The multi-walled carbon nanotubes (MWCNTs) with controlled diameter distribution are useful in the fabrication of composite materials as reinforcement, due to their superior strength and toughness. Chemical vapor deposition (CVD) is a viable process to synthesize MWCNTs. In this investigation, an attempt has been made to study the effect of CVD process parameters (reaction temperature, flow rate of precursor gas, process time) on the mean diameter of MWCNTs. The MWCNTs of controlled diameter distribution was selectively grown on NiO catalyst supported by Al₂O₃ nano particles. The argon and acetylene were used as carrier and carbon precursor gas, respectively. The catalyst and carbon samples were characterized using field emission scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy and thermogravimetric/differential thermal analysis. From this investigation, it is understood that the increase in reaction temperature and flow rate of precursor gas increased the mean diameter of MWCNTs but increase in process time decreased the diameter. The diameter distribution and quality of MWCNTs are strongly influenced by the diameter of the catalyst particles.

Research work published since 2010 on the synthesis of carbon nanotubes (CNTs), carbon nanorings (CNRs), and carbon nanospheres (CNSs) using the chemical vapor deposition (CVD) process is reviewed. The effect of CVD process parameters on carbon nanomaterials morphology, such as diameter, yield, and quality was reviewed. The mechanism of CVD formation and growth of carbon nanomaterials was reviewed in detail. The catalyst materials used to synthesize these carbon allotropies were discussed in detail. The formation mechanism of carbon nanomaterials indicates that the variables of the CVD process parameters that appear to control growth are not directly manipulated in the CVD process. Rather, it is determined by complex interactions between variables. The impact of CNTs, CNRs, and CNSs was discussed using the schematic representation. The researchers who published the articles in the CNTs, CNRs, and CNSs for the past decade were discussed. From the intensive literature review, it was found that as compared to CNTs there is not much research was undertaken in synthesizing spheres and rings. But spheres and rings are capable of performing better than CNTs structure in energy storage, and sensors.

In this research, friction stir processing (FSP) is utilized to develop the graphene-boron nitride-reinforced hybrid magnesium surface composite with varying volume percentages of reinforcements. A Taguchi-coupled Entropy-COPRAS approach is adopted to understand the influence of control factors of wire electrical discharge machining on the developed magnesium surface composite. An optimal combination of machining factors to attain maximum material removal rate (MRR) along with minimal kerf width and surface roughness is to be finalized. The Taguchi method is utilized for planning the experiments with three levels and four factors, namely, reinforcement volume , pulse off time, wire feed rate, and pulse on time. ANOVA results show that pulse on time and reinforcement volume act as the most significant factors for output responses. Using the Entropy-COPRAS approach, an optimal combination for output response was found for a maximum MRR of 16.20mm³/min; minimal surface roughness of 3.86μm; and 0.29μm of kerf width.