Can XuFollow

Date of Award

Summer 5-31-2022

Document Type

Thesis (Ph.D.)

Department or Program

Engineering Sciences

First Advisor

Jifeng Liu

Abstract

This thesis explores spinel-structure transition metal oxide nanoparticle pigmented solar selective coatings with high thermal efficiency (>90%) and high-temperature (~750 ºC) thermodynamic stability via cost-effective and facile fabrication methods. Compared to the preliminary work, we reduce the emittance loss by selecting silicones with a lower emittance loss as the matrix. We further move from purchasing simple commercial oxide nanoparticles to systematically designing and synthesizing spinel-structure based three-transition-metal-incorporated oxide nanoparticles for a better optical response of nanoparticle pigmented coatings. Nanoparticles of three systems are studied, including Ni-Mn-Fe oxide, Cu-Mn-Fe oxide, and Cu-Mn-Cr oxide systems. Among, Cu-Mn-Cr oxide nanoparticle pigmented silicone solar selective coatings on Inconel 625 substrates with an outer diameter of 76mm show an optimal optical-to-thermal conversion performance, with a solar absorbance of 97.9%, thermal emittance of 59.4% and a record-high thermal efficiency up to 94.2% at a temperature of 750 ºC and solar concentration ratio of 1000. According to some electronic structure investigations, the excellent absorbing behaviors are attributed to the joint result of d-d transitions, charge transfer effect and defects in the structure. Simulation results based on the four-flux radiative model confirm no need for precise control over volume and volume fraction of nanoparticles in coatings, and prove that our current recipes lie in the optimized region for absorptance. Up to 60 simulated day (12h)-night (12h) thermal cycles (a total annealing time of 720h) at 750 ºC and/or 800 ºC are conducted for stability verification of Cu-Mn-Fe oxide and Cu-Mn-Cr oxide nanoparticle pigmented solar selective coatings. No more than 1% efficiency loss is observed for coatings after thermal cycles at 750 ºC and 800 ºC, indicating the superior resistance against thermal degradations caused by long-time operations at high temperatures. Inter-diffusion under very high temperatures is confirmed to enhance the adhesion of the interface, and therefore improve the mechanical stability against slight scratches. This study offers a promising approach to high-efficiency, high-temperature stable and economically friendly solar selective coatings with feasibility of scaling up for the next generation CSP systems.

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