Gallium, melting point

Mangum, B. W. and Thornton, D. D., Ed. (1977), The Gallium Melting-Point Standard, NBS Special Publication 481, Government Printing Office, Washington, D.C. 

Mangum BW (1977) The gallium melting-point standard its role in our temperature measurement system. Clin Chem 23 711-718. 

However, in many countries cesium (melting point 28.5°C) and gallium (melting point 29.8°C) are also liquid at room temperature. 

Calibration of the CTD temperature sensor to better than 2mK accuracy thus requires three units (i) a reference temperature bridge that is accurate to 1 mK at a resolution of at least 0.5 mK, (ii) a thermostat bath to obtain the two oceanic primary fixed-point temperatures with a water triple point cell and a gallium melting point cell to control the drift of the reference sensor and (iii) a temperature controlled bath that is stable to better than 0.5 mK while taking a calibration point with the reference thermometer and the immersed CTD. 

Because bismuth expands on solidification and because it alloys with certain other metals to give low melting point alloys, bismuth is particularly weU suited for a number of uses. Alloys of bismuth can be made that expand, shrink, or remain dimensionally stable on solidification. AH other metals except gallium and antimony contract on solidification. Bismuth aHoys and uses are summarized in Table 5. 

From the ventilation point of view, the fixed points -38.83 °C (triple-point of mercury), 0.010 °C (triple-point of water), 29.76 °C (melting point of gallium), and 156.60 °C (freezing point of indium) are of relevance. The triple-point of water is relatively simple to achieve and maintain with a triple-point apparatus. Some freezing point cells are covered in standards. In practical temperature calibration of measuring instruments, the lTS-90 fixed points are not used directly. 

Steels and austenitic stainless steels are susceptible to molten zinc, copper, lead and other metals. Molten mercury, zinc and lead attack aluminum and copper alloys. Mercury, zinc, silver and others attack nickel alloys. Other low-melting-point metals that can attack common constructional materials include tin, cadmium, lithium, indium, sodium and gallium. 

Gallium is one of the few metals that can melt at room temperature. Its melting point is 29.76°C. If you leave solid gallium in your car on an early summer morning when the temperature is 75°F, in what physical state is the gallium when you return to your car and the interior car temperature is 85.0-F ... 

Mendeleev predicted that the melting point of gallium would fall between those of aluminium (660°C) and indium (115°C). In fact gallium has an anomalously low melting point of 30°C. 

Arsenic and antimony are metalloids. They have been known in the pure state since ancient times because they are easily obtained from their ores (Fig. 15.3). In the elemental state, they are used primarily in the semiconductor industry and in the lead alloys used as electrodes in storage batteries. Gallium arsenide is used in lasers, including the lasers used in CD players. Metallic bismuth, with its large, weakly bonded atoms, has a low melting point and is used in alloys that serve as fire detectors in sprinkler systems the alloy melts when a fire breaks out nearby, and the sprinkler system is activated. Like ice, solid bismuth is less dense than the liquid. As a result, molten bismuth does not shrink when it solidifies in molds, and so it is used to make low-temperature castings. 

The volatile metal is separated by distillation and condensed. Mercury is the only metallic element that is liquid at room temperature (gallium and cesium are liquids on warm days). It has a long liquid range, from its melting point of — 39°C to its boiling point of 357°C, and so it is well suited for its use in thermometers, silent electrical switches, and high-vacuum pumps. 

Obviously this method is limited to liquid metals like mercury and gallium and their amalgams respectively alloys. Modifications of this method have been reported [86FIor]. At elevated temperatures with molten salt electrolytes alloys with an appropriately low melting point can be investigated, too. 

Portland cement Isobutyl alcohol Liquid metal alloy of gallium, indium, and tin of melting point Water 63.4-65.0 0.13-0.17 0.13-0.17 up to 100... 

A liquid metal alloy [36] containing gallium, indium, and tin has been proposed as an additive to Portland cement. A formulation is shown in Table 18-10. The liquid metal alloy has a melting point of 11° C. Its presence does not cause corrosion of stainless steel up to 250° C but causes corrosion of steel alloys at temperature above 35° C, and it dissolves aluminum at room temperature. The alloy is harmless to skin and mucous membranes. 

Note that only in the case of gallium, with a deep subcooling, the reference is linked to the melting point instead that to the freezing point. a All substances (except 3 He) are of natural isotopic composition. e-H2 is hydrogen at the equilibrium concenttation of the ortho and para molecular forms. 

B—The system is insulated and no work can be done on or by the system (rigid container) thus, the energy is constant. At the melting point, some of the gallium will melt and some will freeze, the entropy change of these two processes cancel each other so there is no net entropy change. 

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