Dose Deposition and Electrostatic Charging of Kapton Films Irradiated with Electrons

Kapton films are widely utilized in harsh radiation environments where radiation resistant insulating materials are required. For space applications, Kapton polymers are used on satellites as substrates for solar arrays and outer layers of thermal systems. Kapton is also used in nuclear power plants as wire insulation. Kapton materials can be exposed in nuclear reactors to a reactive chemical environment in addition to severe radiation. It is of utmost important to understand how Kapton materials behave under high irradiation conditions and mitigate radiation damage effects. High-energy electrons can deposit ionizing dose and electric charge deeply inside Kapton materials. The charge accumulation grows over time and may exceed the dielectric strength of Kapton resulting in the electrostatic discharge that may cause extensive material damage. The dose deposition and electrostatic charging of Kapton irradiated with electrons has been studied using the Monte Carlo stepping model implemented in the Geant4 software toolkit. The secondary radiation emission (photo-, Auger-, Compton-electrons, and fluorescence photons) generated by primary electrons is taken into account in the redistribution of dose and charge deposition within a Kapton film. The results of this study are the profiles of dose and charge deposited by primary and generated secondary electrons and photons within a thin film of Kapton as a function of its depth. The results also provide insights into distributions of dose and charge in Kapton films under various incidence angles and energies of electrons.https://scholarscompass.vcu.edu/gradposters/1103/thumbnail.jp

High-temperature adhesives for bonding polyimide film

Experimental polyimide resins were developed and evaluated as potential high temperature adhesives for bonding Kapton polyimide film. Lap shear strengths of Kapton/Kapton bonds were obtained as a function of test temperature, adherend thickness, and long term aging at 575 K (575 F) in vacuum. Glass transition temperatures of the polyimide/"Kapton" bondlines were monitored by thermomechanical analysis

High Temperature Adhesives for Bonding Kapton

Experimental polyimide resins were developed and evaluated as potential high temperature adhesives for bonding Kapton polyimide film. Lap shear strengths of Kapton/Kapton bonds were obtained as a function of test temperature, adherend thickness, and long term aging at 575K (575 F) in vacuum. Glass transition temperatures of the polyimide/Kapton bondlines were monitored by thermomechanical analysis

Effects of illumination on the conductivity properties of spacecraft insulating materials

Experimental data on the dark and illuminated conductivities of Kapton V and polyvinylidene fluoride (PVF2) films are described as well as the changes in insulating properties produced in Kapton H, Kapton V, PVF2, and FEP Teflon films as result of prolonged exposure to solar illumination. An overall summary of the results of tests is presented. A general introduction and a description of the experimental apparatus and procedures used are also given

Theoretical models of Kapton heating in solar array geometries

In an effort to understand pyrolysis of Kapton in solar arrays, a computational heat transfer program was developed. This model allows for the different materials and widely divergent length scales of the problem. The present status of the calculation indicates that thin copper traces surrounded by Kapton and carrying large currents can show large temperature increases, but the other configurations seen on solar arrays have adequate heat sinks to prevent substantial heating of the Kapton. Electron currents from the ambient plasma can also contribute to heating of thin traces. Since Kapton is stable at temperatures as high as 600 C, this indicates that it should be suitable for solar array applications. There are indications that the adhesive sued in solar arrays may be a strong contributor to the pyrolysis problem seen in solar array vacuum chamber tests

Sputtered coatings for protection of spacecraft polymers

Kapton polyimide oxidizes at significant rates (4.3x10(-24) gram/incident oxygen atom) when exposed in low Earth orbit to the ram atomic oxygen flux. Ion beam sputter deposited thin films of Al2O3 and SiO2 as well as a codeposited mixture of predominantly SiO2 with a small amount of polytetrafluoroethylene were evaluated and found to be effective in protecting Kapton from oxidation in both laboratory plasma ashing tests as well as in space on board shuttle flight STS-8. A protective film of or = 96 percent SiO2 and or = 4 percent polytetrafluoroethylene was found to be very flexible compared to the pure metal oxide coatings and resulted in mass loss rates that were 0.2 percent of that of the unprotected Kapton. The optical properties of Kapton for wavelengths investigated between 0.33 and 2.2 microns were not significantly altered by the presence of the coatings or changed by exposure of the coated Kapton to the low Earth orbital ram environment

Evaluation of Kapton pyrolysis, arc tracking, and arc propagation on the Space Station Freedom (SSF) solar array Flexible Current Carrier (FCC)

Recent studies involving the use of polyimide Kapton coated wires indicate that if a momentary electrical short circuit occurs between two wires, sufficient heating of the Kapton can occur to thermally char (pyrolyze) the Kapton. Such charred Kapton has sufficient electrical conductivity to create an arc which tracks down the wires and possibly propagates to adjoining wires. These studies prompted an investigation to ascertain the likelihood of the Kapton pyrolysis, arc tracking and propagation phenomena, and the magnitude of destruction conceivably inflicted on Space Station Freedom's (SSF) Flexible Current Carrier (FCC) for the photovoltaic array. The geometric layout of the FCC, having a planar-type orientation as opposed to bundles, may reduce the probability of sustaining an arc. An experimental investigation was conducted to simulate conditions under which an arc can occur on the FCC of SSF, and the consequences of arc initiation

Kapton charging characteristics: Effects of material thickness and electron-energy distribution

Charging characteristics of polyimide (Kapton) of varying thicknesses under irradiation by a very-low-curent-density electron beam, with the back surface of the sample grounded are reported. These charging characteristics are in good agreement with a simple analytical model which predicts that in thin samples at low current density, sample surface potential is limited by conduction leakage through the bulk material. The charging of Kapton in a low-current-density electron beam in which the beam energy was modulated to simulate Maxwellian and biMaxwellian distribution functions is measured

Laboratory studies of Kapton degradation in an oxygen ion beam

Results are presented from a preliminary laboratory investigation of the degradation of the widely used polyimide Kapton under oxygen ion bombardment. Recent space shuttle flights have shown that Kapton and some other materials exposed to the apparent ram flow of residual atmosphere (at orbital velocity in low Earth orbit) lose mass and change their optical properties. It was hypothesized that these changes are caused by chemical interaction with atomic oxygen, aided by the 5-eV impact energy of atmospheric oxygen atoms in the ram. The reaction rate under O(+) bombardment seemed to be independent of incident energy over a wide range of energies. Although the flux of thermal ions in this experiment was much greater than the accelerated flux, the observed Kapton degradation was limited to the beam area and ram flow direction. This is consistent with an activation energy above the thermal energies but well below the beam energies. The results reproduce well the material loss, optical changes, SEM surface structure, and ram directionality of the samples returned by the shuttle. These factors, along with the lack of degradation under argon ion bombardment, are convincing evidence for ram flow oxidation as the mechanism of degradation

Photoconductivity of high voltage space insulating materials: Measurements with metal electrodes

The electrical conductivities of high voltage insulating materials were measured in the dark and under various intensities of illumination. The materials investigated included FEP Teflon, Kapton-H, fused quartz, and parylene. Conductivities were determined as functions of temperature between 22 and 100 C and light intensity between 0 and 2.5 kW/m2. The thickness dependence of the conductivity was determined for Teflon and Kapton, and the influence of spectral wavelengths on the conductivity was determined in several cases. All measurements were made in a vacuum to simulate a space environment, and all samples had metallic electrodes. The conductivity of Kapton was permanently increased by exposure to light; changes as great as five orders of magnitude were observed after six hours of illumination