An in-situ pH measuring system for high temperature aqueous solutions was developed with YSZ membrane tubes and a new pressure balanced regulator system. Air was filled inside the tube, the pressure of which being balanced with that of high temperature aqueous side by the regulator system. The Pt coated inside surface functioned as an oxygen electrode. Owing to the regulator system and some improvement in the shape of the tube and its cooling position, the damage of the full stabilized membrane tubes was almost prevented. In the temperature range from 150 to 275°C, the potential of the YSZ tube electrode was confirmed to show the one to one correlation to the potential of the Pt oxygen electrode in air-saturated aqueous solutions. The pH measurement by the YSZ tube was also confirmed not to be affected by other redox couples contained in solutions.
Influence of dissolved oxygen and temperature on corrosion and elution behaviors of Si3N4 ceramics containing 5wt% MgO as sintering aid in high-temperature pure water were studied using the once-through type experimental loop. Exposure tests were carried out under two different dissolved oxygen concentrations of below 20μg/l and 8mg/l. Exposure temperature was elevated gradually from 120°C to 200°C and then to 275°C, where the indicated temperature was kept for 8 days. The results suggested that dissolved oxygen did not promote corrosion of Si3N4 ceramics, although the weight loss of specimen after exposure was influenced largely by temperature and the amount was increased by almost one order of magnunitude with temperature change. These were considered to be caused by the reaction of Si3N4 grain with H2O, of which rate was increased with temperature. The specimen exposed at 275°C was largely leached and its amount of weight loss attained up to 52mg/cm2 under low dissolved oxygen condition. Then a part of corrosion products remained on the surface and formed the porous corrosion film. In these processes Mg tended to be accumulated in the leached layer. On the other hand, Si3N4 grain was scarecely eluted at 120°C, but the grain boundary contaming Mg was selectively eluted to test solution.
Fatigue crack growth tests were conducted by using CT specimens of butt welded joint of low alloy pressure vessel steel A508 cl. 3 in high temperature pressurized water simulated BWR environments. The butt welded joint was obtained by a submerged arc-welding method. Microstructures of base metal, welded metal and HAZ were all bainitic ones. Grain size of the HAZ was greater than that of the base metal. The welded metal showed dendritic microstructure. Residual stress of the butt welded joint was about 200MPa in maximum and the values of Vickers hardness of the HAZ and the welded metal were higher by 20% than that of the base metal. As the results of the tests, there was no specific difference in fatigue crack growth behaviour of these three microstructures irrespective of grain size, residual stress, specimen orientation and so on. It is, therefore, concluded that fatigue crack growth rate in butt welded joint may be represented by that of the base metal. The tests also revealed that the material used in this work has a sufficient safety margin compared to the reference curves in ASME Boiler and Pressure Vessel Code Sec. XI.
In order to investigate the simultaneous attack behavior of erosion and corrosion of alicyclic epoxy resin, cavitation erosion tests were made by using a magnetostiction vibratory apparatus in pure water and NaOH solution. The results obtained were as follows: (1) By promoting crack initiation and growth, the erosion damage was accelerated by corrosion. (2) By enlarging surface area and removing corrosive products, the corrosion damage was promoted by erosion. (3) It was also found that the synergistic effect in cavitation erosioncorrosion markedly depended on the relative intensity of cavitation erosion to the concentration of corrosive liquids. (4) Based on the theory of crack propagation, an equation for predicting the damage loss was proposed.
Various problems concerning corrosion in ULSI (Ultra-large-scale Integration)'s are discussed. After a brief discussion on Al-line corrosion in plastic packages, two problems connected with ULSI manufacturing are explained and discussed. One is the selection of heat treatment atmosphere which does not oxidize tungsten gate electrodes, but can oxidize silicon at the same time. The other is the high-temperature stability of thin SiO2 films in refractory metal/SiO2/Si structures. Namely, the degradation of SiO2 occurs by H2 atmosphere and by the reaction between SiO2 and Si.
Corrosion protection technique and anti-corrosive agent have been improved extremely, so that troubles and accidents are reduced. But even now corrosion occurred to equipments, so we have to go on inspection based on considering corrosion mechanism. We describe the outline of corrosion examples for refining units are described.