Molybdenum disulfide, decomposition

Tungsten disulfide, like molybdenum disulfide, exists both in the hexagonal and rhombohedral forms15). Thermal decomposition of WS3 is similar to that of MoS3. 

The specific reaction ( activation ) conditions for the conversion of catalyst precursors to unsupported catalysts have a direct effect on the catalytic activity and dispersion. The importance of reaction intermediates in decomposition of ammonium heptamolybdate and ammonium tetrathiomolybdate, and the sensitivity of these intermediates to reaction conditions, were studied in coal liquefaction systems. Recent results indicate that optimization of activation conditions facilitates the formation of a highly dispersed and active form of molybdenum disulfide for coal liquefaction. The use of the catalyst precursors ammonium heptamolybdate, ammonium tetrathiomolybdate, and molybdenum trisulflde for the conversion of coal to soluble products will be discussed. 

In a complementary series of experiments the cobalt/molybdenum disulfide samples were initially treated in hydrogen at S00°C for O.S hours. Under these conditions metal particles which had accumulated at edges were observed to catalyze the removal of material from these regions. When such specimens were subsequently heated in the presence of acetylene there was no evidence for the formation of carbon filaments. It was apparent that when specimens were treated in the hydrocarbon for extended periods at 6S0°C then many of the surface features were obscured by the build up of carbon deposits resulting from uncatalyzcd hydrocarbon decomposition reactions. 

Figure 19-16. Comparison of the effect of temperature on the durability and the friction of films of graphite fluoride and molybdenum disulfide. 440 C stainless steel riders against burnished films on 440 C stainless steel disks. Load 4.6 N. Sliding speed 1.6 m/s. Atmosphere dry air. A Friction of unlubricated metal. B Onset of thermal decomposition of (CF 12 n Fusaro and Sliney [73].

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