Sintering Furnaces

Thermocouple Calibration Furnace

The international temperature scale, ITS-90, uses optical pyrometry to establish temperatures above the freezing points of silver, gold, and copper (around 1000° C).  For many practical applications, a more direct temperature measurement device is desirable, and to that end high temperature thermocouples have been developed. They are widely available for use in certain conditions to 2000° C, and in some cases, even higher.

Calibration and testing of these thermocouples requires a furnace able to stably maintain extreme temperatures for prolonged periods of time.  With few exceptions, simple furnaces designed to operate in air atmospheres are limited to temperatures below 2000° C.  Research laboratories engaged in high temperature studies often employ inexpensive ceramic box or tube furnaces using ceramic-metal composite (cermet) heating elements fabricated from molybdenum or tungsten silicide compositions for use in temperatures from 1600° to 1900° C.  However, in most cases, extreme temperature thermocouples are fabricated from refractory metal alloys that require protection from oxidation.

Increasing, temperatures exceeding 2000° C are needed for these studies, as well as a wide variety of other applications.  The cold wall furnace design is well suited to attaining and maintaining extreme temperatures above 2000° C.  Much of the work done at these extreme temperatures is performed near atmospheric pressure in inert gas rather than in vacuum. This reduces sample and furnace component sublimation.  However, the inexpensive rotary vane mechanical vacuum pump often provided on these furnaces provides rapid evacuation of air from the furnace in a few minutes, avoiding lengthy inert gas purge cycles.  Initial  furnace heating is also done in vacuum to reduce inert gas consumption, which limits inert gas consumption to the higher temperature portions of the heating cycle.

The following figure shows the RD-G, a 2200° C benchtop calibration furnace manufactured by Webb Vacuum Furnaces. It is used in National Standard Laboratories worldwide for the calibration of high temperature thermocouples and melting point standards.

RD-G Vacuum Furnace

RD-G Thermocouple Calibration Furnace