Journal of Central South University最新文献

The evolution of mechanical properties, localized corrosion resistance of a high purity Al-Zn-Mg-Cu alloy during non-isothermal aging (NIA) was investigated by hardness test, electrical conductivity test, tensile test, intergranular corrosion test, exfoliation corrosion test, slow strain rate tensile test and electrochemical test, and the mechanism has been discussed based on microstructure examination by optical microscopy, electron back scattered diffraction, scanning electron microscopy and scanning transmission electron microscopy. The NIA treatment includes a heating stage from 40 °C to 180 °C with a rate of 20 °C/h and a cooling stage from 180 °C to 40 °C with a rate of 10 °C/h. The results show that the hardness and strength increase rapidly during the heating stage of NIA since the increasing temperature favors the nucleation and the growth of strengthening precipitates and promotes the transformation of Guinier-Preston (GPI) zones to η′ phase. During the cooling stage, the sizes of η′ phase increase with a little change in the number density, leading to a further slight increase of the hardness and strength. As NIA proceeds, the corroded morphology in the alloy changes from a layering feature to a wavy feature, the maximum corrosion depth decreases, and the reason has been analyzed based on the microstructural and microchemical feature of precipitates at grain boundaries and subgrain boundaries.

The low-cost Fe-Cu, Fe-Ni, and Cu-based high-entropy alloys exhibit a widespread utilization prospect. However, these potential applications have been limited by their low strength. In this study, a novel Fe₃₁Cu₃₁Ni₂₈Al₄Ti₃Co₃ immiscible high-entropy alloy (HEA) was developed. After vacuum arc melting and copper mold suction casting, this HEA exhibits a unique phase separation microstructure, which consists of striped Cu-rich regions and Fe-rich region. Further magnification of the striped Cu-rich region reveals that it is composed of a Cu-rich dot-like phase and a Fe-rich region. The aging alloy is further strengthened by a L1₂-Ni₃(AlTi) nanoprecipitates, achieving excellent yield strength (1185 MPa) and uniform ductility (∼8.8%). The differential distribution of the L1₂ nanoprecipitate in the striped Cu-rich region and the external Fe-rich region increased the strength difference between these two regions, which increased the strain gradient and thus improved hetero-deformation induced (HDI) hardening. This work provides a new route to improve the HDI hardening of Fe-Cu alloys.

The magnetization reduction of hematite using biomass waste can effectively utilize waste and reduce CO₂ emission to achieve the goals of carbon peaking and carbon neutrality. The effects of temperatures on suspension magnetization roasting of hematite using biomass waste for evolved gases have been investigated using TG-FTIR, Py-GC/MS and gas composition analyzer. The mixture reduction process is divided into four stages. In the temperature range of 200–450 °C for mixture, the release of CO₂, acids, and ketones is dominated in gases products. The yield and concentration of small molecules reducing gases increase when the temperature increases from 450 to 900 °C. At 700 °C, the volume concentrations of CO, H₂ and CH₄ peak at 8.91%, 8.90% and 4.91%, respectively. During the suspension magnetization roasting process, an optimal iron concentrate with an iron grade of 70.86%, a recovery of 98.66% and a magnetic conversion of 45.70% is obtained at 700 °. Therefore, the magnetization reduction could react greatly in the temperature range of 600 to 700 °C owing to the suitable reducing gases. This study shows a detail gaseous evolution of roasting temperature and provides a new insight for studying the reduction process of hematite using biomass waste.

The utilization of prefabricated light modular radiant heating system has demonstrated significant increases in heat transfer efficiency and energy conservation capabilities. Within prefabricated building construction, this new heating method presents an opportunity for the development of comprehensive facilities. The parameters for evaluating the effectiveness of such a system are the upper surface layer’s heat flux and temperature. In this paper, thermal resistance analysis calculation based on a simplified model for this unique radiant heating system analysis is presented with the heat transfer mechanism’s evaluation. The results obtained from thermal resistance analysis calculation and numerical simulation indicate that the thermal resistance analysis method is highly accurate with temperature discrepancies ranging from 0.44 °C to −0.44 °C and a heat flux discrepancy of less than 7.54%, which can meet the requirements of practical engineering applications, suggesting a foundation for the prefabricated radiant heating system

Finding sustainable energy resources is essential to face the increasing energy demand. Trees are an important part of ancient architecture but are becoming rare in urban areas. Trees can control and tune the pedestrian-level wind velocity and thermal condition. In this study, a numerical investigation is employed to assess the role of trees planted in the windward direction of the building complex on the thermal and pedestrian wind velocity conditions around/inside a pre-education building located in the center of the complex. Compared to the previous studies (which considered only outside buildings), this work considers the effects of trees on microclimate change both inside/outside buildings. Effects of different parameters including the leaf area density and number of trees, number of rows, far-field velocity magnitude, and thermal condition around the main building are assessed. The results show that the flow velocity in the spacing between the first-row buildings is reduced by 30%–40% when the one-row trees with 2 m height are planted 15 m farther than the buildings. Furthermore, two rows of trees are more effective in higher velocities and reduce the maximum velocity by about 50%. The investigation shows that trees also could reduce the temperature by about 1°C around the building.

In this paper, equal channel angular pressing and thermomechanical treatment was employed to improve the strength and electrical conductivity of an aging strengthened Cu-Ti-Cr-Mg alloy, and the microstructure and properties of the alloy were investigated in detail. The results showed that the samples deformed by the combination of cryogenic equal channel angular pressing (ECAP) and rolling had good comprehensive properties after aging at 400 °C. The tensile strength of the peak-aged and over-aged samples was 1120 MPa and 940 MPa, with their corresponding electrical conductivity of 14.7%IACS and 22.1%IACS, respectively. ECAP and cryogenic rolling introduced high density dislocations, leading to the inhibition of the softening effects and refinement of the grains. After a long time aging at 400 °C, the alloy exhibited ultra-high strength with obvious increasing electrical conductivity. The high strength was attributed to the synergistic effect of work hardening, grain refinement strengthening and precipitation strengthening. The precipitation of a large amount of Ti atoms from the matrix led to the high electrical conductivity of the over-aged sample.

In order to overcome the limitations of traditional microperforated plate with narrow sound absorption bandwidth and a single structure, two multi-cavity composite sound-absorbing materials were designed based on the shape of monoclinic crystals: uniaxial oblique structure (UOS) and biaxial oblique structure (BOS). Through finite element simulation and experimental research, the theoretical models of UOS and BOS were verified, and their sound absorption mechanisms were revealed. At the same time, the influence of multi-cavity composites on sound absorption performance was analyzed based on the theoretical model, and the influence of structural parameters on sound absorption performance was discussed. The research results show that, in the range of 100–2000 Hz, UOS has three sound absorption peaks and BOS has five sound absorption peaks. The frequency range of the half-absorption bandwidth (α>0.5) of UOS and BOS increases by 242% and 229%, respectively. Compared with traditional microperforated sound-absorbing structures, the series and parallel hybrid methods significantly increase the sound-absorbing bandwidth of the sound-absorbing structure. This research has guiding significance for noise control and has broad application prospects in the fields of transportation, construction, and mechanical design.

Exploitation of sustainable energy sources requires the use of unique conversion and storage systems, such as solar panels, batteries, fuel cells, and electronic equipment. Thermal load management of these energy conversion and storage systems is one of their challenges and concerns. In this article, the thermal management of these systems using thermoelectric modules is reviewed. The results show that by choosing the right option to remove heat from the hot side of the thermoelectric modules, it will be a suitable local cooling, and the thermoelectric modules increase the power and lifespan of the system by reducing the spot temperature. Thermoelectric modules were effective in reducing panel temperature. They increase the time to reach a temperature above 50 °C in batteries by 3 to 4 times. Also, in their integration with fuel cells, they increase the power density of the fuel cell.

In this paper, the experimental investigation on the performance improvement of conventional stepped solar still is conducted. The steps are covered by the porous material to improve the performance of the conventional device and increase the evaporation rate. All the parameters, including the temperature on the glass surface, the water temperature inside the evaporation zone, and the amount of water produced in both conventional and modified stepped solar stills are measured and compared. The efficiency of two devices and their exergy efficiency have been calculated. Finally, the economic analysis of both devices has been done to check the economic feasibility of the modified device. The amount of freshwater generated during one day was 2244.4 and 3076.2 mL/m², respectively for the conventional and modified stepped solar stills. As a result, the amount of water produced in one day by modified stepped solar still is 35.5% more than the conventional one. Also, the costs for the conventional and modified stepped solar stills have been calculated as 0.0359 and 0.029 $/(L·m⁻²), respectively.

The utilization of arsenic-containing gold dressing tailings is an urgent issue faced by gold production companies worldwide. The thermodynamic analysis results indicate that ferrous arsenate (FeAsO₄), pyrite (FeS₂) and sodium cyanide (NaCN) in the arsenic-containing gold metallurgical tailings can be effectively removed using straight grate process, and the removal of pyrite and sodium cyanide is basically completed during the preheating stage, while the removal of ferrous arsenate requires the roasting stage. The pellets undergo a transformation from magnetite to hematite during the preheating process, and are solidified through micro-crystalline bonding and high-temperature recrystallization of hematite (Fe₂O₃) during the roasting process. Ultimately, pellets with removal rates of 80.77% for arsenic, 88.78% for sulfur, and 99.88% for cyanide are obtained, as well as the iron content is 61.1% and the compressive strength is 3071 N, meeting the requirements for blast furnace burden. This study provides an industrially feasible method for treating arsenic-containing gold smelting tailings, benefiting gold production enterprises.