Ultrafine Particle Size Research Articles

Effects of dry grinding on the structure and granularity of calcite and its polymorphic transformation into aragonite

The structure and granularity of calcite were measured during dry grinding in a ball mill by X-ray diffraction, Fourier transform infrared spectroscopy and laser diffraction, and its morphology was observed by a scanning electron microscope. During the early stage of grinding (0–10min), the median particle size and X-ray diffraction intensity of the calcite decreased, while the full width at half maximum increased as grinding progressed. During the middle grinding stage (20–300min), the grain size and crystalline degree of ultrafine calcite particles no longer changed with time; this was attributed to aggregation, which hindered the breakage of particles. During the final grinding stage (360–720min), a polymorphic transformation of calcite into aragonite took place.

Effect of wood combustion conditions on the morphology of freshly emitted fine particles

The physical and chemical properties of biomass combustion-originated particles produced under controlled conditions (efficient, intermediate, and smouldering combustion) were studied. Transmission electron microscopy with energy dispersive X-ray spectroscopy was used to study the morphology and chemical composition of the size-classified samples collected from the flue gas. In addition, online-measured particle number size distributions, chemical analyses of the PM samples, and thermodynamic equilibrium calculations were used to interpret the results. The particles were composed of inorganic species and carbonaceous matter. Zinc oxide particles with an average diameter of <13 nm acted as seeds for the condensation of inorganic vapours and organic material, forming ash particles with a nested structure. The outer layer was composed mainly of alkali salts. Soot and gaseous hydrocarbons were formed in high concentrations during the impaired combustion conditions. Two modes of particle size distribution were observed, with each exhibiting distinctive features. The main particle type found in the ultrafine particle size mode (<100 nm) was ash. Impairing the combustion conditions increased the release of soot and condensable organics into the PM, found mainly in the accumulation particle size mode (>100 nm). TEM observations of the size-classified samples revealed that condensed organic matter influenced the ash particle size and appearance. The soot morphology was also found to change, even after short periods of time, due to the presence of OM; changes in the primary particle diameter and the appearance of the agglomerates were observed. As external mixtures, the soot and ash particles were separated into two particle size modes, but both could be found as internally mixed from the accumulation mode. This result extends the current knowledge of particle formation in wood combustion, showing that the particle formation processes of ash and soot particles are largely separate.

Particle Deposition in Respiratory Tracts of School-Aged Children

Exposure to ultrafine particles poses a potential health risk to school children. While many studies have focused on measuring ultrafine particle (UFP) concentrations in environments where children are at risk of high exposure, few studies have examined the particle deposition in the respiratory tract of children. This study aims to examine the particle deposition in the respiratory tract of school children in different microenvironments. UFP size distribution data were collected in residential homes, school buses, school classrooms, and from school outdoor air in both rural and urban areas of South Texas. The size distribution data were input to the Multiple Path Particle Dosimetry model to calculate regional and total particle deposition fraction. A 24-hour-school-day exposure was simulated by adding the time children spend in each microenvironment. The maximum pulmonary deposition fraction occurs at a diameter ranging from 18 to 40 nm, depending on condition. Age mostly affected the pulmonary region and the total lung deposition with the highest deposition fraction observed for younger children. In addition, comparison of size-dependent regional deposition and particle concentration establishes an accurate depiction of children's exposure and dose profiles. While children only spend 4% of the day in the home source environment, that environment may account for up to 77% of total daily dose intake. Higher deposition fraction occurs at smaller particle size. Younger children show increased levels of particle deposition than older children. Exposure period does not correlate to daily percentage of dose intake. This research can be used to assess children's accumulative exposure to UFPs.

Interconnected carbon-decorated Tio2 nanocrystals with enhanced lithium storage performance

A novel direct preparation method was developed to prepare interconnected carbon-decorated TiO2 nanocrystals. The as-prepared composite exhibited a morphology of interconnected 10nm TiO2 nanocrystals with uniform carbon coverage. As anode in lithium ion batteries, high reversible capacity of 184mAhg−1 with 87.4% initial coulomb efficiency, outstanding rate performance and stable cycle life were observed, which was attributed to ultrafine particle size, uniform carbon coating and high preparation temperature.

Aircraft engine particulate matter: Macro- micro- and nanostructure by HRTEM and chemistry by XPS

Carbonaceous particulate emissions from jet aircraft are a significant source of emissions from airports near urban areas. Physical structure and surface chemistry are relevant towards assessing impacts of combustion-produced soot upon the environment and assessing health impacts. In this report high-resolution electron microscopy (HRTEM) and X-ray photoelectron (XPS) data are presented for particulate emissions from a CFM-56-3 engine aboard a DC-9 aircraft, fueled by JP-8. Engine power levels were varied from 4% to 100%. Soot aggregate macrostructure, microstructure and nanostructure are discussed with respect to combustion conditions. Ultrafine particle size distributions at idle and near full power conditions are highlighted by HRTEM and compare favorably to reported scanning mobility particle sizer (SMPS) measurements. Particle composition, as inferred from the XPS ratio for sp2/sp3 carbon bonding is compared to results from thermo-optical evaluation of organic and elemental carbon analysis at selected powers with excellent agreement. Across engine power levels, these ultra-fine particles appear to be remnants of oxidized larger aggregates.

Microemulsion-assisted synthesis of ultrafine Li4Ti5O12/C nanocomposite with oleic acid as carbon precursor and particle size controller

Ultrafine Li4Ti5O12/C composite is synthesized by microemulsion with oleic acid as carbon precursor and particle size controller. The as-prepared sample is characterized with X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), thermogravimetry analysis (TGA) and nitrogen absorption–desorption isotherms, and its performance as anode of lithium ion battery is determined with charge–discharge test and electrochemical impedance spectroscopy (EIS). The characterizations show that the as-prepared sample is composed of ultrafine Li4Ti5O12 particles with average size of 25 nm, which are uniformly dispersed in carbon matrix with a carbon content as low as 2.69 wt%. Charge–discharge test indicates that the as-prepared sample exhibits excellent rate performance and cycling stability. At 10C, the highest discharge capacity reaches 136.3 mAh g−1 and the capacity retention is 96.4% after 100 cycles. The improved performance of the Li4Ti5O12/C composite is attributed to the ultrafine particle size and the uniform composite of Li4Ti5O12 with carbon.

Exposure to ultrafine particles in hospitality venues with partial smoking bans

Fine particles in hospitality venues with insufficient smoking bans indicate health risks from passive smoking. In a random sample of Viennese inns (restaurants, cafes, bars, pubs and discotheques) effects of partial smoking bans on indoor air quality were examined by measurement of count, size and chargeable surface of ultrafine particles (UFPs) sized 10-300 nm, simultaneously with mass of particles sized 300-2500 nm (PM2.5). Air samples were taken in 134 rooms unannounced during busy hours and analyzed by a diffusion size classifier and an optical particle counter. Highest number concentrations of particles were found in smoking venues and smoking rooms (median 66,011 pt/cm(3)). Even non-smoking rooms adjacent to smoking rooms were highly contaminated (median 25,973 pt/cm(3)), compared with non-smoking venues (median 7408 pt/cm(3)). The particle number concentration was significantly correlated with the fine particle mass (P<0.001). We conclude that the existing tobacco law in Austria is ineffective to protect customers in non-smoking rooms of hospitality premises. Health protection of non-smoking guests and employees from risky UFP concentration is insufficient, even in rooms labeled "non-smoking". Partial smoking bans with separation of smoking rooms failed.

Progress on Porous Ceramic Membrane Reactors for Heterogeneous Catalysis over Ultrafine and Nano-sized Catalysts

Heterogeneous catalysts with ultrafine or nano particle size have currently attracted considerable attentions in the chemical and petrochemical production processes, but their large-scale applications remain challenging because of difficulties associated with their efficient separation from the reaction slurry. A porous ceramic membrane reactor has emerged as a promising method to solve the problem concerning catalysts separation in situ from the reaction mixture and make the production process continuous in heterogeneous catalysis. This article presents a review of the present progress on porous ceramic membrane reactors for heterogeneous catalysis, which covers classification of configurations of porous ceramic membrane reactor, major considerations and some important industrial applications. A special emphasis is paid to major considerations in term of application-oriented ceramic membrane design, optimization of ceramic membrane reactor performance and membrane fouling mechanism. Finally, brief concluding remarks on porous ceramic membrane reactors are given and possible future research interests are also outlined.

Ferritin-Templated Synthesis and Self-Assembly of Pt Nanoparticles on a Monolithic Porous Graphene Network for Electrocatalysis in Fuel Cells

The monolithic three-dimensional (3D) graphene network is used as the support for Pt nanoparticles (NPs) to fabricate an advanced 3D graphene-based electrocatalyst. Distinct from previous strategies, the monodispersed Pt NPs with ultrafine particle size (∼3 nm) are synthesized using ferritin protein nanocages as the template and subsequently self-assembled on the 3D graphene by leveraging on the hydrophobic interaction between the ferritin and the graphene. Following the self-assembly, the ferritins are removed, resulting in a stable Pt NP/3D graphene composite. The composite exhibits much enhanced electrocatalytic activity for methanol oxidation as compared with both Pt NP/chemically reduced graphene oxide (Pt/r-GO) and state-of-the-art Pt/C catalyst. The observed electrocatalytic activity also shows marked improvement over Pt/3D graphene prepared by pulse electrodeposition of Pt. This study demonstrates that protein nanocage templating and assembly are promising strategies for the fabrication of functional composites in catalysis and fuel cell applications.

New Method of Coal Comminution to Ultrafine Size

Research into the use of coal for power generation has become more important to deliver next-generation solutions for advanced coal cleaning technologies required by near-zero emissions. Comminution of coal with waterjets to ultrafine particle size offers a new and promising method for producing coal-water fuel (CWF), which is a replacement for power generation products. In this paper the results of coal comminution in a waterjet-based mill are presented for the range of pressures up to 276 MPa using four groups of feed size ranging from minus 850 micrometers to less than 106 micrometers. The focus of studies was on particle size reduction and distribution. The results presented in this paper are part of ongoing studies of coal-water fuel optimization for power generation.

Cluster analysis of roadside ultrafine particle size distributions

This study reports the diurnal, seasonal, and annual variation of ultrafine particle size distributions in downtown Toronto. The k-means clustering algorithm was applied to five years of size-resolved data for particles with diameters less than 100 nm. Continuous particle number concentrations were measured 16 m from a major arterial roadway between March 2006 and May 2011 using a Fast Mobility Particle Sizer. Eight particle size distribution (PSD) types were identified. The PSD types exhibited distinct weekday–weekend and diurnal patterns. The relative frequency that each PSD occurred varied with season and wind direction and was correlated with other pollutants. These temporal patterns and correlation helped in elucidating the sources and processes that each of the eight PSD represent. Finally, similar PSD types were observed in residential areas located 6 and 15 km away from the central monitoring site suggesting that these PSD types may be generalizable to other sites. Identification of PSD types was found to be a valuable tool to support the interpretation of PSD data so as to elucidate the sources and processes contributing to ultrafine particle concentrations.

Ultrafine LiCoO2 powders derived from electrospun nanofibers for Li-ion batteries

Sol–gel based electrospinning has been developed to synthesize phase pure LiCoO2 powders at relatively low temperature with excellent crystallinity and ultrafine particle size. Compared to LiCoO2 powders synthesized from regular sol–gel processes, the nanofiber derived powders possess high initial discharge capacity and good cyclic stability, and the retention of initial capacity is also much higher than bare LiCoO2 nanofibers reported in literature. With additional surface modification of La2O3 coating, the retention of initial capacity is increased to 91% at 30th cycle and 83% at 50th cycle without decreasing its initial capacity, making it attractive for Li-ion batteries.

Ultrafine particle size distributions near freeways: Effects of differing wind directions on exposure

High ambient ultrafine particle (UFP) concentrations may play an important role in the adverse health effects associated with living near busy roadways. However, UFP size distributions change rapidly as vehicle emissions dilute and age. These size changes can influence UFP lung deposition rates and dose because deposition in the respiratory system is a strong function of particle size. Few studies to date have measured and characterized changes in near-road UFP size distributions in real-time, thus missing transient variations in size distribution due to short-term fluctuations in wind speed, direction, or particle dynamics. In this study we measured important wind direction effects on near-freeway UFP size distributions and gradients using a mobile platform with 5-s time resolution. Compared to more commonly measured perpendicular (downwind) conditions, parallel wind conditions appeared to promote formation of broader and larger size distributions of roughly one-half the particle concentration. Particles during more parallel wind conditions also changed less in size with downwind distance and the fraction of lung-deposited particle number was calculated to be 15% lower than for downwind conditions, giving a combined decrease of about 60%. In addition, a multivariate analysis of several variables found meteorology, particularly wind direction and temperature, to be important in predicting UFP concentrations within 150 m of a freeway (R2 = 0.46, p = 0.014).

3D air filtration modeling for nanofiber based filters in the ultrafine particle size range

In this work, 3D filtration modeling utilizing realistic SEM image-based 3D structure model, transition/free molecular flow regime, Brownian diffusion, particle–fiber interactions, aerodynamic slip and sieve has been proposed and used for different polyurethane nanofiber-based filters. For the model validation purposes, two polyurethane nanofiber layers prepared by the electrospinning process (having identical average fiber diameter, 120nm, but different average pore sizes) were combined to form two pairs of nanofiber-based filters; each pair consists of two filters having comparable mass area and thickness. Filtration characteristics of prepared filters were determined experimentally in the ultrafine particle size range (20–400nm). It has been found that the proposed model is able to reasonably predict the measured filtration efficiency, pressure drop and quality factor for all tested filter samples.

Preparation of Ultra–Fine La&lt;sub&gt;3&lt;/sub&gt;NbO&lt;sub&gt;7&lt;/sub&gt; Powder by Solid State Reaction

As a new candidate material for the ceramic layer in thermal barrier coatings (TBCs) system, La3NbO7 was synthesized with La2O3 powder and Nb2O5 powder by solid state reaction. The stating powders with a mole ratio of La to Nb of 3:1 were mixed and then the mixture was calcined under the different temperatures(800°C, 1000°C, 1200°C) and dwell times(2h, 6h, 10h). The phase structure of the powder was observed by X–ray diffraction(XRD), and the microstructure of the sample was observed by scanning electron microscope(SEM). The effect of calcination temperature and dwell Time on the phase formation were examined. The results indicate that the La3NbO7 powder with single phase can be synthesized successfully at 1200°C for 10h in air, and the La3NbOsub&gt;7 powders synthesized have an ultra-fine particle size of 0.5˜1µm with a granular particle shape. With the temperature increasing, LaNbO4/sub&gt; was synthesized firstly and then La3NbO7 was synthesized with a mole ratio of La2O3 to LaNbO4 of 1:1.

Evolution of Ultrafine Particle Size Distributions Following Indoor Episodic Releases: Relative Importance of Coagulation, Deposition and Ventilation

Indoor ultrafine particles (UFP, 24 nm. The model was parameterized using different values of the Hamaker constant for predicting the coagulation rate. Deposition was determined for two different conditions: central fan on versus central fan off. For the case of a central fan running, deposition rates were measured by using a nonlinear solution to the mass balance equation for the whole building. For the centra...

Investigation of Ultrafine Particle Deposition to Vegetation Branches in a Wind Tunnel

Vegetation is an important sink for atmospheric ultrafine particles (UFP). Prediction of UFP deposition to vegetation, however, is still problematic. In this study, we have investigated size-dependent removal of UFP by two conifer species: pine and juniper. The experiments were performed by placing freshly cut branches into a wind tunnel and measuring UFP size distributions upstream and downstream of the branches. Five air velocities ranging from 0.3 to 1.5 m/s, two packing densities (volume fraction occupied by the branches) and two branch orientations were tested to assess their effect on particle removal. The UFP removal efficiency was found to decrease with increasing particle size, increasing wind speed, and decreasing packing density. The branch orientation did not affect the removal efficiency within the uncertainty of the measurements. To facilitate extrapolation of the measurement results to real-life conditions, we have tested the applicability of filtration theory to particle removal by vegetat...

New Approach to Recycling Asphalt Shingles in Hot-Mix Asphalt

The objective of this study is to introduce a new approach to recycling asphalt shingles in asphalt paving construction in which recycled asphalt shingles (RAS) are ground to ultrafine particle sizes and blended with asphalt binder through a wet process. In the proposed wet process, the ground recycled material is blended with the binder at a high temperature prior to mixing with the aggregates. Two unmodified binders that are classified as PG 64-22 and PG 52-28 were blended with two contrasting sources of RAS at a modification content ranging from 10–40% by weight of the binder. The use of RAS modification through the proposed wet process was successful in the laboratory. Based on the results of the experimental program, the use of RAS modification through the proposed wet process would generally improve or not influence the high temperature grade of the binder, but it may reduce the low temperature grade of the binder. As demonstrated in this study, an optimum shingle content may be identified that will improve the high temperature grade without influencing the low temperature grade of the binder. Using confocal laser-scanning microscopy (CLSM), wax crystals ranging from 4–8 μm in size were successfully detected. However, wax crystals were not detected in the RAS-modified binder, which may indicate that the wax molecules are absorbed by the RAS material. Results of high-pressure gel permeation chromatography (HP-GPC) showed that the proposed wet method of modification produced a slight increase in the high molecular weight (HMW) (>3,000 daltons) content in the prepared blends at higher RAS contents, suggesting that a fraction of the RAS binder contributes to the blend properties.

Synthesis and electrochemical properties of highly dispersed Li4Ti5O12 nanocrystalline for lithium secondary batteries

A sol-gel method using lauric acid as surfactant was used to synthesize Li4Ti5O12 nanocrystals with an ultra-fine particle size distribution between 120 and 250 nm. In order to obtain the electrode materials with the best electrochemical performance, the content of lauric acid during Li4Ti5O12 synthesis was systematically studied. The physical and electrochemical properties of the synthesized samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), laser particle size analysis, alternating current impedance (AC) and galvanostatic charge-discharge experiments. The highly dispersed Li4Ti5O12 nanocrystals obtained at 800 °C for 10 h can deliver a specific capacity of 163.3 mA·h/g at 1C rate without obvious capacity fade up to 50 cycles. The results suggest that well dispersed Li4Ti5O12 nanocrystals shorten the Li-ion diffusion length and enhance the electrochemical kinetics of the samples, which are very crucial to high rate capability.

Simultaneous Elimination of Formaldehyde and Ozone Byproduct Using Noble Metal Modified TiO2Films in the Gaseous VUV Photocatalysis

Simultaneous removal of low concentration formaldehyde (HCHO) and ozone byproduct was investigated in the gaseous VUV (vacuum ultraviolet) photocatalysis by using noble metal modified TiO2films. Noble metal (Pt, Au, or Pd) nanoparticles were deposited on TiO2films with ultrafine particle size and uniform distribution. Under 35 h VUV irradiation, the HCHO gas (ca. 420 ppbv) was dynamically degraded to a level of 10~45 ppbv without catalyst deactivation, and over 50% O3byproduct wasin situdecomposed in the reactor. However, under the same conditions, the outlet HCHO concentration remained at 125~178 ppbv in the O3+ UV254 nmphotocatalysis process and 190~260 ppbv in the UV254 nmphotocatalysis process. And the catalyst deactivation also appeared under UV254 nmirradiation. Metallic Pt or Au could simultaneously increase the elimination of HCHO and ozone, but the PdO oxide seemed to inhibit the HCHO oxidation in the UV254 nmphotocatalysis. Deposition of metallic Pt or Au reduces the recombination of h+/e−pairs and thus increases the HCHO oxidation and O3reduction reactions. In addition, adsorbed O3may be partly decomposed by photogenerated electrons trapped on metallic Pt or Au nanoparticles under UV irradiation.