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Environmental barrier coatings are necessary to protect fibre reinforced ceramics from high recession rates in fast and hot water vapor-containing gases as they typically are found in the hot gas sections of gas turbines. A standard material to protect SiC/SiC composites is atmospherically plasma sprayed (APS) Yb2Si2O7. For this material, it is difficult to obtain at reasonable substrate temperatures both low porosity and high crystallinity levels during APS. In this paper results of coatings prepared by a so-called high velocity APS process and also more conventional processes are presented. All coatings have been prepared by a single layer deposition method which avoids inter passage porosity bands. Furthermore, the samples were heat-treated in air at 1300 °C for 100 h and the influence of the topcoat density on the growth of the silica scale on the used silicon bond coat was studied.

International audience; Silicon carbide (SiC) fiber reinforced SiC ceramic matrix composites (CMCs) are envisaged as structural material for hightemperature parts in next generation aero-engines. A lower density and a higher thermal stability make such composite very attractive for industrial applications but there is a need for a protective coating to prevent the chemical degradation under service conditions. Therefore, Environmental Barrier Coating (EBC) systems consisting of a silicon bond coat and a rare-earth silicate top coat layer deposited by thermal spraying are envisaged and already successfully tested in gas turbine engines. In this work, two different Si/Yb2Si2O7 EBC samples were prepared by plasma spraying involving APS and High-Velocity APS respectively, each exhibiting a different deposition temperature. The non-contacting LASAT method (Laser Shock Adhesion Test) was implemented in order to estimate the potential of this laser shock method and its capability to support the development of optimized spraying parameters leading to enhanced interfacial properties. The LASAT method was previously developed on metal/ceramic systems for thermal barrier coatings (EB-PVD, APS) and also for hydroxyapatite coatings for biomedical applications. This first attempt on SiC/SiC composite substrate coated with an EBC by plasma spray was successful and revealed that the weakest region was located in the silicon layer near the ceramic top-coat. Further observation of damaged regions after laser shock confirmed that the debonding threshold that corresponding to the minimum of laser energy needed to create an interfacial crack was much higher for the APS coating deposited at a higher temperature. Further work is on progress to confirm the role of the deposition temperature on the resulting interface strength and also to address the influence of the composite thickness on the shockwave propagation.

From the literature, it is known that due to their glass formation tendency, it is not possible to deposit fully-crystalline silicate coatings when the conventional atmospheric plasma spraying (APS) process is employed. In APS, rapid quenching of the sprayed material on the substrate facilitates the amorphous deposit formation, which shrinks when exposed to heat and forms pores and/or cracks. This paper explores the feasibility of using a high-velocity oxygen-fuel (HVOF) process for the cost-effective fabrication of dense, stoichiometric, and crystalline Yb2Si2O7 environmental barrier coatings. We report our findings on the HVOF process optimization and its resultant influence on the microstructure development and crystallinity of the Yb2Si2O7 coatings. The results reveal that partially crystalline, dense, and vertical crack-free EBCs can be produced by the HVOF technique. However, the furnace thermal cycling results revealed that the bonding of the Yb2Si2O7 layer to the Silicon bond coat needs to be improved

Bu çalışmada, ilk olarak 5-amino-4-arilazo-3-metil-1-fenilpirazol türevleri sentezlenmiştir. Elde edilen bu 5-amino-4-arilazo-3-metil-1-fenilpirazol türevleridaha sonra diazolanarak 5-hidroksi-3-metil-1H-pirazol ve 5-hidroksi-3-metil-1-fenilpirazol bileşiklerine kenetlenmiş ve yeni pirazol türevi dispers disazoboyarmaddeleri elde edilmiştir. Sentezlenen bu iki seri boyarmadde element analizi,UV, FT-IR ve 1H-NMR gibi spektral yöntemlerle karakterize edilmiş ve pH, çözücüdeğişimi, elektron alıcı ve elektron verici grupların o-, m- ve p- köşelerinde bağlıolmasının bu bileşiklerin absorpsiyon yeteneklerini nasıl etkilediği incelenmiştir.Sentezlenen bu boyarmaddelerin tekstilde kullanımını değerlendirmek üzerePoliamid 6.6 (P.A. 6.6), Polyester (PES) ve Polilaktikasit (PLA) kumaşlar tüm eldeedilen boyarmaddeler ile boyanmış ve ISO standartlarına göre haslıklarıdeğerlendirilmiştir. In this study, mainly 5-amino-4-arylazo-3-methyl-1-phenylpyrazolederivatives were synthesized. These obtained 5-amino-4-arylazo-3-methyl-1-phenylpyrazole derivatives then diazotized and coupled with 5-hydroxy-3-methyl-1H-pyrazole and 5-hydroxy-3-methyl-1-phenylpyrazole and eventually novelpyrazole derivative disperse disazo dyes were synthesized. These compounds werecharacterized by UV-vis, FT-IR, 1H-NMR spectroscopic techniques and elementalanalysis. The effect of varying pH, and solvent upon the absorption ability ofpyrazole substituted with electron-donating and electron-withdrawing groups at theiro-, m-, p- position was examined.To evaluate the use of these dyes in textile, Polyamide 6.6 (P.A. 6.6),Poliester (PES) and Polylacticacid (PLA) fabrics were dyed with all of thesynthesized dyes. Fastness properties were evaluated according to ISO standards. 253

Thermal barrier coating (TBC) research and development is driven by the desirability of further increasing the maximum inlet temperature in a gas turbine engine. A number of new top coat ceramic materials have been proposed during the last decades due to limited temperature capability (1200 °C) of the state-of-the-art yttria-stabilized zirconia (7 wt. %Y$_{2}$O$_{3}$-ZrO$_{2}$, YSZ) at long term operation. Zirconate pyrochlores of the large lanthanides((Gd $\rightarrow$ La)$_{2}$Zr$_{2}$O$_{7}$) have been particularly attractive due to their higher temperature phase stability than that of the YSZ. Nonetheless, the issues related with the implementation of pyrochlores such as low fracture toughness and formation of deleterious interphases with thermally grown oxide (TGO, Al$_{2}$O$_{3}$) were reported. The implication was the requirement of an interlayer between the pyrochlores and TGO, which introduced double-layer systems to the TBC literature. Furthermore, processability issues of pyrochlores associated with the different evaporation rates of lanthanide oxides and zirconia resulting in unfavorable composition variations in the coatings were addressed indifferent studies. After all, although the material properties are available, there is a paucity of data in the literature concerning the properties of the coatings made of pyrochlores. From the processability point of view the most reported pyrochlore is La$_{2}$Zr$_{2}$O$_{7}$. Hence, the goal of this research was to investigate plasma-sprayed Gd$_{2}$Zr$_{2}$O$_{7}$ (GZO) coatings and YSZ/GZO double-layer TBC systems. Three main topics were examined based on processing, performance and properties: (i) the plasma spray processing of the GZO and its impact on the microstructural and compositional properties of the GZO coatings; (ii) the cycling lifetime of the YSZ/GZO double-layer systems under thermal gradient at a surface temperature of 1400 °C; (iii) the properties of the GZO and YSZ coatings such as thermal conductivity, coefficient of thermal expansion as well as time and temperature-dependent elastic and creep deformations. Thermal cycling results displayed that the double-layer YSZ/GZO TBC concept is able to provide signicant lifetime improvement at 1400 °C surface temperature compared to the standard YSZ. The investigations on the chemical composition of the as-sprayed GZO revealed that no signicant gadolinia evaporation, which would compromise the performance of the coating, takes place in the examined spray current range (300 A-525 A). The detailed examination of microstructural properties of the as-sprayed GZO highlighted the importance of the process parameters for achieving the desired porosity features assisting superior lifetime performances. A signicant insight was gained intothe elastic and creep deformation of the plasma-sprayed YSZ and GZO coatings which play a critical role on the development of advanced TBCs. The overarching conclusion of this work is that the GZO has the potential to increase the temperature capability of gasturbines, if it is applied in double-layer TBC systems and if its microstructure is tailoredby adapted processing.

In this study, 8 novel pyrazole disperse dyes which were synthesized in our previous work [1] were applied to polyethylene terephthalate (PET), poly (lactic acid) (PLA) and polyamide 6.6 (PA 6.6) fiber fabrics and their colorimetric and fastness properties were evaluated. The measured a*, b* and hue angle (ho) values of all dyed fabrics exhibited yellow, orange and red colour shades. Quite high colour strength values (K/S) were measured particularly for dyes containing substitute groups; p-OCH3 and o-OCH3. Shade changes of all fabrics after standard washing and sublimation tests were in the commercially adequate range. All dyed PET, PLA and PA 6.6 fabrics exhibited commercially acceptable fastness staining performances with very good to excellent levels. Synthesized novel disperse dyestuffs led to moderate to high light fastness levels particularly in the case of PLA and PET fabrics.