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Role of surface nanocrystallization on corrosion properties of low carbon steel during surface mechanical attrition treatment
No full textSurface mechanical attrition treatment (SMAT) was carried out on low carbon steel (LCS) by varying ball size from 4 to 8 mm diameter. Present work studies the effect of ball size on the electrochemical behaviour of the LCS in 3.5 wt.% NaCl solution, using open circuit potential (OCP), impedance (EIS) and anodic polarization methods. The untreated LCS shows similar to 29 nm grain size, whereas after SMAT with 4 mm ball size exhibited remarkable reduction in grain size i.e., similar to 11 nm. Reduction in grain size was achieved due to the presence of highly densified mechanical twins after SMAT as well as the formation of dislocation tangles that rearrange themselves into nanocrystallites. These factors have a direct impact on the corrosion behaviour of SMATed LCS. The increase in corrosion potential (E-corr) towards positive side and a reduction of 93% in corrosion current density (i(corr)) value were observed after SMAT using 4 mm balls as compared to the untreated LCS. Remarkable improvement in corrosion resistance was due to grain refinement after SMAT processing, hindrance of the corrosive ion, increase in the activity of charge carriers at the interface between solution and substrate, and reduction in surface roughness. Nanocrystalline surface after SMAT effectively hindered the chloride infiltration into the substrate and resisted pit formation, thus the corrosion performance is improved
Recovery of Metal Values from Ni-Cd Cake Waste Residue of an Iranian Zinc Plant by Hydrometallurgical Route
No full textThis paper concerns the development of an environment-friendly hydrometallurgical flowsheet dedicated to the recovery of zinc and nickel from a waste residue collected from an Iranian zinc plant. In particular, valuable metals from Ni-Cd cake waste generated at this plant were recovered by a simple hydrometallurgical process using minimum acid for leaching, and solvent extraction step was designed such that addition of sodium hydroxide was not required and the effluent generated is safe to dispose off. The waste was leached with a mixture of hydrochloric acid and sulfuric acid in the presence of hydrogen peroxide in order to achieve a good selectivity towards iron and calcium. Afterwards, cementation was performed at pH 5 in order to remove cadmium. Liquid-liquid extraction was then implemented to produce high-purity solutions of zinc and nickel. Zinc-nickel separation was obtained at pH 2 by using a mixture of bis-(2-ehtyl-hexyl)-phosphoric acid (HDEHP) and tris-2-ethylhexyl amine (TEHA) diluted in an aliphatic kerosene. TEHA did not directly participate but helped in the extraction of zinc by scavenging the protons released by HDEHP. Therefore, no alkaline solution was necessary for maintaining the equilibrium pH during liquid-liquid extraction. Finally, this flowsheet allowed to recover more than 95% of zinc and nickel from the residue with more than 99% purity
Quench Temperature-Dependent Mechanical Properties During Nonisothermal Partitioning
No full textThe present study demonstrates the role of hot rolling and quench temperature in determining the mechanical properties of low alloy steel processed through quenching and nonisothermal partitioning (Q&P) route. The results indicate that the abrasive wear resistance does not show any significant variation with quench temperature. However, a reduction in tensile strength and an increase in charpy impact toughness and elongation is observed with increasing quench temperature. Interestingly, the retained austenite shows high thermal stability at sub-zero temperature. Furthermore, during deformation through the wear process, the retained austenite experiences the TRIP effect that leads to improvement in wear resistance. The incorporation of hot rolling prior to Q&P led to a significant improvement in strength, energy absorption capability and wear resistance due to a considerable refinement of the microstructural constituents
Essential basics on biomass torrefaction, densification and utilization
No full textTorrefaction and densification are crucial steps in upgrading biomass as feedstock for energy generation and metallurgical applications. This paper attempts to discuss essential basics on biomass torrefaction and densification, which can propel developing nation to take full advantage of them. The most promising clean energy sources that have found applications in various areas are biomass materials, that is, both the lignocellulosic and non-lignocellulosic. However, high moisture contents, low energy density, hydrophilic nature, poor storage and handling properties are the major drawbacks limiting its usefulness. Therefore, torrefaction as one of the major thermal pre-treatment processes to upgrade biomass in terms of improved energy density, hydrophobic, moisture content and grindability has been discussed. The influence of temperature, residence time, particle sizes and gas flow rates on the properties of torrefied biomass has also been discussed. The advantages and disadvantages of various torrefaction technologies have also been highlighted. The possible areas of application of torrefied biomass especially densification into pellets and briquettes alongside the equipment required for it have been reviewed in this paper. The torrefied biomass can be deployed in the metallurgical industries as reducing agent in the development of sponge iron from iron ores of various grade including lean ones. The information gathered in this paper from peer-reviewed articles will reduce the burden of seeking to understand the preliminaries of torrefaction process and its importance
Characterization of Chemical Structure with Relative Density of Three Different Ranks of Coal from India
No full textA comparative study of coals of different ranks having different chemical structure and petrography would be desirable to gain an in-depth knowledge of Indian coals. Here, we report structural and petrographic analyses of three different coals: Coal A (coking coal), Coal B (semi-coking coal) and Coal C (non-coking coal) of Indian origin. The vitrinite reflectances of the three coals were measured to be 1.26, 1.38 and 0.46 for Coal A, Coal B and Coal C, respectively. Size fractionation (- 3.0 + 1.0 mm, - 1.0 + 0.5 mm and - 0.5 mm) followed by density gradient separation (1.2, 1.3, 1.4, 1.6, 1.8 g/cm(3)) were performed for all the coal samples to study mineral matter liberation and distribution of macerals in different density fractions. Petrographic analysis of different density fractions revealed a direct proportionality of vitrinite content to swelling properties. The highest free-swelling indices (7.5 and 6.5) were observed for 1.2 density fraction of Coal A and Coal B, respectively. Fourier transform infrared spectroscopy revealed crucial information relating the degree of aromaticity and aliphaticity with observed coking properties. Specifically, aromaticity (AR1) (CHar stretching/CHal stretching, (3000-3100 cm(-1))/(2800-3000 cm(-1)) and mean reflectance (R-o in %) were found to have a strong positive linear correlation with each other, indicative of an increase in aromaticity with coal rank
Retardation Effect of Tin Multilayer on Sn-3.0Ag-0.5Cu (SAC305)-Based Solder Joint Interface
No full textIn the present study, low alloy steel AISI 4140 pipe in reheated, quenched and tempered (RQT) condition was friction-welded using 6.4 MPa upset pressure followed by post-weld heat treatment as per the manufacturing practice prevailing in the drill pipe industry and compared the same with friction welds made at different upset pressures in the RQT condition and in the as-received condition to evaluate bond quality. The weld region consisted of a mixture of tempered martensite and ferrite in case of RQT condition and mixture of lath martensite/upper bainite and ferrite in the as-received condition. As the upset pressure was increased, the martensite lath size decreased in both as-received and RQT conditions. In general, as the upset pressure was increased, the average microhardness increased. The average microhardness of the material adjacent to partially deformed zone showed lower hardness due to tempering effect because of weld heat. The upset pressure 6.4 MPa showed better notch tensile strength ratio confirming better ductility of the weld zone. The impact strength decreased as the upset pressure increased in both as-received and RQT conditions. But as-received condition showed significantly lower impact strength due to higher carbide content at the weld interface
Influence of Upset Pressure on Microstructure and Mechanical Properties of Friction-Welded AISI 4140 Low Alloy Steel Pipes
No full textIn the present study, low alloy steel AISI 4140 pipe in reheated, quenched and tempered (RQT) condition was friction-welded using 6.4 MPa upset pressure followed by post-weld heat treatment as per the manufacturing practice prevailing in the drill pipe industry and compared the same with friction welds made at different upset pressures in the RQT condition and in the as-received condition to evaluate bond quality. The weld region consisted of a mixture of tempered martensite and ferrite in case of RQT condition and mixture of lath martensite/upper bainite and ferrite in the as-received condition. As the upset pressure was increased, the martensite lath size decreased in both as-received and RQT conditions. In general, as the upset pressure was increased, the average microhardness increased. The average microhardness of the material adjacent to partially deformed zone showed lower hardness due to tempering effect because of weld heat. The upset pressure 6.4 MPa showed better notch tensile strength ratio confirming better ductility of the weld zone. The impact strength decreased as the upset pressure increased in both as-received and RQT conditions. But as-received condition showed significantly lower impact strength due to higher carbide content at the weld interface
Recycling of EV Li-ion batteries to reclaim valuable metals/ materials
No full textDue to the large dependency of Li-ion batteries for various applications such as electric vehicles, consumer electronics and energy storage, the huge amount of waste batteries are generated after the end use. Illegal recycling and disposal to environment are creating hazard to the environment as well as loss of valuables, particularly in developing countries, where environmental regulations are not yet implemented properly. On the other hand, several applications of cobalt and lithium, lack of natural resources, increasing demand and less availability compelled to find alternative resources for its extraction. The present paper is focused on the review as well as process developed by CSIR-NML to recover Co, Li, Mn, Cu, Ni, Fe, plastic, mix metals and graphite from waste Li-ion batteries using various techniques consists of pre-treatment followed by hydrometallurgical processes. First of all, waste Li-ion batteries are crushed and beneficiated to obtain plastics, mix metals and black cathodic materials. Generally it contained in wt. % 5-25 Co, 2-5 Li, 1-3 Ni, 7-10 Al, 6-10 Cu, 5-15 Fe, 5-25 Mn, 10-25 Graphite, 7-10 plastics etc. The contents in the batteries are very heterogeneous in nature depending on variety, quality and uses. Further black material containing Co, Li, Cu, Ni, Mn, Al was processed for metal leaching in suitable lixiviant i.e. 2M sulphuric acid, 10% H2O2 at elevated temperature and mixing time 1 hour. The leach liquor obtained was purified using advance separation techniques (SX/IX/precipitation) to get pure solution of individual metals. After filtration the obtained leach-liquor was processed for recovering MnO2 at optimised pH with the addition of precipitant. Leached residue containing graphite/carbon is saleable product. Further, Mn depleted solution was processed to recover Cu and Ni using cationic extractant LIX-84IC at eq. pH 2.5 and 4, respectively. Now, the solution was processed to get Co selectively by using Cyanex 272 at eq. pH 5.5. The Li from the raffinate was obtained as lithium sulfate by the evaporation process. Further, using crystallization/ electro-winning techniques value added products (salts/ metals) could be produced. The developed processes are eco-friendly, energy-saving and comply with stringent environmental regulations
Optimization of sulfuric acid leaching of a Vietnamese rare earth concentrat
Get PDFThe modeling of Yen Phu (Vietnam) xenotime concentrate leaching by sulfuric acid was studied for the purpose
of optimizing the process. The response surface methodology (RSM) based on a central composite face-centered
(CCF) design was empirically used to model the interactive effect of the independent variables, namely leaching
temperatures of 250–450 °C, acid/concentrate (acid/conc.) mass ratios of 0.8–1.8, and leaching times of 2–6 h,
on the dependent response, namely the leaching yield. And a CCF model for the leaching of the concentrate was
proposed that exhibited good consistency with the experimental data. The shrinking core models for spherical
particles of constant size based on the Arrhenius equation were empirically used to study the kinetics of the
leaching. The activation energies calculated from the kinetic models for the chemical reaction and diffusion rate
stages have the same value of 17.3 kJ·mol−1
, which fitted well to a mixed control model of the chemical reaction
followed by a diffusion stage at leaching temperatures in the range of 473–593 K. The kinetic studies of the
leaching indicated that the leaching percent rate (or leaching yield) is controlled by the leaching temperature.
The optimization of the leaching process was estimated by analyzing the contributions of the coefficients of the
CCF model to the leaching yield. The results indicated that the effect of leaching temperature on leaching yield is
the strongest; it is five times higher than that of the acid/conc. Mass ratio and four times higher than that of the
leaching time. The effects of acid/concentration mass ratio and leaching time on leaching yield are insignificant.
In addition, the optimum data for leaching are as follows: the leaching temperature, acid/conc. Mass ratio, and
leaching time are 320 °C, 1.3, and 4 h, respectively. The proposed CCF model and kinetic study suggested that
the optimization of the Yen Phu xenotime concentrate leaching is controlled by the leaching temperature; and
the CCF model can potentially be applied in the commercial operation of Yen Phu xenotime concentrate leaching
after pilot tests on 50 kg dry concentrate per batc
Role of particle fineness on engineering properties and microstructure of fly ash derived geopolymer
No full textFly ash is ball milled for 30 and 90 min duration to obtain two finer fractions. The degree of size reduction
is very significant at the early stage of milling, then because of agglomeration effect size reduction becomes sluggish. The effect of particle size on physical, mechanical and microstructural properties of resultant geopolymer is elucidated. The physical properties and mechanical strength improvement with milling time is attributed with formation of higher amount of alkaline alumino-silicate (N-A-S-H) hydrated gel. The weight loss profile in Thermo-gravimetric analysis (TGA) indicates more hydrated gel formation and lower carbonation with finer fraction. Different techniques such as Fourier transforms infrared spectroscopy (FTIR), X-ray diffractometer (XRD), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) have been used for microstructural evaluation of geopolymers.
In FTIR, the asymmetric stretching of Si–O–T (T is Si/Al) has been shifted towards lower frequency due to
structural alteration of Al–Si network. The crystalline peak intensity has been decreased because of formation of amorphous gel after geopolymerization, detected by XRD. Under SEM and TEM, finer fraction is characterized with formation of more reaction product. The counts of un-reacted and non-bridge particles are decreased with size reduction