fabrication of porous copper with directional pores through thermal decomposition of compounds hideo...
TRANSCRIPT
Fabrication of Porous Copper with Directional Pores through Thermal
Decomposition of CompoundsHIDEO NAKAJIMA and TAKUYA IDE
Metallurgical and Materials Transactions A. vol. 39A, 390 (2008)
NAKAJIMA Lab.JUNG JONG-SUCK
2008.06.18 M1 Colloquium
Contents
Introduction
1. Characteristics of porous metals2. Pressurized gas method to fabricate lotus-type porous metals and the principle of pore formation
Experimental procedures(Thermal Decomposition Method - TDM)
Experimental results
Conclusions
Introduction - 1
2. Characteristics of porous metals
Foamed and sintered porous metals Lotus-type porous metals
oSuperior mechanical properties
o Light-weighto Energy absorptiono Sound absorption.etc
Difficulty of use as structure materials due to weak strength
Schematic of lotus-type porous metal
Foamed Aluminum
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Problem
J. Banhart : Prog. Mater. Sci., 2001,
Spherical and irregular Cylindrical
o Various functionalities owing to their unique pore structure
1.Porous metal is defined as a metal structure which has a number of pores
H. Nakajima: Prog. Mater. Sci., 2007,
Introduction - 2
Pressurized gas method to fabricate lotus-type porous metals
Inherent inflammable and explosive risks of hydrogen gasA new fabrication method which does not use pressurized hydrogen gas is necessary !!!
Melting Point
Solid
Liquid
Gas
so
lub
ility
Temperature
Principle of pore formationL ( Liquid )→ S(Solid ) + G
( Gas )
Experimental procedures
o Molten Cu temperature : 1573K
1. Argon atmosphere : 0.1 ~ 0.5 MPa2.TiH2 on bottom plate of the mold :0.075g ~ 0.25g
Thermal Decomposition Method with TiH2 containing hydrogen gas
TiH2(S) → Ti(S) + 2H (in the melt)
Mold
Chiller
TiH2 pellets
Graphite crucible Induction
coilMolten Cu
PoreMold
Chiller
TiH2 pellets
Induction coil
Molten Cu
Argon atmosphere
Graphite crucible
Effect of TiH2 addition on pore morphology
TiH2:0.075g 0.10g 0.125g 0.25g
Sol
idifi
catio
n di
rect
ion
(A): Cross - section perpendicular to the solidification direction
(B): Cross - section parallel to the solidification direction
Constant argon atmosphere(0.1MPa)
(B)
(A)
So
lidif
icat
ion
dir
ecti
on
5mm
Constant
Constant(Supersaturation)
Pore morphology dependence on mass of compounds(TiH2)
Constant argon atmosphere (0.1 MPa)
TDM (undersaturated)
TDM(supersaturated)
TiH2:0.075g 0.10g 0.125g 0.25g
(A)
(B)
0.1MPa 0.25MPa 0.5MPa
Effect of Ar pressure on pore morphology
Constant addition mass of TiH2 (0.25g)
(B)
(A) So
lidif
icat
ion
d
irec
tio
n
5mm
Pore morphology dependence on Ar pressure
Porosity and average pore diameter decrease with increasing argon pressure (Boyle-Charles law)
Constant addition mass of TiH2 (0.25g)
p
nRTv
v : pore volumep : external argon pressuren : hydrogen molar numberR : gas constantT : Temperature
(A)
0.1MPa 0.25MPa 0.5MPa
Discussion (1) - Role of Ti of TiH2
Thermal decomposition reaction of TiH2
Titanium is a very reactive element
Ti + O2 TiO2
Nucleation sites for the hydrogen pores !
Liquid
Liquid
TiO2 particles
Chiller
Solid/Liquid interface
Cylindrical pores
Suggestion
TiH2 Ti (?) + 2H (pores)
It is expected that pore size and pore distribution become by uniformly distributed nucleation sites
Discussion (2) - Role of Ti of TiH2
1. Cross-section of lotus copper fabricated by pressurized gas method (H2 pressure : 0.2 MPa, Argon pressure : 0.6 MPa)
2. Cross-section of lotus copper fabricated by TDM (TiH2 : 0.125g, Argon pressure : 0.1 MPa)
More homogeneous pore size and pore distribution
Conclusions
1. This method is simpler and more effective than the pressurized gas method employing high pressure hydrogen gas which may cause inflammable and explosive risks.
2. It was confirmed that it is possible to control the pore morphology by TDM with changing argon pressure and mass of compounds.
3. TDM may have another advantage to fabricate lotus - type porous metals with more homogeneous pore size and pore distribution than those by pressurized gas method.
Lotus - type porous copper was fabricated by thermal decomposition method with compounds containing gas elements