Low Impurity Concentration Research Articles

Effect of diffusion medium on the regeneration of Nd-Fe-B magnet sludge by CaH2 reduction diffusion method

The effects of adding different diffusion medium (KCl and CaCl2) on the regeneration of Nd-Fe-B magnet sludge by CaH2 reduction diffusion (RD) method were investigated. Through thermodynamic calculations, phase-structure and microstructure analysis, we found that the liquid CaCl2 could lower the starting reaction temperature of the CaH2-RD reaction. And the gaseous KCl led to the formation of loose and porous reacted compact, which was beneficial for impurity removal and refining the grains. Besides, CaCl2 would be involved in the CaH2-RD reaction and produce the intermediate product NdOCl, while KCl would not. Therefore, the regenerated Nd-Fe-B powders with finer particle size, low impurity content and uniform particle size distribution were prepared when KCl was used as diffusion medium. The average particle size of the regenerated Nd–Fe–B powders were reduced from 3.49 μm to 1.83 μm. The contents of Ca and O for the regenerated Nd-Fe-B powders were reduced to 0.04 wt% and 0.26 wt%, respectively. The M3T of regenerated Nd-Fe-B powders increased to 152.25 emu/g, which was about 4.1% and 38% higher than CaH2-regenerated Nd-Fe-B powder and initial sludge, respectively. Finally, the regenerated Nd-Fe-B sintered magnets with properties of Hcj = 16.5 kOe, Br = 11.7 kG, and (BH)m = 31.8 MGOe were successfully prepared by adding 40 wt% Nd4Fe14B alloy powders.

Remarkable thermopower property enhancement in two-dimensional SiC via B and N doping and magnetic field

DFT-based tight binding theory calculations and the Kubo conductivity formula were used to investigate the thermopower properties of 2D SiC with different impurity concentrations and magnetic field. The electronic and thermal properties were studied for cases that a carbon replaced with B (BC) and N (NC) atoms. The impurity concentration has been controlled by varying the number of cells from n2 [two unit cells] to n5 [five unit cells]. The electronic structure of the doped SiC has been strongly modified with the impurity type and the created band gap is sensitive to impurity concentration and field strength. In all selected structures, regardless of the impurity type, the subband splitting and the band gap reduction are caused by the magnetic field. Selective doped structures have thermal properties that are dependent on the type and concentration of impurity and the strength of the magnetic field. As a result of the investigations, we are able to conclude (i) structures that contain lower impurity concentrations have larger thermal properties, (ii) doped structures containing BC impurities exhibit higher thermal properties than doped structures containing NC impurities and (iii) magnetic fields have a stronger influence on structures with lower impurity concentrations.

Distillation with separate condensation of components as a new way to prepare especially pure GexTe100−x glasses with precisely desired composition

The study is aimed to develop a method for preparing especially pure GexTe100−x glasses that provides low oxygen impurity content and, at the same time, high accuracy of a given, desired composition. It is shown that the conventional distillation of the Ge20Te80 melt can lead to a deviation in the glass composition from 0.5 to 2.1 at.% depending on the number of stages due to the thermal decomposition of GeTe. Such deviations in the composition have a significant effect on the crystallization of glasses upon heating and the values of the characteristic temperatures. A method for purification of GexTe100−x charge that makes it possible to minimize the deviation of the glass composition from the desired value is developed. The method is based on creating a constant tellurium vapor excess over germanium(II) telluride that suppresses its thermal decomposition. This is achieved by separate condensation of tellurium and GeTe and their subsequent successive evaporation. Two options for practical implementation of the method with the same efficiency, differing in the initial stage of the charge synthesis, are proposed. Using the developed method, Ge20Te80 glass samples with an oxygen impurity content of <10 ppb(wt) and a composition deviation of ≤0.2 at.% are prepared.

Synthesis of submicron ferrous oxalate from red mud with high Fenton catalytic performance on degradation of methylene blue.

Ferrous oxalate dihydrate (FOD) can be used as a photo-Fenton catalyst with remarkable photo-Fenton catalytic and photocatalytic performances on organic pollutant degradation. Various reduction processes were compared in the current study to synthesize FODs from ferric oxalate solutionutilizing the iron source in alumina waste red mud (RM), including natural light exposure (NL-FOD), UV light irradiation (UV-FOD), and hydroxylamine hydrochloride hydrothermal method (HA-FOD). The FODs were characterized and employed as photo-Fenton catalysts for methylene blue (MB) degradation, and the effects of HA-FOD dosage, H2O2 dosage, MB concentration, and the initial pH were investigated. The results show that HA-FOD has submicron sizes and lower impurity contents with more rapid degradation rates and higher degradation efficiencies compared with the other two FOD products. When using 0.1g/L of each obtained FOD, 50mg/L of MB can be rapidly degraded by HA-FOD by 97.64% within 10min with 20mg/L of H2O2 at pH of 5.0, while NL-FOD and UV-FOD achieve 95.52% in 30min and 96.72% in 15min at the same conditions, respectively. Meanwhile, HA-FOD exhibits strong cyclic stability after two recycling experiments. Scavenger experiments reveal that the predominant reactive oxygen species responsible for MB degradation are hydroxyl radicals. These findings demonstrate that submicron FOD catalyst can be synthesized using hydroxylamine hydrochloride hydrothermal process from ferric oxalate solution with high photo-Fenton degradation efficiency and reduced reaction time for wastewater treatment. The study also provides a new pathway of efficient utilization for RM.

Enhancing the separation of Fe/Al/Ca impurities from metallurgical silicon to purify by slagging-directional solidification

Metallurgical silicon (MG-Si) with low content of Fe, Al and Ca impurities is very important for the production of organosilicon. A novel approach of slagging-directional solidification was investigated to remove Fe, Al and Ca impurities. Firstly, the study analyzed the effect of cooling methods and solidification rates on removal of Fe, Al and Ca impurities during directional solidification without the slagging agent. Then, the crystal morphology and impurity micromorphology of silicon ingots obtained with optimal conditions were analyzed and found the shape of the impurity was related to the crystal morphology of the ingot, precipitating at grain boundaries. On this basis, the removal of Fe, Al and Ca impurities by the slagging-directional solidification was studied. The result showed Al and Ca impurities in silicon were few and a small amount of Fe impurity was in the form of Fe–Si. The mechanism of the slagging-directional solidification was analyzed and revealed that it not only effectively removed Al and Ca impurities from MG-Si, but also decreased the effective segregation coefficient of Fe and enhanced the separation of Fe impurity. The method of slagging-directional solidification provides a new idea for the separation of Fe, Al and Ca from MG-Si.

Progress in Isolation and Molecular Profiling of Small Extracellular Vesicles via Bead-Assisted Platforms.

Tremendous interest in research of small extracellular vesicles (sEVs) is driven by the participation of vesicles in a number of biological processes in the human body. Being released by almost all cells of the body, sEVs present in complex bodily fluids form the so-called intercellular communication network. The isolation and profiling of individual fractions of sEVs secreted by pathological cells are significant in revealing their physiological functions and clinical importance. Traditional methods for isolation and purification of sEVs from bodily fluids are facing a number of challenges, such as low yield, presence of contaminants, long-term operation and high costs, which restrict their routine practical applications. Methods providing a high yield of sEVs with a low content of impurities are actively developing. Bead-assisted platforms are very effective for trapping sEVs with high recovery yield and sufficient purity for further molecular profiling. Here, we review recent advances in the enrichment of sEVs via bead-assisted platforms emphasizing the type of binding sEVs to the bead surface, sort of capture and target ligands and isolation performance. Further, we discuss integration-based technologies for the capture and detection of sEVs as well as future research directions in this field.

Self-propagating high-temperature synthesis and sintering of AlN‒Y&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;‒Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; compositions

The results of studies on the synthesis of aluminum nitride and AlN‒Al2O3‒Y2O3 compositions with a low oxygen impurity content by the SHS method are presented. The dependence of the lattice parameter c of aluminum nitride on the oxygen impurity content is shown. The conditions for the synthesis of AlN‒Y2O3 compositions with a low oxygen content in the structure of aluminum nitride are determined. The dependence of the composition of oxide phases in compositions on the content of yttrium oxide in the reaction mixture is shown. The optimal content of yttrium oxide in the compositions has been determined. The results of sintering AlN‒Al2O3‒Y2O3 composite powders with different oxygen content in the aluminum nitride structure are shown.

Growing clean crystals from dirty precursors: Solid-source metal-organic molecular beam epitaxy growth of superconducting Sr2RuO4 films

Ultra-high purity elemental sources have long been considered a prerequisite for obtaining low impurity concentrations in compound semiconductors in the world of molecular beam epitaxy (MBE) since its inception in 1968. However, we demonstrate that a “dirty” solid precursor, ruthenium(III) acetylacetonate [also known as Ru(acac)3], can yield single-phase, epitaxial, and superconducting Sr2RuO4 films with the same ease and control as III–V MBE. A superconducting transition was observed at ∼0.9 K, suggesting a low defect density and a high degree of crystallinity in these films. In contrast to the conventional MBE, which employs the ultra-pure Ru metal evaporated at ∼2000 °C as a Ru source, along with reactive ozone to obtain Ru → Ru4+ oxidation, the use of the Ru(acac)3 precursor significantly simplifies the MBE process by lowering the temperature for Ru sublimation (less than 200 °C) and by eliminating the need for ozone. Combining these results with the recent developments in hybrid MBE, we argue that leveraging the precursor chemistry will be necessary to realize next-generation breakthroughs in the synthesis of atomically precise quantum materials.

Raman spectroscopic study of non‐stoichiometry in cerianite from critical zone

AbstractCerianite (CeO2) is one of the key minerals controlling the behavior of rare earth elements (REE) in supergene environment, yet little is known about the composition and structure of the mineral. We present Raman spectroscopy and compositional data on regolith cerianite from carbonatite‐related supergene REE deposits. Cerianite showed a low content of impurities, distinguishing from high‐temperature environments, where the mineral is characterized by elevated concentrations of lanthanides other than Ce. The Raman spectra are characterized by the shift of the dominant peak located at 464–465 cm−1 in stoichiometric CeO2 to the lower wavenumbers of 450–455 cm−1, the widening of this peak with the increasing shift, and the presence of additional peaks at 225–230, 284, and 604–613 cm−1. The independence of the main spectral characteristics from the laser wavelength (tested by three lasers: 488, 532, and 633 nm) suggests that the features are genuine and not produced by REE luminescence. The anhydrous composition of supergene cerianite is indicated by the absence of Raman bands in the water‐bearing region of the spectra (2700–3200 cm−1). The spectral features of supergene cerianite, combined with the compositional data, suggest non‐stoichiometry in the mineral and the presence of Ce3+ with oxygen vacancies in the mineral structure. Our observations demonstrate the efficiency of Raman spectroscopy for the identification of the non‐stoichiometric composition of cerianite and its common occurrence in the critical zone.

Concentration anomalies of galvanomagnetic properties of (Bi1-хSbх)2Te3 solid solutions based on Sb2Te3 in the (Bi1-хSbх)2Te3 system

Today, solid solutions based on antimony and bismuth tellurides are among the most widely used materials for the p-legs of thermoelectric converters used at room temperature and below. This paper presents the results of a study of galvanomagnetic properties (electrical conductivity σ, Hall coefficient RH, Hall mobility of charge carriers μH) of thermoelectric solid solutions (Bi1-хSbх)2Te3 in the range of compositions close to pure antimony telluride (x = 1 – 0.96) at temperatures T = 80 K and T = 300 K. The study was carried out on cast polycrystalline samples obtained by the method of crystallization from the melt followed by long-term annealing in vacuum at a temperature of T = 650 K. Galvanomagnetic properties were measured by the standard dc-method, the experimental cell was cooled with liquid nitrogen. The measurement error of RH and σ did not exceed ± 5%. It is shown that the introduction of the first portions of Bi2Te3 leads to a sharp decrease in σ, which is associated with a high degree of disorder of the crystal lattice. In the range of compositions x = 0.99 – 0.9825, the concentration dependences of σ(x) and μH(x) revealed anomalous growth of σ and μH. The presence of concentration anomalies is associated with the transition from dilute to concentrated solid solutions. An assumption is made about the percolation nature of the phase transition. Within the framework of the problem of spheres of percolation theory, within the framework of the task of spheres of the theory of percolation the radius of the deformation sphere of an impurity atom (Bi) is estimated. The obtained value is consistent with the short-range potential of the impurity. It is shown that the position of the anomalies in the σ(x) and μH(x) dependences does not change with the decrease in temperature down to 80K. Thus, the observation of concentration anomalies of the properties for the solid solution (Bi1-xSbx)2Te3 is another confirmation of the hypothesis about the universal nature of the behavior of solid solutions at a low impurity concentration. The detected anomalies must be taken into account when developing methods for increasing the thermoelectric performance of materials by creating solid solutions and doping.

Efficient Utilization of Limonite Nickel Laterite to Prepare Ferronickel by the Selective Reduction Smelting Process

Ferronickel products obtained from the traditional process used to treat limonite nickel laterite usually assay very low-grade Ni, only 3–5% Ni due to the high Fe/Ni ratio of limonite nickel laterite. This paper describes an investigation conducted to upgrade limonite nickel laterites for the preparation of ferronickel by using selective reduction smelting technology. By means of thermodynamic calculations and smelting experiments, the smelting separation mechanism and the behavior of P and S removal in the smelting process, as well as the influence of smelting factors, have been systematically identified. The best production index of ferronickel is obtained under optimized conditions as follows: smelting the pre-reduced lumps at 1525 °C for 45 min with a basicity of 0.60, MgO/SiO2 ratio of 0.30, and nickel and iron metallization rate of 94.30% and 10.93%, respectively. The resulting ferronickel features a nickel and iron grade of 12.55% and 84.61% and a nickel and iron recovery of 85.65% and 10.87%, respectively. In addition, the content of S and P contained in ferronickel is only 0.11% and 0.0035%, respectively. The ferronickel obtained from the selective reduction smelting process is a fine material for the subsequent stainless steel smelting due to its high Ni grade and low content of impurities.

Assessment of two-stage anaerobic digestion of blackwater and kitchen waste for reducing environmental impact of residential buildings

In recent years, much attention has been directed towards municipal waste management since these residues has become a global challenge with increasing public health, environmental, social, and economic costs. Therefore, there is an urgent need to adopt widely accepted sustainable alternatives and circular economy approaches. In that sense, the decentralized waste management approach has become a feasible and sustainable strategy to valorise and minimize wastes at source. Among the available technologies, anaerobic digestion is widely used as it allows to recover energy in form of biogas from organic waste. This study proposes a decentralized system based on a two-stage anaerobic digestion for the joint valorisation of organic wastes -blackwater and kitchen wastes-in residential buildings. In the first stage (dark fermentation), different ratios of blackwater:kitchen waste were assessed and a maximum volatile fatty acids production of 5000–7000 mg L−1 was reached when 5 kg of black water and 0.30 kg of kitchen waste were added to the system. Then, during second stage, the volatile fatty acids rich stream was valorised in an upflow anaerobic sludge blanket reactor resulting in a biogas production of 5.45 ± 1.34 L d−1, containing 75.6 ± 7.3% of methane and 22.8 ± 5.7% of carbon dioxide while reporting a low content of impurities - 0.02% of hydrogen sulphide and 0.002% of hydrogen -.

Effect of Hf x Zr1−x O2/Ge metal–ferroelectrics–insulator–semiconductor interfaces on polarization reversal behavior

To evaluate the polarization characteristics of ferroelectric-gate field-effect transistors, metal–ferroelectrics–insulator–semiconductor (MFIS) structures are often used. This study examines the influence of interface characteristics on polarization characterization in MFIS on low-impurity-concentration substrates by experimentally evaluating the ferroelectric properties of Hf x Zr1−x O2 (HZO)/Ge MFIS capacitors with different interface properties. Usually, polarization reversal behavior is not observed for MFIS capacitors on low-impurity-concentration substrates. However, it is found that, when the interface properties are poor and the interface state density is high, polarization reversal behavior can be observed even on the low-impurity concentration substrates. In lightly-doped MFIS capacitors with many interface states, the response of the interface states at low measurement frequencies suppresses the depletion layer change and voltage drop in the Ge substrate, resulting in the high electric field across the HZO films and observation of polarization reversal behavior.

Influence of powder size on the moldability and sintered properties of irregular iron-based feedstock used in low-pressure powder injection molding

Initially used for shaping irregular ceramic powders, manufacturing metallic parts via low-pressure powder injection molding (LPIM) from irregular powders has received very little attention. This study investigates the processability of irregular powders for fabricating high-density and low-cost metallic parts using the LPIM process. Three irregular iron-based powder lots were mixed with a low-viscosity binder, injected, debound, and sintered to evaluate their molding and sintering performances via viscosity measurements, real-scale injections, metallographic analysis, and tensile tests. The results revealed that feedstocks formulated from fine and coarse powders exhibit good moldability, predicted by their moldability indexes and validated by spiral flow distances. Furthermore, the feedstock formulated with the finer powder (i.e., 1250 mesh providing a powder particle size <10 μm) produced a homogeneous microstructure along with a low content of oxygen impurities, leading to the highest sintered relative density of ∼90%, an ultimate tensile strength of ∼225 MPa, and an elongation at break of ∼24%. These results confirm that the cost-effective irregular iron powders present a promising alternative to fabricating metallic parts via low-pressure powder injection molding compared to their relatively high-cost spherical powder counterparts (i.e., carbonyl iron powder).

The high corrosion-resistance of ultra-high purity Mg–Ge alloy and its discharge performance as anode for Mg–air battery

This study reports cast ultra-high-purity (UHP) Mg–Ge alloys that exhibited remarkably high corrosion resistance and good discharge performance as anodes for Mg-air batteries. The UHP Mg-0.5Ge had a corrosion rate of 0.15 mm y−1, which is twice better than Mg's intrinsic corrosion rate of 0.3 mm y−1. The outstanding corrosion resistance is attributed to the low impurity content, the restricted HER, and the presence of a protective surface film. The energy density of Mg-0.5Ge is 37% higher than UHP Mg at 10 mA cm−2. The better discharge properties are ascribed to the more negative corrosion potential and suppressed NDE.

Electronic transport properties of GeS single crystals grown by vapor transport from molten GeS source

The electrical properties of GeS single-crystal are determined by the Van der Pauw method as a function of the temperature, thus establishing for the first time the dependence of electrical resistivity on both carrier concentration and mobility. This was possible after the repeated growth of GeS by vapor transport from molten GeS so that high-purity (low concentration of Fe and Na impurities) and high-crystalline (XRC FWHM = 2 min.) GeS single-crystals could be obtained. An extraordinary high electrical conductivity is observed between 180 and 450 K, ranging from 1.1 x10-2 to 3.7 x10-5 Ω−1 cm−1. Acceptors are activated over the whole temperature range, while donor activation takes place above 280 K, partially compensating the hole carrier concentration. In contrast, the mobility is proportional to T−2.4 over the whole temperature range, indicating the predominance of lattice scattering. At room temperature the electrical conductivity is as high as 6.7 × 10-3 Ω−1 cm−1, originating from a hole concentration of 1.7 × 1015 cm−3 and mobility of 25 cm2/Vs.

Room temperature d 0 ferromagnetism in carbon doped LaH3: insights from density functional theory simulations

Employing the state-of-the-art density functional theory with both generalized gradient approximation and the hybrid HSE06 functional, along with the incorporation of spin–orbit coupling, we have engineered stable room temperature ferromagnetism (FM) (RTF) in nonmagnetic LaH3 through C substitution at octahedral and tetrahedral H sites where the induced magnetic moment is mostly contributed by the 2p orbital of the C atom. It is interesting that the magnetic signature is switched on with an impurity concentration as low as 1.04 at% with a magnetic moment of ∼1.0 µ B per impurity, where the localized behavior of the 2p states of C, along with significant exchange splitting energy, can be attributed as the origin of the induced magnetic moment. The verification of the Stoner criterion in the material further confirmed the onset of FM in the system, and the computed Curie temperature is found to be well above room temperature. Reduced formation energy and the requirement of lower impurity concentration ensure practical feasibility towards a spintronic device where RTF is established from the nonmagnetic host and the dopant.

Periodical Ripening for MOCVD Growth of Large 2D Transition Metal Dichalcogenide Domains

Abstract2D semiconductors, especially 2D transition metal dichalcogenides (TMDCs), have attracted ever‐growing attention toward extending Moore's law beyond silicon. Metal–organic chemical vapor deposition (MOCVD) has been widely considered as a scalable technique to achieve wafer‐scale TMDC films for applications. However, current MOCVD process usually suffers from small domain size with only hundreds of nanometers, in which dense grain boundary defects degrade the crystalline quality of the films. Here, a periodical varying‐temperature ripening (PVTR) process is demonstrated to grow wafer‐scale high crystalline TMDC films by MOCVD. It is found that the high‐temperature ripening significantly reduces the nucleation density and therefore enables single‐crystal domain size over 20 µm. In this process, no additives or etchants are involved, which facilitates low impurity concentration in the grown films. Atom‐resolved electron microscopy imaging, variable temperature photoluminescence (PL) spectroscopy, and electrical transport results further confirm comparable crystalline quality to those observed in mechanically exfoliated TMDC films. The research provides a scalable route to produce high‐quality 2D semiconducting films for applications in electronics and optoelectronics.

The influence of Al-based powder additives on the sintering behaviour of Ti–6Al

The sintering behaviour of Ti–6Al was studied using DSC, dilatometry and microscopy. Blended elemental (BE) and master alloy (MA) mixtures, each at two powder sizes, were compared. During heating, the elemental Al in the BE mixtures melted, spread and exothermically reacted with the surrounding Ti particles to form an evenly distributed intermetallic layer over these particles. This exothermic reaction, from ∼550 to 700 °C, was associated with an expansion of the material due to a Kirkendall effect. No such reaction occurred in the MA mixtures since their additions were already in intermetallic form. Sintering rates generally increased once Ti transformed to the β phase (above 882 °C). However, in the BE mixtures this increased sintering rate was delayed due to the presence of intermetallic layers that first had to dissolve. When sintering at 1200 °C, the BE mixtures homogenized faster than the MA mixtures as a result of the Al being more evenly distributed in the sample from the BE melting event. MA additions introduced higher levels of O and N as impurities, which broadened the temperature range of the α to β phase transformation. The use of fine scale BE additions for Al, to allow in-situ alloying of Ti, presents an optimal approach when taking into account homogenization, low impurity content and sintering densification.

Structure evolutions of the polymer derived medium-/high-entropy metal carbides

Ceramic powders with low oxygen content are highly demanded in monolithic ceramics. In this work, a series of medium-/high-entropy ceramic (HEC) particles, including (Zr0.25Ta0.25Nb0.25Ti0.25)C, (Zr0.2Ta0.2Nb0.2Ti0.2W0.2)C, (Zr1/6Ta1/6Nb1/6Ti1/6W1/6Hf1/6)C (Zr1/7Ta1/7Nb1/7Ti1/7W1/7Hf1/7V1/7)C, and (Zr1/8Ta1/8Nb1/8Ti1/8W1/8Hf1/8V1/8Mo1/8)C, were successfully fabricated by the polymer-derived ceramic (PDC) route. The structure evolutions of the precursor demonstrated that HEC particles obtained at 1800 °C possessed a single phase and rock-salt structure. All the samples had the similar microstructures (hillock structure) and a low oxygen impurity content (less than 2.00 wt%). The results also demonstrated that the as-obtained HEC particles had a disordered distribution of elements from nanoscale to microscale. This work proved a new method to fabricate the HEC powders with low oxygen impurity content and the HEC precursors for further obtaining the nanofibers or ceramic matrix composites.