Box furnaces are not often used for crystal growth because the convective currents can cause the temperature inside to fluctuate slightly. In addition, maintaining a controlled atmosphere in a box furnace is usually not feasible. No matter what kind of furnace one uses, it is important to keep materials from spilling or depositing on the walls of the furnace. If material spills on the furnace refractory material or heating elements, these can burn out prematurely and are expensive to replace. Prices can go much higher as one adds multiple zones or accessories.
Programmable controllers are very desirable, especially for tube furnaces.
A hypothetical temperature ramp program for single crystal growth in a tube furnace might include ramping to 1000 degrees C at 25 degrees per minute, holding isothermal for several hours, ramping down at 0.2 degrees per hour to 975 degrees C and then ramping down at 0.5 degrees per hour to 500. There are many variations, of course. Send comments, kudos and suggestions to us via email . Some of these figures are adapted from the Chemglass, Inc. catalog and have been reproduced with permission.