Ceramic composites from mesoporous silica coated multi-wall carbon nanotubes

• Mesoporous silica was successfully coated onto a variety of carbon nanotubes.
• Carbon nanotubes with different properties and characteristics can be coated.
• Nanocomposites produced have record hardness's 50% higher than blank silica's.

The addition of multi-wall carbon nanotubes (MWCNTs) to ceramic matrices could provide nanocomposites with enhanced properties. Efforts to produce these materials are normally frustrated by two major issues: firstly, the difficulty of attaining a homogenous distribution of MWCNTs in the matrix and secondly the poor bonding between the MWCNTs and the ceramic matrix. Herein, a processing method that overcomes these problems by using a sol–gel route to produce a low-melting point silica matrix, in combination with a dispersion method for the MWCNTs that is compatible with the sol is reported. This universal method was used to coat mesoporous silica on conventional, nitrogen-doped (CNX) and boron-doped (CBX) produced using aerosol assisted chemical vapour deposition (AACVD) as well as commercially available MWCNTs. After hot-pressing the powders, record improvements (ca. 50%) in hardness for the nanocomposites over the silica were observed and this improvement is enhanced by 50% if spark plasma sintering is used to consolidate the nanocomposites. Nanocomposites containing conventional nanotubes produced from AACVD and commercially available nanotubes have near identical hardness even though the nanotubes have different properties and characteristics.

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