Material

Effect of vacancies and vanadium doping on the structural and magnetic properties of nano LiFe2.5O4

Publication date: November–December 2020

Source: Journal of Materials Research and Technology, Volume 9, Issue 6

Author(s): A.M. El-naggar, Mohamed Bakr Mohamed, A.M. Aldhafiri, Zein K. Heiba

Published

2 months ago

December 18, 2020

Republished by Plato

open access

Abstract

Nano LiFe_2.5-xV_xO₄ and LiFe_2.5-1.667xV_xO₄ systems were prepared by a sol–gel procedure at low temperatures. The influence of vacancies and vanadium doping on the structure parameters; lattice parameter, cation distribution, crystallite size, dislocation density, intrinsic distances, and bond angles between different cations and anions was fully studied by x-ray diffraction analysis applying Rietveld method. The nano nature and the particles morphology of the formed samples were examined by the transmission electron microscope. The change and the splitting, upon doping, of vibration bands obtained by Fourier-transform infrared spectroscopy were discussed. Magnetic measurements manifested that all samples exhibited a superparamagnetic behavior with a single domain characteristic. The change of saturation magnetization (M_s) and remnant magnetization (M_r) was correlated with the change in the crystallite size, and the cation distribution of different ions between different sites. The high concentrations of vacancies presented due to doping with vanadium ions is enhancing the electrochemical charge–storage properties of the samples making them a good potential electrode for Li-ion batteries.

Keywords

Li ferrite

Vanadium

Vacancies

Cation

Magnetic

Structure

Source: https://www.sciencedirect.com/science/article/pii/S2238785420320639?dgcid=rss_sd_all

Material

Microstructural characterization and electrochemical behavior of nano/ ultrafine grained pure copper through constrained groove pressing (CGP)

Publication date: March–April 2021

Source: Journal of Materials Research and Technology, Volume 11

Author(s): Ahmad Keyvani, Majid Naseri, Omid Imantalab, Davood Gholami, Kazem Babaei, Arash Fattah-alhosseini

Published

18 hours ago

February 27, 2021

Republished by Plato

Volume 11, March–April 2021, Pages 1918-1931

Journal of Materials Research and Technology

open access

Abstract

This study presents microstructural, electrochemical, and mechanical characterizations on pure copper fabricated using constrained groove pressing (CGP) in quiescent phosphate buffer solution (pH = 11.73). We tested the effect of surface modifications on electrochemical features using electrochemical impedance spectroscopy (EIS) and Mott–Schottky analysis. A three-dimensional simulation via finite element modeling evaluates the CGP effects on the maximum principal stress and the plastic strain distribution. The transmission electron microscopy (TEM) micrographs confirm that the increasing CGP cycles result in a nano/ultrafine grain microstructure. Our electrochemical study showed that the CGP process can positively impact the passive behavior of pure copper. Mott–Schottky analyses illustrated that the point defect densities decline in the p-type semiconducting passive layer upon receiving CGP. Besides, increasing the CGP cycles lowers the corrosion current density and produces less defective passive films.

Keywords

Electrochemical characteristic

Mott–Schottky (M–S) analysis

Passive film

Electrochemical impedance spectroscopy (EIS)

Constrained groove pressing (CGP)

Source: https://www.sciencedirect.com/science/article/pii/S2238785421001654?dgcid=rss_sd_all

Material

Microstructure, characterization of interfacial phases and mechanical properties of high Nb–TiAl/Al2O3 joints brazed by novel Nb particle-reinforced Ag–Cu filler alloy

Publication date: March–April 2021

Source: Journal of Materials Research and Technology, Volume 11

Author(s): Duo Dong, Dongdong Zhu, Yongfeng Liang, Xiaohong Wang, Shuyuan Zhu, Junpin Lin

Published

18 hours ago

February 27, 2021

Republished by Plato

Volume 11, March–April 2021, Pages 1942-1952

open access

Abstract

High niobium content TiAl alloys and Al₂O₃ ceramics were successfully joined using novel Nb particle-reinforced Ag–Cu composite filler. The changes in microstructure brazing at different temperatures were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The corresponding mechanical properties were studied by shear tests. The results showed that the brazed joints prepared at 900 °C can be divided into three zones. The typical microstructure of the brazed joints is high niobium content TiAl/AlCuTi + AlCu₂Ti/Ag(s,s)+Cu(s,s)+Nb/Ti₃(Cu,Al)₃O/Al₂O₃. The brazing temperature was shown to have a significant influence on the microstructure and reaction layer thickness. After brazing at 810 °C, macrodefects could be observed in the brazing seam. At higher brazing temperatures, brazed joints without any defects were obtained. The addition of Nb particles and the suitable thickness of the Ti₃(Cu,Al)₃O reaction layer are the main reasons for the high shear strength. When brazing at temperatures higher than 900 °C, the volume fraction of the brittle AlCu(Ti, Nb) phase was increased and a thick Ti₃(Cu,Al)₃O reaction layer was formed, which deteriorated the shear strength of the joint. The maximal shear strength joint reached 228 MPa at 870 °C for 10 min, which is a substantial increase compared with conventional brazing processes.

Keywords

Brazing

High Nb–TiAl alloys

Al₂O₃ ceramics

Interfacial microstructures

Mechanical properties

Source: https://www.sciencedirect.com/science/article/pii/S2238785421001745?dgcid=rss_sd_all

Material

Corrosion resistance and electrical contact resistance of a thin permanganate conversion coating on dual-phase LZ91 Mg–Li alloy

Publication date: March–April 2021

Source: Journal of Materials Research and Technology, Volume 11

Author(s): Sung-Mao Hung, Han Lin, Huan-Wen Chen, Siao-Ying Chen, Chao-Sung Lin

Published

18 hours ago

February 27, 2021

Republished by Plato

Volume 11, March–April 2021, Pages 1953-1968

open access

Abstract

A strongly acidic permanganate conversion coating solution containing 0.1 M KMnO₄ at pH 1.5 adjusted with H₂SO₄ was employed for LZ91 magnesium-lithium alloy, realizing the formation of a thin protective coating with a low electrical contact resistance. The corrosion resistance of LZ91 alloy was markedly improved by the permanganate conversion coating, which consisted of MgO, MnO₂, and Mg(OH)₂. Coating formation proceeded on both the α-Mg phase and β-Li phase in this strongly acidic permanganate solution, achieving a full coverage of permanganate conversion coating within a short treatment time. When the immersion was prolonged to 30 s, cracks were present on the permanganate conversion coating, which deteriorated the corrosion resistance substantially. Moreover, the increase in the thickness of the coating elevated the electrical contact resistance. However, the relatively thin areas on the thin permanganate conversion coating became active sites where corrosion commenced. As a result, a thin uniform permanganate conversion coating is crucial for both enhanced corrosion resistance and reduced electrical contact resistance.