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Title: Silane surface modification of boron carbide in epoxy composites
Author: Rodrigues, David D. S.
Awarding Body: Oxford Brookes University
Current Institution: Oxford Brookes University
Date of Award: 2013
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Boron carbide (BC) is used as a radiation absorber in the nuclear industry and particle physics experimentation. BC parts are generally manufactured through a sintering process, which limits the size and shape of components and imparts high cost. On the other hand, a polymeric matrix composite (PMC) with high BC content can be easily obtained through a moulding process, providing lower cost parts whilst accommodating increased complexity of geometry and size. Despite the importance of BC in industry, only a few studies have been carried out on epoxy PMCs containing only small amounts of BC. The lack of adhesion exhibited between BC and resin led to limited mechanical strength and durability. Hence, silane surface modification of BC particles was conducted with γ–glycidoxypropyltrimethoxysilane (GPS) as an aqueous solution to attain an 80%wt BC-epoxy PMC with improved strength and durability. Surface analysis on BC, and physical-chemical characterisation, mechanical testing and durability studies on the PMCs were conducted to better understand the effect of silane treatment and parameters (pH, %GPS). Fourier Transform Infrared (FTIR) and X-ray Photoelectron Spectroscopy (XPS) confirmed boron oxide and hydroxyl groups on the native surface which can offer a means of attachment to the silane. Surface modification was more evident using higher GPS concentrations in pH5-7 solutions. These parameters were found to strongly affect the silane layer structure (crosslinking, density, thickness and coverage). Also, IR bands corresponding to B-O-Si were evident which are typically found on borosilicate glass. Increased hydrophobicity and adhesive wettability confirmed by sessile drop method, led to PMCs with higher density, lower porosity and reduced water permeability. Mechanical testing by means of three-point bending (3PB), Iosipescu and double v-notch (DVN) tests demonstrated correlations between strength improvement and the various surface modifications and physical-chemical characterisation. This was supported by SEM of the PMC failure surfaces, showing enhanced adhesion through distinguishable layers of epoxy and small BC particle clusters, remaining attached to the larger particles. This was due to a better adhesive wetting and stronger interfacial bonding. Optimal mechanical properties and durability were generally obtained using 0.5-1%GPS in pH5 solutions due to the combination of high initial strength and lower reductions in strength after ageing (water immersion).
Supervisor: Not available Sponsor: Science & Technology Facilities Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available