Prompted by John Carmack's report I did a little digging on the web to try to understand the issues with various different types of Teflon. It looks like there are three types: PTFE, FEP, and PFA. I also found a couple of places where ETFE is referred to as Teflon, but it looks like the correct name is actually Tefzel. I didn't find any reference suggesting that any of these were degraded by contact with Teflon. A couple of references suggest PTFE, FEP, PFA, and ETFE are excellent for Peroxide use.
PTFE is polytetraflouroethylene FEP is Tetrafluoroethylene-Hexafluoropropylene PFA is PerFluoroAlkoxy ETFE is Ethylene tetrafluoroethylene There is a good list of flouropolymers, with trade names and suppliers here: http://www.datacable.org/suppliers/supptab.htm Doing google searches on the flouropolymer code and "hydrogen peroxide" didn't yield any references to incompatibility. In fact the only one that didn't turn up a reference suggesting it *is* compatible with hydrogen peroxide is THV (dyneon). Some properties of teflon are listed here: http://www.berghofusa.com/be01006.htm Click through the "next page" links to get to more information. Only PTFE peroxide resistance is given. Hydrogen Peroxide resistance of PTFE, FEP, PFA is listed as "Excellent" here (90% peroxide): http://www.texloc.com/closet/cl_chemical_resist_chart2.html and FEP and PFA are listed as "Excellent" here (30% peroxide): http://www.dualam.com/chem.html - this reference also lists ETFE as "excellent" though the temperature rating is lower (100C as opposed to 120C) All this suggests that the material that failed was either filled teflon (with a peroxide incompatible filler) or not really teflon. Perhaps it might be a good idea to order rebuild kits for all valves and use those for compatibility testing. ......Andrew -- Andrew Case | [EMAIL PROTECTED] | _______________________________________________ ERPS-list mailing list [EMAIL PROTECTED] http://lists.erps.org/mailman/listinfo/erps-list
