2005 Fiscal Year Final Research Report Summary
Infiltration-growth of Superconductive REBCO Oxide and Simulation of Faceted Peritectic Crystal Growth
| Project/Area Number |
15360404
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Metal making engineering
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| Research Institution | KYUSHU UNIVERSITY |
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Principal Investigator |
MORI Nobuyuki KYUSHU UNIVERSITY, Faculty Engineering, Materials Sci.& Eng., Ass.Prof, 大学院・工学研究院, 助教授 (20108666)
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| Co-Investigator(Kenkyū-buntansha) |
OGI Keisaku KYUSHU UNIVERSITY, Faculty Engineering, Materials Sci.& Eng., Prof, 大学院・工学研究院, 教授 (40038005)
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| Project Period (FY) |
2003 – 2005
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| Keywords | crystal growth / facet / YBCO / REBCO / superconductor / superconducting oxide / 123 / 211 / nucleation |
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| Research Abstract |
Growth process and structures of RE123(REBa_2Cu_3O_<7-x>) crystals in superconductive REBCO(RE=Y,Nd) and REBCO/Ag oxides fabricated by infiltration-growth and unidirectional solidification in the atmosphere of air or Ar-1%O_2 were studied experimentally and analytically to clarify the growth and structure-formation mechanism of faceted 123 crystals. To get a sample without shrinkage and with fine microstructure by the infiltration-growth, Ba-Cu-O(-RE,Ag) liquid was infiltrated into sintered porous Y211(/Ag) or Nd422(/Ag) solid, and then cooled under the peritectic temperature(Tp) to grow 123 crystal under a temperature gradient. The critical transition conditions of macrostructures from columnar to equiaxed structures and the change in freezing front temperature of 123 phase during solidification were analyzed to clarify the effects of growth rate(R), temperature gradient(G) and sample size(cross section) by using R-ΔT(undercooling for growth) and ΔT(for formation of a new crystal)-Vc(
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cooling rate) relations.The formation processes of macrostructure such as columnar and/or equiaxed structures of faceted 123 crystals during unidirectional solidification were well simulated by two-dimensional numerical method, in which the effects of crystallographic orientations and the nucleation of crystals in the liquid were considered. Further, the nucleation and growth processes of faceted RE123 (RD=Nd,Sm,Gd) crystals were observed in-situ on MgO(100) by using a high temperature in-situ observation apparatus with zoom-type optical microscope. RE123 crystals nucleated and grew at various undercooling, and the growth rate (u) and incubation time (t_<inc>) for nucleation were measured. u was approximated by a function of ΔTr: u=A_<gp>ΔTr^2/η(T), where A_<gp> is a constant, ΔTr=ΔT/Tp and η(T) is viscosity.Nucleation rate (I_v) was obtained from the relationship between time and number of nucleated crystals, and it was approximated by an exponential function: I_V={A_n/η(T)}exp(-B/ΔTr^2), where An and B are constants. It was clarified that u and Iv depend on not only ΔT but also Tp of RE123. Less
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