Thermal Crystallization Process Research Articles

Thermal Stability and Crystallization Processes of Pd78Au4Si18 Thin Films Visualized via In Situ TEM.

Amorphous alloys or metallic glasses (MGs) thin films have attracted extensive attention in various fields due to their unique functional properties. Here, we use in situ heating transmission electron microscopy (TEM) to investigate the thermal stability and crystallization behavior of Pd-Au-Si thin films prepared by a pulsed laser deposition (PLD) method. Upon heating treatment inside a TEM, we trace the structural changes in the Pd-Au-Si thin films through directly recording high-resolution images and diffraction patterns at different temperatures. TEM observations reveal that the Pd-Au-Si thin films started to nucleate with small crystalline embryos uniformly distributed in the glassy matrix upon approaching the glass transition temperature Tg=625K, and subsequently, the growth of crystalline nuclei into sub-10 nm Pd-Si nanocrystals commenced. Upon further increasing the temperature to 673K, the thin films transformed to micro-sized patches of stacking-faulty lamellae that further crystallized into Pd9Si2 and Pd3Si intermetallic compounds. Interestingly, with prolonged thermal heating at elevated temperatures, the Pd9Si2 transformed to Pd3Si. Simultaneously, the solute Au atoms initially dissolved in glassy alloys and eventually precipitated out of the Pd9Si2 and Pd3Si intermetallics, forming nearly spherical Au nanocrystals. Our TEM results reveal the unique thermal stability and crystallization processes of the PLD-prepared Pd-Au-Si thin films as well as demonstrate a possibility of producing a large quantity of pure nanocrystals out of amorphous solids for various applications.

Perovskite Light-Emitting Devices Based on Solid-State Diffusion In Situ Dynamic Thermal Crystallization.

Due to the excellent photonic and electrical properties of metal halide perovskite materials, perovskite light-emitting devices have the potential to replace OLED devices as the next-generation of commercial light-emitting devices. In this article, we controlled the surface morphology of PbBr2 using an in situ dynamic thermal crystallization process, which increased the specific surface area of the films and promoted the solid-state diffusion rate. The CsPbBr3 PeLEDs prepared using this method achieved a maximum current efficiency of 7.1 cd/A at the voltage of 5 V, which was 200% higher than devices prepared using traditional spin-coating processes. These results proved that the in situ thermal dynamic crystallization process effectively improved the film quality of perovskite materials.

Fabrication of Er3+:YAlO3 fibers by electrospinning method for upconversion luminescence applications

AbstractThis study aimed to prepare YAlO3 fibers doped with 2 mol% Er3+ using electrospinning and a carbon‐free sol system as the precursor. X‐ray diffraction, thermal gravimetry and differential thermal analysis, and Fourier transform infrared were employed to characterize the thermal behavior and crystallization process of the precursor fibers. Scanning electron microscope analysis showed that the Er3+:YAlO3 fibers had a uniform diameter of 1 μm, a dense and crack‐free surface, and a non‐porous cross‐section. Upon excitation at 450 and 488 nm, upconverted luminescence spectra were obtained from the Er3+:YAlO3 fibers. This observation indicates their potential as upconversion luminescent agents capable of converting visible light into ultraviolet light. These properties make the Er3+:YAlO3 fibers promising candidates for various upconversion luminescence applications.

Characterization of flexible aluminosilicate bulk fibers and fibrous mats fabricated by facile electrospinning

This paper reports a facile electrospinning method to synthesize aluminosilicate fibers by using aluminum chloride hexahydrate as single aluminum precursor, which contains no harmful or hazardous chemicals in the precursor sol. The results of Fourier transform infrared, X-ray diffraction, simultaneous thermogravimetry and differential scanning calorimetry show that the sols are diphasic. The thermal decomposition behavior, crystallization process and microstructure of the fibers are discussed in detail. The main components of aluminosilicate fibers heat-treated at 1200 °C are mullite (Al6Si2O13), alumina (α-Al2O3) and amorphous silica, while the alumina phase disappears when the molar ratio of Si to Al is below 1.5. The diameter and microstructure of fibers with different Si/Al molar ratios are obviously different, which is related to the large difference in conductivity of spinning sols. Bulk fibers and fibrous mats with good flexibility can be easily obtained by using alternative collectors. The tensile strength of the fibrous mats can reach 2.63 MPa and 1.52 MPa after heat-treated at 1000 °C and 1200 °C, respectively. The aluminosilicate fibers fabricated in this work has a noticeable potential in high temperature fields and related applications.

Direct precipitation of multilayer graphene on c-plane sapphire using a crystallized Ni catalyst

Graphene was precipitated using crystallized Ni catalyst, which was crystallized using a MBE-grown Ni layer as a seed. In the thermal crystallization process, the additional deposition of amorphous Ni layer was effective to suppress the dewetting of the Ni catalyst. The resulted graphene was flat and free from folds, which are the large wrinkles folded on the substrate and the graphene islands were found smoothly stitched together. It is because the islands were precisely aligned by the crystal information inherited from the Ni layer. The insitu observation of the precipitation was also performed using high intensity X-ray beam from a synchrotron apparatus. Precipitation process was clearly revealed, and the crystallized Ni catalyst was found effectively reduced the formation of defective graphene, which was conventionally produced by the carbons diffused though grain boundaries at low temperature.

Effects of B2O3 on crystallization kinetics, microstructure and properties of Li1.5Al0.5Ge1.5(PO4)3-based glass-ceramics

Lithium-ionic conductors of Li1+xAlxGe2-x(PO4)3 family are considered as one of the most attractive solid electrolytes. Li1.5Al0.5Ge1.5(PO4)3 composition obtained by glass-ceramic route exhibits the highest electrical conductivity at room temperature. The introduction of sintering additives makes it possible to modify the properties of solid electrolytes. Glass-ceramics of the Li1.5Al0.5Ge1.5(PO4)3–xB2O3 series (x = 0, 0.05, 0.1, 0.15, 0.2 wt%) was obtained by glass crystallization at optimal conditions of heat treatment. The influence of B2O3 additive on thermal stability and crystallization process of initial glasses was studied by DSC method. The phase composition, microstructure and transport properties of glass-ceramics were investigated by XRD, SEM and impedance spectroscopy, respectively. The structure of the glass-ceramics was characterized by Raman spectroscopy. Glass-ceramics was found to be single-phase (R-3c) when 0 ≤ x ≤ 0.15, but impurity phases Li4P2O7 and AlPO4 appear at x = 0.20. The conductivity of B2O3-added solid electrolytes is higher compared to the pristine Li1.5Al0.5Ge1.5(PO4)3. Its ionic conductivity reached 5.5 × 10−4 S cm−1 at 25 °C. The obtained glass-ceramic electrolytes are promising for use in all-solid-state lithium-ion batteries.

Investigations of the thermal, structural, and Near-IR emission properties of Ag containing fluorophosphate glasses and their crystallization process

In this work, the impact of Ag2O on the thermal, structural, and Near-IR luminescence of Er3+ doped calcium-fluorophosphate glasses is investigated. The amount of silver oxide in the glass significantly impacts its thermal stability and crystallization process. The increase in the thermal stability of the glasses might be attributed to the depolymerization of the metaphosphate network evidenced using FTIR and Raman spectroscopies. The precipitation of Ag nanoparticles within the glass network, induced by a thermal treatment, has been confirmed by the appearance of a clear visible broad absorption band centered at about 450 nm in the glasses after heat treatment. Such species induce a significant enhancement in the Er3+ IR emission. Transparent glass-ceramics have also been processed by thermally treating the glasses. The XRD analyses have revealed that the addition of Ag2O in the glass promotes the precipitation of new crystalline phases at the expense of CaF2 crystals. The presence of such nanostructures in the glass network induces some modifications in the distribution of Er ion sites.

Synthesis of nanostructured iron oxides and study of the thermal crystallization process using DSC and in situ XRD experiments

Using a coprecipitation route in aqueous medium with different precipitating agents (NH4OH and NaOH), iron-oxide nanostructures were prepared with distinct structural and magnetic properties. X-ray diffraction (XRD), 57Fe Mössbauer spectroscopy and N2 sorption experiments indicated that the sample synthesized with NaOH had nanocrystalline goethite as the dominant phase, with a specific surface area (SSA) of 80 m2/g, whereas the sample synthesized with NH4OH was X-ray amorphous, with SSA = 270 m2/g. The crystallization process of the amorphous material was investigated in detail, using in situ XRD experiments combined with differential scanning calorimetry (DSC). The X-ray diffractograms recorded at high temperatures for this sample showed first the formation of maghemite, which was then converted into hematite as the heat treatment temperature increased. DSC curves recorded at different heating rates allowed the assessment of the kinetics of the crystallization process, with identification of two consecutive steps (formation of maghemite and conversion of maghemite into hematite) and the determination of the corresponding activation energies (166 and 273 kJ/mol, respectively). From the magnetic viewpoint, the nanostructured iron oxide samples showed non zero magnetization values, indicating a strong contribution form the uncompensated iron spins at the particle surfaces, leading to a superparamagnetic regime (i.e., magnetically non-blocked state) observed for temperatures above 50 K for both samples. These results evidenced how the chemical composition and the structural features of nanostructured iron oxides can be controlled by the conditions employed in the synthesis and the posterior thermal treatments performed on these materials.

Crystal growth, defect passivation and strain release via In-situ Self-polymerization strategy enables efficient and stable perovskite solar cells

The perovskite film fabricated by the currently approbatory solution method with high temperature annealing process is inevitably accompanied by the defects and strains, which are two critical factors affecting the photovoltaic performance of perovskite solar cells (PSCs). Herein, we demonstrate an in-situ self-polymerization (ISP) strategy for high-performance PSCs by incorporating self-polymerizable n-methacrylamide (NMA) monomer additives into the perovskite film. It is revealed that NMA could not only regulate crystal growth, but also passivate grain boundary defects through its own carbonyl groups. Moreover, the self-polymerization of NMA monomer could confine the thermal-expansion of perovskite during thermal crystallization process, thereby releasing the tensile strain of perovskite film. As a result, the optimized devices achieve a champion power conversion efficiency (PCE) of 22.9%. These unencapsulated devices could maintain 91% of their initial PCE after aging 1500 h in ambient air (25 ± 5 ℃, 30 ± 5% relative humidity, dark) and 85% efficiency after annealing 600 h at 65 ℃ in nitrogen atmosphere.

Crystallization and Magnetic Properties of Pr-Fe-B Alloys

In the present work, the thermal properties and crystallization process and kinetics of the as-spun Pr6Fe78B16 are thoroughly investigated. The activation energies Ec(x) of crystallization for the Pr2Fe14B phase increase rapidly first and then increase slowly to a maximum value 440 kJ/mol at the crystallization value of 40%, while the Ec(x) of Fe3B phase is mostly lower at the stage of crystallization and then increases gradually with the increase of crystallization fraction. Meanwhile, the enhanced magnetic properties (Hcj, 215 kA/m; Mr, 116 A m2/kg; and (BH)max, 73.9 kJ/m3) have been obtained for the alloy with the annealing temperature at 660 °C. The results of magnetization reversal behavior show that a stronger exchange-coupling interaction between the hard and soft phases can be obtained by the proper annealing temperature.

Thermal decomposition and crystallization behavior of double rare-earth co-doped SrZrO3 precursor used in the solution precursor plasma spray process

A double rare-earth (Yb/Gd) co-doped SrZrO3 [Sr1.1(Zr0.9Yb0.05Gd0.05)O3.05] thermal barrier coating (TBC) was prepared by the solution precursor plasma spray (SPPS) using an aqueous solution precursor of nitrates [Sr(NO3)2, Gd(NO3)3·6H2O, Yb(NO3)3·6H2O] and zirconium acetate [Zr(C2H3O2)4]. The thermal decomposition and crystallization process of the solution precursor powders calcined at elevated temperature (~1400 °C) were studied and characterized by X-ray diffraction (XRD) and synchronous thermal analyzer coupled with Fourier transform infrared spectroscopy and quadrupole mass spectrometry (STA/FTIR/QMS) methods. Zr(C2H3O2)4 precursor decomposed into ZrO2, CH3COCH3 and CO2 firstly, followed by decomposition of hydrated nitrate. ZrO2 reacted with SrO (Yb2O3, Gd2O3) and CO2 to generate Yb/Gd co-doped SrZrO3 and SrCO3 simultaneously. SrCO3 decomposed into SrO again at higher temperature, which reacted with ZrO2 to form SrZrO3. The Sr1.1(Zr0.9Yb0.05Gd0.05)O3.05 coating was characterized as single phase with interpass boundary (IPB) structure, nano- and micrometer porosity, and through-thickness vertical cracks, analysed by XRD and the scanning electron microscope (SEM). The average grain size of the coating was calculated to be ~30 nm by Scherrer formula.

Approach to trace hidden paleo-weathering of basaltic crust through decoupled Mg[sbnd]Sr and Nd isotopes recorded in volcanic rocks

On Earth, chemical weathering of basaltic rocks not only modulates the climate change, but also plays a crucial role on the ocean oxygenation and ecosystem evolution. Records of paleo-weathered crusts are a challenge to identify because they are obscured by subsequent alteration processes and buried by the newly formed volcanic lavas. However, late formed volcanic rocks theoretically could record previously weathered crust via their assimilation and fractional crystallization (AFC) processes. Here, we present a systematic study on major, trace elements and Sr-Nd-Mg isotopes in a suite of Changbaishan early formed basalts and late erupted trachytes from Northeast China. Detailed evidence of field observation, geochemical signature and rhyolite-MELTS simulations suggest that trachytes mainly originated from deep fractional crystallization of basaltic melts. The low abundant trachytes from the stratigraphic layer above the basalts display decoupled MgSr and Nd isotopes. δ26Mg and 87Sr/86Sr in trachytes range from −0.27 up to +0.94‰ (the heaviest isotopic composition ever reported for Mg in the igneous rocks) and 0.70490 to 0.71065, respectively, which are significantly elevated relative to that of their mantle source. However, they preserved mantle source-like 143Nd/144Nd (0.512584 to 0.512656) ratios. These unusual characteristics cannot be explained by thermal diffusion, fractional crystallization or simple crustal contamination processes. Specifically, δ26Mg correlates positively with SiO2 and 87Sr/86Sr, and negatively with MgO, CaO, Al2O3, Sr and Nb/U indicators. The highly elevated Mg and Sr isotopes but limited Nd isotopic changes in trachytes require a component to be the relatively younger weathering residue of basaltic rocks. Taking this component as a wall rock endmember, the well-developed above correlations can be best modelled by AFC processes. This reflects that some trachytes in the aftermath of AFC processes almost fully lost their primary source characteristics, but inherited the intense chemical weathering signature of basalts. This event probably occurred in the middle Miocene as studies of paleosols showed humid and warm climate during that period after the initial eruption of Changbaishan basalts. Therefore, our study as a specific case for the first time provides an efficient way to explore paleo-weathering of basaltic crusts buried in the Earth's surface, through comprehensive investigating Mg, Sr and Nd isotopes of volcanic rocks developed in the late stage of a volcano cone.

Effects of water vapor on the crystallization and microstructure manipulation of MgO ceramic fibers

Magnesium oxide (MgO) ceramic fibers are a promising candidate material in high temperature insulating area, supporting area, adsorption area and catalytic area, and most of the properties are determined by the microstructure. In the present work, MgO precursor fibers were fabricated by the centrifugal-spinning combined with sol-gel method. The thermal decomposition and crystallization process of the ceramic fibers were fully characterized. Different atmosphere preheat treatment results suggested that water vapor promoted the thermal decomposition and crystallization of precursor fibers at a lower temperature. Three kinds of particles, including round particles, polyhedron particles to plate particles in the microstructure of the fibers could be manipulated by adjusting the water vapor preheat treatment. The change in textural properties (BET surface area, pore size and pore volume) of the MgO fibers, heated at different temperatures in air after pre-heated treatment in water vapor, was analyzed. Furthermore, the formation mechanisms of the microstructures of the fibers were also presented. The easy manipulation of the microstructures of MgO ceramic fibers may make it a promising material in various areas.

Electrospun mesoporous zirconia ceramic fibers for catalyst supporting applications

Mesoporous zirconia has been widely used as supporting materials, absorption materials, catalysts and high temperature insulating materials. While seldom has taken a consideration of the mesoporous fiber structure. In the present work, mesoporous zirconia ceramic fibers were fabricated by electrospinning method with CTAB as the template. The thermal decomposition and crystallization process of the mesoporous zirconia fibers were fully studied by TG/DSC, IR spectra and XRD. The highest surface area of the mesoporous zirconia fibers was about 120m2/g. With mesoporous zirconia fibers as the supporting materials, tungstate supported on zirconia fibers catalyst showed that the specific activity of bromination of phenol red was 1.26mmolh−1g−1. The results confirmed that zirconia fibers with the mesoporous structure would be a promising candidate as a supporting material.

Thermal stability and crystallization process in a Fe-based bulk amorphous alloy: The kinetic analysis

In this work, the thermal stability and non-isothermal kinetic analysis of crystallization process in (Fe41Co7Cr15Mo14Y2C15)94B6 amorphous alloy were investigated. The research findings revealed that crystallization process was done in four stages whereby the crystalline phases including Fe23 (B, C)6, Fe3Mo3C, and Mo3Co3C were formed. In order to determine the activation energy of every crystallization stages, the isoconversional methods were used. The activation energies were calculated about 550, 620, 550, and 820kJ/mol for I, II, III, and IV crystallization stages, respectively. Also, values of the rate constant at the peak temperature of crystallization, Kp; Avrami exponent, n; and growth dimensional, m; were determined by means of Augis-Bennett and Gao-Wang methods. Furthermore, for a more accurate determination of kinetic parameters including n, and m, these kinetic parameters were obtained by the Johnson-Mehl-Avrami-Kolmogorov (JMAK) and Matusita. The values of m were calculated equal to 2, 1, 2, and 3 for I, II, III, IV crystallization stages, respectively. Also, the obtained nucleation index, showed that the rate of nucleation in I, II, and III crystallization stages were zero. Therefore, it can be acceptable that a large number of nuclei related to these stages already exist in the specimen.

Mathematical model of the crystallizing blank`s thermal state at the horizontal continuous casting machine

Present article is devoted to the development of the mathematical model, which describes thermal state and crystallization process of the rectangular cross-section blank while continious process of extraction from a horysontal continious casting machine (HCCM).The developed model took cue for the heat-transfer properties of non-iron metal teeming; its temperature on entry to the casting mold; cooling conditions of blank in the carbon molds in the presence of a copper water cooler. Besides, has been considered the asymmetry of heat interchange from blank`s head and drag at mold, coming out from fluid contraction and features of the horizontal casting mold. The developed mathematical model allows to determine alterations in crystallizing blank of the following factors with respect to time: temperature pattern of crystallizing blank under different technical working regimes of HCCM; boundaries of solid two-phase field and liquid two-phase filed; blank`s thickness variation under shrinkage of the ingot`s material

A study of thermal treatment and hydrothermal crystallization stages in production of granulated NaA zeolite from mechanically activated metakaolin

NaA zeolite was synthesized from mechanically activated granulated mixtures of metakaolin, sodium hydroxide, and aluminum oxide. The thermal treatment and hydrothermal crystallization processes were studied. It is shown that the optimal temperature of thermal treatment of grains based on a mechanically activated metakaolin is 600°C at a NaA zeolite content of about 65 wt %. Raising the calcination temperature leads to a decrease in the content of the zeolite and to formation of nepheline. It was found that the optimal concentration of the crystallization solution of NaOH is 2–4 M. Under these conditions, the content of the zeolite exceeds 90 wt %. Raising the alkali concentration leads to a decrease in the content of the zeolite and to its recrystallization into sodalite.

Glass and glass-ceramics along the SrTiO3-NaPO3line

The xSrTiO 3 -(1−x)NaPO 3 (x = 0−0.20 mol%) glasses were prepared by the conventional melt-quenching method. The amorphous state of the samples was verified by X-ray diffraction. The glass-ceramic materials were obtained by the well known thermal controlled crystallization process. It is found that several physical properties such as the density, molar volume, and the glass transition temperature depend strongly on the chemical composition. Vickers test on the glasses showed that the micro-hardness increases with the SrTiO 3 content. The structural approach of the glasses was realized by IR spectroscopy. This technique has highlighted the co-existence of different phosphate and titanium structural units in the glassy-matrix. Crystallization of the glasses was enhanced by heat treatments and followed by X-ray diffraction. A mechanism for this glass crystallization was proposed.

Thermal crystallization kinetic and electrical properties of partly crystallized amorphous indium oxide thin films sputtering deposited in the presence or the absence of water vapor

Partly crystallized amorphous indium oxide thin films were deposited under water vapor atmosphere by magnetron sputtering. XRD analysis revealed that appropriate water vapor could suppress the film's crystallinity. In situ thermal crystallization process was monitored by high-temperature XRD. The crystallization data were analyzed using the Kolmogorov-Johnson-Mehl-Avrami equation. The kinetic exponent n is determined to be approx. 1/2 and 3/2 for film deposited in the absence and the presence of water vapor, respectively. The activation energy of crystallization for film deposited under 1 x 10(-5) Torr water vapor pressure was determined to be 30.7 kJ mol(-1), which is higher than 18.9 kJ mol(-1) for film deposited in the absence of water vapor. The increased activation energy caused by the chemically bonded hydrogen and embedded O-H bonds from the water vapor resulted in the suppression of crystallization. Introduction of appropriate water vapor during the deposition decreased the resistivity because of the increase of Hall mobility. The resistivity of the films after annealing increased due to the evaporation of water vapor resulted in crystal defects.

Water Barrier Properties in Biaxially Drawn Poly(lactic acid) Films

Crystallization is among the easiest ways to improve polymer barrier properties because of the tortuosity increase within the material and the strong coupling between amorphous and crystalline phases. In this work, poly(lactic acid) (PLA) films have undergone α' thermal crystallization or different drawing processes. Although no effect of α' thermal crystallization on water permeability is observed, the drawing processes lead to an enhancement of the PLA barrier properties. This work clearly shows that, in the case of PLA, the crystallinity degree is not the main parameter governing the barrier properties contrary to the crystalline and amorphous phase organizations which play a key role. X-ray analyses confirm that the macromolecular chain orientation in the amorphous phase is the main cause of the improvement of the drawn PLA water barrier property. This improvement is due to the orthotropic structure formation for sufficient draw ratios, particularly when using the Simultaneous Biaxial drawing mode. Moreover, independently of the draw conditions, the drawing process tends to reduce the plasticization coefficient. Consequently, the drawn material barrier properties are not much affected by the water passage.