International Conference Ceramic Processing Science

Abstract:Porous silicon nitride is gaining interest for a number of applications including metal–ceramic thermal engineering components, biomaterials and catalyst supports. This paper describes the fabrication of porous silicon nitride ceramic materials using a fugitive additive, corn starch, which allows samples to be produced with different volume fractions of porosity from ∼0 to 0.25. The initial composition consisted of 92 wt.% Si 3 N 4 , 6 wt.% Y 2 O 3 and 2 wt.% Al 2 O 3 . Sintering was carried out at 1800 °C for 2 h under nitrogen. Relative density as a function of the fugitive additive content has been measured. Microstructural analysis reveals a dense matrix of elongated β-Si 3 N 4 grains surrounded by intergranular glass phase and containing large pores and cavities. Pore size, geometry and grain size have been measured for certain compositions. Young's modulus and modulus of rupture have been determined as a function of the volume fraction of porosity. The Young's modulus–porosity relationship has been compared with previous work in the literature and it was found that this dependency is close to that for a model for spherical pores in cubic stacking arrangement.

Abstract:A comprehensive model for solid state sintering is presented which combines several previous models for partial aspects of sintering and grain coarsening. Some additional aspects are discussed and the model is extended for external loads several times higher than the sintering stress. Model parameters for a SiC powder are presented. For a face seal made of SiC uniaxial die compaction is simulated and different green density distributions after compaction are obtained for two different pressing schedules. Next, the sintering behavior is simulated using these density distributions as initial conditions. The resulting distortions of the face seal differ significantly for the two pressing schedules. For a special element with average green density the predictions of the sintering model are investigated in more detail. Finally, the shape predictions of the model are compared with a simplified model for solid state sintering.

Abstract:Well-defined porous ceramics with controllable pore size and porosity were fabricated via a hetero-coagulation of template/ceramic particle colloidal processing. Monodispersed polymer spheres were used as template and ceramic nanoparticles as inorganic building blocks to create porous structures. The preparation of well-dispersed suspensions of polymers and ceramics is essential for the fabrication of uniformly porous materials. Core-shell composites of polymer/ceramic could be obtained by mixing the oppositely charged two suspensions via electrostatic attraction following by filtration and calcination to produce macroporous ceramic materials. SEM images and pore size distribution results revealed that various materials, such as Al2O3, TiO2 and ZrO2, with ordered and uniform macropores have been obtained by this simple procedure. The pore size could be controlled readily by varying the polymer size and the porosity could be manipulated by modifying the volume ratio of polymer/ceramic particles. (C) 2003 Elsevier Ltd. All rights reserved.

Abstract:Porous piezoelectric materials are of interest for applications such as low frequency hydrophones. This is due to their high hydrostatic figures of merit and low sound velocity, which leads to reduced acoustic impedance and enhanced coupling with water or biological tissue. A wide variety of methods are available to produce porous structures such as using reticulated polymer foams or volatile additives which are burnt out during the sintering process (e.g. polymer spheres). Each processing technique and additive produces its own distinctive microstructure, particularly in terms of pore size, morphology and porosity volume fraction. The aim of this paper is to manufacture a variety of porous microstructures and relate the structures to measured hydrostatic figures of merit.