Synthesized zeolites are extremely important as industrial minerals and are most commonly prepared using organic templates. Because these organic templates present undesirable environmental hazards, a synthesis method which avoids their use is desirable. The objective of the current study was to develop such a synthesis method. Zeolite NaY was synthesized hydrothermally starting from a mixture of 1.0 Al2O3:10 SiO2:4.6 Na2O:180 H2O molar gel composition, without adding any organic additives. Experiments were carried out to investigate the effects of molar compositions including water content (H2O/SiO2), crystallization conditions including temperature, and time on the crystal size and yield of NaY-type zeolite. The results showed that increasing the crystallization time from 5 to 12 h increased the crystal size, while increasing the crystallization temperature from 80 to 100°C also increased crystallinity. The crystal species of zeolite NaY were characterized by X-ray diffraction, X-ray fluorescence, and scanning electron microscopy analysis. Zeolite NaY crystals in the size range 25–150 nm were synthesized successfully over a period of 8 h at 100°C.

The fracture behavior of precracked nanocrystals with grain size gradients is simulated using the molecular dynamics method. A large grain size gradient is found to elevate resistance to crack propagation and transform the fracture mode from intergranular to intragranular when the crack is obstructed by a coarse grain. But the intragranular crack is nipped in its bud due to the difficulty of intragranular fracture. However, intergranular fractures can be always kept in nanocrystals with a small grain size gradient. Both the Schmid factors for the slip systems of grains near the crack tip and the critical stress intensity factors are calculated, and energy partitioning is conducted to analyze the mechanisms behind this phenomenon. The research exhibits the key role of grain size gradient in improving the antifracture ability of nanocrystals.

Monodisperse and uniform γ-Fe2O3 (maghemite) nanocrystals of variable size were prepared by thermal decomposition of iron pentacarbonyl [Fe(CO)5] in the presence of surfactants, following controlled oxidation with trimethylamine N-oxide as a mild oxidant. The influence of carboxylic acids with variable alkyl carbon chain lengths on the synthesis of γ-Fe2O3 nanocrystals was investigated. The effect of the molar ratios of surfactant to iron precursor was also studied. The nanocrystals were characterized by x-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD showed the particles were highly crystalline at the nanometer scale. The results showed that the size and shape of the nanocrystal is strongly influenced by the decomposition temperature of iron pentacarbonyl and closely related to the length of carbon chain of the capping groups and the molar ratio of surfactant to iron precursor. Following controlled evaporation from nonpolar solvents, self-assembly into two-dimensional arrays could be observed by TEM. It was also found that the distance between the nanocrystals in self-assembled structures matched the length of the capping molecules very well.