Formation Of Amorphous Phase Research Articles

Vacancy infilling during the crystallization of Fe-deficient hematite: An in situ synchrotron X-ray diffraction study of non-classical crystal growth

Abstract The crystallization of hematite from precursor ferrihydrite was studied using time-resolved, angle-dispersive synchrotron X-ray diffraction in aqueous solutions at pH 10 and 11 and at temperatures ranging from 80 to 170 °C. Rietveld analyses revealed a non-classical crystallization pathway involving vacancy infilling by Fe as defective hematite nanocrystals evolved. At 90 °C and pH 11, incipient hematite particles exhibited an Fe site occupancy as low as 0.68(2), and after 30 min, Fe occupancy plateaued at 0.84(1), achieving a metastable steady state with a composition corresponding to “hydrohematite.” During crystal growth, unit-cell volume increased with an increase in Fe occupancy. The increase in Fe occupancy in hydrohematite was accomplished by deprotonation, resulting in a shortening of the long Fe-O(H) bonds and decreased distortion of the octahedral sites. Once the occupancy stabilized, the unit-cell volume contracted following further nanoparticle growth. Our study documented various synthetic routes to the formation of “hydrohematite” with an Fe vacancy of 10–20 mol% in the final product. The structure refined for synthetic hydrohematite at 90 °C and pH 11 closely matched that of natural hydrohematite from Salisbury, Connecticut, with a refined Fe occupancy of 0.83(2). Dry heating this natural hydrohematite generated anhydrous, stoichiometric hematite, again by continuous infilling of vacancies. The transformation initiated at 150 °C and was complete at 700 °C, and it was accompanied by the formation of a minor amorphous phase that served as a reservoir for Fe during the inoculation of the defective crystalline phase.

The formation of structural disorder in FeNi-based alloys – Theoretical approach

• Positive values of enthalpy of formation of amorphous phase in Fe-Ni system confirmed on the basis of Miedema’s model. • Insignificant influence of Co doping on the enthalpies of formation in FeNi system. • Promotion of amorphous phase and solid solution formation ability depending on Cu substitution. • Cu as promising candidate when aiming destabilization of FeNi crystalline structure. FeNi-based alloys are known to crystallize in bcc or fcc-structures depending on their composition. In many slowly cooled objects, like meteorites, L 1 0 -type phase (tetrataenite) with its characteristic layered Fe/Ni structure has been found. Nevertheless, the synthesis of L 1 0 FeNi phase in industrial amount in a bulk form has not been possible, mainly due to sluggish diffusion and low order/disorder temperature of this phase. We present results of the calculations of formation enthalpies for solid solution and amorphous phase in Fe-Ni system. Additionally, we performed calculations for Co and Cu substitutions (found in meteoritic matter). Our calculations confirm poor glass forming ability of FeNi system and limited influence of Co in this aspect. In contrast, Cu is a promising candidate when aiming at destabilization of FeNi solid solution, as a starting point in L 1 0 phase formation. Formation enthalpy for some Cu-substituted compositions reaches highly negative values. It is expected that at least local chemical segregation should be facilitated by the presence of Cu atoms (attributed mainly to different values of Cu-Co and Cu-Ni interfacial enthalpies).

Al-Fe-Ni Metallic Glasses via Mechanical Alloying and Its Consolidation

In this paper, the influence of mechanical milling on the microstructural evolution and magnetic properties of Al82Fe14Ni4 alloys prepared by mechanical alloying is investigated. The elemental powder mixture was processed under argon gas at 250 rpm and 350 rpm using a planetary ball mill. The powder particles experienced severe deformation, fragmentation and mutually cold-welding during the collisions of the balls. The diffraction peaks of the Al, Fe and Ni phases gradually disappeared during the milling process, and a halo peak corresponding to the amorphous phase formed. The amorphization of powders milled at 250 rpm was slower than that of 350 rpm. These alloys achieved a fully amorphous structure after milling for 60 h. The amorphous powder alloy milled at 350 rpm exhibited higher thermal stability compared with that of an alloy milled at 250 rpm. The saturation magnetization and coercive of the milled Al82Fe14Ni4 alloy powder were decreased following the formation of a para-magnetic amorphous phase. The highest compressive strength, about 710 MPa, was obtained for the Al82Fe14Ni4 alloy sintered at 600 °C by SPS.

Fabrication of TiFe-Based Electrodes Using High-Energy Ball Mill with Mn Additive for NiMH Batteries

Binary and ternary (with the addition of Mn) TiFe-based intermetallic compound powders were fabricated by high energy ball milling, and their electrochemical behavior as negative electrodes was investigated in 6M-KOH. X-ray diffraction exhibited the single phase of nanostructured binary and ternary TiFe-based crystallites after 20 h of milling followed the amorphous phase formation. Addition of Mn increased peak broadening and in turn decreased the nanocrystallite size of TiFe. Electrode properties of 20, 40, 60, and 70 h binary milled products showed that the discharge capacity of the 60 h one offered a maximum discharge capacity of ~169 mAhg−1. Although substitution of Mn for Ti (Ti1−xFeMnx, x = 0.1, 0.2) caused a decrease in initial discharge capacity, the periodic stability increased compared to the binary TiFe and ternary TiFe1-xMnx (x = 0.1, 0.2). The ternary Ti0.9FeMn0.1 electrode maintained ~53% of its initial discharge capacity after five cycles of charge–discharge; this was just 28% in the case of binary TiFe electrode.

Geopolymerization kinetics of steel slag activated gasification coal fly ash: A case study for amorphous-rich slags

The geopolymer processing of amorphous-rich slag required excessive soluble alkali usage severely limiting the application of geopolymer materials. In this study, industrial solid waste steel slag (SS) was introduced as alkali substitution for stimulating the potential activity of Shell gasification coal fly ash (SFA). Result shows that a 15%–20% addition of SS can reduce 14.5–23.3% NaOH consumption for the preparation of high-strength geopolymers. SS accelerates the dissolution rate of SFA promoting the early strength of geopolymer (ES) via alkalinity adjustment and reducing the wetting angle of refactoring globular particles in the slurry. The long-term strength of geopolymer (LS) is increased to 68.5 MPa with the higher devotion of SFA (67 ω%). During the geopolymerization course, Ca-rich hydrates growth are competed with the polymerization of amorphous minerals. The geopolymerization kinetics enlightens that the soluble tetrahedral SiO4 or AlO4 and hydrates in pozzolanic phase initially generated in paste then transformed to a more stable form of amorphous phase after a series of repeated processes of dissolution, homogeneous nucleation, and heterogeneous growth. This work paves a environmentally friendly way for disposing amorphous-rich slags with low activity and discloses the detailed mechanism of related geopolymerization.

Acid activated smectite clay as pozzolanic supplementary cementitious material

This research has investigated the structural changes and pozzolanic activity produced in acid activated smectite clay. The activation treatment used HCl at different concentrations, using different times and at a range of temperatures. X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy were used to determine the acid dissolution mechanism and characterise the activated clay mineral structure. Acid activation causes dehydroxylation of smectite clay, followed by leaching of octahedral cations. This results in the formation of a silica-rich amorphous phase that exhibits substantial pozzolanic activity compared to the same clay sample that had undergone calcining treatment at 850. The optimum sample was activated for 8 h using 5 M HCl at 90 °C. This was 93 % amorphous. Mortar prisms prepared with 25 % replacement of Portland cement by acid activated smectite produced 93 % compressive strength of plain Portland cement mortar.

Li-Ion Conductive Li1.3Al0.3Ti1.7(PO4)3 (LATP) Solid Electrolyte Prepared by Cold Sintering Process with Various Sintering Additives.

The density, microstructure, and ionic conductivity of solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 (LATP) ceramics prepared by cold sintering using liquid and solid sintering additives are studied. The effects of both liquid (water and water solutions of acetic acid and lithium hydroxide) and solid (lithium acetate) additives on densification are investigated. The properties of cold-sintered LATP are compared to those of conventionally sintered LATP. The materials cold-sintered at temperatures 140–280 °C and pressures 510–600 MPa show relative density in the range of 90–98% of LATP’s theoretical value, comparable or higher than the density of conventionally sintered ceramics. With the relative density of 94%, a total ionic conductivity of 1.26 × 10−5 S/cm (room temperature) is achieved by cold sintering at the temperature of 200 °C and uniaxial pressure of 510 MPa using water as additive. The lower ionic conductivities of the cold-sintered ceramics compared to those prepared by conventional sintering are attributed to the formation of amorphous secondary phases in the intergranular regions depending on the type of additives used and on the processing conditions selected.

Immobilization mechanism of radioactive borate waste in phosphate-based geopolymer waste forms

The solidification of radioactive borate waste (BW), which contains a high concentration of boron ions using cement waste forms is challenging because soluble borate hinders the cement hydration reaction. Here, BW was immobilized using a phosphate-based geopolymer, and the phase change of BW in the geopolymer was investigated. The geopolymers could solidify BW up to 50 wt% depending on the water content and heat curing conditions. In geopolymers cured at high temperatures (60 and 90 °C), the 7-day compressive strength increased as the BW waste loading increased up to 40 wt%. Heat curing promoted geopolymerization and the precipitation of amorphous boron phosphate, leading to an increase in the compressive strength. The formation of a new amorphous boron phosphate phase was confirmed by performing XRD, MAS NMR, and SEM analyses of the geopolymers and reaction products. These results can improve our understanding of the immobilization mechanism of BW in phosphate-based geopolymers.

Exploring the amorphous phase formation and properties of W-Ta-(Cr, Fe, Ni) high-entropy alloy gradient films via a high-throughput technique

A high-throughput technique can realize fast and efficient material screening, and greatly improve the discovery efficiency of advanced materials. In the present work, the gradient composition films of the W-Ta-CrFeNi high-entropy alloy were prepared by the three-target magnetron co-sputtering technique. The gradient alloy films exhibited a body-center-cubic (BCC) structure near the W or Ta element target, and an amorphous structure near the CrFeNi target region. Considering the effect of the undercooling degree, the amorphous formation region (using Ω ~ δ ) was larger than that of the bulk alloys. These alloy films displayed ultra-high nano-indentation hardness, with the maximum hardness reaching ~ 20.6 GPa. The elastic modulus in the high-entropy composition region was lower than that in the low-entropy composition region. There is a nonlinear relationship between the nano-indentation hardness and mix-entropy of the alloys. This study provides a reference and alternative material library for the development of high-performance advanced materials. • The rapid screening with properties and phase structure of the W-Ta-(Cr, Fe, Ni) films via the high-throughput technique. • The W 15.39 Ta 38.81 Cr 14.58 Fe1 5.45 Ni 15.77 high-entropy alloy film possesses ultra-high hardness of ~ 20.6 GPa. • The amorphous phase formation ruler of high-entropy alloy films was investigated. • There is a nonlinear relationship with the mix-entropy and properties in these high-entropy alloy films. • The high mix-entropy is a reason for low elastic modulus in these high-entropy alloy films.

Rapidly quenched heavy rare earth-based ternary Lu-Fe-B alloys: Phase evolution and hard magnetic properties

Aiming to clarify the fundamental properties of Lu-Fe-B alloys and facilitate the application of the Lu in rare earth (RE)-iron-boron permanent magnets, the phase constitutions, phase precipitation behavior, and hard magnetic properties of Lu12+xFe82−xB6 alloys (x = 0–4) prepared by melt spinning were systematically studied. The intrinsic coercivity Hcj= 313 kA/m, remanence Jr = 0.72 T, and maximum energy product (BH)max= 68.5 kJ/m3 were obtained in optimally quenched Lu12Fe82B6 alloy. Different from many other RE-Fe-B alloys, increasing Lu content leads to the formation of the soft magnetic amorphous phase and Lu6Fe23 phase, which eventually increases the exchange coupling effect and decreases Hcj and (BH)max of the Lu-rich alloys (x = 1–4). For the amorphous Lu12+xFe82−xB6 alloys, after annealing treatment, Lu2Fe14B and Fe2B phases precipitate in the alloys with x = 0 and 1, but the crystalline phases change into Lu6Fe23, Lu2Fe14B, and Fe2B phases in the alloys with x = 2–4. For the Lu-rich alloys, all crystalline phases tend to precipitate simultaneously from the amorphous matrix, which is beneficial to obtaining optimized microstructure under various processes. The alloy with x = 2 annealed at 750 °C for 10 min exhibits a good combination of magnetic properties with Jr = 0.69 T, Hcj= 234 kA/m, and (BH)max= 51.9 kJ/m3. The present results can serve as a useful reference for promoting the utilization of Lu in RE permanent magnets.

Interatomic Potential to Predict the Favored Glass-Formation Compositions and Local Atomic Arrangements of Ternary Al-Ni-Ti Metallic Glasses

An empirical potential under the formalism of second-moment approximation of tight-binding potential is constructed for an Al-Ni-Ti ternary system and proven reliable in reproducing the physical properties of pure elements and their various compounds. Based on the constructed potential, molecular dynamic simulations are employed to study metallic glass formations and their local atomic arrangements. First, a glass-formation range is determined by comparing the stability of solid solutions and their corresponding counterparts, reflecting the possible composition region energetically favored for the formation of amorphous phases. Second, a favored glass-formation composition subregion around Al0.05Ni0.35Ti0.60 is determined by calculating the amorphous driving forces from crystalline-to-amorphous transition. Moreover, various structural analysis methods are used to characterize the local atomic arrangements of Al0.05NixTi0.95-x metallic glasses. We find that the amorphous driving force is positively correlated with glass-formation ability. It is worth noting that the addition of Ni significantly increases the amorphous driving force configurations of fivefold symmetry and structural disorder in Al0.05NixTi0.95-x metallic glasses until the content of Ni reaches approximately 35 at%.

Amorphous Phase Formation and Heat Treating Evolution in Mechanically Alloyed Ti–Cu Alloy for Biomedical Applications

The present work aims to produce TixCu100-x (x = 90, 80, 70, and 60) amorphous alloys by using high energy ball mill. The microstructure and possible formation of amorphous phases were characterized employing laser granulometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The amorphous-crystalline transformation at high temperatures was studied according to differential scanning calorimetry (DSC) and XRD. The Ti80Cu20 alloys were obtained in an amorphous state after 30 h of mechanical alloying, and the amorphous phase is stable up to 340 °C. At higher temperatures, this alloy crystallizes, forming the intermetallic compound Ti2Cu, and a substitutional solid solution Ti(Cu).

Concrete/Glass Construction and Demolition Waste (CDW) Synergies in Ternary Eco-Cement-Paste Mineralogy.

The study described sought further understanding of the synergies in a mix of CDW pozzolans, containing (calcareous and siliceous) concrete and glass waste, used to prepare ternary eco-cement paste bearing 7% of the binary blend at concrete/glass ratios of 2:1 and 1:2. The mineralogical phases in the 2-day, 28-day, and 90-day cement matrices were identified and monitored using XRF, XRD-Rietveld, SEM-EDX, FT-IR, and NMR. The findings showed that changes in the reaction kinetics in the ternary blended pastes relative to OPC pastes depended on the nature of the recycled concrete and the glass content. Adding the binary mix bearing calcareous concrete (at a ratio of 2:1) favoured ettringite, portlandite, and amorphous phase formation, whilst the blends with siliceous concrete favoured C-S-H gel formation. Monocarboaluminate was detected in the 90-day siliceous concrete and glass pastes in amounts similar to those found in the reference OPC paste.

A kinetic transition from peritectic crystallization to amorphous solidification of rapidly quenched refractory Nb-Ni alloy

In this study, the kinetic transition of solidification modes for refractory peritectic Nb54Ni46 alloy was revealed using melting spinning experiments combined with molecular dynamics (MD) simulation and classical nucleation theory. This begins with a shift from the usual peritectic solidification to the direct precipitation of the peritectic Nb7Ni6 phase when the roller speed reaches 10 m/s. Once the roller speed exceeds 20 m/s, the nucleation of the Nb7Ni6 phase is suppressed and the amorphous phase forms. The high-resolution transmission electron microscopy images indicate that the stacking fault and twining model of the peritectic Nb7Ni6 phase are {101¯2}/<1¯011> with a misorientation angle of 35.65°. The results of an individual local crystallization zone in amorphous matrix imply that the chemically disordered crystalline structure is more likely to form during the early stages of nucleation and growth, whereas the chemically ordered crystalline structure may evolve during the growth of the complex intermetallic compound Nb7Ni6 phase. Furthermore, the MD simulation of the glass transition temperature agrees well with the experiment, and the Voronoi polyhedron analysis suggests that the Ni-centered 〈0,0,12,0〉, 〈0,2,8,2〉 as well as Nb-centered 〈0,1,10,4〉 icosahedron-like clusters and their medium-range ordered structures play an important role in the formation of amorphous Nb54Ni46 alloy. In addition, the predictions made using classical nucleation theory and the time-temperature-transformation diagram propose that the phase selection rules are consistent with the experimental results as the undercooling and cooling rate increase, with the critical cooling rate for the formation of amorphous phase determined to be 1.71 × 107 K/s.

Kinetics and phase transformation of low-calcium coal fly ash (CFA) under hydrofluoric acid leaching

ABSTRACT The content and depolymerization degree of the glass phase in coal fly ash (CFA) is positively correlated with the activity of CFA, which is one of the key factors in the comprehensive utilization of this ash. At present, the most common and accurate method for quantitative analysis of fly ash is selective dissolution. However, more experimental data are needed to specify the effect of HF concentration on reaction kinetics, the dissolution rate of amorphous phases, and the formation of new amorphous and crystalline phases. In this study, the effects of reaction temperature, reaction time, and hydrofluoric acid concentration on the leaching rate of CFA were investigated with a single-factor condition experiment and orthogonal experiment. Phase composition and transformation of CFA under different conditions were observed with XRD and SEM. The results show that with increasing reaction time (5–120 min), temperature (20–80°C), and HF concentration (5% to 30%), the leaching rate of CFA also increased from 29.4% to 90.2%. The phase transformation of CFA in acid solution is as follows: in 5% hydrofluoric acid concentration solution, the original glass phase disappears totally and a new glass phase is formed; in 15% hydrofluoric acid concentration solution, quartz disappears and a new phase named ralstonite [Na0.5Mg0.5Al1.5F4(OH)2 · (H2O)] is formed; and when the hydrofluoric acid concentration reaches 30%, mullite disappears and a new phase named potassium aluminum fluoride (KAlF4) is formed. Also, when the temperature rises to 80°C, the f-CaO in CFA participates in the reaction to form creedite (Ca3Al2SO4F7.5(OH)2.5 · 2H2O) and fluorite (CaF2). Reaction kinetics demonstrate that the leaching reaction to the glass body of CFA is a diffusion-controlled process, and the apparent activation energy of the Si and Al leaching reaction in glass phase is 11.62 kJ/mol and 26.039 kJ/mol, respectively.

Characterization of kaolinite aqueous suspensions by acoustophoresis: Influence of crystallinity and of the ratio between basal and lateral surface of grains

The electrokinetic properties of aqueous suspensions of two kaolins were studied using the acoustophoretic method by measuring the ultrasonic attenuation spectrum in a wide frequency range (1–20 MHz). Then, the zeta potential is calculated according to the size distribution of grains. A high state of crystallinity of the kaolinite platelets strongly influences the amplitude and the variation of zeta potential versus the pH due to a high density of hydroxyl surface groups. It was also shown that specific adsorption occurs mainly with the hydroxyl surface groups of the platelet edges by using strong electrolytes (NaOH and HCl) and also organic molecules (Tiron and sodium salt of citrate). The variation of the surface chemical properties of platelets during the amorphous phase formation after temperature treatment of kaolin powder is also studied. The electrokinetic properties of kaolin suspensions treated between 200 and 800 °C successively show an increase in the positive contribution to the zeta potential up to 400 °C for the best-crystallized kaolinite and a decrease in the density of surface hydroxyl groups when the sheets delaminate from 400 °C for the less-crystallized kaolinite. This study shows that the characterization in aqueous suspension of surface properties of kaolinite complements other studies carried out on powder and therefore it makes it possible to choose kaolin as a raw material according to the intended application.

HRTEM and XPS characterizations for probable formation of TiBxNy solid solution during sintering process of TiB2–20SiC–5Si3N4 composite

The microstructural characterization of spark plasma sintered (SPSed) TiB2–20SiC–5Si3N4 composite was investigated precisely by high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The in-situ phases generated during SPS process were studied using HSC chemistry software; the result shows the development of plausible reaction between Si3N4 and B2O3, forming h-BN. In addition, the formation of in-situ TiN phase and/or TiBxNy solid solution was confirmed by XPS analysis, attributed to the reaction between TiO2 and Si3N4. The intense interfaces were formed due to the coherency between hexagonal structures of TiB2, SiC, and BN phases as detected by HRTEM. Furthermore, weak interfaces were generated because of the formation of amorphous phases in the junctions. The presence of structural defects and distortions was demonstrated in both TiB2 and h-BN by inverse fast Fourier transform patterns, which can be considered as the main channels for the diffusion and transportation of boron atoms into the Si3N4 matrix for the formation of the in-situ h-BN phase.

Microstructure and Magnetic Properties of Copper Mold Cast Nd–Fe–B Magnets Investigated by Phase‐Field and Micromagnetic Simulations

The effects of several factors, including alloy composition, cooling rate, and external magnetic field, on the microstructures and magnetic properties of Nd–Fe–B ternary alloy are explored in detail by using phase‐field and micromagnetic simulations during the copper mold casting process. It is found that the characteristic of regional distribution is formed due to the temperature gradient in the alloy, and that Nd19Fe71.5B9.5 (at%) exhibits the highest coercivity and pretty good comprehensive magnetic properties among all alloys studied, which can be interpreted by the refinement of Nd2Fe14B grain size and thickness of Nd‐rich grain boundary phase. The cooling rate has significant influence on the average grain size and the amount of amorphous phase. An increase of cooling rate results in a decrease of grain size and an increase of amorphous phase, which then affect the coercivity and remanence of the magnet. Applying an external magnetic field is demonstrated to be a good approach to enhance the coercivity and remanence by refining the grain size and restraining the formation of amorphous phase and T2 phase.

Sulfuric Acid-Activated Silica Gel as a Potential Solid Acid Catalyst

The conversion of silica gels into sulfated silicas (SO4/SiO2) have been carried out. The sulfation process of the catalysts was carried out by impregnation of sulfuric acids at concentrations of 1; 2; and 3 M and calcination temperatures of 500, 600, and 700 °C. Sulfation with 2 M H2SO4 and calcination temperature of 600 °C (SS2-600) produced a catalyst with the highest acidity value (5.13 mmol NH3 g-1). XRD analysis showed the formation of amorphous SiO2 phase, whereas SSA analysis showed that the SS2-600 catalyst had a mesoporous structure with a surface area of 147.728 m2/g, a total pore volume of 0.25 mL/g and a pore diameter of 6.439 nm. Characterization results show that sulfated silica gels have potency as solid acid catalysts.

Formation of nanoscale reaction layer with several crystallinities in the friction-welded 6061 Al alloy/steel joint

Through precise control and manipulation of welding parameters for inertia friction-welded Al alloy/steel joints, the transformation of nanoscale interfacial layer from the amorphous to the mixed phase (co-existence of amorphous and crystallised phases) and then to a fully crystallised Fe2Al5 intermetallic compound (IMC) was observed. The temperature and velocity range for the formation of different phases, including amorphous phase, mixed phase and IMC was exploited. A high level of plastic deformation and flow was found to destabilise the crystallised Fe-Al structure, promoting the formation of amorphous phase and enlarging the formation window of amorphous and mixed phase at a high temperature (∼650 K). The processing temperature was expected to govern the crystallinity of the final interfacial microstructure. The joint failed at the Al alloy side when an amorphous or mixed phase appeared at the interface, but a thicker (>100 nm) IMC layer resulted in a significantly decreased strength. The present study may provide insight on the analysis of the interfacial reaction at the initial stage of friction-based solid-state welded Al alloy/steel, and on controlling the resulting properties.