Investigation of Calcium Aluminate Cement Phases Under High Gaseous Pressure.

The chemical degradation of refractory cement castable liners is important in the coal gasification process. The system CaO-Al2O3-H2O has been investigated at high temperature and pressure. A pseudobinary reaction diagram was constructed for the system CaO-Al2O3-H2O in steam at 1000 psig. Several experiments were conducted in the CaO-Al2O3-H2O system in CO2, CH4, and CO.

Phase Equilibria and Crystal Chemistry of Rubidium Niobates and Rubidium Tantalates.

The phase equilibria relations and crystal chemistry of portions of the Rb2O-Nb2O5 and Rb2O-Ta2O5 systems were investigated for structures potentially useful as ionic conductors. A hexagonal tungsten bronze-type (HTB) structure was found in both systems as well as three hexagonal phases with mixed HTB-pyrochlore type structures. Ion exchange experiments between various alkali ions are described for several phases. Unit cell dimensions and x-ray diffraction powder patterns are reported.

Phase Equilibria and Crystal Growth in the Alkali Antimonate Systems Sb2O4-NaSbO3/ Sb2O4-KSbO3/, and Sb2O4-NaSbO3-NaF.

Phase equilibrium diagrams have been constructed from experimental data for the systems Sb2O4-NaSbO3, Sb2O4-KSbO3, and Sb2O4-NaSbO3-NaF. The system Sb2O4-NaSbO3 contains only an intermediate pyrochlore type solid solution with a maximum melting point of 1490 °C at a Na:Sb atom ratio of 3:5. The Sb2O4-KSbO3 system contains in addition to the pyrochlore phase a compound 3K2O • 5Sb2O5 which melts congruently at about 1450 °C and two polymorphs of K2O • 2Sb2O5. The low temperature form of K2O • 2Sb2O5 was found to be monoclinic P21/c with a = 7.178, b = 13.378, c = 11.985 A, ß = 124°10'. The melting point of Sb2O4 was found to be 1350 ± 5 °C and NaSbO3 and KSbO3 both melt congruently at 1555 ± 5 °C and 1410 ± 5 °C respectively. The previously reported cubic form of KSbO3 was found to be a K+ deficient phase stabilized by reaction with atmospheric moisture. A similar cubic phase which appears to be a good Na+ ion conductor can be synthesized in the ternary system NaSbO3-Sb2O4-NaF.

Effect of Oxide Additions on the Polymorphism of Tantalum Pentoxide: II. "Stabilization" of the High Temperature Structure Type.

The high temperature, apparently tetragonal, polymorph of tantalum pentoxide can be obtained at room temperature by quenching a specimen containing 2-5 mole percent of the following oxides:SnO2, Ga2O3, Cr2O3, Fe2O3, Sc2O3, or MgO. All the x-ray patterns can be indexed on a body centered tetragonal cell with a ≈ 3.830 Å, c ≈ 35.68 Å. However, P2O5, V2O5, Nb2O5, ZrO2, Lu2O3, NiO, or ZnO do not stabilize the tetragonal form at room temperature. Single crystals of scandium "stabilized" Ta2O5 have been grown by the Czochralski technique.

Laser Induced Raman Spectra of Some Tungstates and Molybdates.

The Raman spectra of single crystals of CaWO4, CaMoO4, PbWO4, and PbMoO4 have been recorded using a He-Ne laser (λ = 6328 Å) and an Argon ion laser (λ = 4880 Å) as the exciting radiation sources. The polarization data have enabled us to classify unambiguously the observed fundamentals into the Raman active species of the point group C4h to which these crystals belong. The comparison of the spectra of these crystals in the low frequency region has also enabled us to make a rough classification of the bands into the rotational and the translational lattice vibrations.