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