Correlations between structural and magnetic properties in powder and bulk Mg(B1-xCx)2 prepared using carbon chemical vapour doped boron and silica coated boron
Correlations between structural and magnetic properties in powder and bulk Mg(B1-xCx)2 prepared using carbon chemical vapour doped boron and silica coated boron
The research project has been focused on the preparation and characterization of Mg(B1-xCx)2 powder and bulk samples using chemical vapour coated boron and silica coated boron by sol-gel method. The chemical vapour deposition of carbon on boron powder was achieved by reacting ethylene gas on high purity nano-sized boron particles (20-100nm diameter) with varying deposition temperatures and partial pressures. Undoped and carbon doped boron was then reacted with magnesium rod to produce both Mg(B1-xCx)2 powder and bulk samples. Transmission electron microscopy showed that the chemical vapour deposition achieved a uniformly thick carbon-rich layer on each particle, regardless of particle size. In addition, the analysis of the diffraction peaks and the characterization of the magnetisation has evidenced the coexistence of phases with different levels of carbon resulting in multiple current paths within the Mg(B1-xCx)2 samples. The study of the preparation process for bulk Mg(B1-xCx)2 samples has evidenced that reducing the difference between the time constant of reaction and the time constant of diffusion is crucial to obtain well-sintered samples devoid of cracks. Doping with carbon has shown significant improvements in the field dependence of Jc for the Mg(B1-xCx)2 bulk samples reaching values comparable with the best literature-reported data for bulk samples. However, the Jc values of the Mg(B1-xCx)2 bulk samples were observed to be noticeably lower when compared with the best literature-reported data for wires and tapes, owing to the greater density achievable in the latter. In contrast to the carbon doping, the coating with silica via sol-gel process was found to impair the in-field Jc properties of Mg(B1-xCx)2 bulk samples, presumably due to the huge amount of silica loaded onto the boron powder and to the formation of carbonate and silicate impurities within their reacted microstructure.
Paolella, Maurizio
1355d9ce-bf28-45ae-8ffa-203528fddf8d
July 2015
Paolella, Maurizio
1355d9ce-bf28-45ae-8ffa-203528fddf8d
Young, Edward
d3a881b0-a564-41f5-9843-34ae86da360f
Paolella, Maurizio
(2015)
Correlations between structural and magnetic properties in powder and bulk Mg(B1-xCx)2 prepared using carbon chemical vapour doped boron and silica coated boron.
University of Southampton, Faculty of Engineering and the Environment, Doctoral Thesis, 199pp.
Record type:
Thesis
(Doctoral)
Abstract
The research project has been focused on the preparation and characterization of Mg(B1-xCx)2 powder and bulk samples using chemical vapour coated boron and silica coated boron by sol-gel method. The chemical vapour deposition of carbon on boron powder was achieved by reacting ethylene gas on high purity nano-sized boron particles (20-100nm diameter) with varying deposition temperatures and partial pressures. Undoped and carbon doped boron was then reacted with magnesium rod to produce both Mg(B1-xCx)2 powder and bulk samples. Transmission electron microscopy showed that the chemical vapour deposition achieved a uniformly thick carbon-rich layer on each particle, regardless of particle size. In addition, the analysis of the diffraction peaks and the characterization of the magnetisation has evidenced the coexistence of phases with different levels of carbon resulting in multiple current paths within the Mg(B1-xCx)2 samples. The study of the preparation process for bulk Mg(B1-xCx)2 samples has evidenced that reducing the difference between the time constant of reaction and the time constant of diffusion is crucial to obtain well-sintered samples devoid of cracks. Doping with carbon has shown significant improvements in the field dependence of Jc for the Mg(B1-xCx)2 bulk samples reaching values comparable with the best literature-reported data for bulk samples. However, the Jc values of the Mg(B1-xCx)2 bulk samples were observed to be noticeably lower when compared with the best literature-reported data for wires and tapes, owing to the greater density achievable in the latter. In contrast to the carbon doping, the coating with silica via sol-gel process was found to impair the in-field Jc properties of Mg(B1-xCx)2 bulk samples, presumably due to the huge amount of silica loaded onto the boron powder and to the formation of carbonate and silicate impurities within their reacted microstructure.
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Final e-thesis for e-prints - 24377775.pdf
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Published date: July 2015
Organisations:
University of Southampton, Energy Technology Group
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Local EPrints ID: 397082
URI: http://eprints.soton.ac.uk/id/eprint/397082
PURE UUID: 2d56e64a-d766-48e5-b2d4-1ab478c516ee
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Date deposited: 11 Jul 2016 15:28
Last modified: 15 Mar 2024 01:05
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Author:
Maurizio Paolella
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