Methods of Corrosion Analysis |
129 |
this may be true, one must be very aware of the amount of lubricant used, the pressures applied, and the area of the sample being polished. If the lubricant supply rate is constant, which is generally the case, the material removal rate will peak at about 300–350 rpm. Thus if one is thinking of purchasing automatic grinding and polishing equipment, he should look for something that has automatic lubrication flow rate control. Although many advances have been made in the grinding and polishing of ceramics, this area still is very much an art. Subtle changes in the procedure can make a major difference in the final finish of the sample*.
3.4 SELECTION OF TEST CONDITIONS
Although the selection of appropriate samples can be a major problem, the selection of the appropriate test conditions is an even more difficult task. The goal of the industrial corrosion engineer in selecting test conditions is to simulate actual service conditions. Selection of test conditions is much easier for the scientist, who is attempting to determine mechanisms. The major problem in attempting to simulate service conditions is the lack of detailed documentation. This is caused by not knowing the importance of such data in the corrosion of ceramics, the cost of collecting the data, or both. Thus if one wants to perform meaningful laboratory corrosion studies, it is imperative that the industrial environment of interest be accurately characterized.
When conducting laboratory oxidation studies, a convenient way to obtain a range of oxygen partial pressures is desirable. Very low partial pressures are never attained in practice by the use of a vacuum system. Instead, a mixture of gases in which oxygen is a component is used to establish the low partial pressure. The most important mixtures that are used are
* One should also remember that a perfectly polished surface, although excellent for reports, is not necessary to obtain sufficient data to solve a corrosion problem.
Copyright © 2004 by Marcel Dekker, Inc.