直流电场下湿型砂极化机理分析和等效模型建立

Polarization Mechanism Analysis and Equivalent Model of Green Sand under Direct Current Electric Field

针对直流电阻法测量湿型砂含水量过程中存在的极化现象,运用数学方法深入分析了湿型砂在直流电场下的极化机理.在直流电场作用下,流过湿型砂试样的电流是由贯穿电流和吸收电流组成,贯穿电流不随时间变化,但吸收电流却随着时间的延长按指数规律下降,正是由于吸收电流造成了湿型砂的极化现象.进一步得到了湿型砂等效电学模型,它在电路上可用一个电阻R串联一个电容C再与另一个电阻R'并联表示.为减弱或消除极化现象,可从减慢电子的流动速度、加速电极反应、使阴阳电极上电荷积累不能实现3方面加以考虑,因此,采用小幅值的激励电压、大面积的测量电极和合适频率的交流激励源都有利于极化现象的消除.

Aiming at the polarization phenomenon when the moisture content of green sand is measured by the resistance method, the polarization mechanism of green sand under the direct current electric field is further ana- lyzed. The results show that the current through the sand specimen can be divided into the through-type conduction current and the absorption current, and the former keeps invariable while the latter decreases exponentially with the time. It is the absorption current that causes the polarization of green sand. Further, the equivalent model can be obtained where the serial connection of a resistor R and a capacitor C is in parallel with another resistor R. To weaken or eliminate the polarization effect, three measures can be taken from decelerating the electron movement speed, accelerating the electrode reaction speed and eliminating the charge accumulation on the electrodes. So the small exciting voltage, the large electrode area and the appropriate frequency are helpful to reduce the polarization.