This paper demonstrates that seeding nanocrystalline transition alumina powders is a viable option for producing high quality, alumina-based ceramics. By using α-Al 2 O 3 concentrations of ⩾1.25 wt.% α-Al 2 O 3 seed particles (equivalent to 5 ×10 14 seeds/cm 3 of γ-Al 2 O 3 ) the sintering temperature is reduced from 1600°C for unseeded γ-Al 2 O 3 to 1300–1400°C in dry pressed powders. The scale of the sintered microstructure is related to N v −1/3 and thus a 100-nm grain size is obtained. It is apparent that seeding is necessary for producing dense, alumina-based ceramics from nanocrystalline transition alumina powders.

Sintering of α-Al2O3-seeded nanocrystalline γ-Al2O3 powders

Effective inhibition of Cr(VI) in the Al2O3-CaO-Cr2O3 refractory castables system through silica gel assisted in-situ secondary phase tuning

CaAl2Cr2O7: Formation, synthesis, and characterization of a new Cr(III) compound under air atmosphere in the Al2O3–CaO–Cr2O3 system

This paper demonstrates that seeding nanocrystalline transition alumina powders is a viable option for producing high quality, alumina-based ceramics. By using a-Al2O3 concentrations of 51.25 wt.% a-Al2O3 seed particles (equivalent to 5 � 10 14 seeds/cm 3 of g-Al2O3) the sintering temperature is reduced from 1600 � C for unseeded g-Al2O3 to 1300–1400 � C in dry pressed powders. The scale of the sintered microstructure is related to Nv 1/3 and thus a 100-nm grain size is obtained. It is apparent that seeding is necessary for producing dense, alumina-based ceramics from nanocrystalline transition alumina powders. # 2002 Elsevier Science Ltd. All rights reserved.

Sintering of a-Al2O3-seeded nanocrystalline g-Al2O3 powders

Investigations were carried out on sintering of Al2O3 in presence of (CaO+Fe2O3) and CaO.Fe2O3 synthesized at 1150°c for 50 minutes Effects of different amounts, viz. 0.001, 0.003, 0.005 and 0.01 moles of (CaO+Fe2O3) and CaO.Fe2O3 per 100 gm of Al2O3 on the sintering of alumina were studied at various temperatures (1300°—1600°C) and times (up to 300 minutes). The study revealed that 0.005 moles of (Ca0+Fe2O3) and CaO.Fe2O3 gave maximum densification of alumina at 1600°c.

Sintering of Alumina (γ-Al2O3) in Presence of (CaO + Fe2O3)

Sintering behaviour of various AI2O3-Cr2O3 compacts made out of calcined alumina fines and chromic oxide, upto a temperature of 1700°C and 4 h soaking time was investigated. The amount of chromic oxide was found to have an appreciable impact on densification, rate constants, activation energy, diametrical tensile strengths and microstructures. A maximum density of 3.452 g.cm−3 and a maximum shrinkage of 15.67% were attained with the compacts having 2 wt% Cr2O3 when sintered at 1700°C for 4 h. It has been found that with the increase in Cr2O3 content, the porosity of the compact increases.

Densification of Al2O3-Cr2O3 Compacts at High Temperatures

In the present investigation, densification behaviour and sintering kinetics of different MgO-Al2O3-Cr2O3 compacts have been studied. A maximum density of 3.21 g.cm−3 was obtained at 1650°C with soaking for 4 hours. The value of corresponding linear shrinkage was 12.26%. Diametrical tensile strengths and activation energy of different compacts were determined. Identification of phases using powder X-ray diffraction patterns and microstructural studies using thin section and scanning electron microscope have also been carried out. Microstructure showed rounded and polygonal grains of closely spaced spinel.

G. N. Agrawal

Papers

Sintering of Alumina (γ-Al2O3) in Presence of (CaO + Fe2O3)

Densification of Al2O3-Cr2O3 Compacts at High Temperatures

Sintering Studies of MgO-Al2O3-Cr2O3 Compacts