水合稀土二氯醋酸盐的合成及热分解研究

合成了La,Ce,Nd,Sm,Eu,Gd二氯醋酸盐,经化学分析,热重法和五氧化二磷真空千燥脱水法确定组成为Ln(CHCl2COO)3.nH2O(n=2,Ln=La,Ce,Nd;n=1.5,Ln=Sm;n=1.25,Ln=Eu;n=1,Ln=Gd),它们均属新水合物.用DTA-TG-DTG并用技术并辅以化学分析和红外光谱技术研究了其热分解机理,实验证明,由室温至600℃范围内,它们均发生三步主要反应:水合盐脱水变为无水盐;无水盐分解为中间产物,Ln2(OH)Cl5.3H2O[Eu盐分解为Eu2(OH)Cl5.2H2O];中间产物进一步分解为LnOCl[Ce盐为CeO2].并观察到无水盐和氯氧化物形成温度皆与原子序数呈现镧系"双一双效应".     

Preparation and thermal behaviour of rare earth citrate hydrates

Nine rare earth citrate hydrates (RE(C₆H₅O₇)·nH₂O,RE=La, Nd, Sm) were prepared and characterized by chemical analysis, elementary analysis, thermal analysis and IR spectra. The thermal decomposition processes were studied by using TG-DTG and IR spectra techniques. Dehydration enthalpies and dehydration entropies of 3 neodymium and 3 samarium citrate hydrates were also determined by means of DSC.     

Kinetic analysis of thermogravimetric data. XI thermal decomposition of some metal dithionates

A thermal analytical study of Li, Na, K, Rb, Cs, NH₄, Mg, Ca, Sr, Ba and Zn dithionates is reported. The decomposition of the dithionate ion is endothermic in the case of the Na, K, Rb, Cs and NH₄ salts, but exothermic with Li, Mg, Sr, Ba and Zn. Kinetic parameters have been derived from the TG curves by means of the Coats-Redfern method. The validity of a linear kinetic compensation law is reported for the loss of crystal water and separately for the decomposition of the dithionate ion.

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Zusammenfassung Es wird über eine thermoanalytische Untersuchung der Dithionate von Li, Na, K, Rb, Cs, NH₄, Mg, Ca, Sr, Ba und Zn berichtet. Die Zersetzung des DithionatIons ist im Falle von Na, K, Rb, Cs und NH₄-Salzen endotherm, im Falle von Li, Mg, Sr, Ba und Zn hingegen exotherm. Die kinetischen Parameter wurden aus den TG-Kurven mittels der Coats-Redfern-Methode abgeleitet. Es wird über die Gültigkeit eines linearen kinetischen Kompensationsgesetzes für den Verlust von Kristallwasser berichtet und gesondert für die Zersetzung des Dithionat-Ions.

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Résumé On présente les résultats d'une étude par analyse thermique des dithionates de Li, Na, K, Rb, Cs, NH₄, Mg, Ca, Sr, Ba et Zn. La décomposition est endothermique dans le cas des sels de Na, K, Rb, Cs et ammonium tandis qu'elle est exothermique dans le cas des sels de Li, Mg, Sr, Ba et Zn. Les paramètres cinétiques sont déduits des courbes TG par la méthode de Coats-Redfern. La validité d'une loi de compensation cinétique linéaire est étudiée pour la perte de l'eau d'hydratation ainsi que pour la décomposition de l'ion dithionate.

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Li, Na, K, Rb, Cs,. NH₄, Mg, Ca, Sr, Ba Zn. [ Na, K, Rb, Cs NH₄ , Li, Mg, Sr, Ba Zn . - . .

     

The thermal decomposition of the 5,7-dihalo-8-quinolinol rare earth metal chelates

The thermal decomposition of the 5,7-dichloro-, 5,7-dibromo- and 5,7-duodo-8-quinohnol chelates of lanthanum, cerium, praseodymium, neodymium, samarium and yttrium was investigated on the thermobalance. The chelates decomposed in the temperature range from 65 to 125°C while the oxide levels were obtained from 395 to 805°C Although the chelate thermal stability temperatures varied little with the chelating agent, the minimum oxide level temperatures were largely dependent on the halogen substitution on the 8-quinolinol molecule. Results of this study were correlated with previous studies on the rare earth metal chclatcs with 8-quinolinol and 2-methyl-8-quinolinol.     

Study of the thermal decomposition kinetics of some rare earth carbonates,fluorocarbonates and fluorooxalates

The thermal transformations of Pr and La carbonates, La, Ce, Pr, Nd, Sm, Eu and Gd fluorocarbonates, and La, Nd, Dy and Ho fluorooxalates were investigated. A Derivatograph Q-1000 (MOM, Hungary) was used for thermal analysis. The kinetics of the processes was studied in a flow reactor. The activation energies and preexponential factors for dehydration and decarbonization were calculated. Samples of Pr fluorocarbonate, Ho fluorooxalate, and Pr and La carbonates were exposed to γ-irradiation (dose from 6.2·10⁶ to 6.1·10⁷ rad). The influence of the irradiation dose upon the kinetic parameters (E _a andA) of the processes was investigated.     

The thermal decomposition of alkaline earth metal salicylates

The thermal decompositions of the salicylates of magnesium, calcium, strontium and barium were investigated using thermogravimetry and differential thermal analysis, together with the analysis of intermediate products formed during the decomposition processes. One intermediate product was isolated and identified during the decomposition of the magnesium salt, and two for each of the remaining metal salts.

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Zusammenfassung Die thermische Zersetzung der Salicylate von Magnesium, Calcium, Strontium und Barium sowie die Analyse der während des Vorganges gebildeten Zwischenprodukte wurden durch die thermogravimetrische und Differential-Thermal-Analyse untersucht. Im Verlaufe der Zersetzung des Magnesiumsalzes wurde ein Zwischenprodukt isoliert und identifiziert, bei den übrigen Metallsalzen je zwei.

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Résumé On a étudié par thermogravimétrie et analyse thermique différentielle la décomposition thermique des salicylates de magnésium, calcium, strontium et baryum et l'on a analysé les produits intermédiaires qui se forment pendant la décomposition. C'est ainsi que l'on a isolé et identifié un produit intermédiaire au cours de la décomposition du sel de magnésium et deux pour chacun des autres sels.

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Thermal decomposition of some rare earth metal cupferrates and neocupferrates

The thermal decomposition of the eupferrates and neocupferrates of europium, terbium, dysprosium, holmium, erbium, and ytterbium was studied on the thermobalance. The metal chelates possessed poor thermal stability as well as a pronounced tendency to Coprecipitate reagent. The minimum oxide level temperatures for the metal cupferrates were : Eu, 570°; Tb, 540°; Dy, 550°; Ho, 610°; Er, 550° and Yb, 520°. The minimum oxide level temperatures for the metal neocupferrates were: Eu, 560°; Tb 565°; Dy, 540°; Ho,445°; Er, 530°; and Yb, 485°.     

Isothermal kinetic analysis of the thermal decomposition of magnesium hydroxide using thermogravimetric data

In the present study, the kinetics of the thermal decomposition of magnesium hydroxide is investigated, using isothermal methods of kinetic analysis. For this purpose, experiments in thermogravimetric analyser were carried out in standard values of temperature (350°, 400°, 450° and 500°C) which resulted in weight loss percent as a function of time. The data were further modified to give fraction reacted ‘' versus time to be tested in various forms of ‘' functions. In order to determine the mechanism of the magnesium hydroxide decomposition and the form of the conversion function which governs the dehydroxylation of Mg(OH)₂, four different methods of isothermal kinetic analysis were used. Applying each of these methods to the data, it was concluded that the nucleation mechanism predominates the Mg(OH)₂, decomposition for all values of temperature tested; at 350°C the kinetic model which represents the experimental data is that of reaction at phase boundaries (random nucleation), F₁: ln(1−)=kt) while for the higher temperatures 400°, 450° and 500°C the kinetic equation of nucleation and development in two dimensions, A₂: [−ln (1−)]^1/2=kt was found to fit better the experimental results. The activation energy was evaluated applying two alternative methods; the Arrhenius plot, using maximum rates of reaction, from which the activation energy was evaluated to be 20.54 kcal/mol. An alternative method based on plots of ln t versus 1/T corresponding to the same value of ‘' gave values of 10.72, 13.82 and 16.31 kcal/mol for ‘' values of 0.25, 0.50 and 0.75, respectively.     

Thermal studies and decomposition kinetics of alkaline earth metal trichloroacetates

Alkaline earth metal trichloroacetates M(O₂CCCl₃)₂·nH₂O, where M = Be (1), n = 4; M = Mg (2), n = 6; M = Ca (3) or Sr (4) or Ba (5), n = 4, were synthesized and their thermal behavior analyzed using thermogravimetric analysis (TG/DTG/DSC). A critical examination was made for the apparent activation energy by means of non-isothermal kinetic methods employing multiple heating rates. A systematic and comparative study of thermal decomposition was carried out at different heating rates i.e., 5, 10, 15, and 20 °C min^?1 for various trichloroacetates synthesized. It was observed that the Ca, Sr, and Ba trichloroacetates decompose preferentially to respective metal halides while Be and Mg compounds decompose to metal and metal oxide, respectively. The composition of the final residues was also confirmed using FT-IR spectroscopy. The activation energy follows the order: Mg > Ca > Sr > Ba, Be being the exception. Results reveal that each metal trichloroacetate decomposes through its unique thermolysis mechanism.     

Non-isothermal kinetics of diffusion and its application to thermal analysis

Non-isothermal kinetics of diffusion are derived, extending the fundamental equation of diffusion to non-isothermal conditions, and the equation is solved for a few typical cases. From these theoretical considerations, two methods of analyzing thermoanalytical data of diffusion are proposed. One of the methods is applied to EGA curves of the volatilization of toluene from epoxy resin cured with ethylenediamine. The diffusion constants obtained as a function of temperature for two plate-specimens of different thicknesses at various heating rates are in good agreement with each other. The temperature dependence of the diffusion constant observed for a powdered sample is also in good agreement with those observed for the two plate-specimens.

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Zusammenfassung Die nicht-isotherme Kinetik der Diffusion wird abgeleitet, indem die Grundgleichung der Diffusion auf nicht-isotherme Fälle erweitert und für einige typische Fälle gelöst wird. Von diesen theoretischen Erwägungen ausgehend werden zwei Methoden zur Analyse thermoanalytischer Diffusionsangaben vorgeschlagen. Eine der Methoden wird für die EGA-Kurven der Verflüchtigung von Toluol aus mit Ethyländiamin behandeltem Epoxyharz angewandt. Die an zwei Platten-Arten verschiedener Dicke bei verschiedenen Aufheizgeschwindigkeiten als Funktion der Temperatur erhaltenen Diffusionskonstanten stimmen gut überein. Die an einer pulverförmigen Probe beobachtete Temperaturabhängigkeit der Diffusionskonstante ist ebenfalls in guter Übereinstimmung mit der an den zwei Plattenkörpern erhaltenen.

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Résumé On étudie la cinétique de diffusion en régime non isotherme, en étendant l'équation fondamentale de la diffusion aux cas non isothermes et l'on donne la solution de l'équation pour quelques cas typiques. A partir de ces considérations théoriques, on propose deux méthodes pour analyser les données thermoanalytiques de la diffusion. On applique l'une d'elles aux courbes AGE de stabilisation du toluène à partir des résines époxy traitées à l'éthylène diamine. Les constantes de diffusion obtenues en fonction de la température pour plusieurs vitesses d'échauffement sur deux échantillons en forme de plaquette sont en bon accord, de même que pour des échantillons pulvérulents.

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Synthesis and thermal decomposition of some rare earth tetramethylammonium double sulphates

When reaction mixtures of rare earth(III) sulphates and tetramethylammonium sulphate in molar ratios of from 1∶4 to 1∶12 were evaporated at ambient temperature and the concentrated reaction mixture was treated with ethanol, double sulphates with general empirical formula (CH₃)₄NLn(SO₄)₂·2H₂O (Ln=Ho?Lu and Y) were obtained as reaction products. The crystalline products were identified by quantitative analysis, X-ray powder diffraction patterns and TG, DTG and DTA analysis. They were found to be isostructural. Their thermal decomposition took place in three stages. The temperature range of the dehydration mainly decreased from Ho to Lu. The thermal decomposition in the second and third stages occurred with many thermal events. As final product, Ln₂O(SO₄)₂ was obtained.     

Non-isothermal kinetic study of the thermal decomposition of diaminoglyoxime and diaminofurazan

Data on the thermal stability of organic materials such as diaminofurazan (DAF) and diaminoglyoxime (DAG) was required in order to obtain safety information for handling, storage and use. These compounds have been shown to be a useful intermediate for the preparation of energetic compounds. In the present study, the thermal stability of the DAF and DAG was determined by differential scanning calorimetery (DSC) and simultaneous thermogravimetery-differential thermal analysis (TG-DTA) techniques. The results of TG analysis revealed that the main thermal degradation for the DAF and DAG occurs in the temperature ranges of 230–275°C and 180–230°C, respectively. On the other hand, the TG-DTA analysis of compounds indicates that DAF melts (at about 182°C) before it decomposes. However, the thermal decomposition of the DAG started simultaneously with its melting. The influence of the heating rate (5, 10, 15 and 20°C min⁻¹) on the DSC behaviour of the compounds was verified. The results showed that, as the heating rate was increased, decomposition temperatures of the compounds were increased. Also, the kinetic parameters such as activation energy and frequency factor for the compounds were obtained from the DSC data by non-isothermal methods proposed by ASTM E698 and Ozawa. Based on the values of activation energy obtained by ASTM and Ozawa methods, the following order in the thermal stability was noticed: DAF>DAG.     

Kinetics of the thermal decomposition of alkaline earth metal hydrofluorides

The thermal stability of alkaline earth metal hydrofluorides was studied by means of a Derivatograph. The values of the activation energy, reaction order and rate constant were determined. The comparison of the kinetic parameters of the decomposition process for the complete series of hydrofluorides studied led to a certain regularity in the differences in their thermal stabilities and its correlation with the strength of the hydrogen bond in their structure.

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Zusammenfassung Die thermische Stabilität von Erdalkalihydrofluoriden wurde mit Hilfe eines Derivatographen untersucht, die Werte der Aktivierungsenergien, der Reaktionsordnung und der Geschwindigkeitskonstanten bestimmt. Der Vergleich der kinetischen Parameter des Zersetzungsvorganges wies auf eine gewisse Regelmäßigkeit in ihrer verschiedenen thermischen Stabilität, die in Zusammenhang mit der Stärke ihrer strukturalen Wasserstoffbindung steht.

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Résumé On a étudié la stabilité thermique des hydrogénofluorures des métáux alcalinoterreux et déterminé les valeurs des énergies d'activation, des ordres de réaction et des constantes de vitesse de réaction à l'aide d'un Dérivatographe. Après comparaison des paramètres cinétiques on a pu établir une certaine régularité dans le changement de la stabilité thermique en corrélation avec la force de liaison de l'hydrogène dans la structure.

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Pyrolysis of the hybrid energy cane: thermal decomposition and kinetic modeling using non-isothermal thermogravimetric analysis

Journal of Thermal Analysis and Calorimetry - This work aims to investigate the thermal decomposition and reaction kinetics of the hybrid energy cane, as well as its thermochemical properties....     

Comparative study on thermal behaviors between micrites and thrombolites using thermogravimetric analysis

Journal of Thermal Analysis and Calorimetry - Although micrites (abiotic limestone) and thrombolites (typical biotic limestone), according to the sedimentation and biological action, can be...