High Particle Surface Area Research Articles

Poly(Vinylidene Difluoride) Soft Dendritic Colloids as Li-Ion Battery Separators

As an alternative to Li-ion battery (LIB) microporous membrane separators that are typically comprised of polyolefins, other materials and separator morphologies may yield increased cell performance. Here, we present a new class of LIB separators comprising poly(vinylidene difluoride) (PVDF)-based and highly branched, colloidal polymer particulates, called soft dendritic colloids, that are produced by shear-driven polymer precipitation within a turbulent nonsolvent flow followed by filtration. We show the morphology of the resulting PVDF particulates may be varied from fibrous dendritic colloids to thin and highly porous sheet-like particles. The use of PVDF leads to low thermal shrinkage (5% at 90 °C) and high tensile strength (<0.7% offset at 1000 psi), while the high porosity (up to 80%) and high particle surface area are responsible for high conductivity (1.2 mS cm−1) and electrolyte uptake (325%), and good cell capacity (112 mAh g−1 in Li/LiCoO2 cell) with <10% loss after 50 cycles. Because shear-driven precipitation with filtration is a facile and versatile process to make a new class of polymeric LIB separators, soft dendritic colloids are promising candidates as separators for next-generation batteries.

An Ideal Structure for Li-Ion Battery Separators

Among all types of Li-ion battery (LIB) separators, fibrous mats have the advantage of low cost, low mass, and high porosity. Fibrous Poly(Vinylidene difluoride) (PVDF) shows promising results because of its stability and affinity for electrolytes commonly employed in Li-ion cells. Despite numerous studies published on LIB separators, none reports structure-property relationships for the identification of an ideal structure. We investigated the properties of a melt-blowable PVDF and produced meltblown PVDF mats in scale-up equipment with the objective of elucidating its performance as a LIB separator. We also present a new class of LIB separators, PVDF-based highly-branched, colloidal polymer particulates called soft dendritic colloids that are produced by shear-driven polymer precipitation within a highly turbulent nonsolvent flow, followed by filtration. We show that the morphology of the resulting PVDF particulates can be modulated from fibrous soft dendritic colloids (SDC) to thin and highly porous sheet-like particles.Through a scale-up system, we obtained high-quality meltblown PVDF with high homogeneity, low number of defects, an average fiber diameter of 1.4 μm, and pore size as low as 0.9 μm. Small fiber diameter provides high-surface area and high-electrolyte uptake. We show interactions of the meltblown PVDF with the electrolyte lead to a morphology change in the fibers. The highest ionic conductivity was ~ 9.6 mS/cm, and the first-cycle capacity was 140 mAh/g (Li/LiCoO2). After melt-pressing, the thickness and pore size decrease, but the mats electrolyte absorbency and conductivity decrease commensurately. PVDF SDC separators show high porosity (up to 80%) and high particle surface area, which results in high conductivity (1.2 mS/cm), high-electrolyte uptake (325%), and high-cell capacity (112 mAh/g in Li/LiCoO2 cell) with <10% loss after 50 cycles. Both processes yield separators with low thermal shrinkage (<5% at 90 ºC) and high tensile strength (<0.5% offset at 1000 psi), with the highest-performing separator possessing low average fiber diameter with a wide diameter distribution.Both meltblowing and shear-driven precipitation are facile and versatile processes for high-volume fabrication of LIB separators with one single polymer without necessarily requiring post-processing and with characteristics similar to commercially available battery separators. Our findings show that battery separators should be fabricated with a low pore size (<2 µm) but also with a wide pore distribution. When the strength and openness of the micropores are coupled with a dense net of nanopores, an ideal Li-ion battery separator is obtained.

Guava flavored whey-beverage processed by cold plasma: Physical characteristics, thermal behavior and microstructure

The present study aimed to compare the physicochemical (pH), physical (rheology parameters and particle size), microstructure (optical microscopy) and thermal properties (differential scanning calorimetry) of guava flavored whey-beverages submitted to cold plama technology in different processing time (5, 10, and 15 min) and gas flow (10, 20, and 30 mL min−1) conditions with a conventional pasteurized product. Whey beverages treated by cold plasma presented higher pH values, lower consistency and lower viscosity, and a flow behavior index similar to Newtonian fluids. Milder cold plasma conditions resulted in whey beverages with higher pH, lower viscosity and consistency, and similar particle distribution and microstructure compared to the pasteurized product. In contrast, more severe processing conditions resulted in a higher particle surface area ([D 3,2]) and smaller particles (~10 μM), due to the decrease in the number of larger particles (1000 μM), cell rupture, the formation of cell fragments, and higher viscosity and consistency. The treatments did not affect the thermal properties (enthalpy and bound water) of any sample.

Simulating Biogenic Secondary Organic Aerosol During Summertime in China

AbstractBiogenic secondary organic aerosol (BSOA) contributes significantly to summertime organic particulate matter. In this study, a simulation of BSOA for summer 2012 over China is performed using the Community Multiscale Air Quality model with an explicit representation of BSOA formation via reactive uptake of isoprene‐derived intermediates, species‐specific parameters for monoterpene‐derived BSOA production, and a multigenerational oxidation scheme. Simulated BSOA tracks the measurements well (normalized mean bias of 1% and r2 of 0.59). Elevated BSOA occurs in the Sichuan Basin and southeastern China (except the coastal areas) where concentrations are mostly within the range of 5–7.5 μg/m3. Nitrate oxidation dominates fresh BSOA originating from monoterpenes. Simulated monoterpene‐formed BSOA increases by a factor of 3–11 with multigenerational oxidation. Isoprene‐formed BSOA shows high concentrations in southwestern China, formed primarily by two methyltetrols (2‐MT) and organosulfates (62%–83%). High concentrations in this region are driven by the abundance of IEPOX and high particle surface area of sulfate‐laden aerosols. NOx emissions influence the formation pathways of isoprene‐formed BSOA, as a high ratio of two‐methylglyceric acid (2‐MG)/2‐MT is found in the North China Plain and part of the Yangtze River Delta Region. The simulated isoprene‐formed BSOA is more strongly correlated with sulfate than with particle water mass concentration or particle acidity, in part because sulfate increases the surface area increasing uptake for heterogeneous reactions. Decreases in isoprene‐formed BSOA were simulated with a pH increase of 2, implying that particle acidity mediates the BSOA formation.

Thermal barrier coatings based on alumina microparticles

Abstract Buildings are large consumers of energy everywhere and a substantial share of energy goes to heat and cool buildings. This heating and air-conditioning load can be reduced through many means; a notable possibility is the proper design and selection of the building envelope. Therefore the use of thermal insulation in buildings contributes to reducing the annual energy cost. The objective of this paper is to present a new coating based on waterborne matrix, which is modified with gamma-alumina to form an inorganic–organic composite paint. Characterizations and performance, in terms of thermal conductivity, are presented. Due to both the high surface area of particles and the presence of interstitial cavities in the thin film, the product seems to be very interesting as insulation material.

Electron microscopy of multi-layered polymer-nanocomposite based dielectrics

Vacuum deposited polymer-nanocomposites (PNCs) comprising alternate layers of metal (Al/Ag) (filler) and polymer (nylon-6) (matrix) have been investigated using chemical, impedance spectroscopy and microstructural characterisation techniques. Electron microscopy investigations revealed the morphology, nanostructure and phases of nano-scale core (metal)-shell (oxide) particles and metallic nano-islands in Al and Ag based PNCs respectively. Evaporation of Al yielded islands of angular core-shell nanoparticles in an Al-oxide/nylon-6 matrix whereas Ag yielded rounded, discrete nanoparticles in nylon-6 matrix. The high particle surface area and an affinity for oxygen formed oxide shells in Al nanoparticles and was critical to charge accumulation and enhanced dielectric behaviour; in contrast, Ag showed little oxidation and less charge accumulation. With an increase in the thickness of the deposited metal layer, Al formed a continuous film of particles whereas Ag condensed to form interconnected nano-islands. This microstructural study is useful in conceptualising better dielectrics based on PNCs.

Improving fines recovery by grinding finer

It is commonly believed that fine particles have low flotation recoveries. Indeed, size–recovery graphs often are 'hill shaped' with high recovery in the mid sizes and low recovery at the fine and coarse ends. Yet rather than being due to 'overgrinding', fines recovery may be low because the grind is not fine enough! The different flotation needs of fine and coarse particles have long been recognised, for example, in the old design for separate 'sand and slimes' circuits. Yet the principles may be overlooked in the desire for simpler circuits and larger equipment. Most plants now treat all particles together in one wide size distribution. Reagent conditions are set for the dominant coarser particles, so fines are starved of collector. Worse still, if there are significant mid sized composites, they often have to be rejected in cleaning to achieve target concentrate grade. Yet the conditions which reject mid size composites (collector starvation and high depressants) also reject fine liberated particles. In contrast to this common result, fines flotation can be excellent when flotation chemistry is tailored to them. After first recovering fast floating liberated particles, it is essential to adequately grind remaining composites to enable fines recovery. First, this allows lower depressant and higher collector additions since composites do not have to be rejected from concentrate. Second, finer grinding in appropriate equipment may be managed to narrow the size distribution to flotation, allowing reagent conditions to be set to suit the majority of particles. Third, grinding in an inert attritioning environment like an IsaMill increases fine flotation rates by producing clean mineral surfaces. An excellent case study is the installation of IsaMills in the Mount Isa lead zinc concentrator to grind lead and zinc rougher concentrate to P80 of 12 μm and zinc cleaner tailings to 7 μm. Most plant losses had previously been in the sub 10 μm fraction, yet the finer grinding increased plant recovery by 5% lead and 10% zinc and also increased concentrate grades. Circulating loads dropped, reagent additions dropped in spite of the much higher particle surface area, and the plant became much more operable and responsive.

Mercury–organic matter relationships in pre-pollution sediments of thermokarst lakes from the Mackenzie River Delta, Canada: the role of depositional environment

This study investigates the influence of organic matter (OM) on the historical variations of Hg in sediments from two closely-situated Canadian Arctic lakes, prior to the advent of Hg pollution inputs. Because of variable landscape evolution in the Mackenzie River Delta over the past 1–3 millennia, the lakes provide distinctly different histories of OM sources, types, and degree of aquatic productivity (i.e., depositional environments). They also differ significantly in their pre-1900 Hg concentration profiles. When labile, kerogen-like carbon (“S2”) from aquatic sources (diatoms and other unicellular algae) increased between 750 and 1900 A.D. in the more productive lake (Nesbitt), Hg concentrations also increased by ca. 50%. In contrast, S2 carbon concentrations in the nearby organic-poor lake (Big Lake) were several-times lower than in Nesbitt and decreased over the past millennium, while Hg concentrations showed no trend probably reflecting the stable input of clastic material from tundra soils. The contrast between lakes suggests that OM derived from unicellular algae is more effective at scavenging Hg than OM from terrestrial plants or aquatic macrophytes, possibly because of a higher content of labile, sulphur-rich compounds, high particle surface area and its dispersion throughout the water column. The results indicate that, in the absence of anthropogenic Hg inputs, increasing phytoplankton productivity and Hg scavenging alone can lead to significant increases in the Hg content of lake sediments. This finding is consistent with the hypothesis that increasing lake productivity because of climate warming during the twentieth century has confounded the interpretation of recently increasing Hg levels in northern lake sediments as being unequivocally due to anthropogenic Hg deposition. This study also suggests that sedimentary TOC by itself is a poor and sometimes misleading indicator of possible changes in the source and quality of OM in aquatic systems, which can have a major impact on Hg concentrations in sediments.

Dual Effect of Amino Modified Polystyrene Nanoparticles on Amyloid β Protein Fibrillation

The fibrillation kinetics of the amyloid β peptide is analyzed in presence of cationic polystyrene nanoparticles of different size. The results highlight the importance of the ratio between the peptide and particle concentration. Depending on the specific ratio, the kinetic effects vary from acceleration of the fibrillation process by reducing the lag phase at low particle surface area in solution to inhibition of the fibrillation process at high particle surface area. The kinetic behavior can be explained if we assume a balance between two different pathways: first fibrillation of free monomer in solution and second nucleation and fibrillation promoted at the particle surface. The overall rate of fibrillation will depend on the interplay between these two pathways, and the predominance of one mechanism over the other will be determined by the relative equilibrium and rate constants.

Performance of Mechanical Filters and Respirators for Capturing Nanoparticles ―Limitations and Future Direction

There is an increasing concern about the health hazard posed to workers exposed to inhalation of nanoparticles. Inhaling nanoparticles possess an occupational hazard due to elevated amount emitted to the atmosphere and working environment. Nanoparticles have potential toxic properties: the high particle surface area, number concentration, and surface reactivity. Inhalation, the most common route of nanoparticle exposure, has been shown to cause adverse effects on pulmonary functions and the deposited particles in the lung can be translocated to the blood system by passing through the pulmonary protection barriers. Filtration is the simplest and most common method of aerosol control. It is widely used in mechanical ventilation and respiratory protection. However, concerns have been raised regarding the effectiveness of the filters for capturing nanoparticles. This paper reviews the literature on the filtration performance of mechanical filters and respirators against nanoparticles. It includes the discussion about filtration mechanisms, theoretical models, affecting factors of the filtration efficiency, and testing protocols for respirator and filter certification.

Ultrasmall-angle X-ray scattering (USAXS) studies of morphological trends in high energy milled NaAlH 4 powders

Transition metal dopants added to complex metal hydrides, specifically to sodium aluminum hydride (NaAlH 4), by high energy ball milling enhances dehydrogenation kinetics and induces dehydrogenation reaction reversibility. This study uses the power-law scattering parameter, p, gained from ultrasmall-angle X-ray scattering (USAXS) data to elucidate differences in NaAlH 4 particle morphology as dopant type and mill time is varied. Four dopant types were used. Two dopant types were used to represent the best kinetic enhancements having high desorption rates (e.g. TiCl 2, TiCl 3) and were compared with two dopant types which do not perform as well (e.g. ZrCl 3 and VCl 3). USAXS data for the doped hydrides were compared with undoped and milled NaAlH 4 powders. Mill times used were 0 min (blended), 1, 5, and 25 min. As indicated by the USAXS power-law scattering data, the undoped NaAlH 4 powders are comprised of primary particles each having a high surface area. The high particle surface area in the undoped NaAlH 4 particle system persists as mill time increases—with only the 25 min sample undergoing a marked a decrease in primary particle surface area. Alternatively, the doped powders milled for 1, 5, and 25 min show uniformly decreasing hydride particle surface area. These decreases in particle surface area may be explained by either the colloidal particles increasing in surface smoothness or decreasing internal void space. TiCl 3-doped NaAlH 4 powders show the trend of maintaining particles having a morphology comprised of higher particle surface area during the high energy milling stage of powder processing compared with other dopants.

Evolution of particle concentration and size distribution observed upwind, inside and downwind hill cap clouds at connected flow conditions during FEBUKO

The concentration and size distribution of atmospheric particles were traced upwind, inside and downwind a hill cap cloud within the ground-based cloud passage experiment FEBUKO, which was carried out at the mountain ridge Thüringer Wald (Germany) during October 2001 and 2002. Three cloud events were examined in detail for which the connected flow between all three sites was meteorologically confirmed and the influence of entrainment and local sources on particle concentration and size distribution was only of minor importance. Modifications of the number size distributions between 60 and 300 nm particle diameter that are attributed to cloud processing were observed comparing upwind and downwind dry particle size distributions. Despite a small interference of droplet deposition, a maximum in-cloud mass production of 0.38 μg m−3 was found accounting for 5% of the upwind aerosol mass. The corresponding mass production rate was estimated to 1.16 μg m−3 h−1. A formation of new ultra-fine particles was detected in the outflow of the orographic clouds during nighttime yielding number concentrations up to 300 cm−3 at a pre-existing dry particle surface area of about 300 μm2 cm−3. At a more than twice as high particle surface area, i.e. when adsorption of condensable gases on existing particles became more important, no new particle formation was observed. Whereas the in-cloud mass production proceeded rather continuously throughout the cloud events, the particle production occurred during periods of 15 min up to 2 h within the cloud events. In the absence of actinic radiation, ternary nucleation of gaseous substances outgassing from the evaporating droplets at high relative humidity is hypothesized as the most likely particle formation mechanism but the reason for the temporary appearance of the particle production is not known.

Coupling of HDPE/hydroxyapatite composites by silane-based methodologies.

Several coupling treatments based on silane chemicals were investigated for the development of high density (HDPE)/hydroxyapatite (HA) composites. Two HA powders, sintered HA (HAs) and non sintered HA (HAns), were studied in combination with five silanes, namely y-methacryloxy propyltrimethoxy silane (MEMO), 3-(2-aminoethyl)aminopropyltrimethoxy silane (DAMO), vinyltrimethoxy silane (VTMO), 3-aminopropyltriethoxy silane (AMEO) and trimethoxypropyl silane (PTMO). The HA particles were treated by a dipping in method or by spraying with silane solutions. After drying, the treated powders were compounded with HDPE or HDPE with acrylic acid and/or organic peroxide and subsequently compression molded. The tensile test specimens obtained from the molded plates were tensile tested and their fracture surfaces were observed by scanning electron microscopy (SEM). For the sintered HA (HAs) composites, the most effective coupling treatments concerning stiffness are those based on MEMO and AMEO. The low influence of these coupling procedures on strength is believed to be associated to the low volume fraction and the relatively smooth surface of the used HA particles. For the non-sintered HA (HAns) composites, it was possible to improve significantly both the stiffness and the strength. Amino silanes demonstrated to be highly efficient concerning strength enhancement. The higher effectiveness of the coupling treatments for HAns filled composites is attributed to their higher particle surface area, smaller particle size distribution and expected higher chemical reactivity. For both cases, the improvement in mechanical performance after the coupling treatment is consistent with the enhancement in interfacial adhesion observed by SEM.

Transformation of N-, O-, and S- heterocycles (NOSHs) in estuarine sediments: Effects of redox potential and sediment particle size

The transformation of 19 N-, O-, and S- heterocycles (NOSHs) was examined in estuarine sediment-water microcosms. The effects of redox potential (Eh) and sediment particle size on compound transformation rates were evaluated, and stable products were identified. Results from stirred, controlled Eh/pH microcosms (CEPMs) showed that most of the NOSHs were significantly transformed under oxidized and reduced conditions over 15 week incubations, and the resulting product distributions were similar. In general, the rates and extent of transformation were greater in oxidized sediments of low surface area vs. those with high particle surface area and reduced redox conditions. Further experiments in sealed, unstirred microcosms also showed that NOSH transformation proceeded more slowly and on fewer compounds in fine vs. coarser grained sediments under oxidized conditions. Unlike the stirred systems, however, NOSH transformation rates were similar or greater under reduced vs. oxidized conditions. Thus, reduced, methanogenic clay of high surface area displayed some of the fastest rates of NOSH transformation. Data from liquid-liquid partitioning experiments suggested that this effect was related to the formation of NOSH complexes with iron and perhaps other redox-active metals in sediments.

Enhanced biodegradation of phenanthrene in a biphasic culture system

Degradation of phenanthrene byPseudomonas aeruginosa AK1 was examined in (i) an aqueous mineral salts medium to which phenanthrene particles of varying size (i.e. diameter) were added, and (ii) an aqueous/organic biphasic culture system consisting of mineral salts medium supplemented with 2,2,4,4,6,8,8-heptamethylnonane (HMN) as the phenanthrene-carrying organic phase. In both systems, the rate of phenanthrene biodegradation could be significantly enhanced by manipulations leading to improved phenanthrene mass transfer into the aqueous phase. With crystalline phenanthrene, the rate of biodegradation was found to be directly correlated to the particle surface area, whereas in the biphasic system the rate of biodegradation of the dissolved phenanthrene was mainly governed by the HMN/water interface area. In the latter system, exponential growth with a doubling time t d of 6–8 hours has been achieved under conditions of intensive agitation of the medium indicating that phenanthrene degradation by strain AK1 is limited mainly by physicochemical parameters. Addition of selected surfactants to the culture medium was found to accelerate phenanthrene degradation by strain AK1 only under conditions of low agitation (in the presence of HMN) and after pretreatment of phenanthrene crystals by ultrasonication (in the absence of HMN). Evidence is presented that the stimulating effect of the surfactants was primarily due to improved dispersion of phenanthrene particle agglomerates (in the aqueous mineral salts medium supplemented with phenanthrene crystals) or of the phenanthrene-carrying lipophilic solvent drops (in the aqueous/organic biphasic culture system) whereas the solubilizing activity towards phenanthrene was neglectible. Under conditions of intensive mixing of the culture medium (i.e. if a high particle surface area or HMN/water interface area, respectively, is provided), the addition of surfactants did not enhance phenanthrene biodegradation.