Nanoscale grains, high irreversibility field and large critical current density as a function of high-energy ball milling time in C-doped magnesium diboride

The effects of ball milling on lithium (Li) insertion/extraction properties into/from single-walled carbon nanotubes (SWNTs) were investigated. The SWNTs were synthesized on supported catalysts by thermal chemical-vapor deposition method, purified, and mechanically ball-milled by high-energy ball milling. The purified SWNTs and the ball-milled SWNTs were electrochemically inserted/extracted with Li. The structural and chemical modifications in the ball-milled SWNTs change the insertion/extraction properties of Li ions into/from the ball-milled SWNTs. The reversible capacity (Crev) increases with increase in the ball milling time, from 616 mAh/g (Li1.7C6) for the purified SWNTs to 988 mAh/g (Li2.7C6) for the ball-milled SWNTs. The undesirable irreversible capacity (Cirr) decreases continuously with increase in the ball milling time, from 1573 mAh/g (Li4.2C6) for the purified SWNTs to 845 mAh/g (Li2.3C6) for the ball-milled SWNTs. The enhancedCrevof the ball-milled SWNTs is presumably due to a continuous decrease in theCirrbecause the SWNTs develop a densely packed structure on the ball milling process. The insertion of Li ions into the ball-milled SWNTs is facilitated by various Li insertion sites formed during the ball milling process in spite of small surface area than the purified SWNTs. Lithium ions inserted into various insertion sites enhance theCrevin the ball-milled SWNTs with the large voltage hysteresis by hindrance of the extraction of Li ions from the ball-milled SWNTs. In addition, the ball-milled samples exhibit more stable cycle capacities than the purified samples during the charge/discharge cycling.

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Spark Plasma Sintering of High-Energy Ball-Milled ZrB2 and HfB2 Powders with 20vol% SiC

Materials Science Forum ◽

10.4028/www.scientific.net/msf.941.1990 ◽

2018 ◽

Vol 941 ◽

pp. 1990-1995

Author(s):

Naidu V. Seetala ◽

Cyerra L. Prevo ◽

Lawrence E. Matson ◽

Thomas S. Key ◽

Ilseok I. Park

Keyword(s):

Particle Size ◽

Grain Size ◽

Ball Milling ◽

Milling Time ◽

High Energy ◽

Micro Hardness ◽

Plasma Sintering ◽

Spark Plasma ◽

Energy Ball ◽

Ball Milling Time

ZrB2 and HfB2 with incorporation of SiC are being considered as structural materials for elevated temperature applications. We used high energy ball milling of micron-size powders to increase lattice distortion enhanced inter-diffusion to get uniform distribution of SiC and reduce grain growth during Spark Plasma Sintering (SPS). High-energy planetary ball milling was performed on ZrB2 or HfB2 with 20vol% SiC powders for 24 and 48 hrs. The particle size distribution and crystal micro-strain were examined using Dynamic Light Scattering Technique and x-ray diffraction (XRD), respectively. XRD spectra were analyzed using Williamson-Hall plots to estimate the crystal micro-strain. The particle size decreased, and the crystal micro-strain increased with the increasing ball milling time. The SPS consolidation was performed at 32 MPa and 2,000°C. The SEM observation showed a tremendous decrease in SiC segregation and a reduction in grain size due to high energy ball milling of the precursor powders. Flexural strength of the SPS consolidated composites were studied using Four-Point Bend Beam test, and the micro-hardness was measured using Vickers micro-indenter with 1,000 gf load. Good correlation is observed in SPS consolidated ZrB2+SiC with increased micro-strain as the ball milling time increased: grain size decreased (from 9.7 to 3.2 μm), flexural strength (from 54 to 426 MPa) and micro-hardness (from 1528 to 1952 VHN) increased. The correlation is less evident in HfB2+SiC composites, especially in micro-hardness which showed a decrease with increasing ball milling time.

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CRITICAL CURRENT DENSITY PERFORMANCE OF MALIC ACID DOPED MAGNESIUM DIBORIDE WIRES AT DIFFERENT OPERATING TEMPERATURES

International Journal of Modern Physics B ◽

10.1142/s0217979209062864 ◽

2009 ◽

Vol 23 (17) ◽

pp. 3497-3502

Author(s):

X. XU ◽

J. H. KIM ◽

Y. ZHANG ◽

M. JERCINOVIC ◽

E. BABIC

Keyword(s):

Critical Current Density ◽

Critical Current ◽

Current Density ◽

Malic Acid ◽

Magnesium Diboride ◽

Transport Critical Current Density ◽

Pinning Force ◽

Irreversibility Field ◽

Operating Temperatures ◽

Practical Level

We investigated the effects of different operating temperatures on the performance of transport critical current density, Jc, for MgB 2 + 10 wt % C 4 H 6 O 5 MgB 2/ Fe wires. It was shown that the Jc values of the malic acid doped wires sintered at 900°C reached 104 Acm-2 at 20 K and 5 T. The Jc value extrapolated to 2 T and 20 K exceeds the practical level of 105 Acm-2. According to the Kramer plots, the pinning force, FK = Jc1/2 x B1/4, is expected to be a linear function of magnetic field B. The irreversibility field, B irr , at which extrapolated FK reaches zero, was 1.8 T at 32.8 K, 2.8 T at 30 K, 5.7 T at 25 K, 8.6 T at 20 K, and 12.5 T at 15 K, respectively.

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Nanocrystalline Cu90Nb10 Alloy Produced by Mechanical Alloying

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.750-752.752 ◽

2013 ◽

Vol 750-752 ◽

pp. 752-755

Author(s):

C.J. Li ◽

Q.X. Zhang ◽

Q. Yuan ◽

J. Tan ◽

L. Teng ◽

...

Keyword(s):

Mechanical Alloying ◽

Ball Milling ◽

Milling Time ◽

High Energy ◽

Deformation Degree ◽

Solid Solution Strengthening ◽

Fine Grain ◽

Powder Particles ◽

Energy Ball ◽

Ball Milling Time

Nanocrystalline Cu90Nb10 alloy was produced by high energy ball milling mechanical alloying (MA). The effects of ball milling time on the microstructure and mechanical property of this alloy in the process of MA were investigated. The results show: up to 10 at.% Nb could be dissolved into Cu matrix by MA; the powder particles became compacted and homogeneous with increasing the ball milling time, and the deformation degree also increased synchronously; the grain size of this alloy was refined gradually, and it reached the minimum value of 11.5 nm after 30h milling; the microhardness of this alloy increased with increasing the milling time, and it obtained the maximum value of 328 Hv after 30h milling. The obvious reinforcement of this alloy may be due to the comprehensive effects of the fine grain strengthening, the solid solution strengthening and the strain strengthening.

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