Synthesis and Use of Polyoxychloropropylen-Epoxymethacrylate Oligoesters as Active Modifier of Epoxy Diane Resin Ed-20
Abstract— The synthesis of polyoxychloropropylenepoxymethacrylate oligoesters by esterification of polyoxychloropropylenetriepoxide by methacrylic acid has been carried out. It has been established that by varying the conditions of carrying out of the reaction, one can prepare, mainly, the mono-, di- and trimethacrylic oligoesters. On the basis of epoxy diane ED-20 and synthesized polyoxychloropropylenepoxymethacrylate oligoesters as modifiers there have been prepared the self-extinction compositions, which after curing by N, N1–diaminodiphenylsulfone possess higher physical-mechanical, adhesion and heat-physical properties.
Keywords— polyoxychloropropylenetriepoxide, ED-20, diaminodiphenylsulfone, methacrylic acid, epoxymethacrylate, methacrylate oligoesters, self-extinction compositions.
Abstract—Barium titanate (BaTiO3) doped with rare-earth elements (REE) is used as dielectric in the manufacture of multilayer ceramic capacitors (MLCCs). The most common REE oxide employed as dopant for this application is Y2O3. The behavior of the Y3+ in the BaTiO3 structure depends on its concentration and the sintering conditions, among other factors, which can induce the formation of secondary phases that are a potential cause a detriment to the electrical properties of BaTiO3. The purpose of this work is to perform a phase characterization of BaTiO3 doped with different concentrations of Y2O3, validating its possible contribution to the formation of secondary phases. The role of Y2O3 was evaluated on two kinds of raw materials. The first one is pure BaTiO3 (< 100 ppm Y) and the second kind is a commercial formulation designed for MLCCs known as X7R (-55°C and 125°C, 15% tolerance), which among other elements, already contained 1 wt% of Y2O3. High concentrations of Y2O3 (1% up to 20 wt%) were used aiming to promote structural changes, and even the formation of secondary phases in amounts suitable to be detected by X-ray diffraction. Heat treatment of powder and sintering of ceramics (powder compacted at 2 MPa) were conducted in air (1310°C in air for 3 h, two steps: 1350°C then 1150°C 15 h). A phase transition from tetragonal to a mixture of tetragonal and cubic was observed as Y2O3 concentration increases in the thermally treated powder and in the corresponding ceramics. Commercially formulated powder showed higher densification than pure BaTiO3, and produced cubic structure at higher Y2O3concentrations. The phase Ba6Ti17O40is detected in the 20 wt% Y2O3-doped sample.
Keywords—BaTiO3, doping, Y2O3.
Determination of Radio Frequency Attenuation Signals of Ajilete FM (92.1MHz) and Compared with Existing Friis Formula, along Gambari-Oyo Road, Nigeria
Abstract— This work measured experimentally, and calculated theoretically using the existing Friis Fomula, the Attenuation of 92.1 MHz (Ajilete FM) Signals along Gambari(Lat 8o291N; Long 4o291) – Oyo-Road(Lat 7o501N; Long 3o561E), Oyo State Nigeria. The two results were compared. The experimental Measurement campaign was achieved by using an appropriate design dipole antenna, well matched to (810 GSP Analyser), to determine the attenuation. The calculated results correlated very well with the measurements (Correlation Coefficient Value R2=1). But, they are not accurate when compared with the measurements (Chi- square values equal zero for received power, measured attenuation). The inaccuracies of the results for the existing formula with the measurements may be due to hills, valleys, trees and bends along the links. Hence the accuracy of the model used can only be effectively confirmed in areas free of the obstacles mentioned above. By applying LEAST SQUARE fit method to the experimental measured data, the analytical models, P(x)= 0.0154x2-1.3575x-38.7620 and A(x)= 0132x2 -1.2464x-104.8487, in the form of polynomial of degree two, were obtained respectively for received power and measured attenuation. The analytical model obtained is therefore recommended for use in an area characterised with bends, valleys, hills and trees, since the model has taken into consideration all these factors. In addition, repeater stations should be installed for effective transmission and for wider coverage in forested and valley areas. Moreover, transmitter of higher value like ten kilowatts should be employed for long distance transmission.
Keywords— Attenuation, Dipole, transmitter, model polynomial, Friis Fomula.
Abstract—The present paper reports the kinetics of soybean and sunflower oils’ ethanolysis. The transesterification reaction was carried out using a molar ratio of ethanol to oil of 9:1 and 1.0 wt% of sodium ethoxide as catalyst under stirring of 400 rpm. The reactions were performed in a stirred batch reactor at three different temperatures (308.15, 323.15 and 338.15 K) over a period of 120 min. The concentration of compounds was analyzed by High-Performance Size Exclusion Chromatography (HPSEC). The kinetic model assumed that ethanolysis occurs in a sequence of three reversible steps with the production of di- and monoacylglycerols as intermediate components. Based on the modeling approach it was possible to determine the rate constants of reaction and activation energies for the transesterification process of soybean and sunflower oils. Despite the phase splitting, no mass transfer control was observed and the proposed mathematical model fitted well the experimental data.
Keywords: Ethanol, ethylic biodiesel, kinetics, soybean oil, sunflower oil.
Effect of different sulfur content in Natural Rubber mixtures on their thermo-mechanical and surface properties
Abstract— In this study, a field experiment was conducted to find out the effect of different levels of sulfur on natural rubbers mixtures. Vulcanization is a chemical process for converting natural rubber or related polymers into more durable materials by heating them with sulfur other equivalent curatives with accelerators. These additives modify the polymer by forming cross-links (bridges) between individual polymer chains. Vulcanized materials are less sticky and have superior mechanical properties. The results indicated that the application of sulfur -as a vulcanasing agent-had significant effect on mechanical (Shore A hardness test), thermal (DSC calorimetry) and surface-optical properties (SEM microscopy) of mixtures.
Keywords— vulcanization, sulfur, natural rubber, additives, cross-links.
Abstract— To ensure good adhesion between a 200 nm thick silicon dioxide layer and a 4.5 μm thick hardcoat polymeric coating, a better understanding of mechanisms of adhesion at this interface is needed. To reach this purpose, focus is placed on two axes: characterizing mechanical properties of materials composing the system and in parallel, finding an applicable and effective method to quantify adhesion. Small dimension of SiO2 thin film makes it challenging to accurately characterize it. Hence the use of both nano-indentation and AFM to attempt assessment of SiO2 thin film elastic modulus Ef; taking into account limitations and uncertainty associated with each technique. Elastic modulus of SiO2 thin film determined by nano-indentation is roughly 50 GPa on a wafer substrate and 15 GPa on a lens substrate. As for AFM, modulus measured is approximately 56 GPa on a wafer substrate and 22 GPa on a lens substrate. This highlights significant influence of substrate for both techniques. Impact on mechanical properties between SiO2 thin films under different intrinsic stresses was also investigated. Results suggest that higher density of SiO2 thin film leads to higher elastic modulus.
To quantify adhesion, micro-tensile and micro-compression tests were performed. Micro-tensile experiments give ultimate shear strengths of hardcoat-substrate interface ranging from 9 to 14 MPa. Values of energy release rates of SiO2 / Hardcoat, range from 0.1 J/m² to 0.5 J/m², depending on moduli values found on wafer or lens substrate.
Keywords— Adhesion, mechanical properties, oxide thin film, polymer substrate.