Evaluation of Zinc Oxide: Gallium for High-Speed Thermographic Phosphorescence During Impact Studies

Thermographic phosphors are useful compounds to determine temperature, due to their luminescence characteristics being a function of temperature. In this research, Zinc Oxide: Gallium was evaluated for its ability to measure the temperature of an impact event in a drop weight apparatus. Different solids loadings of the phosphor were placed in a sylgard binder and these samples were then excited by a 355 nm laser as they were impacted. Images of the event were captured through two separate filters with a high-speed camera, from which intensity ratios were formed. These intensity ratios correlated to a temperature, revealing the change in temperature of the sample throughout the impact. Initial testing at a repetition rate of 500 kHz provided insignificant data, due to difficulties with timing. The whole impact event was not able to be captured, and the imprecise timing of the drop did not allow for imaging of a specific area of the impact. Moving to a slower repetition rate of 50 kHz, the entire impact was captured on the high-speed camera, showing three separate areas of interest. The first section of this area was where the impact was first initiated, resulting in a temperature increase. Next, there was a temperature decrease, where the energy from the drop weight transitioned to deforming, rather than heating the sample. Lastly, there was a final temperature rise when the sample was fully compressed, but the impact was still occurring. This trend presented itself in all of the samples, supporting the idea that when combined with the intensity ratio method, ZnO:Ga embedded in a sylgard binder is an appropriate method to determine the temperature changes in a high-speed impact event.