ABSTRACT
Damping materials have attracted much attention for wide potential applications in the industry. Previous research shows that annealing treatment is an effective and costless way of improving the functional properties of conventional shape memory alloys. However, there are few investigations concerning the annealing effect of the ambient-temperature damping behavior. In this paper, we present the influence of annealing treatment on the martensitic transformation and damping behaviors of Ni 55 - x Cu x Mn 25 Ga 20 (x = 0, 2, 4, 6) alloys within the ambient-temperature range. With increasing annealing time, the martensitic transformation temperature and the temperature span of martensitic transformation decrease. Moreover, annealing treatment greatly enhances the twin boundary damping peak of martensite. The X-ray diffraction (XRD) measurement demonstrates that annealing can improve the degree of L2 1 atomic order, which relieves the pinning effects for the twin boundary motion and thus leads to the enhancement of the twin boundary damping of these alloys.
ABSTRACT
A PdO/CeO2 composite with a rod-like nanoporous skeletal structure was prepared by combining the dealloying of Al-Ce-Pd alloy ribbons with calcination. For CO oxidation and CH4 combustion, the nanoporous PdO/CeO2 composite exhibits excellent catalytic activity, and the complete reaction temperatures of CO and CH4 are 80 °C and 380 °C, respectively. In addition, the composite possesses excellent cycle stability, CO2 toxicity, and water resistance, and the catalytic activity hardly decreases after 100 h of long-term stability testing in the presence of water vapour (2 × 105 ppm). The results of a series of characterizations indicate that the enhanced catalytic activity can be attributed to the good dispersion of the PdO nanoparticles, large specific surface area, strong redox capacity, interaction between PdO and CeO2, and more surface active oxygen on PdO. The results of the characterization and experiments also indicate that the PdO nanoparticles, prepared by combining dealloying and calcination, have a stronger catalytic activity than do Pd nanoparticles. Finally, a simple model is used to summarize the catalytic mechanism of the PdO/CeO2 composite. It is hoped that this work will provide insights into the development of high-activity catalysts.
ABSTRACT
A series of Co3O4 catalysts modified by Sm were prepared by a combined dealloying and calcination approach, and the catalytic activities were evaluated using CO catalytic oxidation. The Sm2O3/Co3O4 catalysts were composed of a large number of nanorods and nanosheets, and exhibited a three-dimensional supporting structure with pores. The experimental results revealed that the addition of a small amount of Sm into the precursor AlCo alloy led to a dealloyed sample with improved catalytic activity, and the dealloyed Al90Co9.5Sm0.5 ribbons (0.5 Sm2O3/Co3O4) calcined at 300 °C showed the highest activity for CO oxidation with complete CO conversion at 135 °C, moreover, CO conversion almost no attenuation, even after 70 hours of catalytic oxidation, which is superior to that of Co3O4. The enhanced catalytic activity of the Sm2O3/Co3O4 catalyst can be attributed to the large specific surface area, more reactive oxygen species and Co3+ ion, as well as electronic interactions between Sm and Co.
