Bi-Sn System Research Articles

In-situ observation of alloy phase formation in nanometre-sized particles in the Sn–Bi system

Alloy phase formation in nanometre-sized particles has been studied by in-situ transmission electron microscopy using particles in the Sn–Bi system. Observations have been carried out at a temperature (i.e. 350 K) above the eutectic temperature. For tin-rich compositions, with increasing concentration of bismuth, a particle (approximately 8 nm in size) of the terminal tin solid solution changed directly into a particle of the liquid phase, without going through the stage of solid–liquid coexistence. On the other hand, for bismuth-rich compositions, a particle (approximately 8 nm in size) of the terminal bismuth solid solution changed first to a particle with a crystal–liquid two-phase microstructure and eventually to a particle of the liquid phase, with increasing concentration of tin. Thermodynamic model calculations indicate that the contribution of the solid–liquid interfacial energy to the total Gibbs free energy of an alloy particle with a solid–liquid two-phase microstructure becomes large enough to change the phase equilibrium when the size of the particle is reduced to the nanometre range, and that the difference between the alloy phase formation for the tin-rich and bismuth-rich alloys observed here can be consistently explained in terms of the difference between the relative contributions of the solid–liquid interfacial energy for the two types of alloy.

Thermodynamic Properties of Bi–Sn Melts

The thermodynamic properties of the Bi-Sn system are investigated between 673 and 793 K using liquid-electrolyte emf measurements. The principal thermodynamic functions were evaluated by integrating the Gibbs-Duhem equation. The results indicate that the Bi-Sn melt system is a subregular solution.

Thermodynamic properties of liquid Bi–Sn alloys

Abstract The thermodynamic properties of liquid Bi–Sn alloys were measured over the whole composition range by an electromotive force (emf) method using a liquid electrolyte. The basic thermodynamic functions were calculated from the corresponding excess functions by using the Gibbs–Duhem integration at 723 K. The liquid Bi–Sn system was classified as a subregular solution and an asymmetrical curve of enthalpy of mixing vs. composition was found.

Phase diagram studies of the Ti–Bi–Sn system

The system Ti–Bi–Sn has been studied, using optical and scanning electron microscopy. Ternary Ti–Bi–Sn alloys were prepared by arc melting as well as in quartz ampoules by classical metallurgical methods. The arc-melted alloys have been analyzed as cast while the ampoules have been annealed at 500 and 600 °C. Primary crystals of a ternary compound with approximate formula Ti 3BiSn have been found in the “as cast” alloys. Diffusion layers of this phase have been observed as well. The binary end-systems compounds’ homogeneity ranges have been determined. A tentative isothermal section of the Ti–Bi–Sn phase diagram at 500 °C is constructed taking into account the ternary extensions of the binary phases.

Phase diagram studies of the Ti–Bi–Sn system at 400°C

The phase equilibria in the Ti–Bi–Sn system have been studied at 400 °C using optical and scanning electron microscopy. The homogeneity ranges and the ternary extensions of the relevant binary compounds were determined. The highest contents of the correspondent ternary element (8.2 at.% Sn and 9.0 at.% Bi, respectively) are found in Ti 2Bi and Ti 2Sn. A new formerly unknown ternary compound, having the approximate formula Ti 3BiSn, has been found. An isothermal ternary phase diagram section at 400 °C has been constructed.

In situ HREM study on the structural instability of isolated nanometre-sized alloy particles in the Sn-Bi system.

The structural instability of isolated nm-sized alloy particles has been investigated by in situ transmission electron microscopy, using particles in the Sn-Bi system. In a pure tin (Sn) particle, no structural fluctuation was induced under electron-beam irradiation. In a tin-rich solid solution particle, an orientational fluctuation took place at a rate of approximately once per 1-3 s. In a high concentration alloy particle with a two-phase microstructure, a structural fluctuation occurred at a rate of a few hertz. Namely, the fluctuation became more frequent with increasing bismuth (Bi) concentration, no matter whether it consists of a single phase or multiple phases. A good parallelism can be found between this fluctuation enhancement with bismuth concentration and the fact that the free-energy difference between a solid particle and the corresponding liquid one decreases continuously with bismuth concentration and approaches a value close to zero at the eutectic composition. These results lead to a view that a nm-sized solid particle exhibits a structural instability under electron-beam irradiation when the free-energy difference between a solid particle and the corresponding liquid one is reduced to a value close to zero.

PHASE EQUILIBRIUM IN METALLIC SYSTEMS

Binary phase diagrams represent a rich source of thermochemical information. The mathematical concept of equilibrium that underlies binary phase diagram construction is reviewed using the Sn-Bi and Mg-Si systems as examples. The common methods that provide experimental data useful to modelling include microscopic phase examination, X-ray diffraction (XRD), elecromotive force (emf), vapour pressure, scanning calorimetry and calorimetric techniques. Using the mathematical concept above, information resulting from these diverse techniques can be examined in a self-consistent way and all information contributes to the construction of the phase diagram. As commercial alloys typically contain several elements, the mathematical equations derived for binary systems can be combined and extrapolated to model these multicomponent systems. There are two general cases: a system with one dominant element such as lead acid battery alloys which are represented by the lead-rich region of the Pb-Ag-Ca-Sn system and the general case where the alloy cover the entire compositional domain, such as the phase relationships of noble metal inclusions in nuclear fuel rods, which are represented by the Mo-Rh-Ru-Pd-Tc system.Les diagrammes de phase binaires représentent une source riche en information thermochimique. On examine le concept mathématique d’équilibre qui sous-tend la construction du diagramme de phase binaire en utilisant les systèmes Sn-Bi et Mg-Si, comme exemples. Les méthodes communes fournissant l’information expérimentale utile à la modélisation incluent l’examen de phase par microscopie, la diffraction par rayons X, la force électromotrice (fem), la pression de vapeur, la calorimétrie à balayage et les techniques calorimétriques. Utilisant le concept mathématique ci-dessus, on peut examiner de manière consistante les données qui proviennent de ces techniques variées et toute l’information contribue à la construction du diagramme de phase. Puisque les alliages commerciaux contiennent typiquement plusieurs éléments, on peut combiner et extrapoler les équations mathématiques établies pour les systèmes binaires afin de modéliser ces systèmes à composantes multiples. Il y a deux cas généraux: un système avec un élément dominant, comme les alliages au plomb pour pile qui sont représentés par la région riche en plomb du système Pb-Ag-Ca-Sn; ensuite, le cas général où les alliages couvrent le domaine compositionnel entier, comme les relations de phase des inclusions de métal noble des tiges de combustible nucléaire, qui sont représentées par le système Mo-Rh-Ru-Pd-Tc.

In-situ Observation of Alloy Phase Formation in Isolated Nanometer-sized Particles

Alloy phase formation in isolated nanometer-sized particles has been studied by transmission electron microscopy, using alloy particles in the Au-Sn, Bi-Sn, and In-Sn binary systems. When the size of particles was decreased down to approximately 10 nm in diameter, a thermodynamically stable amorphous phase appeared in the former two systems whereas a liquid phase formed in the latter system. Neither the amorphous nor the liquid phase is an equilibrium phase in bulk materials at room temperature. The formation of these phases at room temperature is ascribed to the large suppression of the eutectic temperature associated with size reduction.

In situobservation of a fluid amorphous phase formed in isolated nanometer-sized particles in the Sn-Bi system

It is revealed by in situ transmission electron microscopy that a unique, fluid amorphous phase is produced in Sn-Bi alloy particles at room temperature when the size of particles is below 10 nm. Bright and dark spots in the granular contrast in the high-resolution electron microscopy images of the fluid amorphous phase exhibited continuous changes in position and intensity with time, suggesting a high atomic mobility in the amorphous phase. Upon heating the fluid amorphous phase went to melt without crystallization and upon cooling it solidified again into the fluid amorphous phase with no traces of crystallization. These results indicate that due to the finite-size effect, the eutectic point ${T}_{\mathrm{eu}}$ in this system is lowered to a temperature below room temperature where observations were carried out, and that the glass transition temperature ${T}_{g},$ where a liquid goes to an amorphous solid, locates near room temperature.

Alloy Phase Formation in Isolated Nanometer-sized Particles in the Au-Sn and Sn-Bi Systems

ABSTRACTAlloy formation in nanometer-sized particles has been studied as a function of the particle size by in-situ transmission electron microscopy using particles in the Au-Sn and Sn-Bi systems. When the size of particles is larger than a critical value, essentially similar phase equilibrium was observed in nanometer-sized particles and bulk materials in the both systems. But a solid amorphous phase was formed over a compositional range near the eutectic composition when the size of particles was smaller than about 7 nm in diameter in the former system, whereas a fluid amorphous phase was formed when the size of particles is smaller than about 10 nm in diameter in the latter system. These amorphous phases directly changed into liquid phases upon heating and solidified into amorphous phases upon subsequent cooling. The formation of these thermodynamically stable amorphous phases can be attributed to the the suppression of the eutectic temperature (Teu) associated with size reduction being so large that Teu is below the glass transition temperature (Tg).

Kinetics of interface reaction in 40Sn-Bi/Cu and 40Sn-Bi-2Ag/Cu systems during aging in solid state

The characteristics of thickening kinetics of the intermetallic compounds (IMC) (Cu/sub 6/Sn/sub 5/+Cu/sub 3/Sn) during aging at 120/spl deg/C and 90/spl deg/C in solid state were studied by quantitative metallographic analysis for three solder alloy systems: 40Sn-Bi/Cu, 40Sn-Bi-2Ag/Cu and Sn-37Pb/Cu. The diffusion couples were prepared by hot immersion in the molten solder bath. The results showed that the rate of the IMC thickening increases in the order Sn-37Pb/Cu<40Sn-Bi/2-Ag/Cu<40Sn-Bi/Cu. The IMC thickening rate in the Sn-Bi eutectic system is one order of magnitude faster than that in Sn-Pb eutectic system. The time exponents are different from each other. The relationship between the increase of IMC and aging time follows a parabolic function in the Sn-Pb system, and a linear relation in the Sn-Bi system. Addition of Ag in Sn-Bi inhibits the IMC thickening process.

Metastable and equilibrium wetting states in the Bi–Sn system

Sessile drop experiments involving a variety of Bi–Sn alloys on solid Bi substrates were performed. Substrates prepared from small- and large-grained polycrystals and single crystals were used to measure equilibrium and metastable contact angles and estimate the surface tension and equilibrium contact angle of the solid–liquid interface. The substrates were also used to investigate the coupling of the dissolution and wetting processes and to investigate the effect of substrate grain size on wetting. It was determined that the equilibrium wetting geometry is independent of linear scale and that grain size has little influence on wetting or dissolution in the Bi–Sn system.

Experimental equilibrium phase diagram of the Ag–Bi–Sn system

The equilibrium phase diagram of Ag–Bi–Sn ternary system was studied by X-ray powder diffraction analysis, differential scanning calorimetry and differential thermal analysis. Three isopletic sections were studied: 10 at.% Bi, 40 at.% Ag and 70 at.% Bi. Three transitory invariant reactions were characterized: two ternary transitory peritectics and one ternary eutectic. Moreover, from all equilibrium temperatures we were able to propose a description of ternary liquidus surface in the whole composition range.

Thermodynamic assessments of the Sn-In and Sn-Bi binary systems

A thermodynamic evaluation of the Sn-ln and Sn-Bi system has been made by using thermodynamic models for the Gibbs energy of the individual phases. An optimized set of thermodynamic parameters was obtained taking into consideration relevant experimental information. The thermodynamic parameters of the Sn-ln and Sn-Bi systems and comparisons between calculation and experimental data are presented.

Melting behavior of SnBi alloy droplets during continuous heating

An increase in the heating rate applied to samples of bct solid solution alloys in the SnBi system was observed to bring about a change in the melting behavior in that an additional melting event appeared between the equilibrium solidus and liquidus temperatures. The measured temperature of this reaction was interpreted as corresponding to invariant melting of retained β of composition C o at the T o temperature. A comparison of the measured values with the T o calculated from thermodynamic analysis showed good agreement (within 1.5°C). A mechanism involving sluggish diffusion in the solid is proposed to account for the retention of C o solid up to its corresponding T o temperature. Moreover, the observed melting behavior has direct relevance to understanding the influence of the recalescence thermal history on the microstructural development during rapid solidification of highly undercooled liquids.

The effect of pressure on metastable phase formation in the undercooled Bi-Sn system

A metastable phase was produced by the solidification of highly undercooled Bi-48.6 at% Sn alloy droplet samples. During heating the metastable phase was observed to melt at 116° C at ambient pressure. The onset of the metastable endotherm was found to increase with increasing pressure, while the liquidus and eutectic temperature for the structure stable at ambient pressure decreased with increasing pressure. Based on the pressure dependence of the melting trend, the metastable phase will be stable at the expense of the stable ambient pressure structure under high hydrostatic pressure conditions (above ∼ 1 GPa). Both microstructural observations and X-ray examinations at ambient pressure revealed that the metastable phase was present in droplet samples and that the X-ray diffraction pattern was close to that of the high-pressure stable phase previously reported as a rhombic cell. High-pressure thermal analysis has also allowed for identification of the effect of pressure in promoting favourable formation kinetics and the kinetic transition from the equilibrium phases to the metastable phase at high undercooling.

Structural Studies on Ni75(SnSi)25 and Ni75(SnBi)25 Alloys

AbstractTernary alloys on the quasi‐binary system Ni3Sn(r) in equilibrium condition. It has been observed that these phases undergo transformations at high temperatures but upto 500 °C room temperature modifications are stable. The two phases do not have any appreciable solid solubility in either of them. The phase Ni3Si(r) crystallizes in to Cu3Au (Li2) structure where as Ni3Sn(r) is based on c.p.h. structure with a = 5.305 A°, c = 4.254 A°. No new ternary phase has been detected in Ni3SnNi3Si section.The investigated alloys of the NiSnBi system contain 75 at.% Ni. All the ternary alloys show simultaneous occurrence of three phases, namely Ni3Sn(r), NiBi and Ni(Sn) in equilibrium state. The phase NiBi has NiAs(B8) type of structure. Due to non‐existence of isostructural phases in the two binary systems (NiSn and NiBi), single solid solution phases are not formed. Widely differing atomic sizes of nickel and bismuth atoms restrict the formation of solid solution of bismuth in nickel in contrast to Ni(Sn) where atomic size factor is favourable.

Heterogeneous nucleation in entrained Sn droplets

Differential thermal analysis has been used in conjunction with entrained droplet specimens to measure the nucleation rates of uncontaminated Sn-rich liquids in contact with solid Bi, Zn and Al. The Bi(Sn) system gave a linear nucleation rate plot and an analysis of the data in terms of the classical theory of heterogeneous nucleation at variable composition, yielded a pre-exponential frequency factor, J s 0, that was in good agreement with the predicted value for pure Sn. On the other hand, the nucleation rates plots for Zn(Sn) and Al(Sn) were irregular and could only be analysed to give approximate estimates of J s 0 for these two systems. The origin of the irregularity was discussed in terms of the surface structure of entrained droplets. In the case of Bi(Sn), the nucleation rate data yielded a catalyst surface energy difference of − 50 ± 26 mJm −2 which agreed with a theoretical estimate for pure Sn nucleating in contact with pure Bi.

Eutectic solidification of the pseudo binary system of polyethylene and 1, 2, 4, 5-tetrachlorobenzene

This paper describes a study on the solidification of the pseudo binary eutectic system, consisting of unfractionated linear polyethylene and the faceted growing diluent 1, 2, 4, 5-tetrachlorobenzene. Crystallization under eutectic conditions resulted in very fine-grained structures, which were found to depend on the growth rate. This rate of solidification was varied by pulling the polymer solutions through a fixed temperature gradient of 3° C mm−1 at different speeds ranging from 1 to 216 mm h−1. Fibrillar polymer crystals with lateral dimensions of about 0.5 μm remained after removal of the solid diluent. At rates of solidification in the region of 2 to 20 mm h−1, the fibrils appeared to be aggregated in domains of well oriented structures, closely resembling the complex regular structures of the eutectic Sn-Bi system. At higher speeds the fibrillar crystals formed an irregular three-dimensional network. The polymeric structures grown from more dilute mixtures were characterized by rectangular holes originating from the growth of faceted primary diluent crystals. Despite the complexity of the crystallization of the highly entangled polymer solutions there appears to be quite some similarities between the eutectic polymeric system investigated and faceted/non-faceted atomic or small molecular eutectics.

Mass Spectrometric Determination of Activities and their Dependence on Temperature in Liquid Bismuth-Tin Alloys

Abstract Liquid alloys of the Bi-Sn system have been studied to determine thermodynamic properties. Ion currents have been measured by a double-focusing mass spectrometer. The thermodynamic values were calculated by application of the monomer-dimer ratio technique and the integration technique. Special attention was paid to the correction of fragmentation effects. Activities of both components versus composition in the temperature range from 1023K to 1323K and values of Gibbs energies and heats of mixing are reported as results. At 1200K the species Bi2 , Bi3, Bi4 , BiSn, and Bi2Sn were observed in the gaseous phase above the Bi50Sn50 alloy. The discussion shows a tendency to segregation of the liquid Bi-Sn alloys.