Zircon dissociation in air plasma through a low power transferred arc plasma torch

Thermal plasma dissociation offers a convenient and attractive route to prepare zirconium oxide from zircon mineral. Transferred and non-transferred arc plasma torches have been used to study zircon dissociation. The major thrust has been to accomplish complete dissociation and make the process simpler and cost effective. Technologically, this has been attempted in argon-fired plasma reactors using higher electrical power. The present work reports a cost effective low power transferred arc plasma (TAP) processing method for dissociating zircon by using air as the plasma forming gas. Phase composition and microstructure formation of the dissociated zircon were examined by XRD and SEM with EDX. Experimental results showed that the torch input power and processing time strongly influenced the dissociation percentage as well as the microstructure formation. Further, obtained results revealed that the air plasma medium significantly improved the percentage of zircon dissociation rather than argon plasma medium at 10 and 15 kW power levels. The air plasma gives complete zircon dissociation at 10 kW power with 5 min of processing

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SrFe12O19 coatings, intended as electromagnetic wave absorbers, were produced by atmospheric plasma spraying (APS) using two different kindsof feedstock powders: spray-dried agglomerates of micrometric SrFe12O19 particles (type-A) or spray-dried agglomerates of raw materials (SrCO3,Fe2O3), reactively sintered at 1100 ◦C (type-B).During spraying, type-A agglomerates either remain unmelted, producing porous coating regions where crystalline hexaferrite is retained, orare disrupted into smaller granules which melt completely, resulting in dense coating regions with no crystalline hexaferrite.The sintered type-B agglomerates possess higher cohesive strength and do not fall apart: the finer ones melt completely, whereas, in the largerones, the outer region melts and infiltrates the porous unmelted core which retains crystalline hexaferrite. Dense coatings can therefore be obtainedwhile preserving high amounts of crystalline hexaferrite even inside the dense areas. Such coatings show magnetic properties that are promisingfor electromagnetic wave absorption applications

Development of matte finishes in electrostatic (EFB) and conventional hot dipping (CHDFB) fluidized bed coating process

This study focuses on the correlation between the thermo-rheological properties of a thermosetting powder coating system with its surface structure build-up. Epoxy powder coating systems, which displayed surface matting and surface wrinkling, were examined. Firstly, the evolution of the complex viscosity was correlated with the cure kinetic. Secondly, the structure build-up on the surface of the coatings was investigated with a combined SEM-CLA profilometry analysis at different stages of curing process for both EFB and CHDFB coating processes. Different finishes were found to characterize the films applied by using EFB and CHDFB coating processes as a result of the different way the film is heated by. Finally, a strict relationship of film morphology to the degree of conversion and to the evolution of the complex viscosity was found out for both EFB and CHDFB coating processes. The surface structure is built up after gelation point and continues to evolve after gelation with a full development of the film fine structure. Differences were observed in the surface structure build-up when different curing temperature was used, thereby indicating an influence of minimum viscosity on achievable finishing. These experimental results lead to further advances in a better understanding of the formation of surface topography and morphology of polymeric films. They also provide important indications for the settings of curing parameters in both EFB and CHDFB coating processes as well as for the development of new powder coating formulations. © 2007 Elsevier B.V. All rights reserved

The structure of ZrO2 phases and devetrification processes in a Ca-Zr-Si-O-based glass ceramic: a combined a-XRD and XAS study

The structure of Zr atomic environment in a CaO-ZrO2-SiO2 glass-ceramic has beenstudied combining x-ray absorption spectroscopy (XAS), X-ray diffraction (XRD) andanomalous-XRD (a-XRD) techniques as a function of thermal treatments. The analysisof XRD patterns demonstrates that the devitrification process, as a function ofthermal treatment, proceeds through the partial segregation of Zr-depleted phases(Wollastonite-like) and Zr-rich phases (Zr-oxides). The XAS and a-XRD measurementsat the Zr K edge have been exploited to get a closer insight on the atomicstructure around Zr ions. In the as quenched glass the Zr is 6-fold coordinated to Oxygenatoms in an amorphous environment rich of Ca and Si. Thermal treatment firstly(T=1000 - 1050 oC) determines the partial segregation of Zr in form of oxide whichcrystalline structure is that of tetragonal Zirconia (t-ZrO2). Raising the temperature(T=1100 oC) provokes the formation of ZrO2 crystallites in the monoclinic crystallographicphase (Baddeleyite: m-ZrO2). The analysis of XAS data demonstrates that aconsiderable amount of Zr still remains in an amorphous Calcium-Silicate phase

The effect of ceramic YSZ powder morphology on coating performance for industrial TBCs

The increasing turbine inlet temperatures in modern gas turbines have raised concerns about the corrosion of ceramic thermal barrier coatings (TBCs) caused by molten silicate deposits, commonly referred to as “CMAS” due to their main constituents (CaO-MgO-Al2O3-SiO2). The objective of this study was to investigate the combined influence of powder morphology and chemical composition on the CMAS resistance and thermal cycling resistance of ceramic monolayer and bi-layer coatings created through Atmospheric Plasma Spraying (APS). Three powder morphologies were examined: porous Agglomerated and Sintered (A&S) granules, Hollow Spherical (HOSP) powders, and dense, irregular Fused and Crushed (F&C) particles. Monolayer 7-8YSZ coatings with both porous and dense vertically cracked (DVC) microstructures, and bi-layer coatings consisting of a bottom layer of porous standard 7-8YSZ and a top layer composed of a porous high‑yttrium ZrO2–55 wt% Y2O3 were obtained using all three powder types (A&S, HOSP, or F&C). Furthermore, the bi-layer systems were deposited with different ratios between the individual layer thicknesses and/or different total thickness. FEG-SEM, EDX, and micro-Raman analyses, were conducted to assess the coatings' performance. Nanoindentation high-speed mapping and pillar splitting test were performed to evaluate the mechanical behaviour. The study on 8YSZ monolayers shows that coatings from a F&C feedstock exhibit higher density, reducing the CMAS penetration. However, these coatings demonstrate poorer thermal cycling performance due to increased stiffness and thermal stresses. Coatings from HOSP and A&S powders allow CMAS penetration but offer stress relief pathways, enhancing the coating's ability to withstand thermal stresses. Bi-layer coatings with a 55YSZ top coat show superior CMAS resistance compared to 7-8YSZ monolayer coatings, with limited penetration causing top coat peeling. The thickness ratio between the layers also affects thermal cycling resistance, where a thinner 55YSZ layer extends the TBC lifetime

EFFETTO DELLO SPESSORE SULLA RESISTENZA AD USURA E CORROSIONE DI RIVESTIMENTI WC-COCR DEPOSITATI SU LEGA DI AL TRAMITE TERMOSPRUZZATURA HVOF

Si sono esaminati gli effetti dello spessore e della presenza/assenza di un sottile bond coat in Ni sulla resistenza ad usura e a corrosione di rivestimenti in materiale cermet WC-CoCr, depositati tramite termospruzzatura HVOF su piastre in lega di alluminio AA 6082T6. Riporti con quattro diversi spessori, compresi nell’intervallo 50 ?m – 150 ?m, sono stati prodotti eseguendo, rispettivamente, un totale di 2, 3, 4 e 5 scansioni consecutive della torcia davanti al substrato. All’aumentare del numero di scansioni, la porosità del rivestimento cermet (sia con, sia senza bond coat) diminuisce; il cambiamento più sensibile si verifica fra i riporti depositati con 2 e 3 passaggi della torcia. Per spiegare questo fenomeno, si sono analizzati i meccanismi di deposizione di singole lamelle di WC-CoCr, esaminandole con tecnica Focused Ion Beam (FIB). All’aumento di densità del rivestimento corrispondono un incremento di microdurezza, un miglioramento della resistenza all’usura per strisciamento (misurata mediante test ball-on-disk) ed una maggior protezione del substrato contro la corrosione (valutata mediante spettroscopia di impedenza elettrochimica e monitoraggio del potenziale di libera corrosione). Rispetto a strati anodizzati, prodotti sulle stesse piastre, tutti riporti WC-CoCr (indipendentemente dallo spessore) sono molto più resistenti ad usura ma meno protettivi contro la corrosione del substrato

Targeted Isolation of Antibodies Directed against Major Sites of SIV Env Vulnerability

The simian immunodeficiency virus (SIV) challenge model of lentiviral infection is often used as a model to human immunodeficiency virus type 1 (HIV-1) for studying vaccine mediated and immune correlates of protection. However, knowledge of the structure of the SIV envelope (Env) glycoprotein is limited, as is knowledge of binding specificity, function and potential efficacy of SIV antibody responses. In this study we describe the use of a competitive probe binding sort strategy as well as scaffolded probes for targeted isolation of SIV Env-specific monoclonal antibodies (mAbs). We isolated nearly 70 SIV-specific mAbs directed against major sites of SIV Env vulnerability analogous to broadly neutralizing antibody (bnAb) targets of HIV-1, namely, the CD4 binding site (CD4bs), CD4-induced (CD4i)-site, peptide epitopes in variable loops 1, 2 and 3 (V1, V2, V3) and potentially glycan targets of SIV Env. The range of SIV mAbs isolated includes those exhibiting varying degrees of neutralization breadth and potency as well as others that demonstrated binding but not neutralization. Several SIV mAbs displayed broad and potent neutralization of a diverse panel of 20 SIV viral isolates with some also neutralizing HIV-27312A. This extensive panel of SIV mAbs will facilitate more effective use of the SIV non-human primate (NHP) model for understanding the variables in development of a HIV vaccine or immunotherapy

Mechanical properties of double-layer and graded composite coatings of YSZ obtained by atmospheric plasma spraying

Double-layer and graded composite coatings of yttria-stabilized zirconia were sprayed on metallic substrates by atmospheric plasma spray. The coating architecture was built up by combining two different feedstocks: one micro- and one nanostructured. Microstructural features and mechanical properties (hardness and elastic modulus) of the coatings were determined by FE-SEM microscopy and nanoindentation technique, respectively. Additional adherence and scratch tests were carried out in order to assess the failure mechanisms occurring between the layers comprising the composites. Microstructural inspection of the coatings confirms the two-zone microstructure. This bimodal microstructure which is exclusive of the layer obtained from the nanostructured feedstock negatively affects the mechanical properties of the whole composite. Nanoindentation tests suitably reproduce the evolution of mechanical properties through coatings thickness on the basis of the position and/or amount of nanostructured feedstock used in the depositing layer. Adhesion and scratch tests show the negative effect on the coating adhesion of layer obtained from the nanostructured feedstock when this layer is deposited on the bond coat. Thus, the poor integrity of this layer results in lower normal stresses required to delaminate the coating in the adhesion test as well as minor critical load registered by using the scratch test.This work has been supported by the Spanish Ministry of Science and Innovation (Project MAT2012-38364-C03) and co-funded by ERDF (European Regional Development Funds).Carpio-Cobo, P.; Rayón Encinas, E.; Salvador Moya, MD.; Lusvarghi, L.; Sanchez, E. (2016). Mechanical properties of double-layer and graded composite coatings of YSZ obtained by atmospheric plasma spraying. 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