Advanced Materials Research Vols. 774-776

Abstract: Zeolitic imidazolate frameworks-8(ZIF-8, Zn (MIM) ₂, MIM=2-methylimidazole) was synthesized by solvothermal (S) method and liquid-phase diffusion (D) method. ZIF-8 was then directly impregnated with phosphortungstic acid (PTA) at room temperature. After impregnation, the ZIF-8 retained its integrity of frameworks as proved by several characterizations. The textural properties are heavily dependent on preparation methods. Diffusion method produced well-crystallized particles with larger surface area, whereas solvothermal method yielded poorly-crystallized particles. ZIF-8 and ZIF-8-PTA were applied in the photo-degradation of methylene blue (MB) with the assistance of electron acceptor hydrogen peroxide, in which both of them were found to be highly active photo-catalytic. Moreover, the impregnation of PTA improved clearly the activity of catalysts due to the fast reversible multi-electron redox transformations.

Abstract: Mechanical properties, microstructure and exfoliation corrosion (EXCO) behavior of spraying forming 7075 alloy underwent retrogression and re-aging (RRA) were studied by tensile test, transmission electron microscopy and EXCO test, and compared with those of T6 peak aging and T73 overaging treatments. The results show that after T6 treatment, abundance transgranular dispersive η phases make tensile strength of the alloy reach 760MPa, elongation and EXCO rating are only 4.8% and ED respectively by dint of continuous η phases at grain boundaries and narrow precipitate free zones (PFZ). After T73 treatment, interrupted η phases at grain boundaries and wide PFZ can improve elongation and EXCO resistance, but depressed volume fraction of coarsening transgranular η phases reduce tensile strength to 676MPa. After RRA treatment (120°C/24h + 200°C/10min + 120°C/24h), abundance transgranular dispersive η phases separate out again, η phases at grain boundaries interrupt, and PFZ widen slightly. Tensile strength, elongation and EXCO rating of alloy are 758MPa, 8.4% and EA respectively.

Abstract: The effects of low energy (1.8 MeV) electron irradiation on enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistors (HEMTs) have been reported. When the dose up to 1.1×10¹⁶ cm^-2, the saturation drain current and maximal transconductance of E-mode AlGaN/GaN HEMTs increase after irradiation. However, almost no change of threshold voltage and gate leakage current is observed. The results are explained by the creation of positive charges in the AlGaN layer by ionizing energy loss, especially the creation of N vacancies and Ga vacancies by non-ionizing energy loss. Moreover, low-energy electron irradiation could recover the electron mobility.

Abstract: Ultrafine TiC powders with a grain size of about 25 nm were synthesized from nanoanatase TiO₂/carbon black mixtures by mechanical activation-assisted vacuum carbothermal reduction (MCR) reaction. The effects of mechanical activation and carbon sources on TiO₂ carbothermal reduction (CR) were also investigated. Results indicated that the CR of nanoTiO₂ was enhanced after pre-milling of the starting powders. The synthesis temperature and holding time of TiC decreased from 1500 °C to 1300 °C and from 4 h to 2 h, respectively. However, phase evolution analysis of the reaction showed that mechanical activation did not alter the phase evolution sequences of the TiO₂ CR. In addition, the relative weight loss of powders in increasing temperatures indicated that nanoTiO₂ MCR can be divided into three stages, in which the reaction rate of the second stage is found to be the fastest. The study on the effect of different carbon sources on the MCR of nanoTiO₂ showed that the use of nanocarbon black as carbon source can cause MCR to react more thoroughly than the use of graphite and active carbon.

Abstract: Thermogravimetric analyzer (TGA) was used to simulate isothermal 60-min oxidation process of Fe-1.5Si alloy under air condition at 700°C-1150°C. Cross-sectional scale morphology and elemental distribution of the oxide layer were investigated by electron probe microanalysis (EPMA). At 700°C-1150°C the oxide scale is composed of external scale and internal Si precipitates zone. And Si-rich oxides can be detected in the inner parts of the outer oxide scale. It was found at 700-1000°C that oxidation mass gain curve obeys the parabolic law but at 1100-1150°C the relationship of mass gain and oxidation time is complex. The parabolic rate constant is lowered at 900-1000°C that should be related with thicker internal oxidation zone at 900°C and formation of the obvious Si-rich layer in external oxide scale at 1000°C.

Abstract: Because of the high abrasive resistance and excellent mechanical property, the Hadifield-steel is widely used in railway, metallurgy, casting and other fields. This article introduces the composition of Hadifield-steel, development situation, the strengthening mechanism, water toughening, the cause of crack and preventive measures.

Abstract: Fiber mats of polycapolactone (PCL) containing tannic acid were prepared by electrospinning from tannic acid-containing PCL solutions in 1:1 v/v dichloromethane/ N,N-dimethylformamide. The base PCL solution was prepared at 12%w/v and the different amounts of tannic acid (5, 10, and 20% w/w based on weight of PCL) were added in the PCL solution. For 5% and 10% tannic acid-loaded PCL fiber mats, the fibers were smooth, with the average fiber diameter of 1.02 and 1.26 μm, respectively. The amounts of water retention and release characteristics of tannic acid-loaded PCL fiber mats and tannic acid-loaded as-cast PCL films in acetate buffer (pH=5.5) at 30°C were studied. Tannic acid-loaded PCL fiber mats exhibited greater amount of water retention and tannic acid released than the tannic acid-loaded as-cast PCL films.

Abstract: Gamma cyclodextrin was produced synthesized from beta cyclodextrin in the presence of glycyrrhizin, using Cyclodextrin glucanotransferase (EC 2.4.1.19) from Alkalophilic Bacillus. The results showed that more than 32.7% of beta cyclodextrin substrate was converted to the corresponding gamma cyclodextrin under the following conditions, viz. 200 units enzyme/g of β-CD, 10mmol/L of β-CD concentration, 3% of glycyrrhizin concentration, 27 h of reaction time, 65°C of temperature and a reaction pH of 7.0.

Abstract: We simulate, fabricate and measure a microwave absorber by introducing metamaterial design method to magnetic material. The proposed absorber is composed of periodic copper wire array, magnetic material coated on copper wires, a foam substrate and a bottom metal plane. The results show a nearly perfect absorption peak around 8.7GHz (simulated) and 7.6GHz (measured). Even though the electric and magnetic field distribution indicate that the absorption is a typical metamaterial absorption, the power loss is neither Ohmic nor dielectric loss but magnetic loss, which is different from typical metamaterial absorber. The skillful introduction of the magnetic loss improves the absorption performance, including the absorption bandwidth and intensity. The designed absorber shows an effective application of the magnetic material, which is only 1/60000 volume proportion of the total absorber. Dependences of the absorption on frequency and the coating volume of the magnetic material manifest that the coated magnetic material can adjust the absorption peak position and intensity. The absorber can be an attractive candidate of electromagnetic wave absorber.

Abstract: Base on the process of asphalt pavement construction, analyse the influence factors of energy-saving and emission-reduction in asphalt pavement construction. Research shows thatduring the asphalt pavement construction process, all kinds of construction machinery are the main source of energy consumption and emissions; Asphalt mixture also emission part of gases itself, which closely related with the heating temperature of the mixture.