Thermal study on structural changes and phase transition in high-energy electron-irradiated blends of P(VDF–TrFE) copolymers

Thermal study of high-energy electron-irradiation binary blends of ferroelectric P(VDF–TrFE) copolymers has been investigated by X-ray diffraction, differential scanning calorimetry (DSC) and thermally stimulated depolarization current (TSDC). X-ray diffraction shows some degree of mixing inside a crystal lattice due to significant changes in the ferroelectric-to-paraelectric phase transition behavior from all-trans to trans-gauche conformation in nanometer range after irradiation. In DSC thermograms, it is found that both the Curie temperature and melting temperature decrease with the dose and that the F–P transition temperatures and enthalpies of two individual copolymers and the blend merge into one with the increase of dose, indicating that there exists a strong lattice coupling between the two copolymers. The peaks observed in TSDC spectra of the blends exhibit the phase transitional characters of the parent copolymers which demonstrates that the miscibility in the crystalline region for their large compositional discrepancy. The distribution of temperature peaks in TSDC also show that the existence of two types of crystallite in the blend which become more clear after irradiation, confirming the X-ray and DSC results.     

On the phase diagram of the system hydroxypropylcellulose-water

The phase diagram of the system hydroxypropylcellulose (HPC)-H₂O has been investigated using differential scanning calorimetry (DSC), X-ray diffraction, optical microscopy and¹H (NMR) nuclear magnetic resonance spectroscopy. A peritectic line at higher temperatures has been found similar to the lytropic systems described before. This phase transition, from a solution consisting of solvate aggregates and free solvent, into a crystal solvate-isotropic phase system is completely reversible. The formation of crystal solvate phases is independent of the water content of the system until the system transforms into a thermotropic system. The solvent molecules are strongly associated with the macromolecules.     

Synthesis, characterization, high temperature phase transition and electrical properties of solid solution AgScMo2O8

AgScMo₂O₈ was synthesized by wet-chemistry method. The samples were characterized by differential thermal analysis/thermogravimetry, differential scanning calorimetry (DTA/TG, DSC), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The novel structure of the sample is different to the other oxide AgLnMo₂O₈ (Ln = lanthanide). The XRD and DTA/TG, DSC results showed that the formation temperature of AgScMo₂O₈ was found to be as low as 450°C, and AgScMo₂O₈ crystallized in a monoclinic-type structure at room temperature. With increasing of the temperature two phase transition processes (monoclinic to hextetrahedral and tetragonal) appeared. The electrical property of the samples was also investigated by using A.C impedance spectroscopy. It showed that an abrupt increase of electrical conductivity was found around 500°C, which attributes to phase transition. The facts indicted that this kind of material shows a potential application in intermediate-temperature solid oxide fuel cells (SOFCs).     

Structural transition and atomic ordering of Ni49.8Mn28.5Ga21.7 ferromagnetic shape memory alloy powders prepared by ball milling

The Ni_49.8Mn_28.5Ga_21.7 powders of micro-scale irregular equiaxial particles are prepared by ball milling method, and characterized by XRD, DSC and SEM techniques. The powders are found to contain disordered fct structure. Upon heating to high temperatures, the crystal structure of the as-milled powder is found to evolve from disordered fct to disordered bcc and then to a Heusler-type structure sequentially. The critical temperature for the transition from the bcc phase to the Heusler phase is 360 °C. This phase transition process is also a disorder–order transition. An atomic ordering model similar to the grain nucleation and growth is established to explain the annealing temperature dependence of the phase transformation temperature.     

Study on the compatibility and crystalline morphology of NBR/PEO binary blends

Compatibility property, as well as crystalline morphology, of NBR/PEO blends has been investigated by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and polarized optical microscopy (POM) thoroughly. There is no apparent shift of nitrile or ether groups in the FTIR spectra of NBR/PEO blends. Based on the calculations from glass transition temperature, the maximum volume fraction of PEO dissolved in NBR phase is about 6.41 % in blend with 5 wt% PEO content (PEO-5), indicating a weak intermolecular interaction in the NBR/PEO blends. From the characteristic absorption bands in the FTIR spectra, XRD and POM graphs, the crystallinity ratio of NBR/PEO blends decreases as the NBR content increases, which is further proved by DSC measurement that the crystallinity ratio and crystal melting temperature of pure PEO are 82.6 %, 69.9 °C, and that of PEO-5 are 16.9 %, 59.5 °C. This illuminates that the weak intermolecular interaction will affect the crystallinity ratio and crystal melting temperature of the NBR/PEO blends.     

Crystalline-amorphous phase transition of hyperbranched polyurethane phase change materials for energy storage

Hyperbranched polyurethane solid–solid phase change material (HB-PUPCM) has been prepared via a two-step process. The phase transition behaviors and morphologies of these HB-PUPCM films were investigated using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarizing optical microscopy (POM). PEG soft segment in the polyurethane was found to be crystalline at room temperature. However, when the temperature was raised to PEG’s melting point, polyurethane did not melt into the liquid state as in the case of pure PEG but changed to an amorphous solid state. In HB-PUPCM, PEG’s molecules probably are tied to the hard segment chain so strongly by the chemical bonds that they cannot change to a liquid state but change to the amorphous state in the transition processing.     

W掺杂二氧化钒的水热晶化机理及其相变性能

以硫酸氧钒为钒源,采用沉淀-胶溶法制备VO_2溶胶。然后向溶胶中加入偏钒酸铵,利用溶胶水热晶化制备出W掺杂二氧化钒(W-VO_2,M相)粉体。通过XRD,FESEM和DSC对合成产物的物相组成、形貌和相变性能进行研究。结果表明:在280℃条件下水热处理4~48h,VO_2溶胶经过水热晶化生成长约1~2μm、直径约100~200nm棒状W-VO_2(B)晶体,伴随着B相向M相晶型转变,W-VO_2(B)逐渐消溶,而W-VO_2(M)逐渐长大,形貌由棒状转变为片状或雪花状;W-VO_2(M)相变温度随着W掺杂量增加而降低,当名义掺杂量为6.0%(原子分数)时,相变温度降低到28℃。根据水热晶化和形貌演变过程,提出了W-VO_2(M)可能的"形核-生长-转化-熟化"形成机理。     

Ferromagnetic-to-Paramagnetic Phase Transition of MnAs Studied by Calorimetry and Magnetic Measurements

Manganese monoarsenide samples have been prepared by the sealed-ampule technique and characterized by X-ray diffraction, differential thermal analysis, and scanning electron microscopy. The hexagonal- to-orthorhombic phase transition of MnAs has been studied using differential scanning calorimetry (DSC) and magnetic measurements. The enthalpy and temperature range of the transition have been determined to be ΔH =–5.6 J/g and 312.5–319 K, respectively. The enthalpy and temperature range of the transition are influenced by the quality of the samples. The samples containing inclusions of the metastable, orthorhombic phase have a lower enthalpy and broader temperature range of the magnetostructural transformation of manganese monoarsenide. It has been demonstrated that DSC is an effective tool for assessing the quality of MnAs samples. Temperature dependences of specific magnetization and magnetic permeability for MnAs lend support to the DSC results. From these data, the Curie temperature of MnAs has been determined to be 40°C, in good agreement with previously reported data.     

Relaxor ferroelectric behavior and structural evaluation in electron-irradiated <Emphasis Type="Italic">P</Emphasis> (vinylidene fluoride-trifluoroethylene) copolymer blends

The effect of high-energy electron-irradiation on binary ferroelectric blends of poly(vinylidene fluoride-trifluoroethylene) 56/44 and 80/20 mol% has been studied in a broad dose ranging from 0 to 120 Mrad. It was found that the blends transformed from a normal ferroelectric to relaxor ferroelectric, obeying the Vogel-Fulcher law, after a proper electron dose by dielectric constants and loss measurements. X-ray diffraction shows significant changes in the ferroelectric-to-paraelectric phase transition behavior from all-trans to trans-gauche conformation after irradiation. In differential scanning calorimetry (DSC) thermograms, the Curie temperature and melting temperature decrease with the dose, indicating that there exists a strong lattice coupling between the two copolymers.     

Organic-inorganic interaction and the growth mechanism of hydroxyapatite crystals in gelatin matrices between 37 and 80 °C

The crystal development of hydroxyapatite[HAp] phase in gelatin[GEL] matrices was investigated in the temperature range 37 to 80 °C by using X-ray diffraction, scanning electron microscopy(SEM), thermoanalytical measurement(DT/TGA), Fourier-Transformed Infra-Red(FT-IR) spectroscopy, and transmission electron microscopy(TEM) with electron diffraction(ED). It was found that during the coprecipitation of apatite phase in GEL matrices and the next aging process the crystallites were formed and developed through the two reaction mechanisms of organic-inorganic interaction between apatite phase and GEL molecules, and thermodynamic reaction for the crystal growing. The analytical evidences showed that there was a definite competition between these two mechanisms with the reaction temperature. Below 50 °C the crystal development of HAp was greatly suppressed by the existence of the GEL molecules, indicating the heterogeneous nucleation by the supposed number of carboxyl groups in GEL. Above 50 °C the effective organic components as a template for the heterogeneous nucleation of apatite crystallites were greatly degraded and so more amount of inorganic ions could be favorably accredited on the preexisting crystallites in virtue of the limited nucleation chance, finally resulting in the crystal growth. At higher temperature pretty big HAp crystals were developed with the depletion of the organics to be bound with crystallites in the slurry solution. Presumably it is believed that the poisoning of the functional groups in GEL molecules was vigorously occurred in the phosphoric acid environment above ∼ 50 °C.     

Simultaneous Measurements of Thermal,Electrical, and Acoustic Properties of BaTiO<Subscript>3</Subscript> – New Feature of 403 K Phase Transition

In order to obtain useful information on the transient process of phase transitions in ferroelectrics by various methods including calorimetry, the “mK-stabilized cell” of a small size has been developed. It is based on the heat flux differential scanning calorimeter (DSC) and has a temperature stability better than 1 mK. The “cell” can be used to change the temperature under nearly quasi-static conditions by an infinitesimally small rate not only on heating but also on cooling while passing through the transition points. It enables simultaneous measurements of endothermic heat and exothermic heat along with dielectric constants, displacement currents, etc. with a high degree of temperature resolution. X-ray diffraction measurements for sensing thermal anomalies are also possible by a minor modification of the “cell.” Precise and simultaneous measurements of thermal, electrical, and acoustic properties were carried out at the 403 K phase transition in BaTiO₃ single crystal grown by the top-seeded solution growth method. It has been clarified that the exothermic heat at the transition on cooling has more useful information than the endothermic heat on heating; in the cooling process two thermal anomalies occur separately at T₁ and T₂ although the transition is in a narrow temperature range. It is recognized from other methods that the nature of the transition on cooling is not of a single but of multiple steps. Resonant ultrasonic measurements using the “cell” were carried out, after developing a new excitation method. The sample does not have a simple softening approaching the transition point on cooling but has different elastic moduli for the two thermal anomalies at T₁ and T₂. The dielectric constant also has an intermediate constant value between T₁ and T₂. The crystal structure in the room temperature phase below the transition point has been determined by X-ray diffraction. In this region, tetragonal and monoclinic structures coordinating with each other exist. Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A.     

Crystallinity of isotactic polypropylene films annealed from the quenched state

Quenched isotactic polypropylene films were annealed at 130, 140 and 155 °C for 24 h. The structural organization, after annealing, was analysed by wide-angle X-ray diffractograms (WAXD), differential scanning calorimetry (DSC), density and sorption of dichloromethane vapour at low activity. The comparison of the different methods used to obtain the crystallinity shows that, even at the highest annealing temperature, the transformation of the smectic phase into the monoclinic phase, is not complete. WAXD and DSC give the amount of monoclinic phase, whereas the amorphous fraction was derived from sorption of dichloromethane vapour at low activity. From the density, it was possible to derive the residual smectic fraction in the different samples. The results indicate that, at temperatures higher than 150 °C, there is an accelerated decrease of smectic phase and an accelerated increase in the crystal dimensions and perfection.     

Synthesis,characterization, and thermodynamic parameters of vanadium dioxide

A novel process was developed for synthesizing pure thermochromic vanadium dioxide (VO₂) by thermal reduction of vanadium pentoxide (V₂O₅) in ammonia gas. The process of thermal reduction of V₂O₅ was optimized by both experiments and modeling of thermodynamic parameters. The product VO₂ was characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS), scanning electron microscopy (SEM), thermogravimetric analysis (TG), and differential scanning calorimetry (DSC). The experimental results indicated that pure thermochromic VO₂ crystal particles were successfully synthesized. The phase transition temperature of the VO₂ is approximately 342.6 K and the enthalpy of phase transition is 44.90 J/g.     

SAXS/DSC/WAXD study of TiO2 nanoparticles and the effect of γ-radiation on nanopolymer electrolyte

Nanostructured polymer electrolytes are very attractive materials for components of batteries and opto-electronic devices. (PEO)₈ZnCl₂ polymer electrolytes and nanocomposites were prepared using Poly(ethylene oxide) (PEO) γ-irradiated with a selected dose of 529 kGy and with an addition of 10% of TiO₂ nanograins. The influence of the added nanosize TiO₂ grains on the polymer electrolytes and the effect of the γ-radiation from a Co-60 source were studied by small-angle X-ray scattering (SAXS) simultaneously recorded with differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) at the synchrotron ELETTRA. Infrared (IR) and impedance spectroscopy (IS) were also performed [1]. It was shown by previously performed IS that the room temperature conductivity of the nanocomposite polymer electrolyte increased more than two times above 65 °C, relative to pure composites of PEO and salts. We observed all changes between 20 °C and 100 °C for treated and as prepared polymer electrolyte in the SAXS, DSC and WAXD spectra and especially during the phase transition to the super-ionic phase at 65 °C [2] and [3]. The SAXS/DSC measurements yielded insight into the temperature-dependent changes of the grains of the electrolyte as well as into the differences due to different heating and cooling rates. The crystal structure and the melting and crystallization temperatures of the nanosize grains were revealed by the simultaneous WAXD measurements.     

Synthesis, characterization and thermal history dependence of the polymorphic structure of nylon6/montmorillonite nanocomposites

Nylon6/clay nanocomposites with 5-wt% montmorillonite (NCN5) were prepared by a twin-screw extruder. The effects of thermal histories including annealing temperature (195 °C, solid-state annealing; 245 °C, melt-state annealing), annealing time and cooling rate on the polymorphic behavior and thermal property of NCN5 have been studied using Modulated Differential Scanning Calorimetry (MDSC) and wide angle X-ray diffraction. It was found that longer annealing time and faster cooling rate favored the formation of the γ crystal when NCN5 samples were annealed at 195 °C. As the annealing temperature was elevated to 245 °C, the α crystal became the absolutely dominating crystalline phase independent on the annealing durations and cooling rate. Moreover, a small endothermic peak was observed around 195 °C in NCN5 samples and this new transition peak was also found to be dependent on the thermal history.     

Shape change and phase transition of needle-like non-stoichiometric apatite crystals

Nanometre-size needle-like non-stoichiometric apatite crystals are made in our laboratory by hydrothermal treatment at 140°C at a pressure of 0.3 MPa for 2 h. The shape change and phase transition of these crystals are studied using transmission electron microscopy (TEM), X-ray diffractometer (XRD) and infrared spectroscopy (IR). The results show that water molecules are present in the crystal structure of non-stoichiometric apatite. The condensation of HPO₄ ^2- ions can happen over a wide temperature range more than 600°C and is followed closely by the reaction of P₂O₇ ^4- ions with OH^- ions. The obvious TCP phase at 750°C is the outcome of the fusion and recrystallization of the needle-like crystals at 650°C and 750°C. Generally, stoichiometric apatite cannot contain water in its crystal structure while non-stoichiometric apatite can. Maybe this is the reason why bone contains non-stoichiometric apatite.     

High-temperature creep and structure investigation of nearly stoichiometric Fe3Si

X-ray diffraction measurements were carried out on powdered single crystals of nearly stoichiometric Fe₃Si. The experimental data obtained in the temperature range from room temperature up to 750‡ C in terms of long-range order, thermal expansion, phase transition and Debye temperature (together with values of the Curie temperature) support the existence of two modifications of the DO₃ structure for Fe-26 at% Si alloys and a phase transition in the DO₃ structure field at 595‡ C. The high-temperature modification has a smaller thermal expansion coefficient, a higher Curie temperature and a higher Debye temperature.     

Annealing and recrystallization of amorphous ZnO thin films deposited under cryogenic conditions by pulsed laser deposition

This article deals with the annealing of amorphous ZnO thin films prepared by pulsed laser deposition (PLD) under cryogenic conditions. The substrate holder was cooled by liquid nitrogen. X-ray diffraction analysis evidenced that as-deposited films had amorphous structures: analysis by scanning electron microscopy (SEM) revealed their fine grained surface and inner structure. Annealing at temperatures in the range of 200-800 °C resulted in a transition in the thin film crystal structure from amorphous to polycrystalline. Various properties of the ZnO films were found depending on the recrystallization temperature. In depth investigations employing SEM, X-ray diffraction, atomic force microscopy and secondary ion mass spectroscopy provided comparisons of the recrystallizations of undoped ZnO thin films during the phase transition processes from amorphous to hexagonal wurtzite structures.     

Superior Functionality by Design: Selective Ozone Sensing Realized by Rationally Constructed High‐Index ZnO Surfaces

A new technique is reported for the transformation of smooth nonpolar ZnO nanowire surfaces to zigzagged high‐index polar surfaces using polycrystalline ZnO thin films deposited by atomic layer deposition (ALD). The c‐axis‐oriented ZnO nanowires with smooth nonpolar surfaces are fabricated using vapor deposition method and subsequently coated by ALD with a ZnO particulate thin film. The synthesized ZnO–ZnO core–shell nanostructures are annealed at 800 °C to transform the smooth ZnO nanowires to zigzagged nanowires with high‐index polar surfaces. Ozone sensing response is compared for all three types of fabricated nanowire morphologies, namely nanowires with smooth surfaces, ZnO–ZnO core–shell nanowires, and zigzagged ZnO nanowires to determine the role of crystallographic surface planes on gas response. While the smooth and core–shell nanowires are largely non‐responsive to varying O₃ concentrations in the experiments, zigzagged nanowires show a significantly higher sensitivity (ppb level) owing to inherent defect‐rich high‐index polar surfaces.     

Thin films of3 He — Implications on the identification of3 He —A

Recently the identification of³He — A with the axial state has been questioned. It is suggested that the A-phase can actually be in the axiplanar state. We point out in the present paper that experiments in a film geometry may be useful to distinguish the above two possibilities. In particular a second order phase transition between an axial and an axiplanar state would occur as a function of thickness or temperature.