University of Illinois Urbana-Champaign

Synthesis and indentation of boride and carbide coated carbon nanotube composite microstructures

Sandin, Carly Renee

Content Files
SANDIN-THESIS-2016.pdf

Permalink

https://hdl.handle.net/2142/95522

Description

Title
Synthesis and indentation of boride and carbide coated carbon nanotube composite microstructures
Author(s)
Sandin, Carly Renee
Issue Date
2016-12-09
Director of Research (if dissertation) or Advisor (if thesis)
Tawfick, Sameh
Department of Study
Mechanical Sci & Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Date of Ingest
2017-03-01T16:37:12Z
Keyword(s)
  • carbon nanotubes
  • carbon nanotube composites
  • hafnium diboride
  • polymer derived ceramics
  • nanoindentation
Abstract
The goal of this thesis is to investigate the synthesis and mechanical behavior of novel refractory coatings for applications subjected to extreme conditions. Starting from aligned carbon nanotube (CNT) forests as scaffolds, composite foams are fabricated by infiltration with refractory materials to achieve desirable mechanical properties such as high stiffness and strength. Similar to naturally occurring materials such as bone and teeth, these properties are dictated by the composition and nanoarchitecture of the material structure. CNTs grown into vertically aligned pillars by chemical vapor deposition (CVD) mimic the microstructure of these natural foams through their porous nanostructure. The CNT pillars are then coated using two methods: (i) static CVD with a hafnium diboride precursor (Hf[BH4]4) leading to coating thicknesses ranging from 3nm to 50 nm; and (ii) through cycles of elasto-capillary imbibition and pyrolysis of a silicon oxycarbide (SiOC) polymer derived ceramic leading to coating thickness from 8 nm to full infiltration. Both coatings enable the infiltration of CNT pillars and lead to a significant increase in stiffness and strength. Nanoindentation tests using a flat punch were performed on the CNT pillars to measure their Young’s modulus and compressive strength. By varying the CNT coating thickness, a trend develops for the Young’s modulus as a function of coating thickness for the CNT pillars where E ~ ρ^1.698 for hafnium diboride coated pillars. The maximum stiffness and strength was 56.49 GPa and 1.94 GPa for the fully infiltrated HfB2 composite and 3.80 GPa and 13.87 MPa for the SiOC pillars. We also identify the different regimes of deformation for the pillars to better understand the coating processes and the material behavior. These results can enable new applications of CNTs in extreme environments where high temperature resistance and high mechanical resilience are needed, such as hypersonic vehicles.
Graduation Semester
2016-12
Type of Resource
text
Permalink
http://hdl.handle.net/2142/95522
Copyright and License Information
© 2016 Carly Renee Sandin

Owning Collections

Graduate Dissertations and Theses at Illinois PRIMARY
Graduate Theses and Dissertations at Illinois
Dissertations and Theses - Mechanical Science and Engineering