| Oxide ceramics have generally been synthesized using traditional preparation methods such as Hot Press Sintering,Hot Isostatic Sintering and so on.These methods require the assistance of high temperature furnaces and have limitations such as many operating steps,long operating time and high energy consumption.The current-controlled rapid sintering technique is characterized by low energy consumption and simple operating equipment.It enables rapid densification and sintering of ceramics in a short period of time.Current-controlled rapid sintering at room temperature or even at low temperatures is a recent research direction of great interest in the field of energy-efficient sintering of ceramics.In this paper,binary oxide represented by magnesium oxide(MgO)and ternary oxide ceramics represented by magnesium aluminium spinel(MgAl2O4)are the targets of research.The sintering aid-assisted current control of sintered ceramic materials is investigated.Solution-assisted room-temperature current-controlled sintering of MgO and Al2O3 ceramics and room-temperature current-controlled reactive sintering of MgAl2O4 ceramics were prepared.Using the current-controlled sintering technique,MgO cylindrical billets with a water content of 10 wt%were sintered under current control for 60 s at a boost rate of 50 V/s,a current density of 57 mA/mm2 and a doping level of 10 mol%LiCl solution to produce MgO ceramics with uniform grain size(average grain size of 18.46 μm),smooth grain boundaries and a density of 94.26%.The MgO ceramics were produced with a uniform grain size(average grain size 18.46μm),smooth grain boundaries and a density of 94.26%.The changes in electrical conductivity of the raw MgO billets were tested during a short period of rapid temperature increase.The mechanism of rapid sintering with triggered sintering currents at room temperature was revealed.The analysis in this paper concludes that a monolayer of water molecules on the surface of MgO particles increases the electrical conductivity of the raw blanks and allows sintering at room temperature.When sintering Al2O3 ceramics,LiAl5O8 phase is produced when the LiCl solution content is greater than or equal to 12.5 mol%.The pure Al2O3 phase can be obtained at less than 12.5 mol%.The densities were 93.23%and the average grain size was 15.19 μm.The results show that the current-controlled sintering technique is suitable for the preparation of binary oxide ceramics.The ternary oxide MgAl2O4 ceramics were successfully prepared by current-controlled reaction sintering with the aid of LiCl solution using MgO and Al2O3 as the initial raw materials.A ternary oxide CuAlO2 ceramic was not prepared using Cu2O and Al2O3 as the initial raw materials.The analysis suggests that the high temperatures generated during the rapid sintering process lead to a reduction reaction of CuAlO2 to produce stable forms of Cu and CuO.The results suggest that room temperature current controlled reaction sintering of ternary oxide ceramics is more complex and requires process improvement on a case by case basis.Current-controlled reactive sintering of MgAl2O4 ceramics yields grain sizes that are ten times larger than those obtained by conventional sintering.By analyzing the defects in MgAl2O4 ceramics at different sintering times,it was found that MgAl2O4 ceramics produce a large number of oxygen vacancies or defect clusters.A rapid grain growth model was constructed to explain the phenomenon of rapid grain growth of MgAl2O4 ceramics in current-controlled reactive sintering.During current-controlled sintering of MgAl2O4 ceramics,a variety of defects can be generated such as oxygen vacancies Vo¨,small defect clusters {3Vo¨:2V’"Al}× and defect coupling {Vo¨:V"Mg}×.As the sintering time increases,the concentration and type of defects increase.These defects can effectively promote grain growth,resulting in larger grain sizes than in conventional sintering. |
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