Isothermal DTA Research Articles

Phase diagram of the eutectic type LiCl-PrCl3-KCl system with wedging liquidus of binary compound

Based on the published experimental data (phase diagrams of three binary systems, four isothermal sections and DTA curves of 33 alloys), a spatial (three-dimensional – 3D) computer model of the LiCl-PrCl3-KCl phase diagram has been constructed. It is shown that, in the general case, the diagram is formed by 66 surfaces and 27 phase regions; however, due to the negligible solubility of the initial chlorides and the stoichiometry of the two binary compounds in reality, it consists of 31 surfaces and 14 phase regions. The evaluation of the quality of the obtained 3D model is a comparison of model and initial isothermal sections and calculation of response functions for 33 alloys with temperature values at the boundaries of the primary crystallization regions shown on DTA traces. The geometric structure of the LiCl-PrCl3-KCl phase diagram is also considered as an illustration of the features of ternary systems of the eutectic type, depending on the nature of the formed in them binary compounds.

Studies on phase evolution, microstructure and crystallization kinetics in Nd2O3 doped Li2O-Al2O3-SiO2 glass system

Nd2O3 doped Lithium Alumino Silicate (LAS) glass of composition (wt.%) 57SiO2–19Al2O3–3.5Li2O-7P2O5–11.5X–2Nd2O3 (X = B2O3, MgO, ZnO, TiO2, ZrO2) was synthesized and transformed into glass ceramic. X Ray Diffraction (XRD) showed formation of TiZrO4 nano crystalline phase at 948 K and major phase β-spodumene (β-LiAlSi2O6) along with some minor phases at temperatures >1073 K. In the intermediate temperature range, γ-spodumene /LixAlxSi3-xO6 (0<x<1)/Virgilite was identified as a major phase which was shown to get converted into stable β-spodumene phase at elevated temperature. Micrographs of heat treated samples revealed nanocrystals of size (<25 nm) of Titanium Zirconate phase at 948 K and shell type microstructure of β-spodumene phase at temperature >1073 K. Decrease in thermal expansion coefficient (α) from 5.5×10−6/K to 2.98×10−6/K (303–573 K) was observed for sample crystallized at around 1073 K. Non isothermal DTA data showed two exothermic peaks, indicating crystallization of two different phases in temperature range of 993 to 1223 K. Activation energy for crystallization (Ea) of first peak was found to be 168±20 kJmol−1 and 187±20 kJmol−1 using Kissinger and Marotta methods, respectively. Model free kinetics was used to find more accurate kinetic parameters such as Ea and predict isothermal reaction progress.

High-temperature (to 1670°C) air oxidation of AlN–Si3N4 and AlN–Si3N4–(Ni–Cr–Al) ceramic materials

The kinetics and mechanism of high-temperature air oxidation of powders and compact materials with different compositions in the AlN–Si3N4 and AlN–Si3N4–(Ni–Cr–Al) systems are studied using nonisothermal (up to 1500°C) and isothermal (1350 and 1670°C) thermogravimetry, DTA, XRD, petrography, and EMPA. During heating, Al4O4–x N x and Si2N2O oxynitrides, α-Al2O3 and α-SiO2 (crystobalite) oxides, and mullite-based Al2O3 ∙ SiO2 solid solution of the boundary composition form during the first oxidation stage, and 3Al2O3 ∙ 2SiO2 mullite forms at higher temperatures (>1350°C) in the upper scale layer and aluminum-nickel chromite spinel in the intermediate (barrier) scale layer. The AlN–Si3N4 and AlN–Si3N4–(Ni–Cr–Al) ceramics may be regarded as hightemperature composites (HTCs) owing to their high corrosion resistance.

Gaseous Products of Dinitromethane Decomposition Determined by DTA/FTIR

Gaseous products of the thermal decomposition of dinitromethane and potassium dinitromethanide were investigated by simultaneous DTA/FTIR analyses. Both isothermal and non-isothermal DTA regimes were applied. Nitrous oxide and carbon dioxide were detected by FTIR.

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.

定温ＤＴＡによる結晶成長速度の評価

Isothermal DTA was performed at various temperatures for nucleated Li2O·2SiO2 glasses and the time neccesary to obtain crystallization peak, t0, was measured. The number density of nuclei in the glass was evaluated from crystallization peak temperature, TC, obtained by DTA with the heating rate of 10°C/min. The crystal growth rate of Li2O·2SiO2 glass was calculated from t0 and TC. By this method, crystal growth rate was measured more conveniently than by the traditional method based on the observation by micsroscope. The accuracy of crystal growth rate obtained was discussed, and it was found that good accuracy is attainable by using the glass samples with proper number density of nuclei.

Stabilisation of LDPE cross-linked in the presence of peroxides I. Kinetic study of the oxidation

The oxidation resistance of LDPE, cross-linked in the presence of dicumyl peroxide and stabilised with a commercial antioxidant, bis[(3- t-butyl-2-hydroxy-5-metyl)phenyl] sulphide (Irganox 1081) was investigated. Oxidation induction time, t i, as found by isothermal DTA, was used as the criterion of evaluation of LDPE resistance to oxidation. Without the peroxide, Irganox 1081, at concentrations in the range 0.1–0.5% w/w, was found to inhibit LDPE oxidation. Its depletion rate at temperatures in the range 195–225°C, as measured by oxidation induction time, t i, may be described as a zero-order reaction with activation energy E=141.4 kJ/mol. Simultaneous addition of 2.0% w/w dicumyl peroxide and 0.1–0.4% w/w Irganox 1081 to LDPE by rolling at 130°C was observed to reduce oxidation induction time to t i=0. After cross-linking at 180°C and 5.0 MPa for 20 min, the same compositions recovered their resistance to oxidation over the whole concentration range of Irganox 1081.

Estimation of Activation Energies for Thermooxidative Degradations of LDPE and NBR from Non-Isothermal and Isothermal DTA Data

Results obtained on the thermooxidative degradations of LDPE (low-density polyethylene) and NBR (nitrile-butadiene rubber) are presented. The activation energies for the thermooxidations leading to solid products were estimated. For LDPE, the activation energies obtained from non-isothermal data are in satisfactory agreement with those obtained from isothermal data. For NBR, the isothermal activation energy is ≉16% higher than the non-isothermal one. This difference is due to the morphological changes undergone by NBR during its heating at the rather high temperatures at which isothermal measurements were performed.

Hydration of Sr- and Ba-bearing sulphoaluminates in the presence of sulphates

The hydration process of Sr- and Ba-bearing sulphoaluminates in the presence of sulphates was investigated by isothermal calorimetry, DTA, XRD and SEM, and compared with that of 3CaO· 3Al2O3 · CaSO4. The strengths of C3A3SrSO4 with sulphates are higher, but the compressive strength of C3A3BaSO4 with sulphate is lower than that of 3CaO·3Al2O3 · CaSO4. The hydration of Sr-bearing sulphoaluminate is accelerated; moreover, the hydration of Ba-bearing sulphoaluminate is delayed in the presence of sulphates. The final hydrates of Sr- and Ba-bearing sulphoaluminates in the presence of sulphates were also defined.

Speciality Polyblend Systems of Crosslinkable Polyethylene and Poly(ethylene-vinyl acetate)

Abstract Malt mixed blends of crosslinkable polyethylene (XLPE) with poly(ethylene-vinyl acetate) are studied over the entire composition range. The effect of increasing amount of EVA in the blend have been studied with respect to cure behaviour, physical properties and thermal behaviour together with failure mode. Both cure rate and scorch time increase as XLPE/EVA ratio decreases. Probable radical cross-linking mechanism is suggested. Thermal stability is governed by EVA content in the blend as is observed from isothermal ageing, DTA and TGA studies. SEM studies supports the change of failure mode from brittle to ductile as EVA content in the blend increases.

Ageing behaviour of hot‐water pipes of polybutene‐1

AbstractIsothermal Differential Thermal Analysis was used to test the thermooxidative stability of pipes of polybutene during internal pressure tests at 110°C. At low hoop stresses and long testing times pipe failure was exclusively caused by thermooxidative degradation of the polymer.The stabilizer distribution in the initial state and its alteration during the pressure tests could easily be measured by isothermal DTA. Leaching of antioxidants from pipe walls could be detected. The decrease of residual thermooxidative stability was degressive.Degradation of pipe material started from the exterior pipe wall. Molecular weight of polybutene decreased rapidly after stabilizer exhaustion which could be observed by isothermal DTA.

Oxidation stability of crosslinked polyethylene. Isothermal DTA method

Isothermal differential thermal analysis has been used to study the thermooxidative stability of two grades of crosslinked polyethylene in the temperature range from 120°C to 230°C. Induction times of thermooxidative degradation were measured from 2 minutes up to 3590 hours. Oxidation Induction time and mechanical failure in oven ageing experiments coincided over the measured temperature range. The degree of crosslinking was not strongly affected by the oxidative reaction. The Arrhenius-plots of DTA results showed curvature at 150°C, so straight line extrapolations from short-term experiments at elevated temperatures to low temperatures and long times are not possible. Thermoanalytically measured residual thermooxidative stability decreased linearly with ageing time and showed great scattering of the results.

Studies of the autoxidation of polybutylene and crosslinked polyethylene by isothermal long-term DTA

The oxidation induction times of two grades of polybutylene and crosslinked polyethylene were investigated by isothermal DTA in the temperature range from 200°C to 130°C. The distribution of stabilizer within the wall thickness of hot water pipes and its alteration during pressure tests was scanned. Finally, the validity of the theory of linear deterioration was checked.

Measurement of oxidation stability of polyolefins by thermal analysis

Isothermal differential thermal analysis has been used to study the thermal stability of polybutene and crosslinked polyethylene in the temperature range from 120°C to 240°C. Oxidation induction times were measured from 2 min up to 7250 h. The Arrhenius-plots of DTA results showed curvature at 150°C, so straight line extrapolations from short-term experiments at elevated temperatures to low temperatures and long times are not possible. Oxidation induction time and mechanical failure in oven ageing experiments coincided over the measured temperature range. Decrease in the molecular weight of polybutene accelerated after the end of the induction period. Thermoanalytically measurable residual thermal stability decreased linearly with ageing time and is a more sensitive indicator of the beginning of thermal degradation than measurement of tensile properties. Finally, the extraction of stabilizer by hot water was measured by isothermal DTA.

The crystallization of small particles and droplets

A general expression is derived for the volume fraction of material crystallized as a function of time for the situation where boundary effects may be important, and it is applied to a sample consisting of a monodisperse array of small particles. It is assumed that crystallization occurs via homogeneous nucleation followed by crystal growth. The crystallization occurs via controlled by a single dimensionless parameter, β. β 1/4 is a dimensionless particle radius which tends to be small when the growth rate is large or when the nucleation rate is small. When β is large, the general expression for the volume fraction transformed reduces to the standard expression valid for bulk samples. When β is small, it reduces to the formula used to compute the volume fraction crystallized in droplet undercooling experiments. Hence, the present results are pertinent for the interpretation of some droplet undercooling experiments as well as isothermal DSC and DTA experiments.

Quantitative differential thermal analysis of the reduction of uranyl fluoride

The enthalpy of the reduction of UO2F2 with hydrogen was obtained from quantitative DTA measurements with a linear heating rate and under isothermal conditions, and the thermodynamic data on UO2F, formed as a stable intermediate in the reduction of UO2F2 to UO2, are also presented. The advantages of isothermal DTA in the reduction of U3O8 to UO2 could be demonstrated.

TG and DTA study of oxygen depletion and reoxidation of bismuth molybdates (2∶1;2∶3)

Oxygen depletion and reoxidation of bismuth molybdates (2∶1; 2∶3) have been studied by means of isothermal thermogravimetry and DTA measurements. From the isothermal curves, Arrhenius energies were obtained between 411 and 683 K. The activation energies for oxygen depletion from Bi2O3·MoO3 were lower than those for Bi2O3·3MoO3. Two kinetically different types of oxygen release were identified for both molybdates. Arrhenius plots were also obtained from reoxidation experiments: Bi2O3·MoO3 was more easily reoxidable than Bi2O3·3MoO3. The substantial closeness of the respective activation energies suggests that depletion and reoxidation follow the same mechanistic steps.

Thermal characterisation of the non-stoichiometry and catalytic activity of Ba xLn 1− xCoO 3 (Ln = La, Nd, Sm and Dy) compounds

The compounds Ba x Ln 1− x CoO 3 (Ln = La, Nd, Sm and Dy) were prepared by ceramic technique. They were characterised for oxygen non-stoichiometry using isothermal DTA under varying oxygen partial pressure and TG in air. Isothermal DTA was also employed to study the catalytic activity of the compounds towards CO oxidation. For a given compound, the oxygen deficiency increases with increasing temperature and decreasing oxygen partial pressure. For a given Ba x Ln 1− x CoO 3 series, in general barium-rich compounds were more oxygen deficient. Isothermal DTA study of CO oxidation over Ba x La 1− x CoO 3 compounds at 600 K suggested that the carbon monoxide takes up lattice-labile oxygen from the sample and is oxidised to CO 2, the percent CO conversion being higher for barium-rich samples.

Evaluation of the efficiency of antioxidants by isothermal DTA

Evaluation of the efficiency of antioxidants by isothermal DTA

Safety Studies on Li / SO 2 Cells: II . Kinetics of Lithium‐Organic Solvent Exothermic Reactions

An isothermal DTA technique was developed for studying the kinetics of the heterogeneous exothermic reactions involving lithium metal and organic solvents used in the batteries. The results showed that while film forming agents such as and PC retard the exothermic reaction (the crucial reaction for cell safety), the organic solvents such as MF, DME, DG, and THF enhance the exothermic reaction most probably due to an enhanced solubilizing effect on the Li film. The above solvents by themselves were found to be quite stable with Li.