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 gas–solid contact, can be associated with the gas–solid 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 µm 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. Please click Additional Files below to see the full abstract

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 TiO₂/SiO₂/TiO₂ coatings were deposited on the surface of ∼27 μm 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, Brunauer–Emmett–Teller 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 TiO₂ and amorphous SiO₂ with a thickness of ∼110 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