Effect of stirring on striae in glass melts

Chemical striae have often negative effect on the glass properties, and hence, elimination of striae has been a key issue in glass science and technology. To produce highly homogeneous glasses, it is necessary to stir melts during the melting process. To explore the physical origin of the stria elimination during stirring, and to optimise the homogenisation process, both simulations of striation and homogenisation experiments are performed. The results show that stirring broadens the stria size distribution in the melt through conversion of larger striae into smaller ones. Only the striae with a size below half the diffusion length in the melt can be eliminated during the melting process. Stirring itself does not homogenise the melt, but enhances the stria elimination rate by generating small striae.     

The optimal parameters of bubble centrifuging in glass melts

The mathematical model of a multicomponent bubble in a glass melt under the influence of gravitational and centrifugal fields has been applied in the model TV glass. The optimal fining conditions have been examined in a rotating cylinder with the aim of determining their general features. All of the dependences between the bubble-removal time and the rotational velocity showed the region of bubble removal by centrifuging at low cylinder rotational velocities and the region of complete bubble dissolution when the rotation was intensive. The low rotational velocities, characterised by the minimal bubble-centrifuging time, appeared to be suitable for industrial application. Consequently, the influence of temperature, pressure and glass-layer thickness on the value of the optimal rotational velocity and optimal fining time of small-critical bubbles has been investigated in detail in a glass melt containing fining agent. The significant role of temperature and minor role of pressure have been proved and the identical features of bubble removal have been identified in cylinders with different radii and filling by glass but with the same average thickness of the glass layer on the cylinder walls.     

Redox behavior and diffusion of copper in soda-lime-silica melts

Glasses with the base mol% composition xNa₂O · 10CaO · (90 ? x)SiO₂ with x = 10, 16, 20 and 26 were investigated at high temperatures using square-wave voltammetry. The recorded voltammograms exhibit two peaks. That at less negative or (depending on temperature and glass composition) even positive potential is attributed to the reduction of Cu²⁺ to Cu⁺, while that observed at more negative potential is caused by the reduction of Cu⁺ to metallic copper. For both redox steps, the peak potentials decrease linearly with temperature. Those of the composition with 10 mol% Na₂O show the most negative values. The diffusion coefficients can be fitted to Arrhenius equation. If referenced to the same viscosity, the diffusion coefficients decrease with increasing Na₂O-concentration. The effect of composition on the thermodynamics as well as on diffusivities is explained by the incorporation of the copper ions into the melt structure.     

Diffusion of the S isotope in soda-lime-silica and sodium trisilicate glass melts

The diffusivity of sulphur in nominal 10 Na₂O-16 CaO-74 SiO₂ (NCS) and 26 Na₂O-74 SiO₂ (NS3) melts was investigated in the temperature range 1273-1473 K using the ³⁵S radioactive isotope in a sandwich setup. Samples were sealed in platinum capsules and run with vertical alignment at 100 MPa confining pressure in an internally heated gas pressure vessel. Using the lowest diffusion coefficient D (m² s^− 1) for each temperature the Arrhenian relations logD = −(4.6 ± 0.3) − (216 ± 7) kJ mol^− 1/RT for NCS and logD = −(6.3 ± 0.6) − (167 ± 17) kJ mol^− 1/RT for NS3 were determined. Viscosity of the melts was used to test the applicability of the Stokes-Einstein (SE) and the Eyring (EY) equations to sulphur diffusion. The SE equation yields unrealistically low radii of the diffusing particles, a consequent of the non-molecular structure of the silicate melts. On the other hand, the Eyring relation yields reasonable jump distances of 550 pm (NCS) and 750 pm (NS3) by fitting the diffusion data to the EY equation. These large values imply that sulphate ions (ionic diameter = 290 pm) migrate as large entities through the silicate network.     

Self-diffusivity of iron in alkali–lime–alumosilicate glass melts

Self-diffusion coefficients of iron were measured in glass melts with the basic mol% composition of 16 R₂O, 10 CaO, x Al₂O₃ and (74 − x) SiO₂ with x=0, 5, 10, 15 and R=Li, Na, K and Cs in the temperature range of 900–1300°C using square-wave voltammetry. All diffusion coefficients had an Arrhenian dependence which depended on the type of alkali present and the Al₂O₃-concentration. Larger alkali cations, e.g. Cs⁺, as well as an increase in the Al₂O₃-content led to a decrease in the diffusion coefficients and also to an increase in viscosity. Within one glass composition, the Stokes–Einstein equation is fulfilled with respect to the dependence of the diffusivity upon viscosity. At constant viscosity, however, increasing size of the alkali cation and increasing Al₂O₃-content led to larger iron diffusion coefficients.     

Change in corrosion behavior of amorphous FePC alloys by alloying with various metallic elements

Comprehensive work to examine the effect of metallic alloying elements M on the corrosion behavior of amorphous FeM13 P7 C alloys was performed. All alloying elements except manganese are effective in increasing the corrosion resistance of amorphous alloys in various acidic and neutral solutions, regardless of anionic species, pH and oxidizability. The addition of elements more active than iron to amorphous FePC alloy decrease the corrosion rate in an active region during immersion tests, depending upon the passivation capabilities of the alloying elements themselves. When elements nobler than iron are added, the nobler is the alloying element, the higher is the corrosion resistance of amorphous FeM13 P7 C alloys.     

Studies of NiO dissolved in alkali silicate melts based on redox potential and visible absorption spectra

The redox behavior of Ni²⁺ ions in alkali silicate melts, xR₂O · (1 - x)SiO₂, (R = Na, K and Cs and x in the range 0.175 – 0.45), was investigated using linear sweep voltammetry and differential pulse polarography. The half-wave potential of Ni²⁺/Ni⁰ depends on the alkali species and contents. It shifted to the positive side when the alkali species changed from sodium through potassium and cesium at a fixed ratio of alkali oxide to silica, indicating that NiO loses its thermodynamic stability in this order. Based on visible absorption spectra, it is shown that the Ni²⁺ ion exists in tetrahedral and octahedral coordinations in the alkali silicate glasses. The relative ratio of tetrahedral to octahedral species of Ni²⁺ also depends on the alkali species, and the content of the tetrahedral species of Ni²⁺ in potassium or cesium silicate is greater than that in sodium silicate. From these two results, it is assumed that, while NiO dissolves in the silicate melts as a weak base, some Ni²⁺ ions change into a tetrahedral coordination in a strongly basic solvent such as cesium silicate.     

Effect of preparation procedure on redox states of iron in soda-lime silicate glass

The redox state of iron in soda-lime silicate glass was determined by analysis of the optical absorption bands due to Fe²⁺ and Fe³⁺ states. When raw materials containing Fe₂O₃ were heated gradually to 1400 °C, the total-Fe content of the glass was 9.4% Fe²⁺, but rapid heating at 1400 °C increased the Fe²⁺ content to 11.7%. The oxygen activity (aO₂) in the corresponding melts was measured using zirconia and Pt electrodes. The value increased with increasing temperature in the gradually heated sample and reached log(aO₂) = 0.03 at 1400 °C, but was about 2.5 times lower in the rapidly heated sample at log(aO₂) = ?0.37. After SnO addition to the raw material, oxygen activity depended strongly on heating speed: log(aO₂) at 1400 °C fell as low as ?1.8 with rapid temperature increase but was about ?0.2 or higher with gradual heating. The Fe²⁺ content of the cooled glass was consistent with the oxygen activity of the melts. The effect of heating speed was attributed to the formation of a melt layer on the surface of the raw material.     

Composition dependence of the optical absorption spectra of cupric ion in sodium borosilicate glass melts

Optical absorption spectra of Cu²⁺ d–d transition peak in sodium borosilicate glasses and their melts were measured from room temperature to 1100 K. In the case of borate glass free from silicon, increase of the temperature above T_g shifts the peak position to the low energy side and decreases the peak height. Peak width is gradually increased with the increase in temperature. On the other hand, in the case of silicate glass free from boron, peak width is decreased with the increase in temperature from room temperature to liquidus temperature. In addition, peak height is slightly decreased with the temperature increase in this temperature range. Further increase of the temperature makes the peak width large. In borosilicate glasses, temperature dependence of the optical absorption spectra is different both from borate and from silicate, and the temperature dependences of the peak position and of the peak height are very small. Temperature dependence of the peak width depends on the boron/silicon ratio.     

Redox behavior of platinum-group metals in nuclear glass

This study highlights the role of two platinum-group metals, ruthenium and palladium, in the redox equilibria of nuclear waste containment glass. Electrochemical measurements in simplified R7/T7 glass melts were used to develop a thermodynamic model of ruthenium redox equilibrium. The oxygen fugacity at equilibrium, corresponding to the coexistence of ruthenium oxide and ruthenium metal dispersed in the molten glass, was measured at different ratios at temperatures ranging from 1000 °C to 1200 °C. Experiments were carried out on glass with and without Pd, revealing the combined role of palladium and tellurium on redox equilibria in the glass. The formation of palladium-tellurium alloys in nuclear glass was observed to result in oxidation of the elements dissolved in the melt.     

Ultrafast modification of elements distribution and local luminescence properties in glass

The success in construction of three-dimensional micro optical components or devices inside transparent materials is highly dependent on the ability to modify materials’ local structure. Especially, the realization of space-selective manipulation of element distribution is highly desirable since most of optical parameters such as refractive index and luminescence are closely related to element distribution. Up to present, the only way to control selective element distribution is local melting of glass. Here, we reported, for the first time to our knowledge, the success in realization of space-selective manipulation of element distribution in glassy state region (i.e., un-melted region) inside glass with the irradiation of high repetition rate femtosecond laser. Confocal fluorescence spectra and micro-Raman spectra show that the luminescence distribution of Cu⁺ ions and the glass network structure can be controlled with femtosecond laser irradiation, revealing the potential applications of this technique in the fabrication of functional waveguides and integrated optical devices.     

Stabilization of color conversion process of various colors in glass production

A new color conversion process has been proposed for minimizing the glass defect occurring during the color conversion caused by the glass flow turbulence in glass melting furnace. Glass flow turbulence is caused by the variation of bottom furnace temperature and also due to the change of high temperature thermal conductivity of glasses. Iron oxide was examined as an additive to control the high temperature conductivity of glasses. The effect of iron oxide on the high temperature thermal conductivity was examined. Based on these results, optimum content of iron oxide needed to keep the high temperature conductivity constant between the glasses of different colors was determined. Finally color coordinate of glasses which contained estimated optimum iron oxide content was also examined to check if it can be used as a panel of cathode ray tube.     

Spin glass behavior in complexes of iron doped coordinated polymers

Magnetization measurements were performed on metal polycarbosilazane complexes polymers doped with Fe(II) and Fe(III)-ions. Zero field cooled (ZFC) and field cooled (FC) magnetization for Fe(II) doped polymer were found to bifurcates at a freezing temperature T_g, showing typical spin glass behavior but at much higher fields (～kOe) than what is commonly observed in metallic spin glass(～Oe). However, the ZFC magnetization of Fe(III) doped polymer did not reveal any spin-glass behavior. The magnetization curves showed very little Hysteresis effects and saturate at about 40 kOe at 2 K then drops sharply at 20 K. The saturation magnetization continues to drop gradually up to room temperature ～300 K.     

A square-wave voltammetric study on the diffusivities of polyvalent elements in CaO/BaO/Al2O3/SiO2 glass melts

Diffusion coefficients of various polyvalent ions (Sn²⁺, As³⁺, As⁵⁺, Sb³⁺, Sb⁵⁺, Cr³⁺, Ti⁴⁺, V⁴⁺, V⁵⁺ and Fe³⁺) were measured in melts with the basic compositions of 10CaO·10 BaO·10Al₂O₃·70SiO₂ and 10CaO·10BaO·15Al₂O₃·65SiO₂ by means of square-wave voltammetry. At temperatures in the range of 1300-1600 °C, linear correlations between logD and 1/T were observed. At 1400 °C, the diffusion coefficients obtained are compared with those obtained from other glass melt compositions.     

Modeling the redox equilibrium of the Ce4+/Ce3+ couple in silicate glass by voltammetry

Square-wave voltammetry was used to determine the characteristic potential of the Ce⁴⁺/Ce³⁺ couple in four glass formulations covering a wide range of silicate glass compositions suitable for nuclear waste containment. The temperature range investigated extended from 1178 K to 1523 K. As the Ce⁴⁺/Ce³⁺ peak potential is situated near the silicate oxidation wall, its position was determined more precisely by superimposing the theoretical peak on voltammetry diagram. The results were then used to develop a model relating the Ce⁴⁺/Ce³⁺ redox ratio to the oxygen fugacity, temperature and optical basicity. In its general expression, the relation accounts for the evolution predicted by the laws of thermodynamics, and is similar to the relations established for the Fe³⁺/Fe²⁺ redox couple by other authors.     

Thermal behavior of biogenic apatite crystals in bone: An X‐ray diffraction study

The thermal behavior of the bovine bone mineral and synthetic stoichiometric hydroxyapatite was investigated by X‐ray diffraction. The bone samples in solid (planar oriented pieces) and in powder form were examined to elucidate how the microstructural and textural properties of bone mineral are modified under heating. As could be expected, the thermal behavior of the bone mineral depends not only on the structural distortions, but also on the crystal habit, texture and ordering of biocrystals in tissue. The temperature growth of biogenic apatite crystals, unlike synthetic hydroxyapatite, is seen to be nonmonotonic and multi‐staged. At 600 to 700°C the biomineral crystallites grow rapidly due to disappearance of the mosaic structure as the lattice imperfections are annealed. After heating between 700°C and 900°C the bone mineral appears to be composed of roughly equidimensional ≥200 nm crystals. The further growth of the crystals in the range from 900 to 1300°C occurs by the mass transport mechanism, supporting the idea that the bone mineral is not a discrete aggregation of crystals, but rather a continuous mineral phase with direct crystal‐crystal bonding. Estimates are presented to show the important role of the surface mass transport mechanism in the growth of apatite crystals. The material obtained by heating a cortical bone fragment between 900°C and 1300°C turns out to be composed of two crystal types: crystals oriented along the bone axis (major morphology) and those of differing shape and orientation (minor morphology). The heating‐induced variations in the longitudinal and transverse dimensions of differing‐morphology crystals are found to be coherent. Small amounts of CaO, MgO and other crystalline phases are seen to be formed in the bone mineral under heating. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Effects of Sn addition on the glass forming ability and crystallization behavior in Ni-Zr-Ti-Si alloys

The effect of Sn substitution for Si on the glass forming ability (GFA) and crystallization behavior has been studied in Ni₅₉Zr₂₀Ti₁₆Si_5 − xSn_x (x=0, 3, 5) alloys. A bulk amorphous Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy with diameter up to 3 mm can be fabricated by injection casting. Partial substitution of Si by Sn in Ni₅₉Zr₂₀Ti₆Si_5 − xSn_x alloys improves the glass forming ability. The improved GFA of the Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy is can be explained based on the lowering of liquidus temperature. The crystallization sequence becomes completely different with addition of Sn. The amorphous Ni₅₉Zr₂₀Ti₁₆Si₅ alloy crystallizes via precipitation of only a cubic NiTi phase in the first crystallization step, whereas the amorphous Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy crystallizes via simultaneous precipitation of orthorhombic Ni₁₀(Zr,Ti)₇ and cubic NiTi phases. Addition of Sn in the Ni₅₉Zr₂₀Ti₁₆Si₅ alloy suppresses the formation of the primary cubic NiTi phase. The bulk amorphous Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy exhibits high compressive fracture strength of about 2.7 GPa with a plastic strain of about 2%.     

Refractive index behavior in phosphate glass from the view point of B3+ and Al3+ coordination

Higher refractive index and higher Abbe value were obtained simultaneously at B₂O₃/Al₂O₃ = 1 in the system of 65P₂O₅–xAl₂O₃–(20 ? x)B₂O₃–10CaO–5Li₂O, although the refractive index generally shows a positive correlation with the dispersion. We investigated the molar volume and the molar refraction by Lorentz–Lorenz’s formula and also studied the coordination number of ¹¹B and ²⁷Al by MAS NMR. By the replacement of Al₂O₃ with B₂O₃, the molar refraction constantly decreased, but the molar volume was minimized at B₂O₃/Al₂O₃ = 1. The refractive index behavior of the glasses was mainly determined by the molar volume in the system. The coordination number of B³⁺ was only IV and it did not change if the composition was changed. On the other hand the coordinations IV, V and VI were observed for Al³⁺. The ratio of Al³⁺(VI) was maximized at B₂O₃/Al₂O₃ = 1. It is considered that the higher coordination of Al³⁺ brings the improvement of the packing and it leads to high refractive index.