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Galinstan is a brand-name and a common name for a liquid metal alloy whose composition is part of a family of eutectic alloys mainly consisting of gallium, indium, and tin. Such eutectic alloys are liquids at room tem`perature, typically melting at +11 °C (52 °F), while commercial Galinstan melts at −19 °C (−2 °F).An example of a typical eutectic mixture is 68% Ga, 22% In, and 10% Sn (by weight) though proportions vary between 62–95% Ga, 5–22% In, 0–16% Sn (by weight) while remaining eutectic; the exact composition of the commercial product “Galinstan” is not publicly known.Due to the low toxicity and low reactivity of its component metals, galinstan finds use as a replacement for many applications that previously employed the toxic liquid mercury or the reactive NaK (sodium–potassium alloy).Physical properties·Boiling point: > 1300°C· Melting point: −19°C· Vapour pressure: < 10−8 Torr (at 500°C)· Density: 6.44 g/cm3 (at 20°C)[3]· Solubility: Insoluble in water or organic solvents· Viscosity: 0.0024 Pa·s (at 20°C)· Thermal conductivity: 16.5 W·m−1·K−1· Electrical conductivity: 3.46×106 S/m (at 20°C)· Surface tension: s = 0.535 - 0.718 N/m (at 20°C, dependent on producer)· Specific heat capacity: 296 J·kg−1·K−1Galinstan tends to be “wet” and adhere to many materials, including glass, which limits its use compared to mercury.UsesGalinstan is commercially used as a mercury replacement in thermometers due to its nontoxic properties, but the inner tube surface must be coated with gallium oxide to prevent the alloy from wetting the glass surface.Galinstan has higher reflectivity and lower density than mercury. In the field of astronomy it is considered as a replacement for mercury in liquid mirror telescopes.Galinstan may be used as a thermal interface for computer hardware cooling solutions, though major obstacles for widespread use are its cost and aggressive corrosive properties (it corrodes many other metals such as aluminium by dissolving them). It is also electrically conductive, and so needs to be applied more carefully than regular non-conductive compounds.It is difficult to use for cooling fission-based nuclear reactors, because indium has a high absorption cross section for thermal neutrons, efficiently absorbing them and inhibiting the fission reaction. Conversely, it is being investigated as a possible coolant for fusion reactors. Unlike other liquid metals used in this application, such as lithium and mercury, the nonreactivity makes galinstan a safer material to use.
Significant manufacturing cost reductions can be realized with lower-temperature surface mount processing by increasing yields and using less expensive components and boards. A lower-melting-point solder alloy (nominal composition Sn-41.75Pb-8Bi-0.5Ag) has been developed that enables significant reductions in peak reflow temperatures during surface-mount assembly. The solder alloy is compatible with standard Pb-Sn surface finishes, melts within the temperature range of ~166-172°C, and has promising mechanical properties.After establishing an optimum ternary composition of Sn-42Pb-8Bi, quaternary additions were examined for additional beneficial effects on the melting character of the alloy. Silver additions were the most beneficial—peak thermal and mechanical benefits were obtained at ~0.5%Ag content. The solidus temperature of this alloy is ~166°C, the primary liquid temperature is ~172°C, and there is a very small (approximately 2-3%) residual amount of lead-rich solids that do not completely melt until 178°C. This melting character suggests that it may be feasible to lower peak reflow temperatures in surface mount assembly processes by as much as 10-15°C using the silver-doped alloy. Compositional fluctuations of silver below 0.2% are not effective in providing melting point depressions and silver contents in excess of 0.8% begin to form phases with melting points well beyond that of eutectic 63Sn-37Pb.Experiments with fully populated boards having greater local thermal masses are in progress to determine the lowest peak reflow temperatures for given applications. However, it does seem quite clear that surface mount soldering with a Sn-41.75Pb-8Bi-0.5Ag solder paste can be done at temperatures significantly lower than those currently in use in order to relieve many yield problems associated with moisture and temperature sensitivity in surface mount assembly.
