“…The percentage of the sintering aids added, as well as the degree to which they homogeneously disperse throughout the samples, determines the pore sizes. The local packing imperfections also contribute to a phenomenon called pore channeling, which actually increases the pore sizes in the initial and intermediate steps of sintering. − In fact, simulations − have confirmed that heterogeneous sintering increases the size of the pores by introducing different shrinkage rates at different spatial locations. 10 Effect of the sintering aid on the cumulative pore size distribution of samples prepared from the P1 powder. 11 Effect of the amount of sintering aid on the permeability and ideal separation factor of samples prepared from the P1 powder. 12 Effect of the sintering aid on the cumulative pore size distribution of samples prepared from the P2 powder. 13 Effect of the amount of sintering aid on the permeability and ideal separation factor of samples prepared from the P2 powder.…”
Silicon carbide (SiC) porous substrates are prepared by pressureless sintering of SiC powders under an inert atmosphere of argon. The porous SiC substrates were characterized by measuring their porosity, pore size distribution, surface characteristics, and structure. Their transport characteristics were investigated using N 2 and He as the test gases. Three different starting powders and four different sintering aids, Al 2 O 3 , B 4 C, carbon black, and phenolic resin, either by themselves or in combination, were investigated in terms of their ability to prepare good quality substrates. It was found that the porosity, pore size distribution, and transport characteristics of the resulting SiC-sintered bodies depend on the nature of the original powder, the particle size in the green SiC samples, and the type and molar ratio of the sintering aid utilized. Depending on the preparation technique, both mesoporous and macroporous materials could be prepared. These supports are currently utilized for the preparation of microporous membranes.
“…The percentage of the sintering aids added, as well as the degree to which they homogeneously disperse throughout the samples, determines the pore sizes. The local packing imperfections also contribute to a phenomenon called pore channeling, which actually increases the pore sizes in the initial and intermediate steps of sintering. − In fact, simulations − have confirmed that heterogeneous sintering increases the size of the pores by introducing different shrinkage rates at different spatial locations. 10 Effect of the sintering aid on the cumulative pore size distribution of samples prepared from the P1 powder. 11 Effect of the amount of sintering aid on the permeability and ideal separation factor of samples prepared from the P1 powder. 12 Effect of the sintering aid on the cumulative pore size distribution of samples prepared from the P2 powder. 13 Effect of the amount of sintering aid on the permeability and ideal separation factor of samples prepared from the P2 powder.…”
Silicon carbide (SiC) porous substrates are prepared by pressureless sintering of SiC powders under an inert atmosphere of argon. The porous SiC substrates were characterized by measuring their porosity, pore size distribution, surface characteristics, and structure. Their transport characteristics were investigated using N 2 and He as the test gases. Three different starting powders and four different sintering aids, Al 2 O 3 , B 4 C, carbon black, and phenolic resin, either by themselves or in combination, were investigated in terms of their ability to prepare good quality substrates. It was found that the porosity, pore size distribution, and transport characteristics of the resulting SiC-sintered bodies depend on the nature of the original powder, the particle size in the green SiC samples, and the type and molar ratio of the sintering aid utilized. Depending on the preparation technique, both mesoporous and macroporous materials could be prepared. These supports are currently utilized for the preparation of microporous membranes.
“…12,17 Today, even more complex arrangements as well as planar sections through samples with irregular pore and particle shapes have been successfully simulated and rearrangement (bulk body movement, i.e., particle rotation and translation) has been integrated in phase field, finite element, discrete element, and Monte Carlo models. 30,31,33,35,82 Furthermore, simulations of anisotropic shrinkage and defect formation during sintering of inhomogeneously packed powder compacts and of constrained films 36,51,67,[83][84][85][86][87][88][89] as well as simulations of nanoparticle sintering and other more complex processes of technical interest (see the recent examples 76,[90][91][92][93][94][95][96] presented together with the present paper at the International Conference on Sintering 2008, La Jolla, CA).…”
Coarsening of porosity during sintering has been observed in powder compacts of metallic, ceramic, and amorphous materials. Monitoring and modelling of the growth of individual (closed) pores in the late sintering stages are well established. Porosity is interconnected up to very high densities. Coarsening of the continuous pore space takes place during the initial and intermediate sintering stages. This coarsening is caused by localized transport of atoms or molecules (diffusion or viscous flow) as well as by bulk particle movement (rearrangement). Its quantitative exploration poses problems both experimentally and theoretically. Ways to characterize the geometry of the interconnected pore space and of closed pores are discussed with emphasis on stereological parameters. Recent and classical approaches, experimental findings with 2D model arrangements (as the formation and opening up of particle contacts, pore coarsening, and particle rearrangement) and some advances of computer simulations are discussed together with open questions.
“…In DEM, each particle is modeled as a sphere that interacts with its neighbors through appropriate sintering laws. DEM simulations of sintering has allowed the investigation of the effect of particle rearrangements 2–6 and of local heterogeneities due to the presence of nonsintering particles 7,8 . Recently it has also been used for the investigation of anisotropic sintering 9 and constrained sintering, 10 which are somewhat related to the problem addressed here.…”
We use discrete element method (DEM) simulations to study the evolution of defects during sintering. In DEM, the particulate nature of the sintering powder is taken explicitly into account because each particle is modeled as a discrete entity interacting with its neighbors. This allows to treat naturally the gain or the loss of contacts between particles, and to explicitly take particle rearrangement into account. These effects are particularly important when looking for the nucleation, growth or healing of local heterogeneities such as defects. We first study the evolution of a crack (generated, e.g., during ejection or drying processes) when no geometrical constraint is imposed. We then investigate how constrained sintering between two parallel planes may lead to crack initiation and growth. We show that the extent of interparticle rearrangement plays a major role in the evolution of the crack under such conditions. The main conclusion of these simulations is that some geometrical constraint is necessary for a defect to grow into a crack and that the presence of an initial defect is not a necessary condition to initiate cracks.
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