模拟近地轨道环境下非线性电导改性聚酰亚胺表面充电机理

The surface dielectrics of Low Earth Orbit spacecraft occur to accumulate the surface charges under low-energy electron irradiation. Due to the high insulation performance of the polyimide, the dissipation rate of the surface charge is far less than the accumulation rate, which leads to the surface climbing to a high charging potential and inducing the electrostatic discharge phenomenon, and generates a serious threat to spacecraft reliability. This project firstly studies the non-linear conduction property and the secondary electron emission property of the polyimide composite. According to the charge transportation theory and the current balance equation among the electron injection current, secondary electron emission current and nonlinear conduction current of the modified polyimide, the surface potential simulation model under electron irradiation and the calculation method of surface potential decay characteristic after electron irradiation are established. Simultaneously, the measurement of polyimide surface potential decay characteristics after low energy electron irradiation is carried out, and the calculation and experimental results are comparatively studied to improve the simulation model. Based on the inversion algorithm of surface potential, the surface charge dissipation characteristic of the modified polyimide are obtained, and the effect of non-linear conduction property on the surface charge dissipation are analyzed. Finally, the bulk infiltration effect on the surface charge by the nonlinear conduction property are proved to produce a rapid dissipation mechanism of the surface charge in the Low Earth Orbit environment, which can significantly reduce the surface potential of the material.

近地轨道航天器表面介质受低能电子辐射时会发生表面电荷沉积现象，由于所用聚酰亚胺材料的高绝缘性能使其表面电荷消散速度远小于积聚速度，致使表面攀升至较高充电电位而诱发静电放电现象，严重威胁航天器可靠性。本项目首先研究改性聚酰亚胺复合材料非线性电导特性与二次电子发射特性，根据电子注入电流、二次电子发射电流与电导电流三者之间电流平衡关系及电荷输运理论，建立电子辐射下改性聚酰亚胺表面电位仿真计算模型，以及辐射后表面电位衰减计算方法。同时，实验研究低能电子辐射后改性聚酰亚胺表面电位衰减特性，对比计算与实验结果，完善仿真模型。通过表面电位反演算法获得电子辐射后改性聚酰亚胺表面电荷消散的时域特性，分析具有非线性电导特性复合材料表面电荷的消散机理。最后证明，利用非线性电导对表面电荷的体内“渗入”作用，产生一种在近地轨道环境下介质表面电荷快速消散机制，显著降低材料表面充电电位。

处在空间极端环境中的航天器表面介质极易受低能电子或等离子体辐射，进而发生表面电荷沉积现象。常见的航天器表面用聚酰亚胺材料的高绝缘性能使其表面电荷消散速度远小于积聚速度，致使表面攀升至较高充电电位而诱发静电放电现象，严重威胁着航天器的可靠性与寿命。按照预期研究目标，本项目主要开展了以下三方面实验与理论研究工作：首先，采用微米氧化锌粒子掺杂的改性方法，完成并制备了五组掺杂含量（0%、1%、2%、3%与5%）聚酰亚胺板状复合电介质样品，并通过复合电介质的基本电气性能验证了其绝缘性能，特别是测量了不同含量氧化锌样品的非线性电导特性并利用空间电荷限制电流模型予以解释。其次，利用微米掺杂聚酰亚胺复合电介质表面/体电导率、二次电子发射系数、非线性电导率等参数，建立了复合电介质表面电荷聚积与消散的动态平衡关系，基于电流平衡方程完成了在3keV与20keV电子辐射下不同粒子含量掺杂聚酰亚胺复合电介质表面充电平衡电位与电位衰减特性的仿真计算工作。特别地，通过数值计算与表面电位衰减特性实验，分析不同掺杂量下聚酰亚胺复合电介质表面陷阱分布特性的变化过程，研究发现3%掺杂量下聚酰亚胺介质表面浅陷阱减少而深陷阱增多，从而揭示了氧化锌掺杂粒子与聚酰亚胺树脂间无机-有机界面对复合电介质表面电荷消散过程的抑制机理。最后，基于大量表面深陷阱对电荷的束缚作用，成功地获得了一种聚酰亚胺复合介质材料表面电荷消散的控制方法，可以有效地提高真空条件下聚酰亚胺复合电介质表面直流放电电压300%以上，并在电子触发极化松弛模型基础上，解释了所提出的表面放电抑制方法的内在机理。项目研究成果为未来航天器表面聚酰亚胺介质抗辐射带电方法提供了有效的理论与技术支撑。