Constitution of Au–AuSn–Pb partial ternary system

Abstract

In the light of recent changes made to the phase diagrams of the Au–Sn and Au–Pb binary systems, the constitution of the Au–AuSn–Pb partial ternary system has been redetermined using thermal analysis, metallography, and X-ray techniques. The equilibria consist of four ternary transition reactions at 63·5Au–26·0Pb–10·5Sn, 382·5°C; 42·5Au–47·5Pb–10·0Sn, 254°C; 30·5Au–60·5Pb–9·0Sn, 224°C; and 20·5Au–75·5Pb–4·0Sn, 214°C; a ternary eutectic equilibrium at 15·0Au–84·0Pb–1·0Sn, 211°C; and a four-phase monotectic equilibrium at 64·0Au–9·0Pb–27·0Sn, 257·5°C (compositions are given in atomic per cent). The phase assemblage of the partial ternary system is characterized by a region of true ternary liquid immiscibility that covers much of the composition triangle. The composition of the second liquid phase at the monotectic reaction temperature is 45·0Au–40·0Pb–15·0Sn. Solid solubilities were not determined.

MST/620     

Formation of microstructure during solidification of Bi–Pb–Sn ternary eutectic

Abstract

To investigate the nature of the Bi–Pb–Sn ternary eutectic, specimens were solidified unidirectionally at very low speeds and quenched to form a representative solid/liquid interface for subsequent study. Specimens made using the generally accepted composition, as reported by Ho et al., did not form all three solid phases from the start of freezing. Specimens produced using the composition reported by Sakurai, i.e., 54 wt-%Bi, 28 wt-%Pb, and 18 wt-%Sn, did give all three phases from the beginning of freezing, indicating that it is the correct eutectic composition. It was found that this eutectic is of the faceted (Bi) non-faceted (X phase) non-faceted (Sn) type. Under the freezing conditions used, a double binary microstructure was formed, with one component consisting of Sn fibres in the X phase and the other of a Bi–Sn complex regular microstructure. While the occurrence of a double binary microstructure was predicted by C. S. Smith for a lamellar ternary eutectic, the current observation shows that it can also occur in a system with one fibrous phase.     

Crystallization of a Bi–Pb–Fe–Cd–O glass under magnetic annealing

Magnetic annealing with a tunable solenoid magnetic field from 0–240 G, was conducted on a Bi–Pb–Fe–Cd–O glass containing 20% Fe2O3, which was prepared by the melt-quenching process. The crystalline phases of the annealed samples were identified as -Bi2O3 and BiFeO3. Evidence of the formation of the crystalline BiFeO3 which was strongly magnetically enhanced at the surface of the samples, was obtained from X-ray diffraction patterns and EPR spectra. Based on the structure transition of Fe3+ ions, a crystallization mechanism for the BiFeO3 crystals under magnetic annealing has been proposed.     

Mechanochemical Synthesis and Structure of New Phases in the Pb–V–O System

The products of mechanochemical synthesis in the Pb–V–O system were characterized by x-ray diffraction and magnetic resonance spectroscopy techniques. The mechanical processing was found to yield only new crystalline compounds, Pb_2.67V_1.33O_5.96and Pb_3.5V_4.5O_14.75. Structural analysis of these phases revealed a low atomic density, mixed-valent states of the constituent cations, the presence of three of four types of vanadium polyhedra, and splitting of crystallographic sites, in line with the views on the mechanisms of mechanochemical reactions developed in the model for the reaction zone.     

Impression creep of Sn–40Pb–2·5Sb peritectic solder alloy

Abstract

The power law creep behaviour of the Sn–40Pb–2·5Sb peritectic solder alloy was investigated using an impression test apparatus. The tests were carried out under constant stress in the range 17 to 39 MPa and at temperatures in the range 296 to 363 K. Assuming a power law relationship between the impression velocity and stress, power law stress exponents in the range 1–3 were determined. Analysis of the data showed that for all loads and temperatures, the activation energy was stress independent with values in the range 51–56 kJ mol^-1. Based on the stress exponents obtained and activation energy data, it is proposed that grain boundary diffusion is the major mechanism for creep of the Sn–Pb–Sb peritectic alloy under these test conditions.     

Microstructure of Zn–Pb immiscible alloys obtained by a rheomixing process

Abstract

A rheomixing process has been developed for processing immiscible metallic liquids. In this paper, a binary Zn–Pb system is used to demonstrate the rheomixing process. During the rheomixing process, liquid Zn and Pb are premixed in the miscibility gap using a propeller mixer to achieve coarse dispersion of Pb liquid droplets in Zn liquid matrix. The coarse mixture is then transferred into a twin-screw rheomixer, where it is continuously cooled down to a temperature below the monotectic temperature to form a semi-solid slurry under the intensive shear mixing action of the twin-screw rheomixer. The semi-solid slurry is finally extruded through a cylindrical extrusion die to form a continuous bar. The microstructure of immiscible alloys produced by this method is characterised by a fine dispersion of Pb particles distributed uniformly throughout a Zn matrix. The effects of rheomixing temperature and alloy composition on the resultant microstructure have been investigated. It has been found that the average size of Pb particles increases linearly with increasing rheomixing temperature and with increasing Pb concentration in the Zn–Pb alloys.     

Effect of medium-density direct current on dendrites of directionally solidified Pb–50Sn alloy

This paper investigated the effect of coupling of direct current (DC) and pulling rate on dendrites and cooling behaviours of directionally solidified Pb–50Sn alloy. Experimental results indicated that the secondary dendritic arm spacing (SDAS) decreased and temperature gradient increased as increasing current densities. Moreover, temperature rise and SDAS under positive DC were higher than those under negative DC. It was speculated that Joule heating and electromigration were obviously induced by the present DC. The effect of DC on the microstructure and solidification parameters was weakened as the pulling rate increases. The coarsening rate reduced from tf^1/3 toward a value of tf^0.29 when DC of ±200?A?cm^–2 were applied. The refinement mechanism of SDAS was discussed.     

Creep of Pb–2·5Sb–0·2Sn alloy at low stresses

Abstract

The creep of a Pb–2·5Sb–0·2Sn alloy has been studied at stresses up to 6·5 MN m^?2 in the temperature range 318–348 K (0·53–0·58T_m) using helical specimens. At 333 K, a transition in the stress exponent from ~1 to 3 occurred at ~3 MN m^?2. The observed good agreements below the transition stress, both for experimental dE/do and predictions for Coble diffusional creep of lead, and for measured activation energy for creep and the activation energy for grain boundary self-diffusion in lead, suggest that grain boundary diffusional creep is the dominant mechanism. at low stresses. The presence of antimony does not seem to affect the magnitude of dE/do appreciably, and the results suggest that the grain boundary self-diffusivity of lead is not influenced by the presence of segregated antimony on the grain boundaries. The diffusional creep occurred above a threshold stress of magnitude ~0·5 MN m^?2, and its temperature dependence was characterised by an activation energy of ~20 kJ mol^?1, similar to the value of 23 ± 7 kJ mol^?1 typical of pure metals in the temperature range investigated. The stress exponent of ~3 observed for the power law regime suggests control by viscous glide of dislocations constrained by dragging of solute atmospheres. Preliminary tests on sagging beam specimens of as-worked material at an applied stress of 2·5 MN m^?2 and a test temperature of 333 K has provided the first direct evidence that anisotropic grain shape affects Coble creep. The specimen with the longest grain dimension along the stress axis underwent slower creep than the specimen with the longest grain dimension perpendicular to the stress axis. This observation is in qualitative agreement with theoretical predictions.

MST/1139     

Choice of Materials for Sorption Treatment of Pb–Bi Coolant to Remove the Accumulated Radionuclides

Sorption and phase distribution of activation products (⁶⁵Zn, ⁵⁴Mn, ⁵⁹Fe, ⁶⁰Со) in systems consisting of Pb–Bi melt and a porous material were studied under laboratory conditions. Radionuclides of elements with minimal oxygen affinity (Ru, Te, and Sb) remain predominantly in the coolant melt and are weakly sorbed by the solid phase. Radionuclides with higher oxygen affinity are well sorbed by structural solid sorbents. The maximum of the ⁶⁰Со sorption onto porous steel is reached at 853 K.     

Study on creep characterization of nano-sized Ag particle-reinforced Sn–Pb composte solder joints

In the present work, the creep strain of solder joints is measured using a stepped load creep test on a single specimen. Based on the experimental results, the constitutive model on the steady-state creep strain is established by applying a linear curve fitting for the nano-sized Ag particle-reinforced Sn37Pb based composite solder joint and the Sn37Pb solder joint, respectively. It is indicated that the activation energy of the Ag particle-reinforced Sn37Pb based composite solder joints is higher than that of Sn37Pb solder joints. It is expected that the creep resistance of the Ag particle-reinforced Sn37Pb based composite solder joints is superior to that of Sn37Pb solder.     

Strengthening Sn60–Pb40 solder alloy by adding trace amount of La

The high temperature tensile strength of traditional Sn60–Pb40 solder alloy has been increased by 70% by adding trace amount of rare earth element La into it. Meanwhile, the thermal fatigue life of solder joints has been increased by two times. Such improvement is attributed to the modification effect of La on the microstructure of Sn60–Pb40 alloy.     

Microstructure and wear performance of Ni–20 wt.% Pb hypomonotectic alloys

The tribological properties of Ni–20 wt.% Pb alloys were measured by using a ball-on-disc reciprocating tribo-tester. The effects of load, sliding speed and melt undercooling on wear rate of the sample were investigated. The worn surface of Ni–20 wt.% Pb was examined using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results show that the wear properties of the samples undercooled by 85 and 390 K are obviously superior, which is attributed to more efficient transfer of Pb from the bulk material to the worn surface. The lubricating film is identified as a mixture of Ni₂O₃ and lead oxide by XPS analysis. At the same load or sliding speed, the predominant wear mechanisms can be identified as oxidative wear for the lower and larger undercooling and plastic deformation for the medium undercooling.     

Electrosynthesis of pinecone-shaped Pt–Pb nanostructures based on the application in glucose detection

The pinecone-shaped Pt–Pb nanostructures were synthesized by electrochemical deposition. The morphology and composition of the pinecone-shaped Pt–Pb nanostructures were characterized by scanning electron microscopy, energy dispersive X-ray detector, transmission electron microscopy and X-ray photoelectron spectroscopy. Cyclic voltammetry and differential pulse voltammetry were used to evaluate the electrocatalytic performance of the pinecone-shaped Pt–Pb nanostructures electrode toward glucose oxidation in neutral media. As a result, the pinecone-shaped Pt–Pb nanostructures electrode exhibited strong current responses to glucose at a negative potential of ? 0.1 V, where the interference from the oxidation of ascorbic acid was effectively avoided. The sensitivity of the sensor was 10.71 μA mM^?1 cm^?2 with a linearity up to 12 mM and a detection limit of 8.4 μM. In addition, the as-prepared nonenzyme glucose sensor exhibited acceptable stability and reproducibility for determination of glucose. The simple preparation method and good analytical performance can potentially pave the way for effective and highly sensitive non-enzyme glucose sensors.     

Phase Relations in the Bi–(Pb)–Sr–Ca–Cu–Sc–O System

The phase relations in the Bi–(Pb)–Sr–Ca–Cu–Sc–O system were studied near Bi₂Sr₂CaCu₂O_{8 +} (Bi-2212) and (Bi,Pb)₂Sr₂Ca₂Cu₃O_{10 +} (Bi-2223) between 850 and 930°C. The introduction of Sc led to the formation of a new compound Sr₂ScBiO₆, which coexisted with Bi-2212 and Bi-2223. Using crystallization from a peritectic melt at different cooling rates, we obtained Bi-2212 matrix composites containing finely dispersed Sr_1.9Ca_0.1ScBiO₆inclusions, with T _cattaining 89 K. The T _cof the Bi-2223–Sr_1.9Ca_0.1ScBiO₆superconducting ceramic prepared by solid-state sintering of a Bi–(Pb)–Sr–Ca–Cu–Sc–O precursor was 108.5 K.     

Differential scanning calorimeter studies on Pb modified Ge–Se–Te glasses

Bulk glasses Pb _x Ge_{42 – x} Se₄₈Te₁₀(0 x 15) and Pb₂₀Ge _x Se_{70 – x} Te₁₀(17 x 24) have been prepared by quenching the melt. The non-isothermal properties of these glasses have been determined using a Differential scanning calorimeter (DSC). The composition dependence of the glass transition temperature, crystallisation temperature, excess heat capacity at glass transition, glass forming tendency and activation energy of glass transition and crystallisation show anomalous features near the composition at which the p- to n-type transition occurs. These observations reflect the changes occurring in the chemical bonding and the nature of the glassy network in these glasses. The results have been interpreted in terms of existing models and the majority charge carrier reversal phenomenon occurring in these glasses.     

On the growth of the minority phase during downward transient directional solidification of hypomonotectic and monotectic Al–Pb alloys

Al–Pb alloys were solidified under non steady heat flow conditions using a casting assembly in order to promote vertical downward directional solidification. The downward configuration enables the effects of gravity-driven convection on the final microstructure to be evaluated since the collective movement of Pb-rich particles downwards is favored, due to density differences between the two coexisting liquid phases. Investigations have been made of the obtained solidification structures. Growth rates (v) and cooling rates ( \mathop T^· \mathop T\limits^{\cdot} ) of the Al–Pb alloys solidified downwards were experimentally determined by the cooling curves recorded along the casting length. The monotectic structure was characterized by metallography and a microstructural transition has been observed in all cases. The microstructure was characterized by well-distributed Pb-rich droplets in the aluminum-rich matrix from the casting cooled surface up to a certain position in the casting, followed by a mixture of fibers and strings of pearls from this point to the bottom of the casting. The increase in alloy lead content delays the formation of fibers for alloys solidified downwards, which occurs for v < 0.48 mm/s and v < 0.15 mm/s for Al–0.9 wt%Pb and Al–1.2 wt%Pb alloys, respectively. Experimental power laws relating the interphase spacing, λ, to v and characterized by −2.0 and −6.5 exponents, were found to represent the growth of droplets and fibers, respectively, for both alloys solidified downwards.     

Effect of La on piezoelectric properties of Pb(Ni1/3Sb2/3)O3–Pb(ZrTi)O3 ferroelectric ceramics

Piezoceramic compositions Pb_1?zLa_z(NiSb)_0.05[(Zr_0.52Ti_0.48)_1?Z/4]_0.95O₃ with Z = 0.01–0.05 were synthesized by mixed oxide route to study the effect of Lanthanum (La) on crystal structure, microstructure, piezoelectric and ferroelectric properties. Calcination was performed at 1,060 °C and sintering at 1,270 °C for 1 h. X-Ray diffraction pattern indicated the polycrystalline microstructure along with co-existence of tetragonal and rhombohedral perovskite phases. Dielectric constant ( $ K_{3}^{T} $ ) was increased whereas piezoelectric voltage constant (g ₃₃) was decreased with increase in lanthanum. Dense microstructure was observed for the composition containing 3 mol% of lanthanum. This was resulted in optimum piezoelectric charge constant (d ₃₃ = 468 × 10^?12 C/N), electromechanical coupling factor (k _p  = 0.68), remanent polarization (P _r = 24.65 μC/cm²) and displacement (D = 2,012 nm). Results indicated that the composition Pb_0.97La_0.03(NiSb)_0.05[(Zr_0.52Ti_0.48)_0.9925]_0.95O₃ could be suitable for actuator applications. The composition Pb_0.98La_0.02(NiSb)_0.05[(Zr_0.52Ti_0.48)_0.995]_0.95O₃ resulted into moderately high value of voltage constant (g ₃₃ = 39.3 × 10^?12 V m/N) and optimum value of Figure of Merit (d ₃₃ × g ₃₃ = 16.2 × 10^?12 C V m/N²) indicated the usefulness for sensor and power harvesting applications.     

Fabrication and Properties of Ag–Ni Bimetallic Sheathed (Bi,Pb)-2223 Tapes

10-meter-long Ag?CNi bimetallic sheathed (Bi,Pb)-2223 tapes with outer nickel sheath and inner silver sheath have been successfully fabricated by the ??Powder in tube?? technique. Microstructure and phase evolution studies by means of SEM and XRD, as well as critical current density (J _c ) measurements have been performed. It is found that the nickel sheath and dwell time in the first sintering process have great influences on the texture evolution, phase transformation and J _c of the Bi-2223/Ag/Ni tapes. Mono-filament (Bi,Pb)-2223 tape with a J _c of 6656?A?cm^?2 and 61-filament tape with a J _c of 12420?A?cm^?2 are obtained. Although using composite bimetallic sheaths can reduce production costs and improve mechanical properties of the Bi-2223 tapes, the Bi-2223 content and J _c of Bi-2223/Ag/Ni tapes are relatively lower than that of traditional Bi-2223/Ag tapes. Meanwhile, due to higher Bi-2223 content and better alignment of Bi-2223 grains, tapes with 61-filament have higher J _c than mono-filament tapes.