Impurity composition and decontamination of the cylindrical surface of CVD polycrystalline tungsten
| Autor: | V. N. Lebedev, V. N. Zykova, Yu. K. Udovichenko, B. M. Zykov, A. V. Bravarets |
|---|---|
| Rok vydání: | 2002 |
| Předmět: | |
| Zdroj: | Technical Physics. 47:1176-1181 |
| ISSN: | 1090-6525 1063-7842 |
| DOI: | 10.1134/1.1508085 |
| Popis: | The impurity composition on and near the cylindrical surface of a CVD polycrystalline tungsten film covering Nb + 1% Zr alloy is determined with SIMS and AES methods. The alloy is used as the collector material in thermionic thermal-to-electrical energy converters of space-borne nuclear power plants. A comparison with the impurity composition of a reference plane-parallel relatively perfect W(110) single crystal is made. At all stages of milling the surface by He+ and Ar+ ion beams, the coating is contaminated greater than the reference. Even after the first heating in vacuo to 1625 K, all the impurities, except carbon, oxygen, and niobium, are removed. The three impurities named are not removed by heating up to 2075 K. Niobium is shown to diffuse toward the surface through a W coating of thickness up to 30 µm. At temperatures above 1925 K, the material is heavily sputtered. After 50 oxidation cycles, the carbon content in the coating is greatly reduced. However, the subsequent 25 cycles fail in further decreasing the carbon content. The fact that oxygen cannot be removed from the surface by heating to 1925–2075 K suggests the presence of high-temperature surface Nb2W2O suboxide. It is recommended that the purity of the W coating raised in order to improve its adhesion to the O-Cs film. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|