Microstructure and photocatalytic activity of suspension plasma sprayed TiO2 coatings on steel and glass substrates

In this study, TiO 2 coatings were deposited by suspension plasma spraying (SPS) from a commercial TiO 2 nanoparticle suspension on two different substrates: a standard stainless steel and a Pyrex glass. Coatings were sprayed on both substrates with an F4-MB monocathode torch; a Triplex Pro tricathode torch was also used to spray coatings just on the stainless steel substrates. Spraying distance and cooling were varied.The anatase content in the coatings, determined by XRD, ranged from 32 to 72 wt% A significant amount of anatase to rutile transformation was found to occur during cooling. Examination of the microstructure revealed that the coating microstructure was bimodal, involving a non-molten region consisting mainly of anatase nanoparticle agglomerates and a molten region. The glass substrate coatings displayed a segregated phase distribution, particularly when the surface to be coated was cooled. Photocatalytic activity was determined by a methylene blue test.The experimental data fitted well to a first-order kinetic. All the coatings exhibited high photocatalytic activity in comparison with that of a commercial sol-gel coating. However, unlike much of the previous research, photocatalytic activity did not correlate with the anatase content determined by XRD. © 2011 Elsevier B.V.This work has been supported by the Spanish Ministry of Science and Education (MAT2009-14144-C03-01), by the Spanish Ministry of Science and Innovation (PID-600200-2009-5) and by the European Commission in the frame of the Interreg IV B Sudoe programme (Eliare: SOE1/P1/F169).Bannier, E.; Darut, G.; Sánchez, E.; Denoirjean, A.; Bordes, M.; Salvador Moya, MD.; Rayón Encinas, E.... (2011). Microstructure and photocatalytic activity of suspension plasma sprayed TiO2 coatings on steel and glass substrates. Surface and Coatings Technology. 206(2):378-386. https://doi.org/10.1016/j.surfcoat.2011.07.039S378386206

Nanoindentation study of the mechanical and damage behaviour of suspension plasma sprayed TiO2 coatings

TiO2 coatings can be used as self-cleaning surfaces owing to their photocatalytic and hydrophilic properties. Suspension plasma spray (SPS) has proven to be a feasible and cheap technique for producing self-cleaning surfaces with acceptable photo-activity. This paper presents a nanoindentation study of the mechanical properties (hardness. Young's modulus and scratch resistance) of photoactive layers of suspension plasma sprayed TiO2 coatings applied on to glass substrates. Microstructure observation showed that the rutile grains were surrounded by fine anatase crystals. Under the same spraying conditions, the resulting anatase/rutile concentrations varied depending on the cooling rate (the substrate being either cooled with water or in air). The results showed that higher concentrations of anatase, which is softer than rutile, reduced the scratch damage and increased the friction coefficient. (C) 2011 Elsevier B.V. All rights reserved.The study was financially supported by the Spanish Ministry of Science and Innovation (PID-600200-2009-5 and MAT2009-14144-C03-01 -02).Rayón Encinas, E.; Bonache Bezares, V.; Salvador Moya, MD.; Bannier, E.; Sánchez, E.; Denoirjean, A.; Ageorges, H. (2012). Nanoindentation study of the mechanical and damage behaviour of suspension plasma sprayed TiO2 coatings. Surface and Coatings Technology. 206(10):2655-2660. doi:10.1016/j.surfcoat.2011.11.010S265526602061

POWDER DENSIFICATION IN A TRANSFERRED ARC REACTOR

Pour améliorer la projection plasma de particules poreuses de zircone produites par atomisation-séchage, les poudres subissent un pré-traitement de densification avant projection. Cette densification doit permettre d'augmenter la tenue mécanique des particules et améliorer leur fusion lors de la réalisation des dépôts. Le pré-traitement de la poudre est réalisé dans un réacteur plasma à arc transféré. Avant et après traitement, les poudres sont caractérisées par leur morphologie, leur répartition granulométrique, leur densité, leur composition chimique et leur résistance mécanique. En jouant essentiellement sur le débit et la nature du gaz plasmagène et sur le débit du gaz porteur de poudre, des particules de forme sphérique avec une densité proche de la densité théorique et une faible teneur en phase monoclinique ont été obtenues.To improve the plasma spraying of porous zirconia particles prepared by spray drying, a pre-treatment of powder has been carried out in a transferred arc plasma. The densification of the agglomeraed particles must raise the resistance of agglomerated particles against mechanical and thermal loads during plasma spraying. Before and after treatment, powders are characterized with regard to morphology, grain size distribution, density, phase composition and mechanical resistance. With the plasma transferred arc reactor, particles with spherical shape, nearly theoretical density and low content of monoclinic phase are produced provided that the particles don't receive a too high thermal flux

Microwave plasma enhanced CVD of aluminum oxide films: Influence of the deposition parameter on the films characteristics

Thin films of aluminum oxide were deposited on silicon wafers at low temperature by remote microwave plasma-enhanced chemical vapor deposition using an oxygen plasma and a mixture of trimethylaluminum and argon injected in the afterglow. Although the pressure and the total flow rate were low (respectively 2 Pa and 178 sccm), the deposition rate was high (250 nm.min-1) and the films contained only hydrogen as impurity. The most influential parameter on the quality of the film was the temperature which had to reach 550°C to obtain good quality films. A lower pressure made possible a better desorption of the by-products which induced a higher deposition rate and a lower etch rate in a 2%wt hydrofluoric acid solution. In the standard conditions, in presence of a large excess of oxygen (oxygen/trimethylaluminum>18), the trimethylaluminum precursor was fully transformed. The quality of the coatings was almost independent on the microwave power

On the oxidation of stainless steel particles in the plasma jet

The in-flight oxidation of stainless steel particles in the plasma jet was investigated in this work. Two types of 316L austenitic stainless steel particles were sprayed by a dc plasma gun in ambient or controlled atmosphere varying gun parameters and surrounding gases composition. The in-flight collected particles were characterized to establish relationship between spray parameters and particle oxidation behavior. The in-flight particle oxidation mechanisms were then suggested. It was shown that besides diffusion based oxidation, convective oxidation in the particles can occur within the plasma jet core if plasma to particle kinematic viscosities ratio and relative Reynolds number (Re) are superior to 55 and 20, respectively. In these conditions, the oxide formed or oxygen dissolved at the surface of the liquid particle can be swept into its interior forming isolated oxide nodules. Fresh liquid metal is transported from interior towards particle surface. The oxidation rates were estimated to be higher compared to diffusion based oxidation which was found to be the dominant phenomenon in the plasma jet plume in the absence of convective oxidation. Spray parameters leading to higher kinematic viscosities ratio and Re, such as increasing arc current, hydrogen content in the plasma forming gases, or decreasing sprayed particle size range, resulted in enhanced convective oxidation in the plasma core. The diffusion based oxidation of particles in the plasma jet plume can be principally controlled by their size (specific surface area), temperature and velocity (dwell time) and the molar fraction of oxidizing and reducing species in the plasma jet. While investigating the influence of the atmosphere of plasma jet on the in-flight particle oxidation, it was found that the surface area of the oxide nodules and the mass percentage of total oxygen in collected particles followed a parabolic and linear relationship with pO2 in the surrounding atmosphere. Keeping surrounding pO2 at 0.1 and altering N2 and Ar content resulted in higher oxygen content in particles sprayed in Ar rich surrounding whereas no distinct difference in oxide nodules surface area was measured

POWDER DENSIFICATION IN A TRANSFERRED ARC REACTOR

To improve the plasma spraying of porous zirconia particles prepared by spray drying, a pre-treatment of powder has been carried out in a transferred arc plasma. The densification of the agglomeraed particles must raise the resistance of agglomerated particles against mechanical and thermal loads during plasma spraying. Before and after treatment, powders are characterized with regard to morphology, grain size distribution, density, phase composition and mechanical resistance. With the plasma transferred arc reactor, particles with spherical shape, nearly theoretical density and low content of monoclinic phase are produced provided that the particles don't receive a too high thermal flux.Pour améliorer la projection plasma de particules poreuses de zircone produites par atomisation-séchage, les poudres subissent un pré-traitement de densification avant projection. Cette densification doit permettre d'augmenter la tenue mécanique des particules et améliorer leur fusion lors de la réalisation des dépôts. Le pré-traitement de la poudre est réalisé dans un réacteur plasma à arc transféré. Avant et après traitement, les poudres sont caractérisées par leur morphologie, leur répartition granulométrique, leur densité, leur composition chimique et leur résistance mécanique. En jouant essentiellement sur le débit et la nature du gaz plasmagène et sur le débit du gaz porteur de poudre, des particules de forme sphérique avec une densité proche de la densité théorique et une faible teneur en phase monoclinique ont été obtenues