ANALYSIS OF RECENT MEASUREMENTS OF THE VISCOSITY OF GLASSES.—II1

Viscosity of two series of four component glasses .—The results recently reported by S. English² are here analyzed by the method used in a previous paper.³ (1) Series 6SiO₂, 1.2Na₂O, 0.8(CaO+MgO). The temperature at which the difference between the viscosity of a glass and the viscosity of 6SiO₂,2Na₂O at the same temperature makes a sharp bend is called the aggregation temperature Ta . It seems to correspond to the devitrification temperature. For this series Ta reaches a sharp minimum for the composition 6SiO₂, 1.15Na₂O, 0.45MgO, 0.39CaO. The viscosity for any temperature also reaches a minimum at or near this composition. (2) Series 6SiO₂, 1.1Na₂O, 0.9(CaO+Al₂O₃). The curves are similar to those for the first series, TA reaching a sharp minimum for the composition 6SiO₂, 1.11Na₂O, 0.81Ca0, 0.14Al₂O₃.     

EFFECT OF COMPOSITION AND TEMPERATURE ON SOLUBILITY OF IRON OXIDE IN GROUND-COAT ENAMEL GLASS*

The solubility of iron oxide in ground-coat enamel glasses at various temperatures was studied by adding varying amounts of ferric oxide to the milled enamel and giving the mixture a heat-treatment to acquire uniformity without devitrification at the desired temperature. The iron oxide solubility was obtained by finding the breaking point in the curve for iron oxide versus index of refraction. The frit solubilities were obtained at 1400°, 1600°, 1800°, and 2000°F. with variations in Na₂O, B₂O₃, A1₂O₃, CaF₂, CaO, F₂, SiO₂, COO, NiO, MnO₂, BaO, and MoO₃. Data are given on a number of commercial frits.     

THE DEVITRIFICATION OF SODA-LIME-SILICA GLASSES1

The isotherms and boundary curves in that portion of the ternary system Na₂O-SiO₂–CaO.SiO₂–SiO₂ of direct application to glass technology, namely, from 64 to 78% SiO₂, 0 to 20% CaO, including the whole of the field of the compound Na₂O.3CaO.6SiO₂, and portions of the adjoining fields of Na₂O.2SiO₂, Na₂O.2CaO.3SiO₂, CaO.SiO₂, tridymite, and quartz, have been determined with greater precision than in a previous study² by greatly increasing the number of mixtures studied, and thereby decreasing the interpolation necessary in the interpretation. An extended discussion is given of the devitrification of glass, in which it is shown that the liquidus temperature is the only datum point which is solely a function of glass composition, and is unaffected by the past history of the glass or by fortuitous circumstances at the time devitrification is taking place. At the liquidus the first trace of crystalline phase is in equilibrium with the glass; above the liquidus the glass will dissolve any such crystals which may have been formed at some previous time, but new crystals cannot form; while only below the liquidus is there a tendency for crystals to separate. The driving force causing this reaction is derived from the difference in free energy between the unstable glass and the stable aggregation of crystalline phases, and this force is opposed by a resistance of the nature of a viscosity. The dissociation in the liquid phase of the compounds which separate on devitrification diminishes the rate at which the devitrification equilibrium is reached, and increasing the complexity of the glass will have a similar effect. The excess in surface energy at the interface glass-crystal may have an influence at the instant of formation of the first infinitesimal crystal, hut after the crystal has grown to a dimension appreciably greater than the sphere of molecular action the excess energy at this interface ceases to be of importance. The only surface tension measurements which have been made on glass refer to the interface glass-air, and the excess energy at this interface has no necessary correlation with the devitrification process.     

VISCOSITY STUDIES OF SYSTEM CaO–MgO–Al2O3–SiO2: 1, 40% SiO2*

The measurement of glass viscosities at elevated temperatures with an oscillating cylinder-type viscometer is described. Viscosity data are presented covering those compositions in the CaO–MgO–Al₂O₃–SiO₂ system which contain 40% SiO₂ and which are liquid at 1500°C. The pattern of the system of isokoms presented indicates that viscosity is closely related to the ratio of basic to acidic components. Theoretical aspects of the variation of viscosity with composition in silicate-aluminate systems are discussed in terms of silica-alumina polymers.     

PRELIMINARY STUDY ON PORTIONS OF SYSTEMS Na2O-CaO-AI2O3-Fe2O3 AND Na2O-CaO-Fe2O3-SiO2*

Portions of the quaternary system Na₂O-CaO-Al₂O₃-Fe₂O₃ have been studied by the exploration of (1) the plane CaO-4CaO.Al₂O₃°Fe₂O₃-(Na₂O + 3Al₂O₃) and (2) planes above the base system CaO.5CaO.3Al₂O3–2CaO.Fe₂O₃ which contain successively increasing amounts of Na₂O up to 6%. A portion of the quaternary system Na₂O-CaO-Fe₂O₃-SiO₂ has been studied by the exploration of a plane containing 5% of Na₂O above the base system CaO-2CaO.SiO₂-CaO.Fe₂O₃. In the pseudosystem CaO-4CaO.Al₂O₃.Fe₂O₃-(Na₂O + 3A1₂O₃) the compound Na₂O.-8CaO.3A1₂O₈ was found to exist as a primary phase, and the area in which the plane cuts the Na₂O.8CaO.3A1₂O₃ primary-phase volume was established. Three points on uni-variant curves were located. The iron phase (4CaO.A1₂O₃.Fe₂O₃ solid solution) was observed to exist in a solid-solution series. In the system Na₂O-CaO-5CaO.3Al₂O_3--2CaO.Fe₂O₃ it was found that the compound Na₂O.8CaO.3Al₂O3 appears at an Na₂O concentration of 4.2%. As soda, however, is taken into solid solution by other phases, it was not feasible at this time to determine the invariant point for Na₂O.8CaO.3A1₂O₃, 3CaO.Al₂O₃, 5CaO.3A1₂O₃, and 4CaO.Al₂O₃.-Fe₂O_a solid solution. In the system Na₂O-CaO-2CaO.SiO₂-CaO.Fe₂O₃ no ternary compounds were observed up to the 5% limit of Na₂O employed. A soda-containing phase occurred in solid solution with α-2CaO.SiO₂, which may precipitate on cooling, forming inclusions in the ß-2CaO.SiO₂, or enter into reaction with the glassy phase.     

Microscopic Origins of Compositional Trends in Aluminosilicate Glass Properties

Revealing and understanding the microscopic origins of the macroscopic properties of aluminosilicate glasses is important for the design of new glasses with optimized properties. In this work, we study the composition‐structure‐property relationships in 20 MgO/CaO sodium aluminosilicate glasses upon Al₂O₃‐for‐SiO₂ and MgO‐for‐CaO substitutions. We find that some properties (density, molar volume, Young's modulus, and shear modulus) are linear through the investigated range of Al₂O₃ compositions, while others (refractive index, coefficient of thermal expansion, Vickers hardness, isokom temperatures, and liquid fragility index) exhibit a change in the slope around the composition with [Al₂O₃] = [Na₂O], which is especially pronounced for the glasses containing MgO. We discuss these phenomena based on structural information obtained by NMR spectroscopy and topological considerations.     

EFFECT OF SUBSTITUTING MgO FOR CaO ON PROPERTIES OF TYPICAL SODA-LIME GLASSES*

In base glasses containing (a) Na₂O 16, CaO 10, and SiO₂ 74% and (b) Na₂O14, CaO 12, and SiO₂ 74%, MgO was substituted in steps of 2% for CaO. The effects of the substitution on liquidus temperature, viscosity, fiber softening point, and the resistance of the glasses to dilute acid and to distilled water are described.     

Synthesis of glass-ceramics in the Na2O/K2O-CaO-MgO-SiO2-P2O5-CaF2 system as candidate materials for dental applications

This study reports on the sintering behavior, crystallization process, and mechanical properties of novel glass-ceramics (CGs) produced by the glass powder compact consolidation method. Substitution of K₂O for Na₂O and MgO for CaO was attempted in the parent glasses belonging to Na₂O-CaO-MgO-SiO₂-P₂O₅-CaF₂ system. Glass powder compacts were heat treated at various temperatures between 700°C and 900°C, taking under consideration the glass transition (T_g) and the crystallization peak (T_p) temperatures, which were experimentally determined for each investigated glass by thermal analysis (dilatometry and differential scanning calorimetry). The experimental results showed that sintering always preceded crystallization, regardless of the type of substitution. In the case of MgO substitution for CaO, crystallization was advanced in the range of 800°C-850°C, resulting in the formation of an assembly of crystalline phases, such as diopside, fluorapatite, and wollastonite. The substitution of K₂O for Na₂O increased the activation energy for crystallization, shifting crystallization process to a high temperature region, with the formation of alpha-potassium magnesium silicate, instead of wollastonite. The GCs produced had values of 22-31 GPa regarding the modulus of elasticity, 5.0-6.1 GPa concerning the microhardness, and 1.4-1.9 MPa⋅m^0.5 as regard the fracture toughness, which are similar to those of the human jawbone.     

Effects of promoters on catalytic activity and carbon deposition of Ni/γ‐Al2O3 catalysts in CO2 reforming of CH4

Catalytic reforming of methane with carbon dioxide was studied in a fixed‐bed reactor using unpromoted and promoted Ni/γ‐Al₂O₃ catalysts. The effects of promoters, such as alkali metal oxide (Na₂O), alkaline‐earth metal oxides (MgO, CaO) and rare‐earth metal oxides (La₂O₃, CeO₂), on the catalytic activity and stability in terms of coking resistance and coke reactivity were systematically examined. CaO‐, La₂O₃‐ and CeO₂‐promoted Ni/γ‐Al₂O₃ catalysts exhibited higher stability whereas MgO‐ and Na₂O‐promoted catalysts demonstrated lower activity and significant deactivation. Metal‐oxide promoters (Na₂O, MgO, La₂O₃, and CeO₂) suppressed the carbon deposition, primarily due to the enhanced basicities of the supports and highly reactive carbon species formed during the reaction. In contrast, CaO increased the carbon deposition; however, it promoted the carbon reactivity. © 2000 Society of Chemical Industry     

EFFECT OF ALUMINA ON DEVITRIFICATION OF SODIUM OXIDE-DOLOMITE LIME-SILICA GLASSES*

The effect of the substitution of A1₂O₃ for the oxides of sodium, silicon, calcium, and magnesium in the ratio in which they occur in dolomite on the liquidus temperatures and phase relations for glasses lying within the composition range, Na₂O 12 to 16%, CaO-MgO 0 to 20%, SiO₂ 63 to 78%, and A1₂O₃ 0 to 10%, has been determined. The results on 116 individual determinations are given. Devitrite is the primary phase in very few glasses. Several glasses were found which cannot be devitrified. A comparison of devitrification temperatures of calcite and dolomite-lime glasses is made.     

RELATION OF ELECTRICAL CONDUCTIVITY TO CHEMICAL COMPOSITION OF GLASS*

The electrical conductivity of some glasses in the soda-lime-silica system was measured at 400 °C. with an apparatus which is described. The specific resistance at this temperature ranged from 0.06 to 5.0 × 10⁵ ohms per cc. Measurements were made on other glasses containing equivalent amounts of various oxides incorporated in a parent soda-lime-silica glass. It was found that an increase in resistance was produced by additions of MnO, ZnO, B₂O₃, Fe₂O₃, BaO, PbO, TiO₂, and K₂O, the resistances increasing in this order. A decreased resistance was produced by Na₂O, CaO, and Al₂O₃. Previously published data on the power factors of these glasses are reviewed.     

Structural and Textural Modifications of Ternary Phosphate Glasses by Thermal Treatment

Phosphate-based glasses of composition xNa₂O−(45+(10−x))CaO−45P₂O₅ with different Na₂O, CaO (x = 1, 5, 10, 15, and 20 mol%), and invariable P₂O₅ (45 mol%) contents were prepared using the rapid melt quench technique. The obtained thermal data from differential thermal analysis revealed a decline in glass transition (T_g) and crystallization (T_c) temperatures of glasses against the compositional changes. The inclusion of Na₂O at the cost of CaO in the glass network led to a reduction in its thermal stability. The thermal treatment carried out on glasses helped to derive their glass-ceramic counterparts. The amorphous and crystalline features of samples were characterized using X-ray diffraction patterns. The crystalline species that emerged out of the calcium phosphate phases confirmed the dominance of Q¹ and Q² structural distributions in the investigated glass-ceramics. The obtained scanning electron micrographs and atomic force microscopic images confirmed the surface crystallization and textural modification of the samples after thermal treatment. The N₂-adsorption–desorption studies explored the reduction of porous structures due to thermal treatment on the melt-driven glass surface. The measured elastic moduli and Vicker's hardness values of the glasses showed an increase after thermal treatment, which were reduced against the inclusion of alkali content in both glass and glass-ceramics.     

THE EFFECT OF BORIC OXIDE ON THE DEVITRIFICATION OF THE SODA-LIME-SILICA GLASSES. THE QUATERNARY SYSTEM,Na2O-CaO-B2O3-SiO21

Commercial glasses of the soda-lime-silica types do not consist solely of these three oxides, but in addition contain significant amounts of other constituents which arc introduced incidentally as impurities or deliberately for some beneficial influence. Such minor additions may have either a favorable or unfavorable influence on the tendency of the glass to devitrify, and an investigation into the effect of such minor components is desirable. Previous results with MgO and with A1₂O₃ have shown that a systematic study of a four-component system is necessary to the understanding of its devitrification relations, and that arbitrary and fragmentary excursions into such a system give little insight into the general effect of the minor constituent and may be misinterpreted to erroneous conclusions as to the effect of this constituent on glasses of slightly different composition. Accordingly, in taking up the study of the effect of B₂O₃ on the devitrification of the soda-lime-silica glasses, it was added to 21 glasses in and near the field of devitrite, Na₂O·3CaO·6SiO₂, in the ternary system, Na₂O–CaO-SiO₂, in amounts up to about 5%. In all cases the liquidus temperature was lowered, and the tendency toward devitrification reduced. Both of these effects are desirable and add to the thermal stability of the glass. With glasses containing 10% CaO, initially in the field of tridymite or so near to it that a small addition of B203 brings the resulting glass into the tridymite field, this initial lowering is replaced by an increase in the liquidus temperature which passed through a maximum at from 4 to 6% B₂O₃. With all other glasses the lowering continues, and the rate of decrease is greatest with glasses originally in the field of Na₂O·2CaO·3SiO₂. An exploration of the quaternary system showed that no new compounds are formed in any mixture that can be obtained by adding B203 in amounts up to 50% to any mixture in or near the devitrite field. It also indicated the probability that a narrow band of immiscible liquids is formed, extending across the ternary system, CaO-B₂O₃–SiO₂, and including the mineral danburite, CaO·B₂O·2SiO₂, but probably not extending far into the quaternary system. The fields of wollastonite and of Na₂O·2CaO·3SiO₂ were found to sweep out regions in the quaternary system extending over the square, Na₂O·SiO₂-Na₂O·B₂O₃-CaO-B₂O₃-CaOSO₂, and the field of Na₂O·CaO·SiO₂ was found to extend over the middle of this square, and is probably adjacent to the fields of wollastonite and of Na₂O· 2CaO·3SiO₂. A compound is formed between Na₂O·B₂O₃ and CaO·B₂O₃. There is included a general survey of the literature relative to the effect of B203 on the properties of glass.     

Reaction of sodium metaphosphate with magnesium and calcium oxides and their mixtures

Conclusions The reactions of MgO and CaO with aqueous solutions of sodium metaphosphate give products in the form of acid orthophosphates. The formation of the acid orthophosphates proceeds in accordance with the schemes: MgO +nNaPO₃=Na_mMgH_2(m–1) (PO₄)_m·aH₂O+(n}-m) NaH₂PO₄·bH₂O, where m=n when n=1, 2, or 3; m=3 when n is greater than 3, and CaO +nNaPO₃=Na _m CaH₂(m–1) (PO₄)_m·aH₂O + (n–m) NaH₂PO₄·bH ₂O. where m=n when n=1 or 2; m=2 when n is greater than 2.The drying process after the reaction of an aqueous solution of sodium metaphosphate with a 11 mix of CaO + MgO results in the formation of NaCaPO₄·nH₂O and Mg(OH)₂ while a 21 mix gives Na₂CaMg(PO₄)₂· nH₂O.When using crystalline sodium metaphosphate the formation of the sodium-calcium orthophosphate and bryanite passes through the intermediate phases Na₂CaP₂O₇ and Na₈Ca₄MgP₈O₂₉.The temperature range of the reaction of the formation of bryanite in the mixes CaO + MgO + 2NaPO₃ depends on the activity of the MgO. When electrofused MgO of varied grain size is used, the formation of bryanite passes through intermediate stages; the temperature range of the reaction giving Na₂CaMg(PO₄)₂ shifts towards higher temperatures with an increase in the grain size of the original MgO.Translated from Ogneupory, No. 5, pp. 51–58, May, 1978.     

REPRESENTATION OF DENSITY AND OPTICAL PROPERTIES OF TERNARY SILICATE GLASS SYSTEMS

A general procedure is outlined for the preparation of contour maps representing such properties as density, refractive index, and Abbe value for ternary glass systems in which one component is silica, using previously published equations and constants. The procedure is illustrated by application to the Na₂O–MgO–SiO₂ and Na₂O–CaO–SiO₂ systems.     

Devitrification and Phase Separation of Zinc Borosilicate Glasses in the Presence of MgO,P2O5, and ZrO2

A base glass composition which undergoes phase separation was chosen in the system Na₂O-ZnO-B₂O₃-SiO₂. Spontaneous and reheat-treatment opal glasses were synthesized by addition of different amounts of oxides such as P₂O₅ and ZrO₂. To clarify devitrification, visible spectroscopy was performed for all samples. Reheat-treated samples showed Tyndall effect in low temperatures, while they were completely opacified after soaking in 800°C for 3 h. P₂O₅-or ZrO₂-containing samples opacified spontaneously. The mechanism of opacification in glasses containing the MgO and ZrO₂ was partial crystallization, while in the mechanism of P₂O₅-bearing one was liquid–liquid phase separation.     

Melting Relations of CaO-Manganese Oxide and MgO-Manganese Oxide Mixtures in Air

Melting relations in the systems CaO-manganese oxide and MgO-manganese oxide in air have been determined at temperatures up to 1705°C. In the system CaO-manganese oxide four crystalline phases have stable existence in equilibrium with liquids: lime (approximate composition CaO-MnO), spinel (approximate composition Mn₃O₄-CaMn₂O₄), and two ternary solid solution phases in which Ca/Mn ratios as well as oxygen contents vary over considerable ranges. One of these ternary solid solution phases may for the sake of simplicity be represented approximately by the formula CaMnO₃ and the other by the formula CaMn₂O₄. Three isobaric invariant situations exist, with temperatures and phase assemblages as follows: At 1588°± 10°C the two crystalline phases lime and CaMnO₃ coexist in equilibrium with liquid (40 wt% CaO, 60 wt% manganese oxide) in a peritectic situation. Another peritectic at 1455°± 5°C is characterized by the equilibrium coexistence of CaMnO₃, CaMn₂O₄, and liquid (25 wt% CaO, 75 wt% manganese oxide). A eutectic situation exists at 1439°± 5°C with CaMn₂O₄, spinel, and liquid (18 wt% CaO, 82 wt% manganese oxide) present together in equilibrium. In the system MgO-manganese oxide in air periclase-manganosite solid solution (approximate composition MgO-MnO) and spinel (approximate composition Mn₃O₄-MgMn₂O₄) are the only crystalline phases present in equilibrium with liquids. Liquidus and solidus temperatures increase with increasing MgO content. A peritectic situation exists at 1587°± 10°C, with the two crystalline phases coexisting in equilibrium with liquid (1 wt% MgO, 99 wt% manganese oxide).     

Studies of the crystallization of the liquid phase in Portland clinker: Effects of MgO and Na2O

Devitrication of a glass containing CaO = 48.9, A?₂O₃ = 23.2, Fe₂O₃ = 14.2, SiO₂ = 5.71, MgO = 5.0, Na₂O = 3.0 (wt %) at 650° - 700°C yields large amounts of a crystalline phase which is rhombohedral, aH = 10.61, $\text{c}\text{H}\text{= 26.18}\text{A}\text{?}$. Partially-indexed powder x-ray data are given. The phase has the approximate composition, relative to 144 oxygens: Ca₅₉.₇Na₃.₅Mg₆.₀A?₂₉.₇Fe₁₃.₄Si₅.₉O₁₄₄. Its crystallization partially suppresses formation of C₃A during devitrification. Compositional data are also given for proto-C₃A formed from this glass. The solubilities of Fe and Si in this unstable variety of C₃A considerably exceed the equilibrium values.     

Waste Form of Silver Iodide (AgI) with Low-Temperature Sintering Glasses

This study focuses on the fabrication and characterization of waste forms of silver iodide (AgI) using low-temperature sintering glasses. We investigated the glass composition of bismuth-phosphate-zinc oxide, which enables low-temperature sintering to fabricate waste forms of AgI. We confirm that novel waste forms were fabricated with Bi₂O₃-P₂O₅-M_xO_y glasses, where M_xO_y is a metal oxide, such as ZnO, CaO (or CaCO₃), MgO, or Na₂O (or Na₂CO₃), at sintering temperatures of 600–650°C. The samples were characterized using X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS), inductively coupled plasma-atomic emission/absorption spectrometry (ICP-AES/AAS), and ion chromatography (IC) used for product consistency testing (PCT). Our findings indicate that chemically durable waste forms of AgI were formed and that the loss of iodine during heat treatment was effectively suppressed by a low sintering temperature.     

The effect of compositional changes on the crystallization behaviour and mechanical properties of diopside–wollastonite glass-ceramics in the SiO2–CaO–MgO (Na2O) system

The crystallization process of ternary system SiO₂–CaO–MgO (Na₂O) was investigated by DTA, XRD and SEM techniques and by strength measurements. The ability of Cr₂O₃+Fe₂O₃ as nucleating agents in inducing bulk nucleation via formation of a spinel phase was proved. Wollastonite and diopside are two major phases that were identified after two-stage heat treatment. The spherulitic growth morphology was observed by SEM. At high growth temperatures for long times the recrystallization process was observed too. The kinetic parameters, such as activation energy and Avrami exponent, were calculated by Kissinger equation.