Abstract
Mechanochemical and microwave-assisted hydrothermal (MicroWave Treatment [MWT]) procedures were applied to prepare crystalline CaCO3. Mechanochemical process was carried out at different speeds of rotation (500 or 850 rpm/min), different duration times (30 or 60 min) and in the aqueous suspensions or in dry state. MWT synthesis was conducted in a saturated water vapour or under the layer of water. The crystalline and porous structures of the prepared samples as well as their morphology were investigated using N2 adsorption, X-ray diffraction and scanning electron microscopy methods. As a result, the calcium carbonate samples in the form of calcite were obtained. The materials prepared by the mechanochemical route performed in the aqueous suspension are characterized by smaller crystallite sizes as compared to those obtained without the addition of water. The samples obtained hydrothermally have the largest size of crystallites. Powders prepared by energetical milling possess higher values of specific surface area in relation to the parameter for those synthesized hydrothermally. In the process of hydrothermal treatment, macroporous structure of the prepared materials is created. With the increasing specific surface area of the sample, the size of the crystallites decreased.
Highlights
Calcium carbonate (CaCO3) is a substance widely distributed in nature
In the case of isotherms for the materials synthesized mechanochemically (Figure 1(b)), it can be seen that elongation of milling process causes drop of the specific surface area and the sorption volume of pores, but the position of the main peak observed in Figure 1(b) for all samples is the same
The values of specific surface area obtained for the tested here materials are at a similar level as in the case of the microparticles of CaCO3 described in work (Sukhorukov et al, 2004)
Summary
It is estimated that 7% of the Earth’s crust, such as marble and limestone, is composed of calcium carbonate It occurs in three crystalline forms, i.e. calcite (rhomboeder), aragonite (needles) and vaterite. (polycrystalline spheres) of different morphology and different shapes of crystals, wherein calcite is the most stable (Peric et al, 1996; Tai and Chen, 1998) This substance has many applications in different branches of industry, among others, as a polymer filler (Gorna et al, 2008), as a pigment (Walton et al, 1973; Yoo et al, 2009), as a template for the encapsulation of bioactive compounds (Sukhorukov et al, 2004) or as an adsorbent for the removal of heavy metals from water (Ahmad et al, 2012; Ma et al, 2012a, 2012b). Its use is defined by a large number of specific parameters, such as crystalline form, morphology, particle sizes and their distribution, specific surface area, chemical purity and the like
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