Papers by Keyword: Silicates

Abstract: In order to achieve the goal of absorption of environmental pollutants, poly-component materials based on magnesium and calcium silicates - metal cations mineralizers – have been synthesized. The study of the processes of mineralization was carried out using model solutions containing soluble sulphates of copper, zinc, manganese and iron. The studies carried out have shown that the synthesized mineralizer based on calcium and magnesium silicates has a multicomponent structure with active electrochemically inhomogeneous centres on its surface as a result of breaking the Ca-O-Si, Mg-O-Si bonds, hydration and leaching of the Ca²⁺ and Mg²⁺ ions. In an acidic environment, the leaching reaction is activated due to H⁺ adsorption and the weakening of the bond between Ca²⁺ and O^2-, thus making the transition of Ca²⁺ into the liquid phase more advantageous. As a result, a negatively charged ≡Si-O-layer enriched with silicon is formed, which is able to interact chemically with heavy metal ions present in the electrolyte solution.

Abstract: The reversibility of phase transformations in Li₂MnSiO₄ and related materials during charge/discharge of the material is an important factor to enable the practical application of the cathode materials. However, the stability of this material is still unattainable. Here we report the computational identification of a new form of Li₂MnSiO₄ as a stable candidate with acceptable characteristics. The stability could arise due to the presence of the three-dimensional structure of the inorganic framework. The presence of a structure with a compact unit cell forms the basis for high capacity. Surprisingly it was found to have a stable analogue occurring in nature – Na₂CaSiO₄ with the same structure. Using this information the possible routes of obtaining such material are presented. The prediction of such material has been not found in the literature previously. Of course the problems such as phase transformations upon delithiation may exist, and to check the data the experimental and computer studies needed.

Abstract: As a potential candidate for the top coating in novel Environmental Barrier Coating systems, one representative of a Barium-Magnesium-Aluminium-Silicate family was produced in the form of the powder. Initial compounds were heat-treated to synthesize and the product was crushed in the ball mill device down to the fraction of 20 micrometers. In the next step, the atmospheric plasma spray (APS) technique was used to form a coating on a steel sheet substrate. The aim of this study was to obtain the most favorable technological parameters for the thermal spraying process and therefore two plasma spraying parameters for pure alumina or yttria stabilized zirconia, and other three experimentally designed ones were tested. Despite the same stand-off distance used for coatings manufacturing, thickness and porosity differed in order of tens of micrometers and several percent, respectively. Resulting coatings consisted of a mixture of amorphous and crystalline Al₂O₃, SiO₂ and MgO phases.

Abstract: The paper presents the results of the study of phase transitions in the system Sr-Sb-Si-O by means of X-ray diffraction, thermal analysis, dielectric spectroscopy. Four effects are observed in the interval from room temperature to 800°C. The first and last are chemical transformations due to dehydration and loss of oxygen, respectively. The second is a transition from tetragonal to cubic perovskite structure, and the third is disordering transition in oxygen sublattice possibly due to the desorption of structural water molecules

Abstract: Many physical effects, such as dc conductivity and percolation, depend on the morphology of the silicate structure and its relationship to adsorbed water. These effects play an important role in numerous technological applications, in geology, oil-extracting industry, and other practical fields. In this study, all the samples: natural montmorillonite, kaolinite, and сlinoptilolite with different exchangeable cations in their structures, – were stored in ambient air humidity. The investigation was carried by using two separate techniques, namely Dielectric Spectroscopy and a fractal analysis of electron micrographs. The aims of this work were to analyze the complex relaxation behavior of the relaxation process in temperature range –70°C ÷ +70°C and to determine the fractal dimensions of silicates from the dielectric response at percolation. Dielectric measurements in the frequency range of 1 Hz ÷ 1 MHz were performed using a BDS 80 Dielectric Spectrometer based on an Alpha Impedance Analyzer (Novocontrol). The micrographs were analyzed using a special Matlab based program. The analysis of aspects of the dielectric relaxation spectra related to percolation was used for the determination of the numerical characteristics of geometric heterogeneity of natural silicates. The percolation temperatures of the studied samples were determined. The percolation phenomenon in the silicates is related to the transfer of the electric excitation within the developed network of open pores due to the migration of protons and ions along the surface of connected pores on the outer surfaces of the granules. The analysis of these processes allows one to extract the fractal dimensions associated with the migration of charge carriers within the porous medium. Fractal dimensions of the silicates calculated in two ways: from dielectric spectroscopy study and from fractal analysis of the micrographs, – are in good agreement with each other. It was demonstrated that conventional method of the spatial fractal dimension determination using fractal analysis of electron micrographs leads to overestimation in the case of spatial fractal bounded by a surface fractal. The dielectric spectroscopy method is free from such overestimation.

Abstract: The objective of this paper is the surface modification of silica pigments layer of polyaniline (PANI), poly (p-phenylendiamine) (PPDA) and chemical layer of zinc ferrite ZnFe₂O₄. This layer promote adhesively-barrier properties of silica particles without surface-treated. This pigment was specified using physico-chemical parameters (oil absorption, critical pigment volume concentration, density, pH extract and the specific electrical conductivity of pigment extracts). An epoxy ester resin was used as binder for the organic coatings investigated. Organic coatings were prepared in the following volume concentration PVC = 10 %. Organic coatings prepared were subjected to measurement of physical-mechanical properties by the following tests: relative surface hardness, adhesion test, bend test, impact test. Organic coatings were subjected to the following corrosion tests: in an atmosphere of SO₂ with water condensation. The results of mechanical and anti-corrosion tests provide evidence that was met premise increase adhesively-barrier properties of newly developed coating films.

Abstract: The opportunity of production of effective non-cement binders with using of different morphological and structural types of aluminosilicates and silicates is studied on the basis of data of phase and structural features of natural raw materials – perlite and quartz sand.

Abstract: The thermal decomposition of wood treated with a series of silicates was characterized by thermogravimetric (TG) analysis, differential thermogravimetry (DTG), and thermogravimetry–mass spectrometry (TG–MS) analysis. The addition of these chemicals caused a decrease in the decomposition temperature, a reduction in weight loss, and an increase in the amount of char produced. The results showed that ion current intensity and ion peak area of the typical representatives of incombustible ion such as m/z = 18 and 44 MS signals were increased by the flame retardants but the inflammable ion such as m/z =12 and 28 MS signals were decreased at the meantime, which indicate that the flame retardants can significantly enhances the dehydration and inhibits the deploymerisation reaction of wood.

Abstract: Polymeric composite electrolytes (PCE) based on poly(ethylene oxide) (PEO) and mesoporous silicates as a filler material were fabricated, and investigated for understanding the effects of filler addition into the polymer matrix on the ionic conductivity. For a lithium battery application, it is necessary to increase ion conductivity of PCE by modification of microstructure. The ionic conductivity was enhanced with increasing MCM-41 contents due to the decreased crystallinity of PEO. Furthermore, the regular mesoporous structure could be functioned as an ion transfer channel for high ion mobility.

Abstract: SiC-composites are candidate structural materials for high temperature applications such as gas turbines. For this purpose, a suitable coating against high temperature oxidation is essential. The coating material selection was made by phase stability/durability under service environment, CTE matching, low elastic modulus and chemical compatibility with SiC. This work is to evaluate the microstructural quality of mullite and erbium silicate coatings on SiC fiber bonded composites. In this work, SiC-fiber bonded 2D-composite (TyrannohexTM) by Ube Industries Ltd., were coated with mullite and erbium silicate by plasma spraying. The thickness of mullite and erbium silicate coatings was determined to be 120 microns and 220 microns, respectively. The fabricated samples were diamond polished for cross-sectional analyses by optical and scanning electron microscopy. The coating-substrate interfaces have been found bit undulating. The bonding between mullite and the substrate was found insufficient as compared to that observed in the erbium silicate coated substrate. The cross-sectional analyses of erbium silicate coating revealed the presence of throughthickness micro- and macro-cracks. The width of the macrocracks was found in the range of 1-3 microns. It is conceived that the evolution of large concentration of through-thickness-cracks is due to the stresses in the coating. The most probable sources of stresses are the precipitation of various second phases in the coating materials and the thermal expansion mismatches that arise during cooling. The mullite coating on the other hand is not found with macrocracks and on the whole the cohesion within the mullite coating is rather strong. The cross-sectional examination also revealed the irregularly distributed pores and cavities in both coating systems that are typical of thermal sprayed coatings. The surfaces of the coatings are characterized of typical lamellar microstructure formed by the flattened platelets of individual particles. The size of these droplets ranges from submicrometer to several micrometers.