bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enrichment of Na and K or 6Li and 7Li by counter current flow of the coexisting phases of Na/K‐ or 6Li/7Li‐ammonia solutions
Authors: Schindewolf U. , Reheis Th. 
Published: July 2012

AbstractMetal‐ammonia solutions (M‐AS) have a miscibility gap, they separate at low temperatures into a diluted, electrolytic phase of high density and a concentrated, metallic phase of low density. In mixed sodium‐potassium solutions (Na/K‐AS) after phase separation sodium is enriched in the metallic phase, the separation factor αNa/K (Eq. (2)) is the larger, the lower the temperature relative to the critical temperature of the miscibility gap or the wider the miscibility gap. Therefore in deuteroammonia solutions (DAS) with higher critical temperatures the enrichment is more effective than in normal ammonia solutions. In Li‐DAS with the two stable isotopes 6Li and 7Li the lighter one is enriched in the metallic phase. The separation factor (Eq. (4)) is αLi ≈ 1.010 at −73°C. By multiplication of the single equilibrium effect in a counter current column, which acts like a solvent‐solvent extraction column, the species can be enriched. The counter current operation of the column was enforced by electrochemical means (application of a dc‐current through the column), and the enrichment was tested around −74°C with equimolar Na/K‐AS and Na/K‐DAS for which αNa/K = 1.61 and 1.70 resp. and with Li‐DAS of natural Li‐isotope abundance. The height of the theoretical plate of the column for all three systems was HTP = 12.9±0.3 cm.
Density equilibration in a near‐critical fluid under reduced gravity
Authors: Ikier C. , Klein H. , Woermann D. 
Published: July 2012

AbstractA quick response of laser beam attenuation is found when a temperature change is imposed on near‐critical SF6 at reduced gravity in space (“piston effect”). The time to reach thermodynamic equilibrium is not correspondingly short. Density equilibration is a long lasting slow process. The times of density equilibration suggest a scaling with the temperature difference (T‐Tc).
The role of solvent structure in perturbation methods applied to the dissolution of an apolar solute in water
Authors: Re Mario , Laria Daniel , Fernández‐Prini Roberto 
Published: July 2012

AbstractIn view of recent experimental and simulation studies which show that solvent reorientation does not play a significant role in the dissolution of small apolar solutes in water, the performance of first order perturbation theories (FOPT) has been reassessed.A contribution which cannot be obtained from classical FOPT is the many‐body effect of the instantaneous solvent electric field which induces a dipole on the apolar solute and contributes an attractive term. The average square electric field was determined by molecular dynamics for solutes of different size and its effect upon the solute's chemical potential was calculated from it with an appropriate extension of the test‐particle method. The contribution of this term to the thermodynamic quantities of dissolution is discussed.
Bond angle distribution in amorphous germania and silica
Authors: Neuefeind Jörg , Liss K.‐D. 
Published: July 2012

AbstractThe distribution of Ge‐O‐Ge and Si‐O‐Si bond angles α in amorphous germania and silica is re‐determined on the basis of diffraction experiments. The bond angle α joining adjacent tetrahedra is the central parameter of any continuous random network description (CRN) of these glasses. New high energy photon diffraction experiments on amorphous germania (at photon energies of 97 and 149 keV) are presented, covering the momentum transfer 0.6–33.5 Å−1. In photon diffraction experiments on GeO2 the contribution of the OO pairs is very small. To obtain a similar information for amorphous SiO2, high energy photon diffraction experiments [1] have been combined with neutron diffraction data [2, 3] on amorphous silica in order to eliminate the OO‐partial structure factor. With this technique it is shown that the Si‐O‐Si angle distribution is fairly narrow (σ = 7.5°) and in fact comparable in width to the Ge‐O‐Ge angle distribution (σ = 8.3°), a result which differs from current opinion. The narrower distribution found in this study are in much better agreement to the determinations based on 29Si‐MAS‐NMR. Among the various models relating the chemical shift to the bond angle, best agreement is found with those models based on the secant model. Sharp components in the bond angle distribution can be excluded within the reached real space resolution of 0.09 Å.
Determination of vapour‐liquid equilibria of two‐centre Lennard‐Jones fluids in the canonical ensemble
Authors: Kristóf Tamás , Liszi János , Szalai István 
Published: July 2012

AbstractVapour‐liquid equilibrium data were determined for a two‐centre Lennard‐Jones fluid with reduced bond length L* = 0.505. The method used is based on the Taylor expansions of both the chemical potential and the pressure calculated by Monte Carlo simulation in the canonical ensemble. New phase coexistence data were obtained at rather low temperatures applying an independent simulation method for the calculation of the chemical potential. Thermodynamic consistency of the vapour pressures as well as the saturated vapour and liquid densities was confirmed on the basis of the Clausius‐Clapeyron equation.
Structural relaxation of glass‐formers confined to sol‐gel‐type porous glasses
Authors: Yan X. , Streck C. , Richert R. 
Published: July 2012

AbstractWe combine the results of dielectric relaxation spectroscopy and solvation dynamics measurements for the glass‐forming liquid 2‐methyltetrahydrofuran spatially confined to the pores of sol‐gel glasses with pore diameters ϕ = 2.5, 5.0, and 7.5 nm. Although both techniques probe the orientational polarization of the polar liquid, a dielectric experiment is bound to sense macroscopic effects, whereas the solvation method probes the molecular dynamics on microscopic scales. When the temperature approaches the glass‐transition at Tg upon cooling, an interfacial liquid layer with strongly frustrated dynamics grows in thickness and is thus able to block the connectivity among the pores. As a result the structural α‐process is subject to an enhanced spatial restriction near Tg and a transition from constant pressure to constant volume conditions might occur as the pore connectivity becomes obstructed by immobile liquid.
Investigating the cooling rate dependence of amorphous silica: A computer simulation study
Authors: Vollmayr K. , Kob W. 
Published: July 2012

AbstractWe use molecular dynamics computer simulations to study the dependence of the properties of amorphous silica on the cooling rate with which the glass has been produced. In particular we show that the density, the glass transition temperature, the radial distribution function and the distribution of the size of the rings depend on the cooling rate.
Surface induced devitrification of glasses: The influence of elastic strains
Authors: Schmelzer J. , Gutzow I. , Möller J. , Pascova R. 
Published: July 2012

AbstractIt is shown that the account of elastic strains evolving in crystallization processes of glasses may be of significant importance for the understanding of the often observed preferential surface devitrification of a variety of vitreous materials. According to the discussed here mechanism the only parameter of the considered system determining the preference to surface crystallization is the misfit parameter δ. δ is a measure of the relative change of the volume of the glass in crystallization. In agreement with experimental results it is found that preferential surface crystallization has to be expected to occur for systems with large values of the misfit parameter δ. Moreover, in comparison with planar interfaces, the inhibiting effect of elastic strains on crystallization is even more decreased for glass powders and rough surface structures of the glass samples. In this way, powders of glass, edges, corners etc. on the glass surface may serve as centers for crystallization.
Application of borophosphosilicate glass (BPSG) in microelectronic processing
Authors: Kirchhoff M. , Ilg M. , Cote D. 
Published: July 2012

AbstractIn semiconductor industry borophosphosilicate glass (BPSG) films formed by chemical vapor deposition (CVD) are widely utilized as dielectric layers between conductor lines. This glass has to provide void‐free fill of 0.2–0.5 μm wide spaces between conducting lines with aspect ratios up to 4:1. Therefore good glass reflow properties, which are a function of boron and phosphorus dopant concentration and of deposition and anneal temperature, are required. Dopant concentrations need to be low enough to avoid undesired surface crystallization phenomena and to provide a stable surface. Anneal temperatures have to be low to fulfill the thermal budget criteria of advanced silicon devices.
Rheological behaviour of textured glass‐ceramic melts produced by the cylinder compression method
Authors: Deubener J. , Brückner R. 
Published: July 2012

AbstractThe rheological behaviour of glass‐ceramic Li‐disilicate melts is characterized by the Newtonian and non‐Newtonian viscosity. These quantities are determined from the thermally corrected rate‐dependent flow curves of the cylinder compression experiments on the basis of equal (Newtonian) equilibrium viscosities (isochomal conditions). Certain crystalline volume fractions in the glass samples are produced by primary nucleation and crystallization treatments.The flow parameters show a characteristic non‐linear decrease with increasing compression rates. This two step shear thinning behaviour is determined, within the range of small deformation rates, by the suspension effect of the initial crystals and at larger deformation rates by the non‐Newtonian flow behaviour of glass melt matrix. The suspension effect is based on a flow orientation mechanism of the crystals, building up a certain texture. The alignment depends on the size, shape and concentration of the specimens. Based on a recently developed flow equation for stress induced changes of viscosity in single‐phase glass melts, a qualitative and quantitative description of the non‐Newtonian flow behaviour of glass melts with suspended crystals is presented.
Influence of pressure and shear flow on the crystallization behaviour of a glass melt based on the Li2Si2O5‐composition
Authors: Durschang B. R. , Carl G. , Rüssel C. , Gutzow I. 
Published: July 2012

AbstractExtrusion experiments of a glass melt, based on lithiumdisilicate, show a different crystallization behaviour in comparison with experiments, where the same glass is heat treated identically, but without the pressure and the shear flow. Therefore, the effect of pressure and shear flow on the nucleation and crystal growth are discussed. It is shown theoretically and practically that at least for the lithiumdisilicate the pressure used is not sufficient to reach significant differences in crystallization. The shear flow is supposed to cause the crystallization catalysis due to the non‐Newtonian flow behaviour of the glass melt used.
In situ electrochemical and spectrophotometric investigation of the oxygen pressure dependence of the [Cr(VI)]/[Cr(III)] ratio in a borosilicate melt
Authors: Claes P. , Duveiller Ph. , Tilquin J.‐Y. , Glibert J. 
Published: July 2012

AbstractThe ratio R = [Cr(VI)]/[Cr(III)] has been measured in a Na2O·1.2SiO2·1.2B2O3 melt at 1000°C by spectrophotometry and by electrochemistry as a function of the partial pressure of oxygen in the gaseous atmosphere above the melt. Spectrochemical and electrochemical determinations are in quite good agreement and fit the linear relationship between log R and logP(O2) which is predicted by a thermodynamic development. This double agreement gives a good degree of confidence to in situ high temperature electrochemical measurements in oxide melts.
Problems of the voltammetric on‐line determination of iron and sulfur in industrial glass melts
Authors: Müller‐Simon H. , Szafarczyk M. 
Published: July 2012

AbstractFor some years efforts have been made in order to utilize voltammetric methods for glass technology. Different boundary conditions and the specific use as an analytical tool lead to some particular requirements in industrial application.For industrial use the electronic equipment has to be protected against electronic perturbation due to electric boosting. In order to shelter the control devices against dust and heat, these devices must be installed at quite a distance from the investigated glass melt, which gives rise to disturbances in the measured voltammograms. The most important problem is the fixing of the area of the measuring electrode, which varies due to glass level variations.The identification of the different influences and some solutions will be presented. In order to take also the influence of different glass compositions into account, the measuring setup should be calibrated for each particular glass melt. If all influences on the measured signal are known, a single point will be sufficient in order to calibrate the system.
About electrochemical reactions between a BaO‐ and a PbO‐Rich melt, short‐circuited by platinum
Authors: Kaps Ch. 
Published: July 2012

AbstractThe “Reboilling” effect is well known. If glass fragments with very different alkali oxide contents are remelted together in a platinum crucible, there can take place a local generation of gas bubbles. Similar effects were observed in a study of the Ba/Pb interdiffusion kinetics between two melts with the same molar composition (MO)33.3(B2O3)66.7‐s(EO2)s (M = Ba and Pb, resp.; E = Ge, s = 0.15 and Si, s = 0.10, resp.). The thermodynamic potential of the melts and the electrochemical mobilities of the ions Ba2+ and Pb2+ will be discussed in connection with the above described phenomenon. At 700°C the Ba/Pb ion‐exchange in the ratio 1/1 shows a dominant viscosity‐controlling. The formation of gas bubbles is caused by reactions, influenced by the experimental arrangement and by the melt compositions.
Kinetics of glass corrosion in acid solutions
Authors: Helebrant Aleš , Pekárková Iveta 
Published: July 2012

AbstractThe interaction of simulated nuclear waste borosilicate glass with acid solutions (pH = 2, pH = 4) was studied under static conditions (i.e. without refreshment of corroding solution) at 30, 60 and 90°C. Tests with stirred and unstirred solution were compared. The rate of glass dissolution (given by the rate of SiO2 transfer into the solution) and the rate of glass leaching (represented by the rate of sodium transfer into the solution) were significantly higher at lower pH and in stirred solution. The first phenomenon can be explained by the more extensive opening of glass structure at lower pH. The second phenomenon can be caused by the creation of thin solution layer adjacent to the glass surface in the case of unstirred corroding media. The SiO2 and sodium concentration in this layer are then higher in comparison to the bulk solution. Due to this fact the driving force of glass matrix dissolution and sodium leaching are lower than in the case of stirred solution. The temperature dependencies of the initial rate of glass matrix dissolution and of the sodium diffusion coefficient can be described using equations of Arrhenius' type.
Investigation of the flaws of container glass introduced by aluminium on the recycled glass cullets by means of ir and raman microspectroscopy
Authors: Meyer K. , Traufelder S. , Stachel D. 
Published: July 2012

AbstractThe introduction of aluminium contained in the recycled glass cullets into the melts of container glass results in the formation of silicon spheres as a well known glass flaw. Besides the glasses of our test melts are inhomogeneous and coloured brown, dark brown, and grey around these silicon spheres. The different coloured regions are investigated by mapping the glass sample using IR and Raman microspectroscopy to find out the nature of the inhomogeneities. Only in the brown regions silicon could be detected. Therefore the brown colour should be caused by silicon particles. The grey regions of the glass contain Al2O3.
Ionic conduction in glass ceramics
Authors: Runge Andreas , Kahnt Hanno 
Published: July 2012

AbstractThe ionic conductivity in glass ceramics depends not only on the partial conductivities of the different phases and their volume fractions but — to large extend — on the structure of the composite material. Moreover, conductivity can be drastically increased by enhancement of ionic mobility along grain boundaries. The conductivity of glass ceramics is discussed in terms of upper and lower bounds depending on the degree of information about the structure. An effective medium approach is used to describe the dc conductivity for some characteristic types of structure. This approach is extended to the frequency dependence of conductivity. The model is applied to experimental data from glass ceramics of the system SiO2‐PbO‐PbF2. In this system different structures have been realized leading to an increase or decrease of conductivity by up to three orders of magnitude compared to the starting glass.
Novel opportunities of structural investigations of glasses by 2D NMR, multiple quantum NMR and 27Al MAS NMR lineshape analysis
Authors: Jäger C. , Hartmann P. , Kunath‐Fandrei G. , Hirsch O. , Rehak P. , Vogel J. , Feike M. , Spiess H. W. , Herzog K. , Thomas B. 
Published: July 2012

AbstractThe recent progress in NMR of glasses is demonstrated using both traditional and improved two‐dimensional (2D) NMR techniques. A novel approach for measuring connectivities Qn units in amorphous and polycrystalline solids is explained. Several examples of phosphate samples are presented to show e.g. how chain end groups can be distinguished from pyrophosphate units. Additionally, novel results of 27Al NMR investigations in mullites and Na2O‐SiO2‐Al2O3 glasses were obtained using a careful lineshape analysis. In mullites three different AlO4 units can be found including an estimation of the relative Al occupancy of the various groups. In ternary Na2O‐Al2O3‐SiO2 glasses we could prove the presence of two AlO4 sites with Al being surrounded by four Q3 units or possibly one terminal oxygen instead of a Q3 unit (60 ppm) and by four Q4 groups (53 ppm). Finally, two different Na sites have been detected for the first time using 23Na MQ NMR in a glass 22.7 Na2O 0.7 B2O 69.8 SiO2.
Order in li‐silicate glasses by diffraction methods
Authors: Uhlig H. , Lamparter P. , Steeb S. 
Published: July 2012

AbstractA silicate glass containing 20 mole % Li2O was investigated by X‐ray diffraction as well as neutron diffraction. In the latter case isotopic substitution was done by replacing Li of natural isotopic abundance by 6Li, 7Li, and 0Li, respectively. 0Li is a mixture of Li‐isotopes with resulting scattering length zero. Using the reverse Monte Carlo method, a cluster containing 3000 atoms is constructed which is in accordance with the experimentally obtained total structure factors. This cluster yields the partial pair correlation functions and various angle correlation functions. Further hints on the three‐dimensional arrangement of the bonds are obtained using the method of Steinhardt et al. All data obtained are compatible with a proposed model for the atomic arrangement in lithium‐silicate glasses. This model is characterized by a distinct increased order compared to the structure of the pure silicate. The order is determined by sixfold rings and an oxygen‐sublattice.
X‐ray spectroscopy of ion‐exchanged glasses
Authors: Dubiel M. , Brunsch S. 
Published: July 2012

AbstractX‐ray absorption Spectroscopy makes it possible to identify the local atomic structure around cations in ion‐exchanged glasses. EXAFS experiments demonstrate that the substitution of sodium by silver leads to local rearrangements below TG whereas the incorporation of Rb or Cs does not generate a cation specific environment. Fe K‐edge XANES spectra confirm that the oxidation of Fe2+ is accompanied by the reduction of silver ions. A structural interpretation of the modified mixed mobile effect as a result of an ion exchange has been developed.
Probe ions for local structure investigations of glasses
Authors: Seeber Wolfgang , Ehrt Doris 
Published: July 2012

AbstractThe successful design of materials for optic and laser technology needs tools of investigation. Besides physical, chemical and optical properties especially the spectroscopic behavior of these materials is important. Knowledge about the local structure of doped active ions may provide the basis for tailoring of spectroscopic properties. Special ions, e.g. Nd3+, Gd3+ or Pb2+ as so‐called probe ions have been incorporated into optical glasses to probe relevant sites of the amorphous network. The Nd3+: 4I9/2→2P1/2 absorption transition has been used to sense the strength of the crystal field in the vicinity of the laser ion and to derive information about emission properties of embedded laser ions. The Gd3+: 6P7/2→8S7/2 emission transition at 315 nm is useful for determination of electron‐phonon interactions. The Pb2+ ion (1S0→3P0 absorption transition) has been applied as probe ion for alkaline earth ion sites. The optical basicity of fluoride phosphate glasses with different phosphate content has been estimated. The application of probe ions for local structure investigations can give assistance in the complex process of material design. However, these methods should not be overestimated because of the huge numbers of parameters affecting the performance of a laser material and complementary investigation methods must be used.
Glasses of sugars and sugar substitutes
Authors: Cammenga H. K. , Zielasko B. 
Published: July 2012

AbstractMany sugars occur in several crystalline and in an amorphous form. The glass transition temperatures of isomalt and its components and the enthalpies of fusion are reported. Amorphous sugars are extremely hygroscopic and sorb large amounts of water. This gives rise to supersaturated sugar solution, from which the sugar recrystallizes in its stable polymorph while the sample loses water, but if the sugar is able to form a hydrate, most of the water is incorporated as water of crystallization and only the non‐bound water is released.
DTA study of rare earth doped ZBYA‐type fluoride glasses
Authors: Rasztovits Z. E. , Szabó I. , Frischat G. H. 
Published: July 2012

AbstractIn the present study the effect of the rare earth elements Ho and Eu on the crystallization behavior of ZBYA‐type fluoride glasses was investigated by means of DTA. Stability criteria like thermal stability range, weighted thermal stability range, crystallization range and Saad and Poulain's criterion were calculated. Furthermore a kinetic analysis was carried out in terms of the Kissinger method and the apparent activation energy of crystallization was evaluated to characterize the crystallization trends as a function of type and concentration of dopants.
Experimental determination of the interface tension of liquid silver halide in a sodium borosilicate melt
Authors: Lembke U. , Blau W. 
Published: July 2012

AbstractA method for the direct measurement of the interface tension of precipitating silver halide in a photochromic glass melt is presented. The technique is based on the determination of the mean radii of curvature of a glass droplet swimming in the silver halide melt at temperatures above the glass transition temperature. The calculation of the interface tension is performed by means of the Laplace equation taking into account the gravitational force and the force of buoyancy. The results obtained for 610°C and 850°C are used to estimate the nucleation rates for the formation of silver halide phases in photochromic glasses.