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What is Galinstan?

A safer alternative to mercury

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What is Galinstan?

A traditional clinical thermometer.

Image © Terence Bell

Galinstan® is a eutectic alloy composed of gallium, indium and tin (hence its name, which is derived from the gallium, indium and stannum, the latin name for tin).

Although galinstan is a registered trademark of the German medical company Geratherm Medical AG, many other companies offer similar alloys, which are non-toxic and have a very low melt temperature.

These properties make galinstan an ideal substitute for mercury, particularly in clinical thermometers, but also in coolants and thermal grease.

Composition:
There is no specific formula for galinstan, but a standard form is composed as follows:

  • Gallium (Ga): 68.5%
  • Indium (In): 21.5%
  • Tin (Sn): 10%

Indium Corporation produces a mercury substitute alloy that is composed of 61% gallium, 25% indium, 13% tin and 1% zinc, and has a melt temperature of roughly 45°F (7°C).

Properties:

  • Appearance: Silvery metallic liquid
  • Odor: Odorless
  • Solubility: Insoluble in water and organic solvents
  • Specific Gravity: 6.4g/cc (room temperature)
  • Melting Point: 2.2°F (-19°C) Boiling Point: >2372°F (>1300°C)
  • Vapor Pressure: <10-8 Torr  (500°C)
  • Viscosity: 0.0024 Pa-s (room temperature)
  • Thermal conductivity: 16.5 (W-m-1-K-1)
  • Electrical Conductivity: 3.46×106 S/m (room temperature)
  • Surface Tension: s= 0.718 N/m (room temperature)

Benefits:
Galinstan medical thermometers are considered more accurate than traditional mercury thermometers and much safer, as galinstan alloy is non-toxic and can be safely cleaned in cases of breakage. Also, as opposed to mercury, disposal of galinstan and galinstan thermometers does not pose any serious environmental threat.

Other:
According to Geratherm Medical, galinstan was awarded the gold medal for best new invention at the 1993 "Eureka" Inventors' Fair in Brussels.

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