Hypersonic plasma particle deposition of nanostructures.

摘要

Nanostructured materials are often found to have superior properties compared to conventional, coarser-grained material. A thermal plasma expansion process called hypersonic plasma particle deposition (HPPD) was used for in-situ synthesis and deposition of nanoparticles and nanostructures. The HPPD process was utilized to synthesize nanoparticulate Si-Ti-N and SiC nanostructures for potential applications in advanced friction and wear-resistant coatings. Hybrid nanostructures consisting of nanoparticle-decorated Si nanowires were also synthesized for a variety of potential applications, including sensors, magnetics, and others.; Si-Ti-N nanoparticle films were deposited over a range of operating conditions. These films were determined to consist of TiN nanocrystallites embedded in a SiNx matrix. In most cases the grain sizes measured by X-ray diffraction correspond closely to the particle sizes measured by an in-situ particle characterization system. Hardness measurements of as-deposited Si-Ti-N coatings typically varied from 16 to 24 GPa. Preliminary results indicate that the hardness of the coatings can be improved through post-deposition densification.; Studies indicate that slight modifications of the HPPD process resulted in nanostructures consisting of single crystal silicon nanowires covered with nanoparticles. These nanowires are believed to grow in a vapor deposition process, catalyzed by the presence of titanium in the underlying nanoparticle film. Nanoparticles are simultaneously nucleated in the nozzle and deposited on the nanowires, producing structures that are formed from a combined chemical vapor deposition and nanoparticle spray process. The combination of these two process paths may open new dimensions in the nanophase materials processing area.; Deposition of SiC nanoparticles and nanostructured coatings showed particles in the sub-10-nm range with primarily crystalline beta-SiC and some crystalline Si particles. These results correlated well with particle size distributions measured using the in-situ particle measurement system. In-situ particle size measurements, in combination with electron microscopy and an analysis of sintering kinetics, demonstrated a possible formation mechanism of SiC nanoparticles in the HPPD system. It is believed that silicon nucleation is the initial step, followed by carburization via surface diffusion for the formation of SiC. Analysis of sintering and coagulation processes indicates that Si particles are likely to grow by collision and coalescence, whereas SiC forms soft agglomerates.