| Blast-furnace slag is one of the by-products and the largest solid waste of iron andsteel industry. Presently, the overall utilization rate of blast-furnace slag in China isrelatively low. The large stacking of blast-furnace slag is not only occupies land resourcesbut also pollutes the surrounding environment of the stacking field, which hinders thesustainable development of iron and steel industry. The main compositions of blast-furnaceslag are CaO, MgO, Al2O3and SiO2, which makes it an ideal raw material for glass-ceramics production. The blast-furnace slag of Baotou Steel contains CaF2, RExOy, K2O,Na2O and other spacial components, making its utilization in large scale difficult. Usingblast-furnace slag as raw material to prepare glass-ceramics provides a high added-valuenew way to Baotou Steel for the comprehensive utilization of blast-furnace slag.In this paper, CaO-MgO-Al2O3-SiO2(CMAS) system glass-ceramics with the maincrystal phase of dioposite alumina were prepared by melting method, using blast-furnaceslag and quartz sand as the main raw materials, and using Cr2O3,CaF2and Fe2O3asnucleating agents. The glass-transition temperature Tg, the crystallization peak temperatureTpand crystallization temperature ranges of the basic glass were analyzed by differentialscanning calorimetry method (DSC) at different heating rates of5℃/min,10℃/min,15℃/min,20℃/min and25℃/min. The crystallization activation energy of E of basicglass was calculated by Kissinger method and Ozawa method. And the crystal growthindex n at different heating rates were calculated thorough Augis-Bennett equation. Basedon the crystallization kinetics calculation results, isothermal heat-treatment schedules andstage heat-treatment schedules were designed taking three-point flexural strength as themain index. Scanning electron microscopy (SEM), X-ray diffraction analysis (XRD) wereused to study the microstructure and crystal phase composition of the glass-ceramicssamples after heat-treatment. The results show that:(1)By the calculations ofcrystallization activation energy E and crystal growth index n, the basic glass at selectedcompositions can realize bulk crystallization,and possess a high crystallization trend;(2)By single-factor studies on the crystallization temperature and the crystallization time at wideranges, the optimum crystallization temperature range and crystallization time range areidentified respectively as930-990℃and30-90min. The optimum isothermal heat-treatment schedule is:crystallizing at960℃and thermal insulate for60min. By this heat-treatment schedule, the glass-ceramics with uniform fine grain can be gained. In this glass-ceramics the glass phase distributes along the grains boundaries and grains ties toughlywith each other, and the main crystal phase is diopside alumina, making its flexuralstrength reached224.8MPa;(3)By four factors and three levels orthogonal tests L9(34) andresults analysis, the optimum step heat-treatment schedule of glass-ceramics is:nucleatingat780℃for60min and crystallizing at960℃for60min. By this step heat-treatmentschedule the gains in glass-ceramics connect closely and formats clusters, the remainingglass phase content is relatively low and its flexural strength reached221.7MPa;(4)Bycomparing the physical properties of glass-ceramics prepared through isothermal heat-treatment schedules and step heat-treatment schedules, and the heat-treatment processcycle time of the two heat-treatment schedules, the isothermal heat-treatment schedulesoverstep step heat-treatment schedules in the two indexes of mechanical properties andprocess cycle time. |
PDF Full Text Request