CONDUCTIVITY METER

PROBLEM TO BE SOLVED: To stabilize the electrical characteristics of an electrode by forming a titanium boride on the surface of the electrode and to enhance the reliability by sustaining high measurement accuracy over a long term. SOLUTION: An AC voltage is applied between a central electrode 1 and a tubular peripheral electrode 2 arranged concentrically thereto through an interval. Each electrode is made of titanium and a titanium boride layer (titanium B, titanium B2 ) is formed thereon. The titanium boride layer can be formed by various methods. In case of molten salt bath method, a mixed salt of borate, potassium borate, potassium carbide, magnesium, or the like, is melted and a material is immersed into the molten salt covered with an inert gas, e.g. argon, in order to protect the material and the molten salt against oxidation before being treated at a temperature of 1023-1323 K, for example. A titanium boride layer thus formed has specific resistivity on the order of 6.4×10 Ω.cm which is lower than the specific resistivity 193×10 Ω.cm of a conventional TiC film and it is evident that the titanium boride layer is suitable as the coating material for the electrode.