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

Al2O3- Si- Al composite specimens with the size of25 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 Al2O3- Si- Al composite during heating from 800 to1 500 ℃ under carbon embedded condition were studied. The results show that:( 1) Al4C3,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 ℃,Al4C3 and AlN disappear,and minor SiA lO N crystals are observed; the nonoxide crystals develop well and they are interlaced in the corundum skeleton structure, which creates strengthening and toughening effects.

Effect of High Temperature Calcination on Structure and Properties of Bauxite-based Homogeneous Clinkers

In this paper,the effect of high temperature calcination on the structure and properties of bauxite-based homogeneous clinkers calcined at different temperatures for different durations was studied.The results show that with the rising of calcination temperature and the prolonging of holding time,the volume density of bauxite-based homogeneous clinkers increases and the apparent porosity decreases.After high temperature calcination,the linear expansion of bauxitebased homogeneous clinker is smaller than that of the non-calcined ones.Whether calcined at high temperatures or not,the thermal shock resistance of bauxite-based homogeneous clinkers is good.The crystalline phases of bauxite-based homogeneous clinkers are mainly mullite and corundum.There is more glass phase in the bauxite-based homogeneous clinkers without calcination.After calcination at high temperatures the glass phase content decreases significantly,and the mullite crystals develop better forming the cross-network structure.

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 magnesite, 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 performance.

Preparation and properties of Ba_3Zn_ZCo_(2-Z)Fe_(24)O_(41)/SiO_2 microcrystalline glass ceramics

Ba 3Zn Z Co 2 Z Fe 24 O 41 /SiO 2 ( Z varies from 0.0 to 1.2 in step of 0.4) microcrystalline glass ceramics were prepared by citrate sol gel process at 1 200 ℃ in the system of BaO Fe 2O 3 CoO ZnO SiO 2. The samples were characterized by X ray diffraction (XRD) and scanning electron microscopy (SEM). The complex dielectric constant and complex permeability of Ba 3Zn Z Co 2 Z Fe 24 O 41 /SiO 2 microcrystalline glass ceramics were measured in the range of 0.16.0 GHz by transmission/reflection coaxial line method. The natural resonance phenomenon was observed in μ ″ spectra for all the Ba 3Zn Z Co 2 Z Fe 24 O 41 /SiO 2 microcrystalline glass ceramics, which was closely affected by the substitution of Zn 2+ ion.

Manufacture of Zn-Co Substituted Y-Type Barium Hexagonal Ferrites by Citrate Precursor Route and Their Microwave Properties

Ba2Zn x Co2- x Fe12O22 hexaferrites with x =0.0, 0.4, 0.8, 1.2, 1.6 and 2.0 were prepared by citrate sol-gel process. The complex dielectric constant and complex permeability of hexaferrites were studied as functions of the measuring frequency, composition and sintering temperature in the range 100 MHz～6 GHz. The natural resonance phenomenon is observed in μ″ spectrum for all Y-type hexaferrites, which resonance frequency is dependent on zinc content and firing temperature. The natural resonance frequencies of Co2Y hexaferrite were calculated, which is in agreement with the measuring results. The reflection loss of those ferrites is measuring frequency as well as absorber thickness dependent, and the higher the frequency and the thickness are, the higher the reflection loss is.

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 sintering at high temperature,using bauxite instead of alumina 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) Al/Si metal bonded Al2O3-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.

Three-dimensional graphitic carbon sphere foams as sorbents for cleaning oil spills

Frequent offshore oil spill accidents, industrial oily sewage, and the indiscriminate disposal of urban oily sewage have caused seri- ous impacts on the human living environment and health. The traditional oil-water separation methods not only cause easily environmental secondary pollution but also a waste of limited resources. Therefore, in this work, three-dimensional (3D) graphitic carbon sphere (GCS) foams (collectively referred hereafter as 3D foams) with a 3D porous structure, pore size distribution of 25-200 μm, and high porosity of 62vol% were prepared for oil adsorption via gel casting using GCS as the starting materials. The results indicate that the water contact angle (WCA) of the as-prepared 3D foams is 130°. The contents of GCS greatly influenced the hydrophobicity, WCA, and microstructure of the as-prepared samples. The adsorption capacities of the as-prepared 3D foams for paraffin oil, vegetable oil, and vacuum pump oil were approximately 12-15 g/g, which were 10 times that of GCS powder. The as-prepared foams are desirable characteristics of a good sorbent and could be widely used in oil spill accidents.

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,in-situ 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 Al addition increases from 0 to 8 mass%, correspondingly,Si addition decreases from 8 mass%to 0,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 1 400℃decreases from 215μm to 90μm;residual strength ratio after 3 thermal shock cycles（1100℃,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 N2 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 rupture （HMOR）,thermal shock resistance < TSR),phase composition and microstructure 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 AT = 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 nonoxides increase appreciably with temperature rising and are well interlaced in periclase skeleton structure at 1 300 -1 400℃.which is beneficial to thermomechanical properties.

Properties and Microstructure Evolution of Al_2O_3-Si Material Fired in Different Atmospheres

Al2O3- Si composite specimens were prepared using fused corundum,ultra-fine α-Al2O3and Si powder as starting materials and resin as binder. Effects of sintering atmospheres on properties,phase composition and microstructure of specimens after firing at 1 500 ℃ were investigated. The results show that:( 1) after firing in oxidizing or weak oxidizing atmosphere,there is some Si in the specimens and some glass phases containing mullite form on specimen surface,the density and strength at room temperature are relatively high,but hot modulus of rupture and thermal shock resistance are relatively poor;( 2) after firing in weak reducing or reducing atmosphere,Si reacts completely with CO or N2forming whisker-like SiC,granular Si2N2O or O'-SiAlON,and the thermo-mechanical properties of specimens are enhanced;( 3) after firing in nitrogen atmosphere,Si reacts completely with N2,CO or C forming whisker-like SiC and columnar β-SiAlON crystals,the hot modulus of rupture and thermal shock resistance of specimens are enhanced noticeably.

Progress and Developing Trend of Purging Plugs for Refining Ladle

Damage reasons of purging plugs for refining ladle and research progress on thermal shock resistance of corundum- spinel purging plugs were summarized. Research achievements and application results of nonoxides bonded corundum purging plugs for refining ladle were briefly reviewed. The further research and developing trend of purging plugs was proposed.

Investigation on Synthesis of Sintered Mullite from Low-medium Grade Kyanite

Sintered mullite is prepared by kyanite powder with Al_2O_3 content of 45% and 50%(Yinshan, Nanyang City, China),and the industrial alumina is added to control the chemical composition. The different series of sintered mullite according to the Al_2O_3 content(45%-70%) are designed. The raw materials are mixed and compacted, and then sintered at different temperatures. Physical properties, phase composition, microstructure and refractoriness under load of the synthesized samples are characterized by physical property test, XRD, SEM and RUL test, in order to confirm the quality of sintering and the relationship between temperature and mullitization reaction. The results show that the sintered mullite from low-medium grade kyanite has well developed mullite crystals and a continuous staggered network structure is formed, which has a significant contribution to increasing the high temperature performance of mullite.

In-situ Formation of Spinel Fibers in MgO-C Refractory Matrixes

In-situ magnesia-rich spinel fiber was formed resulting from the addition of ferrocene into MgO-C refractory matrixes. The formation of in-situ spinel fiber was detected to start at 1300 ℃. The amount, diameter and length of the fibers increased with rising temperature. Ferrocene may have catalytic effects on the growth of the fibers in two aspects. First, the reaction between MgO and C and the decomposition of Al4C3 may be catalyzed at high temperature. Suitable concentration gaseous phase is then created for vapor-vapor reaction which could result in the in-situ formation of fibers. Second, Fe nanoparticle produced from ferrocene can act as catalytic droplets and catalyze the growth of the fibers. The fibers are formed via the vapor-liquid-solid and vapor-solid mechanisms. In terms of chemical thermodynamics, the partial pressure of CO and Mg(g) are found to play an important role in the in-situ fibers formation. Different concentration of vapors affects the size, amount and composition of the fibers at different temperatures. The mechanical properties of MgO-C brick was found to be improved by ferrocene addition.

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 innovative research and development on high quality synthetic refractory raw materials based on bauxite and magnesite and high performance new products such as oxide—non-oxide composites.The next 30—40 years should be a period of steady development for China’ s refractories industry. More efforts should be given to efficient utilization of natural resources,environmental protection and energy conservation,product quality consistency and reliability and innovative development in science and technology. There should be structural 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 materials and high performance new products with Chinese characteristics.

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 rheological behavior of the castables were investigated by means of IBB rheometer V1.0 to measure torque (shear stress) under varying shear rates. The results 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.

Some Influencing Factors on Rheological Properties of Bauxite-based Castable Matrix

The effects of corundum, magnesia and spinel additions on rheological properties of matrix of bauxite-based castables were studied using bauxite, fused white corundum, magnesia, spinel, microsilica, ultra-fine α-Al2O3 and cement as starting materials and trimeric sodium phosphate as dispersant. The results show: (1) the matrix slurry of bauxite-based castables belongs to Bingham fluid and shows thixotropy behavior; (2) appropriate corundum addition improves rheological properties of the matrix; (3) magnesia addition is detrimental to matrix rheological properties; (4) spinel addition has slightly negative effects on matrix rheological properties.

Carbothermal Reduction Synthesis of Al_2O_3-SiC Powders from Coal Gangue

The Al2O3 - SiC composite powders were prepared in argon atmosphere using coal gangue and carbonaceous materials < carbon black,active carbon and anthracite) 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 microstructur e of the Al2O3 -SiC composite powders were investigated. The results indicate that:temperature,soaking time and chloride additive 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 1 550℃.and proper additive addition could reduce the temperature by 50℃.

Effect of Nano Calcium Carbonate on Properties of Corundum-spinel Castables

Using sintered corundum as aggregate,white fused corundum powder,fused spinel powder,ultra-fineα-Al2O3,nano calcium carbonate and hydrated alumina as matrix,effects of nano calcium carbonate additions(0.4%,0.8%,1.2%,1.6% and 2.0% in mass,the same hereinafter)on modulus of rupture,thermal shock resistance and slag resistance of corundum-spinel castables after treating at different temperatures were studied.The results show that nano calcium carbonate decomposes at high temperatures and in-situ forms calcium aluminates,which can significantly increase the CMOR and HMOR of the castables after treating at 800-1400℃;adding nano calcium carbonate obviously improves the thermal shock resistance of the castables,and has little influence on the high basicity slag resistance,however,significantly decreases the corrosion and penetration resistance to low basicity slag.

Effect of Al_2O_3-SiC Composite Powder on Properties of Al_2O_3-SiC一C Bricks

Al2O3- SiC- C specimens were prepared using white fused corundum( 3- 1,≤1 and ≤0. 044 mm),Al2O3- SiC composite powders( d50≤5 μm),α-Al2O3micropowder( d50= 1. 2 μm),SiC powder( ≤0. 044mm),flake graphite( ≤0. 088 mm),Si powder( d50= 42. 8 μm) and B4C powder( d50≤10 μm) as main starting materials,and thermosetting phenolic resin as binder. 4%,8%,12% and 16%( in mass,the same hereinafter) of Al2O3- SiC composite powders substituted the same quantity of α-Al2O3micropowder + SiC powder.Effects of composite powder additions on apparent porosity,bulk density,cold modulus of rupture,cold crushing strength,hot modulus of rupture( 1 400 ℃),therma shock resistance( 1 100 ℃,water quenching) and oxidation resistance( 1 000 and 1 500 ℃) of Al2O3- SiC- C specimens after 180 ℃ curing,1 000 ℃ 3 h carbon-embedded firing and 1 500 ℃ 3 h carbon-embedded firing,respectively,were researched. The results indicate that:( 1) with the increase of Al2O3- SiC composite powder,cold strengths of the cured specimens decline,those of the specimens fired at 1 000 ℃ change a little,and those of the specimens fired at 1 500 ℃ change a little except for an obvious improvement of cold crushing strength;( 2) with the increase of Al2O3- SiC composite powder,hot modulus of rupture at 1 400 ℃ decreasesand thermal shock resistance enhances significantly;( 3) when Al2O3- SiC composite powder addition is4%,the oxidation resistance at 1 500 ℃ is the best,and the reason may be the composite powder is finer and more active,which is beneficial to form dense mullite protective layer to retard the O2diffusion into the specimens.

Research on Copper Matte Corrosion to Periclase-spinel Refractories

Effects of TiO2 or ZrO2 addition on corrosion resistance 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 changes 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 1 200 ℃,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.