The Y3Al5O12 （YAG） nanocrystals were synthesized by ultrasound-assisted and ultrasound- microwave-assisted alkoxide hydrolysis precipitation methods. The structures and morphology of the YAG were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The synthesis kinetics of two kinds of YAG nanocrystals was investigated using differential thermal analysis and thermo gravimetric analysis （DTA-TG） at different heating rates in argon gas. The results show that two kinds of YAG precursors have one obvious endothermic peak at 315-600 K. The apparent activation energy of two kinds of YAG precursors was calculated using the Doyle-Ozawa and Kissinger methods, the coefficients of reaction order, frequency factor and kinetic equations were also determined. The average apparent activation energy for the YAG precursor prepared by ultrasound-microwave assisted was calculated to be 80.76 kJ.mol-1 higher than the YAG precursor prepared by ultrasound-assisted synthesis （56.56 kJ.mol-1）.
Wollastonite glass ceramics were prepared using the reactive crystallization sintering method by mixing waste glass powders with gehlenite.The crystallization property,thermodynamics,and kinetics of the prepared wollastonite glass ceramics were determined by X-ray diffraction analysis,scanning electron microscopy,energy-dispersive spectroscopy,high-resolution transmission electron microscopy,and differential thermal analysis.Results showed that crystals of wollastonite and alumina could be found in the gehlenite through its reaction with silicon dioxide.The wollastonite crystals showed a lath shape with a certain length-to-diameter ratio.The crystals exhibited excellent bridging and reinforcing effects.In the crystallization process,the aluminum ions in gehlenite diffused into the glass and the silicon ions in the glass diffused into gehlenite.Consequently,the three-dimensional frame structure of gehlenite was partially damaged to form a chain-like wollastonite.The results of crystallization thermodynamics and kinetics indicated that crystallization reaction could occur spontaneously under a low temperature(1173 K),with 20 wt%gehlenite added as the reactive crystallization promoter.The crystallization activation energy was evaluated as 261.99 kJ/mol by using the Kissinger method.The compression strength of the wollastonite glass ceramic samples(7.5 cm×7.5 cm)reached 251 MPa.
