Mulberry is a

uranium Uranium is a chemical element; it has chemical symbol, symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Ura ...

alloy An alloy is a mixture of chemical elements of which in most cases at least one is a metal, metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have prop ...

. It is used as a non-corroding or 'stainless' uranium alloy. It has been put forward as a structural material for the casings of the

physics package Nuclear weapons design are physical, chemical, and engineering arrangements that cause the physics package of a nuclear weapon to detonate. There are three existing basic design types: # Pure fission weapons are the simplest, least technically de ...

in nuclear weapons, including those of

North Korea North Korea, officially the Democratic People's Republic of Korea (DPRK), is a country in East Asia. It constitutes the northern half of the Korea, Korean Peninsula and borders China and Russia to the north at the Yalu River, Yalu (Amnok) an ...

. The composition is a ternary alloy, of 7.5%

niobium Niobium is a chemical element; it has chemical symbol, symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and Ductility, ductile transition metal. Pure niobium has a Mohs scale of mineral hardness, Mohs h ...

, 2.5%

zirconium Zirconium is a chemical element; it has Symbol (chemistry), symbol Zr and atomic number 40. First identified in 1789, isolated in impure form in 1824, and manufactured at scale by 1925, pure zirconium is a lustrous transition metal with a greyis ...

, 90% uranium. Mulberry was developed in the 1960s at UCRL.

Binary alloy Binary may refer to: Science and technology Mathematics * Binary number, a representation of numbers using only two values (0 and 1) for each digit * Binary function, a function that takes two arguments * Binary operation, a mathematical op ...

compositions were first studied to avoid the mechanical problems of pure uranium: corrosion, dimensional instability, inability to improve its mechanical properties by heat treatment. Uranium-molybdenum alloys were found susceptible to

stress-corrosion cracking Stress corrosion cracking (SCC) is the growth of crack formation in a corrosive environment. It can lead to unexpected and sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. SCC ...

, uranium-niobium alloys to be weak, and uranium-zirconium alloys to be brittle. Ternary alloys were next studied to try to avoid these drawbacks. Uranium-niobium-zirconium was found to be corrosion resistant and to permit

age hardening Precipitation hardening, also called age hardening or particle hardening, is a heat treatment technique used to increase the yield strength of malleable materials, including most structural alloys of aluminium, magnesium, nickel, titanium, and so ...

, which could increase its hardness from . Multiple crystal phases were observed, with a

critical temperature Critical or Critically may refer to: *Critical, or critical but stable, medical states **Critical, or intensive care medicine *Critical juncture, a discontinuous change studied in the social sciences. *Critical Software, a company specializing in ...

of 650°C. Above this the

body-centered cubic In crystallography, the cubic (or isometric) crystal system is a crystal system where the Crystal structure#Unit cell, unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals. There ...

γ phase Gamma (; uppercase , lowercase ; ) is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. In Ancient Greek, the letter gamma represented a voiced velar stop . In Modern Greek, this letter normally repr ...

was stable. Water quenching to room temperature produces a γ^s transition phase and with

aging Ageing (or aging in American English) is the process of becoming Old age, older until death. The term refers mainly to humans, many other animals, and fungi; whereas for example, bacteria, perennial plants and some simple animals are potentiall ...

this transforms to a

tetragonal In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the Cube (geometry), cube becomes a rectangular Pri ...

γ^o phase. Further aging produces a

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three Vector (geometric), vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in t ...

ɑ phase that is observed metallographically as a

Widmanstätten pattern Widmanstätten patterns (), also known as Thomson structures, are figures of long Phase (matter), phases of nickel–iron, found in the octahedrite shapes of iron meteorite crystals and some pallasites. Iron meteorites are very often formed ...

. The crystal structure of the alloy has been studied, particularly the γ phase. Uranium inclusions have been observed within the alloy although, unlike the binary alloys, niobium-rich inclusions were not. Early studies were uncertain as to whether these were inherent behaviours, or artifacts of their processing.

References

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Jane's Janes is a global open-source intelligence company specialising in military, national security, aerospace and transport topics, whose name derives from British author Fred T. Jane. History Jane's Information Group was founded in 1898 by Fred ...

, url=http://www.janes.com/images/assets/111/75111/North_Korea_bargains_with_nuclear_diplomacy.pdf , ref={{harvid, Jane's, North Korea , page=10 , access-date=2017-11-18 , archive-date=2017-10-25 , archive-url=https://web.archive.org/web/20171025180019/http://www.janes.com/images/assets/111/75111/North_Korea_bargains_with_nuclear_diplomacy.pdf , url-status=live {{Cite report , title=Mechanical Properties of Some Uranium Alloys , last1=Vandervoort , first=R.R. , last2=Peterson , first2=C.A.W. , id=UCRL-7771 , publisher= UCRL , year=1964 , doi=10.2172/4560786 , url=https://digital.library.unt.edu/ark:/67531/metadc1031428/ , access-date=2017-11-18 , archive-date=2017-12-01 , archive-url=https://web.archive.org/web/20171201043252/https://digital.library.unt.edu/ark:/67531/metadc1031428/ , url-status=live {{Cite report , last1=Vandervoort , first=R.R. , last2=Peterson , first2=C.A.W. , title=The Properties of a Metastable Gamma Phase Uranium-base Alloy: U-7.5 Nb 2.5 Zr , publisher= UCRL , id=UCRL-7869 , year=1964 , url=https://digital.library.unt.edu/ark:/67531/metadc867893/ , access-date=2017-11-18 , archive-date=2017-12-01 , archive-url=https://web.archive.org/web/20171201044123/https://digital.library.unt.edu/ark:/67531/metadc867893/ , url-status=live {{Cite report , title=Plutonium and Uranium as Engineering Materials , id=AEC Contract No. W-7405-eng-48 , first=Charles R. , last=Henry , date=February 26, 1965 , publisher= University of California, Lawrence Radiation Laboratory , url=https://www.osti.gov/scitech/servlets/purl/4546042 , pages=7–8 , doi=10.2172/4546042 , access-date=November 18, 2017 , archive-date=July 22, 2022 , archive-url=https://web.archive.org/web/20220722060023/https://www.osti.gov/biblio/4546042 , url-status=live , doi-access=free {{Cite journal , volume=82 , issue=1 , date=June 1979 , pages=184–192 , journal= J. Nucl. Mater. , title=Stability of the body-centered cubic gamma phase in the uranium-zirconium-niobium system , first=R.O. , last=Williams , doi=10.1016/0022-3115(79)90052-7 , bibcode=1979JNuM...82..184W {{Cite journal , journal=

Journal of Vacuum Science and Technology The ''Journal of Vacuum Science and Technology'' is a peer-reviewed scientific journal published in two parts, ''A'' and ''B'', by the American Institute of Physics on behalf of the American Vacuum Society. It was established in 1964 and the editor ...

, volume=8 , issue=1 , page=80 , doi=10.1116/1.1316361 , year=1971 , title=Oxidation of a Ternary Uranium Alloy , first=D.T. , last=Larson , bibcode=1971JVST....8...80L , doi-access=free {{Cite report , title=Flow behavior of mulberry uranium , last1=Hoge , first1=K.G , last2=Kuhn , first2=B.A. , last3=Reshenk , first3=V.L. , publisher=California Univ., Livermore (USA). Lawrence Livermore Lab , id=UCRL-51346 , year=1973 , volume=4 , issue=18 , url=http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/04/075/4075681.pdf?r=1 , journal= , access-date=2017-11-18 , archive-date=2017-12-01 , archive-url=https://web.archive.org/web/20171201034734/http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/04/075/4075681.pdf?r=1 , url-status=live {{Cite report , title=Evaluation of Uranium Alloys , first1=W. C. , last1=Erickson , first2=G. E. , last2=Jaynes , first3=D. J. , last3=Sandstrcsn , first4=R. , last4=Seegmiller , first5=J. M. , last5=Taub , date=September 1972 , publisher= LASL , url=http://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-05002 , pages=8–13 , journal= , access-date=2022-07-22 , archive-date=2017-12-01 , archive-url=https://web.archive.org/web/20171201030232/http://permalink.lanl.gov/object/tr?what=info%3Alanl-repo%2Flareport%2FLA-05002 , url-status=live {{Cite report , title=Recent Observations of Phase Transformations in a U-Nb-Zr Alloy , first1=R.A. , last1=Vandermeer , year=1973 , publisher=Metals and Ceramics Division,

Oak Ridge National Laboratory Oak Ridge National Laboratory (ORNL) is a federally funded research and development centers, federally funded research and development center in Oak Ridge, Tennessee, United States. Founded in 1943, the laboratory is sponsored by the United Sta ...

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Y-12 Plant The Y-12 National Security Complex is a United States Department of Energy National Nuclear Security Administration facility located in Oak Ridge, Tennessee, near the Oak Ridge National Laboratory. It was built as part of the Manhattan Project ...

, url=https://digital.library.unt.edu/ark:/67531/metadc1033722/m2/1/high_res_d/4749751.pdf , access-date=18 November 2017 , archive-date=24 July 2018 , archive-url=https://web.archive.org/web/20180724134105/https://digital.library.unt.edu/ark:/67531/metadc1033722/m2/1/high_res_d/4749751.pdf , url-status=live {{Cite book , title=Electron Microscopy and Structure of Materials , editor=Gareth Thomas , editor2=Richard M. Fulrath , editor3=Robert M. Fisher , publisher=University of California Press , year=1972 , isbn=0520021142 , pages=340–345 , url=https://books.google.com/books?id=1yiRUg7ooO8C&pg=PA340 , access-date=2020-09-30 , archive-date=2022-07-22 , archive-url=https://web.archive.org/web/20220722060022/https://books.google.com/books?id=1yiRUg7ooO8C&pg=PA340 , url-status=live {{Cite journal , journal= J. Less Common Met. , volume=27 , issue=1 , date=April 1972 , pages=9–15 , title=The elastic constants of uranium-7.5% niobium-2.5% zirconium as a function of pressure , first1=A.E. , last1=Abey , first2=E.D. , last2=Joslyn , doi=10.1016/0022-5088(72)90099-9 {{Cite journal , journal=Journal of Nuclear Materials , volume=449, Issues 1–3, June 2014, Pages 23-30 , title=Gamma-phase homogenization and texture in U–7.5Nb–2.5Zr (Mulberry) alloy , first1=Denise Adorno , last1=Lopes , first2=Thomaz Augusto Guisard , last2=Restivo , first3=Nelson Batista , last3=de Lima , first4=Angelo Fernando , last4=Padilha , issue=1–3 , pages=23–30 , doi=10.1016/j.jnucmat.2014.02.030 , bibcode=2014JNuM..449...23L, year=2014 Uranium Alloys