Phase Diagram of Na2O-B2O3-SiO2 System

The binary isopleth Na₂O.B₂O₃-SiO₂ of the Na₂O-B₂O₃ SiO₂ ternary system has been investigated. A phase diagram is presented based upon data from differential thermal analysis studies of prepared glasses and direct observation of the melting behavior using solid-state video imaging. Phase equilibria relations in the Na₂O-B₂O₃-SiO₂ ternary system have been reassessed by combining information from this study with existing data from the literature. A revised liquidus surface for the ternary is presented in which the form of the isotherms is updated.     

Influence of Batch Moisture and Atmosphere on Melting Behavior of Lead Oxide-Containing Glass

Melting behavior in the sand-potash-lead oxide system was found to depend strongly on the amount of H₂O added to the batch (between 0.1 and 9.0 wt%) and also on the melting atmosphere (air, N₂, and air loaded with 30 vol% H₂O). Pb₃O₄ and PbO (red), which were used as raw materials, behave similarly. The newly formed compounds are Pb₃O₄ (formed only when PbO (red) was used as a raw material), PbO (yellow), and K₂Pb₂Si₂O₇. The addition of 2 wt% As₂O₃ to the batch influences the processes of formation and dissolution of compounds only in some cases.     

Studies in Lithium Oxide Systems: XII, Li2O-B2O3-Al2O3

Tentative phase relations in the binary system BnOa-A1₂O₃ are presented as a prerequisite to the understanding of the system Li₂O-B₂O₃-Al₂O₃. Two binary compounds, 2A1₂O₃.B₂O₃ and 9A1₂O₃.-2B₂O₃, melted incongruently at 1030° f 7°C and about 144°C, respectively. Two ternary compounds were isolated, 2Li₂O.A1₂O₃.B₂O₃ and 2Li₂O. 2AI₂O₃. 3B₂0₃. The 2:1:1 compound gave a melting reaction by differential thermal analysis at 870°± 20° C, but the exact nature of the melting behavior was not determined. The 2:2:-3 compound melted at 790°± 20° C to Li_zO.-5Al₂O₃ and liquid. X-ray diffraction data for the compounds are presented and compatibility triangles are shown.     

High-Temperature Energy Relations in the Alkali Borates: Binary Alkali Borate Compounds and Their Glasses

The energy relations existing between the congruently melting compounds Li₂O -2B₂O₃, Na₂O–2B₂O₃, Na₂O-4B₂O₃, and K₂O-4B₂O₃ and their glasses have been determined for the temperature range 25° to 1100°C. High-temperature heat-content, entropy, and heat of solution data are given for both the glasses and the corresponding devitrified materials. A comparison of the heats of fusion of the alkali borates on a gram atom of oxygen basis shows that they follow the order Li > Na > K. The entropy differences between the glass and the corresponding crystalline material have been determined at 25°C. The free-energy change at 25°C. for the reaction crystal → glass has been calculated for the four compounds.     

The Structure of Some B2O3-H2O Glasses

Boron oxide glasses with compositions corresponding to B₂O₃, B₂O₃.0.42H₂O, B₂O₃.0.50H₂O, and B₂O₃.0.63H₂) have been prepared and their structures have been studied. Diffractometric X-ray scattering measurements have been made, and from these, radial distribution functions have been computed. Comparison of the radial distribution functions indicates that the fundamental triangular coordination characteristic of vitreous B₂O₃ is maintained in the water-containing glasses. Consideration of the results of complementary infrared and nuclear magnetic resonance studies along with preliminary results of physical property measurements indicates that the glasses of high water content are heterogeneous. It is probable that disordered regions of high hydrogen bond density, approaching HBO₂ in composition, are embedded in a matrix approximating vitreous B₂O₃.     

Electrochemical Determination of the Activity of Na2O in the Pyrochlore Phase of the Sb2O4-NaSbO3 System

Activity of Na₂O in the pyrochlore phase of the system Sb₂O₄-NaSbO₃ has been measured as a function of temperature in the range 1073–1412 K by electromotive force (emf) measurements of the following solid-state electrochemical cells:
The solid electrolyte used in the above electrochemical cells is Na-ß-Al₂O₃, which is an excellent sodium-ion conductor in the temperature range of the measurements. From the measured reversible emf, the activity of Na₂O in the Sb₂O₄-NaSbO₃ system has been calculated. The temperature dependence of the logarithm of the activity of Na₂O in various two-phase regions of the Sb₂O₄-NaSbO₃ system can be represented as
No thermodynamic data have been reported earlier in the literature for the system Sb₂O₄-NaSbO₃, and the present data constitute the first thermodynamic information.     

The System Al-O

Previous data by other writers who infer the existence of aluminum suboxides in the solid state are critically discussed and alternatively interpreted. High-temperature X-ray diffraction patterns previously attributed to crystalline Al₂O and AlO are identified as those of Al₄C₃ and AlTaO₂, respectively. The melting curve observed by Baur and Brunner, suggesting the existence of a compound of the approximate composition Al₂O₉, corresponds to the pseudobinary system Al₂O₃−Al₄C₃. The T-x melting curve of the system Al₂O₃−Al was determined. There is no indication of the existence of crystalline aluminum suboxide, the only condensed phases being α-Al₂O₃ and Al. The liquidus indicates demixing of liquid Al and molten Al₂O₃. There is very limited intersolubility, and the addition of Al does not lower the melting point of Al₂O₃ measurably. With these facts and some additional information from the literature about the gaseous species, the P-T-x diagram of the system Al-O was constructed.     

Phase Equilibria in the System Na2O – Nb2O5

Phase equilibria data, obtained both by differential thermal analysis and by quenching, are presented for the system Na₂O-Nb₂O₅. Five compounds corresponding to the formulas 3Na₂O.1Nb₂0₆, lNa₂O. 1Nb₂O₅, lNa₂O 4Nb₂O₆, lNa_zO.7Nb₂O₅, and lNa₂O. 10Nb₂O₆ have been found. The compound 3Na_z0.lNb₂O₅ melts congruently at 992°C. The compounds 1Na₂O. 4Nb₂O₆, lNa₂O.7Nb₂O, and 1Na₂O. 1Onb₂O₅ melt incongruently at 1265°, 1275°, and 1290°C., respectively. The well-known perovskite structure phase NaNbO₃ was found to melt congruently at 1412°C. The transition temperatures in NaNbO₅ were checked by thermal analysis and only the major structural changes at 368° and 640°C. could be detected. A new disordered form of NaNbO₃ could be preserved to room temperature by very rapid quenching.     

Effect of Heat-Treatment on the Constitution and Mechanical Properties of Some Hydrated Aluminous Cements

The compound compositions of four aluminous cements were determined on anhydrous as well as hydrated specimens which had been heat-treated at temperatures between room temperature and 1400° C. Phases were identified by X-ray diffraction and differential thermal analysis. Specimens were also tested for transverse strength, dynamic modulus of elasticity, and thermal length change. A study of the dehydration characteristics of CaO - Al₂O₈ - 10H₂O₃ 3CaO.Al₂O₃. 6H₂O, and Al₂O₃. 3H₂O was included. The data indicated that CaO. Al₂O₃ 10H₂O was the primary crystalline hydrate formed in the cements at room temperature. At 50° C., 3 CaO Al₂O₃-6H₂O and Al₂O₃. 3H₂O were formed as by-products of the dehydration of CaO.Al₂O₃.10H₂O. When heated alone in an open system, CaO.Al₂O₃.10H₂O did not convert to 3CaO. Al₂O₃. 6H₂O and A1₂O₃. 3H₂O. A correlation between the mechanical properties and compound compositions was noted.     

Thermal Decomposition of Some Substituted Barium Titanyl Oxalates and Its Effect on the Semiconducting Properties of the Doped Materials

Thermal analysis has been performed on BaTiO(C₂O₄)₂.4H₂O, Ba_0.6Sr_0.4TiO(C₂O₄)₂.4H₂O, Sr(TiO(C₂O₄)₂.4H₂O, Ba_0.9Pb_0.1TiO(C₂O₄)₂.4H₂O, and BaTi_0.9Zr_0.1O(C₂O₄)₂.4H₂O. It was observed that the strontium compound decomposes differently than the others. Previous investigators have proposed conflicting mechanisms for the pyrolysis of the barium salt and these results are discussed in comparison with this work. The electrical resistivity and temperature coefficient of fired lanthanum-doped materials were found to vary with the calcination temperature. Maximum conductivity was observed in samples calcined at 900°C whereas maximum positive temperature coefficient was observed for materials calcined at 1050°C. Particle sizes of the calcined material were compared with grain sizes in the fired pieces and correlated with the electrical properties. A cursory examination was made on the effects of fabrication pressure, 1.25 to 15 tsi, on the electrical conductivity. Both the conductivity and positive temperature coefficient were found to increase with decreasing fabrication pressure.     

Gibbs Energy of Formation of CuGd2O4 and Phase Relations in the Cu-Gd-O System

Oxygen potentials for the coexistence of Cu₂O + Gd₂O₃+ CuGd₂O₄, Cu₂O + CuO + CuGd₂O₄, and Cu + Cu₂O + Gd₂O₃ three-phase equilibrium have been measured by employing the solid-state galvanic cells
between 960 and 1290 K, respectively. The results obtained in this study indicate that the ternary phase, CuGd₂O₄, is nearly stoichiometric. The measured oxygen potentials for the coexistence of various three-phase assemblages are given by the expressions
between 960 and 1290 K, respectively. Combining the oxygen potentials for the coexistence of Cu₂O + Gd₂O₃+ CuGd₂O₄ with that of Cu₂O + CuO gives for the reaction
The results obtained in the present investigation suggest that the formation of CuGd₂O₄ from component oxides is slightly endothermic and the phase CuGd₂O₄ is an entropystabilized compound. The enthalpy and entropy of formation of CuGd₂O₄ from component oxides obtained in this study are in excellent agreement with the recent calorimetric data. Phase relations and oxygen-potential diagram for the Cu-Gd-O ternary system have been constructed at 1273 K by combining the results obtained in this study and the auxiliary thermodynamic data available in the literature.     

The Al2O3-Nd2O3 Phase Diagram

A tentative phase diagram for the system Al₂0₃-Nd₂O₃ is presented. Three compounds were obtained: a β -A1₂O₃-type compound, the perovskite NdAlO₃, and Nd₄Al₂O₉. The perovskite melts congruently (mp 2090°C), and the two other compounds exhibit incongruent melting behavior: β -Nd/Al₂O₃, mp 1900°C; Nd₄Al₂O₉, mp 1905°C. Two eutectics exist with the following compositions and melting points: 80 mol% Al₂O₃, 1750°C; 23 mol% Al₂O₃,1800°C. Nd₄Al₂O9 decomposes in the solid state at 1780°C.     

The System Alumina-Gallia-Water

A study of the system Al₂O₃–Ga₂O₃–H₂O has resulted in the determination of equilibrium diagrams for the systems Al₂O₃–Ga₂O₃ and Al₂O₃.-H₂O–Ga₂O₃.H₂O. Extensive solid solution characterizes the α -Al₂O₃ and β -Ga₂O₃ structures at high temperatures, but it is shown that below 810°C. a compound, GaAlO₃, and a new series of (Al, Ga)₂O₃ structures are stable. Among the hydrates, a complete series of diaspore solid solutions extends from Al₂O₃.H₂O to Ga₂O₃.H₂O. Boehmite solid solutions extend to approximately the composition 70Al₂O₃.H₂O, 30Ga₂O₃.H₂O.     

Studies on 4CaOAl2.O3.13H2O and the Related Natural Mineral Hydrocalumite

Single-crystal X-ray and electron-diffraction studies show the existence in one polymorph of 4CaO.Al₂O₃. 13H₂O of a hexagonal structural element with α= 5.74 a.u., c = 7.92 a. u. and atomic contents Ca₂(OH)₇- 3H₂O. These structural elements are stacked in a complex way and there are probably two or more poly-types as in SiC or ZnS. Hydrocalumite is closely related to 4CaO.A1₂O₃.13H₂O, from which it is derived by substitution of CO₃^2-for 20H^-+ 3H₂O once in every eight structural elements; similar substitutions explain the existence of compounds of the types 3CaO Al₂O₃.Ca Y ₂- xH₂O and 3CaO Al₂O₃ Ca Y xH₂O. On dehydration, 4CaO.Al₂O₃.13H₂O first loses molecular water and undergoes stacking changes and shrinkage along c. At 150° to 250°C., Ca(OH)₂ and 4CaO.3Al₂O₃.3H₂O are formed and, by 1000°C., CaO and 12CaO.7Al₂O₈. The dehydration of hydrocalumite follows a similar course, but no 4CaO.3Al₂O₃.3H₂O is formed.     

The System CaO-Al2O3-H2O

Phase equilibria have been determined in the system CaO-Al₂O₃-H₂O in the temperature range 100° to 1000°C. under water pressures of up to 3000 atmospheres. Only three hydrated phases are formed stably in the system: Ca(OH)₂, 3CaO·Al₂O₃·6H₂O, and 4CaO·3Al₂O₃-3H₂O. Pressure-temperature curves delineating the equilibrium decomposition of each of these phases have been determined, and some ther-mochemical data have been deduced therefrom. It has been established that both the compounds CaO·Al₂O₃ and 3CaO·Al₂O₃ have a minimum temperature of stability which is above 1000°C. The relevance of the new data to some aspects of cement chemistry is discussed.     

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.     

Preparation of Fiberlike Silicon Nitride from Diatomaceous Earth

Fiberlike Si₃N₄ was prepared by the carbothermal reduction of diatomaceous earth in a flow of nitrogen and ammonia. Diatomaceous earth, which is an inexpensive raw material, is composed of 82.5 wt% SiO₂, 5.69 wt% Al₂O₃, and a very small amount of metal oxides (K₂O, CaO, and Fe₂O₃). Two types of fiberlike Si₃N₄ were obtained, short needlelike fiber and woollike fiber with Fe droplets at 1350°C.     

Growth of α-Al2O3 Crystals by Na2O Evaporation

A technique for growing α-Al₂O₃ crystals is described in which Na₂O·11Al₂O₃ is dissolved in a liquid of composition Na₂O·4TiO₂·3Al₂O₃. Alpha Al₂O₃ is precipitated as Na₂O evaporates from the system; Na₂O·11Al₂O₃ serves as a source of Al₂O₃, and Na₂O in the liquid. The content of solids in the mixture is always such that it does not melt completely. The size of the α-Al₂O₃ crystals grown is related to the Na₂O content of the composition. Crystals as large as 4000 by 3000 μm in the α-axis direction and 500 μm in the c -axis direction have been grown.     

Studies in Lithium Oxide Systems: V, Li2O-Li20 B2O3

Nine compositions containing 40 to 68% B₂O₃ were used to study the high-lithia portion of the system Li₂O-B₂O₃ by quenching and differential thermal analysis methods. The compounds 3Li₂O 2B₂O₃ and 3Li₂O B₂O₃ melted incongruently at 700°± 6°C, and 715°± 15°C., respectively. The compound 2Li₂O B₂O₃ is assumed to dissociate slightly below 650°± 15° C., although the data could also be interpreted as in-congruent melting. Below 600°± 6°C. it does dissociate to the 3:2 and 3:1 compounds. In this narrow temperature interval the 2:1 compound had an inversion at 618°± 6°C. Both forms of the 2:1 compound could be quenched to room temperature. X-ray diffraction data for the compounds are tabulated, and the complete phase diagram for the system Li₂O-B₂O₃ is presented.     

Spectroscopic Properties of Er3+-Doped Na2O–La2O3–Al2O3–SiO2 Glasses

Er³⁺-doped sodium lanthanum aluminosilicate glasses with compositions of (90− x )(0.7SiO₂·0.3Al₂O₃)· x Na₂O·8.2La₂O₃· 0.6Er₂O₃·0.2Yb₂O₃·1Sb₂O₃ (in mol%) ( x = 12, 20, 24, 40, 60 mol%) were prepared and their spectroscopic properties were investigated. Judd–Ofelt analysis was used to calculate spectroscopic properties of all glasses. The Judd–Ofelt intensity parameter Ω _t ( t = 2, 4, 6) decreases with increasing Na₂O. Ω₂ decreases rapidly with increasing Na₂O while Ω₄ and Ω₆ decrease slowly. Both the fluorescent lifetime and the radiative transition rate increase with increasing Na₂O. Fluorescence spectra of the ⁴ I _13/2 to ⁴ I _15/2 transition have been measured and the change with Na₂O content is discussed. It is found that the full width at half-maximum decreases with increasing Na₂O.