Core/Shell Structure of TiO2-Coated MWCNTs for Thermal Protection for High-Temperature Processing of Metal Matrix Composites

Laura Angélica Ardila Rodriguez,Dilermando Nagle Travessa

doi:10.1155/2018/7026141

Abstract

The production of metal matrix composites with elevated mechanical properties depends largely on the reinforcing phase properties. Due to the poor oxidation resistance of multiwalled carbon nanotubes (MWCNTs) as well as their high reactivity with molten metal, the processing conditions for the production of MWCNT-reinforced metal matrix composites may be an obstacle to their successful use as reinforcement. Coating MWCNTs with a ceramic material that acts as a thermal protection would be an alternative to improve oxidation stability. In this work, MWCNTs previously functionalized were coated with titanium dioxide (TiO2) layers of different thicknesses, producing a core-shell structure. Heat treatments at three different temperatures (500°C, 750°C, and 1000°C) were performed on coated nanotubes in order to form a stable metal oxide structure. The MWCNT/TiO2 hybrids produced were evaluated in terms of thermal stability. Thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy (RS), and X-ray photoelectron spectroscopy (XPS) were performed in order to investigate TiO2-coated MWCNT structure and thermal stability under oxidative atmosphere. It was found that the thermal stability of the TiO2-coated MWCNTs was dependent of the TiO2 layer morphology that in turn depends on the heat treatment temperature.

Highlights

Since its discovery by Iijima in 1991 [1], carbon nanotubes (CNTs) have been very attractive for different applications due to their unique properties and structure
It seems that the mass relation between multiwalled carbon nanotubes (MWCNTs) core and TiO2 shell is optimized
MWCNTs were uniformly coated with a TiO2 continuous layer with core/shell structure, through the solgel method. e layer thickness formed could be controlled by the repetition of the coating cycles, and a stable and dense coating layer could be reached after calcination at 1000°C

Summary

Introduction

Since its discovery by Iijima in 1991 [1], carbon nanotubes (CNTs) have been very attractive for different applications due to their unique properties and structure. Jo et al [25] coated carbon nanofibers with TiO2 by the sol-gel method and dispersed it in aluminum matrix composites by the liquid pressing process, reporting that the coating protects the carbon nanofiber and improves the mechanical properties of the composite. In this context, the idea of creating a protection system for CNTs that will be subjected to high temperatures during the production of MMCs is promising. Thermogravimetric analysis was employed to assess the TiO2-coated MWCNT stability in the O2 atmosphere

Materials and Methods

Results and Discussion

Conclusions