Boron carbide

Boron carbide (chemical formula approximately B4C) is an extremely hard boroncarbon ceramic, and covalent material used in tank armor, bulletproof vests, engine sabotage powders,[1] as well as numerous industrial applications. With a Vickers Hardness of >30 GPa, it is one of the hardest known materials, behind cubic boron nitride and diamond.[2]

Boron carbide
Boron carbide
Names
IUPAC name
Boron carbide
Other names
Tetrabor
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.031.907
Properties
B4C
Molar mass 55.255 g/mol
Appearance dark gray or black powder, odorless
Density 2.52 g/cm3, solid.
Melting point 2,763 °C (5,005 °F; 3,036 K)
Boiling point 3,500 °C (6,330 °F; 3,770 K)
insoluble
Structure
Rhombohedral
Hazards
Safety data sheet External MSDS
Related compounds
Related compounds
Boron nitride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

History

Boron carbide was discovered in 19th century as a by-product of reactions involving metal borides, but its chemical formula was unknown. It was not until the 1930s that the chemical composition was estimated as B4C.[3] Controversy remained as to whether or not the material had this exact 4:1 stoichiometry, as, in practice the material is always slightly carbon-deficient with regard to this formula, and X-ray crystallography shows that its structure is highly complex, with a mixture of C-B-C chains and B12 icosahedra.

These features argued against a very simple exact B4C empirical formula.[4] Because of the B12 structural unit, the chemical formula of "ideal" boron carbide is often written not as B4C, but as B12C3, and the carbon deficiency of boron carbide described in terms of a combination of the B12C3 and B12CBC units.

Applications

The ability of boron carbide to absorb neutrons without forming long-lived radionuclides makes it attractive as an absorbent for neutron radiation arising in nuclear power plants and from anti-personnel neutron bombs. Nuclear applications of boron carbide include shielding, control rod and shut down pellets. Within control rods, boron carbide is often powdered, to increase its surface area.[5]

Crystal structure

Borfig11a
Unit cell of B4C. The green sphere and icosahedra consist of boron atoms, and black spheres are carbon atoms.[6]
Borfig12a
Fragment of the B4C crystal structure.

Boron carbide has a complex crystal structure typical of icosahedron-based borides. There, B12 icosahedra form a rhombohedral lattice unit (space group: R3m (No. 166), lattice constants: a = 0.56 nm and c = 1.212 nm) surrounding a C-B-C chain that resides at the center of the unit cell, and both carbon atoms bridge the neighboring three icosahedra. This structure is layered: the B12 icosahedra and bridging carbons form a network plane that spreads parallel to the c-plane and stacks along the c-axis. The lattice has two basic structure units – the B12 icosahedron and the B6 octahedron. Because of the small size of the B6 octahedra, they cannot interconnect. Instead, they bond to the B12 icosahedra in the neighboring layer, and this decreases bonding strength in the c-plane.[6]

Because of the B12 structural unit, the chemical formula of "ideal" boron carbide is often written not as B4C, but as B12C3, and the carbon deficiency of boron carbide described in terms of a combination of the B12C3 and B12C2 units.[4][7] Some studies indicate the possibility of incorporation of one or more carbon atoms into the boron icosahedra, giving rise to formulas such as (B11C)CBC = B4C at the carbon-heavy end of the stoichiometry, but formulas such as B12(CBB) = B14C at the boron-rich end. "Boron carbide" is thus not a single compound, but a family of compounds of different compositions. A common intermediate, which approximates a commonly found ratio of elements, is B12(CBC) = B6.5C.[8] Quantum mechanical calculations have demonstrated that configurational disorder between boron and carbon atoms on the different positions in the crystal determines several of the materials properties - in particular, the crystal symmetry of the B4C composition[9] and the non-metallic electrical character of the B13C2 composition.[10]

Properties

Boron carbide is known as a robust material having high hardness, high cross section for absorption of neutrons (i.e. good shielding properties against neutrons), stability to ionizing radiation and most chemicals.[5] Its Vickers hardness (38 GPa), Elastic Modulus (460 GPa)[11] and fracture toughness (3.5 MPa·m1/2) approach the corresponding values for diamond (1150 GPa and 5.3 MPa·m1/2).[12]

As of 2015, boron carbide is the third hardest substance known, after diamond and cubic boron nitride, earning it the nickname "black diamond".[13][14]

Semiconductor properties

Boron carbide is a semiconductor, with electronic properties dominated by hopping-type transport.[8] The energy band gap depends on composition as well as the degree of order. The band gap is estimated at 2.09 eV, with multiple mid-bandgap states which complicate the photoluminescence spectrum.[8] The material is typically p-type.

Preparation

Boron carbide was first synthesized by Henri Moissan in 1899,[7] by reduction of boron trioxide either with carbon or magnesium in presence of carbon in an electric arc furnace. In the case of carbon, the reaction occurs at temperatures above the melting point of B4C and is accompanied by liberation of large amount of carbon monoxide:[15]

2 B2O3 + 7 C → B4C + 6 CO

If magnesium is used, the reaction can be carried out in a graphite crucible, and the magnesium byproducts are removed by treatment with acid.[16]

Uses

Bodyarmor
Boron carbide is used for inner plates of ballistic vests

See also

References

  1. ^ Gray, Theodore (2012-04-03). The Elements: A Visual Exploration of Every Known Atom in the Universe. Black Dog & Leventhal Publishers. ISBN 9781579128951. Retrieved 6 May 2014.
  2. ^ "Rutgers working on body armor". Asbury Park Press. August 11, 2012. Retrieved 2012-08-12. ... boron carbide is the third-hardest material on earth.
  3. ^ Ridgway, Ramond R "Boron Carbide", European Patent CA339873 (A), publication date: 1934-03-06
  4. ^ a b Balakrishnarajan, Musiri M.; Pancharatna, Pattath D.; Hoffmann, Roald (2007). "Structure and bonding in boron carbide: The invincibility of imperfections". New J. Chem. 31 (4): 473. doi:10.1039/b618493f.
  5. ^ a b Weimer, p. 330
  6. ^ a b Zhang FX, Xu FF, Mori T, Liu QL, Sato A, Tanaka T (2001). "Crystal structure of new rare-earth boron-rich solids: REB28.5C4". J. Alloys Compd. 329: 168–172. doi:10.1016/S0925-8388(01)01581-X.
  7. ^ a b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 149. ISBN 0-08-037941-9.
  8. ^ a b c Domnich, Vladislav; Reynaud, Sara; Haber, Richard A.; Chhowalla, Manish (2011). "Boron Carbide: Structure, Properties, and Stability under Stress" (PDF). J. Am. Ceram. Soc. 94 (11): 3605–3628. doi:10.1111/j.1551-2916.2011.04865.x. Retrieved 23 July 2015.
  9. ^ Ektarawong, A.; Simak, S. I.; Hultman, L.; Birch, J.; Alling, B. (2014). "First-principles study of configurational disorder in B4C using a superatom-special quasirandom structure method". Phys. Rev. B. 90 (2): 024204. arXiv:1508.07786. Bibcode:2014PhRvB..90b4204E. doi:10.1103/PhysRevB.90.024204.
  10. ^ Ektarawong, A.; Simak, S. I.; Hultman, L.; Birch, J.; Alling, B. (2015). "Configurational order-disorder induced metal-nonmetal transition in B13C2 studied with first-principles superatom-special quasirandom structure method". Phys. Rev. B. 92: 014202. arXiv:1508.07848. Bibcode:2015PhRvB..92a4202E. doi:10.1103/PhysRevB.92.014202.
  11. ^ Sairam, K.; Sonber, J.K.; Murthy, T.S.R.Ch.; Subramanian, C.; Hubli, R.C.; Suri, A.K. (2012). "Development of B4C-HfB2 composites by reaction hot pressing". Int.J. Ref. Met. Hard Mater. 35: 32–40. doi:10.1016/j.ijrmhm.2012.03.004.
  12. ^ Solozhenko, V. L.; Kurakevych, Oleksandr O.; Le Godec, Yann; Mezouar, Mohamed; Mezouar, Mohamed (2009). "Ultimate Metastable Solubility of Boron in Diamond: Synthesis of Superhard Diamondlike BC5" (PDF). Phys. Rev. Lett. 102 (1): 015506. Bibcode:2009PhRvL.102a5506S. doi:10.1103/PhysRevLett.102.015506. PMID 19257210.
  13. ^ "Boron Carbide". Precision Ceramics. Archived from the original on 2015-06-20. Retrieved 2015-06-20.
  14. ^ A. Sokhansanj; A.M. Hadian (2012). "Purification of Attrition Milled Nano-size Boron Carbide Powder". 2nd International Conference on Ultrafine Grained & Nanostructured Materials (UFGNSM). International Journal of Modern Physics: Conference Series. 5: 94–101. Bibcode:2012IJMPS...5...94S. doi:10.1142/S2010194512001894.
  15. ^ Weimer, p. 131
  16. ^ Patnaik, Pradyot (2002). Handbook of Inorganic Chemicals. McGraw-Hill. ISBN 0-07-049439-8

Bibliography

External links

Armstrong's mixture

Armstrong's mixture is a highly sensitive primary explosive. Its primary ingredients are red phosphorus and strong oxidizer, such as potassium chlorate and potassium perchlorate. Sulfur is used to substitute for some or all of the phosphorus to slightly decrease sensitivity and lower costs; calcium carbonate may also be present in small proportions. Commercially, Armstrong's mixture is used in milligram quantities on the paper caps in toy cap guns and in party poppers. An improvised version can be made with match-heads, ground up into a fine powder, and mixed with another fine powder, this time made of the striker strip found on the side of match boxes.

It has also been considered a suitable mixture for the primer used in guns after boron carbide has been added, and was used during the Second World War.

B4C

B4C may refer to:

the molecular formula of boron carbide

Chevrolet Camaro B4C, an automobileThe Chevrolet Camaro B4C was a police model option produced from 1991-1992, 592 were produced.

Barrett Firearms Manufacturing

Barrett Firearms Manufacturing is an American manufacturer of firearms and ammunition located in the unincorporated town of Christiana, Tennessee. It was founded in 1982 by Ronnie G. Barrett for the single purpose of building semi-automatic rifles chambered for the powerful .50 BMG (12.7×99mm NATO) ammunition, originally developed for and used in M2 Browning machine guns. Barrett began his work in the early 1980s and the first working rifles were available in 1982, hence the designation M82. Barrett designed every single part of the weapon personally and then went on to market the weapon and mass-produce it out of his own pocket. He continued to develop his rifle through the 1980s, and developed the improved M82A1 rifle by 1986.

Boriding

Boriding, also called boronizing, is the process by which boron is introduced to a metal or alloy. It is a type of surface hardening. In this process boron atoms are diffused into the surface of a metal component. The resulting surface contains metal borides, such as iron borides, nickel borides, and cobalt borides, As pure materials, these borides have extremely high hardness and wear resistance. Their favorable properties are manifested even when they are a small fraction of the bulk solid. Boronized metal parts are extremely wear resistant and will often last two to five times longer than components treated with conventional heat treatments such as hardening, carburizing, nitriding, nitrocarburizing or induction hardening. Most borided steel surfaces will have iron boride layer hardnesses ranging from 1200-1600 HV. Nickel-based superalloys such as Inconel and Hastalloys will typically have nickel boride layer hardnesses of 1700-2300 HV.

Boron

Boron is a chemical element with symbol B and atomic number 5. Produced entirely by cosmic ray spallation and supernovae and not by stellar nucleosynthesis, it is a low-abundance element in the Solar system and in the Earth's crust. Boron is concentrated on Earth by the water-solubility of its more common naturally occurring compounds, the borate minerals. These are mined industrially as evaporites, such as borax and kernite. The largest known boron deposits are in Turkey, the largest producer of boron minerals.

Elemental boron is a metalloid that is found in small amounts in meteoroids but chemically uncombined boron is not otherwise found naturally on Earth. Industrially, very pure boron is produced with difficulty because of refractory contamination by carbon or other elements. Several allotropes of boron exist: amorphous boron is a brown powder; crystalline boron is silvery to black, extremely hard (about 9.5 on the Mohs scale), and a poor electrical conductor at room temperature. The primary use of elemental boron is as boron filaments with applications similar to carbon fibers in some high-strength materials.

Boron is primarily used in chemical compounds. About half of all boron consumed globally is an additive in fiberglass for insulation and structural materials. The next leading use is in polymers and ceramics in high-strength, lightweight structural and refractory materials. Borosilicate glass is desired for its greater strength and thermal shock resistance than ordinary soda lime glass. Boron as sodium perborate is used as a bleach. A small amount of boron is used as a dopant in semiconductors, and reagent intermediates in the synthesis of organic fine chemicals. A few boron-containing organic pharmaceuticals are used or are in study. Natural boron is composed of two stable isotopes, one of which (boron-10) has a number of uses as a neutron-capturing agent.

In biology, borates have low toxicity in mammals (similar to table salt), but are more toxic to arthropods and are used as insecticides. Boric acid is mildly antimicrobial, and several natural boron-containing organic antibiotics are known. Boron is an essential plant nutrient and boron compounds such as borax and boric acid are used as fertilizers in agriculture, although it's only required in small amounts, with excess being toxic. Boron compounds play a strengthening role in the cell walls of all plants. There is no consensus on whether boron is an essential nutrient for mammals, including humans, although there is some evidence it supports bone health.

Boron carbides

Boron carbides are boron–carbon compounds.

Bull (armored personnel carrier)

The Ceradyne BULL is an armored personnel carrier with a v-shaped hull designed in a combined effort between Ceradyne, Ideal Innovations Inc (I-3), and Oshkosh Corporation in response to the MRAP II competition. The name Ceradyne Bull is a misnomer; "The Bull" is actually a trade-mark of Ideal Innovations, Inc. (I-3).

The MRAP II competition was announced in 2007 when it became clear that explosively formed penetrator (EFP) type of roadside bomb attacks were increasing in Iraq and the current generation MRAP vehicles could not stop all of them without add-on armor kits. In 2005 Ideal Innovations' President, Robert Kocher, had worked with the U.S. Army Research Laboratory to find an EFP solution, patented it, and then found Ceradyne as a partner in 2006 to produce an armored cab out of it. The U.S. Army's Joint Manufacturing and Technology Center at the Rock Island Arsenal provides the EFP-stopping outer layers of the armor. Kocher had previously been involved in the 1991-93 development of the up-armored Humvee and was part of the team that developed the boron carbide armor now used in Interceptor body armor vests that Ceradyne produces.In 2007 Oshkosh was selected to provide its Medium Tactical Vehicle Replacement (MTVR) chassis, with their TAK-4 independent suspension system and Commercial Off the Shelf (COTS) computer hardware, for the vehicles I3 and Ceradyne intended to enter in the MRAP II competition. Two prototypes were made within 50 days. Team Bull members at Ceradyne, together with almost three dozen employees from I3 and Oshkosh, immediately began working round-the-clock shifts. Engineers rarely left the site, with team members instead grabbing a couple of hours of sleep outside in their cars for refreshment. A six-person version and a ten-person version were delivered to the Aberdeen Proving Grounds for testing.

The EFP simulations were so successful that the military quickly adapted the armor into the Frag kit 6 armor upgrade kits for the Humvee and other MRAP vehicles. Senators Carl Levin (D-Mich) and Joseph Biden (D-Del) took up Bull’s cause. Levin wrote a letter to Defense Secretary Gates promoting the vehicle and Biden asked, during a Senate Foreign Relations Committee event, why the military hadn’t ordered the vehicle. After testing the initial two prototypes, the military awarded the partnership a $18.1 million contract to produce six more Bull vehicles of the six person variant by the first quarter of 2008 for further evaluation. While eight vehicles entered the MRAP II competition, The Bull was one of only two vehicles to receive a contract from it. The other was an uparmored BAE Caiman.

It has been reported that the complete vehicle weighs around 40,000 lbs and costs about $500,000 (three times more than a Humvee). The Bull prototypes had two side hatches at the front (meeting MRAP II specs), used mainly for emergency exits. This design gave more side protection than larger traditional doors. The Bull had no gun ports, but these could be added in the final production model.

CROCUS

CROCUS is a research reactor at École Polytechnique Fédérale de Lausanne, a research institute and university in Lausanne, Switzerland.

The uranium nuclear reactor core is in an aluminum container that measures 130 centimetres (51 in) across with 1.2-centimetre (0.47 in)-thick walls. The aluminum vessel is filled with demineralized light water to both serve as a neutron moderator and neutron reflector.Power output is controlled either by adjusting the water level in the reactor—with a ±0.1-millimetre (0.0039 in) level of control, or with the adjustment of two boron carbide (B4C) control rods—with a ±1-millimetre (0.039 in) level of finesse. The reactor has six separate safety systems: two cadmium shields and four storage tanks, any of which can shut down the reaction in less than second.CROCUS has a license to produce 100 watts (0.13 hp) or a neutron flux of ~2.5 × 109 cm-2s-1 at the core's center.

Cadmium tungstate

Cadmium tungstate (CdWO4 or CWO), the cadmium salt of tungstic acid, is a dense, chemically inert solid which is used as a scintillation crystal to detect gamma rays. It has density of 7.9 g/cm3 and melting point of 1325 °C. It is toxic if inhaled or swallowed. Its crystals are transparent, colorless, with slight yellow tint. It is odorless. Its CAS number is 7790-85-4. It is not hygroscopic.

The crystal is transparent and emits light when it is hit by gamma rays and x-rays, making it useful as a detector of ionizing radiation. Its peak scintillation wavelength is 480 nm (with emission range between 380-660 nm), and efficiency of 13000 photons/MeV. It has a relatively high light yield, its light output is about 40% of NaI(Tl), but the time of scintillation is quite long (12−15 μs). It is often used in computed tomography. Combining the scintillator crystal with externally applied piece of boron carbide allows construction of compact detectors of gamma rays and neutron radiation.

Cadmium tungstate was used as a replacement of calcium tungstate in some fluoroscopes since 1940's. Very high radiopurity allows use of this scintillator as a detector of rare nuclear processes (double beta decay, other rare alpha and beta decays) in low-background applications. For example, the first indication of the natural alpha activity of tungsten (alpha decay of 180W) had been found in 2003 with CWO detectors. Due to different time of light emission for different types of ionizing particles, the alpha-beta discrimination technique has been developed for CWO scintillators.Cadmium tungstate films can be deposited by sol-gel technology. Cadmium tungstate nanorods can be synthesized by a hydrothermal process.Similar materials are calcium tungstate (scheelite) and zinc tungstate.

It is toxic, as are all cadmium compounds.

Carbide

In chemistry, a carbide is a compound composed of carbon and a less electronegative element. Carbides can be generally classified by the chemical bonds type as follows: (i) salt-like, (ii) covalent compounds, (iii) interstitial compounds, and (iv) "intermediate" transition metal carbides. Examples include calcium carbide (CaC2), silicon carbide (SiC), tungsten carbide (WC; often called, simply, carbide when referring to machine tooling), and cementite (Fe3C), each used in key industrial applications. The naming of ionic carbides is not systematic.

Ceramic armor

Ceramic armor is armor used by armored vehicles and in personal armor for its attenuative properties. Ceramics provide projectile resistance through their high hardness and compressive strength and are often used in applications where weight is a limiting factor due to their lightweight nature relative to metals commonly used in armors. Most commonly alumina, boron carbide, silicon carbide, and titanium diboride ceramics are used in armor but other ceramics are used.

Chobham armour

Chobham armour is the informal name of a composite armour developed in the 1960s at the British tank research centre on Chobham Common, Surrey. The name has since become the common generic term for composite ceramic vehicle armour. Other names informally given to Chobham Armour include "Burlington" and "Dorchester." "Special armour" is a broader informal term referring to any armour arrangement comprising "sandwich" reactive plates, including Chobham Armour.

Although the construction details of the Chobham armour remain a secret, it has been described as being composed of ceramic tiles encased within a metal framework and bonded to a backing plate and several elastic layers. Due to the extreme hardness of the ceramics used, they offer superior resistance against shaped charges such as high explosive anti-tank (HEAT) rounds and they shatter kinetic energy penetrators.

The armour was first tested in the context of the development of a British prototype vehicle, the FV4211, and first applied on the preseries of the American M1. Only the M1 Abrams, Challenger 1, and Challenger 2 tanks have been disclosed as being thus armoured. The framework holding the ceramics is usually produced in large blocks, giving these tanks, and especially their turrets, a distinctive angled appearance.

Control rod

Control rods are used in nuclear reactors to control the fission rate of uranium and plutonium. They are composed of chemical elements such as boron, silver, indium and cadmium that are capable of absorbing many neutrons without themselves fissioning. Because these elements have different capture cross sections for neutrons of varying energies, the composition of the control rods must be designed for the reactor's neutron spectrum. Boiling water reactors (BWR), pressurized water reactors (PWR) and heavy water reactors (HWR) operate with thermal neutrons, while breeder reactors operate with fast neutrons.

Niobium diboride

Niobium diboride (NbB2) is a highly covalent refractory ceramic material with a hexagonal crystal structure. NbB2 is an ultra high temperature ceramic (UHTC) with a melting point of 3050 °C. This along with its relatively low density of ~6.97 g/cm3 and good high temperature strength makes it a candidate for high temperature aerospace applications such as hypersonic flight or rocket propulsion systems. It is an unusual ceramic, having relatively high thermal and electrical conductivities (Electrical resistivity of 25.7 µΩ⋅cm, CTE of 7.7⋅10−6 °C−1), properties it shares with isostructural titanium diboride, zirconium diboride, hafnium diboride and tantalum diboride.NbB2 parts are usually hot pressed or spark plasma sintering (mechanical pressure applied to the heated powder) and then machined to shape. Sintering of NbB2 is hindered by the material's covalent nature and presence of surface oxides which increase grain coarsening before densification during sintering. Pressureless sintering of NbB2 is possible with sintering additives such as boron carbide and carbon which react with the surface oxides to increase the driving force for sintering but mechanical properties are degraded compared to hot pressed NbB2.

Nuclear salt-water rocket

A nuclear salt-water rocket (NSWR) is a theoretical type of nuclear thermal rocket which was designed by Robert Zubrin. In place of traditional chemical propellant, such as that in a chemical rocket, the rocket would be fueled by salts of plutonium or 20 percent enriched uranium. The solution would be contained in a bundle of pipes coated in boron carbide (for its properties of neutron absorption). Through a combination of the coating and space between the pipes, the contents would not reach critical mass until the solution is pumped into a reaction chamber, thus reaching a critical mass, and being expelled through a nozzle to generate thrust.

Silicon boride

Silicon borides (also known as boron silicides) are lightweight ceramic compounds formed between silicon and boron. Several stoichiometric silicon boride compounds, SiBn, have been reported: silicon triboride, SiB3, silicon tetraboride, SiB4, silicon hexaboride, SiB6, as well as SiBn (n = 14, 15, 40, etc.). The n = 3 and n = 6 phases were reported as being co-produced together as a mixture for the first time by Henri Moissan and Alfred Stock in 1900 by briefly heating silicon and boron in a clay vessel. The tetraboride was first reported as being synthesized directly from the elements in 1960 by three independent groups: Carl Cline and Donald Sands; Ervin Colton; and Cyrill Brosset and Bengt Magnusson. It has been proposed that the triboride is a silicon-rich version of the tetraboride. Hence, the stoichiometry of either compound could be expressed as SiB4 - x where x = 0 or 1. All the silicon borides are black, crystalline materials of similar density: 2.52 and 2.47 g cm−3, respectively, for the n = 3(4) and 6 compounds. On the Mohs scale of mineral hardness, SiB4 - x and SiB6 are intermediate between diamond (10) and ruby (9). The silicon borides may be grown from boron-saturated silicon in either the solid or liquid state.

The SiB6 crystal structure contains interconnected icosahedra (polyhedra with 20 faces), icosihexahedra (polyhedra with 26 faces), as well as isolated silicon and boron atoms. Due to the size mismatch between the silicon and boron atoms, silicon can be substituted for boron in the B12 icosahedra up to a limiting stoichiometry corresponding to SiB2.89. The structure of the tetraboride SiB4 is isomorphous to that of boron carbide (B4C), B6P, and B6O. It is metastable with respect to the hexaboride. Nevertheless, it can be prepared due to the relative ease of crystal nucleation and growth.Both SiB4 - x and SiB6 become superficially oxidized when heated in air or oxygen and each is attacked by boiling sulfuric acid and by fluorine, chlorine, and bromine at high temperatures. The silicon borides are electrically conducting. The hexaboride has a low coefficient of thermal expansion and a high nuclear cross section for thermal neutrons.

The tetraboride was used in the black coating of some of the space shuttle heat shield tiles.

Small Arms Protective Insert

The Small Arms Protective Insert (SAPI) is a ceramic trauma plate used by the United States Armed Forces. It was first used in the Interceptor body armor, a ballistic vest. It is now also used in the Improved Outer Tactical Vest as well as the Modular Tactical Vest, in addition to commercially available "plate carriers". The Kevlar Interceptor vest itself is designed to stop projectiles up to and including 9×19mm Parabellum submachine gun rounds, in addition to fragmentation. To protect against higher-velocity rifle rounds, SAPI plates are needed.

Strontium hexaboride

Strontium boride (SrB6) is an inorganic compound. At room temperature, it appears as a crystalline black powder. Closer examination reveals slightly translucent dark red crystals capable of scratching quartz. It is very stable and has a high melting point and density. Although not thought to be toxic, it is an irritant to the skin, eyes, and respiratory tract.

Zirconium diboride

Zirconium diboride (ZrB2) is a highly covalent refractory ceramic material with a hexagonal crystal structure. ZrB2 is an ultra high temperature ceramic (UHTC) with a melting point of 3246 °C. This along with its relatively low density of ~6.09 g/cm3 (measured density may be higher due to hafnium impurities) and good high temperature strength makes it a candidate for high temperature aerospace applications such as hypersonic flight or rocket propulsion systems. It is an unusual ceramic, having relatively high thermal and electrical conductivities, properties it shares with isostructural titanium diboride and hafnium diboride.

ZrB2 parts are usually hot pressed (pressure applied to the heated powder) and then machined to shape. Sintering of ZrB2 is hindered by the material's covalent nature and presence of surface oxides which increase grain coarsening before densification during sintering. Pressureless sintering of ZrB2 is possible with sintering additives such as boron carbide and carbon which react with the surface oxides to increase the driving force for sintering but mechanical properties are degraded compared to hot pressed ZrB2.Additions of ~30 vol% SiC to ZrB2 is often added to ZrB2 to improve oxidation resistance through SiC creating a protective oxide layer - similar to aluminum's protective alumina layer.ZrB2 is used in ultra-high temperature ceramic matrix composites (UHTCMCs).Carbon fiber reinforced zirconium diboride composites show high toughness while silicon carbide fiber reinforced zirconium diboride composites are brittle and show a catastrophic failure.

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