Kinetics and mechanism of the thermal dehydration of calcium oxalate monohydrate

Tanaka, Haruhiko; Ohshima, Satoshi; Ichiba, Sumio; Negita, Hisao

doi:10.1016/0040-6031(81)87029-3

Cited by 60 publications

(35 citation statements)

References 30 publications

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“…Therefore, in accordance with the suggested method, we have found a value of the rate constant (K i) invariant with respect to F(~) at isokinetic temperature (T i) for every heating rate used in [14]. Actually, we have obtained concrete relations (1), i.e.…”

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confidence: 64%

“…On the basis of vast experimental material on heterogeneous catalysis obtained by many authors, in [13] the existence of such sets is shown, which is manifested by the validity of the "supercorrelation" B = f-ge (2) which is the Arrhenius equation for the coordinates of the centre of pencils arising from the Arrhenius straight lines according to (1). In the region of non-isothermal kinetics, the validity of (2) is also confirmed by the experimental data of [14] on the kinetics of calcium oxalate dehydration studied by isothermal and non-isothermal methods, The first of these methods was used to find the A and E values invariant with respect to the changes of some experimental conditions and calculation methods. These values range from 10.84 to 11.33 s -1 for IogA and 27.95 to 28.57 kcal mol-1 for E. The non-isothermal experiments with variations of the heating rate and the theoretical model for the fraction conversion function F(~) have revealed much wider ranges of the obtained log A and E: 40.0 to 0.127 and 86.1 to 5.08, respectively.…”

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confidence: 71%

“…In this Figure, -3.2 Fig. 2 The dependence of B on e, determined by treating data [14] are, however, much smaller than the range of uncertainty for log Ai and Ei obtained by the non-isothermal method, even after F((~) is selected on the basis of the isothermal data.…”

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confidence: 80%

“…Non-isothermal kinetic data do not practically permit us to give preference to any function F(~) over the 12 functions tested in [14], since a high correlation coefficient (from 0.9705 to 0.9998) corresponds to each of the function. Therefore, in accordance with the suggested method, we have found a value of the rate constant (K i) invariant with respect to F(~) at isokinetic temperature (T i) for every heating rate used in [14].…”

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confidence: 98%

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A method of finding invariant values of kinetic parameters

Лесникович¹,

Levchik²

1983

Journal of Thermal Analysis

192

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A method of calculating the Arrhenius parameters has been proposed, based on an evaluation of the coordinates of intersection of greatly extended confidence regions determined in solving the inverse kinetic problem. The validity of this method is illustrated by comparison of the Arrhenius parameters found from non-isothermal and isothermal data reported by other investigators.The kinetic parameters characterizing the chemical stage of solid-phase reactions are determined by isothermal kinetic methods, provided certain approaches to the selection of a theoretical model are observed and rigid constraints are imposed on the experiment [1]. Such constraints may yield a positive result in non-isothermal kinetics [2] as well. However, finding t'he kinetic parameters from experimental data, i.e. solving an invers kinetic problem, may run into certain difficulties, for such problems are ill-posed mathematical problems characterized by a poor statement of the problem conditions (the determinant of the information matrix is close to zero). Therefore, such problems have no unique solution unless special methods are used [3]. This problem was analyzed in [4,5] for dynamic thermogravimetry conditions. The poor statement of the problem conditions determines its solution in the form of a greatly extended region, so that experimental data can be described with equal accuracy with the help of Arrhenius parameters A and E variable over a very wide range in this region, the compensative effect being an artefact of computation. Calculated by different methods, A and E characterize the mathematical method used rather than the reaction itself. This also follows from [6][7][8][9]. The artefact can be eliminated, The invariant characteristics of the process can also be calculated with a different, quite general means, by constructing a statistical model of the process as a polynomial [3]. In this paper a method is suggested for determining invariant values of the activation energy (E) and a pre-exponential factor (A), which corresponds to the above general approach. Isokinetic temperature and a polynomial as a polylinear expansion [12] are used in the method. This makes it very simple to use in computation and provides a very clear interpretation that reveals the physical meaning of the invariants

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confidence: 64%

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confidence: 71%

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confidence: 80%

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confidence: 98%

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A method of finding invariant values of kinetic parameters

Лесникович¹,

Levchik²

1983

Journal of Thermal Analysis

192

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“…From the conventional isothermal analysis by means of TG [10], a random nucleation and subsequent growth mechanism, Am, was selected for the dehydration of Li2SO ~ 9 H20. Table 4 shows the correlation coefficient r and error 6 in the least square fitting of F(e) vs. t plot.…”

Section: Kinetic Deuterium Isotope Effectsmentioning

confidence: 99%

Effect of deuteration on the thermal dehydration of lithium sulfate monohydrate

Tanaka

Fujimaru

1982

Journal of Thermal Analysis

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Effects of deuteration on the thermal stability, enthalpy change and kinetic parameters for the thermal dehydration of Li2SO 4 9 H20 were examined by means of TG and DSC. The enthalpy change for the monohydrate was smaller by 1.63 -}-0.75 k J/tool than that for the monodeuterate. The rate constant for the monohydrate was a little larger than that for the monodeuterate. However, the thermal stability, activation energy and frequency factor were practically unaffected by deuteration of the hydrate. It is suggested that the activation entropy as well as the activation energy should be considered in explaining the kinetic deuterium isotope effect in the thermal dehydration of Li2SOa " "H20.Recently, we have determined effects of deuteration on the thermal dehydration processes of CAC204 9 H20 [1], H3BO3 [2,3] and CuSO4 9 5 H20 [4,5] by means of TG and DSC. It was found from these studies that the size or direction of such an isotope effect varies from sample to sample. In addition, these results proved to be useful for the better understanding of the dehydration processes.It thus seems of interest to study the dehydration process of various hydrates extensively by means of TG and DSC. The present paper deals with both thermodynamic and kinetic isotope effects of deuterium in the thermal dehydration of Li2SO4 9 H20 by means of TG-DSC recorded simultaneously, the kinetics [6,7] and thermodynamics [8] having been examined earlier. ExperimentalReagent grade Li2SO 4 9 H20 was ground and sieved to the size fraction of 170-200 mesh. The monohydrate was dehydrated thermally and the anhydrous product was rehydrated with water vapour in a small sealed bottle to give Li2SO 4 9 9 H20. The deuterium analog was prepared with 99.8 % deuterium oxide vapour under identical conditions. The identification was made by means of IR and TG. About 1.56 9 10 -4 tool of the sample was weighed into a platinum crucible 5 mm in diameter and 2.5 mm in depth, a-Alumina was used as a reference material. TG-DSC traces were recorded simultaneously at a heating rate of 1.04 K/rain

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