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A new testing procedure combining in one test two methods for surface tension measurements of liquid metals [the pendant drop (PD) and the sessile drop] and carried out in the same device is discussed. The attention is focused on methodological aspects of the PD method due to the novelty of its application for high temperature metallic systems. It has been claimed that under the conditions applied in the present study, this method can be considered as a quasi-containerless one. Surface tension measurements of pure Cu, Ni, Al, and Fe performed using the new procedure are described. To confirm the validity of this procedure, the experimental results are discussed in the framework of the available literature data, particularly those obtained by the containerless methods. © 2013 The Author(s).

Auger measurements of the surface composition have been performed on solid and molten Pb-5at%Sn alloys. They confirm the theoretical predictions that, in the absence of oxygen, liquid or solid alloys exhibit no significant surface segregation. On the contrary, surface composition measurements and simultaneous surface tension measurements clearly show that oxygen adsorption strongly affects the segregation of tin at the liquid-vapour interface. This surface enrichment is driven by the contribution of the reaction free energy and of the products surface tension.

The problem of oxygen exchange at the interface between a gas and a liquid metal is treated for systems under a “vacuum” (Knudsen regime, pressures lower than 1 Pa), where, due to the large mean free path of gas molecules in a vacuum, transport processes in the gas phase have no influence on the total interphase mass exchange, which is controlled by interface phenomena and by oxygen partition equilibrium inside the liquid. Owing to the double contribution of molecular O2 and volatile oxides to the oxygen flux from the surface, non-equilibrium steady-state conditions can be established, in which no variations in the composition of the two phases occur with time, as the result of opposite oxygen exchanges. The total oxygen and metal evaporation rates are evaluated as a function of the overall thermodynamic driving forces, and an account of the transport kinetics is given by using appropriate coefficients. A steady-state saturation degree s r, is defined which relates the oxygen activity in the liquid metal to the O2 pressure imposed and to the vapour pressures of volatile oxides. When metals able to form volatile oxides are considered, pressures of molecular O2 higher than those defined under equilibrium conditions have to be imposed in the experimental set-up in order to obtain a certain saturation degree, as a consequence of the condensation of the oxide vapours on the reactor walls. Effective oxidation parameters are determined, which define the conditions leading the liquid to a definite steady-state composition under a “vacuum” when it is out of equilibrium. The effective value of the oxygen pressure which corresponds to the complete oxygen saturation of the metal, $$P_{O_{2,} s}^E $$ , is evaluated at different temperatures for the systems Si-O and Al-O. The results are represented as curves of $$P_{O_{2,} s}^E $$ against T, which separate different oxidation regimes; these results agree well with the experimental data found in the literature.

A kinetic and fluodynamic description of processes that may take place near the liquid-vapour interface in the presence of an inert carrier flow containing definite oxygen amounts is presented, in relation to surface tension measurements. The evaluation of the Thiele modulus, φ, and of the parameter e0 (which compares the magnitude of the fluxes of interest to and from the surface), allows definition of the regimes in which fast or slow reactions in the gas phase surrounding a drop of liquid metal are possible in the presence of variable oxygen concentrations. The kinetic features of the process are described in terms of these different reaction regimes, and on the basis of the thermodynamic stability of the possible oxidation products. Diagrams on a plane log φ2/log e0 are drawn, immediately allowing one to know the range of \(P_{O_2 }^0 \) and T in which the reaction considered is thermodynamically possible, and to foresee the evolution in this field from a kinetic point of view, as a function of \(P_{O_2 }^0 \) and T. Therefore, the treatment presented here (and applied to selected cases of technological interest) allows a “stability field” for a chosen oxide on the log φ2/log e0 plane to be defined, and the behaviour of the system from a kinetic-fluodynamic point of view to be predicted when the flow parameters and the geometry of the experimental set-up are known. In particular, the reactive gas fluxes at the liquid-vapour interface can be evaluated as a function of the different experimental conditions. Kinetic-fluodynamic diagrams for liquid metal-oxygen systems containing Pb, Sn, Zn, Cu and Al are presented, as well as an application of the model to surface tension measurements on liquid tin, which gives semi-quantitative confirmation of the theory developed here.

A kinetic and fluodynamic description of processes that may take place near the surface of some liquid metals in the presence of a gas flow containing definite oxygen amounts is given, with a particular regard to the thermodynamic properties of the metal-oxygen system and to the geometry of the experimental set-up. Diagrams have been obtained from which the following items of information are simultaneously available: (1) the range of P02 and T in which the reaction considered is thermodynamically possible; (2) the accessibility of oxygen to the liquid metal surface, and the thermodynamic-kinetic conditions for which this surface can be considered oxygen free. Therefore, the treatment presented here and applied to many cases of technological interest allows us to define (a) the physical and chemical equilibrium conditions of a liquid metal surface in the presence of oxygen diluted in an inert gas carrier, under total pressures ranging from about 10−4 to 0.1 MPa (10−3−1 m), and (b) the kinetic and fluodynamic characteristics of the process through which the quilibrium conditions are reached, the geometry of the experimental set-up having been given.

The mixing behaviour of liquid Sb–Sn alloys has been described in terms of energetics and structure through the study of their thermodynamic, surface, transport and structural properties by using the Complex Formation Model (CFM) in the weak interaction approximation and by postulating SbSn chemical complexes as energetically favoured. The new Sb–Sn surface tension experimental data, obtained by the pinned drop method at temperatures ranging from 513 to 1023 K , have been analysed in the framework of the CFM and compared with the calculated values as well as with the corresponding literature data. The structural characteristics of Sb–Sn melts are described by the two microscopic functions, i.e. the concentration fluctuations in the long-wavelength limit and the Warren–Cowley short-range order parameter.

Surface tension measurements are a central task in the study of surfaces and interfaces. For liquid metals, they are complicated by the high temperatures and the consequently high reactivity characterising these melts. In particular, oxidation of the liquid surface in combination with evaporation phenomena requires a stringent control of the experimental conditions, and an appropriate theoretical treatment. Recently, much progress has been made on both sides. In addition to improving the conventional sessile drop technique, new containerless methods have been developed for surface tension measurements. This paper reviews the experimental progress made in the last few years, and the theoretical framework required for modelling and understanding the relevant physico-chemical surface phenomena.

The surface tension and density of three liquid AlTi-based alloys (AlTiV, AlTiNb, and AlTiTa) have been measured using electromagnetic levitation as a tool for containerless processing. Surface tension has been determined by the oscillating-drop method, while the density was measured using a shadowgraph technique. Both quantities were determined over a wide temperature range, including the undercooled regime. In addition, sessile-drop and pendant-drop experiments to determine the surface tension were performed in a recently built high-temperature furnace. The measured data were compared to thermodynamic calculations using phenomenological models and the Butler equation. Generally, good agreement was found.

Within the Integrated Project IMPRESS, funded by the EU, a concerted action was taken to determine the thermophysical properties of a γ-TiAl-based alloys, suitable for casting of large turbine blades for aero-engines and stationary gas turbines. The challenge was to develop a castable alloy, free of grain refiners and susceptible to heat treatment. Owing to the high reactivity of this class of alloys, many difficulties were encountered to process the liquid phase in a crucible. This prevented also the measurements of specific heat, viscosity and electrical conductivity in the liquid phase. However, surface tension and density could be measured using container-less techniques. For the surface tension determination, both the oscillating droplet method by the electromagnetic levitation as well as a combined method using two methodologies in one test (i.e. the pendant drop and sessile drop) by an advanced experimental complex that has been designed for investigations of high temperature capillarity phenomena were applied. All the quantities have been obtained as a function of temperature, in some cases also in the undercooled liquid. In this article, we report a comparative discussion on the results obtained for the surface tension of Ti–Al–Nb and Ti–Al–Ta alloys, together with the corresponding theoretical values calculated by thermodynamic models.

The mixing behaviour of liquid Bi–In alloys has been described in terms of energetics and structure through the study of their thermodynamic, surface and structural properties by using the Complex Formation Model (CFM) in the weak interaction approximation and by postulating BiIn-chemical complexes as energetically favoured. The new Bi, In and Bi–In surface tension experimental data set, obtained by the large drop method in the temperature range 553–873 K, has been analysed in the framework of the CFM and compared with the calculated values as well as with corresponding literature data. The structural characteristics of Bi–In melts are described by the two microscopic functions, i.e. the concentration fluctuations in the long-wavelength limit and the Warren–Cowley short-range order parameter.

A preliminary, theoretical, analysis of the interfacial oxidization phenomena in a sprayed metal-carrier gas system was made to determine the initial conditions of the process which are compatible or not with surface saturation and the appearance of a separate oxide phase on the droplet surface. This discussion is based on previous theoretical and experimental works on single drop behavior. For the purpose of the discussion the liquid steady state, phase equilibrium and interfacial equilibrium conditions have been discussed; the material balance links of the phases and their coupling with the equilibrium equation have been examined; and the importance of the time variable and the various characteristic times has been underlined. Finally, by coupling the interface steady state conditions and oxygen material balance a set of sufficient conditions for obtaining a clean pure metallic phase has been derived.

A new methodology (Pressure Derivative Method) for measuring the interfacial tension σ between immiscible fluid phases at Δ ρg = 0 (zero Bond number) is presented. This method, which is particularly suitable for measurements under microgravity conditions, is also applicable on earth to liquid pairs with a small density difference. The method consists, essentially, of calculating σ by a linear fitting of experimental capillary pressure and curvature data, collected during the formation of a drop of one of the two liquids inside the other one. The curvature data are derived from the injected drop's volume; thus, any pair of fluids can be used, including opaque liquids, for which optical curvature measurements are not possible. By a specific mathematical treatment of the experimental data, an overall accuracy on the order of less than 1% has been obtained. During the drop growth, a maximum in the pressure is reached, which can also be used to calculate σ by the Maximum Bubble Pressure technique (MBP). This value can be utilized as an internal check on the interfacial tension data obtained by the method proposed.

Immunotherapy of feline immunodeficiency virus (FIV)-infected cats with monocyte-derived dendritic cells (MDCs) loaded with aldrithiol-2 (AT2)-inactivated homologous FIV was performed. Although FIV-specific lymphoproliferative responses were markedly increased, viral loads and CD4+ T cell depletion were unaffected, thus indicating that boosting antiviral cell-mediated immunity may not suffice to modify infection course appreciably.

Dendritic cells are the only antigen-presenting cells that can present exogenous antigens to both helper and cytolytic T cells and prime Th1-type or Th2-type cellular immune responses. Given their unique immune functions, dendritic cells are considered attractive “live adjuvants” for vaccination and immunotherapy against cancer and infectious diseases. The present study was carried out to assess whether the reinjection of autologous monocyte-derived dendritic cells loaded with an aldithriol-2-inactivated primary isolate of feline immune deficiency virus (FIV) was able to elicit protective immune responses against the homologous virus in naive cats. Vaccine efficacy was assessed by monitoring immune responses and, finally, by challenge with the homologous virus of vaccinated, mock-vaccinated, and healthy cats. The outcome of challenge was followed by measuring cellular and antibody responses and viral and proviral loads and quantitating FIV by isolation and a count of CD4 + /CD8 + T cells in blood. Vaccinated animals exhibited clearly evident FIV-specific peripheral blood mononuclear cell proliferation and antibody titers in response to immunization; however, they became infected with the challenge virus at rates comparable to those of control animals.

The present work was carried out in the framework of the study of new lead-free solder alloys for technical applications in electronic devices. In the focus of this characterisation the wetting behaviour of several Sn-rich alloys belonging to the In–Sn, Au–Sn and Cu–Sn systems has been studied by measuring the contact angle variations on Cu and Ni substrates as a function of time and temperature. The interface between the alloy and the substrate has been analysed by the use of optical microscopy and scanning electron microscopy combined with energy-dispersive X-ray spectrometry in order to study the reaction between the alloy and the solid substrate and the possible formation of different compounds at the interface. A remarkable effect of the two different substrates on the behaviour of the contact angle as a function of temperature and on the morphology of the interface between the liquid solder and the solid substrate was observed for the In–Sn and Cu–Sn, while the Au–Sn system shows a very similar wetting behaviour on Cu and Ni.

The surface and interfacial properties of the Cu–Sn system as basic system of the multicomponent alloys proposed as lead-free soldering materials have been studied. The surface tension of the Cu–Sn system has been measured over the whole composition range by using the sessile drop method in the temperature range between 430 and 1300 K. The results obtained are compared with the available literature data and with theoretical values calculated by the compound formation model (CFM) and quasi-chemical approximation for regular solutions (QCA). The study of the wetting behaviour of Cu–Sn on a metal substrate has been performed by measuring the contact angles of four Sn-rich alloys on a pure Ni-substrate and by the metallographic characterization of the solder/Ni interfaces.

Dynamic surface-tension measurements using the sessile drop method and acquisition times of a few seconds make it possible to study the evolution of the surface of molten metals and alloys and so reliably validate the predictive models of the interactions between pure liquid metals and an oxidizing atmosphere, in both an inert gas carrier and in a vacuum. The presence of active oxidation contributes to maintaining surface cleanness and then strongly affects the shape of the boundary separating oxidation and de-oxidation regimes. Recently the general physical–mathematical analysis we developed for pure liquid metals has been extended to liquid binary alloys and their oxides. In this work we present the experimental results of tests on some binary alloys chosen as test systems to try to obtain a preliminary validation of the extended model. The theoretical results obtained, indicating that the behaviour of the alloy towards oxidation tends to be similar to that of the less oxidizable component, have thus been confirmed experimentally.

The surface tension of liquid tin has been measured by the sessile-drop technique as a function of temperature, in the range 232 ⩽T (°C) ⩽ 800 and under different atmospheres. It is shown that oxygen strongly affects the surface tension values and that, under “nominally” very clean conditions, a considerable scatter of experimental results occurs. This scatter can be explained by taking into account kinetic factors, especially those related to the gaseous fluxes around the molten drop. By this procedure, a number of experimental results can be singled out, which corresponds to “clean” surface conditions. On the basis of these results, the following expression for surface tension politherm is proposed: σ(mN m−1 = 581-0.13) (t-232).

Using the monolayer model, a thermodynamic approach is suggested in order to compare the surface reactivity to the volume reactivity under both equilibrium and nonequilibrium conditions (sorption and chemical processes). Capillary parameters, such as surface tension and surface dilation, have a direct influence on the efficiency of chemical reactions and on their stability.

This paper presents a detailed interpretation of the interface saturation data of liquid tin and aluminium drops, on the basis of a mathematical description of the interface evolution described in a previous paper. We also discuss the relevance of evolution times towards the stationary condition for both metal drops, which have given us a better understanding of the interface behaviour and also allowed us to attempt a quantitative estimation of the excess interface concentration.

Dynamic surface tension measurements of molten aluminium have been carried out under different monitored oxygen partial pressures in the temperature range 873–1323 K with the aim of experimentally confirming the behaviour of molten metals in the presence of traces of oxygen as predicted by theoretical models [Ratto M, Ricci E, Arato E, Costa P. Metall Mater Trans B 1998;32B:903; Castello P, Ricci E, Passerone A, Costa P. J Mater Sci 1994;29:6104]. The procedures necessary to obtain experimental validation of the theoretical oxidation–deoxidation curve at high temperatures under both low total pressure and atmospheric pressure are presented.

The lack of experimental data and / or limited experimental information concerning both surface and transport properties of liquid alloys often require the prediction of these quantities. An attempt has been made to link the thermophysical properties of a ternary Cu-Sn-Ti system and its binary Cu-Sn, Cu-Ti and Sn-Ti subsystems with the bulk through the study of the concentration dependence of various thermodynamic, structural, surface and dynamic properties in the frame of the statistical mechanical theory in conjunction with the quasi-lattice theory (QLT). This formalism provides valuable qualitative insight into mixing processes that occur in molten alloys.

The potential of immunotherapy with autologous virus-specific T cells to affect the course of feline immunodeficiency virus (FIV) infection was explored in a group of specific-pathogen-free cats infected with FIV a minimum of 10 months earlier. Popliteal lymph node cells were stimulated by cocultivation with UV-inactivated autologous fibroblasts infected with recombinant vaccinia viruses expressing either FIVgagorenvgene products, followed by expansion in interleukin-2. One or two infusions of both Gag- and Env-stimulated cells resulted in a slow increase in FIV-specific gamma interferon-secreting T cells in the circulation of cats. In the same animals, viral set points fluctuated widely during the first 2 to 3 weeks after adoptive transfer and then returned to pretreatment levels. The preexisting viral quasispecies was also found to be modulated, whereas no novel viral variants were detected. Circulating CD4+counts underwent a dramatic decline early after treatment. CD4/CD8 ratios remained instead essentially unchanged and eventually improved in some animals. In contrast, a single infusion of Gag-stimulated cells alone produced no apparent modulations of infection.

The influence of oxygen on the surface tension of liquid metals is a topic of undoubted interest as the formation of oxide films, or even oxygen contamination of the metal interface, represents the main source of error in determining the surface tension. The evaluation of gas-atmosphere mass exchanges under stationary conditions allows the evaluation of an effective oxygen pressure at which the oxidation of metal becomes evident. This effective oxygen pressure can be considered as a property of the system and, according to experimental evidence, can be many orders of magnitude greater than the equilibrium pressure. The measurement of the surface tension is a good way of studying interface properties, their temporal change and their connections to transport and reaction rates. This paper represents a review of a work undertaken with the aim of understanding oxygen mass transport at the liquid metal surface in relation to the study of capillary phenomena at high temperature.

Thermophysical properties of the Ni-based superalloys CMSX-4, IN738LC, and MM247LC have been measured in the liquid and high-temperature solid phase. Properties included calorimetric, thermal transport, the surface tension, and the viscosity. Experiments have been performed in ground-based laboratory using classical calorimetry and rheometry as well as under reduced gravity conditions in an electromagnetic levitation device on board parabolic flights. In this contribution, an overview of the various properties of three Ni-based superalloys is given with emphasis on the surface tension and viscosity as obtained from the parabolic flight experiments. The measurements were performed within a program called ThermoLab dedicated to the measurement of thermophysical properties of industrial alloys.

In order to point out the interactions of oxygen with a liquid metal and to study the influence of the actual operating conditions, dynamic surface tension measurements of a liquid test metal (tin), were performed under vacuum conditions by using the large drop method. This classical method has been improved by applying a new experimental procedure which allowed to obtain reliable surface tension measurements at high temperature as a function of time and varying the oxygen content. Further, complementary information on molten metal-oxygen interactions can be obtained. In particular, in this work, the trend of the surface tension temperature coefficient has been analysed as a function of different operative parameters, highlighting some crucial points such as the dependence of the temperature coefficient on the accuracy of the surface tension experimental data and the influence of the dissolved oxygen. It was demonstrated that the surface tension and its temperature coefficient do not depend on the quantity of dissolved oxygen when this is inside a certain range of values.

A system made of an atmosphere, a liquid metal and an oxide phase at a given temperature and total pressure is zero-variant and allows only a particular set of partial pressures, compatible with thermodynamic equilibrium. For any different gas composition the system will show a tendency to evolution. Therefore, classical thermodynamics cannot give the answers to a number of problems of major interest, such as those concerning the conditions for interface saturation and oxide formation. Strictly speaking these are kinetic problems, but they can still be treated as pseudo-thermodynamic questions. The key to the problem is in considering the characteristic times of evolution, which suggest stationary state approximation for the condensed phases. In many instances, the evaluation of gas-atmosphere mass exchanges under stationary conditions makes it possible to determine the effective oxygen pressure at which the oxidation of the metal becomes evident. Surface tension measurements allow this condition to be detected with a good accuracy. According to experimental evidence, the effective oxygen pressure can be many orders of magnitude greater than the equilibrium value. The problem needs different theoretical approaches according to the molecular mechanisms involved. Moreover, from the experimental point of view, there are particularly delicate questions regarding the accuracy and the significance of the oxygen control and measurement.

The surface tension and the viscosity of a series of industrial alloys have been measured by the oscillating drop technique with an electromagnetic levitation device under reduced gravity conditions in several parabolic flights. It was demonstrated that the 20 seconds of reduced gravity available in a parabola were sufficient for melting, heating into the liquid phase, and cooling to solidification of typically 7 mm diameter metallic specimen. The surface tension and the viscosity were obtained from the frequency and the damping time constant of the oscillation which were evaluated from the temperature signal of a highresolution pyrometer. Alloys processed included steels, Ni-based superalloys, and Ti-alloys which were supplied by industrial partners to the project. Three to four parabolas were sufficient to obtain the surface tension and the viscosity over a large range in temperature.

This work is aimed to advance the understanding of interfacial saturation phenomena for liquid metal surfaces. The interactions between a liquid metal drop and an oxidising atmosphere can be described by a physical–mathematical description of the liquid metal interface/surrounding environment interface evolution. The closed system and equilibrium assumption were rejected and reference was made to a liquid metal drop as an open system and its related time variation conditions (stationary drop assumption). A better demonstration of the experimental relevance of evolution times towards the stationary condition, in particular for liquid tin is done.

The present work represents an experimentally based investigation on the surface properties of molten Bi, Pb and Bi–Pb alloys. The surface tensions of the two pure elements and of seven alloys were measured by the sessile-drop method over the temperature range 623–773 K. In addition the wetting behaviour of the eutectic Bi–Pb alloy on AISI 316L substrate was also investigated in the same temperature range. The results obtained show general agreement with other reported measurements on pure elements and their alloys as well as with calculated surface tension values obtained by the application of the compound formation model (CFM). # 2003 Elsevier Ltd. All rights reserved.

A theoretical model on oxygen transport at the surface of liquid metals has been validated by dynamic surface tension measurements performed on liquid tin as test metal. The oxygen contamination conditions have been obtained at different oxygen partial pressures under low total pressure conditions (Knudsen regime), confirming that an oxide removal regime occurs under an oxygen partial pressure much higher than the equilibrium one (the “Effective Oxidation Pressure”). Experimental results are reported which give a new insight on the relative importance of the various processes due to the oxygen mass transport between the liquid metal and the gas phase. The critical aspects involved in surface tension measurements of liquid metals, related to the problem of liquid metal–oxygen interactions, are also carefully underlined.

This note considers the problem of the interpretation of experiments of capillary phenomena in molten metals. Reference is made to a previous published paper, where a theoretical analysis of the behaviour of molten metals in the presence of oxygen was presented [1] . Such a theoretical analysis allowed relating the gas phase composition at the surface, which is hardly measurable, to the composition in the feed or at the outlet. The application of the theory was effective for the study of the Si–O system. On the other hand, after the publication of the paper, some aspects of the theory remained unclear or misunderstood. So we deemed necessary to present a further in-depth analysis of the theoretical approach, with the goal to definitely clarify its use and consequences for the experimental praxis. Simple and clear rules will be derived, in the most suitable form for the potential users of the theory, mainly experimentalists of capillary phenomena. Moreover, new relevant experimental results are shown, which corroborate the theory.

The present work represents an experimentally based investigation of the applicability of a statistical mechanical theory in conjunction with a compound formation model (CFM) to describe surface properties of Pb-Bi liquid alloys. The surface tension of molten Pb, Bi and Pb-Bi alloys has been measured by the sessile-drop method over the range of temperatures. The results obtained show general agreement with other reported measurements on pure elements and their alloys as well as with calculated surface tension values. Based on the phase diagram evidence about the existence of the ƒÕ-Pb3Bi intermetallic compound, the phenomenon of compound formation in Pb-Bi liquid alloys has been analysed through the study of surface properties (surface tension and surface composition) and microscopic functions (concentration fluctuations in the long-wavelength limit and chemical short-range order parameter) in the frame of compound formation model (CFM).

In this article, a theoretical analysis of the behavior of metallic materials at high temperature in the presence of gaseous oxygen is presented. A generalized Wagner approach is presented in the limiting scenario of highly reactive vapors, Wagner’s theory being the lower limit for null reactivity. Oxygen transfer from the gas phase to the condensed phase is expressed in terms of oxygen effective pressure, accounting for the contribution of volatile oxides. The theoretical approach allows the prediction of the oxygen partial pressures in the feed gas corresponding to oxidation/deoxidation conditions. Such conditions can be different from those given by thermodynamic equilibrium by several orders of magnitude. Moreover, the actual oxygen partial pressure at the condensed phase interface can be expressed as a function of the feed-gas oxygen content, which is measurable. The theory is applicable for metals and nonmetallic materials, such as semiconductors, both in solid and liquid phase. An application to the molten silicon-oxygen system is presented.

The influence of oxygen on the surface tension of pure liquid metals has been investigated up to the bulk saturation concentration. Two thermodynamic models are proposed to describe the surface tension isotherm. Up to the concentration corresponding to the maximum adsorption (xΓmx) a Fowler-Guggenheim modified isotherm describes, correctly, the experimental surface tension isotherms for various systems. The adsorption energy is shown to depend on bulk thermodynamic quantities and on a surface-composition dependent term. A “surface structure coefficient” is also introduced in order to take into account the stoichiometries of surfaces compounds. For bulk compositions ranging from xΓmx to saturation, the application of Gibbs' adsorption law, with fixed values of the absolute adsorptions, is able to take into account the experimental findings. On the basis of this treatment, some general rules are suggested, that allow xΓmx and the corresponding σ value to be estimated for unknown systems.

The surface tension and the density and their dependence on temperature between 20 °C and 80 °C are reported for the system dioctylphthalate-silicone oil (viscosity, 5 cSt) over the complete composition range.

The surface tension and the density of some gold alloys have been measured and their wetting behaviour investigated in relation to different ceramic supports. Relationships between surface tension and density as a function of temperature are proposed.

A theoretical model on oxygen transport at the surface of liquid metals has been validated by dynamic surface tension measurements performed on liquid Indium as test metal. The oxygen contamination conditions have been obtained at different oxygen partial pressures under both low total pressure (Knudsen regime) and inert atmospheric pressure (Fick regime) conditions, confirming that an oxide removal regime occurs under an oxygen partial pressure much higher than the equilibrium one (the "Effective Oxidation Pressure"). Experimental results are reported which give a further insight on the relative importance of the various processes due to the oxygen mass transport between the liquid metal and the gas phase. The critical aspects involved in surface tension measurements of liquid metals, related to the problem of liquid metal-oxygen interactions, are also underlined.

A theoretical analysis of the behaviour of molten metals in the presence of oxygen is presented. A generalised Wagner approach has been adopted for molten metals, forming volatile oxides (Si, Sn, Al, etc.), in which the description of oxygen transfer from the gas phase to the condensed phase must account for the double contribution of molecular oxygen and oxygen linked as oxide, which leads to define the concept of ‘oxygen effective pressure’. From the analysis of the system at varying operating conditions, it was possible to relate the gas-phase composition at the surface, which is hardly measurable, to the composition in the feed or at the outlet. The application of this theory to the molten silicon-oxygen system is presented and the effectiveness of such a theory as a supporting tool for experimental work of capillary phenomena and crystal growth processes is discussed and verified.

Theoretical models have been developed to study the behaviour of liquid metal surfaces in the presence of gaseous surface active elements, relating the mass exchange between the liquid metal and th...

Theoretical models describing the transport of oxygen in metal/atmosphere systems under different fluid-dynamic conditions have been developed by different authors. In the present study, as in previous ones, the molecular diffusion is the process mainly controlling the exchange of matter between the liquid metal and the atmosphere. So, in this paper a diffusional model is proposed accounting for volatile oxides and for gas phase homogeneous reactions by means of two limiting conditions: instantaneous reactions and null reactions. For the boundary conditions, the model assumes a bulk flow composition of the gas layer surrounding the liquid on the upper side and a local equilibrium constraint at the liquid interface. The asymptotic behavior of the system is described, enabling the prediction of the direction of the net oxygen flux. It has been demonstrated that the results obtained are valid for any type of homogeneous gas phase reactivity, provided that no oxide fog is formed in the gas. The model is useful to correctly guide technological processes such as single crystal growth: in the paper the application to the melt silicon/oxygen system is discussed. Finally, the present model can synthesize apparently contradictory experimental measurements of surface tension available in literature into a unique portrait.