Papers by Keyword: Diffusion Coefficient

Abstract: The reasons of white spots appearance in the middle of oak timber are determined. These white spots reduce the cost of the lamina made of oak timbers - the front covering of floorboards. It is proposed to intensify the drying process by using oscillating drying schedules to avoid this defect. A method for calculating the duration of such drying is proposed. This method includes the peculiarities of heating and cooling periods kinetics of oak timbers with 25 mm and 30 mm thickness. The inexpediency of using the oscillation of the drying agent parameters in the range of wood moisture content below 20% has been established. An adequate model for calculating wood temperature and air humidity during wood heating and cooling periods has been developed using heat and mass transfer criteria and experimentally determined oak wood moisture conductivity coefficient. Based on the results of theoretical and experimental studies oscillating drying schedules of different thickness oak timbers are offered. Tests of the proposed schedules in industrial conditions showed no discoloration of the central layers of European oak (Quercus robur) timbers. The drying process duration was reduced by 1.5–2.4 times and energy consumption were reduced by 1.53 times.

Abstract: Permeability is important to ensure the protective properties of coatings based on styrene-acrylic dispersions. This indicator characterizes the complex of insulating properties of coatings, their ability to prevent the penetration of liquids, vapors and gases from the environment to the surface to be protected. It was studied the effect of aluminosilicate microspheres, which are characterized by the hydrophilic nature of the surface and highly dispersed silicate filler aerosil with a hydrophobised surface on the water absorption of styrene-acrylic coatings. Decreased of water absorption of styrene-acrylic coatings filled with aluminosilicate microspheres with the introduction of hydrophobised aerosil is linked to the fact that the fine aerosil with a high specific surface area provides the formation of a more densely packed structure. Thus, partially filling the interspherical space, which is formed by particles of microspheres with a diameter of 10-100 μm and reduces the surface defect of the styrene-acrylic coating. Localization on the surface of defective structures of particles of hydrophobised aerosil leads to a decrease in wetting of defective structures with water. Resulting deteriorating wetting the surface of the styrene-acrylic coating. Micrographs were taken to assess the nature of the distribution of aerosil on the surface of the styrene-acrylic coating. The analysis of the obtained micrographs confirms that the introduction of microspheres form large agglomerates, between which there are vacancies, which will negatively affect the technological and operational properties of the developed coatings. At the same time, the introduction of aerosil allows to obtain a more orderly structure, which allows to obtain a coating with lower internal stresses, increased aggregate stability and, as a consequence, with improved technological and operational properties.

Abstract: The kinetic properties such as diffusivity and viscosity of the metal melt are the foundations to reveal the structure evolutions and the glass formation abilities during solidification of the investigated alloy, thus, to control the microstructures, defects and properties of materials. In this work, ab initio molecular dynamics simulations were utilized to investigate the kinetic and thermodynamic properties and the structural relaxations of Fe-X (X = 10-15 wt% Al, Cr, Mn and Ti, or 1-2wt% B and C) melts under various temperature and external pressure, which are in line with the interested concentration range of multi-component Fe-based alloys. The kinetics and structural relaxations are characterized by mean squared displacement, velocity autocorrelation function and self-intermediate scattering function. The thermodynamics properties including entropy and heat capacity are calculated by combining the vibrational and electronic contributions based on vibrational and electronic density of states. The predicted kinetics and thermodynamics properties under high temperature and pressure agree well with the experimental and theoretical results while the connection among structural relaxations and diffusion are revealed based on the Stokes-Einstein relation and the Hall-Wolynes (HW) relation. This work provides an insight into the structure-property relationships of metal melts, which are essential in the development of advanced multi-component Fe-based alloys.

Abstract: The investigation of silicone rubber properties with the presence of platinum catalyst at different temperature using molecular dynamic simulation was conducted. Visual observation shows that structuring of silicone rubber occurs in the cell where the molecules aggregates closer compared to at the beginning of the simulation and at higher platinum concentration, silicone rubber molecules are more closely packed together. The diffusion coefficient of silicone rubber are the highest in a 10% platinum concentration followed by 25% and lastly 50% indicating that it is harder for the silicone rubber molecules to move from its original position in the system as the platinum concentration increases. Structural changes was also investigated through radial distribution function (RDF) where the position of peaks did not change with time but there is changes observed in the intensity of the peak. At a constant temperature 50°C, it was observed that the intensity of the peak at 1.10Å radius was the highest in the presence of 50%Pt followed by 25%Pt and 10%Pt. This indicates that higher numbers of silicone rubber molecules are present in a 1.10Å radius from the reference molecules in a system with higher concentration of platinum.

Abstract: The discrete Frenkel-Kontorova model for the movement of a foreign atom in a solid, obtained in the local chains approximation, led to the movement of the atom in the Frenkel-Kontorova (F-K) soliton form. This model made it possible to reveal the structure of the F-K soliton, to design the shapes of nanostructures and to take into account their influence on the F-K soliton. The transition to field variables leads the Frenkel-Kontorova equation to the sine-Gordon equation for the displacement field of an atom having solutions also in the form of a soliton. This equation and its solution (soliton) contains coefficients depending on the shape and size of nanostructures. The transition to the sine-Gordon equation allowed us to use the results of Theodorakopoulos 's works related to the consideration of the interaction of elastic vibration modes with a soliton. This made it possible to calculate the diffusion coefficient of the soliton and find the dependence of the diffusion coefficient on the shape and size of nanostructures and temperature.

Abstract: The contribution focuses on the effect of selected input parameters on probabilistic estimation of chloride induced reinforced concrete bridge deck corrosion initiation. The reinforced concrete bridge deck with steel protected by epoxy-coating is considered. A finite element diffusion model in conjunction with a probabilistic method using Monte Carlo technique is used to address the inherited randomness of input variables. Presented parametric study shows the sensitivity of estimation of the corrosion initiation likelihood on variation of input parameters.

Abstract: This study investigates computation and distribution of the diffusion coefficient using fundamentals of electrochemistry for various concrete mixtures. The instrument utilized is a bulk conductivity meter which provides the bulk conductivity data for computation of the diffusion coefficient. Thirty three mixtures are investigated, where majority of them are ternary mixtures along with Ordinary Portland Cement (OPC) and binary mixtures. They are categorized in several groups based on the supplementary cementitious material (SCM) as a second component in ternary and binary based concrete mixtures. The variation and distribution of the diffusion coefficient in individual group is investigated from 7 days to 161 days. In addition, a new methodology is proposed to determine the aging factor of the diffusion coefficient of each concrete mixture. Aging of concrete is related to chloride ingress which leads to significant decrease of the diffusion coefficient with time. If this effect is not taken into account, considerable questions can be raised while predicting reliable and accurate service life of reinforced concrete structures. Further, aging factor is validated using a statistical analysis method based on published literature of Fisher Test permutation approach. Results show that diffusion coefficient in each group varies significantly and the addition of SCM and its varying replacement level influences the reduction of the diffusion coefficient remarkably over extended time period. Overall, this study could provide promising options for computation of the diffusion coefficient and its aging factor in light to its ease of measurement and shorter amount of time than conventional RCPT and other long term migration tests.

Abstract: The area of sorption and diffusion behaviour of wood/plastic composites has gained considerable attention during the last decade owing to the variety of applications it offers. When it comes to polymers filled with wood particles there are essentially two major limiting factors that controls the final products end user applications; 1) diffusion and 2) sorption/solvent uptake of (especially moisture) the product, since these two processes lead to property degradation in the composite materials. The properties and end use application of a given product can be predicted thorough the knowledge of the parameters like diffusion, sorption and permeation coefficients. Transport (sorption, diffusion & permeation) properties of wood plastic composites (WPC’s) are now a day’s one of the most intensively researched areas owing to its significance in materials science. Liquid transport through plastics is one of the most extensively researched fields in materials science. Present chapter provides a brief insight into the transport (mainly moisture/water) properties of wood/plastic composites. Keywords: Wood particles, wood plastic composites, diffusion coefficient

Abstract: Molecular dynamics simulation was used to investigate two models of aqueous solution ofcalcium carbonate system between 283K and 373K. The diffusion coefficients of water moleculesdemonstrated that both the electropositive surface (110) on Model-I and neutral surface (104) onModel-II showed interaction with the water molecules, and the surface (110) exhibited strongerelectrostatic interaction with water molecules than the latter, besides obvious anomaly appeared near343K on Model-I. On the other hand, surface (110) exhibited anomalous influences on Ca2+ andCO32- ions near 313K and 343K on Model-I, and only a broad anomaly on CO32- ions near 343K onModel-II. The binding energies between surface (110) / (104) and Ca2+ /CO32- ions demonstrated thatthe surface (104)were more favorable for the growth of the new crystal but weak for the diffusion.

Abstract: In this paper, ordinary Portland cement concrete (OPC) and high performance concrete (HPC) were used in the marine environment exposure experiments, Using the second Fick’s law, five parameter of life prediction model-binding ability, diffusion coefficient of free C1- time dependent parameters, chloride ion concentration of surface and degradation effect coefficients are confirmed. The service life of OPC and HPC in ocean conditions is calculated and compared using mathematic software in atmosphere region, underwater region and tidal zone.