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Aluminum Melting Point

The temperature accuracy of optical pyrometry measurements can be checked by monitoring release of 40Ar upon melting from a disc of alloy 1100 (ultra corrosion resistant) aluminum that has been enclosed within a standard 3 mm diameter Ta foil packet in the same manner as for unknown silicate samples.  This approach to temperature calibration is possible because Ar is trapped in the alloy 1100 manufacturing process due to the use of argon as purge gas to remove hydrogen gas.  We have determined that a 3mm diameter x 0.05 mm thick disc of Al foil releases ca. 2.5x10-14 mol of 40Ar as it melts.  Based upon incremental heating of Ta-encapsulated Al foil, the current temperature accuracy of optical pyrometry measurements made from the Ta surface is +/- 18oC when 10 samples are run in sucession.  This variability results from mis-allignment of the pyrometer sample region and the laser image upon the sample when moving between samples.  When the pyrometer is alligned for each new sample, the temperature accuracy is improved considerably.