Visual Observation of Tetra-n-butylammonium Bromide Ionic Semiclathrate Hydrate Formation: A Laboratory Experiment

A laboratory experiment was performed using tetra-n-butylammonium bromide (TBAB) ionic semiclathrate hydrate, a crystalline compound. Ionic semiclathrate hydrates have unique properties, and hence, novel technologies utilizing the ionic semiclathrate hydrates have been proposed to date. Thus, students could learn fundamentals of functional materials through ionic semiclathrate hydrates from chemical and engineering points of view. In the experiment, formation of the TBAB hydrate was observed at fixed temperature and under atmospheric pressure by using TBAB aqueous solutions having TBAB mass fractions of wTBAB = 0.10, 0.20, 0.30, 0.40, and 0.50. There are no serious safety hazards. In addition, the experiment can be performed using inexpensive equipment and materials. The amount of the formed TBAB hydrate and its crystal morphology depended on the concentration of the aqueous solution. The students needed to submit a laboratory report describing fundamentals of the ionic semiclathrate hydrates, a relationship between equilibrium conditions and the amount of the formed TBAB hydrate, and an adequate crystal morphology of the TBAB hydrate crystals as a thermal storage material. Most students understood the experiment well, and the average score of the reports was approximately 80%.