微波干燥自发凝固成型氧化铝湿坯

Microwave Drying of Spontaneous-Coagulation-Cast Wet Alumina Green Body

为了解决常规干燥(控温控湿)过程中坯体出现水分梯度问题,利用微波干燥法来干燥湿坯。通过对比常规干燥(温度:40℃;湿度:60%)和微波干燥的方式,研究了湿坯的重量损失、线性收缩、表面温度和水分分布。与常规干燥相比,采用微波干燥(功率250 W)时,干燥结束时间和停止收缩时间分别缩短至1/6.8和1/6。在微波干燥过程中,样品表面温度随时间延长先升高后降低,与体内水分密切相关。而在常规干燥过程中,温度保持恒定在40℃。采用低场核磁共振(NMR)成像技术表征湿坯内部的水分分布情况发现:在微波干燥过程中,水分分布更均匀,表明微波干燥时湿坯的干燥应力更低。在1550℃下烧结6 h后,微波干燥制备得到的氧化铝陶瓷具有更高的抗弯强度,且标准差更小。

To solve moisture gradients in the conventional drying with controlled temperature and relative humidity,microwave heating was employed to dry wet alumina green bodies shaped by spontaneous coagulation casting.The weight loss,linear shrinkage,surface temperature,and moisture distribution of the green bodies by conventional drying(temperature:40℃;humidity:60%)and microwave drying were investigated.The time for no further weight loss and shrinkage of the body by microwave drying(power:250 W)were respectively shortened to 1/6.8 and 1/6 of those by conventional drying.Surface temperature of the green body during the microwave drying increased firstly and then decreased with time,which was strongly correlated with the internal moisture,while the temperature in the conventional drying keeping at 40℃.Low-field nuclear-magnetic-resonance(NMR)imaging revealed that the moisture distribution in the green bodies dried by microwave drying was more uniform than that by conventional drying,indicating that drying stress in the former was lower than that in the latter.After sintering at 1550℃for 6 h,alumina ceramics from microwave drying had a higher flexural strength with a smaller deviation than that from conventional drying.