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Jordi Farjas

Bio: Jordi Farjas is an academic researcher from University of Girona. The author has contributed to research in topics: Thermal analysis & Thermal decomposition. The author has an hindex of 23, co-authored 117 publications receiving 1933 citations. Previous affiliations of Jordi Farjas include University of Barcelona & Autonomous University of Barcelona.


Papers
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TL;DR: In this paper, a quasi-exact analytical solution of Avrami's model when the transformation takes place under continuous heating was obtained with different activation energies for both nucleation and growth rates.

157 citations

Posted Content
TL;DR: In this paper, a quasi-exact analytical solution of Avrami's model when the transformation takes place under continuous heating was obtained with different activation energies for both nucleation and growth rates, which is also a solution of the so-called Kolmogorov-Johnson-Mehl-Avrami transformation rate equation.
Abstract: Avrami's model describes the kinetics of phase transformation under the assumption of spatially random nucleation. In this paper we provide a quasi-exact analytical solution of Avrami's model when the transformation takes place under continuous heating. This solution has been obtained with different activation energies for both nucleation and growth rates. The relation obtained is also a solution of the so-called Kolmogorov-Johnson-Mehl-Avrami transformation rate equation. The corresponding non-isothermal Kolmogorov-Johnson-Mehl-Avrami transformation rate equation only differs from the one obtained under isothermal conditions by a constant parameter, which only depends on the ratio between nucleation and growth rate activation energies. Consequently, a minor correction allows us to extend the Kolmogorov-Johnson-Mehl-Avrami transformation rate equation to continuous heating conditions.

136 citations

Journal ArticleDOI
TL;DR: In this article, the discrepancies between isoconversional methods when applied to complex transformations are analyzed and the authors conclude that conventional integral methods based on integrated equations are essentially incorrect when dealing with variable activation energy.
Abstract: We will analyze the discrepancies between isoconversional methods when applied to complex transformations. The practical analysis of particular transformations leads us to conclude that (a) conventional integral methods based on integrated equations are essentially incorrect when dealing with variable activation energy; and (b) experimental inaccuracies and noise tend to give an apparent evolution of the energy variation, so that, non-constancy of the activation energy does not necessarily mean deviations from single-step transformations with constant activation energy.

123 citations

Journal ArticleDOI
TL;DR: In this paper, the discrepancies between isoconversional methods when applied to complex transformations are analyzed and the authors conclude that conventional integral methods based on integrated equations are essentially incorrect when dealing with variable activation energy.
Abstract: We will analyze the discrepancies between isoconversional methods when applied to complex transformations. The practical analysis of particular transformations leads us to conclude that (a) conventional integral methods based on integrated equations are essentially incorrect when dealing with variable activation energy; and (b) experimental inaccuracies and noise tend to give an apparent evolution of the energy variation, so that, non-constancy of the activation energy does not necessarily mean deviations from single-step transformations with constant activation energy.

59 citations


Cited by
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TL;DR: In this article, the authors have developed recommendations for reliable evaluation of kinetic parameters (the activation energy, the preexponential factor, and the reaction model) from the data obtained by means of thermal analysis methods such as TGA, differential scanning calorimetry (DSC), and differential thermal analysis (DTA).

4,112 citations

Journal ArticleDOI
TL;DR: This Review focuses on the analysis of new approaches and results in the field of solution combustion synthesis (SCS) obtained during recent years, emphasizing the chemical mechanisms that are responsible for rapid self-sustained combustion reactions.
Abstract: Solution combustion is an exciting phenomenon, which involves propagation of self-sustained exothermic reactions along an aqueous or sol–gel media. This process allows for the synthesis of a variety of nanoscale materials, including oxides, metals, alloys, and sulfides. This Review focuses on the analysis of new approaches and results in the field of solution combustion synthesis (SCS) obtained during recent years. Thermodynamics and kinetics of reactive solutions used in different chemical routes are considered, and the role of process parameters is discussed, emphasizing the chemical mechanisms that are responsible for rapid self-sustained combustion reactions. The basic principles for controlling the composition, structure, and nanostructure of SCS products, and routes to regulate the size and morphology of the nanoscale materials are also reviewed. Recently developed systems that lead to the formation of novel materials and unique structures (e.g., thin films and two-dimensional crystals) with unusual...

841 citations

Journal Article
TL;DR: This paper discusses how and why wrinkles/buckles form in various materials, and describes several examples from everyday life that demonstrate that wrinkling or buckling is indeed a commonplace phenomenon that spans a multitude of length scales.
Abstract: The English-language dictionary defines wrinkles as "small furrows, ridges, or creases on a normally smooth surface, caused by crumpling, folding, or shrinking". In this paper we review the scientific aspects of wrinkling and the related phenomenon of buckling. Specifically, we discuss how and why wrinkles/buckles form in various materials. We also describe several examples from everyday life, which demonstrate that wrinkling or buckling is indeed a commonplace phenomenon that spans a multitude of length scales. We will emphasize that wrinkling is not always a frustrating feature (e.g., wrinkles in human skin), as it can help to assemble new structures, understand important physical phenomena, and even assist in characterizing chief material properties.

670 citations

Journal ArticleDOI
TL;DR: Titanium oxide nanotubes were successfully grown from a titanium plate by direct anodic oxidation with 0.2 wt % hydrofluoric acid being the supporting electrolyte and look like honeywell with the structure similar to that of porous alumina obtained by the same technique.
Abstract: Titanium oxide nanotubes were successfully grown from a titanium plate by direct anodic oxidation with 0.2 wt % hydrofluoric acid being the supporting electrolyte. These nanotubes are of uniform size and are well-aligned into high-density arrays. They look like honeywell with the structure similar to that of porous alumina obtained by the same technique. TiO2 anatase phase was identified by X-ray diffraction. Significant blue-shift in the spectrum of UV−vis absorption was observed. The mechanism of the novel, simple, and direct growth of the nanotubes was postulated. To investigate their potentials in environmental applications, degradation of pentachlorophenol (PCP) in aqueous solution was carried out using photoelectrocatalytic (PEC) processes, comparing with electrochemical process (EP) and photocatalytic (PC). A significant photoelectrochemical synergetic effect was observed. The kinetic constant of PEC degradation of PCP using TiO2 nanotubes electrode was 86.5% higher than that using TiO2 film electr...

423 citations