Effects of volatile coatings and coating removal mechanisms on the morphology of graphitic soot

We have measured morphological changes of combustion-generated mature soot with various quantities of hydrocarbon coating and different coating-removal mechanisms. We made these measurements on soot extracted from a burner and then (1) coated with oleic acid, (2) coated with oleic acid and then denuded using a thermodenuder, (3) coated with oleic acid and then heated with a laser, and (4) coated with oleic acid, denuded with a thermodenuder, and then laser heated. We compared these results to results for untreated soot from the burner. The soot samples were size selected using a differential mobility analyzer prior to coating. Uncoated, coated, and denuded particles were characterized by electric-mobility size, particle and coating mass, and particle morphology. Our results show that the particles are restructured (become compact) when coated. Particles sent through the thermodenuder are irreversibly restructured. Laser desorption of coatings with thicknesses ⩾20% by mass, however, returns the soot particles to a less compact morphology with some fragmentation as the coating rapidly vaporizes. A majority of laser-heated heavily coated particles stay associated with unvaporized oleic acid droplets despite some fragment ejection from the droplet. Thermally denuded particles neither return to a less compact morphology nor fragment when laser heated.     

Processing of Soot by Controlled Sulphuric Acid and Water Condensation—Mass and Mobility Relationship

The effects of atmospheric processing on soot particle morphology were studied in the laboratory using the Differential Mobility Analyzer-Aerosol Particle Mass Analyzer (DMA-APM) and the DMA-DMA (Tandem DMA) techniques. To simulate atmospheric processing, combustion soot agglomerates were altered by sulphuric acid vapor condensation, relative humidity (RH) cycling, and evaporation of the sulphuric acid and water by heating. Primary investigated properties were particle mobility size and mass. Secondary properties, derived from these, include effective density, fractal dimension, dynamic shape factor, and the mass fraction of condensed material. A transformation of the soot particles to more compact forms occurs as sulphuric acid and water condense onto fresh soot. The particle mass increases and initially the mobility diameter decreases, indicating restructuring of the soot core, likely due to surface tension forces. For a given soot source and condensing liquid, the degree of compaction depends strongly on the mass (or volume) fraction of condensed material. For water and sulphuric acid condensing on combustion soot, a mass increase of 2–3 times is needed for a transformation to spherical particles. In the limit of spherical particles without voids, the effective density then approaches the inherent material density, the fractal dimension approaches 3 and the dynamic shape factor approaches 1. Our results indicate that under typical atmospheric conditions, soot particles will be fully transformed to spherical droplets on a time scale of several hours. It is expected that the morphology changes and addition of soluble material to soot strongly affect the optical and hygroscopic properties of soot.     

An Inter-Comparison of Instruments Measuring Black Carbon Content of Soot Particles

Inter-comparison studies of well-characterized fractal soot particles were conducted using the following four instruments: Aerosol Mass Spectrometer-Scanning Mobility Particle Sizer (AMS-SMPS), Single Particle Soot Photometer (SP2), Multi-Angle Absorption Photometer (MAAP), and Photoacoustic Spectrometer (PAS). These instruments provided measurements of the refractory mass (AMS-SMPS), incandescent mass (SP2) and optically absorbing mass (MAAP and PAS). The particles studied were in the mobility diameter range from 150 nm to 460 nm and were generated by controlled flames with fuel equivalence ratios ranging between 2.3 and 3.5. The effect of organic coatings (oleic acid and anthracene) on the instrument measurements was determined. For uncoated soot particles, the mass measurements by the AMS-SMPS, SP2, and PAS instruments were in agreement to within 15%, while the MAAP measurement of optically-absorbing mass was higher by ～ 50%. Thin organic coatings (～ 10 nm) did not affect the instrument readings. A thicker (～ 50 nm) oleic acid coating likewise did not affect the instrument readings. The thicker (～60 nm) anthracene coating did not affect the readings provided by the AMS-SMPS or SP2 instruments but increased the reading of the MAAP instrument by ～ 20% and the reading of the PAS by ～ 65%. The response of each instrument to the different particle types is discussed in terms of particle morphology and coating material.     

Characterization of Particulate Matter Morphology and Volatility from a Compression-Ignition Natural-Gas Direct-Injection Engine

The particulate matter (PM) emitted from a single-cylinder compression-ignition, natural-gas engine fitted with a High-Pressure Direct-Injection (HPDI) system distinctly different from a duel fuel engine was investigated, and characterized by size distribution, morphology, mass-mobility exponent, effective density, volatility, mixing state, and primary particle size using transmission electron microscopy (TEM), and tandem measurements from differential mobility analyzers (DMA) and a centrifugal particle mass analyzer (CPMA). Six engine conditions were selected with varying load, speed, exhaust gas recirculation (EGR) fraction, and fuel delivery strategy. An increase in engine load increased both the number concentration and the geometric mean diameter of the particulate. The fraction of the number of purely volatile particles to total number of particles (number volatile fraction, NVF) was found to decrease as load increased, although at the lower speed, partially premixed mode, the lowest NVF. All size distributions were also found to be unimodal. The size-segregated ratio of the mass of internally mixed volatile material to total particle mass (mass volatile fraction, MVF) decreased with load and with particle mobility-equivalent diameter. A roughly constant amount of volatile material is likely produced at each engine mode, and the decrease in MVF is due to the increase in PM number with load. Effective density and mass-mobility exponent of the non-volatile soot at the different engine loads were the same or slightly higher than soot from traditional diesel engines. Denuded effective density trends were observed to collapse to approximately the same line, although engine modes with higher MVFs had slightly higher effective densities suggesting that the soot structures have collapsed into more dense shapes—a suspicion that is confirmed with TEM images. TEM results also indicated that primary particle size first decreases from low to medium load, then increases from medium to high load. An increase in EGR was also seen to increase primary particle size. Coefficients were determined for a relation that gives primary particle diameter as a function of projected area equivalent diameter. A decrease in load or speed results in a stronger correlation.

Copyright 2015 American Association for Aerosol Research     

Superhydrophobic surfaces with silane‐treated diatomaceous earth/resin systems

Superhydrophobic coatings were prepared using fluorosilane‐treated diatomaceous earth (DE) with either polyurethane or epoxy binders. The surface wettability and morphology of the films were analyzed using contact angle measurements and scanning electron microscopy (SEM), respectively. The water contact angles were studied as a function of the fluorocarbon fraction on DE and the particle loadings of treated DE in the coating. The contact angles exceeded 150° for coatings with at least 0.02 fluorocarbon fraction (mass of fluorosilane/mass of particle) on the DE and with 0.2 particle loadings (mass of treated particles/mass of coating). The water contact angles of the surfaces were dependent on the nature of the binder below 0.2 particle loadings of the superhydrophobic DE particles, but were independent of the binder type after attaining superhydrophobicity. The results were consistent with the superhydrophobicity resulting from the migration of the superhydrophobic DE moving to and covering the surfaces completely. It was also shown that the treatment with fluorosilanes restricted the pores in DE and reduces the specific surface area of the material. However, these changes had effectively no effect on the superhydrophobicity of the coatings. The results of this work clearly identify some important considerations relative to producing superhydrophobic coatings from inexpensive diatomaceous earth. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44072.     

Drying and collapse of hollow latex

Hollow latex particles are used as white pigments for paints and paper coatings. In the coating dispersion, each hollow particle is filled with water. As the coating dries, water vacates the latex, leaving an air-filled void sized to scatter light (~0.5 μm) within each particle. Examinations of dried coatings reveal that hollow particles can collapse, decreasing their light scattering efficiency. Cryogenic scanning electron microscopy (cryoSEM) was used to characterize the microstructure of coatings containing hollow latex during drying. Images suggest latex voids empty after air invades into the coating interstitial space and collapse occurs late in the drying process. The effects of temperature (10–60°C), humidity (20–80%), and binder concentration (0–30 wt%) on particle collapse were also studied through SEM of dried coating surfaces. High drying temperature, high humidity, and low binder concentrations promoted collapse. For hollow latex particles with porous shell walls, temperature and humidity had little effect, whereas binder increased collapse. From these results, a theoretical model is proposed. During drying, diffusion of water from the particle creates a vacuum inside the latex. The vacuum is either relieved by nucleation of a gas bubble from the dissolved air in the water-filled particle or it causes the particle to collapse by buckling.     

生物质燃油碳烟颗粒的形貌、结构与组分表征

通过微乳化工艺分别把不同含量的精制生物质裂解油与柴油进行混合(micro-emulsified biomass fuel, MEBF), 研究了该类燃油碳烟颗粒的形貌与结构, 并对其组分进行了表征。结果表明:该类燃油碳烟的一次颗粒形貌均为球形, 而且一次颗粒之间互相连接构成链状团聚物。同时, 精制生物质裂解油含量为20%(质量)(BS20)的混合油碳烟颗粒的平均粒径最小, 约为32 nm, 其他含量混合油碳烟颗粒的平均粒径均在38 nm左右。BS30石墨化程度高于其余碳烟, 且BS20颗粒表面C=O和C-O-C基团含量较高, 可能归因于混合油燃烧过程中复杂含氧组分的氧化程度不同。     

Characterization of Soot Aerosol Produced from Combustion of Propane in a Shock Tube

The knowledge of yields and properties of soot from combustion of hydrocarbon fuels is crucial for accurate evaluation of the impacts of primary aerosols on air quality and climate. This study presents measurements of soot generated from combustion of propane in a shock tube, using independently adjustable fuel equivalence ratio (φ), temperature, and pressure. The characterization of soot yields inside the shock tube by in situ laser extinction is complemented with a set of comprehensive measurements of soot transferred into a fluoropolymer chamber, including particle size distributions, elemental carbon (EC) mass fraction, effective density, mass fractal dimension (Dfm), dynamic shape factor (χ), and optical properties. The properties of soot particles and the soot yield are sensitive to combustion conditions and the duration of the combustion experiment. High-temperature combustion with φ = 2.5 produces small fractal (Dfm = 2) soot particles composed mainly of EC (up to 90%), at a low mass yield. Particles from lower temperature combustion contain a significant fraction of organic material (～50%). Using rich fuel mixtures (φ = 4.0 and 8.0) significantly increases particle size and soot mass yield. At lower temperatures, compact (Dfm = 3) and nearly spherical (χ = 1.1) aggregates with high organic content are formed, whereas at higher temperatures, the particles are fractal and closely resemble those obtained using φ = 2.5. Single scattering albedo (SSA) varies from 0.15 for fractal particles to 0.75 for compact particles. For soot generated at high equivalence ratios, SSA can be used as a proxy for particle morphology and EC content.

Copyright 2012 American Association for Aerosol Research     

Effective Density Characterization of Soot Agglomerates from Various Sources and Comparison to Aggregation Theory

Soot particle (black carbon) morphology is of dual interest, both from a health perspective and due to the influence of soot on the global climate. In this study, the mass-mobility relationships, and thus effective densities, of soot agglomerates from three types of soot emitting sources were determined in situ by combining a differential mobility analyzer (DMA) and an aerosol particle mass analyzer (APM). High-resolution transmission electron microscopy was also used. The soot sources were diesel engines, diffusion flame soot generators, and tapered candles, operated under varying conditions. The soot microstructure was found to be similar for all sources and settings tested, with a distance between the graphene layers of 3.7–3.8 Å. The particle specific surface area was found to vary from 100 to 260 m²/g. The particle mass-mobility relationship could be described by a power law function with an average exponent of 2.3 (±0.1) for sources with a volatile mass fraction <10% and primary particle sizes of 11–29 nm. The diesel exhaust from a heavy duty engine at idling had a substantially higher volatile mass fraction and a higher mass-mobility exponent of 2.6. The mass-mobility exponent was essentially independent of the number of primary particles in the range covered (N_pp = 10–1000). Despite the similar exponents, the effective density varied substantially from source to source. Two parameters were found to alter the effective density: primary particle size and coating mass fraction. A correlation was found between primary particle size and mass-mobility relationship/effective density and an empirical expression relating these parameters is presented. The effects on the DMA-APM results of doubly charged particles and DMA agglomerate alignment were investigated and quantified. Finally, the dataset was compared to three theoretical approaches describing agglomerate particles’ mass-mobility relationship.

Copyright 2013 American Association for Aerosol Research     

A novel inversion method to determine the mass distribution of non-refractory coatings on refractory black carbon using a centrifugal particle mass analyzer and single particle soot photometer

A novel inversion method is presented, which derives the two-variable number distribution for black carbon aerosol, using a coupled centrifugal particle mass analyzer (CPMA) and single particle soot photometer (SP2). The CPMA classifies all particles by their mass-to-charge ratio, and the SP2 detects the mass of refractive black carbon (rBC) in each individual particle. The results of the inversion are the simultaneous number distributions of both rBC mass and total particle mass. Using the distribution, the coating distribution on a population of rBC particles can be identified visually. Furthermore, the distribution can be integrated to find one-variable mass and number concentration distributions as a function of total or rBC particle mass. These capabilities were demonstrated via smog chamber experiments, where an organic (non-rBC) coating was grown onto uncoated rBC aerosol over several hours via photo-oxidation of p-xylene. The particle distributions were constructed using the inversion over a range of 1–60 fg of total particle mass. As the non-rBC coating thickness increased over time, a shift in the number distribution toward higher total mass was observed. At the end of the experiment, uncoated rBC was injected into the chamber, and the distribution was clearly resolved using the inversion. The CPMA-SP2 method offers several advantages over “SP-2 only” methods, namely, (i) coating mass information can be obtained over a wider range of total particle mass, (ii) total particle mass is measured directly, and (iii) it does not make core–shell morphology assumptions.

Copyright © 2018 American Association for Aerosol Research     

A Potential Soot Mass Determination Method from Resistivity Measurement of Thermophoretically Deposited Soot

Miniaturized detection systems for nanometer-sized airborne particles are in demand, for example in applications for onboard diagnostics downstream particulate filters in modern diesel engines. A soot sensor based on resistivity measurements was developed and characterized. This involved generation of soot particles using a quenched co-flow diffusion flame; depositing the particles onto a sensor substrate using thermophoresis and particle detection using a finger electrode structure, patterned on thermally oxidized silicon substrate. The generated soot particles were characterized using techniques including Scanning Mobility Particle Sizer for mobility size distributions, Differential Mobility Analyzer—Aerosol Particle Mass analyzer for the mass–mobility relationship, and Transmission Electron Microscopy for morphology. The generated particles were similar to particles from diesel engines in concentration, mobility size distribution, and mass fractal dimension. The primary particle size, effective density and organic mass fraction were slightly lower than values reported for diesel engines. The response measured with the sensors was largely dependent on particle mass concentration, but increased with increasing soot aggregate mobility size. Detection down to cumulative mass as small as 20–30 μg has been demonstrated. The detection limit can be improved by using a more sensitive resistance meter, modified deposition cell, larger flow rates of soot aerosol and modifying the sensor surface.     

The Detection Efficiency of the Single Particle Soot Photometer

A single particle soot photometer (SP2) uses an intense laser to heat individual aerosol particles of refractory black carbon (rBC) to vaporization, causing them to emit detectable amounts of thermal radiation that are used to quantify rBC mass. This approach is well suited for the detection of the majority of rBC mass loading in the ambient atmosphere, which occurs primarily in the accumulation mode (～ 1–300 fg-rBC/particle). In addition to operator choices about instrument parameters, SP2 detection of rBC number and/or mass can be limited by the physical process inherent in the SP2 detection technique — namely at small rBC mass or low laser intensities, particles fail to heat to vaporization, a requirement for proper detection. In this study, the SP2's ability to correctly detect and count individual flame-generated soot particles was measured at different laser intensities for different rBC particle masses. The flame-generated soot aerosol used for testing was optionally prepared with coatings of organic and non-organic material and/or thermally denuded. These data are used to identify a minimum laser intensity for accurate detection at sea level of total rBC mass in the accumulation mode (300 nW/(220-nm PSL)), a minimum rBC mass (～ 0.7-fg rBC-mass corresponding to 90 nm volume-equivalent diameter) for near-unity number detection efficiency with a typical operating laser intensity (450 nW/(220-nm PSL)), and a methodology using observed color temperature to recognize laser intensity insufficient for accurate rBC mass detection. Additionally, methods for measurement of laser intensity using either laboratory or ambient aerosol are presented.     

A novel approach to the preparation of powder coating—Manufacture of polyacrylate powder coatings via one step minisuspension polymerization

A novel method for manufacturing powder coating through one step minisuspension polymerization is described. The conventional production of powder coating includes six steps—synthesizing resins, mixing the raw material, extrusion, cooling, pre-crushing and pulverization. Comparatively, the present method can simplify the complicated processes, reduce equipment and save energy. Before polymerization, the TiO₂ particles were treated with a reactive silane coupling agent 3-methacryloxypropyltrimethoxysilane (MPTMS) to obtain enough compatibility with the monomers. The powder coating was directly synthesized through employing one step minisuspension polymerization in the presence of titanium dioxide white particles. The powder coating was characterized using Fourier transform infrared spectra (FT-IR) and thermogravimetric analysis (TGA). The results show that TiO₂ particles and polymer are successfully linked up via MPTMS in the powder particles. The morphology of powder coatings produced via different methods was observed by scanning electron microscope (SEM). The powder coatings obtained from minisuspension polymerization consist of regular spherical morphology particles with narrow particle size distribution. The powder flowability and surface film smoothness were enhanced compared to the pulverization powder coating.     

Practical limitations of aerosol separation by a tandem differential mobility analyzer–aerosol particle mass analyzer

A cavity ring-down spectrometer and condensation particle counter were used to investigate the limitations in the separation of singly and multiply charged aerosol particles by a tandem differential mobility analyzer (DMA) and aerosol particle mass analyzer (APM). The impact of particle polydispersity and morphology was investigated using three materials: nearly monodisperse polystyrene latex nanospheres (PSL); polydisperse, nearly spherical ammonium sulfate (AS), and polydisperse lacey fractal soot agglomerates. PSL and AS particles were easily resolved as a function of charge. For soot, the presence of multiply charged particles severely affects the isolation of the singly charged particles. In cases where the DMA–APM was unable to fully resolve the singly charged particles of interest, the peak mass deviated by up to 13% leading to errors in the mass specific extinction cross section of over 100%. For measurements of nonspherical particles, nonsymmetrical distributions of concentration as a function of mass were a sign of the presence of multiply charged particles. Under these conditions, the effects of multiply charged particles can be reduced by using a second charge neutralizer after the DMA and prior to the APM. Dilution of the aerosol stream serves to decrease the total number concentration of particles and does not remove the contributions of multiply charged particles.     

Measuring aerosol active surface area by direct ultraviolet photoionization and charge capture in continuous flow

Abstract

Direct ultraviolet photoionization electrically charges particles using a mechanism distinct from diffusion charging. The purpose of this study is to evaluate aerosol photoemission theory as a function of aerosol particle size, concentration, material, and morphology. Particles are classified using an aerodynamic aerosol classifier (AAC) and subsequently measured with a scanning mobility particle sizer (SMPS) and photoionization measurement system in parallel. This configuration allows direct comparison of photo-emission from high concentrations of initially neutral, monodisperse aerosols with different morphologies or materials. Under all examined conditions, the overall photoelectric yields of particles of self-similar material (silver and unconditioned soot) and morphology (sintered spheres and agglomerates) are each linearly proportional to the second moment of the mobility-equivalent diameter distribution, even in the transition regime (mobility diameter 30–200?nm), with agglomerate silver particles resulting in 5× higher photoelectric yield than unconditioned soot from a propane flame. It is shown for the first time that the photoelectric yield is significantly higher (2.6×) for fractal-like agglomerate silver particles than sintered, close-packed spherical particles of the same material and mobility-equivalent diameter, which is inferred to be due to the larger material surface area exposed externally to the particle surroundings. It is demonstrated that photoelectric measurements of aerosols reflect the photoelectrically active surface area which depends on the particle morphology and therefore the state of sintering.

Copyright © 2019 American Association for Aerosol Research     

Measurements of Morphology Changes of Fractal Soot Particles using Coating and Denuding Experiments: Implications for Optical Absorption and Atmospheric Lifetime

Mobility-selected fractal and non-fractal soot particles (mobility diameters d _m = 135 to 310 nm) were produced at three controlled fuel equivalence ratios (φ = 2.1, 3.5, and 4.5) by an ethylene/oxygen flame. Oleic acid (liquid) and anthracene (solid) coatings were alternately applied to the particles and removed. Simultaneous measurements with an Aerodyne aerosol mass spectrometer and a scanning mobility particle sizer yielded the particle mass, volume, density, composition, dynamic shape factor, fractal dimension, surface area, and the size and number of the primary spherules forming the fractal aggregate. For a given φ, the diameters of the primary spherules are approximately the same, independent of d _m (15 nm, 35 nm, and 55 nm for φ = 2.1, 3.5, and 4.5, respectively). As the coating thickness on a particle increases, the dynamic shape factor decreases but d _m remains constant until the particle reaches a spherical (for oleic acid) or non-fractal but irregular (for anthracene) shape. Under some conditions, liquid oleic acid coating causes the internal BC framework to rearrange into a more compact configuration. The surface area of fractal particles is up to 2.4 times greater than that of a sphere with the same d _m . Using the surface area determinations, the time for a fractal particle to obtain a monolayer of coating material is compared to that of spheres. If it is assumed that the fractal particle is a sphere with the same d _m as the fractal particle, the monolayer coating time is underestimated by a factor of up to 1.7.     

Soot Particle Studies—Instrument Inter-Comparison—Project Overview

An inter-comparison study of instruments designed to measure the microphysical and optical properties of soot particles was completed. The following mass-based instruments were tested: Couette Centrifugal Particle Mass Analyzer (CPMA), Time-of-Flight Aerosol Mass Spectrometer—Scanning Mobility Particle Sizer (AMS-SMPS), Single Particle Soot Photometer (SP2), Soot Particle-Aerosol Mass Spectrometer (SP-AMS) and Photoelectric Aerosol Sensor (PAS2000CE). Optical instruments measured absorption (photoacoustic, interferometric, and filter-based), scattering (in situ), and extinction (light attenuation within an optical cavity). The study covered an experimental matrix consisting of 318 runs that systematically tested the performance of instruments across a range of parameters including: fuel equivalence ratio (1.8 ≤ φ ≤ 5), particle shape (mass-mobility exponent ( D _fm ), 2.0 ≤ D _fm ≤ 3.0), particle mobility size (30 ≤ d _m ≤ 300 nm), black carbon mass (0.07 ≤ m _BC ≤ 4.2 fg) and particle chemical composition. In selected runs, particles were coated with sulfuric acid or dioctyl sebacate (DOS) (0.5 ≤ Δ r _ve ≤ 201 nm) where Δ r _ve is the change in the volume equivalent radius due to the coating material. The effect of non-absorbing coatings on instrument response was determined. Changes in the morphology of fractal soot particles were monitored during coating and denuding processes and the effect of particle shape on instrument response was determined. The combination of optical and mass based measurements was used to determine the mass specific absorption coefficient for denuded soot particles. The single scattering albedo of the particles was also measured. An overview of the experiments and sample results are presented.     

Reduction of diesel particulate emissions by catalytic filtration

Several kinds of diesel soot filters and filter materials of high melting points with eleven different catalytic coatings were prepared. They were calcined at a maximum temperature of 1000°C. The reaction rate and the kinetic parameters of the combustion of diesel soot were determined in a closed loop laboratory reactor. A packed bed of alumina particulates was the most active filter in soot combustion. Catalytic coatings with oxides of vanadium, copper or cerium accelerated the reaction. In each case the effect of the coating was dependent on specific interactions between the catalyst and the filter material. The manner of filtration and the nature of the soot filter are found to be more important for the overall result than the nature of the catalytic coating.     

Nylon 11/silica nanocomposite coatings applied by the HVOF process. II. Mechanical and barrier properties

Nylon 11 coatings filled with nominal 0–15 vol % of nanosized silica or carbon black were produced using the high velocity oxy‐fuel combustion spray process. The scratch and sliding wear resistance, mechanical, and barrier properties of nanocomposite coatings were measured. The effect of powder initial size, filler content, filler chemistry, coating microstructure, and morphology were evaluated. Improvements of up to 35% in scratch and 67% in wear resistance were obtained for coatings with nominal 15 vol % contents of hydrophobic silica or carbon black, respectively, relative to unfilled coatings. This increase appeared to be primarily attributable to filler addition and increased matrix crystallinity. Particle surface chemistry, distribution, and dispersion also contributed to the differences in coating scratch and wear performance. Reinforcement of the polymer matrix resulted in increases of up to 205% in the glass storage modulus of nanocomposite coatings. This increase was shown to be a function of both the surface chemistry and amount of reinforcement. The storage modulus of nanocomposite coatings at temperatures above the glass transition temperature was higher than that of unfilled coatings by up to 195%, depending primarily on the particle size of the starting polymer powder. Results also showed that the water vapor transmission rate through nanoreinforced coatings decreased by up to 50% compared with pure polymer coatings. The aqueous permeability of coatings produced from smaller particle size polymers (D‐30) was lower than the permeability of coatings produced from larger particles because of the lower porosities and higher densities achieved in D‐30 coatings. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2272–2289, 2000     

铝元素对锌镀层耐蚀性的影响

研究了用复合电沉积法制备的锌铝镀层在微酸性腐蚀介质中的耐蚀性。试验结果证明,氢氧化铝也能改善镀层的耐蚀性,但不如铝粉的作用显著。EPMA和ICP显示含氢氧化铝和含铝粉镀层中的铝呈均匀分布状态,但前者铝的含量为50ppm,后者为0.15wt％。x-射线衍射法揭示溶液中的氢氧化铝能使镀层的结晶细致,晶面择优取向程度增加。当镀液中含有铝粉时,所得镀层的结晶晶面的择优程度更大,结构则成为层状的。因此,氢氧化铝和铝粉是通过提高镀层的晶面择优取向程度,从而改善了其耐蚀性能。