Decomposition Of Calcium Oxalate Monohydrate Research Articles

Potentialities of mass spectrometry on activation energy and secondary reactions determination of calcium oxalate thermal decomposition

AbstractThis work investigates the potentialities of the thermal analysis (TA) coupled with the mass spectrometry (MS) technique by studying the thermal decomposition of calcium oxalate monohydrate (CaC2O4·H2O). The aim of this work is twofold: to demonstrate, at first, the efficacy of coupling the thermal gravimetric (TG)‐MS experimental approach to check the presence of intermediate reactions beyond the conventional three‐step decomposition: dehydration, decarbonylation, and decarbonation; second, to test the reliability of different modeling approaches in determining the activation energy (E) including, as innovative alternative, the use of the MS signals. The TA is carried out at selected constant heating rates by recording both the thermal gravimetric analysis, differential thermal analysis) profiles, and, simultaneously from the MS data, the signals of the total ion current and the ion currents selected to monitor the release of the H2O, CO, and CO2 species. These experimental results are effective in determining the E through different modeling approaches based on the maximum reaction rate method and isoconversional procedures including both TG and MS signals. Coupling the TA‐MS technique has allowed us to check the concurrent presence of the dismutation reaction of carbon monoxide, occurring during the decarbonylation event, and to determine the corresponding E value (E = 169.7 kJ/mol). These results present a surprising correlation between the global enthalpy of the two reactions involved in this second step and their activation energy values. On the whole, the results satisfy the conventional constraints usually adopted to test the reliability of the E results and are consistent with the majority of the datasets published in the literature on this subject.

Topochemical Synthesis of Alkali-Metal Hydroxide Layers within Double- and Triple-Layered Perovskites

The formation of alkali-metal hydroxide layers within lamellar perovskites has been accomplished by a two-step topochemical reaction strategy. Reductive intercalation of ALaNb2O7 with alkali metal (A = K, Rb) and RbCa2Nb3O10 with Rb leads to A2LaNb2O7 and Rb2Ca2Nb3O10, respectively. Oxidative intercalation with stoichiometric amounts of water vapor, produced by the decomposition of calcium oxalate monohydrate in a sealed ampule, allows the insertion hydroxide species. Compounds of the form (A2OH)LaNb2O7 (A = K, Rb) and (Rb2OH)Ca2Nb3O10 are accessible. X-ray diffraction data indicates a clear layer expansion of almost 3 Å on the insertion of hydroxide relative to that of the parent. Rietveld refinement of neutron diffraction data collected on deuterated samples of (Rb2OD)LaNb2O7 (P4/mmm space group, a = 3.9348(1) Å, c = 14.7950(7) Å) finds that both rubidium and oxygen species reside in cubic sites forming a CsCl-like interlayer structure between niobate perovskite blocks. Hydrogens, attached to the interlayer oxygens, are disordered over a 4-fold site in the x-y plane and have O-H bond distances (0.98 Å) consistent with known hydroxide species. This synthetic approach expands the library of available topochemical reactions, providing a facile method for the construction of alkali-metal hydroxide layers within receptive perovskite hosts.

A comparative study of non-isothermal kinetics of decomposition of calcium oxalate monohydrate

The kinetics of thermal dehydration and decomposition CaC 2O 4·H 2O was studied using thermogravimetry at four rates of linear increase of temperature and two different sample mass. Four calculation procedures based on single TG curves and iso-conversional method, as well as 35 mechanism functions were used. The comparison of the results obtained with these calculation procedures showed that they strongly depend on the selection of proper mechanism function for the process. Therefore, it is very important to determine the most probable mechanism function. In this respect the iso-conversional calculation procedure turned out to be more appropriate. In the present work, the values of apparent activation energy, pre-exponential factor in Arrhenius equation, as well as the changes of entropy, enthalpy and free Gibbs energy for the stages of dehydration, decarbonylation and decarbonation of calcium oxalate monohydrate are calculated. All calculations were performed using programs compiled by ourselves.

Evolved Gas Analysis-Mass Spectrometry (EGA-MS) Using Skimmer Interface System Equipped with Pressure Control Function

A new evolved gas analysis-mass spectrometry (EGA-MS) equipped with a skimmer interface system and a pressure control function (PCF) has been developed successfully. The skimmer interface system based upon jet separator principle is constructed between a sample chamber surrounded by an electrical furnace and a vacuum chamber. Although the skimmer type is principally more excellent than a capillary type, it is a significant problem that the sensitivity of EGA-MS falls with increasing the temperature. The fall of detection sensitivity of EGA-MS depending on temperature rising has been remarkably improved by introducing the pressure control function (PCF). As the result of evaluating PCF by using the thermal decomposition of calcium oxalate monohydrate, the ionic intensities of the evolved gases increased more than twice. The new EGA-MS was applied to the thermal decomposition of zinc acetylacetonate monohydrate and polymethylmethacrylate (PMMA). It was confirmed that the more sensitive and precise gas analysis which prevented condensation of evolution gases and/or generation of by-products can be performed, by comparing with the capillary interface system of TG-MS.

A description of kinetics of thermal decomposition of calcium oxalate monohydrate by means of the accommodated R n model

The choice of possible kinetic models for a solid state reaction should involve multi-parameters to reduce down specious models which are suggested by using single parameters. For this purpose, in the present work the activation energy estimated from the isoconversional plot was used to check models proposed by the degree of conversion at the maximum reaction rate for the thermal decomposition of calcium oxalate monohydrate. It was found that the basic D2 and D4 models are not a likely description of the kinetics of a three step decomposition. The R n model was also applied.

ANALYSIS OF THE THERMOKINETICS UNDER DYNAMIC CONDITIONS BY RELATIVE RATE OF THERMAL DECOMPOSITION

A novel parameter of the relative rate of thermal decomposition has been defined on the basis of an analysis of equation relating the logarithm of the conversion degree on the temperature. The dependence of this parameter on temperature in the dynamic conditions has been analyzed and discussed. The dependence of the relative rate of thermal decomposition is a linear relationship involving two coefficients. These coefficients can be related to the enthalpy and activation energy. The parameter developed has been used for the analysis of a series of consecutive reactions of thermal decomposition of calcium oxalate monohydrate.

Modification of the integral isoconversional method to account for variation in the activation energy

Integral isoconversional methods may give rise to noticeable systematic error in the activation energy when the latter strongly varies with the extent of conversion. This error is eliminated by using an integration technique that properly accounts for the variation in the activation energy. The technique is implemented as a modification of the earlier proposed advanced isoconversional method [Vyazovkin, S. J Comput Chem 1997, 18, 393]. The applications of the modified method are illustrated by simulations as well as by processing of data on the thermal decomposition of calcium oxalate monohydrate and ammonium nitrate. © 2000 John Wiley & Sons, Inc. J Comput Chem 22: 178–183, 2001

Thermodynamics of the thermal decomposition of calcium oxalate monohydrate examined theoretically

Geometries and energies of isolated CaC2O4·H2O, CaC2O4, CaCO3, CaO, H2O, CO and CO2 were determined at the ab initio level using effective core potential valence basis sets of doublezeta quality, supplemented with polarization functions. The effects of electron correlation were taken into account at the second order Møller-Plesset level of theory. For CaC2O4·H2O, the correlation for the basis set superposition error was also included. Common routines were employed to evaluate entropies, heat capacities, as well as enthalpies and free enthalpies of formation of all entities. The enthalphies and free enthalpies of consecutive dehydration of CaC2O4·H2O, decarbonylation of CaC2O4 and decomposition of CaCO3 towards CaO and CO2 were determined on the basis of avialable data from the literature or those predicted thoretically. Assuming that upon all the above mentioned processes the system maintains equilibrium, the fractions reacted, enthalpy changes and differential dependencies of thesevs. temperature were derived and compared with experimental thermoanalytical data.

Kinetic studies by DSC on the thermal decomposition of calcium oxalate

In the present paper, we have studied the kinetics of the thermal decomposition of calcium oxalate monohydrate, using a new method of kinetic study employing data obtained from differential scanning calorimetry, as previously proposed by us. Initial products and those obtained following decomposition have been identified by infrared spectroscopy and X-ray powder diffraction. A comparison between the results obtained in this paper and those reported in the literature has also been made.

Kinetic analysis of thermal decomposition reactions—III. Irradiation effects on the thermal decomposition of calcium oxalate monohydrate

The effects of gamma radiations on the kinetic parameters of the three stages of isothermal decomposition of calcium oxalate monohydrate were investigated. Radiation did not modify the mechanism of thermal decomposition reactions and kinetic analysis of data showed that the random nucleation and the two-dimensional phase boundary reaction models give the best fit of the results. For the first two stages kinetic analysis showed progressive decrease in both activation energy and frequency factor with greater radiation dose due to the generation of more dislocations and surface etch pits. However, in the third stage, radiation has no effect at the higher doses due to the formation and accumulation of CO 2 molecules and the self-generation of defects during the movement of the phase boundary.

Thermal decomposition kinetics: Part XIV. Kinetics and mechanism of isothermal decomposition of calcium oxalate monohydrate and correlation with sample mass

The mechanisms of the first two stages of the thermal decomposition of calcium oxalate monohydrate have been established from isothermal mass-loss studies. For both stages, the rate-controlling process is phase boundary reaction with cylindrical symmetry. The isothermal kinetic parameters computed from the mechanism-based equation show the same trend as those from the mechanism-non-invoking approach. For the decomposition of calcium oxalate to calcium carbonate and carbon monoxide, the kinetic constants are not appreciably affected by sample mass, while for the dehydration of calcium oxalate monohydrate, they show a systematic decrease with increase in sample mass. The bestfit correlations have been represented as: E (or log A) = C 1 − C 2 m + C 3 m 2

Thermal decomposition kinetics. Part XI. Mechanism of thermal decomposition of calcium oxalate monohydrate from a thermogravimetric study — the effects of heating rate and sample mass on kinetic parameters from mechanistic equations

The mechanisms of the first two stages of the thermal decomposition of calcium oxalate monohydrate ▪ have been established from non-isothermal thermogravimetric studies. For both stages, the rate-controlling processes are phase boundary reactions; the dehydration step assumes spherical symmetry whereas the decomposition step follows cylindrical symmetry. The kinetic parameters calculated from mechanistic equations show the same trend as those from mechanism-non-invoking equations. Thus, for the decomposition of CaC 2O 4 the kinetic parameters are not appreciably affected by heating rate or sample mass. For the dehydration step they show a systematic decrease with increase in either heating rate or sample mass. The best fit correlations can be expressed as follows E(or, log A) = (Constant/Heating rate) + Constant, (at fixed sample mass) E(or, log A) = (Constant) × (Mass) 2 − (Constant) × (Mass) + Constant, (at fixed heating rate)

Thermal decomposition studies: Part X. Thermal decomposition kinetics of calcium oxalate monohydrate — correlations with heating rate and samples mass

Quantitative correlations between kinetic parameters (energy of activation E, pre-exponential factor A) and procedural factors (heating rate, sample mass) in non-isothermal thermogravimetry have been made for the first time. The effect of heating rate and sample mass on the first two stages of thermal decomposition of calcium oxalate monohydrate in a nitrogen atmosphere ▪ has been evaluated in detail using non-isothermal thermogravimetry. Kinetic parameters are calculated from the TG curves using three integral methods (two “exact” and one “approximate”). The values obtained by the “approximate” method are higher than the corresponding values from the “exact” integral methods. For the decomposition of calcium oxalate to carbonate, the kinetic parameters are not much affected by heating rates or sample masses in the ranges studied. For the dehydration of CaC 2O 4 · H 2O, the parameters show a systematic decrease with increase in either heating rate or sample mass. The values of E and log A obtained by all three equations are best correlated to heating rate as rectangular hyperbole of the type: ▪ The best fits for correlation to sample mass are parabolae of the type E (or log A) = constant × (mass) 2 − constant × mass ÷ constant SYMBOLS USED A = pre-exponential factor α = fraction decomposed φ = heating rate in deg min −1 E = energy of activation n = order parameter R = gas constant T i = temperature of inception of reaction T f = temperature of completion of reaction T s = DTG peak temperature Δ T = T − T s

Data Acquisition and Reduction Program for Thermogravimetry

An on-line data acquisition system for thermogravimetry using the IBM S/7 computer followed by data reduction on a 360/195 is described by means of flow charts. The system is designed so that no knowledge of programming is required to acquire, display and manipulate data on an interactive graphics terminal. The program not only extracts weight loss data, but also computes the energies of activation, E, for any selected weight loss interval by two methods, i.e., tabular integral and derivative. The system is demonstrated by a study of the activation energies for loss of water, loss of carbon monoxide, and loss of carbon dioxide during the thermal decomposition of calcium oxalate monohydrate. The results are in good agreement with the best literature values. The derivative method was found to give more consistent results than the tabular integral approach because of problems encountered in the precise measurement of temperature in the thermobalance.

Thermogravimetry system designed for use in dispersion strengthening studies

A thermogravimetry system, designed to study the reduction of oxides in metal and alloy powders to be used in dispersion strengthened materials, is described. The apparatus was devised for use at high temperatures with controlled atmospheres. Experimental weight change and moisture evolution results for the thermal decomposition of calcium oxalate monohydrate in dry helium, and experimental weight change results for the reduction of nickel oxide in dry hydrogen and hydrogen containing 15,000 p.p.m. water vapor are presented. The system is currently being successfully applied to the evaluation of the reduction characteristics and the removal of impurities from metals and alloys to be used for dispersion strengthening.

Differential Gas Analysis Method -Apparatus and Its Applications-

This apparatus was developed to study the solid-state reactions and physico-chemical changes involving absorption or evolution of gases, and structurally consists of a modified gas effluent analysis equipment and a high-precision gas mixer. The new apparatus is more useful in the fields of inorganic chemistry, organic chemistry, metallurgy, etc. than a conventional EGA equipment.The sample is heated or cooled at the constant rate in a mixed flow of two or more different gases such as He-O2, He-CO2, Ar-H2, etc. The changes in the composition of the gas passing through the reactor due to the decomposition or the gas-solid reaction are detected with high sensitivity by a thermal conductivity detector. The sample weight required for the usual measurement is 5∼50 mg. It is applicable to the range from room temperature to 1600°C and the gas flow of any mixing ratio (200: 1∼1: 200). Although the limits of determination are affected by the operating conditions, an evolution or absoption of 0.01-0.0001 ml of oxygen by the sample in the He-O2 mixture can be detected.This paper describes the following reactions as the applications of this apparatus: reduction of vanadium pentaoxide by hydrogen, thermal decomposition of calcium oxalate monohydrate, oxidation and reduction of iron oxide, formation and decarbonation of calcite, and hydrogenation and formation of uranium hydride.

Application of thermogravimetric techniques to reaction kinetics

AbstractAn easier technique for the determination of reaction constants such as order, energy of activation, and frequency factor from the thermogravimetric data has been described. The method requires two TGA curves obtained with different sample weights under similar reaction conditions. Applicability of the method to complex reactions, where simultaneous decomposition occurs, has been discussed. Reaction constants for different steps of the decomposition of calcium oxalate monohydrate are evaluated.