Where do I find a good comprehensive table of friction coefficients between various materials? I'd like, in particular, to be able to compare the coefficient of static friction between tungsten carbide and sapphire and that between sapphire and sapphire. Tables that I have found tend to have sapphire on sapphire, but not tungsten carbide on sapphire. Is there some master table of these things that engineers know about or am I just going to have to get my hands on these materials and test them myself? Thanks!