Electrophoretic deposition of aramid nanofibers and carbon nanomaterials on carbon fibers

Please click Additional Files below to see the full abstract

CMAS interaction with yttrium based systems: Towards a promising solution?

Anti-CMAS coatings are designed to protect thermal barrier coatings against degradations due to CMAS infiltration. They are dedicated to react as fast as possible with CMAS compounds in order to generate a new phase that will not let the CMAS infiltration going on. In addition to the fast kinetics, the preparation of large quantities of phases with as less as anti-CMAS material as possible is sought as well as the obtaining of a dense and impermeable phase. Reference anti-CMAS material is gadolinium zirconate, it has been demonstrated as efficient to block CMAS infiltration. The efficiency of yttria for the same application has been studied by previous works at the CIRIMAT laboratory [1]. The starting point of this work was first, to make a comparative study of the anti-CMAS properties of gadolinium zirconate and yttria based anti-CMAS compositions and secondly, to discuss on the behaviour of a mixed composition i.e. yttrium zirconate. This insight on the mechanism of interactions of CMAS with the yttrium based systems and gadolinium reference is obtained at the light of a large number of interactions experiments and characterizations. Interaction durations between 1h and 100h were investigated, with either 50/50 or 80/20 mass ratio of CMAS/anti-CMAS. Different temperatures of interaction between 1200°C to 1300°C were also scanned. The phases in presence were systematically characterized by XRD, SEM, EDX and Castaing microprobe local analyses and cartographies (Figure 1a)). In particular, the proportion and composition of phases are detailed as a function of the interaction time (Figure 1b)) for each anti-CMAS-CMAS interaction system. From these experiments, the mechanisms of interaction between CMAS and Y2O3, Y2Zr2O7 and Gd2Zr2O7 are evidenced. Whereas Y2O3 interaction leads to the higher proportion of reaction products, the products impermeability is also superior for this composition. The depth of infiltration of CMAS into a dense pellet anti-CMAS material for a given time is longer for Y2Zr2O7 as compared to the two others. However Y2Zr2O7 benefit is due to a higher Ca2+ trapping capability with the formation of Ca4Y6 like phase instead of Ca2Y8 for Y2O3 (Figure 1c)). In this respect, yttrium zirconate demonstrates a synergetic effect as compared to Y2O3 and Gd2Zr2O7. The origin of this synergy is interpreted as coming from the presence of both zirconium and yttrium. A large part of the discussion is based on the study of powders interactions, an insight into the interactions of CMAS with anti-CMAS pellets of the different compositions will also be presented and discussed. Fundamental and applicative aspects will be covered. Please click Additional Files below to see the full abstract

Nucleation and growth mechanisms of trivalent chromium conversion coatings on 2024-T3 aluminium alloy

Nucleation and growth mechanisms of trivalent chromium conversion coatings on 2024 aluminium alloy (AA 2024) were studied. Nucleation of 25 nm diameter nodules was observed on the ridges of the scalloped structure of degreased and desmutted AA 2024 after very short time of conversion treatment corresponding to the formation of a 12 nm thick precursor layer. Then, the composition of this layer evolved and concomitantly a chromium and zirconium outer layer deposited on top of it. Rather long-lasting anticorrosive properties were measured even for conversion coatings formed after short exposure to the conversion bath, except for the precursor layer

Lithium conducting solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 obtained via solution chemistry

NaSICON-type lithium conductor Li1.3Al0.3Ti1.7(PO4)3 (LATP) is synthesized with controlled grain size and composition using solution chemistry. After thermal treatment at 850 C, sub-micronic crystallized powders with high purity are obtained. They are converted into ceramic through Spark Plasma Sintering at 850–1000 C. By varying the processing parameters, pellet with conductivities up to 1.6 * 10−4 S/cm with density of 97% of the theoretical density have been obtained. XRD, FEG-SEM, ac-impedance and Vickers indentation were used to characterize the products. The influence of sintering parameters on pellet composition, microstructure and conductivity is discussed in addition to the analysis of the mechanical behavior of the grains interfaces

Synthesis of yttria by aqueous sol-gel route to develop anti-CMAS coatings for the protection of EBPVD thermal barriers

Anti-CMAS yttria coatings have been prepared by sol-gel routes. Yttria powders with controlled morphology are prepared via auto-combustion of yttrium precursors in a polymerized matrix. The influence of key parameters of the water-based sols is assessed. Indeed, the pH of the initial sol and the temperature of thermal treatment play a major role in the morphology and grain size of yttria powders. To prevent infiltration of CMAS, yttria powders are proposed to be synthesized at pH=1 of the aqueous sol, with drying of the sol and heating at 900 °C. After optimization of the synthesis and deposition conditions via sol-gel route, yttria-based coatings with high specific surface area are obtained. They promote the interaction with melt CMAS and consequently limit the degradation of the thermal barrier coatings situated underneath. It was proved that anti-CMAS yttria coating is effective against the infiltration of CMAS at 1250 °C for 15 min and even 1 h

Dense on Porous Solid LATP Electrolyte System: Preparation and Conductivity Measurement

A dense membrane of lithium aluminum titanium phosphate Li1+xAlxTi2-x(PO4)3, x=0.3 (LATP) is deposited on a porous LATP substrate via wet chemistry. In the polymerized complex process, phosphate precursors with different active groups and steric hindrance are selected to tune precursor’s reactivity. Rheological studies and microstructural observations lead to the selection of an LATP powder slurry charged with lithium, aluminum, titanium, and phosphate ion precursors. The optimized formulation is impregnated into a porous LATP substrate. After thermal treatment, dense LATP membranes on top of a porous LATP substrate are obtained with conductivities as high as 3 x 10-4 S/cm for the dense part, the porous part acting as a mechanical support. An original Van der Pauw impedance setup is validated for the measurement of the ionic conductivity of such dense/ porous systems

Synthesis of yttria by aqueous sol-gel route to develop anti-CMAS coatings for the protection of EBPVD thermal barriers

Anti-CMAS yttria coatings have been prepared by sol-gel routes. Yttria powders with controlled morphology are prepared via auto-combustion of yttrium precursors in a polymerized matrix. The influence of key parameters of the water-based sols is assessed. Indeed, the pH of the initial sol and the temperature of thermal treatment play a major role in the morphology and grain size of yttria powders. To prevent infiltration of CMAS, yttria powders are proposed to be synthesized at pH=1 of the aqueous sol, with drying of the sol and heating at 900 °C. After optimization of the synthesis and deposition conditions via sol-gel route, yttria-based coatings with high specific surface area are obtained. They promote the interaction with melt CMAS and consequently limit the degradation of the thermal barrier coatings situated underneath. It was proved that anti-CMAS yttria coating is effective against the infiltration of CMAS at 1250 °C for 15 min and even 1 h

Advances in the deposition of ceramics by soft chemistry process : example of rare- earth silicate coatings

The dip-coating process consists in immersing a sample to be coated in the liquid medium and then removing it at a controlled speed in order to obtain a film of regular thickness, as shown in Figure 1a). Dip-coating technique is now used in many industrial fields (biomedical, transportation, optics…). It is a very simple, and easy process to implement for the deposition and shaping of different natures of coatings (ceramic, metallic and polymer). In the case of ceramic coatings, after the dip-coating operation, the layers undergo a sintering post-treatment leading to the consolidation and/or the densification of the deposit. The corresponding mechanisms need a rigorous control of many parameters. The parameters involved in the dip-coating process are related to the medium and to the process. Concerning the medium, the dispersion medium nature, the particles concentration, viscosity, and stability are the main ones. The stability of the suspension is a first-order parameter and a preliminary formulation work has been carried out to cope with it. Moreover, parameters relative to the fabrication process such as the number of layers and the thermal profile (intermediary and final temperatures), will also be key factors to be taken into account in the formation of homogeneous and reproducible coatings by dip-coating.This work highlights the influence of these various parameters in the case of rare earth silicates based coatings. The various experiments were carried out in correlation to the coatings quality and microstructure. Homogeneous and conformal ceramic coatings of few tens of micrometers thick, as shown in Figure 1b), were obtained. A multi-layers deposit in a sol loaded at 40% mass generally allows to reach the desired thickness. With these experiments relationship between dip-coating parameters and coatings microstructure and morphology can be established. Please click Additional Files below to see the full abstract

Comparative analysis of the anticorrosive properties of trivalent chromium conversion coatings formed on 2024-T3 and 2024-T351 aluminium alloys

The anticorrosive properties of the trivalent chromium process (TCP) coatings were studied for a 2024 aluminium alloy (AA2024) in both T3 and T351 metallurgical states. Better corrosion resistance was measured for the TCP coated AA2024-T3 compared to AA2024-T351, which was clearly related to the surface copper coverage measured after the pre-treatments for the different samples. The differences were explained considering the reactivity of both the S-phase coarse intermetallics (IMCs) and intergranular Cu-rich precipitates during deoxidation.Large S-phase IMCs and numerous intergranular Cu-rich precipitates constituted critical metallurgical parameters for the anticorrosive properties of the TCP coating

Electrochromic single and two-core viologen derivatives and optical articles containing them

The present invention relates to a group of novel electrochromic materials. More specifically, it relates to electrochromic materials based on either single or two-core viologen systems and the use of these viologen systems as a variable transmittance medium for the manufacture of an optical article, such as an ophthalmic lens