Protective coating against EM Radiation and partical bombardment at high temperatures
This invention concerns a process for protecting a substrate from damage by electromagnetic radiation and/or particle bombardment, in particular a component from aerospace technology, a layer or coating, manufactured or producible by this process and substrates which have such a layer or coating.
Spacecraft such as satellites are exposed to extreme conditions in space, especially near the sun. They are subject to long-term exposure to very hard electromagnetic radiation and particle radiation and also to extreme temperature fluctuations. This makes it possible for the surfaces of the missiles to pass through a temperature range of -200 °C to +500 °C within a few minutes, depending on whether they are facing or away from the sun. Due to the high temperatures near the sun, the outer parts of the room bodies in particular can only be made of special materials such as high-temperature-resistant aluminium and titanium alloys and composite materials. In addition, the extreme conditions make a temperature-regulating coating of the components indispensable.
Innovations & Advantages
State-of-the-art white surface coatings for geostationary applications based on silicone-based, white-pigmented high-temperature inks are known. However, these inks have a very high organic carbon content, which is usually due to organic binder systems and additives or hybrid materials such as polysiloxane. At high temperatures in a vacuum, especially in combination with extreme UV radiation, carbonization can occur, resulting in a black coloration of the surface coating. This can lead to heating of the component and in extreme cases to material fatigue.
Also known are coatings evaporated by PVD (physical vapour deposition) or CVD (chemical vapour deposition), consisting of various transparent or white oxides. However, such a layer is very expensive due to the large amount of equipment required and three-dimensional components with complex geometry can only be coated to a limited extent.
The composition can be applied to the substrate by conventional methods such as spraying, dipping, flooding, etc. Application by spraying is preferred, especially by low-pressure spraying. By adjusting the viscosity of the composition and the spraying parameters (pressure, material flow and distance to the substrate), defined layer thicknesses can be achieved. The viscosity can be adjusted by adding a defined amount of solvent or dispersant to the composition used according to the invention. Ideally, the solvent or dispersant should only contain volatile components that cannot carbonize under the extreme conditions mentioned above. A polar solvent or dispersant is preferred, especially water.
The composition used is particularly preferably an aqueous suspension of the solvent or dispersant, the inorganic particles and/or the particles with the layer lattice structure, in particular the hexagonal boron nitride, with a solids content of between 25 and 60% by weight, preferably between 35 and 45% by weight. This means that only water in a proportion between 40 and 75% by weight is the preferred solvent. In principle, however, the solvent or dispersant may also contain other polar components, such as alcohols, at least in part.
Current and Potential Domains of Application
- aerospace technology
- power generation
- Chemical industry