Phase separation and crystallization of La2O3 doped ZnO-B2O3-SiO2 glass

In order to investigate the effect of the La2O3 on the phase separation and crystallization of ZnO-B2O3-SiO2 glass, after the occurence of the phase separation and crystallization of glasses by heat treatment, the microstructure morphology and distribution of elements in different sample areas were characterized by the scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS); the non-isothermal crystallization kinetics of the glass samples was studied by using a differential scanning calorimeter (DSC) and the precipitated crystals of crystallized glass were determined by the X-ray diffraction (XRD). The results suggest that the phase separation and crystallization of 60ZnO-30B2O3-10SiO2 glass occur at glass surface, and the incorporation of small amount (<4 mol%) of La2O3 significantly inhibits the glass phase separation and consequently improves the thermal stability of glass. Doping of La2O3 accelerates the glass crystallization at the elevated temperature (660 °C), making the depth of crystal layer thicker and diffraction intensity in XRD patterns stronger. However, due to the precipitation of several crystals that occur simultaneously when La2O3 doping amount is 4 mol%, crystallization of the 60ZnO-30B2O3-10SiO2 glass is obviously depressed, the crystallization activation energy Ec and the relative crystallinity Xc of the glass reach the maximum and the minimum values, respectively. Although transition from one-dimensional growth of crystals to two-dimensional growth of crystals results from La2O3 addition, the one-dimensional growth of crystals remains dominant in crystallization process. This work can provide some useful information for preparing glass ceramics with nano-crystals precipitated in the glass surface.