Showing papers in "Journal of Non-crystalline Solids in 1975"

Calculation of bulk modulus, shear modulus and Poisson's ratio of glass

Abstract: Combining Gruneisen's equation with our Young's modulus equation of glass, new formulae were semi-empirically derived for the calculation of bulk modulus, shear modulus and Poisson's ratio of glass. Considering packing density of atoms and bond energy in unit volume the elastic moduli of glass can be calculated. The agreements between calculated and observed values of the moduli of glass are satisfactory for more than 30 glasses.

Interdiffusion of hydrogen and alkali ions in a glass surface

Abstract: Experimental data on the interdiffusion of hydrogen and alkali ions in glass are examined using a concentration-dependent interdiffusion coefficient, taking into account surface dissolution. The comparisons between calculated and experimental concentration profiles and diffusion coefficients are more satisfactory than for a concentration-independent diffusion coefficient, and support the use of the interdiffusion coefficient.

Characterization of the diffusion process in oxide glasses based on the correlation between electric conduction and dielectric relaxation

Abstract: Electric conduction was correlated with dielectric relaxation for many ionically and electronically conducting oxide glasses. On the basis of this correlation, the carrier-diffusion process occurring in the glasses was identified. Of the three types of diffusion processes (localized diffusion process, non-localized diffusion process I and non-localized diffusion process II) one or more were found in each glass. The diffusion process shifted from one type to another with varying glass composition in certain series of glasses. The conditions of preparation of the glasses were found to influence the diffusion processes in these glasses. These facts are discussed in terms of the ‘microstructure’ of glass.

Hydroxyl groups on silica surface

Abstract: Infrared (IR) gravimetric adsorption data show that the major adsorption sites on a silica surface are surface hydroxyl groups. Depending upon the temperature of pretreatment these may be either ‘freely vibrating’ or hydrogen bonded to each other. The adsorptive properties of each type of group are very different. Thus, whereas water will adsorb preferentially on the hydrogen-bonded hydroxyl groups, compounds containing lone-pair electrons adsorb preferentially on the freely vibrating hydroxyl groups. This physical adsorption in turn controls the order of chemical interaction with the groups. The freely vibrating hydroxyl groups are evidenced by a single, sharp IR band at 3747 cm−1. However, both their physical adsorption and chemical reactivity show that they themselves are composed of two types of groups. This is clearly demonstrated by their chemical reactions with silane coupling agents. Small amounts of impurity have a gross effect on the chemical reactivity of the surface. The presence of small amounts of boron on the silica surface not only gives rise to specific adsorption sites of the Lewis acid type, but also alters the reactivity of the silanol group which (spectroscopically) appears unchanged. Thus, the kinetic order of the reaction of dichlorodimethylsilane with the surface hydroxyl groups is reduced from 1.6 order to 1.0 order after the surface has been purposely unpurified by the introduction of boron. The implications of these data in terms of the glass surface are discussed.

The structure of borosilicate glasses studied by Raman scattering

Abstract: Raman spectra of alkali and alkaline earth borosilicate glasses are reported. These spectra are used to discuss the molecular structure of the glasses. The influence of Al 2 O 3 additions on the structure of borosilicate glass is also discussed. It is shown that the same type of groups are present in borosilicate glasses as in borate and silicate glasses. The presence of large borate groups such as tetraborate and metaborate groups is strongly suggested by the Raman spectra. It appears that boron ions are hardly taken up in the silicon-oxygen network. Our results suggest that the region of phase separation is larger than the region presently acknowledged.

Elastic constants, hardness and their implications to flow properties of metallic glasses

Abstract: The longitudinal and transverse sound velocities and Vickers hardness of metallic glasses (Pd1 − xNix)0.80P0.20, (Pd1 − xFex)0.80P0.20 and (Pt1 − xNix)0.75P0.25 have been measured. The elastic constants at room temperature exhibit a positive deviation with composition χ from linearity whereas the hardness shows a negative deviation. The increase in elastic constants has been attributed to a denser packing of the alloys on mixing. The reduced hardness HrH/μ versus χ exhibits a remarkable similarity to a Tg versus χ relationship. This seems to indicate that flow mechanisms involved in metallic glasses above and below the glass-transition temperature are of similar origins. It is the excess entropy of disorder associated with alloying which lowers the hardness as well as the viscosity of metallic glasses. The metallic glasses possess in general a relatively high Poisson's ratio ν ≈ 0.40 and a shear modulus approaching that of the noble metals Cu, Ag and Au. Among the metallic glasses observed, the PtP glasses exhibit the highest ν = 0.42, whereas the glasses containing Fe tend to have lower values. The phenomenon that the conduction electrons in the glassy alloys behave as in the noble metals may be partly attributed to the filling of d shell orbitals of the transition metals in the PtP, PdP and NiP alloys. The high ν of metallic glasses is believed to be responsible for the ductile behavior of these glasses. Poisson's ratio ν of metallic glasses was observed to decrease with decreasing temperature. It is suggested that the decreasing ν with falling temperature causes the rapid increase in the fracture strength of Fe-based glasses.

Devitrification characteristics of GexSe1−x glasses

Abstract: Amorphous Ge x Se 1− x compounds have been prepared and carefully characterized in the range 0 ⩽ x ⩽ 0.43 (density and micro-hardness measurements and DTA experiments). By heating samples from the amorphous phase, the crystallization process has been investigated for 0.15 ⩽ x ⩽ 0.30. An immiscibility gap in the vitreous region is determined by optical microscopy, from phase-separation observations; moreover, a new metastable crystalline phase appearing as an intermediate step between phase separation and stable GeSe 2 is described.

Transformation behavior of PdAuSi metallic glasses

Abstract: The transformation behavior of roller-quenched amorphous Pd 0.82− x Au x Si 0.18 and Pd 0.835− x Au x Si 0.165 alloys, where x ⩽ 0.10, after rapid heating to temperatures near to or above T g , is reported. The calorimetrically determined glass ( T g ) and kinetic crystallization ( T c ) temperatures both increased with x up to x ≈ 0.04. With increasing x , at x ⩾ 0.04, T c decreased rapidly while T g varied little. Binary Pd 0.82 Si 0.18 alloys crystallized to an fcc phase without apparent composition segregation. The tendency to phase separate at T near T g , as manifested by small- (SAXS) and large-angle X-ray scattering and calorimetry, increased with increasing Au substitution. Pd 0.8 Au 0.035 Si 0.165 alloy apparently phase separated by a nucleation and growth mechanism, with a growth rate limited by the melt viscosity, to form an fcc phase dispersed in an amorphous phase which later crystallized. Pd 0.74 Au 0.08 Si 0.18 alloy phase separated initially to two melts, each of which later crystallized in turn. The initial separation behavior was generally consistent with the predictions of the spinodal theory but with some deviation from Cahn's linear relation.

An analysis of the radial distribution function of SIOx

Abstract: A theory is presented for the short-range order (sro) in the SiOx alloy system for 0⩽x⩽2. The parameters of the sro are taken to be fixed by the properties of amorphous Si and SiO2, except that the probability of an Si atom having (i−1) oxygen neighbors is left as a free parameter, Ci(x), for i=1 through 5. The areas of the first three peaks in the radial distribution function (RDF) of SiOx are calculated as a function of x and Ci(x). It is shown that the RDF can be used to differentiate between the two models proposed for the sro in SiOx namely the SiSiO2 mixture model and the random bonding model. In the case of SiO powder, a mixture model at the atomic level is found to be consistent with the RDF. It is suggested that accurate RDF's of SiOx films, which are not currently available, would be useful in determining the sro of the alloy system. The present theory may be extended to analyze the GeOx and SnOx alloy systems.

Characterization of glass corrosion and durability

Abstract: New methods for obtaining a quantitative description of surface structural changes in glass are described. Application of the new methods is established through a systematic analysis of a series of glass compositions and environments. Based upon these investigations it is now possible to describe in quantitative detail the surface and bulk structural state of a glass object independent of its processing or environmental history. It is likewise possible to establish changes in bulk or surface structure of a glass due to processing or environmental conditions. Characterization of glass objects, e.g. relating composition, structure and surface to properties, is now possible since extrinsic processing and environmental variables can be described in terms of intrinsic structural features.

Intrinsic and impurity infrared absorption in As2Se3 glass

Abstract: A quantitative study of infrared absorption in the 250–4000 cm −1 region of As 2 Se 3 glasses doped with small amounts of As 2 O 3 or purified by various procedures has been carried out with particular attention to absorption in the wavelength regions of the CO 2 and CO lasers. The dependence of the relative intensities of the oxide impurity bands in the 650–1340 cm −1 region on the total amount of As 2 O 3 added to the glass indicates the existence of three distinct oxide-impurity species. A number of higher-frequency impurity bands which are due to the presence of hydrogen in the glass and whose intensities are highly dependent on the glass-melting conditions have been observed and classified. Intrinsic multiphonon absorption in the 400–1100 cm −1 region has been interpreted in terms of combination and overtone bands of the two highest-frequency fundamental vibrational modes. Absorption coefficients of As 2 Se 3 glass in the 920–1090 cm −1 CO 2 laser region are limited by intrinsic multiphonon absorption to values of around 10 −2 cm −1 . The lowest absorption coefficients measured in the 1700–2000 cm −1 CO laser region were around 2 × 10 −3 cm −1 and may contain contributions from hydrogen-impurity bands.

Chemical characteristics of float glass surfaces

Abstract: The regions near the top and bottom surfaces of float glass are chemically different from the bulk glass composition. In addition to the presence of tin oxide at the bottom surface and to a lesser extent at the top surface, differences are found in SiO 2 , Na 2 O, CaO, SO 3 and Fe 2 O 3 . The concentrations of Na 2 O, CaO and SO 3 are lower at the top surface than in the bulk glass, while SiO 2 is higher. In the case of tin at the bottom surface and iron at both top and bottom surfaces, the components exist in complex concentration gradients. In addition, there are variations in oxidation state for tin, iron and sulfur. Tin appears to exist in both stannous and stannic states near the bottom surface. So far it has been found that iron at the top surface and sulfur at the bottom are largely in reduced states. Some consequences of these effects have been observed in physical and chemical behavior of the surface.

Infrared absorption of some high-purity chalcogenide glasses☆

Abstract: New compouning techniques were devised to prepare high-purity Ge28Sb12Se60 (TI 1173)and Ge33As12Se55 TI 20). The methods were based on the combination of the reactant purification and compounding steps. The goal of the program was to establish the absorption limit for the glasses and to lower the absorption at 10.6 μm. At the present purity level, the GeSbSe glass is found to have an absorption level of about 0.01 cm−1 at 10.6 μm while the absorption level for the GeAsSe glass is 0.05 cm−1. Underlying causes for the limits are discussed along with the possibilities for improvement.

Effect of thermal history on conductivity and electrical relaxation in alkali silicate glasses

Abstract: Electrical conductivity σ0 and electric field relaxation measurements have been carried out as a function of thermal history for two alkali silicate glasses, Na2O3SiO2 and K2O3SiO2. Specimens of each glass with three different thermal histories, two of the anneal-and-quench type and one of the rate-cool type, were studied. The average structural or fictive temperature Tf of each of the specimens was characterized by measuring their indices of refraction. Effects of thermal history on σ0 and its activation enthalpy Hσ∗ were in accord with results of previous investigators. That is, for a given type of thermal history σ0 was lower and Hσ∗ higher the lower Tf. In addition it was found that for two specimens with the same Tf or index of refraction but different thermal histories the rate-cooled specimen exhibited a lower conductivity than the annealed-and-quenched specimen, in accord with the results of Ritland. The distribution of relaxation times τσ for decay of the electric field due to ionic migration was found to be due primarily to a distribution in the pre-exponential term ln τσ∗ in the equation ln τσ = ln τσ∗ + H∗/RT; the distribution in H∗ was extremely narrow. Differences in thermal history caused small differences in the distribution of τσ, but no difference in the average activation enthalpy 〈H∗〉 for τσ. From this result it appeared that the dependence of the conductivity activation enthalpy Hσ∗ on thermal history was due to the effect of thermal history on the temperature dependence of the distribution in τσ.

The crystallization kinetics of glassy Pd0.775Cu0.06Si0.165

Abstract: The crystallization kinetics of a Pd 0.775 Cu 0.06 Si 0.165 metallic glass have been determined by calorimetry over the temperature interval 665–680 K. We observe a change in the time dependence from t 4 at 665 K to t 3 at 680 K. In this temperature interval the activation enthalpy for crystallization was observed to be (95 ± 5) kcal/mol, in good agreement with the activation enthalpy for viscous flow as determined previously by Chen.

DC electronic transport in binary arsenic chalcogenide glasses

Abstract: dc conductivity and Seebeck measurements have been carried out at temperatures below T g on well characterized bulk samples of amorphous As 2 Te 3 , As 2 Se 3 , and As 2 S 3 . Several models for conduction in these materials have been compared to the data. It is concluded that the models involving polaron hopping conduction are in better agreement with available data than are models involving hopping in the tails of localized band-tail states.

Crystallization and decomposition of amorphous silicon-aluminium films

Abstract: The crystallization and decomposition of vacuum-deposited amorphous silicon-aluminium films have been examined by means of transmission electron microscopy. Depending on the aluminium concentration, the transformation of the metastable amorphous phase into the stable phases of aluminium and silicon proceeds by different reactions such as pre-crystallization of aluminium, polymorphous transformation into supersaturated crystalline solid solutions or eutectic decomposition. The temperature dependence of the eutectic crystallization was measured. The results are discussed in terms of the thermodynamics of amorphous-to-crystalline transformation.

Glass surface analysis by Auger Electron Spectroscopy

Abstract: This paper reviews the application of Auger Electron Spectroscopy (AES) to the analysis of glass surfaces. Attention is drawn to experimental perturbations which may occur when analyzing glasses with absorbed and/or mobile species at the surface. Previous workers [1–4] have shown, for example, that mobile ions (e.g. Na) are very difficult to measure in glasses due to their migration under the electron beam. Special techniques developed to permit the measurement of mobile ions are discussed, and some recent applications of AES in current research at the University of Florida are presented.

Thermal analysis of bulk amorphous arsenic triselenide

Abstract: Through the use of differential scanning calorimetry, the heat capacity and crystallization parameters of amorphous As 2 Se 3 have been studied. It is found that the heat capacity above the glass transition temperature ( T g ) exceeds, by a factor of 1.6, the Dulong-Petit limiting value found below T g . The crystallization process is found to obey first-order kinetics with an activation enthalpy of 1.24 eV and an enthalpy of crystallization of 0.36 eV · molecule −1 . The effect of sample age on the rate constant is also reported.

Effects of humidity on the weathering of glass

Abstract: The weathering of 26 glass compositions was investigated under static conditions of 30%, 50%, 75%, 90% and 98% relative humidity (RH) at 50°C and a cycling condition between 77% and 98% RH at 50°C. The cycling condition was found to be less severe than static 98% RH. The effect of humidity level on weathering was studied and showed that water adsorption increases with time and humidity, whereas alkali generation increases with time, but not always with humidity. Significant weathering occurs for some glasses at 30% RH with the quantitative effect being almost as great as at 90% RH. Visual weathering was observed for some glasses when the level of generated alkali was less than 0.5 μg/cm 2 . Various techniques for evaluating the weathering of glass under humid conditions were investigated. Visual appearance was judged to be the best evaluation method for routine weathering tests. It represents the effect of most concern and is sufficiently precise. Electron microscopy, measurement of sorbed water and alkali generated are principally used for research studies. Weight change and haze measurement lack sensitivity and reproducibility. A standard test was defined. The conditions are 98% RH at 50°C for 12 weeks. The visual ranking system is used. The glasses were generally ranked in the same order by the various evaluation techniques.

Properties of amorphous silicon films— Dependence on deposition conditions

Abstract: We report measurements on the electrical conductivity, optical absorption, electron spin resonance, Raman spectrum and electron diffraction of a set of a-Si films vaccum deposited at room temperature. As revealed by absorption at about 10 μm some of the films grown at deposition rates of about 0.4 A/sec contain considerable amounts of oxygen. All the properties, except Raman spectra and electron diffraction, are found to vary strongly with the deposition rate and the background pressure during evaporation. Qualitatively, these variations show significant correlations. For instance, if the electrical conductivity is higher so is the spin density, the optical absorption and the low-frequency refractive index. Also, increasing oxygen content leads to lower conductivity. In addition, we have tried to establish a rough quantitative relation between the shift in the optical gap and the change in the spin density by connecting each of these changes to the variation in the low-frequency refractive index. The temperature dependence of the electrical conductivity was also measured and it was found that below about 150 K the data are consistent with recent theoretical predictions, i.e., log σ exhibits a ( 1/T) 1 4 dependence.

Crack growth as an interpretation of static fatigue

Abstract: Static fatigue is due to water in the environment which accounts for substantial reductions in the strength of glass. Extensive experimental investigations have shown that static fatigue results from surface cracks that grow when glass is subjected to tensile loads. In this paper evidence for this conclusion is reviewed. First, the earlier studies of strength of glass are summarized. Then, supporting evidence for crack growth obtained from the newer discipline of fracture mechanics is given. Finally, the influence of ion exchange and chemical reactions at crack tips is discussed with regard to crack growth. The chemical composition of the crack-tip solution is shown to play an important role in controlling crack growth.

AC conductivity in amorphous germanium

Abstract: The ac conductivity in evaporated amorphous germanium films has been measured as a function of annealing and has been found to obey the ω 0.8 law, in accordance with the hopping model. The dc conductivity measurements on the same samples show a T 1 4 law behaviour. The densities of localized states near the Fermi level g ( E F ), obtained from both experiments are in reasonable agreement with each other. Both the measurements show a reduction by about a factor of 2 in g ( E F ) when a freshly prepared film is fully annealed. High-temperature substrate films also show the ω 0.8 behaviour. This suggests that the frequency dependence of the ac conductivity is not caused by voids alone. Other possible explanations of our results are also discussed.

The interdependence of physical parameters for infrared transmitting glasses

Abstract: Glasses based on sulfur and selenium were carefully characterized to establish the interdependence between chemical composition and the magnitudes of physical parameters related to their use as infrared optical materials. Parameters considered in this paper are density, volume-expansion coefficient, glass-transition temperature, thermal conductivity, elastic moduli, and Poisson's ratio.

Threshold switching and the on-state in non-crystalline chalcogenide semiconductors: An interpretation of threshold-switching research

Abstract: Experimental research on chalcogenide glasses is reviewed and an interpretation concerning the cause of threshold switching and the basis of the low-impedance on-regime is presented. Observed behavior is consolidated in terms of a single conductivity mechanism and two conducting species governing the off- and on-state electrical characteristics. Phenomenological equations and their consequences are given which are shown to be capable of successfully describing both in functional form and accurate magnitude a very wide variety of experimental data including current — voltage transient characteristics, the Haberland condition, delay time, maximum allowable interruption times, rise and decay characteristics and negative capacitance. Recent research is presented concerning two types of non-thermal radiative emission during the on-regime of a threshold switching event. Various switching models are described and critically discussed in terms of the experimental data and phenomenological equations.

Chemical and physical properties of obsidian: a naturally occuring glass

Abstract: The chemical composition of obsidian samples from 28 sources in Western America is that of a high alumina glass (ca. 12 wt% Al 2 O 3 ) with a silica content exceeding that of normal granite. Considerable complexity of phase states is indicated by a wide range of variability of properties. The results of thermal expansion, density measurements, Vicker's hardness, chemical durability, electrical properties. Mossbauer and infrared spectra are presented. It was found that obsidian is a glass of high chemical durability, comparable to Pyrex, and high hardness, comparable with silica glass. Research in the fields of geochemistry and archaeology has developed a useful chronometric technique based on the reaction and diffusion of water in obsidian for dating geological features and aboriginal obsidian artifacts. Correlation of hydration and radiocarbon data indicates that the hydration rates vary among the obsidian sources.

The kinetics of formation of A AuGeSi metallic glass

Abstract: The glass-forming ability of a Au 0.778 Ge 0.138 Si 0.084 alloy is analyzed theoretically by computing a time-temperature-transformation curve which describes the time required to produce a barely detectable fraction of crystallization, at various temperatures. The calculation is based on an interpolated viscosity-temperature curve, this alloy being exceptional among metallic glass formers in that experimental viscous-flow data are available at both high and low temperatures. Allowing for uncertainties, the critical cooling rate for glass formation lies within the range 10 6 −10 8 K/sec which is in satisfactory agreement with experimental estimates of cooling rates in splat quenching. This and previous comparisons for Ni and PdSi alloys suggest that the approach may have useful and general applicability to metallic glasses.

Pressure effect on vapor-deposited amorphous materials

Abstract: Pressure-induced densification and crystallization of vapor-deposited amorphous Se, As, Ge and GeTe were investigated. In general, the density of the amorphous material increases monotonically with pressure and crystallization occurs after a certain pressure level is reached. For each amorphous material there appears to exist an upper density limit beyond which crystallization occurs. The pressure effect on individual substances is correlated to their short-range order and basic structural character.

Adsorption of proteins on glass surfaces and pertinent parameters for the immobilization of enzymes in the pores of inorganic carriers

Abstract: The forces involved in the adsorption reactions between proteins and glass surfaces are primarily ionic amine-silanol bonding and hydrogen bonding. When protein solutions are exposed to porous glass surfaces, two rates of reaction are noted. The first appears to be dependent upon the relative number of amines on the protein surface and is very rapid. The second reaction is considerably slower than the first and is dependent upon the molecular weight of the protein. This second reaction, then, is governed by the ability of the protein to diffuse into the porous structure of the glass. The surface reaction of glass has been utilized to bind enzymes (biological catalysts) and other biologically active molecules. Enzymes, a precious material, can be immobilized on inorganic oxide surfaces and effectively employed, economically, in a manner similar to that of inorganic catalysts. The pore morphology of the carrier utilized to immobilize the enzyme offers a protected environment for extending the use of this unstable molecule.