摘要
本文研究了炭黑含量为10.6—12.2Vol％的聚乙烯—炭黑导电复合材料的直流I—U特性。按测试电压可分为Ohm区及非Ohm区。电流及电阻和电压的关系可分别用公式I=AU^B和R=A^(-1)U^(1-B)表示,式中A、B为常数,分别表征导电能力和导电的性质。在非Ohm区,B>1,电阻随电压增加而下降。炭黑含量减少或升高温度都使常数B变大、A变小,由于聚乙烯和炭黑的膨胀系数相差很大,升温可看作减少炭黑浓度。热处理使B变小、A变大,这可能是炭黑粒子的运动使导电网络中非Ohm导电的成分减少的缘故,这种变化的不可逆性表明上述炭黑的运动是单方向的,它使导电网络趋于稳定,也使测量的稳定性和重现性有较大的改进。
In order to obtain the proper electric properties of PTC material, testing the threshold cur- rent at constant voltage is essential if the voltage used is not low enough to avoid the influence of Joule heat. It was found that thc I-U characteristics of PE--CB composites which contain CB 10.6—12.2 Vol% can be divided into two regions, ohmic and nonohmic, according to the test voltage. The I—U and R—U behavior of the composites can be expressed by equations I = AU^B and R = A^(-1)U^(I-B) in which constants A and B reflect the electric conduc- tivity and the nature of electron tranport respectivitely. Ih the nonohmic area, B > 1 and the re- sistance decreases as voltage increases. Because of the great difference between the thermoexpansion of PE and CB, increasing temperature enhances the values of A^(-1) and B, the same effect as reducing CB content. As a result of heat treatment, values of A^(-1) and B decrease. Probably, heat treatment, by stimulating the irreversible movement of carbon particles, com- pletes and stabilizes the conductive ntwork in the composites, so that the nonohmic component of conductances was decreased whild the ohmic component was inereased.
