Precious metals from industrial scraps generated by manufacturing processes have been extensively recycled. For these recycles, it is necessary to ensure confidentiality when dealing with the scraps and to perform the recycling operation in an isolated lot with a high recovery ratio, short operation time, and low treatment cost. In recent years, three challenges have emerged in scrap recycling. The first is the decrease in the precious metal content in the scrap, owing to the substitution of precious metals with other non-ferrous metals. The second is the contamination of the scrap with metals that are not present in natural ores. These contaminations pose challenges in the extraction and purification of precious metals. The third challenge is the adherence to Japan’s environmental regulations, which have been tightened recently, restricting the continuous use of some chemicals such as nitric acid. In this report, some efforts of precious metal recycling companies to overcome these challenges are discussed.
This Paper was Originally Published in Japanese in Japan Inst. Met. Mater. 81 (2017) 152–156.
This review briefly discusses the relationship between the crystal structures, electronic structures, and thermoelectric properties of materials such as pseudogap quasicrystals and related approximant crystals, narrow-gap binary intermetallic compounds, and lead chalcogenides. The approach used is to identify the materials’ intrinsic physical properties from experimental data and establish a route for tuning their properties based on theoretical models and first-principles calculations. A possible route for improving thermoelectric performance is to use a band engineering approach, such as band convergence and introducing impurity states near the valence and conduction band edges. This approach was successfully applied to TiSi2-type RuGa2 and the lead chalcogenides PbTe and PbSe.
This Paper was Originally Published in Japanese in J. Thermoelectrics Soc. Japan 14 (2018) 120–125.
First-principles calculations were used to investigate the effects of substituting a Mg atom in Mg2Si with a foreign atom. The aim was to chemically induce a state of negative pressure for Mg2Si, which would theoretically increase its thermoelectric power factor. First, density of states (DOS) calculations were performed for Mg2Si with a Mg atom substituted with Group 3–12 elements (Sc to Zn). The results suggest that Group 3 and 4 elements are good candidates because the main features of the DOS curves for the substituted Mg2Si were the same as that of the undoped semiconductor. Structural optimization and energy calculations were then performed for Mg2Si substituted with Sc, Y, La, Ti, Z, and Hf. Only Sc and Y showed negative energy changes as a result of the substitutional reaction. The volume changes indicate that only Y is an appropriate substitutional element for inducing a state of negative pressure for Mg2Si.
The effect of the substitution of V, Cr, and Fe on the magnetic properties of MnAlGe ternary compounds has been investigated by first-principles electronic calculations. The total energy differences (ΔEs) between the ferromagnetic and nonmagnetic states varied in a similar trend to the variation in their experimental Curie temperatures. Thus, ΔE can be used to make an approximate and systematic estimation of the effect that atomic substitution or the addition of a fourth element will have on the Curie temperature. The results show that the magnetization of MnAlGe compounds (or the magnetic moment of Mn) is sensitive to the variation of the distance between the Mn layer and its adjacent layer comprising Al and Ge atoms. A large distance between the layers corresponds to a large magnitude of magnetization.
To ensure the safe geological disposal of radioactive waste, it is important to determine the permeability (hydraulic conductivity) of clays. The transient pulse method is suitable for low-permeability materials because it requires a relatively short time to determine their permeability. Upstream pore pressure typically increases in the measurement conducted via the transient pulse method. However, this procedure cannot be used to determine the permeability of clays due to the increase in pore pressure. Therefore, the transient pulse method has never been applied to determine clay permeability. In this study, we applied the transient pulse method to a clay sample obtained in the Mizunami Underground Research Laboratory to determine its permeability while decreasing the downstream pore pressure. We found that this method was also appropriate for conducting measurements on granite. The hydraulic conductivity of the clay measured by the proposed method was higher by only one order of magnitude than that determined using the falling head method, indicating that hydraulic conductivity can be determined using the transient pulse method with reasonably small error. The measurement time of the transient pulse method was much shorter than that of the falling head method. We concluded that the transient pulse method is appropriate for determining clay permeability.
This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 67 (2018) 318–323. In order to show the permeability test system more clearly, Fig. 1 was modified by decreasing the abbreviations in this figure.
The effects of elapsed time following gas metal arc welding (GMAW) on the static strength of lap fillet-welded joints were investigated using a static tensile test. It was observed that the static joint strength did not exhibit a time dependency for cases where the fracture was located in each base metal or the softened heat affected zone (HAZ). In addition, the static joint strength was not observed to have a time dependency for cases where a wire with low-hardness weld metal was used and where the fracture was located in the weld metal. However, the static joint strength was low immediately after welding, and increased over time when a wire with high-hardness weld metal was used. It was found that diffusible hydrogen that entered the weld metal during arc welding and was emitted over time was the cause of the time dependency of joint strength. High-hardness weld metal was sensitive to diffusible hydrogen; therefore, time dependency was observed only when wires with high-hardness weld metal were used and the fracture positions were located in the weld metal during tensile tests. In addition, a correlation between the storage temperature following welding and the static strength or diffusible hydrogen content of welded parts was found: the higher the storage temperature, the earlier the joint strength increases, and the earlier the diffusible hydrogen decreases.
Fig. 9 Effects of storage temperature on joint strength (a) and nominal diffusible hydrogen content of welds (b).
The influence of different metallic foam inter-layers on the mechanical properties of self-piercing riveted (SPR) sandwich joints is investigated in this paper. Comparing with the homogeneous sheet of AA5052, the copper, nickel, iron-nickel foams are added in the joints as inter-layers. The tensile-shear test, SEM and EDS experiments are employed to discuss the mechanical properties of SPR sandwich joints. The results indicate that the addition of metallic foam inter-layers can effectively affect the mechanical lock inside of SPR sandwich joints. The SPR sandwich joint with iron-nickel foam inter-layers exhibits the highest peak load. The SPR sandwich joint with nickel foam inter-layers exhibits the maximum failure displacement and the energy absorption value.
Generally, welding is an indispensable process in the assembly of automobile body parts, while resistance spot welding is applied in many cases. However, an efficient welding technique is necessary because an aluminum alloy has lower resistance and higher thermal conductivity than steel. Based on this point of view, laser welding has been studied as a new method to obtain stable welding quality and ensure deep penetration with low heat input, regardless of the type of material used. In this study, the lap joint weldability of the Al 6061-T6 thin plate, which is a heat-treated aluminum alloy, was investigated by varying the focus position, including the laser power and welding speed. The main result showed that the sound bead was formed when the power was 2 kW, the welding speed was 2 mpm (meter per minute), the focus position was at −0.8 mm, and the N2 shielding gas flow rate was at 10 l/min. Also, the strength of the welds under optimum welding condition was 52% compared to the base material. However, the welded part was subjected to ageing heat treatment (170°C, 12 hours), and demonstrated a strength of 295 MPa, which is about 90% of the base metal.
The effect of the intermetallic compound layer formed by atmospheric controlled induction heating fine particle peening (AIH-FPP) treatment on the wear resistance and high-temperature oxidation resistance of titanium alloy was investigated. To form an intermetallic compound layer on a titanium alloy by AIH-FPP treatment, pure titanium, aluminum and nickel particles were mechanically milled using a planetary ball mill, and the prepared particles were used as shot particles in the AIH-FPP treatment. The results showed that intermetallic compound layers, consisted of Ti3Al and Ti2NiAl3, were formed on titanium alloy by AIH-FPP treatment using the prepared particles. The wear resistance and high-temperature oxidation resistance of the AIH-FPP treated specimen were higher than those of the untreated ones.
This Paper was Originally Published in Japanese in J. Jpn. Soc. Heat Treatment 58 (2018) 11–16.
Sumitomo Metal Mining Co., Ltd. (SMM) has gradually increased the mixed sulfide (MS: mixture of nickel and cobalt sulfides) production from nickel laterite ore as raw material for the SMM’s unique Matte Chlorine Leach and Electro-winning (MCLE) process over the past decade. This process has significant cost advantages because it is capable of selectively and effectively leaching nickel from MS; however, chlorine leaching requires expensive corrosion-resistant facilities. A new process that could be operated using lower-cost facilities has therefore been desired. To meet its development needs, this study evaluated a process for nickel-selective leaching from MS, which is similar to the existing process for refining of ZnS. The process uses sulfuric acid, which does not require high-cost facilities.
However, selective nickel leaching from MS, which was the process development goal, could not be achieved. This result is quite different from the case of selective Zn leaching from ZnS.
The mechanism of nickel leaching from MS using sulfuric acid was identified. It was shown that nickel-selective leaching using sulfuric acid is difficult because of the formation of elemental sulfur and NiS2 precipitates on the MS surface that interfere with the leaching reaction.
This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 81 (2017) 320–326.
Ferrite-matrix nodular cast iron has been modified by a laser surface melting process to develop its microstructure and to improve the surface hardness. A YAG laser beam was irradiated on a substrate and the microstructure of the melted layer was investigated as a function of the pulse energy at a constant specimen travel speed. The surface of the specimen is melted and then rapidly solidified up to a depth of 100 µm order. The melted depth increases with increasing pulse energy. In addition, the ferrite-phase matrix around the spheroidal graphite in cast iron preferentially melts because several alloying elements are segregated at the ferrite/graphite interface. The solidified layer consists of three distinctive parts: first, a martensite phase appears in the vicinity of the melted/unmelted substrate interface, then single-phase austenite crystallized on the martensite phase, and finally a ledeburite-austenite hybrid structure unidirectionally solidified from the substrate towards the surface. A cooling rate from 0.3 to 2.4 × 104 K/s is estimated from the austenite primary dendrite arm spacing under our experimental conditions. The micro-Vickers hardness was also examined in relation to the area fractions of the ferrite, austenite and cementite phases. The Vickers hardness varies from 600 to 900 HV in the solidified layer, whereas the initial substrate shows 200 HV. This tendency for the hardness to increase is estimated from the hardnesses and volume fractions of the soft austenite and hard ledeburite.
This Paper was Originally Published in Japanese in J. Japan Thermal Spray Society 54 (2017) 12–17.
Die casting, a highly efficient production method, is widely applied to the manufacturing of automotive components. On the other hand, extending the die life is required to meet the needs of reducing the production cost because die costs are included in the manufacturing costs.
As one of the primary factors leading to die failures, soldering was investigated in this study by observing the adhesion of ADC12 alloy to the die and the reaction between ADC12 alloy and die in die casting process, analyzing the diffusion of concerned elements in ADC12 alloy, and numerically simulating the flow and the solidification of the molten metal. It was revealed that ADC12 alloy adhered to the surface of the die and caused the surface layer of the die castings to remain on the surface of the die by breaking the die castings with shearing stress at the time of ejection. In addition, Al–Si–Fe compounds were found at the interface between the die and the remaining ADC12 alloy layer with the repetition of die casting. These compounds grew gradually with the concentration of Si in the remaining ADC12 alloy layer towards the interface by diffusion with the further increase of shot numbers.
This Paper was Originally Published in Japanese in J. JFS 89 (2017) 757–763.
In this study, we reproduced the hyper-eutectic cast iron made at the end of the Edo period, and considered its new possibility.
It was found that foundry men of that period made non-chill hyper-eutectic cast iron even at very low silicon content. As for ϕ50 × 250 mm T.P, the tensile strength of C4.53% flake graphite cast iron is 107 MPa which is very low for cast iron. It is thought that the produced thick cannon most probably burst in actual combat with this material.
The melt’s flow ability is the best in the eutectic composition but deteriorates suddenly when entering the hyper-eutectic composition, due to the formation of Kish graphite. Plate type carbide forms when silicon content is low and with quick cooling, in the hyper-eutectic composition. It is thought to form, due to the very slow C diffusion from the matrix to the free graphite, during the eutectoid transformation. Test pieces having plate type carbides shows excellent damping capacity.
This Paper was Originally Published in Japanese in J. JFS 89 (2017) 695–700.
Silver nanoparticles (NPs) were fabricated using a high-pressure wet-type jet mill. A mixture containing both aqueous silver nitrate and a cellulose nanofiber (CNF) suspension was processed with the high-pressure wet-type jet mill at a pressure of 150 MPa. An X-ray diffraction pattern of the obtained sample revealed not only cellulose type I crystallites, but also silver metal crystallites. Transmission electron microscopy revealed silver NPs in the obtained sample that were spherical in shape with an average particle size of 7.1 ± 1.6 nm. These were much smaller than those in a sample prepared by a reflux method. Note that the particle size distribution was very narrow; moreover, almost all the silver NPs were well dispersed due to their constituent CNF. It was considered that Ag(I) was reduced to Ag(0) in the mixed suspension due to the many reducing functional groups on the surface of the raw CNF. It was concluded that cellulose acted as both a reducing agent and a dispersant.
Generally, high-purity 99.99% Au wires are mainly used for electrical connection to transmit and receive data between an Al bonding pad and a printed circuit board (PCB) substrate in semiconductor devices. However, there have been several studies to reduce the cost of expensive Au wires due to the sharp increase in the price of Au. Thus, Ag and Cu alloy wires have been mainly considered as alternative materials.
This paper focused on a ternary Ag alloy wire (Au: 1.5%, Pd: 2.5%) and explained free air ball (FAB) shape effects with various electronic flame-off (EFO) conditions in more detail and experimentally showed the susceptibility to bonding failure of the Ag alloy wire after exposure to the atmosphere at room temperature. In particular, a feasible Ag wire bonding process and grain structure effects under N2-free conditions were studied in depth for the first time. With this N2-free condition, weak surface tension of a melting wire led to move FAB quickly to the interface between FAB and heat affected zone (HAZ). In addition, a slender grain structure in the center of FAB area still remained because of the short time current stressing. It made good conductivity and no significant resistance change of a Ag alloy wire. For a Ag alloy wire exposed to the atmosphere for 19 days, the defective percentage during bonding process suddenly started to rise, and reached more than 0.7% in 24 days. According to our results, less than 18 days are highly recommended as a control standard of a Ag alloy wire when it is exposed to the atmosphere. The bonding between a Ag alloy wire and an Al bonding pad was formed without any crack in the lower part of an Al bonding pad. Higher intermetallic compound coverage and minimum Al splash were chosen as key bonding parameters, and KOH cratering tests were performed to secure good bonding quality. Finally, robust Ag wire reliability has been successfully achieved and demonstrated.
Cu is one of the most valuable metals found in waste printed circuit boards (PCBs). In order to recover the metals from the e-waste, PCB recycling process exploiting physical concentration techniques have widely been applied. Size reduction steps including crushing and grinding are done for liberation of Cu from the non-metallic materials such as glass fiber and epoxy resin. Degree of liberation is an important factor by which liberation performance of comminution process is evaluated. The primary purpose of this study was to investigate liberation characteristics of Cu particles in comminuted PCB by using image analysis method. The analysis procedures include image processing such as noise reduction, edge detection and component discrimination so that a set of images of ground PCB particles provides quantitative information such as Cu grade distribution and degree of Cu liberation. The Cu liberation phenomenon was also discussed in terms of its disassociation behavior from non-metallic material and grindability difference.
Fig. 5 Component segmentation algorithm (H: hue, H*: hue criterion, S: saturation, S*: saturation criterion, I: intensity, I*: intensity criterion, NV: pixel number of non-valuable matter, V: pixel number of valuable matter).
Silver nanoparticles (AgNPs) were synthesized from aqueous AgNO3 precursor via an effective and ecofriendly method using Lemon Citrus Latifolia (LCL) extract as the reducing and stabilizing agent under sunlight condition. The AgNPs formation was confirmed by ultraviolet-visible absorption spectroscopy at the wavelength of 400–450 nm. The appropriate conditions and positive effect of direct sunlight on the AgNPs preparation were revealed clearly. The synthesized AgNPs were characterized using multitechniques X-ray diffraction revealed that AgNPs had the crystalline nature of face-centered cubic structure. Scanning electron microscopy and transmission electron microscopy showed the obtained AgNPs was spherical and the size distribution was uniform with the nanosize of 4–24 nm. The obtained AgNPs solution showed an effective antibacterial activity against E. coli, B. subtilis and B. cereus with the average diameter of inhibition zones over 15 mm.
The optical and electrical properties of MnTe films were investigated to ascertain the feasibility of their use in solar cell applications. Three α-MnTe thin films with different composition, i.e., Mn-47.9 at% Te, Mn-49.2 at% Te, and Mn-50.4 at% Te, were prepared using RF magnetron sputtering. All the films demonstrated a high light absorption coefficient (0.2 × 105–0.8 × 106 cm−1) and an optimal indirect band gap (1.37–1.52 eV) for solar cell applications. Furthermore, all of them exhibited p-type conductivity, with the Mn-47.9 at% Te film demonstrating three to four times higher carrier mobility (5.2 cm2·V−1·s−1) than the Mn-50.4 at% Te film (1.6 cm2·V−1·s−1).
Friction stir processing (FSP) was applied to modify the microstructures of Al–36Si composite. FSP resulted in a significant breakup of coarse primary Si particles in the processed zone (PZ), and the size and aspect ratio of the Si particles decreased with increasing the number of FSP passes. The refinement and homogenization of Si particles during FSP can lead to an improvement in both strength and ductility, though FSP caused softening behavior in the PZ due to thermal cycle during the processing. Post-FSP aging treatment partially recovered the microhardness in the PZ of FSP samples, resulting in the enhanced strength and ductility. Furthermore, post-FSP T6 treatment resulted in a considerable enhancement in the microhardness in the PZ which could reach up to a similar level of the base material (BM). Therefore, the tensile strength was significantly improved to 381 MPa, which was much higher than that of the BM (187 MPa). This study provides an effective method of improving the mechanical properties of the Al–36Si composite.
In Microbially Induced Carbonate Precipitation (MICP), bacteria can perform metabolic activities that promote the deposition of carbonate particles in the form of calcite. Previously, purified urease and CaCl2 have been used for hydrolysis of urea to deposit carbonate particles. In our present study, Mg2+ ions were added to investigate the effect on the deposition of carbonate particles, because Mg2+ ions can delay the reaction rate and enhance the crystal deposition rate. Additionally, other parameters (temperature, solvent, bacterial population, and CaCl2 concentration) were taken into consideration to enhance the amount of carbonate deposition by ureolytic bacteria. The aim of this study was to investigate the mechanism of carbonate particle generation using urease producing bacteria (Pararhodobacter sp.) in laboratory test conditions using a translucent cell. In this study, marine ureolytic (Pararhodobacter sp.) bacteria were used and their urease activity was estimated considering bacterial concentration, temperature, and the effect of Ca2+ and Mg2+ ions. Digital microscopy analysis revealed the direct involvement of these parameters on the deposition of carbonate particles. The results of this study also showed that the type of deposited crystals, their shapes, and bacterial growth rate change depending on the medium used, the type of carbonate (metal ion used), CaCl2 concentration, and temperature. In addition, when Mg2+ and Ca2+ ions were used, the amount of particle deposition increased, which enhanced the possibility of becoming a superior binder for sand particles. This study is useful for the various sand solidification experiments and to regulate the most suitable conditions for engineering applications in future studies.
When solderable polymer composites (SPCs) filled with a low-melting-point-alloy (LMPA) was used in the bonding process, the elimination of surface oxide layers of the fillers and electrodes is very important to achieve an excellent conduction path by the proper coalescence-wetting behaviors of molten fillers. In this study, to investigate the influence of reductant content on the conduction path formation, four kinds of SPC with different reductant amounts (0, 7.5, 15, and 30 phr) were examined. The LMPA filler with a reductant concentration of 15 phr exhibits excellent wettability because of the proper elimination of the surface oxide layer of fillers and electrodes. However, the wettability deteriorated with a further increased reductant content due to the rapid curing of the SPC at low temperature conditions caused by increased chemical reactions between the carboxyl groups of the reductant and epoxide groups.
Synchrotron X-ray nanotomography, which offers a state-of-the-art resolution, has been applied for the 3D observations of hydrogen induced nano voids under different strain levels in Al–Zn–Mg–Cu aluminum alloys. A great number of nano voids are initiated uniformly across the whole specimen during a loading process. The average diameter and number density of initiated nano voids is 300 nm and 5 × 1015 m−3, respectively. No evidence has been observed that the formation of nano voids results in the propagation of hydrogen induced quasi-cleavage cracks and premature fracture of Al–Zn–Mg–Cu aluminum alloys. Since nano void is one of the hydrogen trap sites in Al–Zn–Mg–Cu aluminum alloys, the majority of hydrogen can be repartitioned to nano voids during deformation due to their high density.