Design and experimental validation of geopolymer-based refractory insulation with closed porosity for molten salt storage applications

Here, we investigate a sodium-aluminosilicate-based geopolymer refractory insulation (GRI) with an optimized mixture of closed-cell and open-cell porosities as an innovative internal thermal insulation and containment material for high-temperature molten salt storage applications. The closed-cell porosities are achieved via the addition of aluminosilicate cenospheres, a byproduct of coal-fired power plants. The open-cell porosities are minimized by the addition of lightweight aggregates as well as via high-temperature heat treatment. The mixed closed- and open-cell pore structure allows partial permeation of the molten salt into the GRI while maintaining most of its thermal insulation performance. This thermal insulation and containment design allows the molten salt to freeze inside the insulation layer and effectively form a self-containing and self-healing barrier for molten salts. Extensive immersion tests in molten nitrate and molten chloride salts were conducted for >50 days. X-ray computed tomography characterizations and thermal conductivity measurements before and after the immersion tests were performed to understand the stability of the geopolymer matrix and the pore structure during molten salt immersion. The results indicated stable performance and promising applicability of the proposed insulation/containment concept for high-temperature molten salt storage applications. • An innovative geopolymer refractory insulation is investigated as a thermal insulation material for molten salt storage. • The concept enables a self-containing and self-healing barrier to contain molten salts by allowing salt freezing inside. • Closed-cell porosity is key to the GRI’s long-term stability during molten salt interaction. • Characterizations were conducted to assess the performance and degradation of the insulation during molten salt immersion.