Papers by Keyword: Ultrasonic Dispersion

Abstract: Carbon nanotubes have been studied by scanning electron microscopy. Measurement modes - accelerating voltage 10 kV, current in microscopy mode 10^-9 A. The sample was applied to a metal mesh. Spectroscopic data indicate that this sample consists of carbon (peak at 280 eV). There are no other intense peaks in the spectrum; no impurities were detected by this method. Determination of physical and mechanical characteristics was carried out on a testing machine model N5K-S.

Abstract: The factors determining the production of fine-grained high-strength concrete are considered. The effect of micro-and complex nanodisperse additives based on natural mineral components, as well as the packing density of the quartz aggregate, on the strength parameters of fine-grained concrete is studied. The compositions of the fine-grained concrete modified by micro-and complex nanodisperse additives have been developed. The dependence of the fine concrete strength on the ratio of the mineral component and the stabilizer in the nanodisperse additive and the time of ultrasonic dispersion and additive storage is analyzed. The stabilization mechanisms of water dispersions of complex nanodisperse additives by various surface active modifiers are considered. The positive role of ultrasonic dispersion in obtaining nanodispersed additives is shown. The application efficiency of the micro-filler improving the density and strength of fine-grained concrete is revealed. The structure of fine-grained concrete is studied. It has been established by scanning electron microscopy that the introduction of the micro-and nanodispersed additives in the concrete leads to a less defective crystalline structure of the material.

Abstract: The stabilizer nature effect on the aggregative stability of the modifying concrete additives based on halloysite nanotubes in the aquatic environment is shown. The chemical composition and morphology of halloysite nanotubes and their additives, obtained by ultrasonic dispersion in the aquatic environment of the surfactant, are studied. The influence on the processes of charge stabilization on the outer and inner surface of halloysite nanotubes is determined. The dependence of nanotube sizes and specific surface area on the stabilizer type, the time of ultrasonic dispersion, and additive storage is revealed. The stabilization mechanisms of aqueous dispersions of modifying additives based on halloysite nanotubes with anion-and cation-active substances are considered. It is established that the polynaphthalenesulfonate-based modifier S-3 has got the maximum efficiency as a stabilizer of aqueous dispersions of modifying concrete additives with halloysite nanotubes.

Abstract: The technological parameters on synthesis rate of ITO nanometer by chemical coprecipitation were investigated. The effects of process parameters on synthesis rate of ITO nanometer powders were discussed by the range analysis of orthogonal experiment design. The dispersion features of ITO nanometer powder by ultrasonic dispersion or without were compared. The results show that the biggest factor that affects the powder synthesis rate is the pH at the titration end-point. Powder synthesis rate increases with the increase of pH value. When pH is 9, the powder synthesis rates are all above 90%. TEM images show that ITO nanometer powders are well dispersed without obviously agglomeration when anhydrous ethanol is used as dispersant. Particles have diversity of shapes, and the particle sizes distribute widely. After Ultrasonic physical dispersion, ITO nanopowders are well dispersed with no obviously agglomeration, narrow particle sizes of 20-30 nm and the approximation spherical particle morphology.

Abstract: In this paper, a new method of the preparation of mica composite insulation material without making mica paper is introduced. Firstly, the mica pulp and modified starch is mixed, and then preformed by ultrasonic dispersion, finally formed with three separation steps of hot-pressing. The flexural strength of mica composite insulation material can reach 229.5 N/mm2, the dielectric strength can reach 23.80KV/mm.

Abstract: The electrochromic PANI film was prepared by emulsion polymerization with dodecyl benzene sulphonic acid (DBSA) as dopant and ammonium persulfate (APS) as initiator. Ultrasonic dispersion was adopted in the polymerization. The electrochemical properties, the surface morphology and structure of the prepared PANI film was characterized by means of Fourier Transform infrared spectroscopy (FT-IR), cyclic voltammograms (CV) and field emission scanning electron microscope (FE-SEM), respectively. The relationship between the morphology and properties of PANI film was detailedly discussed. The PANI film exhibited an excellent electrochromism with reversible color changes form yellow to purple. The PANI film also had quite good reaction kinetics with fast switching speed, and the response time for oxidation and reduction were 65 ms and 66 ms, respectively.

Abstract: SiC nanoparticles reinforced AZ61 magnesium composites were fabricated by Ultrasonic method. The distribution of nanoparticles in the matrix and the fracture morphology of the composites were observed by SEM, and the mechanical properties of the composites were tested at room temperature. Experimental shows that SiC nanoparticles were dispersed well in the matrix with the pretreatment method. Compared with the matrix, the tensile strength and hardness of the composites were improved respectively. Meanwhile, the ductility of the composites didn’t be obviously decreased. The enhancement function of nano composites was predicted with the dislocation strengthening and Orowan dispersion strengthening mechanisms. The predicted results coincided well with experimental ones.

Abstract: Ever since copious nucleation was shown to be an efficient, cost effective method for producing semi-solid slurry, many processes have been developed to take advantage of the cost savings inherent in this method of slurry production. Despite great advances in various aspects of semi-solid processing, the cost competitive nature of the industry, most noticeably the auto industry, has prevented a wider adoption of semi-solid casting technology. This research aims to realize a more industrial appealing process by combining the synergistic benefits of semi-solid casting technology with metal matrix nanocomposite (MMNC) technology, thus creating higher value products with superior properties cost-effectively. To do this, a process that produces a semi-solid slurry though the nucleation catalysis induced by nanoparticle additions as small as 1 wt. % to alloys is proposed and the results are presented in this paper. Examination of the potential for nano-scale inoculants to catalyze nucleation of solidification showed that despite their small sizes, inoculants on the scale of tens of nanometers are capable of catalyzing nucleation in the zinc and aluminum alloys studied. Employing the differential scanning calorimetry (DSC), differential thermal analysis (DTA), and droplet emulsion techniques with nanocomposite samples showed a significant reduction in undercooling owing to the homogeneous distribution of nanoparticles by ultrasonic mixing and the potency of those nanoparticles to catalyze nucleation. Comparison of undercoolings between different types of nanoparticles, such as silicon carbide (SiC), gamma and alpha alumina (Al2O3), and titanium carbide (TiC), to relative potencies predicted by minimum lattice disregistry showed a strong correlation. Results were also examined in light of free growth and nucleation controlled grain initiation. For nanoparticles predicted to be potent nucleation catalysts by lattice disregistry, the undercoolings observed fell into the free growth controlled grain initiation regime.

Abstract: Semi-solid casting (SSC) techniques have proven useful in the mass production of high integrity castings for the automotive and other industries. Recent research has shown metal matrix nanocomposite (MMNC) materials to have greatly improved properties in comparison to their base metals. However, current methods of MMNC production are costly and time consuming. Thus development of a process that combines the integrity and cost effectiveness of semi-solid casting with the property improvement of MMNCs would have the potential to greatly improve cast part quality available to engineers in a wide variety of industries. This paper presents a method of combining SSC with MMNC in a way that benefits from MMNCs’ tendency to naturally form the globular microstructure necessary for SSC. This method uses ultrasonically dispersed nanoparticles as nucleating agents to achieve globular primary grains such that fluidity is maintained even at high solid fractions. Once particle dispersion is achieved, the material needs no further processing to become a semi-solid slurry of globular primary grains as it cools. This quiescent method of slurry production, while still imposing some constraints on cooling rates, has a large process window making this process capable of industrial rates of throughput. It was found that the key factor to achieving globular microstructure is a sufficiently slow cooling rate at the onset of solidification such that particle-induced nucleation can occur. Once nucleation occurs, continued cooling is virtually unconstrained, with globular microstructure evident in quenched samples as well as samples cooled at rates as slow as 1 °C/min. This method was demonstrated in several material systems using zinc (Zn), aluminum (Al), and magnesium (Mg) alloys and nanoparticles of aluminum oxide (Al2O3), silicon carbide (SiC), and titanium oxide (TiO2). Additionally, several nucleation models are examined for applicability to nanoscale composites.