Abstract
Niobium, as pure metal and alloying element, is used in a variety of applications, among them in nuclear industries. Niobium is incorporated into nuclear fission reactors due to its enormous strength and low density. Surface finishing of niobium is often performed in electrochemical polishing processes in view of improving its smoothness, corrosion resistance and its surface cleanability. However, the presently used electropolishing process (EP) is intrinsically linked to the subsurface hydrogenation of niobium, which measurably degrades its properties. This is why the annealing operation is used to remove hydrogen from electropolished niobium that is a costly and time-consuming process. The traditional electrolyte consisting of a mixture of 96% H2SO4/49% HF acids by volume in a 9:1 ratio has been substituted for the new one, being a mixture of 70% methanesulfonic acid with 49% hydrofluoric acid by volume in a 3:1 ratio. Moreover, the additional imposition of a magnetic field during the electropolishing process (MEP) further increases hydrogen removal, when compared to the hydrogen content achieved by the electropolishing process alone. The aim of the study is to reveal a methodic approach and showing decreasing hydrogenation of niobium samples after consecutive steps of electrochemical polishing. Secondary ion mass spectrometry (SIMS) was used to measure the hydrogen content in the surface layer of as-received AR niobium and in the samples after EP and MEP processes.
Highlights
IntroductionFormerly columbium, is a rare, soft, grey and ductile transition metal with the symbol Nb.It is used in a variety of applications, such as superconducting magnets, medical devices, capacitors, optical lenses, barometers, superconducting radio frequency cavities, or electromagnetic radiation detectors, and nuclear industries [1,2]
Niobium, formerly columbium, is a rare, soft, grey and ductile transition metal with the symbol Nb.It is used in a variety of applications, such as superconducting magnets, medical devices, capacitors, optical lenses, barometers, superconducting radio frequency cavities, or electromagnetic radiation detectors, and nuclear industries [1,2]
One thinnest oxide layer was obtained on magnetic field during the electropolishing process (MEP), after clearly notice that thethe thinnest oxide layer was was obtained on sample sample
Summary
Formerly columbium, is a rare, soft, grey and ductile transition metal with the symbol Nb.It is used in a variety of applications, such as superconducting magnets, medical devices, capacitors, optical lenses, barometers, superconducting radio frequency cavities, or electromagnetic radiation detectors, and nuclear industries [1,2]. Niobium improves the strength of the alloys, especially at low temperatures. It acts as a key element in nuclear fission reactors, due to its enormous strength, low density, high melting point (2477 ◦ C), and low neutron absorption [5]. Niobium is very resistant to corrosion due to a layer of oxide formed on its surface. Its corrosion resistance is not as outstanding as that of tantalum, the lower price and greater availability make niobium attractive for numerous demanding applications. Niobium forms oxides in the oxidation states +5 (Nb2 O5 ), +4, +3, and the rarer oxidation state +2 (NbO). Most common is the pentoxide, precursor to almost all niobium compounds and alloys used in engineering.
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