Differential Thermal Analysis Apparatus Research Articles

Acceleration of Isothermal ω Phase Formation by Oxygen Addition in Ti–Nb Alloys during Cooling Process

The effect of oxygen addition on the microstructure formation during cooling from the β phase in the Ti–Nb alloy was investigated. The alloy ingots of Ti–(13∼20) at%Nb–(0∼3) at%O were arc-melted. They were homogenized at 1200°C for 3.6 ks and then hot-rolled at 850°C into 1.5 mm thick sheets. The disk specimen of 3 mm diameter was heated up to β phase field at 1000°C in the differential thermal analysis apparatus. And then specimen was cooled to room temperature at a cooling rate of 20°C/min. The β → α transformation was accelerated by the oxygen addition in Ti–(13∼15) at%Nb alloys. On the other hand, the oxygen addition promoted β → isothermal ωi transformation in Ti–(16∼20) at%Nb alloys. The promoting effect increased up to 1.5% oxygen, but the effect weakened by adding more than 1.5 at% oxygen in Ti–(18, 20) at%Nb alloys. The addition of oxygen over 3.0 at%O might suppress the β → ωi transformation in Ti–20 at%Nb alloy.

Na2Ca3Si2O8 or γ‐Na2Ca6Si4O15? A hybrid approach combining 3D single‐crystal electron and powder X‐ray diffraction

AbstractPhase assemblages of mixtures containing Na2CO3, CaCO3, and SiO2 in the molar ratio 1:3:2 have been studied at elevated temperatures. Synthesis experiments have been performed at 1000, 1100, and 1200°C within a differential thermal analysis (DTA‐TGA) apparatus. Mass losses during heating and annealing periods of the high‐temperature treatment have been investigated in situ using thermogravimetry. For the run at 1200°C, the solid‐state reactions resulted in almost phase pure polycrystalline material of a previously unknown high‐temperature polymorph of Na2Ca6Si4O15, whose formation was triggered by significant Na2O losses at the reaction temperature. The new so‐called γ‐phase has been structurally characterized by a combination of 3D single‐crystal electron and powder X‐ray diffraction. Basic crystallographic data at ambient conditions are as follows: monoclinic symmetry, space group C 2, a = 17.2066(1) Å, b = 5.47863(3) Å, c = 7.32583(4) Å, β = 91.435(4)°, V = 690.38(1) Å3, Z = 2. Structure solution was accomplished by electron diffraction, whereas the subsequent refinement calculations were based on the Rietveld method using high‐resolution data from a laboratory powder diffractometer. Similar to the other two already known Na2Ca6Si4O15 modifications, the crystal structure of the γ‐phase contains both [Si2O7] dimers and insular [SiO4] moieties. Tetrahedra and [CaO6] octahedra form a three‐dimensional framework whose topological characteristics have been studied. The remaining Ca and Na cations are located on five symmetrically independent positions located in cavities of the network. There are sufficiently strong arguments that previously described “triclinic Na2Ca3Si2O8” is actually misinterpreted γ‐Na2Ca6Si4O15 and that a sodium calcium silicate with a molar ratio of Na2O:CaO:SiO2 = 1:3:2 does probably not exist. Our investigation is an excellent example that 3D electron diffraction has transformed from an exotic technique for crystal‐structure determination into an indispensable method for problems where small sizes of the crystallites is an issue.

New insights of the peritectic phase transition in steel through in-situ measurement of thermal response in a high-temperature confocal microscope

The topic of peritectic phase transition in steel has been widely studied using various in-situ experimental techniques including visual observation on a surface of a sample in a high temperature microscope and measurement of the thermal response from the bulk of the sample using differential thermal analysis (DTA) and differential scanning calorimetry (DSC). These two different techniques have inherent limitations leading to difficulties in interpretation of the results in the case of complex phase transformations such as the peritectic reaction, and there have been discrepancies among the interpretations from many previous studies of the peritectic transition in steel. A new technique was developed through a spatial combination of a DTA apparatus and a high-temperature laser-scanning confocal microscope to overcome these limitations. Solidification experiments with carbon steels of 0.061, 0.182 and 0.451 wt%C were conducted under conditions typical of conventional thermal analysis experiment, i.e. 90 mg of sample mass and 10 °C/min cooling rate, and the findings of earlier studies were revisited. We concluded that whether or not a peritectic reaction in a steel specimen of peritectic composition occurs, largely depends on the size of the sample used in the experiment. Deep undercooling for austenite nucleation can be experienced, in the absence of the occurrence of a peritectic reaction as a result of constrained nucleation of austenite, due to a limited number of nucleation sites in the small samples used.

Heating Conditions Influence on Solidification of Inconel 625-WC System for Additive Manufacturing.

In this study, an Inconel 625–tungsten carbide (WC) composite system was investigated by means of microstructure changes affected by both heating rate and WC content. In order to investigate how the system behaves while exposed to fast thermal processing, controlled melting using a differential thermal analysis (DTA) apparatus was performed on the powders. Two WC powders with different average grain size were used to obtain six compositions of Inconel 625–WC powder mixtures (10, 20, and 30 wt.% WC). They were analyzed under 10 and 30 °C/min heating rate in order to obtain composite samples. Results from DTA together with SEM/energy-dispersive X-ray spectroscopy (EDS) microstructural observations allowed observing material changes during solidification. Because of the extensive microsegregation of alloying elements to liquid and their reactions with C, which derived from dissolved WC, the formation of secondary phases with improved microhardness was possible. The collected results provide a better understanding of material behavior during intensive thermal processing which can be useful when designing materials for the laser additive manufacturing technique.

Effect of oxygen addition on the formation of isothermal ω phase in Ti-Fe alloys

The effect of the addition of oxygen on the formation of microstructure cooled from the β phase of Ti-Fe alloy was examined. The alloy ingots of Ti-(4, 5, 6, 7, 8, 9 and 10) at.% Fe and Ti-8 at.% Fe-(1 and 3) at.% O were arc-melted. They were homogenized at 1200 °C for 3.6 ks and then hot-rolled at 850 °C into 1.5-mm thick sheets. The disk specimen was fabricated and then put in the differential thermal analysis (DTA) apparatus. The disk in the DTA was heated at 1000 °C for 0.6 ks in the β phase and then cooled to room temperature at a rate of 50 °C/min. The microstructure was examined by an optical microscope after the DTA experiment. In the Ti-(7 and 8) Fe alloys the ω phase formed during cooling. The addition of oxygen in the Ti-8Fe alloy promoted the β→α transformation. Furthermore, the addition of one at.% oxygen in the Ti-8Fe alloy promoted β→ωi transformation, while the addition of three at.% oxygen suppressed the β→ωi transformation during cooling.

Experimentally Determined Phase Diagram for the Barium Sulfide-Copper(I) Sulfide System Above 873 K (600 °C)

The phase diagram of the barium sulfide-copper(I) sulfide system was investigated above 873 K (600 °C) using a custom-built differential thermal analysis (DTA) apparatus. The melting point of barium sulfide was determined utilizing a floating zone furnace. Four new compounds, Ba2Cu14S9, Ba2Cu2S3, Ba5Cu4S7, and Ba9Cu2S10, were identified through quench experiments analyzed with wavelength dispersive X-ray spectroscopy (WDS) and energy dispersive X-ray analysis (EDS). A miscibility gap was observed between 72 and 92 mol pct BaS using both DTA experiments and in situ melts observation in a floating zone furnace. A monotectic was observed at 94.5 mol pct BaS and 1288 K (1015 °C).

Hydrothermal synthesis and mechanism of triangular prism-like monocrystalline CeO2 nanotubes via a facile template-free hydrothermal route

Monocrystalline CeO2 tablet-like nanostructures and triangular prism-like nanotubes were synthesized by thermal conversion of cerium carbonate hydroxide (CeOHCO3) precursors prepared by a simple template-free hydrothermal method using Ce(NO3)3·6H2O as cerium source, CO(NH2)2 as both precipitator and carbon source and polyvinylpyrrolidone (PVP) as surfactant. X-ray diffractometer (XRD) images inferred that the as-synthesized Ce(CO3)(OH) has a hexagonal structure, and the CeO2 obtained by calcining the Ce(CO3)(OH) at 500°C for 5h has a cubic fluorite structure. Scanning electron microscope (SEM) was employed to reveal the transformation from tablet-like to triangular prism-like structures, and then to triangular prism-like nanotubes with the increase of temperature from 120 up to 200°C. Monocrystalline structure was revealed by high resolution transmission electron microscope (HRTEM) and select area electron diffraction (SAED) patterns. The thermal decomposition process of the as-synthesized Ce(CO3)(OH) was investigated by thermo-gravimetric differential thermal analysis (TG–DTA) apparatus, and the possible formation mechanism of CeO2 has been discussed. The spectral properties were characterized by Fourier transform infrared spectrum (FT-IR), Raman scattering, Photoluminescence (PL) spectra and UV–vis spectroscopy. There is a red-shifting in the band gap of the material compared to bulk one, which is mainly attributed to the influences of the Ce3+ ions, oxygen vacancies and the change of morphology.

Differential Thermal Analysis of Li-Ion Cells as an Effective Probe of Liquid Electrolyte Evolution during Aging

A technique has been developed to allow for in-situ observation of the state of the liquid electrolyte present in an electrochemical device through exploiting the nature of solid-liquid phase transitions. An apparatus was developed to perform differential thermal analysis (DTA) on complete NMC/graphite lithium-ion pouch cells. The DTA apparatus monitored the temperature of a sample cell alongside that of a thermally inert reference cell during a controlled temperature scan through the melting point of the electrolyte in the sample cell, producing a thermal signature of the sample electrolyte without damage to the cell performance. This signature holds information pertaining to the composition and amount of liquid electrolyte present in the electrochemical device, allowing for detailed study of electrolyte evolution at various points of life and indications of the state-of-health of the device.

Temperature effect on the microstructural development of Al–Ni layered binary couples produced by an unconventional method

In this work, the authors have used an unconventional experimental route that consists of (i) deposition of a nickel coating onto an aluminium substrate and (ii) the subsequent heat treatment of created couple in order to produce intermetallic-layered structures, hypereutectic or bulk aluminide intermetallic alloys. The procedure was conducted by controlling chemical concentrations in the Al-rich corner of Al–Ni binary system. The couple was prepared by high velocity oxyfuel spraying of 99.0wt.% Ni powder onto the surface of 99.999wt.% Al sheet. The specimens for heat treatment were manufactured immediately after the spraying. The heat treatment was carried out in a differential thermal analysis apparatus by using the temperature range of 600–1200°C, thus considering the solid state, transient liquid as well as liquid phase of aluminium, with a constant heating/cooling rate of 5°C/min in an argon atmosphere. Microstructural development of produced alloys was studied by conventional metallography and scanning electron microscopy. Formed intermetallic layers and compounds were evaluated by using energy dispersive microanalysis and image analysis techniques. The development of a novel ultra-fine eutectic alloy is reported.

High-temperature Oxidation Behavior of a High Manganese Austenitic Steel Fe–25Mn–3Cr–3Al–0.3C–0.01N

In this paper, a Fe–Mn–Al–C austenitic steel with certain addition of Cr and N alloy was used as experimental material. By using the SETSYS Evolution synchronous differential thermal analysis apparatus, the scanning electron microscope (SEM), the electron microprobe (EPMA) and the X-ray diffraction (XRD), the high-temperature oxidation behavior microstructure and the phase compositions of this steel in air at 600–1,000 °C for 8 h have been studied. The results show that in the whole oxidation temperature range, there are three distinct stages in the mass gain curves at temperature higher than 800 °C and the oxidation process can be divided into two stages at temperature lower than 800 °C. At the earlier stage the gain rate of the weight oxidized in temperature range of 850 °C to 1,000 °C are extremely lower. The oxidation products having different surface microstructures and phase compositions were produced in oxidation reaction at different temperatures. The phase compositions of oxide scale formed at 1,000 °C are composed of Fe and Mn oxide without Cr. However, protective film of Cr oxide with complicated structure can be formed when the oxidation temperature is lower than 800 °C.

Effect of Heat Treatment on Formation of Al-Al<sub>3</sub>Ni Hypereutectic Alloys

The paper deals with the mechanism of eutectic formation in a nickel coated aluminium system after heat treatment. The initial coating was produced from a nickel powder by means of high velocity oxyfuel (HVOF) spraying onto an aluminium sheet substrate. Specimens for investigations were manufactured immediately after the spraying. The specimens were heat-treated using a differential thermal analysis (DTA) apparatus up to the temperature of 700 or 900 °C and then cooled down to room temperature in argon atmosphere with a constant heating and cooling rate of 5 °C / min, under which Al-Al3Ni + Al3Ni hypereutectic alloys were formed within the initial substrate. Two different alloy microstructures consisting of intermetallic layers and coarse eutectic or an ultrafine well-dispersed eutectic were formed. Formation processes and resulting microstructures were studied by means of DTA, metallography, scanning electron microscopy, focused ion beam, energy dispersive microanalysis and image analysis techniques.

Facile hydrothermal method to synthesise hexagonal rotor‐like cerium carbonate hydroxide and CeO 2 nanostructures

The hexagonal rotor-like cerium carbonate hydroxide (CeCO3OH) and CeO2 nanostructures were successfully synthesised via a facile hydrothermal method using Ce(NO3)3 · 6H2O as the cerium resource, HNO3 additive to form an acidic solution, CO(NH2)2 as both precipitator and carbon source and polyvinylpyrrolidone as surfactant. Characterisation techniques using an X-ray diffractometer, scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy, thermogravimetric differential thermal analysis apparatus and UV–vis absorption spectrum have been used for studying the roles of Ce(NO3)3 · 6H2O and HNO3. It was found that the amount of Ce(NO3)3 · 6H2O has an obvious effect on the morphology of the as-synthesised CeCO3OH and CeO2 nanostructures, whereas HNO3 has a significant influence on the crystalline phase. CeO2 has a higher UV absorption than as-synthesised CeCO3OH, which is likely associated with the charge-transition between Ce3+ and Ce4+.

Microstructure development during isothermal brazing of Ni/BNi-2 couples

Heat treatments of the Ni–BNi-2 assemblies were performed at 1050°C, for different brazing times, in a Differential thermal analysis apparatus. The nature, chemical composition and crystallography of the involved phases were identified. Limited predictive capability of Thermo-Calc software with the TTNI7 data base (developed for Ni-based alloys) was pointed out. The microstructure evolution with brazing time was quantitatively analyzed, and used to discuss the mechanism of isothermal brazing and further solidification during cooling. The fraction of dissolved base metal was found proportional to the initial thickness of brazing material. This suggests that the composition of liquid stays homogeneous with a precise initial equilibrium composition during the brazing process. Finally a specific analysis of DTA curves is proposed to estimate the brazing kinetics.

The kinetics of a polytypic Laves phase transformation in TiCr 2

A systematic investigation of the kinetics of the polytypic C36 ⇄ C14 equilibrium phase (shear) transformation occurring at about 1545 K was performed. A recently developed calibration and desmearing procedure for a differential thermal analysis (DTA) apparatus [Baumann et al. Thermochim. Acta 2008; 472:50] enabled the investigation of the progress of this transformation by isochronal DTA measurements, both upon heating and cooling. A kinetic model was developed on basis of the modular approach, which considers overlapping nucleation, growth and impingement. It was shown that athermal nucleation prevailed, i.e. pre-existing nuclei (here: arrays of dislocations) become activated as function of undercooling/overheating. The model fitting led to values for the equilibrium transformation temperature, the C36/C14 interface energy and the activation energy for growth. Moreover, a quantitative explanation was given of the composition-dependent thermal hysteresis of the transformation.

Construction of an Apparatus for Differential Thermal Analysis under Constant High-Pressure

Construction of an Apparatus for Differential Thermal Analysis under Constant High-Pressure

Behavior of pressure dependence of melting temperatures in aromatic polyesters: Influence of polymer structure

AbstractThe thermal behavior of three aromatic polyesters in a homologous series, poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT), and poly(butylene terephthalate) (PBT) was studied under hydrostatic pressure up to 200 MPa by using a high pressure differential thermal analysis apparatus. Confining fluid high pressure dilatometer was used to establish the volume–temperature curves (in both solid and liquid regions) from which volume change on melting of these polyesters at atmospheric pressure was determined. Single endothermic peak was seen for PET and PTT, whereas PBT showed double peaks above 50 MPa. Pressure coefficient of melting temperature at atmospheric pressure (dTm/dp(0)), was obtained from the quadratic fit. The dTm/dp(0) for PTT was newly determined to be 0.445 KMPa−1, whereas for PET and PBT were 0.503 and 0.455 KMPa−1, respectively, comparable to reported values. The dTm/dp(0) exhibited the odd‐even behavior corresponding to odd and even number of methylene groups in the repeat unit. Enthalpy and entropy of fusion had the most influence on this coefficient. Entropy related to conformational and volume change were evaluated and the former was found to have a significant impact on the value of dTm/dp(0). © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1799–1808, 2009

Design and application of differential thermal analysis apparatus in high magnetic fields

The differential thermal analysis (DTA) apparatus has been developed for a commercial superconducting magnet. The DTA apparatus could detect the kinetics and thermodynamics of phase transformation with and without a magnetic field. Preliminary results for Al-Al2Cu eutectics are presented. The DTA curves indicate the similarity at several rates regardless of a magnetic field; however, at the same rate, melting transformation seems not to be influenced by a magnetic field, while solidification could be delayed via suppressing nucleation and crystal growth in a magnetic field. It will be believed that the DTA apparatus can be used to investigate the phase transformation of substances of interest in a magnetic field.

Characterization and the mechanism of formation of the ternary compoundMgNi2.5B2 inNi-doped MgB2 bulk

(MgB2)1−xNix bulksamples (x = 0.0, 0.04 and 0.06) were synthesized using a differential thermal analysis apparatus at750 °C. Bymeans of scanning electron microscopy and transmission electron microscopy, the secondary phaseMgNi2.5B2 is found for thefirst time in MgB2 samples, as a concentration of clusters. According to the magnetization measurements, the low doping levelof Ni (x<0.04) was observed to have small influence on the grain connectivity, and thus a highJc was maintained at low field. Because of the large grain size ofMgNi2.5B2 concentratedwithin the MgB2 grains, the Jc values at high field all show a significant decrease in the Ni-doped samples. On the basis ofthe analysis of the superconducting properties, the process of formation of theMgNi2.5B2 clusters is discussed in terms of a mechanism of precipitation from grain boundaries toMgB2 intra-grains as the sintering temperature increases.

Phase transition of [Cn-mim][PF6] under high pressure up to 1.0 GPa

Behavior of the phase transition of an ionic liquid, [Cn-mim][PF(6)], has been investigated under pressures up to 1.0 GPa by using a high-pressure differential thermal analysis (DTA) apparatus. The T versus P phase diagrams of [BMIM][PF(6)] and [EMIM][PF(6)] are constructed. The DTA curve of [BMIM][PF(6)] shows one endothermal valley in heating course at each given pressure, which indicates that a simple phase transition from solid to liquid has taken place under high pressure and that the melting point is an increase function of pressure. However, the DTA curve of [EMIM] x [PF(6)] shows two endothermal valleys in the heating course within the tested pressure range, implying that there may exist another phase. After treatment of [EMIM][PF(6)] at different temperatures under high pressure, the structures of the recovered samples are also investigated by wide-angle x-ray scattering. By considering the results above, it indicates that another crystalline phase exists between the solid and liquid of [EMIM][PF(6)].

Melting point of polymers under high pressure: Part II. Influence of gases

The influence of highly compressed gases on the melting of polyethylene was investigated for nitrogen, helium and ethylene. The impact of the particle size of the polymer and the heating rate on the melting point were also analysed. The melting points were determined with a high pressure differential thermal analysis (HPDTA) apparatus. These measurements were compared with independent measurements, done by high pressure differential scanning calorimetry (HPDSC), without gas. From this experimental data it was possible to calculate the concentration of the gas in the molten polymer phase based on equilibrium thermodynamics. For high density polyethylene (HDPE), a concentration of nitrogen at the polymer melting point of 10.4–35.7 mL(SATP) g(polymer) −1, in the pressure interval of 65–315 MPa, was calculated.