Crystal Growth of Hydrogen/Tetra‑<i>n</i>‑butylammonium Bromide Semiclathrates Based on Morphology
Study
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Abstract
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