Dispersion Of Nano-sized Particles Research Articles

DETERMINATION OF THE THERMAL BEHAVIOR OF WATER-BASED Fe3O4 NANOFLUID USING THERMOPHYSICAL PROPERTY MODELS

Nanofluids refers to the mixture containing homogeneously dispersed nano-sized particles in conventional base fluids. Recently, researchers have focused on analyzing the thermal performance of nanofluids, which are utilized as working fluids to raise the efficiency of thermal systems. To survey the heat transfer behavior of nanofluids, it is vital to determine the thermophysical characteristics. Researchers use different models to obtain the specific heat, viscosity and thermal conductivity. In current study, various correlations have been investigated in detail and summarized to predict the thermophysical properties of the Fe3O4/water nanofluid. It is aimed to use the correlations specified in calculating experimental heat transfer coefficient of water-based Fe3O4 nanofluid with weight concentration of 0.5%, which acts as the working fluid in the plate-type heat exchanger. The effects of different models used on the predicted value of the heat transfer coefficient of the nanofluid have been investigated both experimentally and theoretically. The results have been analyzed in detail by making comparisons between experimental data and correlations. The obtained results exhibited good agreement between experimental and correlations results.

Confined-space strategy for anchoring catalytic nanoparticles on Si-OH by ball milling for enhanced O3/PMS oxidation of ciprofloxacin

Design and preparation of effective catalysts for advanced oxidation processes (AOPs) remain challenging, especially concerning the creation of strong interactions between catalytic sites and the support, which is essential for effective charge transfer and generation of reactive oxygen species (ROSs). In the present work, a pore-confinement approach based on a green ball milling method is proposed to anchor Co-Ce nanoparticles on a mesoporous silica support, and its chemical features and advantages are addressed. Remarkably, such a catalyst exhibited high activity due to the enhanced interface-mediated electron transfer, giving superior total organic carbon (TOC) removal (>70%) of ciprofloxacin (CIP) after only 10 min of treatment with O3/peroxymonosulfate (O3/PMS), which was much higher than for a catalyst synthesized by a traditional non-confined space process in previous reported literature. This confinement effect could stretch Co–Co bonds in a tetrahedral coordination and promote the growth of highly dispersed nanosized particles due to the Si-OH anchoring according to the results of X-ray absorption fine structure (XAFS). Furthermore, theoretical analysis revealed that Co3O4 {111} as main active sites significantly raised the adsorption of PMS, CIP and O3 than other phase, thereby favoring catalyst–reactant interaction and boosting electron transfer in this system.

Investigation on flower-shaped Ni-doped Fe3O4/SnS2 formation mechanism through a microcalorimetric method and catalytic property as a Fenton-like catalyst

Flower-shaped Ni-doped Fe3O4/SnS2 composite was synthesized by a one-pot solvothermal method, where nanosized Ni-doped Fe3O4 particles were dispersed on the SnS2 sheets and these sheets built the flower-shaped structure. A microcalorimeter was employed to study the Ni-doped Fe3O4 formation processes with the SnS2. The experimental results indicated that the Ni-doped Fe3O4 formation mechanism is similar with and without the SnS2. Different endothermal processes demonstrated that the interaction between the cations (Fe3+, Fe2+ and Ni2+) and S2− induced various morphologies of the Ni-doped Fe3O4. Cluster-shaped Ni-doped Fe3O4 was synthesized without SnS2. The composite exhibited more excellent Fenton catalytic activity than the Ni-doped Fe3O4, SnS2, and the mixture is composed of the Ni-doped Fe3O4 and SnS2 with the same composition as the composite for the degradation of rhodamine B (RhB). RhB could be removed about 95% in 120 min at natural pH of the RhB solution (6.64) without irradiation for the Ni-doped Fe3O4/SnS2 composite as the catalyst. The present SnS2 enhanced adsorption capacity for RhB and the dispersed nanosized particles of Ni-doped Fe3O4, and the interaction between cations (Fe3+ and Fe2+) and S2− enhanced the conversion from Fe3+ to Fe2+, which induced excellent catalytic activity of the composite.

A new model for the description of creep behaviour of aluminium-based composites reinforced with nanosized particles

A basic model developed to describe the creep response of fcc metals has been used to obtain a new constitutive equation valid for alloys and composites reinforced with a dispersion of nanosized particles. The new model gives an excellent description of the minimum strain rate dependence of applied stress and temperature, and gives reason for the reduced creep rate observed in these composites when compared with conventional alloys. The reason for the different behaviour is that the dislocation mean free path becomes equivalent to the distance between nanosized particles. The volume fraction and size of the nanosized particulate thus assumes a key-role in determining the creep response of these materials. In addition, the strengthening effect due to the interaction between particles and dislocation has been described by introducing a back stress, which is in general proportional to the Orowan stress and has the nature of a true threshold stress.

Formulation and Development of Stable Metaxalone Nanosuspension Using 32 Factorial Design

Nanosuspensions are the dispersions of nanosized particles in a suitable vehicle prepared using surfactants or solubilizers to aid in nanosize distribution. Nanosuspension is best suited for dosage form development of poorly soluble drugs. According to the biopharmaceutical classification system, drugs with poor solubility fall either in BCS class II or BCS class IV. BCS class II drugs show poor solubility and good permeability; hence their bioavailability problems can be overcome by improving their solubility. Metaxalone is one such BCS class II drug from an oxazolidin-2-one class of centrally acting muscle relaxant drugs, indicated for relief of discomforts associated with acute, painful musculoskeletal conditions. Therefore, in present investigation, nanosuspension of Metaxalone has been formulated as an attempt to improve solubility and hence the overall bioavailability of Metaxalone. Media milling technique has been employed for nanosuspension preparation. Surfactant concentration (Poloxamer 407) and stirring time has been optimized using 32 factorial design to achieve desired particle size and saturation solubility responses as dependent variables. The particle size (PS) of 215.3 nm and maximum saturation solubility (SS) of 2805μg/ml was obtained as suggested solutions from factorial design which was further confirmed using check point analysis. Interaction of surfactant concentration and stirring time and their effect on particle size and saturation solubility was predicted using the contour plots and response surface plots. The optimized formulation showed around 99% metaxalone in vitro dissolution in comparison to around 46% dissolution from SKELAXIN® tablet at 30 minutes. These methodologies could therefore be employed successfully to improve solubility of any BCS class II drug and to predict effects and interactions of many experimental variables at the same time.

Thermophysical properties and thermal characteristics of phase change emulsion for thermal energy storage media

A great deal of attention has been paid to energy saving devices in place of conventional air-cooled and water-cooled devices. The thermal energy storage system that uses the latent heat of a PCM (phase change material) for air-conditioning or heating has recently become popular because it does not require high electric power and it saves energy. An emulsion dispersed nano-size particles of phase change material is produced. We discuss with the thermophysical properties, the stability of emulsion, and the heat transport characteristics as a thermal functional fluid. The testing emulsion, which has nano-size particles as the discrete phase, is produced with a d-phase emulsification method. The diameter of discrete phase in the emulsion is measured for evaluation of the long-term stability of emulsion. In addition, the DSC (differential scanning calorimetry) curve of emulsion is determined. Thermophysical properties such as viscosity and thermal conductivity of emulsions were studied in this work, and was compared with that of the base fluid. The results reveal that the emulsion with the d-phase emulsification method has the superior stability. From the differential thermal analysis, the DSC curve of present emulsion indicates a discontinuous change at the phase change temperature of phase change material due to its latent heat.

Grains versus subgrains: How growth kinetics is affected by the presence of nanosized dispersoids

Abstract In this study, a Monte Carlo (MC) simulation framework is developed to predict and analyze subgrain growth in Al–4.5Zn–1Mg alloy influenced by dispersion of nanosized particles. The simulation is performed at a definite temperature and certain volume fraction of dispersoids. In order to convert Monte Carlo simulation time to real time, the activation energy and pre-exponential factor for determining the coefficient of diffusion of high angle grain boundaries are utilized. It was found that the outputs are not compatible with experimental results. Therefore, grain boundary diffusion coefficient ( D GB ) is best-fit into experimental results to improve the precision of the simulation and temperature dependent values for D GB are estimated. Kinetics of the subgrain growth in the presence of and without nanosized dispersoids is investigated using power law approach and values of growth exponent are predicted to be 2.8 and 2.2, respectively. The growth exponent is a constant in subgrain growth power law with a direct relation to the rate of subgrain growth. This reduction in growth rate exponent indicates the significance of the presence of second phase particles on diminishing subgrain growth rate.

Enhancement of electrorheological effect by particle-fluid interaction

The influence of interactions between particle surface and host fluids in electrorheological suspensions is explored. It is observed that dispersions of nanosized particles of titania in octanoid acid exhibit an anomalously large electrorheologic effect when compared with a similar dispersion of micrometric particles or with a more conventional colloidal suspension of silica in silicone oil. The effect is interpreted as originated by the formation of a thin layer of octanoid acid molecules with the surface of the titania solid particle. The experimental data are fitted with the outcomes of a modified version of conductive models existing in the literature. It is suggested that anomalous large electrorheological effect is mainly originated by the increasing of the effective radius of the nanometric particles, which results in an increasing of the effective volume fraction of the dispersed phase. It is also shown that the deformation of the soft shell around the solid particles, induced by Coulombic force, plays a not negligible role. Some hints for tailoring electrorheologic fluids suitable for different applications are proposed.

Nanoparticle Aerosols: Boon or Bane for Breathing?

Nanoparticle aerosols represent an emerging area of nanobiotechnology and nanotoxicology. The dispersion of nanosized particles within aerosol droplets have different effects on biological systems depending on the nature of the nanoparticle aerosol. Degradable, drug-loaded nanoparticle aerosols can directly deliver actives in the lungs in a noninvasive and safe manner for treatment of respiratory diseases. However, many environmental nanoparticle aerosols of fine suspended matter act as pollutants and increase the risks of respiratory problems.

Effect of Diamond Nanolubricant on R134a Pool Boiling Heat Transfer

This paper quantifies the influence of diamond nanoparticles on the pool boiling performance of R134a/polyolester mixtures on a roughened, horizontal, and flat surface. Nanofluids are liquids that contain dispersed nanosize particles. A lubricant based nanofluid (nanolubricant) was made by suspending 10 nm diameter diamond particles in a synthetic ester to roughly a 2.6% volume fraction. For the 0.5% nanolubricant mass fraction, the nanoparticles caused a heat transfer enhancement relative to the heat transfer of pure R134a/polyolester (99.5/0.5) up to 129%. A similar enhancement was observed for the R134a/nanolubricant (99/1) mixture, which had a heat flux that was on average 91% larger than that of the R134a/polyolester (99/1) mixture. Further increase in the nanolubricant mass fraction to 2% resulted in boiling heat transfer degradation of approximately 19% for the best performing tests. It was speculated that the poor quality of the nanolubricant suspension caused the performance of the (99.5/0.5), and the (98/2) nanolubricant mixtures to decay over time to, on average, 36% and 76% of the of pure R134a/polyolester performance, respectively. Thermal conductivity and viscosity measurements and a refrigerant\lubricant mixture pool-boiling model were used to suggest that increases in thermal conductivity and lubricant viscosity are mainly responsible for the heat transfer enhancement due to nanoparticles. Particle size measurements were used to suggest that particle agglomeration induced a lack of performance repeatability for the (99.5/0.5) and the (98/2) mixtures. From the results of the present study, it is speculated that if a good dispersion of nanoparticles in the lubricant is not obtained, then the agglomerated nanoparticles will not provide interaction with bubbles, which is favorable for heat transfer. Further research with nanolubricants and refrigerants are required to establish a fundamental understanding of the mechanisms that control nanofluid heat transfer.

Effect of particle size in Ni screen printing paste of incompatible polymer binders

Dispersion of nano-sized particles at high solid content has attracted attention in many industrial applications such as printed electronic products. However, the material design and processing heavily depends on experience with little quantitative measure. For fabrication of thinner dielectric layers, Ni size is getting smaller when used as an inner electrode in multilayer chip capacitor (MLCC). In the present study, we investigate the rheological properties and printing performance of the pastes with two different sizes of Ni particles in the same incompatible binder mixtures of ethyl cellulose (EC) and polyvinyl butyral (PVB). The difference in particle size causes different microstructural heterogeneity and highly nonlinear rheological properties upon the external flow field. The printing pattern and the surface profile are also analyzed by confocal images after screen printing. For smaller particle size of Ni, the more heterogeneous microstructure is observed with increasing PVB content, which is evidenced by the screen printing images as well as its rheological behavior. We explain the difference of spatial heterogeneity in terms of different interactions between particle–particle and particle–polymer. This work is believed to contribute to better design of inner electrodes and processing in MLCC manufacturing.

Elastomer–Carbon Nanotube Composites as Prospective Multifunctional Sensing Materials

Carbon nanotubes offer attractive possibilities for developing new sensors because of superior mechanical and electrical properties. So far most studies relate to the mechanical deformation and to the change of nano-scale electrical properties. We present an attempt to utilize multi wall carbon nanotubes for developing a new flexible composite for macro-scale pressure sensors. Two simultaneously existing effects--mechanical strain sensing and organic solvent vapour sensing--were found and investigated in polyisoprene-multi wall carbon nanotube composites. Elastomer composites containing dispersed nano-size particles, for example, polyisoprene-multi wall carbon nanotube composites were prepared by treatment of the composite matrix with chloroform providing an increase of mobility and better dispersion of the nano-particles within the matrix. Multi wall carbon nanotubes with a small amount of solvent were carefully grinded in a china pestle before adding the polyisoprene matrix. Both the polyisoprene matrix solution and concentrated multi wall carbon nanotube solution in chloroform were blended at room temperature for certain time in a mixer which contained small glass spheres. The product was dried and vulcanized under 3 x 10(6) Pa pressure at 160 degrees C for 20 min. Polyisoprene-multi wall carbon nanotube composites show attractive pressure sensing and gas sensing properties. The maximum sensitivity has been achieved in the region slightly above percolation threshold of the composite. The mechanism of sensing effect is based on changes in tunneling currents due to the strain caused by mechanical forces as well as swelling of composite matrix.

Influence of Ultrasonic Processing on Nano-Sized Particle Dispersion in Magnesium Matrix Nanocomposites

The parameters of ultrasonic processing have important effects on the distribution and dispersion of nano-sized particles in magnesium matrix nanocomposite (MMNC) fabrication. In order to learn more about the above effects and produce guidelines for the fabrication of MMNC, the acoustic cavitation and streaming effects produced by high intensive ultrasonic method with different frequency and power were experimented with water, glycerol, soybean oil and oil-water mixture respectively. The results showed that the acoustic cavitation and streaming were influenced by ultrasonic frequency and power as well as the depth of waveguide dipped into melts. The ultrasonic processing of the MMNC melts with 20kHz and 1.4kW greatly improved the dispersion and distribution of nano-sized reinforcement particles in MMNC.

Effect of CuO Nanoparticle Concentration on R134a/Lubricant Pool-Boiling Heat Transfer

This paper quantifies the influence of copper (II) oxide (CuO) nanoparticle concentration on the boiling performance of R134a/polyolester mixtures on a roughened horizontal flat surface. Nanofluids are liquids that contain dispersed nanosize particles. Two lubricant-based nanofluids (nanolubricants) were made with a synthetic polyolester and 30 nm diameter CuO particles to 1% and 0.5% volume fractions, respectively. As reported in a previous study for the 1% volume fraction nanolubricant, a 0.5% nanolubricant mass fraction with R134a resulted in a heat transfer enhancement relative to the heat transfer of pure R134a/polyolester (99.5/0.5) between 50% and 275%. The same study had shown that increasing the mass fraction of the 1% volume fraction nanolubricant resulted in smaller, but significant, boiling heat transfer enhancements. The present study shows that the use of a nanolubricant with half the concentration of CuO nanoparticles (0.5% by volume) resulted in either no improvement or boiling heat transfer degradations with respect to the R134a/polyolester mixtures without nanoparticles. Consequently, significant refrigerant/lubricant boiling heat transfer enhancements are possible with nanoparticles; however, the nanoparticle concentration is an important determining factor. Further research with nanolubricants and refrigerants is required to establish a fundamental understanding of the mechanisms that control nanofluid heat transfer.

Toughening mechanism and frontal process zone size of ceramics

In order to improve the fracture toughness of intrinsically brittle ceramics, it is essential to expand the frontal process zone (FPZ) ahead of a crack tip. Nanocomposites proposed by Niihara utilize dislocations generated around the dispersed nano-sized particles in matrix and expand the FPZ. In this paper, we discussed the toughening mechanism of ceramics using our experimental data on alumina-based nanocomposites, focusing on fundamental theories of fracture mechanics, such as Griffith-Irwin energy equilibrium and the local fracture criterion. We estimated the FPZ size using an indirect technique proposed recently, and clarified that the FPZ expansion toughening mechanism is achieved in nanocomposites by means of dislocation activities. The results revealed that ceramics with a larger FPZ size had higher fracture toughness and properly annealed nanocomposites had the largest FPZ size. The FPZ expansion mechanism in nanocomposites was considered that sessile dislocations generated around a crack tip in matrix, served as nano-crack nuclei, and hence expanded the FPZ size. It is clarified that the critical local stress is the strength of an infinite plate with no crack, and must be the true strength with no size effect. The fracture toughness, the critical local stress, and the FPZ size are the mutually dependent material properties, and the relation among them is clarified.

Synthesis of YAG powders by the co-precipitation method

YAG (Y 3Al 5O 12) powders have been prepared by co-precipitation technique in which NH 4HCO 3 is used as a precipitant and Y 2O 3, A1((NO 3) 3·9H 2O—as raw materials. Two kinds of surfactant are added into the solution, i.e. Polyethylene glycol (PEG10000) as steric stabilizer and (NH 4) 2SO 4 as electrical stabilizer. The composition of YAG precursor, the phase formation process of YAG and the properties of the powders were investigated by means of differential scanning calorimetry and thermogravimetry analysis (DSC–TG), X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FT-IR) and Scanning electron microscopy (SEM). The results of XRD show that phase YAG crystallite can be obtained as precursors when heated at 900 °C for 2 h. The powders loosely dispersed with narrow size distribution and spherical shapes could be observed by SEM. It has been found that the presence of PEG and (NH 4) 2SO 4 is beneficial for the dispersion of the resulting YAG powder. In the presence of surfactants, the synthesized product consists of highly dispersed nano-sized particles.

Electrophoresis system for high temperature mobility measurements of nanosize particles

The electrophoretic mobility, which reflects the zeta potential of a solid material, is an important experimental quantity providing information about the electrical double layer at the solid/liquid interface. A new high temperature electrophoresis cell was developed suitable for electrophoretic mobility measurements of dispersed nanosize particles up to 150 degrees C and 40 bars. Amorphous silica (SiO(2)) particle size standards were used to test the particle size detection limit of the new instrument at 25, 100, and 150 degrees C and several pH values. The microscopic detection of the particles was enabled by dark-field illumination, which allowed extending the previously available capabilities and provided higher accuracy of the electrophoretic mobility data. The electrophoretic mobility measurements for SiO(2) at temperatures above 100 degrees C were reported for the first time and indicated a gradual increase in particle electrophoretic response with increasing temperature. The obtained data indicated negatively charged SiO(2) surface throughout the pH and temperature ranges studied.

Characterization of MMoO4 (M = Ba, Sr and Ca) with different morphologies prepared using a cyclic microwave radiation

Scheelite molybdates (MMoO4, M=Ba, Sr and Ca) were successfully prepared by the reactions of M(NO3)2·2H2O and Na2MoO4·2H2O in propylene glycol and NaOH using a microwave radiation. The phases were detected using XRD and SAED. TEM analysis revealed the presence of micro-sized bi-pyramids with a square base, nano-sized particles in clusters, and dispersed nano-sized particles for BaMoO4, SrMoO4 and CaMoO4, respectively. Diffraction patterns of the bi-pyramids were simulated, and are in accord with the experimental results. Raman and FTIR spectra provide the evidence of scheelite structure with Mo–O stretching vibration in MoO42− tetrahedrons at 742–901 cm−1.

Polyisoprene—multi-wall carbon nanotube composites for sensing strain

Carbon nanotubes offer attractive possibilities for developing new sensors because of superior mechanical and electrical properties. So far most studies relate the mechanical deformation to the change of nano-scale electrical properties.We present an attempt to use the multi-wall carbon nanotubes (MWCNT) to develop a new material for sensing macro-scale strain. Polymer composites containing dispersed nano-size particles, for example, polyisoprene - multi-wall carbon nanotube composites (PMCNTC) were prepared by treatment of the composite matrix with chloroform providing an increase of mobility and better dispersion of the nano-particles within the matrix. MWCNT with a small amount of solvent was carefully ground in a china pestle before adding to the polyisoprene matrix. Both the polyisoprene matrix solution and concentrated MWCNT product were mixed in a mixer with small glass beads at room temperature for 15 min. The product was dried at 40 °C for over 12 h and vulcanized under high pressure at 160 °C for 20 min. PMCNTC shows attractive tensile and compressive strain sensing properties. A mechanism of sensing effects is being investigated.

Surface Modified Boehmite Aluminas: A Versatile Approach to Nano-scale Particle Dispersion and Nanocomposites

AbstractCertain forms of monohydrate aluminum oxide, commonly known as boehmite or pseudoboehmite alumina, are known to disperse in water at low pH to nano-scale dimensions. The upsurge of interest in nano-scale structures has prompted our study of the surface modification of nano-scale boehmite aluminas with organic acids in order to achieve dispersion of these materials in non-aqueous systems and alkaline aqueous systems.This paper discusses the variety of modifiers used to achieve compatibilization and dispersion of nano-sized particles of these boehmite aluminas in aqueous and organic matrices. Organic modification of a variety of crystallite sizes (5-60 nm) and shapes (plates, needles, blocks) has been achieved, including materials of high aspect ratio. We describe the properties of these dispersions, including primary particle size, dispersed particle size, and surface charge. Finally, we present physical property data of polymer nanocomposites prepared from these materials. These materials are based on a commercial process which has been in operation for over 40 years and which has global production capacities of 70,000 tons per annum.