Glassy Powders Research Articles

Correlation of morphology and photoluminescence properties of gehlenite: Eu glassy phosphors

In this study, gehlenite: Eu glassy powders were synthesized from two common Si sources, silicon tetraethyl orthosilicate (TEOS) and silicon acetate (SiA), using spray pyrolysis. Its morphology and chemical composition were studied. The morphological results suggested that the SiA‐derived powder contained more porous particles than the TEOS‐derived powder. The two gehlenite powders thus formed were found to have similar chemical compositions. Accordingly, porous gehlenite: Eu glassy phosphor seems to exhibit superior PL properties, which have the potential to be exploited in novel phosphor materials.

Development of a novel high-entropy alloy with eminent efficiency of degrading azo dye solutions.

In addition to its scientific importance, the degradation of azo dyes is of practical significance from the perspective of environmental protection. Although encouraging progress has been made on developing degradation approaches and materials, it is still challenging to fully resolve this long-standing problem. Herein, we report that high entropy alloys, which have been emerging as a new class of metallic materials in the last decade, have excellent performance in degradation of azo dyes. In particular, the newly developed AlCoCrTiZn high-entropy alloy synthesized by mechanical alloying exhibits a prominent efficiency in degradation of the azo dye (Direct Blue 6: DB6), as high as that of the best metallic glass reported so far. The newly developed AlCoCrTiZn HEA powder has low activation energy barrier, i.e., 30 kJ/mol, for the degrading reaction and thus make the occurrence of reaction easier as compared with other materials such as the glassy Fe-based powders. The excellent capability of our high-entropy alloys in degrading azo dye is attributed to their unique atomic structure with severe lattice distortion, chemical composition effect, residual stress and high specific surface area. Our findings have important implications in developing novel high-entropy alloys for functional applications as catalyst materials.

Metallic glassy Zr70Ni20Pd10 powders for improving the hydrogenation/dehydrogenation behavior of MgH2.

Because of its low density, storage of hydrogen in the gaseous and liquids states possess technical and economic challenges. One practical solution for utilizing hydrogen in vehicles with proton-exchange fuel cells membranes is storing hydrogen in metal hydrides. Magnesium hydride (MgH2) remains the best hydrogen storage material due to its high hydrogen capacity and low cost of production. Due to its high activation energy and poor hydrogen sorption/desorption kinetics at moderate temperatures, the pure form of MgH2 is usually mechanically treated by high-energy ball mills and catalyzed with different types of catalysts. These steps are necessary for destabilizing MgH2 to enhance its kinetics behaviors. In the present work, we used a small mole fractions (5 wt.%) of metallic glassy of Zr70Ni20Pd10 powders as a new enhancement agent to improve its hydrogenation/dehydrogenation behaviors of MgH2. This short-range ordered material led to lower the decomposition temperature of MgH2 and its activation energy by about 121 °C and 51 kJ/mol, respectively. Complete hydrogenation/dehydrogenation processes were successfully achieved to charge/discharge about 6 wt.%H2 at 100 °C/200 °C within 1.18 min/3.8 min, respectively. In addition, this new nanocomposite system shows high performance of achieving continuous 100 hydrogen charging/discharging cycles without degradation.

Voltammetric determination of sulfonamides using paste electrodes based on various carbon nanomaterials

The authors have performed a comparative study of the performance of various carbonaceous material-based electrochemical sensors in order to identify the most appropriate sensor for determination of sulfonamides. The electro-oxidative power of carbon paste electrodes prepared using carbon black, graphite, carbon nanopowder, acetylene black, multiwalled carbon nanotubes and glassy carbon powder was investigated by square-wave voltammetry at pH 6.0 using sulfamethoxazole (SMX) as the model analyte. It is found that carbon paste electrodes prepared with graphite or carbon nanopowder and operated at a voltage of 0.93 (vs. Ag/AgCl) display the highest sensitivity and lowest detection limit. Next, the sulfonamides sulfadiazine, sulfacetamide, sulfadimethoxine, sulfathiazole, sulfamethiazole and sulfamerazine were also tested. The voltammetric response is linear in the 1 to 75 μM concentrations range, with detection limits range from 0.4 to 1.2 μM, and sensitivities were between 10 and 38 nA⋅μM−1. The carbon nanopowder paste electrode (CNPE) showed the lowest detection limit (0.12 μM) for SMX and was successfully applied to its determination in (spiked) water samples and in pharmaceutical formulation.

Synthesizing and Characterizing of a Novel Zr90Ni6Pd4 Bulk Metallic Glassy Alloy Obtained by Spark Plasma Sintering of Mechanically Alloyed Powders

A single phase of metallic glassy Zr90Ni6Pd4 powders was synthesized by mechanical alloying approach of the elemental powders, using a low-energy ball mill. The solid-solution hcp-ZrNiPd phase obtained after 25 h of the milling time transformed into a single amorphous phase upon ball milling for 100 h to 150 h. This synthesized amorphous alloy transformed into a metallic-glass at a glass transition temperature of 552.8°C. A small volume fraction of this glassy phase transformed into a mixture of two metastable phases of i-phase + big-cube upon annealing at 649.1°C. The supercooled liquid region of the metallic glassy Zr90Ni6Pd4 alloy powders was 69.7°C. A complete crystallization was achieved at a temperature ranged from 649.1°C to 682.2°C through a sharp exothermic reaction with an enthalpy change of crystallization of -76.3 J/g. After this temperature, the formed metallic glassy phase was transformed to polycrystalline mixture of tetragonal Zr2Ni and Zr2Pd phases. The powders obtained after 150 h of milling were subsequently consolidated at 600°C, using spark plasma sintering technique. The sizes of the obtained bulk metallic glassy buttons ranged were 15 mm and 50 mm in diameter with different thicknesses in the range between 0.25 mm to 20 mm. This consolidation step led to the formation of full-dense buttons with relative densities laid in the range between 99.23% to 99.76% without precipitations of any medium- or long-range ordered phase (s). Nanoindentation approach was employed to identify the nanohardness and Young’s modulus that were in the range between 7.74 to 9.32 GPa, and 135.26 to 151.15 GPa, respectively.

Potential applications of cold sprayed Cu50Ti20Ni30 metallic glassy alloy powders for antibacterial protective coating in medical and food sectors

Mechanical alloying was utilized for synthesizing of metallic glassy Cu50Ti20Ni30 alloy powders, using a low energy ball milling technique. The metallic glassy powders obtained after 100 h of ball milling had an average particle size of 1.7 mm in diameter and possessed excellent thermal stability, indexed by a relatively high glass transition temperature (358.3 oC) with a wide supercooled liquid region (61 oC). This amorphous phase crystallized into Ti2Cu and CuTiNi2 ordered phases through two overlapped crystallization temperatures at 419.3 oC and 447.5 oC, respectively. The total enthalpy change of crystallization was −4.8 kJ/mol. The glassy powders were employed as feedstock materials to double-face coating the surface of SUS 304 substrate, using cold spraying process under helium gas pressure at 400 oC. This coating material had an extraordinary high nanohardness value of 3.1 GPa. Moreover, it showed a high resistance to wear with a low value of the coefficient of friction ranging from 0.45 to 0.45. Biofilms were grown on 20-mm2 SUS304 sheets coated coupons inoculated with 1.5 × 108 CFU ml−1E. coli. Significant biofilm inhibition (p The inhibition of biofilm formation by nanocrystalline powders of Cu-based provides a practical approach to achieve the inhibition of biofilms formation.

Characterization of a {(Fe60Co40)75B20Si5}96Nb4 impulse atomized glassy powder by Neutron Diffraction and Differential Scanning Calorimetry

This paper investigates FeCo-based alloy glass formability by high undercooling and high cooling rate solidification technique and the hardness evaluation of the generated samples. For this investigation, Impulse Atomization was used to generate {(Fe60Co40)75B20Si5}96Nb4 powders of different sizes that correspond to different cooling rates and undercoolings. The amorphous fraction and kinetic crystallization properties of the investigated powders were determined by means of Differential Scanning Calorimetry and Neutron Diffraction. The enthalpy of crystallization of a close to amorphous powder produced by gas atomization was used as a reference for the calculation of amorphous fraction by calorimetry in atomized powders. Thus, a quantitative estimation of cooling rate corresponding to each powder size and the variation of amorphous fraction with cooling rate are presented. Higher cooling rate promoted by smaller powder size and helium atomization atmosphere is found to yield higher amorphous fraction. At relatively high cooling rates Neutron Diffraction technique yields higher amorphous fractions than the Differential Scanning Calorimetry technique. The critical cooling rate for amorphous phase formation under unconstrained solidification conditions using Impulse Atomization is found to be ~15,000Ks−1 which corresponds to a powder size of about 100μm atomized in nitrogen or about 200μm atomized in helium.

Fabrication of FePBNbCr Glassy Cores With Good Soft Magnetic Properties by Hot Pressing

Glassy Fe77P7B13Nb2Cr1 alloy powders with the particle size below $100~\mu$ m were synthesized by water atomization using industrial raw materials. The glassy powders were consolidated into bulk forms through sintering them at different temperatures by hot pressing. The resulting glassy core sintered at 771 K, which between the supercooled liquid region, has a high relative density of 91% compared with the master alloy. It also exhibits good soft magnetic properties, i.e., high saturation magnetic flux density ${B_s}$ of 1.13 T, low coercive force ${H_c}$ of 50 A/m, relatively high effective permeability $\mu$ e of 1200 at 1 kHz under a field of 1 A/m, low core loss $P$ of 1393 mW/cm3 at 50 kHz under the maximum magnetic flux density of 0.1 T. The synthesis of Fe-based glassy cores with good soft magnetic properties is encouraging for future applications as functional materials.

Microstructure and mechanical properties of Al-based metal matrix composites reinforced with Al84Gd6Ni7Co3 glassy particles produced by accumulative roll bonding

Al-based metal–matrix composites reinforced with Al84Gd6Ni7Co3 glassy powders have been produced by accumulative roll bonding (ARB) for the first time. Microstructural analyses show that after nine ARB cycles, the Al84Gd6Ni7Co3 particles are homogeneously distributed in the Al matrix. The fractography of the samples indicates that an excellent metallurgical bonding is created at the Al84Gd6Ni7Co3 particles/matrix interface upon ARB cycles. Microhardness and tensile tests demonstrate that the addition of Al84Gd6Ni7Co3 glassy particles significantly improves the mechanical properties, compared to pure ARBed Al.

Fabrication of Al-based composites reinforced with in situ devitrified Al84Ni8.4Y4.8La1.8Co1 particles by hot pressing consolidation

In this study, Al84Ni8.4Y4.8La1.8Co1 particles reinforced Al-based composites were prepared by hot pressing sintering and subsequent hot extrusion. The glassy powders were produced by gas atomization and then employed to mechanical milling. After hot pressing sintering, the nano-scale intermetallic compounds precipitated from metallic glass matrix due to higher temperature than super-cooled liquid region. The mechanical properties of 2024 alloy were improved by addition of glassy particles. The ultimate compressive stress increased from 482 MPa for 2024 alloy to 545 MPa, 627 MPa and 735 MPa for composites with 20 w.t.% 40 w.t.% and 60 w.t.% glassy powders addition, respectively, together with considerable fracture strain ranging between 2.9% and 13.6%. And the mechanical properties could be predicted by using the Rule of Mixture, which predicts the mechanical properties of the bulks from the volume weighed average of the constituent properties.

A new method for estimating the isothermal devitrification and crystallization of mold powder slags from non-isothermal DSC data

Abstract The rate of formation of crystalline phases from liquid and glassy mold powder slags is of foremost importance in the performance of molds used for continuous casting of steel. This study shows how the Induction Period (of Simon and Kolman) and the Kissinger methods can be combined in a kinetic model to evaluate the isothermal rate of formation of crystalline phases from thermo-analytical data – onset temperature, T i , peak maximum temperature, T m , shape index, S , and conversion at peak maximum, x m – collected at various linear heating and cooling rates. The diagram of the extent of isothermal transformation as a function of time calculated for a commercial mold powder, used for casting low carbon steels, shows good agreement with the degree of transformation observed in photomicrographs of glass disks devitrified isothermally, at several temperatures for different times. Additionally, qualitative and quantitative X-ray diffraction results obtained at room-temperature from glass powder samples treated isothermally and quenched also show good accord with the degree of transformation predicted with the kinetic model developed in this work.

Li1.5Al0.5Ge1.5(PO4)3 Li-ion conductor prepared by melt-quench and low temperature pressing

A low temperature hot pressing was used to consolidate Li1.5Al0.5Ge1.5(PO4)3 (LAGP) glassy powder that was fabricated through melt-quench. To fully utilize the special behavior of glass transition of amorphous-structured LAGP, low temperature hot pressing was carried between the glass transition and crystallization temperature. Densified and partially crystallized pellets were obtained after hot pressing and further crystallized at a higher temperature. Ionic conductivity of the final pellet is measured to be 1.64×10−4Scm−1 with activation energy of 0.2994eV.

Bioactivity and cell proliferation in radiopaque gel-derived CaO-P2O5-SiO2-ZrO2 glass and glass-ceramic powders.

In this study, 10 mol% ZrO2 was added to a 27CaO-5P2O5-68SiO2 (mol%) base composition synthesized via a simple sol-gel method. This composition is similar to that of a frequently investigated bioactive gel-glass. The effects of ZrO2 on the in vitro bioactivity and MG-63 cell proliferation of the glass and its derivative polycrystalline (glass-ceramic) powder were investigated. The samples were characterized using thermo-gravimetric and differential thermal analysis (TG/DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) coupled to energy dispersive X-ray spectroscopy (EDS). Release of Si, Ca, P and Zr into simulated body fluid (SBF) was determined by inductively coupled plasma (ICP). Upon heat treatment at 1000 °C, the glass powder crystallized into an apatite-wollastonite-zirconia glass-ceramic powder. Hydroxycarbonate apatite (HCA) formation on the surface of the glass and glass-ceramic particles containing ZrO2 was confirmed by FTIR and SEM. Addition of ZrO2 to the base glass composition decreased the rate of HCA formation in vitro from one day to three days, and hence, ZrO2 could be employed to control the rate of apatite formation. However, the rate of HCA formation on the glass-ceramic powder containing ZrO2 crystal was equal to that in the base glassy powder. Tests with a cultured human osteoblast-like MG-63 cells revealed that the glass and glass-ceramic materials stimulated cell proliferation, indicating that they are biocompatible and are not cytotoxic in vitro. Moreover, zirconia clearly increased osteoblast proliferation over that of the Zr-free samples. This increase is likely associated with the lower solubility of these samples and, consequently, a smaller variation in the media pH. Despite the low solubility of these materials, bioactivity was maintained, indicating that these glassy and polycrystalline powders are potential candidates for bone graft substitutes and bone cements with the special feature of radiopacity.

The critical water activity from dynamic dewpoint isotherms as an indicator of pre-mix powder stability

Premix instant powders offer quick, easy alternatives for making common food products such as gravy, muffins, and beverages. To remain viable, premix instant powders must be free of caking while maintaining their wettability, solubility, and dissolution properties. The main extrinsic factors that influence the stability of powders are temperature and water activity. The critical water activity from dynamic isotherms has been demonstrated to be an effective moisture related specification to maintain the stability of glassy powders. Premix instant powders are often primarily wheat flour, which has a high glass transition, so it is questionable if a critical water activity associated with stability can be found. The purpose of this study was to determine if a critical water activity can be determined for premix instant powders using dynamic isotherms and if this critical water activity is associated with product stability. Instant oatmeal muffin powder and instant chicken gravy powder were found to have a critical water activity at approximately 0.70 aw. Samples of the premix powders were then equilibrated to water activities above and below the critical water activity and examined for changes in caking strength. The mean caking strengths at water activities less than the critical water activity were significantly higher than at higher water activities. The premix samples also experienced color and other appearance changes above the critical water activity. The changes in the premix powders’ matrices that occurred at the critical water activity resulted in degradation of the powder, indicating that the critical water activity provides an effective specification to prevent product loss without requiring an extensive stability study.

Ultrafine grained Ti-based composites with ultrahigh strength and ductility achieved by equiaxing microstructure

Abstract Ultrafine grained Ti-based composites with equiaxed microstructure were fabricated by sintering and crystallizing from glassy powder precursors. The optimized composites exhibit ultimate strength of 2585 MPa and plasticity of exceeding 30%, occupying an unprecedented regime in the strength and ductility space of advanced titanium alloys. Dislocation pile-ups induced by precipitated phases and slip band propagation in the β-Ti matrix are the main reasons for the ultrahigh strength and plasticity respectively. The results provide an innovative route for fabricating titanium alloys with higher mechanical properties.

Amorphous-i phase-big cube-amorphous cyclic phase transformation of mechanically alloyed Zr75Ni20Al5 system

Cyclic glassy-metastable-glassy phase transformations were investigated during mechanical alloying of Zr75Ni20Al5 powders, using high-energy ball milling technique. After 20 h of continuous milling, a single glassy phase was obtained. The synthesized glassy powder, which is homogeneous in structure and composition, showed a glass transition temperature lied at 510 °C and a large supercooled liquid region extended to 86.5 °C. This glassy phase, which crystallized through a single sharp exothermic peak at 596.5 °C, tended to transformed into icosahedral (i-phase) nano-quasicrystalline grains upon further milling to 30 h. This i-phase showed serious instability against the mechanical deformations generated by the milling tools, and hence transformed into big cube phase with increasing the milling time to 45 h. In a cyclic phase transformation the obtained big cube phase subsequently transformed into the same glassy phase after 60 h of milling. This observed cyclic phase transformation was observed twice upon further milling to 90 h without serious compositional changes. The iron contamination contents in the ball-milled powders had constant values of about 0.16 wt.% and did not change with changing the structure of the powders. The present work shows that this phenomenon does not have any obvious analogues with the periodic redox reactions or with diffusive-reactive phenomena known in chemistry. On the basis of our results, the destabilizing effect of the defects created by the milling media (balls), which leads to the cyclic transformations, depends on the milling time.

Length scale-dependent structural relaxation in Zr57.5Ti7.5Nb5Cu12.5Ni10Al7.5 metallic glass

Structural relaxation in ball-milled Zr57.5Ti7.5Nb5Cu12.5Ni10Al7.5 glassy powders has been investigated by in-situ high-energy X-ray diffraction. The studies in reciprocal and real space reveal a contrasting behavior between medium- (MRO) and short-range order (SRO). The free volume is not uniformly distributed across the atoms: annihilation of free volume (i.e. shrinking) during heating is observed in the MRO, whereas an increase of free volume (i.e. expansion) occurs in the SRO, implying a denser SRO in the as-milled powder compared to the structurally relaxed material. This behavior is in agreement with the concepts of free volume and anti-free volume and can be attributed to the change of the coordination number in the first nearest-neighbor shell. Finally, the results demonstrate that the first diffuse diffraction maximum in reciprocal space is a reliable indicator to evaluate the structural changes occurring in the MRO.

The second-harmonic generation in chalcogenide glass-ceramic doped with CdS nanocrystals

An innovative way is proposed here to synthesize chalcogenide glass-ceramic by hot-pressing a combination of Ge20Sb12S68 glassy powder and non-linear CdS nano-particles. The cadmium sulfide nano-particles, which possess the second-harmonic generation property, were synthesized from basic cadmium solution strongly complexed by amine. The obtained glass-ceramics present homogeneous distribution of the crystals. The transmission reaches 30% at 5µm and up to 60% at 10.6µm. The second-harmonic generation at 0.9µm has been detected. This technique can overcome the uncontrollable hetero-crystallization which tends to occur in the glass-ceramics prepared by the conventional thermal treatment method.

Atomization and characterization of a glass forming alloy {(Fe0.6Co0.4)0.75B0.2Si0.05}96Nb4

Metallic glasses require high cooling rates and are therefore generally constrained to small product dimensions. To overcome these limitations, atomization techniques are promising methods to fabricate larger, fully or partially amorphous materials through subsequent metallurgy processing.In this paper, the characterization of iron-based glassy powders, {(Fe0.6Co0.4)0.75B0.2Si0.05}96Nb4 (at.%), formed by using Impulse Atomization (IA) is compared with powder generated by using gas atomization (GA).To quantify the amorphous fraction of IA atomized powder samples, the enthalpy of crystallization for the gas atomized sample was determined. The powders were also characterized by using light microscopy, SEM, XRD, Micro-Vickers hardness tests and DSC. Several isochronal DSC/DPSC measurements were performed at different heating rates to determine the thermal stability and crystallization kinetics of glassy powder samples using the Kissinger approach.The glassy powder samples exhibited high thermal stability against crystallization. The critical cooling rate was computed to be approximately 5000Ks−1. The Micro-Vickers hardness measured in the amorphous region was about 1200–1250HV using 100mN load.

Preparation and soft magnetic properties of spark plasma sintered compacts based on Fe–Si–B glassy powder

Amorphous powder of Fe75Si20B5 (at.%) was prepared by wet mechanical alloying route using benzene as surfactant. The amorphous phase is obtained after 60h of milling. Structural, morphological, and thermal characteristics were investigated. The as-milled powder consists in micrometric particles with a mean diameter of 10.4μm which are formed by the agglomeration of smaller particles. The amorphous powder is thermally stable up to the temperature of 490°C. Spark plasma sintered compacts were prepared from the amorphous powders at sintering temperatures of 800, 850 and 900°C. The phases formation and their evolution was investigated by X-ray diffraction technique showing that Fe3Si and Fe2B are the main phases formed during the spark plasma sintering process. Fe75Si20B5 (at.%) samples in the form of a ring were investigated in DC and AC magnetization regime. It was found that the boride phase formation (during sintering) and the low density of the compacts affect the magnetic properties of the compacts. In addition, a superficial contamination of the compacts with carbon (a layer of 2–3μm) was evidenced, contributing thus to their soft magnetic deterioration. Increasing of the saturation induction, maximum relative permeability and initial relative permeability was observed by increasing both sintering temperature and time. It was generally observed that the compacts with high density have higher total core losses at high frequency.