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Wednesday, October 4, 2023

Metal

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Metal

A metal (from Ancient Greek μέταλλον métallon 'mine, quarry, metal') is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typically ductile (can be drawn into wires) and malleable (they can be hammered into thin sheets). These properties are the result of the metallic bond between the atoms or molecules of the metal.

A metal may be a chemical element such as iron; an alloy such as stainless steel; or a molecular compound such as polymeric sulfur nitride.

In physics, a metal is generally regarded as any substance capable of conducting electricity at a temperature of absolute zero. Many elements and compounds that are not normally classified as metals become metallic under high pressures. For example, the nonmetal iodine gradually becomes a metal at a pressure of between 40 and 170 thousand times atmospheric pressure. Equally, some materials regarded as metals can become nonmetals. Sodium, for example, becomes a nonmetal at pressure of just under two million times atmospheric pressure.

In chemistry, two elements that would otherwise qualify (in physics) as brittle metals—arsenic and antimony—are commonly instead recognised as metalloids due to their chemistry (predominantly non-metallic for arsenic, and balanced between metallicity and nonmetallicity for antimony). Around 95 of the 118 elements in the periodic table are metals (or are likely to be such). The number is inexact as the boundaries between metals, nonmetals, and metalloids fluctuate slightly due to a lack of universally accepted definitions of the categories involved.

In astrophysics the term "metal" is cast more widely to refer to all chemical elements in a star that are heavier than helium, and not just traditional metals. In this sense the first four "metals" collecting in stellar cores through nucleosynthesis are carbon, nitrogen, oxygen, and neon, all of which are strictly non-metals in chemistry. A star fuses lighter atoms, mostly hydrogen and helium, into heavier atoms over its lifetime. Used in that sense, the metallicity of an astronomical object is the proportion of its matter made up of the heavier chemical elements.

Metals, as chemical elements, comprise 25% of the Earth's crust and are present in many aspects of modern life. The strength and resilience of some metals has led to their frequent use in, for example, high-rise building and bridge construction, as well as most vehicles, many home appliances, tools, pipes, and railroad tracks. Precious metals were historically used as coinage, but in the modern era, coinage metals have extended to at least 23 of the chemical elements.

The history of refined metals is thought to begin with the use of copper about 11,000 years ago. Gold, silver, iron (as meteoric iron), lead, and brass were likewise in use before the first known appearance of bronze in the fifth millennium BCE. Subsequent developments include the production of early forms of steel; the discovery of sodium—the first light metal—in 1809; the rise of modern alloy steels; and, since the end of World War II, the development of more sophisticated alloys.

Properties

Form and structure

Metals are shiny and lustrous, at least when freshly prepared, polished, or fractured. Sheets of metal thicker than a few micrometres appear opaque, but gold leaf transmits green light.

The solid or liquid state of metals largely originates in the capacity of the metal atoms involved to readily lose their outer shell electrons. Broadly, the forces holding an individual atom's outer shell electrons in place are weaker than the attractive forces on the same electrons arising from interactions between the atoms in the solid or liquid metal. The electrons involved become delocalised and the atomic structure of a metal can effectively be visualised as a collection of atoms embedded in a cloud of relatively mobile electrons. This type of interaction is called a metallic bond. The strength of metallic bonds for different elemental metals reaches a maximum around the center of the transition metal series, as these elements have large numbers of delocalized electrons.

Although most elemental metals have higher densities than most nonmetals, there is a wide variation in their densities, lithium being the least dense (0.534 g/cm³) and osmium (22.59 g/cm³) the most dense. (Some of the 6d transition metals are expected to be denser than osmium, but predictions on their densities vary widely in the literature, and in any case their known isotopes are too unstable for bulk production to be possible.) Magnesium, aluminium and titanium are light metals of significant commercial importance. Their respective densities of 1.7, 2.7, and 4.5 g/cm³ can be compared to those of the older structural metals, like iron at 7.9 and copper at 8.9 g/cm³. An iron ball would thus weigh about as much as three aluminum balls of equal volume.

Metals are typically malleable and ductile, deforming under stress without cleaving. The nondirectional nature of metallic bonding is thought to contribute significantly to the ductility of most metallic solids. In contrast, in an ionic compound like table salt, when the planes of an ionic bond slide past one another, the resultant change in location shifts ions of the same charge closer, resulting in the cleavage of the crystal. Such a shift is not observed in a covalently bonded crystal, such as a diamond, where fracture and crystal fragmentation occurs. Reversible elastic deformation in metals can be described by Hooke's Law for restoring forces, where the stress is linearly proportional to the strain.

Heat or forces larger than a metal's elastic limit may cause a permanent (irreversible) deformation, known as plastic deformation or plasticity. An applied force may be a tensile (pulling) force, a compressive (pushing) force, or a shear, bending, or torsion (twisting) force. A temperature change may affect the movement or displacement of structural defects in the metal such as grain boundaries, point vacancies, line and screw dislocations, stacking faults and twins in both crystalline and non-crystalline metals. Internal slip, creep, and metal fatigue may ensue.

The atoms of metallic substances are typically arranged in one of three common crystal structures, namely body-centered cubic (bcc), face-centered cubic (fcc), and hexagonal close-packed (hcp). In bcc, each atom is positioned at the center of a cube of eight others. In fcc and hcp, each atom is surrounded by twelve others, but the stacking of the layers differs. Some metals adopt different structures depending on the temperature.

Body-centered cubic crystal structure, with a 2-atom unit cell, as found in e.g. chromium, iron, and tungsten
Face-centered cubic crystal structure, with a 4-atom unit cell, as found in e.g. aluminum, copper, and gold
Hexagonal close-packed crystal structure, with a 6-atom unit cell, as found in e.g. titanium, cobalt, and zinc

The unit cell for each crystal structure is the smallest group of atoms which has the overall symmetry of the crystal, and from which the entire crystalline lattice can be built up by repetition in three dimensions. In the case of the body-centered cubic crystal structure shown above, the unit cell is made up of the central atom plus one-eight of each of the eight corner atoms.

Electrical and thermal

The electronic structure of metals means they are relatively good conductors of electricity. Electrons in matter can only have fixed rather than variable energy levels, and in a metal the energy levels of the electrons in its electron cloud, at least to some degree, correspond to the energy levels at which electrical conduction can occur. In a semiconductor like silicon or a nonmetal like sulfur there is an energy gap between the electrons in the substance and the energy level at which electrical conduction can occur. Consequently, semiconductors and nonmetals are relatively poor conductors.

The elemental metals have electrical conductivity values of from 6.9 × 10³ S/cm for manganese to 6.3 × 10⁵ S/cm for silver. In contrast, a semiconducting metalloid such as boron has an electrical conductivity 1.5 × 10⁻⁶ S/cm. With one exception, metallic elements reduce their electrical conductivity when heated. Plutonium increases its electrical conductivity when heated in the temperature range of around −175 to +125 °C.

Metals are relatively good conductors of heat. The electrons in a metal's electron cloud are highly mobile and easily able to pass on heat-induced vibrational energy.

The contribution of a metal's electrons to its heat capacity and thermal conductivity, and the electrical conductivity of the metal itself can be calculated from the free electron model. However, this does not take into account the detailed structure of the metal's ion lattice. Taking into account the positive potential caused by the arrangement of the ion cores enables consideration of the electronic band structure and binding energy of a metal. Various mathematical models are applicable, the simplest being the nearly free electron model.

Chemical

Metals are usually inclined to form cations through electron loss. Most will react with oxygen in the air to form oxides over various timescales (potassium burns in seconds while iron rusts over years). Some others, like palladium, platinum, and gold, do not react with the atmosphere at all. The oxides of metals are generally basic, as opposed to those of nonmetals, which are acidic or neutral. Exceptions are largely oxides with very high oxidation states such as CrO₃, Mn₂O₇, and OsO₄, which have strictly acidic reactions.

Painting, anodizing, or plating metals are good ways to prevent their corrosion. However, a more reactive metal in the electrochemical series must be chosen for coating, especially when chipping of the coating is expected. Water and the two metals form an electrochemical cell and, if the coating is less reactive than the underlying metal, the coating actually promotes corrosion.

Periodic table distribution

The elements that form metallic structures under ordinary conditions are shown in yellow on the periodic table below. The remaining elements either form giant covalent structures (light blue), molecular covalent structures (dark blue), or remain as single atoms (violet). Astatine (At), francium (Fr), and the elements from fermium (Fm) onwards are shown in gray because they are extremely radioactive and have never been produced in bulk. Theoretical and experimental evidence suggests that almost all these uninvestigated elements should be metals, though there is some doubt for oganesson (Og).

Bonding of simple substances in the periodic table
	1	2															3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
Group →
↓ Period
1	H																															He
2	Li	Be																									B	C	N	O	F	Ne
3	Na	Mg																									Al	Si	P	S	Cl	Ar
4	K	Ca															Sc	Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn	Ga	Ge	As	Se	Br	Kr
5	Rb	Sr															Y	Zr	Nb	Mo	Tc	Ru	Rh	Pd	Ag	Cd	In	Sn	Sb	Te	I	Xe
6	Cs	Ba	La	Ce	Pr	Nd	Pm	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb	Lu	Hf	Ta	W	Re	Os	Ir	Pt	Au	Hg	Tl	Pb	Bi	Po	At	Rn
7	Fr	Ra	Ac	Th	Pa	U	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	Md	No	Lr	Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Cn	Nh	Fl	Mc	Lv	Ts	Og

Metallic Network covalent Molecular covalent Single atoms Unknown Background color shows bonding of simple substances in the periodic table. If there are several, the most stable allotrope is considered.

The situation can change with pressure: at extremely high pressures, all elements (and indeed all substances) are expected to metallize. Arsenic (As) has both a stable metallic allotrope and a metastable semiconducting allotrope at standard conditions.

Elements near the border between metals and nonmetals often have intermediate chemical behavior. As such, a category of metalloids is often used for such in-between elements, but there is no consensus in the literature as to which elements should qualify.

Alloys

An alloy is a substance having metallic properties and which is composed of two or more elements at least one of which is a metal. An alloy may have a variable or fixed composition. For example, gold and silver form an alloy in which the proportions of gold or silver can be freely adjusted; titanium and silicon form an alloy Ti₂Si in which the ratio of the two components is fixed (also known as an intermetallic compound).

Most pure metals are either too soft, brittle, or chemically reactive for practical use. Combining different ratios of metals as alloys modifies the properties of pure metals to produce desirable characteristics. The aim of making alloys is generally to make them less brittle, harder, resistant to corrosion, or have a more desirable color and luster. Of all the metallic alloys in use today, the alloys of iron (steel, stainless steel, cast iron, tool steel, alloy steel) make up the largest proportion both by quantity and commercial value. Iron alloyed with various proportions of carbon gives low-, mid-, and high-carbon steels, with increasing carbon levels reducing ductility and toughness. The addition of silicon will produce cast irons, while the addition of chromium, nickel, and molybdenum to carbon steels (more than 10%) results in stainless steels.

Other significant metallic alloys are those of aluminum, titanium, copper, and magnesium. Copper alloys have been known since prehistory—bronze gave the Bronze Age its name—and have many applications today, most importantly in electrical wiring. The alloys of the other three metals have been developed relatively recently; due to their chemical reactivity they need electrolytic extraction processes. The alloys of aluminum, titanium, and magnesium are valued for their high strength-to-weight ratios; magnesium can also provide electromagnetic shielding. These materials are ideal for situations where high strength-to-weight ratio is more important than material cost, such as in aerospace and some automotive applications.

Alloys specially designed for highly demanding applications, such as jet engines, may contain more than ten elements.

Lifecycle

Formation



	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
1	H																	He
2	Li	Be											B	C	N	O	F	Ne
3	Na	Mg											Al	Si	P	S	Cl	Ar
4	K	Ca	Sc	Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn	Ga	Ge	As	Se	Br	Kr
5	Rb	Sr	Y	Zr	Nb	Mo		Ru	Rh	Pd	Ag	Cd	In	Sn	Sb	Te	I	Xe
6	Cs	Ba	Lu	Hf	Ta	W	Re	Os	Ir	Pt	Au	Hg	Tl	Pb	Bi
7


			La	Ce	Pr	Nd		Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb
				Th		U

Most abundant (up to 82000 ppm)
Abundant (100–999 ppm)
Uncommon (1–99 ppm)
Rare (0.01–0.99 ppm)
Very rare (0.0001–0.0099 ppm)

Metals left of the dividing line occur (or are sourced) mainly as lithophiles; those to the right, as chalcophiles except gold (a siderophile) and tin (a lithophile).

This sub-section deals with the formation of periodic table elemental metals since these form the basis of metallic materials, as defined in this article.

Metals up to the vicinity of iron (in the periodic table) are largely made via stellar nucleosynthesis. In this process, lighter elements from hydrogen to silicon undergo successive fusion reactions inside stars, releasing light and heat and forming heavier elements with higher atomic numbers.

Heavier metals are not usually formed this way since fusion reactions involving such nuclei would consume rather than release energy. Rather, they are largely synthesised (from elements with a lower atomic number) by neutron capture, with the two main modes of this repetitive capture being the s-process and the r-process. In the s-process ("s" stands for "slow"), singular captures are separated by years or decades, allowing the less stable nuclei to beta decay, while in the r-process ("rapid"), captures happen faster than nuclei can decay. Therefore, the s-process takes a more-or-less clear path: for example, stable cadmium-110 nuclei are successively bombarded by free neutrons inside a star until they form cadmium-115 nuclei which are unstable and decay to form indium-115 (which is nearly stable, with a half-life 30000 times the age of the universe). These nuclei capture neutrons and form indium-116, which is unstable, and decays to form tin-116, and so on. In contrast, there is no such path in the r-process. The s-process stops at bismuth due to the short half-lives of the next two elements, polonium and astatine, which decay to bismuth or lead. The r-process is so fast it can skip this zone of instability and go on to create heavier elements such as thorium and uranium.

Metals condense in planets as a result of stellar evolution and destruction processes. Stars lose much of their mass when it is ejected late in their lifetimes, and sometimes thereafter as a result of a neutron star merger, thereby increasing the abundance of elements heavier than helium in the interstellar medium. When gravitational attraction causes this matter to coalesce and collapse new stars and planets are formed.

Abundance and occurrence

A sample of diaspore, an aluminum oxide hydroxide mineral, α-AlO(OH)

The Earth's crust is made of approximately 25% of metals by weight, of which 80% are light metals such as sodium, magnesium, and aluminium. Nonmetals (~75%) make up the rest of the crust. Despite the overall scarcity of some heavier metals such as copper, they can become concentrated in economically extractable quantities as a result of mountain building, erosion, or other geological processes.

Metals are primarily found as lithophiles (rock-loving) or chalcophiles (ore-loving). Lithophile metals are mainly the s-block elements, the more reactive of the d-block elements, and the f-block elements. They have a strong affinity for oxygen and mostly exist as relatively low-density silicate minerals. Chalcophile metals are mainly the less reactive d-block elements, and the period 4–6 p-block metals. They are usually found in (insoluble) sulfide minerals. Being denser than the lithophiles, hence sinking lower into the crust at the time of its solidification, the chalcophiles tend to be less abundant than the lithophiles.

On the other hand, gold is a siderophile, or iron-loving element. It does not readily form compounds with either oxygen or sulfur. At the time of the Earth's formation, and as the most noble (inert) of metals, gold sank into the core due to its tendency to form high-density metallic alloys. Consequently, it is a relatively rare metal. Some other (less) noble metals—molybdenum, rhenium, the platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, and platinum), germanium, and tin—can be counted as siderophiles but only in terms of their primary occurrence in the Earth (core, mantle, and crust), rather the crust. These metals otherwise occur in the crust, in small quantities, chiefly as chalcophiles (less so in their native form).

The rotating fluid outer core of the Earth's interior, which is composed mostly of iron, is thought to be the source of Earth's protective magnetic field. The core lies above Earth's solid inner core and below its mantle. If it could be rearranged into a column having a 5 m² (54 sq ft) footprint it would have a height of nearly 700 light years. The magnetic field shields the Earth from the charged particles of the solar wind, and cosmic rays that would otherwise strip away the upper atmosphere (including the ozone layer that limits the transmission of ultraviolet radiation).

Extraction

Metals are often extracted from the Earth by means of mining ores that are rich sources of the requisite elements, such as bauxite. Ore is located by prospecting techniques, followed by the exploration and examination of deposits. Mineral sources are generally divided into surface mines, which are mined by excavation using heavy equipment, and subsurface mines. In some cases, the sale price of the metal(s) involved make it economically feasible to mine lower concentration sources.

Once the ore is mined, the metals must be extracted, usually by chemical or electrolytic reduction. Pyrometallurgy uses high temperatures to convert ore into raw metals, while hydrometallurgy employs aqueous chemistry for the same purpose. The methods used depend on the metal and their contaminants.

When a metal ore is an ionic compound of that metal and a non-metal, the ore must usually be smelted—heated with a reducing agent—to extract the pure metal. Many common metals, such as iron, are smelted using carbon as a reducing agent. Some metals, such as aluminum and sodium, have no commercially practical reducing agent, and are extracted using electrolysis instead.

Sulfide ores are not reduced directly to the metal but are roasted in air to convert them to oxides.

Uses

A metal bracket — A neodymium compound alloy magnet of composition Nd₂Fe₁₄B on a nickel-iron bracket from a computer hard drive

Metals are present in nearly all aspects of modern life. Iron, a heavy metal, may be the most common as it accounts for 90% of all refined metals; aluminum, a light metal, is the next most commonly refined metal. Pure iron may be the cheapest metallic element of all at cost of about US$0.07 per gram. Its ores are widespread; it is easy to refine; and the technology involved has been developed over hundreds of years. Cast iron is even cheaper, at a fraction of US$0.01 per gram, because there is no need for subsequent purification. Platinum, at a cost of about $27 per gram, may be the most ubiquitous given its very high melting point, resistance to corrosion, electrical conductivity, and durability. It is said to be found in, or used to produce, 20% of all consumer goods. Polonium is likely to be the most expensive metal that is traded, at a notional cost of about $100,000,000 per gram, due to its scarcity and micro-scale production.

Some metals and metal alloys possess high structural strength per unit mass, making them useful materials for carrying large loads or resisting impact damage. Metal alloys can be engineered to have high resistance to shear, torque, and deformation. However the same metal can also be vulnerable to fatigue damage through repeated use or from sudden stress failure when a load capacity is exceeded. The strength and resilience of metals has led to their frequent use in high-rise building and bridge construction, as well as most vehicles, many appliances, tools, pipes, and railroad tracks.

Metals are good conductors, making them valuable in electrical appliances and for carrying an electric current over a distance with little energy lost. Electrical power grids rely on metal cables to distribute electricity. Home electrical systems, for the most part, are wired with copper wire for its good conducting properties.

The thermal conductivity of metals is useful for containers to heat materials over a flame. Metals are also used for heat sinks to protect sensitive equipment from overheating.

The high reflectivity of some metals enables their use in mirrors, including precision astronomical instruments, and adds to the aesthetics of metallic jewelry.

Some metals have specialized uses; mercury is a liquid at room temperature and is used in switches to complete a circuit when it flows over the switch contacts. Radioactive metals such as uranium and plutonium are fuel for nuclear power plants, which produce energy via nuclear fission. Shape-memory alloys are used for applications such as pipes, fasteners, and vascular stents.

Metals can be doped with foreign molecules—organic, inorganic, biological, and polymers. This doping entails the metal with new properties that are induced by the guest molecules. Applications in catalysis, medicine, electrochemical cells, corrosion and more have been developed.

Recycling

A pile of compacted steel scraps, ready for recycling

Demand for metals is closely linked to economic growth given their use in infrastructure, construction, manufacturing, and consumer goods. During the 20th century, the variety of metals used in society grew rapidly. Today, the development of major nations, such as China and India, and technological advances, are fuelling ever more demand. The result is that mining activities are expanding, and more and more of the world's metal stocks are above ground in use, rather than below ground as unused reserves. An example is the in-use stock of copper. Between 1932 and 1999, copper in use in the U.S. rose from 73 g to 238 g per person.

Metals are inherently recyclable, so in principle, can be used over and over again, minimizing these negative environmental impacts and saving energy. For example, 95% of the energy used to make aluminum from bauxite ore is saved by using recycled material.

Globally, metal recycling is generally low. In 2010, the International Resource Panel, hosted by the United Nations Environment Programme published reports on metal stocks that exist within society and their recycling rates. The authors of the report observed that the metal stocks in society can serve as huge mines above ground. They warned that the recycling rates of some rare metals used in applications such as mobile phones, battery packs for hybrid cars and fuel cells are so low that unless future end-of-life recycling rates are dramatically stepped up these critical metals will become unavailable for use in modern technology.

Biological interactions

The role of metallic elements in the evolution of cell biochemistry has been reviewed, including a detailed section on the role of calcium in redox enzymes.

One or more of the elements iron, cobalt, nickel, copper, and zinc are essential to all higher forms of life. Cobalt is an essential component of vitamin B12. Compounds of all other transition elements and post-transition elements are toxic to a greater or lesser extent, with few exceptions such as certain compounds of antimony and tin. Potential sources of metal poisoning include mining, tailings, industrial wastes, agricultural runoff, occupational exposure, paints, and treated timber.

History

Prehistory

Copper, which occurs in native form, may have been the first metal discovered given its distinctive appearance, heaviness, and malleability compared to other stones or pebbles. Gold, silver, and iron (as meteoric iron), and lead were likewise discovered in prehistory. Forms of brass, an alloy of copper and zinc made by concurrently smelting the ores of these metals, originate from this period (although pure zinc was not isolated until the 13th century). The malleability of the solid metals led to the first attempts to craft metal ornaments, tools, and weapons. Meteoric iron containing nickel was discovered from time to time and, in some respects this was superior to any industrial steel manufactured up to the 1880s when alloy steels become prominent.

Native copper
Gold crystals
Crystalline silver
A slice of meteoric iron
oxidised lead nodules and 1 cm³ cube
A brass weight (35 g)

Antiquity

The discovery of bronze (an alloy of copper with arsenic or tin) enabled people to create metal objects which were harder and more durable than previously possible. Bronze tools, weapons, armor, and building materials such as decorative tiles were harder and more durable than their stone and copper ("Chalcolithic") predecessors. Initially, bronze was made of copper and arsenic (forming arsenic bronze) by smelting naturally or artificially mixed ores of copper and arsenic. The earliest artifacts so far known come from the Iranian plateau in the fifth millennium BCE. It was only later that tin was used, becoming the major non-copper ingredient of bronze in the late third millennium BCE. Pure tin itself was first isolated in 1800 BCE by Chinese and Japanese metalworkers.

Mercury was known to ancient Chinese and Indians before 2000 BCE, and found in Egyptian tombs dating from 1500 BCE.

The earliest known production of steel, an iron-carbon alloy, is seen in pieces of ironware excavated from an archaeological site in Anatolia (Kaman-Kalehöyük) and are nearly 4,000 years old, dating from 1800 BCE.

From about 500 BCE sword-makers of Toledo, Spain, were making early forms of alloy steel by adding a mineral called wolframite, which contained tungsten and manganese, to iron ore (and carbon). The resulting Toledo steel came to the attention of Rome when used by Hannibal in the Punic Wars. It soon became the basis for the weaponry of Roman legions; such swords were, "stronger in composition than any existing sword and, because… [they] would not break, provided a psychological advantage to the Roman soldier."

In pre-Columbian America, objects made of tumbaga, an alloy of copper and gold, started being produced in Panama and Costa Rica between 300 and 500 CE. Small metal sculptures were common and an extensive range of tumbaga (and gold) ornaments comprised the usual regalia of persons of high status.

At around the same time indigenous Ecuadorians were combining gold with a naturally-occurring platinum alloy containing small amounts of palladium, rhodium, and iridium, to produce miniatures and masks composed of a white gold-platinum alloy. The metal workers involved heated gold with grains of the platinum alloy until the gold melted at which point the platinum group metals became bound within the gold. After cooling, the resulting conglomeration was hammered and reheated repeatedly until it became as homogenous as if all of the metals concerned had been melted together (attaining the melting points of the platinum group metals concerned was beyond the technology of the day).

A droplet of solidified molten tin
Mercury being poured into a petri dish
Electrum, a natural alloy of silver and gold, was often used for making coins. Shown is the Roman god Apollo, and on the obverse, a Delphi tripod (circa 310–305 BCE).
A plate made of pewter, an alloy of 85–99% tin and (usually) copper. Pewter was first used around the beginning of the Bronze Age in the Near East.
A pectoral (ornamental breastplate) made of tumbaga, an alloy of gold and copper

Middle Ages

Gold is for the mistress—silver for the maid—
Copper for the craftsman cunning at his trade.
"Good!" said the Baron, sitting in his hall,
"But Iron—Cold Iron—is master of them all."

from Cold Iron by Rudyard Kipling

Arabic and medieval alchemists believed that all metals and matter were composed of the principle of sulfur, the father of all metals and carrying the combustible property, and the principle of mercury, the mother of all metals and carrier of the liquidity, fusibility, and volatility properties. These principles were not necessarily the common substances sulfur and mercury found in most laboratories. This theory reinforced the belief that all metals were destined to become gold in the bowels of the earth through the proper combinations of heat, digestion, time, and elimination of contaminants, all of which could be developed and hastened through the knowledge and methods of alchemy.

Arsenic, zinc, antimony, and bismuth became known, although these were at first called semimetals or bastard metals on account of their immalleability. All four may have been used incidentally in earlier times without recognising their nature. Albertus Magnus is believed to have been the first to isolate arsenic from a compound in 1250, by heating soap together with arsenic trisulfide. Metallic zinc, which is brittle if impure, was isolated in India by 1300 AD. The first description of a procedure for isolating antimony is in the 1540 book De la pirotechnia by Vannoccio Biringuccio. Bismuth was described by Agricola in De Natura Fossilium (c. 1546); it had been confused in early times with tin and lead because of its resemblance to those elements.

Arsenic, sealed in a container to prevent tarnishing
Zinc fragments and a 1 cm³ cube
Antimony, showing its brilliant lustre
Bismuth in crystalline form, with a very thin oxidation layer, and a 1 cm³ bismuth cube

The Renaissance

A disc of uranium being held by gloved hands — A disc of highly enriched uranium that was recovered from scrap processed at the Y-12 National Security Complex, in Oak Ridge, Tennessee

The first systematic text on the arts of mining and metallurgy was De la Pirotechnia (1540) by Vannoccio Biringuccio, which treats the examination, fusion, and working of metals.

Sixteen years later, Georgius Agricola published De Re Metallica in 1556, a clear and complete account of the profession of mining, metallurgy, and the accessory arts and sciences, as well as qualifying as the greatest treatise on the chemical industry through the sixteenth century.

He gave the following description of a metal in his De Natura Fossilium (1546):

Metal is a mineral body, by nature either liquid or somewhat hard. The latter may be melted by the heat of the fire, but when it has cooled down again and lost all heat, it becomes hard again and resumes its proper form. In this respect it differs from the stone which melts in the fire, for although the latter regain its hardness, yet it loses its pristine form and properties.
Traditionally there are six different kinds of metals, namely gold, silver, copper, iron, tin, and lead. There are really others, for quicksilver is a metal, although the Alchemists disagree with us on this subject, and bismuth is also. The ancient Greek writers seem to have been ignorant of bismuth, wherefore Ammonius rightly states that there are many species of metals, animals, and plants which are unknown to us. Stibium when smelted in the crucible and refined has as much right to be regarded as a proper metal as is accorded to lead by writers. If when smelted, a certain portion be added to tin, a bookseller's alloy is produced from which the type is made that is used by those who print books on paper.
Each metal has its own form which it preserves when separated from those metals which were mixed with it. Therefore neither electrum nor Stannum [not meaning our tin] is of itself a real metal, but rather an alloy of two metals. Electrum is an alloy of gold and silver, Stannum of lead and silver. And yet if silver be parted from the electrum, then gold remains and not electrum; if silver be taken away from Stannum, then lead remains and not Stannum.
Whether brass, however, is found as a native metal or not, cannot be ascertained with any surety. We only know of the artificial brass, which consists of copper tinted with the colour of the mineral calamine. And yet if any should be dug up, it would be a proper metal. Black and white copper seem to be different from the red kind.
Metal, therefore, is by nature either solid, as I have stated, or fluid, as in the unique case of quicksilver.
But enough now concerning the simple kinds.

Platinum, the third precious metal after gold and silver, was discovered in Ecuador during the period 1736 to 1744, by the Spanish astronomer Antonio de Ulloa and his colleague the mathematician Jorge Juan y Santacilia. Ulloa was the first person to write a scientific description of the metal, in 1748.

In 1789, the German chemist Martin Heinrich Klaproth isolated an oxide of uranium, which he thought was the metal itself. Klaproth was subsequently credited as the discoverer of uranium. It was not until 1841, that the French chemist Eugène-Melchior Péligot, prepared the first sample of uranium metal. Henri Becquerel subsequently discovered radioactivity in 1896 by using uranium.

In the 1790s, Joseph Priestley and the Dutch chemist Martinus van Marum observed the transformative action of metal surfaces on the dehydrogenation of alcohol, a development which subsequently led, in 1831, to the industrial scale synthesis of sulphuric acid using a platinum catalyst.

In 1803, cerium was the first of the lanthanide metals to be discovered, in Bastnäs, Sweden by Jöns Jakob Berzelius and Wilhelm Hisinger, and independently by Martin Heinrich Klaproth in Germany. The lanthanide metals were largely regarded as oddities until the 1960s when methods were developed to more efficiently separate them from one another. They have subsequently found uses in cell phones, magnets, lasers, lighting, batteries, catalytic converters, and in other applications enabling modern technologies.

Other metals discovered and prepared during this time were cobalt, nickel, manganese, molybdenum, tungsten, and chromium; and some of the platinum group metals, palladium, osmium, iridium, and rhodium.

Light metals

All metals discovered until 1809 had relatively high densities; their heaviness was regarded as a singularly distinguishing criterion. From 1809 onward, light metals such as sodium, potassium, and strontium were isolated. Their low densities challenged conventional wisdom as to the nature of metals. They behaved chemically as metals however, and were subsequently recognised as such.

Aluminium was discovered in 1824 but it was not until 1886 that an industrial large-scale production method was developed. Prices of aluminium dropped and aluminium became widely used in jewelry, everyday items, eyeglass frames, optical instruments, tableware, and foil in the 1890s and early 20th century. Aluminium's ability to form hard yet light alloys with other metals provided the metal many uses at the time. During World War I, major governments demanded large shipments of aluminium for light strong airframes. The most common metal in use for electric power transmission today is aluminium-conductor steel-reinforced. Also seeing much use is all-aluminium-alloy conductor. Aluminium is used because it has about half the weight of a comparable resistance copper cable (though larger diameter due to lower specific conductivity), as well as being cheaper. Copper was more popular in the past and is still in use, especially at lower voltages and for grounding.

While pure metallic titanium (99.9%) was first prepared in 1910 it was not used outside the laboratory until 1932. In the 1950s and 1960s, the Soviet Union pioneered the use of titanium in military and submarine applications as part of programs related to the Cold War. Starting in the early 1950s, titanium came into use extensively in military aviation, particularly in high-performance jets, starting with aircraft such as the F-100 Super Sabre and Lockheed A-12 and SR-71.

Metallic scandium was produced for the first time in 1937. The first pound of 99% pure scandium metal was produced in 1960. Production of aluminium-scandium alloys began in 1971 following a U.S. patent. Aluminium-scandium alloys were also developed in the USSR.

Chunks of sodium
Potassium pearls under paraffin oil. Size of the largest pearl is 0.5 cm.
Strontium crystals
Aluminium chunk, 2.6 grams, 1 x 2 cm
A bar of titanium crystals
Scandium, including a 1 cm³ cube

The age of steel

The modern era in steelmaking began with the introduction of Henry Bessemer's Bessemer process in 1855, the raw material for which was pig iron. His method let him produce steel in large quantities cheaply, thus mild steel came to be used for most purposes for which wrought iron was formerly used. The Gilchrist-Thomas process (or basic Bessemer process) was an improvement to the Bessemer process, made by lining the converter with a basic material to remove phosphorus.

Due to its high tensile strength and low cost, steel came to be a major component used in buildings, infrastructure, tools, ships, automobiles, machines, appliances, and weapons.

In 1872, the Englishmen Clark and Woods patented an alloy that would today be considered a stainless steel. The corrosion resistance of iron-chromium alloys had been recognized in 1821 by French metallurgist Pierre Berthier. He noted their resistance against attack by some acids and suggested their use in cutlery. Metallurgists of the 19th century were unable to produce the combination of low carbon and high chromium found in most modern stainless steels, and the high-chromium alloys they could produce were too brittle to be practical. It was not until 1912 that the industrialisation of stainless steel alloys occurred in England, Germany, and the United States.

The last stable metallic elements

By 1900 three metals with atomic numbers less than lead (#82), the heaviest stable metal, remained to be discovered: elements 71, 72, 75.

Von Welsbach, in 1906, proved that the old ytterbium also contained a new element (#71), which he named cassiopeium. Urbain proved this simultaneously, but his samples were very impure and only contained trace quantities of the new element. Despite this, his chosen name lutetium was adopted.

In 1908, Ogawa found element 75 in thorianite but assigned it as element 43 instead of 75 and named it nipponium. In 1925 Walter Noddack, Ida Eva Tacke, and Otto Berg announced its separation from gadolinite and gave it the present name, rhenium.

Georges Urbain claimed to have found element 72 in rare-earth residues, while Vladimir Vernadsky independently found it in orthite. Neither claim was confirmed due to World War I, and neither could be confirmed later, as the chemistry they reported does not match that now known for hafnium. After the war, in 1922, Coster and Hevesy found it by X-ray spectroscopic analysis in Norwegian zircon. Hafnium was thus the last stable element to be discovered, though rhenium was the last to be correctly recognized.

Lutetium, including a 1 cm³ cube
Rhenium, including a 1 cm³ cube
Hafnium, in the form of a 1.7 kg bar

By the end of World War II scientists had synthesized four post-uranium elements, all of which are radioactive (unstable) metals: neptunium (in 1940), plutonium (1940–41), and curium and americium (1944), representing elements 93 to 96. The first two of these were eventually found in nature as well. Curium and americium were by-products of the Manhattan project, which produced the world's first atomic bomb in 1945. The bomb was based on the nuclear fission of uranium, a metal first thought to have been discovered nearly 150 years earlier.

Post-World War II developments

Superalloys

Superalloys composed of combinations of Fe, Ni, Co, and Cr, and lesser amounts of W, Mo, Ta, Nb, Ti, and Al were developed shortly after World War II for use in high performance engines, operating at elevated temperatures (above 650 °C (1,200 °F)). They retain most of their strength under these conditions, for prolonged periods, and combine good low-temperature ductility with resistance to corrosion or oxidation. Superalloys can now be found in a wide range of applications including land, maritime, and aerospace turbines, and chemical and petroleum plants.

Transcurium metals

The successful development of the atomic bomb at the end of World War II sparked further efforts to synthesize new elements, nearly all of which are, or are expected to be, metals, and all of which are radioactive. It was not until 1949 that element 97 (berkelium), next after element 96 (curium), was synthesized by firing alpha particles at an americium target. In 1952, element 100 (fermium) was found in the debris of the first hydrogen bomb explosion; hydrogen, a nonmetal, had been identified as an element nearly 200 years earlier. Since 1952, elements 101 (mendelevium) to 118 (oganesson) have been synthesized.

Bulk metallic glasses

A metallic glass (also known as an amorphous or glassy metal) is a solid metallic material, usually an alloy, with a disordered atomic-scale structure. Most pure and alloyed metals, in their solid state, have atoms arranged in a highly ordered crystalline structure. Amorphous metals have a non-crystalline glass-like structure. But unlike common glasses, such as window glass, which are typically electrical insulators, amorphous metals have good electrical conductivity. Amorphous metals are produced in several ways, including extremely rapid cooling, physical vapor deposition, solid-state reaction, ion irradiation, and mechanical alloying. The first reported metallic glass was an alloy (Au₇₅Si₂₅) produced at Caltech in 1960. More recently, batches of amorphous steel with three times the strength of conventional steel alloys have been produced. Currently, the most important applications rely on the special magnetic properties of some ferromagnetic metallic glasses. The low magnetization loss is used in high-efficiency transformers. Theft control ID tags and other article surveillance schemes often use metallic glasses because of these magnetic properties.

Shape-memory alloys

A shape-memory alloy (SMA) is an alloy that "remembers" its original shape and when deformed returns to its pre-deformed shape when heated. While the shape memory effect had been first observed in 1932, in an Au-Cd alloy, it was not until 1962, with the accidental discovery of the effect in a Ni-Ti alloy that research began in earnest, and another ten years before commercial applications emerged. SMA's have applications in robotics and automotive, aerospace, and biomedical industries. There is another type of SMA, called a ferromagnetic shape-memory alloy (FSMA), that changes shape under strong magnetic fields. These materials are of particular interest as the magnetic response tends to be faster and more efficient than temperature-induced responses.

Quasicyrstalline alloys

A metallic regular dodecahedron — A Ho-Mg-Zn icosahedral quasicrystal formed as a pentagonal dodecahedron, the dual of the icosahedron

In 1984, Israeli chemist Dan Shechtman found an aluminum-manganese alloy having five-fold symmetry, in breach of crystallographic convention at the time which said that crystalline structures could only have two-, three-, four-, or six-fold symmetry. Due to fear of the scientific community's reaction, it took him two years to publish the results for which he was awarded the Nobel Prize in Chemistry in 2011. Since this time, hundreds of quasicrystals have been reported and confirmed. They exist in many metallic alloys (and some polymers). Quasicrystals are found most often in aluminum alloys (Al-Li-Cu, Al-Mn-Si, Al-Ni-Co, Al-Pd-Mn, Al-Cu-Fe, Al-Cu-V, etc.), but numerous other compositions are also known (Cd-Yb, Ti-Zr-Ni, Zn-Mg-Ho, Zn-Mg-Sc, In-Ag-Yb, Pd-U-Si, etc.). Quasicrystals effectively have infinitely large unit cells. Icosahedrite Al₆₃Cu₂₄Fe₁₃, the first quasicrystal found in nature, was discovered in 2009. Most quasicrystals have ceramic-like properties including low electrical conductivity (approaching values seen in insulators) and low thermal conductivity, high hardness, brittleness, and resistance to corrosion, and non-stick properties. Quasicrystals have been used to develop heat insulation, LEDs, diesel engines, and new materials that convert heat to electricity. New applications may take advantage of the low coefficient of friction and the hardness of some quasicrystalline materials, for example embedding particles in plastic to make strong, hard-wearing, low-friction plastic gears. Other potential applications include selective solar absorbers for power conversion, broad-wavelength reflectors, and bone repair and prostheses applications where biocompatibility, low friction, and corrosion resistance are required.

Complex metallic alloys

Complex metallic alloys (CMAs) are intermetallic compounds characterized by large unit cells comprising some tens up to thousands of atoms; the presence of well-defined clusters of atoms (frequently with icosahedral symmetry); and partial disorder within their crystalline lattices. They are composed of two or more metallic elements, sometimes with metalloids or chalcogenides added. They include, for example, NaCd2, with 348 sodium atoms and 768 cadmium atoms in the unit cell. Linus Pauling attempted to describe the structure of NaCd₂ in 1923, but did not succeed until 1955. At first called "giant unit cell crystals", interest in CMAs, as they came to be called, did not pick up until 2002, with the publication of a paper called "Structurally Complex Alloy Phases", given at the 8th International Conference on Quasicrystals. Potential applications of CMAs include as heat insulation; solar heating; magnetic refrigerators; using waste heat to generate electricity; and coatings for turbine blades in military engines.

High-entropy alloys

High-entropy alloys (HEAs) such as AlLiMgScTi are composed of equal or nearly equal quantities of five or more metals. Compared to conventional alloys with only one or two base metals, HEAs have considerably better strength-to-weight ratios, higher tensile strength, and greater resistance to fracturing, corrosion, and oxidation. Although HEAs were described as early as 1981, significant interest did not develop until the 2010s; they continue to be the focus of research in materials science and engineering because of their potential for desirable properties.

MAX phase alloys

MAX phase
alloy examples
MAX	M	A	X
Hf₂SnC	Hf	Sn	C
Ti₄AlN₃	Ti	Al	N
Ti₃SiC₂	Ti	Si	C
Ti₂AlC	Ti	Al	C
Cr₂AlC₂	Cr	Al	C
Ti₃AlC₂	Ti	Al	C

In a MAX phase alloy, M is an early transition metal, A is an A group element (mostly group IIIA and IVA, or groups 13 and 14), and X is either carbon or nitrogen. Examples are Hf₂SnC and Ti₄AlN₃. Such alloys have some of the best properties of metals and ceramics. These properties include high electrical and thermal conductivity, thermal shock resistance, damage tolerance, machinability, high elastic stiffness, and low thermal expansion coefficients. They can be polished to a metallic luster because of their excellent electrical conductivities. During mechanical testing, it has been found that polycrystalline Ti₃SiC₂ cylinders can be repeatedly compressed at room temperature, up to stresses of 1 GPa, and fully recover upon the removal of the load. Some MAX phases are also highly resistant to chemical attack (e.g. Ti₃SiC₂) and high-temperature oxidation in air (Ti₂AlC, Cr₂AlC₂, and Ti₃AlC₂). Potential applications for MAX phase alloys include: as tough, machinable, thermal shock-resistant refractories; high-temperature heating elements; coatings for electrical contacts; and neutron irradiation resistant parts for nuclear applications. While MAX phase alloys were discovered in the 1960s, the first paper on the subject was not published until 1996.

Resource curse

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Resource_curse

The resource curse, also known as the paradox of plenty or the poverty paradox, is the phenomenon of countries with an abundance of natural resources (such as fossil fuels and certain minerals) having less economic growth, less democracy, or worse development outcomes than countries with fewer natural resources. There are many theories and much academic debate about the reasons for and exceptions to the adverse outcomes. Most experts believe the resource curse is not universal or inevitable but affects certain types of countries or regions under certain conditions.

Thesis

As far back as in 1711, The Spectator noted, "It is generally observed, that in countries of the greatest plenty there is the poorest living."

The idea that resources might be more of an economic curse than a blessing emerged in debates in the 1950s and the 1960s about the economic problems of low and middle-income countries. In 1993 Richard Auty first used the term resource curse to describe how countries rich in mineral resources were unable to use that wealth to boost their economies and how, counter-intuitively, these countries had lower economic growth than countries without an abundance of natural resources. An influential 1995 study by Jeffrey Sachs and Andrew Warner found a strong correlation between natural resource abundance and poor economic growth. As of 2016, hundreds of studies have evaluated the effects of resource wealth on a wide range of economic outcomes, and offered many explanations for how, why, and when a resource curse is likely to occur.While "the lottery analogy has value but also has shortcomings", many observers have likened the resource curse to the difficulties that befall lottery winners who struggle to manage the complex side-effects of newfound wealth.

As of 2009, scholarship on the resource curse has increasingly shifted towards explaining why some resource-rich countries succeed and why others do not, as opposed to just investigating the average economic effects of resources. Research suggests that the manner in which resource income is spent, the system of government, institutional quality, type of resources, and early vs. late industrialization all have been used to explain successes and failures.

Since 2018, a discussion has emerged concerning the potential for a resource curse related to critical materials for renewable energy. This could concern either countries with abundant renewable energy resources, such as sunshine, or critical materials for renewable energy technologies, such as neodymium, cobalt, or lithium.

Bruce Bueno de Mesquita, who developed selectorate theory, explains that when an autocratic country has lots of natural resources, the ruler's optimal strategy for political survival is to use that revenue to buy the loyalty of critical support groups and oppress the rest of the population by denying them civil liberties and underfunding education and infrastructure. Education, liberty, and infrastructure can make the people more productive, but they also make it easier for them to organize opposition movements. Since the ruler can obtain sufficient revenue from his country's natural resources, he has no need for a productive populace and therefore does not have to risk liberalization. By contrast, in a dictatorship with few natural resources, there may be a necessity for the ruler to liberalize his society somewhat so that the economy can be organized more efficiently, and to invest in education and healthcare to create a skilled and healthy workforce. Bueno de Mesquita cites Ghana and Taiwan as examples of countries where the rulers permitted democratization out of necessity.

Economic effects

The International Monetary Fund classifies 51 countries as "resource-rich," which are defined as countries that derive at least 20% of exports or 20% of fiscal revenue from nonrenewable natural resources; 29 of those countries are low- and lower-middle-income. Common characteristics of the 29 countries include (i) extreme dependence on resource wealth for fiscal revenues, export sales, or both; (ii) low saving rates; (iii) poor growth performance; and (iv) highly volatile resource revenues.

A 2016 meta-study found weak support for the thesis that resource richness adversely affects long-term economic growth. The authors noted that "approximately 40% of empirical papers finding a negative effect, 40% finding no effect, and 20% finding a positive effect" but "overall support for the resource curse hypothesis is weak when potential publication bias and method heterogeneity are taken into account."

A 2018 study showed that most specifications, the impact of oil correlated with regime leaders as well as being between two and three times larger than the marginal effect of increases during the leader's term.

A 2021 meta-analysis of 46 natural experiments found that price increases in oil and lootable minerals increased the likelihood of conflict. A 2011 study in the journal Comparative Political Studies found that "natural resource wealth can be either a "curse" or a "blessing" and that the distinction is conditioned by domestic and international factors, both amenable to change through public policy, namely, human capital formation and economic openness."

Dutch disease

Dutch disease, defined as the relationship between the increase in the economic development of a specific sector (for example natural resources) and a decline in other sectors, first became apparent after the Dutch discovered a huge natural gas field in Groningen in 1959. The Netherlands sought to tap this resource in an attempt to export the gas for profit. However, when the gas began to flow out of the country, its ability to compete against other countries' exports declined. With the Netherlands focusing primarily on the new gas exports, the Dutch currency began to appreciate, which harmed the country's ability to export other products. With the growing gas market and the shrinking export economy, the Netherlands began to experience a recession.

This process has been witnessed in multiple countries around the world including but not limited to Venezuela (oil), Angola (diamonds, oil), the Democratic Republic of the Congo (diamonds), and various other nations. All of these countries are considered "resource-cursed".

Dutch disease makes tradable goods less competitive in world markets. Absent currency manipulation or a currency peg, appreciation of the currency can damage other sectors, leading to a compensating unfavorable balance of trade. As imports become cheaper in all sectors, internal employment suffers and with it the skill infrastructure and manufacturing capabilities of the nation. To compensate for the loss of local employment opportunities, government resources are used to artificially create employment. The increasing national revenue will often also result in higher government spending on health, welfare, military, and public infrastructure, and if this is done corruptly or inefficiently it can be a burden on the economy. While the decrease in the sectors exposed to international competition leaves the economy vulnerable to price changes in the natural resource and consequently even greater dependence on natural resource revenue, this can be managed by active and effective use of hedge instruments such as forwards, futures, options, and swaps; however, if it is managed inefficiently or corruptly, this can lead to disastrous results. Also, since productivity generally increases faster in the manufacturing sector than in the government, the economy will have lower productivity gains than before.

According to a 2020 study, giant resource discoveries led to a substantial appreciation of the real exchange rate.

Revenue volatility

Prices for some natural resources are subject to wide fluctuation; for example, crude oil prices rose from around $3 per barrel to $12/bbl in 1974 following the 1973 oil crisis and fell from $27/bbl to below $10/bbl during the 1986 glut. In the decade from 1998 to 2008, it rose from $10/bbl to $145/bbl, before falling by more than half to $60/bbl over a few months. When government revenues are dominated by inflows from natural resources (for example, 99.3% of Angola's exports came from just oil and diamonds in 2005), the volatility can disrupt government planning and debt service. Abrupt changes in economic realities that result from this often provoke widespread breaking of contracts or curtailment of social programs, eroding the rule of law and popular support. Responsible use of financial hedges can mitigate that risk to some extent.

Susceptibility to that volatility can be increased when governments choose to borrow heavily in foreign currency. Real exchange rate increases, through capital inflows or the "Dutch disease" can make it appear an attractive option by lowering the cost of interest payments on the foreign debt, and they may be considered more creditworthy because of the existence of natural resources. If the resource prices fall, however, the governments' capacity to meet debt repayments will be reduced. For example, many oil-rich countries like Nigeria and Venezuela saw rapid expansions of their debt burdens during the 1970s oil boom; however, when oil prices fell in the 1980s, bankers stopped lending to them and many of them fell into arrears, triggering penalty interest charges that made their debts grow even more. As Venezuelan oil minister and OPEC co-founder Juan Pablo Pérez Alfonzo presciently warned in 1976: "Ten years from now, twenty years from now, you will see, oil will bring us ruin... It is the devil's excrement."

A 2011 study in The Review of Economics and Statistics found that commodities have historically always shown greater price volatility than manufactured goods and that globalization has reduced this volatility. Commodities are a key reason why poor countries are more volatile than rich countries.

Enclave effects

"Oil production generally takes place in an economic enclave, meaning it has few direct effects on the rest of the economy." Michael Ross describes how there are limited economic linkages with other industries in the economy. Consequently, economic diversification may be delayed or neglected by the authorities in light of the high profits that can be obtained from limited natural resources. The attempts at diversification that do occur are often white elephant public works projects which may be misguided or mismanaged. However, even when the authorities attempt diversification in the economy, this is made difficult because resource extraction is vastly more lucrative and out-competes other industries for the best human capital and capital investment. Successful natural-resource-exporting countries often become increasingly dependent on extractive industries over time, further increasing the levels of investment in this industry as it is necessary to maintain their states' finances. There is a lack of investment in other sectors of the economy which is further exacerbated by declines the commodity's price. While resource sectors tend to produce large financial revenues, they often add few jobs to the economy, and tend to operate as enclaves with few forward and backward connections to the rest of the economy.

Human capital

Another possible effect of the resource curse is the crowding out of human capital; countries that rely on natural resource exports may tend to neglect education because they see no immediate need for it. Resource-poor economies like Singapore, Taiwan or South Korea, by contrast, spent enormous efforts on education, and this contributed in part to their economic success (see East Asian Tigers). Other researchers, however, dispute this conclusion; they argue that natural resources generate easily taxable rents that can result in increased spending on education. However, the evidence for whether this increased spending translates to better education outcomes is mixed. A study on Brazil found that oil revenues were associated with sizable increases in education spending, but only with small improvements in education provision. Similarly, an analysis of early-20th century oil booms in Texas and neighboring states found no effect of oil discoveries on student teacher ratios or school attendance. However, oil-rich regions participated more intensively in the Rosenwald schoolbuilding program. A 2021 study found that European regions with a history of coal mining had 10% smaller per-capita GDP than comparable regions. The authors attribute this to lower investments in human capital.

Adverse effects of natural resources on human capital formation might come through several channels. High wages in the resource extraction industry could induce young workers to drop out of school earlier in order to find employment. Evidence for this has been found for coal and fracking booms. In addition, resource booms can lower the wages of teachers relative to other workers, increasing turnover and impairing students' learning.

Incomes and employment

A study on coal mining in Appalachia suggests that "the presence of coal in the Appalachian region has played a significant part in its slow pace of economic development. Our best estimates indicate that an increase of 0.5 units in the ratio of coal revenues to personal income in a county is associated with a 0.7 percentage point decrease in income growth rates. No doubt, coal mining provides opportunities for relatively high-wage employment in the region, but its effect on prosperity appears to be negative in the longer run."

Another example was the Spanish Empire which obtained enormous wealth from its resource-rich colonies in South America in the sixteenth century. The large cash inflows from silver reduced incentives for industrial development in Spain. Innovation and investment in education were therefore neglected, so that the prerequisites for successful future development were given up. Thus, Spain soon lost its economic strength in comparison to other Western countries.

A study of US oil booms found positive effects on local employment and income during booms but found that after the boom, incomes "per capita" decreased, while "unemployment compensation payments increased relative to what they would have been if the boom had not occurred."

Tradeable sectors

A 2019 study found that active mining activity had an adverse impact on the growth of firms in tradeable sectors but a positive impact on the growth of firms in non-tradeable sectors.

Other effects

Natural resources are a source of economic rent which can generate large revenues for those controlling them even in the absence of political stability and wider economic growth. Their existence is a potential source of conflict between factions fighting for a share of the revenue, which may take the form of armed separatist conflicts in regions where the resources are produced or internal conflict between different government ministries or departments for access to budgetary allocations. This tends to erode governments' abilities to function effectively.

Even when politically stable, countries whose economies are dominated by resource extraction industries tend to be less democratic and more corrupt.

Violence and conflict

A 2019 meta-analysis of 69 studies found "that there is no aggregate relationship between natural resources and conflict." According to a 2017 review study, "while some studies support the link between resource scarcity/abundance and armed conflict, others find no or only weak links." According to one academic study, a country that is otherwise typical but has primary commodity exports around 5% of GDP has a 6% risk of conflict, but when exports are 25% of GDP the chance of conflict rises to 33%. "Ethno-political groups are more likely to resort to rebellion rather than using nonviolent means or becoming terrorists when representing regions rich in oil."

There are several factors behind the relationship between natural resources and armed conflicts. Resource wealth may increase the vulnerability of countries to conflicts by undermining the quality of governance and economic performance (the "resource curse" argument). Secondly, conflicts can occur over the control and exploitation of resources and the allocation of their revenues (the "resource war" argument). Thirdly, access to resource revenues by belligerents can prolong conflicts (the "conflict resource" argument). A 2018 study in the Journal of Conflict Resolution found that rebels were particularly likely to be able to prolong their participation in civil wars when they had access to natural resources that they could smuggle.

A 2004 literature review finds that oil makes the onset of war more likely and that lootable resources lengthen existing conflicts. One study finds the mere discovery (as opposed to just the exploitation) of petroleum resources increases the risk of conflict, as oil revenues have the potential to alter the balance of power between regimes and their opponents, rendering bargains in the present obsolete in the future. One study suggests that the rise in mineral prices over the period 1997–2010 contributed to up to 21 percent of the average country-level violence in Africa. Research shows that declining oil prices make oil-rich states less bellicose. Jeff Colgan observed that oil-rich states have a propensity to instigate international conflicts as well as to be the targets of them, which he referred to as "petro-aggression". Arguable examples include Iraq's invasions of Iran and Kuwait; Libya's repeated incursions into Chad in the 1970s and 1980s; Iran's long-standing suspicion of Western powers; the United States' relations with Iraq and Iran. It is not clear whether the pattern of petro-aggression found in oil-rich countries also applies to other natural resources besides oil. Some scholars argue that the relationship between oil and interstate war is primarily driven by the case of the Iran–Iraq War and that the overall evidence points in the direction of an oil-peace.

A 2016 study finds that "oil production, oil reserves, oil dependence, and oil exports are associated with a higher risk of initiating conflict while countries enjoying large oil reserves are more frequently the target of military actions." As of 2016, the only six countries whose reported military expenditures exceeded 6 percent of GDP were significant oil producers: Oman, South Sudan, Saudi Arabia, Iraq, Libya, Algeria (data for Syria and North Korea were unavailable). A 2017 study in the American Economic Review found that mining extraction contributed to conflicts in Africa at the local level over the period 1997–2010. A 2017 study in Security Studies found that while there is a statistical relationship between oil wealth and ethnic war, the use of qualitative methods reveals "that oil has rarely been a deep cause of ethnic war."

The emergence of the Sicilian Mafia has been attributed to the resource curse. Early Mafia activity is strongly linked to Sicilian municipalities abundant in sulphur, Sicily's most valuable export commodity. A 2017 study in the Journal of Economic History also links the emergence of the Sicilian Mafia to surging demand for oranges and lemons following the late 18th-century discovery that citrus fruits cured scurvy.

A 2016 study argues that petrostates may be emboldened to act more aggressively because of the inability of allied great powers to punish the petrostate. The great powers have strong incentives not to upset the relationship with its client petrostate ally for both strategic and economic reasons.

A 2017 study found evidence of the resource curse in the American frontier period of the [[Western United States] in the 19th century (the Wild West). The study found, "In places where mineral discoveries occurred before formal institutions were established, there were more homicides per capita historically and the effect has persisted to this day. Today, the share of homicides and assaults explained by the historical circumstances of mineral discoveries is comparable to the effect of education or income."

A 2018 study in the Economic Journal found that "oil price shocks are seen to promote coups in onshore-intensive oil countries, while preventing them in offshore-intensive oil countries." The study argues that states which have onshore oil wealth tend to build up their military to protect the oil, whereas states do not do that for offshore oil wealth. A 2020 study determined that low levels of oil and gas revenue actually increases the likelihood of nonviolent resistance in autocratic countries, despite the general logic of the resource curse.

Democracy and human rights

Research shows that oil wealth lowers levels of democracy and strengthens autocratic rule because political leaders in oil-rich countries refuse democratic development because they will have more to give up from losing power. Similarly, political leaders of oil-rich countries refuse democratic development because the political elite collects the revenues from the oil export and use the money for cementing its political, economic, and social power by controlling government and its bureaucracy, Military spending generally increases with oil wealth and so a military coup, one of the strongest tools in toppling autocracies, is less likely in oil-rich countries since dictators can quell resistance through additional funding. According to Michael Ross, "only one type of resource has been consistently correlated with less democracy and worse institutions: petroleum, which is the key variable in the vast majority of the studies that identify some type of curse." A 2014 meta-analysis confirms the negative impact of oil wealth on democratization. A 2016 study challenges the conventional academic wisdom on the relationship between oil and authoritarianism. A 2022 study found that the resource curse is tied only to easily-extractable oil, not to oil that requires complex extraction. Other forms of resource wealth have also been found to strengthen autocratic rule. A 2016 study found that resource windfalls have no political impact on democracies and deeply entrenched authoritarian regimes, but significantly exacerbate the autocratic nature of moderately authoritarian regimes. A third 2016 study finds that while it is accurate that resource richness has an adverse impact on the prospects of democracy, this relationship has held only since the 1970s. A 2017 study found that the presence of multinational oil companies increases the likelihood of state repression. Another 2017 study found that the presence of oil reduced the likelihood that a democracy would be established after the breakdown of an authoritarian regime. A 2018 study found that the relationship between oil and authoritarianism primarily holds after the end of the Cold War. The study argues that without American or Soviet support, resource-poor authoritarian regimes had to democratize, but resource-rich authoritarian regimes resisted domestic pressures to democratize. Prior to the 1970s, oil-producing countries did not have democratization levels that differed from other countries. Oil-abundant authoritarian governments are suggested to earn high levels of income for oil but spend an extremely minimal amount on social expenditures for individuals being ruled and democracies are suggested to do the opposite.

Research by Stephen Haber and Victor Menaldo found that increases in natural resource reliance do not induce authoritarianism but may instead promote democratization. The authors say that their method rectifies the methodological biases of earlier studies which revolve around random effects: "Numerous sources of bias may be driving the results [of earlier studies on the resource curse], the most serious of which is omitted variable bias induced by unobserved country-specific and time-invariant heterogeneity." In other words, this means that countries might have specific, enduring traits that get left out of the model, which could increase the explanation power of the argument. The authors claim that the chances of this happening are larger when assuming random effects, an assumption that does not allow for what the authors call "unobserved country-specific heterogeneity". The criticisms have themselves been subject to criticism. One study reexamined the Haber-Menaldo analysis by using Haber and Menaldo's own data and statistical models. It reported that their conclusions were only valid for the period before the 1970s, but since about 1980, there has been a pronounced resource curse. Authors Andersen and Ross suggest that oil wealth became a hindrance to democratic transitions only after the transformative events of the 1970s, which enabled the governments of developing countries to capture the oil rents that were previously siphoned off by foreign-owned firms.

There are two ways that oil wealth might negatively affect democratization. The first is that oil strengthens authoritarian regimes, making transitions to democracy less likely. The second is that oil wealth weakens democracies. Research generally supports the first theory but is mixed on the second. A 2019 study found that oil wealth is associated with increases in the level of personalism in dictatorships.

Both pathways might result from the ability of oil-rich states to provide citizens with a combination of generous benefits and low taxes. In many economies that are not resource-dependent, governments tax citizens, who demand efficient and responsive government in return. This bargain establishes a political relationship between rulers and subjects. In countries whose economies are dominated by natural resources, however, rulers don't need to tax their citizens because they have a guaranteed source of income from natural resources. Because the country's citizens aren't being taxed, they have less incentive to be watchful with how government spends its money. In addition, those benefiting from mineral resource wealth may perceive an effective and watchful civil service and civil society as a threat to the benefits that they enjoy, and they may take steps to thwart them. As a result, citizens are often poorly served by their rulers, and if the citizens complain, money from the natural resources enables governments to pay for armed forces to keep the citizens in check. It has been argued that rises and falls in the price of petroleum correlate with rises and falls in the implementation of human rights in major oil-producing countries.

Corrupt members of national governments may collude with resource extraction companies to override their own laws and ignore objections made by indigenous inhabitants. The United States Senate Foreign Relations Committee report entitled "Petroleum and Poverty Paradox" states that "too often, oil money that should go to a nation's poor ends up in the pockets of the rich, or it may be squandered on grand palaces and massive showcase projects instead of being invested productively." A 2016 study found that mining in Africa substantially increases corruption; an individual within 50 kilometres (31 mi) of a recently opened mine is 33% more likely to have paid a bribe the past year than a person living within 50 km of mines that "will open" in the future. The former also pay bribes for permits more frequently, and perceive their local councilors to be more corrupt. In a study examining the effects of mining on local communities in Africa, researchers concluded that active mining areas are associated with more bribe payments, particularly police bribes. Their findings were consistent with the hypothesis that mining increases corruption.

The Center for Global Development argues that governance in resource-rich states would be improved by the government making universal, transparent, and regular payments of oil revenues to citizens and then attempting to reclaim it through the tax system, which they argue will fuel public demand for the government to be transparent and accountable in its management of natural resource revenues and in the delivery of public services.

One study found that "oil producing states dependent on exports to the USA exhibit lower human rights performance than those exporting to China". The authors argue that this stems from the fact that US relationships with oil producers were formed decades ago, before human rights became part of its foreign policy agenda.

One study found that resource wealth in authoritarian states lowers the probability of adopting freedom of information laws. However, democracies that are resource-rich are more likely than resource-poor democracies to adopt such laws.

One study looking at oil wealth in Colombia found "that when the price of oil rises, legislators affiliated with right-wing paramilitary groups win office more in oil-producing municipalities. Consistent with the use of force to gain power, positive price shocks also induce an increase in paramilitary violence and reduce electoral competition: fewer candidates run for office, and winners are elected with a wider vote margin. Ultimately, fewer centrist legislators are elected to office, and there is diminished representation at the center."

A 2018 study in International Studies Quarterly found that oil wealth was associated with weaker private liberties (freedom of movement, freedom of religion, the right to property, and freedom from forced labor).

Research by Nathan Jensen indicates that countries that have resource wealth are considered to have a greater political risk for foreign direct investors. He argues that this is because leaders in resource-rich countries are less sensitive to being punished in elections if they take actions that adversely affect foreign investors.

Distribution

According to a 2017 study, "social forces condition the extent to which oil-rich nations provide vital public services to the population. Although it is often assumed that oil wealth leads to the formation of a distributive state that generously provides services in the areas of water, sanitation, education, health care, or infrastructure... quantitative tests reveal that oil-rich nations who experience demonstrations or riots provide better water and sanitation services than oil-rich nations who do not experience such dissent. Subsequent tests find that oil-rich nations who experience nonviolent, mass-based movements provide better water and sanitation services than those who experience violent, mass-based movements."

Gender inequality

Studies suggest countries with abundant natural resources have higher levels of gender inequality in the areas of wages, labor force participation, violence, and education. Research links gender inequality in the Middle East to resource wealth. According to Michael Ross,

Oil production affects gender relations by reducing the presence of women in the labor force. The failure of women to join the nonagricultural labor force has profound social consequences: it leads to higher fertility rates, less education for girls, and less female influence within the family. It also has far-reaching political consequences: when fewer women work outside the home, they are less likely to exchange information and overcome collective action problems; less likely to mobilize politically, and to lobby for expanded rights; and less likely to gain representation in government. That leaves oil-producing states with atypically strong patriarchal cultures and political institutions.

Ross argues that in oil-rich countries, across the Middle East, Africa, Latin America, and Asia, the need for female labor reduces as export-oriented and female-dominated manufacturing is ousted by Dutch disease effects. This hypothesis has received further support by the analysis of mining booms in Africa. For the United States, the evidence is mixed. State-level comparisons suggest that resource wealth leads to lower levels of female labor force participation, lower turnout and fewer seats held by women in legislatures. On the other hand, a county-level analysis of resource booms in the early 20th century found an overall positive effect of resource wealth on single women's labor force participation.

Research has also linked resource wealth to greater domestic violence, and a gender gap in education.

International cooperation

Research finds that the more that states depend on oil exports, the less cooperative they become. They become less likely to join intergovernmental organizations, accept the compulsory jurisdiction of international judicial bodies, and agree to binding arbitration for investment disputes.

Foreign aid

There is an argument in political economy that foreign aid can have the same negative effects in the long run towards development as in the case of the resource curse. The so-called "aid curse" results from giving perverse political incentives to a weak body of civil servants, lowering politicians' accountability towards citizens and decreasing economic pressure thanks to the income of an unearned resource to mitigate economic crisis. When foreign aid represents a major source of revenue to governments, especially in low-income countries, state-building capacity is hindered by undermining responsiveness toward taxpayers or by decreasing the incentive for governments to look for different sources of income or the increase in taxation.

Crime

A 2018 study found that "a 1% increase in the value of oil reserves increases murder by 0.16%, robbery by 0.55% and larceny by 0.18%."

Petro-aggression

Petro-aggression is the tendency for a petrostate to be involved in international conflicts, or to be the target of them. The term was popularized by a 2013 book by Jeff Colgan that found that petrostates (states with 10% or more GDP from petroleum) are 250 percent more likely to instigate international conflicts than a typical country.

Examples of oil-rich countries engaging in conflict include:

Iraq (Invasion of Kuwait)
Iran (Support of Hezbollah and other Shia militias)
Libya (Chadian–Libyan conflict)
Biafra
Indonesia (Operation Lotus)
Saudi Arabia (Saudi Arabian-led intervention in Yemen, Yemeni Civil War (2015–present) )
Russia (War in Donbas, Russian Invasion of Ukraine)
South Sudan (South Sudanese Civil War)

As of 1999, it remained unclear whether the pattern of petro-aggression found in oil-rich countries also applies to other natural resources besides oil.

Oil-rich states also tend to have a poor record of human rights abuses, as well as revolutionary, revisionist ambitions, making them more conflict-prone. Unfortunately, the lack of data allows no way of discerning high oil prices turning petro-states more aggressive as public thought might deduce. Natural disasters turn out to be far more hurtful to the price of oil than any conflict.

Examples in biology and ecology

Microbial ecology studies have also addressed if resource availability modulates the cooperative or competitive behaviour in bacteria populations. When resources availability is high, bacterial populations become competitive and aggressive with each other, but when environmental resources are low, they tend to be cooperative and mutualistic.

Ecological studies have hypothesised that competitive forces between animals are major in high carrying capacity zones (i.e. near the Equator), where biodiversity is higher, because of natural resources abundance. This abundance or excess of resources, causes animal populations to have R reproduction strategies (many offspring, short gestation, less parental care, and a short time until sexual maturity), so competition is affordable for populations. Also, competition could select populations to have R behaviour in a positive feedback regulation.

Contrary, in low carrying capacity zones (i.e. far from the equator), where environmental conditions are harsh K strategies are common (longer life expectancy, produce relatively fewer offspring and tend to be altricial, requiring extensive care by parents when young) and populations tend to have cooperative or mutualistic behaviors. If populations have a competitive behaviour in hostile environmental conditions they mostly are filtered out (die) by environmental selection, hence populations in hostile conditions are selected to be cooperative.

Mutualism hypothesis was first described while Peter Kropotkin studied the fauna of the Siberian steppe, where environmental conditions are harsh, he found animals tend to cooperate in order to survive. Extreme competition is observed in the Amazonian forest where life requires low energy to find resources (i.e. sunlight for plants) hence life could afford being selected by biotic factors (i.e. competition) rather than abiotic factors.

Criticisms

A 2008 study argues that the curse vanishes when looking not at the relative importance of resource exports in the economy but rather at a different measure: the relative abundance of natural resources in the ground. Using that variable to compare countries, it reports that resource wealth in the ground correlates with slightly higher economic growth and slightly fewer armed conflicts. That a high dependency on resource exports correlates with bad policies and effects is not caused by the large degree of resource exportation. The causation goes in the opposite direction: conflicts and bad policies created the heavy dependence on exports of natural resources. When a country's chaos and economic policies scare off foreign investors and send local entrepreneurs abroad to look for better opportunities, the economy becomes skewed. Factories may close and businesses may flee, but petroleum and precious metals remain for the taking. Resource extraction becomes the "default sector" that still functions after other industries have come to a halt.

A 2008 article by Thad Dunning argues that while resource revenues can promote or strengthen authoritarian regimes, in certain circumstances they can also promote democracy. In countries where natural resource rents are a relatively small portion of the overall economy and the non-resource economy is unequal, resources rents can strengthen democracy by reducing economic elites' fear of ceding power since social welfare policies can be funded with resource rents and not redistribution. Dunning proposes Venezuela's democratic consolidation during the oil boom of the 1970s as a key example of this phenomenon.

A 2011 study argues that previous assumptions that oil abundance is a curse were based on methodologies which failed to take into account cross-country differences and dependencies arising from global shocks, such as changes in technology and the price of oil. The researchers studied data from the World Bank over the period 1980–2006 for 53 countries, covering 85% of world GDP and 81% of world proven oil reserves. They found that oil abundance positively affected both short-term growth and long-term income levels. In a companion paper, using data on 118 countries over the period 1970–2007, they show that it is the volatility in commodity prices, rather than abundance per se, that drives the resource curse paradox.

A 2019 article by Indra Overland argues that concerns about a new form of resource curse related to renewable energy are overblown, as renewable energy resources are more evenly distributed around the world than fossil fuel resources. Some countries could still experience windfalls from critical materials for renewable energy technologies, but this depends on how the technologies evolve and which materials they require.

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