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High-temperature Vacuum Furnace

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The high-temperature vacuum furnace is used for melting and step-heating of rocks, minerals and sediments. It has a tantalum resistive heating element and a central Ta crucible. This is surrounded by a series of heat shields and the whole assembly is contained in a water cooled chamber which is independently pumped from the main vacuum line (via a diffusion pump with a backing rotary pump). Cooling is maintained by a dedicated water chiller having a minimum flow rate of 2 l per min. The pressure of the secondary vacuum is monitored using a Penning gauge and furnace power is interlocked to this measurement and the chiller water flow. A disposable Ta liner contains samples dropped into the furnace and minimizes chemical reaction with the crucible walls. Samples are introduced by a low volume carousel that allows up to 12 samples to be loaded under vacuum simultaneously. A viewport enables the viewing of samples during heating, as well as monitoring the crucible temperature independently with an optical pyrometer if desired. The temperature of the furnace is monitored with a W/W-Re thermocouple and controlled using a dedicated controller (Eurotherm 3216) interfaced to a computer. Different heating profiles may be stored for use in different experiments. Maximum temperature measured at the thermocouple is 2000°C.