DTA measurements on polymers under high pressure

The construction of a high-pressure (up to 800 MPa), low-temperature (173–600 K) differential thermal analysis (DTA) apparatus is described. Some results on the phase transitions in polyethylene and poly(diethylsiloxane) under high pressure are presented.

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Zusammenfassung Mittels DSC wurde im Bereich 323 bis 1273 K die spezifische Wärme von Bi₄Ge₃O₁₂- und Bi₄Ti₃O₁₂-Einkristallen untersucht. Unter Zuhilfenahme des normalen Wärmekapazitätskurvenverlaufes für Bi₄Ge₃O₁₂ wurde derjenige Temperaturbereich bestimmt, in dem in Bi₄Ti₃O₁₂ die anomale Umwandlung von einer polarisierten in eine unpolarisierte Phase verläuft. Wärmeeffekt und Entropieänderung für diese Umwandlung wurden ermittelt.

     

Investigation of refractory oxides by high-temperature DTA

Aim of this work in connection with the development of materials in the periclase-forsterite-zirconia system was the determination of melting temperature and melting enthalpy of refractory compounds. The possibility of determination of the melting and solidification of minor phases in refractory materials should be proved.The forsterite melting enthalpy was determined equal 783 J/g with a standard deviation of 22 J/g.The addition of zircon to periclase leads to the formation of an eutectic MgO-ZrO₂-Mg₂SiO₄ melt. 1750°–1755°C was determined as its solidification temperature. Cooling leads to the crystallization of forsterite and cubic-ZrO₂ from the melt.

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Zusammenfassung Ziel dieser Arbeit ist die Bestimmung von Schmelztemperatur und Schmelzenthalpie der feuerfesten Verbindungen in Verbindung mit der Entwicklung von Substanzen im System Periklas-Forsterit-Zirkonerde. Es sollte die Möglichkeit zur Bestimmung von Schmelzen und Erstarren von Minor-Phasen in feuerfesten Substanzen geprüft werden.Die Schmelzenthalpie von Forsterit wurde mit einem Wert von 783 J/g und einer Standarddeviation von 22 J/g ermittelt.Der Zusatz von Zirkonerde zu Periklas führt zur Bildung einer eutektischen MgO-ZrO₂-Mg₂SiO₄-Schmelze, deren Erstarrungstemperatur mit 1750°–1755°C ermittelt wurde. Beim Abkühlen kristallisieren aus der Schmelze Forsterit und kubisches ZrO₂ aus.

     

DTA/TG coupling

With the discovery of high temperature superconductivity an extraordinary field for investigations on new materials containing up to (more than) 8 or 9 components has been open. But, in addition to problems specifically related to superconductivity, we are faced with a prelimary difficulty: the preparation of well defined compounds which may have reproducible properties. This difficulty is smoothed out when the phase relations in the relevant systems are known. Differential Thermal Analysis (DTA) contributes to their establishment. However, in multicomponent systems, an isopletic line is expected to intercept various boundary surfaces and the analysis is obviously complicated, compared to low order systems. In addition, by the nature of high temperature superconductors the oxygen partial pressure used for their preparation is an important thermodynamic parameter which contributes to fix the oxygen content in the solid state. During heat treatments, the composition of the systems may change, due to oxygen or volatile oxides (Tl₂O₃, PbO₂ or HgO) release. A permanent composition control then requires thermogravimetric (TG) measurements associated to DTA.This paper attempts to demonstrate the efficiency of the assembly DTA/TG for the study of high temperature superconductors. Going beyond the frame of preparation and quality control, the system is also particularly useful for kinetic studies. Examples will be principally in the (Tl,Pb)-(Ba,Sr)-Ca-Cu-O systems.It is a pleasure to associate to this lecture my colleagues from research groups with which I collaborate from many years in the difficult field of elaboration and characterization of thalliumbased HTSC: T. K. Jondo, K. Lebbou. R. Abraham and M. T. Cohen-Adad in Lyon (Lab. PCM2), M. Couach and A. F. Khoder at the CEN in Grenoble (SPSMS), J. Muller and R. Flukiger at the DPMC in Geneva and of course C. Opagiste and Ph. Galez at the LSM in Annecy.     

Characterization of carbonaceous products by TG and DTA

Thermogravimetry and differential thermal analysis, using only a combustion step with oxygen, were used to characterize carbonaceous products. Binary composition of alumina and wood charcoal, coke, carbon black, petroleum coke or carbon graphite were prepared containing 5 wt% of each. They were characterized by the burnout onset and DTA and DTG peak temperatures, which range from 476°C for wood charcoal to 790°C for carbon graphite.Complementary characterization of each product was also performed by estimating the ash content from the TG curves, and the calorific value from the DTA curves. The results indicate that these thermal analysis techniques, with only one oxygen burnout step, can be applied both for quality control of each raw material, and to determine the appropriate processing temperatures of the ceramic compositions in which they are used.Funding for this work was provided by the Brazilian PADCT-GTM Project. Participation at the 11th ICTAC was sponsored by Fundação Coordenação de Aperfeiçoamento de Pessoal de Nível Superior — CAPES — and Fundação de Amparo à Pesquisa do Rio de Janeiro — FAPERJ.     

煤系高岭土的DTA特征

利用程序升温热分析法得到煤系高岭土在不同气氛下的ＴＧ／ＤＴＡ谱图。通过比较煤系高岭土与普通高岭土的ＴＧ／ＤＴＡ谱图，可以发现：在惰性气氛下煤系高岭土的ＤＴＡ谱图与普通高岭土的谱图基本一致；而在空气气氛下，由于煤的燃烧反应致使煤系高岭土的吸热谷被部分或全部遮盖，另外在３００℃左右有弱的放热峰出现。比较煤系高岭土与普通高岭土的吸热谷特征可以得出煤系高岭土的结构完整性与结晶度较差。     

Analysis of the thermal decomposition of commercial vegetable oils in air by simultaneous TG/DTA

This work presents a study of the thermal decomposition of commercial vegetable oils and of some of their thermal properties by termogravimetry (TG), derivative termogravimetry (DTG) and by differential thermal analysis (DTA). Canola, sunflower, corn, olive and soybean oils were studied. A simultaneous SDT 2960 TG/DTA from TA Instruments was used, with a heating rate of 10 K min^-1 from 30 to 700°C. A flow of 100 mL min^-1 of air as the purge gas was used in order to burnout the oils during analysis to estimate their heat of combustion. From the extrapolated decomposition onset temperatures obtained from TG curves, it can be seen that corn oil presents the highest thermal stability (306°C), followed by the sunflower one (304°C). Olive oil presents the lowest one (288°C). The heat of combustion of each oil was estimated from DTA curves, showing the highest value for the olive oil. Except for corn oil, which presents a significantly different thermal decomposition behavior than the other oils, a perfect linear correlation is observed, with negative slope, between the heat of combustion of an oil and its respective extrapolated onset temperature of decomposition in air. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study of natural and ion exchanged vermiculite by emanation thermal analysis,TG, DTA and XRD

Emanation thermal analysis (ETA), thermogravimetry, DTA and XRD were used in thermal characterization of natural vermiculite (Santa Olalla, Huelva, Spain) and of Na^+- and - exchanged vermiculite samples during heating in air in the range 25-1100°C. A good agreement between the results of these methods was found. Changes in the radon release rate measured by ETA, which reflected the decrease and collapse of the interlayer space after the release of water as well as the formation of new crystalline phases were evaluated using a mathematical model. The model used for the evaluation was found suitable for the quantitative characterization of microstructure changes during in situ conditions of heating of vermiculite samples. This revised version was published online in July 2006 with corrections to the Cover Date.     

A simultaneous TG–DTA study of the thermal decomposition of 2-hydroxybenzoic acid, 2-carboxyphenyl ester (salsalate)

Simultaneous thermogravimetry–differential thermal analysis (TG–DTA) and gas and liquid chromatography with mass spectrometry detection have been used to study the kinetics and decomposition of 2-hydroxybenzoic acid, 2-carboxyphenyl ester, commercially known as salsalate. Samples of salsalate were heated in the TG–DTA apparatus in an inert atmosphere (100 ml min⁻¹ nitrogen) in the temperature range 30–500 °C. The data indicated that the decomposition of salsalate is a two-stage process. The first decomposition stage (150–250 °C) had a best fit with second-order kinetics with E_a=191–198 kJ/mol. The second decomposition stage (300–400 °C) is described as a zero-order process with E_a=72–80 kJ/mol. The products of the decomposition were investigated in two ways:

(a)Salsalate was heated in a gas chromatograph at various isothermal temperatures in the range 150–280 °C, and the exit gas stream analyzed by mass spectrometry (GC–MS). This approach suggested that salsalate decomposes with the formation of salicylic acid, phenol, phenyl salicylate, and cyclic oligomers of salicylic acid di- and tri-salicylides.

(b)One gram samples of salsalate were heated in a vessel under nitrogen to 150 °C, and the residues were analyzed by liquid chromatography–mass spectrometry (LC–MS). The major compound detected was a linear tetrameric salicylate ester.

     

Crystallization Kinetics of Lithium Diborate Glass by DTA

The crystallization process of Li₂B₄O₇ in the glass of stoichiometric composition, characterized by the crystal growth of pre-existing nuclei, was analyzed kinetically by means of DTA. Because the number of pre-existing nuclei for the subsequent growth varies depending on the cooling rate of the glass-forming melt and heating rate of the as-prepared glass, a modified Kissinger plot was applied for evaluating the apparent activation energy to the crystal growth in the glass samples with three different thermal histories, i.e., the pre-annealed, slowly quenched and quickly quenched glasses. The process was characterized by the three dimensional growth of pre-existing nuclei with the apparent activation energy of ca 340 kJ mol⁻¹. This revised version was published online in August 2006 with corrections to the Cover Date.     

LiAlyCo0.96-yMg0.04O2(y=0.3,0.7)的合成及相行为的DTA研究

用柠檬酸配位聚合法合成了LiAl_yCo_0.96-yMg_0.04O₂(y=0.3,0.7)粉体,采用DTA方法和X射线衍射分析研究了烧结温度对不同铝含量材料相行为的影响.实验结果表明,铝掺杂量低(y=0.3)时,在600℃烧结就可得到具有α-NaFeO₂结构的单相固溶体.而铝掺杂量高(y=0.7)时,在600和700℃烧结都有γ-LiAlO₂相出现,直到烧结温度升高到800℃才得到单相固溶体.     

Determination of Kinetic Parameters of Phase Transition on the Basis of DTA Measurements

A simple method of determination of kinetic parameters by analysis of DTA(t) function was developed for the case of systems undergoing transitions without mass change and when kinetic equation describing transition rate is known. The presented method also permits the determination of transition rate dα/dt (or α(t )) when the kinetic equation of transition is unknown. The developed method was tested using DTA data of crystallization of 2CaO×Al₂ O₃ ×1.95SiO₂ glass pure and doped with Cr³⁺ and Nd³⁺ . This revised version was published online in July 2006 with corrections to the Cover Date.     

Study of a Brazilian spent catalyst as cement aggregate by thermal and mechanical analysis

Fluidized catalytic cracking units of refineries normally use zeolite catalysts to treat heavy oil fractions. This catalyst is regenerated continuously, but due to the reduction of its activity during the process, it is partially substituted by a new catalyst make-up. The spent residue has a high content of silicon and aluminum oxides and usually presents pozzolanic properties. This paper presents the study of a Brazilian spent catalyst, which is being tested as a pozzolanic aggregate in partial substitution to cement. Pastes were prepared with 15, 20 and 25% in substitution to cement mass and analyzed after 28 days of hydration. Hydrated paste samples were analyzed by simultaneous thermogravimetry and differential thermal analysis, to quantify the calcium hydroxide consumption, as well as the content of other main hydrated cement phases. Compressive strength analysis was also performed after 28 days of hydration. Although, as spent catalyst content is increased, the pozzolanic activity is confirmed by the increase of calcium hydroxide consumption on cement mass basis, unlikely to other studied spent FCC catalysts, tested for the same purpose, the compressive strength of respective paste specimens decreases, due to the increase of other hydrated phases formation.     

Aluminum Nitride Oxidation by Simultaneous TG and DTA

This work is a study, by simultaneous thermogravimetry (TG) and differential thermal analysis (DTA), of the oxidation of a water resistant aluminum nitride powder which has a special protective coating, and an uncoated AlN powder which has become partially hydrated during its use. The activation energy for oxidation is estimated by the Kissinger and isoconversional methods. In the former method, the temperatures of the oxidation peaks were obtained from DTA and DTG curves. The activation energies for oxidation of the water resistant AlN, obtained by the Kissinger method, are 357±10 kJ mol^–1, 392±12 kJ mol^–1 using respectively DTG and DTA data. For the uncoated AlN, the values are 243±7 and 257±8 kJ mol^–1, respectively. By the isoconversional method, the average values obtained for coated and uncoated samples are, respectively, 323±10 and 224±7 kJ mol^–1. Therefore, the special coating, which protects the aluminum nitride from humidity action, also provides a higher resistance to oxidation. This revised version was published online in July 2006 with corrections to the Cover Date.     

DTA study of the hydration of systems of interest in the field of building materials manufacture

The hydration processes of mixtures containing calcined gypsum, blastfurnace slag or fly ash, portland cement and/or hydrated lime, able to generate calcium trisulphoaluminate and silicate hydrates, have been studied by means of differential thermal analysis. Samples were aged at 55°,70° and 85°C for 16, 24 and 48 hours, followed by a further curing at room temperature and humidity up to 28 days.In the case of the systems containing slag, the optimum pre-curing temperature is 55°C and increasing the pre-curing time from 16 to 48 hours leaves the hydration degree almost unchanged.In the case of the systems containing fly ash the optimum pre-curing temperature is 85°C. Increasing the pre-curing time from 16 to 24 hours enhances the hydration degree. The further increase to 48 hours reduces the selectivity towards calcium trisulphoaluminate hydrate.In all the systems investigated the post-curing at room temperature and humidity has no significant effect on the hydration degree.Finally, the influence of the nature of raw materials depends not only on the characteristics of each component, but also on those of the others.

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Zusammenfassung Mittels DTA wurden die Hydratationsprozesse von Gemischen aus Gips, Hochofenschlacke oder Flugasche, Portlandzement und/oder Löschkalk untersucht, die zur Bildung von Calciumtrisulfoaluminat und Silikathydraten fähig sind. Die Proben wurden bei 55°, 70° und 85°C für 16, 24 und 48 Stunden lang, im Anschluß daran durch Aushärten bei Raumtemperatur und normaler Luftfeuchte 28 Tage lang gealtert.Bei der Verwendung von Schlacke beträgt die optimale Vorhärtungstemperatur 55°C und die Erhöhung der Vorhärtungsperiode von 16 auf 48 Stunden ließ den Hydratationsgrad unverändert.Bei der Verwendung von Flugasche beträgt die optimale Vorhärtungstemperatur 85°C. Die Erhöhung der Vorhärtungsperiode von 16 auf 14 Stunden steigert auch den Hydratationsgrad. Eine weitere Steigerung auf 48 Stunden setzt die Selektivität gegenüber Calciumtrisulfoaluminat-Hydrat herab.In keinem der untersuchten Systeme hatte das Nachhärten bei Raumtemperatur und normaler Luftfeuchte einen signifikanten Einfluß auf den Hydratationsgrad.Letztendlich hängt der Einfluß der Ausgangsmaterialien nicht nur von den Eigenschaften jeder einzelnen Komponente, sondern auch von denen der anderen Komponenten ab.

     

Use of DTA in the investigations of fly ashes from fluidized bed boilers

DTA method was used to follow the hydration process of cement admixtures containing fluidized bed combustion by-product, formed on joined combustion and desulphurisation in some installations with fluidized bed. Based on endothermic peaks attributed to the dehydration of phases formed on hydration, the conditions leading to the formation of so-called ‘delayed’ ettringite were found. This calcium alumino-sulphate hydrate is responsible for lower durability of fluidized bed ash containing material. DTA method is also beneficial in the studies of fluidized bed combustion by-product itself, giving information about the un-burnt carbon content and pozzolanic properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

DTA and FT-IR analysis of the rehydration of basic magnesium carbonate

The rehydration characteristics of a commercially produced hydromagnesite and two basic magnesium carbonates synthetically produced from Mg(OH)₂, are presented. The products were dehydrated and dehydroxylated at 325°C before rehydration was attempted. DTA and FT-IR were used to follow the structural changes that occurred during the rehydration processes. The results obtained for the commercially and synthetically produced hydromagnesite products indicated that the original symmetry of the groups was reclaimed during rehydration. This was not observed for the synthetically produced unidentified basic magnesium carbonate product. This investigation provides insight into the rehydration characteristics of a select group of basic magnesium carbonates. This revised version was published online in July 2006 with corrections to the Cover Date.     

Investigation of thermal characteristics of a DTA cell block

Prior to evaluating DTA curves a thorough investigation of different types of specimen holders and cell blocks should be made, which means a quantitative appraisal of heat transfer conditions. The empirical approach makes use of the thermal analogue of Ohm's law, whereR=thermal resistance. Calculation ofR gave a graphical correction of about 1 mm, which stresses the merit of computer calculation. Very small differences of the values forR between platinum and alumina sample holders were observed.R was experimentally determined at 500 K and 1000K by means of UO₂ and BaCO₃.

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Zusammenfassung Vor der Auswertung von DTA-Kurven sollte eine gründliche Prüfung der verschiedenen Typen von Probebehältern und Zellenblöcken erfolgen, was für die quantitative Abschätzung der Wärmeübertragungsverhältnisse von Bedeutung ist. Die empirische Annäherung macht von dem thermischen Analogen des Ohmschen Gesetzes Gebrauch, wobeiR der thermische Widerstand ist. Die Berechnung vonR ergab eine graphische Korrektion von etwa 1 mm, was die Vorteile der Komputerberechnung betont. Sehr kleine Unterschiede der Werte fürR wurden bei Platin-, bzw. Aluminium-Probebehältern beobachtet.R wurde bei 500 K und 1000 K mittels UO₂ und BaCO₃ auf dem Versuchswege bestimmt.

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Résumé L'exploitation des courbes ATD devrait Être précédée d'une étude approfondie de l'influence des divers types de supports d'échantillon et de cellules, c'est-à-dire d'un examen quantitatif des conditions du transfert de chaleur. L'approximation empirique utilise l'analogie thermique de la loi d'Ohm oùR est la résistance thermique. Le calcul deR donne une correction graphique d'environ 1 mm, ce qui met en relief les mérites du calcul à l'ordinateur. On n'a observé que de très petites différences entre les creusets en platine ou en aluminium contenant les échantillons. On a déterminéR expérimentalement à 500 K et à 1000 K en utilisant UO₂ et BaCO₃.

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, . R — . R 1 , . , R . R 500 1000 UO₂BaCO₃.

     

DTA and X-ray diffraction investigations of laser-irradiated CeO2 powders

The TG and DTA curves and diffractograms of powdered CeO₂ samples irradiated with a CO₂ laser beam with powers of 0.41–1.39 kW/cm² are presented. The laser treatment induced structural changes and probably generation of a metastable phase. X-ray diffraction coupled with thermal analysis was used to establish the structural modifications in the irradiated samples after heating.     

Closer relation between thermal analysis and calorimetry

Several DTA experiments followed by calorimetric works are reviewed here to emphasise the importance of complementary role of both techniques. The thermal analysis is advantageous in the sense that it gives quickly the overall view of thermal behaviour of a material under various conditions. Calorimetric work provides accurate heat capacity data which enable to derive thermodynamic functions including the enthalpy and entropy. The latter quantity is especially important in judging whether the material obeys the third law of thermodynamics. However, calorimetric work leads occasionally to an erroneous conclusion if the work is not preceded by thermal analysis performed under various conditions. Sometimes, quality of information obtained by DTA exceeds that obtained by laborious calorimetry.