A direct experimental method, involving a two-stage varying-temperature syn
thesis, was utilized to investigate the effects of aging on the nucleation
kinetics for the synthesis of nanosized TPA-silicalite-1 with various silic
a sources, including tetraethoxysilane (TEOS) and amorphous silica Ludox TM
. For TEOS aging had only a mild influence on the nucleation and crystalliz
ation kinetics, whereas for Ludox TM dramatic changes occurred. After exten
ded aging periods, the nucleation kinetics for syntheses with Ludox TM beca
me similar to those for syntheses with TEOS, leading to increasing similari
ties in the properties of the products of the crystallization. Independent
of aging time and silica source, the nucleation processes occurred over a s
ubstantial period of time, extending over the induction period, but were co
mpleted before crystal growth was detected. With increased aging, the nucle
ation period was gradually decreased and tended to be completed earlier in
the induction period. Raman spectra revealed that with Ludox TM, aging enha
nced the interaction between TPA(+) and the silica species, leading to an i
ncrease in the concentration of precursor species for nucleation, which in
turn accelerated the nucleation rate. (C) 2001 Elsevier Science B.V. All ri
ghts reserved.