Paruchuri Kondaiah

Research Associate

Biography

Paruchuri Kondaiah received the Ph.D. degree in Physics and was with the Indian Institute of Science, Bangalore, and the National Aerospace Laboratory, Bangalore, India, prior to joining the Advanced Materials and Technologies Laboratory in 2019. Dr. Kondaiah's interests are in thin films, solar selective coatings, and corrosion resistant coatings for mid and high temperature applications.

Research Projects

Corrosion mitigation in industrial grade molten chloride salts

Molten chloride salt eutectics are attractive candidates for use as thermal energy storage media and heat transfer fluids in generation three concentrating solar thermal power (Gen3 CSP) plants. However, corrosion of alloys in molten chloride salts, especially at high temperatures, is an extremely challenging problem that studies focus on lower temperatures, shorter durations, or analytical grade, and high-purity, salts. To date, there has been no study on corrosion or corrosion mitigation in an industrial-grade salt at a high temperature such as 750 °C. To alleviate this knowledge gap, the study presents new multiscale fractal-textured Ni coatings on various alloy surfaces for effective corrosion mitigation at 750 °C in molten chloride salts. Using the electrodeposition method, durable double-layer textured coatings were formed on stainless steel alloys (SS316, SS310, and SS347) and In800H. The corrosion performance of the coatings is investigated in both analytical-grade purity and, for the first time, practically relevant industrial-grade chloride salts. Ni-coated ferrous alloys showed an exceptionally reduced corrosion rate in the range of 350–480 µm/y in analytical-grade salts, and between 450–490 µm/y in purified industrial-grade salts at 750 °C. Ni coatings on ferrous alloys reduced corrosion rates by as much as 70% compared to uncoated surfaces and were comparable to the expensive Ha230 alloy with a high Ni content. By the use of innovative fractal corrosion mitigation coatings, for the first time, low-cost structural alloys are rendered viable for use with industrial-grade chloride salts, which is profoundly beneficial in practical systems.

All you need to know about corrosion in high temperature heat transfer fluids

Concentrating solar power (CSP) systems have gained considerable eminence in converting solar thermal energy into electrical power in recent years. According to the U.S. Department of Energy’s Gen3 roadmap, the CSP system should operate > 700 °C, as its efficiency depends directly on the operating temperature of the heat transfer fluids (HTFs). A significant challenge, however, is the corrosion of containment materials by the HTFs that is exacerbated at the higher temperatures. A comprehensive review of the high temperature stable HTFs, their properties, corrosion mechanisms on different alloys, and corrosion mitigation measures is of much importance to directing a concerted research and development in the field, which forms the motivation for this compendium. First, molten salt HTFs and their thermophysical properties, along with liquid metals, are introduced. Corrosion of structural materials in different HTFs including molten salts, liquid metals, and supercritical carbon-di-oxide at various temperatures and the corrosion mechanisms are comprehensively reviewed. In addition, several corrosion mitigation methods are discussed. Finally, future directions for HTFs and corrosion mitigation methods in molten salts are proposed. The holistic review presented here will serve as the foundation for further research addressing relevant challenges and enabling the promise of achieving cost-competitive CSP.

Superior corrosion mitigation in molten carbonate salts

Corrosion of metals in contact with molten salts used for thermal energy storage and heat transport at high temperatures is a serious impediment to the development of next-generation concentrating solar thermal systems. Toward addressing this limitation, novel multiscale fractal-textured Ni coatings on a variety of substrate alloys are presented in this study for exceptional corrosion mitigation in molten carbonate salts at a high temperature. Strongly adherent, durable, single-layer and double-layer multiscale fractal coatings were fabricated using the electrodeposition method. Corrosion performance of the coatings on SS310, SS316, SS347, and In800H was studied in molten carbonate salt (32% Li₂CO₃+33% Na₂CO₃+35% K₂CO₃) at 750 °C. Single-layer coatings are stable up to 300 h immersion, whereas double-layer coatings are stable beyond 750 h. The corrosion rate of double-layer Ni coatings on ferrous alloys was reduced by as much as 60% from that of uncoated surfaces and was about 18% below that of higher cost, high Ni content Ha230. The study represents the first-ever report of corrosion characteristics of alloys in carbonate salts at 750 °C and the first demonstration of a means of dramatically reducing corrosion in carbonate salts at a high temperature. The study is further significant in that it provides a viable approach for low-cost structural alloys to be corrosion-resistant to molten carbonate heat transfer fluids and storage media in high-temperature concentrating solar thermal applications. The corrosion-resistant coatings provide opportunities for the use of low-cost, ferritic alloys instead of the expensive nickel-based alloys in practice.

Fractal coatings of Ni and NiYSZ for high-temperature corrosion mitigation in solar salt

This work introduces a novel approach to corrosion mitigation using electrodeposited, fractal Ni and NiYSZ coatings. Highly adherent, durable multiscale coatings with fractal dimensions above 1.80 were fabricated. Corrosion characteristics of coated plain and etched surfaces of In800H, SS310, SS316 and SS347, in comparison to Ha230, were studied in molten 60% NaNO₃ + 40% KNO₃ at 600 °C. The corrosion rate of coated Fe-based alloys reduced by up to 68% compared to uncoated alloys and was on par with or lower than the corrosion rate of Ha230. The corrosion-resistant coatings provide for use of low-cost alloys in high temperature corrosive environments.

Fractal textured surfaces for high temperature corrosion mitigation in molten salts

Mitigation of corrosion of structural materials in contact with molten salts is imperative in high temperature applications such as nuclear and solar thermal power plants. This research introduces, for the first time, a novel approach to corrosion mitigation through fractal surface texturing and details a systematic corrosion study of a variety of structural materials. Multiscale fractal textured surfaces on SS316, In800H, In718, In625, and Ha230 were fabricated via chemical etching, whose parameters were optimized to obtain surface fractal dimensions above 1.90. The influence of grown oxides was examined by annealing the optimized etched surfaces with high fractal dimensions at a high temperature. The corrosion mitigation characteristics of plain, etched and etched-annealed surfaces were systematically studied in molten 60% NaNO₃ + 40% KNO₃ at 600 °C. The fractal textured surfaces are shown to reduce corrosion rate by 30% for ferrous alloys and by over 80% and up to 87% for high nickel content alloys. Elemental composition analysis reveals that the corrosion oxides are correspondingly diminished on fractal textured surfaces compared to plain surfaces. The study is significant in that any existing material may be made more corrosion resistant through this simple surface modification and treatment.