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 Wysłany: Nie 12:28, 16 Sty 2011 Temat postu: ugg stivali On a molten salt coating NbSi2_3275 Nb |
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Molten salt coating on niobium NbSi2
aC1, 36.58% KC1, 21.95% NaF, 4.89% NaESiF. Preparation of a 2OOg 150g of salt, then add silica fume (accounting for 21.85% molar fraction of salt), into the A10, crucible and heated to 9OOK melt. Coating process, the molten salt into the SiO, rod,[link widoczny dla zalogowanych], to supplement the amount of Si4 +. The pure niobium (99.85%) to 3mm thick cold rolled plate, cut into 25mmX7mm sample film. In HF and HNO, acid mixture in a clean. In the atmosphere, using molybdenum wire hanging specimens immersed in molten salt, and then removed, air cooling, dry weight, and then the optical microscope, scanning electron microscopy and anti-oxidation performance analysis. Oxidation resistance by the TGA analysis, heating rate of 2K/min. For comparison, the Ar gas furnace in the preparation of the sample cut into small pieces NbSi casting oxidation test at the same time. In the Nb-Si binary system there are four kinds of silicides: NbSi, d-NbsSi, B-NbsSi and NbSi. Under the experimental conditions,[link widoczny dla zalogowanych], only the d-Nb,[link widoczny dla zalogowanych], NbSi to stable,[link widoczny dla zalogowanych], and NbSi preferentially formed. MoSi Mo deposited on the test, the sample will appear at the corners of the irregular growth of MoSi. The growth in the coating does not appear when NbSi This phenomenon, which shows through the thin layer of Nb and si the supply is very balanced. In practice, the need for coatings are relatively thick. Although there has not been very thick MoSi layer, but under the same conditions, had been prepared successfully in Fe thickness Fesi 2001TI layer. This shows that the supply of molten salt in the si is adequate, but the proliferation of Nb matrix is much slower. Compared with the coating method,[link widoczny dla zalogowanych], the advantages of molten salt is lower the temperature required for reaction 2OOK, but not carried out in a closed system, can be carried out in air. Without the atmosphere of pure Nb sample coated TGA result: start from 658K, the surface generated do not have the protection of Nb20, quality began to increase. By 1173K, lh deposited sample, the temperature reached 750K occurs dangerous oxidation, indicating that molten coating NbSi not fully cover the substrate surface. By 1173K, 3h deposited sample, the formation of NbSi coating prevents oxidation, indicating NbSi layer thick enough to have good oxidation protection. For comparison, also studied the oxidation of Arc's NbSi performance. Generated by the SiO layer of pure NbSi when not in 1OOOK oxidative protection. More than 3h oxide coated specimens than in single-phase NbSi weight gain be less. Coated specimens oxidized in air at 1523K section and surface morphology analysis, the coating is divided into 3 layers, silicon mainly concentrated in the innermost layers, were (mole fraction) was 67.2%. 37.8%. Phase composition are NbSi and NbSi, the outer surface is formed by a mixture of SiO and Nb20 layer. NbSi, stopped in the SiO protective layer and the interface between the matrix cracks and expansion. The results show that two kinds of silicides from time to time than those of niobium and niobium between Nbsi between the bond strength and oxide is much higher. Nb coating after the NbSi than single-phase oxidation resistance is one good reason generated Nbsi. NbO coated NbSi in the presence of so can not cover the entire surface of the sample SiO, so oxidation will occur in the 1100K. Control the morphology of SiO lattice is the key to improving the oxidation resistance. Zhou Hui From (JournalofAlloysandCompounds \One of a calcium copper oxide (BSCCO) 2212 superconducting composite wire is feasible. the wound of superconducting magnets for magnetic resonance imaging. The small business innovation research program objective is to adjust the second phase of powder BSCCO2212 particle size distribution, improved superconductor / silver composite wire thermo-mechanical processing technology, expand production scale. The first two stages of the project is mainly for improving the production process of powder and wire feasibility study aimed to produce a current density of more than 250A/mm (4.2K, 12 km BSCCO2212 length of at least high-temperature superconducting composite wire. 12T superconducting magnets used in medical research is the highest field strength magnet. magazine correspondent From \
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