Session: 04-04-01: (04-04: Advances in Aerospace Structures and Materials & 04-11: Advances in Mechanics, Multiscale Models and Experimental Techniques for Composites)

Paper Number: 95056

95056 - Thermo-Mechanical Properties of SiC-Mineral Binder Composites for Space Applications 

Due to its excellent stiffness, thermal stability and lightweight, silicon carbide (SiC) ceramics are used for the fabrication of lightweight substrates for space mirrors for telescopes and satellites. However, the use of pure SiC is limited due to difficulty in manufacturing which paves way for SiC composites. The current methods for manufacturing dense SiC composites involve thermal oxidation and sintering aids, which are limited by poor oxygen diffusion in SiC and formation of amorphous silica phase. These limitations among others weaken the interfacial bond and compromise the thermo-mechanical properties of SiC. Cordierite and Spodumene are ceramics that are used as mirrors due to their light weight and nearly zero thermal coefficient of expansion. Despite their excellent thermal properties, the mirrors made of cordierite (CO720) by Kyocera® and spodumene (Zerodur) by Schott® have relatively low stiffness and thermal conductivity. We report on the synthesis and characterization of SiC-Cordierite (SiC-Cord) and SiC-Spodumene (SiC-Spod) with superior thermomechanical properties. Dense SiC-mineral composites were prepared by (i) surface activation of SiC particles and (ii) in situ mineralization of the grain boundaries in the temperature range of 800 °C - 1200 °C. The densities of SiC-Cord and SiC-Spod composites were 2.74 g/cc and 2.61 g/cc, respectively. The thermal conductivity of SiC-Cord and SiC-Spod were 6.737 W/m. K and 3.281 W/m. K, respectively. Polishing the SiC-Cord sample with SiC grit numbers 400 – 1200 and diamond/silica slurry resulted in a mirror finished surface. Atomic Force microscopy showed the average roughness (Ra) values to be 2.37 ± 0.28 nm. The nano indentation stiffness of the polished SiC-Cordierite composite measured 239.9 ± 20.6 GPa with SiC component measuring 273.64 ± 20 GPa and the cordierite binder measuring 105 ± 23 GPa. The stiffness of the SiC-Cord composite is superior to that of pure cordierite (140 GPa) or Zerodur (80 GPa). The average Vickers hardness of SiC-Cordierite was 8.12 ± 4.5 GPa which was as same as the pure cordierite (8 – 8.5 GPa) and superior than that of Zerodur (6.08 GPa). Thermal shock resistance test from 1200 ºC to room temperature in water showed comparable compressive strength and dimensional stability. Taken altogether, the thermal and mechanical properties of SiC-Cordierite and SiC-Spodumene are superior to the corresponding ones reported for commercially used Cordierite and Zerodur space mirrors. The innovative surface activation of SiC prior to sintering with mineral binders are responsible for the strong interfacial bone between the SiC particles as well as SiC particles and the mineral binders.

Presenting Author: Sujithra Chandrasekaran University of North Carolina at Charlotte

Presenting Author Biography: Sujithra Chandrasekaran is currently a PhD student at University of North Carolina at Charlotte, North Carolina. She obtained her Masters degree in Materials Science from a prestigious Institute in India. She did her master thesis at the Ceramics and composites division of the Defense Research and Development Organization of India. After her graduation, she joined Carborundum Universal Limited, a leading manufacturers of Abrasives in India as Research Executive in the Research and Development unit. Sujithra joined as a graduate student in bio-ceramics lab in Fall 2019 and working on the thesis titled "Additive manufacturing of 3D printed SiC Composites: Strengthening and Densification using surface modification of SiC and addition of mineral binders". She has co-authored a publication in Journal of Solid State Chemistry and in Procedia Manufacturing by NAMRC2021. She is also a loving wife and a caring mother of a 2 year old beautiful girl.

Authors:

Sujithra Chandrasekaran University of North Carolina at Charlotte
Ahmed El-Ghannam University of North Carolina at charlotte
James A. Monroe ALLVAR
Chengying Xu North Carolina State University