JP2012241231A - Amorphous alloy with excellent corrosion resistance and excellent electrical conductivity, and use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make an amorphous alloy which can resolve the problem of combining corrosion resistance and electrical conductivity and which exhibits ductility and is useful as a regular industrial material applicable to various fields.SOLUTION: The amorphous alloy contains at least 66 at% of Ni and, for example, 5-25 at% of B as a semimetal. It is preferable that the amorphous alloy contains Mo and Nb as additional major elements, and further contains Cu in some cases. The amorphous alloy does not form any passive film, but exhibits corrosion resistance on the basis of the electrical double layer theory.

Description

  The claimed invention relates to an amorphous alloy that can be used in a large amount as an industrial material and has both corrosion resistance and electrical conductivity due to an electric double layer.

  Amorphous alloys have been on the market for nearly 50 years, and many compositions with high corrosion resistance have been discovered. This property is due to the formation of a stable passive film on the surface. Passivation has poor electrical conductivity, so these are not suitable for use in environments where corrosion resistance and electrical conductivity are required simultaneously. This time, this physical property problem has been incorporated and solved.

Fe-based amorphous alloys such as Fe-Cr and Fe-Cr-Mo have excellent corrosion resistance. Therefore, there are many papers and patents that have been studied since ancient times. Its typical are patent No. 3805601 of the Fe-Cr-Mo-P system. The semi-metals for amorphization mainly consist of P (refer to the paper; Koji Hashimoto, Amorphous Stainless Steel, Journal of the Japan Institute of Metals, Vol. 8, No. 5 (1979)), which is useful for forming a highly corrosion-resistant passive state. It is. The main forms are PC and PB. Furthermore, when the Cr content is 25 or more at% and 7 or more at the Mo at%, it has excellent corrosion resistance that is close to zero corrosion even in the room temperature immersion test for 1 month for aqua regia (JP2009- 270152).
As reported above, amorphous alloys with high corrosion resistance form a Cr-enriched passivation.

Other than Fe-based materials, Ni-based amorphous alloys have been studied, and high patent resistance and ductility are considered good, and many patent documents have been issued.
For example, Patent Documents 1 and 2 report the corrosion resistance of Ni—Cr—PB amorphous to dilute hydrochloric acid.
Recently, there are Patent Documents 3 and 4. In particular, Patent Document 3 discloses a wide range of components as “high strength, high corrosion resistance Ni-based amorphous alloy”. That is, a _{Ni (80-wxy) Nb w} Cr x Mo y P 20-z B z with 0.1 ≦ W ≦ 10,4 ≦ X ≦ 18,3 ≦ Y ≦ 12,4 ≦ range of Z ≦ 6 .

JP 60-002641 A JP-A-61-243142 Japanese Patent Laid-Open No. 2001-049407 JP-A-8-225901

Many of these Ni-based amorphous alloys described in the literature have many combinations of PB, PC, and P—Si as semimetals, and many alloys also have the above-mentioned component ratios changed. Recently, many Ni _80-x -Cr _x -P ₁₆ -B ₄ have been introduced as fuel cell separators. In the 1960s and 1970s, Ni-Cr-B products were also introduced.
Since these Ni-based amorphous alloys exhibit high corrosion resistance due to the passivated Cr, they have poor electrical conductivity. Therefore, it is not suitable for use in applications that require electrical conductivity.

Therefore, in the present invention, an amorphous alloy having the following characteristics is manufactured on the assumption that the material does not form a passive state.
・ Excellent corrosion resistance: Confirm that it is superior to SUS316L by immersion test and constant potential electrolytic current density measurement.
・ Excellent electrical conductivity: Confirm that the resistance value is lower than that of the material that forms passivity (SUS316L) by measuring contact resistance.
-Furthermore, preferably it is excellent in ductility: It is confirmed that the ductility evaluation index (according to the adhesion bending test described later) is 4 or more.

The amorphous alloy of the present invention is characterized by exhibiting corrosion resistance by forming an electric double layer without forming a passive film.
Passive films have high corrosion resistance but are also strong insulators. Since the amorphous alloy of the present invention exhibits corrosion resistance by forming an electric double layer without forming a passive state, it has excellent current resistance as well as corrosion resistance. Corrosion resistance based on the electric double layer does not form a passive film on the surface of the amorphous alloy, but exhibits corrosion resistance by forming a portion with high electrical resistance in a narrow liquid phase at the interface between solid and liquid. To do. In that case, since it does not have a highly insulating film such as a passive film, the contact resistance is low, and therefore, the electrical conductivity is very good. In order to provide corrosion resistance based on the electric double layer, the component system of the amorphous alloy is preferably as follows, for example.

  The amorphous alloy of the present invention should not contain Cr. This is because Cr is provided with corrosion resistance that does not depend on the passive state, considering that the oxide easily forms a passive state.

The amorphous alloy of the present invention may further contain 66 at% or more of Ni and further contain Mo, Nb and B.
If the amorphous alloy does not contain Cr as described above, high corrosion resistance is not necessarily exhibited for all chemicals even if it is based on an electric double layer. However, as shown here, if Ni is contained at 66at% or more and Mo, Nb and B are also included, it will become a high concentration chemical such as hydrochloric acid (35%), sulfuric acid (98%), caustic soda (45%). On the other hand, it has excellent corrosion resistance.
Further, it is more preferable in terms of corrosion resistance to contain a trace amount of Cu.

Further, it is more preferable that B is contained as a semimetal for amorphization and P is not contained.
When P is contained as a semimetal for amorphization, this P tends to cause formation of a passive state, and also tends to induce delayed fracture over time because it absorbs hydrogen. In that respect, if B is contained as the metalloid and P is not included, it is difficult to form a passive state and delayed fracture does not occur. Further, if it does not contain P, it can be used for an IC substrate cleaning device or the like that also dislikes slight contamination.

It is particularly preferable that the amorphous alloy of the invention has the following component system.
a) It is represented by the component system Ni _100-xyz Mo _x Nb _y B _z , the amount of Ni is 66 at% ≦ Ni, and x, y, z indicating other component amounts are 0.1 at% ≦ x ≦ 15 at%, 0.1at% ≦ y ≦ 15at%, 5at% ≦ z ≦ 25at%.
b) Component system Ni _100-vxyz Mo _v Nb _x Cu _y B _z , the amount of Ni is 66 at% ≦ Ni, and other component amounts v, x, y, z are 0.1 at% ≦ v ≤15at%, 0.1at% ≤x≤15at%, 0.1at% ≤y≤5at%, 5at% ≤z≤25at%.
These component-based amorphous alloys exhibit high corrosion resistance based on the principle of an electric double layer, not by passive formation, and are therefore excellent in electrical conductivity. It is also preferable in that it has high ductility.

The amorphous alloy of the invention is suitable for use in a polymer electrolyte fuel cell (PEFC) separator that requires corrosion resistance and electrical conductivity.
The polymer electrolyte fuel cell separator is used to create gas (fuel / air) and water flow paths in the fuel cell and to conduct electricity, and is used in an environment where it is in contact with an acidic aqueous solution at 80 to 100 ° C. Therefore, high corrosion resistance and electrical conductivity are required. Since the amorphous alloy of the invention is excellent in corrosion resistance and electrical conductivity as described above, it can be said that it has excellent characteristics for constituting such a separator (or a surface portion of the separator).

The amorphous alloy of the invention is suitable for use as a corrosion-resistant material in a high-temperature environment (such as a material for a high-temperature chemical solution handling apparatus).
This is because sufficient corrosion resistance can be exhibited even in a high temperature (about 100 ° C. or higher) and highly corrosive environment. In addition, as a corrosion-resistant material in a high temperature environment, there exist a heat exchanger used for the heating of a chemical | medical solution, a reaction container, etc., for example.

The amorphous alloy of the present invention can have the following characteristics. That is,
・ Ensuring high ductility However, in an amorphous alloy mainly composed of Ni-Mo-Nb-B, the ductility is lost when the Nb content is increased. In order to ensure ductility while containing Nb in an amount of 8 at% or more, it is important to balance the contents of Mo and B (see FIG. 2).

・ Ensuring high corrosion resistance In order to avoid the formation of passivity, an amorphous alloy containing no Cr was used. Nb is effective for corrosion resistance to ph = 1 sulfuric acid. In addition, addition of Cu to the Ni—Mo—Nb—B based amorphous alloy is also effective in improving the corrosion resistance. As a test for confirming high corrosion resistance, as described later, measurement of weight loss due to sulfuric acid immersion, measurement of DC resistance value change, and measurement of constant potential electrolytic current density change were performed (FIGS. 3, 5, and 6). reference).
The role of each component is as follows.
Mo: Improves corrosion resistance in a reducing environment.
Nb: Excellent corrosion resistance. When combined with Mo, corrosion resistance is further improved.
However, if more are added, ductility is impaired.
Cu; Corrosion resistance is improved by adding a small amount.
B: A semi-metal that increases the ability to form amorphous materials. Does not directly affect corrosion resistance.
In amorphous alloys with these component systems, as a component system corresponding to dilute sulfuric acid in a reducing environment,
Ni-Mo-Nb-B, Ni-Mo-Nb-Cu-B
Is preferred.
In addition, those that are passive and exhibit corrosion resistance are greatly deteriorated in corrosion resistance because the passive state is destroyed at high temperature (about 100 ° C. or higher). It is possible to confirm a difference from the one that exhibits corrosion resistance by the electric double layer principle (see FIG. 7).

-Ensuring electric conductivity About this invention, the electric conductivity was evaluated by contact resistance measurement (refer FIG. 8). Since the inventive material does not contain Cr and does not form a passive state that deteriorates the electrical conductivity, the value is 1/3 or less smaller than SUS316L, which is close to that of graphite. Therefore, high electrical conductivity can be expected.

  The amorphous alloy of the present invention is excellent in both corrosion resistance and electrical conductivity and can be improved in ductility, and can be developed as a full-scale industrial material with a wide application range.

It is an X-ray diffraction profile about the produced amorphous ribbon. It is a diagram which shows the relationship with the ductility evaluation index | exponent in an amorphous ribbon. It is a diagram which shows the weight change in 80 degreeC sulfuric acid of an amorphous ribbon. It is an equivalent circuit used for analysis of impedance measurement. It is a diagram which shows the direct current | flow resistance value of the film | membrane in the impedance measurement of an amorphous ribbon. It is a diagram which shows the constant potential electrolysis current density in 80 degreeC sulfuric acid (ph = 1) of an amorphous ribbon. FIG. 4 is a diagram showing immersion corrosion weight loss in amorphous room temperature 5% phosphoric acid and 140 ° C. 85% phosphoric acid. It is a diagram which shows contact resistance values, such as an amorphous ribbon.

  The amorphous alloy according to the invention can be produced by a so-called single roll method or twin roll method using one or two cooled rolls, or a quenching function in which a cooling gas is blown around a flame for melting metal powder It can manufacture by the thermal spraying method using a thermal spraying apparatus with a mark.

  The inventors produced a ribbon (metal flake) made of an amorphous alloy by the single roll method according to the following procedure. That is, for each amorphous alloy shown in Table 1, first, a mixture of pure metal and semimetal of each corresponding component was melted by high-frequency heating in an Ar atmosphere, and cast with a Cu mold to obtain a master alloy. . The mother alloy was again melted by high frequency heating in an Ar atmosphere and sprayed onto the rotating single roll surface of Cu to obtain an amorphous ribbon. The thickness of the amorphous ribbon was set to 25 μm and 50 μm by changing the rotation speed of the single roll. The ribbon was confirmed to be amorphous by observing a halo peak by X-ray diffraction (see FIG. 1).

[Confirmation of ductility]
Each amorphous ribbon produced above was subjected to a 180 ° adhesion bending test, and the ductility of each amorphous alloy was evaluated based on whether or not the ribbon was cracked. The results are also shown in Table 1 above. The ductility evaluation index is represented by any one of 1 to 4 according to the following criteria.
Evaluation index 1: Adhesive bending with 25μm thick ribbon ×
Evaluation index 2: Adhesion bending with 50μm thick ribbon ×
Evaluation index 3: Adhesive bending with 50μm thick ribbon △
Evaluation index 4: Adhesive bending with 50μm thick ribbon ○
Moreover, the determination of contact | adherence bending (circle), (triangle | delta), and x follows the following references | standards.
×: Cracking occurred at 100% of the total ribbon length △: Cracking occurred at 50% of the total ribbon length ○: No cracking occurred at 100% of the total ribbon length

なお、表１の浸漬試験で使用したアモルファスリボンの厚さは25ミクロンである。H-2（SUS316L）のみバルクで浸漬試験を実施した。
図2は、リボンサンプル（Ni_87-x-yMo_xNb_yB₁₃）の延性を整理したものである。図中の○内数字は、延性評価指数を示し、斜線域は、表1の耐食性評価で減厚量＜5(μm/年)であった組成を示す。これより、延性評価指数４を得るための組成が明らかになった。Ni-Mo-Nb-Bを主成分とするアモルファス合金で、Nbの含有率を上げると延性は失われていく。Nbを8at%以上含有しながら延性を確保するためには、Mo、Bの含有率のバランスが重要となる。 [Confirmation of corrosion resistance (1)]
Each amorphous ribbon produced above was subjected to an immersion test in ph = 1 sulfuric acid at room temperature. The change in weight of the ribbon was observed, the corrosion plate thickness (thickness reduction) was calculated by the weight loss rate, and the corrosion resistance was evaluated. The results are shown in Table 1.

In addition, the thickness of the amorphous ribbon used in the immersion test of Table 1 is 25 microns. Only H-2 (SUS316L) was subjected to immersion test in bulk.
Figure 2 is obtained by organizing the ductility of the ribbon sample _{(Ni 87-xy Mo x Nb} y B 13). The numbers in circles in the figure indicate the ductility evaluation index, and the hatched area indicates the composition whose thickness reduction was <5 (μm / year) in the corrosion resistance evaluation of Table 1. From this, the composition for obtaining the ductility evaluation index 4 became clear. It is an amorphous alloy mainly composed of Ni-Mo-Nb-B, and the ductility is lost when the Nb content is increased. In order to ensure ductility while containing Nb in an amount of 8 at% or more, the balance of the contents of Mo and B is important.

[Confirmation of corrosion resistance (2)]
An immersion test was performed with 80 ° C. sulfuric acid having a concentration of 0.1N and 1N on two samples containing and not containing Cu. The survey sample is a part of the composition where corrosion resistance to sulfuric acid at normal temperature ph = 1 was observed in the above, and [at%] Ni ₇₂ Mo _4.5 Nb ₁₀ B ₁₃ Cu _0.5 (hereinafter referred to as Cu) and Ni _72.5 Mo _4.5 Nb ₁₀ B ₁₃ (hereinafter Cu-free).
Here, the change in the weight of the ribbon sample was investigated, and the measurement time was 240 h (10 days). The result is shown in FIG. 3, and the amount of corrosion on the vertical axis indicates the amount of weight reduction of the ribbon sample. It can be said that those with less corrosion are more corrosion resistant. The results of the four conditions are both excellent in corrosion resistance, but each sulfuric acid concentration shows higher corrosion resistance in the Cu-containing sample.

[Confirmation of corrosion resistance (3)]
The impedance was measured to determine the direct current resistance of the film using the two samples containing Cu and not containing Cu. The test piece was affixed and reinforced with a 1 mm thick vinyl chloride plate, and the free surface side was the measurement target. A 20 mm square platinum plate was used as the counter electrode, and the distance from the test piece was set at about 15 mm. The measurement temperature was 25 ° C. and the sulfuric acid concentration was 0.1N and 1N. Each sulfuric acid concentration was measured before and after being immersed in sulfuric acid of the same concentration at 80 ° C. for 10 hours. At this time, in the measurement after immersion for 10 days, impedance measurement was performed with fresh 25 ° C. sulfuric acid. The measuring device is PAR-STAT-2273 manufactured by Princeton Applied Reserch. In the measurement, alternating current of each frequency obtained by dividing the range of 1,000,000 to 0.01 [Hz] into 40 points by logarithmic values was applied, and the difference between the impedance value and the phase was measured intermittently. In the analysis, R1, R2, and C were calculated using the equivalent circuit shown in FIG.
FIG. 5 shows R2 (the DC resistance of the film, see FIG. 4) obtained by the impedance measurement. The index of corrosion resistance is R1 and R2, and when these values are large, the current density decreases and it can be said that the corrosion resistance is large. The value of R1 increases when it has corrosion resistance due to high Cr-containing passivation, but the value of R2 increases when it shows a corrosion resistant system with an electric double layer. R1 is not shown here because it was only 1/30 or less of R2 in all measurements.
According to FIG. 5, in the Cu-containing sample, each sulfuric acid concentration is a stable value before and after immersion. What should be noted here is the height of the DC resistance of the film. In the case of a material having corrosion resistance due to formation of a passive film, the DC resistance value R1 of the circuit outside the film is high in this measurement, but the reverse result is obtained for the developed material. Such a result is obtained when a structure called an electric double layer is generally used. The corrosion resistance of the developed material can also be judged to be due to this effect. This phenomenon has been put to practical use in capacitors and the like, but has never been confirmed with amorphous alloys.

[Confirmation of corrosion resistance (4)]
The current density was measured at a potential load of 1V. The chemical solution was 80 ° C. sulfuric acid with ph = 1, and continuous measurement was performed for 80,000 seconds or more. Here again, the two samples containing Cu and not containing Cu were used. A test piece, a counter electrode, and a test apparatus are the same as impedance measurement. The results are shown in FIG. Since corrosion weight loss correlates with current density, it can be said that the lower the current density, the better the corrosion resistance. In SUS316L, a result of 1 to 10 μm is also obtained in the same condition test. Both of the survey materials can be said to have better corrosion resistance than SUS316L.

[Confirmation of corrosion resistance (5)]
An immersion test was conducted on Ni ₆₃ Cr ₂₀ B ₁₇ and Ni ₆₆ Mo ₁₅ B ₁₉ ribbons to confirm corrosion resistance. The chemicals used for the immersion were two types of 5% phosphoric acid (room temperature) and 85% phosphoric acid (140 ° C.), and the immersion times were 7 days and 600 hours, respectively. FIG. 7 shows the annual thickness reduction converted from the thickness of the ribbon before immersion and the change in weight during immersion.
Ni ₆₃ Cr ₂₀ B ₁₇ exhibits corrosion resistance due to passivation. Corrosion loss could not be confirmed with 5% phosphoric acid (room temperature), but the corrosion resistance deteriorates rapidly with 85% phosphoric acid (140 ° C.). This is expected because the passive state is destroyed by the high-temperature chemical solution, as has been said conventionally. On the other hand, in Ni ₆₆ Mo ₁₅ B ₁₉ , even 85% phosphoric acid (140 ° C.) does not show much deterioration compared with 5% phosphoric acid (room temperature). This indicates that the resistance to corrosion due to the electric double layer is more resistant to temperature than the passive state.

[Confirmation of electrical conductivity]
The contact resistance was measured by measuring the amount of voltage drop generated by applying a constant current of 1 [A / cm ² ] to a test piece against a gold plate and deriving the resistance based on Ohm's law. The contact area between the gold plate and the test piece is 1 cm ² . The pressing force at this time was 5 MPa. The results are shown in FIG. 8, and the values of SUS316L and graphite are also shown for comparison. The contact resistance is an index for evaluating the conductivity when the materials are overlapped, and it can be determined that the smaller the resistance, the better the conductivity.

Claims (11)

  An amorphous alloy characterized by exhibiting corrosion resistance by forming an electric double layer without forming a passive film.   The amorphous alloy according to claim 1, which does not contain Cr.   3. The amorphous alloy according to claim 2, wherein Ni is contained at 66 at% or more and Mo, Nb and B are further contained.   4. The amorphous alloy according to claim 3, wherein B is contained as a semimetal for amorphization and P is not contained.   The amorphous alloy according to claim 3 or 4, further comprising Cu. Component system Ni _100-xyz Mo _x Nb _y B _z , the amount of Ni is 66 at% ≦ Ni, and x, y, z indicating the amount of other components is 0.1 at% ≦ x ≦ 15 at%, 0.1 at The amorphous alloy according to claim 1, wherein% ≦ y ≦ 15 at% and 5 at% ≦ z ≦ 25 at%. _{Indicated by the} component system Ni _100-vxyz Mo _v Nb _x Cu _y B _z , the amount of Ni is 66 at% ≦ Ni, and v, x, y, z indicating other component amounts are 0.1 at% ≦ v ≦ 15 at The amorphous alloy according to claim 1, wherein%, 0.1 at% ≦ x ≦ 15 at%, 0.1 at% ≦ y ≦ 5 at%, and 5 at% ≦ z ≦ 25 at%.   The use of the amorphous alloy according to any one of claims 1 to 7, wherein the polymer electrolyte fuel cell (PEFC) separator is required to have corrosion resistance and electric conductivity.   The use of the amorphous alloy according to any one of claims 1 to 7, wherein the material is a corrosion-resistant material in a high temperature environment.   A separator for a polymer electrolyte fuel cell, wherein the amorphous alloy according to any one of claims 1 to 7 comprises at least a surface of a portion in contact with an acidic aqueous solution.   A high-temperature chemical solution handling apparatus, wherein the amorphous alloy according to any one of claims 1 to 7 comprises at least a surface of a portion in contact with the chemical solution.

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