Diffusion-driven growth of calcium carbonate polymorphs in microchannels

Area of Science:

• Materials Science
• Chemical Engineering
• Fluid Dynamics

Background:

• Understanding crystal growth is crucial for materials science and chemical processes.
• Microfluidic devices offer controlled environments for studying dynamic phenomena like crystallization.
• Calcium carbonate polymorphs (calcite and vaterite) have diverse industrial applications.

Purpose of the Study:

• To develop and apply a novel microfluidic approach for characterizing individual crystal growth.
• To investigate the influence of reactant stoichiometry and spatial location on calcium carbonate polymorph formation.
• To analyze the kinetics and controlling factors of crystal surface growth.

Main Methods:

• Utilizing a Y-shaped microfluidic reactor to mix calcium chloride and sodium carbonate solutions.
• Monitoring crystal formation and development using in-situ imaging techniques.
• Employing numerical modeling to support experimental observations and understand reaction zones.
• Analyzing crystal morphology and growth patterns from captured images.

Main Results:

• Crystal formation (calcite and vaterite) is dependent on both reactant stoichiometric ratios and their location within the microchannel.
• Significant crystal growth was observed closer to the microchannel confluence.
• Both calcite and vaterite morphologies predominantly form in the carbonate-rich region of the reactor.
• Side growth of calcite particles is diffusion-controlled and independent of crystal orientation and reactant ratios.

Conclusions:

• The microfluidic approach provides detailed insights into crystal growth dynamics.
• Spatial effects within the microfluidic channel significantly impact calcium carbonate polymorph selection and growth.
• Diffusion control governs the side growth of calcite, offering a key parameter for process optimization.