Thesis

Synthesis and evaluation of organic/inorganic hybrid materials for high temperature applications

Creator
Rights statement
Awarding institution
  • University of Strathclyde
Date of award
  • 2024
Thesis identifier
  • T16857
Person Identifier (Local)
  • 201793904
Qualification Level
Qualification Name
Department, School or Faculty
Abstract
  • Organic-inorganic hybrid materials are becoming increasingly used in industry for providing useful properties, including high mechanical strength and thermal resistivity. As part of this thesis, the use of these materials in joining silicon carbide (SiC) rods for use in heating elements was investigated. A phenol-formaldehyde (PF) based resin is used in an organic adhesive-based system for joining SiC heating elements. The thermal profile determined that the thermal stability was low, the variation between resin chemistry was high and porosity was a major issue for the resistance and strength of the weld. Due to this a replacement system was identified. The pre-ceramic polymer Allylhydridopolycarbosilane (AHPCS) was identified as a replacement adhesive. Using thermal volatilisation analysis accompanied with solid-state nuclear magnetic resonance, Fourier-Transform infrared spectroscopy, mass spectrometry, differential scanning calorimetry and thermogravimetric analysis the thermal profile was identified. Three thermal processes were observed between 160-670 °C. AHPCS cross-links through the allyl group and undergoes carbon-silicon rearrangement, with volatilisation of oligomers, chain fragments and compounds such as methane, ethane, methanol, propane, propene. The major volatile released is hydrogen from dehydrocoupling of Si-H and C-Hbonds which leads to radical recombination of silicon and carbon, forming the SiC network which recrystallises to β-SiC by 1100 °C. Dicumyl peroxide at 1 % w/w was used as the thermal initiator which provided AHPCS with the highest final ceramic yield. TVA analysis showed differences in the thermal profile with lower cross-linking temperature, reduced volatilisation and higher Si-C recombination compared to unadulterated AHPCS. The post-fired flexural strength, resistance and porosity were improved in the AHPCS based formulations with only green strength being higher in the PF resin. This, along with both the safety and the consistency between adhesive chemistry, showed that AHPCS with dicumyl peroxide was a successful replacement for the PF resin in joining SiC heating elements.
Advisor / supervisor
  • Liggat, John
Resource Type
DOI
Embargo Note
  • This thesis is restricted to Strathclyde users only until 14th March 2029.

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