Real-time monitoring of liquid–solid phase transition by using an ion-beam-synthesized Au/SiO2 nanocomposite refractive index sensitive element

Au/SiO2 nanocomposite refractive index sensitive element was prepared by implanting 30 keV Au ions into a 0.5-mm-thick SiO2 wafer at a fluence of 4.5 × 1016 ions/cm2. Combining this sensitive element with other components, a device was built to measure the reflection spectra of water and 4 % brine in real time during the cooling courses. With the recorded characteristic reflection peaks’ positions, two media’s refractive indices were calculated, and their phase transition processes were discussed. The results revealed that the water–ice phase transition in the cooled water was a very fast process, and the water freezing and the progressive salt precipitation existed in the cooled brine. These satisfactory and reproducible results demonstrated that the ion-beam-synthesized Au/SiO2 nanocomposite refractive index sensitive element was quite stable in structure, and thus, it could find its niche in the fields of selecting phase transition materials, preserving biological cells, and desalinating frozen seawater, etc.