This appendix gives a few indicators of suitable materials for use in a UHV environment. The main point is simply to emphasize that the materials need to have low outgassing rates per unit area exposed, and that they need to be stable at the temperatures not only of use, but also during bakeout. Some of the obvious candidates in the different categories are as follows. Much of this information can be gleaned from talking to practitioners, from vacuum technology books such as Dushman & Lafferty (1992), O'Hanlon (1989), Roth (1990) or from reading between the lines in design handbooks such as Yates (1997), or increasingly from the web. A page giving properties and some sources for materials is at http://venables.asu.edu/grad/ appmat1.html

Structural materials

The most widely used structural material is 304 stainless steel, which is used to make chambers, flanges, etc., and can also be used for stages and other parts of the experiment itself. At very low temperatures this austenitic (largely f.c.c.) 18–20%Cr, 8–10%Ni Fe-based alloy transforms in part to the b.c.c. (martensitic) structure, and thereby becomes magnetic. If this could be important, then more technical details are needed, such as would be obtained from ASSDA – the Australian Stainless Steel Development Association – or AVS – the American Vacuum Society. Aluminum alloys are used for experimental pieces inside the vacuum system, and have also been used for whole chambers on occasion.