Hasil untuk "Mining engineering. Metallurgy"

Cuixia Liu, Meng Meng, Xian Luo

Based on the innovative mode driven by “data + artificial intelligence”, in this study, three methods, namely Gaussian noise (GAUSS Noise), the Generative Adversarial Network (GAN), and the optimized Generative Adversarial Network (GANPro), are adopted to expand and enhance the collected dataset of element contents and the hardness of the AlCoCrCuFeNi high-entropy alloy. Bayesian optimization with grid search is used to determine the optimal combination of hyperparameters, and two interpretability methods, SHAP and permutation importance, are employed to further explore the relationship between the element features of high-entropy alloys and hardness. The results show that the optimal data augmentation method is Gaussian noise enhancement; its accuracy reaches 97.4% under the addition of medium noise (σ = 0.003), and an optimal performance prediction model based on the existing dataset is finally constructed. Through the interpretability method, it is found that the contributions of Al and Ni are the most prominent. When the Al content exceeds 0.18 mol, it has a positive promoting effect on hardness, while Ni and Cu exhibit a critical effect of promotion–inhibition near 0.175 mol and 0.14 mol, respectively, revealing the nonlinear regulation law of element contents. This study solves the problem of revealing the mutual relationship between the element contents and hardness of high-entropy alloys in the case of a lack of alloy data and provides theoretical guidance for further improving the performance of high-entropy alloys.

Yueyu LEI, Zhonghui LI, He TIAN et al.

In order to study the influence of loading rate on infrared radiation energy of siltstone during loading failure, and quantitatively analyze the change law of infrared radiation energy of siltstone during loading process, the infrared radiation experiments of siltstone under uniaxial compression at different loading rates were carried out. The results show that the peak stress decreases with the increase of loading rate. Under different loading rates, in difference mode, the maximum infrared radiation temperature ΔTmax has a good correspondence with the stress change, which can better reflect the damage of the sample, and the maximum temperature difference of ΔTmax increases by 1.0-1.7 ℃. During the main rupture, cumulative infrared radiant energy increment ΔQ increases slowly with time. There is a power function relationship between ΔQ and mechanical work. With the increase of mechanical work, the cumulative infrared radiation energy increment increases first and then increases slowly. The range of infrared precursor ratio of specimen damage under different loading rates is 0.02-0.285, and decreases with the loading rate.

Lei SI, Jiahao LI, Feng XING et al.

The problem of coal-gangue identification is one of the technical problems that have not been effectively solved for a long time in the coal industry. By analyzing the characteristics and limitations of existing coal-gangue identification methods, the feasibility of coal-gangue identification based on microwave detection technology is discussed. Firstly, the electromagnetic parameters of different coals and gangues are measured and analyzed to provide a basis for the subsequent analysis of sample test results. Then, in order to explore the influence of coal gangue size parameters on microwave propagation, the propagation law of coal gangue dielectric samples with different thickness and cross-sectional area on different frequency bands is studied. Because the coal-gangue mixture is a multi-scale medium composed of coal, gangue and air, the volume and shape are different, and the spatial distribution and mixing form are complex and changeable. The scattering effect in the microwave irradiation area is very complex, resulting in obvious differences in the transmission characteristics of electromagnetic waves in different coal-gangue mixtures. Finally, in order to explore the variation law of microwave propagation characteristics in different coal-gangue media, some microwave detection experiments of coal-gangue mixture under different microwave frequency bands, different particle sizes and different gangue contents are carried out. The results show that: the electromagnetic parameters, thickness and sectional area have obvious influence on the propagation law of microwave in the media. Different particle size and gangue rate have certain influence on microwave propagation in coal-gangue mixture. When microwave with frequency greater than 4 GHz irradiates the coal gangue mixture, the increase of particle size will gradually increase the intensity values of S11 and S21 and the amplitude of O21 signal. When the electromagnetic parameters of coal and gangue in the mixed medium are quite different, after the frequency is greater than 3.5 GHz, the increase of particle size reduces the S21 intensity from −35.3 dB to −38.2 dB, and the O21 signal amplitude from 1.6 mV to 1.26 mV, with certain time delay characteristics. Through the experimental analysis, the differences of the transmitted wave signal intensity value, the time-domain transmitted wave signal amplitude and the transmitted wave signal delay at the sensitive frequency points can be mastered, so as to provide a new idea and method for accurate identification of coal and gangue in top coal caving face.

Shuai Zhang, Tao Wang, Zhipeng Jiang

The contradiction between strength and electrical conductivity of pure aluminum (Al) hinders its wide applications in electrical engineering. In this study, an attempt was made to overcome this limitation by adding carbon nanotubes (CNTs) into Al matrix using friction stir processing (FSP) method. The results showed that CNTs were singly distributed in Al matrix and strong bonded CNTs/Al interfaces without chemical reaction as well as impurity contamination were formed. Interestingly, it was found that the axis of CNTs tended to be parallel to Al (111) planes, which provided a geometric basis for the formation of semi-coherent CNTs/Al interfaces. These semi-coherent CNTs/Al interfaces possessed an extremely low electrical resistivity, which weakened the total electron scattering generated by all CNT/Al interfaces. Meanwhile, strong bonded CNTs/Al interfaces effectively hindered dislocations movement, inducing an improvement of 84 % and 50 % in yield strength and tensile strength of Al respectively. As a result, the strength of Al was significantly improved without losing its electrical conductivity. This study provides a new strategy for breaking through the contradiction between strength and electrical conductivity of Al and then producing CNTs/Al nanocomposites with high strength and high electrical conductivity.

Tarek Bachagha, Joan-Josep Suñol

Heusler alloy research has increased considerably in recent years. This is mostly due to their strong desire to develop future smart device applications. However, many limiting variables remain for researchers to overcome in order to enhance their functional properties. The poor mechanical properties of these alloys restrict their use as solid-state cooling materials in magnetic refrigeration devices. A promising strategy, resulting in novel compounds with better mechanical properties and substantial magnetocaloric effects, is favoring the <i>d</i>–<i>d</i> hybridization with transition-metal elements to replace <i>p</i>–<i>d</i> hybridization. The term given to these materials is “all-<i>d</i>-metal”. In light of recent experimental results of the magnetocaloric effect and the increased mechanical characteristics in these alloys (with complex crystallographic behavior due to off-stoichiometry and disorder), a review of this advanced functional behavior is offered. Moreover, the impact of the substitution of transition metal for the <i>p-</i>group to increase mechanical ductility and considerable magnetocaloric effects has also been addressed. These Heusler alloys are a potential new class of materials for technological applications because of their optimum functional behavior. Finally, we highlighted the potential challenges and unsolved issues in order to guide future studies on this topic.

Elvis Pantaleão Ferreira, Geovana Carla Girondi Delaqua, Gabriela Nunes Sales Barreto et al.

This study examines the potential of adding grape skins to red ceramics to evaluate its effect on the physical and mechanical properties of the clayey body. Five compositions were prepared with different percentages of biomass incorporation: 0%, 2.5%, 5%, 7.5%, and 10%. The specimens were conformed using vacuum extrusion in a laboratory extruder, with dimensions of 120 mm in length and a straight section of 30 × 15 mm. After drying, the pieces were sintered in a laboratory muffle furnace at 700 °C, 800 °C, 900 °C and 1000 °C. Chemical, mineralogical, thermal, physical, morphological, and microscopy tests were conducted on the clayey raw materials. An acceptable formulation was achieved by incorporating up to 5% biomass, fired at 900 °C. For water absorption, the incorporation of up to 5% of biomass fired at 700 °C satisfies the normative limits to produce structural blocks and sealing blocks. From 900 °C onwards, it meets the parameter intended for making roof tiles. The linear shrinkage of the pieces fired up to 900 °C is slightly altered by the incorporation of up to 5% of biomass fired under 800 °C are below 2%. The bending strength, at 700 °C there was an increase in mechanical strength directly proportional to the increase in biomass. However, at 800 and 900 °C, there was a gradual decrease in the bending strength. In turn, at 1000 °C, there was a sudden reduction in bending strenght for all formulations with biomass incorporation.

Chaoyu WANG, Tingye QI, Guorui FENG et al.

As a renewable and clean source, biomass energy is one of the substitutes for traditional fossil energy. However, when biomass is burned as an industrial fuel, it produces a large amount of biomass ash with considerable pozzolanic activity. Currently, the activity of biomass ash is ignored in the utilization of biomass energy. Therefore, research on the regulation mechanism of calcination temperature on the pozzolanic activity of biomass ash will facilitate its efficient utilization. Therefore, we reviewed previous research and selected 500, 700, and 850 ℃ temperatures to calcinate willow leaves. The contents of SiO2, CaO, and other oxides in the willow leaf ash were determined through X-ray fluorescence spectrometer(XRF). The specific surface area of willow leaf ash was determined using a laser particle size analyzer. The mineral composition of willow leaf ash was characterized by X-ray diffraction (XRD), and the characterization of the chemical bonds of the minerals was supplemented by Fourier-transform infrared (FTIR) spectroscopy. The zeta potential of the willow leaf ash–Ca(OH)2 solution was determined through microelectrophoresis to evaluate the system’s stability. After determining the basic physical and chemical properties of willow leaf ash, the mechanical properties of willow leaf ash–cement-based materials were investigated by replacing 20% (mass fraction) cement with the ash, and the factors affecting performance were analyzed. The pozzolanic activity of willow leaf ash at 500, 700, and 850 ℃ was evaluated through the activity index. Rapid evaluation of pozzolanic activity was conducted by active ion extraction capability and inductively coupled plasma-optical emission spectrometer (ICP-OES) analyses. Scanning electron microscopy and XRD characterization methods were combined to analyze the effect of calcination temperature on the structure and composition of the ash and to elucidate the mechanism of the effect of calcination temperature on its pozzolanic activity. The results show that the SiO2 content in the ash was 20% to 30%, and the specific surface area increased with increasing temperature. However, the presence of xonotlite in willow leaf ash was detected through XRD at 850 ℃ Furthermore, the observed FTIR absorption peak at 1120.74 cm−1 corresponded to the stretching vibration of the Si–O–Si structure, which indicated that some amorphous SiO2 was crystallized. The absolute value of the zeta potential of the solution containing willow leaf ash at 500 ℃ and 700℃ was considerably higher than that at 850℃. After replacing a part of the cement with willow leaf ash, the willow leaf ash–cement-based material exhibited the highest compressive strength at 500 ℃ with an activity index of 0.79. The rate of conductivity variation of the willow leaf ash–Ca(OH)2 solution at 500 ℃ and 700 ℃ was higher than that at 850 ℃. The concentration of Si4+ precipitation decreased with the increase in calcination temperature, indicating that willow leaf ash had the highest pozzolanic activity at 500 ℃ followed by 700 ℃. Excessively high calcination temperatures lead to the crystallization of amorphous SiO2 and slagging in willow leaf ash, along with a decrease in the pozzolanic activity. This study provides theoretical support for the regulation of the pozzolanic activity of biomass ash and its applications.

Ju Xu, Mengke Liu, Guojun Ma et al.

As a type of metallurgical solid waste with a significant output, chromium-containing metallurgical dust and slag are gaining increasing attention. They mainly include stainless steel dust, stainless steel slag, ferrochrome dust, and ferrochrome slag, which contain significant amounts of valuable elements, such as chromium, iron, and zinc, as well as large amounts of toxic substances, such as hexavalent chromium. Achieving the harmless and resourceful comprehensive utilization of chromium-containing metallurgical dust and slag is of great significance to ensuring environmental safety and the sustainable development of resources. This paper outlines the physicochemical properties of stainless steel dust, stainless steel slag, ferrochrome dust, and ferrochrome slag. The current treatment technologies of chromium-containing metallurgical dust and slag by hydrometallurgy, the pyrometallurgical process, and the stabilization/solidification process are introduced. Moreover, the comprehensive utilization of resources of chromium-containing metallurgical dust and slag in the preparation processes of construction materials, glass ceramics, and refractories is elaborated. The aim of this paper is to provide guidance for exploring effective technology to solve the problem of chromium-containing metallurgical dust and slag.

Thobile Masinga, Malvin Moyo, Vusumzi Emmanuel Pakade

Contamination of water by hexavalent chromium generated from man–made activities remains one of the challenges for environmental pollution. Activated carbon impregnated with diluted polyethyleneimine (PEI) solutions was investigated as a possible adsorbent for the remediation of water contaminated with toxic Cr(VI). The activated carbon adsorbents were characterized using Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Parameters that influence the adsorptive removal of Cr(VI) were evaluated, and it was observed that high removal efficiency was achieved at pH 3 with a contact time of 120 min and 1 g L−1 dosage concentration. The data were analyzed by kinetic and isotherm models. The data fitted well into the Elovich and Langmuir models, the latter yielding a maximum adsorption capacity of 114 mg g−1. Overall, the MAC-PEI showed promise as a potential adsorbent to remove noxious Cr(VI) in aqueous solution.

Jingyu Zhao, Hanqi Ming, Tao Guo et al.

Abstract Temperature variation and gas generation at different depths and positions in the coal combustion process were studied to determine the propagation and evolution of high temperature regions in the process of coal spontaneous combustion. This study selected coal samples from Mengcun, Shaanxi Province, People’s Republic of China, and developed a semi-enclosed experimental system (furnace) for simulating coal combustion. The thermal mass loss of coal samples under various heating rates (5, 10, and 15 °C/min) was analyzed through thermogravimetric analysis, and the dynamic characteristics of the coal samples were analyzed; the reliability of the semi-enclosed experimental system was verified through the equal proportional method of fuzzy response. The results reveal that the high-temperature zone is distributed nonlinearly from the middle to the front end of the furnace, and the temperatures of points in this zone decreased gradually as the layer depth increased. The apparent activation energy of the coal samples during combustion first increased and then decreased as the conversion degree increased. Furthermore, the proportion of mass loss and the mass loss rate in the coal samples observed in the thermogravimetric experiment is consistent with that observed in the first and second stages of the experiment conducted using the semi-enclosed system. The research findings can provide a theoretical basis for the prevention and control of high-temperature zones in coal combustion.

Hu Xiangpeng, Liu Xinhua, Pang Yihui et al.

The setting load of hydraulic support plays an important role in the roof-control.There are two methods to control the setting load of hydraulic support, one is open-loop control by manual control valve of three position four port, the other is pilot control by solenoid directional control valve of two position three port.However, these two methods can hardly make the setting load reach the expected value and remain stable.Even when the expected value is reached, pressure drop and fluctuation generally exist.Based on this, a mathematical model of electrohydraulic force control system is established, then the stability of the system is analyzed by using MATLAB.It is obtained that there are no open-loop zeros and poles in the right half S plane of the Pole-Zero diagram of the system, so the system is a minimum phase system;the number of cycles of counter-clockwise winding(-1, j0) from the Nyquist diagram is 0, and the system phase margin is 94.1° and the amplitude margin is 10.7 dB, so the system is stable;the step response is stable for 115 s, the impulse response is stable for 90 s.An adaptive PID control method based on BP Neural Network is proposed, and a three-layer neural network control model is established.Quadratic performance index is used to control error.The weight coefficients of the output and hidden layers are updated by using supervised Hebb learning rules and gradient descent algorithm.Then three control parameters of the PID controller are obtained by training.The simulation results show that:it takes about 8.85 s for the setting load to reach the expected value and maintain stability when the expected input is step signal, and 9.1 s when the expected input is the square wave signal.Compared with no BP neural network PID control, the response time is increased by about 13 times.

Ye Cui, Di Liu, Yang Zhang et al.

A TA1 (Ti alloy)/low alloy steel (LAS) composite plate was manufactured by explosive welding. The effects of the bonding interface microstructure on the mechanical properties and fracture behavior of the composite plate were investigated. The results show that the interface has a wavy structure with intermetallic compounds (IMCs) enclosed by a steel matrix. The metallurgical bonding interface was achieved by local diffusion, with a several micrometer-thick diffusion layer. Two kinds of microcracks were formed in the IMC region and the diffusion interface. Microcracks in the IMC region propagate with difficulty due to the impediment of the IMC/steel interface. The microcracks initiated at the interface need to propagate into the fine-grain steel matrix before crack connection and delamination. The shear strength of the TA1/LAS composite plate was over 350 MPa. The composite plate could be bent up to the equipment limit (135 degrees). Excellent mechanical properties were obtained since the crack propagation was hindered by the refined or elongated steel grains induced during explosive welding.

Septriono Hari Nugroho, Purna Sulastya Putra

The Simeulue sub-basin is situated off north-western Sumatra between the outer arc and the mainlands. The sediment and geochemical element characteristics of basins are the important sedimentology variables to recognize the process of sediment deposition. However, the characteristics of the sediment and the geochemical elements in the Simeulue subbasin have not been well explained. This study aims to investigate the textural and geochemical elements characteristics of marine sediments and the distribution of these two variables to determine the sedimentary facies in the Simeulue sub-basin. Samples were taken from various depths in the sub-basin and collected during the 2017 Expedition of “Widya Nusantara” by using the “Baruna Jaya VIII” Research Vessel. The grain size trend analysis showed that the middle part of the basin was dominated by mud, while the edge of the basin near the island (mainland) was mostly dominated by coarser sediments. A geochemical element analysis was performed on each sample to observe the origin of the sediments. The results of these two analyses were subjected to multivariate statistics. This approach was selected because it is appropriate for determining the sedimentary facies and the depositional environments. Based on the multivariate analysis, the sedimentary facies in the Simeulue sub-basin was divided into five facies with similar sediment characteristics and depositional environments. These facies were deposited in the environment with low to medium energy.

Dryelle Nazaré Oliveira do Nascimento, Adriano Reis Lucheta, Maurício César Palmieri et al.

The use of biotechnology to explore low-grade ore deposits and mining tailings is one of the most promising alternatives to reduce environmental impacts and costs of copper extraction. However, such technology still depends on improvements to be fully applied in Brazil under industrial scale. In this way, the bioleaching, by Acidithiobacillus ferrooxidans, in columns and stirred reactors were evaluated regarding to copper extraction of a mineral sulfide and a weathered ore from the Brazilian Amazon region. Samples (granulometry of 2.0/4.75 mm) were characterized by X-ray diffraction (XRD), energy dispersive X-ray fluorescence (EDXRF) spectrometry and scanning electrons microscopy (SEM). The pH and Oxidation-reduction potential (Eh) were daily monitored and leachate samples were collected for copper extraction determination by EDXRF. After 47 days, the columns bioleaching efficiency was 1% (1298 mg Cu&middot;L&minus;1) and 0.95% (985 mg Cu&middot;L&minus;1) for 2.00/4.75 mm sulfide ore, respectively, whereas the stirred reactors bioleaching resulted in 4% (348 mg Cu&middot;L&minus;1) for the mineral sulfide and 47% (295.5 mg Cu&middot;L&minus;1) for the weathered ore.

Md Daniyal, Sabih Akhtar, Ameer Azam

This article presents the effect of 1%, 3% and 5% content of nano-TiO2 (NT) on the fresh, hardened, microstructural and corrosion resistance properties of cementitious composites under different exposure environments (tap water, saline water and acidic solution). Various investigations such as setting time, compressive strength, scanning electron microscope (SEM), energy dispersive x-ray (EDX), X-ray diffraction (XRD) and potentiodynamic polarization studies were carried out. The setting time test confirmed that the NT acts as an accelerator. The 28 days-compressive strength of mortar increased with the addition of NT. The results of SEM and XRD analyses indicate that NT improved the microstructure and increased the amounts of desirable hydration products. The 360 days-compressive strengths of NT admixed mortar exposed under tap water, saline water and acidic solution were found to be higher than control mortar. The corrosion inhibition efficiency of NT was observed to be increasing with the increase in the dosage, in all the exposure environments. Keywords: Nano-TiO2, Setting time, Compressive strength, Microstructure, Corrosion resistance

Koh-ichi Sugimoto, Sho-hei Sato, Junya Kobayashi et al.

In this study, the effects of Cr and Mo additions on mechanical properties of hot-forged medium carbon TRIP-aided bainitic ferrite (TBF) steel were investigated. If 0.5%Cr was added to the base steel with a chemical composition of 0.4%C, 1.5%Si, 1.5%Mn, 0.5%Al, and 0.05%Nb in mass%, the developed steel achieved the best combination of strength and total elongation. The best combination of strength and impact toughness was attained by multiple additions of 0.5%Cr and 0.2%Mo to the base steel. The excellent combination of strength and impact toughness substantially exceeded those of quenched and tempered JIS-SCM420 and 440 steels, although it was as high as those of 0.2%C TBF steels with 1.0%Cr and 0.2%Mo. The good impact toughness was mainly caused by uniform fine bainitic ferrite matrix structure and a large amount of metastable retained austenite.

Reza Alaghmand Fard, Mohsen Kazeminezhad

The application of electropulsing treatment (EPT) is studied on the microstructure and hardness of cold-rolled low carbon steel. The effects of electrical pulses on the grain refinement, precipitate size evolution and hardness are investigated. It is found that applying electrical pulse decreases the grain and precipitate size and increases the hardness in the early stages of electropulsing, but the grain and precipitate size is increased and the hardness is decreased by continuing electropulsing. Also, the effect of electropulsing treatment variables as well as treated time and number of periods are discussed. It is demonstrated that increasing treated time can accelerate achieving maximum hardness in lower number of periods. Keywords: Electropulsing treatment, Hardness, Microstructure, Precipitate, Grain refinement

Alex Poznak, Violet Thole, Paul Sanders

The technological relevance of Al-Mg-Si alloys has been rapidly growing over the last decade. Of particular interest to current and future applications is the problematic negative effect of prior natural aging on subsequent artificial age hardening. The influence of natural aging is dependent on both processing and compositional variables and has origins that are far from well-understood. This work examines the hardenability of 6000 series alloys under a wide range of conditions, paying particular attention to the natural aging effect. Experimental variables include alloy composition (Mg + Si, Mg/Si), cooling rate after solutionization, and duration of prior natural aging. Hardenability was evaluated with full hardness and conductivity aging curves for each condition, as well as select Transmission Electron Microscopy (TEM). Results are discussed based on the actions of naturally aged solute clusters during artificial aging. In particular, a complex interaction between vacancy concentration, cluster stability, and precipitation driving force is suggested.

Zhi Zhu, Min Wang, Huijie Zhang et al.

In this study, a 3D coupled thermo-mechanical finite element model is developed to predict and analyze the defect formation during friction stir welding based on coupled Eulerian Lagrangian method. The model is validated by comparing the estimated welding temperature, processed zone shape and void size with those obtained experimentally. The results compared indicate that the simulated temperature and the data measured are in good agreement with each other. In addition, the model can predict the plasticized zone shape and the presence of a void in the weld quite accurately. However, the void size is overestimated. The effects of welding parameters and tool pin profile are also analyzed. The results reveal that welding at low welding speed or high tool rotational speed could produce a smaller void. Moreover, compared to a smooth tool pin, a featured tool pin can enhance plastic flow in the weld and achieve defect-free weldment. The results are helpful for the optimization of the welding process and the design of welding tools.

Mircea Viorel DRĂGAN

Biomass is one of the Earth’s most abundant and precious resources. It offers not only food but also energy, materials used for construction, chemicals and much more. Biomass has always been used for generating energy since fire was discovered. The term of biomass covers a wide range of products, derived products and waste obtained from agriculture, forestry, including those derived from farming, domestic and industrial waste. This paper aims at investigating the main characteristics of the briquettes made out of wood, wood chips and sawdust.