Precipitation Of Nanoparticles Research Articles

Effect of Mo Alloying on the Precipitation Behavior of B2 Nano-Particles in Fe-Mn-Al-Ni Shape Memory Alloys

In Fe-Mn-Al-Ni shape memory alloys, the stabilization of superelasticity would be affected by the undesired precipitation of B2 nano-particles during natural aging. In order to solve this problem, the effect of Mo alloying on the precipitation behavior of B2 nano-particles during the cooling and natural aging processes was performed by scanning electron microscope, transmission electron microscope and Vickers microhardness test in two Fe-Mn-Al-Ni-Mo shape memory alloys. The results showed that the formation of γ phase was completely suppressed after 15 °C and 80 °C water quenching as well as air cooling. However, B2 nano-particles were still precipitated after the three cooling processes, and their sizes and misfits increased with decreasing the cooling rates. In addition, the Vickers hardness increased after natural aging for 338 days, which indicated that it is not viable to inhibit the precipitation of B2 nano-particles during natural aging by Mo alloying in the Fe-Mn-Al-Ni shape memory alloys.

Influence of Plasmonic Gold Nanoparticles on the Optical Properties of Oxide Glasses Doped with Rare-Earth Ions

We report on the thermally-induced precipitation of gold plasmonic nanoparticles in phosphate and silicate glasses, doped with Eu3+ and Er3+ ions. We studied the structure and optical properties of glasses under the heat treatment below and above glass transition temperature. The heat treatment of the glass at temperatures above transition is shown to facilitate the formation of plasmonic gold nanoparticles and decrease near-infrared luminescence intensity of the ions. The formation of pre-plasmonic gold nanoparticles under the low-temperature heat-treatment leads to the increase of luminescence intensity through the energy transfer process. We showed that nanophase separation in silicate glasses allows precise tuning of localized surface plasmon resonance spectral position of gold nanoparticles and paves the way for the development of new glass-based materials for photonics applications.

Verification of the ability of Cu to dissolve in BCC δ in a δ-γ Solid Solution above 1200 °C and boosting δ nano-hardness in Cu-containing PHSS

Because Cu is an austenite γ stabilizer, it is thought that Cu only dissolves in the FCC γ phase but not in the BCC δ when Cu-containing PHSS are treated in a dual δ-γ solid solution at high temperature. However, the nano precipitation of Cu in the allotriomorphic δ found upon quenching from 1295°C. To study this unexpected phenomenon, thermodynamic calculations were performed. The predicted solubilities of Cu in the γ and δ at 1295°C were 3.52 and 1.99 wt%. Consequently, quenching the solid solution from 1295 to 25°C results in the ultra-supersaturation of Cu in the δ. The vacancy concentration in the δ solution was estimated to change from 1024 vac./m3 at 1295°C to105 vac./m3 at 25°C; quenching yields excess vacancies. Thus, Cu-rich nanoparticles precipitate in the δ matrix through the interdiffusion of the ultra-supersaturated Cu and excess vacancies.

Studies on the Formation of Catalytically Active PGM Nanoparticles from Model Solutions as a Basis for the Recycling of Spent Catalysts.

The paper presents basic studies on the precipitation of platinum, palladium, rhodium, and ruthenium nanoparticles from model acidic solutions using sodium borohydride, ascorbic acid, and sodium formate as reducing agents and polyvinylpyrrolidone as a stabilizing agent. The size of the obtained PGM particles after precipitation with NaBH4 solution does not exceed 55 nm. NaBH4 is an efficient reducer; the precipitation yields for Pt, Pd, Ru, Rh are 75, 90, 65 and 85%, respectively. By precipitation with ascorbic acid, it is possible to efficiently separate Pt, Rh, and Ru from Pd from the two-component mixtures. The obtained Pt, Pd, and Rh precipitates have the catalytic ability of the catalytic reaction of p-nitrophenol to p-aminophenol. The morphological characteristic of the PGM precipitates was analyzed by AFM, SEM-EDS, and TEM.

Inexpensive and Easily Replicable Precipitation of CuO Nanoparticles for Low Temperature Carbon Monoxide and Toluene Catalytic Oxidation

Inexpensive and Easily Replicable Precipitation of CuO Nanoparticles for Low Temperature Carbon Monoxide and Toluene Catalytic Oxidation

Condensation and growth of amorphous aluminosilicate nanoparticles via an aggregation process.

The precipitation of zeolite nanoparticles involves the initial formation of metastable precursors, such as amorphous entities, that crystallize through non-classical pathways. Here, using reactive force field-based simulations, we reveal how aluminosilicate oligomers grow concomitantly to the decondensation of silicate entities during the initial step of the reaction. Aluminate clusters first form in the solution, thus violating the Loewenstein rule in the first instant of the reaction, which is then followed by their connection with silicate oligomers at the terminal silanol groups before reorganization to finally diffuse within the silicate oligomers to form stable amorphous aluminosilicate nanoparticles that do obey the Loewenstein rule. Our results clearly indicate that aluminate does not serve as the nucleation center for the growth of aluminosilicates in a nucleation-like process but rather proceeds via an aggregation process. The coexistence of aluminosilicate oligomers and small silicate entities induces a phase separation that promotes the precipitation of zeolites with aging.

Rare earth nanominerals in bentonite deposits of the Eocene Texas coastal plains

Mineral phases and modes of occurrence of rare earth elements and yttrium (REE) in weathering environments are poorly understood but constitute a potential economic source. In Texas, deposits of bentonite that formed by alteration of rhyolitic ash in a coastal and marine influenced environment show REE enrichment comparable to some North American coal and deposits that are under consideration for extraction. We investigated the post depositional mineralization and modes of REE occurrence in a bentonite deposit from Gonzales, Texas, in which total REE concentration exceeds 450 ppm.Scanning electron microscopy (SEM) revealed the presence of sub-micron to nano-size REE phosphate particles dispersed in the montmorillonite matrix, aggregated at the edge of incompletely altered phenocrysts, or in the void space separating montmorillonite stacks. Chemical composition distinguishes a prevalent group of phosphate with Ce > La ~ Nd > Y > Pr > Sm, also bearing Ca and trace amounts of Th and U, and a less common Y-phosphate with trace amounts of other REEs. Transmission electron microscopy (TEM) analysis indicated that the most common particles exhibit a platy morphology, with a diameter smaller than 200 nm and a thickness of less than 100 nm. Electron diffraction, 3D electron diffraction, and high-resolution TEM clearly showed that the mineral phase was monazite. We interpreted the observed REE geochemistry and mineralogy as dissolution of volcanic glass deposited in an alkaline aqueous environment that released REEs into pore water that became oversaturated due to precipitation of montmorillonite, the availability of P in the solution prompted precipitation of monazite nanoparticles. The reduction in permeability following formation of montmorillonite and precipitation of opal in void spaces facilitated accumulation.

Magnetothermally-responsive nanocarriers using confined phosphorylated halloysite nanoreactor for in situ iron oxide nanoparticle synthesis: A MW-assisted solvothermal approach

A family of easily recoverable magnetic and thermally responsive composite materials, with nanoscale dimensions, were synthesized by a rapid and simple solvothermal approach. The synthesis was thermally activated, accelerated, and controlled using a coaxial antenna to directly apply the microwave energy inside the solvothermal reactor. The composite materials were made up by a confined phosphorylated nanoreactor, namely halloysite nanotubes grafted on the inner lumen with phosphoric acid (HNTs-(H+-PO4)), that promoted the urea hydrolysis thus favoring the formation of a local alkaline environment to catalyze the homogeneous in situ precipitation of superparamagnetic iron oxide nanoparticles (IONs) selectively on their inner or outer surface. Two new MW-assisted solvothermal methodologies were used: 1) in the first the solvent is directly loaded into the MW-assisted reactor together with HNTs-(H+-PO4) mechanically preloaded with iron chloride and urea in the lumen 2) in the second the synthesis is preceded by a further pre-functionalization step of the iron salt with clove essential oil (EO) as a green functionalization agent. Structural, morphological, textural, and magnetic properties were assessed by TEM, N2 physisorption, TG-FTIR, ICP, XRD, magnetic and magnetic hyperthermia measurements. The MW-assisted solvothermal deposition of IONs was fully controlled using the phosphorylated nanoreactor, in short synthesis times, by a simple methodology following the principles of sustainable chemistry. IONs were selectively deposited on the outer surface or in the inner lumen of HNTs yielding easily recoverable superparamagnetic and thermally responsive nanocarriers suitable for applications like targeted hyperthermia therapy.

A refractory multi-principal element alloy with superior elevated-temperature strength

A multiphase AlMo0.8NbTiW0.2Zr refractory multi-principal element alloy (RMPEA) with superior elevated-temperature strength was prepared by the powder metallurgy (PM). The as-sintered RMPEA was composed of BCC matrix, lath-like B2 phase, and two Al-Zr hexagonal structure phases. The alloy (ρ = 7.07 g/cm3) exhibited a superior specific compressive yield strength of 153.3, 107.8 and 54.7 MPa cm3/g at the temperature of 1423, 1523 and 1623 K, respectively, which were remarkable in the current designed refractory alloys. After compressing at 1423 K, the AlMo0.8NbTiW0.2Zr consisted of a band-like or blocky Zr5Al4-type phase and the BCC matrix, in which embedded amounts of spherical B2 nanoparticles with a size of 5–10 nm. The superior elevated-temperature compressive yield strength of the RMPEA at 1423 K is primarily ascribed to both the stabilization of the martensitic-transformation Zr5Al4-type submicron-sized phase and the precipitation of the B2 nanoparticles, afterwards impede the deformation flow.

Controlled assembly of heterogeneous aggregates of clay, iron hydr(oxydes) and polysaccharide: Effects of preparation conditions

The preparation of well-defined organo-mineral assemblies under controlled conditions is required to improve our understanding of the formation and surface reactivity of micrometric aggregates, ubiquitous in soils and continental aquatic media. We aim at investigating the building of organo-mineral assemblies with a specific focus on the assembly mode and its consequence on the final properties of the micrometric aggregates. In this work, the preparation and detailed characterization of clay-size aggregates composed of a clay mineral (illite), organic polymer (Dextran polysaccharide) and iron (hydr)oxide are reported, with a focus on the structural organization of the generated aggregates. A step-by-step strategy was developed, and three sets of clay-size composites were prepared with illite particles as a starting material. In two first steps, two distinct sets of two-component composites were obtained according to different procedures. Illite‑iron (hydr)oxide composites were obtained by alkaline hydrolysis of iron in the presence of illite particles, and illite-Dextran aggregates were obtained through the addition of Dextran polysaccharide to an illite suspension. In a third step, three-component micro-aggregates were obtained by subsequent addition of Dextran to suspensions containing the formed illite‑iron (hydr)oxide composite. The so-prepared 2- and 3- component aggregates were investigated by electrophoresis, electron microscopy, X-ray absorption and FTIR spectroscopies. For materials containing Dextran, electrophoretic mobility measurements evidenced variations of surface charge, combined with an increase of aggregate size highlighted by dynamic light scattering. Electron microscopy and EXAFS at iron K-edge evidenced the precipitation of nanoparticles of iron (hydr)oxide onto clay mineral surfaces. FTIR data in transmission and diffuse reflectance modes supported not only the adsorption of Dextran but also the preferential localization of Dextran at the external surfaces of the aggregates. All in all, data collected on the two- and three-component materials demonstrated that the presence of iron (hydr)oxide nanoparticles on the surface of illite strongly modified the organization of organic and mineral constituents.

Designing co-reinforced in-situ (Cr3C2(w) + Cr2O3(p))/CoCrFeNi composite with excellent strengthening efficiency

A process is developed for fabricating in-situ CoCrFeNi matrix composite co-reinforced with Cr3C2 whiskers and Cr2O3 nanoparticles. Initially, mechanical alloying of the powder was carried out to obtain powder containing laminates of FCC and thin Cr rich layers along with carbon dispersed at the laminate interfaces. The powder was then reaction sintered as the Cr layers reacted with carbon and transformed into Cr3C2 phase. Concomitantly, a uniform precipitation of Cr2O3 nanoparticles took place across the microstructure. The designed microstructure exhibited excellent reinforcement efficiency and a yield strength of over 1 GPa along with elongation of 12% was achieved. According to the calculation based on strengthening mechanism models, the reinforcements were estimated to be responsible for a more than 100% increase in matrix yield strength.

Strengthening-toughening mechanism of cost-saving marine steel plate with 1000 MPa yield strength

One kind of cost-saving marine steel plate with 1000 MPa yield strength was successfully processed based on the alloying concept of nano-particles precipitation in a lath martensitic matrix. The conventional quenching and tempering heat treatment was adopted to optimize the mechanical properties. The experimental steel with lower alloy content exhibited excellent performance, i.e., the yield strength above 1030 MPa at room temperature, and the impact energy above 69 J at −40 °C. The microstructural evolution, precipitation behavior and dislocation density were systematically studied by optical microscopy, field emission scanning electron microscopy, X-ray diffraction and transmission electron microscopy. It was shown that the high strength resulted from grain refinement, dislocation strengthening, solid solution strengthening and precipitation strengthening. The role of every strengthening mechanism was quantitively evaluated so that the yield strength could be accurately estimated. Base on this study, it could be concluded that the precipitation strengthening had a significant contribution to yield strength. In addition, the excellent impact toughness of the steel was attributed to its unique microstructure characteristics of fine film-like stable austenite and delamination structure.

Characterization of nanoparticulated WO3 electrochromic thin films prepared via precipitation reaction of peroxotungstic acid solution

Amorphous WO3 thin films with a nanoparticulated morphology were fabricated using a combination of electrodeposition and electrophoretic deposition via the precipitation reaction of a peroxotungstic acid (PTA) solution. Due to the presence of the precipitated WO3 nanoparticles in the aged PTA solution, the electrophoretic deposition and electrodeposition occur simultaneously, which results in a grainy surface morphology in which nano-sized WO3 particles are embedded on a smooth WO3 thin film. The WAT-5 sample prepared with a PTA solution aged for 5 days exhibited faster ion intercalation/de-intercalation kinetics (coloration time of 3 s and bleaching time of 1 s), a greater transmittance modulation (68.36%), and a higher coloration efficiency (41.29 cm2/C) with better cyclic stability (91% retention during 300 cycles) than a WO3 thin film fabricated using the PTA solution without the aging process. The nanoparticulated morphology enhanced the active reaction area by expanding the interface between the electrolyte and the electrochromic material. Such results indicate that the electrochromic characteristics of WO3 thin films can be improved simply by adjusting the aging period of the PTA solution.

Experimental study and modeling of letrozole (anticancer drug) solubility in subcritical water: Production of nanoparticles using subcritical water precipitation method

A green solvent anti-solvent precipitation was applied, for the first time, to precipitate nanoparticles of letrozole (LTZ) using subcritical water solutions. In this novel technology, subcritical water (SW) and cold water at ambient conditions used as solvent and anti-solvent, respectively, to improve the bioavailability of LTZ as a poorly water-soluble drug. The solubility of LTZ in SW was first measured at different temperatures (298.15–383.15 K) and at the constant pressure of 5 MPa using a static method. Furthermore, two semi-empirical models, including the linear and Apelblat models, were applied to correlate the drug solubility. The statistical result showed the superior performance of the Apelblat model. Then, the influence of procedure parameters, including SW temperature (363.15–383.15 K), polyethylene glycol concentration (0.01–0.03 wt%), and anti-solvent temperature (273.15–293.15 K) were studied on the size and the morphology of the precipitated drug nanoparticles. According to the results, excellent size reduction of the precipitated particles of LTZ from 20 μm (unprocessed drug) to about 79 nm was achieved using green technology with no need for organic solvents and post-processing purification stages.

Surface modification for AlCoCrFeNi2.1 eutectic high-entropy alloy via laser remelting technology and subsequent aging heat treatment

Eutectic high-entropy alloys (EHEAs) are a class of prospective structural material in advanced engineering applications due to their excellent mechanical properties and castability. However, few researchers focused on the surface modification of these EHEAs. This study aimed to propose an effective method combining laser remelting and heat treatment to modify the surface of classical AlCoCrFeNi2.1 EHEA. After surface modification, the surface microhardness of the EHEA increased by 59%, and the average friction coefficient and wear rate decreased by 26% and 68%, respectively. The improved performance was mainly attributed to the decrease in lamellar spacing between face-centered cubic (FCC)/body-centered cubic (BCC) (B2) and coherent precipitation of nanoparticles in both FCC and B2 phases. A semi-empirical model was built to estimate the contribution of lamellar spacing to microhardness. The method and model might be applied to modify the surface properties of other EHEAs with lamellar structures.

Precision Polymer Particles by Flash Nanoprecipitation and Microfluidic Droplet Extraction

We comparatively review two versatile approaches employed in the precise formation of polymer particles, with length scales from 10s of nm to to 100s μm, from ternary polymer(s), solvent and nonsolvent mixtures. Flash nanoprecipitation (FNP) utilizes an opposing jet arrangement to mix a dilute polymer solution and a nonsolvent in confinement, inducing a rapid (∼millisecond) chain collapse and eventual precipitation of nanoparticles (NPs) of 10–1000 nm diameters. FNP of polymer mixtures and block copolymers can yield a range of multiphase morphologies with various functionalities. While droplet solvent extraction (DSE) also involves the exposure of a polymer solution to a nonsolvent, in this case the polymer solution is templated into a droplet prior to solvent extraction, often using microfluidics, resulting in polymer particles of 1–1000 μm diameter. Droplet shrinkage and solvent exchange are generally accompanied by a series of processes including demixing, coarsening, phase inversion, skin formation, and kinetic arrest, which lead to a plethora of possible internal and external particle morphologies. In the absence of external flow fields, DSE corresponds effectively to nonsolvent induced phase separation (NIPS) in a spherical geometry. In this review, we discuss the requirements to implement both approaches, detailing consequences of ternary solution phase behavior and the interplay of the various processes underpinning particle formation and highlighting the similarities, differences, and complementarity of FNP and DSE. In addition to reviewing previous work in the field, we report comparative experimental results on the formation of polystyrene particles by both approaches, emphasizing the importance of solution phase behavior in process design.

Nonequilibrium solidification microstructures and mechanical properties of selective laser-melted Cu–Sn alloy

Cu-based alloys can be used as a selective laser melting (SLM) material for advanced engineering applications, such as aerospace, 5G mobile networks, and high-speed transportation. The mechanical properties and solidification microstructures of Cu alloys prepared using the casting technique differ from those prepared using the SLM technique, and SLM-built alloys can involve more complex microstructures and phase transformations developed in micromolten pools produced by high-power laser beams. However, nonequilibrium solidification microstructures and mechanical properties of SLM-built Cu–Sn alloys have seldom been studied in the literature. In this work, the Cu–5%Sn alloy was investigated using the SLM technique, along with cast Cu–Sn alloys for comparison. The high quality Cu-based alloy samples were fabricated using the SLM technique, with optimized processing parameters of 160 W laser power, 300 mm·s−1 scanning speed, and 0.07 mm line spacing. The samples exhibit a relative density of 99.2%, and virtually no pores and spheroidizing phenomena or warping defects were observed. The microstructural analysis of SLM-built Cu–5% Sn alloy reveals a nonequilibrium solidification feature under high cooling rates and rapid alternative thermal conditions during the SLM fabrication process, in which the α-Cu(Sn) solid solution is the major phase along with γ and δ phases. Columnar grains and reticular microstructures dominate the solidified SLM-built alloy, while segregated Sn appears in the boundaries of all levels within the alloys. The Sn-rich nanoparticles with super-lattice structures precipitates along the grain boundaries and inside the grains. With the combined effects of grain fining, super-lattice-structured nanoparticles precipitation, solid solution, and thermal residual stress, the SLM-built Cu–5%Sn alloy shows significantly enhanced mechanical properties, such as HV 133.83 Vickers hardness, 326 MPa yield strength, 387 MPa tensile strength, and 22.7% fracture extension. Such scientific information is very useful for improving the alloy composition design and optimizing the SLM processing parameters.

Red mud regulates arsenic fate at acidic pH via regulating arsenopyrite bio-oxidation and S, Fe, Al, Si speciation transformation

Red mud (RM) as waste of industrial aluminum production is piling up in huge ponds. RM could be a cost-effective adsorbent for heavy metals, but adsorption is vulnerable to pH changes, metal ions speciation and the occurrence of iron bearing minerals. In this study, the precipitation and elemental speciation transformation relevant to arsenic fate in responding to the addition of RM during arsenopyrite bio-oxidation by Sulfobacillus thermosulfidooxidans was investigated. The results show that the addition of RM significantly changed the arsenic precipitation and the solution chemistry and thus affected the arsenopyrite bio-oxidation and arsenic fate. An addition of a small amount (≤ 4 g/L) of RM substantially promoted arsenopyrite bio-oxidation with formation of SiO2 @ (As, Fe, Al, Si) spherical nanoparticles that can enhance the stability of the immobilized arsenic. The SiO2-based spherical nanoparticles precipitate was mainly composed of jarosites, amorphous ferric arsenate and crystalline scorodite, and its formation were controlled by Fe3+ concentration and solution pH. An addition of increased amount of RM (≥ 6 g/L) resulted in a significant increase of the solution pH and a decrease in the Fe2+ bio-oxidation activity, and spherical nanoparticles were not formed. Consequently, the dissolution of arsenopyrite was inhibited and the release of arsenic was blocked. This study suggests the applicability of RM in mitigation of arsenic pollution from bio-oxidation of As-bearing sulfide minerals.

Emulsion stability of heavy oil with surfactants and nanoparticles

The recovered crude oil is often in form of an emulsion and the recovery is cut off when water to oil ratio exceeds a certain amount. The emulsions vary from water-in-oil to oil-in-water and the step that follows is to coalesce droplets to get two continuous liquids. This is often made difficult because crude contains naturally occurring surfactants, or the oil recovered is by enhanced oil recovery techniques which have additives that also stabilize the droplets. We have considered below a heavy oil (viscosity 650-750 mPa.s) to which has been added one of the three surfactants: a nonionic surfactant or a cationic surfactant or an anionic surfactant. In addition, the mix can have alumina or silica nanoparticles or none. Most of the results have straightforward interpretations. Cationic surfactants appear to give rise to a secondary haze. There is no apparent effect due to nanoparticles. If the system contains nonionic surfactant then it can be destabilized by raising the temperature, except for one notable case. There are also cases of precipitation of nanoparticles.

Overcoming the Inhibition Effects of Citrate: Precipitation of Ferromagnetic Magnetite Nanoparticles with Tunable Morphology, Magnetic Properties, and Surface Charge via Ferrous Citrate Oxidation (Part. Part. Syst. Charact. 8/2021)

In article 2100098, Mandel and co-workers demonstrate how to solve the long known challenge to overcome the inhibition effects of citrate that are believed to hinder iron oxide nanoparticle formation from iron salt precursors when being present during the nanoparticle synthesis. This opens up routes to in-situ modification of nano iron oxides, thus making post-synthesis citrate modification obsolete.