Simulating flash heating in a muffle tube furnace

Very rapid heating is an important chondrule-formation process, and it has not been clear whether conventional equipment, such as a muffle tube furnac e, is adequate for the simulation of heating on a timescale of seconds. We present a met:hod for measuring the internal temperature reached by a charg e during rapid heating when the thermocouple response lags. We have constra ined charge temperatures by monitoring the time required to melt metal wire s of various compositions and melting points placed inside charges with fur nace temperature at 1400, 1500, and 1600 degrees C. The times required for melting of the metal wires define the temperature paths inside the charges. At 1400 degrees C, a charge takes 31 s to reach 1399 degrees C; at 1500 de grees C, a charge takes 10 s to reach 1495 degrees C; and at 1600 degrees C , a charge takes 6 s to reach 1538 degrees C. Heating rates in vertical muf fle tube furnaces are adequate for studying flash melting processes (ie., o f much less than 1 min duration) invoked, for example, in the formation of chondrules.