Synergistic effect on spacetribology in the low earch orbit

本项目的目的是阐明原子氧（AO）和其他环境因素，如紫外线（UV）光或X射线，在低地球轨道（LEO）环境中使用的卫星的摩擦学中的协同效应。本研究采用离子束型和激光诱导击穿型两种原子氧源，在实验室中产生高能原子氧束。本课题取得的研究成果如下：1.通过旋涂技术形成的聚酰亚胺膜的AO的反应效率受到UV照射的影响。只有在AO和UV同时照射时，才检测到显著的质量损失和CO_2的生成。这一研究结果表明，在AO轰击的聚合物表面发生了吸收紫外光的羰基等官能团的光辅助化学反应，在AO攻击下形成羰基.当AO撞击MoS_2（0001）表面时，生成SO。在MoS_2（0001）表面进行AO辐照时，用四极质谱仪检测到了这种挥发性产物。然而，蒸发速率与时间不是线性的。这可能是由于AO向MoS_2块体中的低扩散速率，即，反应仅限于非常表面的区域，在该区域中仅有限量的S被还原。MoS_2（0001）的摩擦学性能受AO侵蚀影响不大。我们看到AO暴露后初始摩擦力最多增加40%。然而，即使在AO暴露之前也观察到类似的效果。一定比例的这种影响是由于磨损痕迹的形成。这种效应显然取决于滑动系统和材料的常数。由于原子氧对溅射MoS_2的摩擦学性能的影响可能与单晶不同，因此需要了解原子氧对实际滑动分量的影响程度。必须对这一点进行进一步研究。

The purpose of this project is to clarify the synergistic effect of atomic oxygen (AO) and the other environmental factors, such as ultraviolet (UV) light or X-rays, in the tribology of satellites used in low earth orbital (LEO) environment. An ion beam type and a laser induced breakdown type AO sources are used in this study to generate energtic AO beam in the laboratory. The research results obtained in this project are as follows :1. The reaction efficiency of AO with the polyimide film formed by a spin-coating technique is influenced by UV irradiation. Only in the simultaneous irradiation of AO and UV,significant mass loss and CO_2 formation is detected. This research result suggests the photo-assisted chemical reaction of the functional groups such as carbonyl, which absorbs UV light, occurs at the AO bombarded polymer surfaces where carbonyl is formed by AO attacks.2. When AO hits MoS_2 (0001) surface, So is formed. This volatile product is detected by a quadrupole mass spectrometer during AO beam exposure on MoS_2 (0001). However, the rate of evaporation is not linear with time. This is probably due to the low diffusion rate of AO into the MoS_2 bulk, i.e., reaction is limited only at the very surface region where only limited amount of S is existed.3. Tribological properties of MoS_2 (0001) is not suffered by AO attack very much. We see maximum 40% increase of initial friction after AO exposure. However, similar effect is also observed even before AO exposure. Certain percentage of this effect is dur to wear track formation. This effect obviously depends on the sliding system and materials' constants. We need to know how much AO influences to the actual sliding component, because the effect of AO on the tribological property of sputtered MoS_2 may be different with single crystal. Further research on this point must be necessary.