Influence of porogen type and copper powder morphology on property of sintering copper porous materials

Copper porous materials have been manufactured by the method of powder metallurgy.Electrolytic copper powders and atomized copper powders are used as matrix material.Methylcellulose and paraffin are used as porogen.The influence of porogen type and copper powder morphology on the property of copper porous materials is investigated as well.The results show that copper porous materials with paraffin as porogen have lower porosity and permeability compared with materials using methylcellulose as porogen,due to the different pore-forming mechanisms.The pore forming mechanism of methylcellulose is thermal decomposition,while the pore forming mechanism of paraffin is melting–evaporation.The morphology of copper powders affects the contact state between adjacent powders,which further influence the sintering shrinkage.The porous materials using arborescent copper powders as matrix have lower porosity,smaller pore size and lower permeability,compared with materials with atomized copper powders as matrix.

Simulation of the neck growth of non-isometric biosphere during initial sintering

Because powders are mostly non-isometric during the sintering process, copper powders were chosen to study the effects of four material transport mechanisms, including surface diffusion, grain-boundary diffusion, volume diffusion, and multi-couplings. These material transport mechanisms were studied with respect to sintering neck growth of a non-isometric biosphere during initial sintering. The evolution of the neck growth in the four transport mechanisms was simulated by Visual C＋＋ as well based on the model of different particles. The results show that the increase of the sintering temperature, both the grain-boundary diffusion and volume diffusion play primary roles in neck growth, while surface diffusion gradually becomes the secondary mechanism. Both the sintered neck and the shrinkage of the two centers increase with increasing temperature by means of the coupling diffusion mechanism. The radius of the sintering neck decreased, and the shrinkage rate of the two centers increased with an increase of the diameter ratio of the two spheres.

Porous Alumina Ceramics Fabricated by Spark Plasma Sintering

Porous alumina of regular spherical particles was fabricated with the spark plasma sintering （SPS） and then compared to those obtained through conventional hot pressing （HP）. The effects of the parameters of the heating process on porosity were also investigated, Microstructural studies suggest that porous ingots including regular pores be made out of regular spherical alumina particles due to the close sphere packages. A comparative study on the relative necks of the specimens produced by SPS and HP indicates an enhancement of neck growth with SPS. Contrasting the theoretical values to the experimental results over the relative necks indicates that a proper relationship between the relative necks and the porosity can be established by a sintering model.

Interface interaction between SiO_(2) and magnetite under high temperature:particle migration and inhibition mechanism

Silicon is one of the main gangue components in iron ore,usually in the form of quartz and olivine.Numerous studies have shown that SiO_(2) has a two-sided effect on the consolidation of pellets during high-temperature oxidation roasting of magnetite.However,it is very difficult to capture the structural evolution and migration mechanisms during high-tem-perature roasting process by existing experimental methods.Therefore,the influence of SiO_(2) on the consolidation behavior of magnetite was studied through a series of roasting experiments and molecular dynamic simulation.The results show that the consolidation index and particle growth index decrease with the increase in SiO_(2) content in the particles.At 1573 K,the liquid phase promotes the recrystallization growth of hematite at high temperature.Molecular dynamic study shows that it is difficult for quartz SiO_(2) to form sintering neck with Fe_(2)O_(3).When the calcination temperature is higher than 1400 K,the Fe_(2)O_(3)-Fe_(2)SiO_(4) system produces a considerable sintering neck structure after relaxation.The atomic migration ability of Fe_(2)SiO_(4) is much higher than that of Fe_(2)O_(3).The higher atomic migration ability of Fe_(2)SiO_(4) is the main reason for the formation of the sintering neck.

Sintering Behavior of Porous Titanium Fiber Materials

The porous titanium fiber materials with open porosity were successfully prepared by the vacuum sintering technology. The morphology characteristics of sintering neck of porous titanium fiber materials were investigated by scanning electron microscopy （SEM）. The results show that the formation and growth of sintering neck of porous ti- tanium fiber material approximately follow the rule that the primary mechanism is grain boundary diffusion and sub- sidiary mechanisms are other diffusion mechanisms during the sintering process. The formation and growth of the sintering neck depend mainly on the sintering temperature and slightly on the soaking time. The sintering system of porous titanium fiber material was determined and the equation of the sintering neck＇s length was established.