Voltammetric potentials of polyaniline varying with electric percolation

The reduction of the emeraldine form of polyaniline film into leucoemeraldine, which corresponds to the conversion of an electric conductor into an insulator, shifted in the positive direction with increasing scan rate and film thickness. Similar dependence was found in the diffusion-controlled voltammograms of dispersed polyaniline latex particles with eight diameters ranging from 0.2 to 7.5 μm. The particles were synthesized by coating dispersed polystyrene latex with polyaniline. These variations were explained in terms of electric percolation of the conducting species to the electrode. The theoretical expression for the Nernst equation was derived on the assumption that the percolated and the un-percolated conducting species took inner potentials of the electrode and the solution phase, respectively. The conducting species does not participate in the determination of the equilibrium potential, though it participates in the Faradaic current. The cathodic peak potential shifted in the negative direction with an increase in particle size, solution viscosity, and film thickness, as predicted from the derived Nernst equation.     

Colloidal submicron-palladium particles stabilized with acetate

Palladium spherical particles 0.23 μm in diameter were synthesized by reducing palladium acetate with hydrazine in the presence of surfactant, with an aim of exhibiting both easy separation by filtration and easy dispersion for a catalyst. The particles in the suspension were sedimented slowly but not aggregated. The suspension showed voltammetric redox waves. The anodic wave was ascribed to the oxidation of Pd to Pd²⁺, whereas the cathodic one was to the reduction of the palladium acetate moiety to Pd. The current ratio of the anodic peak to the cathodic one 4:1, was close to the ratios by the partial chemical oxidation with permanganate and by the thermogravimetry, suggesting the composition of 80% palladium metal and 20% palladium acetate in the molar ratio. Heating the palladium particles at 300 °C yielded palladium metal. The decomposition proceeded to the first-order reaction with the activation energy of 40 kJ mol⁻¹. The particle catalyzed the reduction of methylene blue with hydrazine. The reaction rate was of the first-order with respect to methylene blue. The rate constant was proportional to the geometrical surface area of the palladium particle, suggesting a surface catalysis.     

A case study on suspended particles in a natural gas urban transmission and distribution network

Suspended particles in the natural gas transmission and distribution network of the city of Kerman, Iran were investigated. Particle concentration and size distribution were measured in different locations of the natural gas pipeline network. Particle samplings were carried out in two seasons: summer, when there is the lowest consumption, and winter, when there is the highest consumption of natural gas. Additional particle characterization was carried out by scanning electron microscopy coupled with energy dispersion X-ray (SEM/EDX) and X-ray diffraction(XRD) analyses. Particle concentration was found to be significantly higher in winter as compared to summer. The range of particle concentrations in summer was from 0.12 mg/Nm³ at the end of the pipeline to 4.7 mg/Nm³ at the network entrance, and from 0.30 mg/Nm³ to 22.1 mg/Nm³ in winter. Particle size distribution showed a higher frequency of smaller particles in winter than in summer. Larger particles were more likely to exist at the network entrance as compared to the exit. The average particle size ranged from 181 μm at the network end to 253 μm at the entrance in summer, and from 74 μm to 209 μm in winter. Particle characterization confirmed the presence of corrosion products in the suspended particles.     

Proton exchange membranes based on sulfonated crosslinked polystyrene micro particles dispersed in poly(dimethyl siloxane)

Proton exchange membranes of sulfonated crosslinked polystyrene (SXLPS) particles dispersed in crosslinked poly(dimethyl siloxane) matrix were investigated. Three different sizes of particles—25, 8 and 0.08 μm—were used at loadings from 0 to 50 wt% and the influence of these variables on the water and methanol uptake and proton conductivity were observed. With the reduction in particle size in the composite membrane, more water or methanol uptake was observed. Three different states of water were revealed in the composite membranes by differential scanning calorimetry (DSC). The number of bound water molecules per SO₃H group was 11-15 in membranes with 8- and 25-μm SXLPS. The ratio of bound to unbound water molecules was more than one in these membranes, whereas it was less than one in membranes with 0.08-μm SXLPS. The proton conductivities of the membranes increased with the increase in particle loading. At particle loadings above 35 wt%, membranes containing 8-μm SXLPS had higher conductivity compared to 25-μm SXLPS at room temperature. The conductivity of membranes containing 0.08-μm SXLPS was restricted to 10⁻³ S/cm because of the inherently low IEC of the particles. Increasing the temperature from 30 to 80 °C drastically enhanced the conductivity of the composite membranes compared to Nafion^® 112. At 80 °C, conductivities as high as 0.11±0.04 S/cm were observed for membranes containing more than 30 wt% of 25-μm SXLPS particles.     

Electropolymerized polyaniline coatings on aluminum alloy 3004 and their corrosion protection performance

Homogeneous and adherent polyaniline coatings were electrosynthesized on aluminum (Al) alloy 3004 (AA 3004) from an aqueous solution containing aniline and oxalic acid by using the galvanostatic polarization method. A higher applied current density in the polymerization stage proved to be the best condition to adopt for the synthesis of more compact and strongly adherent polyaniline coatings on Al. The corrosion performances of polyaniline coatings were investigated in 3.5% NaCl solution by the potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS).Potentiodynamic polarization and electrochemical impedance spectroscopy studies reveal that the polyaniline acts as a protective layer on Al against corrosion in 3.5% NaCl solution. The current corrosion decreases significantly from 6.55 μA cm⁻² for uncoated Al to 0.158 μA cm⁻² for polyaniline-coated Al. The corrosion rate of the polyaniline-coated Al is found to be 5.17 × 10⁻⁴ mm year⁻¹, which is ∼40 times lower than that observed for bare Al. The potential corrosion increases from −1.015 V versus SCE for uncoated Al to ∼−0.9 V versus SCE for polyaniline-coated Al electrodes. The positive shift of ∼0.11 V in potential corrosion indicates the protection of the Al surface by the polyaniline coatings.The synthesized coatings were characterized by UV-visible absorption spectrometry, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Optical absorption spectroscopy reveals the formation of the emeraldine form of polyaniline. The results of this study clearly ascertain that the polyaniline has outstanding potential to protect the AA 3004 alloy against corrosion in a chloride environment.     

Influence of catalytic particle size on the performance of fluidized-bed chemical vapor deposition synthesis of carbon nanotubes

In this paper, the impacts of catalytic particle size on the overall reactor performance for carbon nanotubes (CNTs) production using a fluidized-bed chemical vapor deposition (FBCVD) process have been studied. Six different particle size fractions (10-20 μm, 20-53 μm, 53-75 μm, 75-100 μm, 100-200 μm, and 200-300 μm) were selected. It was observed that the smaller the catalytic particle diameter, the greater the carbon deposition efficiency and the greater CNT synthesis selectivity. The 10-20 μm catalytic particles exhibited 30% higher carbon deposition efficiency than the 200-300 μm catalytic particles. The selectivity toward CNTs formation was also approximately 100%. These observations could be explained by the fact that when the diameter of the catalytic particle gets smaller, the breakthrough capacities during frontal diffusion will be bigger due to a shorter diffusion path length within the particle. Moreover, the fine particles ensured high interstitial velocity which subsequently enhances the heat and mass transfer, and consequently improves the CVD reaction.     

Platinum-modified titanium anodes for the electrolytic destruction of nitric acid

Three sets of electrodes, namely Pt electroplated Ti (PET) and diffusion annealed PET (DAPET) of plating thickness 3, 5, 7 and 10 μm and thermochemically glazed mixed oxide coated titanium anode (MOCTA-G) were evaluated for their performance, with a view to optimizing the current density conditions for maximum efficiency during the electrolytic destruction of nitric acid. In the acid killing by electro-reduction process, concentration of nitric acid in the high level waste (HLW) from the spent nuclear fuel reprocessing plant was brought down from about 4 to 0.5 M in order to reduce the amount of HLW by subsequent evaporation and to minimise the corrosion in waste tanks during storage of the concentrated waste solution. The electrochemical reduction of 4 and 8 M nitric acid to near neutral conditions was carried out with the above-said anodes and Ti cathode at various cathodic current densities ranging from 10 to 80 mA cm⁻². At current densities below 15 mA cm⁻² MOCTA-G electrode worked satisfactorily, whereas PET and DAPET electrodes could withstand and function well at much higher cathodic current densities (up to 80 mA cm⁻²). The life assessment of a 3 μm thick PET electrode at a cathodic current density of 60 mA cm⁻² in 8 M HNO₃ for a period of 110 h showed no failure. Phase identification of the plated electrodes was done by XRD measurements and their surface morphology was investigated by SEM.     

Numerical simulation of microparticles penetration and gas dynamics in an axi-symmetric supersonic nozzle for genetic vaccination

This paper describes two phase (solid particles/gas) flow in a supersonic nozzle that is part of a device for micromolecular vaccine/drug delivery. It accelerates micro solid particles to high speeds sufficient to penetrate the viable epidermis layer to achieve the pharmaceutical effect. Helium is used as the driving gas for the solid particles because of its high compressibility factor. A numerical parametric study was performed for gas pressures ranging between 3 and 6 MPa and gold particles of diameters 1.8 μm and 5 μm. The computed results show that uniform particle velocity was achieved at standoff distance of 2 exit diameters (D_e) downstream of the device exit with particles concentrated on the supersonic core jet. Increasing the helium pressure from 3 to 6 MPa caused an increase in the particle velocity of 24% for particles with a diameter of 1.8 μm and 7% for particles of diameter 5 μm at the standoff distance. Furthermore increased gas pressure has adverse effect on particles concentration. As the inlet pressure increases, the particles are concentrated more at the core of the nozzle. Semi-empirical particle penetration calculation confirms the numerical results that the 5 μm particles penetration distance is 45-135 μm and the 1.8 μm diameter penetration is 35-95 μm beneath the skin. Comparison of different geometries has been done in order to understand each section function and to gain optimum performance.     

Numerical optimization and experimental investigation of the aerodynamic performance of a three-stage gas-solid separator

The present research investigates and optimizes the aerodynamic performance of a newly designed compact size three stage mobile gas-solid separator. This separator is designed to collect solid particles with different characteristics at a minimum pressure drop. The minimum particle diameter to be completely collected is 1 μm at solid loading 20 g/m³. The first stage of the separator is a settling chamber which is designed to collect coarse particles (particles down to particle diameter 100 μm). The second stage is a cyclone separator where medium to fine particles (particles down to particle diameter 15 μm) are to be collected. Particles escaping the cyclone separator are collected in the third stage which is a bag filter.A separator conceptual aerodynamic design is first performed to obtain overall separator dimensions. CFD simulation is used in order to optimize the separator aerodynamic performance and reduce the separator size. The separator is then constructed and experimentally investigated. Comparison between CFD results at design point and measured separator total pressure drop shows good agreement.     

Formation of submicron poorly water-soluble drugs by rapid expansion of supercritical solution (RESS): Results for Naproxen

Numerous results of multitude investigations indicate that the particular properties of supercritical fluids can be conveniently exploited for the formation of submicron particles. In case of pharmaceutical substances the poor dissolution behaviour and therewith bioavailability of drugs in biological media can be enhanced dramatically by reduction of the particle size. In this paper we report the application of RESS (Rapid Expansion of Supercritical Solutions) and RESSAS (Rapid Expansion of Supercritical Solution into Aqueous Solution) to produce submicron particles of Naproxen, a poorly water-soluble drug. Thereby the effect of various process conditions on the obtained product properties was investigated. The experimental results show, that the RESS processing of Naproxen leads to particles in the range from 0.56 to 0.82 μm which is about 22 times smaller than the unprocessed powder. RESSAS experiments show, that stabilized Naproxen particles have an average diameter of 0.3 μm for drug concentrations up to 1 g/dm³ in 0.4 wt% PVP solution while expansion into a 0.4 wt% Tween^® 80 solution produced particles 8 μm in diameter. Furthermore, it is shown that the improved dissolution behaviour of the processed powder depends on the particle size and hence increased surface area and on the pH-value of the dissolution media.     

Polyvinylpyrrolidone-assisted synthesis of microscale C-LiFePO4 with high tap density as positive electrode materials for lithium batteries

Carbon-coated LiFePO₄ (C-LiFePO₄) with micron particle size (6 μm) and high tap density (1.6 g cm⁻³) was prepared from spherical FePO₄·2H₂O powder via the co-precipitation method. The C-LiFePO₄ powder was calcined at temperatures between 650 and 800 °C. The 6 μm C-LiFePO₄ prepared at 800 °C exhibited an excellent rate capability, delivering 150 mAh g⁻¹ on discharge at the 0.1 C-rate and 108 mAh g⁻¹ at the 5 C-rate. The volumetric capacity of the 6 μm C-LiFePO₄ corresponded to 225 mAh cm⁻³, since the large secondary particles (6 μm) C-LiFePO₄ sufficiently allowed tight packing of the particles. The 6 μm C-LiFePO₄ powder with high tap density makes an attractive positive electrode candidate for lithium-ion batteries designed for high energy density.     

Fabrication of flat silicon surfaces using ion-exchange particles in ultrapure water

A silicon etching process using an ultrafine particle dispersion is proposed. The ultrafine particles contain quaternary ammonium hydroxide groups as ion-exchange groups, giving an alkaline dispersion. In the etching process, the fine particles and impurity ions can be easily separated by filtration or dialysis. Dialysis led to a decrease in the concentration of impurities in the dispersion, which included heavy metal ions and alkali metal ions known to result in a rough etched surface and affect the electronic properties of the semiconductor. Our proposed method is applicable to the surface planarization of silicon single crystals, manufacture of semiconductor devices, and fabrication of MEMS (micro-electro and mechanical systems). In addition, the etching waste can be reused after removal of the impurity ions by dialysis. Thus, the method has low environmental burden. Using the proposed alkaline etching dispersion, cathodic electrochemical etching of a silicon single crystal was demonstrated. The etching characteristics, properties of the etched surface, and effects of particle size were evaluated. The roughness of a 2 μm × 2 μm etched p-Si(0 0 1) surface was measured to be 0.1228 nm Ra (center line average roughness) by AFM.     

Toughening of polypropylene with calcium carbonate particles

Polypropylene-CaCO₃ composites were prepared on a twin screw extruder with a particle content of 0-32 vol%. The influence of particle size (0.07-1.9 μm) and surface treatment of the particles (with and without stearic acid) on the toughening properties were studied. The matrix molecular weight of the polypropylene was also varied (MFI 0.3-24 dg/min). The experiments included tensile tests, notched Izod impact tests, differential scanning calorimetry (DSC), scanning electron microscopy and rheology experiments. The modulus of the composites increased, while the yield stress was lowered with filler content. This lowering of yield stress was connected to the debonding of the particles from the polypropylene matrix. From DSC experiments it was shown that the particle content had no influence on the melting temperature or crystallinity of the PP phase, also particle size showed no effect on the thermal properties. The impact resistance showed large improvement with particle content. The brittle-to-ductile transition was lowered from 90 to 40 °C with the addition of CaCO₃ particles. Notched Izod fracture energy was increased from 2 up to 40-50 kJ/m². The stearic acid coating on the particle surface showed a large positive effect on the impact strength. This was mainly due to the improved dispersion of the CaCO₃ particles. Aggregates of particles clearly had a detrimental effect on the impact behaviour of the composites. The smaller particle sizes (<0.7 μm) showed coarse morphologies and this lowered the toughening efficiency. The molecular weight of the polypropylene matrix had a profound effect on the toughening properties. A higher molecular mass shifted the brittle-to-ductile transition towards lower temperatures. At the higher filler loads (>20 vol%), however, still problems seem to occur with dispersion, lowering the toughening efficiency. Of all particle types used in this study the stearic acid treated particles of 0.7 μm were found to give the best combination of properties. From the study of the micro-toughening mechanism it was shown that at low strain the particles remain attached to the matrix polymer. At higher strain the particles debond and this leads to a change in stress state at the particle size level. This prevents crazing of the matrix polymer and allows extensive plastic deformation, resulting in large quantities of fracture energy.     

Particle size design of digitoxin in supercritical fluids

Bioavailability of the pharmaceutical substances is very important for their activity. In case of necessity, bioavailability can be improved by reducing the particle size of the drugs. In this study, particle size of digitoxin was reduced by the Rapid Expansion of Supercritical Solutions (RESS). The effects of pre-expansion temperature (90-110 °C), flow rate (2.5-7.5 ml/min), spray distance (3-7 cm) on the size and size distribution of the precipitated digitoxin particles were carried out. The particles were characterized by dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and LC-MS analysis.While the particle size range of the original digitoxin was 0.2-8 μm, it was decreased to 68-458 nm and determined that 97% of the particles were below 200 nm depending on the different experimental conditions.Response surface method (RSM) was used to optimize the process parameters. The flow rate, 7 ml/min; spray distance, 7 cm; pre-expansion temperature, 95 °C were found to be the optimum conditions to achieve the minimum particle size of digitoxin.     

Wastewater filtration performance of multilayer glassy microporous filters

The glassy composition (quartz, clinoptilolite and frit glass mixture) provides a filter having glassy pore wall microstructure and thus enables easily cleaning through the filter recovery by back flushing. The filter was obtained as multilayer compaction by one step slip cast-processing where a cylindrical filter, consisting of filtration layer on granular assemblies with specific interlayer was shaped by a fine particle migration phenomenon. The multilayer compaction has low resistance to liquid flow and thus the filter great potential to use for wastewater filtration. It is known that high capacity filtration also requires correct pore size/interval with respect to filtered particles. In this study, a wastewater overflow from marble factory (0.035 wt.% of solid with a size distribution of 0.58-1.46 μm) was filtered by different pore sizes of the glassy filters (pore size intervals: 0.4-10 μm, 0.2-4 μm, 0.1-1.5 μm and 0.04-2 μm) and significantly different filtering capacities was obtained; the irreversible fouling capacities were determined between 2.9 and 8.5 m³ of filtrate per m² of the filter area through the filtration produced 5 min intervals. The filtration pressure was 5 bar and backflushing was achieved at 1 bar. The high filterability (8.1 m³/m² in 5 min) with high filtrate clarity (∼0.5 nephelometric turbidity units) could be obtained using finer pore sized filters. The large size filter was seriously clogged during the filtration.     

Computational modelling of the impact of particle size to the heat transfer coefficient between biomass particles and a fluidised bed

The fluid-particle interaction and the impact of different heat transfer conditions on pyrolysis of biomass inside a 150 g/h fluidised bed reactor are modelled. Two different size biomass particles (350 μm and 550 μm in diameter) are injected into the fluidised bed. The different biomass particle sizes result in different heat transfer conditions. This is due to the fact that the 350 μm diameter particle is smaller than the sand particles of the reactor (440 μm), while the 550 μm one is larger. The bed-to-particle heat transfer for both cases is calculated according to the literature. Conductive heat transfer is assumed for the larger biomass particle (550 μm) inside the bed, while biomass-sand contacts for the smaller biomass particle (350 μm) were considered unimportant. The Eulerian approach is used to model the bubbling behaviour of the sand, which is treated as a continuum. Biomass reaction kinetics is modelled according to the literature using a two-stage, semi-global model which takes into account secondary reactions. The particle motion inside the reactor is computed using drag laws, dependent on the local volume fraction of each phase. FLUENT 6.2 has been used as the modelling framework of the simulations with the whole pyrolysis model incorporated in the form of User Defined Function (UDF).     

Influence of β-Si3N4 particle size and heat treatment on microstructural evolution of α:β-SiAlON ceramics

In the present study, we report the effects of starting β-Si₃N₄ particle sizes and post-sintering heat treatment on microstructure evolution and mechanical properties of prepared α-β SiAlON ceramics. Three different β-Si₃N₄ starting powders, with particle sizes of 2, 1 and 0.5 μm were used to prepare α-β SiAlON ceramics by gas-pressure sintering. Elongated β-SiAlON grain morphology was identified in the samples prepared using 0.5 μm particle size β-Si₃N₄ powder. Low-aspect ratio grain morphology was observed in samples prepared from starting powders with coarse particles (2 μm and 1 μm). The sintered samples were further heat treated to develop desired microstructure with elongated grains. The hardness and indentation fracture toughness values of sintered and heat treated samples were found to lie in the range of 12.4-14.2 GPa and 5.1-6.4 MPa m^1/2 respectively. It was revealed that fracture toughness increases with decrease in particle size of starting β-Si₃N₄ powder.     

Filling of mesoporous silicon with copper by electrodeposition from an aqueous solution

Copper filling into mesopores formed in highly doped p-type silicon was investigated. When the copper electrodeposition was carried out at a very small constant current density (−6.4 μA cm⁻²), the mesopores with 4 μm depth were filled with copper continuously from the bottom to the opening. When the electrodeposition current was set at an absolute value twice as large as in the above condition, the isolated particles were electrodeposited in the mesopores. The depth also affected the filling behavior. The pores with 8 μm in depth were not continuously filled with copper even in the condition at which the pores of 4 μm in length were completely filled. Electrodeposition behavior in mesopores was also simulated using a simple model. The numerical simulation suggested that the diffusion-limited electrodeposition could be achieved in mesopores at a very small current, at which the diffusion-limited condition had never been realized on a planar electrode.     

Improved capacitive behavior of electrochemically synthesized Mn oxide/PEDOT electrodes utilized as electrochemical capacitors

A sequential synthetic approach and a one-step method were adopted to synthesize Mn oxide/PEDOT electrodes through anodic deposition on Au coated Si substrates from aqueous solutions. In the former case, free standing Mn oxide rods (about 10 μm long and less than 1.5 μm in diameter) were first synthesized without a template through anodic deposition from a dilute solution of Mn acetate, then coated by electro-polymerization of a conducting polymer (PEDOT) giving coaxial rods. The one-step, co-electrodeposition method produced agglomerated Mn oxide/PEDOT particles. The electrochemical behavior of the deposits depended on the morphology and crystal structure of the fabricated electrodes, which were affected by the pH of electrolyte, deposition potential, current density and polymer deposition time. Structural characterization of as-deposited and cycled electrodes was conducted using XPS, SEM, TEM and AES.The Mn oxide/PEDOT coaxial core/shell electrodes prepared by the sequential method showed significantly better specific capacity and redox performance properties relative to both uncoated Mn oxide rods and co-electrodeposited Mn oxide/PEDOT electrodes. The best specific capacitance for Mn oxide/PEDOT rods produced sequentially was ∼285 F g⁻¹ with ∼92% retention after 250 cycles in 0.5 M Na₂SO₄ at 20 mV s⁻¹.     

Electrochemical reduction of Zn(II) ions on l-cysteine coated gold electrodes

Zn(II) ions have been selectively bound to the l-cysteine coated gold electrode in the form of a four-coordinated complex. Voltammograms of the Zn complex on the l-cysteine coated gold electrode showed a cathodic wave at ca. 0.05 V in the pH 7.54 phosphate buffered saline. The charge transfer coefficient and rate constant for the reduction of this Zn complex were 0.65 and 0.003 s⁻¹, respectively. The complexation of Zn(II) ions with l-cysteine on the gold electrode resulted in the maximum surface coverage of the Zn complex of 0.35 nmol cm⁻² and the Gibbs energy change of −27.6 kJ mol⁻¹. The cathodic peak current, influenced by the types of the end functional groups in thiols, the preconcentration time, and pH values of the supporting electrolyte, was linear with the concentration of Zn(II) ions in the range of 5.0 nM to 5 μM with a detection limit of 2.1 nM. The proposed voltammetric method was utilized successfully to detect the concentration of Zn(II) ions in hairs.