Preface

Abstract: The present paper is focused on ceramic–metal composites obtained via different technologies which leads to different microstructures in terms of size and distribution of metal phase. Composites analysed in paper were produced by the following methods:(a) infiltration of porous ceramics by metal, (b) consolidation under high pressure and (c) sintering of ceramic powder coated by metal. Their microstructures were investigated by scanning and transmission electron microscopy methods. The three methods of composite fabrication employed in the present study result in specific spatial distribution and dispersion of metal phase. Presureless infiltration of porous ceramics by liquid metal is driven by capillary force and make it possible to produce microstructure with percolation of metal phase in ceramic matrix. The volume fraction of metal phase in this case depends on the size of pores. The size of pores influence also the kinetics and extent of infiltration. Ceramic preforms with small size of pore are not fully infiltrated. This method is useful for composite with size of metal phase in the range of micrometers. Hot pressing under high pressure produces microstructures of composites with metal phase grain size in the range from nano to micrometers. Moreover, it allows to achieve the nanometric size of ceramic grains. In the case of ceramic powders covered by metal, compression and hot pressing preserves nanometric size of metal. The grain growth of ceramic grains is suppressed.

Abstract: Ceramic foams containing MoSi2 were prepared by a self-blowing process of poly-silsesquioxane with MoSi2 as filler. Ceramic foams prepared by polymer pyrolysis were composed of MoSi2 and silicon oxycarbide glass matrix. Densities, pore sizes and mechanical properties of ceramic foams were depended on the filler content and heating rate for curing of polymer. Depending on the foaming condition, ceramic foams with a density of 1.2∼0.4 and a compressive strength of 3∼30 MPa were obtained.

Abstract: As an important solid tritium breeding ceramic material, Li2TiO3 pebbles with the diameter of 1mm are used in the breeding pebble bed for ITER test blanket module (TBM). Therefore, it is very important to evaluate the densities of Li2TiO3 ceramic pebbles accurately. In this paper, Li2TiO3 ceramic pebbles with the diameter of about 1mm were prepared by wet method using Li2CO3 and TiO2 as the main raw materials. The shape and microstructure are characterized by SEM technique. Densities of the ceramic pebbles were analyzed by both Archimedes principle and Mercury porosimetry methods. The results show that the density measured by Archimedes principle is higher than reality density, while the density measured by mercury porosimetry is accurate.

Abstract: This paper adopted freeze casting method to prepare porous Al₂O₃ ceramic bodies with interconnected pore channels as a preform. The preform was pressureless infiltrated with Nb-Al binary alloy by using electromagnetic induction furnace. The results indicated that the Nb-Al melt solidified as a sphere-like body under the surface tension driving. It was difficult to obtain Nb-Al binary alloy matrix Al₂O₃ ceramic composites. However, the wettability between Nb-Al melt and porous Al₂O₃ ceramic bodies was improved obviously while the Ti and Cr alloying elements were added into Nb-Al binary alloy. Also, the resultant Nb-35Ti-20Al-10Cr melt was filled into the interconnected pore channels existed in the Al₂O₃ preform by pressureless infiltration.

Abstract: Preparation of porous ceramic body foamed by microbe is prone to structure defects such as inequality of pore size and distribution, crack, contraction deformation, etc. Four-level orthogonal tests based on three improving factors such as water content(WC) and carboxymethyl cellulose (CMC) and stirring time(ST) were carried out to improve the method of preparing porous ceramic body foamed by microbe at ordinary tempreature. It is concluded that water content is the key improving facor followed by stirring time and CMC content, and the optimized formula could be A3B3C1 or A3B4C2.