Aluminum nitride oxygen content

All precursors are amorphous up to calcination temperatures of around 600°C. At higher temperatures, in most cases powders with extremely small crystallite sizes of around 20-40 nm are formed (Fig. 7). A further increase in calcination temperature promotes crystal growth. With aluminum nitride, a white powder with a low oxygen and carbon content is obtained [97]. Other main group element precursors exhibit fairly different behaviors Mg and Ca precursors yield metal cyanamide [99]. Calcination of the transition element precursors (Fig. 8) results in the formation of nitrides, carbonitrides, or carbides. For the titanium-containing precursors, TiN/TiC solid solutions can be obtained [96] the quantity of carbon strongly depends on the calcination atmosphere applied (argon, 31 wt% ammonia, 5.1 wt%). 

Aluminum nitride is primarily noted for two very important properties a high thermal conductivity and a TCE closely matching that of silicon. There are several grades of aluminum nitride with different thermal conductivities available. The prime reason for the differences is the oxygen content of the material. It is important to note that even a thin surface layer of oxidation on a fraction of the particles can adversely affect the thermal conductivity. Only with a high degree of material and process control can AIN substrates be made consistent. 

Like silicon nitride, aluminum nitride is not easy to sinter. The high covalent bonding character (60% covalent-40% ionic (13)) of AIN limits the atomic mobility and prevents complete densi-fication. The condition of the starting materials—purity, particle size, particle-size distribution, oxygen content and specific surface area—influences the sinterability and properties of AIN ceramics (14). 

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