Papers by Keyword: Cerium

Abstract: Fusibility curves of FeO–La₂O₃–Al₂O₃, FeO–Ce₂O₃–Al₂O₃, La₂O₃– Ce₂O₃–Al₂O₃ oxide systems are created based on the literature data and modern thermodynamic theories of oxide and metal melts. Admitting the oxide systems conjugation with the area of metal melts existence, we define oxide phases, which can maintain the equilibrium with metal melts of Fe–Ce–Al–O, Fe–La–Ce–Al–O systems. The surfaces of component solubility are created for above mentioned metal melts. For Fe–Ce–Al–O system it is established that the following phases can be at equilibrium with metal: Al₂O₃, Сe₂O₃, FeO∙Al₂O₃, Сe₂O₃∙11Al₂O₃, Сe₂O₃∙Al₂O₃, and the oxide melt (FeO, Al₂O₃, Сe₂O₃, СeO₂). For Fe–La–Ce–Al–O system the following oxide phases can be at equilibrium with the liquid metal: La₂O₃, Al₂O₃, Сe₂O₃, La₂O₃∙Al₂O₃, Сe₂O₃∙11Al₂O₃, Сe₂O₃∙Al₂O₃, and the oxide melt (FeO, La₂O₃, Al₂O₃, Сe₂O₃, СeO₂). Diagrams of active components consumption, which are used to establish the possibility of chosen equilibrium, are created for iron deoxidation with cerium and aluminium as well as with Ce and La at fixed Al content (0.01 wt. %).

Abstract: The reduction behaviour of 3% cerium doped (Ce-Fe₂O₃) and undoped iron oxide (Fe₂O₃) by hydrogen in nitrogen (10%,v/v) and carbon monoxide in nitrogen (10%,v/v) atmospheres have been investigate by temperature programmed reduction (TPR). The phases formed of partially and completely reduced samples were characterized by X-ray diffraction spectroscopy (XRD). TPR results indicate that the reduction of Ce doped and undoped iron oxide in both reductants proceed in three steps reduction (Fe₂O₃ → Fe₃O₄ → FeO → Fe) with Fe₃O₄ and FeO were the intermediate. TPR results also suggested that by adding Ce metal into iron oxide the reduction to metallic Fe by using both reductant gaseous give better reducibility compare to the undoped Fe₂O₃. The reduction process of Ce and undoped Fe₂O₃ become faster when CO was used as a reductant instead of H₂. Furthermore, in CO atmosphere, Ce-Fe₂O₃ give complete reduction to metallic iron at 700 0C which about 200 0C temperature lower than other samples. Meanwhile, XRD analysis indicated that Ce doped iron oxide composed better crystallite phases of Fe₂O₃ with higher intensity and a small amount of FeCe₂O₄.

Abstract: The effect of rare earth additions on diffusion and porosity deformation of Al-11Si-Cu alloy was investigated. The microstructure was characterized by optical microscope. By adding small amount of La and Ce, the porosity can be reduced. As the amount of La and Ce were increased, the porosity defects were diffused and increased in microstructure. RE intermetallic indicates Al-Cu phase interrupted the quality of Al-Si-Cu casting alloy.

Abstract: Aspergillus niger PSSG8 is assisted bioleaching of monazite to recover the constituent metals were investigated. Bioleaching was carried out using Bromfield (BM1/10P & BM-P) and sucrose media (SM1/10P & SM-P) with different levels of Phosphate under rotary and stationary conditions. The growth of the A. niger PSSG8 significantly reduced the media pH to acidic. However, the media pH changed later in rotary shake flasks and were stable in roux bottles. A similar trend was observed for ORP. ORP increased as leaching progressed, but in rotary shake flasks ORP started decreasing after 15 days in Bromfield and 30 days in sucrose media. Fungal growth was maximum in SM when comparing to BM. The reduction and the omission of phosphate in both media did not significantly influence the culture parameters including the yield of biomass. ICP-AES analysis of leach liquor showed highest recovery of cerium (Ce) (1419 µg/L in BM-P) and thorium (Th) (182 µg/L in SM1/10P) in rotary conditions when comparing to the stationary conditions (229 µg/L Ce in BM 1/10P & 159 µg/L in SM-P). Reduction in the metal concentration was observed in the rotary shake flasks after 15 days of incubation. It was due to the biosorption of released metals by the fungal mycelium. Uranium was not detected in any of the media tested. SEM studies of the partially bioleached and control mineral particles show no changes in the surface features.

Abstract: Owing to its beneficial material properties, Al-Mg₂Si in-situ composite has recently received wide attention and application in the manufacture of automotive and aerospace components. Melt treatment of the in-situ composite with the addition of Ce has resulted in a change in the primary and eutectic Mg₂Si phases to refined morphology, which would be expected to improve the mechanical properties of the composite. Characteristic parameters of Mg₂Si particles have been investigated via thermal and microstructural analysis. This has revealed that the addition of 0.8wt.% Ce produced optimum refinement effects on Mg₂Si_P because the coarse structure has been changed to a polygonal shape and reduced in size. Similarly, the flake-like morphology of Mg₂Si_E has been transformed into a rod-like or fibre form in addition to reduction of the eutectic cell area. The result also showed an increase in nucleation temperature T_N of Mg₂Si_P while depressed for Mg₂Si_E, which also corresponds to the refinement morphology effect.

Abstract: This research was to determine the effect of Cerium and cooling rate on the microstructure of eutectic Al-11Si-Cu-Mg cast alloy. The Cerium was added to produce Al-11Si-Cu-Mg-1.5Ce alloys. The microstructure was characterized by optical microscope. The Si structure was modified with the increase of the cooling rate, where smaller area was achieved. Ce formed rich intermetallic phase, such as Al-Si-Ce.

Abstract: Investigations on carburized layers phase composition are usually made ​​by optical microscopy, electron microscopy and X-ray diffraction. A microstructure consisting in different proportions of superior bainite, inferior bainite, martensite and retained austenite was found after carburizing in paste of the 21NiCrMo2 steel which has appropriate bainitic hardenability. The investigations carried out on 21NiCrMo2 steel samples, carburized in paste with additions of about 10% Ce, highlighted a significant change of phase proportions ratio in the carburized layer resulting in an important increasing of the lower bainite ratio. It was also observed, that the carburized layer case depth obtained in the carburizing paste with Ce additions does not significantly differ in relation to that attained in the carburizing paste without Ce additions but the microhardness increases considerably. The reason is connected also to the presence of Ce carbide identified by X-ray diffraction in the carburized layer. The Ce hard affinity towards oxygen and its influence on bainitic hardenability increasing is well known and adopted, however neither Ce transfer mechanism from carburizing paste to the carburizing layer and nor the effects of its high affinity to oxygen (for example) are not addressed in this particular case. The present study proposes a possible transfer mechanism of Ce in the carburized layer and an explanation of the consequences of Ce hard affinity towards oxygen on the phase composition of the carburized layer. Nanoscale iron oxides such as wüstite, magnetite and maghemite were identified in the surface of the carburized layer by Mössbauer spectrometry.

Abstract: The methanation reaction is a promising method for the purification of natural gas, in which the acid gases of CO_2, is eliminated by catalytic conversion. The advantage of catalytic technology is the utilization of CO₂ present in the production of methane gas. The used of alumina supported cerium oxide as the based catalyst in CO₂/H₂ methanation reaction have been investigated in this research by using manganese as the dopant and ruthenium as the co-dopant via wet impregnation technique. The series of cerium oxide catalysts were calcined at 400 °C for 5 hours had been prepared at the screening stage. Then, the catalysts were optimized by different calcination temperatures and different based oxide loadings. The potential catalysts of Ru/Mn/Ce (5:35:60)/Al₂O₃ calcined at 700 °C gave 100 % of CO₂ conversion by using FTIR and yielded about 24 % of CH₄ respectively at reaction temperature of 400 °C. X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscope (FESEM) showed that the supported catalysts were amorphous in structure. FESEM analysis illustrated the surface of the catalysts were covered with small and dispersed spherical particles. EDX analysis revealed that there was 1.02 % reduction of Ru in the Ru/Mn/Ce (5:35:60)/Al₂O₃ used catalysts compared to fresh catalysts. Meanwhile NA analysis showed that Ru/Mn/Ce (5:35:60)/Al₂O₃ catalysts attained surface area of 143.10 m²/g respectively.

Abstract: A novel Mg/Fe/Ce layered double hydroxide (LDHs) and its calcined product (CLDH) were synthesized and CLDH was used as adsorbents for the removal of chlorate ions. Results showed that the initial solution pH was an important factor influencing the chlorate adsorption. The adsorption behavior of chlorate followed the Langmuir adsorption isotherm with a maximum adsorption capacity of 18.2 mg/g. The adsorption kinetics of chlorate on CLDH can be described by the pseudo-second-order kinetic model. It was concluded that the CLDH material is a potential adsorbent for the purification of polluted water with chlorate.

Abstract: The effect of additive elements on impact toughness of Al-11Si-Cu alloy was investigated. The impact test bars were used as impact specimens. The energy of Al-11Si-Cu was improved with Sr modifier addition. The high ability of Ce and La to form large structure intermetallic in Al-Si-Cu will reduce the energy. The RE-intermetallic has an effect on impact analysis, which facilitates to increase the porosity pore.