Using Gold Insulation in Transparent Tube Laboratory Furnaces
Gold (Au) remains one of the most sought-after precious metals in the world for its superficial monetary value, but it also exhibits useful electro- and thermomechanical behavior for engineering and manufacturing applications. With a thermal conductivity of roughly 310 Watts per meter-Kelvin W/(mK) from room temperature up to 225°C (437°F) and outstanding reflectivity to infrared (IR) radiation, it is routinely used to manufacture protective films for satellites and faceplates for space suits. These novel properties are gradually being recognized in a broader range of fields. Most recently, gold has been employed for thermally-efficient heat shieldings in the engine bays of Formula One vehicles. It has also been explored as a potential insulator for innovative transparent tube laboratory furnaces.
The primary challenge of using gold in laboratory furnaces is the excessive operating temperatures of typical heat treatment environments. Typical thermal processing for analytical applications requires heating chambers capable of facilitating temperatures exceeding 1000°C. Gold has a melting point of 1064°C and is subject to thermal warping at significantly lower temperatures.
Thermcraft has developed a unique solution to this problem. In this blog post, we will explore how gold is successfully used as an insulator in our unique Transparent Tube Laboratory Furnace.
Where is Gold Installed on the Laboratory Furnace?
The TransTemp laboratory tube furnace comprises three concentric tubes of Pyrex glass and quartz. Within the outermost Pyrex tube is a thin film of gold approximately 80 nanometers (nm) thick. This reflective layer is designed as a series of gold ‘islands’ separated with uncoated channels of Pyrex. The lightness of the gold film determines the amount of space between these islands.
What Does the Gold Mirror Achieve?
This gold thin film acts as a reflector of the IR energy generated by the brazed coil heating elements inside the second tube. It continuously reflects these wavelengths back into the heating chamber to enhance the thermal uniformity across up to 60% of the process tube. The reflectivity of the gold mirror ensures that very low levels of heat is transmitted through the film itself and is instead redirected back into the heating chamber. The ambient air outside the tube keeps the film at low temperatures and limits the risk of thermal degradation.
The selective reflectivity of gold is ideal for laboratory furnaces as it features high transmissivity of many visible wavelengths of light. Light gold films are fairly transparent, enabling analysts to directly observe process conditions in situ. Heavier gold films naturally increase the opacity of the outer Pyrex tube while enhancing the thermal and electrical efficiency of the Transparent Tub Laboratory Furnace.
If you would like to learn more about how our TransTemp Laboratory Furnace works, read our previous blog post: Transparent Tube Laboratory Oven for Research Applications.
Laboratory Furnaces from Thermcraft
Thermcraft is dedicated to designing, manufacturing, and supplying specialist thermal processing equipment for distinct applications. Our TransTemp Laboratory Furnace was envisaged as a tool for crystal growth and chemical deposition techniques, but its applications have grown significantly to include many of the uses for standard tube furnaces.