Stains and Etches

Perhaps the most thorough treatment of the subject of stains and etches is the work of Ellson and Weymouth of Australia (1968). Their paper lists approximately 43 reagent solutions and their effects on Portland cement and blast furnace slag phases in terms of (a) reaction type (stain or structural etch), (b) time required for the desired effect, (c) recommended temperatures, and (d) concentrations. Futing summarized the application of many varieties of etches in 1986. 

Another helpful procedure in polished section examination is to immerse only one half of the polished surface in water, for example, holding the section with apair of forceps, spray wash the sample with isopropyl alcohol, dry, and then rotate the sample 90 immersing half of the section in nital. Thus the surface is divided by this procedure into quarters one quarter with only water, one quarter with water plus nital, one quarter with only nital, and a quarter remaining with no etch. 

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After cleaning the polished surface with isopropyl alcohol in the sonic cleaner, the section is dried with forced warm air and is ready for study in reflected light. Effects of stains and etches can be removed by repolishing the section with 0.03-pm alumina and Texmet . Suitably polished and etched surfaces can be examined with a scanning electron microscope. 

Marlin, ]., Stains and Etches, First Annual Meeting, International Cement Microscopy Association, sponsored by Gifford-HillCementCo.,Arlington,Texas, 1978,3-page handout. 

Marlin, J., "Staining and Etching of Polished Surfaces," Advanced Microscopy Seminar, Portland Cement Association, Skokie, Illinois, 1979,13 pp. 

It is clear from the preceding discussion that direct examination, staining and etching-replication techniques all have their strengths and weaknesses. They are therefore complementary approaches to the study of polymer microstructure and the choice of technique depends very much upon the precise problem being addressed [144]. 

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