In-situ observation of crystal detachment behavior in NH ₄Cl-H₂O system from chilling metal surface with vibration

The crystal detachment behaviors from a chilling solid surface with vibration were investigated using a transparent NH₄Cl-70H ₂O alloy. The nucleation experiments of NH₄Cl-70H ₂O alloy were performed on a chilling surface generator with various vibration frequency from 20 to 1 000 Hz and vibration acceleration from 10 to 100 m/s². The results indicate that the crystal detach rate increases and the grains are refined with increasing vibration acceleration under a certain vibration frequency. It is interesting to note that, when the frequency is 50 Hz, acceleration is 100 m/s², the crystal detach rate increases sharply and the grain refinement effect is strengthened. A special grain refinement phenomenon can be observed, when the vibration acceleration and frequency are up to a critical value. A power-based definition was introduced in order to describe the relationship between the vibration parameters and imposed power on the system. It is found that a power criterion exists for the grain refinement in the current system.