Disaggregation Behavior And Dispersion Of Nano-Calcium Carbonate In Water Media

Nano-CaCO₃, an important new chemical material, is widely found in many industrial applications at present. Because of its fine particle size,large specific surface area and high surface energies,nano-CaCO₃ powders are very easy to aggregate together. This seriously affects its original superior properties and its applications. Based on extended DLVO theory, this paper studied the disaggregations and dispersions behavior of nano-CaCO₃ in water. And also discussed the dispersion mechanisms of sodium polyacrylate on nano-CaCO₃ particles.The aggregation behavior of nano-CaCO₃ particles in water was investigated by observing the dispersion state of nano- CaCO₃ in water and the effects of ultrasonic wave on dispersion and also observed by means of transmission electron microscope(TEM). The results showed nano-CaCO₃ particles were in an aggregate state. Each aggregates contained many original primary nano-CaCO₃ particles. These particles combined together closely, with large volume and loose structure. The grain size of an agglomeration is up to 1μm, and the median-particle-size d(0.5) is 1.799μm.This paper also studied the disaggregation behavior and dispersion of nano- CaCO₃ particles in water. The results showed high-speed stirring, ultrasonic treatment, mechanical grinding and the addition of disperser could to some extent increase the particle dispersion in water. High-speed stirring could break up agglomerate nano-CaCO₃ and made median-particle-size d(0.5) decrease to 1.444μm. Ultrasonic treatment and mechanical grinding could to a large extent make agglomerate nano-CaCO₃ disaggregate. The optimum dispersion condition was achieved. When the amount of CD458 was 0.1⁰.5% and the pH value of solution 9, the median-particle-size d(0.5) is 0.173μm, which is close to nano-size of primary particle. Sodium hexametaphosphate(SHMP), sodium dodecylbenzenesulfate (SDBS) and sodium polyacrylate (CD458) could all make nano-CaCO₃ disperse well in water. Their dispersion effects were CD458 >SHMP >SDBS.This paper also studied the dispersion mechanism of sodium polyacrylate on nano-CaCO₃ . Zeta potential of nano-CaCO₃ particle in water is negative in large pH range when adding CD458. When pH was 9, the absolute value of zeta potential was maximum and the electrostatic repulsion effect was also maximum, so the nano- CaCO₃ particle were in a best dispersion state. Surface adsorption behavior of sodium polyacrylate on nano-CaCO₃ particle was due to the competitive adsoption of sodium polyacrylate dissolved in water with CO₃^2-,HCO₃^- and OH^-.