Thermal Decomposition Of Calcium Carbonate Research Articles

Hydrogenation of calcium carbonate to carbon monoxide and methane

The current cement, steel, refractory and calcium carbide industries rely on thermal decomposition of calcium carbonate (CaCO3) that forms calcium oxide (CaO) and carbon dioxide (CO2). Hydrogenation of CaCO3 may reduce or eliminate CO2 in CaO generation and simultaneously generate carbon monoxide (CO) and/or methane (CH4). This work mainly investigates CaCO3 hydrogenation conditions for CO and CH4 and establishes the kinetics for these reactions. It is found that CH4 forms at temperatures lower than that of CO2 but higher than that of CO. The rates of CO and CH4 formation increase with increasing hydrogen pressure (PH2) but that of CO peaks at PH2 of 0.05–0.10 MPa. The CO2, CO and CH4 yields are 17.7%, 81.4% and 0.9% at the PH2 of 0.10 MPa while 1.2%, 20.0% and 78.8% at the PH2 of 6.00 MPa. The kinetics of CaCO3 conversion and CO and CH4 formation can be better modeled by the shrinking core model (SCM) than the volume reaction model (VRM) and the gas reaction model (GRM). The activation energy (Ea) for CaCO3 conversion and CO and CH4 formation by SCM is 165.8, 156.4 and 211.9 kJ·mol−1, respectively, with the order of PH2 of 0.108, 0.005 and 0.673, respectively.

Complementary use of thermogravimetric analysis and oven to assess the composition and bound CO2 content of recycled concrete aggregates

The carbonation of recycled concrete aggregates (RCA) has emerged as a possible significant carbon sink to mitigate the increase of CO2 concentration in atmosphere and global warming. A reliable determination of bound CO2 content is thus needed to optimize carbonation processes but there is no real consensus on the existing quantification methods, mainly based on thermal decomposition of calcium carbonate. With the aim of developing a relevant quantification method of bound CO2 during the carbonation of RCA, an experimental study based on the combination of two main techniques – thermogravimetric analysis (TGA) and high-temperature oven – was performed at different scales: paste, mortar, and concrete. XRD analyses allowed highlighting the overlaps between the decomposition of portlandite and calcium carbonate polymorphs during linearly increasing temperatures. Oven and TGA with isothermal steps were found to provide consistent and complementary data on RCA composition and their bound CO2 content from initially dried specimens.

Acceleration Effect of Atmospheric Water Vapor on the Thermal Decomposition of Calcium Carbonate: A Comparison of Various Resources and Kinetic Parameterizations

Acceleration Effect of Atmospheric Water Vapor on the Thermal Decomposition of Calcium Carbonate: A Comparison of Various Resources and Kinetic Parameterizations

Kinetic Parameterization of the Effects of Atmospheric and Self-Generated Carbon Dioxide on the Thermal Decomposition of Calcium Carbonate

Kinetic Parameterization of the Effects of Atmospheric and Self-Generated Carbon Dioxide on the Thermal Decomposition of Calcium Carbonate

A Multifaceted Kinetic Model for the Thermal Decomposition of Calcium Carbonate

The existing kinetic models often consider the influence of a single factor alone on the chemical reaction and this is insufficient to completely describe the decomposition reaction of solids. Therefore, the existing kinetic models were improved using the pore structure model. The proposed model was verified using the thermal decomposition experiment on calcium carbonate. The equation has been modified as fα=n1−α1−1n−ln1−α−1m1−ψln1−α12. This led to the conclusion that the pore structure, generated during the thermal decomposition of calcite, has an important influence on the decomposition kinetics. The existing experimental data show that the improved model, with random pores as the main body, reasonably describes the thermal decomposition process of calcite.

Thermal decomposition of calcium carbonate (calcite polymorph) as examined by in-situ high-temperature X-ray powder diffraction

The temperature dependence of composition, unit cell parameters, thermal expansion coefficients and microstructure during complete thermal decomposition of calcite has been investigated by in-situ high-temperature X-ray powder diffraction. The respective X-ray diffractograms were obtained from 675 to 800 °C at 25 °C intervals. Results indicate that the thermal conversion of calcite to calcium oxide is initiated at a slow rate and rapidly decomposed beyond the temperature of 750 °C. During the period of thermal decomposition, positive and negative expansion of the unit cell is detected parallel to c-axis and perpendicular to a-axis, respectively. A substantial reduction in unit cell volume by 69% is observed during the conversion from trigonal calcite to cubic calcium oxide. It is also found that the rapid composition change and unit cell volume reduction simultaneously accounted for polynomial behavior of thermal expansion coefficients of calcite. Both crystallite size and lattice strain of calcite are increased simultaneously during thermal decomposition. A considerably higher lattice strain is observed for calcite compared to calcium oxide at all decomposition temperatures. The uniform arrangement of small cubic unit cells in newly materialized calcium oxide is accounted for moderate crystallite size and lowest lattice strain at the completion of thermal decomposition.

Effect of Laser Speed on Cutting Characteristics of Cement-Based Materials

The results of an experimental investigation on the physical and chemical characteristics of cement-based materials under laser interactions are presented. The laser cutting tests were conducted using a multi-mode continuous fiber laser with a laser power of 1 kW. The experimental variables were laser speed, water to cement ratio, and material compositions including cement paste, cement mortar, and ultra high-performance concrete (UHPC). In order to evaluate the mass removal mechanisms of cement-based materials under laser interactions, the effect of laser cutting was evaluated in terms of kerf width, penetration depth, and chemical composition changes before and after the interaction with laser using EDX analysis. The test results reveal that adding silica sand in cement-based materials leads to decreasing penetration depth and increasing kerf width. Unlike the cement paste and cement mortar series, UHPC specimens showed no discernible crack observed by the naked eye after laser interaction due to its high strength. Furthermore, the chemical analysis indicates that chemical composition changes were caused by various mechanisms including dehydration of calcium hydroxide and thermal decomposition of calcium carbonate.

Thermogravimetric analysis coupled with mass spectrometry of spent mushroom substrate and its fractions

This study aimed at determination of the char, tar and gas production yield during pyrolysis of the spent mushroom substrate left after cultivation, as well as its individual components, namely the casing layer and the mushroom substrate. The pyrolysis process was carried out in a thermobalance combined with a mass spectrometer. Based on the analysis of mass losses, it was found that the largest amount of flammable gases and tar were released during pyrolysis of the spent mushroom substrate. The yield of char, tar and gas during pyrolysis at 600 °C were respectively equal to 57.1, 14.4 and 14.5 wt.%. The loss of mass at temperature above 600 °C was associated with thermal decomposition of calcium carbonate, calcium sulfate, and oxidation of the char. The deconvolution of DTG curves and volatile products such as H2, CH4, CO, CO2, H2O and tar allowed to determine the decomposition of the compounds contained in the spent mushroom substrate during the pyrolysis process. The kinetic parameters were calculated from the isoconversional model for thermal degradation of biomass. The results could aid in managing organic wastes including the energy production.

Pico-thermogravimetric material properties analysis using diamond cantilever beam

This paper presents a novel technique for pico-thermo gravimetric analysis of material properties using diamond cantilever beam. The thermal decomposition of calcium carbonate (CaCO3) was examined using this method and was detected in picogram range. The diamond cantilever beam with CaCO3 particles attached on the tip was introduced in a thermal chamber and the temperature was raised from room temperature to 600 °C. The cantilever beam was operated in vibration mode and the resonant frequency was monitored in real time during the thermal process. From the resonant frequency behavior, there was evidence that the thermal conversion from CaCO3 to CaO starts around 500 °C. This novel technique used very small amount of material and variations of the analyzed material pico-mass at different temperatures were observed from the cantilever beam measurements. The thermal analysis expects a release of carbon dioxide (CO2) which in turn decreases the sample mass. Variations of the sample mass are an indication that the thermal decomposition of the analyzed material started. In this research the information about the conversion temperature was repeatable and highly accurate. The diamond cantilever beam is well suited for the thermal measurements because large variations of temperature produced small changes of the resonant frequency. This novel thermogravimetic technic provides accurate information about the analyzed material mass variations at picogram range during the thermal process.

SYNTHESIS AND CHARACTERIZATION OF CALCIUM HYDROXIDE OBTAINED FROM AGAVE BAGASSE AND INVESTIGATION OF ITS ANTIBACTERIAL ACTIVITY

Calcium hydroxide (Ca(OH) 2 ) is recognized as an efficient bactericide and is widely applied as a root canal filler in endodontic treatment. Ca(OH) 2 is mainly produced by hydration of calcium oxide (CaO), a product of the thermal decomposition of calcium carbonate (CaCO 3 ) from sources such as limestone. In this work, calcium hydroxide particles were synthetized by the thermochemical transformation of waste biomass from the tequila industry. Agave biomass processed at 600 °C was composed mostly of calcium carbonate (CaCO 3 ), while calcination at 900 °C followed by hydration produced Ca(OH) 2 . The morphology and crystalline nature of the Ca(OH) 2 particles were characterized by micro-Raman spectroscopy, scanning electron microscopy and X-ray diffraction analysis. Bactericidal activity of synthesized calcium hydroxide was evaluated with the agar diffusion assay. Our results provide evidence that Ca(OH) 2 obtained from agave biomass is an effective bactericidal against Escherichia coli and Enterococcus faecalis. Biomass from agave is available in Mexico and the rest of the American continent, the use of processed bagasse for medical applications could provide a venue for the useful disposition of industrial waste.

The validity of nonlinear isoconversional method in the kinetic analysis of calcium carbonate decomposition under isothermal and non-isothermal conditions

• The nonlinear isoconversional method was applied to determine the kinetics parameter. • The activation energy determined by this method varies with the extent of reaction. • The dependence of the activation energy can excellently predict the actual measurement. • It is demonstrated that this method is a trustworthy way for kinetics analysis. The nonlinear isoconversional method has been applied to data for non-isothermal thermal decomposition of calcium carbonate. The activation energy determined by this method is dependent on the extent of reaction. The dependence of the activation energy has been used to predict the isothermal kinetics. It is shown that the dependence derived from non-isothermal data permits reliable predictions of the isothermal kinetics. Therefore, the nonlinear isoconversional method is recommended as a trustworthy way of obtaining consistent kinetic information from isothermal and non-isothermal.

Determined the Activation Energy of the Decomposition of Calcium Carbonate by Nonlinear Isoconversional Method

The nonlinear isoconversional method has been applied to data for nonisothermal thermal decomposition of calcium carbonate. It is shown that the dependence derived from nonisothermal data can reveal the complexity of solid reaction. Therefore, the nonlinear isoconversional method is recommended as a trustworthy way of obtaining the activation energy of solid reaction under nonisothermal conditions.

Thermal decomposition of calcium carbonate polymorphs precipitated in the presence of ammonia and alkylamines

Precipitated calcium carbonate was obtained by CO2 bubbling in CaCl2 solution. Ammonia and alkylamines were used to enhance CO2 absorption and control the polymorphic phases. Vaterite and calcite mixtures were obtained, mainly vaterite in ammonia and mono-methylamine and mostly calcite in tri-methylamine environment. The thermal decomposition of precipitated calcium carbonate leads to high purity CaO. During the thermal decomposition the vaterite to calcite transformation was noticed but the final spherical shape of vaterite was maintained. As the use of CaO as catalyst in biodiesel synthesis may recommend a spherical shape and high contact surface, a precipitated calcium carbonate, rich in vaterite phase, may be a good precursor for CaO catalyst preparation.

An iterative model-free method to determine the activation energy of heterogeneous processes under arbitrary temperature programs

A new iterative model-free (isoconversional) method with integration over a given range of conversion for the determination of the activation energy using non-isothermal data recorded at arbitrary temperature programs has been suggested. The advantages of applying this method in comparison with differential linear and nonlinear methods and advanced nonlinear method are put in evidence. The applicability of the suggested method was checked for simulated data for a single-step process, thermal decomposition of calcium carbonate, and thermal degradation of high density polyethylene.

Concept of Variable Activation Energy and Its Validity in Nonisothermal Kinetics

The concept of variable activation energy in solid-state kinetics under nonisothermal conditions has been suffering from doubt and controversy. Rate equations of nonisothermal kinetics of solid decomposition, which involve the factors of thermodynamics conditions, pressure of gaseous product, structure parameters of solid, and/or extent of conversion, are derived from the models of the interface reaction, the diffusion of gaseous product, and the nuclei growth of the solid product, respectively. The definition of the validity function in the rate equations represents the influence of the factors on the reaction rate. A function of variable activation energy depending on the validity function is also developed. The changing trend and degree of activation energy are extrapolated from the function of variable activation energy and based on the data of nonisothermal thermal decomposition of calcium carbonate. It is shown that the concept of variable activation energy is meaningfully applicable to solid-state reactions under nonisothermal conditions.

Heterogeneous thermochemical decomposition of a semi-transparent particle under direct irradiation

Transient heat and mass transfer in a non-uniform emitting, absorbing and anisotropically scattering medium inside a semi-transparent, optically large and chemically reacting particle directly exposed to an external source of high-flux radiation is analyzed numerically. Thermal decomposition of calcium carbonate is selected as the model chemical reaction. The unsteady mass and energy equations are solved numerically using the finite volume technique and the explicit Euler time-integration scheme. Radiative transport is modeled using the Rosseland diffusion approximation and the Monte Carlo ray tracing method. Direct irradiation and internal radiative transfer in the particle are highly favorable for particle heating and the decomposition reaction, decreasing the total reaction time by a factor of 15, as compared to the case with external and internal radiation neglected in the analysis. In the latter case, the temperatures at the particle center and the particle surface increase monotonically to 1406 and 1417 K for the reacting particle, and 1428 and 1432 K for the non-reacting particle, respectively, after 179 s—the total reaction time of the reacting particle. With radiation included in the analysis, the surface temperatures of both reacting and non-reacting particle increase from the initial 300 to 1300 K in less than 2 s, and at the same rate until the onset of the endothermic chemical reaction at t=1.1 s. The surface temperature of the reacting particle increases further up to 2000 K after 12 s, when the whole particle is calcined. Weak dependence of the temperature, the overall reaction extent, and the total reaction time on the CaO grain size is observed in spite of strong dependence of the radiative properties of porous CaO on the CaO grain size.

Calcium carbonate thermal decomposition in white-body wall tile during firing. I. Kinetic study

This study examines the thermal decomposition of calcium carbonate, contained in disk-shaped test pieces formed from a mixture of raw materials of a similar composition and characteristics to those of the mixtures customarily used for the manufacture of white-body wall tile. The experiments were conducted under isothermal conditions at different temperatures in the range 825–950 °C in an air stream free of carbon dioxide. The experimental results have been interpreted using the Shrinking Unreacted Core kinetic model, assuming that, at low conversion degrees, the process is only controlled by the chemical reaction step of CaCO 3 decomposition, while at high conversion degrees the diffusion of the resulting CO 2 through the porous structure of the reacted ceramic layer also affects the process. The derived equations, which relate the conversion degree of calcium carbonate in the ceramic body to residence time, temperature, and initial porosity of the test pieces, allow the experimental results to be satisfactorily reproduced.

Formation of CaO from thermal decomposition of calcium carbonate in the presence of carboxylic acids

Effect of 5% tartaric, succinic and citric acids on the decomposition of CaCO3 have been studied by TG-DSC and X-ray diffraction techniques. The decomposition temperature of CaCO3 is not decreased and at the same time particle size distribution and morphology of CaO are changed as determined by laser granulometer and SEM studies.

Kinetic analysis of poly(vinyl butyral)/glass ceramic thermal degradation using non-linear heating functions

A kinetic analysis based on a set of non-linear heating functions was developed to evaluate the thermal degradation of poly(vinyl butyral)/glass ceramic composites. The non-linear Arrhenius equation with respect to temperature can be exactly solved by introducing this non-linear heating function (integrating factor). The integral formula can then be used to determine kinetic parameters of solid-state reactions applying the non-linear heating strategies. Thermal decomposition of calcium carbonate in nitrogen and air was utilized to evaluate the reliability of the proposed algorithm using TGA. Results show that the kinetic analysis of this case was quite reasonable compared with the data reported in the literature. This analytical approach was applied on the kinetic analysis of PVB/ceramic thermal degradation. The kinetics of the PVB/ceramic degradation was discussed based on the analytical results. The results can be applied to the design and operation of the ceramic thermal processing.

The A to G of Chemical Equilibrium: Aspects Depicted by Helmholtz Energy Using Its Relationship to Gibbs Energy

The approach to chemical equilibrium at constant V, T is considered for various heterogeneous reactions and processes. Analysis is made showing how A and G conveniently interrelate enabling typical 2-D and 3-D Helmholtz energy curves to be drawn across a range of T to illustrate water vaporization and the thermal decomposition of calcium carbonate and ammonium chloride solids. A dip in free energy forms when gas component(s) change in pressure and amount as each reaction proceeds. Equilibrium is consequently attained by the opposing influence of these changes bringing the free energy to a minimum or the entropy to a corresponding maximum. Significantly this effect does not depend on a contribution from a free energy (or entropy) of mixing. The Helmholtz energy curves for the decomposition of ammonium chloride into ammonia and hydrogen chloride are obtained by using (equilibrium) vapor pressures for this two-gas formation and the effect of adding more of one of these gases is allowed for and depicted in co...