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Focuses on a study which examined the effects of cluster and particle deposition on atmospheric pressure chemical vapor deposition on the silicon dioxide thin film. Details on the use of gaseous organic silicon-containing precursors and ozone gases; Experimental apparatus and method; Results and discussion; Conclusion.

Vapor nucleation induced by seed ions of controlled size and charge is studied for several monovalent positive and negative ions as well as divalent cations. Ions from dissolved salts are transferred into a gas via electrospray, purified by differential mobility selection, and introduced into a condensation nucleus counter of the mixing type using supersaturated dibutyl phthalate vapors. The number of drops nucleated on the ions is then measured as a function of the vapor supersaturation S. None of the anions tested is activated. Singly charged cations with mobilities Z from 0.48 up to 0.93 cm²/V/s are activated at values of ln S 30% smaller than predicted by Thomson's model. All doubly charged cations tested (Z from 0.46 to 1.08 cm²/V/s) fall very near the Thomson curve, independently of their size or of whether the double ionic charge is localized on one metal atom or on two separate monovalent sites. [ABSTRACT FROM AUTHOR]

A continuous-flow mixing apparatus has been developed for the study of binary nucleation. This apparatus has been used to investigate the nucleation of mixed dibutylphthalate/dioctylphthalate vapors, and the interaction of the two vapors in particle formation has been demonstrated. A model that considers competition between nucleation and condensation processes during particle formation is applied in the analysis of the experimental results, allowing comparison of the magnitudes of the theoretical and actual nucleation rates in both the single-component and mixed vapor systems. [ABSTRACT FROM AUTHOR]

Presents a study that evaluated the unipolar charging phenomena of ultrafine aerosol particles by positive gas molecule ions produced by α-ray irradiation. Background on the diffusion charging of ultrafine aerosol particles; Measurement of the effect of ion mass on the quantity of charge on particles; Results and implications.

Abstract: Control of particle size and morphology has increasingly captured the attention of researchers for decades. The exploration of unique sizes and shapes as they relate to various properties has become a great quest for large field applications. To meet these demands, this review covers recent developments in particle processing. An aerosol-assisted self-assembly technique, with a spray-drying method as a representative of it, to create particles is thoroughly reviewed. Its popularity and its broad use in industry for producing particles are the main reason of this review; thus, elucidation of this method is important for the improvement of particle technology. A practical spray-drying method is described from the step-by-step process to the selection of apparatus types (merits and demerits). Elaboration of particle processing of several morphologies (sphere, doughnut, encapsulated, porous, hollow, and hairy) is discussed in terms of the selection of material types, the addition of supporting materials, and the change of process conditions. Controllable size is also discussed in terms of the adjustment of the droplet size, initial precursor concentration, and the addition of specific techniques. A comparison between a theoretical mechanism and current experimental results (over a 15-year period) are shown to clarify how particles with various sizes and morphologies are designed. This method must be considered an art rather than a science because of its advantages in creating wonderful and unique particle shapes. The performance of various particle morphologies is also demonstrated, which is essential for an understanding of the importance that shape can exert on practical use. Because the method outlined here can be broadly applied to the production of various types of functional materials, we believe that this report contributes new information to the field of chemical, material, environmental, and medical engineering. [Copyright &y& Elsevier]

Reference filters with uniformly deposited, known masses of elemental carbon (EC) and organic carbon (OC) were produced by a spray-drying method and a carbon aerosol sampling system. Submicrometer carbon particles were produced by nebulizing a carbon black hydrosol and a potassium hydrogen phthalate (KHP; C6H4(COOK)(COOH)) solution.Total carbon (TC) concentrations measured at three different locations on the filter showed that the carbon particles were uniformly distributed on the filter. Reference filters were analyzed using thermal optical analysis methods (TOA) IMPROVE and NIOSH 5040-NIIH, and the measured concentrationsof TC, EC, and OC were compared to the gravimetrically measured concentrations. TC measurements by both TOA methods used were in excellent agreement with gravimetrically measured TC. It was found that the IMPROVE method produced approximately 3.5 times as much pyrolytically generated elemental carbon (PEC) as did the NIOSH 5040-NIIH method. However, no PEC was detectable on reference filters when both EC and OC were present. This led to discrepancies in EC and OC measurement between the TOA and gravimetric methods. Better agreement was found when PEC generation of pureOCreference filters was taken into account and measurements on filters with both EC and OC deposited were corrected for PEC generation. These data imply that, when both EC and OC are present on the filter, TOA methods are often inaccurate in correctly measuring the amount of PEC generated, with the magnitude of measurement error dependent upon the type of EC and OC present in the sample. In addition, reference filters with OC deposited on top of EC and EC deposited on top of OC were generated and analyzed. From these reference filters, it was found that PEC measurements are also affected by the way in which the EC and OC deposit on the filter. Overall, the method devised here to create reference EC/OC filters is a simple technique in which EC, OC, and mixed EC-OC particles of a controlled size and chemical composition can be deposited uniformly onto filters and such reference filters will be invaluable in evaluation of TOA methods of EC/OC measurement. [ABSTRACT FROM AUTHOR]

When particle dimensions are reduced to the order of several nanometers, their physical and chemical properties deviate significantly from the bulk properties of such materials. Because of this, there is abundant potential for their use in future technologies including electronic and optoelectronic, mechanical, chemical, cosmetic, medical, drug, and food technologies. However, due to their extremely small sizes, the particles suffer from many problems related to their surface and thermal stability, shape preservation, handling, assembly in devices, etc. It is therefore an important challenge to solve these problems by developing slightly larger particles (e.g. on the submicrometer scale) in which the properties generated by the nanoscale material are preserved. One approach to this is to trap nanoparticles in a micrometer-sized inert matrix. This approach allows the nanoscale properties to be retained, since nanoparticles are separated from each other in the inert matrix. The inert matrix also serves as a coating medium that inhibits any chemical changes to the surface of the nanoparticles. Their larger size allows easy handling or assembly in devices. A promising method for designing and fabricating these composite structures is a spray method, in which spherical particles can be produced. In this paper, we review the nanostructural processing (synthesis) of submicrometer-sized particles by a spray method, which provides a restricted reaction environment (such as pores or cages) in the matrix for their synthesis and handling. The characterization and potential applications of these composites are also discussed. [ABSTRACT FROM AUTHOR]

Abstract: Cerium-doped yttrium-gadolinium aluminum garnet, (Y,Gd)3Al5O12:Ce, shortened here to (Y,Gd)AG:Ce, was systematically prepared by a polymer complex method, using high molecular weight polyethylene glycol (PEG). Without PEG, only large flakes several micrometers in size containing nearly pure (Y,Gd)AlO3 were obtained. Adding PEG dramatically reduced the particle size. However, the (Y,Gd)AG phase was not obtained by merely adding PEG. Instead, mainly (Y,Gd)2O3 and small amount of Ce2O3 were obtained. Simultaneous use of PEG and a flux (simple salt) such as BF2 resulted in the formation of small YAG particles. The presence of the (Y,Gd)AG phase results in intense yellow–green luminescence. By selecting various heating routes, the fractions of cubic and hexagonal phases were controlled. It was found that the luminescence intensity is proportional to the fraction of cubic phase, and is probably independent of the hexagonal phase. [Copyright &y& Elsevier]

Several modifications of the particle size magnifier (PSM) developed by Okuyama et al. have been introduced recently for detection of particles at diameters of 1 nm and below. However, their evaluation has been incomplete. Here we provide the first direct measurements of counting efficiencies near unity below 2 nm. We use the modified PSM described by Sgro and Fernández de la Mora, which separates thermally the PSM's original vapor generator from the water-cooled growth chamber by means of a narrow and short T where turbulent mixing with the aerosol takes place. The counting efficiency is seen to depend greatly on the aerosol flow, the amount of vapor, and temperature. With ethylene glycol vapor, under optimal conditions, the counting efficiency is 100% down to 1.6 nm (actual diameter of 1.2 nm), and negative particles are more easily activated than positive particles. The improved PSM is applied to the measurement of gold nanoparticle size distributions, and the results show it is a powerful aerosol detector for nanoparticles. [ABSTRACT FROM AUTHOR]

Light scattering by porous spheroidal silica and several silica/carbon composite particles having different carbon contents was systematically investigated using a laser particle counter coupled with a pulse height analyzer (LPC-PHA). A new and simple method for the measurements of the effective complex refractive index of silica/carbon composite particles using a conventional LPC-PHA system and a differential mobility analyzer was introduced and tested. Challenge particles, from pure silica to silica/carbon compounds having a gradually increasing porous structure, were prepared by spray-drying methods for use in testing of the inversion method. By representing the deviation of the real part of the refractive index of a porous silica particle versus the size on a topographical map, the inversion method for the determination of the real part of the refractive indices was found to have a satisfactory precision. Furthermore, the method can be applied to the measurement of the complex refractive index of silica/carbon composite particles by extending the best fitting method to complex refractive indices. The effective complex refractive index of silica/carbon composite particles as a function of their carbon content is reported. Both the real and imaginary parts of the complex refractive index were increased with increasing carbon content of the composite particles. [ABSTRACT FROM AUTHOR]

The effect of chemical reaction rate on the generation of titania nanoparticles by chemical vapor deposition using two different precursors was investigated by FTIR, XRD, and microscopy. The size of the primary particle exhibited a minimum with increasing reactor temperature. At lower reaction temperatures, the continuous and gradual formation of titania monomers occurred followed by coagulation and/or surface reaction on the existing particles. In addition, unreacted precursor condensed at the reactor exit. As the reaction temperature increased, the rate of monomer production increased, the dominant characteristics of particle growth were coagulation and sintering. The reactor temperature where the minimum primary particle diameter was produced was different for the two precursors due to differences in chemical reaction rates. Phase composition as well as the primary particle diameter of product titania were affected by the chemical reaction rate. Particle-laden reactor wall enhanced the precursor conversion at low reactor temperatures, where surface reactions compete effectively with gas-phase precursor conversion. [Copyright &y& Elsevier]

Nanometer-sized particles (1–100 nm) are of considerable interest for a wide variety of applications, ranging from electronics via ceramics to catalysts, due to their unique or improved properties that are primarily determined by size, composition and structure. In this study, we report a simple, rapid and generalizable aerosol decomposition (spray pyrolysis) process for the continuous synthesis of nanoparticles with adjustable sizes, narrow size distribution, high crystallinity and good stoichiometry. The production of spherical-shaped porous particles with nanoscale ordering porosity and the zinc oxide quantum dots in silica nanoparticles matrix by means of a spray drying method using a colloidal mixture as the precursor and by the combined sol–gel and spray drying method were also reported. [Copyright &y& Elsevier]

The light scattering by granular and macroporous silica spheroids consisting of nanometer-sized primary particles was systematically investigated using a laser particle counter coupled with a pulse height analyzer. The shape- and porosity-controlled spheroids as model particles were prepared using spray drying method by changing the particle size of colloidal suspension. The effect of shape and porosity of dense and porous spheroidal particles on electrical mobility was also studied using a differential mobility analyzer and an electron microscope. The electrical mobility equivalent diameter of particles classified by the differential mobility analyzer was estimated by measuring Feret diameter and the projected area equivalent diameter from the SEM micrographs. The electrical mobility diameter of the spheroids was in good agreement with the projected area equivalent diameter regardless of the primary particle size and porosity. The measured partial scattering cross section of dense and porous silica particles with same mobility diameter showed significant differences. As the primary particle size of granules and the porosity of porous particles increased at parity of electrical mobility diameter, the scattering intensity decreased. The effective refractive indices of dense and porous particles were computed by best fitting of the scattering intensity measurements. The porosities of dense and porous spheroids were calculated using the effective refractive indices as obtained by the effective medium theory. The porosities were also measured by a comparison of particle size before and after annealing at 1700°C. By comparing these porosities, the effective refractive indices of the spheroidal particles were confirmed. [Copyright &y& Elsevier]

A mixing-type condensation nucleus counter (MTCNC) was used to detect nanometer-sized particles suspended under low-pressure conditions. The experimental results show that MTCNC is capable of measuring nanoparticles smaller than 10 nm at low pressures above 65 Torr (8.644 kPa) by adjusting the rate of the aerosol flow, the amount of vapor and temperature depending on the desired operation pressure. At pressures above 160 Torr (21.33 kPa), the optimal operation conditions of a MTCNC, variables such as the saturator temperature, condenser temperature and mixing ratio are similar to those used at atmospheric pressure. Since the condensational growth of particles depends greatly upon the residence time, the current MTCNC needs improvement to increase the growth time under even lower pressure conditions. At the optimal operation conditions, the counting efficiencies for nanoparticle size 3 nm particles are 85% at atmospheric pressure and 40% at an operating pressure of 115 Torr (15.33 kPa), respectively. [Copyright &y& Elsevier]

A metal-free, sub-stoichiometric tungsten oxide (WOX) photocatalyst has been successfully prepared by hydrogenating WO3 plasma nanoparticles at 425 °C. X-ray diffraction (XRD) analysis indicated that the photocatalyst comprised WO3 monoclinic, WO2.9, WO2.7, and WO2.0, depending on the reduction time. Their adsorption and photocatalytic activity on organic contaminants were evaluated by decomposing Rhodamine B (RhB). The prepared WOX demonstrated remarkable capabilities in decomposing 1.2 gL−1 Rhodamine B (RhB) compared to WO3 plasma NPs. WOX-120 exhibited the optimal catalytic performance, with the adsorption capacity for RhB at 174.9 mgg−1, 73 times greater than WO3 plasma NPs. WOX-60 exhibited the highest photodecomposition rate, with a k rate more than 90 times greater than that of WO3 plasma NPs. The investigation into active species in the photocatalytic reaction suggested that superoxide hydroxyl radicals (*OH) and photoinduced holes (h+) were the primary contributors. Furthermore, the photocatalytic degradation of RhB by the synthesized WOX showed improvement when Benzoquinone was introduced into the system as a scavenger, effectively capturing generated electrons and inhibiting their recombination with holes. This research showed the potential for metal-free semiconductor photocatalysts to efficiently remove various organic pollutants through adsorption and photocatalysis under visible light irradiation. Furthermore, the simple reduction process makes this material promising for large-scale catalyst and photocatalyst production. [ABSTRACT FROM AUTHOR]

Investigates an ultraviolet/photoelectron method for removing fine airborne particles under low pressure conditions. Generation of airborne particles; Removal of particulate contaminants on the silicon wafer; Calculation of ion concentration.

The distribution and transport of fine particles trapped in a radio-frequency (rf) plasma-enhanced chemical vapor deposition reactor was investigated using a laser light scattering technique. Structured clouds of particles were observed at localized regions between the holes below the showerhead. Typically, at a high rate of gas flow, particles emerging from the showerhead holes overshoot the equilibrium position of the particle trap, and the particle clouds in the trap were small and thin (winding mode). At a low rate of gas flow, the particles are directly attracted to the trap locations, and large particle clouds (lumping mode) were observed. The particle number concentration of trapped particles tends to increase with increasing rf power and decrease with increasing particle size. When the gas flow rate is increased, a sharp decrease occurs at a certain flow rate. [ABSTRACT FROM AUTHOR]

The influence of Cu doping on the function of dye-sensitized solar cells (DSSCs) dependent on Cu/N-doped TiO 2 photoelectrodes was examined. Cu/N-doped TiO 2 photoelectrodes with diverse Cu concentration were synthesized using the sol–gel process. Upon adequate addition of Cu, the nanoparticles exhibited small particle sizes, high surface area, and a significant red alteration of their absorption to the visible region in relation to Degussa P25 nanomaterials. Furthermore, the traces of Cu/N-doped TiO 2 nanoparticles enhanced the charge transfer and reduced the charge recombination. The addition of sufficient Cu and N increased the surface area, elevating the dye adsorption degree, and decreasing the level of electron recombination. A DSSC fabricated with a 1 mM Cu/N-doped TiO 2 nanoparticles accomplished 11.35% of the highest power conversion efficiency, with a short-circuit current of 22.5 mA/cm 2 . The energy conversion efficiency of this photoelectrode was approximately 37% greater than that of the control, Degussa P25. The increased energy efficiency can be resulted from the extension in surface area, which enabled larger dye charging amount, and the deduction in charge recombination, which accelerated the charge transfer. [ABSTRACT FROM AUTHOR]

Highlights: [•] Recent strategies for functional nanostructured particles were reviewed. [•] We focused on co-precipitation and spray methods in this review. [•] Magnetic, phosphor, catalyst, and adsorbent performances were evaluated. [ABSTRACT FROM AUTHOR]

Doughnut magnesium fluoride particles with controllable size (from 6 to 50 nm) and shape (sphere and cube) were successfully prepared using an electron-beam irradiation method. While common reports typically produced doughnut particles in the micrometer range, the present method succeeded in preparing this type of particles with sizes of nanometers. Different from other methods that pointed out the importance of the additional additive and specific process to support the formation of doughnut structure, we preferred exploiting the electron-beam irradiation method that was simpler and free of additive. Transformation of the particle from its original morphology (dense structure) into doughnut shape were also investigated, along with the analysis of irradiation time and elemental composition. Outer sizes and shapes of the final particles were identical to those of the initial particles (before irradiation process), giving a potential way for controlling the size and the shape of the doughnut particles by adjusting the size and the shape of the initial magnesium fluoride particles only. [ABSTRACT FROM AUTHOR]

Abstract: The use of aluminum trihydroxide (ATH) fillers as non-halogen flame retardants for polymethylmethacrylates (PMMA) creates a conflict between the mechanical properties and heat resistance of the composites. Therefore, to ensure that the PMMA mechanical properties remain satisfactory, improvements in both the filler–polymer interactions and the ability to control the size and size distribution, morphology and dispersion of the fillers are required. Thus, in the present study, bead milling was used to control both the size distribution and dispersion of ATH fillers in MMA, which had an initial average size of 0.75μm. The dispersion was obtained by alteration of the surface characteristics of ATH fillers using a silane-based dispersing agent, (3-acryloxypropyl) trimethoxysilane (APTMS). Bead milling successfully comminuted the ATH particles and prevented the formation of ATH agglomerates. The smallest average size of the ATH particles after bead milling was 300nm. Highly dispersed ATH filler particles were observed in the TEM images of the PMMA/ATH composites. The filler–polymer interaction, i.e. the interaction parameter (B), was calculated. The effects of volume fraction, particle size distribution, and surface modification of the fillers on the results of dynamic mechanical analysis (DMA) are discussed. The thermal stability of the PMMA/ATH composites was also investigated using thermal gravimetric analysis (TGA). [Copyright &y& Elsevier]

Abstract: An anatase titania particle with a honey-comb-like pore structure (200nm-pore size) and a controllable outer diameter (0.2–1μm) was successfully prepared using a spray-drying method. As a precursor, an anatase nanoparticle (5nm) and a polystyrene particle (200nm) were used as a titania source and a colloidal template, respectively. The outer diameter could be controlled by varying the precursor concentration. The photocatalytic performance of a porous particle was faster than that of a dense particle (with a similar outer diameter). [Copyright &y& Elsevier]

Risk assessment of nanoparticles by inhalation experiments is of great importance since inhalation is considered the most significant route of exposure to nanoparticles suspended in air. However, there have been few inhalation experiments using manufactured nanoparticles, mainly because of the difficulty in stably dispersing the nanoparticles in air for a long period of time. In this study, we report for the first time the development of a rational system for stably and continuously dispersing and supplying manufactured nanoparticles for inhalation experiments. The system was developed using a spray-drying technique, in which a nebulizer was used to atomize nickel oxide (NiO) and fullerene (C60) nanoparticle suspensions, and the resulting droplets were dried to generate aerosol nanoparticles. The size, concentration and morphology of the aerosol particles were evaluated by in-line measurements using an aerosol measuring device and off-line measurements based on the collection of the aerosol particles. After examining the effects of the conditions for the suspensions and the aerosol generation, we were able to obtain NiO and C60 aerosol nanoparticles with average diameters of 53-64 and 88-98 nm, respectively. By feeding these aerosols into a whole-body exposure chamber for rats, a stable supply of the aerosol nanoparticles could be achieved for long hourly durations (6 h per day) as well as for long terms (5 days per week for 4 weeks). [ABSTRACT FROM AUTHOR]

Abstract: Selective deposition of metal (Au) and oxide (SiO2) nanoparticles with a size range of 10–30 nm on patterned silicon–silicon oxide substrate was performed using the electrospray method. Electrical charging characteristics of particles produced by the electrospray and patterned area created by contact charging of the electrical conductor with non- or semi-conductors were investigated. Colloidal droplets were electrosprayed and subsequently dried as individual nanoparticles which then were deposited on substrates, and observed using field emission-scanning electron microscopy. The number of elementary charge units on particles generated by the electrospray was 0.4–148, and patterned area created by contact charging contained sufficient negative charges to attract multiple charged particles. Locations where nanoparticles were (reversibly) deposited depended on voltage polarity applied to the spraying colloidal droplet and the substrate, and the existence of additional ions such as those from a stabilizer. [Copyright &y& Elsevier]

BaTiO3 nanocrystals were synthesized by using a low-pressure spray pyrolysis (SP) method. A new strategy was proposed to improve nanocrystal formation and phase evolution by ethanol addition and Ba/Ti molar ratio variation, respectively. A mixture of submicron and nanoparticles was found with SP of precursors without ethanol addition, while only nanoparticles could be obtained by ethanol addition. BaTiO3 crystal growth was improved by increasing the Ba/Ti ratio. In comparison, SP of the same precursor under atmospheric conditions resulted in only submicron particles with smooth surfaces and irregular morphology. [ABSTRACT FROM AUTHOR]

Abstract: A simple method for the synthesis of nanosized gallium nitride (GaN) particles from a mixture of gallium nitrate (Ga(NO3)3) and aqueous ammonia solutions under a flow of ammonia gas in a temperature range of 700–900 °C is described. Nanosized GaN particles with an average diameter of approximately 20–50 nm were obtained. The resulting GaN nanoparticles showed an intense photoluminescence at 364 nm under UV excitation at 254 nm. The effects of the preparation conditions, such as temperature, length of heating time and ammonia concentration on the crystallinity and intensity of the photoluminescence of the particles were also investigated. [Copyright &y& Elsevier]

Abstract: Formation of individually dispersed nanoparticles or compactly aggregated nanoparticles from sols via a spray-drying route at low pressure was investigated experimentally. Silica sol was used as a sample material. Effects of operating temperature, colloid size, sol concentration, pressure, pH and zeta potential of sols on the morphology of product particles were investigated. From the experimental results, it was shown that dispersed nanoparticles could be obtained at a relatively low pressure (20 Torr) and low temperature (200 °C). The experiment also showed that dispersed nanoparticles could be achieved by careful control of the interfacial energy (pH value) of the colloidal precursor. A possible mechanism of sol-to-dry-particle formation in the spray-drying process at low pressure is suggested, based on the experimental results and the available theories. This mechanism was able to explain the experimental results well. [Copyright &y& Elsevier]

Abstract: Patterned deposition of nanoparticles is a prerequisite for the application of unique properties of nanoparticles in future nanodevices. Recent development of nanoxerography requires highly charged aerosol nanoparticles to avoid noise deposition due to random Brownian motion. However, it has been known that it is difficult to charge aerosol nanoparticles with more than two elementary charges. The goal of this work is to develop a simple technique for obtaining highly charged monodisperse aerosol nanoparticles by means of electrospray of colloidal suspension. Highly charged aerosol nanoparticles were produced by electrospraying (ES) and drying colloidal suspensions of monodisperse gold nanoparticles. Size and charge distributions of the resultant particles were measured. We demonstrate that this method successfully charges monodisperse nanoparticles very highly, e.g., 122 elementary charges for 25.0 nm, 23.5 for 10.5 nm, and 4.6 for 4.2 nm. The method described here constitutes a convenient, reliable, and continuous tool for preparing highly charged aerosol nanoparticles from suspensions of nanoparticles produced by either wet chemistry or gas-phase methods. [Copyright &y& Elsevier]

A europium doped ZnO (ZnO:Eu) particle was directly synthesized by the spray pyrolysis method. The crystal structure of samples was designated by the europium ion and the synthesis temperature. We identified the coexistence of Eu2+ and Eu3+ ions in the as prepared ZnO, which was strongly influenced by the doping concentration and the synthesis temperature. With addition of a 0.5mol% concentration of europium ions, only the Eu2+ ion existed in particles, while both Eu2+ and Eu3+ ions existed in sample using 1mol% or higher concentration of europium ions. Changing the wavelength of the excitation source, we also found that both the blue and red luminescence can be obtained. [Copyright &y& Elsevier]

Abstract: Particles of a red phosphor, Pr3+, Al3+-doped strontium titanate (SrTiO3:Pr3+, Al3+), were successfully synthesized by one-step spray pyrolysis. Submicron-sized particles with high crystallinity and high photoluminescence (PL) emission intensity were easily obtainable without post-annealing treatment. The effects of synthesis temperature and the composition and concentration of starting precursor on the physical properties of particles, such as crystallinity and PL, were investigated. An attractive evolution of particle morphology can be created by additional Al3+ ions in the precursor. PL intensity of phosphor particles was dependent on the concentration and composition of the precursor and improved with increasing synthesis temperature up to 1550°C. The effect of the addition of LiNO3 as a flux in the precursor on the photoluminescence properties of the product is also discussed. [Copyright &y& Elsevier]

Composites of zinc oxide (ZnO) nanoparticles in silica matrix can be produced by initially synthesizing a ZnO colloid (containing ZnO nanoparticles in ethanol solution), mixed with tetraethoxysilane (TEOS), followed by spray drying, to produce powder comprised of submicrometer sized particles. The initial size of ZnO nanoparticles in the colloid is about 3 nm when the precursors are first mixed, but the size increases with aging, following an approximate equation D∝tα, α=constant [J. Phys. Chem. B 102 (1998) 2854]. By using ZnO colloids that have been aged for different times, composites containing a specific size of ZnO can be produced. Since the excitation and emission luminescence spectral positions of ZnO are dependent on particle size (shift to blue region with reducing particle size), composites that emit a specific color can be produced using this method. We have been able to produce composites that emit colors from blue (460 nm) up to yellow-green (550 nm). [Copyright &y& Elsevier]

At high concentrations of ambient bipolar ions, charged aerosol particles show a stationary charging state as a function of particle size. When the particle diameter exceeds 0.1 μm, a considerable fraction of multiply charged particles is present, which hinders size classification of particles, when a differential mobility analyzer (DMA) is used. However, at low ion concentrations, particle charging by the ions can be suppressed, and in principle, the production of multiply charged particles can be reduced even when the particle size is larger than 0.1 μm.In this study, a use of a power-adjustable soft X-ray emitter was investigated for the first time as the ionization source of an aerosol charger. The bipolar ion concentration was found to be adjustable between 1010 and 1013 ions/m3. Through proper control of the bipolar ion concentration in the soft X-ray aerosol charger, multiply charged particles were reduced to less than 5% of the singly charged particles, while the singly charged particles remained at a relatively high concentration with most of the particles in size range of 0.1–1.0 μm. Therefore, highly monodisperse aerosol particles in the 0.1–1.0-μm-diameter range could be generated using this technique with a commercialized differential mobility analyzer. [Copyright &y& Elsevier]

The control of the morphology of nanostructured particles prepared by the spray drying of nanoparticle sol was investigated experimentally and the results are qualitatively explained based on available theory. A theoretical analysis indicates that the structural stability of the droplet and the hydrodynamic effects during the drying process play important roles in controlling the morphology of the resulting particles. The size of the sol in the droplet, droplet size, viscosity of droplet, drying temperature, gas flow rate, and addition of surfactant are all crucial parameters that affect the morphology of particles. Experimentally, nanostructured silica particles were prepared from a nanosize silica sol under various preparation conditions. Doughnut-shaped particles can be produced when the droplet size is large, in conjunction with high temperature, high gas flow rate and in the presence of an added surfactant. Appropriate choice of the spray drying method permits control of the particle size and shape, ranging from spheres to ellipsoids as well as doughnut-shaped particles by varying the preparation conditions. The results open a new route to controlling the formation of a wide variety of nanostructured particles. [Copyright &y& Elsevier]

Microencapsulated powders were prepared by an aerosol spray method using a precursor comprised of a mixture of two types of sols as well as a sol-aqueous mixture precursor solution. Two different types of sols were used as precursors to prepare microencapsulated small-SiO[sub 2]/large-SiO[sub 2] and Al[sub 2]O[sub 3]/SiO[sub 2] powders. A microencapsulated ZrO[sub 2]/SiO[sub 2] powder was also prepared from a mixture of SiO[sub 2] sol and an aqueous precursor solution of zirconyl nitrate dihydrate. For preparing small-SiO[sub 2]/large-SiO[sub 2] powders, two different sizes, i.e. 6 and 109 nm, of SiO[sub 2] sols were used as precursors. The results show that the larger SiO2 particles were encapsulated with the smaller ones. A similar result was also observed in the preparation of an Al[sub 2]O[sub 3]/SiO[sub 2] powder prepared from a mixture of Al[sub 2]O[sub 3] (18 nm) and a SiO2 (109 nm) sol precursor. The Al[sub 2]O[sub 3] particles appeared on the surface of the prepared powder. In the case of the ZrO[sub 2]/SiO[sub 2] powder, the morphology indicates that the SiO[sub 2] particles (109 nm) were encapsulated by a ZrO[sub 2] shell. The effect of precursor ratios on the morphology of powders was also investigated. The light scattering characteristics of the prepared particles were also investigated using a laser particle counter coupled with a pulse height analyzer. The effective refractive indices of the microencapsulated powders varied considerably with the content of coating material. [ABSTRACT FROM AUTHOR]

The nucleation of aerosols in a field of high-density free radicals, ions, and secondary thermalized electrons was studied by irradiating air, N2, O2, and Ar containing different water contents with electron beams. The charged nanoparticles in the irradiating gases were analyzed by a cluster differential mobility analyzer equipped with a Faraday cup electrometer. All experiments with humidified gases formed both positively and negatively charged particles with mean mobil. equiv. diameters (Dm) range of 7–10 nm and with the same number concentration (N) as well as water ion clusters with Dm range of 1.0–1.1 nm. The N of these large particles increased with water content and absorbed dose. The experimental result showed that hydrogen peroxide was contained in these large charged particles as its part. In the presence of ppbv-level benzene, the Dm and N of large charged particles increased with benzene concentration, although their Dm were constant at different doses. [Copyright &y& Elsevier]

Effects of NO[sub 2] on particle formation in SO[sub 2]/H[sub 2]O/Air mixtures by α-ray irradiation as a source of hydroxyl radicals are investigated to evaluate the contribution of homogeneous and ion-induced nucleation in the nanometer-sized aerosol particle generation. The total particle number concentration, the charged-particle fraction, and the electrical mobility distribution of particles and hydrated and solvated ions generated in NO[sub 2]/SO[sub 2]/H[sub 2]O/Air mixtures were measured at NO[sub 2] levels of 0-1.98 ppm, SO[sub 2] levels of 0-3.87 ppm, and H[sub 2]O levels of 6480-9889 ppm. Total particle number concen2 tration first tends to increase with increasing NO[sub 2] concentration up to a certain NO[sub 2] level and then decreases for NO[sub 2] concentrations beyond this point. The charged-particle fraction, indicative of particle formation by ion-induced nucleation, tends to decrease with increasing NO[sub 2] concentration, reaching a minimum value. The peak intensity of the electrical mobility distribution for particles significantly exceeded that in the absence of NO[sub 2] at a relatively low concentration of NO[sub 2]. The intensity decreased with increasing NO[sub 2] concentration and fell below that in the absence of NO[sub 2]. The results indicate that 2 opposing mechanisms that enhance and suppress the particle formation work simultaneously in NO[sub 2]/SO[sub 2]/H[sub 2]O/Air mixtures, and the dominant mechanism depends on the NO[sub 2] concentration. [ABSTRACT FROM AUTHOR]

Morphological changes of agglomerates consisting of nanometer primary gold particles were studied experimentally and theoretically. Gold aerosol nanoparticles were produced using the evaporation/condensation method, and the change in agglomerate size by reheating was examined experimentally using a tandem DMA setup. Numerical calculations, based on two extreme mechanisms to reshape agglomerates, i.e., subsequent coalescence of primary particles and subsequent rearrangement of primary particles, were carried out. By comparison with the experimental results, the sintering time and the rate constant of restructuring were obtained. Using these values, the change in particle size for different generation conditions could be calculated. The change in morphology of agglomerates can be explained from the comparison of the experimental results with the theoretical calculations: agglomerates with smaller primary particles will compact mainly by the subsequent coalescence of primary particles, while agglomerates with larger primary particles will compact mainly by a rearrangement of primary particles. [Copyright &y& Elsevier]

Examines the preparation of nickel powders using ultrasonic spray pyrolysis of nickel formate. Range of the particle morphologies; Dependence of pyrolysis on precursor solution and the operating condition; Account on the reducing agent used in the study.

• Strategies for the production of porous particles with controllable structures. • Template-assisted spray drying method with its particle formation mechanism. • Regulation of spray drying process conditions and precursor formulations. • Concentration, size, and electrostatic charges for controlling particle structure. • Porous particles for advanced functional materials (e.g. catalyst, adsorbent, etc.). Developing strategies for the production of porous particles with controllable structures using a spray-drying method has attracted attention of researchers for decades. Although many papers have reported their successful production of porous particles using this method, information on how to create and control the porous structures as well as what parameters involving and what formation mechanism occurring during the synthesis process are still not clear. To meet these demands, the present review covers strategies in the spray-drying developments for the fabrication of porous particles with controllable structure. This information is important for optimizing the production of porous particles with desirable properties. Regulation of process conditions and precursor formulations are also explained, including composition, type, and physicochemical properties of droplet and raw components used (i.e., host component, template, and solvent). The electrostatic interactions between the individual components and the droplets are also presented, while this information tends to be neglected in the conventional spray-drying process. To clarify how the porous particles are designed, current experimental results completed with illustrations for the proposal particle formation mechanism are presented. The review also completed with the opportunities and potential roles of the changing porous structures in practical uses. This review would provide information on how to produce porous particles that can be used for advanced functional materials, such as catalysts, adsorbents, and sensors. [ABSTRACT FROM AUTHOR]

The phenomenon of atomic motion between the nanoparticle and its substrate was examined in constructing perpendicularly aligned FePt nanoparticle structures. Samples of iron-rich FePt nanoparticles synthesized by vapor phase or liquid phase synthesis techniques were deposited on a platinum-(001) buffer layer and annealed in a hydrogen atmosphere. Superconductive quantum interference device and x ray diffraction measurements for the in-plane and out-of-plane direction exhibited perpendicularly oriented magnetization and an L10 ordered phase with a perpendicular easy axis orientation. The coercivity was measured as approximately 4.3 kOe. In addition, high angle annular dark field-scanning transmission electron microscopy showed FePt alloy formation normal to the sample surface. The atomic distribution data showed iron diffusion into the platinum layer. These results might open a new path toward ultrahigh density storage media from chemically synthesized FePt nanoparticles. [ABSTRACT FROM AUTHOR]

An experimental system for the study of ion-induced nucleation in a SO2/H2O/N2 gas mixture was developed, employing a soft x-ray at different pressure and temperature levels. The difficulties associated with these experiments included the changes in physical properties of the gas mixture when temperature and pressure were varied. Changes in the relative humidity (RH) as a function of pressure and temperature also had a significant effect on the different behaviors of the mobility distributions of particles. In order to accomplish reliable measurement and minimize uncertainties, an integrated on-line control system was utilized. As the pressure decreased in a range of 500-980 hPa, the peak concentration of both ions and nanometer-sized particles decreased, which suggests that higher pressure tended to enhance the growth of particles nucleated by ion-induced nucleation. Moreover, the modal diameters of the measured particle size distributions showed a systematic shift to larger sizes with increasing pressure. However, in the temperature range of 5-20 °C, temperature increases had no significant effects on the mobility distribution of particles. The effects of residence time, RH (7%-70%), and SO2 concentration (0.08-6.7 ppm) on ion-induced nucleation were also systematically investigated. The results show that the nucleation and growth were significantly dependent on the residence time, RH, and SO2 concentration, which is in agreement with both a previous model and previous observations. This research will be inevitable for a better understanding of the role of ions in an atmospheric nucleation mechanism. [ABSTRACT FROM AUTHOR]

Cerium-doped yttrium aluminum garnet (YAG:Ce3+; Y3-xAl5O12:Cex3+) phosphor nanofibers were successfully prepared using an electrospinning method followed by a heating process. Aluminum nitrate nonahydrate, yttrium nitrate hexahydrate, and cerium nitrate hexahydrate dissolved in dimethylformadide, poly(vinyl pyrrolidone), and ethanol comprised the precursor. The precursor was electrospun under atmospheric conditions to obtain the as-prepared fibers, which consisted of salts and the polymer composite. The as-prepared fibers were then heated to remove the polymer and to obtain the YAG:Ce3+ crystalline fibers. The morphology of the final fibers was homogeneous; the fibers were approximately 300 nm in diameter and several centimeters in length. The photoluminescence (PL) and crystalline properties of the fibers were studied as a function of both the doping fraction (0.005≤x≤0.4) and the heating temperature (900–1400 °C). High heating temperatures resulted in a high degree of crystallinity, crystallites that ranged from 20 to 55 nm in size, and enhanced PL intensity. A doping concentration of 1% (x=0.01) gave the highest PL intensity under excitation at 470 nm. The PL spectra were centered at 530 nm due to the transition from the 5d state to the 4f state (2A1g→2F5/2 and 2A1g→2F7/2). [ABSTRACT FROM AUTHOR]

The equilibrium and trapping of dust particles in a plasma sheath are investigated, both experimentally and theoretically. A self-consistent sheath model including input power as one of the model parameters is proposed, to predict the equilibrium position of particle trap. The electron temperature and density are estimated from the observed current and power (I-P) characteristics using the sheath model developed. Direct comparisons are made between the measured equilibrium position and the predicted equilibrium position. The equilibrium position moves closer to the electrode with increasing rf power and particle size. The position is apparently related to the sheath thickness, which decreases with increasing rf power. The model can correctly predict the experimentally observed trend in the equilibrium position of particle trap. It is found that the particle charge becomes positive when the particle gets closer to the electrode, due to the dominant influence of ion currents to the particle surface. [ABSTRACT FROM AUTHOR]

FePt nanoparticles have been synthesized using a liquid process, by mixing two precursor liquids: ferric acetyl ferric acetyl acetonate, Fe(acac)[sub 3], and platinum acetyl acetonate, Pt(acac)[sub 2] in polyol solution of sodium hydroxide at high temperatures. To avoid the agglomeration of the produced particle, aminoethoxy ethanol has been used. The particle size was monodisperse and non- agglomerating. The fraction of Fe in Fe[sub x]Pt[sub (100-x)] was a linear function of Fe(acac)[sub 3] molar fraction. The highest room temperature coercivity (up to 10 kOe) was observed in Fe[sub 53]Pt[sub 47] sample after annealed at 580 °C, which also exhibited the most ordered fct structure. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]