Narrow Results

The crystallization of calcium carbonate (CaCO₃) in soil controlled by natural organic material was considered a very important reason to enhance the property of ancient Chinese organic Sanhetu (COS), but how the organic material affected the crystallization of CaCO₃ in COS is still unclear. In this paper, a natural organic material (sticky rice, SR) and a synthetic organic material (anionic polyacrylamide, APAM) were selected as additives to investigate their effect on the crystallization of CaCO₃. The experimental results showed that the morphology and size of CaCO₃ crystals could be affected by the concentration of additives and reaction time, while only the size of CaCO₃ crystals could be affected by the concentration of reactant. Although the morphology and size of CaCO₃ crystals varied greatly with the variation of additive concentration, reactant concentration and reaction time, the polymorph of CaCO₃ crystals were always calcite, according to SEM/EDX, XRD and FTIR analyses. This study may help us to better understand the mechanism of the influence of organic materials on CaCO₃ crystallization and properties of COS.

A method of modifying calcium carbonate particles was investigated by coating sodium stearate or sodium oleate on the surface of calcium carbonate by wet method. The results of FTIR, activation and dispersion index, dispersity in kerosene, surface wettability tests and zeta potential tests show that sodium stearate or sodium oleate has successfully coated on the surfaces of calcium carbonate. The main factors were researched and the optimal parameters were obtained for the best modification effect. Compared with common rubber, the modified calcium carbonate added rubber has larger breaking tensile strength (more than 21%) and larger elongation at break (more than 16%). This research provides a feasible way of modifying calcium carbonate for its use as filler in organic matrix, reduces the cost and has a potential application in large-scale production of modified calcium carbonate.

A detailed quantum chemical calculation is performed at the MP2(full)/6-311G* level to explore the mechanism of calcium carbonate thermal decomposition. Four microscopic pathways are identified. The rate constants of rate-determining steps in four pathways are calculated over a temperature range 298–1200 K. The calculating results show that only path A (R(CaCO₃) → IM₁ → P(CaO + CO₂)) and path B (R(CaCO₃) → IM_B1 → IM_B2 → P(CaO + CO₂) have contributions to the CaCO₃ thermal decomposition, and path A may be more favorable than path B. The present theoretical studies may provide useful information in understanding reaction mechanism of metal carbonates at the molecular level.

Polypropylene (PP)/multi-walled carbon nanotube (MWCNT)/calcium carbonate (CaCO₃) composites are prepared by melt mixing using two types of CaCO₃ of different sizes. The electrical resistivities of the composites with the two types of CaCO₃ are all lower than those of the corresponding PP/MWCNT composites at various MWCNT loadings (1 wt%–5 wt%). The morphology of the composites is investigated by field emission scanning electron microscopy (FESEM). The crystallization behavior of PP in the composites is characterized by differential scanning calorimetry (DSC). The storage modulus, as measured by dynamic mechanical analysis (DMA), increases significantly by the presence of CaCO₃.

Polymethyl methacrylate (PMMA)-coated nano-CaCO₃ particles were prepared by in-situ emulsion polymerization. The mechanical properties of nano-CaCO₃ particles-reinforced PVC were investigated using an AG-2000A universal testing machine and an XJU-2.75 izod impact tester; interfacial adhesion between CaCO₃ nanoparticles and PVC matrix by SEM, and structure of PMMA coated on the surface of CaCO₃ by FTIR and ¹H-NMR. The results indicate that the PMMA coated on the nano CaCO₃ particles consists mainly of syndiotactic structure, and their three tacticity contents were rr 52.8%, mm 7.3% and mr 39.9%, respectively. The interfacial adhesion between CaCO₃ nanoparticles and PVC matrix was significantly improved when the CaCO₃ nanoparticles were coated with PMMA, which led to increased Young's moduli and tensile strengths of the PMMA-coated CaCO₃/PVC composites. The izod impact strengths of the composites were strongly affected by the PMMA coating thickness and increased significantly with increasing the volume fraction of CaCO₃ filler in the composites.

Phosphors based on calcium carbonate, co-doped with various Eu³⁺ and Dy³⁺ concentrations were prepared by microwave co-precipitation method. The prepared phosphors were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry and differential scanning calorimetry (TG-DSC) and photoluminescence and photoluminescence excitation (PL-PLE) spectroscopy. Results showed that Dy³⁺ and Eu³⁺ ions were uniformly introduced into the host lattice of CaCO₃ taking the place of Ca²⁺ ions. Under the excitation at 382 nm, the emission peak wavelengths were at 487 nm (⁴F_9/2 → ⁶H_15/2 of Dy³⁺), 576 nm (⁴F_9/2 → ⁶H_13/2 of Dy³⁺), and 614 nm (⁵D₀ → ⁷F₂ of Eu³⁺). The luminescent intensities and emitting colors of Eu³⁺-Dy³⁺ co-doped CaCO₃ phosphors could be controlled by UV–violet excitations wavelengths or the rare-earth ions concentrations of Eu³⁺ and Dy³⁺ in phosphors. The chromaticity coordinates and photographs of samples under UV light showed the changes of the luminescence color intuitively through the varing UV–violet excitations wavelengths or the rare-earth ions concentrations of Eu³⁺ and Dy³⁺.

Some people think that carbon and sustainable development are not compatible. This textbook shows that carbon dioxide (CO₂) from the air and bio-carbon from biomass are our best allies in the energy transition, towards greater sustainability. We pose the problem of the decarbonation (or decarbonization) of our economy by looking at ways to reduce our dependence on fossil carbon (coal, petroleum, natural gas, bitumen, carbonaceous shales, lignite, peat). The urgent goal is to curb the exponential increase in the concentration of carbon dioxide in the atmosphere and hydrosphere (Figures 1.1 and 1.2) that is directly related to our consumption of fossil carbon for our energy and materials The goal of the Paris agreement (United Nations COP 21, Dec. 12, 2015) of limiting the temperature increase to 1.5 degrees (compared to the pre-industrial era, before 1800) is becoming increasingly unattainable (Intergovermental Panel on Climate Change (IPCC), report of Aug. 6, 2021). On Aug. 9, 2021 Boris Johnson, prime minister of the United Kingdom, declared that coal needs to be consigned to history to limit global warming. CO₂ has an important social cost…

We saw (Section 4.4) that CO₂ (carbon dioxide) reacts with quicklime (calcium oxide) in water at 25°C, under 1 atm generating calcium carbonate or limestone (CaCO₃). The process is a sequence of two reactions (4.14) and (6.1):

This paper develops a polyvinylidene fluoride (PVDF)/ polyacrylic acid (PAA)/calcium carbonate (CaCO₃) composite membrane using the in-situ mineralization method. PAA is used as polyanionic macromolecule to induce the generation of CaCO₃ particles. The mineralization condition was optimized based on CaCl₂ content in the selection process of the casting solution and carbonate source. The structures and surface hydrophilicity were characterized by field emission scanning electron microscope (FESEM), Fourier transform infrared/attenuated total reflection (FT-IR/ATR) spectrometer, energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and water contact angle for the prepared composite membranes. The results demonstrate that CaCO₃ particles consisting of calcite and vaterite disperse uniformly on the membrane surface and in the membrane cross-section; the membrane hydrophilicity increases with the increase of CaCl₂ content in the casting solution. The improved hydrophilicity is resultant of the membrane structure in the in-situ mineralization process and the collapse of PAA chains in the membrane pores, facilitating the tenfold improvement of the membrane’s pure water fluxes. Due to the electrostatic repulsion between the positively charges lysozyme and CaCO³ particles, the mineralized membranes possess a high rejection (85.13%) and flux recovery ratio (77.21%). Therefore, in-situ mineralization is a convenient and effective method to prepare hydrophilic composite PVDF membranes.

Poly (vinylidene fluoride) (PVDF)/poly (acrylic acid) (PAA)/calcium carbonate (CaCO₃) composite membrane were prepared by in-situ mineralization method. PAA is used as polyanionic macromolecule to induce the generation of CaCO₃ particles. The mineralization condition was optimized based on CaCl₂ content in the casting solution and carbonate source selection. Structures were characterized in detail by FESEM and XRD for the prepared composite membranes. Results confirm that CaCO₃ particles consisting of calcite and vaterite disperse uniformly on the membrane surface and in the membrane cross-section. The improved hydrophilicity is resulted from the membrane structure in the in-situ mineralization process and the collapse of PAA chains in the membrane pores. Therefore, pure water fluxes of the membranes were improved about ten times. Our work indicates that the in-situ mineralization method is convenient and beneficial to prepare hydrophilic composite PVDF membranes.