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Selected Application Recommendations Nitric and Chromic Acid Nitric and chromic acid (HNO3 and H2CrO4) are strong oxidizing agents that will gradually attack the composite surface to form a yellow crust which eventually can develop microcracks and lead to structural deterioration. Diluted nitric and chromic acids (5% or less) can be handled at moderate temperatures in accordance with the selection guide. These dilute acids are commonly encountered in metal plating, pickling, or electrowinning processes, where composites often out -perform competitive materials such as rubber -lined steel. When dealing with nitric acid, care should always be given to safe venting of NOX fumes as well as dealing with heat of dilution effects. It is also important to avoid contamination and avoid mixed service of the tank with organic materials, which can react (sometimes explosively) with nitric acid. Hydrofluoric Acid Hydrofluoric acid is a strong oxidizing agent and can attack resin as well as glass reinforcements. This can occur with concentrated as well as diluted acid (to 5%). Synthetic surfacing veil is commonly used. Fluoride salts, as well as fluoride derivatives (such as hydrofluosilicic acid) used in fluoridation of drinking water, can be accommodated with use of vinyl esters or other premium resins as indicated in the material selection guide. HF vapors associated with chemical etching in the electronics industry can be accommodated by resins appropriate for hood and duct service. Acetic Acid Glacial acetic acid causes rapid composite deterioration due to blister formation in the corrosion barrier. This is usually accompanied by swelling and softening. Acetic acid becomes less aggressive when diluted below 75% concentration, and at lower concentrations can be handled by a variety of resins. Perchloric Acid While perchloric acid can be an aggressive chemical, a main issue from a composite standpoint is safety. Dry perchloric acid is ignitable and presents a safety hazard. When a tank used for perchloric acid storage is emptied and allowed to dry out, residual acid may remain on the surface. Subsequent exposure to an ignition source, such as heat or sparks from a grinding wheel may result in spontaneous combustion. Phosphoric Acid Corrosion resistant composites are generally quite resistant to phosphoric and superphosphoric acid. Some technical grades may contain traces of fluorides since fluoride minerals often occur in nature within phosphorous deposits. This is ordinarily not a problem, but is worth checking. Deionized and Distilled Water High purity deionized water, often to the surprise of many, can be a very aggressive environment. The high purity water can effectively act as a solvent to cause wicking and blistering especially at temperature >150' F. Purified water can also extract soluble trace components from the resin or glass reinforcement to thereby compromise purity, conductivity, or other attributes. Good curing, including post -curing, preferably in conjunction with a high temperature co -initiator, such a tertiary butyl perbenzoate (TBPB), is suggested to maximize resistance and to prevent hydrophyllic attack of the resin. It is best to avoid using thixotropic agents which can supply soluble constituents, and where possible any catalyst carriers or plasticizers should be avoided.