REFERENCE MATERIALS FOR THERMAL-EXPANSION - CERTIFIED OR NOT

Many dilatometers in common use can have significant systematic errors in determining linear thermal expansion as evidenced by round-robin m easurements on reproducible materials. The need for reference material s to check these dilatometers can usually be met by rods of OFHC Cu, s emi-conductor grade Si, W, Pt (rather expensive!), sapphire (of specif ied orientation) etc. which are readily available and for which there are now reliable data. For legal reasons there may be a need to use ce rtified materials made from a batch which has been measured in a natio nal laboratory. For some years the NBS (now NIST) supplied Cu (SRM 736 ), sapphire (SRM 732) and W (SRM 737) which are no longer available. P resently available axe SRM 731 (borosilicate glass for 80-680 K), SRM 738 (AISI 446 stainless steel for 293-780 K) and SRM 739 (fused silica for 80-1000K). With some further measurements as a check, MgO and Mo could also be useful reference materials up to high temperatures.