Authors: Zhu Cheng, Jia Lin Sun, Fu Shen Li, Zhao You Chen, Long Gang Wan
Abstract: Fused magnesite, α–Al2O3 micropowder and aluminum powder were used as starting materials to form MgAlON and MgAlON-bonded MgO materials in nitrogen atmosphere. Influence of technical conditions, such as composition, on formation of MgAlON was studied. Influence of vapouring of MgO in low PO2 atmosphere at high temperature on sintering of MgAlON-bonded MgO material was also discussed, showing that vapouring of MgO makes the material porous and damages its sintering.
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Authors: Shao Feng Wang, Chang An Wang, Jia Lin Sun, Li Zhong Zhou, Yong Huang
Abstract: Porous SiC ceramics with high porosity and high strength were fabricated by gelcasting, with tert-butyl alcohol (TBA) as solvent, acrylamide (AM) as monomer, and in-situ reaction bonding with a-Al2O3 as sintering additive. SiC suspension with 10 vol% solid loading was successfully solidified by gel-casting to form high strength green body. The results showed that the compressive strength of the porous SiC ceramics increased with sintering temperature from 1300 to 1450°C, but porosity had little change, due to formation of more volume of cristobalite and mullite phases on the surface of SiC grains, accompanied by a large volume expansion effect. Very narrow single-peak distributions with about 2 mm median pore diameter could be found for the porous SiC ceramics. The porosity and compressive strength of the porous SiC ceramics sintered at 1450°C were 71.21 % and 12.14 MPa, respectively.
608
Authors: Xi Gao Peng, Jia Lin Sun, Gan Shi, Shao Ping Huang
Abstract: Based on an extensive comparison of test methods for abrasion resistance from home and abroad, a new technique for abrasion resistance at elevated temperature has been developed with some improvements. Two connected airtight chambers are designed to prevent compressed air from entering the sample chamber, so that heat loss of the sample chamber can be reduced and the chamber temperature is less disturbed. The sample surface temperature can reach stable within 5 min and the temperature fluctuation on sample surface can be less than 20°C in the course of inleting the compressed air at working temperatures up to1400°C. The repeatability was tested using float-glass plate as reference sample at ambient temperature and using high alumina bricks for elevated temperature. A variation coefficient under 7% at ambient temperature has been achieved. Comparison of abrasion resistance at elevated temperature was tested respectively on a high alumina brick and on a silicon nitride bonded silicon carbide brick and the results could be significantly distinguished. Nitrogen can be blown into sample chamber during heating the furnace to prevent nonoxide bearing samples from being oxidized.
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Authors: Xiao Hui Wei, Yan Jun Wang, Hong Xia Li, Jia Lin Sun
Abstract: The influence of silicon addition on the microstructure and properties of corundum-mullite refractory was studied. Results show that Si addition as raw material of the matrix can accelerate mullite crystal formation. The oxidation of Si leads to nucleation of mullite via liquid phase and gas phase. The network microstructure is formed by tiny mullite crystals with few glass phase. So it enhances obviously the high temperature strength of sintered corundum-mullite refractory.
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Authors: Jian Li Zhao, Chang An Wang, Akira Yamaguchi, Jia Lin Sun, Xin Sheng Zhang
Abstract: Al4SiC4 is probably used as non-oxide raw material for high-temperature ceramics. Al4SiC4 was synthesized by using starting materials of metal-carbon, metal-oxide- carbon or carbides. In this paper, Al4SiC4 has been synthesized by using oxides (Al2O3 and SiO2) and carbon as starting materials through carbothermal reduction process. The oxidation properties in air and O2 atmosphere by TG method and the stability of the synthesized Al4SiC4 heated in moisture were investigated. Pure Al4SiC4 phase was synthesized when heating the mixture powder of Al2O3, SiO2 and C (C : Al2O3 : SiO2 = 8 : 2 : 0.8, in molar ratio) at 1700°C for 8h in flowing Ar atmosphere. The synthesized Al4SiC4 powder consists of platelet shape grains with size of 68μm length, 35μm width and 1μm thickness. Al4SiC4 obviously oxidized from 800°C when heated in flowing air or O2 atmosphere. When keeping Al4SiC4 powder in moisture, it was not observed to be reacted with water by XRD and SEM analysis.
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Authors: Rong Lin Wang, Jing Long Bu, Zhi Fa Wang, Jia Lin Sun
Abstract: Zr-Al-O-N composites were prepared in N2 atmosphere at 1600oC with Ca-PSZ and Al powders as raw materials. Phase composition of the composites and formation reaction mechanism were investigated by XRD and SEM analyses. With Al content increaseing from 1% to 50%, phase composition of the composites were changed step by step. The results showed that phase compositions of the composites are related to Al content.
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Authors: Fu Wang, Wen Bin Cao, Jia Lin Sun, Rong Liang He
Abstract: SiC powder was synthesized by carbothermal reduction method using silica sol and amylum as
reactants in closed and open graphite crucibles, respectively. The phase composition and morphology of
the powders were characterized. Formation of phase-pure silicon carbide can be achieved at 1700°C for
1h. Increasing reaction temperature and extending holding time can greatly promote the production of
SiC. The products synthesized in open graphite crucibles are mainly composed of equiaxial β-SiC
particles while those synthesized in closed graphite crucibles are β-SiC particles and nanorods.
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Authors: Jin Feng Wang, Ya Chun Gao, Xian Feng Yang, Jia Lin Sun, Zhi Peng Xie
Abstract: Ultrafine ZrO2 suspension with stable high solid loading was prepared, and ZrO2 ceramic
materials with uniform structures were fabricated through gelcasting. Zeta potential of the ultrafine ZrO2
suspensions with A-type dispersant, triammonium citrate, and without dispersant was measured. The
influencing factors on suspension flowability as the content of dispersant, pH value, solid loading, and
milling time were studied in detail. And the optimum premixed solution/initiator (APS)/catalyst
(TEMED) ratio for gelcasting was investigated. The results showed that A-type dispersant was suitable
for dispersing of ultrafine ZrO2 particles in aqueous premixed solutions; the optimized content of
dispersant was 2%~2.5% of ZrO2 volume; ZrO2 suspension displayed a minimum viscosity at pH 10.66;
the upper limit of solid loading was 54vol.%; and the appropriate milling time was 12 hours. When
premixed solution/initiator (APS)/catalyst (TEMED) ratio was 100/1/0.5, ZrO2 suspension has a better
gelcasting behavior.
740
Authors: Mu Yun Lei, Cun Xin Huang, Jia Lin Sun
Abstract: In this paper, transparent polycrystalline magnesium aluminate spinel was fabricated by hot
pressing ultra fine high purity spinel powder using LiF as the sintering aid in vacuum, then hot isostatic
pressing (HIPing) the sintered body to improve the optical properties of the sample. The transmittance
and the strength of the samples before and after HIPing were measured; morphologies of the fracture
surface of the samples before and after HIPing were observed. Following hot pressing, the grain size of
the sample is small; the transmission values are low and may varied at different sites in the same sample.
After HIPing, the strength of the sample decreased, the grain size increased obviously, and the
transmittance and the uniformity of transmittance increased significantly. The panel of transparent
spinel up to 200 mm in diameter and 8 mm thick was fabricated by this method; the average
transmittance of the spinel is above 80% in the range between 2 μm and 5 μm .
1200
Authors: Hou Xing Zhang, Y. Huang, Yan Ruo Hong, Jia Lin Sun, N.S. Zhou
Abstract: The isothermal oxidation behaviors of MgAlON/Si3N4 composite which was synthesized by pressureless nitridation reaction sintering have been investigated in flowing air at 1100°C, 1200°C and 1300°C respectively. The results show that the composite represents excellent self-healing property of oxidation at 1300°C, which might be attributed to the formation of protective silicate film with reasonable viscosity, good spreading power and very low oxygen diffusion coefficient, and to the formation of compact surface resulted from the expansion effect of forming mullite from SiO2 and Al2O3. However, the self-healing property of it is relatively poor at 1100°C and 1200°C as compared to 1300°C.
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