Amorphous-crystalline Composites Research Articles

Modeling of the Aqueous Solubility of N-butyl-N-methyl-1-phenylpyrrolo[1,2-a] pyrazine-3-carboxamide: From Micronization to Creation of Amorphous-Crystalline Composites with a Polymer.

N-butyl-N-methyl-1-phenylpyrrole[1,2-a] pyrazine-3-carboxamide (GML-3) is a potential candidate for combination drug therapy due to its anxiolytic and antidepressant activity. The anxiolytic activity of GML-3 is comparable to diazepam. The antidepressant activity of GML-3 is comparable to amitriptyline. GML-3 is an 18 kDa mitochondrial translocator protein (TSPO) ligand and is devoid of most of the side effects of diazepam, which makes the research on the creation of drugs based on it promising. However, its low water solubility and tendency to agglomerate prevented its release. This research aimed to study the effect of dry grinding, the rapid expansion of a supercritical solution (RESS), and the eutectic mixture (composite) of GML-3 with polyvinylpyrrolidone (PVP) on the particle size, dissolution rate, and lattice retention of GML-3. The use of supercritical CO2 in the RESS method was promising in terms of particle size reduction, resulting in a reduction in the particle size of GML-3 to 20-40 nm with a 430-fold increase in dissolution rate. However, in addition to particle size reduction after RESS, GML-3 began to show signs of a polymorphism phenomenon, which was also studied in this article. It was found that coarse grinding reduced particle size by a factor of 2 but did not significantly affect solubility or crystal structure. Co-milling with the polymer made it possible to level the effect of the appearance of a residual electrostatic charge on the particles, as in the case of grinding, and the increased solubility in the resulting mechanical mixtures of GML-3 with the polymer may also indicate the dissolving properties of polymers (an increase in 400-800 times). The best result in terms of GML-3 solubility was demonstrated by the resulting GML-3:PVP composite at a ratio of 1:4, which made it possible to achieve a solubility of about 80% active pharmaceutical ingredient (API) within an hour with an increase in the dissolution rate by 1600 times. Thus, the creation of composites is the most effective method for improving the solubility of GML-3, superior to micronization.

Hierarchical W18O49/NiWO4/NF heterojunction with tuned composition and charge transfer for efficient water splitting

Designing and synthesizing heterojunction electrocatalyst with abundant active sites is critical to optimize the activity of electrochemical water splitting. Herein, a typical hierarchical W18O49/NiWO4 heterojunction grown on nickel foam was successfully synthesized via a multistep synthesis strategy. The electrochemical oxidation and reduction process triggers the amorphization of W18O49 and significantly enhances the interfacial interaction, thereby endowing the composites with enriched active sites. The W18O49/NiWO4/NF is completely reconstructed to NiWO4/NF and NiWO4/NiOOH/NF with amorphous-crystalline interface (denoted as H-AM/NiWO4/NF for HER and O-AM/NiWO4/NiOOH/NF for OER). The valence of tungsten ions is well modulated to achieve a high proportion of tetravalent W (IV) active sites accompanied by abundant oxygen vacancies. The increased Ni (III) ions as OER active sites have strong orbital overlap with reaction intermediate, which stabilize the low-valent W (IV) by producing more NiOOH species during the oxygen evolution reaction. Benefiting from the amorphous–crystalline composites, unsaturated W (IV) sites, abundant oxygen vacancies, and highly active NiOOH species, the activated electrocatalyst exhibits excellent electrocatalytic activity, achieving a small overpotential of 1.53 V at 10 mA·cm−2 for water-splitting and maintaining long-term stability at least 100 h.

Co3O4-ZrO2 and Co3O4-Nb2O5 crystalline-amorphous composites for H2O2 activation via Fenton-like and electroprotic processes – Proof of concept

Generation of reactive oxygen species (ROS) via decomposition of hydrogen peroxide is associated with a cascade of reactions which involves either redox active centers of Fenton-like catalysts or acidic-base surface functional groups of non-redox materials. The latter mediate electroprotic reactions resulting in ROS formation. Such two functions can be utilized jointly by combining two oxide phases, a redox-active crystalline oxide and a non-redox amorphous oxide, into one composite material. As a proof of this concept, two amorphous-crystalline composites constituted by ZrO2 and Nb2O5 gels, and cobalt spinel Co3O4 nanocrystals were synthesized in this work. A thorough structural and chemical characterization was carried out using TEM/STEM combined with EDX spectroscopic mapping, XRD, and XRF techniques. Raman measurements were performed to inspect further the dual nature of the composite materials. The formation of surface-stabilized reactive species upon interaction with H2O2 was monitored with Raman and EPR spectroscopy. In parallel, the detection of hydroxyl radicals OH was performed using spin-trapping experiments with DMPO. The measurements proved the cooperative effect of the crystalline and amorphous phases in ROS generation. The Fenton-type mechanism of H2O2 decomposition was proposed, which involved formation of free hydroxyl radicals. It was augmented with the formation of superoxide radicals and stabilization on the amorphous component. The chemical reactivity of the investigated catalysts was tested in oxidation of OPD, a peroxidase substrate, and methylene blue discoloration exemplifying an advanced oxidation process (AOP).

Enhanced tensile strength and ductility of bulk metallic glasses Zr52.5Cu17.9Al10Ni14.6Ti5 via high-pressure torsion

Zr 52.5 Cu 17.9 Al 10 Ni 14.6 Ti 5 (Vit105) Bulk metallic glass is processed by High-Pressure Torsion up to 30 rotations at room temperature, showing simultaneous enhancement of both strength (2023 MPa) and ductility (0.45%). Nano-crystal precipitates with an average size of 45 nm inside the amorphous matrix are observed after 30 turns HPT. Free volume increases from ~0.9030 Å 3 (as cast) to ~0.9275Å 3 after 30 turn HPT alloy with 2.83% (by volume) of nanocrystal precipitates. Strengthening due to precipitation after 30 turns HPT comply with the phase mixture model. The synergetic effect of free volume and nanocrystal precipitation on the ductility of amorphous-crystallite composite is quantitatively approached through modelling. By implementing the model, a ductilization window between bottom limit and top limit of the inter-crystallite spacing w.r.t the free volume is established, elucidating the necessary conditions required to obtain plasticity in amorphous-crystalline composites. • Both ductility and strength of BMGs are enhanced by HPT processing. • The nanocrystals precipitation during HPT increases the strength. • Free volume increase during HPT enhances ductility and reduces yield stress. • Synergetic effect of free volume and nanocrystals on ductility was observed. • Mechanism based-modelling correctly predict the synergetic effect on ductility.

Microstructures, Martensitic Transformation and Mechanical Properties of TiNi-Based Amorphous-Crystalline Composites

By successively introducing minor Al and Sn into the (Ti46.5Ni46.5Hf2Si5)98Nb2 alloy, the amorphous-crystalline composites were fabricated by rapid solidification. The main microstructures were identified as B2 TiNi dendrites together with a few TiNi martensitic crystals. The intercrystalline regions were composed of amorphous phase, B2 TiNi phase, and Ni3.02Ti2Si0.98 intermetallic compounds, whose morphology gradually transformed into striped microstructures. The segregation of Si within intercrystalline regions leads to the formation of the amorphous phase. During deformation, the amorphous-crystalline composites exhibit a double yielding behavior. The yield strength and fracture strength increase to 1114 ± 10 MPa and 2470 ± 15 MPa, respectively, resulting from the reduction of grain size, the existence of the amorphous phase, Ni3.02Ti2Si0.98 intermetallic compounds, and martensitic transformation. All the samples exhibited plastic strains larger than 10% due to the interaction between martensitic transformation and the shear banding process.

Heat Treatment- and Lamp Processing-Induced Structural Transformations of an Amorphous Fe77B7Nb2.1Si13Cu0.9 Alloy and Nonmonotonic Behavior of Its Mechanical Properties

Using a variety of characterization techniques (differential scanning calorimetry, X-ray diffraction, high-resolution transmission electron microscopy, resistivity measurements, nanoindentation, and uniaxial tension testing), we have studied structural changes produced in the amorphous phase of the Fe77B7Nb2.1Si13Cu0.9 alloy by heating in vacuum to 750°C and lamp processing (LP) with the use of pulsed xenon lamps to a fluence F = 120 J/cm2 on the sample surface. Increasing the temperature or fluence leads to three stages of structural transformations: structural relaxation of the amorphous phase below 450°C and two stages of crystallization, which show up as nonmonotonic behavior of the hardness and local plasticity of the samples. With a common character of the structural changes, the effect of LP shows up as an increase in crystallization rate (the processing time is 200 times shorter). In both cases, the fraction of plastic strain in indentation work in amorphous and crystallized samples is 25% larger than that in amorphous–crystalline composites. It has been shown that irreversible deformation of amorphous samples by uniaxial tension leads to structural relaxation and an increase in the size of the relaxation zone.

Mechanical properties of Fe-based amorphous–crystalline composite: a molecular dynamics simulation and experimental study

A new Fe-based amorphous–crystalline composite without non-metallic elements, Fe55Cr15Mo15Ni10W5, was prepared by melt-spinning. The formation ability and structure information were investigated by X-ray diffractometer (XRD), energy-dispersive spectrometer (EDS) and scanning electron microscope (SEM). The mechanical properties of the amorphous–crystalline composite were investigated by nanoindentation. A molecular dynamics simulation study was performed to simulate the formation of Fe55Cr15Mo15Ni10W5 amorphous alloy. The mechanical properties were obtained by compression simulations simultaneously. The results indicate that the Fe55Cr15Mo15Ni10W5 ribbon is an amorphous–crystalline composite structure with good ductility, and the hardness of the amorphous–crystalline composite is about 75% higher than that of master ingot. The simulation mechanical properties are in good agreement with the results of nanoindentation at the nanoscale.

Application of Laser Design of Amorphous Feco-Based Alloys for the Formation of Amorphous-Crystalline Composites

Morphological and fractographic features of change of FeCo-based amorphous alloy surfaces after laser treatment are studied in detail. Regimes of laser treatment that allow various degrees of crystallization of the examined alloys to be obtained, including thin (<1 ∙m) crystal layers on amorphous alloy surfaces, amorphous-crystalline composites, and completely crystalline alloys are adjusted. The Vickers hardness is estimated in zones of selective laser irradiation. The structure of the examined alloys attendant to the change of their mechanical properties is analyzed.

The Simulation of the Pseudoelastic Behavior for Amorphous-crystalline Shape Memory Alloys

The mechanical behavior and the physical properties of shape memory alloys (SMAs) considerably depend on their structural state. The current research was devoted to the amorphous-crystalline shape memory composites produced by means of the partial isothermal crystallization from melt-spun ribbons. Previous works revealed that such composites contain amorphous matrix with embedded spherical crystalline inclusions and this structure was simulated in the current study with the help of the simple nucleation and growth model. In addition, some aspects of pseudoelastic behavior of the amorphous-crystalline composites were simulated by means of finite element analysis by ANSYS FEA software. This study revealed that pseudoelastic behavior significantly depended on the volume fraction of crystalline phase in the amorphous-crystalline shape memory composite.

Synthesis of amorphous alloys and amorphous–crystalline composites in ternary Ni–Nb–Zr system by ion beam mixing

Six sets of Ni–Nb–Zr multilayered films were designed and prepared with the overall compositions of Ni63Nb28Zr9, Ni48Nb13Zr39, Ni29Nb60Zr11, Ni79Nb12Zr9, Ni31Nb31Zr38, and Ni31Nb11Zr58, and an ion beam mixing experiment was then conducted using 180 keV xenon ions. It is found that the Ni–Nb–Zr system is a readily glass-forming system, and both fully amorphous alloys and amorphous–crystalline composites could be synthesized. A detailed discussion was presented for the formation mechanism of the amorphous alloys and amorphous–crystalline composites. In addition, thermodynamic calculation predicted the glass-forming ability of the system, which is in good agreement with the IBM results. The experimental results and thermodynamic calculation obtained in present study are also supported e.g. by the observations of rapid solidification.

Structure of the Amorphous-Crystalline Fe66Cu6B19Si5Nb4 Alloy Obtained by the Melt-Spinning Process

This paper presents structure investigations of the rapidly cooled Fe66Cu6B19Si5Nb4 alloy. A proper selection of chemical composition enabled in-situ formation of the amorphous-crystalline composite during the melt spinning process. Liquid phase separation into the Fe-rich and the Cu-rich phases was confirmed. The microstructures of alloy, melt-spun from 1723 and 1773 K, are composed of the Fe-rich amorphous matrix and Cu-rich spherical crystalline precipitates. For the higher melt-ejection temperature, no coarse precipitates could be observed. Amorphous nature of the Fe-rich matrix was confirmed by presence of a broad diffraction maximum on the X-ray diffraction patterns, a halo ring on the electron diffraction pattern as well as presence of exothermic effects, related to the crystallization of the Fe-rich amorphous matrix, in the differential scanning calorymetry. Beside presence of copper, revealing positive heat of mixing with iron, relatively large supercooled liquid region, was noticed.

Metastable phase formation and transformation studied by ion mixing and computation for the Cu–Zr–Ni system

Glass-forming ability/range of the Cu–Zr–Ni ternary system was studied by thermodynamic calculations and ion beam mixing of multilayered films. Thermodynamic calculations located an energetically favored composition region for metallic glass formation, and also characterized the composition dependence of the glass-forming ability. Under the guidance of the thermodynamics calculations, four sets of nano-sized Cu–Zr–Ni multilayered samples were designed, prepared and then subjected to irradiation by 200keV xenon ions. It turned out that unique amorphous phases were indeed obtained in the samples Cu21Zr55Ni24 and Cu24Zr45Ni31 that were located in the predicted superior glass-forming ability region, while for the Cu33Zr17Ni50 and Cu68Zr19Ni13 samples that fell within the low glass-forming ability region, ion beam mixing resulted in the formation of amorphous-crystalline dual-phase structures. A brief discussion was also presented for the formation mechanisms of the amorphous phase and the amorphous-crystalline composites.

Surface vitrification of alloys by laser surface treatment

With laser surface treatment (LST) method, the surfaces of Zr-, Cu-, Fe- and Al-based alloys were melted and amorphous or amorphous–crystalline composite structures were synthesized, which were related to the different glass-forming ability of the alloys. Influences of laser processing parameters on glass formation for Cu 60Zr 30Ti 10 alloy were investigated and the laser treated alloy exhibited a gradient structure: amorphous surface, amorphous–crystalline composites transitional region and crystalline substrate. Temperature distributions and thermal profiles of the treated Cu 60Zr 30Ti 10 alloy during the laser process were simulated using finite volume method. The formation mechanism of the gradient structure is discussed based on the experimental and simulated results.

Synthesis of amorphous alloys and amorphous-crystalline composites in the Cu-Nb-Hf system by ion beam mixing

Seven sets of Cu-Nb-Hf multilayered films were designed and prepared with the overall compositions of Cu21Nb65Hf14, Cu33Nb49Hf18, Cu34Nb34Hf32, Cu34Nb10Hf56, Cu50Nb23Hf27, Cu58Nb10Hf32, and Cu70Nb8Hf22, and an ion beam mixing experiment was then conducted using 200 keV xenon ions. It is found that the Cu-Nb-Hf system is a metallic glass forming one, and the single amorphous alloys could be synthesized in the Cu-Nb-based alloys with less than 18 at.% of Hf as a third addition. Also, when the Hf concentration is greater than 18 at.%, i.e., at the compositions of Cu34Nb34Hf32, Cu34Nb10Hf56, Cu50Nb23Hf27, Cu58Nb10Hf32, and Cu70Nb8Hf22, ion beam mixing resulted in the formation of amorphous-crystalline composites, which might have better mechanical properties than single-phase glassy alloys. In addition, a detailed discussion was presented for the formation mechanism of the amorphous alloys and amorphous-crystalline composites.

Microstructure and properties of the in situ formed amorphous-crystalline composites in the Fe–Cu-based immiscible alloys

The paper presents microstructures and mechanical properties of the melt-spun Fe 30Cu 32Si 13B 9Al 8Ni 6Y 2 and Fe 44Cu 18Si 13B 9Al 8Ni 6Y 2 alloys. It was found that liquid phase separation of the initially homogeneous melt occurred due to a positive heat of mixing between two major elements. The microstructures of the melt-spun ribbons were composed of the Fe-rich amorphous and the Cu-rich crystalline phases. A significant effect of the melt ejection temperature and the chemical composition (Fe and Cu content) on microstructures of rapidly solidified alloys was revealed. The microstructures of ribbons melt-spun from the miscibility gap region were non-uniform. On the other hand the microstructures of ribbons melt-spun from homogeneous melt temperature region were composed of the spherical precipitates distributed within the matrix. Superior hardness values of the examined ribbons melt-spun from the same temperature were found for the alloy with higher iron content. An increase of the melt-ejection temperature in the homogeneous melt region resulted in hardness decrease in case of the Fe 30Cu 32Si 13B 9Al 8Ni 6Y 2 alloy and its increase for the Fe 44Cu 18Si 13B 9Al 8Ni 6Y 2 ribbons.

Al-La-Ni-Fe Amorphous Alloys and Amorphous-Crystalline Composites Produced by Mechanical Alloying

Al-La-Ni-Fe alloys of three different compositions (Al82La10Ni4Fe4, Al85La9Ni3Fe3 and Al88La6Ni3Fe3) were prepared high-energy milling in a planetary ball-mill (AGO-2). Complete amorphization was observed for the Al82La10Ni4Fe4 alloy after milling for 350 h at a rotational speed of 300 rpm. In contrast, the Al85La9Ni3Fe3 and Al88La6Ni3Fe3 powders contained the FCC Al phase even for prolonged milling. The amorphization tendency was found to increase in the order of Al88La6Ni3Fe3 &lt; Al85La9Ni3Fe3 &lt; Al82La10Ni4Fe4, which may well be ascribed to the increasing atomic size mismatch of the constituent elements on La addition. DSC analyses of amorphous samples revealed two-stage crystallization processes for all three alloys, however, with strong variations in the thermal stability upon compositional changes. As observed by SEM, amorphous powders consisted of particles with nearly spherical shape and diameters ranging from 5 to 20 µm.

Transport phenomena in some solids under hipping pressure

The effects of pressure in hot isostatic press (HIP) on the transport phenomena have been studied on the following three systems; (1) Fe–WC, (2) Ba(Zr,Ti)O3 and (3) amorphous SiO2–crystalline SiO2. In these cases, mass transports were suppressed by hipping pressure. In the Fe–WC system, WC grains reacted with surrounding Fe, and the pressure appears to suppress the diffusion. In the case of (2), thin plates of Ba(Zr,Ti)O3, having different compositions, were piled to make a functionally graded material (FGM). To suppress the diffusion between the plates, hipping pressure of 200 MPa was applied at 900°C, and then the temperature was raised to 1200°C. The hipped compact revealed a flat temperature dependence of dielectric constant, which was ca. 2000 over the temperature range of 25–120°C. The grain growth was also suppressed by the hipping pressure. In the case of (3), the crystallization of amorphous SiO2 was suppressed under the conditions of 1200°C, 200 MPa and 30 min to prepare the amorphous–crystalline composite of SiO2.