Ceramics tempers

Although x-ray diffraction has been used for many years in the identification of crystalline materials, its special application to the study of ceramic temper and paste minerals is relatively recent. Because many tem-... 

The ceramic analyses on hand were produced in a niunber of laboratories, mostly in connection with different ad hoc experimental schemes largely dedicated to the solution of specific, closed-end archaeological problems. In only a few cases were there studies aimed at a comprehensive knowledge of the chemical compositional profiles of all the ceramics, tempered and non-tempered, and all the clay and temper resources in a particular region of archaeological interest. 

Curing. Some chemically bonded bricks requke some elevated heat treatment that is typically higher than the tempering process mentioned above, but less temperature than that requked to form ceramic bonds. One example is aluminosihcate brick bonded with phosphoric acid. A very strong... 

Ton-exchange approaches and thermal tempering have been evaluated for strengthening dental ceramics (18,19). Both of these approaches are aimed at placing external surfaces of dental ceramic restoration in compression. Only ion exchange is promoted commercially and is not in extensive use. 

Bronitsky, G. and R. Hamer (1986), Experiments in ceramic technology The effects of various tempering materials on impact and thermal-shock resistance, Am. Antiquity 51, 89-101. 

Tempered glasses are useful because failure normally occurs under an applied tensile stress, and failure in ceramics and glasses is almost always initiated at the surface. When a permanent compressive stress, called a residual compressive stress, is placed on a surface, either through thermal or chemical means, the applied stress must first overcome this residual compression before the surface is brought into tension under which failure cau occur (see Figure 5.53). Notice that the residual stress is compressive in nature at the surface of the plate and is tensile in the center (shaded areas). When... 

Figure 5.53 Residual stress, applied stress, and resultant stress distribution for transverse loading of a tempered glass plate. From W. D. Kingery, H. K. Bowen, and D. R. Uhknann, Introduction to Ceramics. Copyright 1976 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

To a much greater extent than either metals or ceramics, the mechanical properties of polymers show a marked dependence on a nnmber of parameters, inclnding temper-atnre, strain rate, and morphology. In addition, factors snch as molecnlar weight and temperature relative to the glass transition play important roles that are not present in other types of materials. Needless to say, it is impossible to cover, even briefly, all of these effects. We concentrate here on the most important effects that can affect selection of polymers from a mechanical design point of view. 

From the correlation between the ancient pottery and modern clay one can draw several significant conclusions in addition to the most immediately obvious one that the matching ancient pots were locally made. The amount of temper in the ancient pottery, as evidenced by our comparison with the clay source, has not diluted or otherwise significantly altered the compositional pattern of the ceramic. Also the pottery must not have significantly changed in composition during burial. In addition we observed a small but significant difference between the composition... 

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