Defect and Diffusion Forum Vol. 364

Abstract: This work applies a 3D multi-scale bottom-up approach for modeling the processes of diffusion and reaction-diffusion in porous catalyst layers. The performance of the random pore model to predict effective transport coefficients are compared with the results of the multi-scale diffusion model. The results of the 3D multi-scale diffusion model are employed in a 1D pseudo-homogeneous reaction-diffusion model with a relative good agreement with the 3D multi-scale reaction-diffusion model. Furthermore, the former multi-scale model was coupled to a full-scale reactor model with good results and high advantages in terms of computational time savings.

Abstract: In this work, the effect of catalysts, temperatures and different types of vegetable oil on the production of synthetic bio-fuel via a hydro-processing process called as a hydro-cracking reaction by high pressure pack bed reactor is investigated. Firstly, H₂ gas (95% purity) was fed into the reactor together with palm oil under two different catalysts (Pd/Al₂O₃ and Pt/Al₂O₃) separately packed in the reactor. The effect of different temperatures (500°C and 530°C) was investigated and the pressure was applied and maintained at 5 MPa for both temperatures. The results revealed that, when the Pd/Al₂O₃ catalyst was used the highest bio-fuel (approximately 90% at 500°C) after distillation can be produced. Then, palm oil and soybean oil were used to compare in the efficiency of kerosene fuel production. The reaction was operated at 500°C, 5 MPa under H₂ pressure on the presence of 0.5% Pd/Al₂O₃. The bio-fuel achieved the highest yields at about 88% and 69% in cases of palm oil and soybean oil. It was also classified as kerosene yield approximately 70% when palm oil was used as a feed stock and at about 55% for soybean oil. Some properties of the kerosene product were characterised. The viscosities were obtained at 1.75 and 1.84 mm²/s and provided 43.06 and 45.85 MJ/kg of heating combustion values when palm oil and soybean oil were used. In addition, the carbon distribution of the synthetic kerosene produced from palm oil was clearly shown to be in the range of C₁₁-C₁₃ which is similar to kerosene fuel obtained from petroleum.

Abstract: The aim of this study is to resolve the phenomenon of formation of mesoscopic structures on the surface of heteroepitaxial thin film system due to surface diffusion by considering the effects of both surface and interface stresses. Elastic stress field caused by curved surface is solved by using the constitutive equations of linear elasticity for the bulk and surface phases. Based on the method of superposition, a boundary perturbation technique, Goursat-Kolosov complex potentials and Muskhelishvili representations, the boundary value problem is reduced to the successive solution of a system of singular and hypersingular integral equations for any order of approximation. This solution and thermodynamic approach allows us to derive a governing equation which gives the amplitude changing of a surface roughness with time.

Abstract: This paper presents some non-destructive evaluation methods of materials and structures, such as: pulse method, resonance method, direct measurement of the propagation velocity, pulse-echo method, impact-echo method, acoustic emission evaluation, interferometry and infrared thermography. The methods are suitable for non-metallic materials, with rugged and non-homogeneous structure, high attenuation coefficients for ultrasound propagation waves into materials, composites multilayer structures, etc. Some relevant measurement parameters are presented too.

Abstract: A nanostructured iron, elaborated from pure elemental powders by mechanical milling at high energy was characterized by different types of technical of analysis. Scanning electron microscopes (SEM) and laser scattering machine have showed the variation in the size and the shape of particles according to different milling times. Powders obtained were characterized with X-ray diffraction (XRD) , the latter diffraction patterns indicated the body centered cubic (bcc) structure. The crystalline grain was about 13 nm size after only a few hours of milling time. The measurement of both coercive field (H_c) and maximal magnetization (M_s) revealed a change in the magnetic behavior of our samples.

Abstract: The structure and morphology of Nb₃Sn layers in superconducting Nb/Cu-Sn composites with ring (tubular) Nb filaments have been studied by transmission (TEM) and scanning (SEM) electron microscopy after various regimes of diffusion annealing. It is demonstrated that the tubular geometry of Nb filaments, in which Sn diffuses from the bronze matrix both from inside and outside, ensures practically complete transformation of Nb into the superconducting Nb₃Sn phase. Besides, at certain regimes of the diffusion annealing this geometry enables the improvement of the superconducting layers morphology compared to that of wires with continuous filaments, namely, to obtain wide Nb₃Sn layers with fine equiaxed grains and to avoid the formation of columnar grains, which promotes enhanced current-carrying capacities of the wires.

Abstract: Grain boundaries in coarse-grained Mo with grain boundaries of recrystallization origin and in ultrafine-grained (UFG) Mo obtained by high pressure torsion have been studied by the emission Mössbauer spectroscopy on the ⁵⁷Co (⁵⁷Fe) nuclei. It is demonstrated that Co atoms diffuse along grain boundaries by interstitials. The temperature dependence of grain-boundary segregation factor of Co in coarse-grained Mo has been determined. It is shown that the state of Co atoms in grain boundaries and near-boundary areas in UFG Mo differs from that in coarse-grained Mo.

Abstract: In this study, a Cu-Sn sintered bronze, used largely for con-rod bushing and automotive transmission, was treated by ultrasonic nanocrystalline surface modification (UNSM). Then, Vickers hardness and microstructural evolution of the treated region were investigated by using scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM). The hardness of the treated surface doubled, which is attributed to the developed of nanoscale grains, deformation twins, and high density of dislocations induced by the UNSM. Microstructural modification beneath the UNSM treated surface was typically characterized with increase of the depth: (i) nanoscale grains (top surface), (ii) intersection of deformation twins (~30 μm), (iii) high density nanoscale twin/matrix lamellae (~50 μm), (iv) interception of micro band and deformation twins (~100 μm), (v) dislocation arrays (~200 μm), (vi) low density dislocations (~300 μm) and (vii) pre-existing coarse grains and annealing twins in unaffected region (400 μm ~deeper).

Abstract: Ti and its alloys are widely used as biomaterials. Their main properties are excellent corrosion resistance, relatively low elastic modulus, high specific strength, and good biocompatibility. The development of new Ti alloys with properties favorable for use in the human body is desired. To this end, Ti alloys with Mo, Nb, Zr, and Ta are being developed, because these elements do not cause cytotoxicity. The presence of interstitial elements (such as oxygen and nitrogen) induces strong changes in the elastic properties of the material, which leads to hardening or softening of the alloy. By means of anelastic spectroscopy, we are able to obtain information on the diffusion of these interstitial elements present in the crystalline lattice. In this paper, the effect of oxygen on the anelastic properties of some binary Ti-based alloys was analyzed with anelastic spectroscopy. The diffusion coefficients, pre-exponential factors, and activation energies were calculated for oxygen and nitrogen in these alloys.

Abstract: Using solid-to-solid couples investigation, this study characterized the reaction products evolved and quantified the diffusion kinetics when pure Mg bonded to AA6061 is subjected to thermal treatment at 300°C for 720 hours, 350°C for 360 hours, and 400°C for 240 hours. Characterization techniques include optical microscopy, scanning electron microscopy with X-ray energy dispersive spectroscopy, and transmission electron microscopy. Parabolic growth constants were determined for γ-Mg₁₇Al₁₂, β-Mg₂Al₃, and the elusive ε-phase. Similarly, the average effective interdiffusion coefficients of major constituents were calculated for Mg (ss), γ-Mg₁₇Al₁₂, β-Mg₂Al₃, and AA6061. The activation energies and pre-exponential factors for both parabolic growth constant and average effective interdiffusion coefficients were computed using the Arrhenius relationship. The activation energy for growth of γ-Mg₁₇Al₁₂ was significantly higher than that for β-Mg₂Al₃ while the activation energy for interdiffusion of γ-Mg₁₇Al₁₂ was only slightly higher than that for β-Mg₂Al₃. Comparisons are made between the results of this study and those of diffusion studies between pure Mg and pure Al [1] to examine the influence of alloying additions in AA6061.