## 3 Results & Discussions
### Effect of Molten Salt Exposure/Prolonged Heating
The presence of glaze on composite containing potassium chloride in Figure 7 could also be attributed to potassium chloride being the most stable of the Group 1 chlorides, and least likely to react, according to the enthalpies of formation as well as slightly lower dwell temperature [51]. It can be hypothesized that the lack, or reduction, of the glaze, is due to some glassy phase material migrating into the bulk of the composite during reheating above the glass softening point of 573 \({}^{\circ}\)C, according to previous work [31]. EDS analysis of geopolymer composites in Figures 6 and 7 show the lack, or presence, of surface glaze via aluminum concentration. Areas of brighter purple indicate higher aluminum content and dimmer areas indicate lower aluminum content. Figure 8 shows lighter discrete alumina while connected irregular medium or darker phases are potassium geopolymer and glassy phase, respectively. No microcracks can be seen in the bulk of samples exposed to molten salt, indicating no chemical degradation occurred to the containment material on a microscopic level. Figure 6: Surfaces of ASH-G composite after heating to 805 \({}^{\circ}\)C for 240 h without (**A**) and with (**B**) NaCl. No glaze is present in either case. Figure 7: Surfaces of ASH-G composite after heating to 775 \({}^{\circ}\)C for 240 h without (**A**) and with (**B**) KCl. A reduced glaze is present in both cases. To further check for the chemical reaction between chloride salts and geopolymer composites, bulk powder XRD analysis of ground salt samples was conducted. Representative salt samples were taken from the as-received supply and post-test crucibles. The salts were dried at 120 \({}^{\circ}\)C for 24 h and ground to \(<\)50 \(\upmu\)m. The results can be seen in Figure 9 and show the presence of potassium chloride in sodium chloride samples and sodium chloride in potassium chloride samples. The exchange of Group 1 elements can be attributed to diffusion, and not dissolution, of the container material. Dissolution of the container material would result in microcracks, which are not present in the EDS micrographs. No other crystalline phases were observed in the recovered salt samples. If chemical degradation occurred, alumina platelets would  
Figure 8: Bulk ASH-G composite after heating to 805 \({}^{\circ}\)C for 240 h with NaCl (**A**) and heating to 775 \({}^{\circ}\)C for 240 h with KCl (**B**). No microcracks are present. Figure 9: X-ray diffraction patterns of NaCl and KCl before and after prolonged heating in ASH-G composites. Salt samples after prolonged exposure to ASH-G show the presence of both Group 1 chlorides. be free to dislodge and appear in the recovered salt samples. The results indicated that the geopolymer composites did not react with air, molten salt, or chemical species generated from molten salt-air interactions to form crystalline phases. The ability of geopolymers to incorporate additive phases of different shapes, sizes, quantities, and chemistries into stable composites is valuable and needs to be explored. There is a range of solutions for the containment of different molten salts in different geometries for different applications is a testament to the utility of engineered geopolymer composites. While no microscopic or macroscopic chemical degradation was found, how the flexural strength of geopolymer composites exposed to both molten salt and temperature changes is of particular interest. Previous work done by [PERSON] et al. found that potassium metakaolin-based geopolymer without additives exhibited superior densification and compressive strengths when heated in molten salt rather than air [46]. Initial heat treatment to 300 \({}^{\circ}\)C in air followed by further sintering in molten salt could not only produce stronger, more dense composites but also eliminate the contamination of molten salt over extended periods.