Magnesium alloy (AZ31) reinforced with carbon nanotubes (CNTs) and grapheme nanoplatelets (GNPs) were fabricated with the method of hot-pressing sintering and hot extrusion processes. GNPs and CNTs were predispersed with Al and Zn powders by ball milling used as precursor for sintering, which effectively guaranteed the integrity and dispersion of them. The microstructure and mechanical properties of the composites (denoted as Mg–3 wt% Al–1 wt% Zn–1 wt% (xCNTs + yGNPs)(x:y = 1:1, 1:2, 1:3) were investigated. The results show that the CNTs and GNPs are uniformly distributed in the matrix and closely combined with the matrix in nanoscale. Among the tested composites, Mg–3 wt% Al–1 wt% Zn–1 wt% (xCNTs + yGNPs)(x:y = 1:2) exhibits the most favorable mechanical properties, and the yield strength, tensile and compressed strength, and elongation of composites are substantially improved by the addition of 0.33 wt% CNTs and 0.67 wt% GNPs. Novel strengthening mechanisms such as three-dimensional reinforced structure formed by CNTs and GNPs are found for the remarkable improvement in mechanical properties.

The vertically aligned carbon nanotubes (CNTs) deposited by microwave plasma-enhanced chemical vapor deposition (MPCVD) were utilized as resistive gas sensors.

The carbon nanotubes were annealed between 200 to 800°C under N2 flow (500 sccm) for 15 minute, respectively. After that, the carbon nanotubes were exposed to an N2 filling and pumping environment. Upon exposure to N2 the electrical resistance of vertically aligned carbon nanotubes was found to increase. It was found that the N2 absorption of unannealed carbon nanotubes was reversible, whereas which of annealing ones was not. However, the sensitivity of the N2 absorption on carbon nanotubes was improved after annealing. From the Raman spectra, the ID/IG ratio of carbon nanotubes also decreased after annealing, indicating that more graphenes were formed by the annealing process. Furthermore, from X-ray photoelectron spectroscopy (XPS), it was observed that the ratio of the oxygen to carbon (O/C) signal intensity increased from 0.094 to 3.943 as the annealing temperature increased. As a consequence, it was suggested that the surface of carbon nanotubes was oxygenated and the absorption of N2 changed from physisorption to chemisorption.