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|PRODUCT DATA of 20: Miscellaneous non-metallic|
|Material||20: Miscellaneous non-metallic|
|General Information||This covers non-metallic materials that do not fall in any other DML material class, i.e. it does not include thermosetting or thermoplastic type polymer-based materials, but does cover ceramic-type materials used for space.
NOTE: These materials are generally known as advanced technical ceramics (ATCs): a term that encompasses a wide range of material types used in engineering applications for mechanical, electrical or thermal characteristics or some combination thereof. It also covers "Functional" ceramics, e.g. piezoelectric, but can include materials for optical applications.
|Use in Spacecraft||Structural uses of ceramics are largely limited to those applications where extreme service temperatures or aggressive environmental conditions preclude the use of any other material (e.g. re-entry surfaces of manned or reusable space vehicles).
Ceramic coatings can be applied selectively to parts to improve resistance to hot, aggressive environments such as those within propulsion systems.
Ceramic-based adhesives can be used for very high-temperature applications (1000ºC) normally for the assembly of ceramics.
Thermal insulation ceramic-based products can be applied to structures and also used in payload experiments (e.g. oven and furnace linings).
Ceramics and glasses are used in electrical and electronic equipment subassemblies (electrical insulators); within the manufacture of electronic components (capacitors; packaging for integrated circuits); and in sensing and measuring devices (transducers).
|Main Categories||Ceramics normally have complex compositions based on one or more oxide, nitride or carbide and often contain glassy constituents. Ceramic-type materials - characterized by their hard, brittle nature - can be in the form of:
A further group of ceramic-type materials are the carbon - (C-C) or ceramic-matrix composites (CMCs) and ceramic variants containing glass (GCMCs). These are finding applications as structural components on the re-entry surfaces of reusable launch vehicles (e.g. panels and flaps), and as specialist high temperature fasteners for their assembly and attachment. Such applications are known as “passive thermal protection systems (TPS)”.
C-C and CMCs are only used for applications when the design requirements, performance and economical factors justify their selection. See ECSS-E-30-04 for information on current materials, design and applications for C-C and CMCs.
|Processing and Assembly||Within the ceramics industry, processing methods include using slurry and powder forms of raw materials to create a shape, followed by drying and high-temperature firing to consolidate the product form. Owing to their extreme hardness and brittleness, most shaped engineering products are produced to the final shape. Some grades of ceramics are “machinable” but this is usually limited to cutting product forms to the specified dimensions or making holes for attachments. In general, extreme care is needed when handling brittle materials to prevent cracking, and the use of diamond or other ceramic tools is advised.
Processing of fibre-based products used for thermal insulation is normally restricted to cutting to shape and attaching the “blanket” to the structure. Some blankets can be “moulded” to a take a shape. Some thermal insulation materials are supplied as blocks or bricks that can be shaped to the specified form by machining (e.g. oven and furnace linings for experimental payloads).
|Precautions||The brittle characteristics of ceramics and glasses, along with the scarcity of reliable characterization of their properties and in-service performance mean that they are not among the routine structural materials applied to spacecraft. The exception is re-entry surfaces on reusable, manned space vehicles for which intensive evaluation studies are necessary, with the final customer reviewing and approving the various design stages.
An evaluation shall be made of the characteristics of ceramics used as insulators in electrical and electronic applications. Many ceramics have a relatively high porosity which makes their potential as contaminant traps a concern; glazed materials effectively seal the surface.
|Hazardous and Precluded||Specialist safety equipment and procedures shall be applied when operators are working with ceramic fibres and fine powders or processing methods that produce dust and debris. Some materials and their common forms are known to provoke respiratory problems; this is a growing subject for legislation worldwide.
The use of asbestos is discontinued because of its carcinogenic nature
|Effects of Space environment|
|Some Representative Products||There are many sources of advanced technical ceramics within Europe (from raw products, standard shapes or forms to finished components). There are also small firms making specific components. Some names can be cited, but the following list is far from complete: