Thermal Decomposition Of CaCO3 Research Articles

Comparative study of CaO and CaCO3 on microstructure refinement, mechanical and corrosion resistance of AM60 alloy

Grain refinement is a crucial technique for enhancing the mechanical properties and corrosion resistance of magnesium alloys. In this study, the addition of 0.3 wt% CaO and 0.3 wt% CaCO3 successfully refined the AM60 alloy, resulting in a significant reduction in the average grain size from 326 μm to 96 μm (when adding CaCO3). The refined grain size of the as-cast AM60 alloy led to an increase in both tensile strength and yield strength to 118.2 MPa and 72.6 MPa, representing a respective increase of 35% and 23% compared to the alloy without the refiner. As results of EBSD, it is verified that the basal slip system (0001)<112‾0> has a higher Schmid factor after adding CaO, which indicates that this system has higher activity. The substitution reaction between CaO and Mg can produce synergistic effects from the solute effect of Ca and the nucleating effect of residual CaO, which play an important role in grain refinement. Due to the fine grain size and diffuse distribution of the second phase in the AM60-CaCO3 alloy and the thermal decomposition of CaCO3, which consumes the aluminum element in the matrix, the content of the β-phase (Mg17Al12) is reduced. Consequently, this reduces the electric coupling effect between the β-phase and the magnesium matrix. The AM60-CaCO3 alloy exhibited the most superior corrosion resistance, achieving a corrosion rate of only 1.01 mm y−1, representing a 48.9% reduction in corrosion rate compared to the AM60 alloy.

Towards a better understanding of historic mortar production\u2014burning experiments on calcareous nannofossils

Calcareous nannofossils are < 30 µm sized calcitic fossil remains of single-celled marine photoautotrophic algae. Carbonate-rich sedimentary rocks, containing these fossils, are used as raw material for lime-based mortars. The carbonates (CaCO3) are heated up to approx. 900 °C. The burning process, which causes the thermal decomposition of CaCO3 into CaO (= quicklime) and CO2, destroys the calcitic fossils. Surprisingly, remains of these calcareous algae were recently encountered in historic mortars and mortar-based materials. To gain a better understanding of the behaviour of calcareous nannofossils during the calcination procedure, four sample sets were heated to nine temperature levels (100 °C, 300 °C, 500 °C, 600 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C). For each sample set, the initial and the heated material of all nine temperature levels were analysed with respect to its nannofossil content and preservation by using settling slides. Our results show a decrease of absolute abundance and preservation from 500 °C onwards; rare nannofossils are preserved up to 900 °C. Changes in the relative abundance of individual species document that certain taxa are more heat resistant than others. This pattern is explained by different crystal sizes and forms of the relevant taxa. Differences in the calcareous nannofossil assemblages, observed in the raw material and in the mortar produced from it, can be used to estimate the temperature reached during quicklime production.

Kinetics of component reactions in calcium looping appeared during the multistep thermal decomposition of Portland cement under various atmospheric conditions

Calcium looping (CaL) reactions in a Ca(OH)2-CaCO3-CaO system for energy storage and CO2 absorption occur during the thermal decomposition of cement and concrete materials. Herein, we report the kinetic behavior of the reactions in a cement matrix as the necessary information for establishing a CaL cycle supported by cement/concrete materials. The thermal decomposition of Portland cement samples, characterized by different Ca(OH)2/CaCO3 ratios, under different atmospheric water vapor and CO2 conditions were investigated to reveal the kinetic behavior of the component reactions and the changes with atmospheric conditions. The multistep thermal decomposition, characteristic of each sample and atmospheric condition, were separated into individual reaction steps through a kinetic deconvolution analysis. Using the extracted kinetic curves for the reactions of Ca(OH)2 and CaCO3, retardation effects of atmospheric water vapor and CO2 on the thermal decompositions of Ca(OH)2 and CaCO3, respectively, were kinetically described by introducing different accommodation functions (AF) comprised of the partial pressures of the gases and their equilibrium pressure. In addition, the kinetic description of the catalytic effect of water vapor on the thermal decomposition of CaCO3 was achieved by introducing alternative AF of water vapor pressure. The thermally induced carbonation of Ca(OH)2, which occurred in the presence of atmospheric CO2, was characterized kinetically as physico-geometrically regulated consecutive reactions of thermal decomposition of Ca(OH)2 and subsequent carbonation of the as-produced CaO. Kinetic information concerning the reactions of Ca(OH)2 and CaCO3 in the cement materials is reported in details.

Study on multi-cycle reaction performance of Fe/Al compound oxygen carriers in chemical-looping pyrolysis of coal tar

Two Fe/Al compound oxygen carriers were prepared by the impregnation method, in which one is CaO-modified, and they were applied in multi-cycle experiments of preparing carbon black (CB) by chemical-looping pyrolysis of coal tar in a small fluidized bed reactor in laboratory. X-ray diffraction, N2 adsorption analysis, and scanning electron microscopy were employed to analyze the variation of composition, the pore distribution, and the surface morphology of the OCs during the cyclic reaction. XRD results show that the oxygen-carrying capacity of both two-compound OCs decreases with the increase of the number of cycles, but the CaO-modified OC performs better for carbonation of CaO and then thermal decomposition of CaCO3 during the cycle reaction. BET and SEM results show that the Fe/Al compound OC can maintain a good porous structure during the first 15 cycles. As the cycle numbers continuously increase, the sintering accumulation appears on the OC surface, resulting in an increase in the tar volatiles’ diffusion resistance on the surface of the particles. The CaO-modified compound OC maintained a good porous structure during 20 cycles. The decrease of the oxygen-carrying capacity and the surface sintering of the OC are the main reasons for the decrease of the reaction activity. The CaO carbonation-decomposition can maintain the porous structure of the compound OC during the multi-cycle reaction and delay the surface sintering effectively, thus improving the reaction performance of the OC.

Effect of the thermal annealing on the phase transitions of biogenic CaCO3 nanostructures

The issue of the present research lays its foundation on the proposal of the Crassostrea virginica waste oyster shells (WOS) reuse to obtain calcium carbonate powder (CaCO3) and calcium hydroxide (Ca(OH)2) nanostructured, using thermal annealing treatments. The oysters shells were subjected to a previous physical grinding process to decrease their size (smaller sizes 0.074 mm). The parameter studied was the effect of annealing temperature (500, 700 and 900 °C in air atmosphere) on the structural properties and morphology of the powders by FTIR, XRD, SEM and HRTEM. The X-ray diffraction results indicate that the WOS in their natural state and thermally annealed at 500 °C have two phases of CaCO3 the rhombohedral form for calcite with crystallite size around 24 nm and aragonite traces in orthorhombic phase. At 700 °C, the WOS powder is transformed into calcium hydroxide, also known as portlandite (Ca(OH)2), attributed to the absorption of water released during the thermal decomposition of CaCO3. This crystalline phase does not change when the temperature increases to 900 °C. The SEM and HRTEM analysis of WOS powders reveals that with a thermal annealing treatment it is possible to obtain nanostructured CaCO3. FTIR analysis demonstrates the biogenic origin of CaCO3, due to amide groups. The nanostructured CaCO3 obtained by grinding and thermal annealing of WOS, can be used as drying agent, or as additive in ceramic and glass. The issue of the present research lays its foundation on the proposal of the Crassostrea virginica waste oyster shells (WOS) reuse to obtain calcium carbonate powder (CaCO3) and calcium hydroxide (Ca(OH)2) nanostructured, using thermal annealing treatments. The oysters shells were subjected to a previous physical grinding process to decrease their size (smaller sizes 0.074 mm). The parameter studied was the effect of annealing temperature (500, 700 and 900 °C in air atmosphere) on the structural properties and morphology of the powders by FTIR, XRD, SEM and HRTEM. The X-ray diffraction results indicate that the WOS in their natural state and thermally annealed at 500 °C have two phases of CaCO3 the rhombohedral form for calcite with crystallite size around 24 nm and aragonite traces in orthorhombic phase. At 700 °C, the WOS powder is transformed into calcium hydroxide, also known as portlandite (Ca(OH)2), attributed to the absorption of water released during the thermal decomposition of CaCO3. This crystalline phase does not change when the temperature increases to 900 °C. The SEM and HRTEM analysis of WOS powders reveals that with a thermal annealing treatment it is possible to obtain nanostructured CaCO3. FTIR analysis demonstrates the biogenic origin of CaCO3, due to amide groups. The nanostructured CaCO3 obtained by grinding and thermal annealing of WOS, can be used as drying agent, or as additive in ceramic and glass.

Blood Cockle Shells Waste as Renewable Source for the Production of Biogenic CaCO3 and Its Characterisation

The prowess to reuse and recycle of blood cockle shells for raw material in bio-ceramics applications is an attractive component of integrated waste management program. In this paper an attempt is made to introduce a simple process to manufacture biogenic CaCO3 powder from blood cockle shells waste. The biogenic CaCO3 powder was produced from rinsing of blood cockle shells waste using deionised water and oxalic acid for cleaning the dirt and stain on the shells, then drying and grinding followed by heat treatment at 500 and 800 °C for 5 h. The powder obtained was characterised by XRF, DTA/TG, SEM, FTIR, and XRD analysis. The amount of 97.1 % CaO was obtained from XRF result. The thermal decomposition of CaCO3 become CaO due to mass loss was observed in the TG curve. The SEM result shows the needle-like aragonite morphology of blood cockle shells powder transformed to cubic-like calcite after heat treated at 500 °C. These results were consistent with FTIR and XRD results.

N&lt;sub&gt;2&lt;/sub&gt;O Reduction and NOx Adsorption in Carbonator of Calcium Looping CO&lt;sub&gt;2&lt;/sub&gt; Capture Process

A dual-fluidized bed solid circulating system that comprised a bubbling bed carbonator and a fast fluidized bed regenerator was operated under a condition of Calcium Looping (CaL) CO2 capture process. Calcined limestone (CaO) was employed as bed material. Gas mixture simulating flue gas from air-blown combustor consisted of CO2, N2O, NO, O2, and N2 was fed to the carbonator. Most part of the fed CO2 was captured by the calcined limestone particles, then the partially carbonated particles were transported to the regenerator, in which thermal decomposition of CaCO3 was carried out in air stream. The carbonator of CaL process was found to be effective for N2O reduction when the sorbent particles had activity to capture CO2. A part of NO in the feed gas was also adsorbed by CaO particles, then the adsorbed NO was transported to the regenerator, and released to the gas phase there, though the net decomposition of NOx was not observed. CaL process was revealed to be a multifunctional process of CO2 capture, N2O decomposition, and removal of a part of NO in the flue gas fed to the carbonator.

Mutual Relationship between Solid-State Aragonite–Calcite Transformation and Thermal Dehydration of Included Water in Coral Aragonite

A specimen sample of coral skeleton (Pavona, Okinawa, Japan) was selected to study the mechanistic relationship between aragonite–calcite transformation and the thermal dehydration of the included water in biogenic aragonite. The sample exhibited three mass loss steps attributed to the thermal dehydration of the included water (2.8% of the sample mass) before the thermal decomposition of CaCO3. The aragonite–calcite transformation simultaneously occurred during the second dehydration step of the included water in a temperature region lower by approximately 100 K than in synthetic and geological aragonites. During the thermal dehydration of the included water and the aragonite–calcite transformation, the root structure of polygonal plate stacking in the biogenic aragonite was preserved. A possible mechanistic relationship between the thermal dehydration of the included water and the aragonite–calcite transformation is explained by the three successive dehydration steps: (a) the diffusional removal of the included water from the interstitial spaces between the polygonal aragonite plates, (b) the dehydration step accompanying the aragonite–calcite transformation in the polygonal aragonite plate, and (c) the diffusional removal of residual water accompanying the growth of as-produced calcite crystals.

Low temperature hydrothermal synthesis of ZrO2-CaO solid solutions

Nanosized powders of ZrO2-CaO solid solutions have been synthesized by hydrothermal treatment at 110°C. Amorphous hydrous ZrO2, CaO freshly prepared by thermal decomposition of CaCO3 and MOH (M = Na, Li) mineralizer solutions were employed as precursors for the hydrothermal synthesis. Calcia-stabilized zirconia (CSZ) with different CaO content and characterized by different crystal sizes have been produced by changing the hydrothermal treatment temperature, the reaction time and the mixture composition of precursors. The combined effect of both MOH and CaO on the crystallization-stabilization of zirconia at low temperature of hydrothermal treatment is discussed.

Thermal decomposition of CaCO3 in the presence of calcium fluoride

The thermal decompositoon of calcium carbonate mixed with calcium fluoride was examined by means of simultaneous TG, DTG and DTA. The temperature range of CaCO3 decomposition shifted to higher temperatures as a result of CaCO3-CaF2 eutectic formation. The temperature of melting of this eutectic was in the temperature range of CaCO3 decomposition, and therefore all factors which increase the partial pressure of CO2 (such as the thickness of the sample layer, the shape of the crucible, the heating rate, etc.) influence the amount of the liquid phase. The DTA curves can be regarded as the sum of three endothermic effects occurring almost simultaneously: decomposition of CaCO3 in the solid phase, melting of the eutectic, and decomposition of CaCO3 present in the liquid phase.

ChemInform Abstract: Preparation of Solid Catalysts for Vapor‐Phase Decomposition of Carbonyl Sulfide.

AbstractComparison of the catalytic activity and selectivity of a series of Al2O3 Catalysts in COS decomposition (reactions Aand B) demonstrate that electron‐donating sites catalyze reaction Awhereas Lewis acid sites catalyze reaction B. CaO Catalysts are prepared by thermal decomposition of CaCO3 and their catalytic activity is related to their amount of electron‐donating sites.

Preparation of Solid Catalysts for Vapor-Phase Decomposition of Carbonyl Sulfide

Abstract The vapor-phase catalytic decomposition of COS (COS→CO+1/xSx and 2COS→CO2+CS2) has been mechanistically investigated so as to prepare solid catalysts which are active and selective for the first reaction. The comparison of the catalytic activity and selectivity of a series of Al2O3 catalysts with their acid-base properties and the different behavior of these two catalytic decomposition reactions in the poisoning of an Al2O3 catalyst with SO2 demonstrate that electron-donating sites catalyze the first reaction whereas Lewis acidic sites do so the second reaction. CaO catalysts are prepared by thermal decomposition of CaCO3 at elevated temperatures and their catalytic activity is compared with their amount of electron-donating sites. The greatest catalytic activity and selectivity for the first reaction(yield of CO+Sx=21.4%, selectivity=80.2% at 873 K) are obtained over CaO catalyst prepared at 1123 K which has the greatest electron-donating ability. These values of the yield and selectivity to CO+Sx are much greater than those obtained over Al2O3 catalysts.

Thermal decomposition of CaCO3 and formation of ?-Ca2SiO4

Thermal decomposition of CaCO3 and formation of ?-Ca2SiO4

Esterification of Benzaldehyde Catalyzed by Alkaline Earth Oxides

When benzaldehyde was treated at 120-200 C over BeO, MgO, CaO, SrO or BaO without any solvent, a large amount of benzyl benzoate and a very small amount of benzyl alcohol were found as the raction products. The time variation of the ester formation gave S-shaped curves including induction periods (Fig.1). After the induction period, the reaction obeyed the first order rate equation with respect to the concentration of benzaldehyde (Fig.3). The induction periods were shortened remarkably by the addition of benzyl alchohol (Fig.6). The catalytic activity was found to increase in order of BeO MgO CaO SrO BaO (Table 1)and the activation energy and entropy were 9.4 kcal/mol and -49 e. u. for CaO and 54 kcal/mol and 54 e. u. for SrO, respectively. A very good correlation was found between the catalytic activity and surface basicity measured by an indicator method (Fig.4). ln the case of CaO, the highest activity was observed for CaO obtained by calcining Ca(OH)2 at 400 C or by thermal decomposition of CaCO3 at 900 C (Table 2), theugh CaO obtained by calcining Ca(OH)2at 900 C did not show any activity.On the basis of the observed results, it has been concluded that the active species of MgO and CaO are the metal alcoholates formed by the reaction of benzyl alcohol with the catalyst surface and the formation of the alcoholate is facilitated by the basic sites(O2- and OH-)on the surface. The reaction mechanism was also discussed.