High-temperature Differential Scanning Calorimetry Research Articles

Formation kinetics and thermodynamic stability of the Aurivillius compounds in Bi4Ti3O12–BiFeO3 system

AbstractThe Aurivillius compounds in the Bi2O3–Fe2O3–TiO2 system, combining ferroelectric, semiconducting, and ferromagnetic properties, have attracted particular interest. Formation kinetics and thermodynamic stability are the fundamental knowledge needed for modeling and predicting the temporal microstructure and property evolution during materials processing but have not yet been addressed by quantitative experimental measurement. This article focuses on the Bin+1Fen–3Ti3O3n+3 Aurivillius compounds on the Bi4Ti3O12–BiFeO3 tie‐line to elucidate the mechanisms and thermodynamic controls responsible for phase formation of compounds with various perovskite‐like layers. Five high‐purity Aurivillius compounds Bi4Ti3O12, Bi5FeTi3O15, Bi6Fe2Ti3O18, Bi7Fe3Ti3O21, and Bi8Fe4Ti3O24 with integer n = 3–7 values were synthesized and their phase transformation properties and enthalpies of formation were studied by X‐ray diffraction in situ, high temperature differential scanning calorimetry, and high temperature oxide melt solution calorimetry. Thermodynamic stability of the compounds decreases with increasing n, and formation kinetics gradually slow down, demonstrating the inherent difficulty to synthesize pure Aurivillius compounds with n larger than 8. This difficulty was confirmed by an impurity phase coexisting with Bi9Fe5Ti3O27.

Experimental investigation of lattice thermal expansion and specific heat capacity of C15–Cr2Zr Laves phase intermetallic compound by HTXRD and DSC

The lattice thermal expansion and specific heat capacity of the C15–Cr2Zr Laves phase intermetallic compound were investigated using high temperature X-ray diffraction (HTXRD) and differential scanning calorimetry (DSC). All these alloys were prepared by arc melting. Through various heat treatments, the intermetallic compound Cr2Zr with both C14/C36–Cr2Zr and cubic C15–Cr2Zr Laves phase structure was obtained from these ingots. Room temperature XRD profile and scanning electron microscope (SEM) along with energy-dispersive X-ray (EDX) experiments on 1573 K/8h homogenized samples have confirmed the homogeneity and C15 (Fd-3m) crystal structure of Cr2Zr. The lattice parameters and relative phase fraction of the constituent phases were evaluated by using Rietveld refinement. The lattice thermal expansion behaviour of the compound was investigated in the temperature range 298 K–1073 K, and the result shows that its unit cell parameters increased exponentially when the temperature increased. The average thermal expansion coefficients were found to be αai = 1.03 × 10−5 K−1 and αvi = 3.08 × 10−5 K−1. The specific heat capacity of the Laves phase Cr2Zr has been measured by using heat-flux DSC by employing the classical three-step method and is being reported for the first time. The heat capacity data obtained in this study have been compared with the theoretical model using quasi-harmonic Debye Grüneisen formalism in the temperature range 0–860 K and shown the various contributions to total heat capacity. The measured heat capacity data was used to obtain enthalpy increment as a function of temperature, which was effectively modelled by first principles based quasi-harmonic approximation and revealed different contributions to total enthalpy. To the best of our knowledge, this is the first experimental report on the thermal expansion and specific heat capacity of C15–Cr2Zr. A comprehensive set of thermodynamic parameters for C15–Cr2Zr has been established using a combination of measurement and modelling.

Experimental and thermodynamic study of high-temperature phase stability of Fe–Zr binary alloy

This work investigated the high-temperature phase stability of Fe–Zr binary alloy using the CALPHAD approach combined with an experimental study. The controversial Fe23Zr6 phase in the Fe–Zr system was recognized as a stable phase by annealing at 1273 K for 1440 h, followed by X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry. The conditions affecting the stability of the Fe23Zr6 phase, such as the cooling rate, annealing time, and atmosphere, were investigated. The experimental results indicated that the Fe23Zr6 phase precipitates more under longer annealing time and faster cooling rate, and the phase is not oxygen stabilized. The liquidus temperature from the Fe2Zr_C15 phase to the Zr end region was measured using high temperature differential scanning calorimetry. A combination of the experimental results and the findings in recent literature enabled us to reoptimize the Fe–Zr system using the CALPHAD approach.

Analysis on phase nucleation in Sn-Ni peritectic alloy combining confocal laser scanning in-situ observation and differential scanning calorimetry

The analysis of the phase nucleation requires not only the in-situ images but also the accurate nucleation information. Thus, the nucleation of both the primary Ni3Sn2 and peritectic Ni3Sn4 phases were studied during peritectic solidification of Sn-Ni alloy using the high temperature confocal laser scanning microscope (HT-CLSM) and differential scanning calorimetry (DSC). The results by both methods confirm that the nucleation undercooling ∆T of the solid phases decrease with increasing cooling rates, which is demonstrated to be caused by higher concentration difference at larger cooling rates. Besides, the freezing range of the alloy is also found to decrease with the increase in cooling rate. However, the nucleation undercooling of the peritectic Ni3Sn4 phase determined by HT-CLSM is larger than that by DSC at each cooling rate. This is attributed to the slower capture of peritectic reaction when using HT-CLSM. Furthermore, the nucleation of peritectic Ni3Sn4 phase is confirmed to be controlled by the heterogeneous nucleation on primary Ni3Sn2 phase by comparison between the HT-CLSM observation and DSC result. In addition, the wetting angles for heterogeneous nucleation of both phases which are important parameters in analyzing the nucleation of solid phases were determined through the entropy of solidification data from the DSC results. The smaller wetting angle of peritectic Ni3Sn4 phase as compared with that of the primary Ni3Sn2 phase further proving the smaller nucleation undercooling of Ni3Sn4 phase during solidification.

Preparation and characterization of chitosan flake and chitosan nanopowder gels: A comparative study of rheological, thermal and morphological perspectives

Chitosan flakes (CF) were modified to chitosan nanopowder (CP), using planetary ball milling for 8 h. Dynamic light scattering (DLS) revealed and high resolution transmission electron microscopy (HRTEM) confirmed the nano size of CP. Least gelation capacity (LGC) of CF (3%) and CP (4%) was manipulated to fabricate gels with 1.5, 2, and 3 fold increase in LGC. The total color difference was higher in CP than CF gels and depended on concentration. Dynamic rheometry under temperature ramping (20–80 °C and 80-20 °C) showed stable viscoelasticity. Besides, optimal structural network was observed in CP8 and CF6. During temperature ramping, the damping factor (tan δ) for all the gels was >0.1 < 1, which confirmed the elastic behavior of the gels. Power law model revealed maximum shear thinning behavior in CP8 and CF6. Rapid increase in temperature of gels during thermogravimetric analysis (TGA) and high temperature differential scanning calorimetry (HDSC) revealed more thermal stability in CP than CF gels. The interconnecting gap of polymer gel matrix revealed through scanning electron microscopy (SEM) was higher in CF than in CP gels. In conclusion, the CP gels have comparable rheology but better thermal and matrix properties that could be explored for food and pharmaceutical applications.

Determining Compositional Variation in Silicon-Metal Alloys by Parsing SEM/EDS Hyperspectral Images.

High-temperature differential scanning calorimetry was used to understand the thermal properties of Si-rich metal–silicon alloys. Insoluble metals (A and B) were found to produce an alloy with discrete ASi2 and BSi2 dispersed phases. In contrast, metals that form a solid solution result in a dispersed phase that has a composition of AxB1−xSi2, where x varies continuously across each inclusion. This complex composition distribution is putatively caused by differences in the solidification temperatures of ASi2 versus BSi2. Though this behavior was observed for several different combinations of metals, we focus here specifically on the Cr/V/Si system. To better understand the range and most probable element concentrations in the dispersed silicide domains, a method was devised to generate histograms of their Cr and V concentrations from energy-dispersive X-ray spectroscopy hyperspectral images. Varying the Cr/V/Si ratio was found to change the shape of the element histograms, indicating that the distribution of silicide compositions that form is controlled by the input composition. Adding aluminum was found to result in dispersed phases that had a single composition rather than a range of Cr and V concentrations. This demonstrates that aluminum can be an effective additive for altering solidification kinetics in silicon alloys.

Influence of sub-Tg annealing on microstructure and crystallization behavior of TiZr-based bulk metallic glass

Herein, the effect of sub-Tg annealing on microstructure, glass transition kinetics and crystallization behavior of Ti33Zr30Cu9Ni5.5Be22.5 bulk metallic glass (BMG) is systematically studied by high-temperature differential scanning calorimetry. The results reveal that sub-Tg annealing can improve the compactness of Ti33Zr30Cu9Ni5.5Be22.5 BMG and expand the supercooled liquid region. Also, the non-isothermal crystallization behavior indicates that the glass transition activation energy (Eg) of Ti33Zr30Cu9Ni5.5Be22.5 BMG decreases and crystallization activation energy (EP1, EP2) increases after sub-Tg annealing. The changes in Eg, EP1 and EP2 exhibit sensitivity to sub-Tg annealing temperature. It is demonstrated that the isothermal crystallization time of Ti33Zr30Cu9Ni5.5Be22.5 BMG is extended by ≈1 min after 593 K annealing, indicating the inhibition of crystallization process. The Avrami indices of as-cast and sub-Tg-annealed Ti33Zr30Cu9Ni5.5Be22.5 BMGs, calculated by the Johnson-Mehl-Avrami equation, range from 2.08 to 2.30 and indicate that the three-dimensional growth process is mainly controlled by the diffusion, which is not influenced by sub-Tg annealing.

TEMPERATURE EFFECT ON THE STRUCTURE OF NdSr2Mn2O7+δ COMPLEX OXIDE

High-temperature Xray diffraction and differential scanning calorimetry are used to study the features of structural changes in NdSr2Mn2O7+δ complex oxide at temperatures from room to 1150 °C. Structural calculations by the Rietveld method establish a relationship between anomalies in the temperature dependences of unit cell parameters and in the DSC curves with changes in the lengths of bonds between Mn and Nd, Sr cations and oxygen atoms.

Synthesis Conditions and Structure of Layered Manganites Ln2BaMn2O7 – δ(Ln = Pr, Nd)

Conditions (temperature, oxygen partial pressure in the gas atmosphere, and heating time) for the synthesis of polycrystalline layered manganites Ln2BaMn2O7 – δ (Ln = Pr, Nd) with an orthorhombic structure (Fmmm) and a specific oxygen non-stoichiometry were proposed for the first time. The temperature boundaries for the orthorhombic (Fmmm) to tetragonal (I4/mmm) structural phase transition were determined using high-temperature X-ray diffraction and differential scanning calorimetry. The temperature of the structural transition increases with increasing atomic number of the rare earth metal present in the manganite.

Techno-functional characterization of chitosan nanoparticles prepared through planetary ball milling

Planetary ball milling of chitosan microparticles (CMP) for 8 h produced chitosan nanoparticles (CNP) having hydrodynamic diameter of 615.18 nm. The ζ-potential decreased from 56.48 mV (CMP) to 31.52 mV (CNP). High resolution transmission electron microscopy (HRTEM) revealed nanosize, irregular shape and surface roughening of CNP. CNP was whiter than CMP having higher water absorption capacity and decreased flow ability. Both CMP and CNP showed negligible swelling and no water solubility. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) revealed no chemical changes and X–ray diffraction (XRD) showed decreased crystallinity in CNP. In CNP, thermogravimetric analysis (TGA) revealed increased thermal degradation; differential thermogravimetric (DTG) revealed increased rate of thermal degradation; and high temperature differential scanning calorimetry (HDSC) revealed broadening of endothermic and exothermic phases and reduction in glass transition temperature as compared to CMP. In conclusion, planetary ball milling for 8 h produces bright, amorphous and rough CNP with improved functional and comparable thermal properties.

Influence of strain rate and strain at temperature on TRIP effect in a metastable austenitic stainless steel

Metastable TRIP (TRansformation-Induced Plasticity) steel strips with a microstructure comprising ferrite, retained austenite and martensite were subjected to tensile tests at different strain rates of 10−5s−1, 10−4s−1, 10−3s−1 and temperatures 27 °C, 50 °C and 100 °C. The TRIP steel specimens exhibited very high tensile strengths (up to ~1700 MPa) in tests carried out at room temperature, which is attributed to the TRIP effect. Thermal stability of the phases present in the TRIP steel in the as-received condition was assessed by in-situ high temperature XRD and DSC (Differential Scanning Calorimetry) analysis to determine the retained austenite decomposition temperature. Microstructural analysis by XRD, optical microscopy and electron microscopy was used before and after the tensile tests to identify the features present at micro- and nano-scales, which are responsible for the observed mechanical properties. Macrographs taken from the surface of the specimens after the tensile tests showed the presence of Lüders bands and their occurrence was concurrent with the TRIP effect. The effect of strain rate and temperature on the TRIP effect and the associated mechanical response are discussed in detail.

Quantitative high temperature calorimetry on precipitation in steel and nickel alloys

This work presents a method for the in-situ analysis of solid-solid-phase transformations in precipitation hardening alloys at high temperatures (typically 600–1100 °C). It shows that the Differential Scanning Calorimetry (DSC) methodology originally introduced for low temperatures (typically below 600 °C, e. g. Al-alloys) can be successfully adapted for continuous heating and even continuous cooling on high temperature alloys such as martensitic precipitation hardening steel X5CrNiCuNb16-4 (17-4 PH) as well as the Ni-based superalloys, Inconel 718 and René 65. The high temperature DSC Setaram Labsys EVO was used with both continuous heating, as well as continuous cooling, experiments being performed, using rates of 0.01 to 0.3 K/s. One challenge for high temperature DSC analysis is to find an appropriate reference material. Hence different strategies to obtain quantitative data are discussed.

Powder X-Ray Diffraction Data on Polymorphism of RbBSi2O6 and Crystal Structure of Its High-Temperature Modification

Structural deformations and phase transformations of Rb-boroleucite RbBSi2O6 obtained by crystallization from glass at 1000 °C are studied by high-temperature X-ray powder diffraction and differential scanning calorimetry in the range 25–1200 °C. At 345 °C the compound undergoes a reversible cubic-cubic polymorphic transition with increasing symmetry \(I\bar 43d \leftrightarrow Ia\bar 3d\). The crystal structure of RbBSi2O6 is refined by the Rietveld method at temperatures of 25 °C, 100 °C, 200 °C, 300 °C, 310 °C, 320 °C, 330 °C, 340 °C, 350 °C, 360 °C, 380 °C, 400 °C, 500 °C, 600 °C, 700 °C, 800 °C, and 900 °C, according to the powder X-ray diffraction data.

Highly branched and high‐molecular‐weight polyethylenes produced by 1‐[2,6‐bis(bis(4‐fluorophenyl)methyl)‐4‐MeOC6H2N]‐2‐aryliminoacenaphthylnickel(II) halides

ABSTRACTA series of unsymmetrical 1‐[2,6‐bis(bis(4‐fluorophenyl)methyl)‐4‐MeOC6H2N]‐2‐aryliminoacenaphthene‐nickel(II) halides has been synthesized and fully characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance (1H NMR), 13C NMR, and 19F NMR spectroscopy as well as elemental analysis. The structures of Ni1 and Ni6 have been confirmed by the single‐crystal X‐ray diffraction. On activation with cocatalysts either ethylaluminum sesquichloride or methylaluminoxane, all the title nickel complexes display high activities toward ethylene polymerization up to 16.14 × 106 g polyethylene (PE) mol−1(Ni) h−1 at 30 °C, affording PEs with both high branches (up to 103 branches/1000 carbons) and molecular weight (1.12 × 106 g mol−1) as well as narrow molecular weight distribution. High branching content of PE can be confirmed by high temperature 13C NMR spectroscopy and differential scanning calorimetry. In addition, the PE exhibited remarkable property of thermoplastic elastomers (TPEs) with high tensile strength (σb = 21.7 MPa) and elongation at break (εb = 937%) as well as elastic recovery (up to 85%), indicating a better alternative to commercial TPEs. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 130–145

Biocompatible silica-based magnesium composites

In this study, an in-situ formed Mg2Si-Mg composite is investigated to understand the formation of Mg2Si and its influence in mechanical properties and corrosion behavior. A starting blend of 2.5 wt% SiO2 nanoparticles and magnesium powders was used to elaborate in-situ composite through mechanical blending followed by spark plasma sintering technique. High temperature X-ray diffraction measurements and differential scanning calorimetry results confirmed the formation of Mg2Si phase. The addition of 2.5 wt% SiO2 enhanced hardness while the stiffness values remained the same. The results of potentiodynamic polarization tests revealed an improved corrosion resistance of Mg reinforced with SiO2 nanoparticles. Thus, this work is an attempt to understand the fabrication (dissociation of silica into Mg2Si in presence of Mg) and corrosion properties of silica reinforced magnesium composites with those of pure magnesium targeting biomedical applications.

Shock synthesis and characterization of titanium dioxide with α-PbO2 structure

The phase transformation behavior of anatase and rutile titanium dioxide with particle sizes of 60 nm and 150 nm under shock compression have been investigated. To increase the shock pressure and reduce the shock temperature, copper powder and a small amount of paraffin were mixed with the TiO2 powder. The shock recovered samples were characterized by x-ray diffraction, Raman spectroscopy, and transmission electron microscope. The results indicate that both anatase and rutile TiO2 can transform to α-PbO2 phase TiO2 through shock-induced phase transition. The transformation rate of α-PbO2 phase TiO2 for anatase TiO2 under shock compression is 100% and pure α-PbO2 phase TiO2 can be obtained, while the transformation rate for rutile TiO2 is over 90%. The influence of the particle size on the yield of α-PbO2 phase TiO2 is not noticeable. The thermal stability of the recovered pure α-PbO2 phase TiO2 was characterized by high temperature x-ray diffraction, thermogravimetric analysis and differential scanning calorimetry. The results show that α-PbO2 phase TiO2 transforms to rutile TiO2 when heated to temperature higher than 560 °C. The mechanisms of the phase transition of TiO2 under shock compression are discussed.

Graphitization Behavior of Loblolly Pine Wood Investigated by in Situ High Temperature X-ray Diffraction

Graphitization is a complex process involving chemical and morphological changes, although the detailed mechanism for different starting materials is not well understood. In this work, in situ high temperature X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to examine the phase transition occurring between 1000 and 1500 °C in loblolly pine wood-derived carbon materials. Electron energy loss spectroscopy (EELS) was also used to study these wood-derived carbon materials. XRD data showed the disappearance of a disordered carbon phase between 1300 and 1400 °C, followed by the formation of a crystalline graphitic phase between 1400 and 1500 °C. Lattice parameters and the crystal structure of the loblolly pine wood-derived graphite were systematically calculated from the empirical data. The presence of a large endothermic peak at 1500 °C in the DSC thermogram supported this observation. Selected area electron diffraction patterns showed the growth of graphitic crystallites after heat treatment. EELS spectra also supported the presence of a well-developed graphite structure.

Dynamics and Thermochemistry of Oxygen Uptake by a Mixed Ce–Pr Oxide

The dynamics of oxygen uptake by mixed Ce0.55Pr0.45O2–x oxide is studied in a pulsed oxygen supply mode using in situ high-temperature heat flow differential scanning calorimetry. It is stated that the oxidation proceeds in two regimes: a fast one at the beginning of the oxidation process, and a slow one, which is controlled by the diffusion of oxygen through the bulk of the solid at the later stages of the process. Analysis of the shape of calorimetric profiles reveals some processes, accompanied by heat release, that occur in the sample in the absence of oxygen in the gas phase. These could be due to both the redistribution of consumed oxygen in the oxide lattice and the lattice relaxation associated with the transformation of phases with different arrangements of oxygen vacancies in them. The heat effect (which diminishes from ~60 to ~40 kJ/mol in the course of oxygen uptake) associated with the oxidation of the reduced form of mixed Ce–Pr oxide, corresponds to the oxidation of praseodymium ions from (3+) to (4+).

Crude and refined oils from Elaeis guineensis: Facile characterization by FTIR and thermal analysis techniques

ABSTRACTFrom an industrial perspective, fast characterization of raw materials provides an important tool for preventing manufacturing problems and contributes to assure the quality of the final products. In this work, several fast, cheap, and simple methods (Fourier transform infrared spectroscopy (FTIR) and various thermoanalytical techniques) were used for screening and characterization of crude and refined palm oils and other palm-derived products. The FTIR spectra allowed for ready distinction between mesocarp-derived products and those obtained from the kernel. The same applied to high-temperature differential scanning calorimetry (DSC) and differential thermal analysis (DTA) thermograms and the low-temperature DSC curves, in which the peak values and the presence or absence of certain peaks also permitted to differentiate among the various oils and fractions. Correspondences of mesocarp-derived oils with olein and kernel-derived oils with stearin were confirmed by both analytical methods and from the crystallization study. The relationship between the triglyceride composition and the FTIR and thermal profiles of the various palm-derived products has potential to be utilized as a facile quality control method in mill plants and laboratories.

Undoped and ytterbium-doped titanium aluminum nitride coatings for improved oxidation behavior of nuclear fuel cladding

In an effort to develop coatings to increase the oxidation resistance of nuclear fuel cladding during a loss-of-coolant-accident (LOCA), undoped and ytterbium-doped titanium aluminum nitride (TixAl1-xN) coatings were deposited onto ZIRLO® and grade-5 titanium substrates using a hybrid coating technique incorporating both resistance evaporation and cathodic arc physical vapor deposition (CA-PVD). The coating systems consisted of a titanium bond layer, an undoped TiAlN layer, and an outer TiAlN layer doped with varying levels of ytterbium (0.44 to 33.24at.%). The coated materials were subjected to high temperature atmospheric oxidation testing and differential scanning calorimetry (DSC) to evaluate the effect of different Yb dopant concentrations on the TixAl1-xN coating oxidation resistance. The results showed that the coatings evaluated in this study protected the tubular ZIRLO® cladding material from oxidation when exposed to air at temperatures up to 1200°C. DSC data showed that the corrosion resistance of coatings with Yb dopant concentrations of 0.44 and 0.64at.% was better than that of undoped TixAl1-xN coatings and of TixAl1-xN coatings with Yb concentrations ≥4.78at.%. Yb doping and the 0.44 and 0.64at.% level also resulted in a lower rate of oxide scale growth and improved scale adherence, which further slowed oxidation kinetics. Peak oxidation resistance was observed in the TiAlN coating with a 0.44at.% ytterbium dopant concentration. Ytterbium concentrations of 4.78at.% and greater led to accelerated oxidation rates for the testing conditions studied compared to undoped TiAlN. These results show that ytterbium doped coatings are possible candidates for high temperature resistance of accident tolerant fuel coatings.