High-temperature aerospace applications

The beryllides continue to be of interest for high temperature aerospace applications because of their oxidation resistance, low density, and high strength at elevated temperature (7). The limited strain capacity of the materials, particulady at low temperatures, has thus far prevented actual use. 

For a general discussion of these high-temperature adhesives, compared with PBI, see Section 5.5. These adhesives are synthetic thermosetting resins formed by the reaction of a diamine and a dianhydride. As with PBIs, they were developed specifically for high-temperature aerospace applications. PI adhesives are superior to PBIs for long-term strength retention, as shown in Figure 5.4. ... 

Materials that come close to the ideal ladder structure are thermosetting polyimides and polybenzimidazoles. These are used primarily in high-temperature aerospace applications as composites and adhesives. 

Polyimides are an important class of polymers for high temperature aerospace applications. Thin polyimide films are ideal candidates for protective coatings on antenna reflectors and other electronic applications. Their properties, both physical and electrical, are expected to be strongly influenced by their morphology. We have developed a novel technique for monitoring microstructural characteristics of thin polymer films. It is based on the sensitivity of the positron lifetimes to the molecular architecture of the polymers. Specifically, positron lifetimes can be used to calculate free volume hole radii and free volume fractions in the test polymers. A free volume model has been developed to calculate dielectric constants of thin polyimide films. It has been tested on a series of special purpose polyimide films developed for aerospace communication networks. The results are described in the following sections. 

This chapter will deal with the chemistry and applications of epoxies, phenolics, urethanes, and a variety of current vogue high-temperature polymers. Applications in fiber-reinforced plastics will be discussed in the individual sections on resin chemistry where appropriate. Separate sections will deal with adhesives and sealants. Adhesives are most important because, as early history demonstrates, they led the way to the application of resins in aerospace. A section is also included on silicone and polysulfide sealants. Although these materials are elastomers rather than resins, no discussion of aerospace polymers would be complete without some mention. Some major thermosetting polymers have been omitted from this review. Among these are the unsaturated polyesters, melamines, ureas, and the vinyl esters. Although these products do find their way into aerospace applications, the uses are so small that a detailed discussion is not warranted. 

High-temperature, aerospace and impact resistant applications... 

Whilst some consider PEEK to be the polymer of last resort there is also polyether ketone ketone from the US Oxford Performance Materials Inc. This material has a high softening point and is capable of maintaining high strength, wear resistance and chemical resistance even in continuous use at high temperatures. Current applications include the aerospace industry. 

Maturation as a technology does not mean that advancement and innovation has ceased. Adhesive bonding is so essential to the aerospace field that as long as there is a desire to go higher, faster and farther more efficiently, there will be an incentive to develop new materials and processes for adhesive bonding. Areas of particular interest for future applications are high-temperature adhesives, fiber-reinforced metal laminates and more efficient bond assembly techniques. 

Polyetheretherketone PEEK is a high-temperature, crystalline engineering TP used for high performance applications such as wire and cable for aerospace applications, military hardware, oil wells and nuclear plants. It holds up well under continuous 450°F (323° C) temperatures with up to 600°F (316° C) limited use. Fire resistance rating is UL 94 V-0 it resists abrasion and long-term mechanical loads. 

The high-temperature glassy or crystalline transitions of the linear aromatic and heterocyclic polymers were an important drawback for die structural aerospace applications, which need a good flow for the adhesive or composite formulations. 

There are two important titanium aluminides Tig A1 which has a hexagonal structure with a density of 4.20 g/cm and a melting point of 1600°C and Ti A1 which has a tetragonal structure with a density of 3.91 g/cm and a melting point of 1445°C. As do all aluminides, they have excellent high temperature oxidation resistance owing to the formation of a thin alumina layer on the surface. They have potential applications in aerospace structures. 

Polymers containing no secondary or tertiary C-H or are aromatic (PEEK or Kevlar ) or perfluorpolymers (PTFE) are generally resistant to oxidation and require no anti-oxidant additives. However, the high temperature necessary for curing or fabrication of high performance polymers (especially for aerospace applications) can cause oxidation. For this reason, these materials are often prepared and fabricated under a nitrogen atmosphere. 

Re-usable containers, such as bottles for carbonated soft drinks, made of PEN have high-temperature tolerance for cleaning and sterilizing [79], The inherent UV resistance of PEN creates opportunities for colorless electronic and pharmaceutical packaging, as well as vacuum-metallized products for aerospace, industry and military applications [80, 81]. 

ISO 7258 1984 Polytetrafluoroethylene (PTFE) tubing for aerospace applications -Methods for the determination of the density and relative density ISO 7313 1984 Aircraft - High temperature convoluted hose assemblies in polytetrafluoroethylene (PTFE)... 

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