Papers by Keyword: Green Body

Abstract: The piezoelectric ceramic of PMN-PZT was prepared by gelcasting using N-hydroxymothl acrylamide(NMAM) as monomer. The green bodies with different microstructure and properties were obtained by changing solid contents of slurry. The effects of solid volume fraction in slurries on properties of PMN-PZT green bodies were investigated. The results that green shrinkage reduced from 5.95% to 1.47%, the green density increased from 3.51g/cm3 to 4.69g/cm³, and green bending strength increased firstly then decreased when solid content of slurry changed from 45vol% to 60vol%. SEM photographs revealed that^{Superscript text} the green body had a uniform microstructure and few agglomerates when the solid loading was 50vol%.

Abstract: The present work observed and analyzed the microstructures of various starting powders including SiC, AlN-R (Y / La) ₂O₃ as additives for LPSing (Liquid Phase Sintering), B/C additives for SSSing (Solid State Sintering), as well as the spray granulated powders as comparison, by using scanning electron microscopy SEM. The microstructure of molded green bodies was also posted. Present paper opens out the characters of the various perfect and defect of microstructures of these samples. Their effect on the processing and properties of SiC ceramics was analyzed and discussed.

Abstract: The gelcasting technique was used to fabricate 95 alumina ceramics green bodies. The gel system based on MAM-MBAM was low-toxicity in this study. The green bodies and the sinter obtained with solid content of 55vol% had high strength, density and quality. The influences of the monomers mole ratio (MAM/MBAM) and the monomers content (MAM and MBAM) on the compressive strength of green bodies, the solid content on the density, compressive strength and the shrinkage rate of green bodies were also discussed. The experimental results showed that the best mole ratio of MAM/MBAM was 12/1. Compressive strength increased with the increase of monomers content (MAM and MBAM). The microstructure of the green bodies indicated that the ceramic powders were connected by polymeric networks, and the ceramic powders in the green body distributed homogeneously and compactly.

Abstract: Friction between powder and tools plays a major role during cold compaction of PM components with results on the inhomogeneous densification. The present work deals with a new method of compaction for PM components by using the friction force between die and compacts as an active pressing force in order to reduce the density gradient. The proposal technique consists in moving the container of the die, during pressing stage to the punch direction with a well determined speed. As a result, the friction force acts in the same sense as the pressing load with better distribution of powder flow during compaction. The experimental results of compaction parameters versus density have proved the decreasing of the density gradient by increasing die/punch speed rate. A sharp density gradient on the specimen height moving container contrarily to the punch.

Abstract: The packing structure in green alumina bodies has been studied using thin sections of prefired bodies impregnated with refractive-index liquid examined with an automatic, polarizedlight microscope equipped with liquid-crystal adjustable quarter-wave plate and analyzer, and circularly polarized light. The combined intrinsic birefringence (caused by the anisotropy of the hexagonal symmetry of the alumina particles) and form birefringence (due to packing of the slightly elongated particles oriented in the green structure), can be quantified on a small scale. Birefringence values and slow-vibration directions are mapped for the anisotropic fine particles and agglomerates circumferentially or radially aligned in the structure. For some pre-sintered bodies, the interference pattern shows three radial dark brushes with relatively low birefringence, coming from the spider in the extruder. Slow-axis distribution shows random particle orientation in the spider region. The birefringence pattern often indicates a relatively high degree of circumferential alignment in the surface area where frictional force is present during forming. A uniform distribution of the birefringence represents a consistent green structure. The improved procedure for characterization of prefired body provides considerable insight to the optical crystallography of powder/particle arrangement in pre-sintered ceramic body and the relationship of the particle alignment with respect to flow and forming.

Abstract: A new ceramic gelcasting system was developed in this paper. The rheological behavior of alumina suspension with an addition of polymer was examined. Particular attention is given to the flexural strength of green body prepared from gelcasting in the presence of polymer.