Abstract
The variations of electric resistance of a thin iron wire (∅0.1mm) in dilute sodium sulfate and sodium chloride solutions (10-6-10-3mol dm-3) have been measured in order to show that the resistmetric technique is suitable for the monitoring of water quality of wire cut discharge machines concerning the corrosion inhibition of ferrous materials being machined. The iron wire was pretreated in various mineral acid solutions. The dissolution rate was about 100 times higher in a nitric acid solution than in other solutions. The subsequent corrosion test in a sodium sulfate solution showed that the corrosion rate of the iron wire pretreated in a nitric acid solution was smaller by one order than those pretreated in other solutions. TOF SIMS analysis showed that organic contamination became slight as the surface layer was removed by nitric acid and perchloric acid solutions but not by a hydrochloric acid solution. Consequently, the pretreatment condition was fixed as 10 minutes in 0.1mol dm-3 perchloric acid solution. Then the corrosion rate of the iron wire was measured as a function of concentration of sodium sulfate and temperature. The corrosion rate of the iron wire was dependent on the concentration of sulfate while that of iron plate was not, because the diffusion of oxygen did not limit the corrosion rate for the iron wire. Thus water quality of wire discharge machines can be evaluated adequate by a resistmetric measurement of corrosion rate of the iron wire.
