A. Ortega

Applicability of the master plots in kinetic analysis of non-isothermal data

Abstract The ability to determine the actual reaction mechanism (RM) of solid state processes from a single non-isothermal curve was analysed and discussed. Owing to the correlation of all kinetic parameters the RM cannot be ascertained without the knowledge of activation energy. However, if the activation energy is known a simple and precise method for the determination of RM can be proposed. The method was used to analyse the experimental data of the thermal decomposition of magnesium carbonate in vacuum. It was found that the reaction follows the R3 mechanism which is in very good agreement with the results of isothermal experiments.

The effect of the CO2 pressure on the thermal decomposition kinetics of calcium carbonate

Abstract The influence of the pressure of carbon dioxide on the thermal decomposition kinetics of calcium carbonate is studied. It is shown that it is possible to obtain meaningful and reliable kinetic parameters from isothermal and non-isothermal data provided that the pressure correction term is included in the kinetic equation.

Possibilities of two non-isothermal procedures (temperature- or rate-controlled) for kinetical studies

The applicability of both conventional Thermal Analysis (TA) and Controlled Rate Thermal Analysis (CRTA) for kinetic analysis is discussed. It is shown that TA method can give a reliable kinetic information and meaningful kinetic parameters especially for solid state transformation. On the other hand the CRTA method is more suitable for decomposition process where one or more gasses are evolved.A consistent and reliable method of kinetic analysis is proposed for both techniques. This method is illustrated to analyze the crystallization process of chalcogenide glass and the decomposition of dolomite.ZusammenfassungEs wird die Anwendbarkeit von herkömmlicher Thermoanalyse (TA) und geschwindigkeitsgesteuerter Thermoanalyse (CRTA) bei kinetischen Untersuchungen diskutiert. Die TA Technik kann eine zuverlässige kinetische Information und sinnvolle kinetische Parameter besonders bei Feststoffumsetzungen liefern. Die CRTA Technik ist andererseits mehr für Zersetzungsprozesse geeignet, bei denen ein oder mehrere Gase freigesetzt werden.Für beide Techniken wird eine einheitliche und geeignete Methode zu kinetischen Analyse vorgeschlagen. Als Beispiel wird diese Methode zur Analyse des Kristallisationsprozesses von Chalkogenidgläsern sowie der Zersetzung von Dolomit angewendet.

Some considerations regarding the determination of the activation energy of solid-state reactions from a series of isothermal data

It has been demonstrated that the kinetic data on solid-state reactions show a good fitting to the expressiong(α)=kt, regardless of the nature of theg(α) function previously assumed for performance of the calculations. Moreover, the activation energy value obtained from the Arrhenius law is quite independent of the kinetic function assumed.ZusammenfassungEs wird gezeigt, daß die kinetischen, Daten von Festkörperreaktionen gut dem Ausdruckg(α)=kt entsprechen, ungeachtet der Natur der zur Ausführung der Berechnungen angenommen Funktiong(α). Darüber hinaus ist der nach dem Arrheniusschen Gesetz erhaltene Wert für die Aktivierungsenergie ganz unabhängig von der angenommenen kinetischen Funktion.РезюмеПоказано, что данные кинетики твердотельлых реакций хорощо описываются быражениемg(α)=kt, независимо от характера характера функцииg(α), ранее учитываемой при проведении вычислений. Кроме того, значение знергии активации, полученной из уравненил Аррениуса, польностью независимо от принимаемой кинетической функции.

Some successes and failures of the methods based on several experiments

Abstract The actual kinetics of a solid state reaction cannot be discerned by means of the kinetic analysis of a single TG curve. The cause of this relates to the fact that different kinetic equations appear to fit a set of kinetic data. This paper shows the advantage of a choice of method based on comparing data from several experiments at the same degree of conversion. But this procedure must be carried out with great care. The limitations are discussed.

A study of the influence of particle size on the thermal decomposition of CaCO3 by means of constant rate thermal analysis

Abstract The influence of particle size on the kinetic parameters of the thermal decomposition of calcite is investigated. The new constant rate thermal analysis (CRTA) technique which allows considerably better control of the heat and mass transfer phenomena has been used. It is found that the activation energy of the thermal decomposition of calcite smoothly increases by increasing the particle size.

A new point of view on the evaluation of the temperature integral

The accuracy of the approximation of the temperature integral of the Arrhenius law proposed by Coats and Redfern, which is one of the simplest and most popular, has been tested. It has been demonstrated that this method leads to accurate values of sufficiently the activation energy of solid state reactions. This means that the use of a tedious and sophisticated approximation of the temperature integral is not necessary.

Errors in the determination of activation energies of solid-state reactions by the Piloyan method, as a function of the reaction mechanism

The errors in the activation energies of solid-state reactions determined with the Piloyan method are more larger than those previously assumed in the literature. On the other hand, the errors in the kinetic parameters are strongly dependent on the kinetic law obeyed by the reaction. A theoretical explanation of this behaviour is given.ZusammenfassungDie Fehler der nach der Piloyan-Methode bestimmten Aktivierungsenergien von Festkörperreaktionen sind grö\er als bisher in der Literatur angenommen und stark abhÄngig von der Reaktionsordnung. Eine theoretische ErklÄrung dieses Verhaltens wird gegeben.РЕжУМЕОтМЕЧАЕтсь, ЧтО ОшИБк И ОпРЕДЕлЕНИь ЁНЕРгИ И АктИВАцИИ тВЕРДОтЕл ьНых РЕАкцИИ пО МЕтОДУ пИлОьНА жНА ЧИтЕльНО БОльшИЕ пО с РАВНЕНИУ с тЕМ, ЧтО РАНЕЕ пРЕДпОл АгАлОсь В лИтЕРАтУРЕ. с ДРУгОИ стОРОНы, пОкАжАНО, ЧтО ОшИькИ ОпРЕДЕлЕНИь кИНЕтИЧ ЕскИх пАРАМЕтРОВ В жНАЧИтЕльНОИ стЕпЕ НИ жАВИсИМы От жАкОНА кИНЕтИкИ, ОпИсыВАУЩЕгО РЕАкцИ У. пРИВЕДЕНО тЕОРЕтИЧЕ скОЕ ОБЩьсНЕНИЕ тАкО гО пОВЕДЕНИь.

On the suitability of controlled transformation rate thermal analysis (CRTA) for kinetic studies: I/ Determination of the activation energy by the rate-jump method

Abstract The rate-jump method is introduced and illustrated in the case of the thermolysis of dolomite Ca Mg(CO 3 ) 2 . It is shown that it leads to a value of the apparent energy of activation which is practically independent, all at once, from the function f(α), from the sample size (20 to 200 mg) and from the rate ratio (4 to 20). This may be considered as an interesting step towards the assessment of kinetic parameters characteristic of the reaction proper.

Discrimination of the kinetic model of overlapping solid-state reactions from non-isothermal data

A method has been developed that allows the deconvolution of up to 15 overlapping solidstate reactions without previous assumptions. Both the kinetic parameters and the reaction mechanisms fitted by the unit reactions can be determined from a series of non-isothermal experiments carried out at different heating rates.ZusammenfassungEs wurde eine methode zur Dekonvolution von bis zu 15 einander überlappenden Festphasenreaktionen entwickelt, die keinerlei vorherige Annahmen notwendig macht. Mittels einer Reihe nichtisothermer Experimente mit unterschiedlichen Aufheizgeschwindigkeiten können sowohl die kinetischen Parameter als auch der Reaktionsmechanismus der Teilreaktionen bestimmt werden.РЕжУМЕРАжРАБОтАН МЕтОД, пОж ВОльУЩИИ РАжДЕлИть пЕРЕкРыВАУЩИЕсь тВЕ РДОтЕльНыЕ РЕАкцИИ с ЧИслОМ Их ДО 15. кИНЕтИЧЕскИЕ пАРАМЕ тРы И РЕАкцИОННыИ МЕхАНИж М кАжДОИ ЕДИНИЧНОИ РЕАкцИИ МОгУт Быть Оп РЕДЕлЕНы НА ОсНОВЕ Рь ДА НЕИжОтЕРМИЧЕскИх Иж МЕРЕНИИ пРОВЕДЕННых пРИ РАжлИЧНых скОРОстьх НАгРЕВА.