ABSTRACT
Here, we present a new crystallization process which, by combining microwaves and metal-induced devitrification, reduces both the time and the temperature of crystallization compared to other known methods. Titania crystallization initiates at a temperature as low as 125 °C within a few minutes of microwave radiation. Several cations induce this low-temperature crystallization, namely, Mn2+, Co2+, Ni2+, Al3+, Cu2+ and Zn2+. The crystallization mechanism is probed with electron microscopy, elemental mapping, single-particle inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, Auger electron spectroscopy, and scanning Auger mapping. These techniques show that the metal ion migration through the vitreous titania under microwave radiation occurs prior to crystallization. The crystalline particles are suspended in solution at the end of the treatment, avoiding particle aggregation and sintering. The crystalline suspensions are thus ready for processing into a material or employment in any other application. This combination of microwaves and metal-induced crystallization is applied here to TiO2, but we are investigating its application to other materials as an ecofriendly crystallization method.
ABSTRACT
Silicon has emerged as the most desirable material for optical dielectric metamaterials, however chemists struggle to obtain the required silicon nanoparticle dimensions. Here the average diameter of silicon nanoparticles is varied between 3 and 15 nm by changing the reaction solvent. Electrochemistry and NMR elucidate the role of solvent on the synthetic mechanism. Surprisingly the solvent does not stabilize the nanoparticles and there is no trend associated with chain length or open-chain versus cyclical solvent molecules. The solvent's main role is to stabilize the by-products, which prolongs the reaction lifetime.
