Hafnium nitrides

Hafnium nitride s high, emissivity in the visible spectmm at high temperature has led to a proposed use (52) as a coating on incandescent light filaments to improve visible light output. 

Most hafnium compounds have been of slight commercial interest aside from intermediates in the production of hafnium metal. However, hafnium oxide, hafnium carbide, and hafnium nitride are quite refractory and have received considerable study as the most refractory compounds of the Group 4 (IVB) elements. Physical properties of some of the hafnium compounds are shown in Table 4. 

Hafnium nitride (HfN) is a refractory which is resistant to chemical attack. It is produced by CVD mostly on an experimental basis. Its properties and characteristics are summarized in Table 10.4. 

Hafnium nitride (HfN) has good oxidation resistance and is developed as a cutting tool material (see Ch. 10).P1... 

Hafnium carbide and hafnium nitride whiskers from HfCl4, CH4 or N2, and H2 in the presence of a nickel catalyst at 1000-1450°C.P l... 

Hafnium metal, analysis of, 13 87 Hafnium nitride, 13 89—90, 93 Hafnium oxide, 13 89, 93—94 reduction of, 73 84 Hafnium sulfides, 73 94 Hafnium tetrabromide, 73 93 Hafnium tetrachloride, 73 92 26 631 vapor reduction of, 73 84-85 Hafnium tetrafluoride, 73 90, 91 Hafnium tetrahydridoborate, 73 90 Hagen-Poiseuille expression/law, 27 726, 729 Hagen-Poiseuille flow, in microfluidics, 26 961... 

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. 

In finely divided form, hafnium is pyrophoric, igniting in air spontaneously. However, bulk metal reacts slowly in oxygen or air above 400°C. The rate of oxidation increases with temperature. The product is hafnium dioxide, Hf02. It combines with nitrogen, carbon, boron, sulfur and silicon at very high temperatures to form hafnium nitride HfN, hafnium boride HfB, hafnium sulfide HfSi2, respectively. Nitride formation occurs at 900°C. 

Fix, R. Gordon, R. G. and Hoffman, D. M., Chemical vapor deposition of titanium, zirconium, and hafnium nitride thin films. Chem. Mater. 3 (1991) 1138-1148. 

Zirconium and hafnium nitrides dissolve in cold 6 M HF but are stable in other acids except when heated (equation 4). 

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