• Journal of Technologic Dentistry
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• v.27 no.1
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• pp.79-88
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• 2005

This study was performed to investigate the surface properties of electrochemically oxidized pure niobium by anodic oxide and hydrothermal treatment technique. Niobium specimens of $10\times10mm$ in dimension were polished sequentially from #600, #800, #1000 emery paper. The surface pure niobium specimens were anodized in an electrolytic solution that was dissolved calcium and phosphate in water. The electrolytic voltage was set in the range of 250 V and the current density was 10 $mA/cm^2$. The specimen was hydrothermal treated in high-pressure steam at 300$^{\circ}C$ for 2 hours using an autoclave. Then, specimens were immersed in the Hanks' solution with pH 7.4 at 37$^{\circ}C$ for 30 days. The surface of specimen was characterized by scanning electron microscope(SEM), energy dispersive X-ray microanalysis(EDX), potentiostat/galvanostat test, and cytotoxicity test. The results obtained was summarized as follows; According to the result of measuring corrosion behavior at 0.9% NaCl, corrosion resistance was improved more specimens treated with anodic oxide than in hydrothermal treated ones. The multi-porous oxide layer on surface treated through anodic oxidation showed a structure that fine pores overlap one another, and the early precipitation of apatite was observed on the surface of hydrothermal treated samples. According to the result of EDX after 30 days deposition in Hanks' solution, Ca/P was 1.69 in hydrothermal treated specimens. In MTT test, specimens treated through anodic oxidation and hydrothermal treated ones showed spectrophotometer similar to that of the control group. Thus no significant difference in cytotoxicity was observed (P>0.05).

• Elastomers and Composites
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• v.49 no.4
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• pp.330-335
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• 2014

Niobium pentoxide ($Nb_2O_5$) nanoparticles were synthesized using niobium (V) chloride and pluronic F108NF as the precursor and templating agent, respectively. The $Nb_2O_5$-graphene nanocomposites were placed in an electric furnace at $700^{\circ}C$ and calcined under Ar atmosphere for 2 h. The morphology, crystallinity, and photocatalytic degradation activity of the samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and UV-vis spectroscopy. The $Nb_2O_5$-graphene nanocomposites acted as a photocatalyst in the photocatalytic degradation of organic dyes under 254 nm UV light; the organic dyes used were methylene blue (MB), methyl orange (MO), rhodamine B (RhB), and brilliant green (BG). The photocatalytic degradation kinetics for the aforesaid dyes were determined in the presence of the $Nb_2O_5$-graphene nanocomposites.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.306.2-306.2
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• 2016

Niobium oxide thin films were synthesized by reactive rf magnetron sputtering. The target was metallic niobium with 2 inch in diameter and the substrate was n-type Si wafer. To control the surface properties of the films, Nb oxide thin films were obtained at various mixing ratios of argon and oxygen gases. Nb oxide thin films were analyzed with alpha step, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The result of alpha step showed that the thickness of Nb oxide thin films were decreased with increasing the oxygen gas ratios. SEM images showed that the granular morphology was formed at 0% of oxygen gas ratio and then disappeared at 20 and 75% of oxygen gas ratio. The amorphous Nb oxide was observed by XRD at all films. The oxidation state of Nb and O were studied with high resolution Ni 2p and O 1s XPS spectra. And the change in the chemical environment of Nb oxide thin films was investigated by XPS with Ar+ sputtering.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.2
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• pp.78-86
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• 2004

Effects of the annealing parameters on the formation of ferrites transformed at low temperatures were studied in cold-rolled ultra low carbon steels with niobium and/or chromium. Niobium and chromium were found to be effective in the formation of the low temperature transformation ferrites. The low temperature transformation ferrites more easily formed when both higher annealing temperature and longer annealing time, allowing substitutional alloying elements to distribute between phases, are in combination with faster cooling rate. It was found from EBSD study that the additions of niobium or chromium resulted in the increase in the numbers of high angle grain boundaries and the decrease in those of the low angle grain boundaries in the microstructures. Both granular bainitic ferrite and bainitic ferrite were characterized by the not clearly etched grain boundaries in light microscopy because of the low angle grain boundaries.

• Progress in Superconductivity and Cryogenics
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• v.15 no.1
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• pp.11-13
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• 2013

We have developed a terahertz time-domain spectroscopy (THz-TDS) system for transmission and reflection measurements of metallic thin films. Using our THz-TDS system, we studied the conventional superconductor niobium (Nb) in the normal state in the spectral range from 5 to $50cm^{-1}$. Both the real and imaginary parts of the conductivity are acquired without Kramers-Kronig analysis. Nb exhibits a nearly frequency independent real conductivity spectrum in the terahertz range, with a very small imaginary part.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.580-581
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• 2006

The present paper investigates the possibilities of niobium using for the mechanical properties of the common low alloyed Cu-Ni-Mo-C sintered structural steels enhancing. On both thermodynamic and experimental bases there were demonstrated the Nb nitrides/carbides/carbonitrides preferential formation in these steels during sintering in dissociated ammonia at both common and elevated temperatures. The obtained results for $0.2\;{\div}\;1.0\;%$ fine Nb powder and 0.3% graphite additions to Distaloy AB iron base powder cold compacted and sintered in dissociated ammonia proved the expected strengthening effect, leading to higher mechanical properties of the processed steels than of the common Cu-Ni-Mo-C ones.

• Tribology and Lubricants
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• v.16 no.3
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• pp.194-200
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• 2000

In order to evaluate the effect of Nb on wear properties of high speed steel(HSS) by powder metallurgy, niobium-alloyed HSS have been prepared by adding 0%, 1%, 3% and 5%Nb to HSS of 6%W-5%Mo-4 %Cr-5%V-5%Co. Sliding wear tests were conducted at various sliding speed conditions under the constant pressure using a pin-on-disc type machine. The results of this study show that the wear resistance of HSS by powder metallurgy was increased by the addition of Nb within the range of sliding speed used in this experimental study. However, the amount of Nb did not improve the wear resistance. It may be due to the thermal stability of carbide and high temperature properties of the matrix containing Nb comparing to that without Nb.

• Journal of Electrochemical Science and Technology
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• v.12 no.2
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• pp.257-265
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• 2021

In this study, we report niobium (Nb) with hierarchical porous structure produced by a one-pot, HF-free electrochemical etching process. It is proved experimentally that a well-defined hierarchical porous structure is produced from the combination of a limited repetition of pulse etching and high concentration of aggressive anion (i.e., SO₄^2-), which results in hierarchical pores with high order over 3. A formula is derived for the surface area of porous Nb as a function of the hierarchical order of pores while the experimental surface area is estimated on the basis of the electrochemical gas evolution rate on porous Nb. From the comparison of the theoretical and experimental surface areas, an in-depth understanding was gained about porous structure produced in this work in terms of the actual pore shape and hierarchical pore order.

• Journal of the Korean Ceramic Society
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• v.46 no.6
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• pp.541-544
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• 2009

In Part III, the paper will show that an alumina-carbon nanotube-niobium nanocomposite produced fracture toughness values that are several times higher than that of pure nanocrystalline alumina. It was possible to take advantage of both fiber-toughening and ductile-metal toughening in this investigation.

• Progress in Medical Physics
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• v.6 no.2
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• pp.3-12
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• 1995

A 50 $\mu\textrm{m}$ thick niobium filter and its quantitatively determined aluminum equivalent filter were evaluated for effects on entrance skin dose, image quality, and x-ray tube loading for three different tube voltages in radiology. There was no significant difference in the reducion in entrance skin dose and increase in tube loading between two filters while keeping radiographic contrast on the film. For the clinical use of the aluminum equivalent filter as an alternative to the niobium filter in radiology, aluminum equivalent filter thickness at the mid energy range of radiology, 90 kVp, was measured and the filter was applied to the other kVp values, 73 and 125 kVps, to evaluate the effect on the entrance skin dose and tube loading. There was no significant difference between two filter cases at the selected kVp. The aluminum filter with equivalent thickness can be used as an inexpensive alternative to the niobium filter.