For many people attempting to make superconductors in a high school laboratory, finding a suitable furnace may be the greatest difficulty. Laboratory muffle furnaces are somewhat uncommon in secondary schools; whereas pottery kilns are quite common in school art departments. This requires the unusual, and sometimes difficult, process of cooperation between the school's science and art departments.
Small electric pottery kilns are quite adequate for making superconductors, although most will require some minor modifications. Any modifications that are required will not impair the use of the kiln for pottery. In fact, the modifications will only enhance their use as a pottery kiln.
Some kilns do not have a pyrometer for measuring temperature. Suitable pyrometers are available from most kiln dealers at a very reasonable cost. (Pyrometers consist of a thermocouple which is connected to a voltmeter having a scale calibrated in degrees of temperature.) Some inexpensive pyrometers are not very accurate, but even the relatively inaccurate pyrometers are usable if they are calibrated to a suitable calibration reference at a temperature near 950 degrees Celsius. The pyrometric cones commonly used in pottery kilns are a suitable calibration reference. These cones are much more accurate than the temperature indicators on most pottery kilns.
On some pottery kilns, accurate temperature control is difficult (or impossible) because the control may have only three positions (such as "high," "low," and "off"). The most straightforward solution to this problem is to add an "Infinite Control" switch to the kiln. This is the same controller that is used in 95 percent of all electric kitchen ranges with rotary controls. A universal replacement "Infinite Control" switch costs about $15 wholesale and is available from most appliance parts dealers for around $25. They can be installed on an electric pottery kiln by anyone familiar with electrical wiring. They provide a very precise control of kiln temperature by cycling the current on and off with a continuously variable duty cycle.
The most common universal replacement "Infinite Control" switch is the Chromalox part #UC120 (for 120 volts) or part #UC240 (for 240 volts).
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