Defect and Diffusion Forum Vols. 273-276

Abstract: Recent results on radiotracer grain boundary diffusion of different solutes in the same high-purity polycrystalline copper are reviewed. The measurements were performed in extended temperature intervals satisfying Harrison’s B and C regime conditions at higher and lower temperatures, respectively. In the B regime, the triple product P = sδDgb was determined, while the grain boundary diffusivity Dgb was directly measured in the C regime (s is the segregation factor and δ the grain boundary width). Consequently, the segregation of different solutes in the copper matrix was determined for the true dilute limit conditions. The results on grain boundary diffusion and segregation are analysed in relation to the solute – solvent binding and solute – vacancy interaction in the bulk and in the grain boundaries. By increasing amount of the applied radiotracer the effect of solute concentration on grain boundary diffusion can thoroughly be examined. Grain boundary diffusion experiments on well-characterised bicrystals have been shown to be most suitable for such a study. In a radiotracer experiment, the complete solute segregation isotherm can be measured beginning already from a dilute solution in both, bulk and grain boundary.

Abstract: The mathematical model which allows us to describe, with the help of calculations of thermodynamic balance, the kinetics of barbotage of oxide melt by various reducing gases is offered. The algorithm of calculation is developed. The model is tested on system NiO-FeO-Al2O3-SiO2-CaO-Mg-COCO2. The comparative analysis of computation and experimental data has shown that the offered model can be used in the qualitative analysis of processes of interaction of multicomponent oxide melts with gasesreducers of various composition. The calculations describing the kinetics of reduction of nickel oxide by hydrogen in system NiO-CaO-B2O3 in an interval of temperatures 1473-1973 K are carried out.

Abstract: Equations for an estimation of hardness and durability of materials of particles of iron powders in various zones are received. The opportunity of reception of materials with physicomechanical properties above separate zones of particles is shown. By development of technological processes of manufacturing sintered details with demanded physicomechanical properties it is necessary to know the physical characteristics of particles of an initial material, and sintered ensemble with them and their possible limiting values. However, definition of separate mechanical characteristics of particles is impossible because of their small sizes and complex form. Authors attempt to define strength and fluidity of various zones of particles of iron powders and sintered materials on their basis, using a method of microhardness testing.

Abstract: Diffusion of fluids in polymers may lead to swelling, which induces stress-diffusion coupling. A simple coupling model is considered, where boundary conditions only are altered, and it leads to a sigmoidal water-uptake curve for a plate in water. Several other models are studied, which are able to induce similar sorption curves by using various boundary conditions, but comparisons between other predictions of the models reveal significant differences. Eventually, none of the models considered is able to reproduce all features of the coupling model.

Abstract: ZnO as a semiconductor is used in many applications such as gas sensor devices, laser and optoelectronic devices, photocatalysts, solar cells, and varistors. The applications and properties of ZnO nanoparticles highly depend on the size and morphology of these particles. In this research ZnO nanoparticles were prepared via chemical bath deposition at various temperatures in order to see the effects of synthesis temperature and also 2- methoxyethanol (2-ME) as a novel solvent on the morphology of obtained nanoparticles. For synthesizing of ZnO nanostructured materials, 2-ME has been highly used in sol-gel process but it is the first time that it is used in the chemical bath deposition process. For this purpose 1 M solutions of zinc acetate dehydrate in 2-ME were prepared and added to the solution of NaOH in the same solvent dropwisely. Monoethanolamine (MEA) was used as surfactant. The synthesis temperatures were 30°C, 60°C and 90°C. After filtering and drying, morphologies of obtained nanoparticles were characterized and compared.

Abstract: ZnO nanoparticles because of their interesting properties and various morphologies, has become one of the most attractive nanomaterials for research objectives. Its significant properties has made it applicable in UV-Light emitters, varistors, transparent high power electronics, gas sensors, etc., [1]. Many approaches have been used to obtain ZnO nanoparticles, including: Hydrothermal [2], Solvothermal [3], Reverse micelles [4], Sol-Gel [4], Sonochemical [5], and Chemical Bath Deposition [6], etc. Among these, hydrothermal and alcohol-thermal methods have been extremely investigated. In this paper, buthanol as a solvent is used for synthesis of Zinc oxide at 130°C and 150°C at different reaction periods. Also the effects of different surfactants including: N_Cetyl_N,N,N,_trimethyl ammonium bromide (CTAB), Poly vinyl pyrolidon-K90 (PVP), Poly ethylene glycol-15000 (PEG) on obtained morphologies were investigated extremely. X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) were used for characterization of nanoparticles.

Abstract: A mechanism for the combustion synthesis of TiC+Al2O3 was proposed in a mechanically activated TiO2-Al-C system. As-milled powder mixture was analyzed using XRD and TEM techniques where no chemical reaction and/or inter-particle diffusion were identified. The results obtained from DTA tests on unmilled powder revealed that the combustion synthesis occurred in a single step at 962 °C while the synthesis of mechanically activated powder mixture occurred in three different stages. The XRD analysis on the synthesized samples of 8 hour premilled powder at different temperatures showed that the three stages were as follows: First the reaction between Al and TiO2 takes place forming Al3Ti, Ti2O3, and Al2O3 at 700 °C. In the second step, Ti-rich titanium aluminides (AlTi, AlTi2, and AlTi3) and TiO, are formed at 923 °C, and finally the formation of TiC+Al2O3 is completed at 1329 °C.

Abstract: The starting reaction in the combustion synthesis process in TiO2-Al-C system leading to TiC+Al2O3 composite was evaluated using a combination of Differential Thermal Analysis (DTA), X-Ray Diffraction (XRD) and Transmission Electron Microscope (TEM). Double phases in 3TiO2- 4Al-3C system were milled separately and then the third phase was added according to the stoichiometric reaction for 3TiC+2Al2O3 composite formation. The combustion synthesis temperature was observed to decrease from 962 °C to 649 °C after mechanical activation of TiO2/Al mixture for 16 hr. On the contrary, the mechanical activation of Al/C and TiO2/C mixtures for 16 hr made the reaction temperature increase to 995 °C and 1024 °C, respectively. TEM and XRD patterns of as-milled powders showed that the reaction temperature changes could be due to increased TiO2 and Al interface area. In addition, DTA experiments showed that for the sample in which TiO2 and Al were mechanically activated the reaction occurred at the temperature even lower than the aluminum melting point.

Abstract: In this paper, a Lattice Monte Carlo method is used to determine the effective thermal conductivity in two dimensional models of adhesively bonded metallic hollow sphere structures (MHSS). In contrast to earlier approaches, more realistic distributions of spheres without the simplification of cubic symmetric arrangements are considered in this study. For the Monte Carlo analyses, two-dimensional periodic lattices representing different cutting planes through MHSS are generated. Therefore, an algorithm is used which sequentially fills the lattice by adding cut spherical shells and inclusions in the matrix. Another focus of this work is the analysis of the influence of different geometric circle distributions on the effective thermal conductivity. The findings of the random arrangements are also compared to a regular primitive cubic arrangement and with a Maxwell-type approach.

Abstract: In this paper, the increase of the effective thermal conductivity of paraffin based heat sinks is investigated by making use of cellular metallic matrixes with open cells which are introduced in the thermal low conductive paraffin wax. Lattice Monte Carlo analyses are conducted on different model geometries of such composites composed of a cellular matrixes and paraffin wax. The dependence of the effective thermal conductivity on the cell geometry and the metal foam matrix material is analysed. Furthermore, a diamond coating is simulated in order to estimate its influence on the effective thermal conductivity.