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Friday, February 27, 2015

Chinese space program


From Wikipedia, the free encyclopedia

The space program of the People's Republic of China is directed by the China National Space Administration (CNSA). Its technological roots can be traced back to the late 1950s, when the People's Republic began a rudimentary ballistic missile program in response to perceived American (and, later, Soviet) threats. However, the first Chinese crewed space program only began several decades later, when an accelerated program of technological development culminated in Yang Liwei's successful 2003 flight aboard Shenzhou 5. This achievement made China the third country to independently send humans into space. Plans currently include a permanent Chinese space station in 2020 and crewed expeditions to the Moon and Mars.

History and recent developments

During the period of Sino-Soviet co-operation

After the United States threatened to use nuclear weapons during the Korean War, Chairman Mao Zedong decided that only a nuclear deterrent of its own would guarantee the security of the newly founded PRC. Additionally, he wanted China to gain status among the world's powers that—as he felt—did not respect him. From this, he decided instead to only implement his new plan with the Republic of China (present-day Taiwan) as "China". Thus, Mao announced his decision to develop China's own strategic weapons, including nuclear bombs and associated missiles for the warheads, during a Communist Party of China (CPC) Central Committee meeting held on January 15, 1955. The Chinese nuclear weapons program was designated by the codename of "02".


The Fifth Academy of the National Defense Ministry (国防部第五研究院) was founded on October 8, 1956, with Qian Xuesen, who had just been deported from the United States after being accused of being a communist during the red scare, as director. The Academy started the development of the first ballistic missile program, adopted on March 1, 1956 and known as the first Twelve-Year-Plan for Chinese aerospace.[1]

After the launch of mankind's first artificial satellite, Sputnik 1, by the Soviet Union on October 4, 1957, Mao decided during the National Congress of the CPC on May 17, 1958 to make China an equal with the superpowers (“我们也要搞人造卫星”)(We need the artificial too), by adopting Project 581 with the objective of placing a satellite in orbit by 1959 to celebrate the 10th anniversary of the PRC's founding.[2] This goal would be achieved in three phases: developing sounding rockets first, then launching small satellites and in the final phase, large satellites.
  • The construction of China's first missile test base, code-named Base 20 (西北综合导弹试验基地), started in April 1958 and it entered service on October 20 of the same year.
  • The first Chinese missile was built in October 1958 as a reverse-engineered copy of the Soviet R-2 short-range ballistic missile (SRBM), itself an upgraded version of a German V-2 rocket. Its range was 590 km, weighing 20.5 tons and propelled with liquid oxygen and alcohol.
  • China's first ever T-7 sounding rocket was successfully launched from the Nanhui launch site on February 19, 1960.[3]
  • China started to develop medium-range ballistic missiles (MRBM) in July 1960, with an increased range double that of the R-2.
During the cordial Sino-Soviet relations of the 1950s, the USSR engaged in a cooperative technology transfer program with the PRC under which they trained Chinese students and provided the fledgling program with a sample R-2 rocket. But when Soviet premier Nikita Khrushchev was denounced as revisionist, with Mao asserting that there had been a counter-revolution in the Soviet Union and that capitalism had been restored, the friendly relationship between the two countries turned to confrontation. As a consequence, all Soviet technological assistance was abruptly withdrawn after the 1960 Sino-Soviet split.

Missile and Space development after the Sino-Soviet split

Only 17 days after the last Soviet expert had left China, the first Soviet built R-2 rocket fueled with Chinese-made propellant was launched with success on September 10, 1960. Due to Cold War tension, Mao decided in December 1963 that China should develop missile defence system capacity. During a conference held on February 2, 1964, directive 640(640指示)was adopted (later known as Project 640).[4]
  • The first successful launch of a Chinese 1059 SRBM missile copy of the R-2 was conducted only two months later on November 5, 1960. The missile was also designated DF-1. The first DF-2 MRBM was tested on March 21, 1962, but failed.
  • Development eventually continued with the redesigned DF-2A MRBM which was successfully tested on June 29, 1964. It would enter service by the end of 1966.
  • The first successful launch and recovery of a T-7A(S1) sounding rocket carrying a biological experiment (transporting eight white mice) was on July 19, 1964 from Base 603(安徽广德誓节渡中国科学院六〇三基地.[5]
  • China started to develop the DF-5 intercontinental ballistic missile (ICBM) program in August 1965. It was designed to carry a single nuclear warhead and has a maximum range of 12000 km. In November 1966, it was decided to build a second ballistic missile test site, the Northern Missile Test Site (华北导弹试验场)) in Shanxi Province, farther away from China's northern border.
  • On October 27, 1966, a nuclear-tipped DF-2A missile was launched from Jiuquan and the 20 kilotons yield nuclear warhead exploded at the height of 569 meters over the target in Lop Nor or Base 21 situated 894 km away.
  • On December 26, 1966, China tested its first indigenously developed DF-3 intermediate-range ballistic missile (IRBM) with success. The DF-3 was a single-stage, single-warhead missile with a maximum range of 2500 km. The development of the DF-4 IRBM began in 1967 in parallel with the single-stage DF-3.
  • In March 1967, development started on the JL-1 submarine-launched ballistic missile to accompany the Type 092 ballistic missile submarine (SSBN) also in development.
As the space race between the two superpowers reached its climax with the conquest of the Moon, Mao and Zhou Enlai decided on July 14, 1967 that the PRC should not be left behind, and started China's own crewed space program.[6]
  • China's first spacecraft designed for human occupancy was named Shuguang-1 (曙光一号) in January 1968.[7] China's Space Medical Institute (航天医学工程研究所) was founded on April 1, 1968, and the Central Military Commission issued the order to start the selection of astronauts.
  • As part of the "third line" effort to relocate critical defense infrastructure to the relatively remote interior (away from the Soviet border), it was decided to construct a new space center in the mountainous region of Xichang in the Sichuan province, code-named Base 27.
  • A first liquid-propellant DF-3 medium-range ballistic missile was successfully launched from the Northern Missile Test Site on December 18, 1968, inaugurating the test site.
  • In August 1969, the development of China's first heavy-lift satellite launch vehicle (SLV), the FB-1 (风暴一号, was started by Shanghai’s 2nd Bureau of Mechanic-Electrical Industry. The all-liquid two-stage launcher was derived from the DF-5 ICBM. Only a few months later, a parallel heavy-lift SLV program, also based on the same DF-5 ICBM and known as CZ-2, was started in Beijing by the First Space Academy.
  • The DF-4 was used to develop the Long March-1 SLV. A newly designed spin-up orbital insertion solid propellant rocket motor third stage was added to the two existing Nitric acid/UDMH liquid propellant stages. An attempt to use this vehicle to launch a Chinese satellite before Japan's first attempt ended in failure on November 16, 1969.[8]
  • The first DF-4 liquid-propellant with two-stage, single-warhead IRBM was tested with success on January 30, 1970. The addition of a second-stage allowed the missile to increased its range to over 4750 km.
  • The second satellite launch attempt on April 24, 1970 was successful. A CZ-1 was used to launch the 173 kg Dong Fang Hong I (东方红一号, meaning The East Is Red I), also known as Mao-1. It was the heaviest first satellite placed into orbit by a nation, exceeding the combined masses of the first satellites of the other four previous countries. The third stage of the CZ-1 was specially equipped with a 40 m2 solar reflector (观察球) deployed by the centrifugal force developed by the spin up orbital insertion solid propellant stage. Therefore, the faint magnitude 5 to 8 brightness of the DFH-1 made the satellite (at best) barely visible with naked eyes was consequently dramatically increased to a comfortable magnitude 2 to 3.
  • The PRC's second satellite was launched with the last of the CZ-1 SLVs on March 3, 1971. The 221 kg ShiJian-1 (SJ-1) was equipped with a magnetometer and cosmic-ray/x-ray detectors.
  • The first crewed space program known as Project 714, was officially adopted in April 1971 with the goal of sending two astronauts into space by 1973 aboard the Shuguang spacecraft. The first screening process for astronauts had already ended on March 15, 1971, with 19 astronauts chosen. The program would soon be cancelled due to political turmoil.
  • A first flight test of the DF-5 ICBM was carried out in October 1971.
  • On August 10, 1972, the new heavy-lift SLV FB-1 made its maiden test flight, with only partial success.[clarification needed]
  • The CZ-2A launcher, originally designed to carry the Shuguang-1 spacecraft, was first tested on November 5, 1974, carrying China’s first FSW-0 recoverable satellite, but failed. After some redesign work, the modified CZ-2C successfully launched the FSW-0 No.1 recoverable satellite (返回式卫星) into orbit on November 26, 1975.
  • After expansion, the Northern Missile Test Site was upgraded as a test base in January 1976 to become the Northern Missile Test Base (华北导弹试验基地) known as Base 25.

After Mao Zedong's death

After Mao died on September 9, 1976, his rival, Deng Xiaoping, denounced during the Cultural Revolution as reactionary and therefore forced to retire from all his offices, slowly re-emerged as China's new leader in 1978. At first, new development was slowed. Then, several key projects deemed unnecessary were simply cancelled—the Fanji ABM system, the Xianfeng Anti-Missile Super Gun, the ICBM Early Warning Network 7010 Tracking Radar and the land-based high-power anti-missile laser program. Nevertheless, some development did proceed.
  • The first Yuanwang-class space tracking ship was commissioned in 1979.
  • The first full-range test of the DF-5 ICBM was conducted on May 18, 1980. The payload reached its target located 9300 km away in the South Pacific (7°0′S 117°33′E / 7.000°S 117.550°E / -7.000; 117.550 (DF-5 ICBM test impact)) and retrieved five minutes later by helicopter.
  • Further development of the Long March rocket series allowed the PRC to initiate a commercial launch program in 1985, which has since launched over 30 foreign satellites, primarily for European and Asian interests.
  • The next crewed space program was even more ambitious and proposed in March 1986, as Astronautics plan 863-2. This consisted of a crewed spacecraft (Project 863-204) used to ferry astronaut crews to a space station (Project 863-205). Several spaceplane designs were rejected two years later and a simpler space capsule was chosen instead. Although the project did not achieve its goals, it would ultimately evolve into the 1992 Project 921.
  • The China Ministry of Aerospace Industry was founded on July 5, 1988.
  • On September 15, 1988, a JL-1 SLBM was launched from a Type 092 submarine. The maximum range of the SLBM is 2150 km.

After the end of the Cold War

Along with Deng's policy of de facto restoration of capitalism in the Chinese economy, implemented in incremental steps, the cultural fabric of the Chinese society was soon his next target. Therefore, names used in the space program, previously all chosen from the revolutionary history of the PRC, were soon replaced with mystical-religious ones. Thus, new Long March carrier rockets were renamed Divine arrow (神箭),[9][10] spacecraft Divine vessel (神舟),[11] space plane Divine dragon (神龙),[12] land-based high-power laser Divine light (神光)[13] and supercomputer Divine might (神威).[14]
  • In June 1993, China Aerospace Industry Corporation (National Space Bureau) was founded in Beijing.
  • On February 15, 1996, during the flight of the first Long March 3B heavy carrier rocket carrying Intelsat 708, the rocket veered off course immediately after clearing the launch platform, crashing 22 seconds later. It crashed 1.85 km (1.15 mi) away from the launch pad into a nearby mountain village. According to the official count, it destroyed 80 houses. More than 500 civilians died as a result, according to unofficial Chinese sources.[15]
  • On the 50th anniversary of the PRC's founding, China launched the Shenzhou 1 spacecraft on November 20, 1999 and recovered it after a flight of 21 hours. The country became the third country with a successful crewed space program by sending an astronaut into space aboard Shenzhou 5 on October 15, 2003 for more than 21 hours.
China has since turned its focus to extraterrestrial exploration starting with the Moon. The first Chinese Lunar Exploration Program un-crewed lunar orbiter Chang'e 1 was successfully launched on October 24, 2007, making China the fifth nation to successfully orbit the Moon.

Chinese space program and the International Community

Dual-use technologies and outer space

The PRC is a member of the United Nations Committee on the Peaceful Uses of Outer Space and a signatory to all United Nations treaties and conventions on space.[citation needed] The United States government has long been resistant to the use of PRC launch services by American industry due to concerns over alleged civilian technology transfer that could have dual-use military applications to countries such as North Korea, Iran or Syria, and announced an official embargo against the PRC in 2000.[citation needed] Thus, financial retaliatory measures have been taken on many occasions against several Chinese space companies.[16]

Chinese exclusion policy of NASA

Due to security concerns, all researchers from the U.S. National Aeronautics and Space Administration (NASA) are prohibited from working with Chinese citizens affiliated with a Chinese state enterprise or entity.[17] In April 2011, the 112th United States Congress banned NASA from using its funds to host Chinese visitors at NASA facilities.[18] In March 2013, the U.S. Congress passed legislation barring Chinese nationals from entering NASA facilities without a waiver from NASA.[17]

Organization

Initially the space program of the PRC was organized under the People's Liberation Army, particularly the Second Artillery Corps. In the 1990s, however, the PRC reorganized the space program as part of a general reorganization of the defense industry to make it resemble Western defense procurement.

The China National Space Administration, an agency within the Commission of Science, Technology and Industry for National Defense currently headed by Sun Laiyan, is now responsible for launches. The Long March rocket is produced by the China Academy of Launch Vehicle Technology, and satellites are produced by the China Aerospace Science and Technology Corporation. The latter organizations are state-owned enterprises; however, it is the intent of the PRC government that they should not be actively state managed and that they should behave much as private companies would in the West.

Universities and institutes

The space program also has close links with:

Space cities

Suborbital launch sites

  • Nanhui (南汇县老港镇东进村) First successful launch of a T-7M sounding rocket on February 19, 1960.[3]
  • Base 603 (安徽广德誓节渡中国科学院六○三基地) Also known as Guangde Launch Site (广德发射场).[23] The first successful flight of a biological experimental T-7A(S1) sounding rocket transporting eight white mice was launched and recovered on July 19, 1964.[24]

Satellite launch centers

The PRC operates 4 satellite launch centers:

Monitoring and control centers

Domestic tracking stations

  • New integrated land-based space monitoring and control network stations, forming a large triangle with Kashi in the north-west of China, Jiamusi in the north-east and Sanya in the south.[29]
  • Weinan Station
  • Changchun Station
  • Qingdao Station
  • Zhanyi Station
  • Nanhai Station
  • Tianshan Station
  • Xiamen Station
  • Lushan Station
  • Jiamusi Station
  • Dongfeng Station
  • Hetian Station

Overseas tracking stations

Plus shared space tracking facilities with France, Brazil, Sweden and Australia.

Crewed spacecraft landing site

Crewed spaceflight programs

Project 714

As the Space Race between the two superpowers reached its climax with the conquest of the Moon, Mao Zedong and Zhou Enlai decided on July 14, 1967 that the PRC should not be left behind, and therefore initiated China's own crewed space program. The top-secret Project 714 aimed to put two people into space by 1973 with the Shuguang spacecraft. Nineteen PLAAF pilots were selected for this goal on March 1971. The Shuguang-1 spacecraft to be launched with the CZ-2A rocket was designed to carry a crew of two. The program was officially cancelled on May 13, 1972 for economic reasons, though the internal politics of the Cultural Revolution likely motivated the closure.
The short-lived second crewed program was based on the successful implementation of landing technology (third in the World after USSR and USA) by FSW satellites. It was announced few times in 1978 with the open publishing of some details including photos, but then was abruptly canceled in 1980. It has been argued that the second crewed program was created solely for propaganda purposes, and was never intended to produce results.[31]

Project 863

A new crewed space program was proposed by the Chinese Academy of Sciences in March 1986, as Astronautics plan 863-2. This consisted of a crewed spacecraft (Project 863-204) used to ferry astronaut crews to a space station (Project 863-205). In September of that year, astronauts in training were presented by the Chinese media. The various proposed crewed spacecraft were mostly spaceplanes. Project 863 ultimately evolved into the 1992 Project 921.

Project 921

Spacecraft

In 1992, authorization and funding was given for the first phase of Project 921, which was a plan to launch a crewed spacecraft. The Shenzhou program had four uncrewed test flights and two crewed missions. The first one was Shenzhou 1 on November 20, 1999. On January 9, 2001 Shenzhou 2 launched carrying test animals. Shenzhou 3 and Shenzhou 4 were launched in 2002, carrying test dummies. Following these was the successful Shenzhou 5, China's first crewed mission in space on October 15, 2003, which carried Yang Liwei in orbit for 21 hours and made China the third nation to launch a human into orbit. Shenzhou 6 followed two years later ending the first phase of the Project 921. Missions are launched on the Long March 2F rocket from the Jiuquan Satellite Launch Center. 
The China Crewed Space Engineering Office provides engineering and administrative support for the crewed Shenzhou missions.[32]

Space laboratory

The second phase of the Project 921 started with Shenzhou 7, China's first spacewalk mission. Then, two crewed missions were planned to the first Chinese space laboratory. The PRC initially designed the Shenzhou spacecraft with docking technologies imported from Russia, therefore compatible with the International Space Station (ISS). On September 29, 2011, China launched Tiangong 1. This target module is intended to be the first step to testing the technology required for a planned space station.
On October 31, 2011, a Long March 2F rocket lifted the Shenzhou 8 uncrewed spacecraft which docked twice with the Tiangong 1 module. The Shenzhou 9 craft took off on 16 June 2012 with a crew of 3. It successfully docked with the Tiangong-1 laboratory on 18 June 2012, at 06:07 UTC, marking China's first manned spacecraft docking.[33] Another manned mission, Shenzhou 10, launched on 11 June 2013 . The Tiangong 1 target module is then expected to be deorbited.[34]

A second space lab, Tiangong 2, is scheduled for launch in 2016.[35] This will be larger than Tiangong 1 at some 20 tons and 14.4 metres length and will be visited by future Shenzhou missions, though exact details are not yet available.

Space station


Shenzhou 5 re-entry module

A larger basic permanent space station (基本型空间站) would be the third and last phase of Project 921. This will be a modular design with an eventual weight of around 60 tons, to be completed sometime before 2020. The first section, designated Tiangong 3, is scheduled for launch after Tiangong 2.[36] Tiangong 3 will weigh 22 tons and be 18.1 metres long. Additional modules will be connected over several missions to build the space station.

This could also be the beginning of China's crewed international cooperation, the existence of which was officially disclosed for the first time after the launch of Shenzhou 7.[37]

The Chinese space station is scheduled to be completed in 2020, just as the International Space Station is scheduled to retire.[38]

Proposed lunar exploration

In February 2004, the PRC formally started the implementation phase of its uncrewed Moon exploration project. According to Sun Laiyan, administrator of the China National Space Administration, the project will involve three phases: orbiting the Moon; landing; and returning samples. The first phase planned to spend 1.4 billion renminbi (approx. US$170 million) to orbit a satellite around the Moon before 2007, which is ongoing. Phase two involves sending a lander before 2010. Phase three involves collecting lunar soil samples before 2020.
On November 27, 2005, the deputy commander of the crewed spaceflight program announced that the PRC planned to complete a space station and a crewed mission to the Moon by 2020, assuming funding was approved by the government.

On December 14, 2005, it was reported "an effort to launch lunar orbiting satellites will be supplanted in 2007 by a program aimed at accomplishing an uncrewed lunar landing. A program to return uncrewed space vehicles from the moon will begin in 2012 and last for five years, until the crewed program gets underway" in 2017, with a crewed Moon landing some time after that.[39]

Nonetheless, the decision to develop a totally new moon rocket in the 1962 Soviet UR-700M-class (Project Aelita) able to launch a 500 ton payload in LTO[dubious – discuss] and a more modest 50 tons LTO payload LV has been discussed in a 2006 conference by academician Zhang Guitian (张贵田), a liquid propellant rocket engine specialist, who developed the CZ-2 and CZ-4A rockets engines.[40][41][42]

On June 22, 2006, Long Lehao, deputy chief architect of the lunar probe project, laid out a schedule for China's lunar exploration. He set 2024 as the date of China's first moonwalk.[43]

In September 2010, it was announced that the country is planning to carry out explorations in deep space by sending a man to the Moon by 2025. China also hopes to bring a moon rock sample back to Earth in 2017, and subsequently build an observatory on the Moon's surface. Ye Peijian, Commander in Chief of the Chang’e programme and an academic at the Chinese Academy of Sciences, added that China has the "full capacity to accomplish Mars exploration by 2013."[44][45]

On December 14, 2013 [46] China's Chang'e 3 became the first object to soft-land on the Moon since Luna 24 in 1976.[47]

As indicated by the official Chinese Lunar Exploration Program insignia, denoted by a calligraphic Moon ideogram (月) in the shape of a nascent lunar crescent, with two human footsteps at its center, the ultimate objective of the program is to establish a permanent human presence on the Earth's natural satellite.

Yang Liwei declared at the 16th Human in Space Symposium of International Academy of Astronautics (IAA) in Beijing, on May 22, 2007 that building a lunar base was a crucial step to realize a flight to Mars and farther planets.[48]

According to practice, since the whole project is only at a very early preparatory research phase, no official crewed Moon program has been announced yet by the authorities. But its existence is nonetheless revealed by regular intentional leaks in the media.[49] A typical example is the Lunar Roving Vehicle (月球车) that was shown on a Chinese TV channel (东方卫视) during the 2008 May Day celebrations.

Mission to Mars and beyond

Sun Laiyan, administrator of the China National Space Administration, said on July 20, 2006 that China would start deep space exploration focusing on Mars over the next five years, during the Eleventh Five-Year Plan (2006–2010) Program period.[50]
The first uncrewed Mars exploration program could take place between 2015–2033, followed by a crewed phase in 2040-2060.[51] The Mars 500 study of 2011 prepared for this manned mission.

Moreover, in order to make crewed flight in deep space toward Mars safer, a space weather forecast system will be completed by 2017 with the Kuafu[52] mission satellites placed at the Lagrangian Point L1.[53]

The Chief designer of the Shenzhou spacecraft has stated in 2006 in an interview that:

Goals

The PRC's space program has several goals. The China National Space Administration policy white paper lists its short term goals as:[55]
  • Build a long term earth observation system
  • Set up an independent satellite telecommunications network
  • Establish an independent satellite navigation and positioning system
  • Provide commercial launch services
  • Set up a remote sensing system
  • Study space science such as microgravity, space materials, life sciences, and astronomy
  • Plan for exploration of the moon
Among their stated longer term goals are:
  • Improve their standing in the world of space science
  • Establish a crewed space station
  • Crewed missions to the moon
  • Establish a crewed lunar base
  • Unmanned mission to Mars

List of projects

Satellites and science

Satellite launch center

  • Hainan Spaceport Fourth and southernmost space center, will be upgraded to suit the new CZ-5 Heavy ELV and crewed lunar missions

Launch vehicles

  • LM-5D
  • Air-Launched SLV able to place a 50 kilogram plus payload to 500 km SSO[63]
  • Kaituozhe-2
  • Kaituozhe-1 (开拓者一号), KT-1A (开拓者一号甲), KT-2 (开拓者二号), KT-2A (开拓者一二甲) New class of all-solid orbital launch vehicles
  • Kaituozhe-1B (开拓者一号乙) with addition of two solid boosters[64]
  • CZ-1D based on a CZ-1 but with a new N2O4/UDMH second stage
  • CZ-2E(A) Intended for launch of Chinese space station modules. Payload capacity up to 14 tons in LEO and 9000 (kN) liftoff thrust developed by 12 rocket engines, with enlarged fairing of 5.20 m in diameter and length of 12.39 m to accommodate large spacecraft[65]
  • CZ-2F/G Modified CZ-2F without escape tower, specially used for launching unmanned missions such as Shenzhou cargo and space laboratory module with payload capacity up to 11.2 tons in LEO[66]
  • CZ-3B(A) More powerful Long March rockets using larger-size liquid propellant strap-on motors, with payload capacity up to 13 tons in LEO
  • CZ-3C Launch vehicle combining CZ-3B core with two boosters from CZ-2E
  • Chang Zheng 5 Second generation ELV with more efficient and nontoxic propellents (25 tonnes in LEO)
  • Chang Zheng 6 or Small Launch Vehicle, with short launch preparation period, low cost and high reliability, to meet the launch need of small satellites up to 500 kg to 700 km SSO, first flight for 2010; with Fan Ruixiang (范瑞祥) as Chief designer of the project[67][68][69]
  • Chang Zheng 7 used for Phase 4 of Lunar Exploration Program (嫦娥-4 工程), that is permanent base (月面驻留) expected for 2024; Second generation Heavy ELV for lunar and deep space trajectory injection (70 tonnes in LEO), capable of supporting a Soviet L1/L3-like lunar landing mission[70]
  • Project 921-3 Space Shuttle—second generation manned spacecraft Shenlong Spaceplane
  • HTS Maglev Launch Assist Space Shuttle New second generation manned, reusable spacecraft
  • Long March 9
  • Long March 11

Space exploration


Insignia of the Chinese Lunar Exploration Program (CLEP)
  • Project 921-1—Shenzhou spacecraft
  • Project 921-11--X-11 spacecraft
  • Project 921-2—Chinese Space Laboratory and Chinese Permanent Space Station, short term and then permanent occupation[71][72]
  • Shenzhou Cargo (货运飞船)— unmanned version of the Shenzhou spacecraft to resupply the Chinese Permanent Space Station and return cargo back to Earth
  • Tianzhou - unmanned cargo vessel to resupply the Chinese Permanent Space Station based on the design of Tiangong-1, not meant for reentry, but usable for garbage disposal.[73][74]
  • Chinese Lunar Exploration Program
    • First phase lunar program (嫦娥-1 工程)—launched in 2007 with CZ-3A: two unmanned lunar orbital probes
    • Second phase lunar program (嫦娥-2 工程)—launched in 2012 with CZ-5/E:first Moon landing of a couple of rovers
    • Third phase lunar program (嫦娥-3 工程)—to be launched in 2017 with CZ-5/E: automated Moon landing and return sample
    • Fourth phase lunar program (嫦娥-4 工程)—to be launched in 2024 with CZ-7: manned mission and permanent bases (月面驻留)[75]
  • Chinese exploration of Mars—The Yinghuo-1 orbiter was launched in November 2011 in the joint Fobos-Grunt mission with Russia, but it failed to leave Earth orbit and underwent destructive re-entry on 15 January 2012. Further planned missions include rover landers and possible crewed missions in the far future. Anatoly Perminov, head of the Russian Space Agency has revealed in September 2006 in RIA Novosti that China was about to sign a contract by the end of 2006 to participate in a Russian project to bring soil back to Earth from Phobos, one of Mars two moons.[76] The mission will also collect samples on Mars, according to Xinhua.[77] Five decades after the first American mission to Mars, the People's Daily announced that China was finally "technically ready to explore Mars".[78]
  • Deep space exploration—spacefaring through the entire Solar system

Research

The Center for Space Science and Applied Research (CSSAR), was founded in 1987 by merging the former Institute of Space Physics (i.e. the Institute of Applied Geophysics founded in 1958) and the Center for Space Science and Technology (founded in 1978). The research fields of CSSAR mainly cover 1. Space Engineering Technology; 2. Space Weather Exploration, Research, and Forecasting; 3. Microwave Remote Sensing and Information Technology.
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Steel



From Wikipedia, the free encyclopedia


The steel cable of a colliery winding tower

Steels are alloys of iron and carbon, widely used in construction and other applications because of their high tensile strengths and low costs. Carbon, other elements, and inclusions within iron act as hardening agents that prevent the movement of dislocations that otherwise occur in the crystal lattices of iron atoms.

The carbon in typical steel alloys may contribute up to 2.1% of its weight. Varying the amount of alloying elements, their formation in the steel either as solute elements, or as precipitated phases, retards the movement of those dislocations that make iron so ductile and weak, and thus controls qualities such as the hardness, ductility, and tensile strength of the resulting steel. Steel's strength compared to pure iron is only possible at the expense of ductility, of which iron has an excess.

Although steel had been produced in bloomery furnaces for thousands of years, steel's use expanded extensively after more efficient production methods were devised in the 17th century for blister steel and then crucible steel. With the invention of the Bessemer process in the mid-19th century, a new era of mass-produced steel began. This was followed by Siemens-Martin process and then Gilchrist-Thomas process that refined the quality of steel. With their introductions, mild steel replaced wrought iron.

Further refinements in the process, such as basic oxygen steelmaking (BOS), largely replaced earlier methods by further lowering the cost of production and increasing the quality of the metal. Today, steel is one of the most common materials in the world, with more than 1.3 billion tons produced annually. It is a major component in buildings, infrastructure, tools, ships, automobiles, machines, appliances, and weapons. Modern steel is generally identified by various grades defined by assorted standards organizations.

Definitions and related materials

The carbon content of steel is between 0.002% and 2.1% by weight for plain iron-carbon alloys. These values vary depending on alloying elements such as manganese, chromium, nickel, iron, tungsten, carbon and so on. Basically, steel is an iron-carbon alloy that does not undergo eutectic reaction. In contrast, cast iron undergoes eutectic reaction. Too little carbon content leaves (pure) iron quite soft, ductile, and weak. Carbon contents higher than those of steel make an alloy commonly called pig iron that is brittle and not malleable. Alloy steel is steel to which alloying elements have been intentionally added to modify the characteristics of steel. Common alloying elements include: manganese, nickel, chromium, molybdenum, boron, titanium, vanadium, and niobium.[1] Additional elements may be present in steel: manganese, phosphorus, sulfur, silicon, and traces of oxygen, nitrogen, and aluminium.

Alloys with a higher than 2.1% carbon content, depending on other element content and possibly on processing, are known as cast iron. Cast iron is not malleable even when hot, but it can be formed by casting as it has a lower melting point than steel and good castability properties.[1] Steel is also distinguishable from wrought iron (now largely obsolete), which may contain a small amount of carbon but large amounts of slag. Note that the percentages of carbon and other elements quoted are on a weight basis.

Material properties


Iron-carbon phase diagram, showing the conditions necessary to form different phases

Iron is commonly found in the Earth's crust in the form of an ore, usually an iron oxide, such as magnetite, hematite etc. Iron is extracted from iron ore by removing the oxygen through combination with a preferred chemical partner such as carbon that is lost to the atmosphere as carbon dioxide. This process, known as smelting, was first applied to metals with lower melting points, such as tin, which melts at approximately 250 °C (482 °F) and copper, which melts at approximately 1,100 °C (2,010 °F). In comparison, cast iron melts at approximately 1,375 °C (2,507 °F).[2] Small quantities of iron were smelted in ancient times, in the solid state, by heating the ore buried in a charcoal fire and welding the metal together with a hammer, squeezing out the impurities. With care, the carbon content could be controlled by moving it around in the fire.

All of these temperatures could be reached with ancient methods that have been used since the Bronze Age. Since the oxidation rate of iron increases rapidly beyond 800 °C (1,470 °F), it is important that smelting take place in a low-oxygen environment. Unlike copper and tin, liquid or solid iron dissolves carbon quite readily. Smelting results in an alloy (pig iron) that contains too much carbon to be called steel.[2] The excess carbon and other impurities are removed in a subsequent step.

Other materials are often added to the iron/carbon mixture to produce steel with desired properties. Nickel and manganese in steel add to its tensile strength and make the austenite form of the iron-carbon solution more stable, chromium increases hardness and melting temperature, and vanadium also increases hardness while making it less prone to metal fatigue.[3]

To inhibit corrosion, at least 11% chromium is added to steel so that a hard oxide forms on the metal surface; this is known as stainless steel. Tungsten interferes with the formation of cementite, allowing martensite to preferentially form at slower quench rates, resulting in high speed steel. On the other hand, sulfur, nitrogen, and phosphorus make steel more brittle, so these commonly found elements must be removed from the steel melt during processing.[3]

The density of steel varies based on the alloying constituents but usually ranges between 7,750 and 8,050 kg/m3 (484 and 503 lb/cu ft), or 7.75 and 8.05 g/cm3 (4.48 and 4.65 oz/cu in).[4]

Even in a narrow range of concentrations of mixtures of carbon and iron that make a steel, a number of different metallurgical structures, with very different properties can form. Understanding such properties is essential to making quality steel. At room temperature, the most stable form of pure iron is the body-centered cubic (BCC) structure called ferrite or α-iron. It is a fairly soft metal that can dissolve only a small concentration of carbon, no more than 0.005% at 0 °C (32 °F) and 0.021 wt% at 723 °C (1,333 °F). At 910°C pure iron transforms into a face-centered cubic (FCC) structure, called austenite or γ-iron. The FCC structure of austenite can dissolve considerably more carbon, as much as 2.1%[5] (38 times that of ferrite) carbon at 1,148 °C (2,098 °F), which reflects the upper carbon content of steel, beyond which is cast iron.[6]

When steels with less than 0.8% carbon (known as a hypoeutectoid steel), are cooled, the austenitic phase (FCC) of the mixture attempts to revert to the ferrite phase (BCC). The carbon no longer fits within the FCC structure, resulting in an excess of carbon. One way for carbon to leave the austenite is for it to precipitate out of solution as cementite, leaving behind a surrounding phase of BCC iron that is low enough in carbon to take the form of ferrite, resulting in a ferrite matrix with cementite inclusions. Cementite is a hard and brittle intermetallic compound with the chemical formula of Fe3C. At the eutectoid, 0.8% carbon, the cooled structure takes the form of pearlite, named for its resemblance to mother of pearl. On a larger scale, it appears as a lamellar structure of ferrite and cementite. For steels that have more than 0.8% carbon, the cooled structure takes the form of pearlite and cementite.[7]

Perhaps the most important polymorphic form of steel is martensite, a metastable phase that is significantly stronger than other steel phases. When the steel is in an austenitic phase and then quenched rapidly, it forms into martensite, as the atoms "freeze" in place when the cell structure changes from FCC to a distorted form of BCC as the atoms do not have time enough to migrate and form the cementite compound. Depending on the carbon content, the martensitic phase takes different forms. Below approximately 0.2% carbon, it takes an α ferrite BCC crystal form, but at higher carbon content it takes a body-centered tetragonal (BCT) structure. There is no thermal activation energy for the transformation from austenite to martensite. Moreover, there is no compositional change so the atoms generally retain their same neighbors.[8]

Martensite has a lower density than does austenite, so that the transformation between them results in a change of volume. In this case, expansion occurs. Internal stresses from this expansion generally take the form of compression on the crystals of martensite and tension on the remaining ferrite, with a fair amount of shear on both constituents. If quenching is done improperly, the internal stresses can cause a part to shatter as it cools. At the very least, they cause internal work hardening and other microscopic imperfections. It is common for quench cracks to form when steel is water quenched, although they may not always be visible.[9]

Heat treatment

There are many types of heat treating processes available to steel. The most common are annealing, quenching, and tempering. Annealing is the process of heating the steel to a sufficiently high temperature to soften it. This process goes through three phases: recovery, recrystallization, and grain growth. The temperature required to anneal steel depends on the type of annealing to be achieved and the constituents of the alloy.[10]
Quenching and tempering first involves heating the steel to the austenite phase then quenching it in water or oil. This rapid cooling results in a hard but brittle martensitic structure.[8] The steel is then tempered, which is just a specialized type of annealing, to reduce brittleness. In this application the annealing (tempering) process transforms some of the martensite into cementite, or spheroidite and hence reduces the internal stresses and defects. The result is a more ductile and fracture-resistant steel.[11]

Steel production

Iron ore pellets for the production of steel

When iron is smelted from its ore, it contains more carbon than is desirable. To become steel, it must be reprocessed to reduce the carbon to the correct amount, at which point other elements can be added. In modern facilities, this liquid is then continuously cast into long slabs or cast into ingots. Approximately 96% of steel is continuously cast, while only 4% is produced as ingots.[12]

The ingots are then heated in a soaking pit and hot rolled into slabs, blooms, or billets. Slabs are hot or cold rolled into sheet metal or plates. Billets are hot or cold rolled into bars, rods, and wire. Blooms are hot or cold rolled into structural steel, such as I-beams and rails. In modern steel mills these processes often occur in one assembly line, with ore coming in and finished steel coming out.[13] Sometimes after a steel's final rolling it is heat treated for strength, however this is relatively rare.[14]

History of steelmaking

Bloomery smelting during the Middle Ages

Ancient steel

Steel was known in antiquity, and may have been produced by managing bloomeries and crucibles, or iron-smelting facilities, in which they contained carbon.[15][16][17]

The earliest known production of steel are pieces of ironware excavated from an archaeological site in Anatolia (Kaman-Kalehoyuk) and are nearly 4,000 years old, dating from 1800 BC.[18][19] Horace identifies steel weapons like the falcata in the Iberian Peninsula, while Noric steel was used by the Roman military.[20]

South Indian and Mediterranean sources including Alexander the Great (3rd c. BC) recount the presentation and export to the Greeks of 100 talents of South Indian steel. The reputation of Seric iron of South India (wootz steel) amongst the Greeks, Romans, Egyptians, East Africans, Chinese and the Middle East grew considerably, a high quality high carbon iron and steel imported from Tamil people of the dynasty Chera.[21] Metal production sites in Sri Lanka utilized these novel techniques using unique wind furnaces driven by the monsoon winds, capable of producing high-carbon steel, as well as imported artefacts of ancient iron and steel from Kodumanal. Large-scale Wootz steel production in Tamilakam using crucibles they invented and carbon sources such as the plant Avāram occurred by the sixth century BC, the pioneering precursor to modern steel production and metallurgy.[22][23]

Steel was produced in large quantities in Sparta around 650 BC.[24][25]

The Chinese of the Warring States period (403–221 BC) had quench-hardened steel,[26] while Chinese of the Han dynasty (202 BC – 220 AD) created steel by melting together wrought iron with cast iron, gaining an ultimate product of a carbon-intermediate steel by the 1st century AD.[27][28] The Haya people of East Africa invented a type of furnace they used to make carbon steel at 1,802 °C (3,276 °F) nearly 2,000 years ago. East African steel has been suggested by Richard Hooker to date back to 1400 BC.[29][30]

Wootz steel and Damascus steel

Evidence of the earliest production of high carbon steel in the Indian Subcontinent are found in Kodumanal in Tamil Nadu area, Golconda in Andhra Pradesh area and Karnataka, and in Samanalawewa areas of Sri Lanka.[31] This came to be known as Wootz steel, produced in South India by about sixth century BC and exported globally.[32][33] The steel technology existed prior to 326 BC in the region as they are mentioned in literature of Sangam Tamil, Arabic and Latin as the finest steel in the world exported to the Romans, Egyptian, Chinese and Arabs worlds at that time - what they called Seric Iron.[34] A 200 BC Tamil trade guild in Tissamaharama, in the South East of Sri Lanka, brought with them some of the oldest iron and steel artefacts and production processes to the island from the classical period.[35][36][37][38] The Chinese and locals in Anuradhapura, Sri Lanka had also adopted the production methods of creating Wootz steel from the Chera Dynasty Tamils of South India by the 5th century AD.[39][40] In Sri Lanka, this early steel-making method employed a unique wind furnace, driven by the monsoon winds, capable of producing high-carbon steel.[41][42] Since the technology was acquired from the Tamilians from South India, the origin of steel technology in India can be conservatively estimated at 400–500 BC.[43][32]
Wootz, also known as Damascus steel, is famous for its durability and ability to hold an edge. It was originally created from a number of different materials including various trace elements, apparently ultimately from the writings of Zosimos of Panopolis. However, the steel was an old technology in India when King Porus presented a steel sword to the Emperor Alexander in 326 BC.[citation needed] It was essentially a complicated alloy with iron as its main component. Recent studies have suggested that carbon nanotubes were included in its structure, which might explain some of its legendary qualities, though given the technology of that time, such qualities were produced by chance rather than by design.[44] Natural wind was used where the soil containing iron was heated by the use of wood. The ancient Sinhalese managed to extract a ton of steel for every 2 tons of soil,[41] a remarkable feat at the time. One such furnace was found in Samanalawewa and archaeologists were able to produce steel as the ancients did.[41][45]

Crucible steel, formed by slowly heating and cooling pure iron and carbon (typically in the form of charcoal) in a crucible, was produced in Merv by the 9th to 10th century AD.[33] In the 11th century, there is evidence of the production of steel in Song China using two techniques: a "berganesque" method that produced inferior, inhomogeneous, steel, and a precursor to the modern Bessemer process that used partial decarbonization via repeated forging under a cold blast.[46]

Modern steelmaking


A Bessemer converter in Sheffield, England

Since the 17th century the first step in European steel production has been the smelting of iron ore into pig iron in a blast furnace.[47] Originally employing charcoal, modern methods use coke, which has proven more economical.[48][49][50]

Processes starting from bar iron

In these processes pig iron was "fined" in a finery forge to produce bar iron (wrought iron), which was then used in steel-making.[47]
The production of steel by the cementation process was described in a treatise published in Prague in 1574 and was in use in Nuremberg from 1601. A similar process for case hardening armour and files was described in a book published in Naples in 1589. The process was introduced to England in about 1614 and used to produce such steel by Sir Basil Brooke at Coalbrookdale during the 1610s.[51]

The raw material for this process were bars of wrought iron. During the 17th century it was realized that the best steel came from oregrounds iron of a region north of Stockholm, Sweden. This was still the usual raw material source in the 19th century, almost as long as the process was used.[52][53]

Crucible steel is steel that has been melted in a crucible rather than having been forged, with the result that it is more homogeneous. Most previous furnaces could not reach high enough temperatures to melt the steel. The early modern crucible steel industry resulted from the invention of Benjamin Huntsman in the 1740s. Blister steel (made as above) was melted in a crucible or in a furnace, and cast (usually) into ingots.[53][54]

Processes starting from pig iron


A Siemens-Martin steel oven from the Brandenburg Museum of Industry.

White-hot steel pouring out of an electric arc furnace.

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.[55] 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.[56] 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.

Another 19th-century steelmaking process was the Siemens-Martin process, which complemented the Bessemer process.[53] It consisted of co-melting bar iron (or steel scrap) with pig iron.

These methods of steel production were rendered obsolete by the Linz-Donawitz process of basic oxygen steelmaking (BOS), developed in the 1950s, and other oxygen steel making methods. Basic oxygen steelmaking is superior to previous steelmaking methods because the oxygen pumped into the furnace limits impurities that previously had entered from the air used.[57] Today, electric arc furnaces (EAF) are a common method of reprocessing scrap metal to create new steel. They can also be used for converting pig iron to steel, but they use a lot of electrical energy (about 440 kWh per metric ton), and are thus generally only economical when there is a plentiful supply of cheap electricity.[58]

Steel industry


Steel production by country in 2007

A steel plant in the United Kingdom.

It is common today to talk about "the iron and steel industry" as if it were a single entity, but historically they were separate products. The steel industry is often considered an indicator of economic progress, because of the critical role played by steel in infrastructural and overall economic development.[59]

In 1980, there were more than 500,000 U.S. steelworkers. By 2000, the number of steelworkers fell to 224,000.[60]

The economic boom in China and India has caused a massive increase in the demand for steel in recent years. Between 2000 and 2005, world steel demand increased by 6%. Since 2000, several Indian[61] and Chinese steel firms have risen to prominence like Tata Steel (which bought Corus Group in 2007), Shanghai Baosteel Group Corporation and Shagang Group. ArcelorMittal is however the world's largest steel producer.

In 2005, the British Geological Survey stated China was the top steel producer with about one-third of the world share; Japan, Russia, and the US followed respectively.[62]

In 2008, steel began trading as a commodity on the London Metal Exchange. At the end of 2008, the steel industry faced a sharp downturn that led to many cut-backs.[63]

The world steel industry peaked in 2007. That year, ThyssenKrupp spent $12 billion to build the two most modern mills in the world, in Calvert, Alabama and Sepetiba, Rio de Janeiro, Brazil. The worldwide Great Recession starting in 2008, however, sharply lowered demand and new construction, and so prices fell. ThyssenKrupp lost $11 billion on its two new plants, which sold steel below the cost of production. Finally in 2013, ThyssenKrupp offered the plants for sale at under $4 billion.[64]

Recycling

Steel is one of the world's most-recycled materials, with a recycling rate of over 60% globally;[65] in the United States alone, over 82,000,000 metric tons (81,000,000 long tons) was recycled in the year 2008, for an overall recycling rate of 83%.[66]

Contemporary steel


Bethlehem Steel in Bethlehem, Pennsylvania was one of the world's largest manufacturers of steel before its 2003 closure and later conversion into a casino.

Carbon steels

Modern steels are made with varying combinations of alloy metals to fulfill many purposes.[3] Carbon steel, composed simply of iron and carbon, accounts for 90% of steel production.[1] Low alloy steel is alloyed with other elements, usually molybdenum, manganese, chromium, or nickel, in amounts of up to 10% by weight to improve the hardenability of thick sections.[1] High strength low alloy steel has small additions (usually < 2% by weight) of other elements, typically 1.5% manganese, to provide additional strength for a modest price increase.[67]

Recent Corporate Average Fuel Economy (CAFE) regulations have given rise to a new variety of steel known as Advanced High Strength Steel (AHSS). This material is both strong and ductile so that vehicle structures can maintain their current safety levels while using less material. There are several commercially available grades of AHSS, such as dual-phase steel, which is heat treated to contain both a ferritic and martensitic microstructure to produce a formable, high strength steel.[68] Transformation Induced Plasticity (TRIP) steel involves special alloying and heat treatments to stabilize amounts of austenite at room temperature in normally austenite-free low-alloy ferritic steels. By applying strain, the austenite undergoes a phase transition to martensite without the addition of heat.[69] Twinning Induced Plasticity (TWIP) steel uses a specific type of strain to increase the effectiveness of work hardening on the alloy.[70]

Carbon Steels are often galvanized, through hot-dip or electroplating in zinc for protection against rust.[71]

Alloy steels

Stainless steels contain a minimum of 11% chromium, often combined with nickel, to resist corrosion. Some stainless steels, such as the ferritic stainless steels are magnetic, while others, such as the austenitic, are nonmagnetic.[72] Corrosion-resistant steels are abbreviated as CRES.

Some more modern steels include tool steels, which are alloyed with large amounts of tungsten and cobalt or other elements to maximize solution hardening. This also allows the use of precipitation hardening and improves the alloy's temperature resistance.[1] Tool steel is generally used in axes, drills, and other devices that need a sharp, long-lasting cutting edge. Other special-purpose alloys include weathering steels such as Cor-ten, which weather by acquiring a stable, rusted surface, and so can be used un-painted.[73] Maraging steel is alloyed with nickel and other elements, but unlike most steel contains little carbon 0.01%). This creates a very strong but still malleable steel.[74]

Eglin steel uses a combination of over a dozen different elements in varying amounts to create a relatively low-cost steel for use in bunker buster weapons. Hadfield steel (after Sir Robert Hadfield) or manganese steel contains 12–14% manganese which when abraded strain hardens to form an incredibly hard skin which resists wearing. Examples include tank tracks, bulldozer blade edges and cutting blades on the jaws of life.[75]

In 2015 a breakthrough in creating a strong light aluminium steel alloy which might be suitable in applications such as aircraft was announced by researchers at Pohang University of Science and Technology. Adding small amounts of nickel was found to result in precipitation as nano particles of brittle B2 intermetallic compounds which had previously resulted in weakness. The result was a cheap strong light steel alloy which is slated for trial production at industrial scale by POSCO, a Korean steelmaker.[76][77]

Standards

Most of the more commonly used steel alloys are categorized into various grades by standards organizations. For example, the Society of Automotive Engineers has a series of grades defining many types of steel.[78] The American Society for Testing and Materials has a separate set of standards, which define alloys such as A36 steel, the most commonly used structural steel in the United States.[79]

Uses


A roll of steel wool

Iron and steel are used widely in the construction of roads, railways, other infrastructure, appliances, and buildings. Most large modern structures, such as stadiums and skyscrapers, bridges, and airports, are supported by a steel skeleton. Even those with a concrete structure employ steel for reinforcing. In addition, it sees widespread use in major appliances and cars. Despite growth in usage of aluminium, it is still the main material for car bodies. Steel is used in a variety of other construction materials, such as bolts, nails, and screws and other household products and cooking utensils. [80]

Other common applications include shipbuilding, pipelines, mining, offshore construction, aerospace, white goods (e.g. washing machines), heavy equipment such as bulldozers, office furniture, steel wool, tools, and armour in the form of personal vests or vehicle armour (better known as rolled homogeneous armour in this role).

Historical


A carbon steel knife

Before the introduction of the Bessemer process and other modern production techniques, steel was expensive and was only used where no cheaper alternative existed, particularly for the cutting edge of knives, razors, swords, and other items where a hard, sharp edge was needed. It was also used for springs, including those used in clocks and watches.[53]

With the advent of speedier and thriftier production methods, steel has become easier to obtain and much cheaper. It has replaced wrought iron for a multitude of purposes. However, the availability of plastics in the latter part of the 20th century allowed these materials to replace steel in some applications due to their lower fabrication cost and weight.[81] Carbon fiber is replacing steel in some cost insensitive applications such as aircraft, sports equipment and high end automobiles.

Long steel


A steel bridge

A steel pylon suspending overhead power lines

Flat carbon steel[edit]

Stainless steel


A stainless steel gravy boat

Low-background steel

Steel manufactured after World War II became contaminated with radionuclides due to nuclear weapons testing. Low-background steel, steel manufactured prior to 1945, is used for certain radiation-sensitive applications such as Geiger counters and radiation shielding.

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