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Tantalum Diboride
Tantalum borides are compounds of tantalum and boron most remarkable for their extreme hardness. Properties The Vickers hardness test, Vickers hardness of TaB and TaB2 films and crystals is ~30 GPa. Those materials are stable to oxidation below 700 °C and to acid corrosion. TaB2 has the same hexagonal structure as most diborides (AlB2, MgB2, etc.). The mentioned borides have the following space groups: TaB (orthorhombic, Thallium(I) iodide-type, Cmcm), Ta5B6 (Cmmm), Ta3B4 (Immm), TaB2 (Hexagonal crystal system, hexagonal, aluminum diboride-type, P6/mmm). Preparation Single crystals of TaB, Ta5B6, Ta3B4 or TaB2 (about 1 cm diameter, 6 cm length) can be produced by the Zone melting, floating zone method. Tantalum boride films can be deposited from a gas mixture of TaCl5-BCl3-H2-Ar in the temperature range 540–800 °C. TaB2 (single-phase) is deposited at a source gas flow ratio (BCl3/TaCl5) of six and a temperature above 600 °C. TaB (single-phase) is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
TlI Structure
Tlia ( ka, თლია) is a village in the Java District of South Ossetia or Shida Kartli, Georgia (country), Georgia. The village is located in the Vaneli Community on the right bank of Tlidoni river, at an altitude of 1,800 m. Distance to the municipality center Java (town), Java is 23 km.''Georgian Soviet Encyclopedia'', v. IV, p. 686, Tbilisi, 1979. Notable people * Lado Ketskhoveli (1877–1903) - writer and revolutionary Notes References Populated places in Dzau District {{SouthOssetia-geo-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tantalum
Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as ''tantalium'', it is named after Tantalus, a villain in Greek mythology. Tantalum is a very hard, ductile, lustrous, blue-gray transition metal that is highly corrosion-resistant. It is part of the refractory metals group, which are widely used as components of strong high-melting-point alloys. It is a group 5 element, along with vanadium and niobium, and it always occurs in geologic sources together with the chemically similar niobium, mainly in the mineral groups tantalite, columbite and coltan. The chemical inertness and very high melting point of tantalum make it valuable for laboratory and industrial equipment such as reaction vessels and vacuum furnaces. It is used in tantalum capacitors for electronic equipment such as computers. Tantalum is considered a technology-critical element by the European Commission. History Tantalum was discovered in Sweden in 1802 by Anders Ekeberg, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Boron
Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the ''boron group'' it has three valence electrons for forming covalent bonds, resulting in many compounds such as boric acid, the mineral borax, sodium borate, and the ultra-hard crystals of boron carbide and boron nitride. Boron is synthesized entirely by cosmic ray spallation and supernovae and not by stellar nucleosynthesis, so it is a low-abundance element in the Solar System and in the Crust (geology), Earth's crust. It constitutes about 0.001 percent by weight of Earth's crust. It 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 deposits are in Turkey, the largest producer of boron minerals. Elemental b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hardness
In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard metals such as titanium and beryllium are harder than soft metals such as sodium and metallic tin, or wood and common plastics. Macroscopic hardness is generally characterized by strong intermolecular bonds, but the behavior of solid materials under force is complex; therefore, hardness can be measured in different ways, such as scratch hardness, indentation hardness, and rebound hardness. Hardness is dependent on ductility, elastic stiffness, plasticity, strain, strength, toughness, viscoelasticity, and viscosity. Common examples of hard matter are ceramics, concrete, certain metals, and superhard materials, which can be contrasted with soft matter. Measuring hardness There are three main types of hardness measurements: ''scratch' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vickers Hardness Test
The Vickers hardness test was developed in 1921 by Robert L. Smith and George E. Sandland at Vickers Ltd as an alternative to the Brinell method to measure the hardness of materials. The Vickers test is often easier to use than other hardness tests since the required calculations are independent of the size of the indenter, and the indenter can be used for all materials irrespective of hardness. The basic principle, as with all common measures of hardness, is to observe a material's ability to resist plastic deformation from a standard source. The Vickers test can be used for all metals and has one of the widest scales among hardness tests. The unit of hardness given by the test is known as the Vickers Pyramid Number (HV) or Diamond Pyramid Hardness (DPH). The hardness number can be converted into units of pascals, but should not be confused with pressure, which uses the same units. The hardness number is determined by the load over the surface area of the indentation and not t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Orthorhombic
In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base (''a'' by ''b'') and height (''c''), such that ''a'', ''b'', and ''c'' are distinct. All three bases intersect at 90° angles, so the three lattice vectors remain mutually orthogonal. Bravais lattices There are four orthorhombic Bravais lattices: primitive orthorhombic, base-centered orthorhombic, body-centered orthorhombic, and face-centered orthorhombic. For the base-centered orthorhombic lattice, the primitive cell has the shape of a right rhombic prism;See , row oC, column Primitive, where the cell parameters are given as a1 = a2, α = β = 90° it can be constructed because the two-dimensional centered rectangular base layer can also be described with primitive rhombic axes. Note that the length a of the primit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thallium(I) Iodide
Thallium(I) iodide is a chemical compound with the formula TlI. It is unusual in being one of the few water-insoluble metal iodides, along with AgI, CuI, SnI2, SnI4, PbI2 and HgI2. Chemistry TlI can be formed in aqueous solution by metathesis of any soluble thallium salt with iodide ion. It is also formed as a by-product in thallium-promoted iodination of phenols with thallium(I) acetate. Attempts to oxidise TlI to thallium(III) iodide fail, since oxidation produces thallium(I) triiodide, . Physical properties The room temperature form of TlI is yellow and has an orthorhombic structure which can be considered to be a distorted NaCl structure. The distorted structure is believed to be caused by favourable thallium-thallium interactions, the closest Tl-Tl distance is 383 pm. At 175 °C the yellow form transforms to a red CsCl form. This phase transition is accompanied by about two orders of magnitude jump in electrical conductivity. The CsI structure can be stabilized ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hexagonal Crystal System
In crystallography, the hexagonal crystal family is one of the six crystal families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the trigonal crystal system and the rhombohedral lattice system are not equivalent (see section crystal systems below). In particular, there are crystals that have trigonal symmetry but belong to the hexagonal lattice (such as α-quartz). The hexagonal crystal family consists of the 12 point groups such that at least one of their space groups has the hexagonal lattice as underlying lattice, and is the union of the hexagonal crystal system and the trigonal crystal system. There are 52 space groups associated with it, which are exactly those whose Bravais lattice is either hexagonal or rhombohedral. __TOC__ Lattice systems The hexagonal crystal family consists of two lattice systems: hexagonal and rhombohedral. Each lattice system consists of one Bravais l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aluminum Diboride
Aluminium diboride (AlB2) is a chemical compound made from the metal aluminium and the metalloid boron. It is one of two compounds of aluminium and boron, the other being AlB12, which are both commonly referred to as aluminium boride. Structurally the B atoms form graphite-like sheets with Al atoms between them, and this is very similar to the structure of magnesium diboride. Single crystals of AlB2 exhibit metallic conductivity along the axis parallel to the basal hexagonal plane. Aluminium boride is considered a hazardous substance as it reacts with acids and hydrogen gas to produce toxic gases. For example, it reacts with hydrochloric acid to release borane and aluminium chloride. The crystal structure of AlB2 is often used as a prototype structure to describe intermetallic compounds. There are a large number of structure types that fall within the AlB2 structural family. See also *Boride A boride is a compound between boron and a less electronegative element, for example ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zone Melting
Zone melting (or zone refining, or floating-zone method, or floating-zone technique) is a group of similar methods of purifying crystals, in which a narrow region of a crystal is melted, and this molten zone is moved along the crystal. The molten region melts impure solid at its forward edge and leaves a wake of purer material solidified behind it as it moves through the ingot. The impurities concentrate in the melt, and are moved to one end of the ingot. Zone refining was invented by John Desmond Bernal and further developed by William G. Pfann William G. Pfann (1966) ''Zone Melting'', 2nd edition, John Wiley & Sons in Bell Labs as a method to prepare high purity materials, mainly semiconductors, for manufacturing transistors. Its first commercial use was in germanium, refined to one atom of impurity per ten billion,”Zone melting”, entry in ''The World Book Encyclopedia'', Volume 21, W-X-Y-Z, 1973, page 501. but the process can be extended to virtually any solute–solvent ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tantalum Compounds
Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as ''tantalium'', it is named after Tantalus, a villain in Greek mythology. Tantalum is a very hard, ductile, lustrous, blue-gray transition metal that is highly corrosion-resistant. It is part of the refractory metals group, which are widely used as components of strong high-melting-point alloys. It is a group 5 element, along with vanadium and niobium, and it always occurs in geologic sources together with the chemically similar niobium, mainly in the mineral groups tantalite, columbite and coltan. The chemical inertness and very high melting point of tantalum make it valuable for laboratory and industrial equipment such as reaction vessels and vacuum furnaces. It is used in tantalum capacitors for electronic equipment such as computers. Tantalum is considered a technology-critical element by the European Commission. History Tantalum was discovered in Sweden in 1802 by Anders Ekebe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
