Gallium: Thermal Conductivity; Supercooling; Negative Pressure

The thermal conductivity of liquid gallium does not appear to have heretofore been measured. The method employed involved a comparison with the known thermal conductivity of mercury. The two liquids were sealed in two thin-walled glass tubes (30 cm long, 10 mm bore), the upper ends being inserted vertically through the bottom of a boiler containing boiling water. The tubes were coated to secure the same thermal emissivity. Two thermocouple loops which could be moved along the tubes served to establish points having the same temperature on the two tubes. The ratio of the squares of the lengths from the thermocouple junctions to the bottom of the boiler gave 3.51±0.03 as the relative thermal conductivity of gallium to that of mercury, or 0.336±0.005 watt/cm (°C) as the thermal conductivity of gallium between 30° and 100°C, based upon 0.0958 for mercury. It was found possible to supercool liquid gallium to —28°C, or 58°C below its melting point, by exposing small drops on paper to a slowly decreasing temperature in a deep-freeze chamber with a circulating atmosphere. An attempt to measure the negative pressure of gallium proved disappointing, for it was found that gallium does not ``wet'' the wall of an evacuated tube. With a partial evacuation, low negative pressures were measured which decreased (like water) as the melting point was approached.