Papers by Author: Janina Setina

Abstract: The new generation of high silica materials with high thermal resistance was created by leaching of chopped glass fibre. These materials with low thermal conductivity are inert to the majority of chemical reagents, resistant to organic and mineral acids, weak alkali, water and highpressure steam. High silica chopped strand mats are non-woven fabrics designed for using in a wide range of insulation and protection applications at temperature till 11000C. The technology and quality of leaching process of initial Si-Al-Na glass widely depends on quality of fibre surface characteristics, i.e., roughness of surface of glass filaments. The surface roughness of the fibre before leaching is a function of chemical durability, therefore it depend on content of Al2O3. The thermal conductivity (within 20…10000C) of chopped strand mats directly depends on the surface roughness. The morphology and compositional profiles of surface of glass fibre before and after leaching were investigated using AFM, SEM, X-ray microanalysis and X-ray powder diffractometer. The different defects for fibre with content of Al2O3 <2.5% and high roughness namely cracking and crystalline deposits of Na2SO4 on top and into pores of fiber after leaching have been identified. The presence of sodium ions on surface of fibre decreases the heat insulation properties of mats. The structure of glass filaments surface was investigated in order to clarify the influence of surface characteristics on thermal conductivity of high silica glass fibre non-woven fabrics.

Abstract: The article gives an overview of suitability of three kinds of phosphorus-containing glass systems: phosphate, alumosilicate phosphate and fluorophosphate for production of thick-films. Amorphous compositions based on metaphosphate glasses characterize high electric resistivity, thermal expansion coefficients matching with substrate, appropriate viscosity-temperature relationship, and suitable chemical reactivity, that they can be applied in thick-film technology for screen printed resistors on alumina substrate as an alternative of lead borosilicate glasses. Alumosilicate phosphate glasses are the base for the wide range of glass-crystalline high temperature materials (operating up to 10000C) for sealing of the silicon chip in microelectronics. Perfect adhesion of glass ceramics with substrate (the transition zone 5-7.5 μm) is provided by the formation of chemical bond with the oxidized surface of silicon and by the occurrence of analogous structural elements on the silicon surface and in the glass-ceramics. Due to the unique optical properties, low melting temperature of fluorine containing borophosphate glasses (FBP) can be used as brazing material (optical glue) for SiO2 glass optical fiber construction knots.

Abstract: Cordierite was obtained from the mixture of aluminum hydroxide, sand, different magnesium compounds by a solid-state reaction method. The effect of dolomite doping on phase-transformation kinetics and microstructure has been investigated during thermal treatment by keeping a stoichiometric cordierite compound. Adding of dolomite has been used as a flux for preparation of a cordierite precursor by a coprecipitation process. Subsequently, DTA and XRD analyses were conducted to identify the phases formed in the sintered products. Morphological changes of the ground mixtures and sintered product were observed using SEM. The crystallization process of metastable quartz like μ-cordierite can be obtained at 1250…13000C. In this range of temperature form other compounds, such as spinel, quartz. Increase of sintering temperature and prolonged holding times promote the formation of only one phase – indialite or α-cordierite, the hexagonal form of cordierite. Experimental observation shows two steps in the solid-state reaction. First step – formation of volatiles compounds and pores, second – formation and growing of crystalline phases. Evolution of CO, CO2 and H2O that occurred during the thermal treatment of compositions is very important fact in the nucleation process. The intensity of crystallization depends on the gas volume and amount of pore in the sample. The experiments indicated that the intrinsic concentration of volatiles like CO, CO2, H2O influence the appearance of the cordierite phase. SEM photographs sowed that crystallization of cordierite start on the surface of pore. Growth of α-cordierite inside of pores is considerably affected by the time of thermal treatment and amount of adding of dolomite. A remarkable change in peak intensity of XRD patterns of the compositions was observed. Up to 20 wt. % addition of dolomite to the precursor allowed the fabrication of synthetic cordierite at lower temperature.