Abstract
Silicides of all the elements belonging to IV a, V a and VI a groups of the periodic table are electrically conductive and have high melting point and oxidizing resistivity. By the utilization of MoSi2 which has the highest oxidizing resistivity among these suicides, a new heating element. has been developed It can be used at temperatures up to 1, 700°C in air.
Powdered MoSi2 including polyvinyle-alcohol as binder was molded in rod through extrusion and then sintered at 1, 600°C in hydrogen atmosphere. The diameter of the heating element was made smaller at its main part and larger at its terminal parts where it was connected with a current-supply conductor, so that heat was mainly generated in the main part. Such construction was realized by manufacturing the main (heat generating) and the terminal parts separately and then welding them at 1900°C.
The flexural strength of the heating rod was 30kg/mm2 at the heating part and still higher at the terminal parts. The electrical resistivity was 3×10-5Ωcm a room temperature, and 5×10-4Ωcm at 1, 700°C. The surface density of electric power to keep the surface temperature at 1, 700°C was 60W/cm2 in the open air and reduced below one third in a closed room. The expansion coefficient was 8×10-6°C-1 at 1, 000°C. The coefficient varied almost linearly with temperature but had a point of inflextion at about 250°C, hence it is necessary for its cooling to be conducted slowly. At the temperature of about 1, 800°C it manifested plasticity and was able to be bent in any shape. This heat element is applicable in any atmosphere of oxidizing and reducing gases, nitrogen or vacuum.
