Papers by Keyword: Calcite

Abstract: Calcite is a widely available biocompatible material and produced naturally by marine seashells. It can function as a host of bioimaging fluorophores or photoluminescent lanthanides. Eu (II) was incorporated into calcite, a polymorph of calcium carbonate (CaCO₃), through co-precipitation to explore the photoluminescence (PL) of Eu-doped calcium carbonate. Eu (II) was incorporated at different mass percentages from 0.625 to 20% at temperatures not exceeding the decomposition of both CaCO₃ and europium carbonate (EuCO₃). The temperature and transformation of Eu were tracked and showed that at a curing temperature of 400°C, for 20% Eu, Eu (II) ions were initially incorporated into the calcium positions in calcite. As the temperature increased to 450°C, the oxidation of Eu (II) and formation of europium sesquioxide (Eu₂O₃), was observed. The reaction was confirmed by X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and mass spectrometry (MS). Eu³⁺, with a smaller crystal radius, was preferentially incorporated into the calcite instead of the larger Eu²⁺ due to the reduction in the lattice parameters and crystal volume. PL results on the samples further showed red luminescence of Eu³⁺ at excitation and emission peaks of 390 and 619 nm, respectively instead of the blue luminescence of Eu²⁺.

Abstract: Efforts to reduce the usage of imported raw materials in the ceramic industry have encouraged usage of local calcite minerals for production of refractory ceramic products. Corundum-mullite ceramics as refractory products were prepared by using clay, alumina and calcite mineral (CaO) via powder pressing method. The effect of CaO addition from 2.9 to 6.5 wt.% (R1, R2 & R3) on the mechanical strengths such as bulk density, apparent porosity, firing shrinkage and compressive strength were systematically studied as well as the reheat shrinkage and crystallinity of mullite ceramic bodies. The results indicated that the sintering process was prevented by the formation of anorthite phase at higher CaO content. The bulk density increased continuously as the CaO content was increased from 2.9 to 6.5 wt.%, while the apparent porosity and water absorption decreased with the increment of CaO content especially at temperature 1400 °C. On the other hand, addition of small amount of CaO have improved compressive strength of the ceramic body due to reduction in porosity and increase of crystalline phase. Addition of CaO content higher than 4.8 wt.%, would result in increment of crystallinity of the body due to formation of anorthite phase. It was observed that the R1 body (2.9 wt.% CaO) has the lowest reheat shrinkage percentage compared to other bodies and has complied with the Japanese Industrial Standard of mullite refractory product which is lower than 0.2% shrinkage percentage at 1300°C in the furnace for 8 hours.

Abstract: Submicron-sized calcium carbonate (CaCO₃) particles were prepared using an aerosol method in which two commercial air humidifiers containing 0.05 M of Na₂CO₃ and CaCl₂ aqueous solutions were utilized as aerosol suppliers. Two streams of aerosols evaporated from the separate humidifiers were allowed to meet in 17-meter long, spiral reaction tube where collisions between two types of droplets containing precursor reagents leaded to grow of CaCO₃ particles and precipitate onto the inner walls. XRD and SEM analysis revealed that CaCO₃ particles were formed in calcite phase almost entirely.

Abstract: The paper describes the process of recrystallization of portlandite of limestone mortar in calcite. The degree of crystallinity of calcite in limestone mortar of some medieval objects of the north of the Byzantine oecumene is shown through the example of Abkhazia and calcite in natural limestone and marble. The work provides a comparative analysis of the calcite crystallinity and the estimated age of the building objects according to historical and architectural data. It is proven that the higher the calcite crystallinity is the elder the lime mortar and, accordingly, the architectural object is.

Abstract: Abstract. In this study, the CaCO₃ powder has been successfully synthesized by mixing CaCl₂ from natural limestone and Na₂CO₃ in the same molar ratio. The mixing process of solutions was carried out by employing the molar contents of 0.125, 0.25, 0.375 and 0.5M at varying temperatures of 30, 40, 60 and 80ᴼC. The produced CaCO3 microparticles were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The highest content of aragonite phase with morphology rod-like of the samples is around 29 wt%, resulting from the process using solution of 0.125 M at 80 ᴼC. While at 30 ᴼC and 40 ᴼC produced 100 wt% calcite phase.

Abstract: In this study, the phonon-based thermal conductivity of magnesite (MgCO₃) and dolomite (CaMg(CO₃)₂) is calculated and compared with an earlier recent calculation on calcite (CaCO₃). Equilibrium molecular dynamics simulation by way of the elegant Green-Kubo formalism is used for calculating the thermal conductivity. The thermal conductivity is investigated over a wide temperature range (from 200 K to 800 K) for all of the above mentioned materials. The most reliable potential parameters are used for characterising the interatomic interactions. In all of the models, two independent mechanisms are considered. The first is temperature independent, which is relevant to the acoustic short-range and optical phonons, and the other is temperature dependent, which is linked to the acoustic long-range phonons. In the study, the heat current autocorrelation function (HCACF) is calculated over the averages of the NPT, NVT and NVE ensembles in the x- and z- directions. In addition, it is shown that the optical, acoustic short- and long-range phonon modes are the main contributors to the decomposition model of the thermal conductivity. In a further investigation, the effects of the computational cell sizes on the thermal conductivity are investigated with five different simulation blocks containing 30, 240, 810, 1920 and 6480 atoms. Finally, this research provides a comparison of the thermal conductivity from this study and experimental studies: they are in good agreement.

Abstract: This paper deals with the verification of the possibility of preparing synthetic ettringite in a way of direct addition of aluminum sulfate and calcium hydroxide as an alternative to the hydration of yeelimite. The stability of the resulting system was studied using the X-ray diffraction (XRD) and differential thermal analysis (DTA) in two different environments, namely in a laboratory environment and the environment of saturated water vapour. The evaluations of X-ray diffraction analysis and thermal analysis show that in the ettringite sample stored in the laboratory environment, evaporation of molecular water and subsequent transformation of ettringite into metaettringite or monosulfate can occur over time. Conversely, exposition of saturated water vapour environment can lead to saturation of the system by free calcium ions due to the slow dissociation of calcium carbonate, and thereby increase the amount of ettringite at the expense of gypsum and aluminum amorphous phase. To verify the above, it is recommended long-term monitoring of samples exposed in monitored environments.

Abstract: Self-healing cement is a novel topic in concrete technology. Concrete is created to have its own ability to heal cracks. Crack closure is due to the material deposition of the gap so causing the crack closed. Materials used in this paper is mortar composition with ordinary portland cement replaced by calcium carbonate (CaCO₃) and rice husk ash. There are three testing presented in this paper. The first is compressive test to determine the compression applied to mortar for initial cracks. The second is an ultrasonic pulse velocity (UPV) test to observe the depth of cracks and density of each composition. The third is macroscopic investigation to observe cracks wide in each mixture. The maximum compressive strength of 22.46 MPa shown by specimens made with 10% rice husk ash and 10% calcium carbonate cement. By the end of healing process, it reached 23.18 MPa. It was also shown that in crack depth decreased from 38 mm to 16 mm. From this analysis, it can be concluded that rice husk ash (RHA) and calcium carbonate (CaCO₃) can be utilized as self-healing concrete materials.

Abstract: The characterization of historic lime mortars is crucial for many cultural heritage conservation issues. In this work, the characterization of a historical lime mortar is described. Samples for chemical analysis were obtained after different milling times and using the RILEM acid digestion method on several replicates. Qualitative and quantitative determination of phases in the mortar and in the residues after acid attack and the potential presence of CaCO₃ polymorphs, were accomplished with X-ray powder diffraction. Results suggest that representativeness of the sample and the homogenisation, although not always achievable in conservation practice, are strongly affecting results.

Abstract: The Importance of this Paper is Determined by the Research of Conditions of Photosorption Processes Occurance on the Surface of Aerosol Particles Resulting in the Removal of Toxic Substances from the Atmosphere. Acid-Base Properties of Oxygen-Containing Calcium Compounds being Components of Troposphere Aerosol Particles were Studied by Methods of Ph-Metry and Hammet’s Indicators. the Basic Properties of the Investigated Compounds Surfaces are Predominant Ones: рН_iis of Calcium Oxide and Hydroxide has a Value of 9.3 – 9.5, and that for Carbonate and Calcite Equals to 12.3-12.4. Indicator Method Distinguishes Three Areas of Spectrum Corresponding to Lewis Base, and Brensted Neutral and Basic Centers. the Intencity of Peaks is much Higher for Ca(OH)₂ and CaO. the Interaction Process of Halogen-Containing Organic Compounds (Freons: 134a, 22 and 12) with Calcium Carbonate Surface under Illumination in Conditions close to Tropospheric Conditions was Studied. it is Shown that the Interaction is the Destructive Photosorption of Freons (134a or 22). the Spectral Dependence of Effective Quantum Yield of Destructive Photosorption is Determined. as a Result of the Interaction Calcium Fluoride and Calcium Chloride are Formed at the Surface.