Oxide Spallation during Post-Isothermal High Temperature Oxidation Cooling of Cr-rich Cast Alloys highly alloyed with Hf
Cobalt, nickel and iron-based alloys containing 25wt.%Cr and strengthened either by chromium carbides or by HfC were oxidized at 1000, 1100 and 1200°C to obtain external oxide scales. The spallation of these oxides during the post-oxidation cooling was studied by exploiting the cooling part of the thermogravimetry curves. The best resistant alloys against scale spallation were the iron-based alloys which did not lose oxide. The nickel-based alloys well behaved too. The worst alloys were the cobalt alloys, principally due to the complex composition of the oxide scales. Beside the base element, the thickness of the oxide was also identified as a major parameter. The presence of Hf with contents much higher than usual was also beneficial for the resistance against spallation.
Oxide scale spallation behaviour of cast chromia-forming TaC-strengthened superalloys
Six {Ni,Co}-based alloys containing TaC were oxidised at 1250°C. The mass variations files were exploited to follow the progress of the spallation of the oxide scales during cooling. The oxides formed on surface were characterised. On average, spallation started after a 300 K cooling, at higher temperature for the nickel-richest alloys than for the others. These results are discussed by considering the effect of the base element and the natures and thicknesses of the external oxides. Tantalum has a negative influence on the scales adherence. The thicker scales formed on the cobalt-richest alloys are less affected by spallation. The CrTaO4 oxide is more deleterious for the adherence of the external oxide scale when it is gathered at the interface.
Heavy metal adsorption from industrial wastewater by PAMAM/TiO2 nanohybrid: Preparation, characterization and adsorption studies
Abstract This study investigates the removal of heavy metals from industrial wastewater using TiO 2 nanoparticles modified with poly-amidoamine dendrimer (PAMAM, G 4 ). The metal ions Cu 2 + , Pb 2 + , and Cd 2 + were selected as model pollutants. FTIR, SEM, BET surface area and Zeta potential measurements, and Dispersion Observing methods have been employed for characterizing the synthetic nanohybrid and these techniques indicated that the PAMAM loaded on to TiO 2 have been favorably synthesized. The effects of several parameters including initial metal ion concentration, temperature, pH solution, the nanohybrid dosage and contact time were studied. The experimental data were analyzed using equilibrium isotherm and kinetics models. The adsorption process was studied using isotherm, kinetics, and thermodynamics models. The analysis shows that the Langmuir isotherm and pseudo-second-order kinetics are appropriate models for the adsorption process. The thermodynamic parameters illustrate that the absorption is endothermic and spontaneous. The findings suggest that the nanohybrid is a good super absorbent for the removal of heavy metals from industrial effluents.