Hollow Structure Formation Mechanism of Calcium Carbonate Particles Synthesized by the CO₂ Bubbling Method

Abstract

The hollow structure formation mechanism of calcium carbonate particles synthesized by the CO 2 bubbling method has been investigated. Samples were sequentially taken during the bubbling process to be structurally evaluated by X-ray diffraction and scanning electron microscopy. As a result, it has been elucidated that there are three development stages (A, B, and C) in the formation of the hollow structure. In stage A, amorphous CaCO 3 precipitates as primary particles with the decreasing pH by CO 2 bubbling. The primary particles then aggregate around pH 9.1 to form secondary particles, and turbidity ensues. Furthermore, because of the decreasing pH, the primary particles on the surface of the secondary particles begin to transform into the vaterite phase and form a shell. During stage B, the surface potential decreases along with a steep decrease in the pH, interparticle attraction of the primary particles on the surface of the secondary particles becomes stronger, and a highly compacted shell is formed. At the same time as vaterite precipitation on the surface, dissolution of the amorphous phase on the inside rapidly proceeds to precipitate vaterite particles by adhesion to the inside of the outer shell. At this time, contraction due to the release of water occurs and the hollow structure is formed. Moreover, it has been elucidated that, at pH ≤7, redissolution of the particulates inside the secondary particles occurs and definite shell structures are formed.

Synthesis and Characterization of Gd2O3 Hollow Microspheres Using a Template-Directed Method

“…Recently, many efforts have been made in the development of different methods for design and preparation of hollow microspheres materials. Among these methods, the most developed seem sto be the template method, including hard templates (such as carbon spheres [ 8 ], silica particles [ 4 ], melamine formaldehyde (MF) microspheres [ 5 ]) and soft templates (such as liquid droplets, vesicles, emulsion, gas bubbles) [ 9 , 10 , 11 ]. However, these methods have some inherent drawbacks in template formation and removal.…”

Synthesis and Applications of Hollow Particles

“…Subsequently, amorphous CaCO 3 particles which just inside the outer shell start to transfer to vaterite cr ystal. During repeat of these dissolution and re-precipitation process, the outer CaCO 3 shell completes to form with columnar structure 135) . Even though the bubble template is a new process and still on the way of investigation, it was indicated that this method is a facile and promising process to prepare hollow particles with the characteristic of low cost and high production.…”

Preparation of superhydrophobic nanocalcite crystals using Box–Behnken design

“…Calcium carbonate can be produced either by: (1) wet carbonation route, through a double decomposition reaction, wherein aqueous CaCl 2 and Na 2 CO 3 , or CaCl 2 and (NH 4 ) 2 CO 3 , or Ca(NO 3 ) 2 and Na 2 CO 3 are combined in an equal molar ratio; or (2) the bubbling carbonation route, in which CO 2 gas is bubbled through an aqueous slurry of Ca(OH) 2 (Barhoum et al, 2014;Ihli et al, 2014;Ukrainczyk et al, 2007;Reeder et al, 2013). The bubbling carbonation route is industrially used because of the availability of its raw materials, high yield as well as simplicity and low cost of production (Tomioka et al, 2012;Garcı´a Carmona et al, 2003). The bubbling carbonation is preferable in terms of environment preservation and the effective use of mineral resources.…”