Cathy Meunier

X-ray diffraction line profile analysis of iron ball milled powders

Abstract The size of coherently diffracting domains and the lattice strain of iron ball milled powders have been determined according to various models. The Williamson–Hall plot, the Voigt model and the Warren–Averbach model have been employed. The analytical expressions of the size and strain Fourier coefficients have been extracted from the integral breadth using the so-called “double Voigt” method. The shock power generated in the planetary ball milling equipment employed has been calculated for each synthesis condition and used to plot the size and the strain. The nature (screw or edge) and the density of the dislocations have been determined for each powder under investigation.

Properties of reactively RF magnetron-sputtered chromium nitride coatings

Abstract Hard coatings for wear and corrosion protection based on chromium nitride were deposited by means of a commercial RF magnetron sputtering unit. Their structural, compositional and mechanical properties were compared. All films were reactively sputtered with a mixture of nitrogen and argon from a target of the pure metal. This paper reports the influence of deposition parameters on coating morphology, crystallographical structure and hardness. We found that the surface morphology of the coatings is hardly influenced by the volume fraction of the reactive gas. Also, the hardness (HV 0.05 =2500) is closely linked to the crystalline structure of the deposit. Finally, we have paid special attention to the evolution of the deposition rate and the total pressure as a function of nitrogen content in the vapor phase.

Nanostructured photocatalytic titania coatings formed by suspension plasma spraying

This paper describes formation of titanium dioxide coatings designed for photocatalytic applications, obtained by suspension plasma spraying (SPS), an alternative of the atmospheric plasma spraying (APS) technique in which the material feedstock is a suspension of the material to be sprayed. Two different TiO2 powders were dispersed in distilled water and ethanol and injected in Ar-H2 or Ar-H2-He plasma under atmospheric conditions. Scanning electron microscopy (SEM) and x-ray diffraction (XRD) analyses were performed to study the microstructure of the titania coatings. Photocatalytic efficiency of the elaborated samples was evaluated from the conversion ratio of different air pollutants: nitrogen oxides (NOx) and sulfur dioxide (SO2). The morphology and crystalline structure of the deposits depended mainly on the nature of the solvent (water or alcohol) used in the preparation of the slurries. Dense coatings were obtained starting from aqueous suspensions and porous deposits were elaborated by plasma spraying of a PC105 alcoholic suspension. A significant phase transformation from anatase to rutile occurred when ethanol was used as a solvent. Different photocatalytic performances were observed as a function of the nature of the liquid material feed-stock, the spraying parameters, and the nature of the pollutant.

Comparison of the photocatalytic behavior of TiO2 coatings elaborated by different thermal spraying processes

This paper proposes 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 oxyfuel spraying). Agglomerated spray dried anatase TiO2 powder was used as feedstock material for spraying. Morphology and microstructural characteristics of the coatings were studied mainly by scanning electron microscopy and x-ray diffraction. The photocatalytic behavior of the TiO2-base surfaces was evaluated from the conversion rate of gaseous nitrogen oxides (NOx). It was found that the crystalline structure depended strongly 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 has allowed retention of the original anatase phase and for very reactive TiO2 surfaces to be obtained for the removal of nitrogen oxides.

X-Ray reflectometry study of diamond-like carbon films obtained by plasma-assisted chemical vapor deposition

X-Ray reflectivity is used to determine the electron density profiles normal to the surface of diamond-like carbon (DLC) films prepared by plasma-enhanced chemical vapor deposition (PE-CVD). Average values of the scattering lengths obtained from the specular reflection data and elastic recoil detection analysis (ERDA) hydrogen measurements are used to calculate the average mass density of the films. The density is shown to be strongly dependent on the hydrogen content. This depends on the plasma parameters. Argon diluted methane plasma produces homogeneous DLC films but generally with a lower density than the films prepared from pure or He diluted plasmas. These later plasmas produce films with a high density contrast and higher densities.

Development of photocatalytic active TiO 2 surfaces by thermal spraying of nanopowders

Titanium dioxide is a very useful photocatalyst for the decomposition and diminution of environmental water and air pollutants. In such applications, it can be used as slurry or as immobilized coating obtained by different deposition methods. The studies performed in the last years showed that thermal spraying could be employed to elaborate TiO2 coatings with high performance for the decomposition of organic compounds. This manuscript presents a comparative study on the microstructure and photocatalytic performance of titania coatings obtained by different thermal spray techniques: atmospheric plasma spraying (APS), suspension plasma spraying (SPS), and high-velocity oxygen fuel spray process (HVOF). Different titania powders and suspensions were used to study the influence of the feedstock materials on the coating characteristics. The deposits were mainly characterised by SEM and X-ray diffraction. The photocatalytic performance was evaluated from the removal of nitrogen oxides. The experimental results showed that a drastic reduction of the pollutant concentration was obtained in presence of coatings elaborated by suspension plasma spraying. TiO2 coatings resulting from the spraying of agglomerated powder presentd less efficiency. That was mainly explained by the significant phase transformation from anatase to rutile that occurred in the enthalpic source during the spray processes.

Cryogenic monolithic sapphire-rutile temperature compensated resonator oscillator

We have tested a new temperature-compensated sapphire resonator as frequency determining element for high-stability microwave oscillator. Temperature compensation has been obtained by coating the sapphire resonator with a thin rutile film. A 2-/spl mu/m rutile thickness is sufficient to reach turnover temperature higher than 40 K, and a 2/spl times/10/sup -12/ short-term frequency stability has been obtained.

Coupled effects of bombarding ions energy on the microstructure and stress level of RFPECVD a-C:H films: correlation with Raman spectroscopy

Abstract In this work a-C:H films have been prepared in a capacitively coupled RF-PECVD device (ν=13.56 MHz) from methane as the gas source. By the use of ERDA, IRTF and X-Ray reflectometry techniques, we have first investigated the structural evolutions of the films as a function of the ion energy. In the second part, we have measured mechanical properties (hardness and Youngs modulus) by nanoindentation. Concerning the stress level, according to Stoneys equation, the magnitude of the internal stress has been determined by substrates deflection measurements: this finally leads to a quantification of the adhesion through the calculation of the interfacial fracture energy (Gic). Raman spectroscopy has been used as a probe of both film quality and mechanical properties. The position of the G band is correlated with the sp3 carbon content and the stress level. One observes that the G peak position moves to high frequencies when the ion energy increases, indicating a graphitization of the samples. The relationship linking the Raman wavenumber shift to stress is discussed.

Environmental Applications of the Reactive Titania Coatings Elaborated by Suspension Plasma Spraying

This paper deals with the elaboration of titanium dioxide coatings, designed for photocatalytic applications, obtained by a non-conventional method of deposition: suspension plasma spraying (SPS). SPS is an alternative of the atmospheric plasma spraying (APS) in which the feedstock material is a suspension of the powder to be sprayed. The method consists in injection and atomization of a slurry (suspension of fine particles in a solvent) in an enthalpic source (plasma). TiO2 P25 powder (Degussa AG) was mechanically dispersed in distilled water and ethanol and injected in Ar-H2 or Ar-H2-He plasma under atmospheric conditions. SEM and XRD were performed to study the microstructure and the crystalline phases of the titania coatings. Photocatalytic efficiency of the elaborated samples was evaluated from the conversion rate of nitrogen oxides. 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.

Microstructural Transformations of Al2O3-TiO2 and Al2O3-ZrO2 Powders Induced by High-Energy Ball-Milling

Superior properties of nanostructured Al2O3 based materials, such as higher hardness and fracture toughness, have been evidenced. In order to optimize their manufacturing, the mechanical activation of the starting powders (Al2O3-TiO2 and Al2O3-ZrO2) was studied. In the present work, Al2O3 powders blended with 13wt% and 44wt% of titania or 20wt% and 80wt% of yttria partially stabilized zirconia have been high-energy ball-milled using a planetary mill, P4 (Fritsch) with steel vials and balls. The effect of the milling time and operating parameters, such as shock energy and friction to total energy ratio, on the powder structural and microstructural evolutions has been determined by SEM, XRD and BET. The transformation of the metastable anatase TiO2 phase into the high pressure TiO2 II phase and rutile phase was evidenced, simultaneously to the decrease of the alumina crystallite size, in the Al2O3-TiO2 system. In the Al2O3-ZrO2 system, the transformation of the monoclinic phase and the decrease of the alumina and tetragonal zirconia crystallite size have been observed.