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New Mexico Geochronology Research Laboratory
Hardware — Resistance Furnace

Note: The description of hardware below is out of date and will be revised soon.

The resistance furnace used by the NMGRL is essentially...

  • Advantages of a resistance furnace
    • homogenous heating of bulk samples
    • good temperature control (necessary for obtaining thermal histories from plutonic potassium feldspar)
    • capable of analyzing large quantities of material (e.g. very young or low potassium samples)
  • Disadvantages of a resistance furnace
    • large extraction background or blank levels
    • single-crystal analysis not feasible for most samples
    • slow in comparison to CO2 laser system




Illustration of the NMGRL furnace and furnace sample loading system.

  1. Double-vacuum furnace with molybdenum crucible which contains an inexpensive, removable molybdenum liner to increase life of the crucible.
  2. Shutter, shaft-mounted onto a linear actuator with 1 inch of travel.
  3. 1.33 inch flange with flex-line connected to analytical vacuum system.
  4. 1.33 inch flange equipped with 0.75 inch zero-length viewport for visual examination of funnel assembly.
  5. VAT Series 48 all-metal gate valve with saphire window welded into the valve. Provides for visual examination of crucible floor during sample heating.
  6. Shutter shaft-mounted onto a linear actuator with 1" of travel. Shutter is equipped with cup to catch any stray sample grains and a 0.25" diameter in-vacuo mirror. The mirror is mounted to provide viewing access, through a zero-length viewport (similar to 4), to the bottom of the crucible during sample heating.
  7. Rotory actuator driven by a DC stepper motor. Actuator drives small in-vacuo gears which in turn drive tubular funnel up and down. The funnel, normally 'nested' in the 7" long nipple, is lowered when a fresh sample (contained in 9) is dropped into the furnace crucible. The apparatus decreases the chance of in-vacuo contamination from earlier samples and allows for computer-controlled sample loading.
  8. 1.33" flange on opposite side of drawing. Provides access to non-analytical "roughing" section.
  9. Linear actuator driven by a DC stepper motor. Computer controlled actuator manuevers one of 17 stainless steel sample buckets into position to be dumped into the furnace crucible.
  10. Three electromagnets, fired successively, to dump samples out of buckets into furnace crucible. A viewport (similar to 4) allows visual access to the sample drop.




Video Clip of furnace sample melting



The field of view in the video is approximately 1 cm across and shows the bottom of the furnace crucible/liner assembly. A sample of material, wrapped in copper foil, has already been dropped into the bottom of the furnace crucible and step-heated up to approximately 1000°C. The resistance furnace is now approaching 1100°C (copper melts at ~1085°C). The square copper packet starts to shimmer and then completely melts into a ball. The sample inside the copper continues to degas its argon so that it can be analyzed by the mass spectrometer.