Temperature broadening of vibrational lines in glasses

The shape of vibrational lines and the temperature dependences of their width for structures with short-range and medium-range orders in oxide glasses have been studied. The relationship describing the contour of the line associated with internal vibrations of glass-forming polyhedra is derived in the framework of the model for deformation broadening of the vibrational spectra of two-level systems. It is found that the line within the width is represented by a Lorentzian contour, and the line wings decay as (ω − ω₀)⁻⁴. It is demonstrated that a similar contour is observed for the lines corresponding to the intrinsic vibrations of clusters with hinged bonds, which form the boson peak. The shape of the line at 806 cm⁻ for vitreous boron oxide, which is calculated in the framework of the proposed model, is in complete agreement with the experimental data in the temperature range 80–1900 K.     

Temperature of nanometer-scale structure appearance in glasses

The structural network of glass is known to be partitioned into quasiordered nanometer regions (clusters). It is considered that the formation of nanometer-scale inhomogeneities occurs still in a liquid state in the process of cooling and substantially affects the ability of the substance to glass transition. In this work, we discuss the problem of determining the temperature at which a glass nanometer-scale structure is formed. Based on the analysis of the inhomogeneous broadening of Raman spectrum lines and the Landau-Placzek ratio, we show that the formation of an inhomogeneous structure starts near the temperature of the transition from the Arrhenius behavior of the relaxation time (viscosity) to non-Arrhenius behavior. This temperature can be determined using the derivative analysis.     

Properties and vibrational spectra of magnesium phosphate glasses for nuclear waste immobilization

The leaching behavior and structure of magnesium phosphate glasses containing 45–55 mol% MgO incorporated with simulated high level nuclear wastes (HLW) were studied. The leach rate of the waste glasses decrease with increasing of the simulated HLW content. The gross leach rate of the glass waste form containing 50 mol% MgO and 45 mass% simulated HLW is of the order of 10⁻⁶ g/cm² day at 90 °C, which is small enough as compared with the corresponding release from a currently used borosilicate glass waste form. The isolated ions such as dimeric (P₂O₇)⁴⁻ and monomeric (PO₄)³⁻ ions increase upon as increasing the incorporating amount of the simulated HLW. The changes in properties can be attributed to the structure changes owing to the incorporation of the simulated HLW.     

Temperature dependence of the modulus of elasticity of industrial glasses

Translated from Steklo i Keramika, No. 2, pp. 12–13, February, 1992.     

Temperature sensors based on silicate porous glasses impregnated by organic compounds

The spectral dependences of light transmission of samples of silicate porous glasses impregnated by anaesthesine and tribenzylamine have been studied in a visible range at temperatures below and above the solid-liquid phase transition point of these substances. The principle of the action of the fiber-optic threshold temperature sensor with the functional element from porous glass has been considered. The possibility of the effective use of impregnated porous glasses has been demonstrated for the developments of fully dielectric fiber-optic temperature sensors dedicated to industrial monitoring systems, as well as fire-alarm elements.     

Temperature dependences of density of sodium borosilicate glasses in equilibrium states at temperatures below a vitrification temperature

The temperature dependences of the density and intensity of SAXRS of a variety of sodium borosilicate glasses in equilibrium states below vitrification temperature are obtained. The existence of a transition of the investigated supercooled liquids in a solid noncrystalline state was discovered that is similar to the one observed in the study of vitreous boron oxide and alkali-borate glasses. The temperature of the transition of supercooled liquids of the investigated compositions to a solid noncrystalline state is about 50°C below the vitrification temperatures determined by the SAXRS data. Thus, the transition occurs at a viscosity of 1014 P in borate and sodium borosilicate glasses.     

Temperature dependences of the density of borate glasses in equilibrium states at temperatures below the glass transition point

The kinetics of density relaxation during isothermal treatment of samples of vitreous boron oxide and sodium borate glasses (containing 15, 20, and 30 mol % Na₂O) cooled from high temperatures and after heating of the samples stabilized at low temperatures is investigated over a wide range of temperatures below the glass transition point T _g . It is established that there exists a temperature T _s below which the density in the equilibrium state does not depend on the temperature, i.e., the temperature at which the supercooled liquid transforms into a new noncrystalline solid state. The distinguishing feature of this state is the absence of structural transformations after a change in the temperature. The temperatures of the transition of the supercooled liquid to the noncrystalline solid state and the ranges of lower temperatures at which the supercooled liquid can reach an equilibrium state within the limits of experimental error coincide with those previously obtained in the study of relaxation processes in these glasses by the small-angle X-ray scattering technique.     

Doping-induced broadening of the hole density-of-states in conducting polymers

The density-of-states distribution in conducting polymers reflects the energy disorder caused by electrostatic and steric interactions resulting from the different environment in which each molecule is placed. In case of p-doping (oxidation), the highest occupied molecular orbital (HOMO) manifold spreads in energy following a distribution as a result of long-range electrostatic (dipolar) interactions with the surrounding disordered host. In this paper the repercussion of the dipolar disorder on electrochemical signals of standard polypyrrole films is explored. The analysis is based on the chemical capacitance variation with the applied potential in experiments performed in quasi-equilibrium conditions. In addition to the Gaussian shape of cyclic voltammograms at low-doping levels, the model is able to qualitatively account for the current plateau usually observed at high oxidation potentials. This approach allows to estimating the dipolar moment associated to the polymer/dopant complex.     

Temperature dependence of the viscosity for some glasses in the Rb2O-B2O3-SiO2 system

The temperature dependences of the shear viscosity of glasses in the Rb₂O-B₂O₃-SiO₂ system are investigated using the bending method on a quartz viscosimeter in the viscosity range 10¹¹-10¹³ P.     

Temperature dependences of the viscosity for some glasses in the Cs2O-B2O3-SiO2 system

The viscosities of glasses in the Cs₂O-B₂O₃-SiO₂ system are measured by the bending method on a quartz viscosimeter in the temperature range 300–670°C. The temperature dependences of the viscosity of the glasses under investigation are determined, and the temperatures corresponding to the viscosities equal to 10¹¹, 10¹², and 10¹³ P are calculated.     

Theory of glasses

It is argued that is possible to define a ‘perfect glass’ which is both preparable experimentally and understandable theoretically. Some basic conditions and statistical thermodynamics are derived. Polymerized glasses are complex substances but it is argued that progress may be possible by considering them to have short range properties, and long range properties. Examples are given of models of glasses with such properties and their behaviour is shown to be amenable to theory.     

Chromatogram broadening of proteins and dextrans in size exclusion chromatography

The mechanisms governing the broadening of experimental chromatograms for proteins and paucidisperse dextrans were studied on TSK-G2000SW and TSK-G3000SW columns. Within the conditions studied, the chromatogram variance for all solutes increased linearly with increasing effluent flow rate. As predicted by current theories of the kinetics of size exclusion chromatography, this flow rate dependence is caused mainly by slow mass transport of the solute within the stationary phase of the column. Restricted diffusion within the stationary phase was dependent upon the ratio of solute molecular size to column pore radius and was similar for both proteins and dextrans. In comparison with results for monodisperse proteins, the broader chromatograms produced by dextrans were due to sample polydispersity and not to differences in solute column spreading. Corrections for column spreading on these columns are small for the determination of integral properties of polymers but may be significant when molecular weight distributions are of interest.     

Enthalpy relaxation in polymeric glasses

Constitutive equations are derived for enthalpy recovery in a glassy polymer after quench from above the glass transition temperature T_g to a temperature T in the sub‐T_g region. The model is based on the trapping concept, which treats a disodered medium as an ensemble of cooperatively rearranging regions (CRR) hopping in potential wells as they are thermally activated. Rearrangement occurs when a CRR reaches some liquid‐like energy level in a hop. The rate of hops is described by the theory of thermally activated processes, whereas the probability to change trap in a hop is determined by the difference between the current and equilibrium concentrations of cages. A nonlinear parabolic equation is developed for the distribution of traps. This equation ia used to describe entropy recivery in amorphous and semicrystalline polymers. Fair agreement is demonstrated between experimental data for poly(ether imide), poly(ethyl terephthalate) and polystyrene and results of numerical simulation. Some phenomenological relations are suggested to predict the effect of temperature, molar mass and degree of crystallinity on material parameters.     

Structural relaxation in chalcogenide glasses

The structural relaxation of chalcogenide glasses is discussed within Tool–Narayanaswamy–Moynihan (TNM) formalism. The TNM parameters for more than 70 different glassy compositions are compared on the basis of the relaxation rate defined as R_f(ΔT) = −(dT_f/dlogt)_i at the inflection point of the isothermal relaxation curve plotted on a logarithmic timescale. The R_f(ΔT) depends on the TNM parameter ß and the parameter σ, combining the nonlinearity parameter x, the effective activation energy h^* or the fragility m. It is shown that R_f(10) estimated at 10 K below T_g is useful for the prediction of structural relaxation kinetics in different amorphous materials. The chalcogenide glasses are, for example, compared with oxide glasses and organic polymers. For all these materials, the R_f(10) versus σ plot shows a well-defined pattern that is thoroughly discussed.