Galinstan
Galinstan, a brand name, is a silver eutectic alloy of gallium, indium and tin. Gallium, indium and STANNUM (Latin for tin) form the word art galinstan. The alloy is a liquid at room temperature and is, according to the manufacturer's instructions at temperatures below -19 ° C in the solid state of aggregation. Galinstan shows the property of adhering to many materials, including glass of which limits the applications. So thermometer galinstan can only be produced when the interior of the tube is previously coated with gallium ( III) oxide. Just as mercury galinstan shows a tendency to alloy with solid metals; for example, aluminum can be dissolved in galinstan.
Composition and melting point
Expressed in weight percent is from 65 to 95% galinstan of gallium, to 5 to 22 % of indium and 0-11 % tin. A particularly low melting point case has according to the manufacturer, the alloy of 68-69 % gallium, 21 to 22 % indium and 9.5 to 10.5 % tin with -19.5 ° C on.
A similar mixture composed of 62% gallium, 22 % indium and 16 % tin, however, shows a melting point of 10.7 ° C.
A mixture of 68.5% gallium, 21.5 % indium and 10% tin has a density of 6.4 g · cm -3 and a melting point of 11 ° C.
In the physico-chemical literature, the ternary eutectic of these three elements with a composition of 59.6% gallium, indium and 26% tin, and 14.4% with a melting point of 11 ° C is specified.
The large deviation of the melting point between the values from the literature and the manufacturer can not be explained sufficiently with the available sources on the composition of the product.
Properties
Galinstan is a silver-colored, odorless liquid and has the following properties:
- Thermal volume expansion coefficient: 0.000126 K-1
- Density: 6.44 g · cm -3
- Melting point: -19.5 ° C
- Boiling Point: > 1300 ° C
- Vapor Pressure: <10-8 Torr (500 ° C)
- Solubility: insoluble in water and organic solvents
Use
Galinstan is mainly used as a non-toxic substitute in many applications where liquid mercury or sodium-potassium eutectic ( NaK ) was used; inter alia, as lubricant in a high vacuum, for example in cathode ray tubes.
Galinstan because of its indium content can not be used as a coolant for nuclear reactors, because indium has a very high cross section for the Neutronenanlagerung, so the reactor would be deprived of too many neutrons.
As metallic thermal paste for heat sink with a thermal conductivity of 16 W / (m · K) it outperforms conventional thermal compounds with thermal conductivities of 1-9 W / ( m · K). Disadvantage is that aluminum heatsink be resolved by galinstan, so it can only be used with ( nickel-plated or nickel-plated non ) copper heatsinks. Unlike ordinary pastes galinstan is electrically conductive; excess quantities can therefore cause short circuits when removing sources.
Brand name
Galinstan is a legally protected brand name which was registered with the German Patent and Trademark Office on December 10, 1996 by Geratherm Medical AG for "essentially consisting of base metal alloys, in particular gallium alloys ".