Concentrated Acids at Elevated Temperatures
A number of elastomers possess good resistance when exposed to dilute acids at room temperature.
These materials include Aflas™, Butyl, Epichlorohydrin, Ethylene Propylene, Fluorocarbon, Fluorosilicone, Hypalon®, Kalrez®, Chemraz®, Natural Rubber, Neoprene®, Nitrile, and Teflon®.
THE ACID RESISTANCE OF THESE COMPOUNDS, HOWEVER, SIGNIFICANTLY LESSENS WITH BOTH INCREASING ACID CONCENTRATIONS AND RISING TEMPERATURES.
Best Choice(s)
As temperatures and concentrations of nitric and hydrochloric acids rise, perfluoroelastomers such as Kalrez or Chemraz have demonstrated good performance in lab tests.
As temperatures rise above 158°F, only the chemical inertness of Teflon can be relied upon for maintenance of a seal exposed to hydrochlolic or nitric acids.
NOTE: Teflon has been laboratory tested (by DuPont) for 168 hours of exposure to 37% hydro-chloric acid, at 248°F, with only 0.03% of observed weight gain. It has further been tested for 12 months of exposure to 10% nitric acid, at 158°F, with 0.1% weight gain. Teflon has also been shown by DuPont to undergo ONLY SLOW OXIDATIVE ATTACK by 70% nitric acid, under pressure, at 480°F.