Characteristics of nFOG, an aerosol-based wet thin film coating technique (original) (raw)
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Applied Mathematical Modelling, 2013
A model is developed of aerosol spray for synthesis of sensor film from solution. The synthesis technique considered involves atomization of a solution of mixed salts in methanol, spraying of solution droplets, droplet deposition on a heated substrate, evaporation and chemical reaction to produce mixed oxides, and subsequent film growth. The precise control of oxide nanoparticle size distribution and inter-particle spacing in the film is crucial to achieving high sensitivity. These in turn largely depend on the droplet characteristics prior to impingement on the substrate. This paper focuses on the development of a model to describe the atomization and spray processes prior to the film growth. Specifically, a mathematical model is developed utilizing computational fluid dynamics solution of the equations governing the transport of atomized droplets from the nozzle to the substrate in order to predict droplet characteristics in flight. The predictions include spatial distribution of droplet size and concentration, and the effect on these characteristics of swirling inlet flow at the spray nozzle.
Controlling factors of film-thickness in improved aerosol deposition method
Journal of the Ceramic Society of Japan, 2009
To understand the controlling factor of film thickness in aerosol deposition method (ADM), the deposition apparatus was improved at first and the effect of pretreatment of raw barium titanate powder was studied. A developed aerosol generator where the carrier gas was separated from the aerosol generating gas was effective to avoid the agglomeration of powders during the deposition. Two dimensional scanning of the substrate decreased the film-thickness distribution caused by the imhomogeneity of deposition rate in a line-type nozzle. Effect of pretreatments of raw powders, including sieving, drying, planetary ball milling and heating was examined, respectively. There was an optimum rotational velocity of planetary milling to increase the film thickness, indicating that adequate agglomeration of raw powders enhance the film deposition. The film thickness decreased as the heating temperature increased. The heating strengthened the agglomeration of raw powders which restricted the film deposition because the kinetic energy of particles in the aerosol was consumed to break the agglomerations rather than making film. Weakly agglomerated powders with optimum size enhanced the film thickness in ADM.
Experimental investigation of droplet deposition on a single particle
Chemical Engineering Journal, 2001
Spray coating or granulation is used to produce coarse granular solid particles by spraying solutions or suspensions in the form of fine droplets on fluidized particles followed by drying in a stream of fluidizing air. The quality and thickness of granulation or coating on the particle should be uniform. A part of the liquid-droplets from the spray-nozzle collide with the particle, of which, a part bounces back and the remaining part adheres on the surface of the particle giving layered-growth. In this work, the granulation process is carried out on a single spherical particle. Experiments are conducted to study the influence of process parameters, drying conditions, impact velocities and physical properties of sprayed solutions on the kinetics of granulation and on the morphology of the end product. A change in the drying condition changes the viscosity and surface tension of the sprayed solution. With increase in droplet velocity, the growth rate decreases. The results are useful to model the droplet deposition behaviour in fluidized bed granulation.
Characterization and mathematical modelling of single fluidised particle coating
Powder Technology, 2011
A study was made of coating single particles with water-based dispersions under realistic fluid dynamic and well-defined operating conditions. The surfaces of the coated particles were observed with atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM was used to study the latex particle packing and the colloid particle coalescence at the nanoscale, while SEM was used to study the film at the droplet size level. The influence of temperature, moisture content and spray rate were investigated. The experiments showed a coating layer built up of rings of colloid particles for all cases studied except for high spray rate. A variation in the degree of coalescence between colloid particles with different glass transition temperatures, T g , was shown in AFM. Cracks in the coating layer were observed when the temperature was lower than T g . Mechanism evaluation using dimensionless numbers showed that a droplet will spread to the equilibrium angle without splashing; the colloid particles accumulate at the interface between the liquid and the air for all cases studied except air with 90% RH and 20°C and a wet-bulb temperature in the coating layer. The evaluation indicated that no skin forms in any of the cases. A model of the drying of a single droplet was developed to describe the experimental results with rings of colloid particles. The simulation of the shape and height of the dried droplet agrees well with the experimental results.
Progress in enhanced fluidization process for particle coating via atomic layer deposition
Chemical Engineering and Processing - Process Intensification, 2021
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Reviews of Geophysics, 1983
Surface-active organic molecules are common constituents of atmospheric aerosol particles, raindrops, and snowflakes. If these compounds are present as surface films, transfer of gases into the atmospheric water systems could be impeded, evaporation could be slowed, and the aqueous chemical reactions could be influenced. To investigate these possibilities, we have reviewed the chemical literature pertaining to organic films on aqueous surfaces: their composition, structure, properties, and effects. We then review the surface-active organic compounds in atmospheric water. We report the results of new measurements of surface tension of aqueous solutions of common atmospheric organic compounds (fi-pinene, n-hexanol, eugenol, and anethole) and demonstrate that the compounds produce films with properties similar to those of the more well known surfactants. We conclude that organic films are probably common on atmospheric aerosol particles and that they may occur under certain circumstances on fog droplets, cloud droplets, and snowflakes. If present, they will increase the lifetimes of aerosol particles, fog droplets, and cloud droplets, both by inhibiting water vapor evaporation and by reducing the efficiency with which these atmospheric components are scavenged. The presence of the films will not cause a significant reduction of solar radiation within the aqueous solution. It appears likely, however, that the transport of gaseous molecules into and out of the aqueous solution will be impeded by factors of several hundred or more when organic films are present. Since incorporated gas molecules provide much of the oxidizing potential of atmospheric water droplets, the organic films will play a major role in droplet chemistry by strongly inhibiting solution oxidation.
Revealing the effects of aerosol deposition on the substrate‐film interface using NaCl coating
Journal of the American Ceramic Society, 2019
Aerosol deposition is a feasible method of fabricating dense ceramic films at room temperature by the impact consolidation of submicron-sized particles on ceramic, metal, glass, and polymer substrates at a rapid rate. Despite the potential usefulness of the aerosol deposition process, there are issues, such as deposition mechanisms and structure of the filmsubstrate interface, that are not well understood. We have used complementary structural and microstructural analysis to capture the state of the substrate surface after the aerosol deposition process. The results reveal that modification of the substrate surface by the ejected submicron-sized particles is essential for the formation of anchoring layer, thereby, a change in internal residual stress state and surface free energy of the substrate is required to deposit film using AD process. Our analysis also suggests that the adhesion between the metal substrate and ceramic particles is possibly contributed by both physical bonding and mechanical interlocking.
Diffusion and Evaporation Control the Spreading of Volatile Droplets Onto Soluble Films
Interfacial Phenomena and Heat Transfer, 2013
The spreading dynamics of a water droplet on a soluble polymer substrate is controlled by the rate of water transfers into the substrate. We provide a comprehensive description of the parameters controlling the wetting dynamics based on the analysis of the transfers between the spreading liquid and the solid substrate. Our model is supported by experimental results obtained on supported films of polymer with thickness e varied over two decades, on which droplets of water spread with a velocity U spanning two decades. Three different transfers are governing the hydration dynamics: (i) Water evaporates from the droplet, condenses on the substrate, and further diffuses through the polymer. (ii) Liquid water at the contact line diffuses in the polymer ahead of the contact line. (iii) Water in the droplet is convected at the droplet velocity U. The evaporative process is the most efficient at hydrating the substrate and controls the hydration of the polymer at distances ranging between a macroscopic cutoff length L and a microscopic length κ. L is set by the diffusion of vapor in air. κ results from a balance between the diffusion of water from the droplet at the contact line and the diffusion of water in the atmosphere. By analyzing the hydration profile at all distances to the contact line between L and κ, we define three different spreading regimes: a thick film regime where the film behaves as a semi-infinite medium, a thin film regime where hydration is homogeneous along the film thickness, and an intermediate regime where both situations coexist along the film away from the contact line.
Wetting Behavior of Polymer Droplets: Effects of Droplet Size and Chain Length
Macromolecules
Monte Carlo computer simulations were utilized to probe the behavior of homopolymer droplets adsorbed at solid surfaces as a function of the number of chains making up the droplets and varying droplet sizes. The wetting behavior is quantified via the ratio of the perpendicular to the parallel component of the effective radii of gyration of the droplets and is analyzed further in terms of the adsorption behavior of the polymer chains and the monomers that constitute the droplets. This analysis is complemented by an account of the shape of the droplets in terms of the principal moments of the radius of gyration tensor. Single-chain droplets are found to lie flatter and wet the substrate more than chemically identical multi-chain droplets, which attain a more globular shape and wet the substrate less. The simulation findings are in good agreement with atomic force microscopy (AFM) experiments. The present investigation illustrates a marked dependence of wetting and adsorption on certain structural arrangements and propose this dependence as a technique through which polymer wetting may be tuned.