Victor V. Ivanov

Determination of dimensions of exfoliating materials in aqueous suspensions

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Synthesis and Characterization of TiO2, Cu2O and Al2O3 Aerosol Nanoparticles Produced by the Multi-Spark Discharge Generator

The morphology, crystal structure and size of aerosol nanoparticles generated by erosion of electrodes made of different materials (titanium, copper and aluminum) in a multi-spark discharge generator were investigated. The aerosol nanoparticle synthesis was carried out in air atmosphere at a capacitor stored energy of 6 J, a repetition rate of discharge of 0.5 Hz and a gas flow velocity of 5.4 m/s. The aerosol nanoparticles were generated in the form of oxides and had various morphologies: agglomerates of primary particles of and or aggregates of primary particles of . The average size of the primary nanoparticles ranged between 6.3 and 7.4 nm for the three substances studied. The average size of the agglomerates and aggregates varied in a wide interval from 24.6 nm for to 46.1 nm for .

Filtration of nanosized particle aerosols by electret fibrous filters

Results of studying the filtration efficiency of various nanoaerosols in an air-cleaning system in which particles are charged in the integrated corona discharge unit and polymer fibers with electret properties serve as the filtration material are presented. The total filtration efficiency for titanium oxide (TiOx), diethyl-hexylsebacate (DEHS), and bovine serum albumin (BSA) aerosols and anti-mosquito smoke (AMS) is 99.9, 99.3, 98.6, and 98.7%, respectively. A significant (5–10%) drop in the filtration efficiency has been observed for DEHS and BSA aerosols and AMS in a particle size range of less than 80 nm. It has been demonstrated that the filtration efficiency can be substantially increased by activating the electrostatic particle-capture mechanism through the charging of particles in the corona discharge unit. In connection with this, the electrostatic mechanism is the dominant one for particles larger than 80 nm, while its contribution decreases in the particle size range of less than 80 nm with a decrease in particle size and a simultaneous increase in the contribution of the capture mechanism due to diffusion. It has also been found that the increase in the filter solidity by a factor of higher than 1.5 has a negligible effect on the filtration efficiency, thus making it reasonable to utilize low-solidity electret filters whose quality factor reaches the maximal values.

Preparation of alumina nanoparticle suspensions with narrow particle size distribution

Dynamic light scattering (DLS) was applied to the study of the process of the preparing deaggregated water suspensions of alumina nanopowders with specific surface areas of 20–140 m2/g. Nanopowders were prepared by the electric explosion of wire and laser evaporation and, according to electron microscopy (TEM), consisted of nonagglomerated spherical nanoparticles with lognormal size distribution. According to DLS, nonsedimenting water suspensions of alumina nanoparticles, stabilized by sodium citrate at a 5 mM concentration, contain substantial fraction of aggregates. The dynamics of the change in the mean average size of aggregates under exhaustive ultrasound treatment of suspensions with 10 g/l concentration for 1.5–4 h by two types of ultrasonic processors was studied. It was shown that the mean average size of aggregates exponentially diminishes by 1.5–2 times and the fraction of individual particles in suspension enlarges from 45 to 85%. Sequentially centrifuging the suspension at 18000 g separates the remaining aggregates and results in suspensions of individual alumina nanoparticles. Particle size distributions in these suspensions obtained by TEM and DLS are the same within experimental error.

Reducing Humidity Response of Gas Sensors for Medical Applications: Use of Spark Discharge Synthesis of Metal Oxide Nanoparticles

The application of gas sensors in breath analysis is an important trend in the early diagnostics of different diseases including lung cancer, ulcers, and enteric infection. However, traditional methods of synthesis of metal oxide gas-sensing materials for semiconductor sensors based on wet sol-gel processes give relatively high sensitivity of the gas sensor to changing humidity. The sol-gel process leading to the formation of superficial hydroxyl groups on oxide particles is responsible for the strong response of the sensing material to this factor. In our work, we investigated the possibility to synthesize metal oxide materials with reduced sensitivity to water vapors. Dry synthesis of SnO2 nanoparticles was implemented in gas phase by spark discharge, enabling the reduction of the hydroxyl concentration on the surface and allowing the production of tin dioxide powder with specific surface area of about 40 m2/g after annealing at 610 °C. The drop in sensor resistance does not exceed 20% when air humidity increases from 40 to 100%, whereas the response to 100 ppm of hydrogen is a factor of 8 with very short response time of about 1 s. The sensor response was tested in mixtures of air with hydrogen, which is the marker of enteric infections and the marker of early stage fire, and in a mixture of air with lactate (marker of stomach cancer) and ammonia gas (marker of Helicobacter pylori, responsible for stomach ulcers).

Synthesis of Nanoparticles in a Pulsed-Periodic Gas Discharge and Their Potential Applications

Conditions for the synthesis of three types nanoparticles (SnO2, Al2O3, and Ag) with typical sizes in the range of 4 to 10 nm and a performance of 0.4 g/h are employed in a pulsed-periodic gas discharge in an atmosphere of air. Spherical Ge nanoparticles with a characteristic size of 13 nm are synthesized by these means for the first time with a performance of around 10 mg/h. The specific energy consumption in the synthesis of nanoparticles is for these materials in the range of 2000 to 5000 kW h/kg. The prospects for using tinoxide nanoparticles in sensor components and jets of silver nanoparticles for aerosol printing are discussed. The merits and demerits of the pulsed gas-discharge method among other gas-phase approaches to the synthesis of nanoparticles are analyzed for the current level of development.

Unipolar Charging of Aerosol Particles in the Size Range 75-500 nm by Needle-plate Corona Charger

A simple unipolar needle-plate corona charger (NPC) was designed, fabricated and tested on aerosol Al 2 O 3 particles in the size range 75-500 nm. The intrinsic charging efficiency, particle electrostatic losses, and extrinsic charging efficiency were investigated depending on the corona current (35-215 μA), corona polarity, and aerosol flow rate (12-250 l/min). It was found that the intrinsic charging efficiency of the NPC is growing with increase in the corona current and the particle size and decrease in the aerosol flow rate. However, the extrinsic charging efficiency is lower than intrinsic one due to the particle electrostatic losses. Although the NPC has very simple design, it provides the extrinsic charging efficiency comparable with that of unipolar corona chargers of other types having more complicated design. The maximum value of the extrinsic charging efficiency was more than 40% for particles in the size range from 98 to 210 nm.

Determination of the critical values of flow parameters characteristic of the alignment of cylindrical nano-objects in suspensions

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Electrostatic Aerosol Deposition Method for the Formation of an Ensemble of Monodisperse Particles on a Substrate

We have developed an aerosol-based technique for deposition of monodisperse ensembles of spherical SiO2 nanoparticles on the surface of single-crystal silicon substrate (1 cm2) with an average surface particle density of about 2.1±0.4 particles per μm2. The obtained samples of monodisperse ensembles SiO2 nanoparticles was characterized by scanning and transmission electron microscopy. The ensemble of deposited nanoparticles is characterized by a narrow size distribution with a modal size of 26.6 nm and a full width at half maximum of 3.5 nm according to the atomic force microscopy data. We have demonstrated the use of the obtained test structure to determine the effective radius of the tip of an atomic force microscope.

Anisotropic spectra of ultrasonic attenuation in aqueous dispersions with oriented carbon nanotubes

The method of acoustic spectroscopy is used for the first time for investigating the spectra of ultrasonic attenuation in the range of 3–100 MHz on oriented carbon nanotubes in the stabilized aqueous dispersion. The anisotropy of attenuation of ultrasound manifests itself in a significant distinction between the attenuation spectra for preferential perpendicular and parallel orientation of carbon nanotubes with respect to the wave-propagation direction. A qualitative agreement of the measured-spectra shape with that of the attenuation spectra calculated from the theoretical model is obtained.