Growth Of Precipitates Research Articles

Carbonate Minerals’ Precipitation in the Presence of Background Electrolytes: Sr, Cs, and Li with Different Transporting Anions

Carbonate minerals are largely associated with many geological and biological environments as well as several industrial and technological processes. The crystalline characteristics of these mineral phases can be modified by background salts present in the solution due to the effect of different electrolytes on the dynamics of ion-water interactions and ionic strength during precipitation. In the current research, we studied the effect of the presence of several electrolytes (i.e., Cs, Li, and Sr), combined with chloride and carbonate as transporting anions, on the growth and mineral evolution processes of carbonate precipitation in solution. The electrolyte composition during the reaction (experimental times from 24 h up to 30 days) determined the formation of specific calcium carbonate polymorphs. The Li presence induced the formation of vaterite which was progressively transformed into calcite during the reaction time, while Cs stabilized the calcite formation. The Sr presence in the system caused the precipitation of strontianite with modifications in its cell parameters and the structural arrangement of the carbonate molecular group. During the mineral evolution considering chloride and carbonate experimental set-ups, several compositional and cell parameters/crystallinity variations of the carbonated phases were also observed. A better understanding of the relationship between the compositional properties of the aqueous solvent and the crystallization mechanisms can contribute to a deeper comprehension of the mineral precipitation and transformation in different multicomponent solutions that occur in natural environments and in controlled synthesis processes.

A-contrario detection and tracking from optical telescope data

The precipitous growth of the Anthropogenic Space Object population demands new approaches to high-volume detection and measurement for orbital analyses and conjunction assessment. Optical sensors, which can be smaller and more cost-effective than other mechanisms such as radar sensors, have potential for rapid network expansion, community-driven data acquisition, and space-based sensing. However, traditional detection methods of source extraction and track filtering require high-fidelity a-priori assumptions of data content and are limited by extensive calibration requirements costing time, resources, and expert knowledge of particular detection pipelines. Machine learning methods mitigate a-priori assumptions but require extensive training data which is costly to manually label and restricts applicable use cases. We instead consider a new approach to optical Space Surveillance and Tracking based on a-contrario analysis, detecting features which cannot be attributed to noise from the hardware, atmosphere, or background celestial environment. In such an approach, we reduce epistemic uncertainty by recursive conditioning and inference of data structures. This approach is implemented and assessed on data from the ASTRIANet telescope network of The University of Texas at Austin, and we demonstrate the capacity for orbit determination by quantifying detection rates for actively tracked objects, discussing applicability to sidereal tracking and object discovery, and evaluating the resulting orbit estimates.

Phase field simulation of segregation and precipitates formation during steel solidification

Multi-phase field modelling using MICRESS® has been used to perform simulations of the nucleation and evolution microstructure in a 2D domain as function of fundamental thermo-physical parameters, time, cooling rate and chemical composition during solidification. In order to have a better understanding of primary precipitates evolution during solidification in a case hardening steel and the precipites chosen were niobium-carbides (NbC) and manganese sulphides (MnS), simulations were done including the nucleation and growth of precipitates and coupled through thermodynamic databases. The results show a good comparison with the experimental microstructure measured with SEM-EDX measurements. The simulated time dependent segregation profiles of Nb and Mn in the interdendritic regions, and the precipitates composition, have a good similarity with the measurements. Even when the size and morphology of the NbC and MnS particles has a difference in the both simulated and experimental situations, this can be explained by the low resolution used in the simulation. This publication shows the modelling results and the comparison with the experimental measurements.

Improving Precipitation in Cryogenic Rolling 6016 Aluminum Alloys during Aging Treatment.

This study systematically investigated the performance and microstructure characterization of cryogenic rolling (CR) and room-temperature rolling (RTR) Al-Mg-Si alloys. The result showed that the hardness of the CR alloys decreased at the early aging stage, but that the hardness of the RTR alloys increased at the early aging stage. Retrogression phenomena were apparent in the CR alloys at the early aging stage. Despite undergoing the same solid solution treatment, a few substructures were still observed in the CR alloys, and the degree of recrystallization in the CR alloys was significantly inferior to that in the RTR alloys. After aging for 50 h, the strength and precipitates' density in the CR 75 alloy were higher than that in the other alloys; this indicated that the substructures were beneficial to precipitation and precipitate growth. A precipitation strength model was employed to illustrate the precipitation contribution at different aging stages. The results showed that the CR 75 alloy obtained the strongest precipitation strengthening.

Precipitation growth of σ-phase along the interface in CoCrFeMnNi high-entropy alloy

The equiatomic CoCrFeMnNi high-entropy alloy (HEA) has a face-centered cubic (FCC) single-phase structure with a good balance of yield strength and elongation due to the twinning-induced plasticity (TWIP). In order to increase the usability of FCC-structured HEA, it is necessary to develop its mechanical properties. The hard precipitation of the σ-phase might be a promising strengthening mechanism. Furthermore, developing an advanced manufacturing process is necessary to apply the σ-phase-containing HEAs. This study focused on σ-phase formation during annealing after hot compression of a CoCrFeMnNi HEA. The σ-phase was primarily observed near the high-angle grain boundaries and acted as the obstacle for the boundary migration, resulting in grain growth during annealing. In addition, the development of the σ-phase according to the interface type was investigated. This microstructure increased the hardness of the alloy and may contribute to the further development of high-strength HEAs.

Modification of MnS inclusion with trace tellurium to improve the machinability of medium-carbon low-sulfur steel

ABSTRACT Under the industrial process conditions, trace tellurium (13 ppm and 22 ppm) was added to medium-carbon low-sulfur steel to optimize the morphology of MnS inclusion and thereby enhance the machinability of the steel. Voller-Beckermann microsegregation model was used to calculate the precipitation thermodynamics and growth kinetics of MnS inclusion. The morphology of observed MnS inclusion is mainly polygonal (type III), the observed microstructures of the steel are bulk-, acicular-ferrite, and pearlite, the inclusions are mainly present in the bulk-ferrite. The calculation results of inclusion relative plasticity show that 13 ppm Te reduces the relative plasticity of inclusions, while at a Te content of 22 ppm, the relative plasticity of inclusions increases by approximately 70%. Compared with the steel without Te, when containing 22 ppm Te, the material has the best machinability, the average cutting force and average surface roughness of steel are reduced by 3.47% and 38.75%, respectively.

Control of Microstructure in Iron–Carbon Thin Films by Means of Electromigration

Herein, it is demonstrated that high DC electric current densities can be used to tailor the microstructure of iron–carbon thin films. Specifically, elongated ferrite grains can be formed in a nanocrystalline matrix via a process involving electromigration‐induced carbide migration. Herein this article, the parameters that are required to produce and control elongated grain formation in the Fe(C) system are mapped out and they are interpreted in terms of carbon electromigration, and the flux divergences need to reach a critical carbon concentration for precipitate growth and migration. Possible approaches to allow more precise control of the elongated grains are discussed, as are the requirements for material systems where microstructure control through electromigration should be feasible.

Warm acidified seawater: a dolomite solution

ABSTRACTThe “dolomite problem” is the product of two distinct observations. First, there are massive amounts of ancient marine limestone (CaCO3) deposits that have been replaced by the mineral dolomite (MgCa(CO3)2). However, recent (Holocene and Pleistocene) marine deposits contain relatively minuscule amounts of dolomite, although the occurrence of small quantities of dolomite is observed in many modern settings, from deep marine to supratidal. Second, low-temperature synthesis of dolomite in laboratory settings has been elusive, particularly in comparison to the ease with which common marine calcium carbonate minerals (aragonite and calcite) can be synthesized. Since low-temperature solid-state diffusion can be discounted as a method for Mg incorporation into calcium carbonate (as it operates on time scales too long to matter), the replacement of CaCO3 by dolomite is one of dissolution followed by precipitation. Therefore, an often overlooked but required factor in the replacement of limestone by dolomite is that of undersaturation regarding the original calcium carbonate mineral during replacement. Such conditions could conceivably be caused by rapid dolomite growth relative to aragonite and calcite dissolution–precipitation reactions, but laboratory studies, modern systems analyses, and observations of ancient deposits all point to this possibility being uncommon because dolomite growth is kinetically inhibited at low temperature. Pressure solution by force of dolomite crystallization is a second possible driver for CaCO3 undersaturation, but requires a confining stress most likely attained through burial. However, based on petrographic observations, significant amounts of ancient dolomite replaced limestone before burial (synsedimentary dolomite), and many such platforms have not suffered any significant burial. Because these possibilities of undersaturation caused by dolomite precipitation and crystal growth can be largely discounted, the undersaturation required for “dolomitization” to proceed is most likely to be externally forced. In modern natural systems, undersaturation and selective CaCO3 dissolution in marine porewaters is very common, even in warm-water environments, being forced by the breakdown of organic matter. Such dissolution is frequently attended, to varying degrees, by precipitation of a kinetically-less-favored but thermodynamically more stable phase of CaCO3. Laboratory studies as well as observations of modern systems show that when undersaturation is reached with respect to all common marine CaCO3 phases, dolomite assumes the role of this kinetically-less-favored precipitate. This degree of undersaturation is uncommon in modern shallow marine pore systems in warm-water settings, but it was more common during times of elevated atmospheric CO2, and ocean acidification. Furthermore, because oxidation of organic matter drives dolomite formation, near-surface organic-rich deposits such as the remains of microbial mat communities, were more predisposed to dolomite replacement in the acidified oceans of the ancient past relative to contemporaneous deposits that contained less organic matter. These observations lend to a more harmonious explanation for the abundance and occurrence of dolomite through time.

Effect of B addition on microstructures and properties of Cu-15Ni-8Sn alloy

The effect of B addition on microstructures and properties of as-cast, solution-treated and aged Cu-15Ni-8Sn alloy was systematically investigated in the present study. It is found that the micron-scale Ni6.67SnB2 phase is identified in as-cast microstructure for B-containing Cu-15Ni-8Sn-xB alloys. Moreover, it is suggested the segregation of Sn element at grain boundary could be alleviated to a certain degree with B addition. After being solution-treated at 850 °C for 4 h, the Ni6.67SnB2 phase is still existed in the matrix, thereby resulting in a significant influence on the microstructures and properties during subsequent aging process. Results demonstrate that, during aging treatment at 400 °C, the transformation of DO22 ordered phase into L12 ordered phase can be increasingly inhibited with increase of B content and completely prevented for 0.3 and 0.5 wt% B addition. Additionally, the appropriate B addition (0.04, 0.08, 0.1 wt%) could remarkably suppress the formation and growth of the discontinuous precipitation. Nevertheless, with excess B addition (0.3, 0.5 wt%), the discontinuous precipitation is instead promoted. More importantly, alloys with appropriate B addition (0.04, 0.08, 0.1 wt%) could also maintain the peak hardness without deterioration as long as 18 h during the aging process, which suggests the tremendous enhancement of softening resistance. It is believed that the suppression of discontinuous precipitation by Ni6.67SnB2 phase should be responsible for such enhancement of softening resistance. It is anticipated that the current work could provide guidance for the multi-component design of high-performance Cu-Ni-Sn alloy.

The effect of quenching on the hinderance of the NbC growth process in a model microalloyed steel

ABSTRACT The effect of vacancies on the evolution of strain-induced NbC precipitates (SIP) was studied in a model austenitic Fe–30Ni–0.1Nb-0.1C steel deformed at 925 °C. Precipitation growth and coarsening characteristics have been investigated in detail by employing high resolution transmission electron microscopy. In general, the SIP preferentially nucleated on the nodes of the periodic dislocation networks constituting microband walls and grew over the varying holding time following the conventional precipitation growth and coarsening theory. Nevertheless, the current results demonstrated unexpected sluggishness in the process of growth and coarsening of the precipitates on the introduction of intermediary population of vacancies by a quenching step added in the thermomechanical processing schedules. It has been suggested that the formation of stable vacancy-solute complexes may reduce the effective availability of solutes for the precipitate growth.

Non-Equilibrium Shells around Precipitates During the Decomposition of a Three-Component Alloy

The kinetic theory of diffusion over vacancies is used to obtain expressions for the fluxes of atoms in a three-component alloy. This hole gas approach allows us to express kinetic coefficients in terms of the coefficients of diffusion of labeled atoms from microscopic considerations. The conditions for the formation of nonequilibrium impurity shells are revealed by studying the kinetics of decomposition using these expressions. These shells can considerably inhibit the growth of precipitates and change the properties of the alloy.

Dynamic Precipitation During Forging of a γ–γ′ Nickel-Based Superalloy

Hot compression and creep tests under different conditions were performed on a typical γ–γ′ polycrystalline nickel base superalloy below the γ′-phase solvus temperature, to shed light on the mechanisms of γ′ precipitation during deformation and the driving forces behind these mechanisms. Scanning Electron Microscopy (SEM) and image analysis were employed to characterize the different populations of γ′ precipitates and their evolutions. The γ′-phase area fractions observed after hot compression are systematically higher than the fraction prior to deformation within the investigated range of thermomechanical conditions. Two new populations of precipitates formed during deformation are identified and characterized. These are interpreted to result from a dynamic precipitation process, the hypothesis of their formation during the quenching step being very unlikely with regards to their size and amount. The fraction of γ′-phase produced during deformation increases with increasing deformation magnitude, decreasing deformation temperature and for slower strain rates. Finally, a scenario for dynamic γ′ precipitate nucleation and growth is proposed to explain the experimental observations and the influence of dislocation density.

Reduction behavior and growth kinetics of metallic iron in slag bath of BGL coal gasifier

The appearance of metallic iron reduced by residual char leads to the serious blockage and unpredictable shut-down of coal gasifiers, especially in moving bed slagging gasifiers. To prevent blockage, the reduction and growth characteristics of metallic iron are required to understand. In this study, slag mixed char and metallic iron from an industrial British Gas-Lurgi (BGL) coal gasifier was separated and analyzed to the properties of metallic iron formation process under gasification conditions. Results showed the relative carbon content (α) had the strongest effect on the content and average particle size of iron at α = 1.2 in this work. The reduction was weakened by poor mass transfer of reduction reaction when α > 1.2. The endothermic reduction reaction was promoted by the increase in high temperature. The iron precipitation and particle growth can be divided into rapid increase and stable stage with the increase of reduction time, corresponding to the reduction and accumulation of iron. The growth model of the metallic iron in slag under gasification condition was established as D = 4.439 × 10^10 × t^(1/1.190) × exp^(−340.716 × 10^3/RT) (t ≤ 900 s) and D = 4.277 × 10^14 × t^(1/3.580) × exp^(−412.253 × 10^3/RT) (t > 900 s, R2 = 0.9868). The growth model of metallic iron in slag can provide guidance for slag tapping operation of fixed-bed slagging gasifier during iron-rich coal gasification.

Interactions between plastic deformation and precipitation in Aluminium alloys: A crystal plasticity model

This work presents a crystal plasticity model for dynamic precipitation in aluminium alloys. It takes into account both the influence of an evolving precipitate distribution on the critical stress for dislocation glide, and the accelerating effect of deformation on precipitation kinetics. The effect of precipitates on deformation behaviour is integrated into the crystal plasticity constitutive law. The effect of deformation on precipitation kinetics is modelled spatio-temporally using a multi-class precipitation kinetic model (KWN) incorporating the effect of deformation through accelerated solute diffusion caused by the production of excess vacancies. The model is applied to growth and coarsening of shearable precipitates in pre-aged AA7075 alloy under deformation at 150°C, which corresponds to an industrially relevant production. This paper first explores the influence of dynamic precipitation on the tensile behaviour, showing that dynamic precipitation might be responsible for a gain in uniform elongation and tensile stress of respectively 2% strain and 50 MPa for the case at hand. The influence of dynamic precipitation on the development of plastic strain heterogeneities is discussed. The model demonstrates how spatial heterogeneities in precipitate distribution may develop during deformation, and how these heterogeneities correlate with the development of strain heterogeneities. The precipitate distributions obtained under static or dynamic ageing are predicted and compared with each other, and the influence of texture is discussed.

The combined effects of Mg2+ and Sr2+ incorporation during CaCO3 precipitation and crystal growth

Calcite (CaCO3) composition and properties are defined by the chemical environment in which CaCO3 forms. However, a complete understanding of the relationship between aqueous chemistry during calcite precipitation and resulting chemical and physical CaCO3 properties remains elusive; therefore, we present an investigation into the coupled effects of divalent cations Sr2+ and Mg2+ on CaCO3 precipitation and subsequent crystal growth. Through chemical analysis of the aqueous phases and microscopy of the resulting calcite phases in compliment with density functional theory calculations, we elucidate the relationship between crystal growth and the resulting composition (elemental and isotopic) of calcite. The results of this experimental and modeling work suggest that Mg2+ and Sr2+ have cation-specific impacts that inhibit calcite crystal growth, including: (1) Sr2+ incorporates more readily into calcite than Mg2+ (DSr > DMg), and increasing [Sr2+]tor [Mg2+]t increases DSr; (2) the inclusion of Mg2+ into structure leads to a reduction in the calcite unit cell volume, whereas Sr2+ leads to an expansion; (3) the inclusion of both Mg2+ and Sr2+ results in a distribution of unit cell impacts based on the relative positions of the Sr2+ and Mg2+ in the lattice. These experiments were conducted at saturation indices of CaCO3 of ∼4.1, favoring rapid precipitation. This rapid precipitation resulted in observed Sr isotope fractionation confirming Sr isotopic fractionation is dependent upon the precipitation rate. We further note that the precipitation and growth of calcite favors the incorporation of the lighter 86Sr isotope over the heavier 87Sr isotope, regardless of the initial solution conditions, and the degree of fractionation increases with DSr. In sum, these results demonstrate the impact of solution environment to influence the incorporation behavior and crystal growth behavior of calcite. These factors are important to understand in order to effectively use geochemical signatures resulting from calcite precipitation or dissolution to gain specific information.

Study on Effect of High-Entropy Alloy Binder on Microstructure and Properties of WC Cemented Carbide Doped with Rare Earth Oxide

The AlCoCrFeNi powder was added to WC powder as a binder and Y2O3/ZrO2 was doped by the wet chemical method as grain-growth inhibitors. The WC-Y2O3-ZrO2-10AlCoCrFeNi composite powders were sintered by spark plasma sintering to obtain an alloy. The microstructure and properties of the cemented carbide were studied. The result showed that the rare-earth-oxide (Y2O3/ZrO2)-refined grain size of the alloy and the high-entropy alloy binder provided the alloy with better hardness and toughness. The AlCoCrFeNi diffused slowly between the WC grains because of a delayed diffusion effect and Cr having a low affinity for the WC matrix. During the dynamic process of the WC particles’ dissolution and precipitation growth, the Fe, Co, and Ni that had a better affinity for the WC matrix diffused and distributed more smoothly, which increased the strength and toughness of the alloy. When the temperature of the SPS sintering was 1250 °C, the WC-Y2O3-ZrO2-10AlCoCrFeNi cemented carbide had the best properties, which was a Vickers hardness of 1888.14 HV and a fracture toughness of 14.76 MPa·m1/2.

Productivity of agricultural crops under climate change in the Central Forest Steppe of Ukraine

Aim. The aim of the study is to analyze climatic parameters, moisture reserves and dynamics of productivity of grain crops (winter wheat and corn) depending on the system of adaptation measures (fertilization, tillage) for the period 1913-2022, to determine their classification features according to fractal properties, to identify trends in further changes in agrocenoses of the Central Left-Bank Forest-Steppe of Ukraine. Methods. To achieve the goals and objectives, the following methods were used: analysis of scientific and methodological literature on the research topic, collection of information, comparison, generalization, systematization, as well as the use of modern methods of descriptive statistics. Results. On the territory of the central part of the Forest-Steppe (1913-2022), there were no periods of deviations of hydrothermal climate conditions towards aridization to the point where they acquired a steppe character. The lower boundary of hydrothermal conditions varied around T=+150C, and the upper boundary around T=+300C. A direct correlation (R=+0.81-0.85±0.02) was found between the amount of annual precipitation and the lower and upper limits of hydrothermal climate conditions, and the trend of annual precipitation growth was more rapid than the increase in temperature. Precipitation was a compensating factor, which can be regarded as self-regulation of the Forest-Steppe zone’s resistance to steppeification. In the age cycle, the climate humidity index reached its highest values in the periods 1981-1990 and 1998-2004, and subsequently, by 2020-2022, the humidity index was decreasing in a downward trend to values close to 100%. The humidity of the climate of the warm season and the period of active vegetation reached its maximum value in the period from 1931 to 1950, and from 1980 to 1990 the humidity index decreased rapidly, reaching values less than 90% in 2020-2022, indicating a deterioration in the conditions of crops’ vegetation to excessively harsh compared to previous periods of the age cycle. Conclusions. Climate change that has already occurred and continues to occur in the Central Forest-Steppe affects grain yields: increased winter temperatures and precipitation, prolonged frost-free periods, and increased CO2 concentrations lead to an increase in the area of land suitable for agriculture. In order to ensure sustainable grain production, agricultural producers in the Forest-Steppe of Ukraine should use modern grain varieties adapted to new climatic conditions and agroecological tillage technologies (shallow moldboardless loosening with flat-cutters or flat-cutting, mulching, use of organic mass of post-harvest residues as fertilizer in the fields, etc.

Effects of solute redistribution during heat treatment on micro-galvanic corrosion behavior of dilute Mg-Al-Ca-Mn alloy

The underlying mechanism of solute redistribution during heat treatment in affecting corrosion behavior of Mg-1.19Al-0.28Ca-0.44Mn (wt%) alloy was systematically clarified. The supersaturated Al and Ca solutes in matrix effectively alleviate the driving force of micro-galvanic corrosion caused by Al-Mn phases, based on positive shift of matrix potential and film densification. After aging treatment, monoatomic-layer G.P. zones realize higher strength and better corrosion resistance of alloy as compared to nanosized Al2Ca, due to higher number density and less solute consumption in matrix. Our work provides guidance to minimize corrosion loss of Mg by regulating nucleation and growth of precipitates.

Pláticas with Latinx preservice teachers: insights about navigating teacher education in the New Latinx South

Purpose The purpose of this study is to examine the experiences of Latinx preservice teachers (PSTs) while enrolled in a teacher preparation program in the New Latinx South, a cluster of states that have seen a precipitous growth in the Latinx population over the last decades. Design/methodology/approach The authors used pláticas, or informal conversations with a group of six female Latinx PSTs. Findings Two main themes were identified: experiences with racism and discrimination and feelings of isolation. These themes, along with the narratives of the participants, reflect the barriers this population experiences in the education field and how professionals in this field can improve to best assist Latinx PSTs. Originality/value Latinx PSTs’ experiences are yet to be fully investigated to improve not only their schooling but also the number of Latinx teachers serving a growing number of Latinx children in US schools. Additionally, the use of pláticas elevates this paper as this is a method valued by the participants and used in their communities.

Precipitation behavior of Cu/Ni(Mn,Al) co-precipitates in the medium-Mn dual-phase steel

• High Mn content promotes the partition of Mn to NiAl by occupying Al sublattice. • Cu/Ni(Mn, Al) co-precipitates are formed just in the martensite of the DP steel. • The growth of precipitates doesn’t follow volumetric diffusion-controlled process. The precipitation behavior of Cu/Ni(Mn,Al) co-precipitates in the medium-Mn dual-phase (DP) steels was investigated through a combination of atom probe tomography (APT) and small-angle neutron scattering (SANS). The results reveal that high Mn content of the DP steel promotes the partition of Mn to NiAl nanoprecipitates by occupying the Al sublattice, thereby forming a Cu/Ni(Mn,Al) co-precipitates in the martensite. The growth of the co-precipitates doesn’t follow the volumetric diffusion-controlled process, which is controlled by the coupled diffusion of multiple chemical elements induced by the synergistic phase transformation. The coarsening coefficient of the co-precipitates in the DP steel are ten times more than it in the previous martensitic steel, leading to the change of precipitation strengthening effect. The mechanism for the co-precipitates’ coarsening is also addressed and discussed.