Refractory Qualifications

The term refractory, as stated in Ch. 1, means a material with a high melting point, arbitrarily fixed at 1800°C, and with a high degree of chemical stability. Only the interstitial and covalent carbides fulfill these two qualifications. The intermediate and salt-like carbides do not meet one or both of these conditions and cannot be considered as refractory, yet they are important materials and are briefly reviewed in Secs. 5.3 and 5.4. 

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As shown in subsequent chapters, most elements form carbides and nitrides and these can be divided into several types with different physico-chemical structures and characteristics. Of these, however, only the interstitial and covalent materials meet the refractory qualification. This includes the carbides and nitrides of the nine transition elements of Groups rv, V, and VI and the 4th, 5th, and 6th Periods, the carbides and nitrides of boron and silicon, and aluminum nitride. 

Handbook of Refractory Carbides and Nitrides 2.2 Refractory Qualifications... 

Job-site qualification of all refractory installers before the actual work is performed... 

Above 900°C, only refractory metals, such as tantalum and tungsten, retain sufficient mechanical strength to serve the required function. Cost and fabricability must be addressed if these lefiiactory metals are required. Experience under 900°C or greater temperature operating conditions is limited at best, and extensive qualification testing would be required to prove the code case. 

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