Nickel-based alloys are generally preferred for hot caustic service. Commercially pure nickel (i.e., Alloy 200 - UNS02200) will handle any concentration of sodium hydroxide up to 300° C. Reactors can be made entirely of nickel or steel tanks with nickel cladding can sometimes be used. The presence of impurities, such as chlorates, in hot caustic solutions can make nickel alloys more vulnerable to corrosive attack. The final choice of a specific material construction should be based on the maximum expected concentration and temperature of sodium hydroxide as well as any impurities that may be present.
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