The Experts below are selected from a list of 50718 Experts worldwide ranked by ideXlab platform

Peter S Liss - One of the best experts on this subject based on the ideXlab platform.

  • metastable equilibrium Adsorption Theory
    Joint International Conference on Information Sciences, 1998
    Co-Authors: Peter S Liss
    Abstract:

    Abstract It is proposed that a fundamental deficiency in the existing theoretical foundation of surface Adsorption is that Adsorption density (Γ) is incorrectly used as a state variable. A metastable-equilibrium inequality is obtained when Γ is not treated as a state variable. The inequality indicates that experimentally measured “equilibrium” Adsorption constants for a given Adsorption system decrease as the actual metastable-equilibrium Adsorption states deviate from the ideal equilibrium state. Isotherms, when expressed in terms of Γ, can therefore be fundamentally influenced by the kinetics of the Adsorption process. This implies that previously measured equilibrium Adsorption data may show a lack of consistency, thereby making the use and comparison of the data problematic. The inequality reveals a simple relationship between the real metastable-equilibrium constant and the ideal equilibrium constant, which provides a possible way to modify some of the existing equilibrium theories into metastable-equilibrium theories. As an application of the method, Langmuir-type and Freundlich-type metastable-equilibrium isotherm equations are obtained which reveal that the Adsorption isotherm declines as the reversibility of the Adsorption process decreases. Based on this concept, it is proposed that particle concentration (Cp) can universally affect Adsorption isotherms, depending on its effect on the metastable-equilibrium Adsorption state or the Adsorption reversibility.

  • metastable equilibrium Adsorption Theory ii experimental
    Journal of Colloid and Interface Science, 1998
    Co-Authors: Peter S Liss
    Abstract:

    Abstract In a controlled simple aqueous system containing Zn–goethite, where a clear particle concentration effect (Cp effect) is observed, an increase in particle concentration (Cp) causes a simultaneous decrease in Adsorption reversibility and in the Adsorption isotherm. At the same time, Zn adsorbed under a lower Cp condition desorbs faster (indicating more Adsorption reversibility) than that under a higher Cp condition. In another controlled simple aqueous system of Cd–goethite, where no Cp effect is observed, changes in Cp does not cause discernible changes in Adsorption hysteresis and in the Adsorption isotherm. Little difference in desorption rate is observed for the Cd adsorbed under different Cp conditions. The experiments were designed to avoid several important sources of error. Both the Cp effect and the non-Cp effect results are qualitatively explained and quantitatively described by the MEA Theory (1).

Yuhping Chang - One of the best experts on this subject based on the ideXlab platform.

  • thin film elastohydrodynamic lubrication a power law fluid model
    Tribology International, 2006
    Co-Authors: Hsiaoming Chu, Yuhping Chang
    Abstract:

    A 1-D modified Reynolds equation for power-law fluid is derived from the viscous Adsorption Theory for thin film elastohydrodynamic lubrication (TFEHL). The lubricating film between solid surfaces is modeled as three fixed layers, which are two Adsorption layers on each surface and a middle layer between them. The comparisons between classical non-Newtonian EHL and non-Newtonian TFEHL are discussed. Results show that the TFEHL model can reasonably calculate the pressure distribution, the film thickness, the velocity distribution and the average viscosity. The thickness and viscosity of the Adsorption layer and the flow index influence the lubrication characteristics of the contact conjunction significantly. The film thickness increases with the increase of flow index. As the flow index becomes greater, the dimple in the film shape moves towards the center of the contacts. The effect of flow index produces an obvious difference in the pressure distribution. The greater the flow index, the greater the pressure spike, and the pressure spike tends to move toward the center. The larger the flow index, the more the velocity varies in both the middle layer and Adsorption layers along the Z-axis. The greater the thickness and viscosity of the Adsorption layer and the flow index, the greater the deviation in central film thickness versus speed between EHL model and TFEHL model produced in the very thin film regime.

Nobuyuki Matubayasi - One of the best experts on this subject based on the ideXlab platform.

  • Fluctuation Adsorption Theory: quantifying adsorbate-adsorbate interaction and interfacial phase transition from an isotherm.
    Physical chemistry chemical physics : PCCP, 2020
    Co-Authors: Seishi Shimizu, Nobuyuki Matubayasi
    Abstract:

    How adsorbate-adsorbate interaction determines the functional shape of an Adsorption isotherm is an important and challenging question. Many models for the Adsorption isotherm have been proposed to answer this question. However, a successful fitting of an isotherm on its own is insufficient to prove the correctness of the model assumptions. Instead, starting from the principles of statistical thermodynamics, we propose how adsorbate-adsorbate interactions can be quantified from an isotherm. This was made possible by extending the key tools of solution statistical thermodynamics to adsorbates at the interface, namely, the Kirkwood-Buff and McMillan-Mayer theories, as well as their relationship to the thermodynamic phase stability condition. When capillary condensation and interfacial phase transition are absent, adsorbate-adsorbate interactions can be quantified from an isotherm using the Kirkwood-Buff integrals, and virial coefficients can yield multiple-body interaction between adsorbates. Such quantities can be obtained directly from the fitting parameters for the well-known isotherm models (e.g., Langmuir, BET). The size of the adsorbate cluster involved in capillary condensation and interfacial phase transition can also be evaluated from the isotherm, which was demonstrated for the Adsorption isotherm of water on activated carbons of varying pore sizes from the literature. Signatures of isotherm classifications by IUPAC have been characterized in terms of multiple-body interactions between adsorbates.

  • preferential solvation dividing surface vs excess numbers
    Journal of Physical Chemistry B, 2014
    Co-Authors: Seishi Shimizu, Nobuyuki Matubayasi
    Abstract:

    How do osmolytes affect the conformation and configuration of supramolecular assembly, such as ion channel opening and actin polymerization? The key to the answer lies in the excess solvation numbers of water and osmolyte molecules; these numbers are determinable solely from experimental data, as guaranteed by the phase rule, as we show through the exact solution Theory of Kirkwood and Buff (KB). The osmotic stress technique (OST), in contrast, purposes to yield alternative hydration numbers through the use of the dividing surface borrowed from the Adsorption Theory. However, we show (i) OST is equivalent, when it becomes exact, to the crowding effect in which the osmolyte exclusion dominates over hydration; (ii) crowding is not the universal driving force of the osmolyte effect (e.g., actin polymerization); (iii) the dividing surface for solvation is useful only for crowding, unlike in the Adsorption Theory which necessitates its use due to the phase rule. KB thus clarifies the true meaning and limitatio...

Georgy Shashurin - One of the best experts on this subject based on the ideXlab platform.

  • crack propagation engineering model stress intensity dependence of crack growth rate in hydrogen embrittlement material
    ECF19, 2013
    Co-Authors: Pavel A Tarakanov, Georgy Shashurin
    Abstract:

    Based on various mechanisms of hydrogen diffusion in metals, different crack propagation models and stress intensity dependence of crack growth rate have been developed. Engineering model of another hydrogen-assisted cracking in metal materials is presented in this paper. This model is based on simultaneous solution of two various problems: diffusion of hydrogen in metal problem and fracture mechanics problem. Special characteristic, which bonds material and environment, is introduced to colligate these two problems together in proposed model. Engineering model is discontinuous in the present case. The value of crack growth is not a constant. Crack moves out when the concentration of hydrogen in the crack tip reaches maximum permissible value. This magnitude is chosen from the special characteristic mentioned above. The stress intensity dependence of crack growth rate, calculated by authors, has a good correlation with Panasyuk`s experimental data. Introduction Hydrogen embrittlement is a form of environmentally assisted failure which is caused by the action of hydrogen often in combination with stress resulting in the reduction of the load bearing capacity of a component. The problem of hydrogen embrittlement in metal alloys is converged in various types of machine components. There are pipelines for oil and gas transportation, significant components of power plants, such as steam generator tubes boilers, steam/water pipe lines among them. Hydrogen embrittlement was main cause accident of fuel cladding in nuclear reactors (Caskey et al 1962), cracking of fossil fuel boilers tubes (Weiss 1993; Speidel & Atrenes 1984; Metals handbook 1987), retaining rings of generator rotors (Speidel &Atrenes 1984), waterside components of condensers (Metals handbook 1987) and in many other components where there is a possibility of hydrogen ingress in the material. These various components are made from metallic alloys, for example, based on Fe, Ni, Al, Ti, Zr, Ta, which are responsive to hydrogen embrittlement. Hydrogen embrittlement has a pernicious influence on life of the mentioned above machine components. There are many well-known researches and various theories (Panasyuk 1981, Cherepanov 1973, Matvienko 2004), which estimate life of a machine component and structures by means of specific crack propagation engineering models. Therefore crack propagation engineering model of hydrogen embrittlement material research is one of the modern mechanics technical problems. In this paper one of the possible variant of engineering model, which describes the crack growth in hydrogenation structure, is presented. Results, calculated by authors, by means of this model have a good correlation with the experimental data (Panasyuk 1988). Crack propagation engineering model: structure Hydrogen penetrates into material through the material-environment interface due to diffusion process. This process is dependent on different variables: temperature, hydrogen concentration, mechanical properties of material etc. There are many various theories, which describe the mechanisms of hydrogen penetration into material [1-10]. Each Theory explains some experimental observations. Pressure Theory (Zappfe & Sims 1941), Surface Adsorption Theory (McMahon C J Jr,Vitek V 1979), Decohesion Theory (Oriani & Josephic, 1974), Hydrogen enhanced localized plasticity mechanism (Sirois & Birnbaum, 1992), Hydride Theory (Matvienko 2004) are well known theories of hydrogen embrittlement of solid materials. In case of unidirectional diffusion and tension of a sample, hydrogen penetration into material describes by Eq. 1. Boundary and initial conditions are presented below too.

  • crack propagation engineering model stress intensity dependence of crack growth rate in hydrogen embrittlement material
    ECF19, 2013
    Co-Authors: Pavel A Tarakanov, Georgy Shashurin
    Abstract:

    Based on various mechanisms of hydrogen diffusion in metals, different crack propagation models and stress intensity dependence of crack growth rate have been developed. Engineering model of another hydrogen-assisted cracking in metal materials is presented in this paper. This model is based on simultaneous solution of two various problems: diffusion of hydrogen in metal problem and fracture mechanics problem. Special characteristic, which bonds material and environment, is introduced to colligate these two problems together in proposed model. Engineering model is discontinuous in the present case. The value of crack growth is not a constant. Crack moves out when the concentration of hydrogen in the crack tip reaches maximum permissible value. This magnitude is chosen from the special characteristic mentioned above. The stress intensity dependence of crack growth rate, calculated by authors, has a good correlation with Panasyuk`s experimental data. Introduction Hydrogen embrittlement is a form of environmentally assisted failure which is caused by the action of hydrogen often in combination with stress resulting in the reduction of the load bearing capacity of a component. The problem of hydrogen embrittlement in metal alloys is converged in various types of machine components. There are pipelines for oil and gas transportation, significant components of power plants, such as steam generator tubes boilers, steam/water pipe lines among them. Hydrogen embrittlement was main cause accident of fuel cladding in nuclear reactors (Caskey et al 1962), cracking of fossil fuel boilers tubes (Weiss 1993; Speidel & Atrenes 1984; Metals handbook 1987), retaining rings of generator rotors (Speidel &Atrenes 1984), waterside components of condensers (Metals handbook 1987) and in many other components where there is a possibility of hydrogen ingress in the material. These various components are made from metallic alloys, for example, based on Fe, Ni, Al, Ti, Zr, Ta, which are responsive to hydrogen embrittlement. Hydrogen embrittlement has a pernicious influence on life of the mentioned above machine components. There are many well-known researches and various theories (Panasyuk 1981, Cherepanov 1973, Matvienko 2004), which estimate life of a machine component and structures by means of specific crack propagation engineering models. Therefore crack propagation engineering model of hydrogen embrittlement material research is one of the modern mechanics technical problems. In this paper one of the possible variant of engineering model, which describes the crack growth in hydrogenation structure, is presented. Results, calculated by authors, by means of this model have a good correlation with the experimental data (Panasyuk 1988). Crack propagation engineering model: structure Hydrogen penetrates into material through the material-environment interface due to diffusion process. This process is dependent on different variables: temperature, hydrogen concentration, mechanical properties of material etc. There are many various theories, which describe the mechanisms of hydrogen penetration into material [1-10]. Each Theory explains some experimental observations. Pressure Theory (Zappfe & Sims 1941), Surface Adsorption Theory (McMahon C J Jr,Vitek V 1979), Decohesion Theory (Oriani & Josephic, 1974), Hydrogen enhanced localized plasticity mechanism (Sirois & Birnbaum, 1992), Hydride Theory (Matvienko 2004) are well known theories of hydrogen embrittlement of solid materials. In case of unidirectional diffusion and tension of a sample, hydrogen penetration into material describes by Eq. 1. Boundary and initial conditions are presented below too.

Fazhong Yang - One of the best experts on this subject based on the ideXlab platform.

  • inhibition effect of nonionic surfactant on the corrosion of cold rolled steel in hydrochloric acid
    Corrosion Science, 2008
    Co-Authors: Xianghong Li, Guannan Mu, Hui Fu, Shuduan Deng, Fazhong Yang
    Abstract:

    Abstract The inhibition effect of Tween-20 as a nonionic surfactant on the corrosion of cold rolled steel (CRS) in 1.0–8.0 M HCl has been studied at different temperatures (20–50 °C) by weight loss and potentiodynamic polarization methods. Atomic force microscope (AFM) provided the CRS surface conditions. The results show that Tween-20 is a good inhibitor in 1.0 M HCl, and the inhibition efficiency (IE) increases with the inhibitor concentration, while decreases with increasing the hydrochloric acid concentration and temperature. Effect of immersion time was also studied and discussed. The Adsorption of inhibitor on the CRS surface obeys the Langmuir Adsorption isotherm equation. Both thermodynamic and kinetic parameters have been obtained by Adsorption Theory and kinetic equations. The inhibition effect is satisfactorily explained by the parameters. Polarization curves show that Tween-20 is a mixed-type inhibitor in hydrochloric acid. The results obtained from weight loss and polarization are in good agreement, and Tween-20 inhibition action could also be evidenced by surface AFM images.