Temperature Coefficient Of Surface Tension Research Articles

Fundamental Research on the Mechanism of High-Speed Welding Undercut

Undercut is one of the most important problems which restrict welding speed. The research indicated that surface flow direction of welding pool near the periphery is the most important reason of undercut occurred. When the existence of surface active element (e.g. the content of S is about 0.02-0.04% in steel) change the sign of surface tension temperature coefficient to positive, undercut always occurs in TIG moveless welding, and not occurs when the content of S in iron is very low( e.g. S% is less 0.01%). Temperature gradient is the most important factor which influences the depth of undercut. The depth of undercut is bigger with the increase of temperature gradient when the other parameters are the same. When filling metal into welding pool, it restrained the molten metal movement from periphery to the pool center. So it can reduce the tendency of undercut, and eliminate undercut as increasing of filling metal ultimately.

Time Dependent Effects in Surface Tension Measurements of an Industrial Fe‐alloy

AbstractThe surface tension of an industrial FeC‐alloy containing Si, Mn and S in the few atomic per cent range was measured by the oscillating drop method in ground based electromagnetic levitation and under reduced gravity conditions on board a parabolic flight. The results from the parabolic flight exhibited a large variation between different heating cycles and a discrepancy with the ground based experiments with regard to the value of the surface tension at the liquidus temperature and the temperature coefficient. The variation of the surface tension temperature coefficient is interpreted as resulting from the loss of volatile surface active components such as S and Si in subsequent heating cycles. The results demonstrate the importance of the time scale of the measurement and ambient atmosphere for surface tension measurements of industrial alloys containing volatile surface active components. For comparison with the experimental values the surface tension and segregation were modelled using different models. As a result of the analysis, the surface tension as a function of temperature best representing the starting industrial alloy is obtained as σ(T) = 1.52–1.53 10‐4 (T–1752K) Nm‐1.

Surface properties of liquid In–Zn alloys

The measurements of surface tension and density of zinc, indium and liquid In–Zn alloys containing 0.9, 0.85, 0.75, 0.70, 0.60, 0.40, 0.25 and 0.10mole fraction of In were carried out using the method of maximum pressure in gaseous bubbles (MBP) as well as dilatometric technique. The technique of sessile drop was additionally applied in the measurements of surface tension for pure indium and zinc. The measurements were performed at temperature range 474–1151K. The isotherms of surface tension calculated based on Butler's equation at 700 and 1100K corresponded well with the experimental values for zinc content lower than 0.6mole fraction. The surface tension calculated for alloys of higher zinc concentrations (0.6<XZn<0.95) had a positive value of the surface tension temperature coefficient (dσ/dT), which did not coincide with the experimental results. The density as well as molar volume of liquid In–Zn alloys showed almost identical behaviour like the ideal solutions. The observed little deviations were contained within assessed experimental errors.

Pressure–volume–temperature data and surface tension of blends of poly(ethylene oxide) and poly(methyl acrylate) in the melt

AbstractThe pressure–volume–temperature behavior of miscible blends of poly(ethylene oxide) (PEO) and poly(methyl acrylate) (PMA) was studied over extended ranges of temperature and pressure. From pressure–volume–temperature data, the reduction parameters for the Flory‐Orwoll‐Vrij equation‐of‐state were determined. It was found that reduction parameters as well as density, thermal expansion coefficient, and isothermal compressibility vary with composition in a nonlinear manner. The surface tension of the blends in the molten state was measured over the whole composition range using the sessile drop method. The surface tension was found to display negative deviation from additivity pointing toward a remarkable surface excess of PMA. Moreover, surface tension displays a minimum in the range of low PEO content at weight fraction of ∼0.19. In addition, the temperature coefficient of surface tension shows negative deviation from linearity. It stays constant when PMA is in excess. Results are discussed in terms of equation‐of‐state thermodynamics. The minimum of surface tension can be well explained by weak self‐association of PEO in the bulk. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1893–1900, 2010

Relation between the temperature coefficient of surface tension and phase diagrams

An equation determining the relation between the temperature coefficient of surface tension and crystallization temperature was obtained. The equation was substantiated experimentally for solutions of NaOH and ZnCl2. The rule governing the alternation of structures in phase diagrams was found. A relation between phase diagram structures and structures in adsorbed surface layers of liquid solutions at microconcentrations of surface-active components was derived.

Monte Carlo simulation of thermophysical properties of Ni-15%Mo alloy melt

The Monte Carlo method with EAM potential is used to simulate the liquid Ni-15%Mo binary alloy system, from which the thermophysical properties hardly measured by experimental measurement can be obtained. The simulated surface tension of liquid Ni-15%Mo alloy at the melting temperature is 1.918 N/m, and the simulated temperature coefficient of surface tension as a function of temperature is σ=1.918-1.130×10-3（T-Tm） N/m. Based on the simulated surface tension, the variation of viscosity and solute diffusion coefficient within the range of from 1500 K to 2000 K can be deduced. The result of the viscosity is η=0.895exp（2.209×104/RT） mPa·s, that is, the viscosity constant is 0.895 mPa·s, and the apparent activation energy is 2.209×104 J/mol. The diffusion coefficient can then be obtained by the Stokes（Sutherland）-Einstein equation as D=9.803×10-8exp（-3.643×104/RT） m/s2， where the activation energy is 3.643×104 J/mol. From the relationship between system energy and temperature, the specific heat of liquid Ni-15%Mo alloy at different temperatures can be determined to be Cp=37.313-1.425×10-2（T-Tm） J·mol-1·K-1.

Numerical and experimental study of molten pool formation during continuous laser welding of AZ91 magnesium alloy

Heat transfer from the laser keyhole to the weld pool and details of the fluid flow play an important role in determining weld shape and size. In this work, both the experiment and the finite volume method (FVM) are utilized to investigate the thermal phenomena during continuous laser keyhole welding. Firstly, the experiments are carried out to examine the effects of laser welding parameters on the pool dimensions. Secondly, 3D FVM model is developed using the hydrodynamic software FLUENT to simulate the keyhole and pool formation during the interaction between continuous laser and AZ91 magnesium alloy sheet. In this simulation, based on a control volume method, a volumetric heat source is used to model the laser beam. Then, the equations of species, mass, momentum and energy are solved. Laser power and welding speed have a strong effect. Using the developed model, it has been found that the shape and size of the molten pool in the workpiece are affected by welding parameters such as welding speed and the incident laser power. Furthermore, it has been observed that the surface tension temperature coefficient, Marangoni convection, is sensitive to the active elements in the magnesium alloy composition. These coefficients also affect the pattern of the fluid flow in the molten pool. Finally, the simulation results were compared with the experimental data. The effectiveness of the developed computational procedure has been confirmed.

Estimation of the temperature coefficient of surface tension of the interface between phases which form a eutectic

Estimation of the temperature coefficient of surface tension of the interface between phases which form a eutectic

A unified model for the cohesive enthalpy, critical temperature, surface tension and volume thermal expansion coefficient of liquid metals of bcc, fcc and hcp crystals

First the cohesive enthalpy of pure liquid metals is modeled, based on experimental critical temperatures of alkali metals. The cohesive enthalpies are scaled to the melting points of pure metals. The temperature coefficient of cohesive enthalpy is the heat capacity of the liquid metal. The surface tension and its temperature coefficient for pure liquid metals are modeled through the excess surface enthalpy, excess surface entropy and molar surface area supposing that the outer two surface layers of liquid metals are similar to the {1 1 1} plane of fcc crystals. The volumetric thermal expansion coefficient of liquid metals is scaled to the ratio of the heat capacity and cohesion enthalpy. From known values of melting point, heat capacity and molar volume the following calculated properties of liquid metals are tabulated: (i) cohesive enthalpy at melting point, (ii) cohesive energy of the solid metal at 0 K, (iii) critical temperature, (iv) surface tension at melting point, (v) volume thermal expansion coefficient, and (vi) temperature coefficient of surface tension. The present models are valid only for liquid metals of bcc, fcc or hcp crystals as only their structure and nature of bonding are similar enough to be treated together.

Marangoni convection and weld shape variation in A-TIG welding process

The flux effect on TIG weld shape variations is investigated by application of the heat transfer and fluid flow model. The simulation makes use of Nimonic 263 alloy, TiO, TiO 2 and Ti 2O 3 as the flux. The arc constriction and the reversed Marangoni convection are considered to be the two main factors for increasing penetration of A-TIG weld pool. And the simulated results show that the latter is the main factor for changing weld shapes. The surface tension temperature coefficient is sensitive to the active elements and affects the pattern of the fluid flow. By controlling the category and quantity of the active elements, different kinds of the weld shapes are obtained. The experimental result shows that increase of active flux on the weld bead tends to increase the penetration of the weld pool at first and then decreases steeply. This does not coincide with the simulated results. It is probably because part of the oxide in the flux is not totally decomposed when the flux reaches a critical value. The solid oxide particles in the weld pool act as the obstacles of the fluid flow and reduce the velocity of the flow.

Surface Tension and Density of Bismuth Germanate Melts as a Function of Composition and Temperature

The surface tension and density of xBi(2)O(3)-(1-x)GeO2 (BGO) melts have been measured systematically from their respective melting points up to around 1480 K within 0.25 <= x <= 0.86. With the addition of Bi2O3, the density of this system increased smoothly with a positive curvature. Deviation of molar volume from ideality of this system melts decreased firstly, past a minimum at about x=0.4, and then increased. Partial molar volumes of Bi2O3 and GeO2 have also been calculated based on the measured density data and compared with those of a binary bismuth borate system. On increasing the content of Bi2O3, the surface tension of BGO melts increased slowly when x <similar to 0.40, past a maximum at about x=0.50, and then decreased rapidly. In addition, the temperature coefficient of surface tension remained positive within the lower content range of Bi2O3, changed sign from positive to negative at about x=0.38, and then was almost independent of the composition within the measured temperature range when the Bi2O3 content was increased further.

Theoretical study of Marangoni convection and weld penetration under influence of high oxygen content in base metal

A 3D mathematical model is developed to simulate the weld pool development in a moving weld pool of 304 stainless steels with different oxygen concentrations. It is shown that the oxygen can cause significant changes in fluid flow patterns and temperature fields. When oxygen content is <280 ppm, the weld penetration and depth/width ratios increase sharply with increasing oxygen content; positive and negative temperature coefficients of surface tension coexist and cause shallow and wide weld pool. When oxygen content is in the range of 280–500 ppm, positive temperature coefficient of surface tension dominates the flow patterns and causes deep and narrow weld pool. The weld penetration and depth/width ratios remain nearly constant. When oxygen content is >500 ppm, the weld penetration and depth/width ratios decrease again. Vortexes that have different positions, strength and directions may be found in the pool. The vortexes with opposite directions caused by positive temperature coefficient of surface tension can efficiently transfer the thermal energy from the arc, creating a deep weld pool.

An Examination of Surface Tension of Binary Lithium Borate Melts as a Function of Composition and Temperature

Surface tensions of xLi2O–(1−x)B2O3 melts, where 0≤x≤0.68, have been measured systematically with a ring method from respective liquidus temperatures up to about 1450 K. For all of the investigated melts, the relationship between surface tension and temperature can be well described by quadratic polynomial functions. With increasing Li2O content, surface tension monotonously increased, whereas the temperature coefficient of surface tension increased slowly up to about x=0.1, changed sign from positive to negative at about x=0.2, and then remained negative with further increasing Li2O content. Together with the physical properties reported in our previous work, such as density, temperature coefficient of density, and volume expansion coefficient, etc., both surface tension and temperature coefficient of surface tension have been comparatively plotted as a function of Li/B molar ratio. Differentiated from the inflections of slope in the plots of physical properties vs. Li/B molar ratio, three characteristic regions have been found in the melts of this system. Within different regions, different effects of temperature and concentration on the physical properties of melts have been observed.

Thermophysical properties of Ni-5%Sn alloy melt

The surface tension and specific heat of Ni-5%Sn alloy melt were measured by the oscillating drop method and the drop calorimetric method using electromagnetic levitation, respectively. The temperature coefficient of surface tension is 6.43×10−4 N·m−1K−1 within the temperature regime of 1464–1931 K. The enthalpy change was measured in the temperature range from 1461 to 1986 K, and the average specific heat was obtained as 43.03 J·mol−1K−1. Some other thermophysical properties, such as viscosity, solute diffusion coefficient, density, thermal diffusivity and thermal conductivity of this alloy melt, were derived based on the experimentally measured surface tension and specific heat. Using these thermophysical parameters, the relation between solute trapping and undercooling in rapidly solidified α-Ni was calculated, and the theoretical prediction shows a good agreement with experimental data.

The study of surface active element on weld pool development in A-TIG welding

A 3D mathematical model was developed to simulate the weld pool development in a moving A-TIG weld pool with different oxygen and sulfur concentrations. It is shown that the surface active elements—oxygen and sulfur, which change the temperature coefficient of surface tension from a negative value to a positive one, can cause significant changes in fluid flow patterns and the weld penetration. When surface active element content increases, the weld penetration and depth/width ratio increase sharply and then remain nearly a constant. Positive temperature coefficient of surface tension dominates the fluid flow and the weld pool is narrow and deep. The further increasing surface active element content leads to an inappreciable difference in the weld pool size and shape when the oxygen content increases beyond 280 ppm and sulfur content beyond 125 ppm. Positive and negative temperature coefficients of surface tension co-exist in the weld pool when surface active element content is less than the critical value. The fluid flows in the weld pool change apparently with different surface active element. Depending upon the oxygen and sulfur concentrations, three, one or two vortexes that have different positions, strength and directions may be found in the weld pool. The vortexes with opposite direction caused by positive temperature coefficient of surface tension can efficiently transfer the thermal energy from the arc, creating a deep weld pool.

Neural network model of heat and fluid flow in gas metal arc fillet welding based on genetic algorithm and conjugate gradient optimisation

Although numerical calculations of heat transfer and fluid flow can provide detailed insights into welding processes and welded materials, these calculations are complex and unsuitable in situations where rapid calculations are needed. A recourse is to train and validate a neural network, using results from a well tested heat and fluid flow model to significantly expedite calculations and ensure that the computed results conform to the basic laws of conservation of mass, momentum and energy. Seven feedforward neural networks were developed for gas metal arc (GMA) fillet welding, one each for predicting penetration, leg length, throat, weld pool length, cooling time between 800°C and 500°C, maximum velocity and peak temperature in the weld pool. Each model considered 22 inputs that included all the welding variables, such as current, voltage, welding speed, wire radius, wire feed rate, arc efficiency, arc radius, power distribution, and material properties such as thermal conductivity, specific heat and temperature coefficient of surface tension. The weights in the neural network models were calculated using the conjugate gradient (CG) method and by a hybrid optimisation scheme involving the CG method and a genetic algorithm (GA). The neural network produced by the hybrid optimisation model produced better results than the networks based on the CG method with various sets of randomised initial weights. The CG method alone was unable to find the best optimal weights for achieving low errors. The hybrid optimisation scheme helped in finding optimal weights through a global search, as evidenced by good agreement between all the outputs from the neural networks and the corresponding results from the heat and fluid flow model.

Measurement and calculation of surface tension of molten Sn–Bi alloy

The surface tension of molten Sn–Bi (mole fraction X Bi = 0.455 ) alloy has been determined by the sessile drop method at oxygen partial pressure ( P O 2 ) of 1.0 × 10 −6 MPa and different temperatures. The experimental results have been analyzed and discussed, and the positive temperature coefficient of surface tension of molten Sn–Bi alloy has been elucidated. The surface tension of this molten alloy has also been obtained by calculation using STCBE based on Butler's equation and thermodynamic data. The experimental results agree well with the calculation values.

The Surface Tension and Density of Liquid Ag–Bi, Ag–Sn, and Bi–Sn Alloys

The sessile drop method has been used to measure density and surface tension for pure Ag, Bi, Sn, and their mixtures. For pure metals and Bi–Sn alloys negative temperature coefficients of surface tension have been obtained. In case of Ag–Bi and Ag–Sn alloys the temperature coefficients of surface tension take negative or positive values depending on composition. Experimental values of the surface tension for Ag–Bi, Ag–Sn, and Bi–Sn are compared with those computed from Butler’s model. A relatively good agreement is observed.

Features of the relief formed on the surface of quartz glass under the action of a moving beam of a cw CO2 laser

This paper discusses the surface-relief profiles of quartz glass after it is acted on by the moving focused beam of a cw CO2 laser. The results are explained well in terms of a thermocapillary mechanism of relief formation, if the temperature coefficient of surface tension of the glass changes sign as the temperature increases. The phenomenon whereby a flat floor is formed in the microchannel that remains after the glass solidifies is detected and qualitatively explained.

Surface tension of PbO-B2O3 and Bi2O3-B2O3 glass melts

The surface tensions of xPbO-(100−x) B2O3 (x = 30–80 mol%) and xBi2O3-(100−x) B2O3 (x = 0–100 mol%) melts were measured using the ring method over the temperature range 973 to 1373 K. The compositional and temperature dependences of surface tension were investigated. Addition of PbO and Bi2O3 to B2O3 increased the surface tensions of their respective PbO-B2O3 and Bi2O3-B2O3 melts. The surface tension showed a maximum at 60 mol% PbO in the PbO-B2O3 melts and at 70–80 mol% Bi2O3 in the Bi2O3-B2O3 melts. The temperature coefficient of surface tension was examined on the basis of its relationship to the structure, and it was suggested that the temperature coefficient of surface tension decreases with an increasing content of four-coordinated boron.