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One major warning emerging during the first worldwide combat against healthcare-associated infections concerns the key role of the surface in the storage and transfer of the virus. Our study is based on the laser coating of surfaces with an inorganic/organic composite mixture of amorphous calcium phosphate–chitosan–tetracycline that is able to fight against infectious agents, but also capable of preserving its activity for a prolonged time, up to several days. The extended release in simulated fluids of the composite mixture containing the drug (tetracycline) was demonstrated by mass loss and UV–VIS investigations. The drug release profile from our composite coatings proceeds via two stages: an initial burst release (during the first hours), followed by a slower evolution active for the next 72 h, and probably more. Optimized coatings strongly inhibit the growth of tested bacteria (Enterococcus faecalis and Escherichia coli), while the drug incorporation has no impact on the in vitro composite’s cytotoxicity, the coatings proving an excellent biocompatibility sustaining the normal development of MG63 bone-like cells. One may, therefore, consider that the proposed coatings’ composition can open the prospective of a new generation of antimicrobial coatings for implants, but also for nosocomial and other large area contamination prevention.

International audience; This review offers an overview on the latest advances in the powder bed selective laser processing, known as selective laser sintering/melting, of calcium phosphate, silicon carbide, zirconia, alumina, and some of their composites. A number of published studies between 1991 and August 2020 was collected, analyzed and an inclusive state of the art was created for this review. The paper focuses on the process description, feedstock criteria and process parameters and strategy. A comparison is made between direct and indirect powder bed selective laser processing of each ceramic, regarding the present achievements, limitations and solutions. In addition, technical aspects and challenges about how to address these issues are presented.

International audience; Amorphous calcium orthophosphates (ACP) are bioactive compounds presenting high interest as bone substitute. However, the synthesis of such metastable products requires special attention as they can rapidly evolve into a crystalline phase during the elaboration process. The resulting increased stability generally leads to less bioactive reactive materials. Among the various strategies developed to obtain stable form of ACP, the use of spray drying is an effective and reproducible route. Compared to previous works, this study aims to demonstrate for the first time the feasibility of ACP elaboration by spray drying directly from a single solution of selected precursors. Moreover, structuration of the spray-dried powders was determined at different length scales, demonstrating a hierarchical organization from nanometric clusters to particles aggregates. These complementary analyses highlighted a thorough mechanism of particles formation during processing. The effect of the initial composition of the solution was observed, and it was demonstrated that there is a correlation with the purity of the final product that may be modulated. In addition, ACP powders were found to be highly reactive in aqueous medium and their fast transformation into low crystalline apatite suggests a good suitability for biomedical use.

International audience; Hydroxyapatite coatings have been currently used on hip prostheses for their ability to promote faster osseointe- gration and bone growth. Nevertheless, post-operative infections remain a recurring problem. To overcome this issue, doping with antibacterial elements has become a new trend. In this work, hydroxyapatite coatings elab- orated by radio-frequency suspension plasma spraying (rf-SPS) were doped with silver and strontium. Several doping strategies were explored thanks to the versatility offered by SPS compared with conventional spraying. First way: calcium phosphate doped powders were synthesized by coprecipitation and then dispersed into water before plasma spraying; second way: undoped powder was dispersed into aqueous medium in which nitrates or nanoparticles of the dopant(s) were respectively dissolved/dispersed. XRD revealed a high level of crystallinity ratio (ISO 13 779) and hydroxyapatite proportion for most of the coatings, with the presence of Ag/Ag 2 O nanopar- ticles whatever the doping route. SEM-EDS and STEM have demonstrated a more homogeneous distribution of the strontium within the coating made from the doped powder. Adherence of the coatings was estimated via a 3-point bending test, while bacteriological tests with S. aureus and proliferation of mesenchymal stem cells (hMSC) were performed. The results indicated a preferential incorporation of strontium into the secondary phases, showed efficient bactericidal properties, excellent mechanical properties in comparison with an APS reference coating, and no evidence of cytotoxic effect. This opens the way of a new type of coatings with a finer structure and a higher homogeneity through a better control of physicochemical properties using a suspension as the precursor.

International audience; This work focuses on the comparison of Ln-Ni-O coatings (Ln = La, Nd, Pr) deposited by reactive magnetron sputtering using Plasma Emission Monitoring (PEM) which allows high deposition rate. Each layer is deposited by different steps. The optimal regulation setpoint for oxide rare-earth deposition is determined and then the current dissipated on the nickel target is adjusted to obtain the convenient Ln/Ni ratio and to achieve the K2NiF4 structure. After an appropriate annealing treatment, all coatings exhibit crystalline structures, which depend on the Ln/Ni ratio. Due to the instability of Pr2NiO4 structure at intermediate temperatures, the crystallization step of praseodymium nickelate is performed at higher temperature than the other materials. This further thermal treatment implies a more porous structure. Each coating exhibits interesting properties. Electrical and electrochemical characterizations performed on these deposits prove better properties of the praseodymium nickelate coating.

Resume L’impression en 3 dimensions est en plein essor dans le domaine medical. Cette technologie accroit les possibilites de traitement personnalise pour les patients tout en abaissant les couts de fabrication. Dans le cadre des reconstructions de mandibule par lambeau libre de fibula, des societes proposent, a l’heure actuelle, des guides de coupe obtenus par moulage a partir de scanner. Outre les delais de realisation importants i.e. minimum 21 jours, ces guides sont vendus a des couts prohibitifs (2000 a 6000 euros). Conjointement avec le CNRS, des etudiants ingenieurs, une societe biomedicale, les auteurs ont mis au point des guides de coupe et des fantomes de mandibule imprimes en 3 dimensions, livrables en 7 jours et a moindre cout. La nouveaute de ce projet reside dans la rapidite d’elaboration des produits et la reduction importante de leur prix. Les auteurs proposent de decrire dans cette note technique la chaine logistique de realisation des fantomes et des guides de coupe ainsi que les resultats apportes. L’objectif est de permettre dans un avenir proche l’acces a cette technologie pour tous les patients.

International audience; Plasma-spray (PS) is the most common technique used to cover orthopaedic titanium-based implant surfaces with hydroxyapatite (HA - Ca10(PO4)6OH2). The objective of the current work was to explore the influence of the precursor nature and characteristics (mainly powder size, Ca/P ratio, and density) on the morphology and the microstructure of HA coatings, deposited either by conventional atmospheric plasma spray (APS) or by rf-suspension plasma spray (rf-SPS). Two powders with different size distribution, density and shape were sprayed with same operating APS conditions. In parallel two water-based suspensions with distinct particle size and chemistry (Ca/P ratio) were implemented in rf-SPS. The morphology of both APS and rf-SPS coatings observed by SEM exhibits micro and sub-micro sized structures respectively, with similar porosity and thickness. The difference in precursor particle size does not affect the coating structure in rf-SPS, unlike in APS conditions. Superimposition of topography and phases maps performed from profilometry and Raman cartographies showed no direct correlation between the surface profile and composition. But such analysis highlighted the heterogeneity of the phases composing the coating surface, opening the possibility of a better understanding of biological behaviour.

International audience; Dental implant manufacturers are looking for new surfaces to improve osseointegration. It is accepted that rough metallic implant surfaces promote bone mechanical anchoring and biomechanical fixation. In addition, calcium phosphate coatings favor both bone healing and apposition on implants and improve bone bonding properties. Among all the available techniques, the soaking process seems particularly attractive because of its simplicity and ability in producing a versatile bioactive coating at low temperature. The objective of the present study is to improve the titanium implant surface roughness and chemistry by optimizing the surface preparation and the soaking process parameters to produce a bioactive and adherent calcium phosphate coating. Titanium samples were sandblasted with alumina particles and acid etched to obtain a surface with an average roughness between 1.4 and 1.8 μm and micro-porosities created by the acid etching. A high surface wettability was also achieved. Moreover, acid etching favors the removal of alumina particles inlaid in the titanium substrate by sandblasting. Coatings were realized by an alternate soaking process including a centrifugation step to create a phosphate solution thin film on the implant that can afterwards react with the calcium contained in the second bath to form a CaP coating. We showed that this centrifugation step is critical and determines the coating formation, coverage and thickness. A thin covering coating (~ 2 μm) composed of apatite analogous to bone mineral was deposited. The adhesion of coating to the substrate was assessed by a pragmatic and convenient screwing/unscrewing test of the coated implant in an artificial jawbone.

International audience; This work demonstrated the possibility to manufacture dense yttria-stabilized zirconia (YSZ) parts by direct laser beam sintering using a commercial 3D SYSTEMS machine. To achieve this, several requirements of the process itself had to be met. First, an efficient laser-matter interaction had to be achieved. Indeed, a major issue to overcome was the intrinsic nonabsorbance property of the YSZ powder at the Nd:YAG laser wavelength. This issue was solved by adding a small amount of graphite to the YSZ powder that resulted in a simple mechanical blending of the two compounds. The graphite adjunction allowed an increase in the absorbance value from 2% to approximately 60%. The chemical composition of the powder blend and the density and the particle size distribution of the starting material used in this work enabled adequate heat transfers due to the appropriate thermophysical properties. Finally, a set of machine parameters that allows to manufacture parts with a high relative density, good geometrical accuracy, and mechanical strength was experimentally determined. Ultimately, it was found that the direct SLS allows the reproducible manufacture of simple YSZ parts with a relative density of 96.5%

International audience; Three-dimensional (3D) printing is booming in the medical field. This technology increases the possibilities of personalized treatment for patients, while lowering manufacturing costs. To facilitate mandibular reconstruction with fibula free flap, some companies propose cutting guides obtained by CT-guided moulding. However, these guides are prohibitively expensive (€2,000 to €6,000). Based on a partnership with the CNRS, engineering students and a biomedical company, the authors have developed cutting guides and 3D-printed mandible templates, deliverable in 7days and at a lower cost. The novelty of this project is the speed of product development at a significantly lower price. In this technical note, the authors describe the logistic chain of production of mandible templates and cutting guides, as well as the results obtained. The goal is to allow access to this technology to all patients in the near future.

Carbonated Biomimetic Nanocrystalline Apatite (BNAc) coatings are obtained for the first time by Cold Spray. The coatings are characterized by FTIR, Raman, XRD, and SEM and compared to the powders. No significant chemical and structural changes are detected and the nanostructure features of these very reactive BNAc are preserved in the coating. These results and preliminary mechanical assays show that Cold Spray can produce an operational biomimetic coatings offering a high potential for implants functionalization and osseointegration. However, these first results need further studies in order to understand the mechanism of adhesion and the interactions at the coating–substrate interface.

International audience; The manufacture of the last generation metal supported IT-SOFC complete cell by dry surface deposition pro-cesses is really challenging. Atmospheric Plasma Spraying (APS) and Reactive Magnetron Sputtering (RMS) processes are respectively adapted to deposit Ni-YSZ anode and YSZ electrolyte layers. RMS is also used to coat a thin and dense La2NiO4 (LNO) cathode layer. In this work, we have realized a complete cell on metallic support (ITM) produced by PLANSEE SE. The innovative LNO cathode layer was compared with screen-printed LNO layers, with and without RMS bonding layer. Electrochemical and Voltammetry tests were performed on these samples. It reveals lower performances than literature due to the high density of the RMS cathode layer, and too high temperature during sintering step which deteriorate layers manufactured by RMS and metallic substrate. Nevertheless, using LNO bonding layer manufactured by RMS seems to be an interesting way to improve the polarization resistance of the cell.

© 2016 Australian Ceramic Society. The additive manufacturing of bioceramic parts has been investigated since the 1980s. This paper offers an overview of the present achievements in the production of alumina, zirconia and hydroxyapatite parts by means of selective laser sintering/melting of a powder bed or stereolithography. A focus is placed on these specific materials because of their widespread use in the biomedical field. It demonstrates that even though the manufacturing of parts with these processes is possible from pure bioceramics, the use of a binder (or another chemical adjuvant) is required in order to achieve good mechanical properties. Still, improvements in the raw material preparation and in the comprehension of the physical phenomena occurring during the processing remain necessary to be able to prevent the formation of cracks or to be able to control the porosity of the parts.

The chapter discusses the physical–chemical properties of calcium phosphates (Ca-P), among the most used bioactive ceramics. The main calcium phosphate compounds are presented with a brief description of their synthesis methods, their characterization, using different techniques, including chemical analyzes, X-ray diffraction, Fourier transform infrared (FTIR) and Raman spectroscopies, solid-state nuclear magnetic resonance (NMR), scanning and transmission electron microscopies (SEM and TEM). Their thermochemical characteristics are given and the thermal stability and relationships between different Ca-P phases are then described. Their solubility, transformations and hydrolysis, nucleation ability, surface properties and reactivity (ion exchange, adsorption) are presented especially in the case of apatites. The biological response regarding bioactivity, biodegradation, and simulated body fluid (SBF) testing is discussed from the point of view of the Ca-P physical chemistry. Several examples of applications and processing techniques are then proposed as nanoparticles, bulk ceramics, coatings, cements, and composite materials.

International audience; This work focuses on the structural, microstructural, electrical and electrochemical characterization of La–Ni–O coatings deposited by reactive magnetron sputtering under different argon partial pressures. Deposition was driven by Plasma Emission Monitoring system (PEM) which allows high deposition rate. For each pressure, the optimal regulation setpoint for lanthanum oxide deposition is determined and then the current dissipated on the nickel target is adjusted to obtain the convenient La/Ni ratio to achieve the K2NiF4 structure. After an appropriate annealing treatment, coatings crystallize in the desired structure with more or less impurities. Increasing the device's pressure from 0.4 to 4.8Pa produces more porous samples with different microstructures. Then, a coating with porosity gradient was built by using these four different total pressures. Its electrical performances were tested and allowed its utilization as cathode layer in intermediate temperature-solid oxide fuel cell (IT-SOFC). This modified architecture cathode allows better performances (71mW·cm−2) than dense cathode produced by the same technique (51mW·cm−2).

International audience; Hydroxyapatite (HAp) coatings were prepared on Ti6Al4V substrate by electrodeposition method from electrolyte solution containing Ca(NO3)2, NH4H2PO4 and NaNO3. The results show that the HAp coatings were single phase crystals of HAp. Scanning electron microscope (SEM) images present that HAp/Ti6Al4V have flake shapes which arrange to form like-coral agglomerates. In vitro test of the Ti6Al4V and HAp/Ti6Al4V in simulated body fluid (SBF) solution was investigated with different immersion times. pH of SBF solution decreased and the mass of materials increased. SEM images prove the formation of apatite on the surface of Ti6Al4V and HAp/Ti6Al4V. The corrosion current density during immersion time of substrate is always higher than the one of HAp/Ti6Al4V because the deposited HAp can protect well for the substrate.

International audience; The properties and performance of plasma-sprayed thermal barrier coatings (TBCs) are strongly dependent on the microstructural defects, which are affected by starting powder morphology and processing conditions. Of particular interest is the use of hollow powders which not only allow for efficient melting of zirconia ceramics but also produce lower conductivity and more compliant coatings. Typical industrial hollow spray powders have an assortment of densities resulting in masking potential advantages of the hollow morphology. In this study, we have conducted process mapping strategies using a novel uniform shell thickness hollow powder to control the defect microstructure and properties. Correlations among coating properties, microstructure, and processing reveal feasibility to produce highly compliant and low conductivity TBC through a combination of optimized feedstock and processing conditions. The results are presented through the framework of process maps establishing correlations among process, microstructure, and properties and providing opportunities for optimization of TBCs.

Yttria Stabilized Zirconia (YSZ) suspensions were injected in an atmospheric plasma jet using two designs of a home-made two-fluid atomizing nozzle. The sprays of drops were visualized and the behavior of the suspension in the plasma jet was investigated by implementing the Particle Image Velocimetry (PIV) method. The effects of the suspension formulation (surface tension, liquid viscosity, and relative gas-to-liquid mass ratio, GLR) on the distribution and median value of the drop size as well as on the velocity maximum value were evaluated. The interactions between the sprays and the plasma jet were studied. The differences in the behavior of the particle velocity along and radial to the torch axis were pointed out. The validity of PIV measurements was finally demonstrated by the relation established between the in-flight particle velocity and the coating structure.

Several alumina and alumina–zirconia composite coatings were manufactured by suspension plasma spraying (SPS), implementing different operating conditions in order to achieve dense and cohesive structures. Temperatures and velocities of the in flight particles were measured with a commercial diagnostic system (Accuraspray®) at the spray distance as a function of the plasma operating parameters. Temperatures around 2000 °C and velocities as high as 450 m/s were detected. Hence, coatings with high amount of α-alumina phase were produced. The microstructure evolution according to the spray parameters was studied as well as the final tribological properties showing efficient wear resistance.

Thermally sprayed coatings present effective properties strongly different from those of the primary bulk material. In particular, the actual thermal conductivity of Yttria Partially Stabilized Zirconia (YPSZ) coatings is typically twice lower than the thermal conductivity of dense YPSZ. The architecture of the porous network plays a major role on this decrease: thin inter-lamellar cracks act as thermal resistance and contribute to decrease the effective thermal conductivity more efficiently than globular pores. From this situation, an in-house code has been developed since a few years: this code implements a finite difference method to perform calculations directly on micrographs of coating cross-sections obtained by SEM. Each pixel of the intermediate binary picture is interpreted as a cell of integration of the heat conduction equation. A thermal gradient is applied between the top and bottom edges and a system of linear equations is formed and solved, providing the thermal flux flowing through the structure and the corresponding effective thermal conductivity. In the present study, the case of YPSZ coatings before and after thermal treatment was considered. The numerical results are in rather good agreement with experimental data: the thermal treatment tends to close a part of the thinnest pores, thus providing a decrease of the pore level and an increase of the effective thermal conductivity of the produced coatings.

Suspension plasma spray is a promising technique that uses fine particles dispersed in a liquid as feedstock material instead of dry powder as in conventional plasma spraying and has been implemented here to produce layers with appropriate morphologies and microstructures for SOFC applications. This study uses a pressurized gas delivery system to feed the slurry through a homemade two-fluid atomizing nozzle to a conventional plasma torch. The electrodes consist of porous NiO–YSZ as anode and lanthanum nickelate as cathode. The anode and respectively the cathode were deposited onto dense or porous ferritic steel substrates in order to be characterized and optimized. The cell components were examined by scanning electron microscopy (SEM), X-ray diffraction and leakage test. This paper aims at studying the influence of the suspension characteristics (surface tension and viscosity were selected as main parameters), the conditions of injection (nozzle design, gas to liquid ratio, injection angle have been identified as major parameters), the plasma conditions (plasma gas nature and flow rates, spray distance are of major importance) and finally the kinematics on the crystalline phases, the chemical composition (distribution of NiO particles into the layer), the thickness and roughness, the pore ratio and the gas permeability. Then the optimized electrodes have been deposited onto ferritic substrate to perform Open Circuit Voltage and impedance tests at a temperature around 800 °C. This work demonstrated the feasibility for the fabrication of electrodes with interesting performance using suspension plasma spraying technique.

SOFC technology is assumed to have significant potential in energy conversion although many obstacles still prevent its widespread use. Among these, the cost of scaling up existing manufacturing processes for mass production is of major concern. With thermal spray technology, SOFCs can be produced without implementing time consuming sintering steps required in wet ceramic processing. Suspensions Plasma Spraying is one of the promising solutions because it produces thin layer with finer and more adapted microstructures. In the present work, water or alcoholic suspensions of sub-micronic, YSZ/NiO for hydrogen electrode and La2NiO4 for oxygen electrode have been studied to achieve a good dispersion and stability. These optimised suspensions have been injected into the plasma spray system to produce porous coatings of 40 µm thick onto ferritic porous substrates. The evolution of the morphology and crystalline structure of the electrodes have been investigated by SEM/EDS and XRD with the operating parameters.

The growing interest for SOFC leads research towards new materials but also towards processes which could be more effective and less expensive to produce fuel cells. Plasma spraying is one of these interesting processes due to its ability to manufacture the whole cell with the same process. The present study uses suspension plasma spraying (SPS) process which consists in injecting a suspension of sub-micrometer particles dispersed in a liquid into a DC plasma torch. This process allows producing finely structured coatings. In the present study, suspensions containing YSZ particles were atomized into a spray by a bi-fluid atomizer. The droplets were then radially injected into an Ar–H2 plasma jet where they were accelerated and heated. This paper aims at studying the importance of the suspension characteristics on the successive steps leading to the coating formation. Various suspensions based on three different media – methanol, azeotropic mixture of methyl–ethyl–ketone/ethanol and water – were evaluated. The amount of dispersant was adjusted in order to obtain well dispersed and stable suspensions. Plasticizers have been used to tailor the viscosity. Each suspension has thus been characterized versus stability, viscosity and surface tension. The influence of these characteristics on the droplets jet (size distribution and jet shape) issued from the atomizer-injector was assessed. In this purpose, two adimensional numbers (We, Re) were determined for the different atomization conditions and were correlated with the droplets jet. Finally, coatings were realised and characterized in terms of porosity by image analysis of SEM pictures. Powder velocity and temperature were evaluated implementing Accuraspray® and drop size distributions (after passing through the plasma jet) were determined as a function of the injection conditions.

The effect of vacancies on structural properties of the perovskite-type oxide was studied using the full-potential linearized augmented plane wave (FP-LAPW) method, within the density functional theory. In this approach, the generalized gradient approximation was used for the exchange-correlation potential. The ground state properties such as lattice parameter, bulk modulus and inter-atomic distances of cubic Ba 1− x ZrO 3 compounds ( x = 0, 0.125 and 0.25) were calculated. Additionally, using a set of total energy versus volume obtained with the FP-LAPW method, the quasi-harmonic Debye model was applied to determine the thermal properties including temperature dependence of bulk modulus, thermal expansion coefficient, specific heats at constant volume and constant pressure. No experimental data are available and our results are considered as purely predictive.

The ground-state equilibrium properties of cubic Ba 1− x Sr x ZrO 3 compounds ( x = 0, 0.125, 0.25, 0.375 and 0.5) were studied by means of ab initio total energy calculations using the full-potential linearized augmented plane wave (FP-LAPW) method. In this approach, the generalized gradient approximation was used for the exchange-correlation potential. These calculations are the first step in the investigation of thermodynamics of Ba 1− x Sr x ZrO 3 compounds. We found out that compressibility decreases with the Sr concentration according to the ionic radii. The sub-stoichiometry also leads to higher hardness of perovskite compounds. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the isothermal bulk modulus, thermal expansion coefficient, specific heats at constant volume and constant pressure as well as Debye temperature were calculated. No experimental data are available and our results are considered as purely predictive. The major trends show that Ba 1− x Sr x ZrO 3 compounds tend to maintain their hardness with the temperature increases. Furthermore, the substitution of Sr 2+ at Ba 2+ sites in BaZrO 3 has a noticeable influence on the thermal expansion behavior which makes Ba 1− x Sr x ZrO 3 compounds unable to be good candidates for application as thermal barrier coating.

Life and thermal properties of plasma sprayed TBCs – widely used in gas turbine engines – are closely related to the microstructure of the ceramic top coating. Especially, the thermal behaviour of this coating is induced by the void shapes and networks which are in turn determined by both the spraying conditions and the feedstock material. A specific hollow yttria partially stabilised zirconia powder was produced in a one-step process by spray drying and an experimental statistical design study was conducted to investigate the influence of spraying variables (primary and secondary gas flow rates, arc current, spraying distance, spraying angle and traverse speed) on structure and properties of resulting plasma sprayed coatings. The coatings were characterized with respect to deposition efficiency, roughness, porosity and thermal conductivity. A reduction of 25% of the thermal conductivity was achieved by improving the spray and powder parameters. A quantitative characterization of the porous structure using image analysis of polished cross-sections was implemented. The parameters that have relevant influence on the coating porous structure were identified, and their relative importance was determined. An attempt was made to identify morphological criteria of the porous network (coarse/fine porosity ratio, cracks total length, cracks orientation) correlating with the thermal conductivity values.

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 TiO2coatings 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. TiO2coatings 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.

Among processes evaluated to produce some parts of or the whole solid-oxide fuel cell, Suspension Plasma Spraying (SPS) is of prime interest. Aqueous suspensions of yttria partially stabilized zirconia atomized into a spray by an internal-mixing co-axial twin-fluid atomizer were injected into a DC plasma jet. The dispersion and stability of the suspensions were enhanced by adjusting the amount of dispersant (ammonium salt of polyacrylic acid, PAA). A polyvinyl alcohol (PVA) was further added to the suspension to tailor its viscosity. The PVA also improved the dispersion and stability of the suspensions. The atomization of optimized formulations is described implementing Weber and Ohnesorge dimensionless numbers as well as gas-to-liquid mass ratio (ALR) value. Drop size distributions changed from monomodal distributions at low We to multimodal distributions when We number increases. The viscosity of the suspensions has a clear influence on the drop size distribution and suspension spray pattern. The secondary fragmentation of the drops due to the plasma jet was evidenced and the final size of the sheared drops was shown to depend on the characteristics of the suspension. Rather dense zirconia coatings have been prepared, which is a promising way to produce electrolyte.

High-energy ball milling of Al2O3–13 wt% TiO2 and Al2O3–44 wt% TiO2 powders have been studied and more precisely the effect of the addition of a milling agent and the relative speed of the vials. The evolution of the microstructure of the milled powders has been studied by X-ray diffraction and the evolution of the specific surface areas has been determined. The pressure and the temperature inside the vials have been recorded. The milling of the powders induces the transformation of the anatase TiO2 phase into the high-pressure TiO2(II) phase and partly into the rutile TiO2 phase. A decrease in the corundum crystallite size is also evidenced. The addition of PVA as a milling agent in order to avoid severe agglomeration appears to be efficient to enhance the milling effect. The formation of the TiO2(II) phase can be controlled thanks to the vials speed and the milling time in order to obtain quite exclusively this high pressure TiO2 phase that could be interesting to manufacture nanostructured deposits.

The full-potential linearized augmented plane wave (FP-LAPW) method within the density functional theory was used to investigate the structural and electronic properties of Y2Ti2O7 and Cd2Nb2O7. In this approach, the generalized gradient approximation was used for the exchange–correlation potential. We have firstly optimized the internal parameter and used it to calculate the ground state properties such as lattice constant, bulk modulus and its derivative as well as angles and inter-atomic distances. The results were in good agreement with available experimental measurements. We find that Y2Ti2O7 and Cd2Nb2O7 are highly incompressible and thus can be good candidates for hard materials. Calculations of band structure, density of state and charge density were also performed to describe the orbital mixing and the nature of chemical bonding. Both Y2Ti2O7 and Cd2Nb2O7 exhibit indirect band gaps. The mixture of B-d and O-2p states emphasis the covalent nature of the B–O bond that should explain the hardness of pyrochlore compounds. The small distances between oxygen and A/B atoms also lead to higher covalency of the bonds.

DOI: 10.1166/jnn.2015.10329; International audience; The deposition of TiN on stainless steel substrates may improve the stability and compatibility of this material with bone, which may be advantageously exploited for the elaboration of advanced prosthetic devices. In this work, TiN-coated 316LSS (by way of DC magnetron sputtering) was used as a starting material for investigating the electrochemical post-deposition of hydroxyapatite (HAp) which has a composition close to that of bone. Electrodeposition was carried out starting from an aqueous medium containing solubilized Ca(NO3)(2) and NH4H2PO4 in the presence of H2O2. We report the influence of experimental conditions on the morphology of the obtained HAp coating on TiN/316LSS. The effect of applied potential, temperature, H2O2 concentration, pH and duration of reaction were thoroughly discussed on the basis of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Infrared (FTIR) spectroscopy and Energy Dispersive X-ray Spectroscopy (EDX) results. This method appears advantageous for producing HAp-coated implant materials.

International audience; Biomimetic apatites are appealing compounds for the elaboration of bioactive bone-repair scaffolds due to their intrinsic similarity to bone mineral. Bone surgeries are however often heavy procedures, and the infiltration of pathogens may not be totally avoided. To prevent their development, systemic antibiotic prophylaxis is widespread but does not specifically target surgical sites and involves doses not always optimized. A relevant alternative is a preliminary functionalization by an infection-fighting agent. In this work, we investigated from a physicochemical viewpoint the association of a wide-spectrum antibiotic, tetracycline (TC), and a biomimetic nanocrystalline apatite previously characterized. TC adsorption kinetics and isotherm were thoroughly explored. Kinetic data were fitted to various models(pseudo-first-order, pseudo-second-order, general kinetic model of order n, Elovich, double-exponential, and purely diffusive models). The best fit was found for a doubleexponential kinetic model or with a decimal reaction order of 1.4, highlighting a complex process with such TC molecules which do not expose high-affinity end groups for the surface of apatite. The adsorption isotherm was perfectly fitted to the Sips (Langmuir−Freundlich) model, while other models failed to describe it, and the Sips exponent greater than unity (1.08) suggested a joint impact of surface heterogeneity and positive cooperativity between adsorbed molecules. Finally, preliminary insights on TC release from pelletized nanocrystalline apatite, in aqueous medium and neutral pH, were obtained using a recirculation cell, indicating a release profile mainly following a Higuchi-like diffusion-limited rate. This work is intended to shed more light on the interaction between polar molecules not exhibiting high-affinity end groups and biomimetic apatites and is a starting point in view of the elaboration of biomimetic apatite-based bone scaffolds functionalized with polar organic drugs for a local delivery.

Chlorapatite can be considered a potential biomaterial for orthopaedic applications. Its use as plasma-sprayed coating could be of interest considering its thermal properties and particularly its ability to melt without decomposition unlike hydroxyapatite. Chlorapatite (ClA) was synthesized by a high-temperature ion exchange reaction starting from commercial stoichiometric hydroxyapatites (HA). The ClA powder showed similar characteristics as the original industrial HA powder, and was obtained in the monoclinic form. The HA and ClA powders were plasma-sprayed using a low-energy plasma spraying system with identical processing parameters. The coatings were characterized by physical-chemical methods, i.e. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy, including distribution mapping of the main phases detected such as amorphous calcium phosphate (ACP), oxyapatite (OA), and HA or ClA. The unexpected formation of oxyapatite in ClA coatings was assigned to a side reaction with contaminating oxygenated species (O2, H2O). ClA coatings exhibited characteristics different from HA, showing a lower content of oxyapatite and amorphous phase. Although their adhesion strength was found to be lower than that of HA coatings, their application could be an interesting alternative, offering, in particular, a larger range of spraying conditions without formation of massive impurities. This study was carried out under a MNT ERA-Net Project named NANOMED. The authors gratefully thank the Midi-Pyrénées region (MNT ERA Net Midi-Pyrénées Région, NANOMED2 project) and the Institute National Polytechnique de Toulouse (BQR INPT 2011, BIOREVE project) for supporting this research work, especially the financial support for research carried out in the CIRIMAT and the LGP laboratories (France), and the Basque government and Tratamientos Superficiales Iontech, S.A. for their financial and technical support under the IG-2007/0000381 grant for the development of the LEPS device and deposition of the coatings carried out in Inasmet-Tecnalia. The French industrial collaborators (TEKNIMED SA and 2PS SA) were financed by the OSEO programs.

The elaboration of the last generation of metal supported IT-SOFCs by physical surface deposition processes is really challenging. Atmospheric Plasma Spraying (APS) process appears to be well adapted to build the porous anode layer [1] whereas Reactive Magnetron Sputtering (RMS) technique is suitable to deposit thin and dense layer. In the present work, we have deposited a Ni-YSZ anode by APS on porous metallic supports (ITM) produced by PLANSEE SE. Then, a thin YSZ electrolyte film was applied by RMS. Details about the elaboration of the half cell could be found in a previous work [2]. Various strategies have been followed to deposit the cathode layer on top of the previously deposited anode and electrolyte coatings. The Mixed Ionic and Electronic Conductor K2NiF4 structured material presents interesting electrocatalytic properties [3] allowing its utilization as cathode layer. Recent studies deal with the use of thin layers as cathodes in IT-SOFCs [4]. Therefore, RMS process was also evaluated to deposit a thin La2NiO4 layer (LNO) according to already optimized operating conditions [5]. In order to compare the efficiency of this dense layer as an individual cathode or a bonding cathode layer, the complete IT-SOFC building was elaborated by replacing and/or adding a screen-printed La2NiO4 coating (SP LNO). This layer was developed and optimized in ICMCB laboratory and has shown interesting performances in LNO/GDC/LNO half cells [6]. GDC diffusion barrier layers were deposited by RMS in order to limit the deleterious interaction between active layers in use. Different cells with RMS LNO, SP LNO, and RMS LNO + SP LNO were produced and tested in a complete cell bench at 973 K. Impedance Spectroscopy and Voltametry measurements were performed on these samples to assess their electrochemical characteristics and performances. The electrochemical resistances of these cells are too high and their performances are still lower than the literature ones. Analyses of the samples after the electrochemical tests permit to identify the density of the RMS LNO layer as the limiting factor lowering the cathodic electrochemical reaction. The sintering step performed on complete cells with SP LNO deteriorates the layers deposited by RMS as well as the metallic support explaining these performances. Nevertheless, using LNO bonding layer manufactured by RMS seems to be an interesting way to improve the polarization resistance of the cell. References [1] D. Stöver, D. Hatiramani, R. Vaβen, R. Damani, Surface and Coatings Technology 201 (2006) 2002-2005. [2] J. Fondard, P. Bertrand, A. Billard, S. Skrabs, Th. Franco, G. Bertrand, P. Briois, Electrochemical Society Transactions 57 (2013) 673-682. [3] E. Boehm, J.-M.Bassat, P.Dordor, F. Mauvy, J-C.Grenier, Ph. Stevens, Solid State Ionics 176 (2005) 2717 – 2725. [4] I. Garbayo, V; Esposito, S. Sanna, A. Morata, D. Pla, L. Fonseca, N. Sabaté, A. Taracon, Journal of Power Sources 248 (2014) 1042-1049. [5] J. Fondard, A. Billard, G. Bertrand, P. Briois, Solid State Ionics 265 (2014) 73-79. [6] B. Philippeau, F. Mauvy, C. Mazataud, S. Fourcade, J-C. Grenier, Solid State Ionics 249-250 (2013) 17-25.

To achieve solid oxide fuel cells (SOFC) at reduced costs, the atmospheric plasma spray (APS) process could be an attractive technique. However, to make dense and thin layers as needed for electrolytes, a suspension is preferably implemented as a feedstock material instead of a conventional powder. Suspensions of yttria-stabilized zirconia particles in methanol have been prepared with various solid loadings and states of dispersion. An external injection system was used to ensure the atomization and radial injection of the suspension into the Ar-H2 plasma under atmospheric conditions. The coatings morphologies were characterized by scanning electron microscopy, and their porosity was evaluated by the Archimedes method. Differences in the microstructure of the deposits were observed depending on the APS operating conditions. Special attention has been dedicated to assess the influence of the suspension as well as the injection on the layer morphology. For this purpose, the atomization has been investigated and efforts have been made to understand relationships among suspension properties, atomization, and coating microstructure.

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.

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.

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), an alternative of the atmospheric plasma spraying (APS) in which the material feedstock is a suspension of the material powder to be sprayed. TiO 2 P25 powder (Degussa AG) mechanically dispersed in distilled water and/or ethanol was injected in argon–hydrogen and argon–hydrogen–helium plasma under atmospheric conditions. Scanning electron microscopy and X-ray diffraction were performed to study the morphology and the crystalline phases of the titania coatings. Surface features were investigated by Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS). Photocatalytic efficiency of the elaborated samples was tested in an environmental test chamber set-up and evaluated from the conversion rate of nitrogen oxides. The results showed that the coating obtained from the injection of an alcoholic suspension contained 23% of anatase ratio and ensured a very low photocatalytic decomposition of nitrogen oxides. In contrast, the injection of an aqueous suspension into the plasma permitted to obtain deposits where the anatase phase and the crystallites size were preserved. Also, a conversion rate of the pollutants of about 40%, slightly better compared to that of the initial P25 powder (around 32%) was noticed. This slightly higher efficiency was correlated with a cleaning of the particles surfaces when crossing the plasma and a higher hydroxylation of the coating surface.

Titanium dioxide is one of the most important photocatalysts that allows the environmental purification of various toxic organic compounds in water and removal of harmful air pollutants. In this paper, two techniques of plasma spraying – plasma spraying from an agglomerated nanopowder and liquid suspension plasma spraying – were used to produce thin deposits. The microstructure of coatings was characterized using scanning electron microscopy and X-ray diffraction. The photocatalytic properties of the coatings were evaluated by the decomposition test of nitrogen oxides and compared with the efficiency of the initial agglomerated nanopowder and that of the Degussa P25 powder. Noticeable different behaviours in the photocatalytic tests were observed for coatings performed either from conventional or liquid plasma spraying. The TiO2 deposits realized by spraying of the liquid suspension exhibited higher photocatalytic efficiency. It is found that the plasma spraying of a slurry is an effective method to retain the original anatase phase and prevent the increase of the crystallite size. This new method of modified spraying is proved to be a promising technique to elaborate photocatalytic coatings for the removal of nitrogen oxide pollutants.

This paper deals with the study of the photocatalytic behaviours of TiO2 and TiO2–10 wt.% Al coatings elaborated by high-velocity oxygen fuel (HVOF) spraying using spray-dried nanosized feedstock powders. In the HVOF 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. Scanning electron microscopy and X-ray diffraction were employed to characterize the microstructure and the crystalline structure of the TiO2-based coatings. The photocatalytic activities were evaluated by the nitrogen oxides removal and compared with that of the initial powders. It was found that the amount of anatase in the coatings depends on the nature of the powder and also on the type of injection method. The TiO2 coatings, as well as, the TiO2–Al coatings elaborated using the external powder injection presented a better photocatalytic activity (the nitrogen oxides conversion rates were about 25–42% for NO and 14–18% for NOx) than those obtained by the conventional HVOF process (

A study has been performed on both the spray drying of ceramic slurries to determine how the characteristics of the spray dried powder can be affected by the process parameters and the sintering of these agglomerated powders. Two materials have been investigated: yttria partially stabilized ziconia (PSZ) and zirconium silicate. Indeed spray drying enables the fabrication of powder by aggregation of different small particles using an appropriate organic binder. The rapid heat and mass transfer which occurs during drying combined with the presence of various slurry compounds result in dried granules having a large variety of shapes, from uniform solid elongated, pancake, donut-shaped, needlelike or hollow granules. First experiments have been focused on the slurry parameters: dispersant amount, binder type and pH. The colloidal stability of aqueous ceramic suspensions as a function of poly(acrylic) acid content, pH and binder nature has been investigated. The addition of a binder may modify the state of dispersion. Thanks to sedimentation tests, stable (dispersed) and unstable (flocculated) suspensions were defined. Then, dried granules have been produced by means of a single droplet drying method. Individual slurry droplets were suspended using a hypodermic syringe in a stream of heated air. The aim was to assess the effect of the state of dispersion and sedimentation stability of the slurry on the drying of a single droplet. It has been shown that granules prepared from a dispersed slurry (low Ratio Sediment Height—RSH 60% for PSZ) result in solid granules. The sedimentation volume, which represents the state of dispersion of the suspension, is the major factor controlling the droplet drying mechanism. According to the former results, powders have been elaborated by the spray drying process using several slurries formulations. Image analyses have been performed on the granules to determine their morphologies. The shape of the agglomerated powder was mostly spherical and hollow. These results confirmed the morphologies predictions of the drying test. Finally, the evolution of the morphology of the PSZ spray dried hollow powder after sintering in an oxyacetylene flame or an atmospheric furnace was investigated. When the powder is sintered in a furnace, low shrinkage and approximately no shape variations were noticed, whereas using an oxyacetylene flame tends to densify the powder.

TiO2 and TiO2–Al composite 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 using relatively low plasma power were composed of two distinct microstructures of well defined lamellar structure, similar to microstructure of conventional plasma sprayed coatings generated by fully melted particles, and embedded nano or sub-micron particles generated by 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 TiO2 increased the spraying efficiency, and also, improved mechanical properties such as microhardness and wear resistance.

The characteristics and consequently the properties of ceramic coatings performed using plasma spraying means depend not only on the operating conditions but also on the powder feedstock. Oxide powders are commonly prepared in one stage or in a combination of stages of fusing, crushing, agglomerating and sintering. The spray drying process (which corresponds to the agglomerating route) is a technique in which small constituent particles dispersed in water (which is called slurry) are sprayed in hot air and granulated thanks to a binder (latex or PVA). Spray drying is carried out for a variety of reasons, two major motivations being the production of composite and shape controlled powders for thermal spray applications. The aim of the present work was to establish a correlation between the slurry formulation and the characteristics of the spray dried granules for two oxide ceramics: Al 2 O 3 and Y 2 O 3 –ZrO 2 . Detailed studies on the dispersion and stability of the slurries were performed using sedimentation tests, electrophoretic mobility measurements as well as adsorption isotherms experiments. Then, a drying experimental test based on the drying of a suspended droplet was developed to assess the drying mechanisms, identify the correlation between the slurry characteristics and the morphology of the dried granules and finally to predict the shapes of the spray-dried powders. It was shown that there is a qualitative relation between the sedimentation behaviour (as measured by the sediment ratio) and the granule shape (solid or hollow) and a quantitative relation between the thickness of the shell (for hollow granule) and the state of dispersion and the nature of the binder used. Finally, several powder batches were prepared in the spray-dryer which confirm the reliability of the drying simulation test.

We studied the removal of nitrogen oxides pollutants via TiO2 Degussa P25 powder by photocatalysis. Parameters such as mass of catalyst, geometric irradiated surface, catalyst morphology, and thermal treatment were tested to explain the photocatalytic concentration decrease of nitrogen oxides. According to our working conditions, the conversion rates increased until an optimal value of the TiO2 weight, 35% of NO concentration and around 20% of NOx, was decomposed by the photocatalysis. The NOx removal increased proportionally with the irradiated geometric surface. The structural transformation of anatase to rutile performed by thermal treatment involved the decrease of the photocatalytic activity.

An artificial neural network (ANN) was built to analyze the decrease of nitrogen oxides relative to TiO 2 powder photocatalytic efficiency. Experimental sets were considered to train and test ANN where it was possible to identify an optimized structure representing the correlations between experimental variables and NO and NO x efficiencies. Predicted results permitted to point out the role of exposed surface and powder mass.

A study has been performed to determine how the characteristics of spray-dried granules prepared from aqueous yttria doped zirconia slurries can be affected by the spray-drying process parameters: dispersant amount, pH and binder type. First, the colloidal stability of aqueous zirconia suspensions as a function of polyacrylic acid content, pH and binder nature has been investigated in order to establish a stability map. The concentration of dispersant required to stabilise the zirconia suspensions decreases with increasing pH (for instance Γmax=0.93 mg m−2 at pH 4 and 0.1 mg m−2 at pH 10). The addition of a binder may modify the state of dispersion. The stability map makes it possible to define regions of stable (dispersed) and unstable (flocculated) suspensions. Then, dried granules have been produced by means of a single droplet drying method. Granules prepared from a dispersed slurry (low Ratio Sediment Height—RSH 62%) result in full granules. The sedimentation volume, which represents the state of dispersion of the suspension, is the major factor controlling the droplet drying mechanism.