Phase relations in the systems ZrO2Y2O3Nd2O3 and ZrO2Y2O3CeO2

The phase relations of ZrO₂Y₂O₃Nd₂O₃ and ZrO₂Y₂O₃CeO₂ systems have been studied at 1100–1600°C. The single region of the fluorite phase was intensively examined using the relation between lattice parameter and composition. In the ZrO₂Y₂O₃Nd₂O₃ system, 37 mol% Nd₂O₃ is soluble in Y₂O₃-stabilized zirconia (fluorite phase) at 1100°C and 42 mol% Nd₂O₃ at 1600°C. In the ZrO₂Y₂O₃CeO₂ system, 40 mol% CeO₂ dissolves into the stabilized zirconia at 1600°C.     

Zeolite synthesis in the system pyrrolidine-Na2OAl2O3SiO2H2O

Crystallization of zeolites from the system pyrrolidine-Na₂OAl₂O₃SiO₂H₂O was investigated. Five zeolites, ZSM—5, ZSM—35, ZSM—39, ZSM—48 and KZ—1, were synthesized as single phases, whose crystallinity was very high. In this work zeolite ZSM—48 was prepared from the pyrrolidine system for the first time. It was suggested that pyrrolidine might stabilize certain aluminosilicate polyanions which have building units of oxygen five-membered rings. It was also presumed that all zeolites, except ZSM—39, have a pore opening of oxygen ten-membered rings.     

SEM/EDX microanalysis of a Na2OCdOSiO2 glass-ceramic containing sulphur

The formation or separation on cooling of a double cadmium-sodium sulfate CdSO₄·3Na₂SO₄ in a glass from the Na₂O-Al₂O₃-CdO-SiO₂ system has been detected by energy dispersive X-ray microanalysis (EDX) in a scanning electron microscope. The existence of prismatic and holed crystals of sulfate grown from the original glass is discussed.     

Formation of zeolite from the system Na20-Al2O3-SiO2-H2O in alkaline medium (pH > 10)

The hydrothermal reactions of three aluminosilicates, i.e., kaolinite, metakaolinite, and sodium aluminosilicate gel, with aqueous sodium hydroxide have been reexamined. The molar composition of the quaternary system Na₂O-Al₂O₃-SiO₂-H₂O was maintained constant in the three systems. Kaolinite gave a partially rehydrated nonbasic hydroxysodalite, whereas zeolite 4A is the product from metakaolinite and gel. The kinetics of the reaction and the crystal habit of the zeolite formed in the metakaolinite-alkali system appear to be different from that of conventional gel route of synthesis. The metakaolinite slowly dissolves in alkali to form a gel that is the direct precursor of zeolite 4A. However, the crystallization seems to start even before the metakaolinite gel conversion is completed. The ion-exchange and water-adsorption capacity and the chemical assay of the precursors and products have been used to substantiate the XRD and spectroscopic (i.r. and MAS n.m.r.) data in establishing the mechanism of the reaction.     

Phase evolution and gas-phase particle size distributions during spray pyrolysis of (Bi,Pb)SrCaCuO and Ag(Bi,Pb)SrCaCuO powders

Phase evolution, gas-phase particle size distributions and lead loss were studied during formation of (Bi,Pb)SrCaCuO powders and their composites with silver by spray pyrolysis starting from nitrate solutions. The 10 wt% Ag/90 wt% Bi_1.8Pb_0.44Sr₂Ca_2.2Cu₃O_x composite powders made at 700°C consisted of 20–60 nm grains of silver and mixed-oxide phases with a fine dispersion of Ag grains within the particles. At 700°C, the primary phases present in (Bi,Pb)SrCaCuO powders were (Bi,Pb)₂Sr₂CuO_x (2201), Ca₂PbO₄ (plumbate), (Bi,Pb)₂Sr₂CaCu₂O_x(2212), and (Bi,Pb)₃Sr₂Ca₂Cu₁O_x(3221). For T≥800°C, the powders were considerably depleted in lead, and the plumbate and 3221 phases were absent. For T = 900°C, a large number of ultrafine particles (<30 nm) were formed, probably from the PbO vapor released from the reactor walls. Using spray pyrolysis, it is easy to control stoichiometry and limit the phase segregation at the nanometer-scale so that homogeneous and phase-pure materials can be obtained rapidly during subsequent processing.     

D2H2 equilibration over γ-irradiated zeolites

D₂H₂ equilibrium was studied at 77 and 298 K over HY, AIHY, HZSM-5 and Al_xO_yHZSM-5 which had been γ-irradiated at 77 and/or 298 K. The exchange rate was found to be higher at the lower temperature regardless of the temperature of irradiation. Moreover, at 77 K the exchange rates were similar and more stable over the individual zeolites than at 298 K, thus indicating a common reaction path at 77 K. The exchange rate at 298 K depended on the zeolite type: it was more stable and higher over HZSM-5 than over HY, and extra-lattice Al increased both these properties on HY as well as on HZSM-5. The reaction mechanism is discussed in connection with the nature of defects generated by γ-irradiation.     

Sputtering of SiO2 in O2Ar atmospheres

The r.f. sputtering of SiO₂ in an ArO₂ atmosphere was studied. The study was carried out to improve the insulating properties of films relative to those produced in a pure argon discharge which showed a clear aging effect on the losses. The O₂ percentage was varied in the range 1%–4% of the total pressure. The improvement in the insulating properties consisted mainly in a stabilization of the electrical properties close to the best values reported for SiO₂. The role of the oxygen is explained on the basis of annihilation of defects associated with oxygen vacancies in the SiO₄ tetrahedral chains.