Avoiding Ceramic Problems by the Use of Chemical Techniques
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AVOIDING CERAMIC PROBLEMS BY THE USE OF CHEMICAL TECHNIQUES
Peter E. D. Morgan Rockwell International Science Center,
Thousand Oaks,
California 91360
INTRODUCTION As the title of this meeting suggests, a paradigm change is underway in the ceramic community; methods of synthesis and use of ceramic powders are being hurriedly reappraised. The imperative for change was all in place by an important meeting that took place in 1977 [1].
POWDER PROBLEMS Nagging problems with the use of powders for the production of ceramics break down into three broad categories: Diffusion Problems Much ceramic research has concerned itself with the way that oxides interact to produce a final polycrystalline product, preferably with high density and strength. It was assumed that the starting materials should be mixed oxides. However, oxides are not generally the large scale primary products of the chemical industry. One of the few that is, -utile TiO2, is available for the paint industry. The only other really large scale products that I can think of that are at least closely related to an oxide are bayerite and boehmite; the former, is the starting material for the production of aluminum and the latter material a by-product of the Zeigler alcohol process. These two hydroxides produce very active oxides as they decompose; first to convert them into calcined oxides prior to producing ceramics is the approach that has been taken previously. Primary products of the chemical industry come directly from the extraction and purification of the elements from their ores. It is these chemicals that should be used directly to produce ceramics. Slow diffusion reactions between oxides and the intermediate and/or metastable products that may be produced before the final ceramic form are problems to be avoided. Rather, one should develop new reactive chemical routes utilizing the naturally available large scale inorganic sources for the final ceramic. This will be illustrated later. The use of reactive compounds can avoid various ceramic problems at high temperatures: the loss of volatiles, excessive grain growth, or eutectics leading to disproportionation, and so on. Apart from large scale bulk chemicals, certain specialty chemicals are becoming much more readily available because of their use in other fields: (for example, alkoxides, e.g. TyzorTM, acetylacetonates for catalysts and interesting stearates used by the paint industry). A present curious feature of the ceramic industry is that the methods used on the relatively large scale are quite similar to methods that would be used by a student studying ceramic forming in the laboratory. The chemical industry on the other hand uses methods almost totally different from the original academic studies. The future ceramic industry must adopt chemical techniques used by the chemical industry on the large scale. This would include highly automated handling of (usually) liquids, control of particle size and shape, and so on, as is already done in the paint industry. If not picked up by the ceramics indu
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