Effect Of Organic Coatings Research Articles

The effect of organic coatings in the magnetization of CoFe2O4 nanoparticles

Cobalt ferrite has attracted considerable attention in recent years due to its unique physical properties, such as high Curie temperature, large magnetocrystalline anisotropy, high coercivity, moderate saturation magnetization, large magnetostrictive coefficient, and excellent chemical stability and mechanical hardness. This work focuses on the neutron scattering results of the magnetic response characteristics of polysaccharide fucan coated cobalt ferrite nanoparticles for their application as a solid support for enzyme immobilization and other biotechnology applications. Here, we unambiguously show that surfactant coating of nanoparticles can significantly affect their magnetic response throughout the nanoparticle volume. While it has been recently suggested that oleic acid may preserve nanoscale magnetism in ferrites, we present evidence that the influence of oleic acid on the magnetic response of CoFe2O4 nanoparticles is more than a surface effect, instead pervading throughout the interior of the nanoparticle.

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.

The AIDA soot aerosol characterisation campaign 1999

Abstract An intensive soot aerosol characterisation campaign was organised in October 1999 at the large aerosol chamber facility AIDA in Karlsruhe, with the participation of scientists from nine Austrian, German, Russian, and Swiss Research Centres and Universities who contributed special equipment and expertise. The main goal was a comprehensive physical and chemical characterisation of soot aerosol from a modern turbo Diesel passenger car equipped with an oxidation catalyst, in comparison with artificial soot aerosol (“Palas” soot) from a commercial spark discharge generator which is often used as a surrogate for combustion soot in laboratory studies. Included were experiments with pure ammonium sulphate aerosol as well as its external mixtures with soot aerosols, and their evolution to partially internal mixtures on time scales up to 45 h . Effects of organic coatings on various aerosol properties, generated in situ by heterogeneous nucleation of products from the reaction of α-pinene with ozone were also investigated. The purpose of this paper is to present an overview of the whole campaign. This includes the description of technical and modelling tools, standard procedures, and the presentation of experimental parameters in tabular form, as a common background for a series of companion papers which focus on selected scientific issues. Included is a comparison between Diesel and spark generated soot in terms of their Raman and ESR spectra. The most remarkable difference is the large spin density in spark generated soot, which exceeds that of Diesel soot by an order of magnitude. However, the spin densities in both materials are too small to affect the surface properties of soot aerosols to a significant extent.

Influence of an organic coating on the reactivity of aqueous aerosols probed by the heterogeneous hydrolysis of N2O5

Surface‐active organic compounds are common constituents of atmospheric aerosol particles. In this work, the effects of organic coatings on the heterogeneous hydrolysis of N2O5 was investigated. For this purpose aqueous NH4HSO4 particles were coated in situ in a large aerosol chamber. The experiments show that films composed of the ozonolysis products of α‐pinene can reduce the reaction probability by more than an order of magnitude. Model calculations indicate that the main cause for the retardation of the hydrolysis is a slower uptake possibly due to a lower solubility of N2O5 in the organic film.

Immobilisation of molybdate by iron oxides: effects of organic coatings

It has been suggested that molybdate penetrates into micropores and interdomains of iron oxides. This process will cause immobilisation of molybdate. The influence of organic matter that may occlude the pores by adsorptive cover has not yet been examined. Thus, the aim of our study is to elucidate the role of organic coatings around iron oxides for intraparticular molybdate diffusion. We used two synthetic goethites of different crystallinity (specific surface G13: 13 m2 g−1 and G83: 83 m2 g−1), in pure form and equilibrated with dissolved organic matter (DOM), that has been extracted from forest floor samples. The iron oxide samples that were characterised by N2 adsorption, X-ray diffraction analysis and scanning electron microscopy were preincubated with molybdate solution (5 g iron oxide l−1, 0.2 mM molybdate, pH 4) for 12, 24 and 48 h. To follow the molybdate immobilisation, molybdate desorption kinetics (desorption periods 0.5–48 h) were determined with ion exchange resins in batch systems after the different incubation times. In addition, the preincubated iron oxides were examined by XPS. Fractional coverage of DOM-treated iron oxides estimated according to the enthalpy of N2 adsorption was 0.33 m2 m−2 for G83 and 1.19 m2 m−2 for G13. The pore volume of G13 decreased after DOM treatment. Furthermore, SEM images show that DOM treatment results in microaggregation of the iron oxides. A combination of the first-order equation and a diffusion term was applicable to the Mo desorption data of both, the pure and the DOM-treated iron oxides. Desorbability and apparent diffusion constants of molybdate decreased with increasing residence time. However, the decrease was less distinct for the DOM treated than for the pure goethites. The Mo/Fe XPS ratios of the iron oxides indicate that in the presence of organic matter a higher percentage of molybdate is sorbed to outer surfaces. The results confirm the hypothesis that molybdate diffuses into the pores of iron oxides. Organic coatings slow down the molybdate immobilisation probably by decreasing the accessibility of diffusion pathways. This mechanism may be relevant even at low molybdate and C concentrations, where no competition effect of sorbed organic molecules can be observed.

Influence of organic coatings on the stability of macrodefect-free cements exposed to water

Abstract It is known that macrodefect-free (MDF) cements show instability in water, with swelling and reduction in strength. The weight and dimensional changes of three MDF cements, formulated from different aluminous cements, during immersion in quiescent tap water, were evaluated. The results show that the cement with the highest Al2O3 percentage had the lowest degradation after prolonged immersion. Hence, this material was selected for further analysis. As the time taken for water to diffuse into the body of MDF composites is considered a key factor in the collapse of their mechanical properties, the effect of organic coatings with different barrier properties on the composite behaviour, when exposed to water, was studied. The water permeability of seven surface coatings was evaluated by electrochemical impedance spectroscopy (EIS). Three of them were chosen for application to the selected MDF cement. The data presented show that the application of organic coatings, not necessarily characterised by extremely low water permeabilities, improves the stability of the composite when subjected to different conditions of exposure to water.

Evaporation of ammonium nitrate aerosol and the effect of organic coatings

The mass transfer rate of ammonium nitrate between the aerosol and gas phases was quantified experimentally by the use of the TDMAISMPS (Tandem Differential Mobility Analyzer/Scanning Mobility Particle Sizer) technique. Experiments were run for both pure and covered with organic films particles. Fresh, ammonium nitrate particles with initial diameters in the submicrometer regime were produced and evaporated in purified air under temperatures of 20 to 40°C and relative humidities of 10 to 80%. Particles were coated with various film thicknesses by exposing the ammonium nitrate particles to an air stream supersaturated with an organic vapor. A differential mobility analyzer was used to extract a nearly monodisperse aerosol which was allowed to evaporate for approximately 30 seconds in an evaporator. A SMPS system was used to measure the size distribution of the evaporated particles with and without the organic coating.

The effect of organic coatings on the cloud condensation nuclei activation of inorganic atmospheric aerosol

Atmospheric aerosols have mixed chemical composition, with a variety of inorganic (e.g., sulfate, nitrate, ammonium, and sodium) and organic species often present in a single particle. In the present study, we investigate experimentally the cloud condensation nuclei (CCN) activation of submicron aerosol consisting of an inorganic core (e.g., ammonium sulfate) coated by an organic film, at typical atmospheric supersaturations. We use two types of organic coatings on the (NH4)2SO4 particles. The first is glutaric acid, a CCN active organic found in the atmosphere, and the second species is dioctylphthalate (DOP), a nonhygroscopic organic. The CCN activation of (NH4)2SO4‐glutaric acid particles was measured at a supersaturation of 0.3%, for different inorganic core sizes and organic film thickness. We found that a coating of glutaric acid increases the CCN activation of an (NH4)2SO4 particle and that this behavior can be predicted by Köhler theory. The deviation from Köhler theory for the mixed aerosol was determined by comparing theoretical and experimental CCN activation diameters for the particles and was found to be within experimental error. A thick coating of DOP (at least 70% by mass) did not hinder the activation of (NH4)2SO4 particles at supersaturations of 0.5 and 1.0%. The values for the measured activation diameters for the DOP coated (NH4)2SO4 particles were within the experimental error determined by the pure inorganic experiments, indicating that DOP was most likely acting as inert mass during activation.