Effects of Fe on Crystallization and Properties of a New High Infrared Radiance Glass-Ceramics

摘要

In our earlier work, a promising new approach of fly ash utilization as converting it into a high infrared radiance glass-ceramic material was proposed. In this paper, pure reagents glass-ceramics were synthesized simulating the previously obtained high infrared radiance fly ash glass-ceramics, and mechanisms of the effects of iron oxide impurity, contained in fly ash, on crystallization behavior, infrared radiation and thermal expansion properties of this material are systematically analyzed. It was originally found that the iron oxide impurity has a significant influence on the crystallization of the MgO-Al_2O_3-SiO_2 system glass-ceramics as it leads to phase separation of this magnesium aluminosilicate glass, and consequently results in changes of the crystallization activation energy and crystallization mechanism. Furthermore, the Fe ion is incorporated into the cordierite crystal structure in the form of Fe~(3+)/ Fe~(2+) that coexists during crystallization, and the substitution of Mg~(2+) by Fe~(3+) forms the vacant site of Mg~(2+) cations. For the effects of impurity, vacancy defects, and lattice distortion, which are caused by the doping of Fe ion, the infrared radiation performance of this cordierite-based glass-ceramic can be improved considerably. By controlling the iron oxide amount (about 4.2%) in this system glass-ceramics, well crystallized (bulk crystallization, granular equiaxed grains, sized 200-400 nm) Fe~(3+)/ Fe~(2+) substituted cordierite-based glass-ceramics with excellent infrared radiation property and low thermal expansion coefficient were obtained. Since high Fe content fly ashes can be used as raw material for the synthesis of this material, the research has both ecological and economic importance.