A muffle furnace is used for many of the same types of protocols as an ashing furnace. The use of mechanical convection in these ovens directs airflow out of an exhaust muffle, so typically does not require placing the furnace within a fume hood.
Common applications for a muffle furnace include high-temperature applications such as fusing glass, creating enamel coatings, ceramics and soldering and brazing articles. Also, advances in materials used for heating elements, such as non-flammable molybdenum disilicide, can now produce working temperatures up to 1,800 degrees Celsius (3,272 degrees Fahrenheit), which facilitate more sophisticated metallurgical applications.
Tube furnaces are used to synthesize and purify compounds, primarily inorganic. These furnaces consist of a cylindrical cavity that is heated via one or more heating elements outside of the chamber. The cavity’s temperatures can reach up to 1,100°C. Additionally, tube furnaces typically have one (or more) heating cavity that can be controlled via thermocoupler feedback, exposing materials to different temperatures for varying periods of time. Transport reactions, for example, requiring multiple temperature zones within the same compartment, can be performed in tube furnaces. The production of crystals also results from transport reactions.
An example of a material prepared using a tube furnace is the superconductor Yttrium barium copper oxide (YBa2Cu3O7), a mixture of CuO, BaO, and Y2O3. The concoction is heated in a tube furnace at several hundred degrees using oxygen to help achieve the desired result. Other superconductors are created using specific tube furnace “recipes,” depending on their individual reaction characteristics and control criteria.