Molecular Dynamics Simulation On Growth Mechanism Of Soft Scale And Hard Scale

During industrial water and living water, water scale deposition in the tube wallcaused a lot of economic and technical problem. The chemical control method andphysical control method are used in industry. But the chemical control method broughtnot only the pollution to the environment but the corrosion to the equipment. In recentyears, the magnetic water treatment technology as a physical method has been appliedin industrial scale inhibitor, and the effect is distinct. Due to confusion of water system,however, the mechanism of anti-scale has not been solved. Study and assessment onmagnetic water treatment technology mostly rely on the collection of the experimentaldata or the theoretical extrapolation, the errors is visible. So a new research approach isin strong demand.In our study, the growth kinetics of the calcium carbonate that is the maincomponents of scale was researched through molecular dynamics simulation. From themicroscopic point of view, we discussed the crystallization mechanism of calcite andagonite which are homogeneous and isomerism. The thesis consists of three partscontent: Firstly, we investigated the present situation of experiment and theory aboutmagnetic anti-scale, and developed the simulation program. Secondly, we built themodel of the calcium carbonate aqueous, obtained the dynamic information of Ca2+andCO32-by molecular dynamics simulation to the calcite and the aragonite of the aqueoussolution. Finally, we calculated the self-diffusion coefficient, the radial distributionfunction, analyzed the binding energy of the ion （Ca2+, CO32-）and the crystal surfacein the two solutions and the essence of antiscale.From our research, the conclusions are showed as the following:①the activity ofthe water molecules increased ceaselessly with the increasing of the temperature. Butthe activity in the two solutions decreased when the temperature is333K, so thecrystallization is easy in this temperature.②The calcite is easy to crystallization thanaragonite at room temperature through contrasts the diffusion coefficient of Ca2+andCO32-in the two aqueous solution.③The first and second peak of the radialdistribution function graph of Ca2+, CO32-and H2O decreased obviously in the aqueoussolution of aragonite. This showed that the structure of water clusters is broken in theaqueous solution of aragonite, that is, the density of CaCO3is lower. So the nucleus isnot easy to grow up, and the loose scale is flow away with water.④The bindingenergy of the ion （Ca2+, CO32-）and the crystal surface in the calcite is higher0.02 kcal/mol than in aragonite. The calcite is the stable structure of the calcium carbonateand the metastable aragonite would eventually transformed into the calcite. Meanwhile,regardless of any kind of the water treatment technology, the energy value provided bythe outside world is at least in the top of the value. So the result provides a theoreticalbasis for the anti-scaling technology.