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Characteristics and applications
This rather expensive polymer is mostly used in aerospace, semiconductor and transportation technology. It combines heat resistance, lubricity, dimensional stability, chemical resistance, and creep resistance, to be used in hostile and extreme environmental conditions.
Unlike most plastics, it does not produce significant outgassing even at high temperatures, which makes it useful for lightweight heat shields and crucible support. It also performs well in vacuum applications, down to extremely low cryogenic temperatures. However, Vespel tends to absorb a small amount of water, resulting in longer pump time while placed in a vacuum.
Although there are polymers superseding polyimide in all of these properties, the combination of them is the main advantage of Vespel.
Another interesting property makes vespel a material of choice in designing high-resolution NMR probes for NMR spectroscopy: its volume magnetic susceptibility is a very close match to that of water at room temperature. For example, in SI units, volume magnetic susceptibility of water at 20 °C is –9.03×10-6 , whereas volume susceptibility of vespel SP-1 at 21.8 °C was measured to be −(9.02±0.25)×10-6 . Negative values indicate that both water and vespel are diamagnetic. Matching volume magnetic susceptibilities of materials surrounding NMR sample to that of the solvent can reduce susceptibility broadening of magnetic resonance lines.
Processing for manufacturing applications
Vespel can be processed by Direct-Forming (DF parts) and Isostatic Molding (basic shapes - plates, rods & tubes). For prototype quantities, basic shapes are typically used for cost efficiency since tooling is quite expensive for DF parts. For large scale CNC production, DF parts are often used to reduce per part costs, at the expense of material properties which are inferior to those of isostatically produced basic shapes.
For different applications, special formulations are blended / compounded. Some examples of standard polyimide compounds are:
Vespel is a polyimide material and for many years was the only option for high-end polyimide parts. It is a proven material in critical applications. It is also out of reach for many applications due to its high cost. Recently, other polyimide materials such as Meldin and Plavis have brought additional options in the polyimide market and may help reduce the overall market cost of polyimide shapes.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Vespel". A list of authors is available in Wikipedia.|