Effects of Pulsed Magnetic Fields of Different Intensities on Dislocation Density, Residual Stress, and Hardness of Cr4Mo4V Steel

To study the effects of pulsed magnetic fields of different intensities on the dislocation density, residual stress, and hardness of Cr4Mo4V steel, magnetic treatment is conducted at 0, 1.0, 1.3, 1.5, 2.0, and 2.5 T. The dislocation density and residual stress are measured using Electron Backscatter Diffraction (EBSD) and X-ray technique, respectively. The results reveal the dislocation density and compressive residual stress decrease at lower magnetic fields such as 1.0 T and 1.3 T, while they increase at higher magnetic fields such as 2.0 T and 2.5 T. The average value of kernel averaged misorientation (KAM) and compressive residual stress decrease about 10.4% and 15.8%, respectively, at 1.0 T, while they increase about 5.88% and 18.2%, respectively, at 2.5 T. The average value of hardness decreases about 3.5% at 1.0 T, from 817 HV to 787 HV. With the increments of intensities, the hardness of the treated samples increases. The hardness essentially remains unchanged at 2.0 T and 2.5 T. The reason for the dislocation motion under the action of pulsed magnetic fields is discussed

Research of cooperative multi-stability composite energy collection with multi-frequency and broadband oscillation

Vibration energy, as a sustainable energy source, has been widely studied. However, due to the low-frequency and randomness of vibration energy, it is difficult to collect vibration energy. Therefore, how to efficiently collect vibration energy is a very challenging task. In order to expand the working bandwidth of vibration energy collection under low frequency vibration excitation, improve the energy collection efficiency with random vibration excitation, this paper studies a piezoelectric-magnetic liquid composite energy collector problem by constructing a multi-frequency cantilever structure. First, we give some theoretical analysis for the designed novel composite energy collection, and then, by several experiment results, the paper further shows the validity and advantage of the collection. Different from existing literature on the issue, combining the advantages of piezoelectric materials (piezoelectric film) and magnetic liquid, the method of the present paper not only greatly expands the working bandwidth of the vibration energy collection, but also significantly improves the energy collection efficiency. The experimental results show that the device possesses the capability of resonant energy collection in the low-frequency range (5Hz–25 Hz), and can also operate effectively across the entire frequency band. Within the frequency sweep range of 5Hz–25Hz, the highest open-circuit voltage of the energy collection device can reach 21.7V, the highest instantaneous power can reach 171.61 μW. Moreover, it can charge the capacitance energy of a 470 μF electrolytic capacitor to 92.39 μJ within 100 s. In some practical application scenarios, comparative experiments between the device and a existing cooperative multi-stable energy collector conducted show that the operating bandwidth increase by 296.43%, the power increase by 1,012%, and the electricity generation raised to 239%, which implies that the novel composite energy collection device significantly enhances the efficiency of low-bandwidth energy collection of vibration energy

Engineering Properties and Microscopic Mechanisms of Composite-Cemented Soil as Backfill of Ultra-Deep and Ultra-Narrow Foundation Trenches

The backfilling of lime soil in ultra-deep and ultra-narrow foundation trenches is a difficult construction link, and ordinary-cemented soil has drawbacks, including poor strength, impermeability, and frost resistance. To solve these problems, fly ash (FA)–water glass (WG)-composite-cemented soil is developed based on a background project. The three-factor orthogonal tests are conducted on the unconfined compressive strength (UCS) of the composite-cemented soil, and the optimal engineering mix proportion is proposed for the FA-WG-composite-cemented soil. Its UCS is compared with that of cemented soil only doped with FA or WG (FA- and WG-cemented soil). In addition, the cyclic wetting–drying tests, cyclic freeze–thaw tests, and impermeability tests are carried out to study the endurance of the composite-cemented soil in cold regions rich in water. The hydration products of the composite-cemented soil are investigated through scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis, and the curing mechanism of the composite-cemented soil is discussed from the microscopic perspective. The research results indicate that the mixing ratio of cement is crucial to the strength development of the cemented soil; the mixing ratio of FA greatly influences the strength development of the cemented soil in the middle and late stages; the mixing ratio of WG only slightly affects the strength. The ratio of cement, FA, and WG of 9%:12%:3% is the optimal engineering mix proportion of the composite-cemented soil. Compared with ordinary-cemented oil and FA- and WG-cemented soil, the composite-cemented soil shows significantly improved compressive load-bearing capacity. The permeability coefficient of the composite-cemented soil is always obviously lower than that of the ordinary-cemented soil after any curing period. Despite the mass loss, the composite-cemented soil is superior to the ordinary one in overall endurance after wetting–drying and freeze–thaw cycles. Through SEM and XRD analysis, the content of hydration products of the composite-cemented soil is found to be obviously higher than that of ordinary-cemented soil after any curing period, and the hydrates exert stronger cementing action on soil particles in the composite-cemented soil. The contents of C-S-H gel and Aft crystals in the composite-cemented soil are apparently larger than those in the ordinary-cemented soil. Under the alkali activation of WG, the FA produces free SiO32− and AlO2−, which undergo the polymerization reaction with Ca2+ to generate C-S-H gel and C-A-H gel, further promoting the hydration of cement

Engineering Properties and Microscopic Mechanisms of Composite-Cemented Soil as Backfill of Ultra-Deep and Ultra-Narrow Foundation Trenches

The backfilling of lime soil in ultra-deep and ultra-narrow foundation trenches is a difficult construction link, and ordinary-cemented soil has drawbacks, including poor strength, impermeability, and frost resistance. To solve these problems, fly ash (FA)–water glass (WG)-composite-cemented soil is developed based on a background project. The three-factor orthogonal tests are conducted on the unconfined compressive strength (UCS) of the composite-cemented soil, and the optimal engineering mix proportion is proposed for the FA-WG-composite-cemented soil. Its UCS is compared with that of cemented soil only doped with FA or WG (FA- and WG-cemented soil). In addition, the cyclic wetting–drying tests, cyclic freeze–thaw tests, and impermeability tests are carried out to study the endurance of the composite-cemented soil in cold regions rich in water. The hydration products of the composite-cemented soil are investigated through scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis, and the curing mechanism of the composite-cemented soil is discussed from the microscopic perspective. The research results indicate that the mixing ratio of cement is crucial to the strength development of the cemented soil; the mixing ratio of FA greatly influences the strength development of the cemented soil in the middle and late stages; the mixing ratio of WG only slightly affects the strength. The ratio of cement, FA, and WG of 9%:12%:3% is the optimal engineering mix proportion of the composite-cemented soil. Compared with ordinary-cemented oil and FA- and WG-cemented soil, the composite-cemented soil shows significantly improved compressive load-bearing capacity. The permeability coefficient of the composite-cemented soil is always obviously lower than that of the ordinary-cemented soil after any curing period. Despite the mass loss, the composite-cemented soil is superior to the ordinary one in overall endurance after wetting–drying and freeze–thaw cycles. Through SEM and XRD analysis, the content of hydration products of the composite-cemented soil is found to be obviously higher than that of ordinary-cemented soil after any curing period, and the hydrates exert stronger cementing action on soil particles in the composite-cemented soil. The contents of C-S-H gel and Aft crystals in the composite-cemented soil are apparently larger than those in the ordinary-cemented soil. Under the alkali activation of WG, the FA produces free SiO32− and AlO2−, which undergo the polymerization reaction with Ca2+ to generate C-S-H gel and C-A-H gel, further promoting the hydration of cement

Application and Residue Pollution of Mulching Films in Xinjiang

In order to study current situation of application, recycling and residue pollution of mulching films in Xinjiang, and accurately grasp pollution degree of residue of mulching films, this paper made an empirical analysis on residue of mulching films in 31 typical counties and cities in Xinjiang. Results indicate that (i) use of mulching films in Xinjiang is wide and there is great difference in use and residue recycling between cities and counties. Planting area and planting structure jointly influence use of mulching films, and the use of mulching films is significantly correlated with recycling of mulching films, but not correlated with recycling rate of mulching films. (ii) There are significant differences in distribution of residue of mulching films, highest in North Xinjiang and South Xinjiang, followed by East Xinjiang, and the lowest in West Xinjiang. (iii) There are significant differences in distribution of residue of mulching films between different crop fields. Residue of mulching films in cotton field is the key problem of pollution

Two-Dimensional π‑Conjugated Metal Bis(dithiolene) Complex Nanosheets as Selective Catalysts for Oxygen Reduction Reaction

Developing high activity and low price catalysts for the oxygen reduction reaction (ORR) is of critical importance for the commercial application of polymer electrolyte membrane fuel cells. On the basis of density functional theory, the catalytic activity of π-conjugated metal bis­(dithiolene) complex nanosheets (MC₄S₄, where M denotes Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt) for the ORR has been investigated systematically. It is found that the ORR activity of MC₄S₄ is sensitive to the selection of the central metal atom. The adsorption energies of ORR intermediates on MC₄S₄ decrease as the central atom varies from group 8 to group 10. The free energy change of the rate-determining step in the ORR increases in the order of IrC₄S₄ < CoC₄S₄ ≈ RhC₄S₄ < FeC₄S₄ < PdC₄S₄ ≈ PtC₄S₄ < NiC₄S₄ < RuC₄S₄ < OsC₄S₄. Due to the optimal adsorption properties, the IrC₄S₄ nanosheet shows the best ORR catalytic activity among the nine studied MC₄S₄ nanosheets. The free energy change of the rate-determining step in the ORR at high electrode potential follows an inverted volcano curve as a function of the adsorption strength of OH. This work may open new avenues for the development of high-performance ORR catalysts