Comparison of nanoparticle generation by two plasma techniques: Dielectric barrier discharge and spark discharge

Dielectric barrier discharge (DBD) and spark discharge, two versatile atmospheric pressure plasma-based techniques, have been employed to generate nanoparticles. This study compares the characteristics of metal nanoparticles generated by a DBD reactor and a spark discharge generator with argon as the working gas. The gas temperature in the discharge region of the DBD reactor remained near room temperature, while that of the spark reactor varied from 470 to 1120 K and generally increased with increasing applied voltage amplitude in the range of 2–10 kV and driving frequency in the range of 1–10 kHz. Comparing to spark-generated nanoparticles under the same voltage, frequency, and flow rate, DBD-generated nanoparticles have smaller sizes, better monodispersity, and lower number concentrations. The number concentration of DBD-generated particles decreases significantly under high working voltage and frequency, while the number concentration of spark-generated particles increases with increasing working voltage. Under continuous operations over several hours, the DBD reactor has better temporal stability in generating nanoparticles than the spark generator.

© 2017 American Association for Aerosol Research     

Study of TiO2 nanoparticle generation for follow-up inhalation experiments with laboratory animals

A method of long-lasting TiO₂ nanoparticle generation was tested for use in follow-up studies of the health impacts of nanoparticles on laboratory animals during several weeks' long exposure experiments. Nanoparticles were synthesized in an externally heated tube reactor by pyrolysis and oxidation of titanium tetraisopropoxide. Particle production was studied under varying reactor temperature, reactor flow rate, and precursor vapor pressure. A total of 264 h of particle generation were performed in four experimental campaigns using one batch of precursor without an observable decrease of particle production. As a result, particle production with number concentrations high above 1.0 × 10⁷ #/cm³ and with primary particle sizes well below 50 nm could be achieved in most of the investigated experimental conditions. Maximum of particle mass concentration reached the value 9500 μg/m³, which corresponds with emission rate 29 μg/min. The dependence of nanoparticle production and characteristics on experimental conditions was evaluated and the most suitable parameters for exposure experiments were specified. A comparison of the results with data from the literature shows that the material of the reactor plays a significant role in the process of particle formation.

Copyright © 2016 American Association for Aerosol Research     

Preparation of dense SiHf(B)CN-based ceramic nanocomposites via rapid spark plasma sintering

Dense SiHf(B)CN-based ceramic nanocomposites were prepared by spark plasma sintering (SPS) using high heating rates (∼450 ^°C/min.) and high pressures (≥100 MPa). The obtained nanocomposites were investigated by X-ray diffraction, Raman spectroscopy and electron microscopy concerning their phase evolution and microstructure.The hardness and the elastic modulus of dense SiHfCN were found to be 26.8 and 367 GPa, respectively. Whereas the SiHfBCN samples exhibited a hardness of 24.6 GPa and an elastic modulus of 284 GPa. The investigation of the oxidation of the prepared dense ceramic nanocomposites at high temperature revealed that the parabolic oxidation rates of SiHfCN were comparable to those of ultra-high temperature ceramics (UHTCs, e.g. HfC-20 vol% SiC); whereas the parabolic oxidation rates of SiHfBCN were several orders of magnitude lower than those. The results obtained within this study indicate the feasibility of SPS for rapid preparation of dense though nano-scaled Hf-containing ceramic nanocomposites that are promising candidates for high-temperature applications in harsh environments.