Papers by Keyword: Diffusion Coefficient

Abstract: This study examined the influence of pH (4, 7, 10), temperature (20 °C, 30 °C, 40 °C), nanoparticle concentration (13 ppm, 26 ppm), and Pb²⁺ addition (0 , 7 ppm) on the dispersion behavior of bentonite nanoclays in water. Using light scattering techniques, the hydrodynamic radius, zeta potential, and diffusion coefficient were measured. Results showed pH as the primary control, with aggregation highest at neutral pH and stability greatest under basic conditions. Concentration changes modestly influenced dispersion, while Pb²⁺ reduced stability through electric double layer compression and induced precipitation at high pH. Temperature effects were minimal. The results highlight the importance of pH and ionic environment in regulating nanoclay behavior and stability, with implications for its use in water treatment and remediation systems.

Abstract: The objective of this study is to suggest a method for judging jumping periods, which means an atom moves significantly in a short time in liquid metal. In this study, molecular dynamics (MD) simulation of liquid Pb at 773 K was performed. The self-diffusion coefficient was calculated to confirm that the simulation adequately reproduces liquid Pb and was almost consistent with the reliable experimental data. In the evaluation of jumping period, atomic motion during jumping was considered. A method for estimating jumping period by using each atomic speed and 1st-peak of pair distribution function was suggested by using a time when speed is at a local minimum value.

Abstract: The article investigates the process of liquid penetration into porous building materials, including concrete, brick, drywall, plaster, aerated concrete, and others. The influence of moisture on the durability, thermal insulation properties, and structural integrity of materials is examined. The relevance of developing mathematical models for predicting moisture ingress in constructions is highlighted, as this enables the minimization of operational costs and enhancement of building energy efficiency. A nonlinear diffusion model is proposed, taking into account the dependence of the diffusion coefficient on moisture concentration. Experimental data were approximated, and model parameters for specific materials were determined. Both stationary and nonstationary moisture transport problems are considered, with analytical solutions and a methodology for their application in predicting the depth of moisture penetration presented. The results can be integrated into BIM systems, opening new perspectives for use in digital construction.

Abstract: A computer program in Python was developed based on the mathematical model, which allows obtaining preliminary calculations of the diffusion coefficient and nitriding time of a punch part. As a result of a numerical experiment, the process of nitrogen diffusion into the depth of the part was studied. The redistribution of nitrogen occurs as a result of diffusion due to the nitrogen concentration gradient in the volume of the part and the high quenching temperature. The numerical experiment confirms the full-scale experiment. Nitrogen penetration into the depth of the metal occurs precisely at the quenching temperature. The nitrogen content in the internal nitriding zone due to the nitrogen released from the surface layer increases and decreases on the surface with the exposure time of the part. Computer modeling and research of the diffusion coefficient in the process of heat treatment after ion nitriding made it possible to establish that for tool steels, diffusion along grain boundaries occurs. Thus, the use of complex ion nitriding (CIN), i.e. ion nitriding and subsequent heat treatment of nitrided parts allows you to change the phase composition and increase the depth of the nitrided layer due to nitrogen doping, control the nitrogen concentration and hardness along the depth of the nitrided layer due to selected modes.

Abstract: It has been demonstrated that thin films of fluorine-doped Bi₂O₃ can be prepared using sol-gel spin coating. An X-ray diffraction (XRD) and energy dispersive analysis were used to examine samples. Using a sol-gel spin-coating technique, different electrolytes and sweep rates were used in the study to characterize fluorine-doped Bi₂O₃ films. In the results of the studies, it was extensively examined whether these films could be used in the fabrication of electrochromic devices. The enhanced properties of fluorine doped samples are due to their increased separation efficiency and strong oxidation potential. For two hours, the samples were exposed to temperatures ranging from 350 °C to 450 °C. F:Bi₂O₃ films have been the subject of an intercalation and deintercalation investigation. Therefore, H₂SO₄ and KCl are used to intercalate H+ and K+ ions in PC electrolytes. Sharp transmittance peaks at the band's edge in a spectrum with good crystallinity signify interfering patterns. Band assignment 3482 cm^-1, stretching vibration of carbohydrate, C-OH, 2432 cm^-1 asymmetric stretching vibration, 1625 cm^-1 unconjugated C=O stretching vibration, and 1383 cm^-1 bending vibration of C-H are among the numerous assignments in Fourier transform infrared spectroscopy. Additionally, 1101 cm^-1 are vibrations of hydroxyl groups and 625 cm^-1 are metallic bond vibrations of F:Bi₂O₃. The surface roughness of F:Bi₂O₃ films was found to have significantly improved. It is probable that a sol-gel spin coating process at 200 °C produced dense, irregularly shaped Bi₂O₃ grains. The thermodynamic characteristics of the corrosion process for Bi in concentrated sulfuric acid solution were studied. These parameters were Ea (activation energy), H (enthalpy change), and S (entropy change).

Abstract: The objective of this study is to quantify the improvement of diffusion experiments in liquid alloys by using two measurement points of in situ X-ray fluorescence analysis (in situ XRF). The impurity diffusion coefficient of Bi in liquid Sn at 573 K was measured by monitoring the temporal change in the Bi concentration at two fixed points using in situ XRF. In the present study, two XRF measurement points were set in order to determine two unknown parameters that corresponded to the diffusion coefficient and the initial concentration at the measurement point just after complete melting. When only one measurement point is set for in situ XRF, the initial concentration is treated as a variable and the obtained impurity diffusion coefficients of Bi deviated by 20-30% from the reliable reference data. By using two measurement points for in situ XRF, the obtained impurity diffusion coefficient of Bi was (2.44±0.08)×10^-9 m²s^-1 and agreed with the reference data in the reported uncertainty of ±10%.

Abstract: Mechanical characteristics, dimensional stability, and bonding strength are all impacted by water sorption in polymer filler materials. The diffusion coefficient (D) of water through polymer composite, should be determined to understand the impact of the deterioration on service life and micro-leakage. In this study, the kinetics and properties of water absorption by short-term immersion in room-temperature plantain fibre reinforced epoxy bio-composites (PFRC), were studied. 5, 10, 20, and 30 percent, plantain fiber (PF) volume fractions of bio-composite specimens were made. Due to the high cellulose content of natural fibers (NF), the percentage of moisture absorption grew as the PF volume fraction increased. The mechanism and kinetics of PFRC's water absorption were found to follow the Fickian diffusion mode and had the propensity to behave in the Fickian mode.

Abstract: To improve the specific capacitance, power and energy of electrical energy storage devices, in particular hybrid capacitors, various methods of cathode material modification are used. One of the methods of modifying nanostructured materials without applying high temperatures, pressures and long reaction times is ultrasonic treatment. Although the interaction of ultrasound with the structure and surface of electrode materials is well enough studied, there are few works that investigate the optimal duration of ultrasonic treatment and its relationship with the capacitive characteristics of these materials. Therefore, we investigated the efficiency of ultrasonic dispersion of nanocrystalline nickel molybdate hydrate for 15, 60 and 90 minutes. The appearance of two cathodic peaks on cyclic voltammetry patterns was analyzed and the charge / discharge mechanism of the electrode based on nanocrystalline NiMoO₄ hydrate was presented. Based on the results of potentiodynamic and galvanostatic studies the specific capacitances of the initial NiMoO₄ and the material modified by ultrasound for 15, 60 and 90 minutes were calculated. The proton diffusion coefficients of nickel molybdate hydrate were determined on the basis of the Randles–Sevcik equation. NiMoO₄ subjected to ultrasonic dispersion for 60 min as a cathode material in a hybrid electrochemical system was tested.

Abstract: Stokes-Einstein relation is a convenient way to evaluate diffusion properties in liquids from viscosity results (and vice-versa). However, the accuracy of this relation in the case of atomic fluids is often debated as it was initially established in the case of a big Brownian particle immersed in a fluid. Especially, the question is raised to properly define the hydrodynamic radius entering the formula, as well as the constant depending on the boundary conditions at the surface of the particle. In this study, we use our results of viscosity and self-diffusion coefficient obtained by molecular dynamics simulations in the case of alkali metals and their alloys to evaluate the applicability of Stokes-Einstein relation in the case of these liquids. In the case of pure metals, its validity is discussed over a wide range of thermodynamic states, from ambient pressure up to several gigapascals. In the case of alloys, the evolution of its accuracy as a function of temperature and composition is considered. Both definitions of hydrodynamic radius and boundary conditions constant are examined.

Abstract: The influence of water-filled nanoscale defects on the total movement of helium atoms through a quartz crystal is considered. The approximation of local chains is used, the interaction constant of which characterizes the interaction of the helium atom with the environment. The appearance of water molecules in defects (pores) leads to the renormalization of this interaction. The D'Alembert principle is used to evaluate this renormalization. The effect of such a renormalization of the interaction on the diffusion coefficient of helium through a crystal with defects filled with water is considered.