Papers by Keyword: Surface Tension

Abstract: The FeSi system is a compound forming alloy which exhibits the interesting behavior with respect to the composition. In present work, the thermophysical properties of FeSimelts at 1873 K have been explored on using four-parameter model which is based on Maclaurin infinite series. The analytical expressions for various thermodynamic and microscopic functions have been deduced using the standard thermodynamic relations. The model parameters are estimated using experimental data of activity coefficients and excess free energy of mixing for FeSi melts at 1873 K. For theoretical calculations of the thermophysical properties of FeSi liquid alloys at 1873 K, the same values of the model parameters are used in order to maintain the consistency. The composition dependence of theoretical data for Gibbs free energy of mixing and thermodynamic activities are in excellent agreement with the corresponding experimental data at 1873 K. On using the temperature dependence of model parameters, the enthalpy of mixing and entropy of mixing of FeSi molten alloys at 1873 K arecomputed. There is a well agreement between the theory and experiment. The theoretical values of concentration-concentration structural factor, known as concentration fluctuations in the long wavelength limit agree well with experimental data for FeSi system in molten state at 1873 K. The microscopic function such as short-range order parameter has also been computed as a function of concentration of FeSi melts at 1873 K. Again, the surface properties such as surface concentration and surface tension of FeSi molten alloys at the temperatures at 1823 K and 1873 Kare analyzed by Butler modelin the framework of four-parameter model. The theoretical values are compared with the data available in the literature at 1823 K which show well agreement. Again, the excess free energy of mixing, heat of mixing, concentration fluctuations and short-range order parameter are explored at 1823 K, 1873 K, 1923 K and 2073 K. Further, the transport properties like diffusivity ratio and viscosity of FeSi liquid alloys at 1823 K, 1873 K, 1923 K and 2073 Kare computed. For this, a simple statisticalmechanical modeli.eMoelwyn-Hughes model isemployed in the framework of four-parameter model. The theoretical data exhibit the qualitative agreement with the data available in the literature. The present study reveals that FeSi melt is an ordered system in the temperature range 1823-2073 K. The model parameters are temperature dependent. The concentration dependence of short-range order parameter and diffusivity ratio indicates that there is a likelihood of the existence of complex in FeSi liquid alloys. Keywords:Free energy of mixing; heat of mixing; concentration fluctuations; short-range order parameter, surface tension; viscosity

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: This work investigated the surface tension and kinematic viscosity of the multicomponent Fe_73.5Cu₁Nb₃Si_13.5B₉ melt. A relationship was found between surface tension and kinematic viscosity, which manifests itself in a synchronous change in these quantities at temperatures of 1600 and 1780 K. In the temperature range 1600–1780 K, there is a sharp increase in surface tension upon heating and the same decrease upon cooling. The increase in surface tension during heating was explained by the appearance of a large number of free Nb atoms as a result of the dissolution of the residual crystalline phase in the mushy zone, and their diffusion to the melt surface. The drop in the surface tension on cooling below 1780 K is associated with the liquid–liquid structure transition (LLST), which stimulates the outflow of Nb atoms from the surface in order to form new stable clusters. The LLST manifests itself in a change in the activation energy of a viscous flow, which is higher in the high-temperature region and corresponds to the motion of larger clusters with a length scale of about 1 nm.

Abstract: Naturally-occurring saturated fatty acids have been classified as the interesting biomaterials. Typically, the interfacial tension and wettability relying on intermolecular forces relate to the well-fitted performance with any target sites of in situ forming matrix. This research aimed to determine surface tension/contact angle of several saturated fatty acids in selected aprotic solvents commonly used in in situ forming system by varying fatty acid concentrations and molecular weights. Six fatty acids were dissolved in the aprotic solvents, namely 2-pyrrolidone (PYR), N-methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide (DMSO). As fatty acid concentrations in binary mixtures increased, surface tension and contact angle became diminished except where DMSO was used as a solvent. The longer chain of fatty acid, the lower the surface tension except when C_14-16 fatty acid was dissolved in NMP. Contact angle was also decreased as the chain of fatty acid increased except for C_14-16 fatty acid-based preparation due to their viscosity. Understanding these fatty acid solution's surface tension/contact angle behaviors is useful for designing the suitable fatty acid-based in situ forming system.

Abstract: The polytherms of density, surface tension of the Cu-Al system melts and wetting angles of Ni-Cr, Co-Cr substrates, 25X18H9C2 stainless steel and titanium were studied by the sessile drop method. The drop contour was processed by dint of current information technologies, in particular, using the ImageJ software package [1]. The equations of density polytherms and surface tension of the Cu-Al system melts were established. It was shown that Cu-Al melts wet the substrates at 1000 K and more. We revealed the features of temperature dependences of the wetting angles.

Abstract: The paper presents experimental results on the dependence of surface tension on the concentration of a suspension of bentonite (0 - 10% by weight). The isotherms σ of aqueous suspensions of bentonite are characterized by local minima in the concentration range of 3-4 mass% of the solid phase. It has been established that a decrease in the average particle size leads to the disappearance of the extremum on the surface tension isotherms. The data obtained led to the conclusion that the most important factors affecting the nature of the isotherms of the surface tension of bentonite suspensions are the degree of dispersion and the presence in the aqueous suspension of bentonite, both colloidal and coarse particles.

Abstract: The experimental study results of the melts concentration dependence of the surface tension of the four-component indium-tin-lead-bismuth system and its constituent binary systems of indium-tin, indium-lead, indium-bismuth, tin-lead, tin-bismuth, lead-bismuth are presented in the paper. It is shown that the concentration dependence of the melts surface tension of the In-Sn-Pb-Bi four-component system can be predicted from the data on ST (surface tension) values of lateral binary systems. Features in the ST isotherms in the form of a minimum are observed only in the indium-tin lateral system from all lateral binaries. A distinctive feature of the detected minimum is that the minimum depth slightly exceeds the experimental error. Therefore, in addition to the fact that the area of average compositions was studied more thoroughly, we carried out the surface tension measurements by two independent methods. The experimental data obtained by both methods coincide within the experimental error and indicate the extremum availability on ST isotherms. Thus, ST experimental studies by two independent methods confirmed the presence of a flat minimum on ST isotherms of the indium-tin binary system increasing the reliability of the obtained data. The obtained outcomes and their comparison with experimental data have shown that the considered models for predicting surface properties based on data due to similar properties of lateral binary systems adequately reflect the experimental dependences. However, the prediction model based on Kohler's method of excess values describes the experimental curves more accurately.

Abstract: This paper discusses the results of experimental studies on the selection of the repair mixture compound for recreating the surface layer of the historical brick of the 18^th century architectural monument “Commercial Bank” in Arkhangelsk. According to the research results, it was found that the historical brick has a relatively higher density and increased calcium content than the modern one. The characteristics of the surfaces of the analyzed materials based on the component indicators of specific surface energy showed that the brick of 1859, characterized by the highest degree of destruction, has the maximum value of the polar energy component. This fact may indicate a greater hydrophilicity of the surface in relation to atmospheric water and, as a result, a more intensive degradation process. It is established that the composition of the repair mixture with the addition of brick crumbs in the amount of 50 % has a value of the polar part of the surface tension equal to similar parameters for historical bricks (1786 and 1859) after their preliminary priming. The use of this mixture to recreate the surface layer of the brick will allow atmospheric water to pass freely through the repair compound and the body of the brick, without concentrating on the interface and without causing its destruction and detachment when drying.

Abstract: The paper presents an analysis of positions, which a theory of a liquid wetting a solid surface is based on, using the sitting drop equilibrium as an example. Certain inconsistencies are indicated in these positions, which is the subject of the discussion. The paper explains why the interfacial tension of solid-gas has no effect on the equilibrium of a drop. It proposes a mechanism to form a liquid-solid interface layer, the tensor of interfacial tensions of which is represented as a pressure tensor. It is established that the surface tension of the interface layer is variable and changes in magnitude and direction depending on the wetting conditions. It is determined that it is not possible to present a range of phenomena accompanying the wetting of a solid surface with a liquid by examining the equilibrium of a three-phase contact line.

Abstract: Borneol and dimethyl sulphoxide (DMSO) have been used as the skin penetration enhancers. Different concentrated borneol solutions in aprotic DMSO were prepared as the binary mixtures and determined their surface tension and contact angle behaviors using goniometer. Low borneol concentration minimized the surface tension and there was nearly stable contact angle for 30-70% borneol solutions. The trend contact angle value was decreased on glass slide, acrylic and LDPE whereas increasing on agarose gel and porcine tissues including buccal mucosa, gum and tongue with borneol concentration dependence. However, the borneol-DMSO binary mixture exhibited high wettability owing to its contact angle on glass surface was less than 90°. The solvent exchange between DMSO of borneol solutions and aqueous phase form agarose gel and porcine tissues including tongue, gum and buccal mucosa initiated the phase transformation from solution into matrix-like and promoted the higher contact angle with borneol concentration dependence. The understanding of surface tension and contact angle behaviors of aprotic borneol-DMSO binary mixture is useful for developing them into in situ forming gel for drug delivery such as in the oral cavity.