Thermogravimetric thin aqueous film corrosion studies of alloy 22;calcium chloride solutions at 150 degC and atmospheric pressure

摘要

The extent of reaction of alloy 22 with limited amounts of aqueous calcium chloride (CaCl_2) was investigated.Alloy 22 is a highly corrosion-resistant nickel-chromium-molybdenum-tungsten alloy.Specimens were polished to a mirror finish prior to aerosol salt deposition.An aqueous film was formed on the specimen surface by deliquescence of deposited CaCl_2 at 150 degC and 22.5% relative humidity (RH).The reactant gas was a continuous flow of purified humidified laboratory air.The reaction progress as a function of time was continuously measured in-situ by a microbalance.An initial weight gain due to CaCl_2 deliquescence was observed.A steady weight loss was observed over the next 24 hours,after which no further weight.Change was apparent.During the period of weight loss,which precipitates formed and the specimen surface became visible dry.Post-test analyses indicated that the precipitates consisted of calcium,chloride,and oxygen.