The Thermcraft TransTemp transparent tube furnace was originally developed at the Lincoln Laboratory on the campus of MIT. Unlike conventional furnaces, the TransTemp becomes transparent at approximately 600°C, which makes it possible to see a process as it takes place inside the furnace.
TransTemp transparent furnaces use a gold mirror that reflects infrared radation and acts as an insulator. The use of only a gold mirror for insulation minimizes mass and allows for very fast heat up and cool down rates. The maximum recommended operating temperature of the TransTemp tube furnace is 1000°C.
Construction
TransTemp tube furnaces are constructed using three coaxially mounted tubes. The outermost tube is Pyrex glass that has a gold mirror on its inner surface. Gold is highly reflective of infrared energy and acts as an insulator. Gold is also ideal for a transparent furnace because it is a poor reflector of visible light. The second tube is a quartz shield that protects the gold mirror. Coaxially mounted inside of the quartz shield is a resistive element. The element is made up of a series of fixed brazed coils. The exact temperature profile will depend on the design of the element. The third tube is a quartz tube or muffle, which extends beyond the ends of the furnace and passes through the center of the heating element.
Temperature Uniformity
In conventional tube furnaces using packed or porous insulation, the temperature is generally uniform over only the central third of the heated length. Outside this region, the temperature decreases significantly due to heat loss at the ends. In the TransTemp tube furnace, uniform reflection of infrared radiation evenly distributes the heat throughout the entire length of the tube. Because the mirror is uniform, it has uniform radial heat loss. With the ends capped, the TransTemp tube furnace will provide a uniform temperature along 60% of its length.
Rapid Cycle Time
The TransTemp tube furnace has a very low thermal mass, which enables it to quickly heat up to temperature and cool down rapidly. The standard 305mm model with a 37mm inside diameter muffle will reach 1000°C in about 15 minutes and cool to 600°C in about 10 minutes.