Microscale Ceramic Additive Manufacturing for Aerospace Applications

Student’s name: Elizabeth Quansah Home Institution: University of Illinois at Urbana-Champaign NNCI Site: CNF at Cornell University REU Principal Investigator: Sadaf Sobhani, Department of Mechanical and Aerospace Engineering, Cornell University REU Mentor: Giancarlo D'Orazio, Department of Mechanical and Aerospace Engineering, Cornell University Abstract: This paper suggests mechanisms for producing silica glass, silicon carbide, or silicon oxycarbide microscale electrospray emitters for spacecraft propulsion systems. The following research is conducted in an effort to replace the tungsten needles currently being used as emitters. This work relies on two-photon photolithography for the additive manufacturing of green bodies that will subsequently undergo thermal processing to produce glass or ceramic. The process begins with GP Silica resin, preceramic polymer Starfire SMP-10, and preceramic polymer Starfire SPR-688. Six different resins are made by mixing Starfire SMP-10 and Starfire SPR-688 with three different photoinitiators, 4,4’-Bis(diethylamino)benzophenone, 2-Isopropylthioxanthone, or (±)-Camphorquinone. Conversion of these six resins, along with the GP Silica resin, into distinct, emitter-shaped green bodies with features on the scale of nanometers is carried out using the Nanoscribe Photonic Professional GT2, a two-photon photolithography printer with a 780nm femtosecond laser. Through optimizing the printing parameters on the Nanoscribe for each resin, successful micro-additive manufacturing of reliable green bodies is achieved. Each green body undergoes thermal processing tailored to its composition in order to produce its corresponding material: glass, silicon carbide ceramic, or silicon oxycarbide ceramic. Microstructure and phase analysis of the resulting structures is performed using a Scanning Electron Microscope and X-ray diffractometer. For each material, a comparison of the effects of using a 2.54 gigahertz, 1 kilowatt microwave furnace to the results of traditional pyrolysis in a Nabertherm furnace is presented. Adjusting the printing parameters on the Nanoscribe along with the thermal processing steps and techniques for each material produces noteworthy characteristics of the emitters.