Contribution of Aggregation to the Growth Mechanism of Seeded Calcium Carbonate Precipitation in the Presence of Polyacrylic Acid

Abstract

Our work investigates the precipitation mechanism of a seeded calcium carbonate reaction, by using cryogenic TEM to observe the early stages of the reaction. The early precipitation of a hydrated phase is proposed as an intermediate phase before transformation into calcite. Thermodynamic modeling in conjunction with pH, surface potential measurements, and colloidal stability modeling demonstrate that calcite growth is dominated by agglomeration. This is in agreement with the cryogenic TEM observations, which suggest oriented attachment dominates early aggregation. The final stage of the reaction is described by a ripening mechanism that is significantly inhibited when high concentrations of polyacrylic acid (PAA) are used. The different concentrations of PAA lead to significant differences in the final particle substructure observed using cross section TEM. At low PAA concentrations, single crystal particles result, coherent with the proposed early oriented attachment mechanism and interfacial energy calculations. A core shell model is proposed for high PAA concentrations, whereas internal ripening of nanosized pores has been observed for low PAA concentrations, suggesting trapped solvent during the rapid initial particle formation at the relatively high supersaturations (S ) 30) investigated.

Growth modification of seeded calcite using carboxylic acids: Atomistic simulations

“…Experimental observations of calcite surfaces [12,54] show a high density of steps, where carbonate dissolution at the pH of interest (around nine) is more favorable [55], which is also predicted by theory [56]. Even stable surfaces such as the ð1 0 1 4Þ surface have been shown to reconstruct in moist air via pit formation and film growth [57], making it reasonable to consider defective stepped surfaces in our simulations.…”

Precipitation of Nanosized and Nanostructured Powders: Process Intensification and Scale‐Out Using a Segmented Flow Tubular Reactor (SFTR)

“…Calcium carbonate precipitation has been studied intensively in our group for more than ten years [16,20,[34][35][36][37]. The precipitation of calcite is controlled by the addition of seeds stabilized by PAA.…”

Synthesis of Submicrometer Calcium Carbonate Particles from Inorganic Salts Using Linear Polymers as Crystallization Modifiers

“…1 Although calcium carbonate is an abundant naturally occurring mineral already largely used in the polymer industry, recently the clever manipulation of particle size and its effects on the material properties has attracted considerable attention. [2][3][4][5][6][7][8][9][10][11][12] Nano-and micrometer calcium carbonate particles can be synthesized by a variety of methods, including controlled gas diffusion, colloidal/microemulsion systems, sonochemistry, hydrothermal synthesis, etc. The simplest approach consists of the precipitation of calcium carbonate from solutions containing inorganic salts as a source of calcium(II) and carbonate ions.…”

“…These include metallic ions, surfactants, 10,13 biopolymers, 2,[14][15][16] and synthetic polymers. [2][3][4][5][6]9,[17][18][19][20][21][22][23][24][25] Indeed, crystallization control is a critical requirement in the synthesis of many important materials.…”

“…One common feature of polymers able to control the crystallization of calcium carbonate, such as poly(styrene sulfonate) 5,9,23 and poly(acrylic acid), 4,17,18,[26][27][28] is that they are anionic (or contain anionic segments) and are therefore capable of interacting with calcium(II) ions and with the crystal surface itself.…”