This work analyzes the mechanism of spray deposition by means of computational fluid dynamics (CFD) in order to reproduce virtually the spraying of a paint gun adopted for use in the automotive industry and to predict paint drop trajectories and film builds on the target surface. The prediction of the flow of the continuous phase was obtained by solving the time averaged Navier-Stokes equations in connection with suitable closure models for turbulence (RNG and Realizable k-ε). The dispersed phase was treated by a Lagrangian approach, by tracking numerically a large number of representative particles from the gun exit to the target surface. The initial conditions for the droplets were estimated from a detailed simulation of the paint jet at the exit of the nozzle. In this way one could evaluate positions and velocities of droplets at impact and estimate the properties of the deposited layer of paint. The method was validated by comparison with experimental data obtained by phase doppler anemometry and, subsequently, the approach was applied to different geometries and operating conditions. S pray deposition processes are used for many industrial applications, mostly in the area of surface coating, but also for the manufacturing of new materials with peculiar properties. One of the reasons for their widespread use is the ability to provide a finish with very fine microstructure that results in remarkable improvement of protective and aesthetic properties.In order to obtain the appropriate characteristics of the coats, the application process of the liquid paint must be well-controlled and reproducible. As illustrated in this work, significant help can be provided by computational fluid dynamics (CFD), which can offer a detailed view of the operation and show the effect of different operating conditions by simulating the flow field generated by the spraying device. CFD can provide significant insight into the painting process and has the ability to show how changes in operating conditions, applicator type, or workpiece geometry may affect performance. A number of advances can be expected from the better understanding of the basic processes of spray painting provided by the computational methods, including: environmental issues, with improvement of paint transfer efficiency and reduction of the paint that escapes to the environment; quality issues, with more uniform coating deposition and easier identification of the reasons for maldistribution of paint; and safety issues, by assessing workers' exposure to paint as a function of work practices and local ventilation. This work will show an example of applying CFD to the simulation of an air spray painting process and to the prediction of film builds on simple surfaces. The results reveal the type of information provided by such an analysis. The approach is quite general and applicable to other conventional paint spray systems.Few authors have tried to measure and model paint sprays originated from pneumatic atomizers so far. Kwok 1 made measurements of the air flow ...

In anoxic environments, the oxidation of organic compounds, such as BTEX fuel components, by dissimilatory Fe(III) reduction can generate reactive mineral-bound Fe(II) species, which in turn are able to reduce other classes of organic and inorganic groundwater contaminants. In this study, we designed and evaluated an anaerobic batch reactor that mimicks iron-reducing conditions to investigate the factors that favor the coupling of microbial toluene oxidation and abiotic reduction of nitroaromatic contaminants. We investigated the influence of different Fe(III)-bearing minerals and combinations thereof on the coupling of these two processes. Results from laboratory model systems show that complete oxidation of toluene to CO2 by Geobacter metallireducens in the presence of Fe(III)-bearing minerals leads to the formation of mineral-bound Fe(II) species capable of the reduction of 4-nitroacetophenone. Whereas significant microbial toluene oxidation was only observed in the presence of amorphous Fe(III) phases, reduction of nitroaromatic compounds only proceeded with Fe(II) species bound to crystalline Fe(III) oxides. Our results suggest that in anoxic soils and sediments containing amorphous and crystalline iron phases simultaneously, coupling of microbial oxidation and abiotic reduction of organic compounds may allow for concurrent natural attenuation of different contaminant classes.

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Purpose – The purpose of the present study is to use an amino-functional polysiloxane for the surface modification of red iron oxide (Fe2O3) pigment particles for their improved dispersion stability and hydrophobicity and to study the chemical interactions of polysiloxanes with the particle surface. Design/methodology/approach – Surface-treated red Fe2O3 pigment particles were prepared by treatment of the particles with different quantities of the (aminopropylmethylsiloxane)-dimethylsiloxane copolymer in concentrated suspensions in water. The samples were analysed with different instrumental and spectroscopic techniques to study the interaction of the polysiloxane with the particle surface and the effect of the surface treatment of the particles on their dispersion stability and hydrophobicity. Findings – Chemisorption of the amino-polysiloxane onto the surface of Fe2O3 particles resulted in stable layers which turned out to be helpful in improving greatly the dispersion stability of the particles as shown by the Static Light Scattering and Dynamic Light Scattering results. Formation of a polysiloxane coating onto the surface of the pigment particles was confirmed by studying the interactions of the polymer molecules with Fe2O3 surfaces by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy techniques. Practical implications – The surface-treated red Fe2O3 particles with improved dispersion stability can be important components of various formulations in applications such as the colouring of the cement or inorganic pigment-based paint formulations. Originality/value – The study provides mechanistic insights about the interactions of amino-polysiloxane with the red Fe2O3 particles. The process of surface modification of red Fe2O3 particles with the amino-functional polysiloxane showed increased hydrophobicity and dispersion stability which is an important requirement of the pigment-based formulations in real applications.

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