Fabrication of Porous Copper with Directional Pores through Thermal Decomposition of Compounds HIDEO NAKAJIMA and TAKUYA IDE Metallurgical and Materials Transactions A. vol. 39A, 390 (2008) NAKAJIMA Lab. JUNG JONG-SUCK M1 Colloquium

Contents  Introduction 1.Characteristics of porous metals 2.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 Characteristics of porous metals Foamed and sintered porous metals Lotus-type porous metals o Superior mechanical properties o Light-weight o Energy absorption o Sound absorption.etc Difficulty of use as structure materials due to weak strength Schematic of lotus-type porous metal Foamed Aluminum 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 gas A new fabrication method which does not use pressurized hydrogen gas is necessary !!!  Principle of pore formation L （ Liquid ） → S(Solid ） ＋ G （ Gas ）

Experimental procedures o Molten Cu temperature : 1573K 1. Argon atmosphere : 0.1 ~ 0.5 MPa 2.TiH 2 on bottom plate of the mold :0.075g ~ 0.25g Thermal Decomposition Method with TiH 2 containing hydrogen gas TiH 2 (S) → Ti(S) + 2H (in the melt) Mold Chiller TiH 2 pellets Graphite crucible Induction coil Molten Cu Pore Mold Chiller TiH 2 pellets Induction coil Molten Cu Argon atmosphere Graphite crucible

Effect of TiH 2 addition on pore morphology TiH 2 :0.075g 0.10g 0.125g0.25g Solidificationdirection (A): Cross - section perpendicular to the solidification direction (B): Cross - section parallel to the solidification direction Constant argon atmosphere(0.1MPa) (B) (A) Solidificationdirection 5mm

Constant (Supersaturation) Pore morphology dependence on mass of compounds(TiH 2 ) Constant argon atmosphere (0.1 MPa) TDM (undersaturated) TDM (supersaturated) TiH 2 :0.075g 0.10g 0.125g0.25g

(A) (B) 0.1MPa 0.25MPa 0.5MPa Effect of Ar pressure on pore morphology Constant addition mass of TiH 2 (0.25g) (B) (A) Solidificationdirection 5mm

Pore morphology dependence on Ar pressure Porosity and average pore diameter decrease with increasing argon pressure (Boyle-Charles law) Constant addition mass of TiH 2 (0.25g) v : pore volume p : external argon pressure n : hydrogen molar number R : gas constant T : Temperature (A) 0.1MPa 0.25MPa 0.5MPa

Discussion (1) - Role of Ti of TiH 2 Thermal decomposition reaction of TiH 2 Titanium is a very reactive element Ti + O 2 TiO 2 Nucleation sites for the hydrogen pores ! Liquid TiO 2 particles Chiller Solid/Liquid interface Cylindrical pores Suggestion TiH 2 Ti (?) + 2H (pores) It is expected that pore size and pore distribution become by uniformly distributed nucleation sites

Discussion (2) - Role of Ti of TiH 2 1. Cross-section of lotus copper fabricated by pressurized gas method (H 2 pressure : 0.2 MPa, Argon pressure : 0.6 MPa) 2. Cross-section of lotus copper fabricated by TDM (TiH 2 : 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