Volume 37, Issue 2 -

Cerium ion was successfully incorporated into Y/SBA-15 micro-mesoporous molecular sieves via the hydrothermal synthesis method to give a series of composite materials. The prepared materials were thoroughly characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray fluorescence spectroscopy (XRF), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and differential thermo gravimetric analysis (TG-DTG). The results showed that the prepared composite materials retained the highly ordered mesoporous two-dimensional hexagonal structure of SBA-15 and the octagonal structure of Y. The catalyst Ce-Y/SBA-15 was prepared and characterized, then the esterification of n-butanol and oleic acid was studied with bismuth phosphotungstate as a catalyst. Using this model reaction, the effects of Ce-HY/SBA-15, molar ratio of alcohol to oleic acid, amount of catalysts, reaction time and reaction temperature were investigated. The experimental results show that the optimal reaction conditions were: 1.8:1 molar ratio of alcohol to acid, 5 % catalyst amount (based on weight of oleic acid), 4 h reaction time and reflux conditions. Under these conditions, the yield of esterification was 90.6 %. The results suggest that the addition of Ce can effectively improve the catalytic properties of composite molecular sieves.

Molecular dynamics simulation is used to analyze tensile strength and elastic modulus under different temperatures and vacancy concentrations. The effects of temperature and vacancy concentration on the mechanical properties of γ-TiAl alloy are investigated. The results show that the ultimate stress, ultimate strain and elastic modulus decrease nonlinearly with increasing temperature and vacancy concentration. As the temperature increases, the plastic of material is reinforced. The influence of temperature on strength and elastic modulus is larger than that of vacancy concentration. The evolution process of vacancy could be observed clearly. Furthermore, vacancies with different concentrations develop into voids first as a function of external forces or other factors, micro cracks evolve from those voids, those micro cracks then converge to a macro crack, and fracture will finally occur. The vacancy evolution process cannot be observed clearly owing to the thermal motion of atoms at high temperature. In addition, potential energy is affected by both temperature and vacancy concentration.

The electrical conductivity of Fe x O-CaO-SiO 2 -Al 2 O 3 slags was measured by a four terminal method. The results show that the temperature dependences of total, electronic and ionic conductivity for different compositions obey the Arrhenius law and all of them increase as increasing the temperature. For all the studied slags, as increasing CO/CO 2 ratio which is used to controlled the oxygen potential, both the total electrical conductivity and electronic conductivity increase, but the ionic conductivity decreases. It was also found that the electronic transference number exhibits a strong correlation with oxygen potential, but is independent of temperature. Under the condition of constant Fe x O content, the higher the basicity of slags is, the higher the total electrical conductivity and ionic/electronic conductivity will be, which is resulted from the increase of free oxygen ion.

Ce-doped YAG/Al 2 O 3 melt-growth composite (MGC) samples were grown by the micro-pulling-down (μ-PD) method, and their physical and chemical properties were investigated. The grown MGC samples exhibit fine-grained granophyric texture at the micron scale. Fluorescence spectra, excited by a blue laser diode, were recorded, and, in particular, the finely textured granophyric MGC sample doped with 0.1 at% Ce and prepared with a growth rate of 3 mm/min shows superior fluorescence properties without high-temperature deterioration of fluorescence intensity. The μ-PD method is demonstrated to be applicable for manufacturing finely textured MGC samples with improved luminous efficiency as phosphors for white LEDs.

The changes in microstructure that take place during aging a low carbon heat resistant alloy at 750°C for a period of time of up to 1,000 h were studied by optical and scanning electron microscopy, X-ray diffraction and mechanical testing. The microstructure of the as-cast alloy consisted of an austenitic matrix and a network of Nb- and Cr-rich primary carbides that were identified by their tonality when viewed in backscattered mode in a scanning electron microscopy. Aging promotes precipitation of secondary carbides and the transformation of the Nb-rich particles. The mechanical properties are affected by the occurrence of the different phenomena.

MD simulations have been accomplished to study the transport properties of molten CaO-SiO 2 -P 2 O 5 -FeO system. The self-diffusion coefficients of Ca, Si, P, Fe and O ions increase with increasing slag basicity and FeO content, while decrease with increasing P 2 O 5 content. The diffusivities of these ions in the quaternary melts follow the sequence of Ca>Fe>O>P>Si. The calculated viscosities are in good agreement with the experimental ones. It is obvious that increasing the amount of network formers (e. g., Si and P ions) leads to larger viscosity and degree of slag polymerization, while adding network modifiers (e. g., Fe and Ca ions) causes viscosity and slag polymerization to decrease. Except for the calculation, the FT-IR analysis also confirmed the relationship between structural properties of the slag and composition. The viscosity of the slag increases linearly with increasing the parameter of Q (Si+P).

The performance of the primary slag in the cohesive zone of blast furnace is critical for smooth operation of blast furnace ironmaking process. In the present work, the CaO–SiO 2 –MgO–TiO 2 –Al 2 O 3 –FeO slag system was studied to identify the influence of the FeO and the TiO 2 on the melting features and viscosity. The temperatures of melting features are found to decrease with increasing FeO from 5 wt% to 20 wt% and increase with increasing TiO 2 from 5 wt% to 15 wt%. The viscosities of the slag change with TiO 2 can be divided into four periods, which are slow period, rapid period, slow down period and dramatically rise period. The introduction of TiO 2 into silicate network performs as network modifier at high temperature and network former at a relative low temperature. FeO can decrease the effect of Ti 2 O 6 4– chain units and decrease the precipitation temperature of the solid phase.

The hot deformation characteristics of a AZ81E magnesium alloy are studied in the RANGE temperatures from 340 to 430 °C and strain rates ranging between 0.003 and 3.0 s −1 utilizing hot compression tests. Combining Arrhenius equation and Zener-Hollomon parameter, the high temperature flow stress model is proposed and the average activation energy is 166.15 kJ/mol. Processing maps for hot working are developed on the basis of the efficiency of power dissipation with changing temperatures and strain rates. The power dissipation map reveals that the optimum hot working domain is the temperature range of 390–400 °C and strain rate range of 0.03–0.3 s −1 .

The predicted flow behaviors of Aermet 100 steel were analyzed within a wide range of temperatures of 1,073 K–1,473 K and strain rates of 0.01 s –1 –50 s –1 based on isothermal compression tests. Using the original Johnson Cook (JC) model and a modified Johnson Cook (MJC) model, the constitutive equations were constructed in the case of elevated temperatures. For both the JC and MJC, and the previously studied (Arrhenius-type model and double-multivariate nonlinear regression (DMNR)) models, their respective predictability levels were evaluated by contrasting both the correlation coefficient R and the average absolute relative error ( AARE ). The results showed that the prediction from the three models meet the accuracy requirement based on the experimental data, the only exception being the JC model. By comparing the predictability and numbers of material constants involved, the modified Johnson Cook model is regarded as an excellent choice for predicting the flow behaviors of Aermet 100 steel within the range being studied.

The high temperature oxidation and hot corrosion behavior of nickel–iron-based superalloy are studied at 900 ° and 1000 °C. The significant role of alloying elements with respect to the exposed medium is studied in detail. The mass change per unit area was catastrophic for the samples exposed at 1000 °C and gradual increase in mass change was observed at 900 °C for both the environments. The exposed samples were further investigated with SEM, EDS and XRD analysis to study the metallurgical characteristics. The surface morphology has expressed the in situ nature of the alloy and its affinity toward the environment. The EDS and XRD analysis has evidently proved the presence of protective oxides formation on prolonged exposure at elevated temperature. The predominant oxide formed during the exposure at high temperature has a major contribution toward the protection of the samples. The nickel–iron-based superalloy is less prone to oxidation and hot corrosion when compared to the existing alloy in gas turbine engine simulating marine environment.

The high-temperature plastic deformation and dynamic recrystallization behavior of BT25y alloy were investigated within the deformation temperatures of 1,213–1,293 K and strain rates of 0.001–1.0 s –1 on a Gleeble-1500 thermo-mechanical simulator. Results showed that the dynamic recrystallization (DRX) mechanism played an important role in the hot deformation of BT25y alloy. Based on the regression analysis of the true stress–strain data, the stress exponent and deformation activation energy of BT25y alloy were calculated to be 3.4912 and 288.0435 kJ/mol, respectively. The θ-σ and d θ /d σ – σ curves were plotted to further obtain the critical stress and critical strain for the occurrence of DRX. Based on the analysis results, the DRX kinetic model was established. The model was validated by the comparison between predicted and experimental volume fraction of DRX. As the DRX evolution was sensitive to deformation temperature and strain rate, quantities of dynamically recrystallized grains appeared at higher temperatures and lower strain rates.