Effect of Firing Temperature on Mechanical Properties of Al2O3-C Sensor for Continuous Measurement of Molten Steel Temperature

Al2O3-C sensor based on the blackbody cavity theory achieved a continuous measurement of molten steel temperature. Its mechanical properties were affected by the firing temperature. Firing temperature has great influences on the weight changing, decalescence/heat release reaction and structure evolution of the resin binder used for Al2O3-C sensor. Results showed that the porosity increased and the strength declined below 750 degrees C, main exothermic reaction and weight loss of the binder occurred. As the firing temperature increased to 800 degrees C, a great enhancement of endothermic reaction and a drastic increase of crystallite size were observed, relating to the rapid shrinkage of the binder. The porosity decreased from 10.3% to 8.8% and the strength improved remarkably from 6.5 to 8.2 MPa in this temperature range. Strengths and porosities of the sensors fired under 800-950 degrees C were similar (8.2-8.5 MPa and 8.8%-8.4% respectively). Moreover, the temperature response and lifetime of the sensor fired at 800 degrees C were almost equal to the sensor fired at 950 degrees C according to industrial tests, which were about 165 s and 24 h.