Uses and limitations of plastics, elastomers, and carbon-graphite have been detailed.
Organic
Plastic materials without hydroxyl groups tend to resist HF within certain parameters (HF is strongly hygroscopic, rapidly attacking polyesters, for example).
Polyvinylidene fluoride (PVDF), polyethylene, and polypropylene are resistant to 70% acid to about 32°C (90°F). Cross-linked polyethylene and chlorobutyl-rubber-lined steel vessels are used for storage of aqueous hydrofluoric acid. The higher fluoropolymers (polytetrafluorethylene [PTFE], perfluoroalkoxy (PFA), fluorinated ethylene propylene [FEP], chlorotrifluoroethylene [CTFE]) are resistant to their normal temperature limits but are subject to permeation with attendant hazard to adjacent metals. Special design features are sometimes incorporated when fluorocarbons are used as liners to minimize the problems caused by permeation. These measures include the use of vent holes in the steel behind the lining. Also PVDF has lower permeation rates than PTFE.
Graphite impregnated with either phenolic or PTFE resins and fluorocarbon tube heat exchangers are used to remove the heat of solution in process equipment used to make aqueous HF from AHF.
Synthetic soft rubbers (butyl, neoprene), and natural rubber filled with carbon black will withstand 60% HF to about 70°C (160°F). (Compounding is critical; silica and magnesia must not be used.)
Inorganic
Of the inorganic materials, glass and siliceous ceramics are not resistant. Carbon and graphite are resistant, but the impregnants may be attacked. Impervious graphite is limited to 48% acid at the boiling point and to 85°C (185°F) in 60% HF.(Dillon 79)