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Number of results: 7
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Abstract

This work aims to analyze the effects of niobium on the bioactivity of a titanium, nickel, aluminum, and niobium alloy obtained by the Plasma Skull Push Pull process (PSPP). Titanium alloys, such as NiTinol (NiTi), are metallic biomaterials that have wide application in health and surgical prostheses. In this work the microstructural and bioactivity characteristics of the alloys are evaluated. The addition of aluminum improves alloy ductility and reduces its cost. The addition of niobium favors the hydroxyapatite nucleation. Therefore, the addition of the combination of the two elements contributes to lower cost and better alloy bioactivity.
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Authors and Affiliations

R.L.P. Teixeira
1
ORCID: ORCID
J.C. de Lacerda
1
ORCID: ORCID
I.C Conceição
1
ORCID: ORCID
S.N. da Silva
2
ORCID: ORCID
G.O. Siqueira
1
ORCID: ORCID
F. Moura Filho
1
ORCID: ORCID

  1. Universidade Federal de Itajubá, Itabira, MG, Brazil
  2. Centro Federal de Educação Tecnológica de Minas Gerais, Belo Horizonte, MG, Brazil
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Abstract

In this study, the effects of adding niobium and vanadium to Fe-based oxide dispersion strengthened alloys are confirmed. The composition of alloys are Fe-20Cr-1Al-0.5Ti-0.5Y2O3 and Fe-20Cr-1Al-0.5Ti-0.3V-0.2Nb-0.5Y2O3. The alloy powders are manufactured by using a planetary mill, and these powders are molded by using a magnetic pulsed compaction. Thereafter, the powders are sintered in a tube furnace to obtain sintered specimens.

The added elements exist in the form of a solid solution in the Fe matrix and suppress the grain growth. These results are confirmed via X-ray diffraction and scanning electron microscopy analyses of the phase and microstructure of alloys. In addition, it was confirmed that the addition of elements, improved the hardness property of Fe-based oxide dispersion strengthened alloys.

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Authors and Affiliations

Chun Woong Park
Jongmin Byun
ORCID: ORCID
Won June Choi
Young Do Kim
ORCID: ORCID
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Abstract

High temperature and high electric field applications in tantalum and niobium capacitors are limited by the mechanism of ion migration and field crystallization in a tantalum or niobium pentoxide insulating layer. The study of leakage current (DCL) variation in time as a result of increasing temperature and electric field might provide information about the physical mechanism of degradation. The experiments were performed on tantalum and niobium oxide capacitors at temperatures of about 125°C and applied voltages ranging up to rated voltages of 35 V and 16 V for tantalum and niobium oxide capacitors, respectively. Homogeneous distribution of oxygen vacancies acting as positive ions within the pentoxide layer was assumed before the experiments. DCL vs. time characteristics at a fixed temperature have several phases. At the beginning of ageing the DCL increases exponentially with time. In this period ions in the insulating layer are being moved in the electric field by drift only. Due to that the concentration of ions near the cathode increases producing a positively charged region near the cathode. The electric field near the cathode increases and the potential barrier between the cathode and insulating layer decreases which results in increasing DCL. However, redistribution of positive ions in the insulator layer leads to creation of a ion concentration gradient which results in a gradual increase of the ion diffusion current in the direction opposite to the ion drift current component. The equilibrium between the two for a given temperature and electric field results in saturation of the leakage current value. DCL vs. time characteristics are described by the exponential stretched law. We found that during the initial part of ageing an exponent n = 1 applies. That corresponds to the ion drift motion only. After long-time application of the electric field at a high temperature the DCL vs. time characteristics are described by the exponential stretched law with an exponent n = 0.5. Here, the equilibrium between the ion drift and diffusion is achieved. The process of leakage current degradation is therefore partially reversible. When the external electric field is lowered, or the samples are shortened, the leakage current for a given voltage decreases with time and the DCL vs. time characteristics are described by the exponential stretched law with an exponent n = 0.5, thus the ion redistribution by diffusion becomes dominant.

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Authors and Affiliations

Martin Kuparowitz
Lubomír Grmela
Vlasta Sedlakova
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Abstract

In this paper, thermal oxidation resistance of silicide-coated niobium substrates was tested in a temperature range of 1300–1450°C using an HVOF burner. Pure niobium specimens were coated using the pack cementation CVD method. Three different silicide thickness coatings were deposited. Thermal oxidation resistance of the coated niobium substrates was tested in a temperature range of 1300–1450°C using an HVOF burner. All samples that passed the test showed their ability to stabilize the temperature over a time of 30 s during the thermal test. The rise time of substrate temperature takes about 10 s, following which it keeps constant values. In order to assess the quality of the Nb-Si coatings before and after the thermal test, light microscopy, scanning electron microscopy (SEM) along with chemical analysis (EDS), X-ray diffraction XRD and Vickers hardness test investigation were performed. Results confirmed the presence of substrate Nb compounds as well as Si addition. The oxygen compounds are a result of high temperature intense oxidizing environment that causes the generation of SiO phase in the form of quartz and cristobalite during thermal testing. Except for one specimen, all substrate surfaces pass the high temperature oxidation test with no damages.
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Authors and Affiliations

Radosław Szklarek
1 2 3
Tomasz Tański
1
ORCID: ORCID
Bogusław Mendala
1
Marcin Staszuk
1
ORCID: ORCID
Łukasz Krzemiński
1
Paweł Nuckowski
1
Kamil Sobczak
3

  1. Silesian University of Technology, ul. Akademicka 2A, 44-100 Gliwice, Poland
  2. Spinex Spinkiewicz Company, Klimontowska 19, 04-672 Warsaw, Poland
  3. Łukasiewicz Research Network – Institute of Aviation, al. Krakowska 110/114, 02-256 Warsaw, Poland
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Abstract

Both corrosion and abrasion remove materials from some engineering components such as impact coal crusher hammers, pulverizer rings, chute liner, and rolls or molds. Intensive research has been done on improving the wear resistance of high chromium alloys, however, studies into corrosion resistance of high chromium alloys are insufficient. In order to determine the amount of ferroniobium addition in the wire to achieve the best corrosion resistance, and find out the mechanism of ferroniobium enhancing the corrosion resistance of the welding overlays, the high-Cr iron-based welding overlays with different niobium addition were fabricated by using self-made self-shielded metal-cored wires and their acidic corrosion resistance in 3.5 wt.% NaCl solution + 0.01 mol/L HCl solution were investigated by electrochemical corrosion test. The microstructure and corrosion morphology were characterized by OM, SEM, XRD and EDS. The polarization curves and values of I corr, E corr and Rc indicate the corrosion resistance is at the highest with 3.6 wt.% niobium addition, and at the lowest when the niobium addition is 10.8 wt.%. The corrosion of welding overlay occurs in the matrix of microstructure. With the increase of niobium addition from 3.6 wt.% to 10.8 wt.%, the proportion of network eutectic structure in the welding overlay is increased. Up to 10.8 wt.%, the microstructure is transformed from hypereutectic structure into eutectic one, leading to a higher acceleration of corrosion rate. When niobium addition reaches 14.4 wt.%, the welding overlay is transformed into a hypoeutectic structure. The addition of niobium element consumes carbon element in the alloy, which makes the increase of chromium content in the final solidified matrix, leading to an improvement in corrosion resistance.
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Authors and Affiliations

Dashuang Liu
1 2 3
Yucheng Wu
1
Weimin Long
2 4
Ping Wei
3
Rui Wang
3
ORCID: ORCID
Wei Zhou
1 5

  1. Hefei University of Technology, School of Material Science and Engineering, Hefei 230009, China
  2. Zhengzhou Research Institute of Mechanical Engineering Co., Ltd., Zhengzhou 450001, China
  3. Jiangsu University of Science and Technology, School of Material Science and Engineering, Zhenjiang 212003, China
  4. China Innovation Academy of Intelligent Equipment (Ningbo) Co., Ltd, Ningbo 315700, China
  5. School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore
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Abstract

This paper introduces an approach for vacuum brazing of niobium-316L stainless steel transition joints for application in superconducting radiofrequency cavity helium jackets. The study takes advantage of good wettability of Ag-Cu-Pd brazing alloy to suppress brittle Fe-Nb intermetallic formation, hence improve the joints’ mechanical performance. The wettability of Ag-Cu-Pd filler metal on niobium, the interface microstructure and mechanical properties of the transition joints were investigated. Two kinds of Ag-Cu-Pd filler metals had been studied and wet well on the niobium, and the wettability of Ag-31.5Cu-10Pd filler metal on niobium was better than Ag-28Cu-20Pd filler metal. Microstructure characterization demonstrated the absence of brittle intermetallic layers in all of the joint interfaces. Mechanical properties of samples prepared with Ag-31.5Cu-10Pd filler metal were also better than their peers made with Ag-28Cu-20Pd filler metal both room temperature (300 K) and liquid nitrogen temperature (77 K). The transition joints displayed shear strengths of 356-375 MPa at 300 K and 440-457 MPa at 77 K, respectively. After undergoing ten thermal cycles between the room temperature and the liquid nitrogen temperature, the transition joints’ leak rates were all lower than 1.1×10 –11 mbar·L/s. Therefore, Ag-Cu-Pd filler metal is applicable to high vacuum vessels used at cryogenic temperatures.
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Authors and Affiliations

Ruoxu Wang
1 2 3
Lubei Liu
1 2
Zongheng Xue
1 2
Teng Tan
1 2

  1. Chinese Academy of Sciences, Institute of Modern Physics, Lanzhou, Gansu 730000, China
  2. The Advanced Energy Science and Technology Guangdong Laboratory, Huizhou, Guangdong 516000, China
  3. Anhui East China Photoelectric Technology Research Institute, Wuhu, Anhui 241002, China
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Abstract

Textile industry emits daily huge amounts of sewage rich in non-biodegradable organic compounds, especially in textile dyes. Such contaminants are highly soluble in water, which makes their removal difficult. Other studies suggest their carcinogenicity, toxicity and mutagenicity. A promising chemical treatment of textile wastewater is the photodegradation of dye molecules in the process of photocatalysis in the presence of a photocatalyst. One-dimensional nanostructures exhibit a high surface-to-volume ratio and a quantum confinement effect, making them ideal candidates for nanophotocatalyst material. Nb2O5 is, among other metal oxides with a wide band gap, gaining popularity in optical applications, and electrospun niobium oxide nanostructures, despite their ease and low cost, can increase the chemical removal of textile dyes from wastewater. Facile synthesis of electrospun one-dimensional niobium oxide nanofibers is presented. The nanophotocatalysts morphology, structure, chemical bonds and optical properties were examined. Based on photodegradation of aqueous solutions (ph=6) of methylene blue and rhodamine B, the photocatalytic activity was established. The photocatalytic efficiency after 180 minutes of ultraviolet irradiation in the presence of Nb2O5 nanofibers was as follows: 84.9% and 31.8% for methylene blue and rhodamine B decolorization, respectively.
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Authors and Affiliations

Marta Zaborowska
1
ORCID: ORCID
Weronika Smok
1
ORCID: ORCID
Tomasz Tański
1
ORCID: ORCID

  1. Department of Engineering Materials and Biomaterials, Silesian University of Technology, Konarskiego 18A, 44-100 Gliwice, Poland

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