Production and dispersion stability of nanoparticles in nanofluids

This paper presents an experimental study on the homogeneous dispersion of nanoparticles in nanofluids. In this study, various physical treatment techniques based on two-step method, including stirrer, ultrasonic bath, ultrasonic disruptor, and high-pressure homogenizer were systematically tested to verify their versatility for preparing stable nanofluids. Initially carbon black and silver nanoparticles dispersed in base fluids with the presence of surfactant were found to be highly agglomerated with the hydrodynamic diameter of 330 nm to 585 nm, respectively. After both CB and Ag nanofluids were treated by various two-step methods, stirrer, ultrasonic bath, and ultrasonic disrupter was found to do a poor performance in deagglomeration process for the initial particle clusters. However, the high-pressure homogenizer produced the average diameter of the CB and Ag particles of 45 nm and 35 nm, respectively, indicating that among various physical treatment techniques employed in this study, the high-pressure homogenizer was the most effective method to break down the agglomerated nanoparticles suspended in base fluids. In order to prepare another nanofluid with much smaller primary nanoparticles, we also employed a modified magnetron sputtering system, in which the sputtered nanoparticles were designed to directly mix with the running surfactant-added silicon oil thin film formed on a rolling drum (i.e. one-step method). We observed that Ag nanoparticles produced by the modified magnetron sputtering system were homogeneously dispersed and long-term stable in the silicon oil-based fluid, and the average diameter of Ag nanoparticles was found to be ~ 3 nm, indicating that the modified magnetron sputtering system is also an effective one-step method to prepare stable nanofluids.     

Characteristics of Nylon 6 nanofilter for removing ultra fine particles

Electrospinning is a fabrication process that uses an electric field to make polymer nanofibers. Nanofibers have a large specific surface area and a small pore size; these are good properties for filtration applications. In this paper, the filtration characteristics of a Nylon 6 nanofilter made by electrospun nanofibers are tested as a function of the fiber diameter. Nanofilter media with diameters in the range of 100–730 nm can be produced in optimized conditions. The pressure drop of a Nylon 6 nanofilter linearly increases with the increasing face velocity. An electrospun Nylon 6 filter (mean fiber diameter: 100 nm) shows a much lower pressure drop performance relative to the commercial HEPA filter media when the filtration efficiency of the Nylon 6 nanofilter and the HEPA filter are over 99.98% with test particles of 0.02–1.0 μm in diameter. The pressure drop at 5 cm/s of the face velocity is measured as 27 mmAq for the Nylon 6 nanofilter media, and 37.1 mmAq for the HEPA filter media. The particle size with minimum efficiency decreases with the decreasing fiber diameter. And the minimum efficiency becomes greater as the fiber diameter is decreased.     

Optimization of adhesive strength to plywood of gelatin processed from dorsal skin of yellowfin tuna (<Emphasis Type="Italic">Thunnus albacares</Emphasis>)

Gelatin from yellowfin tuna (Thunnus albacares) dorsal skin was optimized for adhesive strength to plywood using surface response methodology of a central composite design with a dependent variable of adhesive strength (Y, kg _f /cm²) and two independent variables of gelatin concentration (X₁, %) and hardening time (X₂, hrs). From the above design, a maximum adhesive strength of 49.84 kg _f /cm² was obtained under the optimal treatment condition of 15.85% gelatin concentration and 25.68 hr hardening time. The adhesive strength under optimum conditions was 50.93 kg _f /cm². The adhesive strength of the tuna gelatin was shown to be superior to that of bovine and porcine gelatins which had adhesive strengths of 34.75 and 34.9 kg _f /cm², respectively.     

Performance evaluation of three optical particle counters with an efficient “multimodal” calibration method

The sizing accuracies of two widely used yet hitherto unevaluated optical particle counters (OPCs—Grimm Model 1.109 and Palas Model WELAS 2100) as well as one high-resolution, non-commercial OPC were evaluated. The measured data were compared to scattering intensity calculations based on Mie theory. Additionally, the counting efficiency for all three counters was measured, as was the influence of coincidence effects for the OPC with the lowest (manufacturer specified) upper concentration limit.Beside the traditional polystyrene latex calibration, a little-known, very fast and precise “multimodal” calibration method was used, which is based on the simultaneous generation of up to eight sharp multiple-charge modes from polydisperse di-ethyl-hexyl-sebacate (DEHS) particles by electrical mobility classification.     

Synthesis and characterization of polypyrrole rod doped with p‐toluenesulfonic acid via micelle formation

Rod‐type polypyrrole (PPY) doped with p‐toluenesulfonic acid (TSA) was synthesized by chemical oxidative polymerization via a self‐assembly process. The shape of the PPY particles is mainly determined by the ratio of TSA/pyrrole (PY) and feed rate of the oxidant. Particle of different shapes (rod, grain, and partially rod) exhibit differences in morphology, electrical properties, dispersity, and thermal properties. Wide‐angle X‐ray diffraction patterning analysis was used to investigate the mechanism of rod formation. The effect of the TSA concentration on the PPY structure was investigated using Fourier transform infrared spectroscopy. The PPY rods doped with TSA exhibited better electrical conductivity than granular PPY doped with TSA, and their dispersity and thermal stability were also higher. Self‐orientation of PPY in the micelles of TSA and high crystallinity of the rod particles led to improved thermal stability. Hence, the decomposition temperature of the polymer chain was considerably increased. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

A self-sensing technology of active magnetic bearings using a phase modulation algorithm based on a high frequency voltage injection method

Conventional AMB(active magnetic bearings) systems consist of electromagnetic coils, position sensors, power amplifiers and a feedback controller. This hardware configuration can lead to a structural complexity, problems of space limitations for the installation, and position control difficulties due to the non-collocation of actuators and sensors. In this paper, a self-sensing mechanism is proposed to resolve such limitations of the general AMB system. The proposed self-sensing scheme uses a phase difference of the injected current of two opposite electromagnetic actuators while an object is levitating between the actuators. The relationship between the phase difference of injected currents and the position of a levitated object was theoretically derived and linearized. In order to realize the proposed self-sensing scheme, a signal processing algorithm was developed. The frequency response of the estimator was measured to verify the performance of the proposed self-sensing scheme. In addition, a magnetic levitation and a disturbance rejection response were experimentally obtained to verify the feasibility of the proposed self-sensing mechanism. Experimental results showed that the developed self-sensing technique has similar performance as a practical gap sensor.     

Electroless coating of tungsten oxide on the surface of copper powder

Tungsten oxide was successfully deposited on the surface of copper powder and the thickness of coating layer was dependent on deposition time. Because a spontaneous reaction occurred on the interface between copper and tungsten-peroxo electrolyte, there was a maximum thickness that could be obtained, as confirmed from XRD and EDX results. Mesoporous tungsten oxide was also deposited using SDS as a structure directing agent. As-synthesized tungsten oxide was amorphous and, after calcination at 450 °C, crystallized tungsten oxide was produced. Compared to pure tungsten oxide, the tungsten oxide coated copper oxide showed enhanced absorption in the visible region.     

Structural and optical properties of ZnS thin films deposited by RF magnetron sputtering

Zinc sulfide [ZnS] thin films were deposited on glass substrates using radio frequency magnetron sputtering. The substrate temperature was varied in the range of 100°C to 400°C. The structural and optical properties of ZnS thin films were characterized with X-ray diffraction [XRD], field emission scanning electron microscopy [FESEM], energy dispersive analysis of X-rays and UV-visible transmission spectra. The XRD analyses indicate that ZnS films have zinc blende structures with (111) preferential orientation, whereas the diffraction patterns sharpen with the increase in substrate temperatures. The FESEM data also reveal that the films have nano-size grains with a grain size of approximately 69 nm. The films grown at 350°C exhibit a relatively high transmittance of 80% in the visible region, with an energy band gap of 3.79 eV. These results show that ZnS films are suitable for use as the buffer layer of the Cu(In, Ga)Se₂ solar cells.