New bio-aerosol collector using a micromachined virtual impactor

For collection and concentration of bioaerosols, we designed and evaluated a single stage virtual impactor, which was fabricated by micro-electro-mechanical systems (MEMS) process. The cut-off diameter of 1 μm was selected, since 1 μm is the lowest size as used in the US Government Joint Biological Point Detection System [Haglund, J. S., & McFarland, A. R. (2004). A circumferential slot virtual impactor. Aerosol Science and Technology, 38, 664–674; Moshier, T., & Buonaugurio, T. (2000). Joint Biological Point Detection System (JBPDS) requirements and design interplay. Proceedings of the First Joint Conference on Point Detection for Chemical and Biological Defense, October 23–27, 2000, Williamsburg, VA.] The design value of a 1 μm cut-off diameter required a nozzle width and thickness of 880 and 200 μm, respectively. The virtual impactor was evaluated for physical and biological collection efficiencies. For the performance evaluation of physical collection efficiency and wall loss, polystyrene latex (PSL) particles were generated from an atomizer and their size distribution was measured using an aerodynamic particle sizer (APS, TSI model 3321) and a scanning mobility particle sizer (SMPS, TSI model 3936). The measured cut-off diameter was 0.95 μm, which agreed with the calculated results (=0.94 μm) determined with a commercial computational fluid dynamics (CFD) package, FLUENT, and the measured wall loss was below 33.5%. For the performance evaluation of biological collection efficiency, Staphylococcus epidermidis bioaerosols were dispersed into air by a nebulizer. The bioaerosols were measured using APS and sampled with a bioaerosol sampler. The overall physical collection efficiency based on the number concentration was 73.8±3%, which was similar to the one based on the number of colonies (=76.7±7%). We found that most of the bioaerosols collected and concentrated by our virtual impactor were viable.     

Ball milling assisted hydrothermal synthesis of ZrO2 nanopowders

The formation of ZrO₂ nanopowders under various hydrothermal conditions such as temperature, time, autoclave rotation speed, heating rate and particularly assistance of ball milling during reaction was investigated. Full ZrO₂ formation (with monoclinic phase) from zirconium solution was completed at shorter times with increasing temperature such as after 4 h at 150 °C, 2 h at 175 °C and less than 2 h at 200 °C. Crystallite size increased from 2.9 to 4 nm with increasing reaction temperature from 125 °C to 200 °C, respectively. Ball milling assisted hydrothermal runs were performed to understand the effect of mechanical force on phase formation, crystallinity and particle size distribution. Monoclinic ZrO₂ was formed in both milled and non-milled runs when zirconium solution was used. Mean particle size for the 2 M solution was measured to be 94 nm for the milled and 117 nm for the non-milled powders. However, when amorphous aqueous zirconia gels (precipitated at pH 5.8) were used, tetragonal phase was also formed in addition to monoclinic phase. Mean particle size was measured to be 0.7 μm (d₉₀≅1.3 μm) for the milled and 7.9 μm (d₉₀≅13 μm) for the non-milled powders. Ball milling during hydrothermal reactions of both zirconium solution and aqueous zirconium gel resulted in smaller crystallite size and mean particle size and, at the same time, effectively controlled particle size distribution (or agglomeration) of nanopowders.     

Effect of particle size on the mechanical properties of reaction bonded boron carbide ceramics

In the present communication, effect of boron carbide particle size on the mechanical properties such as hardness, fracture toughness and flexural strength of reaction bonded boron carbide (RBBC) ceramics were investigated. RBBC composites were produced by the reactive infiltration of molten silicon into porous preform containing boron carbide and free carbon. Boron carbide powders with mean particle size of 18.65 μm, 33.70 μm and 63.35 μm were chosen for the RBBC composites. The experimental results show that hardness increases from 1261.70±64.74 kg/mm² to 1674.90±100.00 kg/mm² and fracture toughness drops from 5.76±0.26 MPa m^1/2 to 3.4±0.37 MPa m^1/2. However, flexural strength decreases from 403.41±5.70 MPa to 256.15±25.05 MPa with the increase in particle size. Indentation induced cracks in RBBC are mainly median type and number of cracks increase with the increase of starting particle size.     

Preparation of kanamycin powder by an optimized spray freeze-drying method

The physical and antibiotic properties of kanamycin powders obtained by spray freeze drying (SFD) were compared with those of raw kanamycin. The SFD procedures were optimized to prepare kanamycin for use as an inhaled drug. Scanning electron microscopy (SEM) and a laser particle size analyzer were applied to estimate physical structure and properties of the particle. In addition, the disk diffusion method was used to compare the antibiotic activity of raw kanamycin and that produced by SFD. According to SEM, the kanamycin particles had various sizes and shapes with porous structures at different SFD conditions. The diameters of the kanamycin powders were between 13.5 μm and 21.8 μm, and their aerodynamic particle sizes were between 3.58 μm and 6.39 μm. The antibiotic activities of the raw and spray freeze-dried kanamycin samples were not significantly different (P > 0.05). The optimized conditions for annealing temperature, annealing time, kanamycin concentration, pressure, and nozzle tip lift were ? 15 °C, 5 h, 10% kanamycin, 100 kPa, and, 1 mm, respectively.     

Micronization of ketoprofen by the rapid expansion of supercritical solution process

The particle size of the pharmaceutical substances is important for their bioavailability (the percentage of the drug absorbed compared to its initial dosage). The absorption rate can be increased by reducing particle size of the drug particles. This study was conducted to investigate the effects of the extraction pressure (140–220 bar), extraction temperature (308–338 K), nozzle length (2–15 mm), effective nozzle diameter (450–1700 μm), and collection distance (1–10 cm) on the size and morphology of the precipitated ketoprofen particles. The characterization (size and morphology) of the particles was investigated using scanning electron microscopy (SEM). The average particle size of the original material was 115.42 μm, while the average particle size of the micronized particles is between 0.35 and 7.03 μm near to quisi-spherical, needle and irregular shape depending upon the experimental conditions.     

Grain size effect on the structural and dielectric properties of Pb0.85La0.15TiO3 ferroelectric ceramic compound

This paper presents a study of the influence of particle size on the structural and dielectric properties of Pb_0.85La_0.15TiO₃ (PLT15) ferroelectric ceramic samples. The samples were prepared with average grain size of 1.69 ± 0.08 μm and 146 ± 8 nm using, respectively, conventional and spark plasma sintering techniques. A decrease in the tetragonality degree as the crystallite size decreased was explained by an internal stress caused by the existence of a large amount of grain boundaries. The local structure exhibited no significant modification and the dielectric measurements showed a diffuse phase transition and a reduction in the permittivity magnitude at T_m as the average grain size decreased. The nanostructured ceramic sample prepared at a relatively lower temperature and sintering time presented a dielectric constant value of approximately 2000 at room temperature.     

Micronization and characterization of squid lecithin/polyethylene glycol composite using particles from gas saturated solutions (PGSS) process

Lecithin was isolated from squid viscera residues after supercritical carbon dioxide (SC-CO₂) extraction at 25 MPa and 45 °C. The particle formation of squid lecithin with biodegradable polymer, polyethylene glycol (PEG) was performed by PGSS using SC-CO₂ in a thermostatted stirred vessel. By applying different temperatures (40 and 50 °C) and pressures (20–30 MPa), conditions were optimized. Two nozzles of different diameters (250 and 300 μm) were used for PGSS and the reaction time was 1 h. The average diameter of the particles obtained by PGSS at different conditions was about 0.74–1.62 μm. The lowest average size of lecithin particle with PEG was found by the highest SC-CO₂ density conditions with the stirring speed of 400 rpm and nozzle size of 250 μm. The inclusion of lecithin in PEG was quantified by HPLC. Acid value and peroxide value was measured after micronization of lecithin.     

Microstructure and high temperature 4-point bending creep of sol–gel derived mullite ceramics

Four-point bending creep behavior of mullite ceramics with monomodal and bimodal distribution of grain sizes was studied in the temperature range of 1320–1400 °C under the stresses between 40 and 160 MPa. Mullite ceramic with bimodal grain size distribution was prepared using aluminum nitrate nonahydrate as alumina precursor. When γ-Al₂O₃ or boehmite were used as alumina precursors, mullite grains are equiaxial with mean particle size of 0.6 μm for the former and 1.3 μm for the latter alumina precursor. The highest creep rate exhibited the sample with monomodal morphology and grains in size of 0.6 μm, which is about one order of magnitude greater than that for the monomodal morphology but with grains in size of 1.3 μm. The highest activation energy for creep (Q = 742 ± 33 kJ/mol) exhibits mullite with equiaxial grains of 1.3 μm, whereas for sample with smaller equiaxial grains the activation energy is much smaller and similar to mullite ceramics with bimodal grain morphology. Intergranular fracture is predominant near the tension surface, while transgranular more planar fracture is predominant near the compression surface zone.     

Polymethylmethacrylate (PMMA) sub-microparticles produced by Supercritical Assisted Injection in a Liquid Antisolvent

A recently developed supercritical assisted process, called Supercritical Assisted Injection in a Liquid Antisolvent (SAILA) is proposed to produce polymer micro and nanoparticles in water stabilized suspensions. Polymethylmethacrylate (PMMA) has been selected as the model polymer for a systematic study of the influence of the SAILA operating parameters on particle morphology and diameter. The effect of expanded liquid injection pressure on particle size and distribution was studied and different expanded liquid temperatures and compositions were also explored. Successful precipitation of the polymer in a water stabilized suspension was obtained and narrow particle size distributions were obtained using 70 and 90 bar injection pressures. PMMA particles controlled diameter were produced ranging between 0.2 ± 0.04 μm and 0.9 ± 0.2 μm. Particles are formed from the expanded liquid solution as a consequence of very fast supersaturation produced by spraying it the liquid antisolvent.     

Development of a system to rapidly measure sampler penetration up to 20 μm aerodynamic diameter in calm air,using the aerodynamic particle sizer

Although the use of monodisperse aerosols to measure penetration through sampling devices results in accurate measurements, it is time consuming and expensive. Measurement methods using polydisperse aerosols are orders of magnitude faster, but tend to be restricted to smaller particle diameters. This is particularly the case with systems using the Aerodynamic Particle Sizer (APS) in calm air, which are limited by poorly characterised aspiration efficiency and low detection efficiency above approximately 10 μm. By measuring the aspiration of such a system in calm air, and introducing a virtual impactor to act as an aerosol concentrator above 10 μm, we have developed an APS-based penetration measurement system that may be used successfully up to 20 μm. Experimental errors (±1 S.D.) are typically less than 20–25% at 20 μm, reducing to below an estimated 10% at 15 μm. Errors below 10 μm are of the order of a few percent. The system is ideally suited to the rapid and inexpensive development of size selective aerosol samplers with cut points below 15 μm, and is capable of quantifying the performance of such samplers under calm air conditions.     

Physicochemical properties of talc ore from three deposits of Lamal Pougue area (Yaounde Pan-African Belt,Cameroon), in relation to industrial uses

Three talc deposits were discovered at Ngoung, Lamal Pougue and Bibodi Lamal (Cameroon). They derived from ultramafic rocks and are enclosed in a Pan-African garnet and muscovite-bearing mica schist of the Yaoundé series. The physico-chemical properties of these talc deposits have been investigated by different techniques including Scanning Electron and Transmission Microscopy (SEM and TEM), chemical analyses, X-ray diffraction (XRD), infrared spectroscopy, particle size analysis by laser diffraction and low temperature gas absorption–desorption. The mineralogical composition deduced from XRD is wide (talc + chlorite + tremolite ± anthophyllite ± chromite ±serpentine ± brucite ± magnesite ± dolomite), but due to the high talc contents (≈ 90%) the samples are close to monomineralic. SEM studies reveal that all talc deposits comprise bundles of platy talc and a few prismatic crystals of amphiboles and other contaminating minerals. Laser diffraction confirms the coarse particle size of the talc crystals. Mode values are as high as 105–170 μm (except two samples displaying 76 and 42 μm) and d50 ranges from 107 to 25 μm. The values of specific surface area measured by BET and t-plot methods range from 1 to 6 m²/g and are correlated with external specific surface area measured by laser diffraction. Discrepancies from the trend are due to the semi-crystalline texture of the samples and mostly to intra-crystalline structural defects revealed by TEM observations. In infrared spectra, specific absorption bands are distinguished for talc, chlorite, tremolite, carbonates, serpentine, brucite and water. Occasional substitutions in minerals led to a shift in some absorption bands. The chemical composition criteria important for most of the industrial applications such as ceramics and pharmaceutics are closely complied with in untreated samples from these deposits. In summary, high talc proportions, chemical compositions, platy morphology and coarse grain size of its crystals lead to the conclusion that the studied deposits are economically attractive. The data set of the present work is an important tool for choosing the beneficiation methods for specific applications.     

Micronization of salicylic acid and taxol (paclitaxel) by rapid expansion of supercritical fluids (RESS)

The particle sizes of the pharmaceutical substances are important for their bioavailability. The bioavailability can be improved by reducing the particle size of the drug. In this study, salicylic acid and taxol were micronized by the rapid expansion of supercritical fluids (RESS). Supercritical CO₂ and CO₂ + ethanol mixture were used as solvent. Experiments were carried out to investigate the effect of extraction temperature (318–333 K) and pressure (15–25 MPa), pre-expansion temperature (353–413 K), expansion chamber temperature (273–293 K), spray distance (6–13 cm), co-solvent concentration (ethanol, 1, 2, 3, v/v, %) and nozzle configuration (capillary and orifice nozzle) on the size and morphology of the precipitated salicylic acid particles. For taxol, the effects of extraction pressure (25, 30, 35 MPa) and co-solvent concentration (ethanol, 2, 5, 7, v/v, %) were investigated. The characterization of the particles was determined by scanning electron microscopy (SEM), optical microscopy, and LC–MS analysis.The particle size of the original salicylic acid particles was L/D: 171/29–34/14 μm/μm. Depending upon the different experimental conditions, smaller particles (L/D: 15.73/4.06 μm/μm) were obtained. The particle size of taxol like white crystal powders was reduced from 0.6–17 μm to 0.3–1.7 μm The results showed that the size of the precipitated salicylic acid and taxol particles were smaller than that of original particles and RESS parameters affect the particle size.     

Effects of inert filler addition on the structure and properties of porous SiOC ceramics derived from silicone resin

Porous SiOC ceramics were obtained from a new self-blowing precursor silicone resin DC217, by pyrolysis at 1200 °C in argon. Silicon carbide powders were incorporated into the silicone resin as inert fillers. The effects of the mean particle size of SiC fillers on the porosity, compressive strength and microstructure of the porous ceramics were investigated. With the mean particle size of SiC powders increasing from 5 μm to 10 μm, the porosity (total and open) of the porous ceramic increased and the compressive strength decreased. However, the porosity, compressive strength and cell morphology of the porous ceramics showed no evident changes when the mean particle size of fillers increased from 10 μm to 15 μm. Micrographs indicated that, when the mean particle size of fillers exceeded 5 μm, the porous ceramics could have a well-defined and regular pore structure. Furthermore, comparing with the porous ceramics which fabricated under the same condition with the SiOC powders as fillers, the cell morphology was similar. But the compressive strength and the oxidation resistance of the porous ceramics with SiC powders as fillers were much better.     

Foam-gelcasting preparation,microstructure and thermal insulation performance of porous diatomite ceramics with hierarchical pore structures

Hierarchically pore-structured porous diatomite ceramics containing 82.9∼84.5% porosity were successfully prepared for the first time via foam-gelcasting using diatomite powder as the main raw material. Sizes of mesopores derived from the raw material and macropores formed mainly from foaming were 0.02∼0.1 μm and 109.7∼130.5 μm, respectively. The effect of sintering temperature, additive content and solid loading of slurry on pore size and distribution, and mechanical and thermal properties of as-prepared porous ceramics were investigated. Compressive strength of as-prepared porous ceramics increased with sintering temperature, and the one containing 82.9% porosity showed the highest compressive strength of 2.1 ± 0.14 MPa. In addition, the one containing 84.5% porosity and having compressive strength of 1.1 ± 0.07 MPa showed the lowest thermal conductivity of 0.097 ± 0.001 W/(m·K) at a test temperature of 200 ̊C, suggesting that as-prepared porous ceramics could be potentially used as good thermal insulation materials.     

Preparation of porous silver particles using ammonium formate and its formation mechanism

Here we report the preparation of two different types of macroporous silver particles (round and coral) by simple chemical reduction using ammonium formate. We also discuss the chemical mechanism of silver particle and macroporous silver particle formation. The synthesized round type and coral-type porous silver particles were 20–50 μm and 30–150 μm in size and their pores were 100–200 nm and 1–2 μm across, respectively. They were characterized by particle distribution analysis, X-ray diffraction, and scanning electron microscopy.     

Synthesis of a biocompatible polymer using siloxane-based surfactants in supercritical carbon dioxide

Poly(N-vinyl-2-pyrrolidone) (PVP) particles were prepared by dispersion polymerization in the presence of 2,2′-azobisisobutyronitrile as the initiator and siloxane-based surfactant in supercritical carbon dioxide (scCO₂). The dispersants used in this study were non-ionic, non-reactive and commercially produced siloxane-based surfactants (Monasil PCA and KF-6017). We investigated the effect of kinds and concentrations of the surfactants, in addition to the reaction temperature and the concentration of the monomer on the particle size and morphology. PVP microspheres were prepared in 0.23–0.74 μm size range with Monasil PCA and 0.71–1.98 μm size range with KF-6017, respectively. The resulting polymer particle of >90% yield was obtained. Particle size slightly increased with the amount of monomer in polymerization with Monasil PCA. In the case of KF-6017 as the surfactant, there was not an obvious variation in particle size with increasing monomer. Particle size of PVP decreased as surfactant concentration increased from 5.0 to 15.0 wt.% basis on concentration of monomer. The narrow particle size distribution (D_n = 0.23 μm and PSD = 1.06) was presented at the high concentration of Monasil PCA (15 wt.% on monomer concentration). As indicated by the reaction temperature and the addition of organic solvent, which affected solubility of monomer, polymer and surfactant in scCO₂, particle size and particle size distribution of PVP varied. PVP particles with Monasil PCA strongly aggregated at 75 °C in contrast to KF-6017 which showed discrete particles at 65 and 70 °C, but particle size distribution was broad. Particle size was slightly reduced with a little amount of hexane, with an inverse relationship of adding hexane reduced the particle size. The amount of the relative residual surfactants on surface of the polymer after extracting with supercritical fluid process (SFE) was measured by using SEM/EDS and EPMA analysis to map out the distribution of silicon element qualitatively. The original polymer particle before the extraction using CO₂ had the high level of silicon element, but the average level of silicon element became low after CO₂ extraction.     

Precise micromachining of yttria-tetragonal zirconia polycrystal ceramic using 532 nm nanosecond laser

High quality micro-sized steps and blind hole structures without microcracks, chips or spatter deposition were machined on yttria-tetragonal zirconia polycrystal (Y-TZP, 3 mol% yttria) by nanosecond laser (wavelength=532 nm, pulse width ~6 ns). The diameter of blind hole is 500 μm and each step is 500±10 μm wide and 100±5 μm deep. The 1.35 mm³/min removal rate and the smooth machined surface with Ra=2.824 μm roughness depicting the high precise and efficient processing were achieved. The ablation characteristics of nanosecond laser process of Y-TZP ceramic were also studied. Based on the study, a reasonable design of the processing path for micromachining of a finer embedded step with 24±2 μm width (smaller than the 60 μm focused spot size) around the inner-wall of a 2×2 mm² cavity was developed. These results and discussion offer new possibilities in the manufacturing of bio-ceramic products by nanosecond laser with high processing quality and efficient.     

SEM investigation of domain structure in (Ba,Ca,Pb)TiO3

In the present paper the microstructure and domain structure in modified BaTiO₃ with Pb and Ca as additives have been investigated using SEM technique. The (Ba,Pb)TiO₃ and (Ba,Ca,Pb)TiO₃ ceramics show a slight difference in grain size, being smaller in composites with Ca additives which acts as grain growth inhibitor. The domain configuration is almost the same. The small grain microstructure with tiny domains have been observed in specimen sintered at 1300°C and the average grain size is in the range 1–3 μm. For those specimens sintered at 1320°C the homogenous microstructure is also obtained with grain size around 2–4 μm. For both types of specimens, the single domain structure is associated with grain which size is lower than 2 μm. The banded domain structure could be observed in grains with size bigger than 3 μm. The bar shape grains and elongated grains together with some large region in microstructure are free of domain structure. The observed domain patterns reveal mainly the straight domain boundary lines with 90° domains walls. The wall thickness ranged from 0·03 μm to 0·15 μm, while the domain width is in the range of 0·1 μm–1 μm.     

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.     

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.