Xiao Shan Ning

Preparation and properties of hydroxyapatite filters for microbial filtration

Abstract Preparation and properties of two kinds of hydroxyapatite filters, filter cloths and porous ceramics, were investigated. The filter cloth was prepared by depositing nanosize ceramic hydroxyapatite on a cotton fabric. The porous ceramic with pore size of several micrometers or less was fabricated by using water soluble starch as a pore former, and its permeability was controlled by adding insoluble starch. Bacterial filtration tests showed that the six-layer filter cloth can clear bacteria effectively, and the porous ceramic can remove 100% of the bacteria. Both the filter cloth and the porous ceramic can be used to clear or separate microbes.

Development of a directly bonded aluminum/alumina power electronic substrate

Abstract A process for manufacturing a directly bonded aluminum/alumina (DBA) power electronic substrate was developed in the present work. The bonding interface of the substrate was studied using transmission electron microscopy to elucidate the bonding mechanism of aluminum to alumina. The bonding strength, the wetting ability, the wire bonding capacity, the break down voltage and the thermal resistance of the DBA substrate were studied in comparison with those of a widely used directly bonded copper/alumina substrate. The results show that the DBA substrate has an excellent thermal cycle tolerance, and it is most suitable for assembling power electronic devices that are used under severe condition such as in vehicles.

Study on the thermal conductivity of silicon nitride ceramics with magnesia and yttria as sintering additives

Abstract In this work, the thermal conductivity of Si 3 N 4 ceramics sintered with 5 wt.% Y 2 O 3 and different amounts of MgO as additives at different temperatures was studied. Mg 5 Y 6 Si 5 O 24 was detected by X-ray diffraction (XRD) and experimental results showed that the amount of Mg 5 Y 6 Si 5 O 24 and the thermal conductivity of Si 3 N 4 ceramics were affected by both the sintering temperature and the amount of MgO. The relationship between Mg 5 Y 6 Si 5 O 24 and the thermal conductivity of Si 3 N 4 ceramics was discussed.

Interface Of Aluminum/Ceramic Power Substrates Manufactured By Casting-Bonding Process

New processes for manufacturing Al/ceramic power substrates have been developed. These processes use a casting-bonding method to bond Al plates to the both sides of ceramic plates. The Al plates formed on the substrates are then chemically etched to be a desired shape using the conventional technology, followed by plating nickel on them. The power substrates manufactured by the process have both a perfect interface and an excellent thermal stress tolerance. Hence, these processes are especially suitable for assembling high reliability power devices such as IGBT power modules.

Study on the thermal conductivity and microstructure of silicon nitride used for power electronic substrate

Abstract The thermal conductivity and microstructure of Si 3 N 4 ceramics used for power electronic substrate were studied in present paper. Thermal conductivity of Si 3 N 4 ceramics sintered at different temperatures varied greatly. The microstructure of the specimens was studied with X-ray diffraction, EDS and transmission electronic microscope to reveal the difference in thermal conductivity. The experimental results showed that microstructure of Si 3 N 4 ceramics sintered at different temperatures had different components in their grain phase and grain boundary phase, while electrical properties showed not much difference with different sintering temperatures.

The study and fabrication of Al/AlN substrate

Abstract In this work, by the die-casting–bonding process at 948–1098 K and under N2 atmosphere, Al/AlN substrates is produced successfully. The bonding strength of Al and AlN substrate, which is more than 15.56 MPa, is tested by a mechanic testing equipment. The microstructure of the performance of the Al/AlN substrates is investigated by SEM and optical microscope. There is no reaction product in the interface of Al/AlN; the crystal of aluminium grow directly on the surface of AlN.

Particle Size Control in Sol-Gel Synthesis of Nano Hydroxyapatite

Sol-gel method is one of the most potential techniques for mass-production of nano hydroxyapatite. In this paper, particle size control techniques, including dripping speed control, addition of several dispersants such as ammonium citrate, castor oil and silane coupling agent, as well as usage of insoluble and water soluble starch additives, were investigated. The particle size and microstructures of as synthesized hydroxyapatite were studied by X-ray diffraction, Scanning electron microscopy and dynamic light scattering. The results indicated that all the control techniques had considerable effects on decreasing the crystallite size, and the starch additives also exhibited obvious effect on preventing the agglomeration of nano crystallites during the synthesizing process.

Study on Thermal Conductivity of SPS-Sintered Si3N4 Ceramics after Heat-Treatment

α-Si3N4 ceramics were sintered at a low temperature of 1773K by using a spark-plasma-sintering (SPS) method with different heating rates, and then they were further heat-treated at different temperatures from 1773K to 2273K, to study the effect of the heating rate of SPS on the microstructure and the thermal conductivity of Si3N4 ceramics after the heat-treatment. Results show that the heating rate of SPS has great influence on the phase transformation and the microstructure of the β-Si3N4, but it has little influence on the thermal conductivity of the ceramics. This proves that the thermal conductivity of the ceramics does not have an obvious relationship with the ratio and the size of the columnar β-Si3N4 grain.

Thermal Conductivity and Mechanical Property of Si3N4 Ceramics Sintered with CeF3/LaF3 Additives

In this paper, rare-earth fluorides were used as sintering additives instead of rare-earth oxides, the influence of the type and the amount of the fluoride on the thermal conductivity, hardness and strength of Si3N4 ceramics was studied. Results show that the thermal conductivity of a sample sintered with CeF3 is nearly 10% higher than that of the sample sintered with Ce2O3, while the samples sintered with LaF3 increases further 15% as comparing with the samples sintered with CeF3. The strength of the samples changes reversely. These results express that the thermal conductivity of Si3N4 ceramics can be improved by using rare-earth fluoride additives instead of the oxides, and the type of rare-earth fluorides has a significant impact on the properties of Si3N4 ceramics.

Effects of Technical Parameters on the Phase Composition and Microstructure of Yb α-SiAlON Prepared by Combustion Synthesis

In this paper, Yb a-sialon powders with elongated grains have been prepared by combustion synthesis. The effects of diluents, nitrogen pressure, adding a-sialon seeds and NH4F on the phase transformation and microstructure development of the samples are discussed systematically. The experimental results show that the addition of diluents, proper nitrogen pressure and additive NH4F can facilitate the nitridation of Si. It was also found that the added a-sialon seeds and NH4F are beneficial to the nucleation and growth of elongated grains.