Characterization of expiration air jets and droplet size distributions immediately at the mouth opening

Size distributions of expiratory droplets expelled during coughing and speaking and the velocities of the expiration air jets of healthy volunteers were measured. Droplet size was measured using the interferometric Mie imaging (IMI) technique while the particle image velocimetry (PIV) technique was used for measuring air velocity. These techniques allowed measurements in close proximity to the mouth and avoided air sampling losses. The average expiration air velocity was 11.7 m/s for coughing and 3.9 m/s for speaking. Under the experimental setting, evaporation and condensation effects had negligible impact on the measured droplet size. The geometric mean diameter of droplets from coughing was 13.5 μm and it was 16.0 μm for speaking (counting 1–100). The estimated total number of droplets expelled ranged from 947 to 2085 per cough and 112–6720 for speaking. The estimated droplet concentrations for coughing ranged from 2.4 to 5.2 cm^?3 per cough and 0.004–0.223 cm^?3 for speaking.     

Exposure to welding particles in automotive plants

This work presents a monitoring study designed to evaluate workers' exposure to particles in several body shops within automotive plants. Concentrations in the proximity of welding activities were measured by a Fast Mobility Particle Sizer, several Condensation Particle Counters, a Nanoparticle Surface Area Monitor and a laser photometer, as well as by several gravimetric samplers. Average concentrations were found to be 1×10⁵ part cm^?3, 3×10³ μm² cm^?3 and 0.4 mg m^?3 for number, surface area and PM₁ concentration, respectively (worst case). Very high concentrations, particularly for surface area, were observed in locations with a high density of manual resistance welding activities or close to oxyacetylene welding activities. Welding emission factors in the automotive plants were also evaluated and in the most critical body shop, the overall welding activities led to emission factors of 2.8×10¹⁵ part min^?1, 7.0×10⁶ μm² min^?1 and 7.9 g min^?1 for number, surface area and PM₁ concentrations, respectively. Finally, particle concentration characterization, along with air exchange ratio measurements in the body shop, showed that the indoor concentrations and, hence, worker particle exposure can be reduced through the use of local exhaust ventilation.     

Impactor designed to increase mass output rate of nanoparticles from a pneumatic nebulizer

A modular impactor was designed to remove large droplets from aerosols generated by a pneumatic nebulizer, the Six-Jet Atomizer from TSI Inc. (Shoreview, MN), with the aim of generating dry nanoparticles. Three interchangeable nozzle heads were designed to provide droplet cutoff diameters of 0.5, 1, and 2 μm at an air flow rate of 8.3×10^?4 m³ s^?1 (50 L min^?1), which corresponds to all six jets of the nebulizer operated at 25 °C and an air pressure of 241 kPa (35 psi). The collection and output characteristics of the 0.5 μm impactor were evaluated from dry particle size distributions produced by nebulizing an aqueous solution with a NaCl mass fraction of 1% both with and without the impactor present. The impactor characteristic cutoff curve was sharp (impactor geometric standard deviation, GSD_imp=1.15–1.19) with a 50% cutoff diameter d₅₀ that ranged from 0.48 μm at 3.0×10^?4 m³ s^?1 to 0.74 μm at 11.7×10^?4 m³ s^?1. The rate of dry NaCl particle generation ranged from 0.5 to 5 g s^?1 (0.04 to 0.4 g day^?1) with mass median diameters MMD_p=80–123 nm and geometric standard deviations GSD_p=1.6–1.8 (depending on flow rate). Anomalous negative impactor efficiencies were observed at flow rates >8.3×10^?4 m³ s^?1 for 100 to 400 nm droplets and at all flow rates for droplets smaller than 100 nm. This phenomenon will be investigated further as a way to increase the generation rate of nanoparticles. A step-by-step procedure is presented for the selection of an appropriate impactor design and operating flow rate for a desired maximum aerosol particle size.     

Characteristics of samaria-doped ceria nanoparticles prepared by spray pyrolysis

Samaria-doped ceria (SDC) nanoparticles were prepared by spray pyrolysis. The means sizes of the samaria-doped ceria nanoparticles were controlled from 21 to 150 nm by changing the calcination temperatures between 700 and 1200 °C. The pellets formed from the SDC particles calcined at temperatures between 700 and 1000 °C had similar grain sizes between 0.75 and 0.82 μm. However, pellet formed from the SDC particles calcined at a temperature of 1200 °C had large grain size of 1.22 μm. The pellet formed from the SDC particles calcined at a temperature of 1000 °C had slightly smaller resistance of grain-boundary than those of the pellets formed from the SDC particles calcined at temperatures between 700 and 900 °C. However, the pellet formed from the SDC particles calcined at a temperature of 1200 °C had low resistance of grain-boundary. The pellet formed from the SDC particles calcined at a temperature of 1200 °C had conductivity of 44.65 × 10^?3 S cm^?1 at a measuring temperature of 700 °C that more twice than those of the pellets formed from the SDC calcined below 1000 °C.     

Application of the dusty plasma method for preparation of diamond ceramics

Diamond particles 3–7 μm in size sustained in plasma in a high-dispersion state were coated with cobalt by magnetron sputtering. The relative concentration of cobalt in obtained powders was 2–3 mass. %. Sintering the diamond powders with the cobalt coating under the pressure of 8 GPa and the temperatures of 2000–2100 K resulted in the production of homogeneous specimens having the density of 3.6 ± 0.1 g cm^− 3. The produced diamond compacts demonstrated high values of the ultrasonic wave propagation velocity and elastic moduli.     

Particle size effects in flash sintering

The study of 3 mol% yttria stabilized zirconia (3YSZ) with different particle sizes provides new insights into flash sintering. Four powders, all with the same crystallite size but various particle size were investigated: described as nominally 1 μm (D80 = 0.51 μm, meaning 80 vol% has a size less than 0.51 μm), 2 μm (D80 = 0.90 μm), 5 μm (D80 = 2.11 μm) and 10 μm (D80 = 3.09 μm). While the furnace temperature for flash sintering, at a field of 100 V cm^?1, increased from 920 °C to 1040 °C with particle size, the specimen temperature in all instances remained at ～1200 °C. The quantum increase in density decreased with larger particles. The grain size distribution of conventionally and flash sintered specimens remained similar, with some evidence of a preponderance of nanograins in the flash sintered specimens. Joule heating was well below the temperatures that would have been required for sintering in a few seconds. An explanation based upon the nucleation of Frenkel pairs is proposed.     

The effect of fast neutron irradiation on the performance of synthetic single crystal diamond particle detectors

Diamond is known for its extreme hardness which may allow it to operate as a particle detector in high fluence environments even after absorption of large radiation doses. We present a study of the deterioration of the charge collection efficiency (CCE) due to neutrons produced by ²³⁵U fission, with irradiation fluences up to 1 × 10¹⁶ n cm^?2. The planar devices were fabricated by thermal evaporation of Au onto approx. 300 μm thick high purity chemical vapour deposited diamond produced by Element Six Ltd., UK. The detector performance was investigated as a function of bias voltage at room temperature using ²⁴¹Am α-particles and minimum ionising particles (MIPs) of a ⁹⁰Sr source. At low fluences up to 2 × 10¹³ n cm^? 2, the detectors reach the initial saturated signal amplitude after irradiation. However, the signal is less stable and deteriorates due to polarisation. This effect can be reduced by initial priming with X-rays. No peak could be distinguished in the detector response in the unprimed state after 10¹⁶ n cm^? 2 with bias voltages up to 1000 V (equivalent to 32 kV cm^?1). However, a peak at about 18% CCE could be recovered after priming.     

Zn2+-imprinted porous polymer beads: Synthesis,structure, and selective adsorption behavior for template ion

Zn²⁺-imprinted polymer was synthesized in porous spherical forms via a self-assembled complex between 2,2′-bipyridyl/4-vinylpyridine complexant/functional monomer and Zn²⁺ template ion. Diameters of particles ranged from 250 to 550 μm to enlarge the surface area and thus enhance the adsorption capacity. The presence/absence of the template ion in the preparation of the imprinted polymer was confirmed by EDX spectroscopy, and the physical structure of the particles was investigated using ESEM and BET analysis. The particle and the pore size were controlled by the cross-linker/monomer feed ratio. The adsorption capacity of the imprinted polymers was 210.61 μmol g^?1 for Zn²⁺, while those for Cu²⁺, Ni²⁺, and Pb²⁺, were 37.92 μmol g^?1, 33.02 μmol g^?1, and 9.70 μmol g^?1, respectively. This big discrepancy of the adsorption capacities illustrates the excellent separation selectivity of the imprinted polymers. The adsorption capacity decreased significantly at pH below 4.5, as the polymers are easily protonated. The imprinted particles lost only 10 % of their adsorption ability after 10 repeated uses.     

Micromoulding of PZT film structures using electrohydrodynamic atomization mould filling

In this work, electrohydrodynamic atomization combined with a photolithography polymeric micromoulding technique was used to form PZT ceramic structures. PZT thick film structures consisting of squares and rectangles of various sizes and separations were produced and used to evaluate the process. An expansion effect of approximately 10 μm on the ceramic structure width relative to the 200 μm wide mould design was observed. The minimum continuous gap between features achieved using this process was 13.5 μm, and the smallest regular PZT square structure obtainable was 106 μm in width. A sloping side wall of the PZT structures caused by the shielding of the photoresist mould was also observed in the process. The resulting PZT structures had a homogenous microstructure and exhibited a relative permittivity of 250, d_33, f of 67 pCN^?1 and remnant polarisation of 8.8 μC/cm².     

Removal of aqueous Fe2+ using MnO2–clinoptilolite in a batch slurry reactor: Catalyst synthesis,characterization and modeling of catalytic behavior

An Iranian clinoptilolite has been modified with MnO₂ for the catalytic removal of Fe²⁺ cations from water in a batch slurry reactor. The modified zeolite was subjected to FESEM, XRD, WDX, XRF and specific surface area analysis. A correlation for the intrinsic catalytic reaction rate incorporating both Fe²⁺ and dissolved oxygen concentration as a function of reaction temperature has been presented. The effect of the modified zeolite aggregate particle size on the iron removal kinetics has been investigated. It was shown that for particles larger than 150 μm, diffusion through the mesopores of the zeolite aggregate is rate controlling. The effective diffusion coefficient through the particles at RT has been calculated as 2.3 × 10^?6 cm² s^?1. It is shown that liquid phase molecular diffusion within the mesopores is the dominating mass transfer mechanism.     

Titania ultrafiltration membrane: Preparation,characterization and photocatalytic activity

A mesoporous photocatalytic titania (TiO₂) membrane on alumina support is successfully fabricated via the sol–gel processing method. Several techniques such as dynamic light scattering, X-ray diffraction (XRD), TGA, N₂-sorption, and SEM are utilized to investigate the optimized processing parameters and their influence on the final properties of the developed membrane. The prepared titania sol containing organic additives (HPC and PVA) has an average particle size of 55.6 nm with a narrow distribution. The resulting TiO₂ membrane with thickness of 1 μm exhibits homogeneity with no cracks or pinholes. It also maintains small pore size (4.7 nm), large specific surface area (75 m²/g), and small crystallite size (8.3 nm).The permeability and photocatalytic properties of the titania membrane were measured. The permeability coefficient of the fabricated membrane is 30.09 cm³ min^?1 bar^?1 cm^?2. These measurements indicate an optimum processing condition for the preparation of the membrane. The prepared titania membrane has a great potential in developing high efficient water treatment and reuse systems because of its multifunctional capability such as decomposition of organic pollutants and physical separation of contaminants.     

COAGULATION OF CIGARETTE SMOKE PARTICLES

Experimental measurements on the deposition of cigarette smoke particles (CSP) in the human airways have produced results that are inconsistent with typical deposition data based on particle size. Previous work relating to hygroscopic growth indicates that hygroscopicity alone can not account for this discrepancy. The present study investigates coagulation of CSP modeled as a polydisperse-charged aerosol as a possible explanation. The results of the model more accurately predict the experimental coagulation data for mainstream CSP than models that treat CSP as a monodisperse or polydisperse-uncharged aerosol. An aerosol with an initial charge distribution based on Boltzmann equilibrium yields slightly larger coagulation rates than the mainstream CSP polydisperse-charged model. The numerical results indicate that the size and charge distribution of sidestream CSP, with a concentration of 10⁶ particles cm^-3, remain stable. In 2 s, the size distribution of mainstream CSP, with a concentration of 10⁹ particles cm^-3, shifts to a larger size while becoming flatter and wider. The diameter of average mass increases from 0.29 to 0.5 μm. Numerical results confirm experimental reports for mainstream CSP, which indicate that the total number of charged particles increases with time and, in the early stages of coagulation, the amount of charge per particle cannot be estimated based on the particle size. This study shows that polydisperse-charged CSP, allowed to coagulate for 2 s in the mouth, will not produce size distributions that yield the observed deposition of CSP. However, additional coagulation will take place as the CSP travels through the respiratory tract, which will be investigated in future work.     

Production of silica aerogel microparticles loaded with ammonia borane by batch and semicontinuous supercritical drying techniques

Silica aerogel microparticles were prepared by supercritical drying and used as support for hydrogen-storing ammonia borane (AB). The formation of aerogel microparticles was done using two different processes: batch supercritical fluid extraction and a semicontinuous drying process. Silica aerogel microparticles with a surface area ranging from 400 to 800 m²/g, a volume of pores of 1 cm³/g, and a mean particle diameter ranging from 12 to 27 μm were produced using the two drying techniques. The particle size distribution (PSD) of the microparticles was influenced by shear rate, amount of catalyst, hydrophilic–hydrophobic solvent ratio and hydrophobic surface modification. In particular, irregular aerogel particles were obtained from hydrophilic gels, while regular, spherical particles with smooth surfaces were obtained from hydrophobic gels. AB was loaded into silica aerogel microparticles in concentrations ranging from 1% till 5% wt. Hydrogen release kinetics from the hydride-loaded aerogel was analyzed with a volumetric cell at 80 °C. By stabilization of AB into the silica aerogel microparticles, an improvement of the release rate of hydrogen from AB was observed.     

Formation of PZT micro-scale structures using electrohydrodynamic atomization filling of metallic moulds

In our previous work electrohydrodynamic atomization (EHDA) combined with a photolithography polymeric micromoulding technique was used to form PZT ceramic micro-scale structures. The major drawback of this technique was the deformation of the polymeric mould resulting in irregular PZT structures.In order to overcome the above drawback, nickel micromoulds were used in this work to form PZT structures. It was observed that the PZT structures presented more regular features compared with those obtained from polymeric micromoulds. The smallest PZT square sizes and separations achieved were 78 μm and 31 μm, which correspond to the minimum nickel micromould cavity obtainable. The side wall angle was increased by using a release agent to prevent excessive build up of PZT at the edges of the mould cavity. The resulting PZT structures exhibited a relative permittivity of 240, d_33,f of 70 pCN^?1 and remnant polarisation of 9.3 μC cm^?2 at 35 V μm^?1.     

Direct electron transfer in a mediator-free glucose oxidase-based carbon nanotube-coated biosensor

A novel biosensor was prepared by immobilizing glucose oxidase on multi-walled carbon nanotube (MWCNT)-coated electrospun gold fibers. Homogeneous coating of the electrospun gold fibers by MWCNTs was achieved by electrophoretic deposition at 20 V (40 V cm^?1), a deposition time of 30 s and a solution concentration of 0.25 mg mL^?1. Scanning electron microscopy confirmed the complete coverage of MWCNTs on the fiber surface. The carboxylated MWCNTs on the gold fibers provided an anchor for covalent immobilization of glucose oxidase (GOX). GOX covalently coupled to conductive carbon nanotubes demonstrated direct electron transfer between the enzyme and the electrode surface without the need for a redox active mediator. Electrochemical characterization of the fabricated sensor by cyclic voltammetry revealed that the immobilized GOX exhibited a surface-confined reversible two-electron and two-proton reaction, with an electron transfer rate constant, k_s, of 1.12 s^?1 and a surface coverage of 1.1 × 10^?12 mol cm^?2. The sensor produced a linear response to glucose concentration up to 30.0 mM with a sensitivity of 0.47 μA mM^?1 cm^?2 and a detection limit of 4 μM.     

Vertical structure Schottky barrier diode fabrication using insulating diamond substrate

To obtain high current operation of the diamond SBDs, the device should be designed in a vertical type structure in order to minimize the device on-resistance. In this research, we have designed and developed the technology for fabrication of diamond vertical structure Schottky barrier diodes (vSBD) by utilizing Inductively Coupled Plasma etching technique. Free standing CVD grown epilayers (p⁺/p^? = 100 μm/5 μm) were obtained by removing the base Ib substrate on which the epi-layers were grown, using ICP etching process. After ICP etching, ohmic contact (Ti/Pt/Au) was made at the bottom of p⁺ layer, and Schottky contact (Mo) was made at top side on oxidized surface of p^? layer, to realize Diamond/Mo vSBDs and were analyzed for their electrical characteristics. The SBDs showed a reproducible ideality factor close to 1.0, and a barrier height of 1.4 eV, with a small standard deviation of 0.06 and 0.12 eV respectively. Diodes in the vertical structure exhibited R_on with a battery uniformity irrespective of their location on the wafer, compared the diodes in a pseudo-vertical structure. Room temperature I–V analysis of the fabricated vSBDs (70 μm size) exhibited a high forward current density of 2980 A/cm² (= 0.115 A) with a low R_onS of 8 mΩ cm², which could be attained due to the vertical geometry of the diodes. At the high temperature operation, still higher current density could be obtained. Satisfactory reverse blocking characteristics also could be achieved with a breakdown field of 2.7 MV/cm for small size diodes.     

The formation and growth of Fe2O3 nanoparticles from the photo-oxidation of iron pentacarbonyl

Particle size distributions from a series of experiments involving the photo-oxidation of iron pentacarbonyl [Fe(CO)₅] in ozone at atmospheric pressure and 295 K are reported for a range of initial reactant concentrations, varying photolysis rates and particle growth times. These data sets were used to test a model which describes the formation of FeO₃ in the gas phase, followed by clustering to produce primary Fe₂O₃ particles. These subsequently coagulate to form fractal-like structures as a result of magnetic dipole coupling of the primary particles.For the smallest size, spherical particles, Smoluchowski theory was used to determine a coagulation constant (k_S) of 7.0×10^?10 cm³ s^?1, indicating a primary particle diameter of 6.6 nm, in very good agreement with the optimised value used in the particle growth model for this system.Finally, these findings are used in discussion of the formation and growth of Fe₂O₃ ‘meteoric smoke’ particles in the upper atmosphere.     

Size distribution of exhaled particles in the range from 0.01 to 2.0 μm

This study investigates the number size distribution of endogenously produced exhaled particles during tidal breathing and breathing with airway closure. This is the first time that the region below 0.4 μm has been investigated. The particle concentration was generally lower for tidal breathing than for airway closure, although the inter-individual variation was large. During tidal breathing, the size distribution peaks at around 0.07 μm. This peak is still present during the airway closure manoeuvre, but an additional broad and strong peak is found between 0.2 and 0.5 μm. This suggests that different mechanisms govern the generation of particles in the two cases. The particles produced from airway closure may be attributed to formation of film droplets in the distal bronchioles during inhalation. It is speculated that the very small particles are film droplets originating from the alveolar region.     

Low cost preparation of high thermal conductivity carbon blocks with ultra-high anisotropy from a commercial graphite paper

A carbon block with ultra-high anisotropy was produced from a commercial graphite paper as the thermal reinforcement and a thermosetting phenolic resin as the binder. Hot-pressing at a maximum temperature of 200 °C was used to densify and integrate the graphite paper stacks. It has been found that the graphite paper blocks have high thermal conductivities in the paper direction and low ones perpendicular. An anisotropy of 98.8% and a thermal conductivity of 197.8 W m^?1 K^?1 in the paper direction were achieved when the density was 1.1 g cm^?3. The thermal conductivity increased to 284.8 W m^?1 K^?1 with a decrease of anisotropy to 98.3% with a density of 1.56 g cm^?3.     

Grain size effect on electrical properties of Mn-modified 0.67BiFeO3–0.33BaTiO3 lead-free piezoelectric ceramics

To investigate how grain size affects the dielectric, ferroelectric, and piezoelectric properties of Mn-modified 0.67BiFeO₃–0.33BaTiO₃ ceramics, we prepared samples with a wide variety of grain sizes from 4.1 μm to 0.59 μm via a conventional solid-state process that use the normal and the two-step sintering methods. Small-signal dielectric measurements show that all the samples exhibit a relaxor-like behavior and that grain size has little influence on the room-temperature dielectric permittivity. For grain sizes below 2 μm, the remanent polarization P_r and piezoelectric coefficient d₃₃ decrease with the grain size, whereas they remain almost constant near P_r = 27 μC/cm² and d₃₃ = 70 pC/N in samples with grain sizes exceeding 2 μm. The mechanism underlying the observed grain size effect is discussed in terms of the electric-field-induced formation of macroscopic ferroelectric domains.