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.     

Thermal behaviour of ground vermiculite

Thermal behaviour of natural vermiculite (Santa Olalla, Huelva, Spain) was investigated by TG, DTA, emanation thermal analysis (ETA) and high temperature XRD on heating in the temperature range from 30 to 1100°C before and after vibratory mill grinding. Microstructure changes of natural and ground vermiculite samples were characterized by using ETA under in situ conditions of heating. By comparing the ETA and XRD results it was demonstrated that a decrease of radon release rate measured by ETA characterized the decrease in the interlayer spacing of the vermiculite samples that followed the dehydration. Dedicated to the memory of Professor Dr. Ferenc Paulik who passed away on October 12, 2005.     

Thermal Behaviour of Titania Based Materials: Mathematical modeling of emanation thermal analysis results

Emanation thermal analysis (ETA) was used in the characterization of microstructure changes during heating ofprecursors for the titania based materials: hydrous titania, TiO₂nH₂O (n=0.58) and hydrous titania containing 10% ruthenia,(TiO₂)_0.9(RuO₂)_0.1nH₂O (n=1.5). The precursors were heated at the constant rate 6 K min^–1 in argon flow in the range 20–1000°C. ETA results were compared with the theoretical curves simulating the temperature dependences of radon release rate, E(T). Two mathematical models were used in the simulation. The models considered either subsequent or simultaneous solid state processes (i.e. dehydration, crystallization orphase transition, resp.) during thermal treatment of titania based materials. A good agreement was found between experimental and the simulated ETA curves. The results of ETA were confirmed by XRD patterns of intermediate products of thermal treatment of the precursors.This revised version was published online in November 2005 with corrections to the Cover Date.     

Formation of B-C-N Ceramics Investigated by Emanation Thermal Analysis, TG and DTA

Processes taking place during formation of B-C-N ceramics by thermal treatment of organic precursors were investigated using emanation thermal analysis (ETA), differential thermal analysis (DTA) and thermogravimetry (TG). An additional information about thermal behavior of precursors used for preparation of BC4N, BN and CNx ceramic systems by heating in argon up to 1100°C was obtained. The ETA enabled us to characterize microstructure changes in the samples at in situ conditions of thermal treatment. A good agreement of ETA, TG and DTA results was found. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

Transport properties and microstructure changes of alumina coatings characterized by emanation thermal analysis

Emanation thermal analysis was used to characterize the thermal behaviour of alumina coatings as deposited on EUROFER 97 steel surface by filtered vacuum arc technique. Temperature ranges of the healing of cracks and structure irregularities observed by SEM were determined from the ETA results. Transport properties of the alumina coatings were assessed from the ETA results by the evaluation of radon diffusion parameters in the temperature range from 50 to 300°C. Healing microstructure irregularities of the alumina coatings can be expected in the range 300–700°C as indicated by the decrease of the radon release rate. From the ETA results it followed that the onset of healing the cracks observed by the SEM on the surface of one alumina coating sample can be expected at 430°C. Dedicated to Dr. K. Habersberger, Past-Chairman of the thermal analysis working group of the Czech Chemcial Society, at the occasion of his 75^th birthday     

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.     

Combined DTA and XRD Study of Sintering Steps Towards YAl3(BO3)4

Sintering processes in the Y₂O₃–Al₂O₃–B₂ O₃ system and its subsystems (Y₂O₃–B₂O₃ and Al₂ O₃–B₂O₃) have been investigated by using combined DTA and XRD measurements to get a better understanding of solid state chemical changes resulting in the formation of yttrium aluminum borate (YAl₃(BO₃)₄, YAB) phase and to study the possible role and contribution of various simple borates formed also in the former processes. Two new exothermic heat effects of YBO₃ formation have been detected by DTA in the Y₂O₃–B₂O₃ system between 720 and 980°C. In the Al₂O₃–B₂O₃ system a new experimental XRD profile of Al₄B₂O₉ was observed. Formation of these borates seems to promote the nucleation of double borate YAB below 1000°C. Conversion of Al₄B₂O₉ to Al₁₈B₄ O₃₃ was observed after a long term (10 h) sintering at 1050°C. Similarly, an increased formation of YAB has been observed as a product of the sintering reaction between YBO₃ and Al₁₈B₄O₃₃ at 1150°C. The two latter single borates are found to be identical with the high temperature decomposition products of YAB. This revised version was published online in July 2006 with corrections to the Cover Date.     

Use of emanation thermal analysis to characterize thermal reactivity of brannerite mineral

Emanation thermal analysis (ETA) was used to characterize the thermal reactivity of amorphous brannerite mineral of general formula U_1–xTi_2+xO₆ (locality El Cabril, near Cordoba, Spain). It was demonstrated that on sample heating up to 880°C microstructure changes taking place in the sample were accompanied by the formation of new radon diffusion paths, followed by their closing up during the final transformation of amorphous to crystalline brannerite in the range 900–1020 °C. Relative changes in structure irregularities that served as radon diffusion paths during heating and subsequent cooling of the sample to temperatures of 300, 550, 750, 880, 1020 and 1130°C, respectively, were determined from the ETA results. Mass losses in temperature ranges of 230–315, 570–760 and 840–1040°C were observed by thermogravimetry. Mass spectrometry indicated the release of CO2 mainly due to the decomposition of minor carbon amount in the brannerite mineral sample.     

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.     

The study of the dehydration and dehydroxylation of smectites by emanation thermal analysis

The dehydration and dehydroxylation of the smectites, beidellite and montmorillonite (dioctahedral) and saponite and laponite (trioctahedral), were investigated by ETA, DTA, TG and X-ray diffractions. There are differences between the behaviors of di- and trioctahedral clays which are due to the differences in the ability of the exchangeable cations to migrate into hexagonal holes of the SiO₄ network and due to the fact that the dehydroxylation and recrystallization of dehydroxylated trioctahedral smectites occur simultaneously, whereas there is a temperature gap of about 300°C between the dehydroxylation and the recrystallization of dioctahedral smectites.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthdayThe authors wish to thank Laporte Industries, Inc. UK for the laponite sample.This research was supported under Project No. C12-219, Grant No. HRN5544 G002069, U.S.-IsraelCooperative Development Research Program, Office of the Science Advisor, U.S. Agency for International Development.     

Effect of Na+ and NH 4 + Cations on Microstructure Changes of Natural Vermiculite During Heat Treatment

Emanation thermal analysis (ETA), DTA, SEM, and XRD were applied for the characterization of the effect of Na⁺ and NH ₄ ⁺ ions used for saturation of natural Mg-vermiculite on the microstructure during heating. The microstructure changes were characterized by ETA under in situ conditions of samples heating in air in the temperature range 20–1300°C. It was found that Na⁺ and NH ₄ ⁺ ions have a significant effect on the microstructure changes during heat treatment of the natural Mg-vermiculite sample saturated with these ions. For Mg-vermiculite and Na⁺ saturated vermiculite thet emperatures of the onset of the collapse of interlaminar space were determined by ETA. Differences in thermal stability of the microstructure of dehydrated vermiculite samples were observed by ETA: the microstructure of dehydrated Mg-vermiculite, and Na-vermiculite was found stable until 650 and 350°C, respectively. For dehydrated NH₄-vermiculite the annealing of the microstructure started at 730°C. The onset temperatures of the formation of new crystalline phases were indicated by ETA as the increase of the radon release rate. The onset temperatures of the ordering of the vermiculite structure or sintering under presence of the glassy stage (for Na-vermiculite), respectively, were determined from the decrease of the radon release rate. The ETA results were confirmed by DTA, XRD and SEM.This revised version was published online in November 2005 with corrections to the Cover Date.     

The influence of exchangeable cation on thermal behaviour of ground vermiculite

Grinding and contact with water or salt solution increased the specific surface (ssa) but lowered the first dehydration effect (escaping up to 150°C) and increased the second dehydration effect (150 to 500°C). The dehydroxylation was moved to lower temperatures and was only ΔM(500-1100°C)=3.7±0.3 % as compared to 5.5% in the parent vermiculite (V). Except ΔM(20-150°C), the mass losses measured at the remaining T ranges, were consistent in the ground samples, thus the grinding for 2 min caused the homogenization of the crystal structure of vermiculite [ΔM(150-500°C)=7.6±0.7%]. DTA curves after grinding and cation exchange indicate an important exothermal peak at 795-870°C, its temperature depending on exchangeable cation. It indicates the formation of high temperature phases (enstatite, forsterite, spinel). The lowest temperature of the peak (795°C) was observed in V-gr-Li, here lithium silicate was formed. The highest peak temperature (870°C) was found in V-gr-K, where almost only forsterite developed. These exothermal peaks were very weak in unground V with various exchangeable cations. This revised version was published online in July 2006 with corrections to the Cover Date.     

用Diamond TG/DTA热重/差热综合热分析仪在外加磁场下研究磁性材料相转变

介绍综合热分析仪Diamond TG/DTA在磁性材料研究中的应用.提出在外加磁场作用下,得到样品的热重曲线(TG),由TG曲线分析样品磁性相变及样品居里温度变化的原因,看到稀土铁基金属间化合物样品替代的Co元素的站位和元素之间相互作用对居里温度有很大影响.作为一种测量居里温度的方法,拓展Diamond TG/DTA热分析仪应用研究领域.     

Thermal decomposition of silver cyano complex and characterization its decomposition products by ETA,DSC, DTA and TG

It was found by DTA and TG that [Phenyl₂I][Ag(CN)₂] in the solid state is chemically stable on heating in argon up to 160°C. During heating to higher temperatures it decomposes, forming volatile products such as [Phenyl]I, [Phenyl]NC and (CN)₂ [1]. After heating the sample to 500°C metallic silver resulted. The volatile and intermediate solid products were analysed by IR-spectroscopy.It was found by means of DTA and ETA that an isophase reversible transition takes place when the sample is heated and cooled, not higher than 100°C. At heating higher than 100°C the sample melts (melting pointT _m=135°C). The enthalpy melting was determined by means of DSC (H=–28 kJ·mol^–1).By means of ETA the disorder degree of the final decomposition product was estimated. The value of the activation energy of radon diffusion in the temperature range 720°–500°C equals 32.6 kJ·mol^–1.Dedicated to Prof. I. N. Bekman Moscow State University at the occasion of his 50th birthday     

Oxidation of Metal Sulphides and Determination of Characteristic Temperatures by DTA and TG

The oxidation of metal sulphides and sulphide concentrates was studied by means of DTA, TG and DTG curves. The behaviour of ZnS, CdS, GaS, Tl₂S, Sb₂S₃ and Sb₂S₅ during thermal treatment in an oxidizing medium was investigated. The properties of these sulphides were compared and conclusions were drawn about their probable oxidation reactions and the kind of end-products obtained. The characteristic temperatures of the studied sulphides were determined on the basis of curves (DTA). The values obtained were used to compare the behaviour of the sulphides during the oxidation process in a fluid bed. The results can be used to improve the technological and economic indices in the industrial production of zinc. This revised version was published online in July 2006 with corrections to the Cover Date.     

The role of various compounds in humic acids stability studied by TG and DTA

Simultaneous DTA/TG technique has been used to study the influence of various model compounds (aromatics, organic acids, alkanes, ketone, heterocyclic and sterole) on the thermo-oxidative behavior of lignite humic acids. As a measure of stability the shift of the onset temperature of the exothermic degradation peak has been used. Further, the ratio of mass loss recorded in the high and low temperature ranges (thermogravimetric index) was used to evaluate the role of added compounds on the recombination reactions occurring during the thermooxidative degradation of humic acids. It has been demonstrated that most of added compounds play a role during those processes at relatively low concentrations (1% mass/mass) and affect the humic acid stability as well as the value of thermogravimetric index (i.e. the degree of the apparent aromaticity). It has been clearly shown, that the latter parameter reflects more the ‘qualitative’ than the ‘quantitative’ relationship between biodegradable humified parts in the extracted pool of organic matter.     

TG/DTA/MS of poly(methyl methacrylate), The Role of the Oxidative Environment

Degradation of relatively large particle size, 0.5 mm of Type-G PMMA (Rohm and Haas) were conducted with thermogravimetric analysis and evolved gas measurements using quadrupole mass spectrometer under conditions of mass transport limitation. In addition, differential thermal analysis was performed in order to furnish information with regards to exothermic or endothermic reactions associated with the degradation. The tests were conducted in an inert environment of pure N₂ and oxygenated environment. The results indicated one step degradation process in pure N₂ and the degradation process is endothermic. As the O₂ fraction increases the degradation process is transformed to exothermic. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evaluation of pozzolanic activity of natural and artificial pozzolans by thermal analysis

In this research, the pozzolanic activity of natural and artificial pozzolan used for preparation of restoration mortars was evaluated. For this purpose, several pastes were prepared, by mixing two artificial pozzolans and a natural one with commercial hydrated lime, in different ratios. The pastes were cured in standard conditions (RH = 98%, T = 25 °C). The pozzolanic activity was evaluated by using simultaneous differential thermal and thermogravimetric analysis (DTA/TG) after curing for 3, 7, 14, 28 days. The obtained results revealed that the various lime/pozzolan pastes displayed different reaction kinetics and therefore the various pozzolans present different reactivity, in proportion to its mineralogical, physical and chemical characteristics.     

Characterization of some new alkali metal molybdate hydrates by thermal and X-ray methods

Preparation and characterization of four new hydrated alkali metal molybdates Na₂Mo₄O₁₃·6H₂O, K₂Mo₄O₁₃·3H₂O, Rb₂Mo₄O₁₃·2H₂O and Cs₂Mo₄O₁₃·2H₂O are described. The compounds were prepared by crystallizing the solution obtained by dissolving MoO₃ and corresponding alkali metal carbonates A₂CO₃ or molybdate A₂MoO₄ in stoichiometric amount in distilled water. The hydrated molybdates were characterized by thermal (TG/DTA) and X-ray diffraction (XRD) methods. The number of water molecules in the compounds were determined from their TG /DTA curves recorded in air and identification of their dehydration products was done by XRD. The cell parameters of the compounds were obtained by indexing their XRD patterns. Attempt to prepare the corresponding hydrated compound of lithium was not successful. This revised version was published online in July 2006 with corrections to the Cover Date.