| The zirconia as a novel material, the development and application of zirconia have been demonstrating its importance because of its excellent characteristics of physics and chemistry. But ,the zirconia will take place the phase transition in the heating and cooling process, accompanied by the shear stress and volume change so that the pure zirconia will be destroyed; however, due to its low thermal expansion coefficient, high thermal conductivity and good thermal shock resistance stability, the partially stabilized zirconia has been used widespreadly as the high-quality refractory material in modern metallurgical field, high temperature thermal insulation material field, etc. Though the partially stabilized zirconia is produced industrialy in the tunnel kiln through cleavage and high temperature heat treatment using the stabilized zirconia obtained by EAF (electric arc furance) smelting as the raw material, during the practical production process, the traditional technique showed some tough problems, such as higher heat treatment temperature, larger energy consumption, longer production time, higher equipment movement cost and maintenance of equipment difficultly, etc. The thesis firstly put forward to produce the partially stabilized zirconia using microwave heating combined with the superiority of the microwave heating, and could create an new approach for energy-saving in the production of the partially stabilized zirconia.In this paper, the experimental studies on the production of the partially stabilized zirconia by the conventional heating and microwave heating have been carried out on the basis of the summaries of the domestic and foreign research situation of zirconia, using the X-ray diffraction, scanning electron microscope (SEM) analysis techniques. The basic rules of phase transition of EAF smelting zirconia and the optimal conditions were obtained through investigating the conditions of the experimental temperature, holding time, temperature of droping rate, hardening temperature, temperature of rising rate and aging treatment at a certain temperature point in temperature droping process.The phase transition basic rule of EAF smelting zirconia under the conditions of traditional heating is that: The monoclinic zirconia is obtained in the temperature decreasing process, the starting temperature of phase transition is about 1000℃in the process of temperature rising, the ending temperature of phase transition is about 950℃in the process of temperature droping. The reaction temperature of front and behind is inconsistent, and presents the temperature lagging; and the higher the temperature, the more favorabl to the formation of monoclinic zirconia, making the stability droping; under the condition (1450℃) of the highest experiment temperature, the longer holding time is propitious to the monoclinic zirconia formation in the process of temperature droping, but, after holding 4 h, the content of monoclinic zirconia does not increase obviously, indicating that the phase equilibrium has been reached; under certain temperature condition (1450℃), the slower the temperature droping rate, the more favorable to the monoclinic zirconia formation, but the excessively faster temperature droping rate may suppress the monoclinic zirconia formation; the phase transition in the process of temperature droping has the certain temperature range, the phase transition is finished at the temperature approximately 950℃; the temperature of rising rate has no effects on the monoclinic zirconia formation; the content of monoclinic zirconia can not be increased at a certain temperature point through holding long time in the process of temperature droping.The communicating double insulation layer structures in the self-made microwave high temperature reactor can keep temperature constant. The special designed thermo-couple shielding cover can guarantee measuring temperature accurately. The rising temperature characteristic experiment of EAF smelting zirconia in the microwave field indicates that the EAF smelting zirconia can absorb microwave well. The temperature can be increased to the 1450℃rapidly in 3-4 min at the heating rates from 400 to 500℃/min under the microwave power of 1000 W.The basic rules of phase transition of EAF smelting zirconia by the microwave heating is the same as those of the traditional heating, but, the content of monoclinic zirconia does not increase obviously after holding 2 h at 1450℃, it can be thought that the phase equilibrium has been achieved; the starting temperature of phase transition is about 950℃in the process of temperature rising, the ending temperature of phase transition is about 950℃in the process of temperature droping.According to the content of monoclinic zirconia 30% (index of stability 70%) about the material resisted heat theknocking to be best, Under the conditions of traditional heating, the optimal experimental conditions of producing partially stabilized zirconia is as follow: The rising rate of temperature of the muffle furnace is 4℃/min; holding 4h at 1450℃; the droping rate of temperature is 2℃/min, hardening at 950℃, the stability is 70.0%. Under the conditions of microwave heating, the optimal experimental conditions of producing partially stabilized zirconia is as follow: the rising rate of temperature of EAF smelting zirconia in the microwave field is 4℃/min, hardening at 850℃, the stability is 71.0%; The partially stabilized zirconia obtained under the optimal conditions is all yellow colour and its microstructure was observed using the scanning electron microscope (SEM) and it was found that there were few air bubbles and has no cracks in the partially stabilized zirconia, it meets the requirements of the high-quality zirconia material; and under the conditions of equal stability, the time needed of producing the partially stabilized zirconia by microwave heatintg is shorten about 70% compared to that of conventional heating, showing the advantages of microwave heating, and providing the production of the partially stabilized zirconia with processing parameters. |
PDF Full Text Request