Experimental study of continuous ultrasonic reactors for mixing and precipitation of nanoparticles (original) (raw)
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Applied Sciences, 2018
The qualification of a unique ultrasonic instrument for real-time monitoring of the size and concentration of nanoparticles during bottom-up liquid phase synthesis is presented in this paper. The presented results of the ultrasonic instrument are verified with a dynamic light scattering device and a transmission electron microscope. Nanoparticles are increasingly used in numerous applications, such as in coatings, paints, cosmetics, etc. Both in the design and the production of nanoparticles there is a need for real-time measurements of their size and concentration. Ultrasound-based instruments are particularly suitable for measuring particle size and concentration, as they are non-destructive, fast, relatively cheap, and can measure in highly concentrated opaque dispersions. Also, the ultrasound sensors are robust enough to be placed inside a chemical reactor, allowing for real-time measurements of the particle size and concentration during synthesis.
Ultrasonic Dispersion of TiO 2 Nanoparticles in Aqueous Suspension
Aggregation and dispersion behavior of nanometer and submicrometer scale TiO 2 particles in aqueous suspension were investigated using three kinds of mechanical dispersion methods: ultrasonic irradiation, milling with 5-mm-diameter balls, and milling with 50 lm beads. Polyacrylic acids with molecular weights ranging from 1200 to 30 000 g/mol were used as a dispersant, and the molecular weight for each dispersion condition was optimized. Viscosities and aggregate sizes of the submicrometer powder suspensions were not appreciably changed in the ultrasonic irradiation and 5-mm-ball milling trials. In contrast, in the trials in which nanoparticle suspension was used, ultrasonic irradiation produced better results than 5-mm-ball milling. Use of ultrasonication enabled dispersion of aggregates to primary particle sizes, which was determined based on the specific surface area of the starting TiO 2 powders, even for relatively high solid content suspensions of up to 15 vol%. Fiftymicrometer-bead milling was also able to disperse aggregates to the same sizes as the ultrasonic irradiation method, but 50-lmbead milling can be used only in relatively low solid content suspensions. It was concluded that the ultrasonic dispersion method was a useful way to prepare concentrated and highly dispersed nanoparticle suspensions.
Production of fine powders by ultrasonic standing wave atomization
Powder Technology, 1996
Ultrasonic standing-wave atomization using two sonolrocles (20 kHzL both osciltating against each other, allows the disintegration of extremely viscoes fluids (synthetic resins, highly concentrated suspensions) or fluids with high surface tension (metal melts) into narrowsized, extremely small droplets and therefrom the production of fine spherical powders. The fundamentals of this new technique as well as its application in viscous fluid and melt alomizatioa are described. Rapid sotidification rates of metal powders (lin panicles with mean diameters oflesslhan 10pro) upto2×10 ~K~sf~rachievingu~ra-~ec~u~armicr~stm~ureswi~hin~hepowde~pani~esa~d~th~s.f~rinstsnc~ supersaturation effects ate further important advantages of this lechnique.
Studies on ultrasonic microfeeding of fine powders
Journal of Physics D: Applied Physics, 2006
Microfeeding can be used, inter alia, for solid freeforming, colour management and pharmaceutical dosing. In this work, a computer-controlled microfeeding system using ultrasonic vibration of a capillary was built. This paper describes the powder structures in the microfeeding process and defines the main processing factors affecting the mean dose mass. The experimental results show that the particle structures in the capillary tube can be divided into three types: arching, plugging and blocking. The nozzle diameter, transmission fluid depth, waveforms, voltage amplitude, frequency and oscillation duration all influence the dose mass. Among these factors, the nozzle diameter, voltage amplitude and oscillation duration can be used to control the dose mass.
Ultrasonic Properties of Nanoparticles-liquid Suspensions
A polymer colloidal solution having dispersed nanoparticles of Cu and Au metals have been developed using a novel chemical method. Average size of the nanoparticles could be varied in the 4-10 nm range by conducting the reaction at an elevated temperature of 50-70°C. Colloidal solutions of representative concentrations of 0.1-2.0 wt% Cu/Au contents in the primary solutions are used to study the modified ultrasonic attenuation and ultrasonic velocity in PVA polymer molecules on incorporating the Cu/Au particles. A characteristic behaviour of the ultrasonic velocity and the attenuation are observed at the particular temperature/particle concentration. The results demonstrate that the primary reaction during the nanoparticles-PVA colloidal formation occurs in divided groups in small micelles. The results are analyzed predicting the enhanced thermal conductivity of the samples.
On the performance of a Taylor-Couette reactor for nano-particle precipitation
In this work a Taylor-Couette reactor is employed for nano-particles precipitation. Its main features are the promotion of large shear rates (for mixing promotion) and almost uniform fluid dynamic conditions that make for reliable characterization and scale up, as well as for the generation of easier to interpret experimental data in the realm of kinetic models build up. Experimental information on the apparatus performance in the precipitation of Barium Sulphate is presented. Results show that particle size is only slightly affected by rotational speed, while a much larger influence is brought about by the presence of excess Barium ions, thus highlighting the importance of agglomeration phenomena in the investigated apparatus.
Investigation of the Precipitation of Barium Sulfate Nanoparticles
Chemical Engineering & Technology, 2008
Precipitation is a promising process for nanoparticle production because it is a fast, economic process and simple to design. In the present work, barium sulfate particles were produced by discontinuous precipitation in a stirred tank reactor. Particle sizes of less than 100 nm were achieved. Particle size distributions strongly depend on the mechanical mixing and the molar ratio of the reactants as well as on the stabilization of the particles in the suspension.
2019
Ultrasonic streaming and cavitation are the most predominant factors to consider for the efficient ultrasonic treatment of melts. In order to achieve a good distribution of reinforcement particles for making a Metal Matrix Composites (MMCs), the cavitation zone and velocity of fluid must be maximum enough to disperse the particles in a homogeneous way. In normal practice, stirring takes place in a closed vessel or crucible, where efficiency cannot be seen, and simulation methods are required to inform experimental research. In this work, ultrasonic streaming in water, glycerol, and the aluminum melt was numerically simulated and compared by introducing SiC particles. And the simulated results of same in water and glycerol were validated by experimental results to observe sonochemiluminescence which can lead to validate the simulated result of aluminum melt indirectly. In this work, COMSOL Multiphysics is used for the challenging coupling of pressure acoustic and particle trajectorie...
Nanopowder Fluidization and Mixing Under the Effect of Acoustic Fields
Chemical Engineering Transactions
Gas fluidization is one of the best available techniques to disperse and process large quantities of nanosized powders. Nevertheless, on the basis of their primary particle size and material density, fine powders fall under the Geldart group C (<30 μm) classification, which means that fluidization is expected to be particularly difficult because of cohesive forces existing between particles. In order to overcome these inter-particle forces and achieve a smooth fluidization regime, externally assisted fluidization can be used, thus involving the application of additional forces. Among all the available techniques, sound assisted fluidization has been indicated as one of the best technological option. The present work is focused on the study of the fluidization and mixing of nanoparticles under sound assisted conditions. All the fluidization tests have been performed at ambient temperature and pressure in a laboratory scale sound assisted apparatus. In particular, the first section...