Volume Size Distribution Research Articles

On-line measurement of pulverized coal fineness on a 300 MWe power plant with pulsed digital inline holography

Pulverized coal fineness (PCF) is a key parameter in coal-fired power plants, demanding accurate and on-line monitoring. This study presents on-line measurement of PCF on a 300 MWe coal-fired power plant with pulsed digital inline holography (DIH). A prototypal instrumentation system, comprised of sampling, measurement, collection, and output, is established and tested on the two mills of the plant. Fineness characterized by the size-area distribution (SAD) and various size-volume distributions (SVD) obtained by DIH are compared to the size-mass distribution (SMD) by the off-line sieving method. The absolute R90 deviations of SAD are 3.60% and 3.72% for the two mills, respectively, with the equivalent area circle diameter (Deac) to estimate the sieve size (Ds). A SVD for which Ds is estimated by the maximum inscribed circle diameter (Dmic) and the particle volume (VSeac) by the equivalent sphere with diameter of Deac yields the deviations of 2.18% and − 0.25%.DIH is applied to the on-line coal fineness monitoring on a 300 MWe power plant. An on-line holographic instrumentation system is established. Fineness results indicate the operation conditions of the tested mills. Different fineness characterizations are compared and two optimums are recommended.

Free volume characteristics of 2,2‐bistrifluoromethyl‐4,5‐difluoro‐1,3‐dioxole‐co‐tetrafluoroethylene copolymers: Effect of composition and molecular weight

Abstract2,2‐bistrifluoromethyl‐4,5‐difluoro‐1,3‐dioxole‐co‐tetrafluoroethylene (PDD‐TFE) copolymer is a good candidate to prepare gas separation membranes with excellent permeability due to its free volume characteristics. However, the influence of PDD‐TFE copolymer structure on its free volume characteristics is less studied. In this paper, PDD‐TFE copolymers with different compositions and molecular weights were synthesized, and their free volume characteristics were analyzed by positron annihilation lifetime spectroscopy and a molecular dynamics simulation. It indicated that the molar fraction of PDD in copolymers had a significant effect on free volume characteristics, while the molecular weight of copolymers exerted a slight influence on free volume when the molecular weight exceeded a critical region (intrinsic viscosity [η] > 68 ml g−1). PDD‐TFE copolymers with greater PDD molar fractions (i.e., 72% and 84%) showed bimodal distributions in positron lifetime and free volume size distributions, while PDD‐TFE copolymers with lower PDD molar fractions (i.e., 27% and 35%) exhibited a single peak. The long‐lifetime parameter τ3 was assigned to micro‐cavities formed by [‐(TFE)y‐PDD‐] segments and τ4 was attributed to micro‐cavities formed by [‐(PDD)x‐TFE‐] segments. The cis and trans transitions of PDD led to a local multilayer spiral structure with a 2.6–4.3 Å layer spacing, which would also increase the free volume of copolymers.

X-ray microtomography for conventional grinding wheel structure analysis

Grinding wheel content characterization is still mainly based on empirical tests, lacking the necessary scientific approach. To further develop the current existing methodology, this study introduces a method to characterize the grinding wheel structure and content, using microscale X-ray tomography allied with image processing techniques. An X-ray tomography characterization was performed on four different conventional grinding wheels, each containing a specific mixture of electro-fused and sol-gel aluminum oxide abrasives as grits. The grinding wheels were evaluated in terms of volumetric phase fraction, representative elementary volume, phase, and pore size distribution. The results showcased that even though the grinding wheels presented the same manufacturing label (in terms of mechanical properties), the volumetric phase fraction between the grinding wheels was significantly different. This study aggregates the empirical knowledge used to characterize grinding wheels, opening possibilities for academic and industrial research.

Synopsis of Factors Affecting Hydrogen Storage in Biomass-Derived Activated Carbons

Hydrogen (H2) is largely regarded as a potential cost-efficient clean fuel primarily due to its beneficial properties, such as its high energy content and sustainability. With the rising demand for H2 in the past decades and its favorable characteristics as an energy carrier, the escalating USA consumption of pure H2 can be projected to reach 63 million tons by 2050. Despite the tremendous potential of H2 generation and its widespread application, transportation and storage of H2 have remained the major challenges of a sustainable H2 economy. Various efforts have been undertaken by storing H2 in activated carbons, metal organic frameworks (MOFs), covalent organic frameworks (COFs), etc. Recently, the literature has been stressing the need to develop biomass-based activated carbons as an effective H2 storage material, as these are inexpensive adsorbents with tunable chemical, mechanical, and morphological properties. This article reviews the current research trends and perspectives on the role of various properties of biomass-based activated carbons on its H2 uptake capacity. The critical aspects of the governing factors of H2 storage, namely, the surface morphology (specific surface area, pore volume, and pore size distribution), surface functionality (heteroatom and functional groups), physical condition of H2 storage (temperature and pressure), and thermodynamic properties (heat of adsorption and desorption), are discussed. A comprehensive survey of the literature showed that an “ideal” biomass-based activated carbon sorbent with a micropore size typically below 10 Å, micropore volume greater than 1.5 cm3/g, and high surface area of 4000 m2/g or more may help in substantial gravimetric H2 uptake of >10 wt% at cryogenic conditions (−196 °C), as smaller pores benefit by stronger physisorption due to the high heat of adsorption.

Template-free method for the synthesis of high-pore-volume γ-Al2O3 nanofibers in a membrane dispersion microreactor

Mesoporous γ-Al2O3 nanofibers with high pore volume and uniform pore size distributions were successfully synthesized via a template-free method in a membrane dispersion microreactor followed by calcination. The effects of crystal temperature, pH values, continuous phase concentration and washing solvent on the γ-Al2O3 nanofibers were carefully studied. The results showed that the as-obtained γ-Al2O3 nanofibers showed a length of 40–60 nm and a width of 3.2–3.4 nm, which were attributed to the high microscopic mixing rate in the membrane dispersion microreactor. Moreover, the precursors of γ-Al2O3 nanofibers treated with deionized water and mixed deionized water/alcohol solution had high pore volumes, reaching to 1.60 ml g−1 and 2.00 ml g−1, respectively. Furthermore, the adsorption performance of γ-Al2O3 nanofibers with high pore volumes was also investigated. These fibers showed an excellent adsorption capacity of 1323.68 mg g−1 for the removal of Congo red from aqueous solution, thereby indicating their potential for applications in adsorption and other related areas.

Experimental study on spray characteristics, combustion stability, and emission performance of a CRDI diesel engine operated with biodiesel–ethanol blends

Biodiesel is a promising alternative fuel for diesel engines, but its high viscosity and low volatility have limitations in decreasing emissions. As a renewable alternative fuel with a high oxygen content, ethanol blended with biodiesel can decrease kinematic viscosity and improve fuel evaporation. In this study, the effects of the ethanol addition ratio on the spray, combustion, and emission performances of a diesel engine fuelled with biodiesel were investigated. The spray characteristics were measured using a high-speed camera and Malvern laser analysis, whereas the combustion and emission performances were tested on a turbocharged common rail direct injection (CRDI) diesel engine. The results show that adding ethanol to biodiesel enlarges the spray cone angle (SCA) and shortens spray tip penetration (STP). In addition, the curves of the size–volume distribution (SVD) of the atomized fuel droplets move toward a smaller diameter, and the Sauter mean diameter (SMD) of the biodiesel–ethanol (BE) blends gradually decreases with increasing ethanol proportion. At low loads, the fuel injection strategy is multi-injection, and the peak cylinder pressures (PCPs) of BE blends are 0.77–1.96% higher than that of diesel at different ethanol blending ratios. However, the peak heat release rates (PHRRs) of BE blends are 9.3–11.5% higher than that of diesel owing to a faster combustion rate, longer main-injection duration, and more hydroxyl radicals generated in the pilot-injection stage. At medium–high loads, the injection strategy changes to single injection, the PCPs of BE blends are roughly equivalent to that of diesel, and the PHRRs of BE blends for different ethanol blending ratios are 9.76–11.91% lower than that of diesel. This is because of the lower diffusion combustion ratio, lower heat value, and change of injection duration corresponding to the variation in fuel properties. In addition, the results of the peak pressure rise rate and the cyclic variation indicate that the higher ethanol addition ratio increases the combustion noise and decreases the combustion stability. In terms of exhaust emissions, compared with biodiesel, with increasing ethanol blending ratio, the soot emissions for different BE blends decrease by 11.28–47.23%, the NOx emissions increase by 2.68–7.04%, and the HC emissions increase by 9.99–21.47%. Considering the engine performance comprehensively, a 20% ethanol blending ratio in biodiesel is recommended.

Machine learning-based accelerated property prediction of two-phase materials using microstructural descriptors and finite element analysis

This study explores the use of supervised machine learning (ML) to predict the mechanical properties of a family of two-phase materials using their microstructural images. Random two-phase microstructures with a diversity of inclusion volume fractions, size distributions, and/or shapes are input into a finite element analysis program to determine the elastic modulus, Poisson’s ratio, and phase stresses. The finite element analysis results establish the “ground truth” to train the supervised ML models. Two-point correlation (TPC) functions and principal component (PC) analysis are applied to the microstructures before training and testing the artificial neural network (ANN) and forest ensemble MLs. The chosen ML methods are found to accurately predict the homogenized elastic properties. Although the PCs for each set of microstructures are unique, recognizable patterns are detected that signify microstructural features that are key to microstructure-based property prediction. This work enables the development of ML algorithms to predict the mechanical properties of complex, multi-phase microstructural composites, based on microstructural images.

The Pore-filling Effect of Bulk Graphite According to Viscosity of Impregnant

Pores produced by carbonization in bulk graphite process degrade the mechanical and electrical properties of bulk graphite. Therefore, the pores of bulk graphite must be reduced and an impregnation process needs to be performed for this reason. In this study, bulk graphite is impregnated by varying the viscosity of the impregnant. The pore volume and pore size distribution, according to the viscosity of the impregnant, are analyzed using a porosimeter. The total pore volume of bulk graphite is analyzed from the cumulative amount of mercury penetrated. The volume for a specific pore size is interpreted as the amount of mercury penetrating into that pore size. This decreases the cumulative amount of mercury penetrating into the recarbonized bulk graphite after impregnation because the viscosity of the impregnant is lower. The cumulative amount of mercury penetrating into bulk graphite before impregnation and after three times of impregnation with 5.1cP are 0.144 mL/g and 0.125 mL/gm, respectively. Therefore, it is confirmed that the impregnant filled the pores of the bulk graphite well. In this study, the impregnant with 5.1 cP, which is the lowest viscosity, shows the best effect for reducing the total pore volume. In addition, it is confirmed by Raman analysis that the impregnant is filled inside the pores. It is confirmed that phenolic resin, the impregnant, exists inside the pores through micro-Raman analysis from the inside of the pore to the outside.

Interpreting rheological behaviour of sugar-fat mixtures as a function of solids phase volume

Abstract Many confectionary items and food components are based on complex suspensions of hydrophilic sugar particles in a hydrophobic fat phase. We hypothesise that the rheology of these suspensions is defined by either the Maron-Pierce-Quemada (MPQ) model, which theoretically predicts the viscosity of hard spheres, or by the percolation model describing a network of attractive particles (gel). The rheology of two sugar-fat mixtures, sugar-shortening based biscuit-creams and chocolate, are characterised as a function of phase volume, particle size distribution (PSD) and emulsifier concentration. It is found that their rheological behaviour shows the formation of a network gel structure at sufficient concentration of sugar particles. We find that, upon addition of sufficient emulsifier, the suspension viscosity follows the MPQ hard sphere model, which only depends on phase volume and particle size distribution. Combining the use of the theoretical model and emulsifiers, we are able to decouple the effects of phase volume and particle size distribution from that of particle interactions. The results provide a theoretical basis for identifying levers to control the rheological behaviour of molten chocolate, biscuit-creams, and other sugar-fat based systems, which is relevant to food processing and sensory perception during consumption.

Aerosol Particles Generated by Coughing and Sneezing of a SARS-CoV-2 (COVID-19) Host Travel over 30 m Distance

A fast-computational 3D model comprising fluid dynamics with heat transfer, mass transfer and diffusion of diluted species has been adapted and employed to evaluate dispersion of aerosol particles in various environments. Effects of convection flow, atmospheric diffusivity and humidity on evolution and travel distances of exhaled aerosol clouds by an infected person are modelled. The modelling clearly demonstrates how aerosol particle dispersion is influenced by weather and geometry of the environment. The results obtained demonstrate that aerosol particles of sizes from 10 µm to 100 µm that potentially can carry SARS-CoV-2 (COVID-19) viruses travel over 30 m in some atmospheric conditions. Modelling of the evolution of aerosol clouds generated by coughing and sneezing enables us to evaluate the deposition dose of aerosol particles in healthy individuals. In realistic weather scenarios viruses can be deposited in the respiratory tract of a healthy individual at up to 200 virus copies in several minutes. A metric based on aerosol particle (volume) size distribution and the ICRP lung deposition model is suggested.

Air pollution in the Gobi Desert region: Analysis of dust‐storm events

AbstractAir pollutants in nine cities of the Gobi Desert region are examined in this study. Mean concentrations of PM2.5 and PM10, retrieved from ground‐based air quality monitoring stations, were 36.2 ± 23.7 and 97.3 ± 84.5 μg·m−3, respectively. The highest concentrations of pollutants were in spring and winter. This can be explained by wind‐borne dust in the spring and emissions from domestic sources during the winter heating season. The highest PM2.5 and PM10 concentrations were registered in a period of dust‐storm activity with values of 343 μg·m−3 and 1,642 μg·m−3. Generally, clean continental (CC) was the dominant aerosol type (73.9%), followed by mixed (MX) aerosol type (20.4%) with insignificant contribution of clean marine (CM) (2.1%), urban/industrial and biomass burning (UI/BB) (0.9%) and desert dust (DD) (2.7%) aerosol types. The various measures of pollution retrieved from AERONET stations, including aerosol optical depth (AOD), Ångström exponent (AE), asymmetry parameter (AP), single scattering albedo (SSA) and aerosol volume size distribution (AVSD), specify the content of coarse aerosol fractions in the period of dust activity. The aerosol radiative forcing at the bottom of the atmosphere (ARFBOA) and the top of the atmosphere (ARFTOA) during dust days were estimated to be −115.76 and −241.31 W·m−2, with a corresponding heating rate of 3.52 K·day−1. According to the backward and forward trajectories of air masses, the dust cloud moved to the east and southeast from the epicentre, affecting the eastern and the central parts of the country. This study may advise environmental policy, as it showed how controlling causes of pollution can improve air quality.

A novel method of retrieving low visibility during heavily polluted episodes in the North China plain

Abstract The prediction of visibility is an ongoing problem in air quality models, particularly that of low visibility during heavily polluted episodes. In this study, a new method of calculating visibility based on the particle mass concentration of PM2.5 (particles with diameter ≤ 2.5 μm) and relative humidity (RH), data for which are generally available in most regions of China, is developed. The method also considers the particle number size distribution (PNSD) and hygroscopic parameter (κ), and focuses on visibility below 10 km. First, the PNSD was re-constructed under dry condition (PNSDdry,rec) based on the relationship between PM2.5 and the particle volume size distribution modal parameters obtained in a previous study conducted in the North China Plain. Then, the ambient PNSD (PNSDamb,rec) was retrieved based on the PNSDdry,rec and κ, and the light extinction was calculated by applying the Mie code (σext,amb). Finally, the visibility was calculated based on the Koschmieder experimental equation, and denoted as Viscal. A parameterization scheme was proposed based on the σext,amb, PM2.5, and RH to simulate the visibility (Vissimu), which is more applicable than the theoretical calculation described above. This method was validated at different locations in different regions in China. The values calculated by the scheme showed agreed well with the observed data in general, especially for low visibility of ≤5 km, associated with severe haze. Although a large bias occurred at some sites, both the hourly and daily averages for almost every event with visibility lower than 5 km were captured. The method reported in this work exhibited smaller bias below 2 km than the other visibility parameterization scheme, and will be available for improving the prediction of visibility in air quality models.

Experimental characterization of cyclopentane adsorption/desorption in microporous activated carbons

In this work, the adsorption of cyclopentane (CP) is investigated and characterized on four activated carbons (ACs) of complementary textural properties by combining characterization (pore volume, pore and particle size distributions), adsorption/desorption isotherms of CP and adsorption enthalpy measurements. On the one hand, the adsorption/desorption isotherms measured with a magnetic suspension balance have shown that between nearly 30% to 50% of CP adsorbed at saturation remains trapped in the ACs even after prolonged evacuation under primary vacuum. On the other hand, calorimetric/manometric measurements have evidenced that high-energy adsorption occurs at the lowest CP-loadings. Gas porosimetry before and after CP adsorption/desorption has made it possible to identify that the pore size distribution is the key parameter that controls cyclopentane trapping and that micropores smaller than 1.1 nm are responsible for hardly-reversible CP adsorption. Coupling of TGA with gas porosimetry has shown that temperatures must be higher than 550 K to remove CP trapped in the ultramicroporosity.

A machine learning field calibration method for improving the performance of low-cost particle sensors

Measurements of airborne particles in buildings with low-cost optical particle counters (OPCs) are often inaccurate and subject to uncertainties. This study introduces a methodology to improve the performance of low-cost OPCs in measuring indoor particles through machine learning. A two-month field measurement campaign was conducted in an occupied net-zero energy house. The studied OPCs (OPC–N2, Alphasense Ltd.) report size fractionated concentrations from 0.38 to 17.5 μm. Co-located reference instrumentation included a scanning mobility particle sizer (SMPS: 0.01–0.30 μm) and an optical particle sizer (OPS: 0.30–10 μm). The machine learning field calibration method applies Gaussian Process Regression (GPR) and includes two components: (1.) correction of the size-resolved OPC counting efficiency from 0.38 to 10 μm and (2.) prediction of volume size distributions (mass proxy) below the 0.38 μm detection limit of the OPC. The field calibration method is applicable to OPCs that report size fractionated concentrations. In (1.), a GPR function was used to correct the size-resolved counting efficiency of the OPCs between 0.38 and 10 μm using the OPS as reference. In (2.), a second GPR function was used to predict the volume size distribution below 0.38 μm using the SMPS/OPS as reference. This was done given the significant contribution of sub-0.38 μm particles to volume concentrations in the accumulation mode. The machine learning field calibration method resulted in a significant improvement in the accuracy of size-integrated volume concentrations (PV2.5, PV10) reported by the OPCs as compared to the SMPS/OPS. Improvements were seen in the Pearson coefficient (before correction: 0.59–0.83; after correction: 0.98–0.99); coefficient of determination (before correction: 0.35–0.69; after correction: 0.97–0.98); and mean absolute percentage error (before correction: 35–69%; after correction: 19–25%).

Aerosol properties in the atmosphere of Natal/Brazil measured by an AERONET Sun-photometer.

We analyzed data measured by a Sun-photometer of the RIMA-AERONET network with the purpose to characterize the aerosol properties in the atmosphere over Natal, state capital of Rio Grande do Norte, at the coast of Northeast Brazil. Aerosol Optical Depth, Ångström Exponent, Volume Size Distribution, Single Scattering Albedo, Complex Refractive Index, Asymmetry Factor, and Precipitable Water were analyzed from August 2017 to March 2018. In addition, MODIS and CALIOP observations, local Lidar measurements, and modeled backward trajectories were analyzed in a case study on February 9, 2018, that consistently confirmed the identification of a persistent aerosol layer below 4 km agl. Aerosols present in the atmosphere of Natal showed monthly mean Aerosol Optical Depth at 500 nm below 0.15 (~ 75%), monthly means of the Ångström Exponent at 440-670 nm between 0.30 and 0.70 (~ 69%), bimodal Volume Size Distribution is dominantly coarse mode, Single Scattering Albedo at 440 nm is 0.80, Refractive Index - Real Part around 1.50, Refractive Index - Imaginary Part ranging from 0.01 to 0.04, and the Asymmetry Factor ranged from 0.73 to 0.80. The aerosol typing during the measurement period showed that atmospheric aerosol over Natal is mostly composed of mixed aerosol (58.10%), marine aerosol (34.80%), mineral dust (6.30%), and biomass burning aerosols (0.80%). Backward trajectories identified that 51% of the analyzed air masses over Natal originated from the African continent.

Production Conditions of Nanoporous Ceramics Based on Mullite

A technology for producing nanoporous ceramics based on mullite (3Al2O3 ⋅ 2SiO2) is developed. The mechanochemical activation of oxides involved in the synthesis of mullite (γ-Al2O3 and amorphous SiO2) makes it possible to obtain single-phase 3Al2O3 ⋅ 2SiO2 and to reduce its sintering temperature to 1300°С. The effect of the pressing pressure and the amount of pore-forming additive (ammonium carbonate) on the value of open porosity, pore volume, and pore size distribution in sintered ceramics 3Al2O3 ⋅ 2SiO2 is established. Mullite nanoceramics with open porosity of 42–47%, pore size <200 nm, and compressive strength 50–65 MPa is obtained.

Assessment of activated carbon fibers from commercial Kevlar® as nanostructured material for gas storage: Effect of activation procedure and adsorption of CO2 and CH4

Carbon-based nanostructures are considered promising materials for gas storage thanks to robust structure, tunable porosity, lightweight, high thermal/chemical stability and easy production. This study reports the development of activated carbon fibers prepared from commercial Kevlar® through an innovative pyrolysis method, consisting of carbonization in inert ambient and subsequent physical activation in oxidizing atmosphere, using a unique apparatus. Varying three key parameters, time (range 60−240 min), temperature (range 1023−1123 K) and gas-flow (0.3/0.9/1.2 Nl/min of CO2), the correlation between the activation procedure and the resulting samples structure was evaluated. The best results in terms of microporosity and gas adsorption properties have been obtained by reducing the activation times of the material. Furthermore, the purpose has been to optimize the characteristics in terms of Specific Surface Area, Total Pore Volume and optimal Pore Size Distribution. The method made it possible to develop an adsorbent material with a high fraction of micropores up to 94 % of the total pore volume, straddling the supermicroporosity (0.7−2 nm) and ultramicroporosity (<0.7 nm) region. Such textural properties have resulted in high gases storage capacities, tested at different temperatures (280, 298, 314 K), with maximum uptake of 46 wt% for CO2 and almost 10 wt% for CH4. All produced samples were characterized by helium picnometry to estimate skeletal density, Scanning Electron Microscopy to obtain morphological information, porosimetry to know structural properties. The adsorption behaviour was tested using a Sievert-type apparatus in the pressure range of 0−15 bar for CO2 and 0−40 bar for CH4.

Investigation of the microporous organization of 1,2-disubstituted polyacetylenes using low-temperature argon sorption and small-angle X-ray scattering

The extra free volume of glassy, highly permeable 1,2-disubstituted polyacetylenes is associated with the microporous organization of these polymers. In this work, the microporosity of poly(1-trimethylsilyl-1-propyne) (PTMSP) and poly(4-methyl-2-pentyne) (PMP) is investigated by two independent methods—convenient low-temperature Ar sorption and less commonly used small-angle X-ray scattering (SAXS). The Ar sorption data were analyzed in connection with the specific surface area, pore volume, and micropore size distribution. It is shown that the higher specific surface area, total pore volume, and micropore volume of PTMSP than those of PMP are associated with higher gas permeability coefficients. It was found that the Brunauer–Emmett–Teller-specific surface values obtained for PTMSP and PMP from argon sorption isotherms correlate with the specific surface values obtained from the SAXS method. The correlation of the specific surface values obtained from fundamentally different methods makes it possible to evaluate the small-angle scattering method as adequate for assessing the microporosity of polymeric materials. The microporosity of poly(1-trimethylsilyl-1-propyne) (PTMSP) and poly(4-methyl-2-pentyne) (PMP) is investigated by two independent methods—convenient low-temperature Ar sorption and less commonly used small-angle X-ray scattering (SAXS). The Brunauer–Emmett–Teller-specific surface values obtained for PTMSP and PMP from Ar sorption isotherms correlate with the specific surface values obtained from the SAXS method. The correlation of the specific surface values obtained from fundamentally different methods makes it possible to evaluate the small-angle scattering method as adequate for assessing the microporosity of polymeric materials.

Inter-annual and seasonal variations in optical and physical characteristics of columnar aerosols over the Pokhara Valley in the Himalayan foothills

ABSTRACT This study reports comprehensive analysis of seasonal and inter-annual variations of aerosol optical and physical properties over the Pokhara Valley in the foothills of central Himalayas in Nepal utilizing the high-quality multi-year columnar aerosol data observed recently from January 2010 to December 2017. The influence of forest fires and agro-residue fires on aerosol properties is also investigated. Seasonal mean aerosol optical depth (AOD) over Pokhara is ≥0.3 during the year, highest in pre-monsoon and lowest in monsoon season. AOD exhibits a consistent seasonal cycle every year with a peak in pre-monsoon. Fine mode fraction contributing to AOD and Angstrom exponent (α) corroborate seasonal pattern of AODs. AODs show good correlation with fire counts in the Pokhara Valley and surrounding region. The aerosol volume size distributions are bimodal. The peaks in volume size distribution and volume concentrations obtained in 2016 pre-monsoon are the highest during the 8-year observation period which coincided with peaks in the occurrence of highest number of fires in the Pokhara Valley and surrounding region. Effective radius of coarse mode aerosols is an order of magnitude larger than fine mode aerosols. The analysis of optical and physical properties of aerosols over the Pokhara Valley suggest that the aerosols observed over the Himalayan foothills are of urban/industrial, biomass burning and dust origin with proportional contributions varying in different seasons. The study provides observational constraints on aerosol physical and optical properties that can serve as inputs for model simulation of aerosol physiochemical processes and quantification of impacts on air quality, climate and sensitive ecosystems in this data-sparse region.

Fabrication and characterization of highly porous Ti6Al4V/xTa composites for orthopedic applications

This paper presents the processing and properties of Ti6Al4V/xTa porous materials for potential use as bone implants. The processing route includes powder mixing, die pressing and solid state sintering. The porosity was created by 30 or 40 vol.% of salt particles with controlled volume fraction and size distribution, acting as space holders. The microstructure of the sintered materials was characterized by SEM and microtomography. Mechanical properties were deduced from simple compression tests, and permeability was evaluated by numerical simulations performed with real 3D microstructures. The obtained results showed various advantages of the fabricated materials. Their weight densities of the materials processed with 40 vol.% of salt particles were in the range of those of human bones. As a consequence of Ta diffusion, the final microstructures included Ta-stabilized β-Ti phase, conventional α-Ti phase, martensitic α′-Ti phase, and small residual Ta particles. Also, it was found that both Ta and salt additions reduced the Young’s modulus and the yield stress, while the permeability strongly increased with increasing vol.% of salt particles. Notably, the properties of the material processed with 30 vol.% of Ta particles and 40 vol.% of salt particles were close to those required for trabecular bone implants.