Crystal Growth of Hydrogen/Tetra‑n‑butylammonium Bromide Semiclathrates Based on Morphology Study

Morphology studies were conducted for the first time on the mixed hydrogen/tetrabutylammonium bromide (TBAB) semiclathrates. Morphology study dealt with the observation of nucleation of the first hydrate crystal, the growth of hydrates and the characteristic appearance of crystals through the microscope. Morphology changes occurring during the formation of mixed hydrogen hydrates using TBAB as a promoter were observed through the microscope. Concentration of TBAB was varied and the influence of concentration on the hydrate crystal morphology was studied. At lower TBAB concentration (1 and 2 mol %) needle like and equiaxial crystals were formed initially which later developed into columnar crystals having high transmittance and retained their individual structure. However, at higher TBAB concentration (2.5 mol % and above), cylinder like crystals were observed which developed into dense irregular shaped crystals with lower transmittance. The individual crystals cannot be distinguished, they become mushy and grow as layers. Characteristic wave formations were observed during crystal formation in all the cases. With the decrease in subcooling or with the increase in experimental pressure (driving force), the dimensions of the formed crystals was initially same but later increased to around 2–4 times the original size.