Showing papers on "Devitrification published in 1980"

Properties and applications of glass

Abstract: 1. Some Aspects of the Nature of Inorganic Glasses. Definition of the term ``Glass''. The transformation range. The chemical nature of inorganic glasses. Devitrification. Immiscibility in melts and glasses. The structure of oxide glasses. II. Viscosity. Definition. Viscosity values. Analysis of some simple problems in viscous laminar flow. Measurement of viscosity. Variation of viscosity with temperature. Flow properties in the transformation range. Effects of glass composition. III. Thermal Expansion. The shape of the thermal expansion curve. Methods of measurement. Effects of glass composition. Stresses in glass seals. Thermal stresses. Annealing. Measurement of internal stresses in glassware. IV. The Strength of Glass. The theoretical strength of glass. Effect of surface flaws on the strength of glass - the Griffith equation. Methods for measuring glass strength. High strength glass surfaces. Damage to glass surfaces. Factors affecting the strength of damaged surfaces. Increasing the strength of glass. V. The Strength of Glassware. Determination of service stresses. The simulated service testing of glass containers. Fracture analysis. VI. Refractive Index and Dispersion. Introduction. Refractive index. Dispersion. Optical glasses. The significance of optical properties in lens design. Glass optical fibres. VII. The Absorption of Radiation by Glasses. Introduction. Units and nomenclature. Transition metal ion colours. The absorptivity of oxide glasses in the UV. Colloidal colours. Absorption in the IR. Decolourizing of commercial glasses. Laser glasses. VIII. Electrical Properties. Introduction. Ionically conducting glasses. Semi-conducting glasses. Dielectric loss in oxide glasses. IX. Chemical Durability. Introduction. Weathering. Reactions of silicate glasses with aqueous solutions. Standard tests for chemical durability. Methods of improving the durability of glassware or reducing the attack by specific reagents. References. Author Index. Subject Index.

TBA studies of prepreg curing behavior

Abstract: : The torsional braid analysis (TBA) equipment has been used as an automated torsion pendulum to characterize prepreg materials in the form of single ply strips (2-1/2 x 1/8 inch). Compared to the use of coated glass braids, the main difference was a marked weakening of the gelation mechanical damping peak in isothermal runs. However, prepreg materials consisting of epoxy resins on glass, carbon or aramid fibers were successfully run isothermally to provide gelation and vitrification times as a function of temperature, or in constant heating rate scans to reveal the T Tg and the Tg relaxations of the uncured resins, and at higher temperatures phenomena associated with gelation, vitrification and devitrification. (Author)

Stability of Glass in the Geologic Environment: Some Evidence from Studies of Natural Silicate Glasses

Abstract: The geologic literature contains numerous studies of the stability of natural silicate glasses under a variety of environmental conditions. The processes of glass hydration, devitrification, and di...

Molecular glasses for nuclear waste encapsulation

Abstract: A molecular glass based upon a phosphate of aluminum, or other trivalent metal, provides significant improvement over prior art glasses for encapsulation of high level radioactive nuclear waste. When containing a controlled amount of those elemental oxides found in a typical nuclear waste, the waste-glass would not devitrify under conditions which produced devitrification in the non-nuclear-waste-containing glass, exhibited hydrolysis losses lower by an order of magnitude, had high solvency power for those elemental oxides, exhibited little tendency for internal crystallite formation, and possessed other desirable physical characteristics, all in direct antithesis to the properties of the best prior-known glasses used for this application.

Directionally Crystallized Sodium Lead Silicate Glass-Ceramic

Abstract: The iron-nucleated devitrification of a sodium lead silicate glass was studied; it produces a glass-ceramic consisting of sodium metasilicate crystals in a lead silicate glass matrix. The nucleating agent is not incorporated in the crystal phase, Anisotropic devitrification of the glass in a thermal gradient produces an aligned microstructure with needles of sodium metasilicate oriented with the c axis parallel to the direction of crystallization.

Devitrification of Nuclear Waste Glasses

Abstract: Devitrification studies of waste glasses are undertaken for a variety of reasons, but mainly to determine processing conditions through which significant crystallization can be avoided. The first detailed kinetic study by Turcotte and Wald (1) demonstrated that although behavior is complex, the kinetics follow expected trends, based on simple theoretical models of simple glasses.

Glass composition for alkali resistant filament

Abstract: PURPOSE:To provide the title compsn having a low liquid phase temp, superior meltability and superior fiber collecting work efficiency, and causing no devitrification phenomenon by mixing SO3 into a SiO2-Al2O3-CaO-MgO type glass compsn for alkali resistant glass filaments CONSTITUTION:The title glass compsn consists of, by wt, SiO2; 45-52%, Al2O3; 7-12%, RO; 20-40%, R'2O; 0-10%, ZrO2; 0-13%, Fe2O3: 0-5% and SO3: 005-05% (R; Ca, Mg, Zn or Ba and R'; Na or K) In this compsin the total amt of SiO2, Al2O3, RO and ZrO2 is pref above 90%, RO is pref based on CaO and MgO, and part (up to 5 wt%) of CaO may be replaced with ZrO or BaO

Chemical Chain Reactions in the Devitrification of the Matrix

Abstract: The results of studies of the mechanisms of chain reactions occurring in the devitrification of vitreous matrices are surveyed and the characteristics of the kinetics and the mechanisms of the chain reactions accompanying the devitrification process are examined: chlorination of hydrocarbons, polymerisation, copolymerisation, and graft polymerisation. The possible applied aspects of chain reactions in the devitrification of the matrix are also considered. The bibliography includes 64 references.

High refraction high dispersion optical glass

Abstract: PURPOSE:To provide optical glass consisting basically of SiO2, TiO2, ZrO2, Nb2O3, divalent metal oxides, monovalent metal oxides and As2O3 and/or F2 exhibiting superior devitrification resistance, uncolorability and chemical durability, and having low specific gravity. CONSTITUTION:The high refraction high dispersion optical glass consists of, by wt., SiO2 20-37%, TiO2 26-33%, ZrO2 1-8%, Nb2O3 1-12%, (BaO+MgO+ SrO+ZnO) 9-18%, (Na2O+K2O+Li2O) 10-18% and As2O3 and/or F2 in fluorides substd. for the metal oxides 0.02-5% in total. In the compsn. Na2O 4-12%, K2O 2-10%, Li2O 0-5% and As2O3 0-0.5%. This glass has such optical constants as a refractive index of 1.75-1.85 and an Abbe 's no. (nud) of 29-23. Since it is superior to conventional glass in devitrification resistance, it is manufactured easily, and starting materials for this glass are cheap.

Study of the region of glass formation and electrical properties of the AsSeSb system

Abstract: Glassy samples containing As, Se and Sb in different ratios are synthesized under a vacuum of the order of 10−5 Torr and at a temperature of (950 ± 20)°C. The region of glass formation of this system is determined. It is found that antimony can be added in amounts of up to approximately 19 at.% in As2Se3 while the glassy state is still preserved. Thermal activation energy for the samples is found to decrease with the increase of antimony content. The conductivity at 20°C and the logarithmic value of the constant σ0 are determined for each composition investigated. Annealing of the samples (induces crystallization) reduces both thermal activation energy and room temperature resistivity. Preliminary devitrification characteristics of some samples in this system using X-ray and differential thermal analysis are given.

Boron containing transistion metal alloys comprising a dispersion of an ultrafine crystalline metallic phase and method for making said alloys, method of making an article from a metallic glass body

Abstract: Boron-containing transition metal alloys based on one 'or more of iron, cobalt and nickel, and containing at least two metal components, are characterized by being composed of ultrafine grains of a primary solid-solution phase randomly interspersed with particles of complex borides which are predominantly located at the junctions of at least three grains of the primary solid-solution phase. These alloys are obtained by devitrification of the solid, amorphous state under specific heat-treatment conditions. These alloys can be consolidated into three-dimensional bodies.

Fluorophosphate optical glass

Abstract: PURPOSE:To reduce the dispersion of a compsn. and improve the stability thereof to devitrification by determining the optimum content of LiF in the compsn.; reducing the P and O contents; introducing much CaF2; and specifying the ratio of F /O . CONSTITUTION:Cations in glass are represented by fluorides as follows: by mol, PF5 5-20%, AlF3 18-42%, CaF2 17-35%, SrF2 0-25%, SrF2+BaF2 8-33%, LiF 0.8-7%, MgF2 0-22%, ZnF2 0-5%, PbF2 0-2%, YF3 0-7%, LaF3 0- 7% and ZrF4 0-3%. Oxygen ions are substd. for part of the fluorine ions to regulate the ratio of F /O to 2.5-15. By this compsn. low dispersion, Be-free fluorophosphate optical glass excellent in charcteristics such as refractive index and Abbe's no. is obtd. without lowering the softening point.

The structure of vapour-deposited arsenic sulphides prepared using a cooled (78 K) substrate

Abstract: Amorphous molecular As4S4 and non-stoichiometric “As2S3” evaporated films have been prepared by condensing onto a substrate at liquid nitrogen temperature in situ in the X-ray diffractometer. The structures of these films are shown to be similar, thus confirming the importance of As4S4 (realgar-type) molecules in amorphous films prepared by evaporation of “As2S3” glass. The local molecular packing in the as-deposited amorphous As4S4 film shows a preference for a packing arrangement similar to that found in the α-crystalline phase. Both as-deposited films contain gross structural defects such as molecular clusters and/or voids which irreversibly reduce in importance as the film structures relax on warming to ambient temperatures. Also, the As4S4 film partially devitrifies to the high-temperature β-crystalline phase on warming to ambient, but no devitrification occurs in the non-stoichiometeric film due to the presence of more than one molecular type.

Borosilicate glass frit with MgO and BaO

Abstract: Borosilicate glass frit with MgO as a major component for forming partially devitrified porcelain compositions are provided which are comprised of a mixture, based on its oxide content, of barium oxide (BaO), magnesium oxide (McO) or a mixture of magnesium oxide with certain other oxides, boron trioxide (B2 O3) and silicon dioxide (SiO2) In accordance with this invention the porcelain compositions are applied to the metal core and fired to provide a partially devitrified porcelain coating on the metal core The coating has a very low viscosity at its initial fusion point and then almost instantaneous high viscosity due to partial devitrification The fired coating has a deformation temperature of at least 700° C and a high coefficient of thermal expansion of at least about 110×10-7 /°C

Process for preparing bodies containing highly radioactive wastes

Abstract: 1. Method for the production of high-level waste containing moulded materials by which the wastes and the glass, glass ceramic or ceramic matrix surrounding them are sintered by means of pressure and temperature, with 1) the wastes a) in the form of a dry or nearly dry powder being mechanically mixed in a conventional way with the glass, glass ceramic or ceramic matrix present as a granulate or powder ; or b) in the form of a sludge being concentrated with glass, glass ceramic or ceramic powder, mechanically mixed and dried, and 2) the mixture, without previous encapsulation, being directly either c) cold pressed initially at a pressure of 50 MPa to 500 MPa and subsequently sintered below the matrix melting zone in the devitrification range at a temperature between 500 K and 800 K ; or d) pressure sintered at a pressure of 10 to 50 MPa and a temperature in the range of 500 K to 800 K (hot isostatic pressing excepted).

Development Of Fluorophosphate Optical Glasses

Abstract: The requirements of high-energy laser systems have stimulated the development of low-refractive index, low-dispersion optical glasses, thus extending the range of available glasses in the Abbe diagram. Fluorophosphate glasses are the prime candidates to meet these requirements, but their preparation is complicated by fluorine volatilization on melting and devitrification and cracking on casting. The latter difficulties are caused by low viscosity at the crystallization temperature and by high thermal expansion. Exploration of glassforming regions and simultaneous optimization of the optical properties has led to the identification of compositions with commercial potential. A representative 100-gram melt contained 60 mol % RF2 (R = Mg, Ca, Sr, Ba), 36.7 mol % A1F3' 3.3 mol % Al(P03)3' with nD = 1.439 and vD = 95. After annealing it was optically homogeneous and strain-free.

A nuclear-waste block for the storage of high level radioactive waste and a process of encapsulating high level radioactive waste

Abstract: A molecular glass based upon a phosphate of aluminum, or other trivalent metal, provides significant improvement over prior art glasses for encapsulation of high level radioactive nuclear waste. When containing a controlled amount of those elemental oxides found in a typical nuclear waste, the waste-glass would not devitrify under conditions which produced devitrification in the non-nuclear-waste- containing glass, exhibited hydrolysis losses lower by an order of magnitude, had high solvency power for those elemental oxides, exhibited little tendency for internal crystallite formation, and possessed other desirable physical characteristics, all in direct antithesis to the properties of the best prior-known glasses used for this application.

Optical glass with high refractive index, but contg. no thorium - contains lanthanum oxide, boric oxide, zinc oxide, zirconia, tungstic oxide, and alkaline earth metal oxide

Abstract: The glass has a low dispersion, and contains by wt. 22-31% B203, 27-44% La203, 5-14% ZnO, 1-9% RO, 11-19% ZnO + RO, 1-9% Zr02, 1-20% W03, 0-4% Si02, 0-4.5% Y203, 0-7% PbO, 0-5% Al203. The pref. glass contains neither PbO nor Al203. The above compsn. produces a refractive index(nd) of 1.75-1.80, and an Abbe number(vd) of 43-48; and the term RO refers to one or more of MgO, CaO, SrO, BaO. In the past, glass with a high nd value was made using thorium oxide; but Th is radioactive and harmful to humans, so the use of Th02 must be avoided. In addn. to contg. no Th, the glass can easily be mass produced, and has excellent resistance to chemicals and to devitrification.

Non-ferroelectric pyroelectric: Piezoelectric glass ceramics

Abstract: In many glass systems where the recrystallization processes of devitrification have been extensively studied, the crystalline phases produced have symmetries consistent with both pyroelectric and piezoelectric properties in the individual crystallite. Heretofore, however, except for the ferroelectric glass ceramic, where preferred orientation and the associated macroscopic piezoelectric and pyroelectric properties were induced by an electric poling of the ferroelectric domain texture after the recrystallization process, little attention appears to have been given to other possible techniques for inducing a proper orientation texture.

DTA-Investigations in the System PbO — SiO2 — GeO2

Abstract: In the PbO rich part of the System PbO — SiO2 — GeO2 the equilibrium phase diagram of the section Pb3SiO5. — Pb3GeO5 was found to be partially binary and partially ternary, with extended solid solutions of all phases observed.Over a wide composition range glasses can be quenched, which show rather complicated devitrification effects.All the various crystalline phases obtained during DTA up to 600 C turned out to be metastable.

Water resistant step type light transmitting body - has core glass of high refractive index and specified compsn.

Abstract: The body has a core of glass of refractive index 1.60-1.66 and compsn. 15-40 wt.% SiO2, 8-15% ZrO2, 7-12% B2O3, 30-45% BaO, 5-12% Na2O, 0-30% GeO2, 0-3% TiO2, 0-5% Al2O3, 0-5% La2O3, 0-5% MgO, 0-7% CaO, 0-7% ZnO, O-5% SrO, 0-8% Li2O, 0-10% K2O, 0-5% Rb2O and 0-8% Cs2O; with SiO2+GeO2=15-15%; ZrO2+BaO=38-50%; Na2O+Li2O+K2O+Rb2O+Cs2O=5-15% and MgO+CaO+ZnO+SrO+TiO2+Al2O3+ La2O3=0-12%. The body is a glass fibre. The core glass has excellent water resistance (160-250 hr. to loss of surface gloss for silicone coated glass in distilled water), is easily drawn, has low loss and has reduced tendency to devitrification, with expansion coefft. and viscosity readily matched to coating glass. A body having a numerical aperture of 0.50-0.69 can be provided.

Effect of low molecular weight plasticizing liquids on the glass temperature of aromatic polyamides

Abstract: A study was made of temperature limits of physical states of aromatic polyamides of different chemical structure in plasticizing liquid media. It was established that the glass temperature of polymers examined in liquid media decreases considerably. It was concluded that for most plasticized polyamides there are two temperature ranges of devitrification. The plasticizing activity of a low molecular weight liquid in polyamide depends on its ability to form hydrogen bonds with the polymer, the number of reactive groups and geometrical dimensions of molecules. In poly-3,3′-diphenylenesulphone isophthalamide intermolecular donor-acceptor interactions are intensified, compared with poly-4,4′-diphenylenesulphone terephthalamide, resulting in a lower reduction of the glass temperature during plasticization. Temperature boundaries of physical states of polymers under conditions of contact and sorption e equilibrium with liquid media may be the upper limits of operating temperatures of polyamide materials in the media investigated.

Directionally crystallized sodium lead silicate glass‐ceramic

Abstract: The iron-nucleated devitrification of a sodium lead silicate glass was studied; it produces a glass-ceramic consisting of sodium metasilicate crystals in a lead silicate glass matrix. The nucleating agent is not incorporated in the crystal phase, Anisotropic devitrification of the glass in a thermal gradient produces an aligned microstructure with needles of sodium metasilicate oriented with the c axis parallel to the direction of crystallization.

Glass fiber and production thereof

Abstract: PURPOSE:To cheaply obtain superior glass fiber by dissolving carbon in glass starting material in a colloidal state to enhance the spinnability followed by spinning. CONSTITUTION:20wt% or less of carbon is dissolved in glass starting material in a colloidal state in a process prior to a glass fiber spinning process. Carbon shows its effect in a very slight amt., yet the amt. is pref. 0.05wt% or more, and 0.5-5wt% of carbon results in an esp. remarkably effect. By spinning the carbon-added material and acid-treating the resulting glass fiber with a soln. of an inorg. acid such as hydrochloric acid, sulfuric acid or nitric acid, an org. acid or a mixt. thereof, high silicate glass can be produced. As the carbon is dissolved, it acts as reducing agent to form bubbles in molten glass as well as to inhibit devitrification, and the bubbles take innumerable fine bubbles present in the glass therein to facilitate bubble separation. In addn., a thickening action appears, and it is considered that the action minimizes cutting is spinning.