Immersion-type temperature measuring apparatus using thermocouple

In an immersion-type temperature measuring apparatus using a thermocouple for measuring temperature of a melt, which comprises:

• a replaceable cartridge-type temperature sensor (11) for detecting a thermoelectromotive force corresponding to a temperature of a melt, said temperature sensor (11) comprising a thermocouple (13), a protecting tube (12) covering at least a lower portion of said thermocouple (13), for protecting said thermocouple (13) from said melt, and a connector (16);
• a holder (26) for releasably supporting said temperature sensor (11);
• a measuring instrument (28) for processing said thermoelectromotive force detected by said temperature sensor (11) to determine the temperature of said melt;
• and
• an extension lead wire (25), arranged through said holder (26), for connecting said temperature sensor (11) with said measuring instrument (28), said extension lead wire (25) being connected with said temperature sensor (11) through said connector (16);
• the improvement wherein:
• said protecting tube (12) which protects said thermocouple (13) comprises an outer layer and an inner layer, said outer layer is formed of a molybdenum-zirconia (Mo-ZrO.sub.2) refractory which consists essentially of:
• molybdenum (Mo):
• from 20 to 95 wt. %,
• and
• zirconia (ZrO.sub.2):
• from 5 to 80 wt. %,
• and said inner layer is comprised of an alumina (Al.sub.2 O.sub.3) refractory.