Effect Of Li₂O Contents And Spodumene Proportion On Crystallization Of Lithium Aluminosilicate Glass-ceramic

Glass ceramics obtained by controlling the crystallization of glass is a kind of multi-phases materials. Lithium aluminum silicate (LAS) glass ceramic is one of the most valuable and widely used glass ceramic systems because of its low expansion, high heat resistance and excellent mechanical properties.The industrial and electrical glass-ceramic plate is one of the important applications of glass ceramic and develops quickly. At present, the production cost and energy consumption are too high for LAS glass ceramic and enhancing its performance is too difficult, which restricts its application. How to resolve these problems has been one of imperative problems.On the basis of present states of LAS glass ceramic, Li2O was partly replaced by other oxide, the expensive chemical material Li2CO3 was partly replaced by cheap spodumene and fluoride was added into LAS glass. The crystallization mechanism, structure and performance of different glass were studied and compared to reduce the content of Li2O, increase the proportion of spodumene and establish the suitable heat-treatment parameters. The researches were benefical for the actual production of LAS glass ceramic materials.The crystallization mechanism of LAS glass had been analyzed by DTA method. The results showed that when the content of Li2O decreased from 4.5% to 3.0%, crystallization peak tempareture increased by 100 ℃ and crystallization activation energy (E) increased from 333.05kJ/mol to 369.973kJ/mol. When the proportion of spodumene increased from 25% to 75%, the E of LAS glass reached its lowest value of 297.64 kJ/mol when the proportion of spodumene was 50%. As the proportion of spodumene increased, the E increased rapidly. The reduction of the content of Li2O restrained the crystallization of LAS glass, while spodumene proportion improved the crystallization.The result of the study on the LAS glass nucleation shows that with the decrease of Li2O content, the tempareture of glass pahse transition and crystallization peak tempareture incresead and the best nucleation tempareture increased from 770℃ to 810℃ when the nucleation time kept stable. As the proportion of spodumene increased, the crystallization peak tempareture increased from 871.4 ℃ to 853.9℃ and the best nucleation tempareture increased a little. When the content of Li2O is 4.0% and 3.5% , the content of fluoride is 0.5 %, the best nucleation tempareture is 680 ℃ and 730 ℃ which is well below the sample that did not include fluoride. The incresea of the content of Li2O incresead the nucleation tempareture of the LAS glass while the add of fluoride sharply reduced the nucleationtempareture. Spodumene increased the nucleation tempareture.The result of the study on the LAS glass crystallizati showed that the replacement of Li2O increased the crystallization tempareture. As the crystallization tempareture increased, the main crystal phase is β - spodumene. The crystallization tempareture increased from 880 ℃ to 970℃ while the crystallization time did not change a lot. The crystal phase of the sample into which spodumene was added changed from β - spodumene to LiAlSi3O8 as the crystallization tempareture growing. With the increase of the proportion of spodumene, the crystallization tempareture decreased and the crystallization time did not change. When the fluoride was added into the LAS glass, the main crystal phase is β - spodumene, the crystallization tempareture decreased and the crystallization time did not change a lot. Decreasing the content of Li2O increased the crystallization tempareture. Increasing the proportion of spodumene decresed the crystallization tempareture and changed the main crystal phase. Adding fluoride decresed the crystallization tempareture.The result of the study on the LAS glass perfonnance shows that decreasing the content of Li2O , increasing the proportion of the spodumene and adding fluoride did not play a important part on the density of LAS glass but reduced the chemical stability of the symtem. The replacement of Li2O increased the thermal expansion coefficient ,but the adding of fluoride and spodumene decreased it. Decreasing the the content Li2O which is one of the necessary elements in forming the crystal phase restrained the formation and growth of grains, which resulted the increase of the nucleation and crystallization tempareture. The other compound which was brought by spodumene improved the melting and crystallization, changed the crystal phase, improved the structure and performance of LAS glass. When adding fluoride into the system , the Si—O—Si bond was replaced by Si—F bond, which reduced the stability of the symtem .advanced the formation and growth of the grain and improved the structure and performance of LAS glass.As shown in the aboved studies, the proper addition of spodumene and fluoride in LAS glass accelerates phase separation, nucleation and crystallization to obtain glass ceramics with a fine grain, high performance and low cost, which is important to low-cost production of glass ceramic materials.