The viscosities of lead,tin, and Pb-Sn alloys

The viscosities of lead, tin, and Pb-Sn alloys have been determined by an absolute technique using an oscillational viscosimeter. By careful experimentation, it has been possible to obtain results which are accurate to within ±0.5 pct. For the pure metals, the data are in good agreement with some recent work. The results obey Andrade’s equation ηv^1/3 = A expC/vT, the constants having values ofA = 2.54 × 10⁻³ and C = 86.30 for lead, andA = 2.75 × 10⁻³ and C = 88.49 for tin. No evidence has been found to support the reports of some investigators that Pb-Sn alloys experience structural changes or abnormal interatomic reactions in any specific composition ranges such as around the eutectic. The results confirm recent work that isothermal viscosities vary with composition in a linear manner. Formerly Research Scientist, Department of Energy, Mines and Resources, Ottawa, Canada     

Nucleation-controlled microstructures and anomalous eutectic formation in undercooled Co-Sn and Ni-Si eutectic melts

Co-20.5 at. pct Sn and Ni-21.4 at. pct Si eutectic alloys have been levitated and undercooled in an electromagnetic levitator (EML) and then solidified spontaneously at different undercoolings. The original surface and cross-sectional morphologies of these solidified samples consist of separate eutectic colonies regardless of melt undercooling, indicating that microstructures in the free solidification of the eutectic systems are nucleation controlled. Regular lamellae always grow from the periphery of an independent anomalous eutectic grain in each eutectic colony. This typical morphology shows that the basic unit should be a single eutectic colony, when discussing the solidification behavior. Special emphasis is focused on the anomalous eutectic formation after a significant difference in linear kinetic coefficients is recognized for terminal eutectic phases, in particular when a eutectic reaction contains a nonfaceted disordered solid solution and a faceted ordered intermetallic compound as the terminal eutectic phases. It is this remarkable difference in the linear kinetic coefficients that leads to a pronounced difference in kinetic undercoolings. The sluggish kinetics in the interface atomic attachment of the intermetallic compound originates the occurrence of the decoupled growth of two eutectic phases. Hence, the current eutectic models are modified to incorporate kinetic undercooling, in order to account for the competitive growth behavior of eutectic phases in a single eutectic colony. The critical condition for generating the decoupled growth of eutectic phases is proposed. Further analysis reveals that a dimensionless critical undercooling may be appropriate to show the tendency for the anomalous eutectic-forming ability when considering the difference in linear kinetic coefficients of terminal eutectic phases. This qualitative criterion, albeit crude with several approximations and assumptions, can elucidate most of the published experimental results with the correct order of magnitude. Solidification modes in some eutectic alloys are predicted on the basis of the present criterion. Future work that may result in some probable errors is briefly directed to improve the model.     

Tensile test behavior of the eutectic Sn-Ag solder joint in ball grid array assemblies

In this study, the mechanical behavior of a eutectic Sn-3.5Ag ball-grid array (BGA) assembly was evaluated by tensile testing at strain rates of 10⁻⁴ and 10⁻⁵ s⁻¹ at various homologous temperatures. The maximum strength of the eutectic Sn-3.5Ag ball-grid array assembly decreased as the testing temperatures increased and the testing strain rates decreased. Two types of fracture modes were found during the tensile tests depending on the strain rates and homologous temperatures. At a strain rate of 10⁻⁴ s⁻¹ and at homologous temperatures lower than 0.65, the crack propagation occurred at the angle 45 deg with the tensile axis and along the Ag₃Sn/Sn interfaces. However, at strain rates lower than 10⁻⁴ s⁻¹ or at homologous temperatures higher than 0.65, the tensile crack formed by linking the creep voids that propagate normal to the tensile axis. A transgranular creep fracture was found on the failed surfaces of Sn-3.5Ag ball-grid array assemblies.     

Thermodynamics of antimony,arsenic, and tin in CaO—CaF2 melts

In view of the importance of tramp element contamination of steel products through a large volume of scrap consumption in the near future, the thermodynamic behaviour of Sb, As, Sn and Cu in CaO—CaF₂ melts under reducing conditions was studied by examining the dependences of distribution of each element between Cu, Ag or Sn alloys and CaO—CaF₂ melts on the CaO activity, oxygen partial pressure and temperature around 1 500°C. As a result, the reaction products on treatment by Ca compounds were demonstrated to be Ca₃Sb₂, Ca₃As₂, Ca₂Sn and CaCu. Experimentally obtained distributions were extrapolated to lower oxygen partial pressures less than 10^?18 atm to estimate the feasibility of removing those tramp elements from molten iron. It is thermodynamically indicated that if the prevailing oxygen partial pressure of the environment is below 10^?23 atm, these impurities, except Cu, would be substantially removed from molten steel.     

Estimation of the viscosities of binary metallic melts using Gibbs energies of mixing

In the present work, information on the integral molar Gibbs energies of mixing is employed to calculate the viscosities of binary substitutional metallic melts. A correlation has been established between the second derivative of the integral molar Gibbs energy of mixing with respect to composition and the corresponding function for the Gibbs energy of activation for viscosity. The viscosities predicted from available thermodynamic data in the case of a number of binary metallic systems using this correlation show satisfactory agreement with the values reported from experimental measurements. The value of this correlation in predicting the viscosities of complex metallic melts is also examined.     

Estimation of viscosities of ternary silicate melts using the excess gibbs energy of mixing

A correlation to predict the viscosities of ternary silicates using the Gibbs energies of mixing of the silicate melts has been developed. This correlation has been employed to predict the viscosities of liquid slags in the systems FeO-MnO-SiO₂, FeO-MgO-SiO₂, CaO-FeO-SiO₂, CaO-MnO-SiO₂, and CaO-MgO-SiO₂. The good agreement between the calculated viscosities and the experimental data in the ternary silicate systems has indicated that this approach can be successfully employed to predict the viscosities of ternary silicate melts.     

Dynamic properties of Aluminum-Lithium and Aluminum-Magnesium melts

A comparison of calculated concentration dependences of the electrical resistivities of the Al-Li and Al-Mg systems suggests that a metal-nonmetal phase transition takes place in the Al-Li system. This assumption casts some doubt on the mechanism of quasi-chemical electron localization used to explain the metal-nonmetal phase transition in Pb-Li and Sn-Li melts.     

Control of the manganese-oxygen reaction in pure iron melts

EMF sensor measurements using ZrO₂(CaO) or ThO₂(Y₂O₃) plug-type sensors with a Cr-Cr₂O₃ reference were performed to redetermine the Mn-O equilibrium reaction. In these experiments a strong effect of deoxidation of manganese was ascertained at saturation with solid deoxidation products. The measuring interval of the sensors at MnO saturation was limited to about 12 min due to chemical corrosion of the used Al₂O₃ sheaths. In the case of double saturation with solid MnO · Al₂O₃ (MA) and Al₂O₃ (A) the sensors could be used as long as desirable. Moreover, the combined deoxidation of the iron melt with Mn and Al was investigated. An auxiliary electrode at the tip of the sensor ensured rapid saturation of the iron melt with solid MnO or MnO · Al₂O₃ + Al₂O₃.     

Control of the aluminium-oxygen reaction in pure iron melts

Modified electrochemical oxygen sensors based on CaO-doped ZrO₂ and Y₂O₃-doped ThO₂ were developed and applied to study the aluminium-oxygen reaction in pure liquid iron with special regard to the provision of reliable experimental conditions and the attainment of true chemical equilibrium. The sensors represent valuable tools particularly for EMF long-term measurements over several hours. At 1600 °C, values of the constant and of the interaction parameters and were determined. When Fe-O-Al melts are covered with a slag phase at an activity a(Al₂O₃) < 1, e.g., CaO-saturated CaO-Al₂O₃ slag, the Al-O relationship in the iron may nevertheless be controlled by an equilibrium oxide phase at an activity a(Al₂O₃) = 1, presumably represented by inclusion particles consisting of pure Al₂O₃.     

Control of the chromium-oxygen reaction in pure iron melts

Oxygen activities in Fe-O-Cr melts, equilibrated with chromium oxide, were determined as a function of chromium content by EMF measurements using ZrO₂(CaO) plug-type sensors with a Cr-Cr₂O₃ reference. Plug-type sensors with or without Cr₂O₃ saturator were used in the experiments. From the experimental results values for the activity coefficient f_O and the interaction parameters and were evaluated. Raoultian chromium activity features a slight positive deviation from ideal solution behaviour in the temperature range from 1550 to 1650°C. Taking into account the calculated interaction parameters, the equilibrium constant K_Cr-O was redetermined at 1550 to 1650°C. In comparison with previous studies a better agreement was obtained with existing thermochemical data.     

Dynamic and kinetic properties of Al-Li melts

The dynamic and kinetic properties of Al-Li melts are calculated. The liquid phase of this system is shown to be characterized by three states with different ion distributions and different degrees of electron localization.     

Settling of undissolved zirconium particles in pure magnesium melts

Zirconium is a remarkable grain refiner for magnesium alloys and is currently introduced into magnesium alloys primarily in the form of a Mg–Zr master alloy (Zirmax^® a Mg–33.3Zr alloy supplied by Magnesium Elektron). Owing to the difficulties of attaining complete dissolution, undissolved zirconium particles are often observed in Zirmax^® alloyed magnesium microstructures in the form of both isolated individual particles varying from submicrometre to greater than 10 μm, and various sizes of clusters that contain a number of zirconium particles. Aimed at improving the alloying efficiency with Zirmax^® and eliminating these undesirable large zirconium inclusions prior to pouring, this paper provides a detailed theoretical and experimental study of the settling behaviour of undissolved zirconium particles in pure magnesium melts. Various characteristics of the settling behaviour of zirconium particles are clarified based on the good agreement achieved between the experimental observations and theoretical predictions. In addition, it is also shown that wet chemical analysis of the total zirconium content in samples taken after different settling times at temperature can be an effective approach for evaluating the settling behaviour of undissolved zirconium particles in pure magnesium melts.     

Creep of tin, Sb-solution-strengthened tin, and SbSn-precipitate-strengthened tin

The creep properties of tin-antimony alloys were studied up to the peritectic composition. For tin at temperatures below approximately 150 °C, creep is dominated by pipe diffusion-controlled climb with a stress exponent of 8 and activation energy of 70 kJ/mol. At high stresses, small amounts of impurities cause a transition to a less stress sensitive, most likely solute drag-controlled mechanism. Antimony atoms in solution have only a minor effect on these creep properties. Alloys with higher compositions of antimony contain whiskerlike SbSn precipitates. These alloys exhibit a discontinuous transition in stress exponent and activation energy at an intermediate stress. The creep behavior of these alloys is described fairly well by a composite theory in which the power law stress is divided by a strengthening coefficient, and the strengthening coefficient is related to the precipitate volume fraction and the aspect ratio. Using a friction stress and a strengthening coefficient simultaneously, the behavior of these alloys can be described entirely in terms of tin creep constants. Aging at 100 °C has little effect on the creep properties of the precipitation-strengthened alloys. It is expected that solder alloys strengthened by these precipitates would maintain a significant fraction of their creep strength for significant periods at temperatures below 100 °C.     

Interaction of exogenous zirconium oxide nanophases with sulfur and tin in nickel melts

The interaction of exogenous refractory compound (ZrO₂) nanoparticles with sulfur and tin, which are present as surfactants in model nickel melts, is studied. Thermodynamic calculations are performed to consider the versions of removal of sulfur and tin from a melt in the form of S₂, SO₂, H₂S, Sn, and SnO. It is shown that the probability of their removal under melting conditions is low. Their contents is found to decrease when ZrO₂ nanoparticles are introduced: the degree of removal is α = 12–18% S in a model Ni–S alloy and 14–20% Sn in a model Ni–Sn alloy.     

Diffusional breakdown of nickel protective coatings on copper substrate in silver-copper eutectic melts

Diffusion couples with electrolessly plated nickel diffusion barriers between copper substrates and silver-copper eutectic alloys were tested at 800 °C and 850 °C, respectively. Growth of (Cu, Ni, Ag) ternary solid solution into the melt was observed at both temperatures. The growth pattern changed from cellular to dendritic as the temperature was increased from 800 °C to 850 °C. The nonplanar growth morphology can be explained in terms of constitutional supercooling in the melt. Kinetics of (Cu, Ni, Ag) solid solution growth were found to be controlled by interdiffusion at the interface of the nickel barrier and the growing solid-state phase. Local breakdown of the nickel diffusion barrier started once the (Cu, Ni, Ag) solid solution reached the copper substrate. Silver diffused from the silver-copper melt, through the ternary solid solution, dissolving copper and forming silver-copper liquid along copper grain boundaries. Ultimately, the nickel barrier was totally converted to the ternary solid solution, broke up, and floated into the liquid. Dissolution of the copper substrate occurred subsequently. A thin layer of chromium undercoating proved to be very effective in extending the protection time of the nickel diffusion barrier, due to the extremely low solubility of both copper and silver in chromium at these test temperatures.     

Electroreduction of neodymium and praseodymium ions in equimolar KCl-NaCl and eutectic KCl-NaCl-CsCl melts at a tungsten electrode

Cyclic voltammetry is used to study the processes that occur during the electroreduction of neodymium and praseodymium ions in equimolar KCl-NaCl (at 973 K) and eutectic KCl-NaCl-CsCl (at 823 K) melts at a tungsten electrode. The kinetics parameters and the diffusion coefficients of neodymium and praseodymium ions are calculated.