Particle Size Distribution,Powder Agglomerates and Their Effects on Sinterability of Ultrafine Alumina Powders

An intensive study of the particle size distribution of four commercial ultrafine alumina powders to obtain information about the powder agglomeration and relate them to the compactibility and the sinterability has been made.

Effect of Various Alumina Powders on Properties of Castables

To satisfy the requirements of alumina castables in specific environment and enhance their properties,alumina castables were prepared using tabular alumina,various alumina powders(07RAL,15RA,22RABL,40CA,99-20um,and 99-325mesh),and calcium aluminate cement as main raw materials,and heat treating at 110,1000,1600℃,respectively.Their flowability and physical properties were tested,and the morphology was researched.The results show that compared with calcined alumina and tabular alumina powders,reactive alumina has higher specific surface area and better filling performance leading to lower water demand and higher viscosity,and the castables prepared with reactive alumina have higher CCS and CMOR after heat treating at 110,1000 and 1600℃as well as lower PLC than those with calcined alumina and tabular alumina powders.

Aluminum and Activated Alumina Powder Additions on Microwave Synthesis of Al_(4)SiC_(4)

Aiming at improving the properties of magnesia carbon materials,silicon aluminum carbide(Al_(4)SiC_(4))containing materials were prepared using industrial aluminum powder,silicon carbide powder,and graphite as raw materials,and activated alumina powder as an additive,mixing thoroughly,pressing into cylinders and then firing at 1200℃for 30 min in a carbon embedded atmosphere by the microwave method.The effects of the aluminum powder addition(20%and 24%,by mass)and activated alumina powder addition(0,3%,5%and 7%,by mass)on the microwave synthesis of Al_(4)SiC_(4) as well as the effect of the obtained Al_(4)SiC_(4) containing material on the properties of magnesia carbon bricks were studied.The results show that:compared with the samples with 20%aluminum powder,those with 24%aluminum powder generate more Al_(4)SiC_(4).With the activated alumina powder addition increasing from 0 to 7%,the amount of Al_(4)SiC_(4) generated increases first and then decreases.Compared with the sample without activated alumina powder,the samples with activated alumina powder show lower bulk density and higher apparent porosity.With the activated alumina powder addition increasing from 3%to 7%,the bulk density of the samples increases first and then decreases,while the apparent porosity of the samples shows an opposite trend.The optimal additions are 24%aluminum powder and 5%activated alumina powder,and Al_(4)SiC_(4) synthesized in this sample has a hexagonal plate structure.With the synthesized Al_(4)SiC_(4) containing material added,the magnesia carbon brick has slightly increased cold modulus of rupture,basically the same modulus of elasticity and improved oxidation resistance.

Microstructure and Tensile Properties of Yttria Coated-Alumina Particulates Reinforced Aluminum Matrix Composites

The liquid-phase coating method was used to deposit Y2O3 ceramic on the surface of α-Al2O3. The coated-Al2O3p/6061AI composites were produced using squeeze casting technology. The microstructure and tensile properties of the composites were analysed and studied. The results showed that the coated AI2O3 particles are able to disperse homogeneously in the aluminum liquid. The microstructure of the composites is more even in comparison with that of as-received powders. The tensile testing indicated that mechanical properties of the coated-AI2O3p/6061AI composites are better than those of uncoated particles. In the composite with 30% volume fraction, the tensile strength, yield strength as well as elongation is increased by 29.8%, 38.4% and 10.3%, respectively. The SEM analysis of fracture indicated that the dimples of the coated-Al2O3p/6061Al composites are more even.

A Novel Processing Route for Ni-doped Alumina Composites

Alumina-based composites containing 0-15wt% Ni metallic phase were produced by hot press-sintering Ni-coated alumina powders. The Ni-coated alumina powders were prepared by the aqueous heterogeneous precipitation of alumina micro-powders and nickel sulfate salt followed by reduction process. The microstructural features and dispersion of Ni phase in Ni-coated alumina powders and the subsequent alumina-Ni cermets were investigated using scanning electron microscope （SEM）, X-ray diffractometer （XRD）, and transmission electron microscope （TEM）. The relative density of the hot press-sintered composites was measured with the Archimedes＇ method while the fracture strength and the fracture toughness were defined with the three-point bending method and the micro-indentation fracture method. In the formation of alumina-Ni cermets from sintered Ni-coated alumina powders, Ni phase to some extent limits the densification rate and stifles the coarsening and growing process of alumina grains. The Ni phase is found to be located at the interfaces and the triple-joint junctions of alumina grains which results into alteration of the fracture mode of alumina and its increased fracture strength and fracture toughness if compared with monolithic alumina.

Influence of Synthesized Super Al_2O_3 Powder on the Properties of Alumina Castable

The influence of three different Al2O3 powder art self-flowing alumina castabie was studied , Max-imum compaction of sample wascomputed by An-dresen Equation . The result showed that the Al2O3 powder, which has much smaller particle size, could improve the microstructure and the mechanical properties of castabie under room temperature and high temperature. With the same powder size, the room temperature strength of the castabie added with Al2O3 powder properties of which were altered by adding mineralizing agent, was higher than that of the castabie added with common Al2O3 powder, but the flowability of these three different castabie was almost thesame.

Effect of Industrial Alumina Powder Particle Size on Preparation of Active α-Al_(2)O_(3) Micropowder

To study the effect of the particle size of industrial alumina powder on the properties of active alumina micropowder(α-Al_(2)O_(3) micropowder),the fine powders with the median diameter of 50,30,10,and 5 pm,respectively,were obtained by grinding industrial alumina powder(the median diameter of 80 pm),and the active alumina micropowders were prepared by firing the industrial alumina powders before and after grinding at 1320℃ for 5 h.The effect of the particle size of the industrial alumina powder on the microstructure and properties of the active alumina micropowder was researched.The results indicate that the initial particle size of the industrial alumina powder has a great influence on the grain morphology of the active alumina micropowder;when the median diameter is larger than 30 pm,the α-Al_(2)O_(3) grains show wormlike aggregates state after calcination and when it is around or less than 10 pm,the α-Al_(2)O_(3) are round,spherical and well dispersed grains with the particle size of 0.3-1.0 pm.With the initial particle size of the industrial alumina powder decreasing,the α-Al_(2)O_(3) phase transition rate increases and the true density gradually increases;moreover,the α-Al_(2)O_(3) powder shows better dispersity and flowability.

Shape Memory Effect During Preparation of Alumia Ceramic Tubes

Pure alumina ceramic tube and 95 alumina ceramic （the ceramic with 95.84% alumina） tube were prepared by using self-prepared alumina micrometer powder without agglomeration as raw material. The ceramic green was shaped by isostatic pressing and sintered at different temperature from 800 to 1 600 ℃ for 2 h. The 95 ceramic tube sintered at 1 550 ℃ for 2 h had mean particle size of 4 μm, bend strength of 437 MPa and volume density of 3.714 g/cm3. Shape memory effect during sintering was observed. XRD results showed that no phase transition occurred during shape memory process, which indicated that shape memory effect was not caused by phase transition. Several probable causes of the alumina ceramic shape memory effect were discussed in this paper.