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4.2.41Performing Accelerated Outdoor Weathering of Nonmetallic Materials Using Concentrated Natural Sunlight, G-90
This standard practice describes the use of a Fresnel-reflector to concentrate sunlight onto samples in the absence of moisture. A variation in the procedure allows the spraying of purified water at regular intervals on the samples.
4.3 NONSTANDARD TESTS
Many individual laboratories use test procedures that are similar to ASTM standard procedures; however, they have been modified to suit their own particular needs or capabilities. Although a particular ASTM test was developed for a certain material under specific conditions, it does not imply that other materials cannot be tested in the same manner. For example, C-621 for corrosion of refractories by molten glass could be used to test nonrefractories by various other liquids. A variation of this test has been used by some glass technologists where the refractory samples are rotated to simulate a forced convection situation. The real problem with this test is that one generally does not know the glass velocity distribution along the sample with sufficient accuracy to extrapolate laboratory results to commercial furnaces. A more appropriate test to evaluate forced convection upon dissolution is the rotating disk test, shown in Fig. 4.1. In this setup, the diffusion boundary layer across the lower disk face has a constant value for any experimental temperature and rotational velocity. The dissolution of the solid disk is therefore constant, a situation that does not occur in the finger test (see also Chap. 2, page 15 on Attack by Molten Glasses). Any test that is used should be subjected to ruggedness testing first to determine the important variables.
It is almost impossible to test the corrosion of ceramics and maintain all samples equivalent since variations in density and porosity are generally present. Thus it is important to test more
Copyright © 2004 by Marcel Dekker, Inc.
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FIGURE 4.1 Rotating disk setup.
than one sample under a particular set of conditions and average the results or normalize the test results to constant porosity.
4.4 ADDITIONAL RELATED READING
Youden, W.J. Experimental design and ASTM committees, Mater. Res. Stand. 1961, 1(11), 862–867.
Copyright © 2004 by Marcel Dekker, Inc.
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Wernimont, G. Ruggedness evaluation of test procedures. ASTM Standard. News March 1977, 13–16.
Smith G.L.; Marschman, S.C. Nuclear waste analytical round robins 1–6 summary report, Mater. Res. Soc. Symp. Proc. 1994, 333, 461–472.
Sterling, J. The importance of international standards. ASTM Standard. News June 2001, 24, 27 pp.
4.5EXERCISES, QUESTIONS, AND PROBLEMS
1.Why is it important to determine the factors that cause variation during testing? What ASTM standard addresses these factors?
2.What is the difference between a standard method and a standard practice?
3.Are there situations when a nonstandard test may be used? If yes, what precautions should be taken?
4.Discuss the importance of developing International Standards related to corrosion of ceramic materials.
REFERENCES
4.1.Form and Style for ASTM Standards, 7th Ed. ASTM: Philadelphia, March 1986.
4.2.Mendel, J.E. (compiler). Nuclear Waste Materials HandbookWaste Form Test Methods, Materials Characterization Center, Pacific Northwest Laboratories, Richland, WA, U.S. DOE Report DOE/TIC-11400, 1981.
Copyright © 2004 by Marcel Dekker, Inc.