The investigation of calcium carbonate formation using micro-Raman spectroscopy

Calcium carbonate (CaCO3) has got significant importance in nature and in several industrial processes. In its different mineral modifications, calcium carbonate is highly abundant in the earth crust, occurring as calcite, aragonite and vaterite (anhydrous crystalline polymorphs) or ikaite (calcium carbonate hexahydrate), calcium carbonate monohydrate, (hydrated crystal forms) and amorphous calcium carbonate (ACC). The CaCO3 can be formed during the process of biomineralization or synthetically with using gas diffusion method or mixing supersaturated solutions containing calcium cations and carbonate anions. The so-called carbonation reaction, plays a crucial role in hardening of lime mortars, a class of binders of relevance in culture heritage conservation. During this process, the CaCO3 is formed from Ca(OH)2 that uptake atmospheric CO2 in aqueous medium. This contribution is focused on the investigation with micro-Raman spectroscopy of CaCO3 modifications appeared during the synthesis from supersaturated aqueous calcium chloride and potassium carbonate solutions, under different reaction conditions [1], as well as during the carbonation reaction [2,3]

Microstructure of lime pastes with the addition of vegetable oils

Vegetable oils can be used as water- repellent additives for mortars and coatings for improving their durability when applied in the protection of structures exposed to severe weathering conditions involving water ingress. Previous studies have shown that, besides imparting water -repellence, vegetable oils can significantly affect the microstructure of the lime paste. The influence of the addition of different amounts (0.5 and 1.5 wt%) of linseed, stand, and rapeseed oil on the microstructure of lime pastes has been investigated with thermogravimetry, Fourier transform infrared spectroscopy, X -ray powder diffraction, and scanning electron microscopy, up to 18 0 days of age. The wettability of the pastes was analysed by measuring the contact angle of water drops on the pastes’ surface. The overall results indicate that linseed and rapeseed oil are more reactive with lime than stand oil, thus , affecting the microstructure of the paste more significantly. The lower reactivity of stand oil is assigned to the considerably lower amount of carbon -carbon double bonds as compared with the other oils. A higher amount of stand oil may be required to achieve water -repellence in the lime paste

Characterization of vaterite synthesized at various temperatures and stirring velocities without use of additives

Conditions for the synthesis of vaterite without additives have been investigated (T = 30 - 90 degrees C, stirring velocity = 200-600 rpm). The obtained different CaCO3 polymorphs were characterized with Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM). Quantitative phase analysis (QPA) was performed by the Rietveld method. To describe vaterite diffraction patterns, two structural models were employed. Their relative abundance was found to change with the temperature of synthesis. The optimal synthesis conditions for preparing pure vaterite (>= 99 wt.%) were found at 60 degrees C and 600 rpm. This is the first time pure vaterite is obtained at such high temperature without additives. The conditions under which the different polymorphs formed, and their microstructural features, are discussed. In addition, nanoindentation measurements on synthesized vaterite and calcite are firstly reported. The vaterite elastic modulus is higher than that of calcite (E = 16-48 GPa and E = 9-35 GPa, respectively), whereas the range in hardness was found to be the same for both polymorphs (H = 0.4-2.8). (C) 2015 Elsevier B.V. All rights reserved