Preparation of ZrB_(2)-ZrO_(2)-SiC Composite Powder by Carbothermal Reduction from Zircon

Using zircon,boric acid and carbon black as starting materials,ZrB_(2)-ZrO_(2)-SiC composite powder was synthesized by calcining at 1500℃in flowing argon atmosphere.The effects of the soaking time(3,6 and 9 h)and the addition of additive AlF_(3)(0,0.5%,1.0%,1.5%,2.0%and 2.5%,by mass)on the phase composition and the microstructure of the synthesized products were investigated.The results show that:(1)ZrB_(2)-ZrO_(2)-SiC composite powder can be synthesized by carbothermal reduction at 1500℃in flowing argon atmosphere;ZrB_(2) and ZrO_(2) are granular-like,and SiC crystals are fiberous;(2)with the soaking time increasing,the amount of ZrB_(2) increases,the amounts of m-ZrO_(2) and SiC decrease,and the total amount of non-oxides ZrB_(2),SiC and ZrC gradually increases;the optimal soaking time is 3 h;(3)compared with the sample without AlF_(3),the sample with 0.5% AlF_(3) has decreased m-ZrO_(2)amount,noticeably increased ZrB_(2) amount but decreased SiC amount;however,when the addition of AlF_(3) increases from 0.5%to 2.5%,the m-ZrO_(2) amount increases,the ZrB_(2)amount decreases,and the SiC amount changes slightly;the optimum AlF_(3)addition is 0.5%.

引入镁砂对矾土基刚玉-莫来石均质料性能的影响

在以两种不同化学组成的矾土生料为原料制备的80级矾土基均质料的基础上,研究了通过外加不同比例(加入质量分数分别为0、2%、4%、8%)、不同粒度(分别为3~1和1~0. 5 mm)的烧结镁砂对其烧结性能、物相组成和显微结构的影响。结果显示:以两种铝矾土生料为原料在最佳烧结条件为1 570℃保温3 h,可制备w(Al_2O_3)≈80%的矾土基均质料,其主要物相为莫来石和刚玉,二者分布均匀且交叉排列形成无序结构。以此为基础,外加4%(w)粒度为3~1 mm的烧结镁砂时,可在保证矾土基刚玉-莫来石均质料耐高温性和体积密度不降低的前提下,减少低熔点物,促进晶体发育,同时还能引入尖晶石相。

Progress in Research and Development of Refractory Oxide-Nonoxide Composites

Some of the progress made in our laboratories in collaboration with industry in research and development work on high performance oxide-nonoxide composites for metallurgical applications has been reviewed. （1） SiAlON bonded corundum composites for blast furnace usage have been produced by reduction-nitridation sinte-ring at high temperature, using bauxite instead of alu-mina in the matrix. （2） Low carbon Al2O3 - SiAlON slide plate materials successfully used in high quality steel continuous casting have been developed in which most or all of the graphite in Al2O3 - C brick is replaced by bauxite-based β-SiAlON. （3） A1/Si metal bonded A12 03 - C material characterized by low carbon content, low firing temperature and in-situ formation of carbides and nitrides at high temperature during service are found to possess very high hot strength and very good thermal shock resistance and have also been successfully used as slide plates in ladles and tundishes for high quality steel casting.

Some Aspects in the Development of High Performance Refractories for Iron and Steel Making in China

In the past 25 years in China, to meet with the rapid increase in steel production accompanied by adoption of advanced metallurgical technologies, there has been fast development of China＇ s refractories industry in production capacity, in quality improvement and in development of new products. Sophisticated high performance refractory materials mainly based on our rich reserves of magncsite, bauxite and flake graphite have been developed, such as carbon-bonded products, high purity oxide products, bauxite-based low creep and high strength high alumina bricks and LC, ULC and ZC castables. They have been used in blast furnaces, BOFs, EAFs, secondary refining and continuous casting with considerable improvement in service pecformance.

Evolution of Phase Composition and Microstructure of Al_2O_3-Si-Al Composite at High Temperatures in Reducing Atmosphere

Al2 O3-Si-Al composite specimens with the size of 25 mm × 25 mm × 125 mm were prepared using fused alumina （as aggregates and fines）,ultra-fine α-Al2O3,Si and Al powders as starting materials,liquid phenol formaldehyde resin as the binder,pressing and heating at 800-1 500 ℃ for 3 h under carbon embedded condition.Evolution of phase composition and microstructure of Al2 O3-Si-Al composite during heating from 800 to 1 500 ℃ under carbon embedded condition were studied.The results show that：（1） Al4 C3,AlN and SiC are initially formed at 800-900 ℃ due to reactions of Al and Si with C or CO and N2 ; （2） at 1 000-1 300 ℃,the amounts of Al4C3,AlN and SiC increase with temperature rising and their crystals grow; （3） at 1 400-1 500 ℃,Al4 C3 and AlN disappear,and minor SiAlON crystals are observed; the nonoxide crystals develop well and they are interlaced in the corundum skeleton structure,which creates strengthening and toughening

Thermo-mechanical Properties of Al/Si Incorporated Low Carbon Al_2O_3-C Slide Plate Materials

Low carbon Al2O3- C refractory materials were prepared by ＂Al/Si metal incorporated, insitu formed non-oxides＂ method using corundum, Al powder, Si powder and flake graphite as starting materials. High temperature strength, stress -strain relationship and thermal shock resistance of these composites were investigated. The results show that these composites possess improved high temperature strength and good thermal shock resistance. When A1 addition increases from 0 to 8 mass%, correspondingly, Si addition decreases from 8 mass% to O, hot modulus of rupture at 1 400 ℃ increases significantly from 10. 4 MPa to 32. 4 MPa; the maximum strain under 6.5 MPa stress at 1400 ℃ decreases from 215 t.tm to 90 μm; residual strength ratio after 3 thermal shock cycles （1 100 ℃ , air quenching） decreases from 80% to 65%. This may be attributed to in-situ formation of nonoxides because Al and Si react with C, CO and N, to form Al4C3 , AlN and SiC creating strengthening and toughening effects.

Effects of Al-Si Addition on Thermomechanical Properties of Low-carbon MgO-C Materials

Effects of Al- Si addition on hot modulus of rup- ture ~ HMOR） . thermal shock resistance ~ TSR~ . phase composition and mierostructure of low-carbon MgO - C materials were investigated. The results show that： Al and Si addition to low-carbon MgO - C materials leads to dramatic increase in MOR at elevated temperatures; it increases from 4 MPa to 11 -21 MPa at 1 200 ℃ and from 2 MPa to 21 -29 MPa at 1 400 ℃. Al and Si addition to low-carbon MgO - C materials also improves TSR： residual strength ratio after thermal shock when △T = 1 200 ℃ is increased,from 44% to 73% - 77%. Al reacts with C and N2 to form, Al4C3 and AlN, Si reacts with C to form SiC. Ultimately. in-situ formed non- oxides increase appreciably with temperature rising and are well interlaced in periclase skeleton structure at 1 300 -1 400 ℃. which is beneficial to thermomechanical properties.

Sintering Behavior and Microstructure of diphasic β-Sialon /Al_2O_3 Composites

Six compositions with different ratio of β-Sialon/Al2O3 were synthesized from Al2O3, Si3,N4 and SiO2 by sintering with 3%Y2O3(mass fraction) as addition under the cover with powders of SiC+C and at nitrogen atmosphere. Theeffects of atmosphere, sintering temperature and composition on the sintering behavior were studied. The results showedthat the composites reached the best sintering behavior with the highest density about 92% at 1 650℃ under the weakreduction atmosphere. Finally the relative density of diphasic β-Sialon and p-Sialon/Al2O3 composites were studied andpredicted using ANN (Artificial Neural Networks) method and the results were experimental examined by fore randomsamples.

Rheological Behavior of Zero Cement Al_2O_3-MgO Castables

Al2O3 -MgO castables have been widely used for working linings of steel ladle due to their superior hot strength and corrosion resistance. In this- work, effects of＂ microsilica, ultrafine alumina and MgO fines additions on the rh, eological behavior of the castables were investi- gated by means of IBB rheometer V1. 0 to measure torque （shear stress） under varying shear rates. The re- sults show that rheological properties of castables at varying shear rates are significantly improved with increase of microsilica additions （from 1 mass% to 5 mass% ） and corresponding decrease in water addition; there is only little change in rheological behavior with variation of ultrafine alumina and MgO fines additions. Optimum ultrafine alumina and microsilica additions are recommended for castables with good rheological behavior.

Uprise of China's Refractories Industry

The development of refractories industry in China in the past 62 years since 1949 is reviewed. In 1949 - 1979, China＇s refractories industry developed to become a comprehensive industrial sector with sizable production capacity and elevated technical level. In 1979 - 2010, refractories production increased at fast tempo partly due to the rapid uprise of private enterprises and partly due to structural reform and improved management of state owned companies. Important progress was made in inno- vative research and development on high quality synthetic refractory raw materials based on bauxite and magnesite and high performance new products such as oxide -nonoxide composites. The next 30 -40 years should be a period of steady development for China＇s refractories industry More efferts should be given to efficient utilization of natural resottrces, environmental protection and energy consen：alion, prodlwt qualio consistency and reliability and innovative development in science and technology. There sho.ld be strucral readjustment and technical reconstruction of the hundreds of refractories mining and manufacturing companies. There should be more innovative achievements in developing high quality synthetic raw material.s and high performance new products with Chinese characteristics.

Research on Copper Matte Corrosion to Periclase-spinel Refractories

Effects of TiO2 or ZrO2 addition on corrosion resist; ance of periclase -spinel refractories to copper matte at different temperatures were investigated using static crucible method, and the results were compared with those of fused rebonded magnesite -chrome bricks. The chartges in chemical compositions and microstructure in different zones of the specimens after corrosion tests were studied by means of EDAX and SEM. The results show that ： （ 1 ） the reaction between periclase - spinel refractories and copper matte is very weak with the reaction layer thinner than 1 mm. Penetration is the main cause of copper matte corrosion and the penetration depth increases with temperature rising. When temperature exceeds 1200 ℃ , the penetration depth increases significantly; （2） appropriate TiO2 addition can improve penetration resistance （even better than that of magnesia chrome brick）, the optimum addition is 2 %. But ZrO2 has no remarkable effect on penetration resistance to copper matte of periclase - spinel refractories ; （ 3 ） SEM and EDAX analysis indicates that, Cu2S penetrates much further into the specimens than FeS.

Carbothermal Reduction Synthesis of Al_2O_3-SiC Powders from Coal Gangue

The Al2O3 -SiC composite powders were prepared in argon atmosphere rising coal gangue and carbonaceous materials （ carbon black, active carbon and antbravite） as starting materials by carbothermal reduction. Effects of excessive carbon addition, carbon types. temperature, soaking time. shaping pressure, types and amount of additives on phase composition and micro-structure of the Al2O3 - SiC composite powders were investigated. The re.suits indicate that： temperature, soaking time and chloride additi＇ve have significant influence on the synthesized Al2O3 -SiC composite powders. Based on the results, the optimized Al2O3 -SiC composite powders , Al2O3 58 mass% and SiC 42 mass%, with particle size d50 ≤5μm were prepared using coal gangue and carbon black as starting materials after 3 h firing at 1550 ℃. and proper additive addition could reduce the temperattlre by 50 ℃.