Influences of temperature on the property of ITO/Teflon/Ag in atomic oxygen environment

This paper uses ground simulation equipment for an atomic oxygen environment to conduct experimental research on ITO/Teflon/Ag, which is used in spacecraft using an atomic oxygen environment. The atomic oxygen integrated flux selected in the study is 9.1× 1019 atoms/cm2, with a vacuum degree of 10-2 Pa, and sample temperatures of 20°C, 70°C, and 120°C, respectively, were selected to investigate the possible impact of sample temperature on atomic oxygen environment simulation experiments. After the test, a high-precision microelectronic balance was used to test the mass loss of the sample and calculate the reaction rate of the material. The thermal emissivity and solar absorption ratio of the sample were tested using TEMP 2000A and LPSR 300, respectively. Through experiments and analysis, it was found that as the sample temperature increased, the ITO/Teflon/Ag reaction rate with atomic oxygen gradually increased but remained at 10-25. Atomic oxygen and temperature have a significant impact on the thermal physical properties of the material.


Introduction
Atomic oxygen (from now on referred to as AO) mainly exists in the low Earth orbit atmospheric environment.When the spacecraft is in orbit, AO will collide with the outer surface material of the spacecraft at a relative speed of 7-8 km/s and undergo chemical reactions with it, causing mass loss of the outer surface material of the spacecraft, thereby reducing its various performance and ultimately affecting the on-orbit life of the spacecraft [1,2] .
Chemical reactions are influenced by various factors, and environmental temperature is one of the important factors affecting the speed of chemical reactions.In foreign in-orbit experiments, polyimide films were selected as the research object to investigate the various performance changes of polyimide films in AO environments under different temperature conditions [3,4,5] .Some universities and scientific research institutions in China have also conducted extensive research on the performance changes of surface materials used in spacecraft under an AO environment and formed a series of research results, providing data support for the selection of thermal control materials used in spacecraft, especially in the field of manned spaceflight.However, there is relatively little research on the material performance changes in the AO environment under different temperature conditions in China [6] .
ITO/Teflon/Ag, a commonly used thermal control material for spacecraft, is widely used in the outer surface coating of aerospace.This article will take ITO/Teflon/Ag as the research object, select AO environments under different temperature conditions, and study its performance changes.

Ground simulation equipment
This research-oriented experiment was conducted on the ground AO simulation equipment, consisting mainly of a vacuum container, a vacuum pumping system, a three-dimensional moving mechanism, a beam emission device, a microwave generation system, and an overall control and data acquisition system [5] .Figure 1

Test device
The experimental device used in this experiment is shown in Figure 2. The sample target platform and sample temperature control device are installed on the existing three-dimensional moving mechanism, and the installation diagram of the entire device is shown in Figure 3.The sample target has good contact with the cooling water tank to control the temperature of the sample.The sample temperature control mainly consists of cooling and thermal cycles.In addition, effective connection methods are adopted to disassemble the sample target rapidly.

Test parameters
Before the experiment, the AO beam was calibrated at different distances from the axial center of the AO source to the neutralization plate.The selected material was Kapton H thin film.The AO beam density at different distances from the neutralization plate was calculated based on the mass changes of the Kapton H thin film before and after the experiment.The beam density of AO calculated by this formula is 2.1×10 15 atoms/cm 2 •s.The AO integrated flux was selected as 9.1×10 19 atoms/cm 2 .During the test, the vacuum degree inside the container is better than 2×10 -2 Pa.The sample temperatures were selected as 20℃, 70℃, and 120℃, with a temperature deviation of ± 2℃.
Before the experiment, a cesium telluride detector was used for VUV testing, and the results indicate that there is no accompanying VUV near the sample installation device.

Testing instrument
Before and after the experiment, the surface morphology of the sample was observed using an OLYMPUS GX51 optical microscope.A ME215S high-precision microelectronic balance measured the quality change of the sample.The thermal emissivity and solar absorption ratio of the sample were measured by TEMP 2000A and LPSR 300, respectively.

Appearance changes
The surface morphology of ITO/Teflon/Ag samples was shown in Figure 4, observed using an OLYMPUS GX51 optical microscope before and after the experiment.It can be seen that after the AO exposure test with the fluence of 9.1×10 19 atoms/cm 2 , the surface morphology of ITO/Teflon/Ag showed significant changes compared to before the test.Figure 3 shows that as the sample temperature increases, the surface defect density of ITO/Teflon/Ag gradually increases.

Reaction rate of materials
Before and after the experiment, the mass of ITO/Teflon/Ag samples was tested using a ME215S high-precision microelectronic balance (with a measurement accuracy of 10 -5 g) produced by the German company Sedoris.The reaction rate between the sample and AO was calculated based on the mass change of the sample, as shown in Table 1.From Table 1, it can be seen that sample temperatures of 20℃, 70℃, and 120℃, after the AO exposure test with the fluence of 9.1×10 19 atoms/cm 2 , the mass loss of ITO/Teflon/Ag samples gradually increased, and the reaction rate of the material also increased with the increase of sample temperature.

Performance variation in thermophysical properties
The test measured the thermal emissivity and solar absorption ratio of ITO/Teflon/Ag using TEMP 2000A and LPSR 300.For effective comparison, a new sample is selected at each target temperature, and only the sample is heated to the target temperature without AO irradiation.The other test environments are the same, and the results are shown in Table 2.
From Table 2, it can be seen that as the sample temperature increases after the AO exposure test with the fluence of 9.1×10 19 atoms/cm 2 , the change trend of the thermal emissivity of ITO/Teflon/Ag samples is consistent with the joint effect of AO and temperature and the single temperature effect.Based on the data, it can be determined that the change in the thermal emissivity of ITO/Teflon/Ag is mainly caused by temperature.

Figure 1 .
Figure 1.The schematic structure of the AO environmental simulation equipment.

Figure 2 .
Figure 2. The schematic structure of the experimental device.

Figure 3 .
Figure 3.The schematic installation of the experimental device.

Table 1 .
Quality changes and ITO/Teflon/Ag reaction rate in AO and temperature composite effect test.