The Pt/Pd thermocouple had been made of reference grade platinum of 99.999% purity and palladium of 99.997% purity thermocouple wires 0.5-mm diameter and 150-cm length supplied by Johnson Matthey England. The wires were cleaned with alcohol, annealed electrically in air for 10 h at about 1300 C for palladium wire and 1100 C for platinum [1] and then cooled to ambient temper-ature by switching off the current. Rapid cooling is essential to prevent oxidation of the Pd wire in the range 500–800 C [10]. The wires were inserted in twin bore alumina tube 3.5 mm outer diameter and 0.8 mm bore, 750 mm length. The Pt and Pd thermoelements were connected at the measuring junction by expansion coil constructed from 0.2 mm Pt wire that was wound into a coil of four turns of 1 mm diameter.