A Carbon Particle Resistance Electric Furnace designed for the Preparation of Synthetic Mica Crystals

Synthetic Mica Research, XXXVI

Abstract

In the experiment of preparing synthetic mica crystals, it is necessary first to melt the mixture of raw materials to a clear liquid by heating it at about 1450°C and then to maintain it for many hours at the temperature within a range of several tens of degrees around its crystallizing temperature which is about 1350°C. The temperature of the melt must be controlled precisely to obtain the desired rate of cooling. High-aluminouns clay crucibles used as containers must be sintered sufficiently at about 1650°C in order to withstand the corrosion of the melt. A carbon particle resistance furnace was constructed to meet the above requirements.
Here in this paper, the construction features and characteristics of the furnace are described.
Usually the carbon particle resistance furnace is said to be unsuitable for precise temperature control and moreover the furnace atomosphere is apt to become reducing.
As a preliminary step, characteristic values, such as the electric power input per unit surface area of heating zone and the specific resistance of carbon particle heating element, were investigated by critical examination of several commercial furnaces of the carbon particle resistance type.
A furnace of 2kg. melting capacity of this type was designed and constructed by applying these charactristics as the basis of planning.
Again, based on the close examination of both calculated and observed characteristics of the experimental furnace, a large furnace of 30kg. melting capacity for large scale experiments in crystal growing was constructed.
The larger furnace was equipped with a crucible-lifting device and two voltage stabilizers were used in sequence, i.e., a moter-driven induction regulator controlled with an electronic switch was used with a saturable reactor combined with a magnetic amplifier and a D. C. voltage stabilizer.
The temperature of the furnace could be controlled within ±2 to 3°C in the temperature range of 1300° to 1400°C by regulating the terminal voltage within ±0.05% with these devices.
The heat balance of the furnace was calculated and empirical formulae of power consumption were computed by using experimental data of several runnings of the furnace.