In the present study, tungsten carbide‐cobalt was coated on the austenitic stainless steel using high velocity oxy‐fuel spraying. The as‐deposited coatings were heat treated at 750 °C in air and ...argon gas environments. Structural characteristics of these coatings were studied using x‐ray diffraction and Raman spectrum analysis. Further, the microhardness of the polished coated samples was also evaluated. The hardness of the coatings was significantly improved after heat treatment in air and argon gas environment. However, the highest hardness was observed with the coatings treated in argon gas environment. The formation of oxide phases such as tungsten trioxide and cobalt tungstate was observed after heat treatment in the air environment, whereas under the argon environment, no oxide phases were observed.
Tungsten carbide‐cobalt coating was prepared using high velocity oxy‐fuel process and the effect of heat treatment environment on the structural characteristics and microhardness was investigated. Oxidation of the coating under air environment was observed to be responsible for the decreased microhardness as compared with the coating treated under the argon environment.
Radioactive cobalt is one of the most abundant radionuclides in radioactive waste. This study investigated the removal of radioactive cobalt (60Co) by adsorption with zeolite 3A and 5A from aqua ...solution. The response surface methodology was employed to constitute the predictive regression model to guess the decontamination factor for radioactive cobalt removal. The experimental maximum decontamination factor 30.37 and 15.9 were obtained for zeolite 3A and zeolite 5A, respectively. The calculated model was significant for both zeolite 3A and 5A (p<0.05). The predicted maximum decontamination factor was 30.05 and 15.19 in optimum conditions for zeolite 3A and zeolite 5A, respectively. Zeolite 3A has a higher adsorbent capacity than zeolite 5A for the removal of radioactive cobalt from aqueous solution.
Radyoaktif kobalt, radyoaktif atıkta en bol bulunan radyonüklidlerden biridir. Bu çalışmada, radyoaktif kobaltın (60Co) su çözeltisinden zeolit 3A ve 5A ile adsorpsiyon yoluyla uzaklaştırılması araştırılmıştır. Cevap yüzey yöntemi, radyoaktif kobaltın uzaklaştırılmasında dekontaminasyon faktörünü tahmin etmek için öngörücü regresyon modelini oluşturmada kullanılmıştır. Deneysel maksimum dekontaminasyon faktörü zeolit 3A ve zeolit 5A için sırasıyla 30.37 ve 15.9 olarak elde edilmiştir. Hesaplanan model zeolit 3A ve 5A için anlamlıydı (p <0.05). Zeolit 3A ve zeolit 5A için tahmin edilen maksimum dekontaminasyon faktörü, optimum koşullarda sırasıyla 30.05 ve 15.19'dur. Sulu çözeltiden radyoaktif kobaltın uzaklaştırılmasında zeolit 3A, zeolit 5A'dan daha yüksek adsorban kapasitesine sahiptir.
The effect of sodium promoter on cobalt–zinc oxide catalysts was studied. Catalysts with different sodium contents (up to 1% (w/w)) were prepared by a coprecipitation method. They were studied in the ...steam reforming of ethanol between 523 and 723 K and characterized by transmission electron microscopy, X-ray diffraction, Raman and infrared spectroscopies, X-ray photoelectron spectroscopy, and in situ diffuse reflectance infrared spectroscopy. A high segregation of sodium on the surface of catalysts took place. The sodium addition had a positive effect on the steam-reforming reaction of ethanol. Under total conversion and in the 623–723 K temperature range, the production of hydrogen from an ethanol–water (C
2H
5OH:H
2O=1:13 molar) mixture (bioethanol) increased (5–8%) with sodium content. In addition, the incorporation of sodium resulted in the stabilization of the catalysts toward deactivation. In particular, the sodium-promoter effect was related to a decrease in carbon deposition, as evidenced by transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy.
We report a novel modulation strategy by introducing transition metals into NiS2 nanosheets (NSs) to flexibly optimize the electronic configurations and atomic arrangement. The Co‐NiS2 NSs exhibit ...excellent hydrogen evolution reaction (HER) performance with an overpotential of 80 mV at j=10 mA cm−2 and long‐term stability of 90 h in alkaline media. The turnover frequencies (TOFs) of 0.55 and 4.1 s−1 at an overpotential of 100 and 200 mV also confirm their remarkable performance. DFT calculations reveal that the surface dopants abnormally sensitize surface Ni‐3d bands in the long‐range order towards higher electron‐transfer activity, acting as the electron‐depletion center. Meanwhile, the high lying surface S‐sites possess substantially high selectivity for splitting the adsorbing H2O that guarantee the high HER performance within alkaline conditions. This work opens opportunities for enhancing water splitting by atomic‐arrangement‐assisted electronic modulation via a facile doping strategy.
Co dotiert: Kobalt‐dotierte NiS2‐Nanoschichten (NSs) mit optimalen eg1‐Elektronenkonfigurationen und erhöhtem Ni3+‐Gehalt zeigen eine ausgezeichnete Aktivität und Stabilität für die Wasserstoffentwicklung (HER) in alkalischen Medien. DFT‐Berechnungen zeigen, dass Co‐NiS2 NSs‐Oberflächen die Ni‐3d‐Bänder abnormal aktivieren, um einen besseren Elektronentransfer zu erreichen.
Catalyst productivity and selectivity to C
5+ hydrocarbons are critical design criteria in the choice of Fischer-Tropsch synthesis (FTS) catalysts and reactors. Cobalt-based catalysts appear to ...provide the best compromise between performance and cost for the synthesis of hydrocarbons from CO/H
2 mixtures. Optimum catalysts with high cobalt concentration and site density can be prepared by controlled reduction of nitrate precursors introduced via melt or aqueous impregnation methods. FTS turnover rates are independent of Co dispersion and support identity over the accessible dispersion range (0.01–0.12) at typical FTS conditions. At low reactant pressures or conversions, water increases FTS reaction rates and the selectivity to olefins and to C
5+ hydrocarbons. These water effects depend on the identity of the support and lead to support effects on turnover rates at low CO conversions. Turnover rates increase when small amounts of Ru (Ru/Co<0.008 at.) are added to Co catalysts. C
5+ selectivity increases with increasing Co site density because diffusion-enhanced readsorption of α-olefins reverses, β-hydrogen abstraction steps and inhibits chain termination. Severe diffusional restrictions, however, can also deplete CO within catalyst pellets and decrease chain growth probabilities. Therefore, optimum C
5+ selectivities are obtained on catalysts with moderate diffusional restrictions. Diffusional constraints depend on pellet size and porosity and on the density and radial location of Co sites within catalyst pellets. Slurry bubble column reactors and the use of eggshell catalyst pellets in packed-bed reactors introduce design flexibility by decoupling the characteristic diffusion distance in catalyst pellets from pressure drop and other reactor constraints.
Numerous studies already identified that the fatigue strength of 316 L parts processed by laser beam melting (LBM) is distinctly affected by the surface integrity. Among others, surface defects as ...well as residual stresses are of crucial importance. Despite new findings in the field of surface engineering of laser beam melting (LBM) parts, the low cycle fatigue strength of thermally sprayed additively manufactured substrates has not been in the focus of research to date. This study aims at evaluating the effect of different pre‐treatments onto 316 L substrates processed by laser beam melting (LBM) prior to the deposition of a high velocity oxy‐fuel (HVOF) sprayed tungsten carbide‐cobalt coating and their effect on the low cycle fatigue strength. Therefore, 316 L substrates were examined in their as‐built state as well as after grit blasting with regards to the surface roughness, strain hardening effects, and residual stresses. To differentiate between topographical effects and residual stress related phenomena, stress‐relieved 316 L substrates served as reference throughout the investigations. The tungsten carbide‐cobalt coated and differently pre‐treated 316 L substrates were mechanically tested under quasi‐static and dynamic load conditions. Besides the low cycle fatigue strength, the fracture toughness as well as the fracture mechanism were identified based on fracture surface analysis.
This study aims at evaluating the correlation between the effect of different substrate surface conditions (i. e. grit blasted, as‐built) and the fatigue strength of the produced tungsten carbide‐cobalt coated 316 L additive manufactured substrate composites under quasi‐static and dynamic load conditions.
The present work aims to improve the wear resistance of the austenitic stainless steel X6CrNiMoTi17‐12‐2. In view of the potential use of this alloy, however, corrosion resistance should be ...maintained where possible. An electron beam surface treatment (cladding) was performed, and the cobalt‐based alloy Stellite® 12 was used as the wear‐resistant material. The presented results show the effects of several electron beam oscillation figures during the cladding process with regard to layer bonding, microstructure formation and hardness. The surface hardness achieved was 576±18 HV 0.3, almost three times higher than that of the base material (203±3 HV 0.3). The scratch energy density – which represents the resistance to abrasive wear – could be increased by a factor of 1.5. Under abrasive‐adhesive stress loading conditions, the determined wear volume decreased by a factor of almost 5. Based on the corrosion investigations carried out, it was possible to prove that in comparison to the base material, the tendency towards pitting corrosion could be almost completely suppressed.
Translation
Das Ziel der vorliegenden Arbeit ist die Verbesserung des Verschleißwiderstandes des korrosionsbeständigen austenitischen Stahls X6CrNiMoTi17‐12‐2. Unter Berücksichtigung des Einsatzgebietes dieses Werkstoffes soll die Korrosionsbeständigkeit dabei weitestgehend erhalten bleiben. Hierfür wurde eine Elektronenstrahloberflächenbehandlung (Auftragschweißen), durchgeführt, bei dem die Kobalt‐Basislegierung Stellite® 12 in Form eines verschleißbeständigen Fülldrahts Verwendung fand. Die vorgestellten Ergebnisse zeigen die Auswirkung unterschiedlicher Oszillationsfiguren des Elektronenstrahls, welche während des Auftragsprozesses verwendet wurden, auf die Anbindung der Auftragsschicht, das sich einstellende Gefüge sowie die Härte. Die maximal erreichte Oberflächenhärte betrug mit 576±18 HV 0,3 nahezu das Dreifache der Substrathärte (203±3 HV 0,3). Die Ritzenergiedichte, welche den Widerstand gegen abrasiven Verschleiß charakterisiert, konnte um einen Faktor von 1,5 gesteigert werden. Unter abrasiv‐adhesiven Verschleißbedingungen verminderte sich das Verschleißvolumen annähernd um den Faktor 5. Auf der Grundlage der durchgeführten Korrosionsuntersuchungen konnte gezeigt werden, dass, im Vergleich zum Grundwerkstoff, die Anfälligkeit gegenüber Lochfraßkorrosion beinahe vollständig verhindert werden konnte.
Nickel‐cobalt alloys were electrodeposited on copper sheets in sulfate bath containing 288.5 g/l NiSO4·6H2O, 30 g/l CoSO4·7H2O, 40 g/l HBO3, 15 g/l NaCl and 0.08 g/l lauryl sodium sulfate. The ...effects of cobalt content on microstructure, microhardness, and wear resistance of electroplating nickel‐cobalt alloys were studied by using SEM and XRD techniques, and microhardness tester and wear tester. The relationship between the microhardness of nickel‐cobalt alloy coatings and heat treatment procedures was also investigated. The experimental results show that cobalt content (Wt) in coating increases with Co2+/(Co2+ + Ni2+)% (X) in plating solution. Fitted regression equation is as following: Wt = –0.7399 + 2.2847X – 0.0133X2. The increase of cobalt content leads to that the longitudinal section morphology of coating transforms from the cone into sphericity and at last into the shape of willow leaf, and its structure transforms from face centered cubic (fcc) nickel solid solution into fcc cobalt solid solution and at last into hcp cobalt solid solution. The increase of cobalt content results in the increase of microhardness of nickel‐cobalt alloy coatings, and the hardness reaches a maximum value (363 HV) when cobalt content is 54.9%. After heat treatment at 400°C and 600°C, the microhardness of coatings begins to decrease except the coating containing 79.2% Co. Moreover, the wear resistance of electroplated coatings increases with the increase of cobalt content.
Oxides of cobalt supported on various supports such as SiO2 and Al2O3 have been prepared by using incipient wetness technique (IMP), the sol–gel (SG) route and the combination of the two methods ...(ISG). The solids formed, after calcination of the corresponding precursors, were characterised by X-ray diffraction, BET area measurements, metal dispersion, and by X-ray photoelectron spectroscopy. Using metal loading of 8%, a high catalytic activity was demonstrated for ethanol steam reforming. Products distribution of the reaction has been found to be dependent on the nature of the support and of the preparation method of the catalysts.
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