Effects of (B2O3, P2O5) Additives on Microstructural Development and Phase-Transformation Kinetics of Stoichiometric Cordierite Glasses

The microstructural development and phase-transformation kinetics of stoichiometric cordierite glasses containing B₂O₃ and/or P₂O₅ additives were highly affected by the microstructural characteristics of the μ-cordierite and the type of additives. The addition of B₂O₃ tended to cause the formation of μ-spherulitic dendrites with thin dendritic arms, which promoted the formation of α-cordierite, either from crystallization of the residual glass or from transformation of μ-cordierite. P₂O₅ had the opposite effect: Increasing the temperature increased the growth rate of α-cordierite more than that of μ-cordierite.     

Effect of Crystallizing the Grain-Boundary Glass Phase on the High-Temperature Strength of Hot-Pressed Si3N4 Containing Y2O3

The effects of fabrication variables on the high-temperature strength of hot-pressed Si₃N₄ containing 5 wt% Y₂O₃ were studied. Materials containing a crystalline grain-boundary phase, formed as a consequence of a high-temperature presintering heat treatment and identified as Si₃N₄·Y₂O₃, had high-temperature strengths significantly superior to those observed for materials containing a glass phase.     

Dielectric Constant and Optical Reflectance of Ceramic Filler-Added BaO–ZnO–B2O3–P2O5 Glass Composites

This study examined the influence of the addition of ceramic fillers (up to 20 wt% of TiO₂, Al₂O₃, and ZnO, respectively) to a BaO–ZnO–B₂O₃–P₂O₅ glass matrix on the dielectric and optical properties with the aim of using this material as the barrier ribs in plasma display panels. The modification of the dielectric constant by the fillers was related to the formation of secondary phases, the changes in the glass composition by the partial dissolution of the fillers, and the presence of pores. The reflectance of the composites ranged from 60% to 80% with the addition of 20 wt% filler.     

Microstructural Development of ZnO Pellets Doped with Different Vanadium Oxides (V2O5 and V2O3)

This work presents the effect of zinc oxide (ZnO) ceramics, doped with different percentages of vanadium trioxide (V₂O₃) and vanadium pentoxide (V₂O₅). Samples were analyzed by X-ray diffraction and scanning electron microscopy. The addition of V₂O₃ or V₂O₅ produced changes in the composition and morphology of the pellets. In both cases, different zinc vanadates were detected as secondary phases: α-Zn₃(VO₄)₂ and Zn₄V₂O₉. Furthermore, when the vanadium concentration was equal to or higher than 3 wt%, the presence of filaments was detected on the surface of the pellets. These filaments were produced due to vanadium segregation. However, this effect was only observed at the surface of the pellets. On the bulk, the filaments were not observed. Instead, vanadium was found at the interfaces between the ZnO grains and at triple points, as it could be expected.     

Sub-Sub-Tg Enthalpy Relaxation in a B2O3 Glass

Enthalpy relaxation processes in a B,O₃ glass were investigated calorimetrically in the temperature region from well below to near the glass-transition temperature T_g . The low-temperature ( T_aT_g- 100 K) or sub-sub- T_g anneals stabilize the glass structure. On heating, the annealed sample shows an excess endothermic peak above the annealing temperature T_a , and gradually recovers the original enthalpy without heating through T_g . The enthalpy relaxation evolves in a continuous manner with annealing time as seen in the recovery process. As T_a approaches T_g , a gradual transformation of the sub-sub- T_g behavior to that characteristic of the sub- T_g anneal occurs. The relaxation spectrum exhibits a broad distribution of relaxation times with activation energies of ∼ 10⁵ J/mol. The so-called β distribution commonly used in the analysis of the sub- T_g relaxation processes is seen to be too narrow to describe the sub-sub- T_g behavior. Possible mechanisms for the sub-sub- T_g relaxation phenomena are proposed.     

Crystallization Behavior of CaO–P2O5 Glass with TiO2, SiO2, and Al2O3 Additions

TiO₂ above 4 mol% is an effective nucleating agent for CaO–P₂O₅ glass which also contains substantial SiO₂ and Al₂O₃ additions. Glass ceramics can be made from this glass using a single slow heating ramp with no need for a nucleating heat treatment step. Powder of this composition crystallizes rapidly to β-Ca₂P₂O₇, whereas bulk glass crystallizes from diphasic nuclei consisting of a central cubic Ca-P-Ti-Si-Al oxide phase surrounded by impure AlPO₄ dendrites. Metastable calcium phosphate grows on the AlPO₄ dendrites and later transforms to β-Ca₂P₂O₇.     

Studies in Lithium Oxide Systems: XI, Li2O–B2O3–P2O5

The glassforming region in the system was roughly outlined and liquidus data were obtained for the three joins LiPO₃-BPO₄, Li₄P₂O₇-BPO₄, and Li₃PO₄-Li₂B₄O₇. Compatibility relations for the ternary subsystems Li₄P₂O₇-BPO₄-P₂O₅ and Li₂O-Li₃PO₄-Li₂B₈O₁₃ were established. Two ternary compounds with the probable compositions 22Li₂O - 11B₂O₃ - 13P₂O₅ and 2Li₂O 3B₂O₃ P₂O₅ were detected.     

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.     

Boron Coordination in PbO.2B2O3 and BaO·2B2O3 Melts

A partial molar volume technique was used to estimate the coordination number of oxygen ions around a boron ion in PbO·2B₂O₃ and BaO·2B₂O₃ melts. The boron coordination number appeared to be lower in the melt than in the crystal of PbO·2B₂O₃, whereas it was nearly the same in the melt and crystal of BaO·2B₂O₃.     

Sintering, Crystallization, and Properties of B2O3/P2O5-Doped Li2O·Al2O3·4SiO2 Glass-Ceramics

Sintering, crystallization, microstructure, and thermal expansion of Li₂O·Al₂O₃·4SiO₂ glass-ceramics doped with B₂O₃, P₂O₅, or (B₂O₃+ P₂O₅) have been investigated. On heating the glass powder compacts, the glassy phase first crystallized into high-quartz s.s., which transformed into β-spodumene after the crystallization process was essentially complete. The effects of dopants on the crystallization of glass to high-quartz s.s. and the subsequent transformation of high-quartz s.s. to β-spodumene were discussed. The major densification occurred only in the early stage of sintering time due to the rapid crystallization. All dopants were found to promote the densification of the glass powders. The effect of doping on the densification can fairly well be explained by the crystallization tendency. All samples heated to 950°C exhibited a negative coefficient of thermal expansion ranging from about −4.7 × 10^-6 to −0.1 × 10^-6 K^-1. Codoping of B₂O₃ and P₂O₅ resulted in the highest densification and an extremely low coefficient of thermal expansion.     

Correlation of Structure and Electrical Properties of 55FeO-45P2O5 Glass

The ac and dc characteristics of 55 mol% FeO-45 mol% P₂O₅ glass were measured as functions of time of heat treatment at 600° and of the ratio Fe³⁺/Fe_total. The dc resistivity behavior at constant temperature (for bulk specimens) was correlated with the appearance and growth of crystals in a glassy matrix, as indicated by data obtained with a Guinier-De Wolff X-ray camera. Dispersions appeared in plots of tan δ_ne vs frequency; a hypothesis explaining the appearance of these peaks is presented.     

Densification and Microstructural Development of SrTiO3 Sintered with V2O5

Precipitation of TiO₂ occurs during the sintering of SrTiO₃ with V₂O₅ added as a liquid-phase sintering agent. Satisfactory densification can be obtained at 1250°C when using a high content of V₂O₅ during sintering. However, a microstructure of fine grains and large pores results along with the precipitation of TiO₂. The precipitation of TiO₂ can be repressed by the addition of excess SrO. A well-sintered microstructure with superior densification can thus be obtained at 125O°C from specimens sintered with a low content of V₂O₅ and an appropriate amount of excess SrO.     

Electrical Conductivity of Glasses in the Systems P4O10-V2O5 and P4O10-WO3

The electrical conductivities of P₄O₁₀-V₂O₅ and P₄O₁₀-WO₃ glasses were compared. The P₄O₁₀ content of a glass from each system was replaced by increasing amounts of several oxides. The conductivity of the vanadium phosphate glass was insensitive to oxide replacement, in contrast to the conductivity of the tungsten phosphate glass, which decreased by almost five decades when a small amount of V₂O₅ was introduced. The change was attributed to the effect of oxidation-reduction on the tungsten ions.     

Relaxation of Volume and Index of Refraction in Pressure-Compacted B2O3 Glass

Relaxation processes were studied in bulk B₂O₃ glasses compacted under hydrostatic pressures up to 21 kbars at room temperature. Measurements of room-temperature density and refractive index at 1 atm revealed that (1) more than one ordering parameter is required to describe observed time-dependent volumetric behavior and (2) the refractive index is not a single-valued function of density, so that the Lorentz-Lorenz equation must be modified to account for changes in molecular configuration.     

Silica Glass Segregation in 3 wt% LiF-Doped Hot-Pressed Y2Si2O7

Hot-pressed yttrium disilicate ceramics have been characterized using analytical transmission electron microscopy (TEM). The microstructure consists of large grains of the γ phase of stoichiometric γ-Y₂Si₂O₇ containing rounded glassy Y-doped SiO₂ inclusions; excess glassy SiO₂-rich material is also found at the grain boundaries. Two main reasons are found for the inhomogeneity: a slight SiO₂ excess is inferred from the composition measurements, and the LiF flux used in hot pressing would also promote glass formation. Improved high-temperature mechanical properties would only be possible if residual glass formation was minimized, strategies for doing so are discussed, and the importance of analytical TEM for studying such submicron scale inhomogeneity is underlined.