| Cryo-SEM Imaging of Microstructures
in a Chelated Sol-Gel Process |
MANOJ M. HARIDAS, AsHoK MENoN, NrriN GoYAL, SANJAY CHANDRAN AND JAYEsH R. BEI.LARE
Pages : 152-155
DOI : 10.1080/0371750X.1995.10804709 |
| Abstract |
| Cryogenic scanning electron microscopy as a tool to image
wet sol to gel transformations, has been applied for the
first time to obtain microstructural information during
controlled hydrolysis. Aluminium sec-butoxide was
chelated with a 1:1 mole ratio of ethyl acetoacetate. About
5.0 ml of isopropanol per gram of alkoxide was added to
the chelated batch, and a powerful contact mode probe
type ultrasonication performed to yield an intimately
blended alumina sol. A controlled water addition at the
rate of 0.4 ml per hour per gram of alkoxide was done on
the sol. About 100 microlitre of samples in varying stages
of sonogelation was extracted using a micropipette and
sandwiched between two 300 mesh TEM nickel grids
placed on copper plate supports. The sandwiched sample
was plunged into liquid freon at high speeds to achieve a
rapidly solidified state without crystallization. The sample
was thermally fixed and placed in the microscope which
was previously cooled to -170°C using liquid N2• Microscopic
contrast achieved from a variation in topology, after
fast-freeze and freeze-fracture, showed the existence of a
growing alumina species as well as a reduction of the
chelated agglomerated species with increasing water addition
to the system. This paper studies aU microstructural
changes and the approach is novel in the sense that the characterization
of wet alkoxide microstructures based on a
direct and in situ visualization has not been attempted earlier. |
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