Cristobalite Phase Formation in Glass/Ceramic Composites

The effect of several different aluminum-containing ceramic additions to borosilicate glass on suppressing cris-tobalite precipitation has been examined. The results showed that mullite or aluminum nitride suppresses cristo-balite formation more effectively than alumina or spinel. Although both follow a simple rule of mixtures, glass/mullite composites can be fabricated with lower dielectric constants than glass/alumina composites, while maintaining a thermal expansion coefficient close to Si. Electron micro-analysis using X-ray energy dispersive spectroscope showed that the measured interdiffusion coefficient between alumina and glass is in good agreement with the data which have already been published.     

Glass Formation and Properties in the System Calcia-Gallia-Germania

The critical cooling rate for glass formation, R^c, was measured for four compositions in the system calcia-gallia-germania. The activation energy, E, and frequency factor, u, for the crystallization process were determined by reheating the glasses at varied constant heating rates and measuring the temperature of crystallization. Both E and v increased, with increasing germania content of the glass, whereas R^c decreased. The density, refractive index, and Abbe number were also measured; all decreased with increasing GeO² content. These results are compared with those for calcia-gallia-silica glasses of comparable compositions.     

Glass Formation and Properties in the System Calcia-Gallia-Silica

The glass-formation region of the calcia-gallia-silica system was determined. The glasses within this region were measured to have a density of 3 to 4 g/cm³, a refractive index of 1.6 to 1.73, an Abbe number between 35 and 58, a thermal expansion coefficient of 6.5 × 10⁻⁷/°C to 11.5 × 10⁻⁷/°C, softening temperatures between 730° and 790°C, and a Vickers microhardness of 5.2 to 7.3 GPa. Crystalline phases were identified along the glass-formation boundary. Infrared transmission spectra were used to explain glass structures and their effect on glass properties. The results suggest that the role of calcia in the glass structure is similar to that for calcia in calcium aluminosilicate glasses.     

Phase Relations and Ordering in the System Erbia-Hafnia

The system erbia-hafnia was investigated using thermal expansion measurements and room-temperature X-ray diffraction of quenched and annealed samples. The range of existence of the solid solutions based on HfO₂ and Er₂O₃ was determined by the precision lattice parameter method. Three compounds with hexagonal structure are reported: the first is an ordered fluorite-related phase with the ideal formula Er₄Hf₃O₁₂ and decomposes with increasing temperature at ∼1500°C into a solid solution of the fluorite type; the second is formed at ∼55 mol% Er₂O₃, corresponding closely to the formula Er₅Hf₂O_11.5, and undergoes a transformation at ∼1650°C into cubic solid solutions to fluorite and C type. The third compound is formed within the concentration range between 60 and 90 mol% Er₂O₃. This compound, Er₆HfO₁₁, decomposes at ∼1700°C into a cubic solid solution of the C type. A proposed phase diagram for the system erbia-hafnia is presented.     

Phase Relations in the System Lead—Oxygen

Most of the known oxides of lead including the intermediate oxides Pb₁₂O₁₉ and Pb₂O₃ have been prepared under equilibrium conditions. Precise X-ray powder data have been obtained for the intermediate oxide phases. Solid-vapor equilibrium data have been obtained for reactions in the system lead-oxygen over the range 200° to 900° C and 3 to 1400 bars Po₂. Pressure-temperature univariant equilibrium curves are presented for the reactions PbO₂⇋ Pb₁₂O₁₉+ oxygen, Pb₁₂O₁₉⇋ Pb₃O₄+ oxygen, and Pb₃O₄⇋ PbO + oxygen. The enthalpies of reaction are, respectively, 26.8, 34.6, and 33.7 kcal per mole. Eutectic melting between PbO and Pb₃O₄ occurs at 875° C and 124 bars. A stability field for Pb₂O₃ exists above 1000 bars PO₂ at 600° C. Approximate resistivity data are presented.     

Phase Relations in the System Uranium—Nitrogen

To supplement efforts to develop UN as a nuclear fuel material, a study of the phase relations in the system uranium-nitrogen was conducted. The decomposition behavior and melting point of UN was studied in a controlled nitrogen-pressure apparatus in which cast specimens of UN were heated and observed. UN decomposed at pressures of nitrogen below 2.5 atm at temperatures below 2850° C and melted congruently at 2850° C and pressures of 2.5 atm or greater. The nitrogen content of the liquid uranium phase in equilibrium with UN was determined by heating uranium in a UN crucible and then quenching and analyzing the equilibrated phase. The solubility of nitrogen in atomic percent can be expressed as S = 2.45 × 10⁴ exp (-38,800/RT) for temperatures in OK. Studies in the region U₂N₃-UN₂ of the system which were performed using a Sievert-type apparatus showed that although these compounds are structurally dissimilar, they form a series of continuous solid solutions. Only UN₂ formed at high pressures and low temperatures. A pressure-temperature schematic diagram and a temperature-composition schematic diagram for a nitrogen pressure of 1 atm for the system uranium-nitrogen are presented. At this pressure, UN decomposed at 2800° C and U₂N₃ decomposed at 1345° C.     

Phase Relations at Low Temperatures in the Fe-Mg-O System

Even when magnesiowustite is rapidly cooled in a reducing atmosphere, a small volume fraction of spinel forms. These results provide a basis for understanding the large discrepancies in M-H curves and the observed quadrupole splitting in Moessbauer spectra reported by various workers. In addition, it is shown that, with modern monochromatic X-ray diffraction techniques, a volume percent <0.10 can readily be measured.     

Phase Relations in the System Boron Oxide–Silica

The suggested phase diagrams for the system B₂O₃-SiO₂ as drawn from the findings of previous investigators are presented. These diagrams show the wide controversy regarding this system. The principal difficulties in obtaining reliable equilibrium data are the volatilization of B₂O₃, the hydration of B₂O₃-rich glasses, and the great viscosity of B₂O_rSiO_z melts. In this investigation firings were made in sealed platinum capsules. Where necessary, they were opened and studied under xylene to eliminate hydration. Phases were identified by optical and X-ray methods. The liquidus was obtained by determination of the temperatures at which the stable phases of SiO₂ completely dissolved in the borosilicate melts. The criteria used for equilibrium are discussed.     

Subsolidus Phase Relations and Transparent Conductors in the Cadmium-Indium-Tin Oxide System

Subsolidus phase relations have been determined in the CdO–InO_1.5–SnO₂ system at 1175°C. A cubic-bixbyite solution In_{2−2 x} (Cd,Sn)_{2 x} O₃ (0 < x < 0.34), a cubic spinel solution (1− x )CdIn₂O₄– x Cd₂SnO₄ (0 < x < 0.75), and an orthorhombic-perovskite solution Cd_{1− x} Sn_{1− x} In_{2 x} O₃ (0 < x < 0.045) having the GdFeO₃ structure have been discovered. The CdO phase field exists over a small range of InO_1.5 (<3%) and SnO₂ (<1%). Orthorhombic Cd₂SnO₄ (Sr₂PbO₄ structure) and rutile SnO₂ appear to be point compounds with negligible solubility. The vertical section between spinel CdIn₂O₄ and orthorhombic Cd₂SnO₄ was determined between 900° and 1175°C. The spinel phase field (1− x )CdIn₂O₄– x Cd₂SnO₄ was found to extend between x = 0 and x = 0.75 at 1175°C or x = 0.78 at 900°C. All of the phases in this system appear to allow small excess quantities of the donors In and/or Sn (vs cation stoichiometry) which may be the source of the electrons that give these oxides their n-type character. The electrical and optical properties of bulk and thin-film specimens in this system are compared and contrasted with each other and the relative merits of each are assessed.     

Glass Formation in the PbO–GeO 2 System

The glass-forming region in the PbO–GeO2 system is studied. To increase the glass-forming limit in this system, the tempering rate of the samples has to be increased using special methodological practices. The dependence of the temperature of the synthesis of lead germanate glass on the PbO content is obtained. It is shown that the corrosion of alumina crucibles proceeded during the synthesis of lead germanate glass. The dependence of the thickness of the corroded layer of the alumina crucible wall on the time of the synthesis of the glass of the 55PbO · 45GeO2 composition, mol % at 900°С is obtained. It is proved that the obtained glass is X-ray amorphous within the whole range of compositions in the PbO–GeO2 system.     

Formation of the Liquid Phase in the System Bi-Pb-Sr-Ca-Cu-O

Differential thermal analysis (DTA), powder X-ray diffraction (XRD), and scanning electron microscopy (SEM) were carried out to investigate the origin of the partial melting which is closely related to the formation of the 110 K superconducting phase in the Bi-Pb-Sr-Ca-Cu-O system. The occurrence of a liquid phase in the presence of the Bi₂Sr₂Ca-Cu₂O _y , Ca₂PbO₄, and CuO phases was demonstrated. Large grain growth and promotion of the 223 phase formation resulting from the reactive liquid-phase-aided sintering were also observed.     

Phase Relations in the System Uranium—Carbon—Oxygen

The ternary system U-C-O was investigated and a diagram is given expressing the phase relations in specimens which were reacted at 1800°C in vacuum or in inert atmospheres and furnace cooled. A U(C,O) single-phase area exists in this diagram. The limit of substitutional solid solution of oxygen atoms for carbon atoms in UC is 12.5 at.%, which means that only 25% of the carbon atoms in UC can be replaced by oxygen atoms. The oxygen-saturated UC phase, U(C_0.75O_0.25), has a lattice parameter of 4.953 ± 0.001 A. The carbon monoxide partial pressures in equilibrium with this phase were determined for temperatures between 1705° and 1855°C.     

Phase Relations and Thermal Expansion Studies in the Ceria–Yttria System

The synthesis, characterization, and bulk and lattice thermal expansions of a series of compounds with general composition Ce_{1– x} Y _x O_{2– x /2} (0.0 ≤ x ≤ 1.0) are reported. The XRD pattern of each product was refined to learn the solid solubility limit and the homogeneity range. The solid solubility limit of YO_1.5 in CeO₂ lattice, under the conditions of slow cooling from 1400°C, is represented as Ce_0.55Y_0.45O_1.775 (i.e., 45 mol% of YO_1.5). The subsequent compositions were biphase. There was no solubility of CeO₂ into the lattice of YO_1.5. The bulk thermal expansion measurements from ambient to 1123 K, as investigated using a dilatometer, revealed that the α_l (293–1123 K) values, within the homogeneity range, decreased on increased Y³⁺ content. A similar trend was observed for average lattice thermal expansion coefficient, α_a (293–1473 K), as investigated using high-temperature XRD. No ordered phases were obtained in this system under the used conditions. These studies on Ce_{1– x} Y _x O_{2– x /2} (0.0 ≤ x ≤ 1.0) system can be used to simulate the phase relation and thermal expansion behavior of Pu_{1– x} Y _x O_{2– x /2} (0.0 ≤ x ≤ 1.0), because CeO₂ is widely used as a surrogate material for PuO₂.     

Solid-state Reactions and Phase Relations in the Ti-Si-O System at 1373 K

Reactions between Ti and SiO₂ were studied at 1373 K (1100°C) under vacuum conditions using planar diffusion couples. A method to correct for the presence of surface oxide was developed which led to improved oxygen measurements with the electron probe microanalyzer. An isothermal section through the Ti-Si-O phase diagram at 1373 K was determined using measured diffusion paths and phase compositions in equilibrated alloys. The experimentally determined isothermal section was compared to isothermal sections calculated using thermodynamic data. In addition the sequence of reaction layers formed in the diffusion couples is discussed in terms of thermodynamic activity diagrams.     

Glass Formation

The ability to form a glass, i.e., the ability to form bonds which lead to a vitreous network, appears periodically in the classification chart of the elements. Thus simple glasses containing only one kind of atom are formed by the elements of Group VI of the periodic table (O, S, Se, and Te). Only these elements are known to form monatomic (primary) glasses and they retain the ability to form a vitreous network when mixed or chemically bound to each other. The elements of Group VI also form binary glasses, i.e., glasses containing two kinds of atoms, with the elements of Groups III, IV, and V. Experimental evidence of the glassforming capacities of these elements and compounds is given; about twenty new glasses suggested by the foregoing were prepared in the author's laboratory. Binary glasses are also known to exist composed of an element of Group VII (F, Cl, I, or Br) and an element of one of Groups II, III, and IV or a transition element. Experimental evidence for these glasses is presented.     

Morphology and Stability of the Glass Phase in Glass Ceramic Systems

An explanation is given for the apparent stability of a minor phase in a two-phase system, such as a glass in a glass ceramic, even though normally the glass would be expected to dissolve completely into the crystalline phase. It is shown that the glass would be stable only if it is segregated to the triple-junction nodes and only if the dihedral angle is <π/3. The size and morphology of the glass pocket are obtained in terms of the interface energies, the undercooling below the solidus temperature, and the dihedral angle.     

Glass Formation, a Contemporary View

The process of glass formation is discussed from several perspectives. Particular attention is directed to kinetic treatments of glass formation and to the question of how fast a given liquid must be cooled in order to form a glass. Specific consideration is paid to the calculation of critical cooling rates for glass formation, to the effects of nucleating heterogeneities and transients in nucleation on the critical cooling rates, to crystallization on reheating a glass, to the experimental determination of nucleation rates and barriers to crystal nucleation, and to the characteristics of materials which are most conducive to glass formation.