Please consider attending the following: MATERIALS ENGINEERING SEMINAR "Evaluation of Rare-Earth Element Dopants (Sm and Er) Effect on the Ablation Resistance and Emittance Tailoring of ZrB2/SiC Sintered Billets" By Angel Antonio Pena Purdue MSE Ph.D. Final Exam Advisor: Professor Rodney W. Trice ABSTRACT Hypersonic flight causes ultra-high surface temperatures which are most intense on sharp leading edges. One way of reducing the surface temperature is to apply a high emittance ceramic on the leading edge, increasing the radiation component of heat transfer. An ideal HEC must have a high emittance, while also possess a strong ablation resistance. From a scientific standpoint, it would be helpful if emittance could be tailored at different wavelengths. The approach used to create a ceramic with tailorable emittance was the use two different rare-earth elements, adding them to a ultra-high temperature ceramic (UHTC) in small quantities. The samarium element was added to increase the emittance of the UHTC over a large wavelength range, and the erbium element was added to decrease the emittance at specific wavelength ranges. The goal of this study was to create an UHTC with tailorable emittance while maintaining the required ablation resistance. Therefore, ZBS billets with five different Sm to Er ratios and with a nominal total amount of 3 mol.% dopant incorporated were prepared by sintering in vacuum to 2000 °C. The ablation resistance was evaluated by using an oxyacetylene torch and observing at exposure times of 60s and 300s, whereas the emittance was evaluated at the Air Force Research Lab facilities via a laser heating testing. The results for the ablation testing showed that ZBS billets co-doped with Sm and Er formed a beneficial c1-(Sm/Er)0.2Zr0.8O1.9 oxide scale as the majority phase, which is more thermally stable than the m-ZrO2 oxide scale typically formed in oxidized ZBS systems. The crystalline and the amorphous phases were formed by a convection cell mechanism. Differences in surface temperatures between ZBS samples with different dopant ratios suggest differences in spectral absorptance/emittance between each of the five compositions evaluated. Despite the emittance profiles by varying the Sm:Er molar ratios were similar because m-ZrO2 was formed as the major oxide phase, the emittance study showed that the erbium oxide influences the emittance profile, as can be noted by the maximum and minimum emittance peaks. Results showed that the emittance changes as a function of the Sm:Er molar ratios and temperature at shorter wavelength ranges. These changes in the emittance are caused by the different Sm and Er concentrations on the surface. Future work should be focused on producing the beneficial c1-(Sm/Er)0.2Zr0.9O1.8 phase directly from the manufacturing process, and therefore, maximize the effect of varying the Sm:Er molar ratios to tailor the emittance. This study represents the first generation and reported emittance data of UHTC doping ZBS systems with both Sm and Er elements. Date: Thursday, April 4, 2019 Time: 9:00 A.M. Place: ARMS 3115