Abstract: As a simulation of surface solidification of materials,quasi-two dimensional dendritic deposition of ammonium chloride(NH_4Cl)crystals from an aqueous solution film with free surface by vapourization was investigated by the in- situ observation technique.The depositing morphologies of NH_4Cl crystals are faceted and of growth laws differing from the three-dimensional case.Under low supersaturation,faceted dendrites formed,whereas the anisotropy in growth kinetics decreases with the increase of supersaturation.When vapourizing rate(supersaturation)is not very low, oscillations of growth rate.tip-radius and second arm spacing of the dendrites were observed.It is suggested that this dynamic phenomenon is attributed to the correlation between the convection-transfer effect induced by the surface tension gradient of solution film.and the driving force for deposition.

Key words: surface deposition, dendrite, surface tension, oscillation