J. M. Criado

Universidad de Sevilla, Hispalis, Andalusia, Spain

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Publications (137)166.33 Total impact

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  • M. D. ALCALA, C. REAL, J. M. CRIADO
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 01/2010; 27(43).
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    ABSTRACT: The micro and nanostructure of Cu-Al, Cu-V and Cu-Ti alloys produced by reactive milling were analyzed using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Samples with different milling times (t= 0, 10, 20 and 30 h) were considered. The grain size, dislocation density and residual microstrain were evaluated form the XRD data using the Williamson-Hall and Klug-Alexander methods. The evolution of texture as a function of milling time was also studied using XRD. It was found, using TEM, that the grain size and dispersoid size were nanometric in all three alloys considered.Se analizó la micro y nano estructura de aleaciones Cu-Al, Cu-V y Cu-Ti obtenidas por molienda reactiva, mediante difracción de rayos X (XRD) y microscopía electrónica de transmisión (TEM). Se consideraron muestras con distintos tiempos de molienda (t= 0, 10, 20 y 30 h). A partir de los datos XRD, usando los métodos de Williamson- Hall y Klug-Alexander, se evaluaron el tamaño de grano, la densidad de dislocaciones y la microdeformación residual; también se estudió la evolución de la textura de la matriz de cobre en función del tiempo de molienda. En los polvos molidos durante 30 h, de las tres aleaciones consideradas, se encontró, por TEM, que los tamaños de grano y de los dispersoides desarrollados son nanométricos.
    Revista de Metalurgia. 01/2010;
  • C. REAL, M. D. ALCALA, J. M. CRIADO
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 01/2010; 27(49).
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    ABSTRACT: The precipitation processes in a Cu–1.0at.%Co–0.5at.%Ti (Cu–1.5at.%Co2Ti) alloy were studied using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and microhardeness measurements. The analysis of the calorimetric curves from room temperature to 900K shows the presence of two exothermic reactions attributed to the formation of CoTi and Co2Ti particles in the copper matrix. On the basis of enthalpy calculations, it was found that the decomposition begins with the precipitation of CoTi, followed by the formation of Co2Ti particles. The activation energies calculated using the modified Kissinger method were lower than the ones corresponding to diffusion of cobalt and titanium in copper. Kinetic parameters were obtained by a convolution method based on the Johnson–Mehl–Avrami (JMA) formalism. The values obtained for the parameter n were indicative of a particle nucleation process from preexistent nuclei. Microhardness measurements and TEM micrographs confirmed the formation of the mentioned phases. KeywordsCopper alloys-DSC-Kinetics-Precipitation-Cu–Co–Ti alloys
    Journal of Thermal Analysis and Calorimetry 01/2010; 100(3):975-980. · 1.98 Impact Factor
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    ABSTRACT: Combined kinetic analysis has been applied for the first time to the thermal degradation of polymeric materials. The combined kinetic analysis allows the determination of the kinetic parameters from the simultaneous analysis of a set of experimental curves recorded under any thermal schedule. The method does not make any assumptions about the kinetic model or activation energy and allows analysis even when the process does not follow one of the ideal kinetic models already proposed in the literature. In the present paper the kinetics of the thermal degradation of both polytetrafluoroethylene (PTFE) and polyethylene (PE) have been analysed. It has been concluded, without previous assumptions on the kinetic model, that the thermal degradation of PTFE obeys a first order kinetic law, while the thermal degradation of PE follows a diffusion-controlled kinetic model.
    Polymer Degradation and Stability 07/2009; 94(11):2079-2085. · 2.77 Impact Factor
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    ABSTRACT: The dynamic heating rate method developed by TA Instruments (Hi-ResTM) is a kind of sample controlled thermal analysis in which a linear relationship between the logarithm of the heating rate and the rate of mass change is imposed. It is shown in this paper that the reacted fraction at the maximum reaction rate strongly depends on the parameters selected for the Hi-Res heating algorithm, what invalidates the use of the Kissinger method for analysing Hi-Res data unless that the reaction fits a first order kinetic law. Only in this latter case, it has been demonstrated that it is not required that a constant value of the reacted fraction at the maximum reaction rate is fulfilled for determining the activation energy from the Kissinger method. In such a case the Kissinger plot gives the real activation energy, independently of both the heating schedule used and the value of the reacted fraction, αm, at the maximum.
    Journal of Thermal Analysis and Calorimetry 11/2008; 94(2):427-432. · 1.98 Impact Factor
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    ABSTRACT: A critical study of the use of isoconversional methods for the kinetic analysis of non-isothermal data corresponding to processes with either a real or an apparent variation of the activation energy, E, with the reacted fraction, α, has been carried out using for the first time simulated curves. It has been shown that the activation energies obtained from model-free methods are independent of the heating rate. However, the activation energy shows a very strong dependence of the range of heating rates used for simulating the curves if the apparent change of E with α is caused by overlapping processes with different individual activation energies. This criterion perhaps could be used for determining if a real dependence between E and α is really occurring.
    Journal of Thermal Analysis and Calorimetry 01/2008; 92(1):199-203. · 1.98 Impact Factor
  • E. Donoso, G. Díaz, J. M. Criado
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    ABSTRACT: The precipitation process for a concentration of CoTi of super-saturated solutions of Cu-0.50 at.% Co-0.45 at.% Ti (Cu-1 at.% CoTi) was studied through differential scanning calorimetry (DSC) and microhardness measurements. The analysis of the calorimetric curves between the environmental temperature and 900 K shows the presence of only one exothermic reaction attributed to the formation of CoTi particles in the matrix of copper. The energy of activation estimated by using the modified Kissinger method came out much lower than the corresponding to the diffusion of the cobalt and titanium in copper. We may attribute this fact to the strong contribution of the vacancies introduced by quenching. We used the formalism of Johnson-Mehl-Avrami (JMA) to assess the kinetic parameters. The energetic and kinetic evaluations and the molar heats of precipitation obtained from the isochor of van’t Hoff allow us to infer that the reaction corresponds to the formation of CoTi precipitates. The isothermal kinetics of precipitation reaction could be represented satisfactory by an overall kinetic function based in a macroscopic parameter (Vickers hardness). The kinetic parameters obtained from microhardness model are in agreements with those obtained from DSC traces.
    Journal of Thermal Analysis and Calorimetry 01/2008; 91(2):491-495. · 1.98 Impact Factor
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    ABSTRACT: The SCTA method implies to control the temperature in such a way that the reaction rate changes with the time according to a function previously defined by the user. Constant Rate Thermal Analysis (CRTA) is one of the most commonly used SCTA methods and implies achieving a temperature profile at which the reaction rate remains constant all over the process at a value previously selected by the user. This method permits to minimize the influence of heat and mass transfer phenomena on the forward reaction. The scope of this work is to develop a universal CRTA temperature controller that could be adapted to any thermoanalytical device. The thermoanalytical signal is programmed to follow a preset linear trend by means of a conventional controller that at the time controls a second conventional temperature programmer that forces the temperature to change for achieving the trend programmed for the thermoanalytical signal. Examples of the performance of this control system with a Thermobalance and a Thermomechanical Analyser (TMA) are given.
    Journal of Thermal Analysis and Calorimetry 01/2007; 87(1):297-300. · 1.98 Impact Factor
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    ABSTRACT: The influence of grinding and surrounding atmosphere on the thermal transformations of zirconia gel has been studied. The XRD analysis of the products obtained by thermal decomposition of zirconia gel has shown that pure tetragonal phase is obtained if the gel decomposition is carried out under high vacuum or dry inert atmosphere, while monoclinic zirconia results from the decomposition of the zirconia gel under air or inert gas saturated with water vapour. A mechanism for the thermal crystallisation of zirconia gel has been proposed from the study of the variation of the crystal size of the monoclinic and tetragonal zirconia phases formed as a function of the temperature and the surrounding atmosphere.The thermal decomposition of ground zirconia leads to the formation of ZrO2 with a percentage of tetragonal phase closed to 90% irrespectively of the surrounding atmosphere. The stabilisation of the tetragonal phase by grinding seems to be connected with the formation of tetragonal zirconia nuclei that cannot be observed by XRD. The crystallisation enthalpy measurements carried out by DSC support this conclusion.
    Journal of Physics and Chemistry of Solids - J PHYS CHEM SOLIDS. 01/2007; 68(5):824-829.
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    ABSTRACT: Using differential scanning calorimetry (DSC), the precipitation process of nickel and aluminium atoms from a solid solution of Cu-Ni-Al were studied. Analysis of calorimetric traces displayed shows the presence of two exothermic reactions (stage 1 and 2), which were interpreted as the formation of two types of precipitates. The first stage corresponds to the formation of an equilibrium b (NiAl) phase, whilst stage 2 corresponds to the formation of g’ precipitate with Ni3Al stoichiometric composition. It is observed the shift of the traces to lower temperatures while linear heating rate decrease. The activation reaction energies were evaluated from modified Kissinger’s method. Kinetic parameters were calculated by means Johnson-Mehl-Avrami formalism. The values obtained for parameter n were indicative of a particle nucleation process from pre-existent nucleus. Microhardness measurements and micrographies obtained by transmission electron microscopy were helpful to confirm the formation and the dissolution of the mentioned phases.Mediante calorimetría diferencial de barrido (DSC), se estudió el proceso de precipitación de átomos de níquel y aluminio a partir de una solución sólida de Cu-Ni-Al. El análisis de las curvas calorimétricas muestra la presencia de dos reacciones exotérmicas (etapas 1 y 2), que se interpretan como la formación de dos tipos de precipitados. La primera etapa corresponde a la formación de la fase de equilibrio b (NiAl), en tanto que la etapa 2 corresponde a la formación del precipitado g’ de composición estequiométrica Ni3Al. Además, se observa que las curvas se desplazan a temperaturas más bajas a medida que la velocidad de calentamiento lineal decrece. Las energías de activación de las reacciones fueron evaluadas a partir de un método de Kissinger modificado. Los parámetros cinéticos se calcularon mediante el formalismo de Johnson- Mehl-Avrami. Los valores de n obtenidos son indicativos de un proceso de nucleación de partículas a partir de núcleos pre existentes. Las medidas de microdureza y las micrografías obtenidas por microscopía electrónica de transmisión ayudaron a confirmar la formación de las fases antes indicadas.
    Revista de Metalurgia. 01/2007;
  • Revista De Metalurgia - REV METALURGIA. 01/2007; 43(2).
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    ABSTRACT: The combined kinetic analysis implies a simultaneous analysis of experimental data representative of the forward solid-state reaction obtained under any experimental conditions. The analysis is based on the fact that when a solid-state reaction is described by a single activation energy, preexponetial factor and kinetic model, every experimental T-alpha-dalpha/dt triplet should fit the general differential equation independently of the experimental conditions used for recording such a triplet. Thus, only the correct kinetic model would fit all of the experimental data yielding a unique activation energy and preexponential factor. Nevertheless, a limitation of the method should be considered; thus, the proposed solid-state kinetic models have been derived by supposing ideal conditions, such as unique particle size and morphology. In real systems, deviations from such ideal conditions are expected, and therefore, experimental data might deviate from ideal equations. In this paper, we propose a modification in the combined kinetic analysis by using an empirical equation that fits every f(alpha) of the ideal kinetic models most extensively used in the literature and even their deviations produced by particle size distributions or heterogeneities in particle morphologies. The procedure here proposed allows the combined kinetic analysis of data obtained under any experimental conditions without any previous assumption about the kinetic model followed by the reaction. The procedure has been verified with simulated and experimental data.
    The Journal of Physical Chemistry A 12/2006; 110(45):12456-62. · 2.77 Impact Factor
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    ABSTRACT: β-SiALON has been obtained from carbothermal reduction of kaolinite by applying the sample controlled reaction temperature (SCRT) method. By using this technique for the synthesis it has been possible to obtain composites with different percentages of SiALON and with different microstructures.
    Journal of Materials Science 03/2006; 41(7):1933-1938. · 2.31 Impact Factor
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    ABSTRACT: Thermal behaviour of mechanochemically synthesized nanocrystalline CuS particles by high-energy milling in an industrial mill has been studied. Structure properties were characterized by X-ray powder diffraction that reveals the formation of copper sulphide CuS as well as of copper sulphate CuSO4·5H2O. Thermal properties of the as-prepared products were studied by the differential scanning calorimetry together with X-ray inspection for detection by pass products formed. The decomposition of the as-prepared sample has been studied too. Thermal stability of the anhydrous CuSO4 formed by the thermal decomposition is lower than the thermal stability of non-milled samples. The final product of the thermal decomposition is metallic copper instead of Cu2O, which is stable up to 1100°C. Differential scanning calorimetry (DSC) analysis proved that the percentage of chalcantite in the covellite mechanochemically synthesized by high-energy milling is 48–51%.
    Thermochimica Acta - THERMOCHIM ACTA. 01/2006; 440(1):19-22.
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    ABSTRACT: The integral methods are extensively used for the kinetic analysis of solid-state reactions. As the Arrhenius integral function [p(x)] does not have an exact analytical solution, different approximated equations have been proposed in the literature for performing the kinetic analysis of experimental integral data. Since the first approximation of Van Krevelen, a large number of equations have been proposed with the objective of increasing the precision in the determination of the Arrhenius integral, as checked from the standard deviation of the approximated function with regard to the real exact value of the integral. However, the main application of these equations is the determination of the kinetic parameters, in particular activation energies, and not the computation of the Arrhenius integral. A systematic analysis of the errors involved in the determination of the activation energy from these integral methods is still missing. A comparative study of the precision of the activation energy as a function of x and T computed from the different integral methods has been carried out. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 658–666, 2005
    International Journal of Chemical Kinetics 09/2005; 37(11):658 - 666. · 1.19 Impact Factor
  • J. M. Criado, L. A. Pérez-Maqueda
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    ABSTRACT: The SCTA methods for the kinetic analysis of solid-state reactions have been reviewed. It has been shown that these methods present two important advantages with regards to the more conventional rising temperature experiments. Firstly, they have a higher resolution power for discriminating among the reaction kinetic models and, secondly, SCTA is a powerful tool for minimizing the influence of the experimental conditions on the forward reaction.
    Journal of Thermal Analysis and Calorimetry 02/2005; 80(1):27-33. · 1.98 Impact Factor
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    ABSTRACT: The dependence of the preexponential factor on the temperature has been examined and the errors involved in the activation energy calculated from isothermal and non-isothermal methods without considering such dependence have been estimated. It has been shown that the error in the determination of the activation energy calculated ignoring the dependence of Aon Tcan be rather large and it is dependent on x=E/RT, but independent of the experimental method used. It has been also shown that the error introduced by omitting the dependence of the preexponential factor on the temperature is considerably larger than the error due to the Arrhenius integral approach used for carrying out the kinetic analysis of TG data.
    Journal of Thermal Analysis and Calorimetry 01/2005; 82(3). · 1.60 Impact Factor

Publication Stats

758 Citations
166.33 Total Impact Points

Institutions

  • 1979–2010
    • Universidad de Sevilla
      • Inorganic Chemistry
      Hispalis, Andalusia, Spain
  • 1999–2000
    • Scientific Research Centre "Isla de la Cartuja"
      • Institute of Materials Science
      Hispalis, Andalusia, Spain
  • 1990–1992
    • Materials Science Institute of Barcelona
      Barcino, Catalonia, Spain