Defect and Diffusion Forum Vol. 332

Abstract: In this paper, the application of the photo-acoustic method to study the thermal properties of modified 9Cr-1Mo Steel is described. The photo-acoustic measurements are carried out for the thermal properties of modified 9Cr-1Mo steel samples of various thicknesses. The theoretical basis for quantitative measurements is discussed, together with the advantages and limitations of these methods as compared with conventional measurements.

Abstract: The present study aims to develop silica sand nanoparticles using the ball-milling process and to utilize these nanoparticles as reinforcement for iron-based metal matrix composites. Iron-based metal-matrix composites with 5, 10, 15 and 20wt.% of the processed silica sand nanoparticles were developed using powder metallurgy technique and sintered at 900°C, 1000°C and 1100°C. The results showed that the addition of silica sand nanoparticles to iron as reinforcement decreased the green density, albeit with an improvement in sintered densities. It was also observed that the increase in the sintering temperature results in an improvement of microstructure and microhardness of the composites. The maximum hardness of 168HV in iron-based composites was found with the addition of 20wt.% of silica sand nanoparticles at a 1100°C sintering temperature. It is proposed that the mechanism for the occurrence of this observed increment in microhardness is due to diffusion of silica sand nanoparticles into porous sites of the composites, resulting in the formation of FeSi phase.

Abstract: The result of positron lifetime measurements of a defected 5251 Al alloy is reported. Positron lifetime is measured as a function of the thickness reduction of the sample which shows a nearly linear increase and then becomes constant; which can be considered to be a reason for the defect movement saturation. The trapping rate, trapping efficiency, trapping cross-section, defect concentration and defect density of positrons are also measured for the sample concerned. The behaviors of these parameters are matched with theoretical calculations. Data are analyzed using the PATFIT88 computer program.

Abstract: Al 6061 alloy matrix reinforced with the coated B₄C particles have been used to investigate the accuracy of a novel optimization method. Population-based optimization was inspired by the swarming behavior as is displayed by a social behavior being influenced by other individuals. The present article focuses on a method of re-evaluating a number of randomly chosen sentry particles to detect the change of environments. A comprehensive population-based optimization method was developed to optimize the mechanical and tribological properties in metal matrix composites using Multi-strategy ensemble particle swarm optimization. In this method, the particles are divided into two parts which are considered to play different roles in searching for dynamic environments by using different strategies. The global best used in part one is the best solution found by all particles, both in part one and part two.

Abstract: To the best of our knowledge the difference in the magnetic properties of ions like Gd (7.94 μB) and Pr (3.58 μB) on the electrical properties of ZnO-varistor have not been studied. To clarify this effect, the binary systems, ZnO-Gd₂O₃, ZnO-Pr₆O₁₁ and the ternary system ZnO-Gd₂O₃-Pr₆O₁₁ were studied. The ceramics were prepared according to the chemical formula; (100-X) mol% ZnO - (X) mol% Y, where X = 0.5, 1, 2, 3.5, 5, 6, 7.5, 9 and 15, Y is Gd₂O₃, Pr₆O₁₁ or Gd₂O_{3 +} Pr₆O₁₁. The samples have been sintered at 1200°C, 1250°C, 1300°C, 1350°C and 1400°C for 1 hr. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDAX), (JxE), (CxV) and Electron Spin Resonance (ESR) have been studied and discussed. Utilizing J-E characteristics, the non-linearity coefficient (α), leakage current (Lg) and breakdown electric field (E_o) have been determined. In the present study, the effect of the magnetic properties on the non-linearity parameters was not clear and the non-linearity characteristics mainly depend upon the microstructure of the system. The ternary system (94%ZnO-4%Pr₆O₁₁- 2%Gd₂O₃) is superior to the binary systems, and can readily serve as a high-voltage varistor.

Abstract: Production of saline formation water from the storage formation in sufficient amounts helps to control the pressure increase during CO₂ storage in saline aquifers. In this paper, we present an engineering design to control the pressure build-up during CO₂ storage in deep saline aquifers and we propose that the extracted saline formation water can be processed at the industrial level in order to produce commercial salt. We investigated the effects on various aquifer properties of pressure increases. Several design options for the injection operations are investigated: injection of CO₂ without saline formation water production, injection of CO₂ with one production well and, finally, injection of CO₂ with one left side and one right side production wells. We showed that an increase in saline formation water production rate leads to pressure build-up decreases, when the production rate was tripled (from 61.42kg/s to 184.26kg/s); the maximum pressure was decreased by about 15bar. About a half of base case temperature (89°C to 45°C) increased the maximum pressure by about 35bar. The pore compressibility which is a key parameter defining the pressure response to CO₂ injection has also been investigated whereby an increase in pore compressibility leads to decreases in pressure build-up. Simulation results showed that the introduction of two wells (left side and right side of the production well) increases more or less the horizontal migration of the CO₂.

Abstract: Positron annihilation lifetime spectroscopy (PALS) is one of the unique tools for studying free-volume defects in solid media. The microhardness test offers a simple and nondestructive tool for investigating the mechanical behavior of polymer materials. Polyallyl diglycol carbonate (CR-39) track detectors have a variety of applications in science and technology. PALS measurements and microhardness tests were verified for CR-39 irradiated with different doses of alpha particles (0 - 69.20 mGy). The variations in free volume hole size and fractional free volume were obtained by using the PALS method. The small free volume hole sizes were found at doses 27.68 and 44.98 mGy. The microhardness test for the two doses yielded medium values.