Hafnium melting point

The silvery, shiny, ductile metal is passivated with an oxide layer. Chemically very similar to and always found with zirconium (like chemical twins, with almost identical ionic radii) the two are difficult to separate. Used in control rods in nuclear reactors (e.g. in nuclear submarines), as it absorbs electrons more effectively than any other element. Also used in special lamps and flash devices. Alloys with niobium and tantalum are used in the construction of chemical plants. Hafnium dioxide is a better insulator than Si02. Hafnium carbide (HfC) has the highest melting point of all solid substances (3890 °C record ). 

H acid ORGCHEM H2NCioH4(OH)(S03H)2 a gray powder or crystalline substance that Is soluble in water, ether, and alcohol used as a dye Intermediate. ach as-od ) hafnium chem A metallic element, symbol Hf, atomic number 72, atomic weight 178.49 melting point 2000°C, boiling point above 5400°C. haf ne am )... 

Hafnium s melting point is 2,227°C, its boiling point varies from about 2,500°C to 5,000°C depending on its purity, and its density is 13.29 g/cm. The compound hafnium nitride (HfN) has the highest melting point (over 3,300°C) of any two-element compound. 

Hafnium carbide (HfC) This alloy has one of the highest melting points of any binary compound (3.890°C). It is extremely hard and resists corrosion while absorbing slow neutrons. Therefore, it is an ideal metal in the manufacture of control rods for nuclear reactors. 

Hafnium carbide has an extremely high melting point (3887 °C) and may find use as an alternative to tantalum carbide in the production of very hard metal components.28... 

Zirconium tetrachloride is a white crystalline solid with specific gravity 2.803.4 The solid sublimes under atmospheric pressure at 331° [log pBin. = — (26,000/4.57T) + 12.30] but melts at 437° under its own pressure, which is about 25 atm. at this temperature.18 The vapor density shows normal behavior up to 500°, at which point dissociation is suspected.16 Electron-diffraction results show tetrahedral symmetry with the Zr-Cl distance 2.33 A.17 Todd18 has recently determined the heat capacity of zirconium tetrachloride at low temperatures (extrapolated below —222°) and calculated the usual thermodynamic constants for the compound. The melting point of hafnium tetrachloride has been estimated as 432° under its own pressure, but the solid sublimes under atmospheric pressure at 317°.12 Both metal chlorides are extremely hygroscopic. They are easily soluble in water, although extensively hydrolyzed. All high-purity samples should be desiccated as well as possible. 

Garg and Ackermann ( ), using pyrometric techniques, measured the melting point of hafnium as 2501t3 K. Hultgren (2) reviewed nine studies available through 1955 and recommended T = 2500 20 K. We adopted = 2500 20 K. 

Hafnium is a bright, silvery-gray metal that is very ductile. Ductile means capable of being drawn into thin wires. Its melting point is about 3,900°F... 

Hafnium carbide has a melting point of 3890°C and exhibits extreme hardness and good electrical conductivity. It is used as an oxidation-resistant coating for composites and as a coating for superalloys [10]. The material is prepared by the CVD of a mixture of hafnium tetrachloride, methane and hydrogen [193, 194]. 

Hafnium is a lustrous, silvery, ductile metal with a high melting point. The mechanical properties of the metal are markedly affected by traces of impurities such as O, N, and C which have an embrittling effect on the metal, making it difficult to fabricate. The alloy tantalum hafnium carbide (Ta4HfCs), with a melting point of 4215 °C, is one of the most refractory substances known. 

Zirconium (Zr, CAS 7440-67-7, atomic number 40, atomic mass 91.22) has a melting point of 1852 °C and a boiling point of 4377 °C. It is a hard, lustrous, silvery metal, in contrast to fine zirconium powder, which is black. Zirconium belongs to Subgroup IV of the Periodic Table of the elements, between the elements titanium and hafnium - two metals with which it is often found in nature. Zirconium has oxidation states ranging from II to IV, of which the tetravalent is relatively stable and abundant (Venugopal and Luckey 1979). Zirconium is very corrosion-resistant and is unaffected by alkalis or acids (except for HF). 

DEA/HAY] Deardorff, D. K., Hayes, E. T., Melting point determination of hafnium, zirconium, and titanium, Trans. Metall. Soc. AIME, 206, (1956), 509-511. Cited on page 83. 

Uses. The metallic derivatives of the 1,3-diketones have been used in chemical separations that depend on their volatility and on differences in their solubilities. There is the further possibility of their use in such difficult separations as for zirconium and hafnium and the individual members of rare earths. Since many of these metallic derivatives decompose on strong heating, it is necessary to find a 1,3-diketone that will yield more stable metallic derivatives. Some progress has been made with fluorine-substituted 2,4-pentandiones. In general, the substitution of hydrogen by fluorine in organic molecules increases the stability and lowers the melting point. 

Ceramic borides, carbides and nitrides are characterized by high melting points, chemical inertness and relatively good oxidation resistance in extreme environments, such as conditions experienced during reentry. This family of ceramic materials has come to be known as Ultra High Temperature Ceramics (UHTCs). Some of the earliest work on UHTCs was conducted by the Air Force in the 1960 s and 1970 s. Since then, work has continued sporadically and has primarily been funded by NASA, the Navy and the Air Force. This article summarizes some of the early works, with a focus on hafnium diboride and zirconium diboride-based compositions. These works focused on identifying additives, such as SiC, to improve mechanical or thermal properties, and/or to improve oxidation resistance in extreme environments at temperatures greater than 2000°C. 

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