Abstract
The plasma-based aerosol process developed for the direct coating of particles in gases with silicon oxide in a continuous chemical vapor deposition (CVD) process is presented. It is shown that non-thermal plasma filaments induced in a dielectric barrier discharge (DBD) at atmospheric pressure trigger post-DBD gas phase reactions. DBD operating conditions are first scanned to produce ozone and dinitrogen pentoxide. In the selected conditions, these plasma species react with gaseous tetraethyl orthosilicate (TEOS) precursor downstream of the DBD. The gaseous intermediates then condense on the surface of nanoparticles and self-reactions lead to homogeneous solid SiOx coatings, with thickness from nanometer to micrometer. This confirms the interest of post-DBD injection of the organo-silicon precursor to achieve stable production of actives species with subsequent controlled thickness of SiOx coatings. SiOx coatings of spherical and agglomerated metal and metal oxide nanoparticles (Pt, CuO, TiO2) are achieved. In the selected DBD operating conditions, the thickness of homogeneous nanometer sized coatings of spherical nanoparticles depends on the reaction duration and on the precursor concentration. For agglomerates, operating conditions can be tuned to cover preferentially the interparticle contact zones between primary particles, shifting the sintering of platinum agglomerates to much higher temperatures than the usual sintering temperature. Potential applications for enhanced thermal stability and tunable photoactivity of coated agglomerates are presented.
Highlights
The coating of nanoparticles is an essential step to improve the particle thermostability [1], to create a protective layer between particle and environment [2] or to enhance particle dispersion in liquids
The plasma filaments originate from the edges of the inner electrode until they cover the whole surface of the smaller electrode for higher applied voltages
Since deposition and coating inside the agglomerates will affect much less the agglomerate mobility compared to the coating of a sphere, the SMPS measurements can only provide a qualitative picture of the coating progress. Another surface sensitive in situ technique is used here to follow the degree of surface coverage, i.e., the aerosol photoemission (APE) [29]
Summary
The coating of nanoparticles is an essential step to improve the particle thermostability [1], to create a protective layer between particle and environment [2] or to enhance particle dispersion in liquids. Post-DBD injection of the organo-silicon precursor is tested to avoid electrode coating so reacting with plasma species in the gap, to particles electro-collection on surfaces in the gap and to as to achieve stable DBD production of active species with subsequent controlled thickness of SiOx discharge destabilization that hampers the economics of the process. In that the selected conditions, trigger the post-DBD conversion of TEOS into solid SiOx coatings of nanoparticles. DBD operating subsequent sections present the coating of spherical particles and of agglomerates separately versus conditions are scanned to produce ozone and dinitrogen pentoxide. Properties present the coating of spherical particles and of agglomerates separately versus of coated agglomerates for thermal stabilization catalyst particles and for photoactivity reaction duration and concentrations of reactantsof (plasma species and TEOS). Coated agglomerates for thermal stabilization of catalyst particles and for photoactivity control are depicted
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
