| 摘要 |
The piston for a precision-metering instrument having a glass barrel comprises a cylindrical core of glass, ceramic or metal onto which a rigid sheath of filled PTFE has been shrunk thermally and is subsequently precision-ground. The PTFE of the sheath is filled with from 10 to 40% by weight of electrographitised artificial coal grit containing less than 50% of graphite, the remainder amorphous carbon, and more than 98% by weight of carbon, the remainder non-volatile and non-extractable constituents. The particle size distribution of the artificial carbon grit particles is 99% by weight < 63 mu m. A piston of this type is completely chemically inert and is distinguished by particularly good swelling resistance.
|
