Papers by Keyword: Glass

Abstract: The structural, electronic, and optical properties of an amorphous SiO₂ (a-SiO₂) model is investigated by using first-principles calculation. Most research works used beta-cristobalite glass structure as a reference to amorphous silica structure. However, only the electronic properties were been presented without any link towards the optical properties. Here, we demonstrate simultaneous electronic and optical properties, which closely matched to a-SiO₂ properties by generating small sample of amorphous quartz glass. Using the Rietveld refinement, amorphous silica structure was generated and optimized using density functional theory in CASTEP computer code. A thorough analysis of the amorphous quartz structure obtained from different thermal treatment was carried out. The structure of amorphous silica was validated with previous theoretical and experimental works. It is shown that small sample of amorphous silica have similar structural, electronic and optical properties with a larger sample. The calculated optical and electronic properties from the a-SiO₂ glass match closely to previous theoretical and experimental data from others. The a-SiO₂ band gap of 5.853 eV is found to be smaller than the experimental value of ~9 eV. This is due to the underestimation and assumption made in DFT. However, the band gap value is in good agreement with the other theoretical works. Apart from the absorption edge at around 6.5 eV, the refractive index is 1.5 at 0eV. Therefore, this atomic structure can served as a reference model for future research works on amorphous structures.

Abstract: Despite several advantages of phosphate glass systems, their hygroscopic tendency (absorbing or attracting moisture from the atmosphere) remain a major limiting factor for widespread industrial applications. Dedicated efforts are made to improve the hygroscopic nature of such glasses for making them chemically durable and greatly resistant towards moisture attack. Guided by this requirement, we prepared five phosphate glass samples of composition (70-x) P₂O₅–xFe₂O₃–25ZnO–5CaO with controlled manipulation of iron-oxide contents (Fe₂O₃: x = 0 to 20 mol %) using melt-quenching method. The influence of Fe₂O₃ (as modifier) contents variation on the improvement of structural and chemical strength is determined. As-synthesized glass samples are immersed in acidic solutions for corrosion test. In this test, glass samples are engrossed in the aqueous hydrochloric acid (HCl) media at 90 °C and soaked for a period of 4 h. The corrosion rate (CR) was calculated from the weight loss obtained after the test. The least number of CR indicates that the inclusion of Fe₂O₃ in the glass network improved the network rigidity and made the glass much stronger as well as more water resistant. However, it is also established that there is an optimum limit of Fe₂O₃ content beyond which the durability cannot be further improved. The AFM analysis of pre- and post- chemically treated glass samples informed the surface roughness and 3D topography. Present observation must be validated with other supporting experiments and model calculation which is underway. In this study, it revealed that the lowest corrosion rate was sample S3 (10% of Fe₂O₃) which have CR value of 1.02±0.12 ´ 10^-3gcm^-2h^-1 .

Abstract: The main objective of this experimental work is to study the effect of Hydro Fluoric acid in ultrasonic machining of polycarbonate bullet proof UL-752 and Acrylic Heat resistant BS 476 Glass. In which, mixture of abrasive particle are also used as the input machining parameter. Three types of abrasive; Alumina, Silicon Carbide and Boron Carbide are used for machining. Experiment has been performed with 8mm of high carbon high chromium tool steel (D2), high carbon steel (HCS) and high speed tool steel (HSS) tools. The material removal rate was father enhanced by HF acid. The experimentation date represent the main effect plots for tool wear rate and material removal rate. After analysis, results reveals that Al₂O₃+SiC+B₂C mixed slurry (1:1:1), Hydro Fluoric acid with 1% concentration and High Speed tool Steel material produce the higher material removal affect.

Abstract: Polycarbonate bullet proof glass and acrylic heat resistant glass are used as the functional material in many application. In this research paper, Taguchi modal is utilized for the ultrasonic machining of these material. Surface roughness is significant output parameter, because it define accuracy of the process. Taguchi modal suggest that 40% concentration, mixture of Alumina, Silicon carbide and Boron carbide abrasive in 1:1:1, 600 abrasive grit size and 1.5% HF acid gives best results in polycarbonate bullet proof glass material and for acrylic heat resistant glass, mixture of Silicon carbide and Boron Carbide abrasive in 1:1, 600 abrasive grit size and 1% HF acid gives the best results. More significant parameters contribution in surface roughness are concentration of slurry, grit size of abrasive and HF acid. Optimum parameters improved the surface roughness by 23% and 24% in polycarbonate bullet proof glass and acrylic heat resistant glass respectively.

Abstract: The use of Fiber Reinforced Polymer (FRP) composites has become a popular solution for retrofitting and strengthening of existing concrete and masonry structures. However, some drawbacks of this technique, mainly associated with the use of organic resins, have been reported. To overcome such drawbacks, the development of composite materials in which the organic resins are replaced with inorganic matrices has recently caught the attention of the civil engineering industry. Among these newly developed systems, Fiber Reinforced Cementitious Matrix (FRCM) composites, which are comprised of high strength fibers embedded within an inorganic matrix, have shown promising results. However, research on this topic is still limited and important aspects, such as the bond behavior between the composite and the substrate, are not fully understood and require further study. This paper presents the results of an experimental campaign aimed at investigating the influence of the type of matrix and substrate on the bond behavior of FRCM composites. Glass-FRCM composite strips were applied onto concrete and masonry substrates and then tested by means of a classical push-pull single-lap direct-shear test set-up. A cementitious and a lime-based matrix were employed to apply the same type of fiber on concrete and masonry substrates, respectively. FRCM-concrete and FRCM-masonry joints reported the same failure mode. However, higher values of the peak load were obtained for the lime-based glass-FRCM composite applied onto masonry substrates than with the cementitious glass-FRCM composite applied onto concrete substrates.

Abstract: The viscoelastic properties of glass under different temperature are essential for the high-precision thermo-plastic-forming of glass. But it is exceptionally difficult to establish a quantitative relation between the thermal history and the viscoelasticity owing to the lack of constitutive model of glassy materials’ relaxation. The present work investigates the validity of Young’s modulus measurement in impulse excitation technology and then the viscosity predicted by Kelvin and Maxwell model. It is demonstrated that the classical Kelvin model, leads to the seemingly unphysical result that viscosity increases with temperature since the experimental loss rate of damped vibration increases with temperature. Although Maxwell model can be employed to explain the positive temperature dependence of loss rate, the magnitude is even smaller than the viscosity at glass transition temperature and is therefore also unreasonable. The further theoretical work suggests the intermediate zone of Kelvin and Maxwell model.

Abstract: The contribution deals with the importance of low-emissivity glazing layers in improving the energy balance of building interiors. It describes the effects of changes in surface emissivity of glass, depending on the position of low-emissivity layer. It also discusses principles, advantages and disadvantages of the most common glazing combinations with regard to interior visual and thermal comfort and also slightly misleading interpretations caused by complexity of the matter. The discussion (and comparison) is based on methods and tools used in computer-aided building performance modelling and simulation and on recent information from glass industry.

Abstract: This work aims to investigate the crystallization kinetics of β-spodumene/cordierite glass-ceramics. Thus, three glasses with compositions based predominantly on cordierite (C), β-spodumene (L) and in a molar ratio 1:1 of both phases (CL) were prepared. The kinetics parameters such as activation energy for crystallization (ranging from 160 to 358 kJ/mol) and Avrami exponent (ranging from 1.4 to 10.7) were determined by means of non-isothermal methods using differential scanning calorimetry (DSC). Additionally, the samples were crystalized according to DSC analyses and characterized by using x-ray diffraction (XRD). The main detected crystalline phases were β-spodumene to the glass L, cordierite to the glass C and β-quartz, mulite and spinel to the glass CL. Considering the thermal and electrical properties of these crystalline phases, these glass-ceramics have potential use for LTCC (Low Thermal Co-fired Ceramics) applications.

Abstract: The aim of this work was to fabricate glass-ceramic substrates using aqueous tape casting technique of the parent glass powder in the SiO₂-Al₂O₃-MgO-Li₂O system with addition of ZrO₂ and B₂O_3. The powder mixture was melted at 1650°C/1h and the obtained glass (frit) was milled and processed by tape casting in thin substrates with 700 μm thickness. Suspensions were prepared by aqueous medium and latex emulsion binder. Flexible green tapes with few defects were obtained using suspensions prepared with 7 and 10 wt% of binder in relation to glass powder. Substrates were submitted to burn out at 700 °C and thermal treatment at 950 oC/30min, 950 oC/4h and 1000 °C/1h. The green density of the substrates was around 1.55 g/cm³ and 2.10 g/cm³ after sintering/crystallization. Microstructure in all treatments showed high porosity. The major crystalline phases identified by XRD were Li_0,6Al_0,6Si_2,4O₆, ZrO₂ and ZrSiO₄.

Abstract: Dental prostheses made of ceramic composites infiltrated with glasses have been used due to their biocompatibility and possibility to mimic the natural teeth. In this study, the devitrification behavior of 20SiO₂-25B₂O₃-25Al₂O₃-15La₂O₃-15TiO₂ glass during the infiltration process in a porous alumina preform was investigated. Glass frits were prepared by melting the raw materials at 1500 °C for 60 min. The glass was infiltrated into the alumina preform at 1,150 or 1,200 °C for 60 min. The specimens were characterized by X-ray diffraction analysis and scanning electron microscopy. After the infiltration, it was possible to note that the devitrification process occurred in the remaining glass (excess glass that did not infiltrate in the preform), forming mostly aluminum borate and mullite crystalline phases. However, within the infiltrated composite no devitrification was noticed in the infiltrated glass. Possible explanations for this behavior are discussed.