Hikal Walid M, Bhattacharia Sanjoy K, Vaughn Mark W, Weeks Brandon L
Department of Chemical Engineering, Texas Tech University, Lubbock, TX 79409, USA.
College of Engineering, West Texas A&M University, Canyon, TX 79016, USA.
Molecules. 2022 Aug 26;27(17):5482. doi: 10.3390/molecules27175482.
In this article, we report the in-situ nanoscale experimental measurement of sublimation rates, activation energy of sublimation, and diffusion coefficients of 2,4,6-trinitrotoluene (TNT) single crystals in air using atomic force microscopy (AFM). The crystals were prepared by slow evaporation at 5 °C using acetone-dissolved TNT. The mass loss was calculated by monitoring the shrinkage of the surface area of layered islands formed on the surface of the TNT crystals due to sublimation upon isothermal heating at temperatures below the melting point. The results suggest the sublimation process occurs via two-dimensional detachment of TNT molecules from the non-prominent facets on the crystal surface which imitates the nucleation and crystal growth process. Sublimation rates are one order of magnitude smaller than previously reported values. However, the calculated activation energy (112.15 ± 3.2 kJ/mol) and temperature-dependent sublimation rates agree well with the reported values for TNT thin films and microcrystals determined by UV-vis absorbance spectroscopy and quartz crystal microscopy (QCM) (90-141 kJ/mol). The average diffusion coefficient is (4.35 × 10 m/s) which is within the range of the reported theoretical values with an average of 5.59 × 10 m/s, and about 25% less than that determined using thermogravimetric analysis for powder TNT.
在本文中，我们报告了使用原子力显微镜（AFM）对2,4,6-三硝基甲苯（TNT）单晶在空气中的升华速率、升华活化能和扩散系数进行的原位纳米级实验测量。晶体是通过在5°C下使用丙酮溶解的TNT缓慢蒸发制备的。通过监测在低于熔点的温度下等温加热时由于升华而在TNT晶体表面形成的层状岛的表面积收缩来计算质量损失。结果表明，升华过程是通过TNT分子从晶体表面不突出的晶面进行二维脱离而发生的，这类似于成核和晶体生长过程。升华速率比先前报道的值小一个数量级。然而，计算得到的活化能（112.15±3.2 kJ/mol）和与温度相关的升华速率与通过紫外可见吸收光谱和石英晶体显微镜（QCM）测定的TNT薄膜和微晶的报道值（90 - 141 kJ/mol）吻合良好。平均扩散系数为（4.35×10 m/s），在报道的理论值范围内，平均值为5.59×10 m/s，比使用热重分析法测定的粉末TNT的扩散系数小约25%。
