DTA Heating Research Articles

3D model of a stable triangle LiF–NaBr–KBr four-component reciprocal system Li+, Na+, K+ || F-, Вr-

A 3D model of the phase equilibrium states of the quasi-three-component system LiF–NaBr–KBr, which is a stable triangle of the four-component reciprocal system Li+, Na+, K+ || F-, Br-, has been constructed. Based on the 3D-model, polythermal, isothermal sections and the polytherm of phase crystallization were constructed for the first time. Two polythermal sections contain wide areas of boundary solid solutions based on sodium and potassium bromide. In an isothermal section at 650 оC, the fields of the liquid phase and the coexisting two and three phases are delimited. The crystallization polytherm is represented by three fields. In the crystallization field of lithium fluoride, the area of separation of two liquids is limited. The direction of the ion exchange reaction 2LiBr + NaF + KF = 2LiF + NaBr + KBr was confirmed by thermodynamic calculations at temperatures of 400, 600, 800, 1000K. The exothermic nature of the exchange reaction is confirmed by taking a DTA heating curve for a mixture of powders from 50% LiBr + 25% NaF + 25% KF, and the phase composition of the reaction products LiF + NaBr(OTR) + KBr(OTR) is confirmed by X-ray phase analysis data, where OTR is limited solid solution.

Study of phase equilibria in a two-component system diphenyloxide <i>- n -</i> nonadecane

Using the Schroeder, UNIFAC and UNIFAC Dortmund methods, the fusibility diagram of the diphenyloxide – n –nonadecane system was calculated and it was shown that it belongs to the eutectic type. Individual substances and their mixtures were studied experimentally using a differential scanning microcalorimeter. On the DTA heating curve of the eutectic alloy, two endo-effects are noted, corresponding to the polymorphic transition of n–nonadecane and the melting of the eutectic. A comparison of the eutectic coordinates calculated by these methods with experimental data is presented. For a eutectic alloy, the specific enthalpy of fusion, molar values of entropy and enthalpy of fusion, volumetric specific enthalpy of fusion and density for standard conditions are calculated. The eutectic mixture can be recommended for use as a coolant, as well as the working fluid of a heat accumulator.

Study of phase equilibria in the two-component organic system biphenyl – n-docosane

The fusibility diagram of the diphenyl – n-docosane system was calculated by Schroeder, UNIFAC and UNIFAC Dortmund methods, and it was shown that it belongs to the eutectic type. Individual substances and their mixtures were studied experimentally using a differential scanning microcalorimeter. The endo-effect corresponding to the melting of the eutectic was noted on the DTA heating curve of the eutectic alloy. A comparison of the eutectic coordinates calculated by these methods with experimental data is presented. Specific fusion enthalpy, molar values of entropy and enthalpy of fusion, volumetric specific fusion enthalpy and density for standard conditions were calculated for an eutectic alloy. The eutectic mixture can be used as a heat carrier, as well as a working fluid of a heat accumulator.

DTA study and thermodynamic prediction of the solidification interval of boron 500HB abrasion-resistant steel

Special wear-resistant steels are essential in applications with extreme abrasion conditions. Main applications of low-alloyed, weldable abrasion-resistant steels are found in mining, agriculture, and elsewhere. They are normally produced via continuous casting process and then hot rolled into heavy plates of desired thickness and width. This paper focuses on the strand casting part where the solidification interval of boron 500HB steel is studied through DTA heating curves and compared with thermodynamic predictions using Thermo-Calc (TCFE7 and TCFE9 database) and JMatPro with internal database General steel. Liquidus temperatures measured from the second heating curve are in good agreement with the thermodynamic approach using both commercial software. Additionally, the invariant peritectic temperature was experimentally determined and a reasonable agreement is achieved with predictions. All databases revealed a similar solidus temperature if the calculation was performed without boron included. By including 23 ppm of boron into the calculation, only one commercial software predicted the solidus temperature in good agreement with the measured value determined by DTA, the other result differed significantly. This study shows that important variation of the predicted metallurgical length in the strand slab caster exists if the solidus position is estimated using thermodynamic prediction. As the studied samples were taken directly from an industrial plate, a qualitative evaluation of micro-segregation through the cross-section of the thickness was also done and taken into account with thermal analysis.

Chemical Interactions in Na+,Sr2+||Cl–,$${\text{EO}}_{4}^{{2 - }}$$ (E = Mo,W) and Na+,Sr2+||Cl–,$${\text{MoO}}_{4}^{{2 - }}$$,$${\text{WO}}_{4}^{{2 - }}$$ Reciprocal Systems: Description and Study

Chemical interactions of salts in the four-component reciprocal system comprised of chlorides, molybdates, and tungstates of sodium and strontium are studied by the ion-balance method. DTA heating curves feature exotherms due to the interaction of Na2EO4 + SrCl2 (E = Mo,W) and Na2MoO4 + Na2WO4 + SrCl2 homogenized powdery batches. Cooling curves feature exotherms indicating the formation of exchange reaction products upon crystallization of batches from NaCl + SrEO4 melts in the Na+,Sr2+||Cl–, $${\text{EO}}_{4}^{{2 - }}$$ and NaCl + SrMoxW1 – xO4 ternary reciprocal systems and in the Na+,Sr2+||Cl–, $${\text{MoO}}_{4}^{{2 - }}$$ , $${\text{WO}}_{4}^{{2 - }}$$ four-component reciprocal system. Reaction products are identified by X-ray powder diffraction. The presence of double compounds Na3ClMoO4 and Na3ClWO4 in reaction products in the Na+,Sr2+||Cl–, $${\text{EO}}_{4}^{{2 - }}$$ systems and the presence of Na3ClMoxW1 – xO4 solid solutions (ss) in the Na+,Sr2+||Cl–, $${\text{MoO}}_{4}^{{2 - }}$$ , $${\text{WO}}_{4}^{{2 - }}$$ system is considered in terms of divergence phenomena.

Structure of orthorhombic martensite in the Ti92.5Nb5Mo2.5 alloy, its deformation and thermal stability

A ternary alloy Ti92.5Nb5Mo2.5 was obtained by arc melting on crystallization of water-cooled copper hearth followed by homogenization treatment, rolling, annealing and quenching in ice water. In this work, the formation of orthorhombic martensite α″ and its stability under deformation and in the course of thermal processing were investigated by a combination of X-ray diffraction, differential thermal analysis and optical microscopy. A set of the Wyckoff positions has been proposed based on the symmetry of the Cmcm space group, which allows the movement of atoms without breaking the space group symmetry. Experimental evidences indicate that a deformation-induced transformation of martensite to austenite (α″ → β) occurs after the above-mentioned heat treatment. It is also shown that during of DTA heating this martensite begins to transform into the β-phase at the temperature of 724 °C. On cooling this β-phase decomposes into α and β phases of nonequilibrium compositions.

Physical, thermal and structural properties of Calcium Borotellurite glass system

In this work the glass forming ability in Calcium Borotellurite (CBTx) glass system was studied. Six glass samples were prepared by melt-quenching technique and the obtained samples are transparent, lightly yellowish, with no visible crystallites. The structural studies were carried out by using XRD, FTIR, Raman Spectra, density measurements, and the thermal analysis by using DTA and specific heat. The results are discussed in terms of tellurium oxide content and their changes in structural and thermal properties of glass samples. The addition of TeO2 increased the density and thermal stability values and decreased glass transition temperature (Tg). Raman and FTIR spectroscopies indicated that the network structure of CBTx glasses is formed by BO3, BO4, TeO3, TeO3+1 and TeO4 units. CBTx system showed good glass formation ability and good thermal stability, which make CBTx glasses suitable for manufacturing process and a candidate for rare-earth doping for several optical applications.

The Minor Precipitation at the Final Stage of U720Li Solidification

The minor precipitations caused by B and Zr which are the normal constituents of U720Li alloy have been studied by analyzing the solidification process and the composition evolution. The present study aims to supply the elementary information about the existing form of B and Zr in the as-cast microstructure, which is helpful for the subsequent processing, such as homogenization treatment. The M 3B2 and Ni5Zr phases were observed in the U720Li alloy in as-cast state, which were usually accompanying with each other together with η-Ni3Ti phase at the edge of eutectic (γ + γ′). Combining the DTA analysis and heating and quenching tests, the solidification sequence was determined to be the following: γ matrix, eutectic (γ + γ′), η-Ni3Ti, M 3B2 and Ni5Zr. The in situ composition analysis by EDS and EPMA revealed that the precipitation and microstructure were governed by the composition evolution in the liquids. The solidification of γ matrix increased the Ti concentration in the residual liquids and resulted in the eutectic (γ + γ′) formation; the (γ + γ′) formation increased the Ti/Al radio in the liquids and the η-Ni3Ti was formed in front of the eutectic (γ + γ′); the η-Ni3Ti precipitation consumed up Al and Ti and increased the concentration of B, Mo and Cr, and M 3B2 boride is formed; the previous precipitation of the phases consumed up most of the elements other than Ni and Zr, and Ni5Zr is formed finally. The melting points are in the ranges of 1130–1140 °C for Ni5Zr phase, 1180–1190 °C for M 3B2 boride and 1190–1200 °C for η-Ni3Ti phase.

Study of anneal hardening in cold worked Cu–Au alloy

An experimental study was carried out on cold worked Cu-12.7 wt.%Au alloy and pure copper, in order to compare the properties change during thermo-mechanical treatment. Hardness, microhardness, and electrical conductivity were studied as a function of annealing temperature and annealing time with the purpose of investigating the intensity of anneal hardening effect in cold worked Cu-12.7 wt.%Au alloy. Isochronal (up to 350 °C) and isothermal (at 250 °C for 100 h) annealing of cold worked alloy caused a two-stage increase in all of the measured properties. The mechanism responsible for this increase was analyzed using DTA, XRD, and TEM studies. The four stages observed in DTA heating curve were discussed in connection with the occurring processes. The reduction in the lattice parameter of cold worked Cu-12.7 wt.%Au alloy during annealing at 260 °C caused by the solute clustering, was observed. TEM studies did not show any presence of precipitates, other than disk-shaped areas with a higher degree of ordering. The achievement of high mechanical properties and high electrical conductivity in cold worked Cu-12.7 wt.%Au alloy after low temperature annealing was ascribed to the comparative effects of short-range ordering and solute segregation to lattice defects.

XIV International conference on thermal analysis and calorimetry in Russia 2013 and hot topic discussion

The XIV International conference on thermal analysis and calorimetry held in St Petersburg, Russia 2013, which would restarted the regular periodicity of these meetings in Russia, is described including history of these conferences. The paper portrayed in details highlighting plenary lectures. Two addressed subjects dealing with yet unaccepted theory of thermal decomposition of solids and the overlooked impact of DTA heat inertia are discussed.

Single crystal growth of ninhydrin by unidirectional Sankaranarayanan–Ramasamy (SR) method by using a glass ampoule for nonlinear optical applications

An organic nonlinear optical single crystal of ninhydrin was grown by Sankaranarayanan–Ramasamy (SR) method by using specially designed glass ampoule. The good quality seed crystal has been prepared by conventional solution growth technique using double distilled water as the solvent. The lattice dimension of the grown specimen was identified from the powder X-ray diffraction analysis and found that it crystallized in a monoclinic system with non-centrosymmetric space group P21. The presence of functional groups was examined by Fourier transform infrared (FTIR) analysis and it was found that there was no incorporation of foreign elements during crystallization. The surface defects were assessed by optical microscope and the dielectric constant and dielectric loss were carried out by LCR meter. Laser damaged threshold, relative second harmonic generation (SHG) and phase matching were measured by using a high intensity Nd:YAG laser as a source having the wavelength of 1064 nm. Its thermal stability has been assessed by TG–DTA and specific heat measurements with respect to different temperatures. The optical studies show that the crystal has transmittance ability of light in the entire visible region.

Phase transition temperatures of Sn–Zn–Al system and their comparison with calculated phase diagrams

The Sn–Zn–Al system was studied in connection with the possible substitution of lead-based solders for temperatures up to 350 °C. Ternary alloys with up to 3 wt% of aluminium were prepared. The investigated alloys lie close to the monovariant line (eutectic valley) of the Sn–Zn–Al system. The temperatures of phase transitions of six binary Sn–Zn reference alloys and fourteen ternary Sn–Zn–Al alloys using DTA method were investigated in this paper. DTA experiments were performed at the heating/cooling rate of 4 °C min−1 using Setaram SETSYS 18TM experimental equipment. The temperatures of phase transitions in the ternary Sn–Zn–Al system were obtained, namely, the temperature of ternary eutectic reaction T E1 (197.7 ± 0.7 °C), temperature of ternary transition reaction T U1 (278.6 ± 0.7 °C), temperatures of liquidus and other transition temperatures for studied alloys. Temperatures obtained during DTA heating runs were used as authoritative. DTA curves obtained during cooling enabled realising better differentiation of the obtained overlapped heat effects (peaks) during heating. Theoretical isopleths of the Sn–Zn–Al phase diagram were calculated using the Thermocalc software and MP0602 thermodynamic database. Experimental data were compared with the calculated temperatures, and a good agreement was obtained.

Silica doped bismuth lead oxyfluoride glass ionic conductors

Doping of bismuth lead oxyfluorides by silica (30 at.%) makes it possible to stabilize a large vitreous domain. The presented study relates to the stability of the vitreous phase and the variation of conductivity versus temperature, as well as composition. DTA heating analyses evidenced the temperature of vitreous transition followed by the material recrystallization. The crystallized phase was identified by high temperature Guinier Lenné pattern. The best conductivity, about 3 × 10 − 3 Scm − 1 at 220 °C, was obtained for the fluorine richest material.

Preparation and Catalytic Activity of Co/CNTs Nanocomposites via Microwave Irradiation

AbstractCo nanoparticles supported on carbon nanotubes (CNTs) were prepared by microwave‐assisted heating of the hydrazine reduction in ethylene glycol (EG). The Co/CNT nanocomposites prepared by the microwave‐irradiation method (MIM‐Co/CNTs) were characterized by XRD, SEM, EDS, and BET. It was found that MIM‐Co/CNTs had compact coating, high cobalt loading, and large BET surface area. The obtained products for the thermal decomposition of ammonium perchlorate (AP) were investigated by DTA. The catalytic activity of MIM‐Co/CNTs was better than that of pure Co nanoparticles and Co/CNT nanocomposites by water‐bath method (WBM‐Co/CNTs). The addition of 5 wt.‐% MIM‐Co/CNTs decreased the high decomposition temperature of AP by 174.05 °C and increased the total DTA heat release by 0.799 kJ g−1.

Mineralogical characterization of silica sinters from the El Tatio geothermal field, Chile

Silica sinters, deposited from alkali chloride waters in the El Tatio geothermal field in northern Chile (22°20'S, 68°01'W), have been characterized by XRD, SEM, TG-DTA, and FTIR. The dominant silica phase is opal-A. Minor contents of opal-A/-CT and opal-CT are also present together with halite (NaCl), sylvite (KCl), and realgar (AsS). Accessory phases include teruggite [Ca4MgAs2B12O22(OH)12·12(H2O)], sassolite (H3BO3), and detrital quartz (SiO2). FWHM values reflect the immature nature of the studied opal-A. DTA heating experiments of opal-A show cristobalite crystallization at ~1000 °C, whereas DTA cooling experiments show the β → α-cristobalite transformation at ~200 °C. The total weight loss is related to changes in the sinter microtextures, mineral phases, and organic matter contents. FTIR spectra show the effects of silica maturation as consequence of the loss of trapped and absorbed water attached to silanols.

Structural transformations in amorphous selenium as studied by the differential thermal analysis and exoelectron emission technique

The parameters (temperature, activation energy) of the surface and volume glass transition (retrification process) in amorphous selenium produced by rapid quenching of the liquid phase have been determined using the EEE and DTA techniques. EEE is a surface effect connected with structural transformations in the surface layer whereas the DTA measurements give the information about the transformations occurring in the volume of the sample. It has been found that the surface retrification of selenium occurs with activation energy smaller than the volume retrification, both observed in the first heating run. The value of activation energy for the volume retrification measured in the second DTA heating run is higher compared with that measured in the first heating run. Irradiation with X-rays accelerates both the surface and volume retrification of amorphous selenium.

On the solubility of [formula omitted] in [formula omitted

Neodymium doped yttrium aluminum garnet powders (Nd:YAG or ( Y 1 − x Nd x ) 3 Al 5 O 12 , x = 0.15 , 0.25, or 0.30, respectively) were prepared by a sol–gel technique. By DTA measurements up to 2000 ° C eutectic and liquidus temperatures could be determined. Exothermal peaks in the second and subsequent DTA heating runs indicate that the crystallized DTA samples are not in equilibrium. The section Y 3 Al 5 O 12 –Nd 3 Al 5 O 12 of the concentration triangle Al 2 O 3–Nd 2 O 3–Y 2 O 3 is proposed on the basis of thermodynamic calculations that allows to explain the experimental results by the balance of metastable phase states in the previously crystallized DTA samples.

Investigation of the thermal degradation of the aged pyrotechnic titanium hydride/potassium perchlorate

Titanium hydride/potassium perchlorate (THPP) is a pressure producing pyrotechnic composition consisting of a mixture of titanium dihydride and potassium perchlorate with a small percentage of a Viton binder. The initial phase of the study focused upon chemical analysis of THPP downloaded from parts ranging up to 25 years in age. The DSC curves were too erratic for kinetic analysis; however, high resolution TG curves for the THPP samples revealed a significant difference in the temperature at which the aged materials began displaying mass loss. Isothermal DTA and variable heating rate TG kinetic analysis were employed to determine the activation energy of the THPP.

Crystallization behaviour of glasses produced from fly ash

Abstract The crystallization behaviour of fly ash based glass samples annealed at 600°C for 2 and 10 h was investigated by DTA, XRD and SEM. On the basis of DTA, nucleation experiments of two glass samples were carried out at 680 and 687°C for 5 h and crystallization experiments were performed at 924 and 892°C for 20 min. The Avrami constant for both glass samples was calculated as 4, which indicates bulk crystallization, predicted by the Ozawa equation. Using the modified Kissinger equation, activation energies of crystal growth were determined as 318 and 312 kJ/mol for samples annealed at 2 and 10 h, respectively. Single peak analysis technique proved that the activation energy is independent of DTA heating rate. SEM observations indicated that the produced glass–ceramic samples have fine grained microstructure. The crystallized phase was identified as diopside [Ca(Mg,Al)(Si,Al)2O6] by X-ray diffraction analysis. The results of Vickers microhardness tests showed that the hardness values of the produced glass–ceramic samples decreased with the increase in holding time at the annealing temperature.

Comportement Thermique du Polypropylene au Cours du Vieillissement

Several samples of polypropylene were studied by thermal analysis. The photo-oxidation and the aging of polypropylene films showed a mass loss more than 7% in heating from 20 to 220°C (5°C min-1), cooling to 20°C and reheating to 220°C. The authors observed also a decrease of the melting and crystallization temperatures. The non aged samples or these ones with preservatives are thermo-oxidised and presented an exothermic peak at about 200°C in DTA heating.