Defect and Diffusion Forum Vols. 326-328

Abstract: This work presents a new analytical method for solving nonlinear heat conduction problems in arbitrary domains. The method is based on approximate mappings which transforms nonlinear partial differential equations into linear models which can be solved using standard techniques. In order to verify whether the proposed formulation can be employed to conceive new online control systems, numerical results are reported.

Abstract: This work presents a three-dimensional numerical solution for the diffusion equation in transient state, in an arbitrary domain. For this end, the diffusion equation was discretized using the finite volume method with a fully implicit formulation and generalized coordinates, for the equilibrium boundary condition. For each time step, the system of equations obtained for a given structured mesh was solved by the Gauss-Seidel method. The computational code was developed in FORTRAN, using the CFV 6.6.0 Studio, in a Windows platform. The proposed solution was validated using analytical and numerical solutions of the diffusion equation for different geometries (orthogonal and non-orthogonal meshes). The analysis and comparison of the results showed that the proposed solution provides correct results for the cases investigated. The developed computational code was applied in the simulation of the drying of ceramic roof tiles for the following temperature: 55.6 °C. The analysis of the results makes it possible to affirm that the developed numerical solution satisfactorily describes the drying processes in this temperature.

Abstract: Defect formation in yttria with a small content of acceptor impurities in equilibrium with a hydrogen-containing gas phase is studied theoretically. A statistical-thermodynamic description of the yttriagas equilibrium is based on the approach developed for compounds with a complex electronic structure [Phys. Stat. Sol. B (1991) Vol. 168, p. 233]. The considered model of electronic structure for Y₂O₃ includes, besides valence and conduction bands, acceptor and F-center states. The energy of F-centers was calculated in the framework of the variational quantum-mechanical approach combined with the molecular statics method. It is shown that acceptor states appreciably affect the thermodynamics of defect formation, while the F-centers contribution in a wide range of external parameters is small. The concentrations of defects (protons, oxygen vacancies, electronic defects) and the Fermi level position are determined as functions of temperature and gas phase parameters.

Abstract: A theoretical model, to predict effective heat storage coefficient (HSC) from the values of HSCs of the constituent phases and their volume fractions for real two-phase systems is presented and is extended to three-phase moist materials, assuming an effective continuous medium (ECM) approach. Particles are assumed to be ellipsoidal in shape and arranged in three-dimensional cubic array. The arrangement has been divided into unit cells, each of which contains an ellipsoid. The HSC of the unit cell has been determined by applying resistor model. To take account of the non-linear flow of heat flux lines in real systems, incorporating an empirical correction factor in the place of physical porosity modifies an expression for HSC. An effort is made to correlate it in terms of the ratio of HSCs of the constituents and the physical porosity. To test the validity of the derived expression, the HSC of some building materials saturated with different liquids have been determined. The HSC of metal powders and metallic oxides at varying temperatures have also been determined. A good agreement has been found between the experimental and the predicted values reported in the literature.

Abstract: In this work the effects of volume fraction at different milling times and impact forces, defined as the ball-to-powder weight ratio (BPR), on the elemental diffusion during mechanical alloying process of Al-4.5wt%Mg/TiC composite were evaluated and compared with the TiC free samples (Al-4.5wt%Mg alloy). X-ray diffraction patterns of the monolithic and composite samples imply the fact that a higher level of mutual diffusion of constituents, Al and Mg, happened in the matrix in the presence of TiC particles. This effect of the reinforcing particles can be attributed to the increased densities of dislocation and vacancy caused by the presence of TiC particles within the matrix-giving rise to increasing the micro-strain, lattice parameter and decreasing the crystallite size. Scanning electron microscopy (SEM) was used not only to study the morphology of the powders but also to show the fact that the TiC powders were distributed during MA process. The TEM and HRTEM results showed that powder produced in this work has a nanosize.

Abstract: In_0.25Co_4-xNi_xSb₁₂ skutterudites were synthesized by encapsulated induction melting and consolidated by hot pressing, and their thermoelectric properties were examined at temperatures from 323 to 823 K. A single δ-phase was obtained successfully by subsequent heat treatment at 823 K for 24 h. In_0.25Co_4-xNi_xSb₁₂ was an n-type semiconductor at all temperatures examined, indicating that Ni atoms acted as electron donors by substituting for Co atoms. The thermal conductivity was reduced considerably by In filling and Ni doping due to an increase in phonon scattering and impurity scattering. The thermoelectric properties were improved due to the low thermal conductivity as a result of In filling and the optimum carrier concentration caused by Ni doping.

Abstract: The area of actual contact of surfaces is essential for longevity and successful operation of mobile and immobile interfaces of machine parts. Wear resistance of friction surfaces, reliability adjustments, heat conduction, conductivity and several other functional characteristics of parts are closely related to actual contact area, and thus they influence the working ability of part surfaces. In this regards, the area of actual contact can be considered as one of the parameters of surface quality. This contact area presents a formed surface of plastic deformation, after the contact of the vibro-percussion treated environment or device, and is the essential process of consolidation of vibratory treatment and finishing. The formed plastic deformation surface is also a kind of micro relief surface, characterized by multitude closed and superimposed on each other traces of contact with the particles working environment cultivated surface. This paper presents the results of vibro-mechanical treatment research, its influence on treated surface quality and working ability of the samples contact surface made by hardened steel ShKh-15, the nickel steel 40HNS2MA and bronze alloy BROF7-0,2.

Abstract: Resin Transfer Moulding (RTM) as it is most known process in the Resin Injections family, is an extensively studied and used processing method. This process is used to manufacture advanced composite materials made of fibres embedded in a thermoset polymer matrix. Fibre reinforcement in RTM processing of polymer composites is considered as a fibrous porous medium regarding its infiltration by the polymer resin. In this sense, the present work aims the computational analysis of a fluid in a porous media for a RTM composite moulding by using the ANSYS CFX^® commercial software. In order to validate the numerical study of the fluid flow in a known RTM system, experiments was carried out in laboratory to characterize the fluid (vegetal oil) flowing into the porous media (0/90 glass fibre woven), were pressure and fibre volume fraction have been fixed. The numerical simulation provides information about volume fraction, pressure and velocity distribution of the phases (resin and air) inside the porous media. The predicted results were compared with the experimental data and its has shown a solid relationship between them.

Abstract: This paper presents a mathematical model to predict the behaviour of the God particle, the Higgs boson, which adds mass to elementary particles appearing and disappearing in the time of Planck. The phenomenon of turbulence in the Planck scale in the modelling of space-time is the base on which is sustained this work. We measured the flow of fluid through the boundary that contains the studied mass (composed of virtual particles with characteristics similar to the Higgs boson) in full bubbling in a gravitational field with enormous surface gravity by calculating the divergence, the rotational and circulation of the fluid. The results show evidence of mass transfer of the particles consistent with the Theory of Special Relativity. The gravitational field (with mass like field source) acts as a conservative field, since its circulation along any closed curve is zero. By Stokes theorem, the flow is irrotational and therefore without vortices. In two arbitrary points of the gravitational field is found that the mechanical energy (sum of kinetic and potential energy) of the particles is constant, satisfying the theorem of conservation of energy in this inertial system isolated from conservative forces. Green's theorem defines sources and sinks of particles around a singularity in the mass center. For heat flow, the sources represent the heat production and the sinks represent its consumption. The irrotational gravitational field where is hosted the God particle has electrostatic and gravitational potential energy.

Abstract: Chitosan is an abundant, natural polysaccaride obtained from fishing industry waste and films of chitosan also provide an efficient oxygen barrier. However, they are a poor water vapor barrier, which can be improved by incorporation of a hydrophobic compound, forming a emulsified film. Chitosan films were produced with the addition of palmitic acid lipid analysis and then the process in parallel with the diffusive permeability to water vapor. The objective of this work was to characterize the diffusion and water vapor permeability behavior of chitosan films and chitosan emulsified films.