A certain level of porosity is always presented in thermal spray ceramic coatings. LPPS or some specific APS processes can allow to reduce it but it is difficult to obtain coatings with a low thickness (less than 100 m) which are fully gas-tight because of cracks or interconnected pores. This gas-tight property is for example very suitable for the ceramic electrolyte of solid oxide fuel cells (SOFC). Some ZrO 2 -Y 2 O 3 coatings were obtained by the VLPPS process, a LPPS system operating at a pressure of about 100 Pa. The specific structure of these coatings is a mixture of condensed vapors and splats. The results are very satisfying because ZrO 2 -Y 2 O 3 coatings with a thickness of about 70 micrometers are tight under a hydrogen pressure of 2x105 Pa. This paper presents some ZrO 2 -Y 2 O 3 coatings obtained by different processes (APS, LPPS and VLPPS) and their properties.

In this paper a comparative study on the microstructure and photocatalytic performances of titanium dioxide coatings elaborated by various thermal spraying methods (plasma spraying in atmospheric conditions, suspension plasma spraying and high-velocity oxy-fuel spraying) was proposed. Agglomerated spray-dried anatase TiO 2 powder was used as feedstock material for spraying. Morphology and microstructural characteristics of the coatings were mainly studied by scanning electron microscopy and X-ray diffraction. The photocatalytic behavior of the TiO 2 -based surfaces was evaluated from the conversion rate of gaseous nitrogen oxides (NOx). It was found that the crystalline structure strongly depended on the technique of thermal spraying deposition. Moreover, a high amount of anatase was suitable for the photocatalytic degradation of the pollutants. Suspension plasma spraying permitted to retain the original anatase phase and to obtain very reactive TiO 2 surfaces for the nitrogen oxides removal.

The suspension plasma spraying using a liquid as material feedstock is a promising technique to elaborate thin and nanostructured coatings. This work deals with the study of suspensions in order to obtain specific microstructural coatings. The slurries were prepared starting from nanosized titania powders. Distilled water and alcohol were used as solvents and appropriate dispersing agents were employed to stabilize the suspensions. An external injection system that ensures the atomisation and radial injection of the suspension into Ar-H 2 plasma under atmospheric conditions was designed. The coatings were characterized by scanning electron microscopy and differences in the microstructure of the deposits were observed. Efforts were made to understand the relationship between liquid feedstock properties, injection/plasma parameters and coatings microstructural characteristics.

This paper deals with the elaboration of titanium dioxide coatings designed for photocatalytic applications, obtained by suspension plasma spraying (SPS), an alternative of the atmospheric plasma spraying (APS) in which the material feedstock is a suspension of the powder to be sprayed. Two different TiO 2 powders were dispersed in distilled water and ethanol and injected in Ar-H 2 or Ar-H 2 -He plasma under atmospheric conditions. SEM and XRD analysis were performed to study the microstructure and surface features of the titania coatings. Photocatalytic efficiency of the elaborated samples was evaluated from the conversion rate of different air pollutants: NOx and SO 2 . The present results showed that the suspension plasma spraying allows to produce reactive surfaces for the removal of air pollutants that in the same working conditions, present a higher photocatalytic activity compared to that of the initial raw powders.

Very low pressure plasma spraying (LPPS) is the objective of numerous studies for the past years. However, numerical simulations and experiments revealed some difficulties such as the presence of successive expansions and constrictions of the plasma jet that has an influence on the deposition efficiency and on the coating structure. Optimization of the plasma gun is thus required and the use of bell-contoured De Laval nozzle extensions seems particularly promising. In this paper, new developments concerning the use of an in-house bell-contoured nozzle extension are presented and both numerical calculations and experiments were performed.

Characteristics of in flight particles before they impact on the substrate influence strongly the quality of coating obtained by plasma spraying. Various optical techniques can be used to measure the in-flight particle characteristics; some of these techniques require the use of high- speed two-color pyrometers to collect the light emitted by the particle during the in-flight period when they pass through the measurement volume. However, the intense radiation coming from the plasma can affect the particle thermal radiation and lead to erroneous measurements. This work was dedicated to the study of reflected light coming from the plasma and scattered by the injected particles. To achieve this goal, sprayed particles were analyzed by optical emission spectrometry. The light scattered by the particles was found to influence significantly the measured temperature. This work allows thus the estimation of the accuracy of temperature measurements on particle surface for the thermal spraying process. Abstract only; no full-text paper available.

The knowledge of thermal fluxes transferred from impinging high temperature jets is always important. For example, during thermal spray applications, the impinging jet acts directly on the transient surface temperature of the substrate. For preheating applications, it acts on the time required to reach the required surface temperature. It is also important to estimate it for some other applications like thermal cycling tests of parts for example. In the present paper, both CFD computations and experiments were carried out in order to quantify thermal fluxes from an impinging HVOF jet. The case of a CDS gun fueled by natural gas was considered. Stand-off distances ranging from 50 mm up to 300 mm were investigated. The model incorporates a 2-layer extension to k-å models for a better estimation of thermal exchanges through the viscous layer on the front body surface. The experiments were performed using a system incorporating two square calorimeters positioned one beside the other in order to attempt defining a radial profile. Abstract only; no full-text paper available.

LERMPS laboratory has been implementing a Quality Management System (QMS) for one year now. Only few Research organisms in the world have begun such process, which has up to now mostly been applied to industrial companies. Hence, the path leading to Quality excellence will be long, but LERMPS is on the way for at least certification, and some interesting results have already been achieved. This QMS implementation is mainly focused for the moment on characterisation team, which are the main support of Thermal Spray and PVD coatings activities in LERMPS. Nevertheless it slightly expands its application area to the whole activity of the laboratory, including administrative support processes. Abstract only; no full-text paper available.

Thermal sprayed protective coatings have gained widespread acceptance for a variety of industrials applications. This technology can be split into air plasma spraying (APS) and vacuum plasma spraying (VPS) according to the atmosphere during the deposition process. A number of advantages of VPS process such as avoiding oxidation or contamination of projectile, substrate and deposed coating; reducing the interaction between the plasma jet and the environment are obvious before the APS. The flexibility of process gives the largest possibility in aeronautics, gas turbine, medical field and other applications using different parameters, deposited and target materials. Low pressure plasma spraying (LPPS) is considered with some particular features so the range of pressure is about 10- 250 mbar, the dimensions of the plasma jet and its homogeneity are important. The adaptation of modern pumping and control systems allow to reduce the worked pressure to 0,1 mbar and to have conditions close to physical vapour deposition (PVD). This paper presents the results of the deposition of a copper alloy powder using the very low pressure plasma spraying performed by a new system developed in the LERMPS

In this paper, the modified method of plasma spraying using liquid suspension feedstock was used to elaborate thin titanium dioxide coatings. TiO 2 Degussa P25 powder were dispersed by continuous stirring in distilled water and alcoholic solutions and injected in an Ar-H 2 or Ar-H 2 -He plasma plume under atmospheric conditions. Scanning electron microscopy and X-ray diffraction were performed to study the microstructure and crystalline phases of titanium dioxide coatings. The anatase content in the elaborated TiO 2 deposits strongly depended on the type of the suspension solvent. The photocatalytic activity of the titanium dioxide coatings was evaluated from the conversion rate of nitrogen oxides and compared with that of the initial powder. The obtained results allowed to affirm that the method of the liquid plasma spraying proved to be a promising technique to elaborate photocatalytic TiO 2 coatings for the removal of nitrogen oxides pollutants.

In the present study, TiO 2 and TiO 2 -Al composite coatings were prepared by HVOF spraying using reconstituted nanosized feedstock powders prepared via the spray drying technique. In the flame, the powders were injected by two methods: internal injection i.e. as in conventional HVOF process and external injection i.e. outside the torch nozzle. The microstructure of the coatings was characterized by scanning electron microscopy and X-ray diffraction. It was found that the amount of anatase in the coatings depends on the nature of the powder and also on the type of the injection method. The coatings were tested for their photocatalytic properties regarding the conversion rate of nitrogen oxides. Coatings elaborated by external injection presented a better photocatalytic activity than those obtained by the conventional HVOF process.

Conventional equipments used for low pressure plasma spraying are designed for a chamber pressure of a few tens of mbar. During the past three years, an increasing interest for thermal spray under very low pressure conditions (as low as 1 mbar) was encountered but no significant advances concerning the spray gun design was proposed. However, it is clear that actual tools do not allow providing uniform plasma jets and that the produced jets present successive expansions and constrictions due to a poor adaptation of the nozzle exit pressure regarding to the chamber one. In the present paper, the use of a nozzle extension is proposed. The holding nozzle is a lengthened F4 type one and the diverging part of the nozzle is formed by a fastened external extension. The design of the nozzle extension is a bell-contoured Laval type one and its dimensions (exit diameter and length) are much higher than for conventional diverging nozzles. An improvement in the jet homogeneity and uniformity is expected.

TiO 2 and TiO 2 -Al composites coatings were prepared by plasma spraying using a reconstituted nanosized feedstock via a spray drying method. Effects of various spray conditions on the microstructure, porosity, microhardness and wear resistance related to the mechanical performance of coatings were evaluated. The coatings sprayed at relatively low plasma power were composed of two distinct microstructures of well defined lamellar structure, similar to microstructure of conventional plasma sprayed coatings typically observed from fully melted particles, and embedded nano or sub-micron particles originated from partial/non-molten particles of feedstock materials. The fraction of partial/non-molten particles in coating layers was increased by Al additive. Such a characteristic of blended microstructure of coatings was clearly confirmed from a bimodal distribution of microhardness described by Weibull plots. The optimized addition of Al into TiO 2 improved mechanical properties such as microhardness and wear resistance.

Titanium dioxide (TiO 2 ) is one of the most important photocatalyst that allows the environmental purification of water and air by the decomposition of toxic organic compounds and removal of harmful gases. In the photocatalytic applications, TiO 2 can be used in form of powder or coating. In this paper, two techniques of deposition were used to elaborate thin deposits starting from an agglomerated TiO 2 anatase nanopowder: conventional plasma spraying in atmospheric conditions and suspension plasma spraying. The photocatalytic efficiency of the coatings was performed with respect to nitrogen oxides (NOx) and compared with the photocatalytic activity of the TiO 2 Degussa P25 powder. Differences in the photocatalytic efficiencies of the nanocoatings obtained by the two techniques of plasma spraying were obtained. The coatings elaborated by suspension plasma spraying have poor mechanical properties but better photocatalytic efficiencies. This method is a promising technique to elaborate photocatalytic coatings for the removal of different air pollutants.

Titanium dioxide (TiO 2 ) has emerged as an excellent photocatalyst material for environmental purification about two decades ago but only recently few works have focused on the photocatalytic properties of sprayed titanium oxide coatings. So far, the role of oxygen deficiency which can appear as a result of the spray process or by use of titanium suboxide powders on the photocatalytic activity has not been investigated. Also the possible influence of the shear plane structure of titanium suboxides (Magnéli phases) on the photocatalytic activity was not taken into consideration. In the present work, the photocatalytic properties of three powders and coatings sprayed from these powders by APS and VPS are investigated: (1) a commercial fused and crushed titanium oxide powder, (2) an agglomerated and sintered titanium suboxide powder consisting predominantly of Magnéli phases Ti 6 O 11 and Ti 5 O 9 , (3) an agglomerated and sintered powder consisting of Ti 2 Cr 2 O 7 and Ti 6 Cr 2 O 15 (Magnéli phases in the TiO 2 - Cr 2 O 3 phase diagram). The phase compositions of the powders and the coatings were investigated by X-ray diffraction. Neither for the spray powders nor for the coatings any ability to reduce the NOx concentration by the photocatalysis was found. From this it is concluded that both oxygen deficiency as well as Magnéli phase structure are not responsible for photocatalytic properties of materials in the Ti-O phase diagram.

The aim of the present study concerns the effect of the chamber pressure on the structure of a plasma jet. Conventional vacuum plasma spray equipments are currently designed to operate at chamber pressures higher than 10 mbar. Nevertheless, recently, the exploration of lower pressure level conditions seems to have become a new challenge. In the present study, pressure levels as low as 0.5 mbar have been achieved and tested. It is shown that a decrease in the chamber pressure provides a longer and enlarged plasma jet whose length may be longer than one meter for the lowest pressure levels considered. CFD modeling results and photographs performed under vacuum conditions are proposed for the case a standard conical nozzle. Some additional characterizations (using thermocouples and emission spectroscopy) were also conducted but the results are currently being analyzed.

Titanium dioxide (TiO 2 ) is an attractive material for numerous technological applications such as photocatalytic applications. The photocatalysts allow the environmental purification of air and water by the decomposition of toxic organic compounds and removal of harmful gases. This work was focused on the production and evaluation of the environmental properties of titanium dioxide coatings obtained by the plasma spray technique. To carry out the step of validation of the TiO 2 coatings for their environmental functionalities, a control test of the photocatalytic effectiveness was performed with respect to nitrogen oxides. A custom-designed test chamber has been developed. The photocatalytic properties of different coatings were studied as a function of various parameters (porosity, anatase/rutile ratio, nature of the substrate).

The electronic structure of the bulk and the surface of rutile titanium dioxide (TiO 2 ) are analyzed from band calculation based on quantum mechanics formalism. The surface density of states and charge distributions of bulk and (001) surface are compared to better understand the mechanism of adsorption and photodegradation processes.

This paper presents a detailed numerical analysis that shows why Laval nozzles are used for vacuum plasma spraying and how to optimize their design to achieve a uniform plasma jet free of expansion waves under different spraying conditions. A Laval nozzle prototype is tested against a commercially available conical nozzle and is found to deliver a longer core jet with less turbulent scattering. Paper includes a German-language abstract.