Amorphous Grain Research Articles

Moderate strategy for efficient recovery of rare earth elements from scintillation crystal waste

The lutetium has been known to be used in medical imaging materials, but its scarcity in the Earth’s crust makes it expensive. In this work, we present a process for efficient lutetium recovery from the lutetium-yttrium oxyorthosilicate crystals (LYSO) waste. The process involves preliminary mechanical activation, followed by rare earth extraction via acid leaching. The key factors for activation and leaching were studied and optimized. The mechanism of mechanical activation promoting rare earth leaching was revealed by employing the characterizations of morphology and crystal structure of LYSO. It was found that the mechanical activation process could destroy the crystal structure of LYSO waste, forming numerous amorphous phases and grain boundaries, which facilitated the breaking of existing bonds and mass transfer of acid. It was also discovered that the formation of silica gel during leaching impedes the leaching of rare earth, and low concentrations of hydrochloric acid, combined with stirring during acid leaching, could reduce the impact of silica gel. Ultimately, following a mechanical activation pretreatment at 300 rpm for 90 min, 98.7 % of lutetium could be leached after 60 min of acid leaching in 3 mol/L hydrochloric acid. This process addresses the problems associated with high energy consumption and excessive usage of acidic and alkaline reagents in conventional recycling techniques. Compared to conventional methods, the mechanical activation-acid leaching method has a minimum economic benefit improvement of 20.8 % in the process of recovery from LYSO waste. It offers an alternative and more energy-efficient and economical recycling route for waste scintillation crystals.

Solar driven photocatalytic colored co–TixOyNz amorphous film prepared through air plasma treatment of sputtered titanium film

Colored co–titanium oxides and oxynitride amorphous thin film were fabricated through air plasma treatment of sputtered titanium films. Air plasma treatment led to the removal of the passive film that developed on the titanium film surface, and changes in the structural and optical properties of the films. The amorphous nature, grain size, and thickness of the films remained invariant after the treatment process. The surface roughness of the films increased upon plasma treatment. UV-vis spectroscopy study showed the reduction of the bandgap energy of the films after the air plasma treatment and the maximum reduction was found for the thinner film. The 60min air plasma treatment of the thinner film (AD5: film with 5 min deposition time) leads to the changes in bandgap from 4.11 eV to 3.26 eV, and significant Urbach energy values pointed to the formation of defect states. XPS analysis highlighted that the plasma treatment process led to the formation of titanium oxides (TiO2, Ti2O3) and oxynitrides (TiON), accompanied with Ti2+ defect states in the bandgap. The degradation of methylene blue dye solution with plasma-treated film (PT5) as the photocatalyst resulted in 88% degradation efficiency under 240min irradiation of solar simulator. The degradation has also been checked with natural solar illumination and is found to have a 90% degradation efficiency in 480min.

Effect of micro-diamond and nano-polycrystalline diamond interfacial microstructure on OLC phase transition

The interfacial microstructure of micro-diamond and nano-polycrystalline diamond (nPCD), as well as their effect on the phase transition of complete structure onion-like carbon (OLC), were investigated using molecular dynamics simulations and experimental methods under high pressure and temperature (HPHT). Introducing micro-diamond disrupted the symmetric equilibrium structure of complete structure OLC, reduced the diamond nucleation process, and formed a coherent interface ((111)CD // (002)Gr), where cubic diamond (111) crystal plane was parallel to graphite (002) crystal plane. This transformed the initial diffusionless phase transition path of complete structure OLC into a low potential path for phase transition along the graphite crystal direction [002] by (111)CD // (002)Gr, thereby reducing the phase transition conditions. Additionally, due to different stacking orders or breakages in the graphite layers of the complete structure OLC, micro-diamond, and nPCD formed four interfacial microstructures containing twin boundaries (TB), cubic diamond, stacking fault (SF), and amorphous grain boundary (aB). Furthermore, under HPHT effects, numerous TBs and SFs were generated inside micro-diamonds as well as at their edges, resulting in a Vickers hardness of 167 GPa for polycrystalline diamond (PCD) composite. This simple yet effective method reduces synthesis conditions for OLC precursors while producing high-performance PCD composites with promising applications.

Electrodeposition of ReMo alloys

The electrodeposition of superconducting ReMo alloys is investigated using highly concentrated electrolytes with acetate, citrate, and the two oxometallate anions, MoO42− and ReO4−. The effects of applied deposition current, the concentrations of acetate, citrate, and metal source in the electrolyte on the film composition, faraday efficiency as well as the partial current densities of Re and Mo are systematically studied. A hybrid complex species, such as (MoO42−)(ReO4−)(HCit3−)2 and its partially reduced form, is proposed to form and mediate the co-deposition reaction. The morphology and superconductivity of alloy films are characterized using microscopy and cryogenic four-probe measurements. The electrodeposited ReMo alloy films maintain the same amorphous grain structure and the same enhanced superconducting transition temperature as pure Re films.

Synergistic influence mechanism of B-Ga content on microstructures and magnetic properties of Nd-Fe-B ribbons

To understand the influence mechanism of B and Ga content on magnetic properties of NdFeB ribbons, Nd29.89FebalGayCo5.93Bx (wt%, x = 0.80–0.98, y = 0.24–1.04) alloys were prepared and magnetic properties, phase composition, coercivity mechanism, and microstructure of these alloys were investigated systematically. The melt-spun ribbons exhibited 2:14:1 phase grains with varying grain sizes and amorphous grain boundary phases at a wheel speed of 25 m/s. By reducing the B content within a specific range, grain refinement was achieved, resulting in narrower triangular grain boundaries, more uniform and continuous thin grain boundaries. Meanwhile, further increasing the Ga content, the grain shape changes from elongated to equiaxed, and the grain size is greatly refined. However, for x = 0.89, y = 0.84 strip, the coercivity is still reduced due to the large number of directly contacted grains. Consequently, an alloy composition of Nd29.89FebalGa0.64Co5.93B0.89 yielded excellent comprehensive magnetic properties, including a remanence of 8.5 kGs and a coercivity of 18.01 kOe. The corresponding magnetic properties enhancement mechanism is further discussed.

Photo-ionization structures of Planetary Nebula IC 2003 with [WR] central star

We present ionization structures of IC 2003, a planetary nebula with [WR] central star, using a 1-D dusty photo-ionization code: ”CLOUDY 17.03”. The photo-ionization model is constrained by archival UV emission line fluxes, medium-resolution optical spectroscopy, IRAS25μm flux, absolute Hβ flux, and the mean angular size of the nearly spherical optical nebula. To constrain the carbon abundance and the effect of photo-electric heating in the ionized gas, we used UV emission lines. We considered an amorphous carbon dust grain with MRN and KMH size distributions to address the importance of photo-electric heating in the ionized nebula. We show that KMH grain size distribution with quantum dust heating reproduces the observations quite well. We construct the ionization structures of different elements at their different ionization stages in the nebula. We derive the physical properties of the planetary nebula and its chemical composition, as well as the parameters of its central star. The estimated nebular dust-to-gas mass ratio is 2.37×10-3, and the enhanced photo-electric heating yielded by small dust grains is 9.4% of the total heating. We considered the H-poor model atmosphere for the central star; the effective temperature of the central star is 177 kK, the specific gravity log(g) is 6, and its luminosity (L∗) is 6425 L⊙. The derived central star parameters plotted on stellar evolutionary tracks correspond to a central star mass of 0.636 M⊙ and to a progenitor mass of 3.26 M⊙.

A cost-effective dual-layer grain boundary diffusion strategy to significantly enhance coercivity of sintered Nd-Ce-Fe-B magnets

In an attempt to obtain cost-effective sintered Nd-Ce-Fe-B magnet and overcome the coercivity-remanence trade-off challenge caused by heavy rare earth (HRE) diffusion, a novel dual-layer coating method has been proposed for the grain boundary diffusion process (GBDP). A high coercivity increment of 8.56 kOe is achieved by dual-layer coated DyHx/Pr80Al20 (DH/PA) diffusion with 0.8 wt% DyHx and a slight remanence reduction from 12.85 to 12.71 kG. Although the DyHx diffused magnet has a coercivity increment of 9.24 kOe, it consumes twice as much DyHx as the DH/PA diffused magnet at the great sacrifice of remanence. This can be attributed to the formation of continuous grain boundary phase and thin Dy-rich shell via microstructural observations. Further TEM characterization indicates that the amorphous triple junction grain boundary phase (TJP) gradually transforms into the crystalline Nd2O3 structure after GBDP. The coexistence of cubic-Nd2O3 phase and hexagonal-Nd2O3 phase found in the dual-layer coated Pr80Al20/DyHx (PA/DH) diffused magnet creates a more intricate grain boundary phase structure, hindering the diffusion of Dy. Comparably, the formation of single cubic-Nd2O3 (Ia3̅ structure) grain boundary phase in the DH/PA and DyHx diffused magnets is an important reason for the significant increase in coercivity. Based on the evaluation of magnetic performance and cost, the DH/PA diffused magnet achieves a higher price-performance ratio (PPR). This cost-effective bilayer grain boundary diffusion strategy provides a valuable reference for high PPR Nd-Ce-Fe-B magnet fabrication.

Enhancing coercivity through grain boundary phase modification in SmxFe10V2

ThMn12-type Sm(FeV)12 magnets with high coercivity (Hc) demonstrate promising potential as alternative rare-earth-lean permanent magnets. This study delves into the microstructure and magnetic properties influenced by the Sm content in the SmxFe10V2 (x = 1.4–1.9) alloy. High-density SmFe10V2 bulks were prepared through a jet-milling process, followed by high-pressure pressing and heat treatment. Upon increasing the Sm content beyond 1.6, the heat-treated bulks exhibited a predominant ThMn12 phase, accompanied by a secondary phase – Sm oxides. Additionally, Sm played a pivotal role in influencing the ThMn12 crystal structure, with the c/a value reaching the smallest in the Sm1.7Fe10V2 bulk. This change contributed to heightened anisotropy constants and Tc values. The introduction of an amorphous Sm-rich grain boundary phase, with the thickness of 1.2 nm, was observed in bulks within a specific Sm content range, influenced by the heat-treatment time. Notably, this phase was absent in bulks with insufficient or excessive Sm. The grain boundary phase had a substantial impact on improving Hc, reaching 10.6 kOe in the Sm1.7Fe10V2 bulk heat-treated for 25 min. However, Hc exhibited a gradual decrease with prolonged heat treatment, attributed to the evaporation of Sm leading to the disappearance of the grain boundary phase. This nuanced relationship underscores the importance of optimizing heat treatment conditions to harness the full potential of ThMn12-type Sm(FeV)12 magnets for enhanced Hc.

Aluminum nitride‐based ceramics with excellent thermal shock resistances

AbstractCeramics were susceptible to thermal shock failure. In this work, aluminum nitride‐based ceramics with excellent thermal shock resistance were developed. Thermal shock resistance was evaluated in the temperature range of 1200–1600°C by thermal cycling of 10, 20, 30, and 50 times. The phase composition, microstructure, and mechanical properties of the ceramics before and after the thermal shock were investigated. After 50 thermal cycles, the retention rates of the flexural strength and fracture toughness were 81.7% and 113.1%, respectively. The excellent thermal shock resistance was attributed to the combined effects of amorphous grain boundaries that passivate the propagation of microcracks and in‐situ precipitation of nanocrystalline particles during thermal cycles, both of which provide useful guidelines for developing ceramics with better thermal shock resistances.

Effect of Ce replacing La on the electrochemical performance of amorphous grain boundaries Mg-Ni-based materials

Aiming at enhancing the electrochemical characteristic of RE-Mg-based composite, the partial substituting La with Ce experiment in the composites was conducted, and the surface modification treatment of the alloys was performed by mechanical coating Ni. By means of mechanical trituration, The La10-xCexMg80Ni5 (x = 0–2) + y wt% Ni (y = 50–200) compound materials which have the structures of nanocrystalline and amorphous were synthesized. In order to make sense of the principle action of Ce and Ni elements in structural and electrochemical properties of the material, some deep research were carried out. According to the final results, the as-milled composites have the electrochemical hydrogen absorption and hydrogen desorption abilities at room temperature. Having no use for activation, the as-milled composites can reach the maximum discharge capacities when the first cycling was carried out. With the Ni value x changed from 50 to 200, the discharge capacity was varied from 70.5 mAh/g to 902.1 mAh/g; moreover, the capacity retention rate at 20th cycle (S20) and high rate dischargeability (HRD) of the (x = 0) composite were heightened from 67.2 % to 82.3 %, from 50.6 % to 55.7 % respectively. The composites' (y = 100) discharge capacity has a maximum value 118.5 mAh/g when the Ce value x is 1. The capacity retention rate (S20) is enhanced from 53.3 % to 68.5 % by lifting Ce content from x = 0 to x = 2. what's more, the high-rate discharge ability (HRD), the electrochemical impedance spectrum (EIS), potentiodynamic polarization curves, and potential-step measurements all intimate that substituting La with Ce clearly promotes the composites' electrochemical kinetic properties, but maximum values emerge only when the x value is 1.

Ferricretes in fluvial archives of a tropical iron province: Records of the Late Quaternary landscape dynamics in the Brazilian Atlantic Plateau

AbstractThe occurrence of iron‐rich rocks in some areas makes possible the formation of duricrusts in positions from the relief tops to the slopes and valley bottoms, as is the case of the Quadrilátero Ferrífero (QF—‘Iron Quadrangle’) in the Brazilian Atlantic Plateau. This study aimed to analyse these materials in the Late Pleistocene fluvial archives of the QF to contribute to the understanding of the complex processes involved in the evolution of surface coverage in tropical regions. The results showed an essential external iron source for the Fe‐cemented alluvium, that is, they are ferricretes. Two ferricrete facies were identified: plate‐shaped and conglomeratic. They are characterised by the infilling of a primary porous system with crystalline and amorphous ferruginous phases or grain coatings by ferruginous materials. In plate‐shaped ferricretes, the size of the cemented grains differentiates the identified subtypes. Conglomeratic ferricretes can be subdivided into ferruginous and aluminous, and feature two types of cementing microstructures: septary and microlaminar. The results of the X‐ray diffraction analysis of the conglomeratic ferricretes highlight the strong presence of goethite (more common) and hematite. The chemical composition corroborated the mineralogical analysis, with the septa having an average iron‐rich composition. Aluminous conglomeratic ferricretes also occur and are the oldest in the area; their cement is composed mainly of gibbsite. Thus, it can be considered (i) a possible past source area of aluminous sediments or (ii) the in situ deferruginisation of a first level of ferricretes. A certain granulometric control in both ferricrete facies reinforces the importance of transport and deposition during ferricrete genesis. However, the cementing of sediments under supergene conditions and their microstructural variety suggest that their formation and evolution also occurred as a result of lateritic processes. Furthermore, the ferricretes revealed integration with the regional relief evolution, and the conglomeratic ones may be associated with lower rates of drainage incisions in some valleys.

Enhanced Radiation Damage Tolerance of Amorphous Interphase and Grain Boundary Complexions in Cu-Ta

Enhanced Radiation Damage Tolerance of Amorphous Interphase and Grain Boundary Complexions in Cu-Ta

ELSSIE: A compact stereo spectral imager for planetary surface morphology and composition

Here we describe the design, prototyping, testing, and simulations that were conducted to demonstrate the technology for a concept of the next generation landed planetary spectral imager, the Europa Lander Stereo Spectral Imaging Experiment (ELSSIE). The concept was developed originally for a Europa Lander mission, but the design is applicable, with simplifications, to any ocean world of the outer solar system or to non-icy bodies, including Enceladus, the Moon, Mars, or the surface of Ceres. ELSSIE's design consists of two subassemblies. A Sensor melds a high-resolution, 20-filter, 0.4–3.65 μm, adjustable-focus multispectral stereo imager with a 0.8–3.6 μm point spectrometer, sharing a radiation-shielded single Teledyne H2RG 2048 × 2048 pixel focal plane array (FPA). Each camera includes two 6-position filter wheels with 5 filters and a blank position, providing 10 bandpasses for each of the 2 stereo eyes, and uses 700 × 700 pixels of the FPA. The point spectrometer uses a 6 ×350 pixel strip of the FPA. The Sensor provides stereo and imaging/spectroscopic measurements of reflected light from visible to medium wave-infrared (MWIR) wavelengths to characterize surface morphology, search for pyroclastic plumes, search for organics, identify salts and possible biominerals, characterize crystalline vs. amorphous ice and ice grain sizes, and map the distributions of key phases. In addition to addressing important geologic questions, these measurements support selection of a site for in situ sampling and analysis. A Data Processing Unit (DPU) performs mitigation of radiation that penetrates the shielding using sets of same-filter image frames or spectra of a single spot by removing image spatial pixels with radiation hits, and coadding the remainder for the same spatial pixel, improving signal-to-noise ratio (SNR). The DPU also performs onboard calibration of imager and spectrometer data, co-registration of multispectral images, and calculation of spectral index (“summary parameter”) images for efficient use of lander downlink. Co-registered multispectral image sets and spectra are retained onboard and can be downlinked upon query.

Tribological properties of laser-cladded Fe-based amorphous composite coatings under dry and lubricated sliding

Fe-based amorphous composite coatings are promising surface coating materials, because of their low cost, high hardness, and superior wear resistance. In the present study, Fe-based composite coatings with various amorphous contents (35.9–59.3%) were deposited onto 1045 steel via laser cladding, and the influence of laser-cladding parameters on the amorphous content was analysed. The cross sections of the coating layer and ground coating surface were then characterised in terms of the microstructure, phase composition, amorphous content, grain size, and microhardness. Importantly, the tribological properties of coatings with various amorphous contents under both dry and lubricated sliding conditions with light and heavy loads were systematically investigated. The microstructure of the crystalline/amorphous mixture was found to be a function of the temperature gradient, cooling rate, and chemical composition. The high microhardness was related to the amorphous content and grain size. The tribological properties were found to be insensitive to the amorphous content under both dry and lubricated conditions under light and heavy loads. The manifold morphologies of the wear tracks and the transition of the wear mechanism were the result of the combined effects of the amorphous content, phase composition, and size and distribution of the crystalline phase.

Binary nanocrystalline alloys with strong glass forming interfacial regions: Complexion stability, segregation competition, and diffusion pathways

Stabilization of grain structure is important for nanocrystalline alloys, and grain boundary segregation is a common approach to restrict coarsening. Doping can alter grain boundary structure, with high temperature states such as amorphous complexions being particularly promising for stabilization. Dopant enrichment at grain boundaries may also result in precipitate formation, giving rise to dopant partitioning between these two types of features. The present study elucidates the effect of dopant choice on the retention of amorphous complexions and the stabilization of grain size due to various forms of interfacial segregation in three binary nanocrystalline Al-rich systems, AlMg, AlNi, and AlY as investigated in detail using transmission electron microscopy. Amorphous complexions were retained in AlY even for very slow cooling conditions, suggesting that Y is the most efficient complexion stabilizer. Moreover, this system exhibited the highest number density of nanorod precipitates, reinforcing a recently observed correlation between amorphous complexions and grain boundary precipitation events. The dopant concentration at the grain boundaries in AlY is lower than in the other two systems, although enrichment compared to the matrix is similar, while secondary segregation to nanorod precipitate edges is much stronger in AlY than in AlMg and AlNi. Y is generally observed to be an efficient doping additive, as it stabilizes amorphous features and nanorod precipitates, and leaves very few atoms trapped in the matrix. As a result, all grains in AlY remained nanosized whereas abnormal grain growth occurred in the AlMg and AlNi alloys. The present study demonstrates nanocrystalline stability via simple alloy formulations and fewer dopant elements, which further encourage the usage of bulk nanostructured materials.

Assessing Li accommodation at amorphous ZrO2 grain boundaries

Nuclear Pressurised Water Reactors (PWRs) use zirconium alloys as a fuel cladding, preventing the cooling water, at elevated pH using lithium hydroxide, from interacting with the fuel. Boron, as boric acid, is added to the coolant as a reactivity shim. Future reactor designs are considering removing soluble boron reactivity control to aid plant simplification. The presence of lithium in the absence of boron in the coolant has, however, been found to accelerate the corrosion of zirconium-based alloys under certain conditions and the mechanisms by which this occurs is under investigation. The ingress of lithium into the bulk oxide layer of zirconium alloy has been addressed in a previous study and was found to be unlikely. Here, atomistic simulations were used to produce Brouwer diagrams from which the solubility of lithium in amorphous structures representing complex grain boundaries have been predicted. The solubility of lithium in these amorphous structures is predicted to be high and will produce an elevated concentration of oxygen defects within the amorphous structure. This could offer a mode for transport of oxygen to the metal oxide interface and, potentially, offer a mechanism or part of a mechanism for observed lithium-accelerated corrosion of Zr-based alloys.

Local structural ordering determines the mechanical damage tolerance of amorphous grain boundary complexions

Amorphous grain boundary complexions act as toughening features within a microstructure because they can absorb dislocations more efficiently than traditional grain boundaries. This toughening effect should be a strong function of the local internal structure of the complexion, which has recently been shown to be determined by grain boundary crystallography. To test this hypothesis, molecular dynamics are used here to simulate dislocation absorption and damage nucleation for complexions with different distributions of structural short-range order. The complexion with a more disordered structure away from the dislocation absorption site is actually found to better resist crack nucleation, as damage tolerance requires delocalized deformation and the operation of shear-transformation zones through the complexion thickness. The more damage tolerant complexion accommodates plastic strain efficiently within the entire complexion, providing the key mechanistic insight that local patterning and asymmetry of structural short-range order controls the toughening effect of amorphous complexions.

Amorphous-crystalline nanostructured Nd-Fe-B permanent magnets using laser powder bed fusion: Metallurgy and magnetic properties

Laser powder-bed fusion (PBF-LB), a class of additive manufacturing (AM), has attracted wide interest in the production of Nd-Fe-B permanent magnets, benefiting from the minimisation of waste of rare-earth elements and the post-processing requirements. Most research on PBF-LB Nd-Fe-B has focused on reducing defects in printed parts alongside the improvement of the resultant magnetic properties. Detailed analysis of the microstructure that results in permanent magnetic properties is yet to be published. In this research, a combination of high-resolution microstructural investigations was conducted for this purpose. For the first time, an in-depth analysis of the grain structure in terms of morphology, size distribution, and texture is presented and correlated to the permanent magnetic performance. Melt pools showed a hierarchical grain size distribution of primary Nd2Fe14B phase grains with a polygonal morphology and random crystalline alignment, in addition to a small amount of Nd-rich and Nd-lean precipitates in the matrix of the Ti-rich amorphous grain boundaries. The permanent magnetic properties of this material are mainly determined by the nanostructured Nd2Fe14B grains and the amorphous Ti-rich iron-based intergranular phase but could be weakened by precipitates that act as magnetic pores. Remelting during PBF-LB led to the transformation of the coarse grains of the previously solidified layer to fine ones, favourable for the permanent magnetic properties. The mechanisms of these complex phase formations and transformations during processing and the development of the nanocrystalline microstructure are elucidated in this paper as a basis for informing the optimisation process for microstructural development.

Quantitative measurement of amorphous grain boundary phase of aluminum nitride ceramics and correlation of microstructure and other physical properties with thermal conductivity

Quantitative measurement of amorphous grain boundary phase of aluminum nitride ceramics and correlation of microstructure and other physical properties with thermal conductivity

Protonation Process of Porous Silica Cluster Surface using Molecular Dynamics Method

Using molecular dynamic simulation, we developed an algorithm to protonate the surface of an amorphous porous silica grain particle model and study its effect. In this work, the silica grain model can be used to study cosmic dust coagulation. The surface of the silica cluster was protonated by placing H atoms on oxygen atoms having only a single bond, namely, the non-bridging oxygens. The H atoms are placed opposite the Si–O bond with a distance of around 1 Å to form silanol (Si–O–H) group termination on the silica surface. The angular conformation of the silanol was optimized by relaxing the surface at low temperature. We evaluated the number of silanol groups, the angular distribution of the Si-O-H bond, and the average distance between Si-O particles using the radial distribution function (RDF). The result of the study shows that minimizing the energy of the silica surface changes the angular distribution of the silanol from 180° to about 110° and between 140°-160°. However, the average distance between Si-O particles remains at 1 Å, which demonstrates the correctness of the atomic interaction model. The addition of protons on the silica surface is an essential factor in the simulation of cosmic dust collision since the modification of the surface chemistry may alter the contact surface energy, thus changing the probability of particle coagulation.