This review describes current trend in research and development of a slight degree of corrosion of stainless steel for semiconductor processing. Although organic materials such as polyvinyl chloride have been used for ultra-pure water piping in semiconductor processing, it has been pointed out that there are several problems of impurities release from the piping surface, insufficiency of heatproofing in heat-sterilizing etc. It has been reported that the amount of metal dissolution from electro-polished stainless steel in ultra-pure water was very small, and that controlled oxidation treatment after electropolishing gave more excellent corrosion resistance. On the other hand, the electropolished stainless steel pipe are used mainly for gas piping in semiconductor processing. However, it is reported that it is subject to a slight degree of corrosion in corrosive chlorine gas and other halogen gases. Moreover, it is proved that the corrosion resistance in halogen gases is improved by controlling the heat treatment condition of oxygen partial pressure and other factors, and the pre-heating suface polishing methods.
The quantitative evaluation of tarnish of stainless steel was carried out using cyclic corrosion test (CCT) and computer image analysis. Test samples were austenitic stainless steels which contained 10-18wt%Cr and had various roughness of surface. Effect of surface finish on tarnish has been studied, and main results are as follows. Total area of tarnish (AR) after CCT depends on Cr concentration in passive film and roughness of surface. AR increases with decreasing of the former and with increasing of the latter. Among conventional surface finishes such as 2B, HL, BA and Miller of stainless steel Type 304, sample of 2B-finished indicates the worst resistance against tarnish after CCT. Compared with the resistance against tarnish of another sample which has the same Cr concentration in passive film and roughness of surface, sample of 2B-finished indicates worse resistance. This result could be persuaded by the fact that sample of 2B-finished has the intergranular corrosion at the grainboundary on the surface because of the pickling treatment in the surface finish process.
A Nb-19 at%Al alloy, which composed of Nb3Al-phase and a small amount of Nb-phase, was heated in a technical-grade nitrogen and in an artificial air at a rate of 2°C/min up to 1000°C. The reactions were compared with those in pure nitrogen, on which a paper has already been published. In both gases weight increase started at ca. 800°C, as did in pure oxygen. The weight increases at 1000°C were, however, ca. 10% in the nitrogen and ca. 40% in the artificial air respectively of that in the oxygen. In the case of the nitrogen, major components of the scale were oxides, although nitrogen compounds were detected in the X-ray diffraction pattern (XRDP). The major reaction was considered to be the oxidation caused by oxygen and moisture in the nitrogen, whose process was identical with that in the oxygen. In the cases of the air, no nitrogen compound was detected in XRDP, although the surface was in a color specific to reactions in nitrogen. The reaction was considered to be akin to that in the oxygen. A comparison with the reaction in Ar-20 vol%O2 revealed nitrogen retarding the reaction.
In order to develop pH sensors which can be used in highly corrosive solutions having pH values lower than 1 or higher than 13, electrolyte-insulator-semiconductor (EIS) capacitor pH sensors were examined. A thin oxide film was used as an insulator layer and a p-type Si semiconductor was used as a substrate. Ta2O5 and ZrO2 thin films were formed by low pressure CVD technique at several deposition temperatures and used as the insulator layer. Capacitance, C, versus voltage, V, curves of the capacitors were measured in solutions of pH=-1.9 to 15.5. A gate voltage value, VR, at a given capacitance was obtained from a measured C-V curve and a VR-pH plot was made for each insulator oxide. The pH response characteristics of the sensor were evaluated from the gradient of the VR-pH plot. Corrosion resistances of the insulator oxides were measured by immersion tests in 10kmol·m-3 H2SO4 and 10kmol·m-3 NaOH. It has been found that a Ta2O5 thin film deposited at 723K shows the large gradient of VR-pH plot, a low limit pH for response in acid solutions, and a high corrosion resistance against acid. A ZrO2 thin film deposited at 573K shows a high limit pH for response in alkali solutions and relatively high corrosion resistance against alkali. EIS capacitor pH sensors using the Ta2O5 film as the insulator layer are suitable for measurement in strong acid and those using the ZrO2 film are suitable for measurement in strong alkali.
The corrosion protective properties of (1) No treatment, (2) Rust preventing agent and nontar epoxy paint, (3) Non tar epoxy paint, (4) Aluminum flame spraying, (5) Hot dip galvanizing, (6) Etching primer and nontar epoxy paint and (7) Uni-chrome plating of steels for retaining wall were investigated by the electrochemical measurements (the open circuit potential and tan δ) and visual observation for 15 years. In field test, the aluminum flame spraying on steel plates, the nontar epoxy paint on bolt nut and the nontar epoxy paint on anchor showed the best corrosion protective property for 15 years. The corrosion protective property of anchor was further enhanced by using jointly together with the cathodic protection.
This research aims to study the SCC fracture dynamics of a AISI 304 steel in 42wt% MgCl2 solution at temperature at 413±4K using the advanced acoustic emission (AE) signal processing. AE signals (out-plane displacement) from the Mode-I fracture were monitored by the special AE monitoring system. Source wave was estimated by using the transfer function experimentally determined. It was revealed that the brittle fracture in size of 10 to 40μm generated at the maximum velocity of 40m/s.