Particle Size Distribution Measurements Research Articles

Study of a gemini surface active ionic liquid 1,2-bis(3-hexylimidazolium-1-yl) ethane bromide as a high performance shale inhibitor and inhibition mechanism

It is an urgent subject to search high-performance shale inhibitors used in water-based drilling fluids for drilling safety. In the present work, two imidazolium-based ionic liquids (ILs), 1-hexyl −3-methylimidazolium bromide (BMH) and its corresponding gemini type, 1,2-bis(3-hexylimidazolium-1-yl) ethane bromide (HMH), were introduced as promising shale inhibitors. The inhibition performances were assessed and compared with the conventional inhibitors potassium chloride and polyether diamine (PDA) via the inhibition evaluation tests including sodium bentonite (Na-bent) pellets immersing tests, linear swelling tests and shale hot-rolling recovery tests. Both ILs inhibitors, especially HMH, shown terrific inhibition performance with lower dosages and maintained high-performance at temperature up to 160 °C. The inhibition mechanism was analyzed by FTIR, X-ray diffraction (XRD), Zeta potential tests, particle size distribution measurement, contact angle measurement and surface tension measurement. The results demonstrated both BMH and HMH effectively inhibit the shale hydration and swelling. HMH, with two positively charged headgroups and two hydrophobic tails, was better than BMH in entering the interlayer space of clay, reducing Zeta potential, forming hydrophobic shield and reducing the surface tension, which was responsible for its superior inhibition performance.

Characterization of AISI 304L stainless steel powder recycled in the laser powder-bed fusion process

During part fabrication by laser powder-bed fusion (L-PBF), an Additive Manufacturing process, a large amount of energy is input from the laser into the melt pool, causing generation of spatter and condensate, both of which have the potential to settle in the surrounding powder-bed compromising its reusability. In this study, AISI 304 L stainless steel powder is subjected to seven reuses in the L-PBF process to assess the changes in powder properties that occur as a result of successive recycling. The powder was characterized morphologically by particle size and shape distribution measurements, chemically through inert gas fusion for evaluation of oxygen content, and microstructurally by X-ray diffraction for phase identification. The evolution in powder properties was used to explain observed performance differences obtained by the Hausner ratio and a Revolution Powder Analyzer for quantifying flowability. The results show that recycled powder coarsens and becomes more spherical, accrues oxygen, and accumulates delta ferrite as it is reused. Due to the change in powder morphology, recycled powder exhibited improved flowability in comparison to the virgin powder.

Electrostatic precipitator dust density measurements in a Mars-like atmosphere

Mars atmospheric in-situ resource utilization processes will require dust filtration of large gaseous volumes. An electrostatic precipitator capable of operating in the Martian environment is under development to meet this need. We performed experimentation to aerosolize and inject Martian simulant particles with a representative dust density and size range into the precipitator intake and to measure removal efficiency. The experimental set up added to the existing electrostatic precipitator system included two customized dust particle analyzers, a laser, and optical sensors to measure particle size distribution, particle morphology, and collection efficiency. In this paper, we describe the methods used to determine particle density and collection efficiency using the fine particle analyzers along with the laser extinction method. We also describe the method used to introduce and aerosolize simulant dust particles with the desired size and particle concentration into the precipitator at the required gas flow rates. Results of precipitator dust removal efficiency obtained from the fine particle analyzers and from the laser extinction method are shown along with a description of the assumptions made and the limitations of each method.

Determination of particle size distribution based on dynamic light scattering measurements in the near field

Particle size distribution (PSD) measurement is important for improving product quality, inhibiting environmental pollution, and safeguarding human health. The near-field scattering (NFS) technique offers many substantial advantages over conventional techniques. However, the reconstruction equations are ill-posed and it is difficult to get a reliable solution. In this paper, we propose a new method that can solve the reconstruction equations. This method combines the Backus-Gilbert eclectic theory with truncated singular value decomposition (TSVD) method to obtain a non-negative approximation solution as the initial value of Chahine algorithm for fine calculation. Our method exhibited good performance with several numerical cases of unimodal and bimodal PSDs. It was then used for PSD measurement of two standard particles (GBW(E) 120,028 and 120,047) using the NFS techniques. The relative errors of the length mean diameter, with respect to the peak size of these two standard particles, were 0.18% and 0.76%, respectively.

Transition Metal Catalysts for Boron Combustion

ABSTRACT Composite powders comprising 95 wt% boron and 5 wt% metal additives including Fe, Co, Ni, Hf, and Zr, were prepared by high energy mechanical milling in a planetary mill using hexane as a process control agent (PCA). Additionally, composites with Fe were prepared using acetonitrile and stearic acid as PCA. Single particles of boron and all prepared materials were fed into the combustion products of a pre-mixed air-acetylene flame, in a diffusion air-hydrogen flame, and ignited in air using a CO2 laser beam. Infrared emission pulses of burning particles were recorded. Distribution of burn times for each powder was obtained based on the durations of these pulses. Correlating the time distributions with measured particle size distributions yielded trends showing the effect of particle size on its burn time for all materials. Color temperatures were also recovered from the recorded emission signals. Additionally, constant volume explosion experiments were performed with all materials aerosolized in air. Results show that the morphology of the prepared composite powders is similar to that of boron. Single particle combustion experiments show that adding Hf leads to the most significant acceleration of combustion compared to boron. A positive effect of Hf as an additive is noted in different oxidizing environments. Adding Fe leads to an improved burn rate in air; however, there is no clear advantage in other oxidizing environments. No clear improvement is observed when other metal additives are used. Preparing B-Fe composites using different PCAs suggests that both a greater refinement of iron and a stronger acceleration in the burn rates of the prepared powders particles in air occur when acetonitrile and stearic acid are used as PCA. The results of the present cloud combustion experiments were found to be affected by multiple parameters and processes making it difficult to offer their meaningful interpretation.

Evaluation of Second-Hand Exposure to Electronic Cigarette Vaping under a Real Scenario: Measurements of Ultrafine Particle Number Concentration and Size Distribution and Comparison with Traditional Tobacco Smoke.

The present study aims to evaluate the impact of e-cig second-hand aerosol on indoor air quality in terms of ultrafine particles (UFPs) and potential inhalation exposure levels of passive bystanders. E-cig second-hand aerosol characteristics in terms of UFPs number concentration and size distribution exhaled by two volunteers vaping 15 different e-liquids inside a 49 m3 room and comparison with tobacco smoke are discussed. High temporal resolution measurements were performed under natural ventilation conditions to simulate a realistic exposure scenario. Results showed a systematic increase in UFPs number concentration (part cm−3) related to a 20-min vaping session (from 6.56 × 103 to 4.01 × 104 part cm−3), although this was one up to two order of magnitude lower than that produced by one tobacco cigarette consumption (from 1.12 × 105 to 1.46 × 105 part cm−3). E-cig second-hand aerosol size distribution exhibits a bimodal behavior with modes at 10.8 and 29.4 nm in contrast with the unimodal typical size distribution of tobacco smoke with peak mode at 100 nm. In the size range 6–26 nm, particles concentration in e-cig second-hand aerosol were from 2- (Dp = 25.5 nm) to 3800-fold (Dp = 9.31 nm) higher than in tobacco smoke highlighting that particles exhaled by users and potentially inhaled by bystanders are nano-sized with high penetration capacity into human airways.

Bio-compatible flotation of Chlorella vulgaris: Study of zeta potential and flotation efficiency

The energy-intensive dewatering of algae biomass, the first step of most downstream processes, remains one of the big challenges for economically relevant photoautotrophic bioprocesses. Due to its scalability and easy construction, froth flotation using the interactions between cells and bubbles shows considerable potential for this type of cost-efficient initial dewatering step. Comprehensive knowledge on both the physico-chemical conditions and the cellular surface properties are an important precondition to harvest cells by flotation. This study investigates the impact of changing the medium composition, specifically varying the pH and adding (bio-) collectors, on the zeta potential of Chlorella vulgaris SAG 211-1b. Decreasing the pH value from physiological to acidic conditions (pH 1–1.5) resulted in a strongly reduced cellular zeta potential. As validated by dispersed-air flotation, this yields a significantly enhanced cell recovery R>95 %. The impact of the synthetic collector cetyltrimethylammonium bromide and the biopolymer chitosan on the cellular zeta potential and flotation performance was studied, resulting in a 3.3-fold decrease in the surfactant dose when chitosan was used . The basic mechanisms of cell-chitosan interaction were analysed in terms of particle size distribution and surface tension measurements, revealing interactions between flocculation and adsorption during the dispersed-air flotation of C.vulgarisSAG 211-1b.

Characterization of laser spatter and condensate generated during the selective laser melting of 304L stainless steel powder

The selective laser melting process, commonly referred to as laser powder-bed fusion (L-PBF), is an Additive Manufacturing (AM) technique that uses a laser to fuse successive layers of powder into near fully dense components. Due to the large energy input from the laser during processing, vaporization causes instabilities in the melt pool leading to the formation of laser spatter and condensate, collectively known as heat-affected powder. Since heat-affected powder settles into the powder bed, the properties of the unconsolidated powder may be altered compromising its reusability. In this study, characterization of 304 L heat-affected powder was performed through particle size and shape distribution measurements, energy-dispersive spectroscopy, Raman spectroscopy, inert gas fusion, metallography, and x-ray diffraction. The results show morphological, chemical, and microstructural differences between the virgin powder and heat-affected powder formed during processing which aid in the understanding of laser spatter and condensate that form in the L-PBF process.

Effects of reformed fuel on dual-fuel combustion particulate morphology

Advancements in catalytic reforming have demonstrated the ability to generate syngas (a mixture of CO and hydrogen) from a single hydrocarbon stream. This syngas mixture can then be used to replace diesel fuel and enable dual-fuel combustion strategies. The role of port-fuel injected syngas, composed of equal parts hydrogen and carbon monoxide by volume, was investigated experimentally for soot reduction benefits under diesel pilot ignition and reactivity controlled compression ignition strategies. Particle size distribution measurements were made with a scanning mobility particle sizer and condensation particle counter for different levels of syngas substitution. To explain the experimental results, computational fluid dynamics simulations utilizing a detailed stochastic soot model were used to validate and initialize additional simulations that isolate mixing and chemistry effects. Based on these simulations, the influence of adding syngas on soot particle size and quantity is discussed.

Comparing Fly Ash Samples from Different Types of Incinerators for Their Potential as Storage Materials for Thermochemical Energy and CO2.

This study aims to investigate the physical and chemical characterization of six fly ash samples obtained from different municipal solid waste incinerators (MSWIs), namely grate furnaces, rotary kiln, and fluidized bed reactor, to determine their potential for CO2 and thermochemical energy storage (TCES). Representative samples were characterized via simultaneous thermal analysis (STA) in different atmospheres, i.e., N2, air, H2O, CO2, and H2O/CO2, to identify fly ash samples that can meet the minimum requirements, i.e., charging, discharging, and cycling stability, for its consideration as TCES and CO2-storage materials and to determine their energy contents. Furthermore, other techniques, such as inductively coupled plasma optical emission spectroscopy, X-ray fluorescence (XRF) spectrometry, X-ray diffraction (XRD), scanning electron microscopy, leachability tests, specific surface area measurement based on the Brunauer–Emmett–Teller method, and particle-size distribution measurement, were performed. XRF analysis showed that calcium oxide is one of the main components in fly ash, which is a potentially suitable component for TCES systems. XRD results revealed information regarding the crystal structure and phases of various elements, including that of Ca. The STA measurements showed that the samples can store thermal heat with energy contents of 50–394 kJ/kg (charging step). For one fly ash sample obtained from a grate furnace, the release of the stored thermal heat under the selected experimental conditions (discharging step) was demonstrated. The cycling stability tests were conducted thrice, and they were successful for the selected sample. One fly ash sample could store CO2 with a storage capacity of 27 kg CO2/ton based on results obtained under the selected experimental conditions in STA. Samples from rotary kiln and fluidized bed were heated up to 1150 °C in an N2 atmosphere, resulting in complete melting of samples in crucibles; however, other samples obtained from grate furnaces formed compacted powders after undergoing the same thermal treatment in STA. Samples from different grate furnaces showed similarities in their chemical and physical characterization. The leachability test according to the standard (EN 12457-4 (2002)) using water in a ratio of 10 L/S and showed that the leachate of heavy metals is below the maximum permissible values for nonhazardous materials (except for Pb), excluding the fly ash sample obtained using fluidized bed technology. The leachate contents of Cd and Mn in the fly ash samples obtained from the rotary kiln were higher than those in other samples. Characterization performed herein helped in determining the suitable fly ash samples that can be considered as potential CO2-storage and TCES materials.

Fabrication of Thymoquinone‐Loaded Albumin Nanoparticles by Microfluidic Particle Synthesis and Their Effect on Planarian Regeneration

Thymoquinone is the main bioactive component of the plant Nigella sativa, which is commonly known as black seeds and has several therapeutic effects. However, clinical applications of thymoquinone are limited due to its hydrophobic nature. In this study, thymoquinone is encapsulated in albumin nanoparticles by using a microfluidic platform to overcome this limitation. The mean particle sizes of empty and thymoquinone-loaded nanoparticles are determined as 271.3 and 315.6 nm, respectively, with polydispersity index values both lower than 0.25. In addition to particle size distribution measurements, characterizations of the prepared nanoparticles such as zeta potential measurements, in vitro release studies, as well as scanning electron microscopy, Fourier-transform infrared, and differential scanning calorimetry analyses are also carried out. To determine the effect of thymoquinone on neural regeneration, planarians are used as the model organism. After application of free and encapsulated thymoquinone, planarians are amputated and the fragments are observed in terms of head and tail regeneration, swimming pattern, and behavior. The results indicate that thymoquinone affects their behavior and primarily enhances head regeneration of planarians. In addition, it is shown that encapsulation of thymoquinone not only enhances the thermal stability of the molecule but also decreases its toxicity.

Investigating the synergetic dispersing effect of hydrolyzed biomacromolecule Cellulase and SDS on CuPc pigment

In this paper, the dispersion performance of biomacromolecule hydrolyzed cellulase from Trichoderma reesei on copper phthalocyanine (CuPc) pigment was first studied. The effect of hydrolysis time, cellulase concentration and environmental pH on the dispersion performance was investigated by particle size distribution and suspension transmittance measurement. The hydrolysis degree of cellulase was determined by FTIR, XRD, UV–vis and fluorescence spectra, potential and particle size analysis, respectively. Subsequently, the hydrolyzed cellulase was combined with sodium dodecyl sulfate (SDS) for acquiring better CuPc suspension based on their synergetic effects on dispersion. The optimal mass ratio of hydrolyzed cellulase to SDS was found to be 1:9. The resulting CuPc dispersion by this hydrolyzed cellulase/SDS composite was characterized by FTIR, TG, TEM, XRD analysis, respectively. This study demonstrated that there were strong interactions between hydrolyzed cellulase and SDS to result in synergistic dispersing effect on CuPc for better stability.

Particle emissions of direct injection internal combustion engine fed with a hydrogen-rich reformate

Thermochemical Recuperation is a promising waste heat recovery method that enables utilization of the engine waste heat together with onboard hydrogen production resulting in a significant improvement in thermal efficiency and a massive reduction in gaseous pollutants emission. However, an unexpectedly high particle emission level as compared to the gasoline-fed engine was measured despite the combustion of a hydrocarbon-free hydrogen-rich methanol steam reforming (MSR) products, containing 75% mol. H2 and 25% mol. CO2. In the existing literature, this phenomenon has not described yet.In this reported study, experiments are performed to investigate reasons of the elevated particle emissions by a direct injection spark ignition engine fed with MSR reformate, and results are compared with a baseline engine fed with gasoline at the same engine loads and speeds. Results of particle number concentration and size distribution measurements show that the total particle number concentration emission of engine fed with MSR reformate is 170% higher compared to gasoline. A direct experimental comparison between the port and the direct reformate injection performed on the same engine shows an increase in particles formation with a direct injection method. Based on these findings, several hypotheses are presented attributing to excessive lubricant involvement in the combustion process. The peculiarities specific for direct reformate injection that could result to the enhanced particles formation are jet – lubricated wall interaction, lubricant vapor entrainment into the reformate jet and shorter flame quenching distance of hydrogen compared to gasoline.

Heterogeneous reaction kinetics for oxidation and combustion of boron

Non-isothermal thermogravimetric (TG) analysis was used to study the oxidation kinetics for 95% pure amorphous boron powder. Commercial boron powders were pre-treated with acetonitrile and water to reduce the thickness of their initial hydrated oxide layer and to achieve a narrower particle size distribution. The samples were oxidized at different heating rates in an oxygen-argon gas mixture. Boron particles comprising aggregates of finer primary particles were modeled as spheres with porous shells and solid cores. Experimental TG traces were split among particles of different sizes. The split was based on the measured particle size distribution and accounted for the fraction of the measured mass gain assigned to different powder particle size bins using the core-shell particle model. Further, the reactive shell was assumed to consist of densely packed spherical primary particles. The reaction kinetics was quantified to obtain both activation energy and pre-factor describing oxidation of the primary particles. The early stage of oxidation is well described with the activation energy of 148 ± 6 kJ/mol. The oxidation rate of boron particle of any size can be obtained considering the rate of oxidation of the primary particle and the introduced core-shell particle structure. The obtained oxidation model was extrapolated to the range of temperatures typical of boron combustion. A change in the particle morphology occurring when boron melts and the aggregates of primary particles coalesce into a single droplet was accounted for. Burn times predicted at different temperatures were close to those measured for boron particles burning in room air. Comparisons suggest that the particle surface temperature varies in the range of 3500–4500 K, approaching boron boiling point. It is concluded that the same heterogeneous kinetics governs both low-temperature oxidation of boron when the oxide film thickness is small and its full-fledged combustion occurring at much higher temperatures.

A novel nano-lignin-based amphoteric copolymer as fluid-loss reducer in water-based drilling fluids

In the study, nano-lignin (Nano-LS) was gradually formed from inside to outside via layer-by-layer self-assembly owing to the interaction of π-π bonds, and a novel amphoteric polymer, Nano-LS-g-DAD, was synthesized by grafting N, N-dimethylacrylamide (DMAM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), diallyl dimethyl ammonium chloride (DMDAAC) onto the Nano-LS in an aqueous solution using ammonium persulfate and sodium bisulfite as initiators. The structure of the resulting graft copolymer was characterized via Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (1H-NMR) methods. Thermogravimetric analysis (TGA) revealed the thermal stability of Nano-LS-g-DAD, and the thermal decomposition of Nano-LS-g-DAD was observed above 281 ℃. Nano-LS-g-DAD were prepared also for water-based drilling fluids (WBDFs), and rheological and filtration properties were evaluated before and after aging at 260 ℃ for 16 h. The results revealed that the fluid loss (FLAPI) of WBDFs with Nano-LS-g-DAD was only 8.0 mL after aging at 260 ℃ for 16 h in a filtration test conducted as per American Petroleum Institute (API) standards. It indicated that the Nano-LS-g-DAD still maintained positive filtration reduction performance in WBDFs at ultra-high temperature. The fluid-loss control mechanism of Nano-LS-g-DAD for WBDFs was investigated via Zeta potential analysis and clay particle size distribution measurement. Simultaneously, WBDFs with Nano-LS-g-DAD also maintained positive rheological and filtration properties under the invasion of salt and calcium ions. Furthermore, the acute toxicity value (EC50) of Nano-LS-g-DAD was 54,800 mg/L, which indicated that it was environmentally friendly.

Inversion of particle size distribution based on iterative non-negative Philips-Twomey algorithm

The precision of particle size distribution (PSD) is a key indicator to evaluate inversion algorithms. In the light scattering particle sizing technology, constructed on the inversion method of the traditional non-negative Philips-Twomey (NNPT) algorithm, an iterative NNPT (INNPT) algorithm was proposed in this paper, applied for the inversion of PSD. In simulations, the inversion accuracy performance of NNPT and INNPT algorithms were compared and analyzed by using different widths of PSD that conform to Johnson’s SB unimodal and bimodal functions. A small angle forward scattering method of PSD measurement system using Charge Coupled Device (CCD) as a photodetector was constructed and the national standard particles were tested. Both the results of simulations and experiments show that the inverse accuracy and stability of INNPT algorithm are superior to NNPT algorithm especially in the conditions of narrow distribution.

Particulate Matter Measurement Indoors: A Review of Metrics, Sensors, Needs, and Applications.

Many populations spend ∼90% of their time indoors, with household particulate matter being linked to millions of premature deaths worldwide. Particulate matter is currently measured using particle mass, particle number, and particle size distribution metrics, with other metrics, such as particle surface area, likely to be of increasing importance in the future. Particulate mass is measured using gravimetric methods, tapered element oscillating microbalances, and beta attenuation instruments and is best suited to use in compliance monitoring, trend analysis, and high spatial resolution measurements. Particle number concentration is measured by condensation particle counters, optical particle counters, and diffusion chargers. Particle number measurements are best suited to source characterization, trend analysis and ultrafine particle investigations. Particle size distributions are measured by gravimetric impactors, scanning mobility particle sizers, aerodynamic particle sizers, and fast mobility particle sizers. Particle size distribution measurements are most useful in source characterization and particulate matter property investigations, but most measurement options remain expensive and intrusive. However, we are on the cusp of a revolution in indoor air quality monitoring and management. Low-cost sensors have potential to facilitate personalized information about indoor air quality (IAQ), allowing citizens to reduce exposures to PM indoors and to resolve potential dichotomies between promoting healthy IAQ and energy efficient buildings. Indeed, the low cost will put this simple technology in the hands of citizens who wish to monitor their own IAQ in the home or workplace, to inform lifestyle decisions. Low-cost sensor networks also look promising as the solution to measuring spatial distributions of PM indoors, however, there are important sensor/data quality, technological, and ethical barriers to address with this technology. An improved understanding of epidemiology is essential to identify which metrics correlate most with health effects, allowing indoor specific PM standards to be developed and to inform the future of experimental applications.

Application a novel thermo-sensitive copolymer as a potential rheological modifier for deepwater water-based drilling fluids

In deepwater drilling, rheological properties of water-base drilling fluids (WBDF) varied remarkably within the wide temperatures range, causing problems including equivalent circulating densities control, lost circulation, etc. To solve these problems, the key was how to reduce the temperature dependence of rheological properties. In this study, the combination of thermo-sensitive polymer and clay particles was used to solve this problem due to the distinct thermo-rheological properties of these two components. In detail, a novel thermo-sensitive copolymer (PANA) of acrylamide (AM), sodium 2-acrylamido-2-methylpropane sulfonate (NaAMPS) and N-vinylcaprolactam (NVCL) was synthesized by free radical polymerization under optimal conditions. And the structure of PANA was characterized by FTIR, elemental analysis, and gel permeation chromatographic measurements. The thermo-rheological properties of PANA in solution and slurry were investigated through viscometer. Results from rheological tests illustrated that PANA showed certain thermo-thickening phenomenon in the temperature range of 4–95 °C due to the thermo-associative behavior of thermo-responsive caprolactam (CL) moieties. And the temperature dependence of rheology of PANA based drilling fluids was further studied over the temperature range of 4–75 °C according to the American Petroleum Institute (API) standard. Results illustrated that the rheology of PANA based fluids were found to be more stable than those of typical WBDF. The change rate of main rheological parameters of PANA fluids, such as, apparent viscosity (AV), yield value (YP), and low shear rate viscosity (LSRV), was less than 15%, while parameters of typical WBDFs varied dramatically (near or over 30%). Therefore, the relatively stable rheological properties of fluids with temperature changes could be achieved through the synergistic effect between the novel thermo-sensitive copolymer and bentonite particles. In addition, the rheological control mechanism of PANA was further investigated through transmittance tests, Environmental Scanning Electron Microscope (ESEM), zeta potential experiments, and particle size distribution measurements.

Nanopowders explosion: Influence of the dispersion characteristics

This work aims to study the influence of the dispersion conditions in a standard 20L sphere on the explosibility of a nanopowder. Even more than for micropowders, the dispersion conditions have a strong impact on the dust cloud homogeneity and its particle size distribution (PSD). Due to their high surface energy, nanoparticles are prone to agglomeration, but such structures can be broken during the dispersion process. Varying the dispersion procedure, the ignition delay time and even the nozzle type (rebound or symmetric) leads to modifications of the dust specific surface area, and thus of its reactivity. Tests were performed on aluminum and carbon black nanopowders. They were characterized before and during their dispersion in the sphere, notably using in situ laser PSD measurement. The initial turbulence level of the dust cloud was determined by particle image velocimetry. A lower shear stress is exerted on the agglomerates by using the symmetric nozzle, which causes less fragmentation and decreases the explosion severity. However, the results obtained with this nozzle are more reproducible than with the rebound nozzle.Because pre-ignition phenomenon was observed for aluminum nanopowders during their injection through the electrovalve, the dust dispersion by dust lifting was experimented. With regard to the standard procedure, the maximum rate of pressure rise decreased by approximately 30% whereas the maximum overpressure remains nearly unchanged. It means that the same amount of dust reacts in both kinds of experiments but that less fragmentation occurs, which is confirmed by PSD measurements. This work brings some questions about the interpretation of the explosivity results related to nanopowders and highlights the potential need to introduce recommendations in the current standards.

W-Band (95 GHz) Radar Attenuation in Tropical Stratiform Ice Anvils

AbstractAttenuation of the W-band (95 GHz) radar signal by atmospheric ice particles has long been neglected in cloud microphysics studies. In this work, 95-GHz airborne multibeam cloud radar observations in tropical stratiform ice anvils are used to estimate vertical profiles of 95-GHz attenuation. Two techniques are developed and compared, using very different assumptions. The first technique examines statistical reflectivity differences between repeated aircraft passes through the same cloud mass at different altitudes. The second technique exploits reflectivity differences between two different pathlengths through the same cloud, using the multibeam capabilities of the cloud radar. Using the first technique, the two-way attenuation coefficient produced by stratiform ice particles ranges between 1 and 1.6 dB km−1 for reflectivities between 13 and 18 dBZ, with an expected increase of attenuation with reflectivity. Using the second technique, the multibeam results confirm these high attenuation coefficient values and expand the reflectivity range, with typical attenuation coefficient values of up to 3–4 dB km−1 for reflectivities of 20 dBZ. The potential impact of attenuation on precipitating-ice-cloud microphysics retrievals is quantified using vertical profiles of the mean and the 99th percentile of ice water content derived from noncorrected and attenuation-corrected reflectivities. A large impact is found on the 99th percentile of ice water content, which increases by 0.3–0.4 g m−3 up to 11-km height. Finally, T-matrix calculations of attenuation constrained by measured particle size distributions, ice crystal mass–size, and projected area–size relationships are found to largely underestimate cloud radar attenuation estimates.