THE STABILIZATION OF SILICONE LUBRICATING LIQUIDS ABOVE 200°CnPART I - CONVENTIONAL OXIDATION INHIBITORS AND SOME HIGH-SURFACE SOLIDS

摘要

A study of the stabilization of silicone oils at temperatures between 250° and 371°C has shown that the useful life of the com?mercially available types may be extended from three to five times by the use of certain oxidation inhibitors known to be effective in other systems. The relative value of different inhibitors varies with the temperature and the aromatic content of the oil. The dete?rioration of silicones in this temperature range is primarily an oxidative process. This oxidation is inhibited by high-surface solids such as Shawanigan black, copper phthalocyanine, and ferric oxide, by conventional inhibitors of the arylamine type, and by dilauryl selenide. Dilauryl selenide was ineffective at 300°C and higher; phenylalphanaphthylamine caused a relatively uniform improvement at 250° and 300°C. The gains from any inhibitor were small at 371°C. The chemical diversity of the effective inhibitors and the relatively high temperatures at which they are effective suggest that the mechanism of inhibition differs from that operating in con?ventional oils at temperatures below 200°C.nThe improvements shown with lightly phenylated silicones per?mit formulation of lubricants having acceptable viscosity charac?teristics and oxidation stability over the range from -55°C or lower to 305°C. This work has led to the discovery of new types of inhib?itors, specifically for use with silicone liquids, which are an order of magnitude more effective than conventional inhibitors.