TG and autoignition studies on forest fuels

The autoignition delay times of some important Mediterranean forest species: Arbutus adrachne, Abies cephallonica, Pinus brutia, Pinus halepensis, Pistacia lentiscus, Cupressus semprevirens, Olea europaea, Cistus incanus were determined in the range 460–600°C under precisely controlled temperature and airflow conditions. Based on these data the forest fuels examined were classified into two groups: the least and the most flammable species. The autoignition delay data were related to the thermal analysis measurements. The themogravimetric analysis in an inert (nitrogen) atmosphere showed that the thermal decomposition of cellulose in the range of 300–400°C as well as the mass residue at 600°C are directly related to the ignition behavior.This revised version was published online in November 2005 with corrections to the Cover Date.     

Magnetic Temperature Standards for TG

Magnetic transition temperatures, Tc, are measured by simultaneous TM/DTA for Alumel, cobalt, nickel, and three alloys of Ni and Co. The observed values of Tc are corrected using the values for the melting temperatures of pure metals used to define the International Temperature Scale. These corrections are based on the simultaneous melting of these pure metals alongside, but separate from, the magnetic sample. Nine investigators, using a wide variety of instrumentation, have made these measurements utilizing a standard protocol. The results are compared for several heating rates. It is planned to make these same magnetic materials ultimately available to the public for calibration of temperature of their TG instruments. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Factors affecting the experimentally resolved shapes of TG curves

From a theoretical consideration concerning the factors affecting the experimentally resolved shapes of thermogravimetric curves, the possible way to increase the accuracy of the thermogravimetric measurements were discussed.

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Zusammenfassung Unter theoretischen Aspekten bezüglich derjenigen Faktoren, die die experimentelle Auflösung thermogravimetrischer Kurven beeinflussen, wird ein möglicher Weg zur Steigerung der Genauigkeit thermogravimetrischer Untersuchungen diskutiert.

     

Fractional analysis of technical polyoxaalkyl borates by TG

Results of preliminary thermoanalytical investigations (DSC/TG) of polyoxaalkyl esters of boric acid are presented. One aim of these investigations was the development of a method of characterization of the technical esterificate. The optimum parameters of quantitative thermogravimetric analysis of boric acid esters and the excess of polyoxaalkanols were assumed. The precision and accuracy of the developed method are discussed.     

镍钴锌纳米铁氧体的制备及磁热性能

以乙酰丙酮盐为前驱体,三乙二醇为溶剂,采用多元醇法制备了纳米Ni0.5-xCoxZn0.5Fe2O4(x=0,0.1,0.2,0.3和0.4)铁氧体.通过X射线衍射仪(XRD)、透射电子显微镜(TEM)、傅里叶变换红外光谱仪(FTIR)和振动样品磁强计(VSM)等对样品的结构、形貌和磁性能进行了表征.结果表明,所得纳米Ni0.5-xCoxZn0.5Fe2O4铁氧体的分散性较好,尺寸均一.在室温下产物的剩磁和矫顽力均较小,表现出亚铁磁性.纳米Ni0.3Co0.2Zn0.5Fe2O4铁氧体的饱和磁化强度达到41.34 A·m2·kg-1,其在交变磁场中升温可达到55℃,表现出较好的磁热性能.     

Evaluating the logistic mixture model on real and simulated TG curves

The aim of this paper is to evaluate and explain the fitting of dynamic TG curves by a mixture of logistic functions. This model assumes that more than one physical process may be involved in each mass loss step and that each physical process may extend along all the experiment. One of the main sources of difficulties in TG is that, very often, different stages of decomposition substantially overlap each other. Several real and simulated TG curves were analysed in this paper. An optimal fitting of the TG curves was obtained by a mixture of logistics. In many cases the optimal fitting reproduces accurately the TG curve. Accordingly, the TG curve can be understood as a sum of parallel reactions, where each single reaction is represented by one or a small number of logistic components. Additionally, making use of the analytical derivative of the fitting, a mixture of Arrhenius reaction order equations was applied to the same curves. In all the cases, the fitting obtained with the mixture of Arrhenius was worse than the obtained with the mixture of logistics. A software was developed to automatically perform these tasks. The physical meaning of the fitting was explained.     

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.     

TG and DSC studies on plaster residues as recycled material

The aim of the present work is to study plaster residues produced in industries in Goiás State (Brazil). The study analyzes the trituration and dehydrating processes of the plaster and compares its chemical, mechanical and physical characteristics to the natural plaster samples aiming its possible recycling. Plaster samples were submitted to X-ray diffraction, infrared spectroscopy, thermogravimetric (TG) and differential scanning calorimetry (DSC) analyses. By the comparison of the results obtained for both samples it was observed that they have similar chemical characteristics. No reason was found against the use of recycled plaster.     

Analysis of the vaporization process in TG apparatus and its incidence in pyrolysis

An analysis of the evaporation process of n-hexadecane in a thermogravimetric apparatus was carried out. n-Hexadecane represents a typical example of a high boiling point compound and its study is interesting for understanding those processes where vaporization takes place in parallel with pyrolysis during thermal treatment. The process has been studied under different operating conditions: nitrogen and air atmospheres, and isothermal and dynamic runs with three different heating rates from 5 K/min to 20 K/min. The experimental data were satisfactorily correlated to a n-order model with zero process order and the same apparent activation energy for all runs, but the exponential factors of the different runs depended on the initial mass and the heating rate. The experimental results were compared with those predicted considering the diffusion process inside the crucible, taking into account the vapor pressure and the diffusion coefficient of n-hexadecane. A parameter, product of these two variables, can be estimated from a single TG run, so the vaporization process in other equipment and/or operating conditions can also be estimated.     

High-resolution TG for the Characterization of Diesel Fuel Additives

High-resolution thermogravimetric analysis (Hi-Res^TM TG) in its variable heating rate mode was applied to commercially available diesel fuel additives under a nitrogen atmosphere. A TGA 2950 from TA Instruments was used to run the experiments. For the selected diesel fuel additives, the use of variable heating rate resulted in sharper transitions and clearer onset of degradation than in traditional constant heating rate experiments. Moreover, the time required for experiments giving reasonable resolution was remarkably reduced compared to constant heating rate experiments. The technique proved to be very useful in the study of multi-component systems, such as diesel fuel additives, since it provides more detailed information regarding mass changes in the sample as a result of heat treatment when total decomposition involves more than one stage i.e. mass changes stem from consecutive reactions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Application of Constant Reaction Rate TG to the Determination of Kinetic Parameters by Hi-Res TG

A simple operation mode to determine the apparent activation energy E _a is introduced. E _a can be determined with a double-curve method by using a constant reaction rate (CRR) approach of Hi-Res TG. The most appropriate mechanism function f(α) and frequency factor A are determined by a single-curve method when the activation energies provided by the two methods are in good agreement with each other. The deacetylation of EVA copolymer has been used for illustration. Advantages of the CRR are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

热重质谱联用(TG/MS)系统的建立和应用

将两种商品型分析仪器热重（TG）和质谱（MS）联用，并将这一热重质谱联用系统（TG／MS）应用于含酚废水的催化氧化和煤燃烧的过程研究，在获取样品重量变化的同时对逸出气相产物进行了在线检测，获取了苯酚氧化反应的历程和煤燃烧过程中氮、硫氧化物的逸出信息。     

Pyrolysis and TG Analysis of Shivee Ovoo Coal from Mongolia

The coal sample of the Shivee Ovoo deposits has been non-isothermally pyrolysed in a thermogravimetric analyser to determine the influence of temperature, heating rate and purge gas employed on the thermal degradation of the sample. The heating rates investigated in the TG were 10–50 K min^–1 to final temperature of 1000°C. N₂or CO₂ were employed as well as type of purge gas on the process of thermal degradation of the coal sample. The coal was also investigated in a fixed bed reactor to determine the influence of temperature and heating rate of the pyrolysis on the yield of products and composition of the gases evolved. The main gases produced were H₂, CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆ and C₃H₈ and also minor concentrations of other gases. This revised version was published online in August 2006 with corrections to the Cover Date.     

Phase Analysis of High-calcium Lime by TG

A thermogravimetric method has been developed and is suggested for both the qualitative and quantitative phase analyses of high-calcium lime and calcium speciation as well. Two complementary TG measurements are proved to be satisfactory for the determination of moisture, calcium oxide, calcium hydroxide and calcium carbonate contents as well as total mineral impurities in high-calcium limes: quicklime, hydrated lime and limestone. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal Characterization of Warifteine by Means of TG and a DSC Photovisual System

This work proposes thermal characterization as analytical methodology for the identification and purity assay of warifteine, an alkaloid in Cissampelos sympodialis Eichl. Thermal and kinetic parameters were determined by means of TG and DSC photovisual studies. The TG results showed that the decomposition of warifteine in air and nitrogen atmospheres proceeds in three and four steps, respectively. The TG data allowed calculation of the kinetic parameters of warifteine. The activation energy values obtained by different methods displayed a good correlation. With the DSC photovisual system applied it is possible to detect the impurity level in warifteine after its purification. This revised version was published online in July 2006 with corrections to the Cover Date.     

Three model-free methods for calculation of activation energy in TG

Two well-known isoconversion methods, the first one developed by Ozawa-Flynn-Wall and the second one developed by Friedman, are confronted with calculations made using modulated thermogravimetry (MTG). The latter variant is free from a number of assumptions and restrictions made in the isoconversion computations. In particular, it allows the use of a single decomposition curve and it remains in force even in the case of multistage decomposition with conjugated processes.To obtain the model-fitting methods from the model-free methods one should replace some functions averaged over isoconversion levels by the functions calculated on the basis of kinetic models. In the Ozawa-Flynn-Wall method it is the averaged reduced time (integral of Arrhenius exponential over time). In the method of Friedman it is the averaged differential conversion function.In MTG, the perturbations caused by the sinusoidal temperature modulation are connected with derivatives of mass loss by simple scaling, where activation energy plays a role of a scaling parameter. The ratio of the experimentally measured perturbations to the experimental derivative is used for the model-free computation of activation energy. If a theoretical derivative replaces the experimental one, this procedure leads to the model-fitting method. Even a rough approximation of the experimental derivative should not lead to an excessive error in activation energy. If in a vicinity of peaks maxima in derivatives of mass loss the decomposition is controlled by single rate-limiting processes, modulated thermogravimetry should give realistic activation energies for these processes. Inasmuch as the results of MTG are weakly sensitive to selection of kinetic models, this method should have a high predictive force.     

球形尖晶石型钴铁氧体:合成方法及其影响因素

实现了在低温、常压条件下由含铁水滑石微晶到球形尖晶石型铁氧体的合成。结果表明,所合成的铁氧体系平均粒径为1.0μm的规整球。进一步研究发现,铁氧体微球的成型过程受到很多因素影响,例如,球型铁氧体磁性粒子的大小随着晶化过程中溶液的酸碱度的升高而变大;同时外加磁场的存在不但会使球型铁氧体磁性粒子的粒径变大,而且也会使晶化产物的粒子形貌更加趋于规整。另外,还对不同组成的尖晶石型铁氧体微球的形成进行横向比较时发现,合成初期的化合物投料组成对终产物形貌的影响是巨大的,随着投料组成中Fe2+含量的增加,转化过程变得容易,且在投料金属离子组成nCo2+∶nFe2+∶nFe3+为1∶1∶1时,所得的球型铁氧体磁性粒子的粒径最大。相同条件下不同组成的铁氧体微球粒径差异明显,MgFe2O4不能形成球形颗粒,NiFe2O4和CoFe2O4可以形成球形颗粒,其中CoFe2O4形成的颗粒粒径最大。     

TG and DSC as tools for confirming hybrid vermiculites derived from intercalation

Vermiculite was prepared to react with aliphatic diamines (ethylene-, trimethylene-, tetramethylene- and hexamethylene-) diamine. The products were characterized by elemental analysis, infrared spectroscopy and X-ray diffraction. The amounts of diamines adsorbed were 0.89, 0.86, 0.79 and 0.68 mmol g^–1, respectively for NH₂(CH₂)⋅nNH₂ where n=2, 3, 4, 6. The basal spacings of the intercalated vermiculites varied between 1300 and 1470 pm. Thermogravimetry and DSC data confirmed intercalation of diamines in gallery space of vermiculite.     

程序升温热重法研究扎赉诺尔煤的气化动力学

用程序升温热重法对扎赉诺尔煤（ＺＬ）的８００℃半焦进行ＣＯ２气化研究，考察了升温速率对ＴＧ／ＤＴＧ谱图的影响，分析讨论了ＤＴＧ参数（Ｔｍ和Ｒｍ）的变化；用单一升温速率法和多个升温速率组合法分别作了动力学计算，并对结果进行了分析讨论。结果表明：Ｔｍ和Ｒｍ均随升温速率的增高而增大，两种计算方法得到的动力学参数是不同的，单一升温速率法计算出的表观活化能Ｅ和指前因子Ａ遵循关系式：ｌｏｇＡ＝０．１０Ｅ－８．