摘要:

The topochemical sintering of barium hexaferrite utilizing stoichiometric mixtures of BaCO3and αFe2O3/α-FeOOH raw materials has been investigated. The densification behaviour of BaO.6Fe2O3in the temperature range of 1273 to 1573 K is studied with the help of a dilatometer. The nonisothermal dcnsification kinetics is derived from dilatometrie results. A kinetic relation of the type mentioned in the equation In

ISSN:0371-750X    

DOI:10.1080/0371750X.1997.10804780

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor

摘要:

Diphasic mullite gel (Si/Al=1/3) has been synthesizedin.situby hydrolyzing an aqueous solution of silica sol and aluminium salt with the help of NH4OH solution. It has been characterized by DTA. The formation of Si-Al spinel during non-eqilibrium heating of the gel and its subsequent transformation have been recorded by XRD technique. The result shows that Si—Al spinel crystallizes very slowly at 500°-800°C and then very rapidly at ∼ 1200°C which corresponds with the exhibition of a broad exotherm between 1100° and 1300°C in DTA. Accordingly, this exotherm is attributed to the formation of Si—Al spinel. It suddenly transforms to predominant amount of orthorhombic form of mullite with consequent exhibition of an exotherm at 1320°C in DTA. The residual non-crystalline aluminosilicate phase also crystallizes into mullite and accounts for the second mullitization process in diphasic gel.

ISSN:0371-750X    

DOI:10.1080/0371750X.1997.10804781

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor

摘要:

Garnets from high P—T granulite field of Sittampundi, Tamil Nadu were investigated by57Fe Mössbauer spectroscopy. The room temperature (298 K) three-band spectra, which have been splitted to two doublets, reveal Fe2+ions to be exclusively located at dodecahedral site (IS = 1.303–1.389 mm/s; QS = 3.423–3.822 mm/s) and Fe3+at tetrahedral site (IS = 0.0060.163 mm/s; QS = 0.520–0.663 mm/s). The Fe3+/∑Fe ratios vary between 0.073 and 0.150, which indicate its formation at high P—T field. The high values of QS of tetrahedral Fe3+suggest that the occupied site is very regular with little distortion. The fairly broad line-width (FWHM, 0.455–0.596 mm/s) of Fe3+doublet may arise from a substitution of some tetrahedral Si by (OH)−group. The strong partition and ordering of Fe2+and Fe3+in dodecahedral and tetrahedral sites, having octahedral sites totally free from iron, suggest in a strong measure of slow cooling and recrystallization of garnet through decompression. The presence of tetrahedral Fe3+strongly depicts the existence of octahedral Si, amounting to an excess of saturation value for tetrahedral sites by Si + Fe3+ions together at these sites.

ISSN:0371-750X    

DOI:10.1080/0371750X.1997.10804782

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor

ISSN:0371-750X    

DOI:10.1080/0371750X.1997.10804783

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor