Formation Of Secondary Phases Research Articles

Secondary phase formation during electrokinetic in situ leaching of intact copper sulphide ore

Electrokinetic in situ leaching (EK-ISL) of copper sulphides is a novel mining technology aimed at recovering copper from orebodies without physical excavation, thereby significantly reducing the environmental footprint of the mining operation. Its viability at larger scale is, however, highly dependent on developing a comprehensive understanding of the geochemical processes occurring inside the pore space of the intact rocks during leaching. One of the critical issues affecting the efficiency of copper sulphide leaching operations is the formation of secondary layers. So far, the details of their formation have only been studied under ex situ conditions and for ground samples. Therefore, this study was aimed at a detailed characterisation of the secondary leaching products under EK-ISL induced leaching conditions and how they evolved over time. We conducted time-dependant leaching tests on intact core samples with either ferric chloride or ferric sulphate as lixiviant. SEM-EDS and laser Raman microspectroscopy showed the formation of elemental sulphur as a result of the oxidation of longer-chain polysulphides. The neo-formed phases showed to slow down copper recovery, yet did not completely halt the leaching progress. Our conceptual model of the secondary layer formation suggests that the sustained dissolution of polysulphides during EK-ISL-induced leaching under the induced geochemical conditions exposes new mineral surfaces to attack. Importantly, this creates the opportunity for secondary phase re-solubilisation and therefore enhanced copper recovery.

Revealing strengthening contribution of grain refinement and phase precipitation in CrMnFeCoNi high-entropy alloy prepared from different powders

Equiatomic CrMnFeCoNi high-entropy alloys (HEAs) were prepared by vacuum hot-pressing sintering with single phase precursor powders made from mechanical alloying (MA) or spray-drying (SD), respectively. MA process was found beneficial for the following precipitation and formation of secondary phases during sintering, after which multiphase bulk HEAs were formed consisting of FCC, M23C6, and precipitated nanoscale σ phases. The tensile and compressive yield strengths of bulk HEAs fabricated from MA powders reached 1150 and 1200 MPa, respectively, which were about three times than SD powders. The excellent mechanical properties of the former were found due to the precipitation of nanoscale σ phase and M23C6 intermetallic resulted from the MA treatment and sintering processing. Nanoscale σ and M23C6 phase can effectively strengthen the alloy not only by self-reinforcement but also through the grain boundaries of the refined grains induced by the precipitation.

Cr deposition and poisoning on SrCo0.9Ta0.1O3-δ cathode of solid oxide fuel cells

Perovskite type SrCo0.9Ta0.1O3-δ (SCT10) is a promising cathode for solid oxide fuel cell (SOFC), but its stability towards Cr impurities is not yet exploited. Herein, the Cr deposition on the electrochemical performance of SCT10 cathodes is evaluated at 700 °C with a cathodic constant current density of 200 mA cm−2. Both polarization and impedance results reveal that Cr impurities lead to serious performance degradation, especially in wet condition. Significant morphology damages occur after Cr exposure and the formation of SrCrO4 and Co3O4 secondary phases on the cathode surface are determined, which greatly deteriorates the oxygen reduction kinetics and thereby the cathode activity. Our study highlights that surface Sr segregation plays a vital role for Cr deposition and special attention should be paid for the practical applications in SOFC.

Morphological evolution in nanostructured secondary phases in entropy stabilized oxides

High entropy oxides (HEO), containing equimolar ratios of five or more oxide components, have emerged recently as an important class of materials with a variety of interesting properties. Some, but not all, HEO systems can be classified as entropy stabilized oxide (ESO) materials, which means they have a phase state that is stabilized by entropy. In these materials, the competition between the metastable entropy stabilized and equilibrium enthalpy stabilized phase states leads to a reversible entropic phase transformation and the formation of secondary phases after heat treatment. The morphologies of the secondary phases (i.e., Cu-rich tenorite and Co-rich spinel) in bulk (Co,Cu,Mg,Ni,Zn)O were visualized in three dimensions for the first time by using focused ion beam (FIB) tomography. The Cu-rich tenorite secondary phase is observed to manifest as several highly complex particle morphologies with features in the nanometric regime. These morphologies are influenced by heat treatment conditions and the interaction with the Co-rich spinel secondary phase. Additionally, the morphology is dependent on the size of the secondary phase particles themselves, with the morphology evolving from spheres, to needles, to plates as the particles get larger. These results indicate that several strategies can be implemented to manipulate the morphologies of the secondary phases, making it possible to engineer bulk ESO materials with specific microstructural features. The ability to form complex nanostructured architectures will provide a powerful strategy for controlling behavior and expanding the possible applications of ESO materials. • Cu-rich tenorite and Co-rich spinel phases segregate in ESOs during heat treatment. • FIB tomography was used to examine the secondary phase particles in 3D. • Particles have complex geometries with sphere, needle, and plate morphologies. • Most particles have a nanostructured dimension, regardless of overall size. • Cu-rich tenorite phase particles have a size dependent morphological evolution.

Strength-plasticity regulation via nanoscale precipitation and coprecipitation in cobalt-free medium-entropy alloys

Nanoprecipitate-strengthened Co-free medium- and high-entropy alloys represent a new candidate for nuclear applications because of their low costs and excellent radiation resistance. However, the premature stress concentration around the nanoprecipitates during deformation tends to greatly reduce the tensile ductility. In this work, L1 2 and D0 22 nanoprecipitates were introduced for the primary purpose of strengthening Co-free Cr 25 Fe 32 Ni 35 Mo 3 Al 5- x Nb x alloys ( x = 1, 2, or 3). The Al/Nb content can influence both the secondary phase formation and the type of nanoprecipitates. Calculations show that order and coherent strengthening play a major role in the D0 22 nanoprecipitation strengthening. In contrast, the strengthening effect of the L1 2 nanoprecipitates was dominated by an order strengthening mechanism. Precipitation not only increases the strength, but also controls the deformation mechanism, which can activate an abnormal deformation mechanism under the condition of low stacking fault energies. This abnormal deformation mechanism originates from the regulation of nanoprecipitates, which determines whether to induce stacking faults or suppress stacking faults to induce microbands, thereby contributing a large ductility. These discoveries provide new insights into the development of alloys with excellent mechanical properties. • D0 22 /L1 2 nanoprecipitates-strengthened Co-free MEAs were designed. • The Al/Nb content affects the phase composition and the type of the nanoprecipitates. • Precipitation not only increases the strength, but also controls the deformation mechanism. • SFs and microbands improve the ductility and strain hardening rate to overcome the strength-ductility tradeoff.

Formation mechanism of coronal composite secondary phase in titanium-zirconium-molybdenum alloy

The coronal composite secondary phase has a high mismatch tolerance with the molybdenum matrix. TiO 2 particles located within the coronal structure that provide a semi-coherent interface with a mismatch degree of 8.70%, and ZrO 2 particles located outside the coronal structure that provide an incoherent interface with a mismatch degree as high as 41.61%. The ZrO 2 particles of the coronal composite secondary phase are partially attached to the TiO 2 in a coronal structure, which endows the ZrO 2 with the molybdenum matrix's higher interfacial bonding force. Titanium sulfate and zirconium nitrate are realized the mixing of Ti/Zr, TiO 2 /ZrO 2 molecules at atomic levels. Compared with Ti, Zr is more easily combined with oxygen, which leads to Zr in Ti/Zr solid solution being attracted by oxygen at high temperature to form ZrO 2 . The small addition of zirconium element lacks nucleation particles to form of ZrO 2 , so ZrO 2 can only adhere to more TiO 2 particles and nucleate, forming the second phase of the coronal composite structure. This study can guide the design of high-performance secondary phase strengthening alloys. • The coronal composite secondary phase and the Mo matrix have a high tolerance of mismatch degree. • ZrO 2 particles are attached to TiO 2 , which endows ZrO 2 with a higher interfacial bonding force with Mo. • The secondary phase particles have a fine particle size, uniform distribution, and strong adhesion. • Mixing at the molecular or atomic level, Zr is oxyphilic, enabling the formation of the coronal composite secondary phase.

Mechanisms of secondary phases formation and resultant mechanical properties of a beta-type Ti-13.3Mo-7.2Al–4Zr-0.25Ni alloy fabricated by laser aided additive manufacturing

The microstructures of Ti alloys are sensitive to the thermal history during the laser aided additive manufacturing (LAAM) process, which inevitably affects the mechanical properties. The dimension of the deposited part is one of the important factors influencing the heat accumulation and dissipation. In this work, the effect of sample size on the LAAM-built β-titanium Ti-13.3Mo-7.2Al–4Zr-0.25Ni (wt.%) was investigated. The results demonstrate that the vertical sample with smaller cross-section area has larger grain size than the horizontal sample with larger cross-section area. In addition, three types of secondary phases, i.e., Ti3Al, Ti2Ni and TiNi, are formed in the vertical sample due to thermal accumulation caused by the smaller cross-section area. The formation of the secondary phases leads to higher Vickers hardness and brittle failure of the vertical sample. However, the horizontal sample with no secondary phase demonstrates excellent combination of high yield strength (923 MPa) and low elastic modulus (68.7 GPa), which is beneficial for structural and biomedical application. Furthermore, the low modulus is mainly ascribed to the crystallographic texture along <001> direction.

Nucleation and growth behavior of multicomponent secondary phases in entropy-stabilized oxides

The rocksalt structured (Co,Cu,Mg,Ni,Zn)O entropy-stabilized oxide (ESO) exhibits a reversible phase transformation that leads to the formation of Cu-rich tenorite and Co-rich spinel secondary phases. Using atom probe tomography, kinetic analysis, and thermodynamic modeling, we uncover the nucleation and growth mechanisms governing the formation of these two secondary phases. We find that these phases do not nucleate directly, but rather they first form Cu-rich and Co-rich precursor phases, which nucleate in regions rich in Cu and cation vacancies, respectively. These precursor phases then grow through cation diffusion and exhibit a rocksalt-like crystal structure. The Cu-rich precursor phase subsequently transforms into the Cu-rich tenorite phase through a structural distortion-based transformation, while the Co-rich precursor phase transforms into the Co-rich spinel phase through a defect-mediated transformation. Further growth of the secondary phases is controlled by cation diffusion within the primary rocksalt phase, whose diffusion behavior resembles other common rocksalt oxides.Graphical abstract

Synergetic Effects of Complex Additions of Mo and Ni on the Phase Transformation Behavior and Mechanical Properties of Austenitic Lightweight Steels

Fe–30Mn–10.5Al–1.1C alloys with different Mo and Ni contents are prepared to investigate the phase transformation behavior and mechanical properties of austenitic lightweight steels. Solution‐treated samples have microstructures consisting of an austenite matrix and ordered κ‐carbides, and the size of the κ‐carbides decreases with the addition of Mo or Ni. In addition, the ordered body‐centered cubic (BCC) phases of B2 and DO3 also form when 3wt%Mo and 3wt%Ni are complexly added, resulting in a large decrease of the austenite grain size. Nanoindentation experiments show that the intrinsic strength of the austenite matrix changes depending on the precipitation behavior of the κ‐carbide; i.e., the addition of 3wt%Mo or 3wt%Ni decreases the intrinsic strength of the austenite by suppressing κ‐carbide precipitation, while complex additions of 3wt%Mo and 3wt%Ni increase them again. The results of tensile tests show that the alloy containing both 3wt%Mo and 3wt%Ni exhibits the highest yield (1102 MPa) and tensile strength (1155 MPa) with large tensile ductility (33%) due to the effects of grain refinement of the austenite grains and formation of secondary hard phases of DO3 and B2, as well as κ‐carbides. Finally, the changes in the precipitation behavior of the κ‐carbide are investigated via transmission electron microscopy and atom probe tomography analyses.

Controlled Surface Morphology and Electrical Properties of Sputtered Titanium Nitride Thin Film for Metal–Insulator–Metal Structures

Titanium nitride (TiN) is a material of interest for electrodes owing to its high-temperature stability, robustness, low-cost, and suitable electrical properties. Herein, we studied the surface morphology and electrical properties of TiN thin film deposited onto an Si/SiO2 &lt;100&gt; substrate through direct current (DC) sputtering with a high-purity TiN target in an argon-gas environment. The electrical properties and surface morphology of TiN thin film significantly improved with increased source power and decreased working pressure. The improved electrical properties could be attributed to the suppressed secondary phase (Ti2N) formation and the reduced electron scattering on smoother surface. Consequently, high-quality TiN thin film with the lowest resistivity (ρ = 0.1 mΩ·cm) and the smallest surface roughness (RMS roughness, Rq = 0.3 nm) was obtained under the optimized condition. The TiN film was further used as the bottom electrode for a metal–insulator–metal (MIM) capacitor. Results demonstrated that the electrical properties of TiN film were comparable to those of noble-metal thin films. Therefore, the TiN thin film fabricated by DC sputtering method had excellent electrical properties and good Rq, indicating its potential applications in MIM capacitors and Si technology.

Highly Durable Solid Oxide Fuel Cells: Prevention of Chemical Inter-Diffusion By Introducing a 4-Layered Structure

Solid oxide fuel cell (SOFC) poses great potential for stationary power generation. Nevertheless, its full-scale commercialization has lagged due to the inadequacy of long-term durability. Along with diverse background of performance deterioration, the inter-diffusion between the cathode and electrolyte have been identified as a leading fatal factor. Herein, we introduced a robust GDC layer by sequential lamination approach that completely suppresses the detrimental phase of SrZrO3 at electrolyte interface during high temperature operation. This buffer layer is fabricated via green film sequential lamination, in which the anode support, anode functional layer, electrolyte and GDC layers were sequentially co-laminated by iso-static pressing and co-sintered at 1300-1400°C. The enhanced interfacial connectivity and desired packing density of electrolyte and buffer layer were attained by controlling the shrinkages behaviors of each component. Thus, the formation of detrimental secondary phases (SrZrO3) at interface of electrolyte and decomposition of cathode are successfully restrained during fabrication and operation at critical current density. The scale-able and mass production are also confirmed through the fabrication of large area cells (144cm2) having active area 100cm2. The sequentially co-laminated GDC layer exhibited extreme low degradation rate of 0.2%/khr, which fulfils the critical longevity benchmark for commercialization of technology. This work features a cost-effective, scalable, and reproducible method for larger scale production of robust multi-layer anode supported SOFC.Keywords: Durability, Sequential lamination, life expectancy, Detrimental phases, iso-static pressing

Robust ferromagnetism of (Co, Er) co-implanted ZnO-based diluted magnetic semiconductor

The present study reports room temperature ferromagnetism observed in Co implanted, Er implanted and (Co, Er) co-implanted ZnO films deposited by filtered cathode vacuum arc (FCVA) on sapphire substrates. The microstructures, surface morphologies, electrical and magnetic properties of pure and implanted ZnO films were investigated. X-ray diffraction results confirm that the implantation of Co and Er ions cause the substitution of Zn ions without the formation of secondary phases. The results of X-ray photoelectron spectroscopy indicate that the Er ions and Co ions are in trivalent and divalent states, respectively. After ions implantation, the electrical properties of the films are improved and the carrier concentration of Er implanted ZnO film is higher than that of Co implanted ZnO film. Substantial intrinsic ferromagnetism has been observed for all the implanted ZnO films. The saturation magnetization for the Er implanted ZnO film is higher than that of the Co implanted ZnO film and the magnetization is further enhanced by (Co, Er) co-implanting. The carrier mediated exchange mechanism can well describe the origin of ferromagnetism in the doped ZnO films. Our results can provide a reference for preparing high-quality diluted magnetic semiconductors (DMSs) by RE elements and TM elements co-doping in ZnO films. The saturation magnetization for the Er implanted ZnO film is higher than that of the Co implanted ZnO film and the magnetization is further enhanced by (Co, Er) co-implanting. • A filtered cathode vacuum arc (FCVA) deposition system was used to grow ZnO films on sapphire substrates. • The saturation magnetization for the Er implanted ZnO film is higher than that of Co implanted ZnO. • The magnetization is enhanced by Co-Er co-doping compared with Co doped and Er doped film. • The magnetization shows carrier concentration-dependent behavior.

Reactivity evaluation of NASICON-type solid electrolyte LATP, LAGP and Olivine-type cathode LCP

• The solid-state reaction and phase decomposition were remarkable between LAGP-LCP. • LATP-LCP has high thermal stability, no formation of secondary phases at 800 °C. • Co diffused from LCP to LATP and dissolved into the LATP. • Co is a key element that improves the low-temperature sinterability of LATP-LCP. The chemical reactivity and thermal stability of the NASICON-type Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) and Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP) solid lithium-ion conductive materials with the Olivine-type LiCoPO 4 (LCP) cathode active material were evaluated. The LATP or LAGP and LCP powders were mixed, uniaxially-pressed, and heat-treated in the air at 800, 900, and 1000 °C for 10 h. The obtained sintered bodies were crushed into powders, then characterized by X-ray diffraction and scanning electron microscopy together with energy-dispersive X-ray spectroscopy. LAGP-LCP decomposes and melts at 800 °C, and produces some different phases. On the other hand, LATP-LCP produces different phases at 900 °C, although it does not produce a different phase at 800 °C, thus forming a dense microstructure. This shows that the LATP-LCP system is an excellent combination of electrolyte and cathode active material that can be sintered in air. This mixed composite can also be used as a composite electrode in bulk-type lithium-ion batteries.

Effect of Al concentration on the structural and thermoelectric properties of ZnAlS alloy

In the present study, we have successfully controlled the structural and thermoelectric properties of ZnAlS nanoparticles alloy by varying the concentration of Al atoms (1, 2, 3 and 4 %). The samples under investigation were prepared by the solid state reaction method and were characterized using X-ray Diffraction (XRD), Raman spectroscopy measurements and Seebeck data. XRD data have confirmed the cubic phase of ZnS with specific planes 100), (1 1 1), (2 2 0), and (3 1 1). XRD data also verified that structure quality of prepared samples was found to be decreased as we increased the concentration of Al atoms up to 4 %. Raman data demonstrated two peaks at 285 and 348 cm−1 which are assigned as TO and LO modes of cubic ZnS respectively. Seebeck coefficient/thermomotive force and electrical conductivity values are increased to 153.5 μV/°C and 1011.11 S/µm respectively, when the concentration of Al atoms increased to 4 % and measurement temperature reached at 100 °C. The simultaneous enhancement in conductivity and Seebeck data suggested the formation of secondary phases when we increased the concentration of Al atoms because extra Al atoms are unattended by the ZnS structure therefore these atoms are involved in the formation of secondary phases.

Assessment of the laser floating zone processing of thermoelectric CuFe1–xNixO2 delafossites and their magnetic characterisation

This work assesses the feasibility of processing CuFe1-xNixO2 (x = 0, 0.02) using the Laser Floating Zone (LFZ) technique to grow fibres with different pulling rates, to tune their thermoelectric performance. Structural analysis showed CuFeO2 as the major phase. Formation of secondary phases is promoted by Ni addition, diminishing with decreasing pulling rate. Grain alignment and crystallite size of the fibres increase with the puling rate and doping. Electrical conductivity is enhanced by decreasing the pulling rate, while Ni-doping decreases the conductivity, and Seebeck coefficient demonstrates quite complex behaviour. Thermal conductivity decreases with temperature and with the pulling rate and Ni-doping. A maximum ZT value of 0.17 was achieved for 10 mm h-1 sample at 1000 K for pure, and 700 K for Ni-doped samples. These ZT values are higher than found in the literature, demonstrating the feasibility of the LFZ method for processing thermoelectric delafossites, indicating a proper optimisation process.

The Effect of Grain Boundary Mobility on the Formation of Second Phases in Nanostructured Binary Alloys

The Effect of Grain Boundary Mobility on the Formation of Second Phases in Nanostructured Binary Alloys

Influence of Nb content on the mechanical behavior of zirconium alloys

Zirconium alloys are basically used in the core structural components of a nuclear reactor. For further understanding mechanical behaviors of zirconium alloy, several alloys with various Nb content are investigated. Microstructure observation, Vickers hardness and mechanical stress-strain curves have been investigated and numerically extracted. Conclusions confirm that the precipitation content of the second phases in Zr-Sn-Nb-Fe-Cr alloys increases with the gradual increment of Nb content. When Nb content reaches to 1.2 wt.%, the excess Nb participates in the formation of second phase containing Nb, which increases the amount of second phases. Moreover, the increase of alloy strength and hardness is mainly attributed to the precipitation strengthening mechanism of second phases.

Role of Al additions in secondary phase formation in CoCrFeNi high entropy alloys

AlxCoCrFeNi High Entropy Alloys (HEAs), also referred to as multiprincipal element alloys, have attracted significant interest due to their promising mechanical and structural properties. Despite these attributes, AlxCoCrFeNi HEAs are susceptible to phase separation, forming a wide range of secondary phases upon aging, including NiAl–B2 and Cr-rich phases. Controlling the formation of these phases will enable the design of age-hardenable alloys with optimized corrosion resistance. In this study, we examine the critical role of Al additions and their concentration on the stability of the CoCrFeNi base alloy, uncovering the connections between Al composition and the resulting microstructure. Addition of 0.1 mol fraction of Al destabilizes the single-phase microstructure and results in the formation of Cr-rich body-centered-cubic (bcc) phases. Increasing the composition of Al (0.3–0.5 mol fraction) results in the formation of more complex coprecipitates, NiAl–B2 and Cr-rich bcc. Interestingly, we find that the increase of the Al content stimulates the formation of NiAl–B2 phases, increases the overall density of secondary phases, and influences the content of Cr in Cr-rich bcc phases. Density functional theory calculations of simple decomposition reactions of AlxCoCrFeNi HEAs corroborate the tendency for precipitate formation of these phases upon increased Al composition. Additionally, these calculations support previous results, indicating the base CoCrFeNi alloy to be unstable at low temperature. This work provides a foundation for predictive understanding of phase evolution, opening the window toward designing innovative alloys for targeted applications.

Laser-based powder bed fusion of pre-alloyed oxide dispersion strengthened steel containing yttrium

In this study, the pre-alloyed powder Fe-22Cr-5.1Al-0.5Ti-0.26Y (wt%) was prepared by nitrogen atomization and characterized with the aid of focused ion beam (FIB) and transmission electron microscopy (TEM). The oxide dispersion strengthened (ODS) bulk material was successfully fabricated using laser-based powder bed fusion (PBF-LB). Micro-scale Y-Al-O complex oxides and nanoscale Y 2 O 3 @TiN core-shell structures were found in the as-built material. The importance of the presence of residual oxygen in the atomization system and the building chamber for the formation of dual-scale secondary phases was revealed. In addition, the formation mechanism of the dual-scale secondary phases was elucidated by investigating the phase and composition of the as-built ODS steel. Columnar crystals with {001}< 100 > cubic alignments grew epitaxially from the bottom of the molten pool during the PBF-LB process, forming a weak cubic texture in the as-built material. This cubic texture led to anisotropic tensile properties of the as-built material, where the room-temperature ultimate tensile strength in the XY-45° direction was higher than that in the building direction (Z). Our work provides a feasible scheme to shorten the preparation process of ODS alloys, which is usually carried out using complicated means. • The Y-containing pre-alloyed powder was prepared by nitrogen atomization. • Primary precipitates in the powder were characterized by FIB and TEM. • Residual oxygen participated in the alloying reaction in the molten metal. • Formation mechanisms of oxides and cubic texture were revealed.

Stable pure-iodide wide-band-gap perovskites for efficient Si tandem cells via kinetically controlled phase evolution

<h2>Summary</h2> Halide perovskites, promising top-cell materials for efficient Si tandem solar cells, suffer from halide segregation, which results from the halide mixing necessary for achieving band-gap widening. We report pure-iodide wide-band-gap perovskite top cells that are fundamentally free of halide segregation. Cs and dimethylammonium cations were incorporated simultaneously into the A-site of perovskite structure to increase the band gap while maintaining the tolerance factor. However, the incorporation of dual cations resulted in the simultaneous formation of orthorhombic and hexagonal secondary phases rather than forming the pure perovskite phase, owing to the different precipitation kinetics between cations. We demonstrated that this strategy can only be implemented by the phase-controlled nucleation of the Cs-rich composition that governs the desired phase evolution. The pure-iodide perovskite top cell exhibited excellent photo-stability (1% degradation after 1,000 h of continuous operation; ISOS-L-1I, white LED), and its Si tandem exhibited a high conversion efficiency of 29.4% (28.37% certified).