Effect of Hydrogen Pressure on Moisture-Based Fabrication of Lotus-Type Porous Nickel

Abstract

Lotus-type porous nickel, which has long straight pores aligned in one direction, was fabricated by utilizing moisture during unidirectional solidification in argon atmosphere. We studied the effect of the quantity of hydrogen in the atmosphere on the fabrication of lotus-type porous nickel. Adding hydrogen in the atmosphere, it was expected that the porosity of the lotus-type porous nickel with a smaller pore diameter became larger because not only the moisture but also hydrogen gas in the atmosphere were the supply source of hydrogen bubble. However, in fact, the pore diameter and the porosity of lotus-type porous nickel gradually decreased as the hydrogen partial pressure increased up to a point. When hydrogen was further added to the atmosphere, the pore diameter and porosity increased while the number of pores decreased dramatically. As a result of the fabrication under various pressures, the partial pressure of hydrogen at the border was 0.05 MPa. No moisture can be dissociated when a large amount of hydrogen is dissolved in the molten nickel.

Fabrication of Lotus-Type Porous Aluminum Utilizing Decomposition of Moisture

“…The chamber was evacuated to a vacuum of about 10 Pa, or filled with argon (99.998%) or hydrogen (99.995%) gas of 0.2 MPa after the evacuation. Here, it is to be noted that the mass of moisture decreases at a rate of about 60% 15) after the evacuation owing to the evaporation. Thus, the mass of moisture was evaluated taking into account this 60% reduction.…”

“…12,13) In the present study, lotus aluminum with pores oriented in one direction is fabricated by a casting method, in which hydrogen decomposed from moisture is utilized as a source of hydrogen. The moisture is a very cheap source of hydrogen, and it was used to fabricate lotus nickel, 14,15) cobalt and silicon. 16) In order to establish a method to fabricate lotus aluminum using moisture, the effects of the moisture amount, temperature of melts, and ambient pressure on the pore morphology of lotus aluminum are examined.…”

Fabrication of Lotus-Type Porous Cobalt and Silicon through Decomposition of Moisture

“…15 work can be found in a previous article. [12] The solidification occurs from the bottom of the mold to the top. During melting and solidification, the constant pressure in the chamber was maintained.…”

Pore Morphology of Porous Al-Ti Alloy Fabricated by Continuous Casting in Hydrogen Atmosphere

“…13,14) It should be noted that it is difficult to fabricate lotus Al alloys, with high porosity because the hydrogen solubility gap in Al alloys is rather low compared with that in other metals such as copper, iron and nickel. [10][11][12] However, previous research efforts have clarified that the pore formation and growth are strongly affected by the solidification process of matrix metal; the formation of equiaxed crystals prevents the growth of pores elongated along the solidification direction, while cylindrical pores can grow along the solidification direction when columnar crystals are formed during the solidification. On the other hand, in alloys with other solidification processes such as peritectic and monotectic solidification, the pore formation and growth behaviors have not been clarified yet.…”

“…[10][11][12] In particular, in Al-Si and Al-Cu alloy systems with eutectic solidification, the pore formation and growth behaviors have been investigated. 13,14) It should be noted that it is difficult to fabricate lotus Al alloys, with high porosity because the hydrogen solubility gap in Al alloys is rather low compared with that in other metals such as copper, iron and nickel.…”