A Few Approved Methods of Measurement of Coating Growth
The measurement of the course of the oxide-layer growth with time, especially at higher temperatures, is generally carried out from the determination of the weight increase of the metal or alloy sample with time, caused, for example, by the quantity of oxygen taken up by the oxide formation. In this technique one frequently carries out the determination of the weight increase as a measure of the rate of oxidation by placing several samples in the furnace at a definite temperature and gas composition. The samples are removed from the furnace at different times at suitable time intervals and their weight increase is determined on an analytical balance. With similar pretreatment of the samples the weight increases which are found at different times permit the construction of a continuous weight increase-time curve as long as no secondary disturbances, such as bursting and spalling of the oxide layers or recrystallization processes, appear. For further evaluation one can try to obtain a straight line with the measured points, corresponding to a linear, parabolic, cubic, or logarithmic rate law. As long as the material which is to be investigated,e.g., steel, is available in large quantities, this “large-number measurement method” is quite useful. Frequently, especially with nonadherent scaling layers, the oxide layer is removed after oxidation and the weight loss of the metal sample is determined. Here the scale is removed with a steel wire brush or by a chemical or electrochemical pickling. This procedure is to be recommended only with larger technological samples.
KeywordsWeight Increase Null Point Metal Sample Balance Beam Diethyl Phthalate
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