Particle Size Agglomeration Research Articles

Detection of agglomeration and gradual particle size changes in circulating fluidized beds

The monitoring of fluidized bed processes is valuable for the optimization of operational efficiency and avoiding unscheduled shut-downs in industrial practice. We here focus on two important applications for the industrially widely applied circulating fluidized beds (CFBs): the detection of small, gradual changes in particle size and the early detection of agglomeration. Based on high-frequency (200 Hz) pressure fluctuation measurements we have applied the attractor comparison method in different CFBs to investigate its suitability as a monitoring tool for the two proposed applications. Attractor comparison has shown to be generally sensitive to small, gradual particle size changes in a lab-scale CFB. The sensitivity normally depends on the measurement location (downcomer, return system, riser) and is often larger in the downcomer section. From the results, detection limits for the particle size have been identified. In an industrial installation the sensitivity and applicability of the method for measurements in the riser has been confirmed. With the help of model agglomerates it has been shown that attractor comparison can also detect the presence of small shares of agglomerates on lab-scale; here, filtering the pressure fluctuation data before the analysis has shown to improve the method. The suitability of the method for agglomeration detection has been confirmed with an agglomeration incident in a hot lab-scale facility; in this case the approaching defluidization has been detected with an early time of about 30 min based on measurements in horizontal return-leg and lower riser.

Analysis of agglomerate dispersion mechanisms of multiwalled carbon nanotubes during melt mixing in polycarbonate

Dispersion of primary nanotube agglomerates in polymer melts is one of the difficult tasks when applying melt mixing for nanocomposite preparation. Hence, there is a need for a better understanding of the ongoing processes. Filler agglomerates generally undergo dispersion by rupture and erosion mechanisms, which usually occur simultaneously. To analyse these mechanisms and their corresponding dispersion kinetics 1 wt% multiwalled carbon nanotubes (MWNT) were incorporated into polycarbonate using a microcompounder. Different mixing speeds at constant melt temperature were applied thereby changing the applied stress. The states of MWNT agglomerate dispersion at different mixing times were assessed by quantifying the agglomerate area ratio and particle size distribution using image analysis of optical transmission micrographs. A model is proposed to estimate the fractions of rupture and erosion mechanisms during agglomerate dispersion. At low mixing speeds, the dispersion was found to be governed by both mechanisms, whereas rupture dominance increases with increasing mixing speed. Further, the relationship between electrical resistivity and dispersion was studied indicating a critical behaviour. A dependency on the amount of dispersed nanotubes was found only in a certain range of state of dispersion.

Solution combustion synthesis and sintering behavior of porous MgAl2O4 powders

Porous MgAl2O4 powders were synthesized with a solution combustion route using a mixture of glycine and urea with the glycine/urea molar ratio of 2/9 as fuel. For the comparison purpose, denser powders were also combustion synthesized using urea as fuel. The porous/denser structure, characteristics (e.g. crystallite size and specific surface areas) and sinterability of the two powders were investigated in detail. Experimental results disclosed that the as-prepared porous powders exhibited a much lower degree of agglomeration, smaller average agglomerate particle size and larger surface areas and thus far higher sintering behavior than the denser powders.

A magnetic poly(dimethylesiloxane) composite membrane incorporated with uniformly dispersed, coated iron oxide nanoparticles

We report a new magnetic polymer membrane for MEMS application. The polymeric magnetic composite has coated iron oxide nanoparticles incorporated in a polydimethylsiloxane (PDMS) matrix. Existing magnetic polymeric materials have particle agglomeration problems, which result in rough surfaces and uneven mechanical and optical properties. We show that the use of iron oxide nanoparticles (10 nm in diameter) with fatty acid and hydrophobic coatings inhibits aggregation of particles in the PDMS polymer matrix. Agglomerated particle sizes in thin-film PDMS composites incorporated with uncoated and coated particles are 51 ± 24 µm and 1.6 ± 0.25 µm, respectively. The PDMS composites exhibit saturation magnetization of 22.8 to 23.94 emu g−1. Stress–strain curves of the composites are characterized by tensile tests. Free-standing magnetic PDMS membranes are fabricated in different sizes from 4 mm to 7 mm in diameter and with the thickness of 35.5 ± 1.5 µm. The membrane of 7 mm diameter achieves deflection of 625 µm in a 0.417 T magnetic field. The magnetic PDMS membranes may be used in micro-pumps and lab-on-a-chip applications.

Characterization of Carbon Based Nanoparticles Dispersion in Aqueous Solution Using Dynamic Light Scattering Technique

AbstractCharacterization of physicochemical properties of nanoparticles in aqueous environment prior to conducting hazard studies is strongly recommended by many scientific organizations. In this work we studied the dissolution behaviour and physicochemical properties of carbon based nanoparticles in aqueous solution. The time evolution of the size distribution and the state of dispersion of carbon black and carbon nanotubes in physiological solution have been investigated by means of Dynamic Light Scattering technique. The influence of mechanical agitation such as sonication and stirring on the agglomeration state and particle size distribution has been investigated. However, such processes seem to have little or no effect as far as agglomeration is concerned.

Airway Exposure to Silica-Coated TiO2 Nanoparticles Induces Pulmonary Neutrophilia in Mice

The importance of nanotechnologies and engineered nanoparticles has grown rapidly. It is therefore crucial to acquire up-to-date knowledge of the possible harmful health effects of these materials. Since a multitude of different types of nanosized titanium dioxide (TiO(2)) particles are used in industry, we explored their inflammatory potential using mouse and cell models. BALB/c mice were exposed by inhalation for 2 h, 2 h on 4 consecutive days, or 2 h on 4 consecutive days for 4 weeks to several commercial TiO(2) nanoparticles, SiO(2) nanoparticles, and to nanosized TiO(2) generated in a gas-to-particle conversion process at 10 mg/m(3). In addition, effects of in vitro exposure of human macrophages and fibroblasts (MRC-9) to the different particles were assessed. SiO(2)-coated rutile TiO(2) nanoparticles (cnTiO(2)) was the only sample tested that elicited clear-cut pulmonary neutrophilia. Uncoated rutile and anatase as well as nanosized SiO(2) did not induce significant inflammation. Pulmonary neutrophilia was accompanied by increased expression of tumor necrosis factor-alpha (TNF-alpha) and neutrophil-attracting chemokine CXCL1 in the lung tissue. TiO(2) particles accumulated almost exclusively in the alveolar macrophages. In vitro exposure of murine and human macrophages to cnTiO(2) elicited significant induction of TNF-alpha and neutrophil-attracting chemokines. Stimulation of human fibroblasts with cnTiO(2)-activated macrophage supernatant induced high expression of neutrophil-attracting chemokines, CXCL1 and CXCL8. Interestingly, the level of lung inflammation could not be explained by the surface area of the particles, their primary or agglomerate particle size, or radical formation capacity but is rather explained by the surface coating. Our findings emphasize that it is vitally important to take into account in the risk assessment that alterations of nanoparticles, e.g., by surface coating, may drastically change their toxicological potential.

Sonochemical coating of magnetite nanoparticles with silica

Magnetite nanoparticles were coated with silica through the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) under ultrasonic irradiation. The ultrasonic irradiation was used to prevent the agglomeration of the magnetite particles and accelerate the hydrolysis and condensation of TEOS. TEM, DLS, XRF, VSM, TG and sedimentation test were used to characterize the silica-coated magnetite particles. The dispersibility of silica-coated magnetite particles in aqueous solution was improved significantly and the agglomerate particle size was decreased to 110 nm. It was found that the agglomerate particle size of silica-coated magnetite particles was mainly decided by the coating temperature and the pH value in the silica-coating process. The weight ratio of silica in silica-coated magnetite particles was mainly decided by the pH value in the silica-coating process. The dispersibility of silica-coated magnetite particles was mainly decided by the agglomerate particle size of the suspension. The oxidation of magnetite particles in air was limited through the coated silica. The magnetism of silica-coated magnetite particles decreased slightly after silica-coating.

SrAl12O19:Pr3+nanodisks and nanoplates: New processing technique and photon cascade emission

High-quality SrAl12O19:Pr3+nanodisks and nanoplates were fabricated via a new processing technique based on a modified polymer steric entrapment method. Serious agglomeration and large particle size distribution of final products, which usually occurred in the conventional method, were eliminated completely. The effects of new synthetic processes on the morphology, crystallization, and yield of products and the relevant mechanisms were discussed. As far as we know, SrAl12O19:Pr3+nanodisks with mean diameter ∼60 nm and thickness between 5 and 10 nm were successfully synthesized for the first time by this low-cost technique. The new synthetic method may provide a general route to synthesize other refractory mixed-oxide nanocrystals. Photon cascade emission involving transitions1S0–1I6followed by3P0–3H4in SrAl12O19:1% Pr3+nanodisks was investigated. Size-effect-induced blue shift of the 4f5dstates of Pr3+was observed in SrAl12O19:1% Pr3+nanodisks, in which the quantum efficiency was preserved, as in the bulk counterparts.

Comparing fate and effects of three particles of different surface properties: Nano-TiO2, pigmentary TiO2 and quartz

The fate of nano-TiO(2) particles in the body was investigated after inhalation exposure or intravenous (i.v.) injection, and compared with pigmentary TiO(2) and quartz. For this purpose, a 5-day inhalation study (6h/day, head/nose exposure) was carried out in male Wistar rats using nano-TiO(2) (100mg/m(3)), pigmentary TiO(2) (250mg/m(3)) and quartz dust DQ 12 (100mg/m(3)). Deposition in the lung and tissue distribution was evaluated, and histological examination of the respiratory tract was performed upon termination of exposure, and 2 weeks after the last exposure. Broncho-alveolar lavage (BAL) was carried out 3 and 14 days after the last exposure. Rats were also injected with a single intravenous dose of a suspension of TiO(2) in serum (5mg/kg body weight), and tissue content of TiO(2) was determined 1, 14 and 28 days later. The majority of the inhaled nano-TiO(2) was deposited in the lung. Translocation to the mediastinal lymph nodes was also noted, although to smaller amounts than following inhalation of pigmentary TiO(2), but much higher amounts than after exposure to quartz. Systemically available nano-TiO(2), as simulated by the i.v. injection, was trapped mainly in the liver and spleen. The (agglomerate) particle size of lung deposited nano-TiO(2) was virtually the same as in the test atmosphere. Changes in BAL fluid composition and histological examination indicated mild neutrophilic inflammation and activation of macrophages in the lung. The effects were reversible for nano- and pigmentary TiO(2), but progressive for quartz. The effects observed after 5-day inhalation exposure to nano-TiO(2) were qualitatively similar to those reported in sub-chronic studies.

Characterization of Visible Light Response N-F Codoped TiO 2 Photocatalyst Prepared by Acid Catalyzed Hydrolysis

N-F codoped TiO 2 (TONF) photocatalysts were prepared using acid catalyzed hydrolysis method from mixed aqueous solution of TiCl 4 and NH 4F. The photocatalytic activity of the TONF was evaluated through the degradation of phenol under both visible and UV light irradiation. X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), scanning electron microscope (SEM), and N 2 adsorption isotherm were used to characterize the obtained powders. The results showed that N-F codoped TiO 2 exhibited significant improvement of visible light catalytic activity. N-F codoping could improve dispersion of TiO 2, inhibit particle size agglomeration, and retard phase transformation. Doped N could extend the light response of TiO 2 to visible light region. In addition, narrower band gap formed by F-doping was beneficial to the high visible light photocatalytic activity.

Effect of grain size on the sinterability of yttria nanopowders synthesized by carbonate-precipitation process

Yttria nanopowders have been synthesized by carbonate precipitation process. The thermal decomposition behavior of the carbonate precipitate, crystal phase, microstructure and sinterability of the powders were examined. The precipitate precursor was decomposed completely at 700 °C and then crystallized well into cubic yttria phase. Our results suggested that the most favorable calcination temperature was 1100 °C for obtaining good dispersion, high-reactive yttria nanopowders. The nanopowders were almost spherical and had weak agglomeration and narrow particle size distribution with a mean grain size of about 80 nm. Using these yttria nanopowders, nearly full dense yttria ceramic with ∼99.2% of theoretical density was obtained at 1600 °C for 2 h without any additives.

The effects of temperature, volume fraction and vibration time on the thermo-physicalproperties of a carbon nanotube suspension (carbon nanofluid)

In this investigation, nanofluids of carbon nanotubes are prepared and the thermalconductivity and volumetric heat capacity of these fluids are measured using a thin layertechnique as a function of time of ultrasonication, temperature, and volume fraction. It hasbeen observed that after using the ultrasonic disrupter, the size of agglomeratedparticles and number of primary particles in a particle cluster was significantlydecreased and that the thermal conductivity increased with elapsed ultrasonicationtime. The clustering of carbon nanotubes was also confirmed microscopically.The strong dependence of the effective thermal conductivity on temperature and volumefraction of nanofluids was attributed to Brownian motion and the interparticle potential,which influences the particle motion.The effect of temperature will become much more evident with an increase in the volumefraction and the agglomeration of the nanoparticles, as observed experimentally.The data obtained from this work have been compared with those of other studies andalso with mathematical models at present proven for suspensions. Using a 2.5%volumetric concentration of carbon nanotubes resulted in a 20% increase in thethermal conductivity of the base fluid (ethylene glycol).The volumetric heat capacityalso showed a pronounced increase with respect to that of the pure base fluid.

Ionic conductivity and electrical relaxation of nanocrystalline scandia-stabilized c-zirconia using complex impedance analysis

A solid solution of 8 mol% of scandia-stabilized cubic-zirconia (8ScSZ) has been prepared by co-precipitation technique. The synthesized powder has an average crystallite size ∼40 nm, surface area of 8.49 m 2/g, and agglomerated particle size of 150 nm. The activation energy of 8ScSZ has been calculated from impedance loss spectra; electrical modulus spectra are in the range of 0.90–1.30 eV. The frequency and temperature-dependent conductivities and impedance were measured in range of 50 Hz–1 MHz and 300–900 K, respectively. Complex impedance spectra, complex modulus formalism and complex conductivity spectra have been carefully analyzed in order to separate the grain, grain boundary and electrode–electrolyte effects. Analysis of ac impedance data using complex impedance indicates a typical negative temperature coefficient of resistance (NTCR) behavior of the materials. The intrinsic conductivity is mainly due to hopping of mobile ions among the available localized site. Relaxation time obtained from complex conductivity spectra are matched well with the impedance loss and modulus loss spectra. Impedance analysis suggests the presence of temperature-dependent electrical relaxation process in the material.

Anomalous Particle Size Shift During Post-milling Storage

To investigate the anomalous phenomenon of particle size shift during post-milling storage. Crystallised and ball-milled adipic acid were stored under different humidity conditions. Analyses were carried out to characterise changes in particle size distribution (laser diffraction), morphology (SEM), bulk flow properties (annular shear tester), surface adhesion forces (AFM) and crystallinity (PXRD and DVS). It was observed that the particle size distribution of milled adipic acid can shift to finer fractions, remain unchanged, or even shift to coarser fractions depending on storage conditions. SEM analysis showed that milled adipic acid is composed of agglomerates, which can undergo de-aggregation or further agglomeration via re-crystallisation. Empirical analysis ruled out the effects of electrostatic charges on the particle size shift. In addition, an improvement in powder flow in terms of bulk tensile strength was seen for milled adipic acid stored under high relative humidity but not under low humidity. Storage of milled adipic acid below the critical relative humidity led to localised disintegration from the agglomerate surface and particle size reduction, which was not influenced by moisture sorption or loss. This evidence supports that "stress relaxation" mechanism behind particle breakage of post-milled particles. Appropriate storage conditions are important in maintaining the stability of milled powders.

A NOVEL CHEMICAL ROUTE FOR PREPARATION OF NANOCRYSTALLINE α-Al2O3 POWDER

A novel chemical method for preparing nanocrystalline α-Al2O3 powder has been developed in this study. The aluminum hydroxide precipitates were initially formed in a three-dimensional space network micro-area of the wet gel, and then the precursor was obtained after the wet gel was dried. The nanocrystalline α-Al2O3 powders were obtained after the precursor was calcined at 1100°C. The precursor and as-calcined powders were characterized using TGA-DTA, XRD, and TEM. The α-Al2O3 powders calcined at 1100°C for 2 h are of narrow distribution, little agglomeration, and small particle size of ∼51 nm. The reason for the synthesis of the high-quality powders is explained.

Synthesis of BaTiO 3 powders by a ball milling-assisted hydrothermal reaction

The effects of ball milling during the hydrothermal BaTiO 3 synthesis from nano- and sub-micron sized TiO 2 powders were studied. The synthesized BaTiO 3 powders were characterized by X-ray diffraction (XRD), a laser light scattering particle size distribution analyzer, and field emission scanning electron microscopy (FE-SEM). The XRD patterns showed that BaTiO 3 powders could be synthesized using the ball milling system at 100 °C and for 5 h with little contamination. The BaTiO 3 powders observed by FE-SEM were agglomerated. The agglomerated particle sizes of BaTiO 3 prepared from nano- and sub-miron sized TiO 2 particles were 152 ± 42 and 148 ± 21 nm, respectively. Furthermore, it was found that the rate constant of BaTiO 3 powder prepared from Ba(OH) 2 and sub-micrometer sized TiO 2 powder with the ball milling process was twice as large compared to a hydrothermal route without ball milling.

Manufacture Process of Light Calcium Carbonate from Limestone

This process and parameters of fabricating light calcium carbonate from limestone were discussed in the paper. Raw limestone in experiment comes from Luquan city, Hebei province. The results of chemistry and XRD analysis indicate that ingredient of this limestone is mainly calcium carbonate, dolomite, silicon dioxide, which takes 83.81%, 11.03% and 1.67% separately, and a few of other impurities. The process includes calcinations, assimilation, carbonation, drying and others. It was ascertainable that the time of calcinations exceeded 5 hours at 850~ 950 and loss of calcinations was 42%. The time of assimilation was around 25 minutes at 70~90The time of carbonation was about 30 minutes at 50~90, and the airflow was about 160L/min and PH of latex after carbonation was 7.2~7.4. The light calcium carbonate product was obtained in experiment, whose fine sphere size was about 10 nanometer, with the agglomeration particle size 2~3μm. The degree of white improved from 42 to 76. As a result, the comprehensive properties of the produce were improved consumedly.

A new design strategy for dispersion stabilization of Ni particles based on the surface acid and base properties of Ni particles

A dispersion technology for Ni particles suspended in a non-aqueous medium based on the quantitative evaluation of surface acid–base properties of Ni particles is described. A quantitative analysis of surface acid–base properties of Ni particles was performed using non-aqueous titration. Dimethylamino ethanol and acetic acid were used as probe molecules to detect surface acid–base amounts of Ni particles. The dispersion system was designed on the basis of the amounts of surface acid–base sites on the Ni particle surface. Rheological behavior and agglomerate particle size data demonstrate that the dispersion stability of the designed Ni suspension is markedly improved, as expected. Therefore, the design strategy to improve the dispersion stability of Ni particles was successful. This strategy is expected to be applicable to dispersion systems of other particles suspended in a non-aqueous medium.

Decolorization of organic dyes on Pilkington Activ™ photocatalytic glass

The air–solid photocatalytic degradation of organic dye films Acid Blue 9 (AB9) and Reactive Black 5 (RBk5) is studied on Pilkington Activ™ glass. The Activ™ glass comprises of a colorless TiO2 layer deposited on clear glass. The Activ™ glass is characterized using atomic force microscopy (AFM) and X-ray diffraction (XRD). Using AFM, the TiO2 average agglomerate particle size is 95nm, with an apparent TiO2 thickness of 12nm. The XRD results indicate the anatase phase of TiO2, with a calculated crystallite size of 18nm.Dyes AB9 and RBk5 are deposited in a liquid film and dried on the Activ™ glass to test for photodecolorization in air, using eight UVA blacklight-blue fluorescent lamps with an average UVA irradiance of 1.4mW/cm2. A novel horizontal coat method is used for dye deposition, minimizing the amount of solution used while forming a fairly uniform dye layer. About 35–75 monolayers of dye are placed on the Activ™ glass, with a covered area of 7–10cm2. Dye degradation is observed visually and via UV–vis spectroscopy.The kinetics of photodecolorization satisfactorily fit a two-step series reaction model, indicating that the dye degrades to a single colored intermediate compound before reaching its final colorless product(s). Each reaction step follows a simple irreversible first-order reaction rate form. The average k1 is 0.017 and 0.021min−1 for AB9 and RBk5, respectively, and the corresponding average k2 is 2.0×10−3 and 1.5×10−3min−1. Variable light intensity experiments reveal a p=0.44±0.02 exponent dependency of initial decolorization rate on the UV irradiance. Solar experiments are conducted outdoors with an average temperature, water vapor density, and UVA irradiance of 30.8°C, 6.4gwater/m3 dry air, and 1.5mW/cm2, respectively. For AB9, the average solar k1 is 0.041min−1 and k2 is 5.7×10−3min−1.

Effect of Nafion® ionomer aggregation on the structure of the cathode catalyst layer of a DMFC

The effect of Nafion® ionomer aggregation in solution on the structure of the cathode catalyst layer of a direct methanol fuel cell (DMFC) was investigated by dynamic light scattering (DLS), laser particle sizer, electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). The results showed that large aggregation particles were suppressed by the addition of NaOH to aqueous solutions of Nafion®, which led to a smaller agglomerate particle size distribution in the catalyst ink. The cathode catalyst layer made from the catalyst ink with NaOH addition showed a more uniform distribution of sulfur and Pt elements, a higher electrochemical active surface area (48% increase) and achieved a better performance in the DMFC than one made from the catalyst ink without NaOH addition.