An important, rather novel procedure for the synthesis of submicron crystalline multicomponent oxide ceramic powders has been studied. The synthesis of powder, a ferrite material, has been used as a model system for understanding the synthesis process. The effect of the fuel content, powder packing, and surface heat loss has been investigated in terms of the maximum reaction temperature and reaction period, phase formation, and particle size and morphology. It has been shown that the maximum temperature and reaction period can be tailored to produce different phases. The submicron features of the synthesized powders are indicated by the large surface area values obtained from BET measurement.
Abstract-A theoretical model has been developed to describe simultaneous momentum, heat, and mass transfer phenomena in disordered porous materials. The model can be applied to a wide variety of engineering-related fields, e.g., the drying and/or burnout of processing aids in the colloidal processing of advanced ceramic materials. Simulations based on the model predict the local temperature and mass distribution of the porous body as a function of time and position. This information can then be coupled with known mechanical properties of the body to predict internal stresses generated during removal of liquid from the body. The theoretical model has potential application to many engineering problems, e.g., the optimization of processing conditions in the design of an improved binder removal process. The model is evaluated using experimental data on binder removal from a ceramic green compact consisting of submicron a-Al,O,
A combined experimental and theoretical investigation of the sedimentation of unstable colloidal ceramic suspensions has been performed. Suspensions containing submicron-sized a -A l 2 O 3 particles were prepared at various pH values in order to modify suspension stability. Particle volume fraction during sedimentation was determined as a function of position and time by gamma-ray densitometry. A population balance model was developed to account for various coagulation and decoagulation mechanisms that affect sedimentation behavior in flocculating suspensions. Model predictions were then compared with experimental measurements, in order to establish the validity of the theoretical model.
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