Low-temperature flux synthesis of potassium hexatitanate whiskers: Growth mechanism and applications in high-temperature infrared thermal insulation

Potassium hexatitanate whiskers (PHWs, K2Ti6O13) area promising functional material with high thermal insulation capacity. In this study, PHWs were successfully synthesized using the flux method at temperatures ranging from 725 degrees C to 1100 degrees C. The crystal growth mechanism of PHWs in the KCl flux follows a series- parallel pattern. The synthesized PHWs have a near-infrared reflectivity (NIR) exceeding 95%, and the cause of high reflectivity was theoretically analyzed based on the Kubelka-Munk equation. The high temperature stability of near-infrared reflectivity and the thermal stability of the PHWs were further assessed using TG-DSC, XRD, SEM, and UV-VIS-NIR analysis. It was found that PHWs prepared at 800 degrees C begin to decompose into TiO2 at approximately 1375 degrees C. Nevertheless, the near-infrared reflectivity remains stable even after heat treatment. Additionally, PHWs were prepared as a composite thermal insulating coating, showing thermal conductivity between 0.177 and 0.569 W/(m K) across the temperature range of 200 degrees C to 900 degrees C. The temperature difference between the hot and cold surfaces of the composite coating was significantly greater compared to the control groups at various temperatures, with a p-value of less than 0.01 in the paired t-test. This result demonstrates the great application potential of PHWs as a high-temperature near-infrared thermal insulation material.