Synthesis and Thermochromic Properties of Cr-Doped Al2O3 for a Reversible Thermochromic Sensor

Abstract

An inorganic thermochromic material based on Cr-doped Al2O3 is synthesized using a solid-state method. The crystal structure, chemical composition, and morphology of the synthesized material are analyzed using X-ray diffraction, scanning electron microscopy coupled with an energy-dispersive X-ray spectrometer, and Fourier transform infrared (FT-IR) spectroscopy. The color performances of the synthesized material are analyzed using a UV-VIS spectrometer. Finally, the thermochromism exhibited by the powdered samples at high temperatures is investigated. The material exhibits exceptional thermochromic property, transitioning from pink to gray or green in a temperature range of 25–600 °C. The change in color is reversible and is dependent on the surrounding temperature and chromium concentration; however, it is independent of the exposure time. This novel property of Cr-doped Al2O3 can be potentially employed in reversible thermochromic sensors that could be used not only for warning users of damage due to overheating when the environmental temperature exceeds certain limits, but also for detecting and monitoring the temperature of various devices, such as aeronautical engine components, hotplates, and furnaces.

Preparation, structural and spectroscopic study of sol-gel-synthesized $$\hbox {Cr}^{3+}$$:$$\hbox {Al}_{2}\hbox {O}_{3}$$ powder

“…Ruby powder is typically obtained by the conventional solid-state reaction [25][26][27]. To attain wanted phase purity, the solid-state reaction process takes up to 10 h at 1200 • C treatment and up to 6 h in ball mill mixing [26], which might introduce further impurities and defects to the end product.…”

Synthesis of Ultrafine Aluminum-Rich Corundum Nanocrystals

“…This color change is known to be associated with bulk solid solution formation for materials with similar overall composition annealed at temperatures in the range of 1400−1600 °C. 6 All three core sizes demonstrated one set of corundum diffraction peaks in their respective XRD patterns, indicating complete homogenization into a single solid solution (Figure 4). Additionally, the corundum peaks shifted closer to the pure α-Al 2 O 3 pattern as a result of annealing at 1000 °C, indicating Al-rich corundum had been formed.…”

Reversible Thermochromic Ink based on Crystal Violet Lactone/Boric Acid/Hexadecyl Alcohol for Anti-Counterfeiting Printing

“…According to whether the thermochromic ink can be recovered after discoloration, it can be divided into reversible thermochromic ink and irreversible thermochromic ink. In recent years, thermochromic materials have been extensively researched because of their potential applications in anti-counterfeiting signs, temperature indicators, wearable electronic devices, medical diagnostics, safety materials, aerospace and other fields [1][2][3][4][5][6][7][8]. Thermochromic material has special thermal memory function, and the color of compounds and mixtures will change significantly during heating or cooling [9][10][11][12][13].…”