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The oxidation behaviour of Incoloy 909 superalloy subjected to diffusion boronizing treatments was studied at 750 and 850°C in atmospheres of dry air and a mixture of dry air + water vapour for times up to 10 h. The oxidation behaviour of the coated samples was described by the parabolic rate law with activation energies of 26 and 21 kJ mol−1 when oxidation was conducted in dry air or in the mixture dry air + water vapour respectively. Oxidation kinetics of the boronized coatings were sensitive to temperature and the oxidation environment promoting the development of a thick SiO2 layer on top of the coatings which also included minor additions of other oxides that acted as a barrier that reduced oxidation. However, in the conditions that included water vapour boron-rich oxides were also formed and a different oxidation behaviour was experienced. [ABSTRACT FROM AUTHOR]

In this study, it was evaluated the chemical interaction between iron ore (Fe2O3) and a refractory concrete based on Al2O3- MgAl2O4 at 1650 °C for 4 h using an air atmosphere, in order to determine the chemical behavior and possible reactions between these materials. After testing, the refractory concrete was microstructurally characterized by optical microscopy and scanning electron microscopy (SEM-EDS), as well as X-ray diffraction and Raman spectroscopy. The results showed that magnesium aluminate phase incorporates in solid solution Fe+2 ions, resulting in the formation of (Fe, Mg) (Al2O4) spinels and after their saturation, the rest of Fe+2 ions tends to precipitate at the grain boundaries of alumina and magnesium aluminate phases. This fact promotes during the concrete cooling, the formation of wustite, hematite and magnetite phases (detected in the microstructure as a dendritic and widmanstätten morphologies). The presence of hematite phase was corroborated by X-ray diffraction; likewise the presence of modified spinel phase whose hkl reflections width is higher compared with the original spinel, due to the incorporation of Fe+2 in the initial MgAl2O4 phase. For Raman spectroscopy, it was confirmed the presence of corundum (alumina) phase at characteristic frequencies of 378, 416 and 644 cm-1, hematite phase at 226, 292, 411 and 612 cm-1, magnetite phase at 520 and 668 cm-1 and spinel MgAl2O4 and (Fe, Mg) (Al2O4) ) with its main frequencies at 406 and 666 major cm-1. [ABSTRACT FROM AUTHOR]

Nanosized IrO electrocatalysts ( d ~ 7-9 nm) with specific surface area up to 100 m g were synthesized and characterized for the oxygen evolution reaction in a solid polymer electrolyte (SPE) electrolyzer. The catalysts were prepared by a colloidal method in aqueous solution and a subsequent thermal treatment. An iridium hydroxide hydrate precursor was obtained at ~100 °C, which was, successively, calcined at different temperatures from 200 to 500 °C. The physico-chemical characterization was carried out by X-ray diffraction (XRD), thermogravimetry-differential scanning calorimetry (TG-DSC) and transmission electron microscopy (TEM). IrO catalysts were sprayed onto a Nafion 115 membrane up to a loading of 3 mg cm. A Pt catalyst was used at the cathode compartment with a loading of 0.6 mg cm. The electrochemical activity for water electrolysis of the membrane-electrode assemblies (MEAs) was investigated in a single cell SPE electrolyzer by steady-state polarization curves, impedance spectroscopy and chrono-amperometric measurements. A maximum current density of 1.3 A cm was obtained at 1.8 V and 80 °C for the IrO catalyst calcined at 400 °C for 1 h. A stable performance was recorded in single cell for this anode catalyst at 80 °C. The suitable catalytic activity and stability of the most performing catalyst were interpreted in terms of proper combination between nanostructure and suitable morphology. [ABSTRACT FROM AUTHOR]

Fired porcelain scrap has been recycled as filler to obtain a sustainable high voltage porcelain insulator. Quartz was progressively replaced by 5, 10, 15 and 25 wt% of porcelain scraps in a traditional siliceous porcelain composition. The replacement effect on sintered samples at 1250 °C under industrial scheduling using a manufacturing kiln was evaluated by measuring the linear shrinkage, bulk density, porosity, flexural strength, and microhardness. Phase analysis was carried out by X-ray diffraction and microstructural characteristics were studied using a scanning electronic microscope. The results showed that scrap containing samples reached bulk densities around 2.38 g/cm3 and a porosity percentage close to zero. The maximum flexural strength at both unglazed and glazed state was 67.5 MPa and 89.7 MPa, respectively for 5 wt% scrap containing samples. X-ray diffraction studies revealed higher mullite phase in scrap containing samples. Scanning electronic microscopy images of the polished and etched specimens show the presence of quartz grains and secondary mullite needles embedded in a feldspathic vitreous matrix. The properties displayed by the scrap containing samples are highly attractive, since they show similar and, in some cases, superior values in flexural strength, density, and porosity in comparison to those reported for traditional siliceous porcelain. The most outstanding result was found in the flexural resistance, for unglazed porcelain bodies it was improved around 7%, while in glazed porcelain bodies it was improved around 15% with the addition of chamotte in a traditional porcelain composition. These new porcelain compositions can be used to produce noble porcelain insulators as a more sustainable, affordable, and environmentally-friendly alternative. • The higher mechanical strength was for 5 wt% scrap containing samples. • The mechanical strength improvement was attributed to higher mullite concentrations. • Scrap containing samples are highly attractive to produce sustainable insulators. • Scrap containing insulators are an environmentally-friendly alternative. [ABSTRACT FROM AUTHOR]

The influence of MgAl2O4 spinel addition as a ceramic bonding in the MgO–CaZrO3 refractory was established by the evaluation of physical and microstructural characteristics in terms of density, porosity, crystalline phases, phase distribution and morphology. X-ray diffraction analyses and scanning electron microscopy with microanalysis have been used. The mechanical behavior has been evaluated in terms of cold crushing strength at room temperature and modulus of rupture at 25 and 1260°C. Static and dynamic resistances tested by chemical attack of clinker raw constituents have been carried out at 1450°C. Results showed that thermo-mechanical properties significantly improved with increasing the content of spinel. Microstructural analysis revealed that spinel phase aided to develop a strong bond between MgO and CaZrO3 refractory aggregates. Finally, the refractory bodies exhibited a good thermal stability and an excellent chemical resistance against the clinker raw material. [ABSTRACT FROM AUTHOR]

Abstract: An IrO2 catalyst was prepared using a colloidal method followed by a thermal treatment. The catalyst was later mixed with Pt-Black and supported on the Sb-doped SnO2 (ATO), synthesized through the same colloidal method. ATO was investigated as a possible catalyst support in an electrode of a regenerative fuel cell (URFC), where Pt–IrO2 was used as the catalyst for the oxygen evolution and reduction reactions. The morphology and composition of the ATO support was investigated through transmission electron microscopy, X-ray diffraction (including Rietveld Refinement), BET analysis, and X-ray fluorescence. An ATO support was obtained with a highly homogeneous distribution and crystal sizes, measuring approximately 4–6 nm. The Pt–IrO2/ATO material was deposited on a Nafion 115 membrane with 0.5 mg cm−2 of catalyst loading. Pt/Vulcan XC-72 (30 wt. %, E-TEK) was used as the catalyst in the H2 compartment with a Pt loading of 0.4 mg cm−2. The electrochemical activity of the Pt–IrO2/ATO for oxygen evolution/reduction in the URFC system was investigated by AC-impedance spectroscopy, linear voltammetry, and chronoamperometry techniques. The maximum mass current activity was 1118 A g−1 at 1.8 V in proton-exchange membrane water electrolyser mode (PEMWE) and 565 A g−1 at 0.3 V in proton-exchange membrane fuel cell mode (PEMFC), both at 80 °C. The value of the round-trip energy efficiency was approximately 48% at 50 A g−1. [Copyright &y& Elsevier]

Abstract: IrO2 electrocatalysts were prepared and electrochemically characterized for the oxygen evolution reaction in a Solid Polymer Electrolyte (SPE) electrolyzer. By using a sulfite complex-based preparation procedure, an amorphous iridium oxide precursor was obtained at 80 °C, which was, successively, calcined at different temperatures: 350 °C, 400 °C and 450 °C. A physico-chemical characterization was carried out by X Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and X-ray-photoelectron spectroscopy (XPS). The various IrO2 catalysts were sprayed onto a Nafion 115 membrane with a loading of 2.5 mg cm−2 to form the anode. A Pt/C catalyst (Pt loading 0.5 mg cm−2) was used as cathode. The best electrochemical performance was obtained for the cell based on the IrO2 calcined at 350 °C. The maximum current density at high potentials (1.8  V) was about 1.75 A cm−2. Accelerated time-tests at 2 A cm−2 demonstrated a suitable stability of the IrO2 calcined at 350 °C; however, the intrinsic stability appeared to increase with the calcination temperature. The sample calcined at 400 °C could represent a good compromise between performance and intrinsic stability. [Copyright &y& Elsevier]