Sintered ceramic heater element

DETAILED DESCRIPTION It is an object of the present invention to provide a ceramic heater which is superior in the rapidly heating property and can accurately control the temperature thereof by the resistance detecting method.
It is another object of the present invention to provide a ceramic heater which exhibits such excellent durability as to be exposed to the high temperature atmosphere, and has a large temperature coefficient of resistance.
The ceramic heater of the present invention comprises a ceramic heater element which generates heat upon receiving electric current, a heater support member made of an electrically insulating ceramic for supporting the heater element and an electric current supply means for supplying electric current to the heater element.
The heater element of the present invention is formed by sintering a mixture composed of MoSi.
sub.
2 powder having an average particle diameter of not greater than 2 .
mu.
m and 35 to 75 mol% of Si.
sub.
3 N.
sub.
4 powder having an average particle diameter of at least twice as large as that of MoSi.
sub.
2 powder.
The heater element of the present invention has such a structure that MoSi.
sub.
2 particles having a smaller particle diameter are interconnected and surround Si.
sub.
3 N.
sub.
4 particles having a larger particle diameter.
Therefore, the resistance of the heater element becomes equal to that of MoSi.
sub.
2 itself.
In contrast, in case that the particle diameter of the MoSi.
sub.
2 particle is the same as that of the Si.
sub.
3 N.
sub.
4 particle, the obtained heater element has such a structure that the Si.
sub.
3 N.
sub.
4 particles intervene among the MoSi.
sub.
2 particles so that the resistance of the heater element becomes larger than that of MoSi.
sub.
2.
MoSi.
sub.
2 has a large positive temperature coefficient of resistance of 6.
4.
times.
10.
sup.
-3 /deg.
while Si.
sub.
3 N.
sub.
4 has a negative temperature coefficient of resistance.
According to the present invention, since the ceramic heater has such a structure that the interconnecting MoSi