We monitored the effect of different
gel aging temperatures (from
−20 to 40 °C) and gel aging times (from 7 to 21 days)
on the particle size and crystalline structure of template-free Linde
type A zeolites through scanning electron microscopy, transmission
electron microscopy, X-ray diffraction, and Raman spectroscopy. We
demonstrate the synthesis of zeolite LTA with average particle sizes
of 0.45 ± 0.07 μm by preliminary heat treatment of the
precursor gel at −8 °C followed by crystallization at
100 °C. Here, we found that aging the precursor gels for 2 weeks
at 40 °C decreases the size of particles by 59% compared with
particles formed from unaged gels, and aging gels for 2 weeks at −8
°C results in particles that have a 95% smaller diameter compared
with particles formed from the unaged gel. We hypothesize that decreasing
the precursor aging temperature below 0 °C leads to the occurrence
of spinodal decomposition at which the nucleation barrier vanishes.
Consequently, a very large number of nuclei form. Decreasing the gel
aging temperature from 40 to 0 °C leads to an increase in the
average size of zeolite particles by the Ostwald ripening phenomena
(coarsening). Additionally, we found aging the precursor gels for
2 weeks at 40 °C leads to the formation of 27% zeolite X (an
undesirable product), while aging at −8 °C for 2 weeks
leads to the formation of only 2% zeolite X. The primary purpose of
our paper is to explore the two experimentally observed phenomena
that occur during low temperature aging of zeolite gel precursors
that result in significant effects on particle size.
Photocurable nanocomposites have tremendous potential in tissue engineering, advanced manufacturing, and structural, multifunctional materials. This project investigates the effect of silica (SiO 2 ) nanoparticle loading content on the thermal, mechanical, physical, and morphological characteristics of the nanocomposite. An increased concentration of SiO 2 nanoparticles causes a decrease in the gel fraction of the nanocomposite, which, at low nanoparticle loading, degrades the thermal and mechanical properties. However, further addition (>3.8 wt %) causes an increase in the glass-transition temperature, Young's modulus, and ultimate compressive strength. The addition of the nanoparticles had no significant effect on the hydrophilicity according to water uptake experiments. Small-angle X-ray scattering experiments, in conjunction with scanning electron microscopy and transmission electron microscopy, indicated a multimodal particle size distribution and the presence of largescale aggregates.
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