Evaluation of the effects of molten CuCl on corrosion resistant coatings

Abstract

The world is facing energy crisis and pollution problems. Clean and renewable energy resources are gaining popularity day by day. Hydrogen is considered as clean energy carrier which is present in on earth in abundance either in the form of water or other chemical. The target is to produce hydrogen by thermo-chemical decomposition of water. Cu-Cl cycle is selected and preferred on other cycles based on its low operating temperature and cost. Plans for the design and construction of a hydrogen production pilot plant using the CuCl thermochemical cycle are being proposed. Currently researchers are facing several challenges to bring this pilot plant in operation. One of the important challenges is to develop materials for the containment vessels and pipes that will encounter the highly corrosive and harsh environment produced by the molten salts at the high temperature of 5000C. This research is done to evaluate corrosion resistant coatings. Different coating materials were tested in high temperature molten copper chloride environment to evaluate the coating performance. Super hard steel, Diamalloy 4006, YSZ (ZrO2 18TiO2 10Y2O3) and alumina are the candidate materials selected for corrosion test. High Velocity Oxy fuel and Air Plasma Spray are the coating methods used to coat the samples. Series of tests were conducted in the absence of oxygen in a specially designed apparatus. Temperature was selected 5000C, based on Cu-Cl cycle maximum temperature. Tests were conducted for 50 and 100 hours. Six coating combinations of bond and ceramic coats were tested in this research. Results suggested that, combination of Diamalloy 4006 (Diamalloy, Diamalloy+YSZ, Diamalloy+Al2O3) performed much better than SHS combination (SHS, SHS+YSZ, SHS+Al2O3). All super hard steel coatings fell off completely. Diamalloy 4006 coatings survived for 100 hours on the walls of the sample but the sample tips corroded badly. Corrosion products along with the deposits of pure copper appeared on the samples, in most of the cases. The study showed that alumina and YSZ can prevent diffusion of molten salt if these coatings do not crack. It was concluded that porosity may be the issue of coating failure. To investigate the issue of porosity, solid samples of coating material (alumina) was tested in CuCl environment. There was no change in shape, size, weight and appearance of these samples after hundred-hour immersion test. It was concluded that the porosity of coating layers has to be minimized to protect the underlying material.