Showing papers on "Particle published in 1995"
TL;DR: In this article, the design and initial characterization of two-dimensional arrays of colloidal Au particles are reported, which are prepared by self-assembly of 12 nm diameter colloidal particles onto immobilized polymers having pendant functional groups with high affinity for Au (i.e., CN, SH, and NH 2 ).
Abstract: The design and initial characterization of two-dimensional arrays of colloidal Au particles are reported. These surfaces are prepared by self-assembly of 12 nm diameter colloidal Au particles onto immobilized polymers having pendant functional groups with high affinity for Au (i.e., CN, SH, and NH 2 ). The polymers are formed by condensation of functionalized alkoxysilanes onto cleaned quartz, glass, and SiO 2 surfaces. The assembly protocol is carried out completely in solution: cleaned substrates are immersed in methanolic solutions of organosilane, rinsed, and subsequently immersed in aqueous colloidal Au solutions. Two-dimensional arrays spontaneously form on the polymer surface. The resulting substrates have been characterized by UV-vis spectroscopy, transmission electron microscopy (TEM), and surface-enhanced Raman scattering (SERS). TEM data show that the particles are spatially separated but close enough to interact electromagnetically (small spacing compared to λ). The UV-vis data show that collective particle surface plasmon modes are present in the 650-750 nm region, suggesting that these assemblies are SERS-active. This is indeed the case, with enhancement factors of roughly. Au colloid monolayers possess a set of features that make them very attractive for both basic and applied uses, including uniform roughness, high stability, and biocompatibility
2,710 citations
TL;DR: Aerosol concentrations and particle size distributions were measured indoors and outdoors at a two-storey residence in California during the summer months as discussed by the authors, where a single central sampling point in the downstairs living area was used for all indoor samples.
824 citations
TL;DR: In this article, dynamic mechanical measurements on several polymers filled with very fine silica particles revealed that these composites exhibit two tan δ peaks, one related to the usual polymer glass transition, while the other, occurring at a higher temperature, was assigned to the glass transition of regions containing reduced mobility.
Abstract: The dynamic mechanical measurements on several polymers filled with very fine silica particles revealed that these composites exhibit two tan δ peaks. One was related to the usual polymer glass transition, while the other, occurring at a higher temperature, was assigned to the glass transition of regions containing chains of reduced mobility. Since many aspects of this behavior were found to be analogous to those of random ionomers, the results support the validity of the EHM model of ionomer morphology. The particle content, the number of monomer units interacting strongly with the surface of the particles, the thermal history of the sample, and the average MW of the polymer were all found to have a significant effect on the area and the maximum of the new tan δ peak. These effects are discussed in terms of a model which is based on the EHM ionomer model but takes into account the formation of tightly bound and loosely bond polymer chains around the filler particles.
594 citations
TL;DR: In this paper, the authors analyzed concurrent observations of particle chemical composition and water content from a continental nonurban (Grand Canyon) and an urban (Los Angeles) location to determine whether the water content of atmospheric particles is influenced by the presence of organics.
Abstract: The optical and chemical properties of atmospheric particles and their ability to act as cloud condensation nuclei (CCN) depend strongly upon their affinity for water. Laboratory experiments have shown that water soluble substances such as ammonium sulfate, ammonium nitrate, and sodium chloride, which are major inorganic components of atmospheric particles, absorb water in an amount proportional to water vapor pressure. Analogous information about the interactions between water and organics, which are another major component of atmospheric particles, is lacking. Here we analyze concurrent observations of particle chemical composition and water content from a continental nonurban (Grand Canyon) and an urban (Los Angeles) location to determine whether the water content of atmospheric particles is influenced by the presence of organics. By comparing the observed water content with the water content expected to be associated with the inorganic fraction, we find that the aggregate hygroscopic properties of inorganic particles are altered substantially when organics are also present. Furthermore, the alterations can be positive or negative. For the nonurban location, organics enhance water absorption by inorganics. In the relative humidity (RH) range of 80–88% organics account for 25–40% of the total water uptake, on average. For the urban location, on the other hand, the net effect of organics is to diminish water absorption of the inorganics by 25–35% in the RH range of 83–93%.
590 citations
TL;DR: The Regional Particulate Model (RPM) as discussed by the authors is a three-dimensional Eulerian model that simulates the chemistry, transport, and dynamics of sulfuric acid aerosol resulting from primary emissions and the gas phase oxidation of sulfur dioxide.
Abstract: The Regional Acid Deposition Model has been modified to create the Regional Particulate Model, a three-dimensional Eulerian model that simulates the chemistry, transport, and dynamics of sulfuric acid aerosol resulting from primary emissions and the gas phase oxidation of sulfur dioxide. The new model uses a bimodal lognormal distribution to represent particles in the submicrometer size range. In addition to including the horizontal and vertical advection and vertical diffusion of the aerosol number concentration and sulfate mass concentration fields, the model now explicitly treats the response of the distribution parameters to particle coagulation within and between the modes, condensation of sulfate vapor onto existing particles, formation of new particles, evaporation and condensation of ambient water vapor in the presence of ammonia, and particle-size-dependent dry deposition. The model has been used to study how the degree of sulfuric acid neutralization by ambient ammonia affects the total aerosol concentrations and particle size distributions over eastern North America. Preliminary results for three representative locations, rural, near-source, and nominal downwind of source, show that the effect is greatest for the rural and smallest for the near-source regions, which corresponds with the largest and smallest values, respectively, of ammonium-to-sulfate molar ratios. The results indicate that the model could provide a tool for investigating the effects of various pollution control strategies, as well as new or alternative formulations of important aerosol processes.
578 citations
TL;DR: In this paper, the theoretical basis of a novel method for producing highly collimated and tightly focused particle beams is discussed, which is to pass the particle-laden gas through a series of axisymmetric contractions and enlargements (so-called aerodynamic lenses) before the nozzle expansion.
Abstract: A particle beam is produced when a particle-laden gas expands through a nozzle into a vacuum. This work discusses the theoretical basis of a novel method for producing highly collimated and tightly focused particle beams. The approach is to pass the particle-laden gas through a series of axisymmetric contractions and enlargements (so-called aerodynamic lenses) before the nozzle expansion. Particles are moved closer to the axis by a lens if the particle sizes are less than a critical value and particles can be confined very closely to the axis by using multiple lenses in series. Since particles close to the axis experience small radial drag forces, they stay close to the axis during nozzle expansion and therefore form a narrow particle beam downstream. The major effects that limit the minimum beam width are Brownian motion and lift forces on particles during the nozzle expansion. Simple theoretical models are developed in this work to estimate the minimum particle beam width set by these effects. While the...
501 citations
TL;DR: In this article, a phase diagram of aqueous dispersions of colloidal plate-like charged particles (300 A x 10 A) is discussed and the role of particle anisotropy coupled with diffuse layer repulsion is discussed.
Abstract: We discuss the phase diagram of aqueous dispersions of colloidal platelike charged particles (300 A x 10 A). Particle concentration and ionic strength are the two parameters controlling the system. The suspensions undergo a sol/gel transition without macroscopic phase separation. Shear rheology is used to monitor this transition and to locate the appearance of the mechanical gel phase. Increasing the ionic strength shifts the sol/gel transition to lower volume fraction. Direct inspection of this gel phase by cryofracture, TEM and SAXS shows correlated but well-separated particle populations. In order to check the reversibility and the equilibrium properties of this transition, the equation of state was determined by osmotic stress. At fixed ionic strength, the osmotic pressure first increases at low particle concentration, then reaches a pseudoplateau, and increases again for higher concentrations. The location of such a singularity in the equation of state of the suspension defines a thermodynamical transition coinciding with the mechanical phase transition. In order to analyze the origin of this gel or glassy phase, the role of particle anisotropy, coupled with diffuse layer repulsion, is discussed.
417 citations
TL;DR: In this article, a particle-beam-forming apparatus for producing narrow particle beams was developed based on the theory discussed in paper I of this series, which consists of a variable number of aerodynamic lenses (short capillaries and/or thin-plate orifices with diameters ranging from 3.5 to 7.0 mm) followed by an accelerating nozzle (3 mm).
Abstract: A particle-beam-forming apparatus for producing narrow particle beams was developed based on the theory discussed in paper I of this series. It consists of a variable number of aerodynamic lenses (short capillaries and/or thin-plate orifices with diameters ranging from 3.5 to 7.0 mm) followed by an accelerating nozzle (3 mm). It was evaluated using monodisperse DOS and NaCl particles (0.02–0.24 μm) at upstream pressures on the order of 1 torr. The particle beams produced by the lens-nozzle system were focused through a skimmer (1 mm) into a high vacuum chamber (10−4–10−5 torr) where the beam widths, velocities and transport efficiencies were measured. The experiments showed that as more lenses were added the particle beam widths were reduced asymptotically to the minimum values. For spherical particles (DOS) these minimum values are in good agreement with the Brownian limit derived in paper I. For nonspherical particles (NaCl) these minimum widths are much larger than the Brownian limit, indicating that b...
401 citations
TL;DR: In this paper, the effects of both particle shape and size on the dissolution rate of sparingly soluble micro-particles have been studied, and the product of the surface shape factor and mean particle diameter was used to discuss the combined effect of these factors on dissolution rates of the microparticles.
383 citations
TL;DR: In this article, the authors made modifications to the procedure used for absorption measurements of aquatic particles retained on glass-fiber filters that extend the procedure's application range to waters with high suspended sediment content and allow the determination of phytoplankton pigment absorption in situations where the standard solvent extraction method is not effective.
Abstract: We made modifications to the procedure used for absorption measurements of aquatic particles retained on glass-fiber filters that extend the procedure’s application range to “case 2” waters with high suspended sediment content and allow the determination of phytoplankton pigment absorption in situations where the standard solvent extraction method is not effective. The first result was achieved by combining light-transmission and light-reflection measurements (the latter made possible by the use of a commercially available integrating-sphere attachment for the dual-beam spectrophotometer) so as to remove the spurious contribution to the measured absorption caused by sample backscattering. The second result was obtained by bleaching the sample with a NaClO solution-a method that proved satisfactory even with water-soluble pigments (e.g. the important class of the phycobilins) and solvent-resistant Chlorophyceae. This process also allows for depigmentation of the particle suspension, and thus it was used to evaluate the empirical expression for converting the filter-retained sample absorbance to the equivalent particle suspension value. Both features of the modified procedure have been positively tested through measurements carried out on solvent-resistant phytoplankton species and on samples of inorganic suspended sediment. Light-transmission measurements on particles retained in glass-fiber filters (Yentsch 1962) are convenient for determining the light absorption spectrum of particle suspensions consisting mainly of natural phytoplankton and organic and inorganic detritus (Gordon and Morel 1983). The procedure has two basic advantages: particles can be concentrated so that instrumental accuracy requirements can be met regardless of the high dilution occurring in situ, and information is provided on the absorption of the cells in vivo. The main problem in data analysis arises from the large modification of light transmission due to multiple scattering by the filter, which results in an overestimate of particle absorption relative to suspension state (Butler 1962). Several empirical expressions have been derived for converting the absorption of filter-retained particles (for convenience also referred to as “sample” in the following) to the equivalent absorption of particle suspension. A review on this subject is given by Cleveland and Weidemann ( 199 3). Kishino et al. (1984, 1985) proposed a procedure for discriminating absorption by phytoplankton pigments from absorption by detritus based on measurements performed before and after pigment extraction by methanol. Although some doubts remain about the effectiveness of the procedure (Bricaud and Stramski 1990) and its validity range shows some limitations (little or no effect on some algal species), solvent extraction is the method generally used to identify pigment absorption in natural phytoplankton populations. It is current practice to minimize the loss of forward
375 citations
TL;DR: A general review of the methods available for the physical characterization of pharmaceutical solids is presented in this article, which is classified as being on the molecular level, the particulate level, and the bulk level.
Abstract: A general review of the methods available for the physical characterization of pharmaceutical solids is presented. The techniques are classified as being on the molecular level (properties capable of being detected in an ensemble of individual molecules), the particulate level (properties which can be detected through the analysis of an ensemble of particles), and the bulk level (properties which can be measured only using a relatively large amount of material). The molecular-level properties discussed are infrared spectroscopy and nuclear magnetic resonance spectrometry, the particulate-level properties discussed are particle morphology, particle size distribution, powder X-ray diffraction, and thermal methods of analysis, and the bulk-level properties discussed are surface area, porosity and pore size distribution, and powder flow characteristics. Full physical characterization of three modifications of lactose (hydrous, anhydrous, and Fast-Flo) is presented to illustrate the type of information which can be obtained using each of the techniques discussed.
TL;DR: In this paper, an improved theoretical model for quantifying the dynamics of colloid deposition in granular porous media is presented, which characterizes the transient aspects of reversible particle deposition onto spherical collector surfaces where repulsive electrostatic forces between colloidal particles limit deposition to monolayer coverage.
Abstract: An improved theoretical model is presented for quantifying the dynamics of colloid deposition in granular porous media. The model characterizes the transient aspects ofirreversible particle deposition onto spherical collector surfaces where repulsive electrostatic forces between colloidal particles limit deposition to monolayer coverage. The transient deposition rate normally associated with particle deposition is depicted in the model by a dynamic blocking function derived from random sequential adsorption (RSA) mechanics. The RSA blocking function has a nonlinear power law dependence on surface coverage, in contrast to the linear Langmuirian blocking function used in previous dynamic deposition models for porous media. A technique involving the calculation of the jamming limit from experimental particle breakthrough curves is utilized for determining the excluded area parameter, an integral component of the dynamic blocking function. Parameter estimation and curve fitting techniques are not required by the model as all parameter values are calculated a priori using available theoretical principles. Parameter values are incorporated into the theoretical model to produce theoretical particle breakthrough curves based on both RSA and Langmuirian dynamic blocking functions. A comparison of theoretical results with experimental particle breakthrough curves demonstrates the utility of RSA mechanics as a means of describing particle blocking dynamics associated with colloid deposition in granular porous media.
TL;DR: The real-space structure of hard-sphere glasses quenched from colloidal liquids in thermodynamic equilibrium has been determined by combining the optical sectioning capability of confocal fluorescence microscopy with the structure of specially prepared fluorescent silica colloids as discussed by the authors.
Abstract: The real-space structure of hard-sphere glasses quenched from colloidal liquids in thermodynamic equilibrium has been determined. Particle coordinates were obtained by combining the optical sectioning capability of confocal fluorescence microscopy with the structure of specially prepared fluorescent silica colloids. Both the average structure and the local structure of glasses, with volume fractions ranging from 0.60 to 0.64, were in good agreement with glasses and random close packings generated by computer simulations. No evidence of a divergent correlation length was found. The method used to obtain the three-dimensional particle coordinates is directly applicable to other colloidal structures, such as crystals, gels, and flocs.
TL;DR: In this article, a semi-empirical model of a particle as a sphere with an exactly determined surface is proposed, which is not adequate in the nanometer size range.
TL;DR: In this article, the effect of the particle size of carbon-supported Pt catalysts on the electrooxidation of methanol was studied and different methods were used to prepare Pt C catalysts with particle sizes ranging between 1.2 and 10 nm.
TL;DR: The formation of a stable finely dispersed aqueous colloidal solution of fullerenes C60 and C70 with particle sizes ⩽0.22 µm is reported in this article.
Abstract: The formation of a stable finely dispersed aqueous colloidal solution of fullerenes C60 and C70 with particle sizes ⩽0.22 µm is reported and hypotheses concerning the nature of the aqueous solutions are discussed.
Patent•
30 Jun 1995
TL;DR: In this article, a method for forming particles of a substance, by co-introducing into a particle formation vessel, in which the temperature and pressure are controlled, of a supercritical fluid; a solution or suspension of the substance in a first vehicle; and a second vehicle which is both substantially miscible with the first vehicle and substantially soluble in the super-critical fluid, in such a way that dispersion of the solution and suspension and the second vehicle, and extraction of the vehicles, occur substantially simultaneously and substantially immediately on introduction of the fluids into the vessel, by the action
Abstract: The invention provides a method for forming particles of a substance, by co-introducing into a particle formation vessel, in which the temperature and pressure are controlled, of a supercritical fluid; a solution or suspension of the substance in a first vehicle; and a second vehicle which is both substantially miscible with the first vehicle and substantially soluble in the supercritical fluid, in such a way that dispersion of the solution or suspension and the second vehicle, and extraction of the vehicles, occur substantially simultaneously and substantially immediately on introduction of the fluids into the vessel, by the action of the supercritical fluid. Preferably the solution/suspension of the substance is introduced separately from the second vehicle, in such a way that contact between the solution/suspension and the second vehicle occurs either substantially simultaneously with, or immediately before, their dispersion by the supercritical fluid and extraction of the vehicles by the supercritical fluid. The method allows a high degree of control over the size, shape, crystalline form and other physico-chemical properties of the particulate product. The invention also provides apparatus for carrying out such a method, using a coaxial nozzle to introduce the fluids into the particle formation vessel, and a particulate product made using the method or the apparatus.
TL;DR: The data indicate that particulate prosthetic debris in the tissues around failed femoral components that have been inserted without cement constitutes a class of particles that are predominantly less than one micrometer in size and are present in amounts of more than one billion particles per gram of tissue.
Abstract: Wear particles from thirty-five membranes obtained during revision hip-replacement operations were studied after digestion of the soft tissue with papain. The particles were isolated and were characterized with use of light and scanning electron microscopic techniques, x-ray microanalysis, and an automated particle analyzer. The mean size of the polyethylene particles was 0.5 micrometer, and the metal particles were a mean of 0.7 micrometer, as determined with scanning electron microscopy. The automated particle analyzer revealed a mean particle diameter of 0.63 micrometer (more than 90 per cent of all particles were less than 0.95 micrometer) and a mean of 1.7 billion particles per gram of tissue, compared with only 143 million per gram of tissue for the control samples. X-ray microanalysis revealed metal debris in sixteen (46 per cent) of the thirty-five membranes after digestion. Thirteen (50 per cent) of the twenty-six membranes surrounding a titanium-alloy stem contained metal particles, compared with three of the nine membranes surrounding a chromium-cobalt stem. Metal debris was present in only one of the twelve membranes surrounding a titanium-alloy stem without a porous coating, compared with twelve of the fourteen membranes surrounding a titanium-alloy stem with a porous coating. This tenfold difference in prevalence was significant (p < 0.005). On the average, the total number of particles (expressed in millions per gram of tissue) associated with the bipolar acetabular components was twice that associated with the fixed acetabular components. In addition, there was a trend toward a larger mean size of the polyethylene particles in association with the bipolar cups. Our data indicate that particulate prosthetic debris in the tissues around failed femoral components that have been inserted without cement constitutes a class of particles that are predominantly less than one micrometer in size and are present in amounts of more than one billion particles per gram of tissue. Routine histological methods did not detect this class of wear debris and led to a gross underestimation of the amount of debris in these membranes.
TL;DR: The authors have reformulated outer sphere relaxation theory to incorporate progressive magnetic saturation of solute nanoparticles and indicate how to use empirical magnetization data for realistic particles when their magnetic properties are not ideal.
Abstract: Organically coated iron oxide crystallites with diameters of 5-50 nm ("nanoparticles") are potential magnetic resonance imaging contrast agents. 1/T1 and 1/T2 of solvent water protons are increased dramatically by magnetic interactions in the "outer sphere" environment of the nanoparticles; subsequent diffusive mixing distributes this relaxation throughout the solvent. Published theory, valid for the solute magnetic energy small compared with thermal energy, is applicable to small magnetic solutes (e.g., gadolinium and manganese diethylenetriaminopentaacetic acid, and nitroxide free radicals) at generally accessible fields (< or = 50 T). It fails for nanoparticles at fields above approximately 0.05 T, i.e., at most imaging fields. The authors have reformulated outer sphere relaxation theory to incorporate progressive magnetic saturation of solute nanoparticles and, in addition, indicate how to use empirical magnetization data for realistic particles when their magnetic properties are not ideal. It is important to handle the effects of rapid thermally induced reorientation of the magnetization of the nanoparticles (their "superparamagnetism") effectively, including their sensitivity to particle size. The theoretical results are presented as the magnetic field dependence (NMRD profiles) of 1/T1 and 1/T2, normalized to Fe content, for three sizes of particles, and then compared with the limited data extant for well-characterized material.
TL;DR: In this article, the motion of solid particles near the wall in a turbulent boundary layer was investigated experimentally in a water flume by flow visualization techniques and by LDA, and the results showed that particle motion, as well as entrainment and deposition processes, are controlled by the action of coherent wall structures, which appear to be funnel vortices.
Abstract: The motion of solid particles near the wall in a turbulent boundary layer was investigated experimentally in a water flume by flow visualization techniques and by LDA. The particles were of polystyrene (specific density ∼1.05) with diameters ranging from 100 to 900 μm. Results show that particle motion, as well as entrainment and deposition processes, are controlled by the action of coherent wall structures, which appear to be funnel vortices. The behavior of the particles is consistent with the motion and effects of such vortices. The vortices appear to cause the formation of particle streaks near the wall, to create suitable conditions for particle entrainment, and to assist in particle deposition by conveying them from the outer flow to the wall region.
TL;DR: In this article, a micro-emulsion technique was used to synthesize metallic cobalt particles in the size range 18 to 44 \AA{} diameter, and the effects of small size were seen in: (1) the anisotropy constant increased markedly as particle size decreased, and (2) the total magnetic moment per atom in the Co particles was enhanced with decreasing particle size.
Abstract: We have used a microemulsion technique to synthesize metallic cobalt particles in the size range 18 to 44 \AA{} diameter. The particles are spherical, not aggregated due to their surfactant coating, and free of oxide. Magnetic properties such as total moment per particle, blocking temperature, and hysteresis all show reasonable size dependencies. The effects of small size are seen in: (1) the anisotropy constant increased markedly as particle size decreased, and (2) the total magnetic moment per atom in the Co particles was enhanced with decreasing particle size by as much as 30% over the bulk value. Magnetization versus applied field curves indicate the particles are heterogeneous with two magnetic phases, possibly a core-shell structure. The core phase has a large total moment and the shell phase is superparamagnetic with an effective moment of 7.5\ifmmode\pm\else\textpm\fi{}1${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ for all sizes. We propose that the shell phase is responsible for the enhanced anisotropy and magnetization.
TL;DR: In this paper, the authors proposed a super-resolution method for high-image-density particle image velocimetry (PIV), which combines correlation analysis of the group of particles in a spot with sub-interrogation-spot particle tracking.
Abstract: The spatial resolution of conventional high-image-density particle image velocimetry (PIV) is determined by the size of the interrogation volume, which is typically a fraction of a millimetre. An improved method of PIV analysis is proposed in which the ultimate resolution of PIV is determined by the smaller of the mean spacing between particles and the displacement of the particles between light pulses. Since these distances must be smaller than the interrogation spot size in the high-image-density limit, the new procedure is referred to as super-resolution. The method combines correlation analysis of the group of particles in a spot with sub-interrogation-spot particle tracking. The theory of the procedure is described and evaluated using Monte Carlo simulations. The feasibility of enhancing resolution significantly is demonstrated by re-analysing turbulent flow PIV data reported by Urushihara et al. (1993). The in-plane resolution has been improved from 250 to 100 mu m.
TL;DR: In this paper, a few glass spheres, marked with a thin coating of silver, were tracked in a suspension of unmarked glass spheres made optically transparent by matching the index of refraction of the suspending fluid to that of the glass spheres.
Abstract: The motion of non‐Brownian spheres settling in the midst of a suspension of like spheres has been experimentally studied under creeping flow conditions. A few glass spheres, marked with a thin coating of silver, were tracked in a suspension of unmarked glass spheres, made optically transparent by matching the index of refraction of the suspending fluid to that of the glass spheres. Particles were tracked with a real time digital imaging processing system. Particle trajectories were examined in the bulk region of the suspension for particle volume fractions ranging from 0% to 40% in 5% steps. Statistical analyses of local particle velocities yield the mean settling velocity, the RMS of the fluctuations of the vertical and horizontal particle velocity and the particle velocity autocorrelation functions. The long time fluctuating particle motion is demonstrated to be diffusive in nature. Vertical and horizontal correlation times and self‐diffusivities are found as a function of particle volume fraction, and a strongly anisotropic diffusion noted.
TL;DR: The question in the title may be answered by considering the outcome of a ``weak measurement'' in the sense of Aharonov, Albert, and Vaidman, and various properties of the resulting time are discussed.
Abstract: The question in the title may be answered by considering the outcome of a ``weak measurement'' in the sense of Aharonov, Albert, and Vaidman. Various properties of the resulting time are discussed, including its close relation to the Larmor times. It is a universal description of a broad class of measurement interactions, and its physical implications are unambiguous.
TL;DR: The experiments show the dynamic nature of micronized albuterol sulfate and aid in the determination of the actual physical state of this pharmaceutical powder.
Abstract: Pharmaceutical powders are often milled to achieve the optimum particle size. These size reduction processes can introduce dislocations and/or defects onto particle surfaces affecting the overall crystallinity of the powder. If enough energy is imparted, amorphous regions on the particle surfaces may be produced. These amorphous regions have the propensity to absorb significant quantities of water. In this study the effect of sorbed water on the physical characteristics of albuterol sulfate is investigated. Physical properties of this compound are studied in both micronized and unmicronized states using scanning electron microscopy, differential scanning calorimetry, powder x-ray diffraction, solution microcalorimetry, laser diffraction particle size analysis and water vapor sorption analysis. Subtle differences in crystallinity induced by air jet micronization are detected by several analytical methods. Amorphous to crystalline conversions are observed, the kinetics of which are found to be both temperature and relative humidity dependent. These experiments show the dynamic nature of micronized albuterol sulfate and aid in the determination of the actual physical state of this pharmaceutical powder.
TL;DR: In this paper, a measurement system consisting of two high speed two-color pyrometers was used to monitor the flattening degree and cooling rate of zirconia particles on a smooth steel substrate at 75 or 150 °C during plasma spray deposition.
Abstract: A measurement system consisting of two high- speed two- color pyrometers was used to monitor the flattening degree and cooling rate of zirconia particles on a smooth steel substrate at 75 or 150 °C during plasma spray deposition This instrument provided data on the deformation behavior and freezing of a particle when it impinged on the surface, in connection with its velocity, size, and molten state at impact The results emphasized the influence of temperature and surface conditions on particle spreading and cooling When the substrate temperature was 150 °C, the splats had a perfect lenticular shape, and the thermal interface resistance between the lamella and the substrate ranged from 10− 7 to 10− 8 W/m2 · K The dependence of the flattening degree on the Reynolds number was investigated
TL;DR: In this article, the authors used backscattering spectrometers, thermogravimetric analysis, and high-resolution transmission electron microscopy to investigate the oxidation behavior of ultrafine grain aluminum powder.
Abstract: Rutherford backscattering spectrometry, thermogravimetric analysis, and high‐resolution transmission electron microscopy were used to investigate the oxidation behavior of ultrafine grain aluminum powder. Fractional change in mass of Al powder samples were obtained as a function of temperature and exposure time for samples with different particle size distributions. As expected from surface energy considerations, the activation energy for oxidation of ultrafine grain particles is less than that for nominally flat surfaces. Activation energy for oxidation of powder samples with average particle diameters from 240 to 650 A was determined to be 0.5 eV, which is smaller than the value of 1.7 eV known for flat Al samples.
TL;DR: In this article, the velocity, flux, and concentration distribution of solid particles in a turbulent boundary layer of a horizontal water flume were investigated experimentally by means of LDA and visualization techniques.
Abstract: The velocity, flux, and concentration distribution of solid particles in a turbulent boundary layer of a horizontal water flume were investigated experimentally by means of LDA and visualization techniques. The particles were of polystyrene (specific density ∼1.05). Results show that coherent wall structures are responsible for most of the characteristics of particle behavior throughout the boundary layer. Particles are often concentrated in regions of low velocity, associated with wall structures, and as a result the average particle velocity is lower than the fluid’s. This was also noted previously by Rashidi et al., but not explained. The actual relative velocity between the particles and the surrounding fluid is often small. In addition, the data suggest that as the shear rate increases, the particle flux profiles asymptotically approach a shape where a strong gradient of particle flux exists in the lower part of the boundary layer (y+≤250), while it is relatively constant at higher elevations. This phenomenon may also be attributable to interactions with the wall structures.
TL;DR: In this article, the dynamical behavior of collisional ring systems via a local simulation which includes mutual gravitational forces between particles is studied via direct force calculations involving up to a few thousand identical particles with parameter values appropriate to Saturn's rings.
TL;DR: In this article, a ternary nucleation model for the H2SO4-NH3-H2O system is presented in an effort to examine the effect of NH3 on heteromolecular homogeneous nucleation in the marine boundary layer (MBL).
Abstract: A ternary nucleation model for the H2SO4-NH3-H2O system is presented in an effort to examine the effect of NH3 on heteromolecular homogeneous nucleation in the marine boundary layer (MBL). The results from this nucleation model suggest that ammonia could, in fact, enhance the nucleation rate over that of the binary system, H2SO4-H2O. The magnitude of this enhancement is introduced as an enhancement ratio, which, in principle, is applicable to any binary nucleation rate for H2SO4-H2O. Also presented are preliminary results from a simple aerosol model using this enhancement ratio. These results suggest that under conditions typical of the marine environment it may be possible to produce enough particles to balance the various particle sinks characteristic of the MBL.