This study reports on the evolutions of surface structure and composition of Fe-30Cr alloys that were first oxidised in oxygen atmosphere then followed by an exposure in gaseous KCl environment. After the pre-oxidation treatment at 800uC for 10 h, a continuous, dense and protective chromia scale was produced. During the following exposure in KCl contaminated atmospheres at 650uC, the surface chromia layer was gradually transformed into worm-like potassium chromate textures, which quickly coalesced on the substrate surface along with simultaneous volatility. The protective oxide layer was then severely deteriorated by enhancing cracking, spallation, volatility and porosity. Voluminous iron migrated outward through these defective sites and iron oxide became the dominating reaction products. Both chromate and residual chromia were finally incorporated into the thick and porous iron oxide scale. This process accounts for the major catastrophic destruction of chromia forming materials involving reactions with alkali chloride salts, even at minor amounts.
Well-aligned diamond nanotips are fabricated by etching as-grown diamond thin films using a Kaufman type broad ion beam source. The nanotips have nanometre-size heads, micrometre-size roots and the same apex angle. All of the nanotips consistently point in the direction against the incident ion beam. The orientation of diamond nanotips can be controlled by adjusting the incident direction of the ion beam. The Raman spectrum does not show a significant increase in graphitic peak intensity after etching, indicating that the quality of diamond is barely degraded by ion beam etching. Near-edge x-ray absorption fine structure spectra show that the diamond sp3 structure is dominant in the spectra of both as-grown and ion etched diamond. The sp2 fraction is found to increase by about 12% at the surface layer of the diamond nanotips as compared with as-grown diamond. The formation of diamond nanotips is explained by Sigmund's sputtering theory and the angle-dependent sputtering mechanism. This method to produce diamond nanotips has the advantage of excellent orientation control and the capability to produce nanotip arrays on a large area.
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