J.M. Criado

Hallmarks of mechanochemistry: from nanoparticles to technology

The aim of this review article on recent developments of mechanochemistry (nowadays established as a part of chemistry) is to provide a comprehensive overview of advances achieved in the field of atomistic processes, phase transformations, simple and multicomponent nanosystems and peculiarities of mechanochemical reactions. Industrial aspects with successful penetration into fields like materials engineering, heterogeneous catalysis and extractive metallurgy are also reviewed. The hallmarks of mechanochemistry include influencing reactivity of solids by the presence of solid-state defects, interphases and relaxation phenomena, enabling processes to take place under non-equilibrium conditions, creating a well-crystallized core of nanoparticles with disordered near-surface shell regions and performing simple dry time-convenient one-step syntheses. Underlying these hallmarks are technological consequences like preparing new nanomaterials with the desired properties or producing these materials in a reproducible way with high yield and under simple and easy operating conditions. The last but not least hallmark is enabling work under environmentally friendly and essentially waste-free conditions (822 references).

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.

Kinetic Analysis of Complex Solid-State Reactions. A New Deconvolution Procedure

The kinetic analysis of complex solid-state reactions that involve simultaneous overlapping processes is challenging. A method that involves the deconvolution of the individual processes from the overall differential kinetic curves obtained under linear heating rate conditions, followed by the kinetic analysis of the discrete processes using combined kinetic analysis, is proposed. Different conventional mathematical fitting functions have been tested for deconvolution, paying special attention to the shape analysis of the kinetic curves. It has been shown that many conventional mathematical curves such as the Gaussian and Lorentzian ones fit kinetic curves inaccurately and the subsequent kinetic analysis yields incorrect kinetic parameters. Alternatively, other fitting functions such as the Fraser-Suzuki one properly fit the kinetic curves independently of the kinetic model followed by the reaction and their kinetic parameters, and moreover, the subsequent kinetic analysis yields the correct kinetic parameters. The method has been tested with the kinetic analysis of complex processes, both simulated and experimental.

Correlation between the shape of controlled-rate thermal analysis curves and the kinetics of solid-state reactions

Abstract A method for determining the real kinetics of solid-state reactions from analysis of the shape of controlled-rate thermal analysis curves is proposed. It is shown that this procedure provides an easy way for discriminating between “ n -order”, Avrami-Erofeev and diffusion kinetic laws. The theoretical conclusions were checked experimentally by studying the thermal decomposition of anhydrous nickel nitrate.

Thermal decomposition reactions of solids controlled by diffusion and phase-boundary processes: possible misinterpretation of the mechanism from thermogravimetric data

Abstract A comparative study of phase -boundary and diffusion-controlled reactions has been carried out using thermogravimetric data. The results reported support the hypothesis that a single TG diagram does not allow the determination of whether a solid decomposition reaction is controlled by a diffusion mechanism or governed by the movement of an interface coming from a nucleation process. However, the analysis of both a single TG diagram and an isothermal curve might be a quick and valid way for discerning between these mechanisms. These statements are confirmed by studying the thermal decomposition kinetics of Ba(OH) 2 and CaCO 3 .

Kinetic analysis of solid-state processes

A simple method for kinetic analysis of solid-state processes has been developed. A criteria capable of classifying different processes is explored here with a view toward visualizing the complexity of solid-state kinetics. They provide a useful tool for the determination of the most suitable kinetic model. The method has been applied to the analysis of crystallization processes in amorphous ZrO 2 and RuO 2 . It is found that the crystallization kinetics of as-prepared sample exhibits a complex behavior under nonisothermal conditions. This is probably due to an overlapping of the nucleation- and crystal-growth processes at the beginning of crystallization. As a consequence, the Johnson–Mehl–Avrami nucleation-growth model cannot be applied. A two-parameter autocatalytic model provides a good description of the crystallization process under isothermal and nonisothermal conditions.

A unified theory for the kinetic analysis of solid state reactions under any thermal pathway

The Ozawa concept of generalized time has been used for developing master plots for the different kinetic models describing solid state reactions. These plots can be indistinctly used for analysing isothermal or non-isothermal experimental data. It is demonstrated that it is not possible to discriminate the kinetic model from a single non-isothermal curve without a previous knowledge of the activation energy. However, it has been shown that the ln [(da/dt)/f(a)] data taken from a set of DTG curves obtained at different heating rates lie on a single straight line when represented as a function of 1/T only if the kinetic model really obeyed by the reaction is considered. Moreover, the true values of E and A are obtained from the slope and the intercept of this straight line.

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.

Non-isothermal transformation kinetics: remarks on the Kissinger method

It has been demonstrated that the activation energy of a solid state reaction can be determined by Kissingers method whatever the reaction mechanism. On the other hand the influence of both the kinetic law obeyed by the reaction and the values of E/RT on the error in the activation energy determined from Kissingers method has been analyzed. It has been shown that whatever the reaction mechanism this error is lower than 5%, provided that E/RT > 10.

The Accuracy of Senum and Yang's Approximations to the Arrhenius Integral

The accuracy of the integral of the Arrhenius equation, as determined from the 1st to the 4th degree rational approximation proposed by Senum and Yang, has been calculated. The precision of the 5th to 8th rational approximations, here proposed for the first time, has also been analyzed. It has been concluded that the accuracy increases by increasing the order of the rational approximation. It has been shown that these approximations to the Arrhenius equation integral would allow an accuracy better than 10−8 % in the E/RT range generally observed for solid state reactions. Moreover, it has been demonstrated that errors closed to 10−2 % can be obtained even for E/RT=1, provided that high enough degrees of rational approximation have been used. Thus, it would be reasonable to assume that high degree rational approximations for the Arrhenius integral could be used for the kinetic analysis of processes, like adsorption or desorption of gases on solid surfaces, which can take place at low temperatures with very low values of E/RT.