| Nano-sized cordierite glass-ceramic is cordierite crystal gains in the order of nano-scale. Because of its excellent performance in the dielectric, thermal shock, infrared radiation and other aspects, it is widely used in power electronics, high temperature heating energy, catalyst carrier and many other fields.In this paper, nano-sized cordierite glass-ceramic was prepared by the secondary melting method and the two-step heat treatment system under the stoichiometric ratio of cordierite. Based on the modified Kissinger equation, Ozawa equation and the principle of non-isothermal thermal analysis,the effects of addition of ZrO2, GeO2, P2O5 and TiO2 on the crystallization and performance of glass were studied. The controlled crystallization results of the glass were analyzed and studied by means of Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM).At the same time, the performance such as dielectric constant, dielectric loss, coefficient of thermal expansion, resistivity and Vickers hardness were tested by high frequency dielectric impedance spectroscopy, thermal expansion meter and high impedance instrument, the effects of dopant and crystallization temperature on its performance were investigated.The results show that ZrO2,GeO2, NH4H2P2O4 and TiO2 are the nucleation agents based on the samples without the nucleation agent. It was found that TiO2 had the strongest effect of reducing the potential barrier of glass crystallization. The activation energy calculated from the modified Kissinger method was reduced from 526.178 KJ·mol-1 to 446.053 KJ·mol-1. The Avrami index (n) is about 3, showing the overall crystallization,while the without nucleation agent sample's Avrami index is about 2, tends to crystallize on the surface. Moreover,the introduction of TiO2 has the most obvious effect on reducing the dielectric constant and dielectric loss, 2 hours after crystallization,the dielectric constant from 7.0 to 4.6, dielectric loss from 0.040 to 0.017.With the introduction of TiO2, when the content is less than or equal to 5.36wt.%, the a-cordierite phase is obtained. When the introduction amount is increased to 7.44wt.%, the spinel phase containing low iron is appeared, and when the amount of TiO2 is increased to 10.72wt.%, the a-cordierite phase disappears completely, so the maximum amount of TiO2 is 10.72wt.%,. The dielectric constant showed a tendency to decrease first and then increase, when the amount of TiO2 is increased from 0 to 2.68wt.%, the dielectric constant deceases from 7.0 to a minimum of 4.6. When the amount of TiO2 continuously increased to 10.72wt.%, the dielectric constant increases from 4.6 to 7.2. The dielectric constant of the samples with different crystallization temperature also showed the trend of decreasing first and then increasing. The cordierite glass samples with crystallization temperature of 913?had a minimum dielectric constant (4.3) and a dielectric loss (0.009). In addition, the nano-sized cordierite glass-ceramic samples obtained in this study have unique dendritic microstructure and combine the effect of nano-effect and alkali metal doping to make the sample shave a quartz-level coefficient of thermal expansion (10-7?-1). At the same time,the effects of different contents of Fe2O3 doping on the crystallization of glass were studied.The results show that the addition of Fe2O3 reduces the crystallization temperature to above 45?, and when the doping amount of Fe2O3 reaches 7.44wt.%, the main crystal phase of the crystallized glass is changed from cordierite to iron spinel phase. |
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