Ceramics chemical data

This chapter is an attempt to refine the classification of Mexican majolica ceramics from Spanish Colonial sites by using chemical data obtained by neutron activation analysis. The ceramics examined came primarily from excavations in Mexico City and from the Santa Catalina de Guale Mission site, St. Catherines Island, GA. The majolica types from these sites are both Spanish and Mexican and date from the 16th to the late 17th century. A rationale for the chemical classification of Mexico City and Puebla production is proposed. 

Unlike chemical provenience studies of geological materials, the compositions of which normally remain unchanged by human choices, the composition of ceramics are the result of human choice, making the interpretation of such chemical data much more problematic. Potters at a given location can and do choose different recipes for different pots with different functions or styles. For example, water jars from Veracruz can give a different mix of clays and tempers for the base of the jar, for the filter, and for the funnel at the top, giving three different compositions for the same vessel. 

In addition to chemical data on ceramic materials, information on the mineralogical constituents by speciat-ion can be vital to a complete understanding of the material (see above). Both X-ray diffraction (XRD) and microscopic examination can provide such mineralogical information. Additional structural knowledge must be obtained using microscopic techniques. 

Here we will demonstrate the problem of overfitting with some examples of chemical data processing. Table 1.2 demonstrates a set of data about the preparation of bismuth-based high-temperature superconductors. And Table 1.3 demonstrates a set of data about the preparation of VPTC ceramic semiconductors. In these tables, the samples of class 1 are those with good properties, and those of class 2 with unsatisfactory properties. 

Silica sintering (dashed curves) and crystallization (solid curves) under dry and wet" conditions upper and lower sintering bounds correspond to assumed pore diameters of SOO and 5 nm, respectively. The lower viscosity observed by Sacks and Tseng [48] shifts all curves to lower times at any temperature. Their data for sol-gel derived glasses are also included X marks treatments that resulted in crystallization with little sintering and S marks treatments that produced sintered glasses free of crystallinity. From Uhlmann et al. [122], pp. 173-183 in Science of Ceramic Chemical Processing, eds. L.L. Hench and D.R. Ulrich (Wiley, New York, 1986). 

F-200 ActivatedMlumina forMdsorption Applications, Product Data, Alcoa Chemicals Division, Aluminum Company of America, Pittsburgh, Pa., 1985. R. D. Woosley, "Activated Alumina Desiccants," in L. D. Hart, ed.. Alumina Chemicals Science and Technology Handbook, American Ceramic Society, Westerville, Ohio, 1990. 

Electronic Ceramic Stannates Technical Data Sheet CER-322, M T Chemicals, Inc., Rahway, N.., 1969. 

Figure 9-44. Gas-liquid hold-up data for ceramic rings and saddles. Used by permission of Leva, M. Tbwer Packings and Packed Tower Design, 2nd ed., U.S. Stoneware Co. (now, Norton Chemical Process Equipment Corp.) (1953).

In most cases, glass-ceramics possess good chemical stability and certainly compare favourably in this respect with other ceramic materials. Table 18.7 summarises makers data for chemical attack on commercially available materials. 

Table 18.7 Chemical resistance data for some commercially available glass-ceramics...

Various ceramic membranes, for example, possess differing degrees of acid/base resistance, depending on the pH value, particular phase of the membrane material, porosity, contact time and temperature. However, no quantitative data are available on the kinetics of chemical dissolution of ceramic membranes as a guide for chemical corrosion considerations. 

In earlier literature reports, x-ray data of a-based ceramics, the /3-like phase observed in certain silica minerals was explained by a structural model based on disordered Q -tridymite. However, others have suggested that the structure of the stabilized jS-cristobalite-like ceramics is closer to that of a-cristobalite than that of Q -tridymite, based on the 29Si nuclear magnetic resonance (NMR) chemical shifts (Perrota et al 1989). Therefore, in the absence of ED data it is impossible to determine the microstructure of the stabilized jS-cristobalite-like phase. ED and HRTEM have provided details of the ceramic microstructure and NMR has provided information about the environments of silicon atoms in the structure. Infrared spectroscopy views the structure on a molecular level. 

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