Hafnium Nitride HfN

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 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. 

The cubic phases of zirconium- and hafnium nitride display properties quite similar to those of TiN. These compositions have been studied to some extent, however, the number of reports dealing with the CVD of ZrN and HfN is considerably lower than those describing the CVD of TiN. Zirconium and hafnium nitride can be prepared by the decomposition of the appropriate metal tetrakis(dialkylamide) compounds [155]. Zirconium and hafnium nitrides of the stoichiometry M3N4 also have been prepared by CVD. The compounds are formed when M(NEt2)4 is reacted with NH3 at 200-450°C [144]. The films thus produced are crystalline, yellow, transparent and insulating. It has been suggested that these phases are related to the MN phase by a rhombohedral distortion. 

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