Abstract: The evaporation by decomposition of NH4NO3 microdroplet has been investigated under atmospheric pressure and temperature. During the experiments, a single microdroplet with an initial radius of 5-30 μm. was suspended in an electrodynamic balance and the change of its light-scattering intensity with time at a scattering angle of 34.5°-68.4° was measured by a 512 element linear photodiode array. The microdroplet size was determined by comparing the experimental data with Mie theory. The change of the microdroplet size in the process of evaporation by decomposition was thus determined precisely. A diffusion controlled surface reaction model based on the experimental data was proposed to describe this process. The process of evaporation by decomposition of NH4NO3 microdroplets can be described as follows: when a single microdroplet was suspended in an electrodynamic balance, moisture first evaporated with the decomposition of NH4NO3. As a result, a microdroplet of metastable pure NH4NO3 was obtained. Since it was thermodynamically unstable, the microdroplet would change into a solid crystal, after having experienced further evaporation.

摘要： 在常温常压下,一个初始半径为5～30μm的硝酸铵水溶液微滴被悬浮在电动平衡仪内,同时该微滴受到一束激光的照射.在34.5°～68.4°散射角内使用一个512点线性光电列阵,测定不同时间里硝酸铵微滴的光散射强度变化.借助于计算机上Mie理论计算,可以容易地比较出硝酸铵微滴的尺寸.根据这种方法,可以精确地测定硝酸铵微滴在分解蒸发过程的尺寸变化.在实验基础上,提出了一个扩散控制的表面反应模型以描述硝酸铵微滴的分解蒸发过程,并得到硝酸铵微滴在25℃、26℃和27℃时的平衡压力.