Separator material for polymer electrolyte fuel cell having excellent corrosion resistance, conductivity and formability, and method for manufacturing same

Abstract

A thin plate is prepared by an ultraquenching transition control injector with a mixture of a metal powder having corrosion resistance to form a matrix and a powder having conductivity, as a raw material. When the matrix of the thin plate is crystal-structure metal, the plate can be formed at room temperature, and when the matrix is metallic glass, the plate can be formed in a supercooled liquid state. Therefore the plate can be finished into a separator with an intended shape.

Claims

1. A thin plate comprising a conductive material component that exists, without dissolving, in a metal matrix exhibiting corrosion resistance by passivation, and the thin plate being subjected to press forming, wherein the metal matrix includes an amorphous structure at a rate of 85% or more.

2. The thin plate according to claim 1, wherein the conductive material component is C or B.sub.4C.

3. The thin plate according to claim 1, wherein an internal pore is crimped by the press forming.

4. A method for manufacturing a thin plate, the thin plate comprising a conductive material component that exists, without dissolving, in an amorphous metal matrix which includes an amorphous structure at a rate of 85% or more and exhibiting corrosion resistance by passivation, the method comprising: injecting metal used for the metal matrix and the conductive material from an injection gun with flame toward a substrate so that the metal is melted, and then cooling with cooling gas before the flame reaches the substrate so as to provide a composite plate with a coating laminated on the substrate; and applying press-forming to the coating.

5. The method for manufacturing the thin plate, according to claim 4, wherein the coating is released from the composite plate to provide the thin plate.

6. The method for manufacturing the thin plate, according to claim 4, wherein the press-forming crimps a pore in the coating and the thin plate.

7. The method for manufacturing the thin plate, according to claim 4, wherein metal having a composition that becomes amorphous by quenching is used as the metal, to make the metal matrix in the coating and the thin plate include an amorphous structure.

8. A separator for a polymer electrolyte fuel cell, the separator being formed of the thin plate made by the method according to claim 4.

9. The thin plate according to claim 2, wherein an internal pore is crimped by the press forming.

10. The method for manufacturing the thin plate according to claim 5, wherein the press-forming is applied to the coating after the coating is released from the composite plate.

11. The method for manufacturing the thin plate according to claim 4, wherein the conductive material component is C or B.sub.4C.

12. A thin plate obtainable by the method according to claim 4, wherein the thin plate comprises a conductive material component that exists, without dissolving, in an amorphous metal matrix exhibiting corrosion resistance by passivation, and the thin plate is subjected to press-forming, having an internal pore crimped by the press-forming.

13. The thin plate according to claim 1, wherein the amorphous structure rate is 89-95%.

14. The thin plate according to claim 12, wherein the amorphous structure rate is 89-95%.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a side view showing the usage of an ultraquenching transition control injector.

(2) FIG. 2A is a side view and FIG. 2B is a bottom view each showing a large ultraquenching transition control injector.

(3) FIG. 3 is a side view showing the overall production line of thin plates.

(4) FIG. 4 is microscopic structure photography showing the cross section of a SUS316L thin plate mixed with B.sub.4C at 2.5 wt %.

(5) FIG. 5 is a graph showing the EDX result of a SUS316L matrix of FIG. 4.

(6) FIG. 6 is a side view showing upstream and downstream mist angles of the ultraquenching transition control injector of FIG. 2.

(7) FIG. 7 is microscopic structure photography showing the cross section of a Ni.sub.65Cr.sub.15P.sub.16B.sub.4 thin plate mixed with C at 0.3 wt %.

(8) FIG. 8 is a diagram illustrating a circuit 1 of measurement.

(9) FIG. 9 is a diagram illustrating a circuit 2 of measurement.

(10) FIG. 10 is a graph showing the result of contact resistance measurement.

(11) FIG. 11 is microscopic structure photography showing the cross section of a pressed Ni.sub.65Cr.sub.15P.sub.16B.sub.4 thin plate mixed with C at 0.3 wt %.

DESCRIPTION OF EMBODIMENTS

(12) 1. Preparation of Thin Plate and Test Specimen (Corrosion Resistance, Contact Resistance)

(13) For a metal material for use in an injection gun (ultraquenching transition control injector), a gas atomized powder having the composition of Ni.sub.65Cr.sub.15P.sub.16B.sub.4 (at %) and being classified as +38/63 m in diameter was used. This is a composition that solidifies as metallic glass when quenched, and this composition was selected also in the present invention in order to achieve the formation in a supercooled liquid range.

(14) For a conductive powder to be mixed in the metal material mentioned above, artificial graphite (AGB-5 from Ito Graphite Co., Ltd.) having the average particle size of 5 m was used (hereinafter, referred to as carbon). This powder is obtained by pulverizing artificial graphite electrodes, and is available at low cost.

(15) Ni.sub.65Cr.sub.15P.sub.16B.sub.4 and 0.3 wt % of carbon powder were mixed and stirred to obtain a material for injection. After mixing, water was removed by keeping the material warm in a drying oven under the condition of 80 C. for two hours. This is performed for a purpose of achieving stable powder supply without clogging or the like inside a supply path during the injection of the powder material.

(16) For the injection gun, the ultraquenching transition control injector shown in FIG. 2 was used. Mixed gas of oxygen and propane is used for fuel, and combustion flame is ejected from flame vents 5 outside of powder ejection ports 6, which are arranged at equal intervals in the widthwise direction. The powder material ejected from the powder ejection ports 6 is completely melted once in the combustion flame. The material is deposited on the surface of a substrate while being quenched, right after being melted, with a refrigerant mist ejected from a mist ejection port 3 arranged outside the powder ejection ports 6, thereby forming a film. This injection gun injects the material uniformly in the widthwise direction, and thus, it is possible to prepare a thin plate having a uniform thickness in the widthwise direction.

(17) The above-described ultraquenching transition control injector was installed in the thin plate production line shown in FIG. 3. A pickled steel coil of 2 mm in thickness300 mm in width is set between a payoff reel 7 and a coil winder 13, and the coil is moved toward the coil winder 13. First, the coil is heated with propane flame by a preheater 8. Then, after the coil shape was corrected by a leveler 9, the coil was heated up to the target temperature of 250 C. by a thin plate substrate heating and heat-equalizing device 10.

(18) On the surface of the coil that was heated up to the target temperature of 250 C., a film was formed with the mixed powder by an ultraquenching transition control injector 11. Immediately after the film formation, 10% reduction was applied thereon with a rolling mill 12. Before being wound on the coil winder 13, the film was released from the coil, thus obtaining a thin plate 14. At this time, the film temperature is 220 to 280 C. right after the reduction applied with the rolling mill 12. It is noted that in a series of operations, a coil speed was constant at 5.7 m/min. The above-described condition for manufacturing thin plates is shown in Table 1. An upstream mist angle and a downstream mist angle in Table 1 show a positional relationship, relative to the coil movement direction, of a mist ejection nozzle 2 and an inclination from the direction at right angles to the plane of the coil. The conditions are illustrated in FIG. 6.

(19) TABLE-US-00001 TABLE 1 Feed Rate of Alloy Powder (g/s) 30 Flow Rate of Propane Gas (m.sup.3/h) 34 Oxygen Flow Rate (m.sup.3/h) 120 Rectified Nitrogen Flow Rate (m.sup.3/h) 400 Injection Distance to Coil (mm) 600 Upstream Mist Angle () 9 Upstream Mist Flow Rate (liter/min) 4 Downstream Mist Angle () 9 Downstream Mist Flow Rate (liter/min) 4 Coil Surface Temperature Before Injection 250 Rolling Speed (m/min) 5.7

(20) The thin plate obtained thereby had a size of 300 m in thickness300 mm in width. The thin plate was confirmed by DSC to have 85% amorphous rate in comparison with an amorphous ribbon material which has 100% amorphous rate. FIG. 7 is a cross-sectional picture of the thin plate obtained thereby. It is observed that C (in a dotted circle) remains in the Ni.sub.65Cr.sub.15P.sub.16B.sub.4 matrix.

(21) Further, in order to confirm a difference in contact resistance between the cases with or without the conductive powder, an amorphous thin plate was also prepared from Ni.sub.65Cr.sub.15P.sub.16B.sub.4 powder having no mixed carbon powder, in the same procedures as described above. Finally, the following two types of thin plates were prepared.

(22) TABLE-US-00002 TABLE 2 Sample Composition of Conductive Mixing Rate of No. Metal Matrix (at %) Powder Conductive Powder (wt %) 1 Ni.sub.65Cr.sub.15P.sub.16B.sub.4 None 2 Ni.sub.65Cr.sub.15P.sub.16B.sub.4 C 0.3

(23) 2. Contact Resistance Test

(24) The prepared thin plates were cut out in the size of 35-mm square with a micro cutter. The amorphous thin plates were treated by a router to have a flat and smooth surface on the side opposite to the coil (having had a surface roughness of about Ra 10 m since they remained as they were after injection).

(25) In order to passivate the material surface, the plates were immersed for two hours in sulfuric acid of ph=3 at 80 C. and then experimented on.

(26) A constant current of 1 A was applied to a circuit shown in FIG. 8 to measure a potential difference between gold layers (Au-1-Au-2), and a resistance value was calculated on the basis of Ohm's law. This resistance value, being a contact resistance of Au-Carbon (C) paper existing at two locations in the circuit, was divided by 2 to give Rc (contact resistance of AuC paper). To determine Rc per 1 kgf/cm.sup.2, contact pressure was changed from 1 to 7 kgf/cm.sup.2.

(27) Then, a constant current of 1 A was similarly applied to a circuit shown in FIG. 9 to measure a potential difference between Au-1 and the test specimen, and a resistance value Ra was calculated on the basis of Ohm's law. Similar to the above description, to determine Ra per 1 kgf/cm.sup.2, contact pressure was changed from 1 to 7 kgf/cm.sup.2. Finally, according to the formula below, a contact resistance value Rs between the test specimen and the C paper was calculated, and conductivity was evaluated on the basis of this value.
Rs=RaRc

(28) FIG. 10 shows the measurement result of contact resistance. The amorphous material of Ni.sub.65Cr.sub.15P.sub.16B.sub.4 exhibits corrosion resistance by passivation on its surface. On the surface of both test specimens, a passive layer is formed during the sulfuric acid immersing process before the test. A reason why the contact resistance value of the C admixture is low at any contact pressure may be that C, a conductor, is present also in the passive layer. Accordingly, it is possible to say that the contact resistance that increases with passivation may be reduced by preparing a metallic thin plate with a powder material mixed with C by using an ultraquenching transition control injector.

(29) 3. Corrosion Resistance Test

(30) The prepared No. 2 thin plate (with mixed C) was cut out in the size of 20-mm square with a micro cutter, and was then experimented. As an immersion solution, sulfuric acid of ph=3 (80 C.) was prepared, and immersion was performed for 24 hours. The weight of the test specimen was measured before and after immersion, and corrosion rate (m/year) was calculated from weight changes and specific gravity.

(31) The result was 3 m/year, confirming that it had sufficient corrosion resistance as a separator for PEFCs.

(32) 4. Press Formability

(33) The prepared No. 2 thin plate was cut out in the size of 100-mm square, and was then experimented. Before processing, both upper and lower dies of a press machine were sufficiently preheated. A test specimen was set between the upper and lower dies warmed to a preset temperature of 390 C., held for two minutes under a micro load and then held for another two minutes with plastic deformation being applied thereto.

(34) FIG. 11 is a cross-sectional picture after the pressing is applied. It was observed that a flat thin plate of 300 m in thickness was formed by the punch with the upper and lower dies without cracked. Additionally, at a location in a dotted circle where a distance between the dies becomes small, 150 m, pores in the thin plate have disappeared due to compressive deformation, which leads to an improvement in internal quality as well as in forming.

(35) The test specimens after the press forming also measured by DSC to detect the presence of progression to crystallization. However, there was no change in amorphous rates before and after the press processing, and it was also found that there was no degradation issue in characteristics such as corrosion resistance.

(36) It is noted that the matrix was metallic glass in the above description, therefore, forming was performed in a supercooled liquid state, however, when the matrix of the thin plate is crystal-structure metal, forming can be performed at room temperature. In any case, by the press forming or the like of the thin plate according to the invention, the plate may be finished into the intended separator shape.

(37) As described above, it was confirmed that a thin plate with a mixed conductive powder of the present invention can satisfy conductivity, corrosion resistance, and press formability necessary for a separator for PEFCs.

REFERENCE SIGNS LIST

(38) 1 Powder Supply Pipe

(39) 2 Mist Ejection Nozzle

(40) 3 Mist Ejection Port

(41) 4 Inert Gas Ejection Port

(42) 5 Flame Vent

(43) 6 Powder Ejection Port

(44) 7 Payoff Reel

(45) 8 Preheater

(46) 9 Leveler

(47) 10 Thin plate substrate heating and heat-equalizing device

(48) 11 Ultraquenching Transition Control Injector

(49) 12 Rolling Mill

(50) 13 Coil Winder

(51) 14 Released Thin Plate