Tungsten disulphide oxidation

Sliney indicated that the comparison between tungsten disulphide and molybdenum disulphide is more complicated. He showed that both compounds oxidise at temperatures as low as 300°C, and that below 340°C tungsten disulphide oxidises more rapidly than molybdenum disulphide. The oxidation rates in that temperature range are very low, and with loosely-compacted powders of 1jt/m average particle size the time required to oxidise 50% of the materials at 300 C was approximately one to two weeks. Above 340°C molybdenum disulphide oxidises more rapidly than tungsten disulphide, and it is at these higher temperatures that the relative oxidation resistance is more important. The relationships are shown in Figure 14.4. 

Figure 14.4 Oxidation Rates of Molybdenum Disulphide and Tungsten Disulphide (Ref.533)...

The changes in friction and wear behaviour with change in temperature in air are presumably determined by oxidation. Figure 14.5 shows that at low temperatures both molybdenum disulphide and tungsten disulphide have similar coefficients of friction of about 0.07 to 0.08, but a marked increase in friction occurs at 400°C with molybdenum disulphide and 600"C with tungsten disulphide. The corresponding temperatures for increasing friction reported by Tsuya were 300 C and 450°C. 

The higher possible operating temperature with tungsten disulphide, due to its greater oxidation resistance, and the resulting maintenance of low friction to higher temperature, have been the main reasons for its use in practical engineering... 

Tungsten diselenide Similar to molybdenum disulphide but better oxidation resistance at high temperatures. ., Nuclear plant... 

Beryllium Sulphide.—Wohler (1828 2) supposed he had made a sulphide by heating the metal with sulphur, but Fremy (1853 1) states that it was the only sulphide he could not produce by I>assing the vapor of carbon disulphide over the hot oxide. De-bray (1855 i) and Nilson and Pettersson (1873 3) state that beryllium and sulphur do not combine when heated together. Berzelius (1826 2) supposed he produced a double sulphide of bci yllium and tungsten, but his results lack confirmation. Lebeau (1899 ii) at last made the sulphide by heating the anhydrous chloride and iodide with. sulphur or with hydrc en sulphide. Also by the action of sulphim vapor on the carbide at a high temperature, lire. sulphide is a white solid, immediately decomposed by water. No other details are given nor further study of this compound been made. 

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