Fraction Of Crystalline Phase Research Articles

The impact of different volume fractions of crystalline structures on the electrochemical behaviour of Mg67Zn29Ca4 alloys for biomedical applications

ABSTRACTIn this work, the influence of various volume fractions of the crystalline phase in an amorphous matrix of Mg67Zn29Ca4 alloys was investigated for its corrosion resistance for biodegradable applications. An amorphous Mg67Zn29Ca4 alloy was successfully fabricated using melt casting into a copper mould. Then, to obtain different ratios of the crystalline phase in an amorphous matrix, the obtained amorphous rods with 3 mm diameters were annealed at 190, 230, 250, and 400°C. The volume fraction of the crystalline phase was measured by X-ray diffraction, and the microstructures of the obtained alloys were determined based on scanning electron microscopy images. Electrochemical testing was conducted in simulated body fluid at 37°C. This report shows that the ratio of the volume fractions of amorphous and crystalline phases in alloy microstructures strongly influences their corrosion behaviours. The alloy with a fully amorphous structure was the most resistive in the analysed media.

Infrared Glass–Ceramics with Multidispersion and Gradient Refractive Index Attributes

AbstractInfrared (IR) glass–ceramics (GCs) hold the potential to dramatically expand the range of optical material solutions available for use in bulk and planar optical systems in the IR. Current material solutions are limited to single‐ or polycrystalline materials and traditional IR‐transparent optical glasses. GCs that can be processed with spatial control and extent of induced crystallization present the opportunity to realize an effective refractive index variation, enabling arbitrary gradient refractive index elements with tailored optical function. This work discusses the role of the parent glass composition and morphology on nanocrystal phase formation in a multicomponent chalcogenide glass. Through a two‐step heat treatment protocol, a Ge–As–Pb–Se glass is converted to an optical nanocomposite where the type, volume fraction, and refractive index of the precipitated crystalline phase(s) define the resulting nanocomposite's optical properties. This modification results in a giant variation in infrared Abbe number, the magnitude of which can be tuned with control of crystal phase formation. The impact of these attributes on the GCs' refractive index, transmission, dispersion, and thermo‐optic coefficient is discussed. A systematic protocol for engineering homogeneous or gradient changes in optical function is presented and validated through experimental demonstration employing this understanding.

Effect of titanium dioxide and zinc oxide fillers on morphology, electrochemical and mechanical properties of the PEO-based nanofibers, applicable as an electrolyte for lithium-ion batteries

In this study, preparation and characterization of filler-filled nanofibrous electrolytes based on polyethylene oxide (PEO) matrix are studied. The electrospun electrolytes are fabricated by an electrospinning method, using PEO, lithium perchlorate (LiClO4) as a salt, ethylene carbonate as a plasticizer and titanium dioxide (TiO2) and zinc oxide (ZnO) as fillers. Surface morphology, fraction of free ions and crystalline phases of the electrolytes are examined. The highest ion conductivities of 0.045 mS.cm−1 and 0.035 mS.cm−1 are obtained with incorporation of 0.21 wt% of the TiO2 and ZnO fillers into the electrospun nanofibers, respectively. However, film electrolytes embedded with the TiO2 and ZnO nano particles, synthesized by a film casting method, present ion conductivities of 0.0044 mS.cm−1 and 0.0147 mS.cm−1, respectively. In addition, it is identified that ion migration follows Arrhenius behavior in the as-spun electrolytes. The filler-filled nanofibrous electrolytes loss about 40% of their capacity after 45 cycles. Moreover, mechanical strength improves in filler-filled nanofibers up to an optimum ratio. The results imply that nanofibrous structures can be a great candidate as solid-state electrolytes for lithium ion batteries.

In situ study of the shear band features of a CuZr-based bulk metallic glass composite

To understand the shear banding evolution and the effect of individual shear band on deformation mechanisms of bulk metallic glass composites (BMGCs), tensile tests of CuZrAlNb BMGCs have been in situ studied. It is found that the type and sequence of shear bands are independent of volume fraction of crystalline phase. All the types of shear bands can be considered as shear bands controlled by stress affected zones (SAZs) at crystal/matrix interface and those far away from SAZs. Based on the analysis of elastic energy dissipation, the shear bands far away from SAZs play a dominant role in the deformation stability. For current BMGCs, the propagation of shear bands far away from SAZs can be delayed by reducing the average elastic energy dissipation. High Young's modulus and volume fraction of crystalline phase are effective for decreasing the average elastic energy stored in shear bands. It is expected that the obtained results can offer better understanding of deformation mechanism in bulk metallic glass composites, which should be beneficial to design bulk metallic glass composites with improved mechanical performances.

Crack-healing during two-stage crystallization of biomedical lithium (di)silicate glass-ceramics

ObjectiveThe study is aimed to evaluate the two single commercially available two-step lithium-(di)silicate systems by analyzing their parent glass composition and studying the quantitative crystalline and glass phase evolution during the second stage heat-treatment. The mechanical repercussions of the crystallization firing were evaluated using strength and fracture toughness tests. MethodsXRF and ICP-OES were used to determine the oxide composition of the parent glasses in Suprinity PC (Vita Zahnfabrik) and IPS e.max CAD (Ivoclar-Vivadent). The crystalline phase of both materials was determined by quantitative XRD and the G-factor method in the partially and post-crystallization states. The oxide composition of the residual glass phase was derived by subtracting the chemistry of the crystalline phase fractions from the parent glass composition. Mechanical testing of biaxial flexural strength and fracture toughness were used to demonstrate how crack-like defects behave during crystallization. ResultsThe two tested lithium (di)silicate systems showed strong differences in oxide composition of the parent glass. This showed to influence the transformation of lithium metasilicate in lithium disilicate, with the former remaining in high vol.% fraction in the post-crystallization Suprinity PC. In IPS e.max CAD cristobalite precipitated at the surface during the second-heat treatment. Strength and fracture toughness tests revealed that crack in both materials, whether introduced by grinding or indentation, heal during the crystallization firing. Cristobalite seemed to have contributed to a surface strengthening effect in IPS e.max CAD. SignificanceAccurate crystalline phase quantification aids in the determination of the residual glass composition in dental glass-ceramics. For both systems crystallization firing induced healing of cracks generated by CAM grinding.

Mechanical behavior of CuZr dual-phase nanocrystal-metallic glass composites

Molecular dynamics (MD) simulations are conducted to investigate the influence of various critical structural aspects such as crystallographic direction, spatial distribution and size/volume fraction of nanoscale crystalline secondary phase on the mechanical behavior of dual-phase nanocrystal-metallic glass composites (NCMGCs). The results of MD simulations show that the ‘softer’ amorphous matrix and amorphous-crystal interfaces serve as the nucleation sites of the shear transformation zones, and eventually developing into mature shear bands (SBs). We find that the different crystallographic directions of the nanocrystals have great influence on elastic modulus of composites. Moreover, the spatial distribution of nanocrystals plays an important role in SBs propagation direction. In particular, by increasing the volume fraction of the crystalline phase, plastic co-deformation of the SBs and stacking faults is achieved for the NCMGCs with nanocrystals of [1 1 0] and [1 1 1] directions. Moreover, the presence of stacking faults releases most of the stress of nanocrystals and retards the formation of a mature SB. By systematically varying the characteristics of the B2 CuZr nanoscale crystalline phase one can design composites with improved mechanical properties.

Microstructure and thermal conductivity of wire-arc sprayed FeCrNbBSiC amorphous coating

For the aim of thermal barrier application in vehicle engines, a specific FeCrNbBSiC cored wire of consideration was produced to fabricate amorphous coating by wire-arc spraying. The microstructure and thermal conductivity of the as-deposited coating were characterized in detail. The results show that the FeCrNbBSiC coating (FB coating) primarily consists of amorphous phase owing to the combination of proper composition design and rapid quenching of wire-arc spraying. However, a fraction of crystalline phases coexists with the amorphous matrix, due to the both effects of partially incomplete alloying and continuous annealing. Depending on the expected amorphous structure, thermal conductivity of the developed FB coating is as low as 2.15 W/mK at room temperature, almost half of the referenced 316L stainless steel coating (SS coating, 4.20 W/mK), and displays relatively slow and limited increase with elevated temperature up to 500 °C. By means of temperature distribution analysis, an obviously higher temperature is found on the top surface of FB coating covered piston, which implies a benefit of enhancing heat energy conversion. Simultaneously, the temperature of aluminium alloy substrate could also be reduced by covered coating as the role of thermal insulation. Therefore, the wire-arc sprayed FeCrNbBSiC amorphous coating developed here with excellent thermal barrier performance and economic advantage could be a promising innovation and candidate for metal-based thermal barrier coatings applied in vehicle engines.

Mechanochemistry approach to produce in-situ tungsten borides and carbides nanopowders: Experimental study and modeling

Mechanically-induced self-sustaining reactions (MSRs) in WO3–B2O3–Mg–C powder mixtures were investigated in terms of reductant content. Also, two different predictive intelligent-based techniques including Adaptive Neuro-Fuzzy Inference System (ANFIS) and Multi-Layer Perceptron Artificial Neural Network (MLP-ANN) were developed to estimate the structural features of the mechanosynthesized powders, where different statistical analysis were performed to prove the precision and robustness of proposed models. The phase compositions were changed as the concentration of ductile reductant (Mg) reduced in the system. Accordingly, the fraction of crystalline phases was dramatically altered after the leaching process. The structural assessment showed that the dislocation density significantly varied as the graphite content increased, however, the rate of these alterations was not linear. FESEM observations indicated that the leached product had a typical flower-like cluster configuration, which consisted of loosely organized nano-sheets with a side length and thickness of around 250 and 12 nm, respectively. Meanwhile, the results achieved from the intelligent-based techniques showed that both ANFIS and ANN are very powerful in estimating the structural characteristics of the mechanosynthesized powders. However, ANFIS was more accurate than MLP-ANN.

Giant enhancement of free charge carrier concentration in boron-doped amorphous hydrogenated silicon under femtosecond laser crystallization

The modification of boron-doped amorphous hydrogenated silicon films [a-Si:H(B)] with femtosecond laser radiation is studied in this work. It is demonstrated that femtosecond laser crystallization of the a-Si:H(B) film area leads to extremely high values of the free charge carrier (hole) concentration, which is typical for degenerated semiconductors. The free charge carrier concentration is locally determined by measuring the Raman spectra in the modified areas. The shape of Raman spectra is typical for Fano resonance. It is found that the charge carrier concentration in the modified areas may exceed 1020 cm−3 depending on the femtosecond irradiation conditions. The areas with such a high concentration of free charge carriers are also characterized by high volume fraction of crystalline phase (more than 90%). Such a sharp increase in the free charge carrier concentration in the modified areas may be explained by an increase in concentration of electrically active boron atoms. The activation energy of the temperature dependence of the conductivity for laser beam treated areas is in full agreement with the data obtained from the analysis of the Raman scattering spectra.

Effect of Cu Presence on Evolution of Mechanical and Magnetic Properties in a Novel Fe-Based Bulk Metallic Glass During Partial Annealing Process

Fe-based bulk metallic glasses (BMGs) often demonstrate extremely poor toughness at room temperature, which seriously limit their widespread application. This study is focused on the improvement of mechanical properties (especially toughness) and ferromagnetic manner of a new Fe-based BMG by using partial annealing and minor addition of Cu as an alloying element simultaneously. The results revealed that the volume fraction of crystalline phases increased with the minor addition of Cu during the partial annealing process. Therefore, maximum hardness and toughness were observed in the alloy with 0.25 at. pct Cu after annealing within a temperature range of the fourth crystallization stage due to the high Poisson’s ratios (υ) of this element and the presence of nano-crystalline phases in the amorphous matrix with an optimal average size. Also, saturation magnetization of the as-cast BMG increased with the minor addition of Cu due to the formation of short-range order regions. While with addition of Cu, this magnetic parameter was reduced in annealed alloys due to an increase in the concentration of non-magnetic Cu atoms around the α-Fe nano-crystals.

Investigation of fluctuation behavior in viscosity of coal slags used in entrained-flow gasifiers

Entrained-flow gasification has attracted extensive attention because of its clean and efficient utilization of coal as well as flexible application in industry for power generation and chemical production. Numerous theoretical and experimental investigations on slag flow in entrained-flow gasifiers have been performed to ensure a smooth operation, but an unscheduled shutdown due to slag tap blockage remains an ongoing challenge. A fluctuation phenomenon of slag viscosity gives a rise in the risk of slag tap blockage. In this work, three Chinese coal slags with low silicon content and high iron content were used to investigate the viscosity fluctuation phenomenon. It was found that the crystalline phases and suspended bubbles can cause the fluctuation phenomenon. The fluctuation degree is related to the volume fraction of crystalline phases and the crystallization rate. In the search for the mechanism of the viscosity fluctuation, an in-situ observation using a high temperature stage microscope system (HTSM) in combination with XRD and SEM analyses was carried out. In addition, the viscosity of investigated slags with the suppression of solid phases as well as the phase distribution at high temperatures was calculated. Based on a comprehensive analysis of the results, a possible mechanism has been proposed that the viscosity fluctuation is attributed to an instant local change in the macrostructure such as the deformation of suspended bubbles, the change of the orientation of acicular crystals and the interaction of the acicular crystals and suspended bubbles.

Effect of microstructure on the hardness and dry sliding behavior of electroless Ni–B coating

Dry sliding test were performed following ball-on-flat test geometry against an EN31 steel counterface on four different heat treated electroless Ni–B coatings: as-deposited (amorphous), 385 °C/4 h (completely crystalline), 300 °C/10 h (mix of amorphous and crystalline Ni3B), and 300 °C/48 h (minor amount of amorphous phase with crystalline Ni3B and metallic Ni) to evaluate the tribo response of the coating as a function of coating's microstructures. Hardness, wear, and friction behavior of the coatings are strongly dependent on the volume fraction and length scale of the boride phases produced upon crystallization of the as-deposited coating. Formation of nanocrystalline boride precipitates is governed by the complex phase transformation behavior of the as-deposited amorphous coating. Presence of local composition modulation in the as-deposited amorphous structure, induced by the deposition process, controls overall microstructure development of the coating. Two dominant wear mechanisms: oxidative and adhesive have been observed for the present experimental conditions, where the transition from the oxidative to adhesive wear regime depends on the coating's microstructure and contact pressure. Synergistic effects of the volume fraction of crystalline boride phases and its sizes, metallic Ni, and presence of remnant amorphous phase on determining the hardness and wear mechanism transition have been explained in relation to the worn track microstructure and chemical characterizations. A microstructure-based guideline for designing an optimal heat treatment scheme has been proposed.

Flame-made TiO2(B)

Titania nanoparticles containing both monoclinic (TiO2(B) – a promising battery material and catalyst) and anatase crystal phases are synthesized with a low-cost, scalable flame spray pyrolysis (FSP) process, as confirmed by X-ray diffraction, transmission electron microscopy and Raman spectroscopy. The latter reveals TiO2(B) contents of up to 27% in the crystalline phase fraction. The amount of TiO2(B) increases as the time for nanoparticle growth in the flame decreases through quenching with ambient air. It can be controlled by varying the flow rates of precursor solution and dispersion oxygen into the flame. The FSP-made titania outperforms commercial titania P25 in the photocuring of epoxy, indicating its potential as a photocatalyst.

Relationship of the Structure and the Effective Diffusion Properties of Porous Zinc- and Copper-Containing Calcium Phosphate Coatings

The morphology and the structure of zinc- or copper-containing calcium phosphate coatings deposited by the microarc oxidation (MAO) method at different voltages on pure titanium and low-modulus Ti-40 wt % Nb alloy substrates are investigated. The morphology of the MAO coatings on both substrates is composed of sphere-shaped structural elements 8–42 μm in size and pores 1–15 μm in size. When the process voltage is increased from 200 to 300 V, these structural elements grow and partially destruct. It is ascertained that the MAO voltage increase leads to the linear increase in the surface porosity of the coatings from 14 to 24%. It is established that the effective diffusion coefficients of the model biological fluid in porous coatings vary from 0.85 × 10–10 to 9.0 × 10–10 m2/s. Under the increase in the structure element size, the effective diffusion coefficient of the model biological fluid increases in the MAO coatings deposited on a titanium substrate and decreases in those deposited on Ti-40 wt % Nb alloy. The observed difference is related to the increase in the crystalline phase fraction.

Electron Diffraction Analysis of the Structure of Carbon Nanopillars along the Growth Direction

The structure of carbon nanopillars grown without catalysis by low-temperature plasmaenhanced-chemical-vapor deposition on a silicon substrate is investigated using the suggested focused ion beam technique for preparing a sample composed of several thin plan-view foils. Studying the prepared sample by electron diffraction and bright-field transmission electron microscopy allows determination of the variation of the two-dimensionally ordered crystallite fraction along the growth direction. It us established that the crystalline phase fraction inside the nanopillars gradually decreases during the growth process. Nearly 90% of the crystalline material is located between the base and the middle of the nanopillars while their upper parts almost entirely consist of amorphous carbon.

Direct derivation (DD) of weight fractions of individual crystalline phases from observed intensities and chemical composition data: incorporation of the DD method into the whole-powder-pattern fitting procedure

A formula for quantitative phase analysis (QPA), called the intensity–composition (IC) formula, can be used for deriving weight fractions of individual crystalline phases in a mixture from sets of observed integrated intensities, measured in a wide 2θ range, with chemical composition data [Toraya (2016). J. Appl. Cryst. 49, 1508–1516; Toraya (2017). J. Appl. Cryst. 50, 820–829]. In this study, the IC formula has been incorporated into the whole-powder-pattern fitting (WPPF) procedure to conduct QPA. The fitting function for calculating the profile intensity at each step of the scattering angle consists of three sub-functions that represent the individual component diffraction patterns. The first sub-function calculates the diffraction pattern using a set of integrated intensities, the parameter values of which are determined by the least-squares fitting of the whole-powder pattern as is usually done by the whole-powder-pattern decomposition (WPPD) method. The second sub-function uses a set of integrated intensity parameters, which are preliminarily prepared by WPPD or may be calculated from a crystal structure model. These intensity parameters, multiplied by a scale factor, are fixed at their original values while the scale factor is adjusted in WPPF. The third sub-function uses an observed or calculated diffraction pattern multiplied by a scale factor. This diffraction pattern can be fitted directly by adjusting the scale factor. Therefore, one can fit patterns consisting of heavily broadened and degraded diffraction lines, like those of clay minerals, without being concerned with the problem of peak overlap in decomposing the diffraction pattern. The IC formula uses the total sums of the intensities under the diffraction patterns of individual phases as observed data sets; therefore, it can equally treat these intensity data sets irrespective of differences in the profile models used by the three sub-functions. The three sub-functions can arbitrarily be chosen and linearly combined, and then they can simultaneously be fitted to the observed diffraction pattern of a target mixture. The capability of the above method has been demonstrated with QPA of mixtures consisting of α-quartz, albite and kaolinite. Theories of currently used QPA techniques are reviewed from a viewpoint of the present theory and they can be interpreted as being based on the same principle, whereby the total observed intensities of individual phases are divided by the standard reference intensity per unit weight.

Microstructural and phase evolutions: Their dependent mechanical and magnetic properties in a Fe-based amorphous alloy during annealing process

In this study, the microstructural and phase evolutions of Fe41Co7Cr15Mo14Y2C15B6 amorphous alloy were investigated during annealing process to enhance the its mechanical and magnetic properties. The results showed that the crystalline phases including Fe23(B,C)6, Mo3Fe3C, and Mo3Co3C were formed during the annealing process, so that the volume fraction of these phases increased up to 32.3% by annealing at 928 °C. The mechanical behavior of investigated bulk metallic glass (BMG) was investigated by means of indentation testing. The cracking system types consist in Palmqvist cracks were obtained by means of stepwise polishing. Hardness and indentation toughness increased by an increase in crystallization temperature, simultaneously. Also, the ferromagnetic properties were significantly improved by increasing the volume fraction of crystalline phases.

Preparation and characterization of blend polymer electrolyte film based on poly(vinyl alcohol)-poly(acrylonitrile)/MgCl2 for energy storage devices

The development of magnesium electrolytes for battery applications has been the demand for electrochemical devices. To meet such demand, in this work solid blend polymer electrolytes were prepared using polyvinyl alcohol (PVA) and polyacrylonitrile (PAN) (92.5PVA:7.5PAN) as host polymer, magnesium chloride (MgCl2) of different molar mass percentage (m.m.%) (0.1, 0.2, 0.3, 0.4, 0.5, and 0.6%) as salt and dimethylformamide (DMF) as solvent. Structural, vibrational, thermal, electrical, and electrochemical properties of the prepared electrolytes were investigated using different techniques such as X-ray diffraction pattern, FTIR spectroscopy analysis, differential scanning calorimetry (DSC), AC impedance measurement, and transference number measurement. X-ray diffraction studies confirm the minimum volume fraction of crystalline phase for the polymer electrolyte with 0.5 m.m.% of MgCl2. FTIR confirms the complex formation between host polymer and salt. DSC analysis proves the thermal transition of the prepared films are affected by salt concentration. The optimized material with 0.5 m.m.% of MgCl2 offers a maximum electrical conductivity of 1.01 × 10−3 S cm−1 at room temperature. The Mg2+ ion conduction in the blend polymer electrolyte is confirmed from transference number measurement. Electrochemical analysis demonstrates the promising characteristic of these polymer films suitable as electrolytes for primary magnesium batteries. Output potential and discharge characteristics have been analyzed for primary magnesium battery which is constructed using optimized conducting electrolyte.

Structure and thermomechanical properties of fast-quenched Ti2NiCu alloy ribbons with various crystalline phase fractions obtained by means of annealing by electric current

New promising functional materials—amorphous-crystalline fast-quenched Ti2NiCu alloys exhibiting the shape memory effect (SME)—are studied. A method for annealing amorphous alloys by electric current pulses is proposed. This method allows one to obtain the needed degree of crystallinity. It is demonstrated that a microcrystalline structure with spherical grains exists in amorphous-crystalline samples. These grains increase in size from 150 nm to 3.2 μm as the degree of annealing increases. The SME is not observed in nontreated samples and is clearly manifested in completely annealed samples. A two-way SME and a trend toward lowering of the martensitic transition temperature are observed in partially annealed samples.

Quantitative phase analysis using observed integrated intensities and chemical composition data of individual crystalline phases: quantification of materials with indefinite chemical compositions

In a previous report, a new method for quantitative phase analysis (QPA) of multi-component mixtures using a conventional X-ray powder diffractometer was proposed. The formula for deriving weight fractions of individual crystalline phases presented therein includes sets of observed integrated intensities measured in a wide 2\theta range, chemical formula weights and sums of squared numbers of electrons belonging to atoms in respective chemical formula units [Toraya (2016).J. Appl. Cryst.49, 1508–1516]. The latter two parameters required to perform QPA could be calculated from only the information of chemical formulae of individual phases. In the present study, these two parameters are replaced with a single parameter in the form new parameter = (chemical formula weight)/(sum of squared numbers of electrons). As will be expected from this definition, the parameter has nearly equal values for groups of materials consisting of similar kinds of atoms, and its value becomes identical for polytypes or polymorphs having the same chemical composition. That characteristic of this parameter makes it possible to estimate the parameter value not only directly from the chemical composition of the target material itself but also from database-stored chemical analysis data sorted on the basis of mineral or chemical composition. The parameter value is also hardly changed as a result of small compositional variations of the target component material. Therefore, the present method can be applied to QPA of materials not only of definite chemical compositions but also of indefinite chemical compositions without degrading the accuracy of the analysis. This is expected to widen the application to QPA of, for example, natural products containing many kinds of trace elements, industrial materials with complex substitutional replacement of atoms, nonstoichiometric compoundsetc. The theory and some examples of applications are presented. A procedure for quantifying unknown material is also proposed.