Field-assisted ion exchange between molten alloys and soda lime glass

Using molten alloys, the electrolysis of soda lime glass has been studied. Ions from a molten anode can be driven into soda lime glass by applying a modest electric potential. The anode current densities have been measured. The temperature and potential dependences have also been measured. The current-time behavior depends on the ion exchange. In a molten alloy the most easily oxidized metal is suited for exchange.     

Optical spectroscopy of silver ion-exchanged As-doped glass

Soda-lime-silicate glass containing arsenic oxide and undoped soda-lime-silicate glass (blank) are prepared by melting from pure sand (iron concentration lower than 0.01 wt%). The effect of arsenic on the optical properties of the glass with and without silver ion exchange at 325 °C for various times is investigated by optical absorption and photoluminescence spectroscopy. Emission/excitation spectra of silver ion exchanged glass allow differentiation of three stages in the silver incorporation into the glass network. First and second stages are only observed in the undoped glass ion exchanged for short times. Such stages are associated with the presence of isolated Ag⁺-ions and Ag⁺-Ag⁺ pairs, respectively. The third stage appears in the undoped glass ion exchanged for times longer than 10 min and in the arsenic-doped glass even for exchange times as short as 1 min. Then, this stage is characterised by molecular mixed species formed with Ag⁺ and Ag⁰, which coexist with nanoparticles of metallic silver. The presence of those Ag⁰-aggregates gives a yellow colour to the glasses, which show the well-know absorption band at about 400 nm due to surface plasmon resonance.     

Modeling and measurement of residual stresses in a bulk metallic glass plate

The recent advent of multi-component alloys with exceptional glass forming ability has allowed the processing of large metallic specimens with amorphous structure. The possibility of formation of thermal tempering stresses during the processing of these bulk metallic glass (BMG) specimens was investigated using two models: (i) instant freezing model, and (ii) viscoelastic model. The first one assumed a sudden transition between liquid and elastic solid at the glass transition temperature. The second model considered the equilibrium viscosity of BMG. Both models yielded similar results although from vastly different approaches. It was shown that convective cooling of Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 plates with high heat transfer coefficients could potentially generate significant compressive stresses on the surfaces balanced with mid-plane tension. The crack compliance (slitting) method was then employed to measure the stress profiles in a BMG plate that was cast in a copper mold. These profiles were roughly parabolic suggesting that thermal tempering was indeed the dominant residual stress generation mechanism. However, the magnitude of the measured stresses (with peak values of only about 1.5% of the yield strength) was significantly lower than the modeling predictions. Possible reasons for this discrepancy are described in relation to the actual casting process and material properties. The extremely low residual stresses measured in these BMG specimens, combined with their high strength and toughness, serve to further increase the advantages of BMGs over their crystalline metal counterparts.     

Activation volume and free volume in some ion-conducting glasses and molten salts

In an ion-conducting glass or molten salt the ions conduct via the voids. The void volume is characterized in terms of the free volume. On the other hand, when the material is pressurized, its ionic conductivity decreases. This reduction is expressed using a parameter denoted as the activation volume. The present author proposed recently that the free volume is made of the structural part, due to the disordered structure, and the atomic part which is inherent in the constituent atoms themselves. Comparison is made between the free volume and the activation volume.     

Molecular dynamics simulation of high-pressure densification of fluorozirconate glass

Molecular dynamics simulations have been performed for a fluorozirconate glass and its model crystals in order to investigate the mechanism of the peculiar high-pressure densification phenomenon of the glass. All the polymorphs and the pressure-induced phase-transition of the model crystals were satisfactorily reproduced. The changes in the density, the F⁻ coordination number and the connectivity of ZrF_n polyhedra during the compression-decompression process are investigated under the glassy state. The density increases under high pressure, accompanying the increases in the coordination number and the connectivity. The effect of annealing treatment near T_g is also investigated. The effect was significant around 20 GPa, around which a maximum was found in the treatment-pressure dependence of density after decompression, only for the samples with the annealing treatment before decompression.     

Glass microstructure evaluations using high temperature mechanical spectroscopy measurements

This paper compares the microstructures of several glasses by measuring the Young’s modulus and internal friction as a function of temperature, using the impulse excitation technique (IET). IET is based on the analysis of the resonant vibration of a solid material sample, induced by an impulse excitation. IET determines the mechanical resonant frequencies (f_r) from which the elastic moduli can be calculated, and for each f_r the corresponding internal friction (Q⁻¹). It was found that the stiffness of quartz and borosilicate glasses increases with temperature. The stiffness of soda-lime and alumino-silicate glasses decreases with the increase of temperature. The change of stiffness of quartz and alumino-silicate glasses during heat-treatment is reversible, but that of borosilicate and soda-lime glasses is not. Explanations for the irreversibility are suggested based on the Q⁻¹-features of the glasses. Diffusion of network modifier ions in the glass network holes is proposed to cause a non-reversible stiffness change, whereas localised anelastic relaxation of network modifier ions leads to a reversible stiffness change.     

Synthesis, modeling of the structure and kinetic study of the thermal decomposition of La(III) and Nd(III) complexes with 3-hydroxypicolinic acid

Synthesis, spectroscopic studies, prediction of the structure and thermal decomposition of the La(3-OHpic)₃ · 3H₂O and Nd(3-OHpic)₃ · 3H₂O (3-OHpic = 3-hydroxypicolinic acid) complexes are described. Elemental analysis and the IR vibrational data are consistent with the complex formulae. The absorption spectra in ethanol of the La(3-OHpic)₃ · 3H₂O and Nd(3-OHpic)₃ · 3H₂O show maximum absorptions at 214 and 211 nm, respectively, which are shifted to 225 nm in the free ligand. The ab initio method RHF/STO-3G/ECP(MWB52) was used to optimize the geometry and the INDO/S-CI model for calculating the electronic spectra of these complexes. A good agreement between theoretical and experimental UV absorption spectra has been obtained. The thermal decomposition was studied by non-isothermal thermogravimetry. Thermal decomposition reactions of the complexes La(3-OHpic)₃ · 3H₂O and Nd(3-OHpic)₃ · 3H₂O are best described by R2 and R3 kinetic models.     

Ionic conduction, diffusion and glass transition in 0.2[XNa2O · (1−X)Rb2O] · 0.8B2O3

We have investigated the ionic transport in the 0.2[XNa₂O · (1−X)Rb₂O] · 0.8B₂O₃ mixed-alkali system with X=0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 in the glassy and the undercooled-liquid state by means of impedance spectroscopy and tracer diffusion experiments. The calorimetric glass-transition temperature T_g obtained by differential scanning calorimetry shows a minimum with composition. The composition dependence of the electrical conductivity below T_g exhibits a minimum, as well. These deviations from an ‘ideal’ linear mixing rule are usually denoted as mixed-alkali effect. The dc conductivities times temperature σ_dc×T follow the Arrhenius law in the range below and above T_g, respectively. The glass transition appears as a kink in the Arrhenius presentation of σ_dc×T. Below the glass-transition temperature the onset frequency ν_on of the conductivity dispersion has an Arrhenius-like temperature dependence. According to ‘Summerfield scaling’ the activation enthalpies of σ_dc×T and ν_on are expected to be the same. This is indeed observed but only for the single-alkali compositions. The activation enthalpies of σ_dc×T as a function of composition show a classical mixed-alkali maximum, however the activation enthalpies of the onset frequencies as a function of composition exhibit a nearly constant behavior in contrast to the expectation from Summerfield scaling. The tracer diffusion measurements reveal a major difference in diffusion of ⁸⁶Rb and ²²Na in mixed-alkali glasses. A diffusivity crossover of tracer diffusion coefficients of ²²Na and ⁸⁶Rb occurs near X=0.2. By comparison of tracer and conductivity diffusivities the Haven ratio is deduced which shows a maximum near the conductivity minimum composition.     

Electrical current and laser radiation effects on amorphous solids

In the present paper a phenomenological theory of external factor effects upon amorphous solid properties is presented and applied to some examples. Electric current and laser light effects are considered, but the theory can be generalized to include other effects, e.g., ionizing radiation, chemical reactants etc. Changes of amorphous solid properties are considered as initiated locally and propagated along certain lines, narrow stripes or tubes, which will be called current- or laser traces. The proposed theory consists of the kinetics of the traces’ appearance, development and disappearance, and of the kinetics of processes (physical, chemical a. o.) which occur inside traces. This phenomenological theory is applied to determine the molecular mechanisms of the considered processes by comparing the kinetics obtained theoretically and experimentally for relevant cases. The comparison also allows determination of constants and functions that cannot be calculated theoretically. A possibility was considered that properties change by crystallization, e.g., initiated by resonance electron collisions with atoms, molecules and ions within the amorphous solid. It is shown how the obtained kinetic dependencies can be compared with experimental data to check the hypothesis itself on the resonance mechanism and to determine what are namely resonances contributing to these processes.     

Ion exchange between glass melts of the system Na2ORb2OSiO2

Ion exchange between glass melts of the quasi-binary system Na₂O · 3SiO₂Rb₂O₂ was investigated at 700—1300°C by means of a special capillary method. Concentration profiles were obtained by electron microprobe analysis and were evaluated for a concentration-dependent quasi-binary interdiffusion coefficient $\text{tilde}\text{D}$ using a modified Boltzmann-Matano method. At 700–1000°C interdiffusion could be obtained in pure form with $\text{tilde}\text{D}$ values ranging from about 10^?7 ?5 × 10^?6 cm² s^?1. Above 1000°C convection processes superimposed interdiffusion, making a further evaluation impossible. The data are compared with those from a 0g rocket experiment and are discussed with respect to a mixed-alkali effect and in terms of the Nernst-Planck diffusion model.     

Diffusion and viscosity in molten Pd40Ni40P20 and Pd40Cu30Ni10P20 alloys

The self diffusion of ⁶²Ni and the shear viscosity in liquid Pd₄₀Ni₄₀P₂₀ and Pd₄₀Cu₃₀Ni₁₀P₂₀ have been measured. The used methods were the long-capillary technique for diffusion measurement and the gas-film-levitation for viscosity measurement. The temperature dependence of diffusion in the equilibrium melt follows the prediction of the mode-coupling theory. The Stokes-Einstein relation describes well the momentum and mass transport in both melts. The ⁶²Ni diffusion is equal in both alloys whereas the normalized bulk viscosity is higher in Pd₄₀Cu₃₀Ni₁₀P₂₀. Thermodynamic and structural considerations are invoked to propose a qualitative explanation for this behavior.     

Internal friction and dynamic modulus of metaphosphate glass

Internal friction and dynamic modulus were measured by a forced torsional vibration method at 0.5-5 Hz in the range of −120 to 300 °C for four kinds of metaphosphate glasses, 50MgO · 50P₂O₅(MgP), 48SrO · 52 P₂O₅(SrP), 25MgO · 25SrO · 50P₂O₅(MgSrP) and 25Na₂O · 25MgO · 50P₂O₅(NaMgP). Three internal friction peaks appeared for MgP at ∼−30, ∼105 and ∼230 °C, and the activation energies of the relaxation behavior obtained from the low, intermediate and high temperature regions were ∼110, ∼250 and ∼580 kJ/mol, respectively. For SrP, those three peaks were also obtained at ∼−45, ∼60 and ∼195 °C, and the activation energies were estimated as ∼95, ∼200 and ∼600 kJ/mol at each temperature, respectively. Two peaks appeared at ∼−50 and ∼160 °C for MgSrP, and ∼−55 and ∼70 °C for NaMgP, respectively. The obtained activation energies were ∼100 and ∼180 kJ/mol for MgSrP, and ∼75 and ∼200 kJ/mol for NaMgP, respectively. It is assumed that the primary peaks (the low temperature region) were influenced by the behavior of Mg²⁺, Sr²⁺ and Na¹⁺ ions, and the secondary peaks (the intermediate temperature region) were based on non-bridging oxygen associated with Mg²⁺, Sr²⁺ and Na¹⁺ ions. Dynamic modulus showed a decreased gradually with increasing temperature in the present temperature range for all the compositions.     

Interpretation and modeling of IR-reflectance spectra of glasses considering medium range order

Conventional qualitative and quantitative IR-reflectance spectrum interpretation of glasses is discussed in light of new findings on the optics of polycrystalline materials and the close relation of the structure of crystallites and regions of medium range order in related glasses. According to these findings, a glass spectrum must not be compared in general with the spectrum of a related polycrystalline material, if the crystallite size exceeds the resolution limit of light. As a consequence of the similarities between the spectra of glassy and related polycrystalline compounds (optically small crystallites) and based on medium range order, the macroscopic optical properties of glasses result not only from disorder and fluctuations, but also from an orientational average of the optical properties of the medium range regions similar to the macroscopic optical properties of polycrystalline materials. Consequently, the assumption of cubic symmetry, which underlies all conventional types of dispersion analysis used for glasses, is inadequate. Based on ARIT (average refractive index theory), [Appl. Spectrosc. 56 (2002) 1194], which permits modeling the optical properties of polycrystalline materials with optically small crystallites, a method is proposed to generate artificial glass spectra from single crystal data. This method is particularly useful if polycrystalline bulk samples with optically small crystallites are not available, since it enables us to determine glass structure on a semi-quantitative level by comparing measured and artificial spectra. The value of the approach is demonstrated for fresnoite glass (Ba₂TiSi₂O₈), Sr-fresnoite glass (Sr₂TiSi₂O₈) and Ge-fresnoite glass (Ba₂TiGe₂O₈). An important consequence of the assumption of an orientational average of the microscopic optical properties of medium range order regions is the prediction of the occurrence of mixed TO-LO modes in glasses. This is confirmed by the resemblance between peak shapes of model oscillators with large oscillator strengths and small damping constants and the prominent high wave number feature of vitreous silica.     

Proton conduction in glass - an impedance and infrared spectroscopic study on hydrous BaSi2O5 glass

Hydrous barium disilicate glasses (BaSi₂O₅) containing 2.75 and 3.54 wt% dissolved water (corresponding to a molar concentration of hydrogen atoms of 11.1 and 14.2 mol/l, respectively) were synthesized by high temperature fusion in an internally heated gas pressure vessel. Near-infrared spectroscopy gives evidence that both OH groups and H₂O molecules are present in the glasses. The maximum intensity in the range of OH stretching vibrations is at 2800 cm⁻¹ indicating strong hydrogen bonding in the glasses. Electric conductivity measurements were carried out at temperatures up to 523 K without significant alteration of the sample. At higher temperatures, OH groups are converted to molecular H₂O and water diffuses out of the sample resulting in a continuous decrease of the conductivity. An activation energy of 87 kJ/mol was derived for the dc conductivity in the unaltered glasses similar to the activation energy for bulk water diffusion in other silicate glasses. Because the dry barium disilicate glass is an electrical insulator at experimental conditions, we infer that the dc conductivity of the hydrous glasses is due to proton conduction.     

Sensitivity of structural results to initial configurations and quench algorithms of lead silicate glass

The sensitivity of resulting structures to starting configurations and quench algorithms were characterized using molecular dynamics (MD) simulations. The classical potential model introduced by Damodaran, Rao, and Rao (DRR) Phys. Chem. Glasses 31 (1990) 212 for lead silicate glass was used. Glasses were prepared using five distinct initial configurations and four glass forming algorithms. In previous MD work of bulk lead silicate glasses the ability of this potential model to provide good structural results were established by comparing to experimental results. Here the sensitivity of the results to the simulation methodology and the persistence of clustering with attention to details of molecular structure are determined.     

Structural changes between soda-lime silicate glass and melt

Neutron diffraction has been used to study the structure of a glass and melt of composition 75SiO₂-15Na₂O-10CaO. RMC modeling of the neutron and X-ray diffraction data for the glass allowed the determination of the Na and Ca environment. The structure has been investigated at 300K, just below the glass transition at 823 K and in the melt at 1273 K. The short range order does not present important modifications with temperature while significant reorganization appears at the medium range order. These latter changes can be associated with the Si and O pairs and indicate the relaxation of the silicate network. This indicates that the glass formation involved structural rearrangement during cooling.     

The structure of zinc polyphosphate glass studied by diffraction methods and P NMR

Zinc polyphosphate glasses with molar ratios, y=n(ZnO)/n(P₂O₅), ranging from 1.0 to 2.5 have been examined by using X-ray and neutron diffraction and ³¹P magic angle spinning nuclear magnetic resonance spectroscopy to extract information on their short-range, intermediate-range and submicroscopic structure. The depolymerization of the PO₄ chains with decreasing P₂O₅ mol% content is quantitatively described by the Qⁿ distributions determined by NMR. The shortening of the real-space distances, r_m, extracted from the diffraction experiments, indicates a structural densification with progressive depolymerization. This effect correlates with the continuous increase in packing density of the ions, ρ_p. The Zn-O coordination number, N_ZnO, was found to be four across the entire polyphosphate concentration range. The presence of two differently-sized heterogeneity regions of electron density is indicated by the measured small angle X-ray scattering.     

Spectroscopic and magnetic behavior of xNd2O3(1−x)(3Bi2O3 · PbO) glasses

Glasses of the xNd₂O₃(1−x)(3Bi₂O₃ · PbO) system with 0?x?0.30 were obtained and studied by IR spectroscopy, X-ray photoelectron spectroscopy (XPS), density and magnetic susceptibility measurements. IR and density measurements show that the addition of neodymium ions produces structural changes and the neodymium ions play a network modifier role in the host glass matrix. XPS investigation permitted following the evolution of the structural disorder, of the degree of polymerization of bismuthate chains and of the fraction of bridging oxygens with respect to the neodymium ion concentration of the studied glasses. Magnetic susceptibility data show that the Nd³⁺ ions are present as isolated species for x?0.05 and as both isolated and exchange coupled species for higher x values.     

Comparison of the energy histograms and conformations between different lattice models of copolymers

Based on large-scale Monte Carlo simulations the energy probability distribution functions are investigated for a large set of primary sequences in distinct lattice models of copolymers at low temperatures below transitions to compacted states. Amphiphilic copolymers with hydrophobic and hydrophilic units are found to produce single or double peak energy distributions corresponding to mono- or multi-meric micellar conformations. However, copolymers with short-ranged random ‘charge’ interactions in some cases are found to produce energy distribution functions with a well pronounced lowest energy state and a gap separating it from the rest of the spectrum. These, however have rather peculiar conformations corresponding to effectively immiscible domains comprised from monomers of likewise species. The relevance of these observations for coarse-grained models for protein folding is discussed.