Journal of Mining and Metallurgy, Section B: Metallurgy

Effect of regular thicknesses on the microstructural and quantitative analysis for a hypo-eutectic ductile iron alloyed with Ni and V

2024-08-26T12:20:02+02:00

Ductile iron contains free graphite nodules inside of the metallic matrix, which generally consists of ferrite and pearlite in the as-cast condition. The cooling rate has a great influence on the size, shape, and quantity of the microconstituents of the metallic matrix and the graphite nodules and, therefore, on the mechanical properties. In this investigation, the effect of the cooling rate on the metallic matrix and the nodular characteristics of a ductile iron alloyed with low concentrations of Ni and V was studied. The ductile iron was obtained using the sandwich technique with ladle inoculation. Six plates of different thicknesses from 4.3 mm to 25.4 mm were fabricated in a sand mold using a cooling time of 30 minutes. The microstructural characterization was performed by optical microscopy (OM) and scanning electron microscopy (SEM). The quantitative analysis of the graphite nodules and the microconstituents of the metallic matrix was carried out with the Image J software. The mechanical characterization was carried out by the hardness test on the Rockwell C scale. The results show that the decrease in thickness improves the nodular characteristics; In this case, the plate thickness of 4.3 mm obtained the highest nodule count of 414 Nod/mm², the smallest nodule size (15.30 µm), a space between particles of 18.23 µm, sphericity close to 0 .96 and nodularity of 96.21%. In addition, the highest volume fraction of pearlite (33.7%) and carbides (4.5%) was obtained and consequently the highest hardness (31.56 HRC).

Mechanical properties and failure analysis of PLA/Copper composites fabricated by Fused Deposition Modelling

2024-08-26T12:20:03+02:00

Fused Deposition Modelling process is an additive manufacturing process influenced by numerous parameters that has an impact on strength of the components. This paper is dedicated to study the impact of Fused Deposition Modelling parameters on the strength of PLA/Copper infill composites. Influence on tensile, impact and flexural strengths were studied by varying the process parameters. Nozzle Temperature, Layer Thickness, Printing speed and Infill density are the major fused deposition modelling parameters considered in this study. Mathematical models were developed to predict the strength of composites by varying the process parameters. Strength of the composites diminished with rise in layer thickness and printing speed. On the other hand, increase in nozzle temperature and infill density increased the strength of the composites. The composite samples were subjected to characterization analysis to have an idea on the fracture mechanisms. Both brittle and tensile mode of failure is observed in the samples influenced by the process parameters that affect bonding of layers and porosity.

Milling parameter optimization for refinement of NiO/Al mixtures and synthesis of Ni/Al2O3 nanocomposites.

2024-08-26T12:20:03+02:00

This study examined the effect of milling parameters on the development of Ni/Al₂O₃ nanocomposites and refinement of NiO and Al powders. Ball milling of certain mixtures was followed by sintering at 800 and 1100 °C for 2 h. The X-ray diffraction results of the dry-milled powders indicated that increasing the ball-to-powder weight ratio from 20:1 to 42:1 produced finer particles, resulting in the synthesis of Ni/Al₂O₃ nanocomposites by milling at 200 rpm for 1.5 h. Extending the milling duration at lower rotational speeds yielded powders with nanoscale particle sizes. However, as observed under scanning electron microscopy and energy dispersive spectroscopy, a metallic matrix nanocomposite was formed via the mechanochemical reaction, and the crystallite size was estimated using the Williamson–Hall plot. Furthermore, using differential scanning calorimetry plots, we analysed the effect of milling on the temperatures of phase transformation and/or reduction reactions. The tribological performance of the developed nickel metal matrix composite was examined by employing a ball-on-disc tribometer at various load conditions. Indeed, the friction coefficient increases with applied forces and decreases with milling. Comprehensive examinations of the worn surfaces were conducted through the utilization of a scanning electron microscope and a 3D optical profiler.

Study on the behavior of impurity removal from lithium iron phosphate slag using the ultrasonic-assisted sulphuric acid leaching

2024-08-26T12:20:03+02:00

Recovery of iron phosphate from the leaching slag of used lithium iron phosphate cathode materials is an important link to achieving closed-loop recovery of lithium iron phosphate, which has not yet been effectively achieved. The study used ultrasonic-assisted sulfuric acid leaching to remove impurity elements in iron phosphate to meet the requirements of battery-grade iron phosphate on the content of impurity elements. By optimizing the leaching conditions of sulfuric acid concentration of 0.2 mol∙L^-1, ultrasonic acid leaching time of 30 min, ultrasonic power of 50 W, and reaction temperature of 80 ℃, the removal efficiencies of Cr, Cu, Ni, and Zn, the impurity elements in iron phosphate, were 26.09%, 83.0%, 75.9%, and 96.3%, respectively. At this time, the content of impurity elements Cr and Zn is in accordance with the standard for battery-grade iron phosphate (HG/T 4701-2021), with the content of 50ppm and 10ppm. The leaching results show that ultrasound is beneficial to the removal of impurity elements in iron phosphate in sulfuric acid solution. The results of XRD, particle size, TEM, and XPS analyses showed that the surface of the iron phosphate particles cavitated after ultrasonic acid leaching to form a large number of pores and the particles collided with the particle size became smaller, but there were no other by-products produced during the process. This process provides ideas to achieve the reuse of leaching slag (iron phosphate) and guides the recovery of metals from waste lithium iron phosphate cathode materials.

Hydrometallurgical processing of molybdenum middlings from Shatyrkul-Zhaysan cluster ore

2024-08-26T12:20:03+02:00

The results of physical-chemical studies with determination of the material composition of the sample and studies on nitric acid leaching of molybdenum, extraction processing of solutions from molybdenum middlings from the ore of the Shatyrkul-Zhaysan cluster (Republic of Kazakhstan) are presented. Molybdenum intermediate product obtained after the selective flotation of copper-molybdenum concentrate was used in the experiment with a yield of 0.07% with a molybdenum content of 22.23% with an extraction of 74.91%. Studying of ore minerals was carried out in reflected light with the use of a microscope OLYMPUS BX53. During the mineralographic study of the molybdenum intermediate product, an approximate ratio of ore and non-ore minerals was visually established as 80:20%. The process of the intermediate product processing was carried out using one-stage counter-current leaching at atmospheric pressure to reduce the consumption of nitric acid and, consequently, to reduce the residual acidity of the productive solutions, directed to the extraction of valuable components through extraction/re-extraction solutions and precipitation of calcium molybdate. In the process of leaching, the reduction of the residual acidity of the pregnant solution (from 2.3 to 0.89 g-eq/l) due to two-stage leaching allows to considerably increase the extraction/re-extraction stage molybdenum recovery from 58.46% to 94.28%.

Diffusion bonding of RAFM steels: evolution of interfacial oxide layer with pressure and microstructure and mechanical property after post bonding heat treatment

2024-08-26T12:20:04+02:00

The effect of elevating the bonding pressure from 10 to 20 MPa (5 MPa interval) at 1050 ^oC for 60 minutes on the diffusion bonded joint of reduced activation ferritic/martensitic (RAFM) steel was studied. The results indicate that as the bonding pressure increases, the joint quality correspondingly improves. The oxide layer at the bonding interface underwent an evolution process from continuous to discontinuous and ultimately disappeared with the increase of bonding pressure. The optimal joint was achieved at the pressure of 20 MPa in this work. Considering the exploration of joint reliability in engineering applications, the optimal joint was subjected to a post bonding heat treatment (PBHT) of 750 ^oC for 90 minutes. The diffusion bonding sample subjected to PBHT displays microstructural characteristics and tensile properties similar to those of the base metal. Notably, tensile fracture does not occur at the bonding interface, but in the base metal far from the interface.

Prediction of End-point Phosphorus Content of Molten Steel in BOF with Machine Learning Models

2024-08-26T12:20:04+02:00

The main task of basic oxygen furnace (BOF) steelmaking is dephosphorization, thus the prediction and control of End-point phosphorus content of molten steel is of great significance. Four machine learning regression models (Lasso, Random Forest, Xgboost, and Neural Network) were established to predict end-point phosphorus content of molten steel in BOF according to raw and auxiliary material data, process parameters, and data of production quality. The prediction effect of four models were further compared, and their prediction results were interpreted via model’s interpretability and Permutation Importance Method. Results showed that compared with linear regression and Neural Network regression model, two kinds of ensemble tree model had higher prediction accuracy, better stability in small data sets, and lower requirements on data pre-processing. The influencing factors of end-point phosphorus (P) content in BOF were ranked by importance as: Tapping temperature > Turning down times > Steel scrap amount > Operation habits of different work groups > Blowing oxygen amount > Sulfur and Phosphorus content of molten iron > Addition amount of lime, limestone, and light-burned dolomite in slagging agents > Slag-splashing amount.

Electrochemical investigation and thermodynamic assessment of the Mg-Pd system

2024-08-26T12:20:04+02:00

This work presents the results of electromotive force measurements, by coulometric titration technique, for liquid and solid Mg-Pd alloys with concentrations up to 0.70 mole fraction of Mg at 918 K. These measurements enabled verification of the range of homogeneity of the occurring phases and phase boundaries in the studied system.

Based on the obtained results and other thermodynamic values found in the literature, the phase diagram of the Mg-Pd system was optimized using the CALPHAD method and ab initio calculations. The thermodynamic calculations successfully reproduced the phase diagram.

Effect of oxidizing agents on the treatment of a Colombian lead ore through hydrometallurgical alternative processes

2024-08-26T12:20:04+02:00

The lead recovery from a Colombian ore of low metallic richness was studied, the research was developed in carboxylic media at ambient conditions. A preliminary chemical treatment was necessary to improve the metal extraction. For this, two hydrometallurgical treatments were used: i) pneumatic agitation with ozone injection and ii) mechanical agitation with hydrogen peroxide dosing. Lead extractions from the pretreated ore were similar to those from the leach without pretreatment. This situation attributed the dissolution of lead to the complexing action of the carboxylic agent rather than to the effect of the pretreatments. Direct dosing of peroxide to the citrate leach achieved extractions of 50% of the metal, improving by more than 30% that was achieved by leaching without the oxidizing agent addition.

The leaching of the ore with 0.5M citrate and pH 4.5 yielded a redox potential of 926 mV, which ensured the high activity of the electrons in the chemical reaction and therefore the lead ions dissolution.

Carbonitriding Reduction of TiO2 in the CH4-H2-N2 System: Reduction Temperature Effect and Kinetics

2024-08-26T12:20:05+02:00

Understanding of the reaction kinetics can provide valuable information for the design and optimization of a reaction process. In this study, the reduction degree and carbonitriding ratio of TiO₂ in the CH₄-H₂-N₂ system were investigated to understand the carbonitriding reduction kinetics. The experimental results revealed the following key findings. The reduction degree of TiO₂ showed a significant increase within the temperature range of 1000 °C to 1200 °C. Simultaneously, the complete carbonitride time decreased as the temperature increased. However, it was observed that excessively high temperatures (1200 °C) had a detrimental effect on the reduction degree. Consequently, the optimal reduction temperature was determined to be 1100 °C, enabling a balance between reduction degree and reaction time. The carbonitriding reduction process of TiO₂ in the CH₄-H₂-N₂ system exhibited conformity with the unreacted nuclear model, with chemical reactions primarily controlling the process. A calculated apparent activation energy of 99.35 kJ/mol was obtained for the carbonitriding reduction process. The identification of the optimal reduction temperature and the dominant role of chemical reactions offer valuable insights for the design and optimization of carbonitriding processes involving titanium compounds.

Effects of CeO2/Y2O3 rare earth oxides on microstructure and properties of in-situ synthesized WC-reinforced Ni-based cladding layer

2024-08-26T12:20:05+02:00

A novel tungsten carbide (WC)-reinforced nickel (Ni)-based laser cladding layer prepared by in-situ synthesized process. The growth mechanism of the cladding layer was explored. Furthermore, the mechanism of the influence of different concentrations for CeO₂/Y₂O₃ doping on the microstructures, wear and corrosion resistance of in-situ synthesized WC-reinforced Ni-based cladding layer were analyzed. The results revealed that the optimal content of rare earth oxides using the CeO₂ content of 0.75% and the Y₂O₃ content of 1.50%, which exhibit outstanding hardness (660HV0.2) and excellent wear resistance. In addition, the minimum corrosion rate of the coating were 0.002770 mm/a and 0.0022548 mm/a, with the noble E_corr (-0.12549 V/-0.49924 V) and lower I_corr (2.3550×10^-7 A·cm²/1.9170×10^-7 A·cm²). The doping of rare earth oxides in the cladding layer excellently enhances the wear and corrosion resistance, which was mainly ascribed to the rare earth oxides have better refining grain and purifying effect on the cladding layer organization.

Recovery of pure lithium phosphate from sulfuric acid leaching solutions of spent LiFePO4 batteries by solvent extraction and chemical precipitation

2024-08-26T12:20:05+02:00

With the increasing use of electric vehicles, the demand for lithium iron phosphate (LiFePO₄) batteries has sharply increased. Hence, the recycling of metals from these batteries after end-of-life is necessary. In this study, a hydrometallurgical process for recovering lithium phosphate from spent LiFePO₄ batteries was developed. The effect of parameters on the recovery process consisting of leaching, solvent extraction, and precipitation were investigated. The addition of H₂O₂ to the H₂SO₄solution was ineffective for the selective leaching of Li(I) over iron. The results showed that Li(I) and iron were completely dissolved by 1.5 mol/L H₂SO₄, 100 g/L pulp density at 25^oC for 60 mins and 300 rpm. After oxidizing the Fe(II) in the leaching solution by adding H₂O₂, Fe(III) was completely separated from the solution by five stages of cross-current extraction with 1.0 mol/L D2EHPA at room temperature. The loaded Fe(III) was successfully stripped by four stages of cross-current stripping with 50% (v/v) aqua regia solution. Finally, most of Li(I) was recovered by precipitation of lithium phosphate from the iron free raffinate by maintaining solution pH at 11 and at 95^oC for 30 mins. The optimum conditions for the complete dissolution of LiFePO₄ batteries by sulfuric acid solution and for the separation of iron and lithium ions from the leaching solutions were obtained. A hydrometallurgical process was proposed for the recovery of pure lithium phosphate from spent LiFePO₄ batteries.

Aluminizing as a method of improvement of Mar-M247 alloy lifetime

2024-08-26T12:20:05+02:00

Environmentally friendly HTHA and HTLA CVD aluminizing processes were realized on the Mar-M247 heat resistant superalloy substrate, that is widely used in the hot part of aircraft engines. Additionally, commercially aluminide coatings deposited in the above-the-pack aluminiznig process were analyzed. Aluminizing of the Mar-M247 superalloy by the HTHA, HTLA and above-the-pack processes led to formation of two layers of the coatings. The outer layer of coatings formed by the above-the-pack process consisted of the β-NiAl phase with substrate precipitates, while the outer layer of coatings formed by the HTHA and HTLA processes consisted of the pure β-NiAl phase. Aluminizing successfully improved lifetime of Mar-M247 superalloy. Despite the fact that coatings formed by the above-the-pack process is thicker and more aluminium concentration was found than those formed by the HTLA aluminizing and process, the lifetime of coated superalloy was lower. Moreover the oxidation resistance of the coated superalloy in the HTLA aluminizing process was better than those coated by the HTHA aluminizing process. The removal of impurities in the HTLA aluminizing process ensured a “pure” outer layer of coatings. Clean aluminide coatings may create a purer alumina oxide and may prolong its lifetime.

Recent advances in electrochemical recovery of rare earth elements from NdFeB magnets

2024-08-26T12:20:05+02:00

Recent advances in electrochemical methods show promise for more sustainable recycling of rare earth elements (REEs) from end-of-life NdFeB permanent magnets. Demand for NdFeB magnets is rapidly growing for clean energy applications, motivating recycling efforts to diversify REE supplies. Core electrochemical steps involve selective dissolution of REE-rich phases at the anode and reduction of REE ions at the cathode. Pretreatment including demagnetization, mechanical size reduction, and leaching help liberate and concentrate the REEs. Thermal demagnetization and mechanical crushing make the magnets brittle and improve leachant penetration. Acid leaching dissolves REEs but co-dissolves iron. Molten salt electrolytes such as chlorides enable high temperature REE recovery while ionic liquids allow milder conditions but can decompose. Aqueous solutions have been most thoroughly investigated for versatility and affordability. Cathode materials like titanium, molybdenum, and stainless steel facilitate REE deposition while avoiding co-reduction of iron and cobalt. Additional purification is needed to isolate high purity REE oxides and metals, using techniques like solvent extraction, selective precipitation, and electroseparation. Key factors for optimal electrochemical recycling are maximizing selectivity for REEs, minimizing energy use and waste generation, and simplifying integration. While technical challenges remain, recent advances demonstrate electrochemical technologies can improve the sustainability of recycling critical REEs from permanent magnets.