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.     

Role of P2O5 in TiO2-Opacified Porcelain Enamels

Phosphorus pentoxide is known to affect the reflectance and color of TiO₂-opacified porcelain enamels. It has been postulated that P₂O₅, impedes the anatase-to-rutile phase transformation. This hypothesis was tested by applying recently developed analytical procedures based on X-ray diffraction analysis to a typical porcelain enamel cover coat system. The inversion of anatase to rutile was not significantly affected by P₂O₅. Instead, in the range 0.5 to 4%, as P₂O₅ concentration was increased in the frit, the rate of crystallization of both anatase and rutile also increased, with the rate of increase of anatase being about twice that of rutile.     

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.     

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.     

Subsolidus Reactions in the System Fe2O3- TiO2

A study has been made of the binary system Fe₂O₂-TiO₂ by solid-state reactions under dry and hydrothermal conditions. Under dry conditions only one binary compound, pseudobrookite (Fe₂O₃-TiO₂), was formed and no evidence of solid solution on either side of this compound at temperatures up to 1200°C. was obtained. The system under these conditions is a simple binary with a single binary compound. Under hydrothermal conditions of 300° C. and 1200 Ib. per sq. in. the system is apparently also binary, with a single unstable compound closely resembling, if not identical with, the naturally occurring mineral arizonite (ferric metatitanate, Fe₂(TiO₃)₃).     

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.     

Microstructural Development on Crystallizing Hot-Pressed Pellets of Cordierite Melt-derived Glass Containing B2O3 and P2O5

Comparing the crystallization mechanism of stoichiometric and B₂O₃ and P₂O₅ containing glass reveals that the additives extend the gap between the glass transition and crystallization temperatures and suppress formation of μ, cordierite while promoting direct crystallization of α cordierite. Detailed TEM analysis of nucleation and growth of crystals in hot-pressed pellets of B₂O₃/P₂O₅-containing glass particles shows that nucleation occurs on unidentified heterogeneous nuclei at the sites of the previous particle surfaces. Growth of α cordierite with a cellular morphology or μ cordierite with a dendritic morphology is most likely controlled by the glass composition directly ahead of the growth front.     

Elastic Moduli and Refractive Indices of Aluminosilicate Glasses Containing Y2O3, La2O3, and TiO2

Glasses in the system Al₂O₃-Y₂O₃-SiO₂, containing TiO₂ and La₂O₃, were investigated. Glasses of high refractive index and elastic modulus were developed. The observed Young's and shear moduli of these glasses show good agreement with theoretical values. Agreement was also found between the observed and calculated values of refractive index when the Appen's empirical coefficients were used.     

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.     

Free Volume of Network-Forming Oxide Glasses in the Systems P2O5-(GeO2,TeO2,Sb2O3,V2O5)

The free-volume fraction (V_f) defined by Simha and Boyer was measured for network-forming oxide glasses in the systems P₂O₅-(GeO₂, TeO₂,Sb₂O₃.V₂O₅). The V_f values varied from 0.06 to 0.25. The systems P₂O₅-TeO₂: and P₂O₅-Sb₂O₃ have V_f∼0.1, which is near the magnitude of the free-volume fraction for normal metaphosphate glasses and many organic high polymers.     

Internal Friction of Network-Forming Oxide Glasses in the System P2O5-(GeO2, TeO2, Sb2O3, V2O5)

The internal friction of only network-forming oxide glasses containing a P₂O₅ component, i.e., in the systems P₂O₅-GeO₂, P₂O₅-TeO₂, P₂O₅-Sb₂O₃, and P₂O₅-V₂O₅, was measured as a function of temperature by a free torsional vibration method. P₂O₅-TeO₂ and P₂O₅-Sb₂O₃ glasses exhibited clearly high-temperature peaks in a plot of internal friction vs temperature in spite of the absence of nonbridging oxygens and network modifiers. Therefore, we conclude that the high-temperature peaks appeared when strong and weak parts coexisted in the network structure.     

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.     

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.     

Porous Glass-Ceramic in the CαO–TiO2–P2O5 System

A porous glass-ceramic in the CaO–TiO₂—P₂O₅ system has been prepared by crystallization and subsequent chemical leaching of the corresponding glass. By applying a two-step heat treatment to 45CaO · 25TiO₂· 30P₂O₅ glasses containing a few mol% of Na₂O, volume crystallization results in the formation of dense glass-ceramics composed of CaTi₄(PO₄)₆ and β-Ca₃(PO₄)₂ phases. By leaching the resultant glass ceramics with HCI, β-Ca₃(PO₄)₂ is selectively dissolved out, leaving a crystalline CaTi₄(PO₄)₆ skeleton. The surface area and mean pore radius of the porous glass-ceramics were approximately 40 m²/g and 13 nm, respectively.     

Studies in Lithium Oxide Systems: I, Li2O B2O3–B2O3

Phase relationships in the system Li₂O, B₂O₃-B₂O₃ were studied by the quenching method using twenty compositions. The crystalline phases encountered were (a) Li₂O, B₂O₃, which melts congruently at 849°± 2°C., (b) Li₂O.-2B₂O₃, which melts congruently at 917°± 2°C., (c) a new compound, 2Li₂O-5B₂O₃, which melts incongruently at 856°± 2°C. and dissociates below 696°± 4°C., (d) Li₂O.3B₂O₃, which melts incongruently at 834°± 4°C. and dissociates below 595°± 20°C., and (e) probably Li₂O.4B₂O₃, which melts incongruently at 635°± 10°C. Reactions were sluggish at temperatures near 600°C., resulting in metastable relations. Hence phase equilibrium data relating to the lower stability limit of Li₂O.3B₂O₃ and to the upper stability limit of Li₂O.4B₂O₃ are considered to be tentative. Properties of the glasses and crystalline phases were studied. The refractive index of the glasses increased with the addition of Li₂O up to 22%, but further additions up to 40% had no substantial effect. Glasses containing less than 30% Li₂O were water soluble. Limited data on the density and thermal expansion of the glasses are presented. Li₂OB₂O₃ was euhedral, lath-shaped, length-fast, biaxial negative (2V = 27°), with n_α= 1.540, n_β= 1.612, n_γ= 1.616. Li₂O.2B₂O₃ was uniaxial negative, with n_e= 1.560, n_w= 1.605. Li₂O.3B₂O₃ was biaxial negative (2V = 75° to 80°), with n_α= 1.576, n_β= 1.602, n_γ= 1.605. X-ray powder diffraction data for the five crystalline compounds are presented. Thermal expansion data for Li₂O-B₂O₃ and Li₂O.2B₂O₃ and limited data on the fluorescent properties of the compounds are given. X-ray diffraction data are also presented for Li₂O.B₂O₃.4H₂O and Li₂O.-5B₂O₃. 10H₂O. Li₂O B₂O₃ was obtained by heating the first hydrate at 450° to 680° C. X-ray diffraction showed Li₂O.4B₂O₃ and Li₂O-3B₂O₃ to be the crystalline products obtained during heating the decahydrate at 500°C. and 600°C., respectively.     

Structure, Thermal Behavior, Chemical Durability, and Optical Properties of the Na2O–Al2O3–TiO2–Nb2O5–P2O5 Glass System

The FTIR, Raman, UV-Vis, ³¹P MAS-NMR, DTA, and refractive index measurements have been combined to investigate a series of glasses with the general formula 20Na₂O–5Al₂O₃− x TiO₂–(45− x )Nb₂O₅–30P₂O₅, 15≤ x ≤45. The glass structure, as well as thermal, optical, and chemical durability properties, were then described as functions of the f _Nb/ f _Ti ratio. An increase of the f _Nb/ f _Ti ratio correlates with a decrease in length of the average phosphate chains linked through Nb–O–P and Ti–O–P bonds, with an increase in the glass stability and with increase in the linear refractive indices at 632.8 nm from 1.79 to 1.89. Furthermore, niobium is more effective than titanium in improving chemical durability.     

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.     

Ionically Conducting Composite Membranes from the Li2O–Al2O3–TiO2–P2O5 Glass–Ceramic

This paper reports processing of lithium ion-conducting, composite membranes comprised of 14Li₂O·9Al₂O₃·38 TiO₂·39P₂O₅ glass–ceramic and polyethylene. The processing involved tape casting of 14Li₂O·9Al₂O₃·38TiO₂·39P₂O₅ glass powder with organic additives into tapes, subjecting the green tape to binder burnout and thermal soaking in the temperature range of 950°–1100°C, and finally infiltrating the porous tape with polyethylene solution. The ionic conductivity and microstructure of 150–350 μm thick membranes were characterized and are discussed in this paper. The crystallites of the glass–ceramic show liquid-like conductivity at ambient temperature, whereas the grain boundary conductivity is lower by a factor of five. The lower grain boundary conductivity is explained on the basis of crystallographic mismatch and the existence of AlPO₄ at the grain boundary. The polyethylene infiltration in the porous membrane improved mechanical resilience with a minor adverse effect on conductivity.