13 research outputs found
Conformal multilayer coatings on fine silica microspheres by atmospheric pressure fluidized bed chemical vapor deposition
Surface properties of fine particles can be tuned through deposition of films or coatings. This approach is an area of science and technology of interest in numerous fields such as catalysis, energy production, microelectronics, optoelectronics, etc. Surface coating of powders can be applied by a dry technique (i.e., the use of a reactive gas phase), so-called chemical vapor deposition (CVD). However, conventional CVD processes cannot provide an efficient conformal deposition while fine particles are considered as substrates. This is due to the fact that mixing of particles, in such a way that their entire surface is exposed to the reactive gas phase, is rather complicated and not often addressed. Therefore, fluidization, as a recognized particle treatment process which meets the requirement of gasâsolid contact, can be associated with the gasâsolid reactions that are often used in the context of various CVD processes. The combination of such mature techniques, namely fluidized bed chemical vapor deposition (FBCVD) leads to innovative, flexible and cost-effective particle treatment processes [1].
In the present investigation, soda lime spherical particles with a particle size of ca. 27 ”m were used as the substrate. Single- and multi-layer depositions composed of TiO2 and SiO2 films were applied to the surface of the particles by the FBCVD at atmospheric pressure, while employing, respectively, titanium and silicon tetrachloride as precursors, and using water as an oxidation agent. TiO2 and SiO2 films were deposited at 300oC and ambient temperatures, respectively.
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Chemical vapour deposition synthetic diamond: materials, technology and applications
Substantial developments have been achieved in the synthesis of chemical
vapour deposition (CVD) diamond in recent years, providing engineers and
designers with access to a large range of new diamond materials. CVD diamond
has a number of outstanding material properties that can enable exceptional
performance in applications as diverse as medical diagnostics, water treatment,
radiation detection, high power electronics, consumer audio, magnetometry and
novel lasers. Often the material is synthesized in planar form, however
non-planar geometries are also possible and enable a number of key
applications. This article reviews the material properties and characteristics
of single crystal and polycrystalline CVD diamond, and how these can be
utilized, focusing particularly on optics, electronics and electrochemistry. It
also summarizes how CVD diamond can be tailored for specific applications,
based on the ability to synthesize a consistent and engineered high performance
product.Comment: 51 pages, 16 figure
Conformal Multilayer Photocatalytic Thin Films on Fine Particles by Atmospheric Pressure Fluidized Bed Chemical Vapor Deposition
Conformal
multilayer TiO<sub>2</sub>/SiO<sub>2</sub>/TiO<sub>2</sub> coatings
were deposited on the surface of âŒ27 ÎŒm spherical
soda lime glass (SLG) particles using fluidized bed chemical vapor
deposition at atmospheric pressure. Cost-effective precursors of titanium
and silicon chlorides together with water were employed to deposit
titania and silica films at 300 °C and room temperature, respectively.
Focused ion beam cross-sectional transmission electron microscopy,
scanning electron microscopy, energy-dispersive spectroscopy, X-ray
photoelectron spectroscopy, BrunauerâEmmettâTeller surface
area analysis, and X-ray diffraction were used to characterize the
multilayer-coated particles. The results revealed a pinhole-free and
uniform multilayer of anatase TiO<sub>2</sub> and amorphous SiO<sub>2</sub> with a thickness of âŒ110 and 20 nm. Moreover, the
photodegradation performance of the coated particles was examined
by the degradation of methylene blue as the model reaction. It was
found that a multilayer thin film of titania and silica can effectively
prevent sodium ion diffusion from the SLG microsphere substrates,
thus improving the photocatalytic performance of such system