Subsolidus Phase Relationships in Part of the System Si,Al,Y/N,O: The System Si3N4─AIN─YN─Al2O3─Y2O3

The subsolidus phase relationships in the system Si,Al,Y/N,O were determined. Thirty-nine compatibility tetrahedra were established in the region Si₃N₄─AIN─Al₂O₃─Y₂O₃. The subsolidus phase relationships in the region Si₃N₄─AIN─YN─Y₂O₃ have also been studied. Only one compound, 2YN:Si₃N₄, was confirmed in the binary system Si₃N₄─YN. The solubility limits of the α'─SiAION on the Si₃N₄─YN:3AIN join were determined to range from m = 1.3 to m = 2.4 in the formula Y _{m /3}Si_{12- m} Al _m N₁₆. No quinary compound was found. Seven compatibility tetrahedra were established in the region Si₃N₄─AIN─YN─Y₂O₃.     

Properties of Sm2O3─Al2O3─SiO2 Glasses for In Vivo Applications

The compositional range for glass formation below 1600°C in the Sm₂O₃─Al₂O₃─SiO₂ system is (9–25)Sm₂O₃─(10–35)Al₂O₃─(40–75)SiO₂ (mol%). Selected properties of the Sm₂O₃─Al₂O₃─SiO₂ (SmAS) glasses were evaluated as a function of composition. The density, refractive index, microhardness, and thermal expansion coefficient increased as the Sm₂O₃ content increased from 9 to 25 mol%, the values exceeding those for fused silica. The dissolution rate in 1 N HCl and in deionized water increased with increasing Sm₂O₃ content and with increasing temperature to 70°C. The transformation temperature ( T _g ) and dilatometric softening temperature ( T _d ) of the SmAS glasses exceeded 800° and 850°C, respectively.     

Thermal Analysis of a SiO2─Al2O3─CaO─CaF2 Glass

A SiO₂─Al₂O₃─CaO─CaF₂ ionomer glass was investigated using thermal analysis, X-ray diffraction, and scanning electron microscopy. The purpose of this investigation was to control the susceptibility of the glass to acid attack. The differential thermal analysis trace exhibited a sharp glass transition at about 645°C and two exotherms. The first exotherm corresponded to liquid–liquid phase separation followed by crystallization of fluorite. The second, much larger, exotherm was the result of crystallization of the remaining glass phase to form anorthite. Prolonged heat treatment below the glass-transition temperature demonstrated that crystallization of fluorite can occur without prior liquid–liquid phase separation.     

Subsolidus Phase Equilibria of the MgO─V2O5─SiO2 System

The subsolidus phase equilibria of the MgO─V₂O₅─SiO₂ system was studied by solid-state reaction and powder X-ray diffractometry. The resulting ternary is discussed with respect to corrosion of magnesia- and silica-containing refractories by vanadium-containing fuels.     

Subsolidus Relations in the La2O3─CuO─CaO Phase Diagram and the La2O3─CuO Binary Join

The phase diagram for the CuO-rich part of the La₂O₃─CuO join was redetermined. La₂Cu₂O₅ was found to have a lower limit of stability at 1002°± 5°C and an incongruent melting temperature of ∼1035°C. LagCu₇O₁₉ had both a lower (1012°± 5°C) and an upper (1027°± 5°C) limit of stability. Subsolidus phase relations were studied in the La₂O₃─CuO─CaO system at 1000°, 1020°, and 1050°C in air. Two ternary phases, La_1.9Ca_1.1Cu₂O_5.9 and LaCa₂Cu₃O_8.6, were stable at these temperatures, with three binary phases, Ca₂CuO₃, CaCu₂O₃, and La₂CuO₄. La₂Cu₂O₅ and La₈Cu₇O₁₉ were stable only at 1020°C, and did not support solid-solution formation.     

Li2O─SiO2─Al2O3─MeIIO Glass-Ceramic Systems for Tile Glaze Applications

In order to verify the possibility of using glass-ceramic materials as tile coatings, the devitrification processes of three industrial formulations belonging to the Li₂O─Al₂O₃─SiO₂ glass-ceramic system were investigated by differential thermal analysis, X-ray diffractometry, scanning electron microscopy, and IR spectroscopy. Compositional variations were made by addition of large amounts of MgO or CaO or PbO (ZnO) oxides as well as through smaller additions of other oxides. In these systems the surface crystallization contributes appreciably to the bulk crystallization mechanism. All the systems investigated show a high tendency toward crystallization even at very high heating rates, developing a very close network of interlocked crystals of synthetic β-spodumene-silica solid solutions (LiAlSi₄O₁₀). The results of this research are expected to establish the conditions under which these glass-ceramic systems can be practically used as tile glazes.     

Thermodynamics of Nitrogen in B2O3, B2O3─SiO2, and B2O3─CaO Systems

The BN solubilities for B₂O₃, B₂O₃─SiO₂, and B₂O₃─CaO systems have been measured mainly at 1823 K using a graphite crucible. The capability of the systems for nitrogen dissolution is compared with that of silicate systems in terms of nitride capacity. The dependence of nitrogen solubility in molten CaO containing 15 mol% of B₂O₃ on oxygen and nitrogen partial pressures is also investigated. It has been found that there are two mechanisms for nitrogen dissolution, namely as chemically bonded nitrogen and as physically dissolved nitrogen gas.     

Effect of Carbon Reduction on the Properties of 13 mol% Tio2─3 mol% Y2O3─84 mol% ZrO2

Fully tetragonal and sintered 13 mol% TiO₂─3 mol% Y₂O₃─84 mol% ZrO₂ was thermally treated at 1300°C for 1 h in argon in the presence of carbon. No phase changes occurred on the as-received surface and in the bulk of the material, but t → m transformation occurred on polished surfaces under reducing conditions, and it resulted in increased fracture toughness, Young's modulus, and modulus of rigidity. Deoxidation of the system occurred and 0.174 wt% of carbon was found in the sample. This seemed to stabilize the tetragonal phase.     

Viscosity of Molten Na2O─B2O3 Slags

The viscosity of sodium borate slags at high Na₂O concentrations (37.3 to 49.4 mol%) and high temperatures (1000° to 1300°C) follows an Arrhenius-type relationship. This relationship was also observed for sodium borate slags (mass% Na₂O/mass% B₂O₃= 0.86) containing CaO and CaF₂ for the same temperature range. There has been a reduction in viscosity of the sodium borate slags (mass% Na₂O₃mass% B₂O = 0.53 to 0.86) with increase in Na₂O concentration. On adding CaO (10 to 50 mass%) to the sodium borate slag (mass% Na₂O/mass% B₂O₃= 0.86), the viscosity increased considerably, while an addition of CaF₂ (S to 15 mass%) to the slag (30.9 mass% Na₂O₃ 35.8 mass% B₂O₃, 33.3 mass% CaO) decreased the viscosity. The average activation energies of Na₂O─B₂O₃, Na₂O─B₂O₃─CaO₃ and Na₂O─B₂O₃─CaO─CaF₂ slag systems have been estimated as 14.6, 124.7, and 41.4 kJ/mol, respectively, for the given composition ranges and 1000° to 1300°C temperature range.     

The System MgO─P2O5─H2O at 25°C

The phase diagram for the ternary system MgO─P₂O₅─H₂O at 25°C has been constructed. The magnesium phosphates represented are Mg(H₂PO₄)₂· n H₂O ( n = 4, 2, 0), MgHPO₄·3H₂O, and Mg₃(PO₄)₂· m H₂O ( m = 8, 22). Because of the large differences in the solubilities of these compounds, the technique which involves plotting the mole fractions of MgO and P₂O₅ as their 10th roots has been employed. With the exception of MgHPO₄·3H₂O, the magnesium phosphates are incongruently soluble. Because incongruency is associated with a peritectic-like reaction, the phase Mg₂(PO₄)₃· 8H₂O persists metastably for an extended period.     

Thermodynamic Assessment of the ZrO2─YO1.5 System

An optimal set of thermodynamic functions for the ZrO₂─YO_1.5 system are obtained using phase diagram and thermodynamic data. The liquid is described by a subregular solution model. Both cubic ZrO₂ and YO_1.5 solid solutions are regarded as one cubic solution, which is also treated as a subregular solution. The ordered Zr₃Y₄O₁₂ phase is treated as a stoichiometric compound. A regular solution model is applied to the other solid solutions. Tentative equilibrium boundaries between monoclinic and tetragonal ZrO₂ solid solutions are evaluated from information about the T ₀ line. The calculated phase diagram and thermodynamic functions agree well with experimental data.     

Ionic Conductivity of the Fluorite-Type Hafnia–R2O3 Solid Solutions

The ionic conductivity of the hafnia-scandia, hafnia-yttria, and hafnia-rare earth solid solutions with high dopant concentrations of 8, 10, and 14 mol% was measured in air at 600° to 1050°C. Impedance spectroscopy was used to obtain lattice conductivity. A majority of the investigated samples exhibited linear Arrhenius plots of the lattice conductivity as a function of temperature. For all investigated dopant concentrations the ionic conductivity was shown to decrease as the dopant radius increased. The activation enthalpy for conduction was found to increase with dopant ionic radius. The fact that the highest ionic conductivity among 14-mol%-doped systems was obtained with HfO₂─Sc₂O₃ suggested that the radius ratio approach should be used to predict the electrical conductivity behavior of HfO₂─R₂O₃ systems. A qualitative model based on the Kilner's lattice parameter map does not seem to apply to these systems. For the three systems HfO₂─Yb₂O₃, HfO₂─Y₂O₃, and Hf₂O₃─Sm₂O₃ a conductivity maximum was observed near the dopant concentration of 10 mol%. Deep vacancy trapping is responsible for the decrease in the ionic conductivity at high dopant concentrations. Formation of microdomains of an ordered compound cannot explain the obtained results. A comparison between the ionic conductivities of doped HfO₂ and ZrO₂ systems indicated that the ionic conductivities of HfO₂ systems are 1.5 to 2.2 times lower than the ionic conductivities of ZrO₂ systems.     

Grain-Size Distribution in Al2O3─ZrO2 Generated by High-Temperature Annealing

Grain-size distribution in various Al₂O₃─ZrO₂ (2.5 mol% Y₂O₃) ceramics during high-temperature annealing was examined. In alumina-rich alloys, the grain size of major and minor phases was very different, while grain size was almost uniform in zirconia-rich alloys. This difference in grainsize distribution was related to the difference in grain growth rate of the major phase and to the effectiveness of grain-boundary pinning by minor-phase grains.     

Phase Equilibria in the System ZrO2─InO1.5

Phase equilibria in the system ZrO₂─InO_1.5 have been investigated in the temperature range from 800° to 1700°C Up to 4 mol%, InO_1.5 is soluble in t -ZrO₂ at 1500°C. The martensitic transformation temperature m → t of ZrO₂ containing InO_1.5 is compared with that of ZrO₂ solid solutions with various other trivalent ions with different ionic radii. The diffusionless c → t ' A phase transformation is discussed. Extended solid solubility from 12.4 ± 0.8 to 56.5 ± 3 mol% InO_1.5 is found at 1700°C in the cubic ZrO₂ phase. The eutectoid composition and temperature for the decomposition of c -ZrO₂ solid solution into t -ZrO₂+InO_1.5 solid solutions were determined. A maximum of about 1 mol% ZrO₂ is soluble in bcc InO_1.5 phase. Metastable supersaturation of ZrO₂ in bcc InO _1.5 and conditions for phase separation are discussed.     

Formation of the Perovskite Phase in the PbMg1/3Nb2/3O3─PbTiO3 System

The reaction sequences during calcination of oxide mixtures were studied for the PbMg_1/3Nb_2/3O₃─PbTiO₃ (PMN-PT) system. The effect of reactivity and composition of the starting mixtures was investigated. In the present study, a B-site-deficient, cubic pyrochlore phase in the PbO-Nb₂O₅ system was formed at 500°C. The perovskite phase of PMN was formed at 7007deg;C through the diffusion of MgO into the pyrochlore phase. The lattice parameter of the pyrochlore phase decreased as this transformation to perovskite progressed.     

Thermopower of YBa2Cu3O7-δ–Ag Composites

The percolation behavior of normal-state thermopower, resistivity, and superconductivity have been studied in YBa₂Cu₃O_7-δ─Ag (YBCO─Ag) composite systems. The normal-state resistivity and thermopower show a percolation threshold at a Ag volume fraction ( V _Ag) of 20% to 30%, whereas the superconducting network shows a threshold at a V _Ag of ≅70% to 80%. The results obtained from this study show that the YBCO─Ag composite obtained from Ag₂O and YBCO powders is uniformly distributed with Ag and YBCO remaining as separate phases without changing their characteristics. The measurements of thermopower indicate that the normal-state thermopower and phonon-drag thermopower are affected by the Ag addition. The stability of YBCO is increased when it is in composite form.     

Thermal Expansion of Homogeneous and Gradient Solid Solutions in the System KZr2(PO4)3─KTi2(PO4)3

Low-thermal-expansion ceramics having arbitrary thermal expansion coefficients were synthesized from homogeneous solid solutions in the system KZr₂(PO₄)₃─KTi₂(PO₄)₃ (KZP–KTP). Dense and strong ceramics were fabricated by sintering at 1100° to 1200°C with 2 wt% MgO. The thermal expansion coefficient increased from 0 to +3 × 10⁻⁶/°C with increasing x in KZr_{2 − x}Ti_x (PO₄)₃ (KZTP). In addition, a functionally gradient material with respect to thermal expansion was prepared by forming a series of KZTP solid solutions in a single ceramic body. By heating a pile of KZP and KTP ceramics in contact with each other, KZP and KTP bonded together to form a KZTP gradient solid solution near the interface.     

Effect of Aqueous Processing Conditions on the Microstructure and Transformation Behavior in Al2O3─ZrO2(CeO2) Composites

Aqueous processing of Al₂O₃─ZrO₂ (123 mol% CeO₂) composites, combined with sintering conditions, was used to control the microstructure and its influence on the martensitic transformation temperature of t -ZrO₂ and the transformation-toughening contribution at room temperature. The resultant ZrO₂ grain sizes in the dense composites were related to the transformation-toughening behavior of t -ZrO₂. The data show that (1) the best processing conditions exist when the electrophoretic mobilities of the two solids are positive, adequately high to ensure colloidal stability, efficient packing,and uniform ZrO₂ distribution but differ greatly in magnitude, (2) the colloidal stability of ZrO₂ controls the overall stability and the rheological and processing behavior of this mixture, (3) the grain size distribution in dense pieces sintered for 1 h at 1500°C is comparable to the particle size distribution of the powders, (4) the martensite start temperature for the tetragonal to-monoclinic transformation in Al₂O₃ containing 20 and 40 vol% ZrO₂ increases and can approach 0°C with increasing average ZrO₂ grain size, and as a result, (5) the fracture toughness values at room temperature are raised from 4–5 MPa.m^1/2 to 9–12 MPa.m^1/2 for these two compositions.     

Porous Glass-Ceramics with a Skeleton of the Fast-Lithium-Conducting Crystal Li1+xTi2−xAlx(PO4)3

Porous glass-ceramics with a skeleton of the fast-lithium-conducting crystal Li_{1+ x} Ti_{2− x} Al _x (PO₄)₃ (where x = 0.3–0.5) were prepared by crystallization of glasses in the Li₂O─CaO─TiO₂─Al₂O₃–P₂O₅ system and subsequent acid leaching of the resulting dense glass-ceramics composed of the interlocking of Li_{1+ x} Ti_{2− x} Al _x (PO₄)₃ and β-Ca₃(PO₄)₂ phases. The median pore diameter and surface area of the resulting porous Li_{1+ x} Ti_{2− x} Al _x (PO₄)₃ glass-ceramics were approximately 0.2 μm and 50 m²/g, respectively. The electrical conductivity of the porous glass-ceramics after heating in LiNO₃ aqueous solution was 8 × 10⁻⁵ S/cm at 300 K or 2 × 10⁻² S/cm at 600 K.     

Color and Selected Properties of PbO─BiO1.5─GaO1.5 Glasses

The density; molar volume; thermal expansion coefficient; dissolution rate in water, HC1, and NaOH; glass transition and crystallization temperatures; and the absorption edge in the ultraviolet-visible and infrared were measured for PbO─BiO1.5─GaO1.5 glasses. The range of compositions investigated was x PbO (100 − (x + y) )BiO_1.5. yGaO_1.5 for x between 20 and 60 cat% and y of 20, 25, 30, and 35 cat%. The glass-forming tendency increased with increased GaO_1.5 and decreased with increased PbO or BiO_1.5. The compositional dependence of these properties was consistent with the weight, size, charge, and bond strength of the cations. The Ga^{3 +} ions in these glasses are believed to act primarily as network-forming cations, whereas the majority of the Bi³⁺ and Pb²⁺ ions behave as network-modifying cations. It is suggested that a small friction of the lead ions are present as Pb⁴⁺. Depending upon melting conditions, these glasses ranged in color from brown to yellow. Various attempts, including containerless melting, were made to obtain colorless glasses, but no conditions were found which totally eliminated the color. The least color (pale yellow) was obtained when the glasses were melted in an air or nitrogen atmosphere in an alumina or gold crucible.