Fraktionsfreisetzungsgrad – Ein neuer Ansatz zur Quantifizierung der Staubungsneigung von Pulvern

The handling of dispersed solids may lead to undesirable release of particles. Size and quantity of the particles transferred into the gas depend on the holding and separating forces in the powder. These in turn are determined by characteristic parameters of the powder and of the process. Analogous to the fractional collection efficiency describing the dust separation, a fractional release rate to quantify the release of dust is introduced. The application is demonstrated by an example and the way to further development of this new approach is demonstrated.     

A method for estimating the dust yield of powders

A method is described by which powders may be compared with respect to their potential to liberate airborne dust during certain manufacturing processes. Thus it is possible to select quickly from a range of otherwise suitable powders the powder with the lowest dust yield, which reduces the precautions required to prevent exposure of factory personnel to the dust.A weighed quantity of the powder is poured through a standard height in a cabinet. Airborne dust, irrespective of particle size (“total” dust), is collected on a weighed filter in an open filter holder and, in a separate test, after passage through a horizontal elutriator which separates respirable dust capable of penetrating to and being deposited in the human lung. The weights of respirable and “total” dust are expressed in relation to the weight of powder tested.     

Atmospheric Aging of Asian Dust Particles During Long Range Transport

Variations of mixing state and chemical constituents of Asian dust (AD) particles having different transport pathways were investigated by measuring hygroscopicity and volatility of size-selected (1 μm) dust particles, and their morphology and elemental composition in Gwangju, Korea. Also, hygroscopicity and volatility of possible candidate chemical species that can be included in the dust particles was measured in a laboratory for comparison with field data. A significant amount of dust particles were found to be aged by internally mixing with hygroscopic and volatile species in different ways, depending on their transport pathway. Formation of hygroscopic CaCl₂ and/or cloud processing of dust particles with sea-salt species were proposed as being central to the formation of hygroscopic species in the “less polluted AD” (in which the air mass arrived at sampling site without passing over significant industrial areas), and the existence of hygroscopic species in the “highly polluted AD” (in which the air mass passed over major industrial areas) was explained by the interaction of dust particles with anthropogenic pollutants (i.e., Ca(NO₃)₂ formation by heterogeneous reaction of HNO₃ with dust particles and condensation of hygroscopic H₂SO₄ or (NH₄)₂SO₄ onto the dust particles). Volatile carbonaceous species, which would exist on the surface of the dust particles, were also observed and their fraction significantly increased in the highly polluted AD due to a higher possibility to encounter air masses containing a significant amount of carbonaceous species. Morphological and elemental data identified three types of aged dust particles (reacted dust, cloud-processed dust, and aggregated dust). The production of various aged dust particles depending on their transport pathways has important implications on their different effects on cloud formation, radiation balance, and human health from original dust particles.

Copyright 2012 American Association for Aerosol Research     

The Relationship between Microstructure and Properties in PP/Rubber Powder/nano‐CaCO3 Ternary Blends

Summary: A new kind of rubber powder with “salami” structure (RPS) was prepared by spray drying the mixture of styrene‐butadiene rubber latex and nano‐CaCO₃ slurry. It was found that RPS is an effective toughener with synergistic toughening effect on poly(propylene) (PP). The Izod impact strength of PP/RPS blend is not only higher than that of PP/rubber powder or PP/nano‐CaCO₃ blends, but also higher than that of a PP/rubber powder/CaCO₃ blend. TEM images show that the microstructure of the PP/RPS blend is an “island‐sea” structure with “salami” structure in RPS, in which nano‐CaCO₃ particles are embedded in styrene‐butadiene rubber particles. The relationship between properties and microstructure has been studied by using TEM, SEM, DSC, etc.

     

IN SITU AERODYNAMIC SIZE CLASSIFICATION OF AEROSOLS IN THE SIZE RANGE BETWEEN 0.1 AND 100 μm FOR DUSTINESS TESTS AND POWDER CHARACTERIZATION

Airborne particles can be released by mechanical processes such as resuspension, powder handling, break-up of solids due to mechanical energy input, i.e. crushing, comminution or accidental mechanical impact. In this study, we describe a new device that collects and classifies the dust generated under lab-scale simulation of these release processes. The release process takes place within a vertical elutriator where the airborne particles are separated from the non-airborne material. The airborne fraction is subsequently classified in situ in the size range between 0.1 and 100 μm by a combination of a centrifugal classifier and a conventional cascade impactor. The system was designed to overcome possible sampling errors due to spatial dust inhomogeneities caused by the release process and to minimize wall losses during the classification process. In this paper we describe the classifier, discuss procedures for data inversion, and present calibration and performance experiments.     

Coatings for plastics. Dispersions of clean metal particles in polymer matrices

Oxides are frequently used to improve the mechanical properties of plastics. Here we report how oxides of zinc, lead, cadmium, and indium, when embedded in a polymer matrix, can be electrochemically reduced, resulting in a polymer-metal “composite” of high electrical conductivity. This method of preparation provides a uniform dispersion of small, clean metal particles, not obtainable by blending metal powder and polymer. The “composites” are somewhat porous, and other metals can be deposited on the “composites” from either electroplating or electroless plating solutions.     

FREE OBJECT MOTION IN A GAS FLUIDIZED BED

The presence probability, the characteristic motions and the velocity of various “light” objects freely immersed in a gas fluidized bed of “heavy” fine particles have been investigated as a function of superficial fluid velocity, powder characteristics and bed height. The displacement of objects through the bed has been shown to result from both a “deterministic” dynamic force equilibrium and a “stochastic” stirring effect due to bubbles. A specific gas velocity exists at which a deep change in mixing occurs: above it the stirring effect is fairly noticeable, while below it pseudo-hydrostatic effects prevail. A method has been proposed to estimate this characteristic value.     

Polymeric Additives for Poly(Vinyl Chloride)

The melt and physical properties of PVC compounds and articles are strongly influenced by the morphology of the PVC. PVC powder exists as various agglomerates [l-41 wherein the primary particles are bound together as “grains” which in turn may be collected and enveloped in a “skin” in the case of the most common, suspension polymerized, PVC. We will discuss the influence on and interaction with these various PVC structures and the polymeric additives classified as processing aids, impact modifiers, and surfacealtering agents.     

No more ‘core-shell’ in binderjetting of bioceramics: Novel solution and experimental validation in microstructure and mechanical properties

During binderjetting of bioceramics, many commercial 3D printers dispense binder in a default ‘core-shell’ manner. Using such a conventional approach, more binder is dispensed at the periphery (shell) and less binder at the ‘core’ of the structure. The inhomogeneous binding of the powder particles from the shell to the core significantly impacts the microstructure and biomechanical properties. To address this, we hypothesised ‘segmentation’ of a 3D printable design file by slicing and discretising with an array of thin solid “segments”, separated with an infinitesimal gap in a periodic manner. In this novel approach, the printing software commands the printhead to print each of the “segments” individually. The inter-segment and intra-segment binder “bleeding” among the segments results in a printed part with a homogeneously bound cross-section, without any “core-shell” effect. This hypothesis was experimentally validated by better microstructure, improved density, and enhanced mechanical strength properties in binderjet printed 3 mol% yttria stabilised ZrO₂.     

Generation of Submicron Arizona Test Dust Aerosol: Chemical and Hygroscopic Properties

This article describes a submicron dust aerosol generation system based on a commercially available dust disperser intended for use in laboratory studies of heterogeneous gas–aerosol interactions. Mineral dust particles are resuspended from Arizona Test Dust (ATD) powder as a case study. The system output in terms of number and surface area is adjustable and stable enough for aerosol flow reactor studies. Particles produced are in the 30–1000 nm size range with a lognormal shape of the number size distribution. The particles are characterized with respect to morphology, electrical properties, hygroscopic properties, and chemical composition. Submicron particle elemental composition is found to be similar for the particle surface and bulk as revealed by X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP-OES), respectively. A significant difference in chemical composition is found between the submicron aerosol and the ATD bulk powder from which it was generated. The anionic composition of the water-soluble fraction of this dust sample is dominated by sulfate. Resuspended dust particles show, as expected, nonhygroscopic behavior in a humid environment. Small hygroscopic growth of about 1% (relative change in mobility diameter) was observed for 100 nm particles when the relative humidity (RH) was changed from 12 to 94%. Particles larger than 100–200 nm shrank about 1% once exposed to RH > 90%. This was interpreted as a restructuring of the larger agglomerates of dust to particles of smaller mobility diameter, under the influence of water vapor.     

Dominant environmental parameters for dust deposition and resuspension in desert climates

Field studies of dry deposition usually measure dust accumulation over periods of days or weeks. However, long measurement periods obscure the effects of meteorological conditions on the deposition rate. Previously we developed an “outdoor soiling microscope” (OSM) in order to measure dust deposition and detachment every 10 min in the field. In this study a greased/ungreased pair of OSMs was deployed for 51 days in the desert climate of Doha, Qatar. Stepwise regression analysis was performed to quantify the explanatory power of meteorological parameters on dust deposition and detachment rates. It was found that wind speed dominated deposition and rebound of dust particles, and produced a distinctive “threshold” response in deposition. The dry deposition results were highly consistent with a model by Kim et al. (2000) derived from outdoor experiments. By comparison, relative humidity and particulate matter concentration had less influence on dust flux rates.

Copyright © 2018 American Association for Aerosol Research     

Toughness enhancement of poly(ethylene terephthalate) with functionalized ultrahigh molecular weight polyethylene

Ultrahigh molecular weight polyethylene (UHMWPE) is available commercially in the form of powder, consisting of fine primary particles, 1–5 μm in diameter, agglomerated into secondary “free‐flowing” particles with overall dimensions in the region of 50 to 150 μm. These are normally sufficiently coherent and retain their conglomerated particulate structure when blended with other polymers because of the extremely high viscosity of UHMWPE. In this study the surface of the agglomerated primary particles was acid functionalized by reactions with aqueous solutions of acrylic acid, after being irradiated with γ‐radiation at 15–45 kGy. The acid groups were used to introduce a glycidoxyl functionality through reactions with a difunctional cycloaliphatic epoxy resin and also to a “partial” metal carboxylate functionality through reactions with zinc acetyl acetonate. When blended with polyethylene terephthalate (PET) in either a small‐batch mixer or in a twin‐screw extruder all the treated powders, except those functionalized with acrylic acid, were broken down to their primary size and were uniformly dispersed and strongly bonded to the surrounding matrix. The blends containing the deglomerated particles were found to have much greater ductility and toughness than those produced from both untreated and acid functionalized powder. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2972–2986, 2001     

Experimental analysis of static pressure in bins

A pressure transducer with a pressure-high sensitive semiconductor gauge was used to measure distribution of vertical pressure at the base and horizontal wall pressure in a bin packed with glass beads, which are typical cohesionless particles.Even when the glass beads were uniformly supplied to the bin, the vertical pressure at the base was distributed unevenly, with the maximum and minimum values. This seems to be attributable to the “arching” which results from its nonhomogeneous configuration. In addition, the results indicate that the larger the diameter of the bin, the more numerous the extreme values of vertical and horizontal pressure become.This implies that the distribution of particles is the principal mechanism affecting the distribution of pressure in a powder bed. Consequently, to analyze the mechanism of a powder bed, the transference of force among the particles should be evaluated considering the distribution of the particles and paying careful attention to each of the particles in the powder bed.     

Small Electrocyclone Performance

Cyclone Separators and Electrostatic Precipitators (ESPs) are both effective particle separators. The former are more efficient at removing the larger particles, while the latter more suited to removing the smaller size classes. We explore the performance of an “Electrocyclone”, constructed by simply retrofitting an electrode coaxially to a small existing “Whitby” cyclone. Tests were performed with respect to particle size, resitivity, loading and various other operating parameters. Non‐electrical separation efficiencies ranged from 71 to 75 % and with the application of additional electrical forces the increase in separation efficiency was between 17 and 21 % at a cyclone Reynolds number of 19000, with the most conductive particle most easily separated. Further parametric testing correlated the effects of dust loading, electrocyclone Reynolds Number and particle cut upon separation efficiency. In particular we show that the separation of the smallest size cuts (D < 38 μm) of the dust sample almost doubled upon application of the corona. We conclude, based on this initial study of small devices, the range of use of cyclones may be extended significantly by the application of additional electrophoretic separation.     

Powder mechanics in tribology

Recently considerable progress has been made in understanding the interactions between a surface and a solid lubricant layer deposited or formed by various physical and chemical methods. Very few studies have been conducted on how these films lubricate and fail from a microscopic point of view. In some of them it has been observed that lubrication and failure criteria are usually arbitrary and that particle interactions play a fundamental role as constituent elements of lubricant layers or as wear debris.To understand these mechanisms, “lubricating” and “abrasive” powders were studied from tribological and rheological point of view.Via classical mechanics, the flow properties of micronized powders were analysed in terms of size, shape and stress-strain relations. Starting from the cumminution process, crushing and grinding phenomena were analysed to determine experimentally through packing, cohesion and consolidation and ultimate shear strength and to predict the boundary friction coefficient in powder lubrication. The rupture surface and instability phenomena were involved for cohesive and noncohesive, “lubricating” and “abrasive” powders.The librication process was found to be very instable, consisting of the plastic flow of thin laminated films formed of coalesced fine particles and reactive films. The effect of substrate surface finish in terms of statistical moments criteria was demonstrated.The tribological process, analysed as particle mechanics of wear debris and as lubricating or abrasive powder interactions, was elucidated.     

提铝粉煤灰蒸压砖的试验研究

粉煤灰是从烧煤粉的锅炉中收集的粉状灰粒,国外把它叫做"飞灰"然而伴随着科技的进步以及人们环保意识的提高,粉煤灰得到了广泛的应用。本文通过SEM、XRD等仪器对提取Al2O3后的粉煤灰进行了各种化学成分、烧失量、细度、活性分析,测得其活性仅为47。最终利用提铝粉煤灰的废料通过正交设计的方法成功研制出实验室小试指标达到JC239-2001《粉煤灰砖》中合格品、MU10.0等级各项指标要求的新型高掺量粉煤灰蒸压砖。     

Alkali-activated waste ceramics: Importance of precursor particle size distribution

The waste ceramics belongs to wide range of aluminosilicate materials which can be alkaline-activated to geopolymer cement – possible “green” alternative to conventional Portland cement. The studied ceramic material is generated during the size adjustment of ceramic building blocks by means of grinding. It means that most of the material is very fine, but it contains also some larger shards. This ceramic powder was used as geopolymer precursor “as received” and after removal of particles retained on 1, 0.5 and 0.125 mm sieves. These four types of precursor were activated by sodium silicate (SiO₂/Na₂O = 1) solution. The prepared mortars were tested for strength, basic physical properties, transport parameters and characterized by help of XRD and thermal analysis. It was found that the best mechanical performance provided the precursor after removal of particles retained on 0.5 mm sieve thanks to the highest geopolymerization rate. The presence of coarser particles in precursor gave rise to porosity, what consequently influenced transport parameter of geopolymers towards the lower thermal conductivity and faster moisture transport.     

Cellulose and Xylan Based Prodrug of Diclofenac Sodium: Synthesis,Physicochemical Characterization and In Vitro Release

Present research has been made to reduce frequency of administration and increase therapeutic efficacy by developing sustained release of diclofenac sodium. In this regard, prodrugs have been synthesized by using eco-friendly “green” materials such as cellulose and xylan by activation of carboxylic acid via N,N′-carbonyldiimidazole. The polymer–drug interactions were evaluated by means of FT-IR, powder X-ray diffraction, and thermal analysis techniques. In vitro release study of synthesized prodrugs might be suggested regarding protection of drug in the upper gastrointestinal tract, and, thereby, it is expected to reach the targeted site specifically to colon.     

Investigation of a wet dust scrubber with a pneumatic nozzle: Dust collection based on turbulent diffusion

The “nozzle scrubber” is a wet scrubber in which the scrubbing water is dispersed in dust laden gas stream by means of one or more pneumatic nozzle. This scrubber is distinguished by an excellent collection efficiency for submicron dust at an unusually low energy and water consumption. So far, the physical effects affecting the separation cannot be explained by a well-defined theory. Therefore, it is sensible to investigate the collection efficiency with regard to the mechanisms of inertial impaction, turbulent diffusion and coalescence induced by turbulence. The experimental equipment is of a very simple design. A light scattering device was used to measure the particle distributions. In addition, electron micrographs were analyzed to obtain information about the submicron particles. The influence of operating parameters on grade efficiency has been demonstrated by their systematic variation. The contribution of turbulent diffusion to the collection efficiency has been confirmed; nevertheless, grade efficiencies were also measured when inertial impaction prevailed.     

Characteristics and pozzolanic reactivity of glass powders

This paper deals with the morphology, fineness and pozzolanic activity of four glass powders: one (GP-fine) from the screening of crushed waste glasses, one (GP-dust) from a dust collector for the glass crushing process and two (GP-4000 and GP-6000) from further grinding of the powder from the dust collector in a ball mill. GP-fine and GP-dust consist mainly of large flaky particles, while GP-4000 and GP-6000 consist mainly of small angular particles. The finenesses of these glass powders are measured by particle size distribution and Blaine fineness method. For a similar particle size distribution, ground glass powder has a higher Blaine specific surface area than Portland cement due to the angular morphology of glass particles. Finely ground glass powders exhibited very high pozzolanic activity. The finer the glass powder is, the higher its pozzolanic reactivity is. An increase in curing temperature accelerates the activation of pozzolanic reactivity of both glass powder and coal fly ash in terms of strength development rate. Mortar cube strength results (ASTM C109) indicated that curing temperature has a greater influence on the glass powder than on fly ash. The rapid mortar bar expansion test (ASTM C1260) results indicate that the replacement of Portland cement with ground glass powder also reduces the expansion due to alkali-aggregate reactions, although it is not as effective as coal fly ash.