The comparative kinetic analysis of the non-isothermal crystallization process of Eu3 + doped Zn2SiO4 powders prepared via polymer induced sol–gel method

• Eu3 +-doped Zn2SiO4 powders were prepared via polymer (PEG) induced sol–gel procedure.
• Comparative kinetic analysis for conventional and microwave heating treatments
• The diffusion-controlled transition, with instantaneous nucleation mechanism
• Autocatalytic model adequate for the crystallization of fine powders

The comparative kinetic analysis of the non-isothermal crystallization was performed for Eu3 + doped Zn2SiO4 samples, prepared by the polymer induced sol–gel procedure and thermally treated in the conventional furnace and in a microwave oven. This comparison is done using various thermal analysis techniques and is supported by SEM investigation. It was found that low values of Avrami constant (n), identified in the primary crystallization stage resulted from a not constant radial growth rate. One possible mechanism that could alter the linear crystal growth rate is a diffusion-controlled transition, with instantaneous nucleation mechanism. In the secondary crystallization stage, observed for both samples, it was found that the probability for two-dimensional crystal growth increases, especially at higher heating rates. It was found that the substitution of zinc ions by europium ions in Zn2SiO4 matrix can lead to some defects due to different radius and charges, which induces autocatalytic behavior of the tested systems. It was shown that the two-parameter Šesták–Berggren (SB) autocatalytic model best describes the non-isothermal crystallization of doped samples. It has been shown that SB model is adequate to describe the crystallization kinetics for the fine powder samples (crystallite size of 60–65 nm).

Crystallization half-time decreased with an increasing heating rate by almost the same mathematical law, in the case of both investigated samples. The growth rate for conventional furnace sample exhibits a concave upward behavior with heating rate, while for microwave sample exhibits changing behavior, with convex downward and then concave upward features, at high heating rates.Figure optionsDownload as PowerPoint slide