Synthesis and Processing of Nano Scaled Ceramic Powders and Composite Coatings Using Sol-Gel and Related Techniques

Abstract

Nanoscaled particles are of interest from various reasons for different types of materials, since many material properties change dramatically when dimensions are reduced to the manometer scale. An impressive example is the significant decrease of the sintering temperature of ceramic powders [1], allowing new ceramic coatings and cofiring techniques, the preparation of new types of ceramic membranes, [2,3,4] and the increase of mechanical strength of ceramic bodies, caused by the decreased size of defects. The decrease of processing temperatures is also used for the preparation of high purity Si02 glasses from dispersed Aerosil powders [5] particulate silica gels or by the combined alkoxide-particulate method [6,7]. In the case of polycrystalline nano phased metals and metal alloys, where the material properties are determined by grain boundary phases, some interesting physical phenomena as plastic behaviour or extremely high coefficients of diffusion have been reported [8] in the last years. Composites with nano sized metallic or semiconductor (e. g. metal halides) particles in glasses have been developed for photochromics [9,10] or are applied since ancient times for glass staining. In these metal colloid composites the optical properties base on a plasmon resonance effect in combination with quantum size effects [11] and therefore depend on the colloid size and concentration and are strongly influenced by the geometric shape of the nano particles [12,13,14]. Recently gol-gel synthesis routes are investigated for the synthesis of noble metal colloid containing organic-inorganic layers [15,16] or glass like coatings [17] since they offer interesting non linear optical properties (χ3-effects). Since investigations of stabilized metal colloids in alcoholic solutions [18,19] have shown that the particle size distribution has a strong impact on the non linear optical properties, the main goal for the synthesis and processing is to control the size of the quantum dots in the case of metal colloids as well as for semiconductor quantum dots, that have been intensively investigated in the last years (metal chalcogenides) [18,19,20,21,22].