DTA Experiments Research Articles

A revision of the Ni-Zn phase diagram based on vapor-solid diffusion experiments

The technique of vapor-solid diffusion couples was systematically studied for its potential in phase diagram investigation using the well-established Ni-Zn system which is highly suitable for this purpose due to the high vapor pressure difference of the two constituents. More than 50 samples synthesized by direct vapor-solid reaction, varying the parameters temperature, time and overall system composition, were investigated by SEM/EDX focusing on diffusion profile line-scans. Supporting powder-XRD and DTA experiments were performed as well. Based on these experimental results, significant changes to the currently accepted Ni-Zn phase diagram, specifically concerning the β, β1, and γ phase fields, are proposed. Furthermore, a relatively simple experimental procedure to prepare vapor-solid diffusion experiments is introduced and its application in phase diagram investigation is discussed in detail.

Tailored Liquid Phases for Enhanced Sintering of Advanced PM - Steels

The application of “masteralloys” as alloying carriers in Powder Metallurgy (PM) steels enables the introduction of highly oxygen‑sensitive alloying elements for advanced PM‑steels, by using a tailored liquid phase. The characteristics of the liquid and its interaction with the iron base powder are determining factors for final microstructure and dimensional behaviour. In this study, theoretical calculations and experimental findings are presented for the masteralloy systems Fe_Mn_Si_C, Fe_Cr_Si_C and Fe_Mn_Cr_Si_C. Lowered melting temperatures and narrow melting temperature intervals could be achieved. The interaction between Fe base material and the masteralloys was studied by infiltration and DTA experiments. It was found that by adjusting the C and Si content in the masteralloy, liquids with widely varying properties could be obtained. This might be a key for tailoring microstructures, properties and dimensional stability of advanced PM‑steels.

Type I kerogen-rich oil shale from the Democratic Republic of the Congo: mineralogical description and pyrolysis kinetics

The Democratic Republic of the Congo holds important reserves of oil shale which is still under geological status. Herein, the characterization and pyrolysis kinetics of type I kerogen-rich oil shale of the western Central Kongo (CK) were investigated. X-ray diffraction, Fourier-transform infrared spectroscopy and thermal analysis (TG/DTA) showed that CK oil shale exhibits a siliceous mineral matrix with a consistent organic matter rich in aliphatic chains. The pyrolysis behavior of kerogen revealed the presence of a single mass loss between 300 and 550 °C, estimated at 12.5% and attributed to the oil production stage. Non-isothermal kinetics was performed by determining the activation energy using the iterative isoconversional model-free methods and exhibits a constant value with E = 211.5 ± 4.7 kJ mol−1. The most probable kinetic model describing the kerogen pyrolysis mechanism was obtained using the Coats–Redfern and Arrhenius plot methods. The results showed a unique kinetic triplet confirming the nature of kerogen, predominantly type I and reinforcing the previously reported geochemical characteristics of the CK oil shale. Besides, the calculation of thermodynamic parameters (ΔH*, ΔS* and ΔG*) corresponding to the pyrolysis of type I kerogen revealed that the process is non-spontaneous, in agreement with DTA experiments.

Syntheses and nanocrystallization of Na2O–M2O3–P2O5 alluaudite-like phosphate glasses (M = V, Fe, Mn)

In this decade, an interest in alluaudites as potential cathode materials for sodium batteries revived. However, only crystalline compounds have been studied so far. In this work, alluaudite-like glasses of nominal composition Na2M3(PO4)3 (where M3 = Fe3, VFe2, VFeMn) were successfully synthesized using standard melt-quenching technique. Temperatures of glass transition and crystallization were determined at various heating rates in DTA experiments and the activation energies of these processes were calculated using Kissinger’s model. XRD studies confirmed that heat-treatment of the glasses led to nanocrystalline materials with alluaudite structure. Glasses exhibited modest, predominant electronic conductivity. After their thermal nanocrystallization, the conductivity increased approximately 2–4 orders of magnitude and the activation energy decreased noticeably. The ionic counterpart of the conductivity became much more pronounced. These preliminary electrical results show that there is a room for further optimization, which may result in highly-conducting nanocrystalline alluaudite-like cathode materials for sodium-ion batteries.

Experimental Investigations of Phase Equilibria in Ternary Ag-Cu-Ga System

Experimental study of phase equilibria in the ternary Ag-Cu-Ga system was carried out by using DTA/DSC, isothermal equilibration and microscopic as well as x-ray analyses. DTA experiments were conducted for alloys, whose concentrations varied along two cross-sections determined by the ratio of mole fractions xAg/xCu = 1:1 and xAg/xGa = 1:1. Equilibration of samples was carried out at 200, 450 and 650 °C. The obtained information about phases in equilibrium was compared with the results of calculations of the phase diagram for conditions identical to our experiments. It was demonstrated that the results of calculations are compatible with the experimental data.

Physical properties and biocompatibility effects of doping SiO2 and TiO2 into phosphate-based glass for bone tissue engineering.

Phosphate glass is continuing to gain more attention as potential bone substitutes. The ternary (P2O5-CaO-Na2O) is investigated in terms of both physical properties and biocompatibility by doping different percentages of SiO2 and TiO2. Two groups were prepared; the first has different percentages of TiO2 and SiO2, whereas the second group compositions have 5 mol% TiO2 and 5 mol% SiO2 being added to compensate the network-forming oxide P2O5 and the network-modifying oxide CaO. Density, mass loss, pH, DTA, XRD, and cation release experiments were performed to study the physicochemical properties of the compositions, while MG63 and hMS cells were used within in vitro cell culture to study their biocompatibility. Results showed that an increase in TiO2 content correlated with an increase in glass density, decreased mass loss, increased trend of Tg and Tm values, and Na+ and Ca2+ release in group 1. There was no improvement in the MG63 viability or the ability of hMSCs to differentiate into osteoblasts where TiO2 decreased in favour of SiO2. Furthermore, in group 2, 50P2O5-25CaO was less dense than 45P2O5-30CaO, degraded dramatically less, had lower Tg and Tm values and released less Na+ and Ca(2+). The synergistic effect of doping 5 mol% TiO2 and 5 mol% SiO2 increased the MG63 viability in both compositions and was found 45P2O5-30CaO to have promising results in terms of the ability of hMSCs to differentiate into osteoblasts. To conclude, substituting TiO2 in place of SiO2 improved the physical properties and the biocompatibility of (P2O5-CaO-Na2O) glass system, whereas doping 5 mol% SiO2 and 5 mol% TiO2 together in place of P2O5 and CaO had a synergistic effect in controlling their degradation rate and improving their biological responses.

Rapid Redox Cycle Stability of Doped CaMnO3 Particles for High-Temperature Thermochemical Energy Storage

A-site doped Ca1-xSrxMnO3-δ and B-site doped CaCryMn1-yO3-δ have been studied for high specific thermochemical energy storage (TCES) in concentrating solar power and other high-temperature applications. With low levels of doping (5 and 10%) for both compositions, these perovskites have demonstrated significant reduction in high temperatures at O2 partial pressures P O2 ≈10-4 bar with as much as 450 kJ/kg of chemical energy can be stored (for Ca0.95Sr0.05MnO3-δ) at 900 ºC on top of sensible energy in a TCES system [1]. The viability of such high specific TCES in these perovskites depends on their rates of energy accommodation during heating cycles and their phase and morphological stability during rapid reduction and reoxidation for energy capture and release respectively. In this study, Ca1-xSrxMnO3-δ and CaCryMn1-yO3-δ were studied for reduction at temperatures up to 1000 ºC and tested in extended redox cycling to explore their stability for energy storage and release at such high-temperatures where the materials undergo expansion/compression and phase transitions during these cycles. The results as highlighted below suggest that these materials have significant promise for high-temperature large-scale TCES. Ca1-xSrxMnO3-δ (x = 0.05 and 0.10) and CaCryMn1-yO3-δ (y = 0.05 and 0.10) were synthesized as particles with solid-state-reactive sintering [1] and cycled as particles (diameter range of 250-425 μm) between air P O2 (≈ 0.17 bar) and P O2 ≈10-4 bar both in isothermal experiments up to 1000 ºC and in long-term cycling experiments between 500 and 900 ºC to simulate TCES system operation. Over these conditions, the doped CaMnO3-δ perovskites undergo significant reduction (δ > 0.2 at 1000 ºC) at phase transitions (orthorhombic to cubic to tetragonal perovskite phase), reduction, and associated lattice expansion as observed in hot-stage XRD for similar composition [1]. The isothermal redox cycling tests in conjunction with thermodynamics derived from TGA/DSC measurements as reported elsewhere [2,3] provided a basis for fitting thermodynamically consistent surface reaction rates [4,5] and bulk ionic transport properties to measured transient evolution in oxygen non-stoichiometry δ which went as high as 0.3 for Ca0.95Sr0.05MnO3-δ at 1000 ºC. These experiments are illustrated with ten-cycle averaged plots in Figure 1 with data for Ca0.9Sr0.1MnO3-δ compared to packed bed models [4] used to fit surface kinetic and bulk transport rate expressions. Figure 1 also shows the chemical energy incorporated into the perovskite with increasing δ during reduction based on thermodynamics derived from fitting equilibrium δ over a range of T and P O2. The packed bed results and model fits show fast rates of reoxidation relative to reduction. The rapid reoxidation i.e., oxygen incorporation rates are limited by the inlet flow supply for a substantial fraction of the experiments. The high-degree of reduction and the rapid rates of reoxidation and associated phase transitions raise questions about the stability of these materials in non-isothermal redox cycling for high-temperature TCES system applications. The selected perovskite materials were thus cycled for over 1000 times under non-isothermal conditions to simulate TCES system operation. The long-term cycling for all four doped CaMnO3-δ perovskites occurred with heating from a fully oxidized state at 500 ºC to a reduced state at 900 ºC in P O2 ≈10-4 bar followed by subsequent reoxidation and cooling in air back to 500 ºC. Figure 2 shows the transient evolution of δ during reduction and heating, averaged over successive 100 cycles for all four materials. An initial induction period of increasing maximum δ is followed by a stable period of redox cycling in spite of the rapid reoxidation. Only CaCr0.05Mn0.95O3-δ shows evidence of a significant loss in maximum δ, and this composition showed the slowest to undergo phase transitions in DTA experiments. Ex situ X-ray diffraction shown in Figure 3 of the particles before and after the long-term non-isothermal redox testing show that the particles maintain their dominant perovskite phase with evidence of small fractions of a secondary spinel phase. The stability of these cyclic tests particular for the Ca1-xSrxMnO3-δ reveal the promise of these materials as a media for effective TCES in a range of high-temperature energy storage applications. Reference [1] E.I. Leonidova, I.A. Leonidov, M.V. Patrakeev, V.L. Kozhevnikov, Journal of Solid State Electrochemistry, 15 (2011) 1071-1075. [2] L. Imponenti, K.J. Albrecht, R.J. Braun, G.S. Jackson, ECS Transactions, 72 (2016) 11-22. [3] L. Imponenti, K.J. Albrecht, J.W. Wands, M.D. Sanders, G.S. Jackson, Solar Energy, 151 (2017) 1-13. [4] K.J. Albrecht, "Multiscale Modeling and Experimental Interpretation of Perovskite Oxide Materials in Thermochemical Energy Storage and Conversion in Applications for Concentrating Solar Power", Ph.D. Dissertation, Colorado School of Mines, 2016. [5] R. Merkle, J. Maier, Angewandte Chemie-International Edition, 47 (2008) 3874-3894. Figure 1

Investigation of Nanocrystalline Co–P Coated by Pulsed Electrodeposition

In this study, nanocrystalline Co-(1–2)wt %P coatings were obtained by pulsed elec[trodeposition method on 1.6959 steel substrate. Coating operation carried out with current density of 150 mA/cm2 on the basis of the preliminary studies and tests, coating was accomplished in 5 different pulsed current. XRD studies and EDX analysis results showed that the coatings all had the same phosphorous-cobalt composition with Co-1.5% P. XRD studies demonstrated the amorphous structure in all coatings. Heat treatment on the coatings showed that annealing the coatings at 400°C for 1 hour causes development of crystal nanostructure coatings and increases the hardness. XRD studies on nanocrystal coatings prove that the least size of the Nano grains belongs to coatings with higher off times. Heat stability of the coatings was proved with the help of DTA experiments on coatings up to 650°C.

New metal(II) complexes with ceftazidime Schiff base

Complexes of Co(II), Ni(II) and Cu(II) with the Schiff base (LH) derived from ceftazidime and salicylaldehyde were synthesized. The proposed structures of the new metal complexes based on the results of elemental analyses, molar conductivity, IR, DRUV and 1H NMR spectra, effective magnetic moment and thermal analysis were discussed. The surface morphology of Schiff base and metal complexes was studied by SEM. The composition of the metal complexes was ML2, where L is the deprotonated Schiff base ligand and M = Co(II), Ni(II) and Cu(II). IR spectral data indicated the Schiff base ligand being bidentately coordinated to the metallic ions with N and O atoms from azomethine and phenolic groups. All the complexes have square-planar geometry and are nonelectrolytes. The thermal analysis recorded that TG, DTG, DTA and DSC experiments confirmed the assigned composition and gave information about the thermal stability of complexes in dynamic air atmosphere. Theoretical investigation of the molecular structure of Schiff base ligand and its complexes was studied using programs dedicated to chemical modeling and quantomolecular calculation of chemical properties. The newly synthesized complexes were tested for in vitro antibacterial activity against selected Gram-negative and Gram-positive bacterial strains, and they exhibited an antibacterial activity superior to that of the Schiff base ligand.

Lessons learned from fires of the wood caused by the spontaneous combustion of coal dust in underground mines

Undesired fires from self-ignition of energy would bring serious economic losses and cause emission of carbon dioxide and toxic gases. Recently, a wood burning accident caused by self-heating of coal in underground mines was investigated. The combination of calorific value, TG, DTG, DTA and SEM experiments provided sufficient information to understand the spontaneous combustion or pyrolysis behavior of wood in coal dust. Numerical simulation and Frank-Kamenetskii theoretical method were employed to study the distribution of coal dust for the purpose of verifying the source of the heat from coal dust. Eventually, wood burning happened when the heat produced by the coal dust spontaneous combustion around wood was not readily dissipated. A large amount of heat and flammable gases were generated, while the charring of wood happened slowly and the pyrolysis reaction rate was high enough. Spontaneous ignition occurred when the smoldering developed into flame combustion. In order to prevent such accidents, coal dust near the belt conveyor in underground mines was needed to be regularly checked and cleaned up. And underground wood or other related materials were required to be fire-retardant-treated in order to eliminate fire hazards.

Determination of pyrolysis properties of sirnak (Avgamasya) asphaltite by thermal analysis methods

ABSTRACTIn this study, pyrolysis properties of Sırnak asphaltite have been determined by thermal analysis methods. According to proximate and elemental analysis results, air-dried sample contains 0.56% moisture, 46.51% ash, 34.02% volatile matter, 18.91% fixed carbon, 42.1% C, 3.57% H, 0.50% N, 5.55% S, and 48.28% O by weight. For the determination of pyrolysis properties of the sample, DTA and TGA of thermal analysis methods have been used. DTA and TGA experiments have been carried out by using approximately 10 mg sample, under 50 ml/min nitrogen gas flow rate, from ambient to 900°C temperature range. To investigate the effects of particle size and heating rate on pyrolysis properties, TGA experiments have been carried out by using three different particle sizes and five different heating rates. By examining the TG/DTG thermograms, three different temperature regions have been found that depend on moisture loss, volatile release, and mineral matter decomposition. Also, by using TG/DTG data of the samples, apparent activation energies and Arrhenius constants were calculated by Arrhenius and Coats-Redfern kinetic models, and the results were compared with each other.

Thermodynamic Study and Re-optimization of the Au-Ga Binary System

Activities of gallium in the liquid Au-Ga alloys were determined using galvanic cells with the solid oxide electrolyte. The cells of the type:AuxGa(1-x)//ZrO2+Y2O3//Fe,FeO\\documentclass[12pt]{minimal}\t\t\t\t\\usepackage{amsmath}\t\t\t\t\\usepackage{wasysym}\t\t\t\t\\usepackage{amsfonts}\t\t\t\t\\usepackage{amssymb}\t\t\t\t\\usepackage{amsbsy}\t\t\t\t\\usepackage{mathrsfs}\t\t\t\t\\usepackage{upgreek}\t\t\t\t\\setlength{\\oddsidemargin}{-69pt}\t\t\t\t\\begin{document}$${\\text{Au}}_{x} {\\text{Ga}}_{(1 - x)} //{\\text{ ZrO}}_{2} + {\\text{Y}}_{2} {\\text{O}}_{3} //{\\text{ Fe}},\\,{\\text{FeO}}$$\\end{document}were used in the temperature range from 1050 to 1273 K, and for four alloy compositions xGa = 0.2, 0.4, 0.6 and 0.8. From the measured e.m.f.’s the activity of gallium was derived, which taken together with the recently measured heat of mixing provided precise description of the thermodynamic properties of the liquid phase. This study was supplemented with DTA experiments which were performed for three alloy compositions, namely 0.15, 0.25 and 0.40 gallium mole fraction. The results of these experiments verified with temperature of respective invariant reactions. Finally, present results, taken together with the information existing in the literature, were used for the calculation of the optimized Au-Ga phase diagram. ThermoCalc software was applied to complete these calculations.

The Sn-rich corner of the system Ni-Pd-Sn: A phase diagram study

The Sn-rich corner (50–100 at.% Sn) of the ternary system Ni-Pd-Sn was studied for two partial isothermal sections at 250 and 500 °C by a combination of powder XRD, optical microscopy and SEM/EDX. The ternary solubility ranges at both temperatures of investigation are found between 3 and 12 at.% Ni for the compounds PdSn4, PdSn3, PdSn2 and PdSn, while the binary phase Ni3Sn4 was found to dissolve up to 33.5 at. Pd. The monoclinic lattice parameters for this phase were studied in detail as function of composition in the entire composition range between Ni3Sn4 and Ni0.7Pd2.3Sn4. DTA experiments were used to explore the ternary phase reactions in the Sn-rich corner, and a total number of six new invariant reactions were identified. A ternary reaction scheme (Scheil diagram) and a liquidus projection are given.

Dependence of a glass transition temperature on a heating rate in DTA experiments for glasses containing transition metal oxides

It has been known for >60years that thermal events taking place during DTA measurements (e.g. glass transition or crystallization) depend on heating rate. In this paper, we collected numerous data of DTA measurements of various glasses containing transition metal oxides (V2O5, FeO, Ti2O3) carried out at different heating rates (1 to 25°C/min). We showed that glass transition temperature vs. heating rate can be well described by both Kissinger's and Lasocka's formulas. Additionally, we discuss an accuracy of extrapolation based on data taken at high heating rates to low heating rates. Our result show that glass transition temperatures at low heating rates can be satisfactorily extrapolated from higher ones, with a relative error <3.5% in every case (and mostly <1%), due to linear change with heating rate both in Kissinger's and Lasocka's plots.

Equilibrium conditions and the region of metastable states of Freon-12 gas hydrate

The results from DTA experiments to determine the thermodynamic parameters of equilibrium of Freon-12 gas hydrate with water (super cooled water), gas, and ice are analyzed. Empirical relations are obtained for determining the positions of the boundaries in the region of metastable states of Freon-12 gas hydrate in the P–T phase diagram. The enthalpies of dissociation of gas hydrate to water and ice are calculated. The size of pores in Freon-12 hydrate formed from granules of ground ice is estimated from the magnitude of the shift in the quadrupole point at temperatures below 273 K.

Charge-transfer Complexes Formed between the Sweeteners Saccharin Drug and Acido Acceptors: Structural, Thermal and Morphological Features

A B S T R A C T Saccharin (sacH) is a sugar substitute sweetening agent used extensively in dietary products. It is about 300 times sweeter than sucrose. This study highlighted the structural chemistry of Charge Transfer (CT) complexes formed from the interactions of two acido acceptors (CLA and PA) with sacH. The IR and 1 H NMR revealed evidence of significant intermolecular interactions between N-H group in the sacH and O-H group in the acido acceptors based on their characteristic shifts. The TG and DTA experiments were carried out to investigate the thermal properties of the obtained complexes. Their morphological features were also investigated using Optical Light Microscope (OLM). The OLM micrograph patterns indicate the formation of high quality colored crystals. This study provided the essential basics for understanding the complexation chemistry of saccharin.

Water, the other network modifier in borate glasses

In the present study we have investigated whether the effect of water on properties of borate glasses resembles that of alkali oxide. Soda–lime–borate glasses with nominal compositions of x Na2O, 10 CaO, (90-x) B2O3 (x=5, 15 and 25mol%) were doped with up to 8wt.% H2O by processing glass powder+distilled water in platinum capsules in an internally heated gas pressure vessel at 1523K and 500MPa. The water content of hydrous glasses was determined by Karl-Fischer titration and near-infrared spectroscopy. The glass transition temperature Tg. was derived from DTA and micropenetration experiments for which the effect of water loss at the surface of the hydrous glasses was studied. Heating glass samples at 10Kmin−1 in the DTA resulted in Tg values which are close to T12 isokom temperatures confirming the equivalence of enthalpy relaxation and viscous relaxation for borate glasses. For all three glass series it is shown that Tg strongly decreases whereas the liquid fragility strongly increases upon the addition of water. These findings reveal that H2O primarily causes breaking of B–O–B bonds rather than supporting 4-fold coordinated boron as it is well-known for alkali oxides in this concentration range.

ChemInform Abstract: Heat Transfer and Phase Transition in DTA Experiments

AbstractReview: 85 refs.

Thermodynamic assessment of the palladium–selenium (Pd–Se) system

Palladium and selenium are fission products produced in the nuclear fuel under irradiation. To better understand the high temperature thermochemistry of these elements, the Pd–Se phase diagram was assessed using the Calphad method. The Pd–Se binary description was optimized using thermodynamic and phase diagram data from the literature and some DTA experiments performed in this work. The calculated phase diagram and thermodynamic properties are consistent with the experimental results in the whole Pd–Se composition range.

Phase Relations in the A356 Alloy: Experimental Study and Thermodynamic Calculations

A thermodynamic database of the Al‐rich side of the Al–Fe–Mg–Si system was derived and it was used to calculate phase transitions and solidification behavior of a commercial A356 alloy. The predicted phase transitions were examined by DTA experiments and micrograph investigations using SEM/EDX/EBSD. The experimental results are in a good agreement with the calculated Scheil‐solidification behavior.