Papers by Keyword: Diffusion

Abstract: The research presented in this scientific paper focuses on modeling the dynamics of multicomponent systems with particles of different geometries using the GROMACS software package. Three main types of particles were analyzed in the study: spheres, ellipsoids, and plates, each of which has its own unique geometric characteristics that affect their behavior in the environment. The modeling allowed us to investigate the influence of particle shape on their diffusion, self-organization, and interaction between particles of different shapes. In particular, spherical particles, having an isotropic geometry, show the highest diffusion coefficient, since their symmetrical structure minimizes the resistance of the environment. This, in turn, makes them ideal for modeling simple interactions in liquids or colloids. Ellipsoidal particles, due to their anisotropy, have a slightly reduced diffusion coefficient, since their orientation in space affects the motion. Plates, which have a significant surface area relative to the volume, demonstrate the lowest diffusion rate, which is associated with a large interaction with the environment and the resistance created by their geometry. The results of the study also showed that the diffusion coefficient decreases with increasing particle size for all types. At the same time, spheres demonstrated the highest diffusion coefficient at the same size compared to other geometries, while plates have the lowest values ​​of this indicator. Analysis of the trajectories of particle motion in space using the GROMACS software allowed us to assess the influence of geometry on particle mobility. It was found that spheres exhibit the largest displacement amplitude, which indicates their high mobility and chaotic nature of the motion. Ellipsoids have a more stable motion with smaller displacements, which is associated with their geometric anisotropy. Plates, due to the large resistance of the environment, have the smallest displacements, which indicates limited mobility. It should be noted that the obtained research results open up opportunities for a deeper understanding of interactions in complex multicomponent systems and can be useful for further research in various fields. It is also worth noting that the comparison of different types of particles with different geometries and their influence on diffusion processes allowed us to obtain valuable information for improving models and practical applications in relevant fields of science and technology.

Abstract: Titanium is widely used in aerospace and medical industries for its high strength-to-weight ratio and corrosion resistance, while Inconel 718 is favored in aerospace and power generation for its exceptional mechanical strength and oxidation resistance at high temperatures. It’s challenging to directly combine the Inconel 718 and the titanium, so the interlayer of vanadium is used which causes the strengthening of the bond by the formation of inter-metallics (TiaNib, NixVy). In this study, the RVE model was developed in order to examine the mechanical properties (i.e. Modulus, Poisson ratio) of the inter-metallics, by examining their microstructures. Furthermore, nanoindentation techniques are employed across different zones of the weldment to determine the modulus and hardness values. At the vanadium-Inconel interface, hardness and modulus values were observed to range from 2 to 8.5GPa and 130 to 205GPa respectively. The maximum error in hardness between the experimental and simulation was 3.75%. The pile up behavior was also examined in the simulation setup to determine the amount of plastic zone in the indent.

Abstract: This study investigates the drying kinetics of Irish potato slices using an Arduino controlled convective heat dryer. The experiment examines drying temperatures of 60, 65, 70, and 75°C, coupled with potato slice thicknesses of 3 and 5 mm. The drying process is crucial in preserving food products and extending their shelf life. Understanding the drying kinetics of potato slices under different conditions is essential for optimizing the drying process and maintaining product quality. The experimental setup allows for precise control of drying parameters, facilitating accurate data collection. The research aims to analyze the drying characteristics, including drying rate, moisture content, and drying time, at various temperature and thickness combinations. From the mathematical models obtained, it is evident that correlation coefficients closest to unity is at 70°C for chip thickness of 3 mm whereas the correlation coefficients closest to unity is at 60°C for chip thickness of 5 mm. Also, it is clearly observed that the efficiency of the system is highest with chip thickness of 3 mm dried at 70°C and performance evaluation results indicate that dryer efficiency is contingent on both temperature and thickness of the chips. These findings contribute to enhancing the efficiency and effectiveness of convective heat drying methods for potato slices, offering insights into temperature and thickness effects on the drying process. This study provides valuable information for food processing industries seeking to improve drying techniques for potato products.

Abstract: Semiconductor devices rely on the incorporation of donor and acceptor atoms into the crystal lattice to form locally doped regions. For dopant atoms incorporated into SiC by ion implantation, a high-temperature annealing step is required to achieve electrical activation. This annealing step is accompanied by redistribution of the implanted atoms. The influence of the annealing parameters on dopant redistribution is crucial when aiming for ever smaller device dimensions. In this work, we present a consistent analysis of the diffusion of Al implanted in 4H-SiC after high-temperature annealing at 1650 °C and 1800 °C for different annealing times. We identify the equilibrium diffusion coefficient at long annealing times from Al profiles obtained by SIMS analyses for both annealing temperatures. The temperature dependence is determined using an Arrhenius representation. This allows to quantify the equilibrium diffusion lengths for the actual temperature profiles, including heating and cooling rates. We find that the measured diffusion lengths for short annealing times are larger than expected from equilibrium diffusion and attribute the excess length to transient enhanced diffusion. Comparing the transient diffusion lengths of room-temperature and 500 °C-implanted samples, we conclude that the transient behavior is likely related to residual crystal damage induced during the implantation process.

Abstract: Hydrogen is an impurity that is often present in LiXO₃ (X= Nb, Ta) single crystals and related materials. In this context, the diffusion of hydrogen is an important process because it may influence the overall conductivity of the material. We investigated the diffusional hydrogen uptake in LiNb_0.15Ta_0.85O₃ single crystals at 600 °C. For the experiments, O₂ is bubbled through liquid deuterated water (D₂O), which leads to a saturation of the gas atmosphere with D₂O that is incorporated into the crystal during isothermal annealing. The diffusivities of deuterium during uptake were determined by infra-red spectroscopy. We identified a fast process that can be associated with tracer diffusion and a second slower process with an almost three times lower diffusivity.

Abstract: In sintering simulation, there are basically two approaches: microscale simulation, in which distinct particles or pores are regarded, and macroscale, where the porous body is regarded as continuum with variable density.Material parameters of the latter can be determined by experiment or by microscale models.Current microscale sintering models mainly use circular resp.~spherical particle geometries to represent the actual shape of real particles.However, sintering behavior is heavily dependent on the morphology of the powder particles, since sintering progress is driven by reduction of the bound surface energy.So current models neglect the influence of local contact morphology.Here, a finite differences based microscopic sintering model is presented, which is capable to work with irregular particle geometries.Asymmetric particle contacts in shape and substance are possible within.The differences between circular particle contacts and asymmetric ones are investigated.Furthermore, a statistical way of describing the morphology of powder particles and its inclusion into sintering simulation using Monte Carlo techniques are shown.Morphology data are obtained from microscopic imaging by extracting the 2D contours.The particles' contour lines are fitted to a parameterized shape function including ovality and first order waves to obtain a description of the particles' fine shapes.From the statistical distribution of the shape parameters, randomized particle groupings are sampled as input for microscopic sintering simulation.Statistical analysis of the samples' sintering behaviors leads to statements about the powder's.Comparisons to classical spherical modelling are given.

Abstract: The temperature dependence of the diffusion coefficient in metallic glass-forming systems do not follow the Arrhenius behavior over a wide temperature range. Instead, it exhibits a kink behavior at around the glass transition temperature. Some researchers associate this behavior to the difference in the diffusion mechanism operating in the glassy and the supercooled liquid state, whereas others do not support this view. In addition, usually, the temperature dependence of the diffusion coefficient is analyzed by splitting the temperature range into two regions, above and below the glass transition temperature. In the present study, we developed an analytical theory that describes the continuous variation of the diffusion coefficient across a temperature where the kink behavior is observed. According to the theory, the kink behavior arises from the freezing of free volume available for diffusion by lowering the temperature. A connection to the vacancy mechanism of diffusion has been also pointed out.

Abstract: Aluminium and titanium are currently in demand as lightweight materials. However, their combination is challenging due to their significantly different thermo-mechanical properties. Here, solid-state joining processes such as Friction Stir Welding open up new opportunities. Within this study, four commercial aluminium alloys (AA2024, AA5754, AA6056 and AA7050) were welded to Ti6Al4V. The results show a direct relationship between the solidus temperature of the aluminium alloys, the process temperature, energy input and resulting lap-shear strength. Regardless of the process parameters, AA5754 and AA6056 with higher solidus temperatures (600 °C and 555 °C) show superior bonding strength compared to AA2024 and AA7050, having a lower solidus temperature of 500 °C and 490 °C, respectively. Therefore, it is assumed that the maximum process temperature, proportional to the solidus temperature, has a major influence on the bonding. This, conversely, would imply that there is a physical limitation in the achievable joint strength between aluminium and titanium alloys as the required process temperature would exceed the solidus temperature of certain alloys. This assumption is verified for AA7050 by systematic variation of the rotation speed and therefore process temperature.

Abstract: In this work, the preparation and processing of aluminum-copper alloys, which added amounts of copper to aluminum in different parentages (2, 4, 5%) so that it does not exceed the saturation limit for aluminum (6% Copper). After adding these specific amounts of copper to aluminum, have been melting each alloy to thaw copper in aluminum fully and diffusion copper atoms in it, and after that the specimens were prepared and quenched at 8-30 hours and rapid cooling in the water, and then were studied parameters of heat treatment and different percentages of copper. It is clear from the schemes and experimental results that each weight ratio of copper in aluminum has a different approach to reach the best mechanical properties. After performing mechanical tests and tests, it was found that the highest hardness of the (aluminum-copper) alloy in the case of (2% Cu) amounted to (120 HB) and in the case of (4% Cu) the amount (211 HB) and in the case of (5% Cu) the amount (188 HB).

Abstract: The term San Mai is used for the manufacture of knife blades consisting of three layered steel composites. The middle layer, which forms the cutting edge, consists of hard steel and on the outside a soft stainless steel is forged. Mr. Benjamin Kamon, an Austrian blacksmith, provided the examined sample. Three different steels and a thin Ni layer are symmetrically connected (1.4301/1.3520/Ni/1.2519/Ni/1.3520/1.4301). The middle layer is a cold work steel (1.2519) and the Ni layer is to prevent diffusion processes. 1.3520 is a heat treatable steel for rolling bearings, followed by an austenitic stainless steel (1.4301). Metallography and SEM-EDX were used to study the microstructure, the interfaces between the different steels as well as diffusion zones. It can be stated that all layers are well connected and no defects are evident.