Abstract: In this research, the effects of SrFe12O19: SF on optical and dielectric properties of Na2O-CaO-P2O5 glasses were investigated. From the study, the optically transparent glass, SF/Na2O-CaO-P2O5, system was successfully prepared by melt-quench method. The composition of SF/Na2O-CaO-P2O5 used in this study are ranging between 5-20 wt.% SF. It was found that the addition of SF enhanced the conductivity, but in turn reduced the percentage of transmittance in the glasses. The glasses subjected to be adding SF contents at higher than 15 wt% were opaque, while the lower range gave highly transparent glass ceramics. The dielectric constant (ɛr) of the SF/Na2O-CaO-P2O5 glasses were improved by increasing the content of SF, which in turn plays an important role in controlling the properties of the glass ceramics, including physical, optical, and dielectric properties.
Abstract: Various ancient glass beads in prehistorical - historical period (around 2500-1200 BP) from the collection of the Banraiprachasawan local museum (A. Pisalee, Nakhon Sawan) were studied to determine elemental compositions and morphologies using electron probe microanalysis (EPMA) and scanning electron microscopy/energy dispersive x-ray analysis (SEM/EDX). The colors of the beads range from blue to red brown. From the EPMA data, all beads contain copper in the glass matrices. The SEM/EDX showed differences in the microstructures of the glass beads. The transparent blue, greenish blue and light green beads contain small particles of tin oxide while the opaque orange or red brown beads contain both copper oxide and tin oxide particles. The forms of copper oxide in the orange and red brown beads were proposed from previous work: Cu2O in the orange glass and copper metal in the red brown glass.
Abstract: This paper reports neodymium doped bismuth borosilicate glasses in composition (40-x)B2O3-40Bi2O3-20SiO2-xNd2O3 where x = 0, 0.5, 1.0, 1.5, 2.0 and 2.5 mol%, have been prepared by melt quenching technique and are characterized through physical properties structural properties, optical absorption spectra and emission spectra measurements. The density is found to increase with the increase in concentration of Nd2O3. The molar volumes of glass decrease where concentration of Nd2O3 where concentration of Nd2O3 is 0-0.5 mol% and beyond 0.5 mol% that molar volumes were increased. The absorption spectra of Nd3+-doped glass centered at 512 nm (4I9/2→2K13/2+4G9/2), 526 nm (4I9/2→4G7/2), 584 nm (4I9/2→4G5/2+2G7/2), 625 nm (4I9/2→2H11/2), 681 nm (4I9/2→4F9/2), 747 nm (4I9/2→4F7/2+4S3/2), 804 nm (4I9/2→4F5/2+2H9/2) and 877 nm (4I9/2→4F3/2) have been observed. The emission spectra of glass were also investigated.
Abstract: The effect of adding TeO2 into (100-x)[0.5Ag2O−0.1B2O3−0.4P2O5]−xTeO2 glasses, with 0−80 mol% TeO2, on the structural changes and electrical properties has been investigated. The structure was studied by Raman spectroscopy and electrical properties have been studied over a wide temperature and frequency range by impedance spectroscopy. The addition of the third glass former, TeO2, to the glass network causes the structural transformation from TeO3 (tp) to TeO4 (tbp) which contributes to the changes in conductivity. The glasses with low TeO2 content show only a slow decrease in dc conductivity with addition of TeO2 due to the increase of the number of non-bridging oxygens, which increases the mobility of Ag+ ions. The steep decrease in conductivity for glasses containing more than 40 mol% TeO2 is a result of decrease of the Ag2O content and stronger cross-linkage in glass network through the formation of more Te-eqOax-Te bonds in TeO4 tbp units. The glasses obey scaling of the ac conductivity with respect to temperature indicating that the dynamic process is independent of temperature. However, the scaling of the spectra for different glasses revealed deviations from the Summerfield scaling due to the local structural disorder caused by structural transition in tellurite glass network.
Abstract: The objective of this research is to focus improving the properties of machinable mica-based glass-ceramics in order for restorative dental materials. The glass-ceramics derived from the SiO2- Al2O3-MgO-MgF2-SrCO3-CaCO3-CaF2-P2O5 system were produced by a two-stage heat treatment. It was elucidated that the optimum nucleation and the crystallization temperatures were at 643°C and 892°C. The various heat treatment times in the first stage were applied as 3, 6, 12, 24, 48 and 72 h, respectively, on the optimum nucleation temperature to produce mica-based glass-ceramics. XRD results showed that specimens of variety of nucleation time had similar crystalline structures such as calcium-mica, fluorapatite, stishovite, anorthite, strontiumapatite and forsterite phases. The microstructures of glass-ceramics were observed by SEM basically as interlocked plate-like and needle-like microstructures of mica and fluorapatite, respectively, in all specimens. Furthermore, different heat treatment times influenced on the revealed crystal size of the glass-ceramics; the longer heat treatment, the smaller crystals. The resultant glass-ceramics gave the results of biaxial flexural strength (178-224 MPa) and Vickers hardness (295-393 HV) increasing with the formation of the interconnected mica phases which contributed to improve the machinability. The values of the properties were comparable to those of human enamel and suitable for some restorative dental applications.
Abstract: Glass ceramic materials are widely used in dental application because of their strong similarity with natural teeth. In this study LAS glass ceramic/glass materials were prepared by glazing processing and characterized in terms of mechanical flexural strength. The selected glass ceramic support derives from an industrial process. Different glasses were applied to the glass ceramic support in order to investigate firstly their effect on the glass ceramic/glass interface and secondly how these structural changes are correlated to the flexural strength property. Different thermal cycles were applied to the glass ceramic in order to promote the increasing of mechanical flexural strength. Preliminary results clearly points out that the application of a glass on the support leads to the decrease of the flexural strength if compared to the materials without any coating applied.
Abstract: Chemical strengthening is a method of generating compressive stress on the glass surfaces by ion-exchange to improve their strengths since old ages. As its targets have been expanding to larger and thinner glasses recently, different strength profiles are required depending on the applications and selecting appropriate ion-exchange parameters becomes even more important. Therefore, we developed a simulation model of chemical strengthening which enables predicting the stress profiles by ion-exchange in order to help optimizing the ion-exchanging parameters. Parameter study using the simulation model with change of temperature results in precise stress prediction, the compressive stress on the surface with a margin of error of ± 3% and the depth of layer with that of ± 10%. Furthermore, the parameter study introduced following two technical findings; (1) both inter-diffusion coefficient and mass-transfer coefficient could obey the Arrhenius equation, (2) both actual temperature and fictive temperature could influence on the stress relaxation. These findings are of great importance in comprehending the phenomena associated with ion-exchange. It has possibilities for beneficial feedback to the composition development and optimum stress design in accordance with each application.
Abstract: Chalcogenide glasses switches from a high-resistance (OFF) state to a low-resistance (ON) state at a threshold voltage (Vth) under high electric fields. This electrical switching is of two types: (i) Threshold switching and (i) memory switching. Threshold switching device revert back to the OFF state immediately upon the removal of the applied voltage, whereas a memory device retains the ON state even after the removal of the applied voltage. Due to Joule heating, a filament is formed between the electrodes and the current is confined within this filament and there is an increase in current density. This increases the temperature inside the filament and there is a transition from high resistive amorphous/glass phase to a low resistive crystalline phase in memory switching materials. In the threshold switching glasses electronic processes like space charge, Poole-Frenkel effect, etc., are responsible. The structural transitions are irreversible whereas the electronic processes are reversible and hence the threshold glasses regain their original state (OFF) and memory glasses remain in the ON state.Interestingly, differential scanning calorimetric studies (DSC) show that both the threshold and memory switching glasses exhibit crystallization (structural transition). Accordingly, glasses which crystallize upon heating should exhibit memory switching behaviour. But the switching experiments indicate that among the glasses which undergo structural transition (crystallization) some show threshold switching and some show memory switching. To understand this, Cu-As-Se, Al-As-Te, Ge-As-Se-Te, Al-As-Se-Te glasses were thermally crystallized under vacuum in two ways: (i) by annealing at their respective crystallization temperatures (Tc) and (ii) heated up to their melting temperatures (Tm) and cooled back to room temperature. Interestingly, most of the threshold switching glasses shows amorphous nature or a huge amorphous background with crystalline peaks when cooled from their melting temperatures. The memory switching glasses crystallize in both the cases.We propose that both threshold and memory glasses undergo phase change and the crystalline phases formed from the melt state are responsible for switching to occur. Hence, at the time of switching the sample in between the electrodes undergo phase change by glass → melt → crystal transformation and not by the direct glass → crystal transformation.
Abstract: Amorphous solids prepared from their melt state exhibit glass transition phenomena upon heating. Derivatives of volume like viscosity, specific heat and thermal expansion coefficient show rapid changes at the glass transition temperature (Tg). In general, application f high pressure increases the Tg (a positive dTg/dP). This positive dTg/dP has been well understood with the Free Volume and Entropy models. However, there are few exceptions where a negative dTg/dP has been observed. It has been proposed that the glasses which undergo negative thermal expansion can exhibit a negative dTg/dP. In this study, electrical resistivity of semiconducting Ge20Te80 glass at high pressures as a function of temperature has been measured in a Bridgman anvil apparatus. Electrical resistivity showed a pronounced change at Tg. The pressure dependence of Tg (dTg/dP) shows a decreasing trend (-dTg/dP). Chalcogenide glasses like Se, As2Se3 and As30Se30Te40 show a positive dTg/dP in contradiction to the present observation of negative dTg/dP. A model proposed by deNeufville and Rockstad finds a linear relationship between Tg and the optical band gap (Eg) when they are grouped according to their connectivity (Zav).Application of high pressure decreases the interatomic distance which in turn decreases the separation between the valence and conduction bands (optical band gap). This reduction in optical band gap shifts the glass transition to lower values. It is also suggested that the sign of the pressure derivative of Tg can be negative (-dTg/dP) if the thermal expansion coefficient is negative. Inelastic neutron diffraction studies show a negative thermal expansion coefficient for most of the Te based chalcogenide glasses. Hence, Ge20Te80 glass is uniquethat its pressure dependence of Tgobeys both thermodynamic and the Tg-Eg-Zav models.
Abstract: The aim of this study is to develop soda lime borate (SLB) doped with Dy3+ glass and investigate their optical and luminescence properties, for different applications in photonics and optoelectronics. The glass were melt by conventional melt quenching technique. Optical properties have been determined by measuring their absorption spectra and luminescence properties were studied by photo luminescence spectra. From optical absorption measurements, there are ten peaks with transition 6H15/2 to 6F11/2 + 6H9/2 at 1262 nm has higher spectral intensity and is a hypersensitive transition. As a result of 350 nm excitation the photoluminescence spectra have four peaks. Higher luminescence intensity peak was observed for 0.5 mol% Dy3+ doped SLB glass at 4F9/2 to 6H13/2 (575 nm). Hence it is suggest from the chromaticity results that SLB glasses with different Dy2O3 concentration may be a promising glass for white LED under 350 nm excitation wavelength. Further investigation is under way for the optimization of different dopend concentration in the SLB glass.