Nitride formation rate

There is a reaction between beryllium and nitrogen that starts at about 750°C and is appreciable at 850°C, beryllium nitride being formed". The reaction with oxygen is less sluggish and at 900°C in oxygen oxidation proceeds at about twice the rate of nitride formation. Thus when beryllium is heated in air, beryllium nitride forms only a small proportion of the total scale —about 0-75% after 1 h at 1 000°C. 

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 failure of NH3 or H2 to strongly influence the film deposition rate or refractive index suggests that the intramolecular nitride formation process is fast, relative to substitution by NH3, or hydrogenation. One significant drawback with the azido precursors is their stability. They are explosive with an equivalent force to TNT and conflagrate upon ignition ... 

The work hardening effect may also cause this tendency together with possibilities of surface oxide or carbide/nitride formation at a certain period of sliding, thus leading to an equilibrium condition of constant wear rate. However, no evidence is available to explain the exact reasons of these wear phenomena... 

There is very different behavior for the two-type adsorption states. For instance, H-type nitrogen has no effect on CO adsorption, while L-type nitrogen inhibits CO adsorption. L-type is more active for ammonia synthesis than H-type. If iron nitride was hydrogenated to ammonia, the formation rate of ammonia was also proportional to P, indicating that the H-tjrpe adsorption state of nitrogen is similar to that on iron nitride, i.e., one nitrogen atom is coordinated with several iron atoms,... 

The technical problem in die high teiiiperamre application of Si3N4 is that unlike the pure material, which can be prepared in small quantities by CVD for example, die commercial material is made by sintering the nitride with additives, such as MgO. The presence of the additive increases the rate of oxidation, when compared with the pure material, by an order of magnitude, probably due to the formation of liquid magnesia-silica solutions, which provide short-circuits for oxygen diffusion. These solutions are also known to reduce the mechanical strength at these temperatures. 

One of the simplest calorimetric methods is combustion bomb calorimetry . In essence this involves the direct reaction of a sample material and a gas, such as O or F, within a sealed container and the measurement of the heat which is produced by the reaction. As the heat involved can be very large, and the rate of reaction very fast, the reaction may be explosive, hence the term combustion bomb . The calorimeter must be calibrated so that heat absorbed by the calorimeter is well characterised and the heat necessary to initiate reaction taken into account. The technique has no constraints concerning adiabatic or isothermal conditions hut is severely limited if the amount of reactants are small and/or the heat evolved is small. It is also not particularly suitable for intermetallic compounds where combustion is not part of the process during its formation. Its main use is in materials thermochemistry where it has been used in the determination of enthalpies of formation of carbides, borides, nitrides, etc. 

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