粗糙铝片表面NH_4Cl晶体形核特性研究

Research on Nucleation Characteristics of NH_4Cl Crystal on Coarse Aluminum Surfaces

制备了润湿特性不同的纯铝表面,并考察了以其作为基底激冷触发30%NH4Cl(质量分数)水溶液中的NH4Cl晶粒形核过程。结果表明:随在空气中暴露时间的延长,具有微纳米层级结构的纯铝表面的润湿性会由强润湿转变为不可润湿,NH4Cl晶粒在强润湿表面的形核点密度明显高于不可润湿表面。分析认为:强润湿性表面产生的毛细作用易于使溶液渗入表面结构中,因而表面凹陷能够有效地促进形核;而不可润湿表面易于存留气体,这会减少利于形核的凹陷结构,同时凹陷结构中气泡的存在使得形核功增大,导致形核困难。

Different wettability was acquired on aluminum surface by eroding, and then nucleation characteristics of NH4Cl crystal on the coarse surface were investigated by immerging the obtained surface into 30% NH4Cl （mass fraction）water solution. Experiment results indicate that： surface wettability shows a transformation from strong wettability to non-wettability on the pure aluminum surface which has a micron and nanometer double roughness structure during its exposure in the atmosphere. Nucleation density on the strongly wetting surface is significantly higher than that of the non-wetting surface. Analysis results show that the capillary effect helps the solution infiltrate into the surface rough structure and drive the air out of the coarse surface, so nucleation is promoted effectively by the sharp corners and hollows of the surface. The number of nucleation sites decreased significantly on the non-wetting surface. The reasons can be attributed to the air bubbles trapped in the surface structures which decrease the effective nucleation sites, moreover, the existing of air bubbles on the nucleation substrates leads to a higher nucleation energy barrier, thus the nucleation density is decreased on the non-wetting surface.