A Method for Measuring the Flow Point of Glass

The need for a new reference point for glasses, at a temperature substantially above the softening point, is discussed from the standpoint of development of. new glasses, control of properties, and behavior in applications where reworking is required. An apparatus and a procedure are described by which a fiber elongation test indicates the "flow point," or temperature at which a glass reaches a viscosity of 10⁵ poises. A short section of a glass fiber, nominally 0.65 mm. in diameter, is heated under specified conditions of load and heat application. The heating time required for the fiber to draw down to a thread indicates the temperature attained. When properly standardized with one or more known glasses, the precision is equivalent to from 1°C. for soft glasses to 5°C. for hard glasses. The effect of infrared absorption by the sample is examined, and a correction curve is given for use when such absorption is abnormally great.     

THE MANUFACTURE OF FUSED BIFOCAL SPECTACLE LENSES1

I. The process of making fused bifocal spectacle lenses is based on patents taken out about 1906. Such lenses are made by fusing a crown glass with an index of refraction of 1.5230 with a lead glass having indexes of refraction of 1.616, 1.66, and 1.69. 11. Problems in making satisfactory glass involved thermal expansion, surface crystallization, surface bubbles, and the softening temperatures of the glasses. The effect of composition of the glass in curing these defects is discussed and satisfactory compositions are given. Testing methods for control are given. III. A later development is the so-called colorless fused bifocal in which a barium glass replaces the lead glass of the normal lens. The use of barium glass introduces new problems, especially the quality of the glass and the tarnishing of the surface. The relative softening temperatures of the barium and crown glass as well as the thermal expansion had to be controlled.     

Optical, Structural, and Chemical Characteristics of Lead-Indium Phosphate and Lead-Scandium Phosphate Glasses

Two new glass systems based on a range of lead-indium phosphate and lead-scandium phosphate compositions have been developed and characterized. These glasses have a relatively high index of refraction ( n = 1.75 to 1.83) in the visible region and exhibit moderate dispersion (Abbe number ∼30). The ultraviolet absorption edge occurs near 300 nm and the glasses strongly absorb in the infrared at wavelengths greater than 2800 nm. Both glass types can be prepared at relatively low temperatures (900° to 1000°C) and are easily poured down to ∼800°C because of their low melt viscosities. The glasses exhibit good chemical durability and resistance to both weathering and intense γ-radiation. These materials have a glass transition temperature of about 430°C, a softening point of about 460°C, and thermal expansion coefficients in the range of 10.8 × 10⁻⁶ to 12.0 × 10⁻⁶/°C. The structure of these phosphate glasses is shown to consist of a distribution of chains of PO₄ tetrahedra held together by bonding between the non-bridging oxygens of the tetrahedra and the metal cations. The polyphosphate chain length distribution was determined by a liquid chromatographic technique. Potential aqueous corrosion mechanisms are discussed and some general guidelines for forming a chemically durable phosphate glass are given.     

A SIMPLE EXPANSIBILITY TEST FOR DETERMINING THE WELDING PROPERTIES OF GLASSES1

Simple method of determining the relative expansibilities of two glasses.—Place two rods of glass side by side with the ends flush, heat these ends, weld together by pinching with forceps and then pull out a thread or thin strip with the two glasses forming opposite sides. When cool the thread will bend toward the glass having the higher total expansion up to the softening point of the softer glass. This test may be used for quantitative determination of coefficieots of expansion if a series of glasses of known expansibilities are available for comparison. The method is of particular value for investigating the welding properties of glasses , for whether or not two glasses can safely be welded together may be determined directly from the amount of curvature of the thread.     

玻璃丝形状尺寸对玻璃软化点温度测量影响研究

通过机械拉丝工艺法制备不同直径(Φ0.50~Φ0.90 mm)、不同圆柱度(ΔΦ0.01~ΔΦ0.06mm)和不同圆度(ΔΦ0.01~ΔΦ0.2 mm)3种形态的玻璃丝,采用Littleton法测试玻璃软化点温度,探究玻璃丝直径、圆柱度和圆度对软化点测量结果的影响作用规律。研究结果表明:随着玻璃丝直径增大,测试的玻璃软化点温度逐渐降低;对于不同圆柱度的玻璃丝,上下两端直径差ΔФ增大,软化点温度变化量增大;对于不同圆度的玻璃丝,其软化点温度取决于玻璃丝断面最小直径,最小直径一定时,随着最大直径增大,软化点温度变化不大。     

Review: Elaboration,structure, and mechanical properties of oxynitride glasses

Oxynitride glasses are glasses where threefold coordinated nitrogen atoms substitute for twofold oxygen ones, hence resulting in a larger interatomic cross-linking degree. Such glasses were first observed at the grain boundary in silicon nitride ceramics, where they govern the high-temperature behavior. Later, they were prepared as bulk materials and motivated numerous researches, thanks to their large viscosity, glass transition range, elastic moduli, hardness, and fracture toughness among inorganic and non-metallic glasses. In different chemical systems that were investigated, the synthesis routes and the sources for these exceptional mechanical properties are reviewed. Oxynitride glasses are not easy to process and suffer from the loss of transparency as nitrogen is incorporated over some critical content. Nevertheless, they are attractive “specialty” glasses in various niche areas, thanks to their large refractive index and dielectric constant, improved chemical durability, high softening point, etc., and majorly to their exceptional mechanical properties.     

EXPANSION MEASUREMENTS OF SEVERAL GLASSES BY MEANS OF A SELF-REGISTERING APPARATUS1

Applying an apparatus which registers photographically, and using quartz glass as control material, the expansion behavior of several glasses upon heating to temperatures above the softening point was investigated. It is shown that, with the help of the arrangement developed, even slight variations in the expansion-temperature curve, which might easily escape visual observation, can be detected. It is possible, by utilizing the results of these measurements, to regulate the annealing process of the glasses in the most useful manner.     

Transformation Range Behavior of Lithium Galliosilicate Glasses

The transformation range viscosity and thermal expansion behavior of lithium galliosilicate glasses were studied. The glass transformation and dilatometric softening temperatures exhibit maxima at gallium to lithium ratios of somewhat greater than one. Similar behavior was observed for the transformation range viscosity. The effect of phase separation on the dilatometric softening temperature is discussed in detail. These results are compared with those obtained for lithium alumino-silicate glasses in other studies. The results are discussed in terms of the structural role of aluminum and gallium in the glass network.     

Prospects of the use of aluminosilicate refractories for aluminum electrolyzers. Part 3. The role of the glass phase formed in the operation of aluminum electrolyzers

The compositions of glasses formed in the process of operation of an aluminum electrolyzer, the lowest content of aluminum at which the glass is separated into aluminosilicate and oxyfluoride components, and the temperatures of softening and of formation of drops of titanium-bearing glasses composition close to the glass in ShPD-45 refractory (with an additive of mullite-corundum chamotte) are determined. It is shown that the oxyfluoride glasses consist of both a silica skeleton and a corundum skeleton. The titanium-bearing glass phase can hinder penetration of aggressive gaseous byproducts of electrolysis. __________ Translated from Novye Ogneupory, No. 12, pp. 10–12, December, 2007. Parts 1 and 2 of the paper appear in “Novye Ogneupory” Nos. 9 and 10 of 2007.     

Silica-Uranium Fuel Systems

Presented are the irradiation results on two uranium-silica systems: a uranium oxide Vycor-brand glass system and a 10% uranium oxide glass prepared by melting. The glasses were irradiated up to 15% depletion of the uranium at temperatures up to the softening points with no appreciable loss of fission-product gases. Included is an outline of a procedure for impregnating leached, unfired Vycor-brand glass with uranium.     

Preparation and Properties of Nitrogen-Doped Phosphate Glasses

Techniques for preparation and the properties of phosphorus oxynitride glasses produced from sodium metaphosphate and nitride compounds are reported. Properties reported include nitrogen content, dissolution rate in water, thermal expansion coefficient, softening point, glass transformation temperature, density, refractive index, microhardness, and infrared absorption.     

R2O3对SnO-ZnO-P2O5无铅玻璃性能的影响

以SnO-ZnO-P2O5(SZP)系统作为低温玻璃材料的研究对象,结合其形成区域,研究了R2O3(Al2O3、B2O3)对SZP玻璃化学稳定性、膨胀系数、转变温度和软化温度等性能的影响。     

Thermal properties of ecological phosphate and silicate glasses

The present work deals with ecological phosphate and silicate glasses that belong to the oxide systems: Li₂O-MgO-P₂O₅, Li₂O-CaO-P₂O₅, Li₂O-MgO-P₂O₅-Fe₂O₃; Li₂O-CaO-P₂O₅-Fe₂O₃ and SiO₂-R₂O-R′O (R = Na, K; R′ = Mg, Ca), the last system contains certain amounts of ZrO₂, ZnO, TiO₂. These ecological glasses do not contain toxic substances as BaO, PbO, As₂O₃, As₂O₅, fluorine, CdS, CdSe and they have applications as regards the retention and counteracting action of the harmful compounds resulted from the nuclear plants. The replacement of MgO by CaO leads to an insignificant increasing of the thermal expansion index and a slight decreasing of the characteristic temperatures, except the softening point where the effect is opposite. Adding of iron oxide in the phosphate glass composition causes the increasing of characteristic temperatures and the decreasing of thermal expansion index, both in MgO and CaO-containing phosphate glasses. The ecological silicate glasses are used as opal glasses free of fluorine as well as for lead-free crystal glass (CFP) where BaO and PbO are replaced by non-toxic oxides as K₂O, MgO, ZrO₂, and TiO₂. The paper presents different glass compositions and the technological parameters to prepare the ecological glass samples. Both ecological phosphate and silicate glasses have been characterized as regards the characteristic temperatures (vitreous transition point, low and high annealing points, softening point) and the thermal expansion coefficient. This study presents the changes of the thermal parameters when CaO replaces MgO in phosphate glass samples and the role of iron oxide in the vitreous network. In the case of silicate glasses, the viscosity and wetting angle dependency of temperature are presented. The elemental analysis of the ecological glasses was made by XPS (X-ray photoelectron spectroscopy) which also put in evidence the iron species from the vitreous network.     

Spontaneous Deformation Phenomena in Partially Crystallized Glasses

Unusual deformation phenomena accompanying partial crystallization were observed during heat treatment in the softening temperature range of Li-Na-Si glasses. Glassy lumps or protuberances formed at the surfaces of fibers 0.5 mm in diameter; rods and plates showed even greater distortions, their original shapes often becoming unrecognizable. Liquid-liquid immiscibility accompanying the crystallization of a 0.7Li₂O.0.3Na₂O.2SiO₂ glass was believed to follow, rather than precede, crystallization. Explanations of these phenomena are proposed.     

DISINTEGRATION OF SODA LIME GLASSES IN WATER1

Soda lime glasses have been treated in water at temperatures helow boiling point, at boiling point, and up to 25 lb. pressure in an autoclave. Effects produced are illustrated with photographs and show that glass disintegrates, i. e., cracks, spalls, and loses weight when treated at any temperature used. The rate of disintegration depends upon time, temperature, composition, and heat treatment of glass surface during forming, the latter factor apparently affecting considerably the tendency to spall or chip. Treatment given glasses conforms in many ways to treatment glass receives in service, either when sterilized when used for food packing or continued washing and sterilizing as when used for delivering or serving food daily. The relative endurance of glasses may be studied by the methods used, and standard methods of testing based upon them can be worked out. An article must stand at least six hours in boiling water without apparent disintegration or chipping to be of good quality. Spalling always appeared on the exterior only of pressed or blown ware. Disintegration of the glass is cumulative with time of treatment whether it be periodic or continuous treatment. Treating glass in hot water with increasing pressures does not seem to give greatly increased disintegration as the temperature and pressure rises. Surfaces of blown or pressed articles are shown to be laminated rather than smooth and impervious.     

Role of Copper Ions in Low-Melting Solder Glasses

Controlled melting conditions for Cu-containing solder glasses yielded a variety of Cu⁺/Cu²⁺ ratios from a single glass starting composition. Measurements of softening point, thermal expansion, chemical durability, plus chemical analysis revealed that the well-known viscosity effect of adding copper oxide to solder glasses is caused primarily by the Cu⁺ ion; Cu²⁺ plays a minor role, if any.     

Sintering of β.q.SS and gahnite glass ceramics

The sinterability of β.quartz solid solution, β.q._ss, and ZnAl₂O₄ glass ceramics was studied. It was found that the sinterability of glass powders with mean particle sizes greater than a threshold value rapidly decreases. Quantitative measurement of the crystalline phases and the shift of the dilatometric softening point of the residual glasses as determined by DTA, indicate that in addition to the amount of crystalline phases, the composition and viscosity of the residual glass influence the maximum densification temperature. ©     

Physical Properties of Quenched Glasses in the Li2O-ZrO2-SiO2 System

The behavior and some physical and thermal properties of a 30Li₂O-70SiO₂ base glass composition with addition of ZrSiO₄ in the as-quenched state was investigated with the aid of X-ray diffraction (XRD), differential thermal analysis (DTA), thermal expansion and microhardness measurements, as well as density measurements. Transparent glasses prepared by the addition of ZrSiO₄ up to 10.30 mol% were obtained. ZrSiO₄ was found to decrease the expansion coefficient of the investigated glasses from 11.0 × 10⁻⁶ to 7.96 × 10⁻⁶°C⁻¹. The glass transition and softening point temperatures of the glasses showed a reverse behavior. On the other hand, both hardness and density increased for successive increases of the ZrSiO₄ amounts, with the highest values of 6.3 GPa and 2.65 g/cm³, respectively.     

Sol-Gel Processing of Neodymia–Silica Glass

Neodymia-doped glasses are currently commercially available for use in laser systems. Typically, these glasses are low-softening-temperature borates, phosphates, silicates, and fluorides. With its high softening temperature, high thermal shock resistance, and low nonlinear index of refraction, silica may be an ideal candidate for a neodymia bost glass for high-power laser applications. Conventional glass processing methods, however, have thus far succeeded in incorporating only low levels of neodymia in silica. In this paper, the fabrication of neodymia–silica glasses with high neodymia content by the sol-gel route is described. A possible structure for neodymia in silica is discussed.