Sintering In Presence Research Articles

Investigation of Glass- Steel Slag Foam Composite Sintering in Presence of SiC

Investigation of Glass- Steel Slag Foam Composite Sintering in Presence of SiC

Production of porous SiC by liquid phase sintering using graphite as sacrificial phase: Influence of SiO2 and graphite on the sintering mechanisms

Porous silicon carbide (SiC) is a promising ceramic for high-temperature applications due to its unique combination of properties. In the present work, a fabrication route for porous SiC is presented using graphite spherical powder as sacrificial phase to introduce porosity. By varying the initial amount of sacrificial phase, high-performance SiC materials with porosities in the range 30–50% were manufactured and characterized in terms of microstructure, density, thermal conductivity and flexural strength. The materials were fabricated by liquid phase sintering in presence of 2.5 wt.% Al2O3 and Y2O3 as sintering additives. The results indicate that the SiO2 present in the starting SiC powders interacts with the sintering additives forming liquid phases that promote densification and weight loss. Besides, an Al-Si liquid phase is formed at higher sintering temperatures, whose contribution to densification is inhibited in presence of graphite due to the formation of Al-rich carbides.

Investigation of europium titanate EuTiO3 obtaining process by method of Eu2O3 and TiO2 solid-phase sintering in presence of carbon

Investigation of europium titanate EuTiO3 obtaining process by method of Eu2O3 and TiO2 solid-phase sintering in presence of carbon

FAST/SPS sintering of nanocrystalline zinc oxide—Part I: Enhanced densification and formation of hydrogen-related defects in presence of adsorbed water

This part is focused on the effect of surface bound water on the densification behavior and defect stoichiometry of zinc oxide. The second part [doi: 10.1016/j.jeurceramsoc.2015.12.008] concentrates on the effect of hydroxide complexions on the microstructural development, texture formation and anisotropic grain morphology. Nanocrystalline zinc oxide powder was humidified or dried followed by quick heating (100K/min) with field-assisted sintering technique/spark plasma sintering (FAST/SPS). Densification is strongly enhanced due to hydroxide-ion-diffusion mechanism, which shows species with lower valence and ionic radius in comparison to oxygen ions. The lowered activation energy for densification exhibits no impact of the sintering electric current on this enhanced densification behavior. The defect stoichiometry and structure of sintered zinc oxide was analyzed by several spectroscopic methods, indicating the formation of hydrogen-related defects for sintering in presence of bound water, while no hydrogen was detected for sintering of dried powder.

Theory of Sintering in Presence of Pressure and Torque

Experiments like the sintering of single crystal spheres on a single crystal plate, the sintering of particle rows or 2D arrangements of powder particles as well as recent experiments by in‐situ Synchrotron Computer Tomography show movements of entire particles beyond the particle center approach described by the well‐known two particle model. Several attempts exist to describe these cooperative material transport processes by an analytical model of the sintering of two wires by grain‐boundary diffusion. The described mechanisms are either rotations caused by asymmetric sintering necks or the application of a torque or changes of the rate of sintering by a normal stress in the sintering neck. To develop a more comprehensive model of sintering, volume diffusion was included in addition to grain‐boundary diffusion and all driving forces mentioned above are used. As a result, the influence of normal stress, torque, and ratio of the sintering neck curvatures on the stress along the contact grain boundary, the diffusion current and the rate of removal along the sintering neck are shown. The contribution of volume diffusion and grain‐boundary diffusion to sintering was also investigated, confirming that a large sintering neck and high sintering temperatures result in a dominating influence of volume diffusion. The shrinkage rate and the rate of rotation provided by this model were used in a subsequent numerical simulation. For several stages of sintering, the influence of particle radius and sintering temperature on the rolling angle of sintering particles was analyzed in 2D. Furthermore, the impact of external normal stresses on the rolling angle is shown. The simulation model gives a surprising result: The speed of wire rolling shows the same behavior as sintering kinetics—a high speed for small particles, small sintering neck diameter and high temperature, but the cumulated rolling angle for small particles is low compared to that for larger particles. Finally, a new approach for simulating particle rotation and rolling caused by torques due to grain‐boundary anisotropy in 3D is presented, which is based on an existing Discrete Element Method sintering model. This model is applied to a row of particles confirming previous observations from the 2D sintering simulations.

Analysis of final stage of sintering in presence of a liquid phase : K-H. Kim, S-J.L. Kang. (Korea Advanced Institute of Science and Technology, Daejon, Korea)

Analysis of final stage of sintering in presence of a liquid phase : K-H. Kim, S-J.L. Kang. (Korea Advanced Institute of Science and Technology, Daejon, Korea)

Structure development in powder processing of polyphenylene sulfide

AbstractThe thermal and crystallization behavior of polyphenylene sulfide (PPS) in the context of its structure development in solid‐state processing is reported. The solid‐state processing of polymers involves cold compaction of the powder, followed by sintering. Since this process comprises of heat treatment at high temperatures for extended periods, the structure of PPS would be expected to be affected. An attempt has been made to elucidate the effect of compaction and sintering process parameters on the physical and chemical structures of the polymer. The changes in the structure of the polymer were monitored by characterizing its melting and crystallization behavior. It was observed that compaction resulted in changes only in the physical structure, leading to destruction of the smaller/less stable crystallities. The thermal treatment at high temperatures led not only to physical changes involving crystal growth and perfection but also to chemical changes in the structure, resulting in modification of crystallization behavior. The extent of change was found to be different for PPS in the powder form and in the pellet form, which is explained on the basis of the restricted diffusion of air in pellet form as compared to the powder. Such changes observed in the samples were also dependent on the type of sintering medium. The sintering in presence of nitrogen did not show significant changes in the crystallization or melting behavior. Thus, the structure development in solid‐state processing of PPS was influenced by the sintering time, temperature, and sintering medium, leading to physical and/or chemical changes.