ABSTRACT
Heat treatment is an important process for optimizing the microstructures of superalloys, and the cooling rate after solid solution treatment is one of the most critical parameters. In this work, we treated solid solution MAR-M247 alloys with water quenching, air cooling, and furnace cooling. Microstructure characterization, hardness, and room temperature tensile tests were conducted to investigate the effect of cooling rate on the microstructure and mechanical properties of MAR-M247 alloys. The results showed that the cooling rate after solid solution treatment mainly affected the precipitation behavior of the secondary γ' phase, but it had few effects on other microstructure characterizations, including grain size, γ/γ' eutectic, and MC carbide. The water-quenched sample had the highest cooling rate (400 °C/s) and hardness (400 HV) but suffered from premature fracture because of quenching cracks. A further decrease in cooling rate from 1.5 °C/s to 0.1 °C/s deteriorated hardness (384 HV to 364 HV) and yield strength (960 MPa to 771 MPa) but increased elongation (8.5% to 13.5%). Moreover, the deformation mechanism was transformed from dislocation shearing to Orowan bypassing. The decreased yield strength was mainly due to the weakened precipitation strengthening resulting from γ'-phase coarsening. The improved elongation was attributed to not only the higher work-hardening index caused by interface dislocation networks but also the more uniform deformation, which delayed necking.
ABSTRACT
Exploring visible light responsive media remains a challenge for solar energy photocatalysis applications. We report the Ni3S2-reduced graphene oxide (NG) hybrid composites with sheet-on-sheet structures synthesized by a facile microwave-assisted method. Their morphology, structure and photocatalytic activity in the reduction of Cr(VI) were characterized by scanning electron microscopy, X-ray diffraction, UV-Vis absorption spectroscopy, and electrochemical impedance spectra, respectively. The results show that NG hybrid composites show excellent visible light photocatalytic activity in the reduction of Cr(VI) compared to pure Ni3S2. The Cr(VI) reduction rate of higher than 90% has been achieved with 1wt.% reduced graphene oxide under visible light irradiation at 180min. Improvement is attributed to its efficient charge separation and more active sites due to the integrative effect and good interfacial contact between Ni3S2 and reduced graphene oxide.
ABSTRACT
OBJECTIVE: To study the sequences of amino-acids and their related genes of rifampin-dependent Mycobacterium tuberculosis. METHODS: The strains of rifampin-dependent, rifampin-resistant and rifampin-sensitive Mycobacterium tuberculosis were evaluated by L-J method. The proteins of 134 strains were analyzed by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (SDS-PAGE). The sequences of amino-acids of the proteins with differential expressions were determined by Q-TOF2 liquid chromatography-electra mist spray-quadrupole -time of flight cascade mass spectrograph (LC-ESI-MS-MS, Q-TOF2). The corresponding gene codes for the proteins were analyzed. RESULTS: The protein SDS-PAGE profile of 41 of 49 (41/49) rifampin-dependent strains showed a high expression of a protein band (molecular weight 43,000), representative of 30%-50% of the total proteins differed from rifampin resistance and the control strains. The protein profile of H(37)Rv standard strains, 28 (28/30) rifampin-sensitive strains and 44 (44/54) rifampin-resistant strains showed no relevant high expression. The protein of high expression was identified as the hypothetical protein Rv0341 of Mycobacterium tuberculosis H(37)Rv with a molecular weight (M) of 43,894, a iso-potential point of 5.25 and a score of 183. No mutation was found in the 1,440 bp encoding sequence in various strains. CONCLUSIONS: The hypothetical protein Rv0341 is related to the rifampin-dependent strains, so it can be regarded as an indicator for rifampin-dependent Mycobacterium tuberculosis. Rifampin upregulated the expression of Rv0341 in rifampin-dependent Mycobacterium tuberculosis. Whether the hypothetical protein Rv0341 is related to virulence and synthesis of the cell wall of Mycobacterium tuberculosis needs further study.
