Papers by Keyword: Diffusivity

Abstract: This study investigates Halloysite Nanotube (HNT) dispersibility in ethanol-water mixtures – 0% and 10% ethanol at 100, 300, and 500 ppm HNT concentrations. Overall, the study finds that changes in HNT concentration linearly affect the response variables and showed that the 10% ethanol solvent has a higher zeta potential, smaller particle size, higher viscosity, and settling velocity. The enlargement of HNT particles at 10% ethanol while keeping better stability than water solvent is unexpected and can open novel studies about the dispersion of HNT in this solvent system.

Abstract: The thermodynamic, structural, surface and transport properties of PbSn eutectic alloys at 1050 K have been analyzed employing self association model. The model parameters have been evaluated on utilizing the experimental data of free energy of mixing of PbSn liquid alloys at 1050 K. For the validation of the model parameters, the calculated values of the excess free energy of mixing and activity of the components of PbSn liquid alloys have been compared with the experimentally measured data. Further, the estimated model parameters have been used to determine the thermodynamic functions i.e. the free energy of mixing, thermodynamic activity, entropy of mixing and heat (or enthalpy) of mixing, and the structural properties such as the concentration fluctuations and shortrange order parameter. The theoretical and experimental values are compared. A good agreement is observed. Again, the surface properties of PbSn liquid alloys at 1050 K have been investigated using the Butler model in the framework of self association model. The calculated values of surface tension of PbSn liquid alloys at 1050 K are in reasonable agreement with the data available in the literature. The transport properties like the diffusivity and viscosity of PbSn liquid alloys at 1050 K have been theoretically analyzed. For the computation of viscosity, the simple formula developed by Moelwin- Hughes has been used in conjunction with self association model. The present study reveals that PbSn eutectic liquid alloys at 1050 K are segregating in nature. Further, the model parameters are found to depend on temperature.Keywords: Gibbsfree energy; concentration fluctuations; short-range order parameter; surface tension; diffusivity; viscosity

Abstract: The ITZ (interfacial transition zone) in concrete has very high porosity and permeability, which affects concrete’s macroscopic mechanical properties and transport properties. Two-dimensional (2D) areal analysis and one-dimensional (1D) linear analysis are usually used to study ITZ’s microstructure. However, 3D microstructure is difficult to be characterized by 1D and 2D information. For example, 2D cross-section planes do not always intercept both the ITZ and the corresponding aggregate, which causes some ITZ regions are ignored by researchers. Therefore, ITZ’s volume and thickness will be misestimated, and leads to the misestimation of the diffusivity. In this paper, the effect of aggregate’s shape on the misestimation of ITZ thickness t is studied. The results reveal that the misestimation increases with the increasing sphericity s of aggregates.

Abstract: Polymeric plastic boxes (named Front Opening Unified Pods (FOUP)) were widely used in semiconductor manufacture to maintain the cleanliness of processed wafer substrates in a controlled mini-environment. Polymeric materials, however, are able to sorb airborne molecular contaminants (AMCs) and subsequently to outgas the sorbed AMCs backward to FOUP’s atmosphere, causing the transfer of AMCs to sensitive stored substrates, named cross-contamination. As a type of AMCs, the NH₃ cross-contamination could cause a severe yield loss to integrated circuits (crystals (haze), resist-development defects (T-topping) or metallic corrosion). Experiments were carried out to establish the NH₃ sorption and desorption kinetics in polyetherimide (PEI), Entegris Barrier Material (EBM)), and EBM/carbon nanotubes (EBMCNT) at NH₃ concentration of 800-ppbv, 21°C, and relative humidity of 40%. The transport coefficients i.e. solubility and diffusivity (D_NH3 and S_NH3) were then determined. The study on NH₃ provides an additional guideline to choose the best raw materials for FOUP formulation in taking into account the potential cross-contamination of AMCs. Numerical simulation model based on obtained solubility and diffusivity values was conducted to demonstrate NH₃ concentration profiles in FOUP walls during contamination and FOUP decontamination, which are inaccessible by conventional experiments.

Abstract: The paper is devoted to the study of thermal parameters (specific heat capacity, diffusivity and thermal conductivity) changes after thermally induced aging of BMC Mensolite 3100. Results of several measurements are statistically treated. From obtained results it is visible the greatest correlation in the diffusivity values, i.e. the heat irradiation effect is the smallest on the diffusivity values dispersion, the influence of the heat irradiation on the thermal capacity has approximately the same trend as the thermal conductivity. From the starting point represented by the virgin sample both values decrease and for the sample heated at 300°C it is visible an increase of the above mentioned values under investigation. Results are interpreted by using of the thermogravimetric analysis (TGA). All physical values under this investigation have a dominant decreasing tendency after the thermal treatment described.

Abstract: A coupling interface between phase-field model with finite interface dissipation and the CALPHAD (CALculation of PHAse Diagram) thermodynamic and atomic mobility databases is developed. It robotizes the procedures that provides the composition and temperature dependent properties in multicomponent and multi-phase systems. Based on the developed coupling interface, different CALPHAD properties can be directly coupling in the phase-field simulation.

Abstract: In this paper was followed the processing flow of aluminum-alumina compositions (10÷20% alumina) in powder state, aiming to obtain aluminum matrix composites reinforced with alumina particles, starting from selecting and mixing the grading fraction of both components reaching up to sintering; it was analyzed the way in which reflects the variation of grading fraction ratio (expressed through average particle diameter in the analyzed fractions limits) on the level of technological interest features: apparent density, tapped density, flowability, presability and on densification after sintering (in various environments). By transmission electron microscopy was observed that aluminum particles showed on the surface a nanoscale oxide film, so the sintering occurs between congeneric areas – by solid phase sintering mechanisms [1, 2, 3]. The analysis of thermophysical properties revealed a decrease of thermal diffusivity at an increase of alumina, simultaneous with the decrease of the densification level.

Abstract: Diffusion coefficients of methane (CH₄) have been obtained by Molecular Dynamics (MD) simulations combined with Einstein fluid equation. Three polymers were considered, namely polyethylene, polypropylene and poly (cis-1,4-butadiene). All calculations were performed by means of Polymer Builder and Amorphous Cell modules within Materials Studio (Accelrys). The obtained diffusivity results are within the range of published results for similar small molecules. Molecular dynamics simulations proved to be a useful tool for understanding the detailed descriptions and transport mechanisms occurring within the material.

Abstract: This paper describes the numerical investigation on the adsorption () of nanoparticles (NPs) scale inhibitor (SI) using Eulerian Computational Fluid Dynamics (CFD) solver ANSYS/FLUENT® based on a scaled down flow model. The simulation were done to investigate theof normal and nanoscaled Calcium-phosphonate. The phosphonate used was 1-hydroxyethylidene-1, 1-disphosphonic acid (HEDP) SI in order to determine the enhancement in adsorption achieved by the nanoscaled SI. This was done by looking at the change in concentration of the SI particles throughout the simulation time. It was found that the two sizes (normal and nanostructured) of the SI particles result in different change in concentration, hence indicates that the two yields different adsorption to the active sites. For the normal SI, the concentration distribution throughout the column remains almost the same as its initial concentration () of 2000 ppm except for very narrow regions in the vicinity of the wall boundaries. This suggests that the rate of process (of the SI onto the wall) is very slow. Consequently, it will take longer time for the SI to be adsorbed to the column wall, hence indicates that it is less efficient. Meanwhile, the nanoscaled Calcium-HEDP SI rapidly shows a significant change in concentration. At 200 s its concentration has distributed evenly in the range of 1960 ppm to 2000 ppm. This shows a really high rate. The results from this study indicates that the nanoscaled Calcium-HEDP SI has better which shows that it is more efficient than normal-scaled Calcium-HEDP SI.

Abstract: Diffusion phenomena are of great importance in materials processing wherein atomic, molecular or ionic species are distributed within a phase or among different phases. Though the phenomenological equation describing the diffusion phenomena including the bulk flow arising out of diffusion in fluid and the phenomena of Kirkendall shift in substitutional solids are the same, these processes are often treated independently. Some discussion on this aspect is presented in the theoretical aspects of diffusion. Owing to the complexity of atomic interactions, prediction of diffusion coefficients in condensed systems from first principles may not be that reliable; Experimental determination of diffusion coefficients is essential. In the second section, some novel experimental techniques developed recently to measure diffusion coefficients in the solid state as well as liquid systems including those in slags are described. In the last section, two case studies on application of diffusion phenomena in process metallurgy are presented emphasizing the importance of these in metallurgical processing.