Aspects Of Chemistry and Chemical Processing Of Organically Modified Ceramics
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ASPECTS OF CHEMISTRY AND CHEMICAL PROCESSING OF ORGANICALLY MODIFIED CERAMICS HELMUT K. SCHMIDT Fraunhofer-Institut fUr Silicatforchung, Neunerplatz 2, D-8700 WUrzburg, Federal Republic of Germany fUr Neue Materialien, Universitat des New address: Institut Saarlandes, Geb~ude 43, Im Stadtwald, D-6600 SaarbrUcken, Federal Republic of Germany ABSTRACT For the synthesis of composites on a nano or molecular level, chemical or physical methods have to be used since mechanical procedures cannot be employed for these systems. If organics have to be included, low temperature processing has to be used for the synthesis of the inorganic component in order not to damage the organic component. Sol-gel techniques are an appropriate means to synthesize oxidic networks by soft chemistry, and various systems of organically modified ceramics (ORMOCERs) have been developed so far. It has been shown that the material prothe synthesis parameter can be used to tailor perties in a wide range. A review over the chemistry and chemical properties of ORMOCERs and several examples of material developments will be given. INTRODUCTION The aim of this paper is to point out special chemical aspects of organically modified ceramics of the ORMOCER type, mainly developed in the Fraunhofer-Institut fUr Silicatforschung in WUrzburg, FRG. Due to the limited amount of space and with respect to the review, in several cases details were not reported here, but are foreseen for later publication or are found in the cited literature. In numerous cases of materials application in technology one-component systems do not meet the complex practical requirements and, therefore, composites have to be used. The vast majority are so-called macroscopic composites like laminates or fiber reinforced materials. The lower limit of the component size in these cases is the pm range and is limited by mechanical processing (e.g. mixing, coating, blending). For coatings, layer thicknesses in the nano range can easily be achieved by deposition techniques and, as shown in [1], composites consisting of several hundreds of thin layers can be prepared by microwave assisted chemical vapor deposition. That means layered composites with one very small dimension can be obtained. Particulate phases, e.g. ceramic phases in ceramic maare obtained by nucleation and crystallization protrices, to obtain very cesses at high temperatures. It is difficult from conventional crystalline small grain sizes if one starts raw materials like oxides. Amorphous gels, however, can be transformed into ceramics with extremely small particle sizes (2]. If growth and agglomeration processes can be controlled
Mat. Res. Soc. Symp. Proc. Vol. 180. @1990 Materials Research Society
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particulate raw materials for ceramics in the nano range can be prepared (3]. In controlled sol-gel reactions, fine particles can be formed by a controlled growth mechanism in solution. To obtain glasses or ceramics from gels or from ultrafine particles, the material has to be densified by heat treatment during a sintering pr
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