Kinetics and Mechanism of the Reaction Between Zinc Oxide and Barium Carbonate
01 Sep 1967-Journal of the American Ceramic Society (Blackwell Publishing Ltd)-Vol. 50, Iss: 9, pp 484-488
TL;DR: In this paper, the authors used thermogravimetric analysis to monitor the percent reaction versus time of BaCO3 and ZnO and found that the activation energy for the reaction of pure Znoxide was 54.6 kcal/mole, which cannot be explained by the quasi-chemical theory of solids.
Abstract: The kinetics of reaction between BaCO3 and ZnO were studied using thermogravimetric analysis to monitor the percent reaction versus time. Solid state reaction models based on (a) product growth controlled by diffusion through a continuous product layer, (b) product growth controlled by phase boundary reactions, and (c) the concept of an order of reaction, were invalid for the reaction studied. The kinetics of the reaction were described by the kt=–ln (1 –x)⅔ nuclei growth equation. The defect nature of the zinc oxide studied was altered by doping with Li2O and Cr2O3. The activation energy for the reaction of BaCO3 and pure ZnO was 54.6 kcal/mole. The changes in activation energy with the type and amount of ZnO doping cannot be accounted for by the quasi-chemical theory of solids.
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TL;DR: In this article, the effects of particle size distributions, shape variations and time distributions for the beginning of the reaction on each one of the particles composing the powder are quantitatively analyzed and their interference in the SPA procedure is estimated.
125 citations
TL;DR: In this article, an extensive in situ and ex situ structural study is performed on the mechanism of crystallization from solution of 3D formamidinium tin iodide (FASnI(3)), 2D phenylethylammonium tin ionide (PEA(2)SnI(4)), and hybrid PEA(2)-FA(n)(-1)Sn(n)I(+1) Ruddlesden-Popper perovskites.
Abstract: Knowledge of the mechanism of formation, orientation, and location of phases inside thin perovskite films is essential to optimize their optoelectronic properties. Among the most promising, low toxicity, lead-free perovskites, the tin-based ones are receiving much attention. Here, an extensive in situ and ex situ structural study is performed on the mechanism of crystallization from solution of 3D formamidinium tin iodide (FASnI(3)), 2D phenylethylammonium tin iodide (PEA(2)SnI(4)), and hybrid PEA(2)FA(n)(-1)Sn(n)I(3)(n)(+1) Ruddlesden-Popper perovskites. Addition of small amounts of low-dimensional component promotes oriented 3D-like crystallite growth in the top part of the film, together with an aligned quasi-2D bottom-rich phase. The sporadic bulk nucleation occurring in the pure 3D system is negligible in the pure 2D and in the hybrid systems with sufficiently high PEA content, where only surface crystallization occurs. Moreover, tin-based perovskites form through a direct conversion of a disordered precursor phase without forming ordered solvated intermediates and thus without the need of thermal annealing steps. The findings are used to explain the device performances over a wide range of composition and shed light onto the mechanism of the formation of one of the most promising Sn-based perovskites, providing opportunities to further improve the performances of these interesting Pb-free materials.
85 citations
TL;DR: In this article, the thermal decomposition of manganese(II) acetate tetrahydrate was studied using isothermal and dynamic thermogravimetric techniques, and it was shown that the reactions are best described by the phase boundary and random nucleation models.
64 citations
TL;DR: In this paper, the formation of BaZrO 3 from very fine (70-90 nm) ZrO 2 powders and coarser (∼1 μm) BaCO 3 powders has been studied in dry and humid air up to 1300°C using TGA/DTA, XRD, SEM, TEM, and EDS microanalysis.
Abstract: The formation of BaZrO 3 from very fine (70-90 nm) ZrO 2 powders and coarser (∼1 μm) BaCO 3 powders has been studied in dry and humid air up to 1300°C using TGA/DTA, XRD, SEM, TEM, and EDS microanalysis. In the temperature range 900°-1100°C, barium is rapidly transported at the surface of the ZrO 2 particles and reacts, forming BaZrO 3 . The compound grows as a concentric layer with gradual consumption of the central ZrO 2 particle. The overall formation kinetics of BaZrO 3 is well described by a diminishing core model, and the most likely rate-determining step is a phase-boundary process at the ZrO 2 -BaZrO 3 moving interface. The size and shape of the final particles is generally determined by the morphology of the starting ZrO 2 particles and not by that of the BaCO 3 . The reaction is faster in humid air than in dry air, and the activation energy decreases from 294 kJ.mol- 1 (dry air) to 220 kJ.mol- 1 (humid air). When the fraction reacted is >80-90 mol%, the reaction rate rapidly decreases.
43 citations
TL;DR: In this article, the kinetics of the reaction MgO+A12O3+MgAl2O4 were studied using both unsized "small" and sized "large" particles of the reactants within narrow size distributions and uniform shapes.
Abstract: The kinetics of the reaction MgO+A12O3+MgAl2O4 was studied using both unsized “small” (∼1 to 3 pm) and sized “large” (∼50 and 100 μm) particles of the reactants within narrow size distributions and uniform shapes. The data were fitted to various equations commonly used in kinetic analyses of isothermal reactions of solids, analyzed by graphical analysis and linear regression analysis, and compared in terms of the predictive mean square error (MSE) criterion. Graphical and linear regression analysis showed that the reaction could be described almost equally well by first-order kinetics, the equation derived by Avrami-Erofe'ev for the nucleation and growth model, and the equations of Jander, Carter, and Ginstling-Brounshtein for diffusion models. The MSE method gave similar results, except that the model of Avrami-Erofe'ev was marginally better than the other four equations. The results are compared with those of the systems BaCO3+Fe2O3 and MgO+Fe2O3 studied previously.
39 citations
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TL;DR: In this paper, the theory of phase change is developed with the experimentally supported assumptions that the new phase is nucleated by germ nuclei which already exist in the old phase, and whose number can be altered by previous treatment.
Abstract: The theory of the kinetics of phase change is developed with the experimentally supported assumptions that the new phase is nucleated by germ nuclei which already exist in the old phase, and whose number can be altered by previous treatment. The density of germ nuclei diminishes through activation of some of them to become growth nuclei for grains of the new phase, and ingestion of others by these growing grains. The quantitative relations between the density of germ nuclei, growth nuclei, and transformed volume are derived and expressed in terms of a characteristic time scale for any given substance and process. The geometry and kinetics of a crystal aggregate are studied from this point of view, and it is shown that there is strong evidence of the existence, for any given substance, of an isokinetic range of temperatures and concentrations in which the characteristic kinetics of phase change remains the same. The determination of phase reaction kinetics is shown to depend upon the solution of a functional equation of a certain type. Some of the general properties of temperature‐time and transformation‐time curves, respectively, are described and explained.
9,458 citations
TL;DR: In this paper, the authors give numerical tables of F(α) in relation to α, and to (t/t0.5) where t 0.5 is the time for 50% reaction and A is a calculable constant depending on the form of F (α).
Abstract: Many solid state reactions can be represented by equations of the type F(α) =kt, where α is the fraction of material reacted in time, t. These equations can be expressed in the form F(α) =A(t/t0.5) where t0.5 is the time for 50% reaction and A is a calculable constant depending on the form of F(α). Numerical tables are given of F(α) in relation to α, and to (t/t0.5), for nine equations corresponding to reactions which are diffusion controlled, or are reaction-rate controlled, or obey first order kinetics, or follow the equations of Avrami and Erofe'ev. The application of the tables to the analysis of experimental data is described.
801 citations
TL;DR: In this paper, a model for solid-solid or solid-gas reactions between spherical particles and a fine powder or gas has been developed, and the oxidation of uniformly sized nickel spheres has been shown to fit this model to 100% reaction.
Abstract: A model for solid‐solid or solid‐gas reactions between spherical particles and a fine powder or gas has been developed. The oxidation of uniformly sized nickel spheres has been shown to fit this model to 100% reaction. Previously reported models are inadequate because they do not meet the boundary conditions set down and because the volume of the product was assumed to equal that of one of the reactants. The inadequacy of earlier experimental results has been explained by the failure to experimentally meet the boundary conditions imposed.
401 citations
TL;DR: In this article, the diffusion of zinc ions through the spinel layer is the rate controlling mechanism for spinel formation and the activation energy for the process is 54,200 cal/mole.
Abstract: Quantitative X-ray diffraction methods were used to define the kinetics of spinel formation. Diffusion controlled reaction rate constants were calculated on the basis of the reaction models of Jander, Dunwald-Wagner, Valensi, Zhuravlev et al., Ginstling-Brounshte'n, and Kroger-Ziegler. The model proposed by Valensi is valid for describing solid-solid reaction rates in the later stages of the reaction. Inert markers indicated that diffusion of zinc ions through the spinel layer is the rate controlling mechanism. The activation energy for the process is 54,200 cal/mole. In the early stages of the reaction there is a second-order phase boundary kinetic process with an activation energy of 28,700 cal/ mole. The rate of chemical combination at the zinc-oxide-spinel phase boundary is believed to be rate controlling.
73 citations