Papers by Author: Yong Li

Abstract: This paper studied the high temperature creep properties of high-alumina bauxite (the mass fraction of Al₂O₃ in the new ore is about 78, the following abbreviations for Al₂O₃~78). The results indicated that the Al₂O₃~78 high-alumina bauxite mainly are corundum phase after high temperature sintered.When the temperature is 1100°C, corundum exists as crystal phase and the connections between grains are directly. The creep resistance of samples is very good at this temperature and the creep rate of 50 hours heat preservation is-0.266%. When the temperature is 1200°C, liquid phase starts to produce in a large number and the creep rate in 50 hours heat preservation is-1.589%. When the temperature is 1300°C, because of the further increase on the amount of liquid phase and wetting coated corundum particle, the direct connections between corundum particles are broken and the creep resistance is greatly reduced, the creep rate in 50 hours heat preservation is-4.088%. The creep curve fitting after 25 hours indicated that the creep property shows linear relations in three different temperatures after 25 hours. When the temperature is 1200°C and 1300°C, the creep variables arise rapidly in linear which declare the creep resistance of corundum is poor and increasing with temperature go up, more corundum phase is covered by glass phase and the creep resistance reduces dramatically.

Abstract: Specimens were prepared by using iron-rich magnesia and high-pure magnesia as the main starting materials, and introducing fused corundum of 3%(in mass), 6%, 9%, 12%, 15% respectively and sintered at 1420°C.The samples were characterized by XRD and SEM. The results show that in-situ synthesized composite spinel solid solution were formed in the reaction between iron-rich magnesia and fused corundum. Iron oxides play a key role on the formation of spinel solid solution. When fused corundum was added in a certain particle size, the material showed core-shell structure. Outer layer of core-shell structure were spinel solid solution and the inside were corundum. These core-shell structure make the synthesis of spinel solid solution bonded periclase material at low temperature happen.

Abstract: This paper takes Al₂O₃-70% natural mullite raw bauxite ore (Referred to 70-ore) and Al₂O₃-70% bauxite based homogenized grogs green adobe (Referred to 70-grog), produced by Beijing Tongda Refractory Technologies Co.,Ltd.through wet homogenization and vacuum pug process, as raw materials. 70-ore and 70-grog are fired respectively at 1100°C, 1300°C, 1400°C, 1600°C for 4 hours. Research on the influence of sintering temperature on the phase compositin, microstructure and bulk density. Analysis on the phase reaction during the sintering process. The results show that: Phase distribution of 70-ore is uneven. α-Al₂O₃ decomposed by diaspore is difficult to contact with amorphous SiO₂ decomposed by kaolinite, this makes α-Al₂O₃ particle be unable to dissolve into amorphous SiO₂, and causes twice crystallizing of mullite reaction hardly to happen. After a series of homogenizing treament, diasepore and kaolinite phase of 70-grog distribute more uniformly, which don’t destory the ore structure, and accelerate the twice crystallizing of mullite reaction. Compared with 70-ore, the twice crystallizing of mullite reaction extent of 70-gorg is more thoroughly. Rising the sintering temperature is beneficial for the twice crystallizing of mullite reaction, the growth of mullite and the bulk density of mateials. The adobes produced through wet homogenization and vacuum pug process have a big volume shrinkage, so controlling the removal of crystal water,the formation and growth of mullite are the keys to get dense bauxite based homogenized grogs.

Abstract: The present explains sintering characters of the Al₂O₃-86 homogenized bauxite under wet processes homogenization, which includes classified bauxite mine, wet grinding, vacuum extrusion, sintering in tunnel kiln,etc. DSC and TG reveal an evident peak of absorption heat at 531°C, resulting from the dehydroxylation of bauxite. Green samples held at 550°C*6hrs were heated up to different temperatures, and the properties of weight loss, linear change, bulk density and apparent porosity were measured. The data show that liquid-phase emerge and sintering process goes slowly above 1100°C. At 1500°C, large amounts of liquid-phase form, making liquid-phase sintering have a positive effect. The analysis of XRD and SEM indicate that, corundum grains develop more inadequate and most of the corundums interlace in a compact way, which can separate the widespread liquid phase and improve the sintering capability of homogenized bauxite.

Abstract: This paper explains sintering properties of Al2O3-70(referred to as the 70 green sample) natural mullite that was prepared by the process of homogenization, wet grinding, vacuum extrusion and high-temperature tunnel kiln sintering. The results show that 70 green sample's dehydroxylation temperature started in 528 °C; 70 green sample's sintering densification started in 1500 °C; 70 green sample had not completed sintering in the 1600 °C, and at this temperature, to prolong the holding time also won't realize densification. After sintering at 1600 °C, the sample's bulk density is 2.82. In this sample, the mullite phase was uniform distribution, density, low porosity and most are closed porosity.

Abstract: Using alumina-rich MgAl₂O₄ spinel AR78 and 97 fused magnesite as raw materials, brine as the binder, magnesia alumina spinel bricks close to theoretical composition and spinel bricks with zirconia have been prepared. Then the influences of zirconia on the properties of MgAl₂O₄ spinel bricks are researched. The results show that: (1) After the addition of zirconia, the direct bonding structure formed between spinel and zirconia can strengthen matrix structure and promote sintering, so the structural properties, the alkali resistance performance and the creep property of MgAl₂O₄ spinel bricks are all improved. (2) The optimal addition of zirconia is 6%, with which the spinel bricks have well alkali resistance performance and creep property of which the final creep rate is -1.46% after creep experiment for 50h.

Abstract: Using alumina-rich MgAl₂O₄ spinel AR78 and 97 fused magnesite as raw materials, brine as the binder, magnesia alumina spinel bricks close to theoretical composition have been prepared. Then the high temperature creep experiments are carried on. The creep property is analyzed by microstructure and creep curve. The results show that: (1) The magnesia alumina spinel bricks close to theoretical composition prepared have well sintering performance and compact structure.(2) The specimen 1# has the best creep property, of which the final creep rate was -1.45% after creep experiment for 50h. (3) Under high temperature and pressure for a long time in creep experiment, the internal of spinel is further sintered, the pores of the specimens are rearranged.

Abstract: α-Si₃N₄ possesses excellent sintering activity, which is used to prepare high performance Si₃N₄-based ceramics and composite refractory. Si₃N₄ powder is always synthesized by nitriding silicon in controlled-atmosphere furnace whose furnace volume is very small(effective volume: 1840×1420×1660mm), the extreme reaction heat is difficult to diffuse, which leads to high reaction temperature and conversion of α-Si₃N₄ to β-Si₃N₄, thus α-Si₃N₄ is difficult to be obtained in controlled-atmosphere furnace. While flame-isolation nitridation shuttle kiln has much larger furnace volume to conduct reaction heat (effective volume: 11500×4190×1684mm), so it owns homogeneous temperature field and stable low-temperature environment which benefits the preparation of α-Si₃N₄. Thermodynamic analysis of Si-N system is shown that Si₃N₄ can be formed by two formats: direct nitridation of Si(s) and indirect nitridation of SiO(g); to ensure completely nitridation, the particle size of silicon powder should be less than 88μm. With reclaimed powder from polysilicon cutting slurry as starting materials, both reactive α-Si₃N₄ and SiC mixed powder were successfully prepared in flame-isolation nitridation shuttle kiln. Because of the gas-gas reaction between SiO(g) and N₂(g), α-Si₃N₄ is fiber-like and in favor of processing high quality Si₃N₄-based materials.

Abstract: Using alumina-rich MgAl2O4 spinel AR78 and 97 fused magnesite as raw materials, brine as the binder, magnesia alumina spinel bricks close to theoretical composition have been prepared. The phase composition and microstructure of the specimens were analyzed and characterized. The alkali resistance property of specimens was researched using static crucible method. The erosion mechanism of alkali vapor to specimens was studied by XRD, SEM and EDS. The results show that: (1) The alkali resistance property of MgAl2O4 spinel bricks were improved obviously when the addition of magnesite is more than 7%. (2) The alkali resistance property of MgAl2O4 spinel bricks is the best when the addition of magnesite is 10.3%.

Abstract: The theoretical composition was made from MgO-rich MgAl2O4 (MR66) and alumina powder. The static crucible method was used to study alkali-resistance of the block samples. It has been observed that alkali steam permeated into the hole and reacted with corundum particles that produced β-Al2O3 by means of XRD, SEM and EDS. It led to volume expansion, cracks and melting erosion of corundum particles. The specimen of the 32% content of MgO has good physical and chemical properties and excellent alkali erosion performance. So the specimen is suitable for oxy-fuel combustion for glass melting furnace.