Subsolidus equilibria and metastable phase development in the system ZrO₂-Al₂O₃-SiO₂

Subsolidus equilibria in the low silica portion of the system ZrO₂-Al₂O₃-SiO₂ were studied by X-ray diffraction of quenched samples fired at 1300°, 1400°, and 1480°C. Samples prepared as powders from combinations of a-Al₂O₃, Al(OH)₃, silicic acid, ZrO₂, and kaolinite reacted very slowly at 1300° and 1400°C and the trends toward equilibria are not apparent. A mixture of zircon and Al(OH)₃ reacted slowly at 1480°C to form mullite and ZrO₂, indicating that the latter phases are the stable assemblage rather than zircon and alumina. A gel prepared from aluminum nitrate, zirconyl nitrate, and colloidal silica reacted at 1480°C to form alumina, zirconia, zircon, and mullite; with continued firing, however, the zirconia and mullite developed further at the expense of aluminia and zircon. A tetragonal, pseudocubic, metastable phase developed in the calcined gel and was quite persistent, even at 1480°C. Hypothetical ternary liquidus surfaces have been proposed on the basis of available binary data from the literature --Abstract, page ii

Thermal Expansion Of Tetragonal PbO

Thermal expansion of tetragonal PbO, investigated by high‐temperature X‐ray diffraction in vacuum, is nearly isotropic, with the coefficient in the c0 direction only slightly greater than that in the a0 direction. Volume thermal expansion is only slightly greater than in massicot. Retardation of the litharge‐massicot transformation is tentatively interpreted as the result of very low oxygen partial pressures caused by catastrophic oxidation of the stainless‐steel sample holder and resulting oxygen scavenging by lead vapor. Copyright © 1970, Wiley Blackwell. All rights reserve

Thermal Expansion Of Orthorhombic PbO

Thermal expansion of orthorhombic PbO was investigated by high‐temperature X‐ray diffraction. The coefficients in the a0, and c0 directions are equal and Pb–O chains extended in the a0 direction and bonded into layers in the b0 direction; appreciable Pb–Pb bonding is indicated. Coordination and bond distances observed in PbSiO3 and lead silicate glasses, which are similar to those of massicot, and PbnOn polymeric units reported in PbO vapor are interpreted as additional evidence of the importance of PbO chains as structural entities. Copyright © 1970, Wiley Blackwell. All rights reserve

Subsolidus Equilibria And Stabilization Of Tetragonal ZrO2 In The System ZrO2‐Al2O3‐SiO2

The irreversible reaction between zircon and alumina to form mullite and zirconia was observed to proceed very slowly at 1480°C, confirming the existence of a stable join between mullite and zirconia in addition to the join between mullite and zircon. Attempts to determine equilibrium assemblages in powder samples of several combinations of the constituents at 1300° and 1400°C were unsuccessful. Metastable tetragonal ZrO2 was observed in fired powder samples containing kaolinite, in fired zircon‐alumina samples, and in calcined gels prepared from zirconyl nitrate, aluminum nitrate, and colloidal silica in water. Tetragonal ZrO2 was the dominant crystalline phase in gels fired for 24 h at 800°, 950°, and 1100°C; the thermal stability of the phase was enhanced by Al2O3 and by SiO2, but most effectively by mixtures of the two. Line broadening measurements and electron microscope observation indicate that the tetragonal ZrO2, with apparent crystallite sizes between 0.009 and 0.1 μm, develops as an intergrowth with, and is stabilized by, the amorphous matrix of Al2O3 and SiO2. Copyright © 1977, Wiley Blackwell. All rights reserve

Thermal Expansion Of Pb3O4

Thermal expansion of Pb3O4 was investigated by high‐temperature X‐ray diffraction. The coefficient in the a0 direction is 14.6x10−6/°C. Expansion in the c0 direction is 32% greater, with a coefficient of 19.3x10−6/°C. Coefficients of expansion are linear from 25° to 490°C and are comparable with those of tetragonal and orthorhombic PbO. Copyright © 1971, Wiley Blackwell. All rights reserve

Review of the anatase to rutile phase transformation

International audienceTitanium dioxide, TiO 2 , is an important pho-tocatalytic material that exists as two main polymorphs, anatase and rutile. The presence of either or both of these phases impacts on the photocatalytic performance of the material. The present work reviews the anatase to rutile phase transformation. The synthesis and properties of anatase and rutile are examined, followed by a discussion of the thermodynamics of the phase transformation and the factors affecting its observation. A comprehensive analysis of the reported effects of dopants on the anatase to rutile phase transformation and the mechanisms by which these effects are brought about is presented in this review, yielding a plot of the cationic radius versus the valence characterised by a distinct boundary between inhibitors and promoters of the phase transformation. Further, the likely effects of dopant elements, including those for which experimental data are unavailable, on the phase transformation are deduced and presented on the basis of this analysis

X-Ray Powder Data And Unit Cell Parameters Of MgCl2.6H2O

Detailed X-ray powder data for MgCl2·6H2O were obtained by diffractometry by use of CuKα radiation at 22°C. The data were indexed on a bimolecular monoclinic unit cell, space group C2/m, with a = 9.858 ± 0.001 Å; b = 7.107 ± 0.001 Å; c = 6.069 ± 0.001 Å; ß = 93° 47′ ± 10′. Calculated density was 1.591 g/cm3, compared with a measured density of 1.593 ± 0.003 g/cm3. © 1974, American Chemical Society. All rights reserved