Fick's 2nd Law Research Articles

Experimental and modeling approaches to determine drug diffusion coefficients in artificial mucus

Asthma, usually characterized by inflammation and mucus accumulation, causes restricted airflow and impaired lung function. The physiological and biochemical characteristics of mucus pose a strong barrier for drugs administered orally or via the pulmonary route for asthma treatment. In this study, two drugs commonly employed in the treatment of asthma, theophylline and albuterol, were placed in contact with an artificial mucus layer, measuring their interface concentrations, and modeling the concentration profiles to determine their diffusion coefficients. To monitor the diffusion process, the upper surface of a mucus layer was placed in contact with the drug solutions and the lower mucus surface was in contact with a zinc selenide crystal to allow for time-resolved Fourier transform infrared spectroscopy (FTIR) measurements. FTIR spectra were collected at constant time intervals and monitored for quantitative changes in spectral peaks corresponding to functional groups specific to each of these drugs. Changes in peak heights were correlated to concentration via Beer's Law. Fick's 2nd Law of Diffusion was used along with Crank's trigonometric series solution for a planar semi-infinite sheet to analyze the concentration data and determine diffusion coefficients. Using this method, fitting the experimental data resulted in diffusivity coefficients of D = 6.56 x 10−6 cm2/s for theophylline and D = 4.66 x 10−6 cm2/s for albuterol through artificial mucus. The drug diffusivity coefficients align closely with literature reports, wherein, diffusivity data was obtained experimentally using a rotating-disk apparatus and intrinsic dissolution technique. By coupling analytical and experimentally determined drug diffusion data, this approach provides a fast, non-invasive method for quickly assessing drug diffusion profiles through complex media.

Effect of process parameters on the extraction kinetics of Leptocarpha rivularis DC. in a packed bed extractor using supercritical carbon dioxide

The kinetics of supercritical extraction from L. rivularis stalks using CO2 were studied in terms of temperature (40−60ºC), pressure (18–30 MPa), specific CO2 consumption (30−50 kg/kg d.s.), and particle diameter (0.5−1.1 mm). The extraction yield was found to range from 17.30 to 27.23 g/kg d.s. The highest extraction yield was obtained at 40°C, 30 MPa, 30 kg CO2/kg d.s., and mean particle size of 0.5 mm. The yield increased with pressure and decreased with temperature and particle size (p≤0.05). The diffusion model based on Fick's 2nd law adequately described the cumulative extraction curves, using the effective diffusion coefficient (De) as the adjusted parameter, which ranged between 3.50 and 19.26×10−12 m2/s. The Biot number was estimated, indicating a prevalence of internal control to mass transfer resistance. Additionally, the “apparent solubility” was obtained from the initial slope of the cumulative extraction curves. The extraction yield correlated positively with apparent solubility (p≤0.05) and De coefficient (p≤0.05).

Sensitivity analysis of a physicochemical model of chloride ingress into real concrete structures subjected to long-term exposure to tidal cycles

In marine environments, reinforced concrete structures are exposed to tidal conditions and therefore susceptible to chloride ingress. Reliable models of transport are crucial in order to evaluate the service life of these structures. Unlike engineering models based on Fick's 2nd law and empirical coefficients, this study proposes a model based on a physicochemical description of the transport phenomena and on some assumptions restricting the number of inputs to 9 parameters and the computational costs. This model is validated for a long exposure to tidal cycles (28 years). Then, the sensitivity analysis, based on the Morris method, is performed through 100 simulations of tidal exposure considering different sets of the 9 input parameters. According to the critical times of initiation of corrosion predicted, the most sensitive parameters are the critical chloride concentration and the chloride diffusivity factors. The effects of moisture sorption and chloride binding parameters are moderate after long exposure. Then, the results of the simulations are compared to data of the literature in terms of convection depths and total chloride concentrations at the limit of the convection / diffusion zones. Finally, by quantitative considerations, the analysis goes further, providing analytical relations expressing the convection depth and the associated total chloride concentration as functions of input parameters. These provide physically informed guidelines in using an engineering model based on Fick's 2nd law in order to estimate the critical time of initiation of corrosion.

Multiscale molecular simulations on the rejuvenation of recycled asphalt mixture: An insight into molecular impact of rejuvenators in aged asphalt binders

Asphalt rejuvenation technology is an effective method to recycle reclaimed asphalt pavement (RAP) for the production of high-quality recycled asphalt mixtures. This approach contributes to mitigating environmental pollution and facilitating resource recycling. In this study, the impact of rejuvenator molecules on the rejuvenation process was explored by utilizing theoretical models and dynamics simulations. Free volume theory models were used to calculate the diffusion coefficient, while molecular dynamics (MD) simulations revealed the internal energy changes during diffusion. Molecules with high interaction with aged asphalt are easier to reach the homogeneous state in diffusion systems under higher temperatures. The quantification of blending by Fick's 2nd law suggests that the blending process consists of three stages: an intense diffusion phase, a stabilization phase, and a homogeneous state phase. The time taken to reach the homogeneous stage depends on the chemical structure of the rejuvenators and the temperature. This study elucidates the molecular-scale mechanism of RAP rejuvenation and provides a roadmap for improving environmentally friendly RAP rejuvenation technology.

Electrical properties of BaZr0.5Ce0.3Y0.1Yb0.1O3-δ proton conductor for reversible proton-conducting solid oxide electrochemical cells

Proton-conducting oxide-based reversible solid oxide electrochemical cells (protonic-SOEC, P-SOEC) have a great potential to be the most efficient transition technology operating at intermediate temperatures. Here, we have introduced a perovskite-type proton conductor BaZr0.5Ce0.3Y0.1Yb0.1O3-δ (BZCYYb5311) and evaluated its electrochemical and transport properties. The chemical stability of BZCYYb5311 was confirmed by thermo-gravimetric analysis (TGA) under pure CO2 conditions and X-ray diffraction analysis. The total and partial conductivities were obtained using DC four-probe conductivity measurements under various pO2 and pH2O conditions. The ratio of proton conductivity to ionic conductivity including the oxygen-ion conductivity of this material was 98% at 600 °C, indicating that it is a relatively pure proton conductor with most of the ionic conduction almost exclusively carried out by protons. Chemical diffusivities were calculated from Fick's 2nd law by non-linear least squares fitting during oxidation/reduction and hydration/dehydration processes and were faster than other proton conductor BZCY (Y-doped BaCeO3-BaZrO3) series, which have a similar zirconium contents. In addition, the theoretical performance and efficiency of the reversible P-SOEC were determined from the spatial distribution of oxygen and hydrogen partial pressure in BZCYYb5311, calculating the maximum power density (4.5 Wcm−2 at 600 °C, 3% of water vapor pressure) for the fuel cell mode and current density (12.3 Acm−2 at 1.5 V, 600 °C, and 20% of water vapor pressure) for the electrolysis mode. The fuel consumption efficiency is high (99.1% at 0.6 V at 600 °C), while the electrolysis efficiency is low (72.3% at 1.6 V) due to the dominant p-type regime in the electrolyte during electrolysis. This low electrolysis efficiency can be enhanced by recovering the electrolyte regime by increasing pH2O or decreasing pO2 in the air electrode; however, it will still have low efficiency. Consequently, BZCYYb5311 is not an efficient electrolyte material for electrolyzers, but is promising for fuel cells because of its superior chemical stability, exceptional pure proton conductivity, and better bulk diffusion than those of the BZCY system.

Migration of Energetic Plasticizer in Advanced Energetic Composite Propellant Grains

AbstractStudies on the migration of nitrate ester plasticizers from advanced energetic nitrate ester plasticized polyester polyol (NEPE) propellants stored at 27o and 55 °C using HPLC showed that the nitrate ester content is depleting from the bulk of the propellant with time, upto 125 weeks, till equilibrium is reached. Diffussion coefficient for migration of nitrate ester estimated by Fick's 2nd law of diffusion reveals that the magnitude of estimated diffussion coefficient is high for the propellant sample stored at elevated temperature as compared to the samples stored at ambient condition, indicating the higher rate of plasticizer migration at high temperature. Also, the estimated diffussion coefficient for NG migration is higher than that for BTTN which is inline with its higher rate of migration. The diffussion coefficients have also been estimated by the tensile strength data of the stored propellants and its magnitude is marginally higher than the one estimated by the physical phenomenon of plasticizer migration as described by Fick's law. Hence it can be inferred that along with the post cure reaction, the plasticizer migration is also responsible for toughening of propellant during storage.

Determination of the concentration-dependent effective diffusivity of CO2 in unconsolidated porous media saturated with heavy oil by considering the swelling effect

Effective diffusivity of CO2 in the unconsolidated sandpack saturated with a Lloydminster heavy oil was determined in the form of an exponential function of CO2 concentration in the diluted and swollen liquid-phase. For such a purpose, two pressure-decay experiments were executed at different pressure ranges (i.e., 855–817 kPa and 1993–1905 kPa) and a temperature of 299.65 K. First, the sandpack saturated with heavy oil was prepared under an increased temperature of 348.15 K because the reduced heavy oil viscosity was required to saturate the sand column with heavy oil in a diffusion cell. Next, the diffusion cell containing the Lloydminster heavy oil-saturated sand column was integrated into a pressure-decay experimental system with pressure-monitoring devices. Then, pressure-history curves of both the diffusion experiments were continuously recorded to be compared with the theoretically calculated ones. The Fick's 2nd law incorporated with the volume-translated Peng-Robinson equation of state (PR-EOS) was implemented to determine the concentration-dependent effective diffusivity of CO2 in a sandpack saturated with heavy oil considering its swelling effect through minimizing the deviations between the theoretically computed pressure-history curves with the experimentally recorded ones. For the computation of the Fick's 2nd law, the Crank-Nicolson scheme finite difference method (FDM) was applied to take the local oil swelling into account for enhancing the accuracy of such a determined diffusivity. The excellent agreements between the theoretically computed and experimentally measured pressure-history curves at both the pressure ranges signify that such a determined effective diffusivity considering the CO2 concentration is accurate and reliable.

Modeling Drug Dissolution in 3-Dimensional Space.

The purpose of the study is to present a mathematical model capable of describing drug particle dissolution in 3-dimensional (3D) space, and to provide experimental model verification. Through this study, we also aim to elaborate limitations of the classic, 1D-based Nernst-Brunner formalism in dissolution modeling. The 3D dissolution model was derived by treating the dissolution of a spherical particle as a diffusion-driven process, and by solving Fick's 2nd law of diffusion in spherical coordinates using numerical methods. The resulting model was experimentally verified through analyzing the dissolution behavior of single succinic acid particles in un-stirred water droplet under polarized light microscopy, in combination with image segmentation techniques. A set of working equations was developed to describe drug particle dissolution in 3D space. The predicted dissolution time and profile are in good agreement with the experimental results. The model clearly shows that the concentration gradient within the diffusion layer, in realistic 3D condition, must not be a constant value as implicated in the Nernst-Brunner formalism. The actual concentration profile is a hyperbola, and the concentration gradient at the surface of the particle can be significantly higher than the classic 1D-based dissolution model. The study demonstrates that the classic, 1D-based dissolution models may lead to significant under-estimation of drug dissolution rates. In contrast, modeling dissolution in 3D space yields more reliable results. This study merits further development of comprehensive 3D drug dissolution models, by considering polydispersed particle ensemble and imposing the changes of diffusion layer thickness during dissolution.

Development of Complex Hydrogen Penetration Ratio As a New Transfer Function for Analysis on Hydrogen Penetration Mechanisms into Metals

Degradation of steels related to the hydrogen embrittlement is a serious problem from the standpoint of infrastructure preservation. The hydrogen embrittlement is related to the hydrogen penetration reaction (HPR) into steel. Some electrochemical methods [1-4] were employed to investigate the HPR mechanisms. One of the major electrochemical methods is electrochemical impedance spectroscopy (EIS). The EIS was applied to the investigation of HPR mechanisms because the time constants observed in impedance spectrum can be discriminated [5]. Another one is Devanatnan-Stachurski permeation technique [6, 7]. In this technique, two independent electrochemical cells are arranged on two surfaces of metal sheet and anodic and cathodic polarizations can be performed with each cell using the three-electrode system. The amount of hydrogen penetration rate can be evaluated by measuring the oxidation current of hydrogen atoms diffused in the metal sheet at the anode side. In this study, we proposed a new transfer function based on the electrochemical reactions and mass transfer during HPR by combining EIS and Devanatnan-Stachurski permeation technique. The complex hydrogen penetration ratio (CHPR), ι, as a new transfer function is defined from ratio of ΔI per and ΔI ent. ι = ΔI per / ΔI ent (1)In this equation, the ΔI per is the current response related to the hydrogen penetrated through metal sheet at anode (detection) side, and the ΔI ent is the current response of cathode (entry) side. The equation (1) can be expressed by the following equation as the theoretical equations for ΔI per and ΔI ent were derived based on Fick's 2nd law,. ι = 1 / K ab exp (-h (jω / D)1 / 2) (2)In the equation (2), K ab is the hydrogen entry ratio against the total cathodic reaction rate, h is the thickness of metal sheet, j is imaginary number unit, and D is the hydrogen diffusion coefficient.The simulations of ι were conducted with the equation (2) assuming arbitrary values of D. The simulation results indicated that the phase shift of ι became large with the decrease of D. The new method to determine the value of D from the phase shift of CHPR was developed.

Partition coefficient and diffusion coefficient determinations of 50 compounds in human intact skin, isolated skin layers and isolated stratum corneum lipids

A standard protocol was used to determine partition (K) and diffusion (D) coefficients in dermatomed human skin and isolated human skin layers for 50 compounds relevant to cosmetics ingredients. K values were measured in dermatomed skin, isolated dermis, whole epidermis, intact stratum corneum (SC), delipidized SC and SC lipids by direct measurements of the radioactivity in the tissue layers/lipid component vs. buffer samples. D determinations were made in dermatomed skin, isolated dermis, whole epidermis and intact SC using a non-linear regression of the cumulative receptor fluid content of radiolabeled compound, fit to the solution of Fick's 2nd Law. Correlation analysis was completed between K, D, and physicochemical properties. The amount of interindividual (donor) and intraindividual (replicate) variability in the K and D data was characterized for each skin layer and chemical. These data can be further used to help inform the factors that influence skin bioavailability and to help improve in silico models of dermal penetration.

Effects of processing parameters on phase, morphology, mechanical and corrosion properties of W–Cu nanocomposite powder prepared by electroless copper plating

Because of excellent physical properties and wide range of applications in electrodes, electrical connections, microelectronic packaging, and heating mineral, Tungsten–copper (W–Cu) composite powders have been significantly remarkable. The substantial differences in the density and lack of fusion of copper and tungsten in both solid and liquid phases, led to occur some problems in W–Cu composite powders. Among the various methods of preparing tungsten–copper composites, the electroless plating process is one of the conventional methods as it is easy to use, efficient, and inexpensive. In this paper, the copper electrolyte solution containing copper sulfate as the main salt, formaldehyde as the reducing agent, sodium ethylene diamine tetra-acetate as the sophisticated agent, has been employed in the electroless copper plating process of tungsten powder. The effects of main parameters of electroless copper plating including NaOH concentration, time and operating temperature, and pre-activation of tungsten powder on the amount of deposited copper layer were investigated. Then, the phase behavior, morphology, mechanical, and corrosion behavior were evaluated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy(EDS), Vickers hardness tester, and electrochemical impedance spectroscopy (EIS), respectively. Results demonstrated an improvement in the morphology and amount of the copper, which was deposited on the surface of the activated tungsten powder. Indeed, the defects formed on the surface of the tungsten powder increased the sites for nucleation and growth of copper particles. In agreement with the Fick's 2nd law, the maximum deposition rate of 7.9 vol% was obtained at 14 g/l NaOH, 100 °C and processing time of 90 min, with a (111) orientation on the activated tungsten powder surface. The higher capacitance and the charge transfer resistance along with the highest ndl at the 14 g/l NaOH concentration demonstrated the homogeneity and integrity of W–Cu composite, the lowest hardness of 149.0 ± 2.8 Hv and a compressive strength of 187 ± 11 MPa.

Contribuição para estimativa do grau de saturação a partir das condições ambientais aplicada à análise de confiabilidade de estruturas de concreto sujeitas ao ataque por cloretos

A durabilidade de elementos estruturais de concreto armado sujeitos a condições ambientais de severa agressividade apresenta-se como um dos principais problemas enfrentados na construção civil. Dentre os agentes de deterioração dessas estruturas destacam-se os íons cloretos, amplamente difundidos em ambiente marinho, que causam a corrosão de armaduras. A estimativa de vida útil de elementos de concreto armado surge como uma temática fundamental na avaliação da durabilidade das estruturas. Embora outros processos causem penetração de íons cloreto no concreto, é praticamente consenso que a difusão é o mecanismo predominante. Um modelo clássico de caracterização da penetração de cloretos é a 2ª Lei de Fick. Guimarães (2000) demonstrou que o grau de saturação (GS) do concreto é um parâmetro que exerce forte influência sobre o coeficiente de difusão de cloretos (D). Embora tenham sido desenvolvidas metodologias de medição do GS, estas se apresentam onerosas em termos de tempo e recursos. O objetivo deste trabalho é apresentar estimativas de GS com base nas condições ambientais a que o material é exposto e posteriormente analisar a influência deste parâmetro na avaliação da estimativa de vida de elementos estruturais através da confiabilidade. São utilizados dados meteorológicos e de medição do GS obtidas em duas regiões litorâneas: Rio Grande, Brasil e Santa Pola, Espanha. Obteve-se modelos de estimativa do GS a partir das variáveis ambientais de cada região e também de ambas em conjunto. Avaliou-se então a influência destes modelos na estimativa de vida útil através da probabilidade de falha da estrutura.

Computational modeling for predicting corrosion initiation in reinforced concrete structures

Abstract This article presents a model for penetration of chloride by diffusion in reinforced concrete structures based on the solution of the Fick's 2nd Law, using the finite element method (FEM) in two-dimensional domain. This model predicts the time, in a given situation, so that a certain limit of chlorides for depassivation of reinforcement is reached, characterizing the end of service life. Several approaches for the chloride surface concentration and for the diffusion coefficient are used, parameter which must be corrected due to the effects of temperature, solar radiation, exposure time, and relative humidity. Moreover, a parametric analysis is carried out in order to study the factors involved and their impact on the ingress of chlorides by diffusion, contributing to a better understanding of the phenomenon. In addition, the developed model is applied to the cities of Vitória (ES) and Florianópolis (SC) to analyze the service life for different concrete covers, making a comparison with the Brazilian standard.

Predictive model for depressurization-induced blistering of type IV tank liners for hydrogen storage

The work described in this study represents the first effort to model the complex phenomenon of plastic liner blistering during the depressurization of type IV hydrogen storage tanks. Blistering occurs because gas is absorbed by the plastic liner at high pressure and stresses are generated when the decompression rate exceeds the rate by which absorbed gas can escape by diffusion. It is important to eliminate blistering because type IV tanks are the lightest hydrogen storage option for GM and Honda's first generation of fuel cell vehicles. This report details the implementation of a simple polymer liner blistering model which is based on Henry's law, Fick's 2nd law, and a simple material yield criterion derived from continuum mechanics. Since the model agreed well with experiment, a parametric study was conducted to predict the onset of blistering as a function of liner thickness and depressurization rate. The model sets the basis for a predictive tool for the pre-selection of liner materials and designs. The pre-selection approach reduces the number of experiments that need to be conducted which potentially reduces the cost of hydrogen storage system development.

Impact of calcium leaching on chloride diffusion behavior of cement pastes exposed to ammonium chloride aqueous solution

Calcium leaching is a procedure being able to greatly impact the internal chemical environment and the microstructure, which mainly decide the chloride diffusion behavior of concrete. However, the detailed rules and mechanisms were rarely studied in the current literatures. In this paper, pure cement pastes were casted for the immersion test. Ammonium chloride aqueous solution was employed as the source solution to simulate the coupling interaction of calcium leaching and chloride diffusion. Vickers hardness and chloride profiles were measured to present the effects of calcium leaching on chloride diffusion behavior. Morphology and EDS linear scanning results of degraded pastes were also given to reveal the micro-mechanism. Results show that leaching can greatly change the internal chemical environment and the microstructure of cement pastes, thereby changing the chloride diffusion behavior and degrading the chloride-ingress resistance. In the leached specimens, chloride profiles are remarkably different from the classical curves predicted by Fick's 2nd law. Losing the binding matrix, the total chloride contents of the degraded zones turn smaller and almost approximate to the water-soluble ones. Due to the microstructure degradation, chloride profile fronts in degraded zones move faster towards the deep.

Design considerations to minimize the impact of drug absorption in polymer-based organ-on-a-chip platforms.

Biocompatible polymers, such as polydimethylsiloxane (PDMS), are the materials of choice for creating organ-on-a-chip microfluidic platforms. Desirable qualities include ease of fabrication, optical clarity, and hydrophobicity, the latter of which facilitates oxygen transport to encased cells. An emerging and important application of organ-on-a-chip technology is drug discovery; however, a potential issue for polymer-based microfluidic devices has been highlighted by recent studies with PDMS, which have demonstrated absorption (and thus loss) of hydrophobic drugs into PDMS under certain experimental conditions. Absorption of drug in the polymer can also lead to undesirable transfer of drug between adjacent microfluidic lines. Given the benefits of polymers, it is essential to develop a comprehensive understanding of drug absorption. In this study, we considered convection, dissolution, and diffusion of a drug within a polymer-based microfluidic device to characterize the dynamics of drug loss in a quantitative manner. We solved Fick's 2nd law of diffusion (unsteady diffusion-convection) by finite element analysis in COMSOL®, and experimentally validated the numerical model for loss of three hydrophobic molecules (rhodamine B, cyanine NHS ester, and paclitaxel) in PDMS. Drug loss, as well as the unintended mixing of drugs by adjacent microfluidic channels, depends strongly on platform design parameters, experimental conditions, and the physico-chemical properties of the drug, and can be captured in a simple quantitate relationship that employs four scalable dimensionless numbers. This simple quantitative framework can be used in the design of a wide range of polymer-based microfluidic devices to minimize the impact of drug absorption.

Corrosion Resistance of Zinc-Rich Metallic Coatings on Aluminum

Thin walled aluminum heat exchanger tubes, with solid-solution Zn-rich surface are widely used by the automotive industry and considered by the HVAC&R (Heat, Ventilation, Air Conditioning and Refrigeration) market for improved corrosion resistance against pitting. It is well known that alloying Al with Zn causes decrease in the corrosion potential in chloride solution.1 Thus, Zn-rich coating can provide cathodic protection to the aluminum substrate, in particular prevent pitting corrosion. However, corrosion rate of Zn itself is quite high in chloride solution.2 This work investigates the extent to which the self-corrosion of the Zn-rich layer can be a limiting factor in determining the service life time of the heat exchanger tubes. Zinc was applied on AlMn alloy extruded tubes by thermal arc spraying immediately after extrusion. Typical Zn load on the surface was 0.8 ± 0.2 mg/cm2. The tubes were subsequently subjected to heat treatment at various temperatures (350 - 430°C) and durations to obtain solid-state AlZn alloy diffusion layer with varying thickness and Zn-concentration profiles at the surface of the AlMn substrate. The Zn depth profiles were characterized by glow discharge optical emission spectroscopy (GD-OES). Corrosion rate was determined by weight loss resulting from immersion for predetermined times in acidified artificial sea water solution of pH 3 at 25°C for slight acceleration of the corrosion rate, during which the open circuit potential change was recorded with respect to time. The morphology and composition of the Zn-rich layer before and after corrosion were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS).The Zn concentration distribution in the layer could be modeled by the solution to Fick's 2nd law with appropriate boundary conditions, giving an effective diffusion coefficient for Zn in the Al substrate of order 10-10 cm2/s in the temperature range of interest, varying according to the Arrhenius law with respect to temperature. Zn-rich layer thickness obtained on the samples heat treated at selected conditions varied approximately in the range 35 to 80 µm with increasing heat treatment temperature and time, corresponding to Zn surface concentrations of 28 to 7 wt%, respectively. Reduction in thickness due to corrosion, calculated from the weight loss measurements by taking into consideration the density depth-profile of Zn, which was obtained from the GD-OES data, increased with increasing thickness of the Zn-rich layer. Unexpectedly, decreasing Zn concentration level in the layer did not have a significant effect on the corrosion rate, unless it was lower than a threshold of a few wt%, which appeared to be sufficient to give the necessary protection. The results confirmed also that Zn gave satisfactory protection against pitting corrosion. Corrosion potential of samples as coated with Zn (no heat treatment) reached the pitting potential of the AlMn substrate in about 4 days. After 11 days of immersion, corrosion potential of the samples heat treated at 350°C for 2 hours increased up to about 30 mV below the pitting potential of the substrate, while the corrosion potential of the samples heat treated at 430°C for 4 hours remained about 120 mV lower than the pitting potential of the substrate. The reduction in thickness after 11 days of immersion for those heat treatment conditions was 23 µm and 54 µm, respectively. These results indicate that optimal Zn concentration and Zn-rich layer thickness, in terms of service life and loss of thickness, lie at levels much lower than those used in this study. The optimal concentration needs to maintain the corrosion potential at a level lower than the critical pitting potential. At the same time, the Zn concentration level in the layer has to be low enough to restrict the rate of self-corrosion, such that the layer thickness can also be reduced to give sufficiently long service life time. The well-known relationship between the corrosion potential of AlZn alloys and Zn concentration1 was extended over a wide concentration range and related further to the corrosion rate in acidified synthetic seawater. The database thus developed is useful for optimizing the Zn-rich layer thickness and Zn concentration profile in the layer to minimize uniform corrosion, and therefore maximize service lifetime, without reducing the protection against pitting.

Effect of pulsed electric fields on mass transfer and quality of osmotically dehydrated kiwifruit

The effects of pulsed electric fields (PEF) on mass transfer and quality during osmotic dehydration (OD) of kiwifruit were investigated. Whole peeled kiwifruit was subjected to different PEF (field strengths E, 0.7, 1.1 and 1.8kV/cm) process conditions. PEF processed and non processed samples were cut into discs and treated by immersion in OD solution consisting of glycerol, trehalose, maltodextrin, ascorbic acid, sodium chloride, calcium chloride and citric acid (wfood/wsolution=1/5) for 240min at different temperatures (T 25, 35 and 45°C). Water loss (WL), solid gain (SG), water activity (aw) as well as main quality indices (colour, texture, vitamin C) were estimated during processing. OD resulted in substantial WL and SG. Application of PEF significantly enhanced rates. Fick's 2nd law for diffusion was used for the calculation of the effective diffusivities of water with higher temperature and field strength showing higher values. The effect of temperature and PEF field strength on the effective diffusivity coefficient of water was mathematically modelled. Shorter OD times, when PEF pretreatment is applied, may be adequate to remarkably improve diffusion kinetics leading to a level of WL/SG that allows the product to retain optimum quality characteristics and adequate decrease of aw. PEF OD processed kiwifruit presented high quality (acceptable level of colour change, increased firmness, high vitamin C content) suggesting that PEF and OD combination can be an effective processing step in the production of intermediate moisture products.

Methodology of calculating required chloride diffusion coefficient for intended service life as function of concrete cover in reinforced marine structures

For marine reinforced concrete (RC) structures, chloride initiated corrosion of reinforcement is generally accepted as the service life limiting degradation mechanism. A methodology is described for how the maximum required chloride diffusion coefficient (D) of a concrete for achieving an intended service life (t) can simply be calculated as a function of concrete cover thickness (x) over the reinforcement by D = constant·x2/t.The principle is based on the usual mathematical solution to Fick's 2nd law of diffusion. The constant is broken down into 3 factors; chloride concentration factor, aging factor and temperature factor, in which input parameters have to be selected. These factors are calculated for a range of selected input parameters illustrating their sensitivity. The largest uncertainty lays in proper selection of the aging factor of the diffusion coefficient. Some concrete recipes satisfying estimated chloride diffusion coefficients are proposed as part of the methodology.

다층구조확산을 고려한 제설제에 노출된 콘크리트의 염화물 해석

Concrete is cost-benefit and high-durable construction material, however durability problem can be caused due to steel corrosion under chloride attack. Recently deicing salt has been widely spread in snowing season, which accelerates micro-cracks and scaling in surface concrete and the melted deicing salt causes corrosion in embedded steel. The previous governing equation of Fick's 2nd Law cannot evaluate the deteriorated surface concrete so that another technique is needed for the surface effect. This paper presents chloride penetration analysis technique for concrete subjected to deicing salt utilizing multi-layer diffusion model and time-dependent diffusion behavior. For the work, field investigation results of concrete pavement exposed deicing salt for 18 years are adopted. Through reverse analysis, deteriorated depth and increased diffusion coefficient in the depth are evaluated, which shows 12.5∼15.0mm of deteriorated depth and increased diffusion coefficient by 2.0 times. The proposed technique can be effectively applied to concrete with two different diffusion coefficients considering enhanced or deteriorated surface conditions. ■ keyword :∣Deicing Salt∣Multi-layered Concrete∣Chloride Attack∣Freezing and Thawing∣Time-dependent Diffusion∣