DuPont Krytox XHT-BD, XHT-BDX, & XHT-BDZ High-Temperature Greases
DuPont™ Krytox® XHT-BD, XHT-BDX, and XHT-BDZ series greases are special extreme high temperature greases with low oil evaporation and are thickened with a non-melting thickener to allow use at temperatures above the melting point of common greases. They have excellent lubrication over a broad temperature range. Krytox® XHT-BD series greases are nonflammable and chemically inert. Krytox® allows extended lubrication intervals and longer equipment life.
Krytox® XHT-BD greases are designed for use where the temperatures are in the 288 °C (500 °F) range and higher, where there is a danger of melting the standard PTFE thickener. This grease uses a special non-melting high temperature thickener. The base oil is an extremely viscous oil that provides good viscosity and lower evaporation at high temperatures. Krytox® XHT-BD greases are for use in low speed bearings or in pillow housings and will shear at high speeds, causing loss of oil in sealed bearings. The oil in the grease can begin to slowly degrade at temperatures above 330 °C (626 °F) and this will occur at an increasing rate as temperatures increase. Relubrication could be required at these temperatures to achieve optimum life.
Due to their low surface tensions, Krytox® oils easily wet metallic surfaces and because of their inertness, Krytox® oils have little or no adverse effect on metals when the oil temperature is lower than 288 °C (550 °F). The behavior of Krytox® oils in the presence of many alloys has been studied using the Micro Oxidation-Corrosion Test developed by the Air Force Materials Laboratory.
In general, nickel and cobalt alloys are the most resistant to corrosion and are suitable for use with Krytox® up to 371 °C (700 °F). Carbon steel alloy suitability should be studied for uses above 288 °C (550 °F). Some types of stainless steel are satisfactory at 316 °C (600 °F). A summary of metals compatible with Krytox® oils at various temperatures is given below.
Certain alloys have been found to cause catalytic depolymerization of Krytox® at high temperatures. At 316 °C (600 °F), for example, titanium alloys that contain aluminum function in this way. Aluminum alloy 2024 also catalytically depolymerizes Krytox® at 371 °C (700 °F). This depolymerization is considerably reduced in the absence of oxygen when an inert gas is substituted for the dry air flow. This suggests that the reactions involved are between the Krytox® and the oxide coating on the metal surface.