Alkali Glasses Research Articles

Distribution of Cs + ions in single and mixed alkali silicate glasses from energy dispersive x-ray diffraction

The present study uses the energy dispersive X-ray diffraction (EDXD) technique to determine the average local distributions of Cs+ ions in silicate glasses with the compositions Cs2O·3.4 SiO2 and (0.405 Cs2O + 0.595 Na2O) · 3 SiO2. The data show that the local structure around Cs+ ions is very similar in the single and mixed alkali glasses, despite large differences in their ionicconductivities. No evidence of pairing or mixing of Cs+ and Na+ ions is seen, suggesting that the different ions may segregate submicroscopically into separate regions in the glass.

Immiscibility of glass forming systems

The immiscibility boundaries of various simple glass forming systems were examined in terms of the regular solution model and the following observations were made: a) The two different types of alkali in mixed alkali glasses have a positive interaction energy parameter; they tend to segregate into like species; b) Alkali borates other than the lithium borate system are unlikely to show a glass-in-glass phase separation; c) The SiO 2B 2O 3 system does not show a phase separation. On the contrary, it has a negative interaction energy parameter; d) The distribution coefficient, or the ratio of the third component in the two separated phases, is related to the binary interaction energy parameters; e) The phase separation of the H 2O-containing system is important in the chemical durability of glasses.

Mechanical vs electrical relaxation in Agl-based fast ion conducting glasses

Results of a low frequency mechanical relaxation study of a fast ion conducting system, and comparison of mechanical with electrical conductivity relaxation in the same system, are reported, using the system AgI + AgPO 3. As predicted from conductivity studies, the mechanical relaxation in the highest conducting glasses occurs at very low temperatures ∼ −170°C. Studies of the system AgIAgBO 2 and exploratory work on mixed oxyanion glasses are also reported. The tensile (Young's) moduli are consistent with values recently obtained from GHz range light-scattering studies. The dispersion in Young's modulus due to the fast ion relaxation is very large, even exceeding those seen in mixed alkali glasses, and it occurs over a much wider temperature range than the corresponding dispersion in the electrical modulus, even though the loss peaks occur within 3 K of one another. The electrical and mechanical loss peaks are found to have the same temperature dependence, and this fact is used to develop a reduced representation of the mechanical relaxation data, suitably normalized in frequency space (ωτ). Both the normalized loss peak height and halfwidth in this representation imply exceptional departures from exponential relaxation with β = 0.25 in the Kohlrausch decay function Θ( t) = exp − ([ t/ τ] β ). The mechanical relaxation evidently has elements both slower and faster than those characterizing the electrical relaxation. A general “relaxation map” of τ vs 1/ T for mechanical and electrical phenomena in this system is proved.

Relationships between conductivity and apparent glass basicity. Conductivity maximum in glass

Studies of the compositionally dependent conductivity in pseudo-binary xNa 2 O·(1− x)[ nB 2· Al 2 O 3] glasses have been carried out to 60 mol% Na 2O. For n=4.0, at x = 0.50 Na 2O, a local maximum conductivity is observed. Due to a simultaneous exponentially increasing conductivity preexponent, A, the conductivity maximum is not persistent. In the same composition region, however, E act, the conductivity activation energy, passes through a minimum value of 55kJmol −1. The activation energy minimum in these glasses is analyzed in terms of the competition, with increasing alkali, between decreasing jump distances tending to decrease E act and the increasing post-polarization charge density residing at the non-bridging oxygens tending to increase E act. The analysis suggests that the coulombic energy, to which both these effects contribute, in the high alkali glasses, is dominated by the latter effect. These observations are analyzed in terms of the glass micro-structure and the conduction energetics-topologies recently correlated by the author.

Ion Exchange Equilibria between Glasses and Molten Salts and Thermodynamical Properties in Mixed Alkali Glasses

The isotherms in ion exchange equilibrium between alkali silicate glasses and molten salts have been determined for Na+-K+ ion exchange reactions. The distribution equilibria for alkali were obtained for some glasses with different alkali fractions in a series of mixed alkali glasses. The distribution curves at 500°C were almost the same for all glasses. However, at 350°C the distribution data were not represented by a single curve probably due to the fact that the exchange distribution is influenced by the starting composition. Thermodynamical approach was made on the basis of the exchange isotherms according to the Ekedahl analysis. The activity coefficient of each alkali ion at 500° and 350°C was derived from the experimental data, and the heat of mixing was calculated for an imaginary mixed system of two end-members (Na-glass/K-glass). Thermodynamical behavior of the glass is regarded as that of a regular solution above Tg. Then, alkali ion mobitity in mixed alkali glasses was discussed in term of mixing enthalpy, and the ion exchange kinetics was analyzed using activity coefficients of alkalis and other data.

Particle adhesion in coagulation and bridging flocculation

The adhesive forces between solid particles mutually attached during coagulation or bridging flocculation are important for modelling floc stability. Results are presented in this study which are obtained from experiments on the adhesion of glass or quartz particles to a flat glass substrate (centrifugal method) or to the wall of a glass capillary through which an aqueous electrolyte solution was passed. Coagulation experiments carried out in 10−2 mole/1 MgCl2 showed the action of hydration layers on hydrophilic surfaces, whereas surface methylation is associated with adhesion in the inner potential minimum. In addition essential ageing effects interpreted as interparticle gelation were observed, especially on the interaction of alkali glass surfaces. Adhesive strength in the case of flocculation with hydrolysed polyacrylamide and a cationic Praestol mainly depends on the polymer concentration and on the preadsorption conditions before the particle-substrate attachment. A significant strengthening of adhesion due to reconformation of the bridging agents was not observed for a contact time greater than 3 min. The effect of steric stabilization with polymer overdosing could be proved by a special preparation technique.

Vibrational spectra of single and mixed alkali pentasilicate glasses

Abstract The far infrared and laser Raman spectra of single and mixed alkali pentasilicate glasses, M 2 O·5SiO 2 (M = Li, Na, Kb, Cs), and x Cs 2 O(1 − x )Na 2 O·5SiO 2 are reported in both the annealed and unannealed forms. Study of the cation-motion bands in the far infrared shows that the vibrationally significant cation-network interactions are unaffected by either introduction of a second cation or by annealing, and these results are discussed in terms of the glass formation and annealing. The spectra of the network show the existence of intrinsic network strain, changes in distributions of bond angles related to alkali mixing and annealing, and evidence for the nature of the distribution of cations in the glass. The results are discussed in relation to the composition dependence of other properties of these and related mixed alkali glasses.

Bond character and properties of the mixed alkali system Na 2OK 2OAl 2O 3SiO 2

The mixed alkali glass system Na 2OK 2OAl 2O 3SiO 2 was investigated. Density, transformation temperature, refractive index, and chemical durability were studied. Optical absorption and ESR spectra of the CuO-doped glasses were determined. Calculations of the polarizability of O 2−, bonding parameters of the Cu 2+ complex, and the packing density are presented. It was found that for the mixed alkali glasses, the oxygen- alkali bond has a more ionic character than expected from additivity. This fact enables the non-linear changes of the refractive index, of the shift of the Cu 2+ absorption band, and of the covalency to be interpreted as the Na mole fraction is varied. It is also possible to explain qualitatively the density, T g and chemical durability non-linear variations with change of the Na content by the ionicity deviations of the bond character and the postulated pairs of Na + and K + ions in the mixed alkali glasses.

Healing of tracks on the surface of alkali glass

Thus, within the framework of the model used, the deviations of the absorption of xenon from the limiting value at ~= ~ have a considerable effect on reactor power, but neutron entrainment under these conditions appears as a considerable stabilizing factor. We have been talking about the stationary state. A change in the velocity could give rise to a transient process according to the following scheme: increase in ~§ decrease in ~§ growth of Xe§ further decrease in ~.

Mechanism of Glass Darkening by a Low Pressure Mercury Discharge

A study was made of the darkening of sodium and potassium silicate glasses by a low pressure mercury discharge, using electron spectroscopy, Rutherford backscattering, and transmission electron microscopy. Initial changes in glass exposed to a mercury discharge are twofold: (i) mercury from the discharge penetrates very rapidly into the glass to depths of the order of 1 nm. (ii) Alkali ions migrate more slowly away from the surface in a photoelectric field that is caused mainly by trapping of photoelectrons. However, mercury entering the glass does not replace alkali ions. Rather, the mercury penetrates into voids in the glass network that are sufficiently close to the surface. From this “surface reservoir” mercury migrates slowly deeper into the glass. This migration is slower in mixed than in single alkali glasses. We assume that mercury migrates as ions in a photoelectric field, assisted by photoelectrons. Ultimately the mercury ions are reduced by photoelectrons to atoms that agglomerate into droplets of metallic mercury reponsible for glass darkening. A mercury discharge provides not only (i) mercury ions and (excited) atoms entering the glass and (ii) photons, creating a photoelectric field in the glass. The discharge also provides (iii) low energy electrons flooding the glass. The latter greatly enhance the strength of the photoelectric field in the glass by recombination with photoholes in the glass near the surface. As regards the effect on the darkening of the glass composition, not only the overall composition is considered (e.g., conductivity, molar volume, shear modulus), but also superficial changes in the composition.

Polymerization of silicate and aluminate tetrahedra in glasses, melts, and aqueous solutions—III. Local silicon environments and internal nucleation in silicate glasses

The local, up to second nearest neighbor, around Si atoms in alkali and alkaline earth-silicate glasses has been characterized by SiKβ X-ray emission spectroscopy. Principally two types of Si atoms can be distinguished. These are Si atoms with only other Si atoms as second nearest neighbours, and those with one or more alkali or alkaline earth atoms in their second coordination sphere. The spectroscopic results indicate that the lower molecular weight alkali and alkaline earth-silicate glasses tend towards a bimodal distribution of local Si environments, which is designated Q 4-Q 0 following the assignment by Engelhardt et al. (1975) for silica species in aqueous solutions. From a different perspective the outcome of these experiments suggests that, though the concentration of bridging oxygens (O(br)) and non-bridging oxygens (O(nbr)) is fixed by the stoichiometry of the glass, the distribution of O(nbr) in the glass varies according to the kind of alkali or alkaline earth atom present. From observed nucleation data on R 2O-SiO 2 ( R = Li, Na, K) glasses it is inferred that a bimodal Q distribution and in particular the presence of Q 0 species dominates the internal nucleation process in the alkali and alkaline earth-silicate glasses studied. Using this inference rationalizations can readily be found to explain the observed resistance to thermal shock and devitrification rates of these glasses.

Brillouin spectra of mixed alkali glasses: xCs 2O(1− x)Na 2O5SiO 2

The Brillouin spectra of a series of mixed alkali glasses, of the composition x Cs 2O(1− x)Na 2O5SiO 2, have been measured and analyzed. Significant nonlinearities are found for the variation of the isothermal compressibility [ K T,0 ( T f )] and Landau-Placzeck ratio, with a minimum observed in each as a function of x, while the longitudinal and transverse sound velocities and related elastic constants, C 11, C 44 and Young's modulus, E, vary monotonically (nearly linearly) with x. The results are interpreted in connection with related ultrasonic data and the effect of varying composition on the mechanical properties of mixed alkali glasses.

Comparative Raman study of mixed alkali and similar ion-exchanged glasses

The Raman spectra of analogous ion-exchanged and mixed alkali disilicate and aluminodisilicate glasses of the same relative composition of dissimilar cations have been determined and employed to investigate the origin of the similarity of the mechanical loss features exhibited by them. Ion-exchange of Na + for Li + in Li 2O · Al 2 O 3 · 2 SiO 2 glasses is shown to yield glasses whose network structure is different from that of the mixed alkali glasses of the same stoichiometry, but to attain that structure upon annealing. The network structure of ion-exchanged and conventionally mixed alkali disilicate glasses are apparently identical. These results are interpreted in light of the mechanical loss spectra of the analogous glasses prepared in the two ways.

Thermal expansion of doped alkali halides and glasses at low temperatures

The anomalous large thermal expansion of doped alkali halides is related to the pressure dependent change in the tunneling matrix element Δ as obtained from infrared measurements. We find that the changes in Δ give the correct magnitude of the experimentally observed giant thermal expansions. Our results suggest that the thermal expansion of glasses may also arise from changes in the tunneling matrix element, contrary to the currently accepted view.

Adopting the melting technology of a high silica alkali glass

Adopting the melting technology of a high silica alkali glass

Glass capillary gas chromatography of highly polar solutes like diols, acids and amines deactivation of fused silica and pretreated alkali glass support surfaces

The method of support surface deactivation by PSD (alkylpolysiloxane degradation) at temperature between 300 and 450°C previously described was used to deactivate both fused silica and alkali glass surfaces of capillary columns. The latter surfaces had to be pretreated before deactivation with aqueous HCl leaching or by the “dealkalisation” method using flowing HCl gas at 450°C and subsequent rinsing with water for alkali removal. Excellent alkylpolysiloxane columns with regard to tailing and irreversible adsorption of highly polar solutes have been obtained on both fused silica and the pretreated alkali glass. Fused silica does not require pretreatment before deactivation by the PSD-method, however. Good polyethyleneglycol (Carbowax 20 M) columns can also be obtained by coating the two types of surfaces when no deactivation is necessary. Deactivation by the PSD method cannot be applied in this case because polar stationary liquids do not adhere to alkylpolysiloxane deactivated surfaces. Sample capacity problems arising when separating highly polar solutes with non-polar stationary phases have also been investigated.

Application of the Rheovibron to inorganic glass problems I. The mixed alkali effect loss spectrum

A mechanical spectrometer with four decade frequency range has been used to characterize the isothermal mechanical loss spectrum of a mixed alkali silicate glass. The half width of the mechanical loss spectrum is very much greater than that for electrical relaxation at the same temperature despite the fact that both relaxations are due to alkali ion motion. It is suggested that the difference, which is also present in single alkali glasses is primarily a consequence of the fact that the mechanical relaxation is by nature a secondary relaxation (probably one of a sequence of broad secondary relaxations) while the electrical relaxation is a primary relaxation insofar as it is the process producing the largest of all changes of electrical modulus.

Secondary relaxation transitions in alkali silicate glasses

Methods of internal friction (IF), thermomechanical and DSC were used in investigation of relaxation transitions and static deformation at T<T g for one-, two-, and Three-alkali silicate glasses. For the first time mixed alkali and high-temperature (similar to ß-transition in polymers) secondary transitions were found with the aid of calorimetry. A direct connection between static deformation including creep and the IF spectrum was established. Abnormally high values of elastic modulus for different mixed alkali glasses were shown to exist, the effect disappearing at temperatures above that of mixed alkali peak. On the basis of the data obtained a new interpretation of secondary transitions is suggested. According to it, the transition phenomenon is a result of silica-oxygen skeleton depolymerization and manifestation of skeleton segments (with possible alkali cations) mobility.

Structure peculiarities of mixed alkali silicate glasses

The thermal properties and structure of alkali and mixed alkali (Li, Na, K) silicate glasses by means of differential scanning calorimetry (DSC), the positron annihilation method, X-ray fluorescence and infrared (300-30 cm −1) spectroscopy were studied. Introduction of different alkali cations in glass results in nonadditive change in their electron structure (bond “covalence degree” growth) and the thermal behaviour. The different manifestations of mixed alkali effect can be explained by the lessening of long-distance Coulomb interactions and strengthening the short-range forces in the mixed alkali glasses.

Alkylpolysiloxane glass capillary columns combining high temperature stability of the stationary liquid and deactivation of the surface

A new method of making alkylpolysiloxane (OV 1, OV 101, OV 17, Dexsil 400, SE 52, SE 54) columns with high stability at temperatures above 300°C of both the stationary liquid itself (low bleeding) and of the surface deactivation (no tailing of polar solutes with extended use at temperatures beyond 250°C) is described. The best results were achieved on dealkalinized alkali glass but also on borosilicate surfaces which have been additionally HF treated before coating in both cases. The procedure can also be applied to leached alkali and borosilicate surfaces successfully. The best deactivations of the glass surface are attained in a two step procedure: firstly by treatment with gaseous HF/N2 mixture and secondly by simple heating of the coated and closed column at temperatures between 350° and 450°C for several hours. The tailing behaviour of such columns for polar solutes is considerably improved by this procedure as shown by test chromatograms. The procedure can also be applied to leached alkali and borosilicate surfaces successfully.