Study On Mechanism Of Pulse Electric Current Sintering Of Ceramic Materials

Pulse electric current sintering is an advanced technology for materials synthesis and processing with potential application. But the sintering mechanism is in dispute. In order to get best sintering effects,the mechanism of pulse electric current sintering was investigated in present dissertation.Main efforts were put on mechanism of sintering of non-conductive materials. The effects of magnetic and electric fields as well as high frequency wave were believed to exist in sintering of non-conductive materials,which have relationship with the current turning direction at the surface of punch.XRD analysis at different depth of A12O3 sintered body indicates that the temperature at top surface is much higher than that at bottom surface,and it has trace to be bombarded by high-energy particles at top surface. Further XPS analysis shows that:the difference of Cls peak site between practical and standard for SPS top surface and bottom surface as well as HP surface increase gradually which indicate that the escaping energy of C particles from body bonding increase gradually. These results are the evidence for the existence of pulse electric field. As the electrons and C particles sprayed by electric field are more at top surface than at bottom,the top surface get more bombardment and make the temperature higher. The result of magnetic particles migrating in sintering of Al2O3-ZrO2-Ni sample is the evidence for the existence of pulse magnetic field. Cu body bathed in BN is heated in edge side indicates that conductive metal material absorbs magnetic energy easy. The results of crack analysis for reaction sintering of ZnO-Al2O3 indicate that periodic high temperature region exists in sintering body. And the periodicity has relationship with die diameter. As the graphite die has all of the conditions to induce high frequency electric-magnetic wave,and the frequency of resonance body also has relationship with diameter,which is the evidence for existence of high frequency electric-magnetic wave.The results of sintering conductive TiB2 indicate that the spark effect between powders and tending-to-skin of pulse current exist at the same time. It behaves the tending-to-skin effect with lower heating rate,and it behaves spark effect with higher heating rate. Powder surfaces are activated by spark. The grain sizes are controlled not only by sintering time but also by activation energy,so optimum heating rate exists in order to get smallest grain size.TiB2 nano-powders were prepared by ball milling and acid treatment. The investigation of nano mechanism indicates that it has relationship with absorbing H+ of Ti and layered structure of TiB2. The composite powders exhibit semi-conductive property because of the absorption of nano-powders. It exhibits non-conductive property when its resistance is much higher than circle materials;while it exhibits conductive property when its resistance is much lower than circle materials.