Titanium metal corrosion-resistant electrodes

Abstract

To provide a corrosion-resistant titanium electrode comprising a glassy carbon layer having strong adhesiveness to withstand bending deformation or sufficient adhesiveness at corners and edges, and making the glassy carbon layer difficult to crack or peel off from the titanium electrode substrate, especially when the titanium electrode substrate in a plate or mesh shape is bent or deformed into a curved shape. [Solution] A corrosion-resistant titanium metal electrode has a conductive and corrosion-resistant coating consisting of a glassy carbon layer 2 with a thickness of 0.1 to 2 μm provided on the surface of a titanium metal electrode substrate 3, the mesh-like electrode substrate 3 having a surface roughness Ra of 0.1 to 1.0 μm, and the surface of the electrode substrate 3 is a chemically polished or electrolytically polished surface that does not have a titanium oxide coating.

Description

[Technical Field]

[0001] The present invention relates to a corrosion-resistant electrode made of titanium metal, which is used for electrodes in electrochemical cells, and a method for producing the same. [Background technology]

[0002] In general, corrosion-resistant metal members used as current collectors for storage batteries, electrode components for electrochemical reaction devices such as those used in the electrolysis of electrolytes such as salt water, and the inner surfaces of battery cell casings are made of materials that have excellent corrosion resistance when used in contact with electrolytes containing highly corrosive halide ions such as fluoride ions and chloride ions.

[0003] For example, electrodes used in electrochemical reaction devices such as bulk electrolysis cells are made of gold, platinum, stainless steel, or the like, which have excellent electrical properties, so that they are insoluble in the electrolyte and conductive at the current density required for the electrochemical reaction. These are made into a mesh or porous graphite is used to increase the surface area of ​​the electrode and increase the current density, thereby achieving the required electrode performance.

[0004] However, electrode materials such as gold and platinum, which have good corrosion resistance, are expensive, and it is difficult to mold porous graphite into thin shapes, making it difficult to practically mass-produce corrosion-resistant electrodes using such materials.

[0005] On the other hand, glassy carbon (GLC) films, which are amorphous carbon films, have corrosion resistance comparable to that of platinum and are also highly impermeable to liquids, making them a promising material for practical use as insoluble electrodes.

[0006] Incidentally, glassy carbon (GLC) has a C=C sp structure compared to diamond-like carbon (DLC). 2 Bond is sp 3 It differs from DLC in that it has more bonds, a low hydrogen content (less than 20%), and low electrical resistance.

[0007] However, when a structure is adopted in which a thin film made of glassy carbon is overlaid on a sheet-like electrode substrate and integrated with it, it is necessary to process it into a cylindrical shape or a partially bent shape to match the shape of the battery, and the glassy carbon thin film also needs to have the required flexibility. However, it has been difficult to impart such flexibility, that is, bending deformability that allows the glassy carbon thin film to conform to the electrode substrate.

[0008] As a well-known technique for improving the bending deformability of a thin glassy carbon film, for example, there is a method for manufacturing a corrosion-resistant metal member in which a thin glassy carbon film layer of 0.5 to 1 μm is formed on the surface of a sheet-like, carburization-resistant metal material that comes into contact with a battery electrolyte by plasma carburization treatment using a hydrocarbon gas at a pressure of 100 to 2666 Pa and an atmospheric gas temperature range of 500 to 700°C (Patent Document 1).

[0009] It is also known that the surface of titanium metal is formed to an appropriate surface roughness Ra of 0.01 to 0.8 μm, and a flat glassy carbon layer is formed on top of the titanium oxide layer, thereby preventing localized stress concentration in the glassy carbon layer (Patent Document 2). [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent No. 6302163 [Patent Document 2] Patent No. 5657940 Summary of the Invention [Problem to be solved by the invention]

[0011] However, even when no localized stress concentration occurs in the glassy carbon layer, the adhesion of the coating is insufficient, and when a glassy carbon layer is provided over a titanium metal electrode substrate, peeling between the layers tends to occur when the substrate is bent. This poses a problem in that the adhesion of the glassy carbon layer, which serves as a coating for an electrode substrate, particularly an electrode substrate with an intricate mesh-like structure, to the electrode substrate is insufficient.

[0012] Such problems are also likely to occur when a sheet-like, plate-like, or mesh-like titanium electrode substrate is bent or deformed into a curved shape, and the glassy carbon layer, which cannot follow the deformation of the electrode substrate, is prone to cracking and peeling off from the electrode substrate.

[0013] Furthermore, not only in the case of a sheet-like or mesh-like electrode substrate, but also in the case of an electrode substrate having, for example, a shape in which a columnar portion is superimposed on a plate-like base, or an electrode substrate having a plate-like base with a circular or polygonal hole, the adhesion of the glassy carbon layer to the electrode substrate at corners or edges where flat or curved surfaces intersect cannot be said to be sufficient.

[0014] Therefore, an object of the present invention is to solve the above-mentioned problems and to provide a corrosion-resistant titanium metal electrode having a conductive and corrosion-resistant coating consisting of a glassy carbon layer on the surface of a three-dimensional titanium metal electrode base material, which has strong adhesion that can withstand bending deformation, and further has sufficient adhesion of the glassy carbon layer at the corners and edges of the three-dimensional electrode base material, so that the glassy carbon layer is not likely to crack or peel off from the titanium electrode base material, even when a flat or mesh-shaped titanium electrode base material is bent or deformed into a curved shape. [Means for solving the problem]

[0015] In order to solve the above problems, the present invention provides a corrosion-resistant titanium metal electrode in which a conductive and corrosion-resistant coating made of a glassy carbon layer is provided on the surface of an electrode base material made of unoxidized titanium metal with a surface roughness Ra of 0.1 to 1.0 μm.

[0016] The corrosion-resistant titanium electrode of the present invention constructed as described above has a titanium electrode substrate having a surface roughness within a predetermined range of Ra 0.1 to 1.0 μm, and the surface is in a non-oxidized state free from titanium oxides, and a glassy carbon layer is provided on the surface with good adhesion.

[0017] Titanium metal normally has a strong bond with oxygen, and an oxide film instantly forms on its surface in air. Therefore, glassy carbon is normally formed on a titanium oxide layer, but the adhesive properties of a glassy carbon layer formed directly on a non-oxidized titanium metal surface were not anticipated.

[0018] Furthermore, the relatively fine irregularities on the surface of unoxidized titanium metal, with a surface roughness of Ra 0.1 to 1.0 μm, allow the glassy carbon layer, which is a plasma CVD coating, to come into direct contact with the titanium metal, which has a high specific surface area, providing an anchoring effect to the titanium metal.

[0019] However, the anchor effect alone is not enough to ensure the adhesion of the glassy carbon layer (coating) to titanium metal or the flexibility of the coating, and when the coating is bent and deformed, cracks will occur due to the strain inherent in the glassy carbon layer.

[0020] Furthermore, as a result of extensive research, the inventors of the present application have found that in order to minimize the occurrence of distortion in the glassy carbon coating, it is necessary to use a titanium metal surface that has as low a carbon absorption capacity as possible, which serves as the substrate for the coating. They have found that in such a case, the glassy carbon layer is formed into a uniform thin film, and they believe that this may also improve the adhesion of the coating and prevent cracks due to bending deformation.

[0021] Therefore, in this invention, titanium metal that meets the specific conditions of having a surface roughness Ra of 0.1 to 1.0 μm and being in a non-oxidized state is identified, and a glassy carbon layer is formed on the surface of that titanium metal. It has been confirmed that such a glassy carbon coating has strain relief and high flexibility, and furthermore, that this coating has good adhesion to the titanium metal surface, and that the flexibility of the glassy carbon layer and its ability to prevent cracks during bending deformation are also improved, leading to the completion of this invention.

[0022] Because the flexible glassy carbon layer is tightly adhered to and integrated with the surface of unoxidized titanium metal in this manner, the glassy carbon layer will not crack even if a flat or mesh-shaped titanium electrode substrate with a glassy carbon layer is bent or deformed into a curved shape. Furthermore, the glassy carbon layer also adheres sufficiently well to corners and edges where flat or curved surfaces intersect in titanium electrode substrates with well-known three-dimensional shapes, preventing it from peeling off from the titanium electrode substrate.

[0023] In order to fully obtain these effects, it is preferable that the non-oxidized surface of the titanium metal electrode substrate is a chemically polished or electrolytically polished surface that does not have a titanium oxide coating. Furthermore, the glassy carbon layer is a thin film having a thickness in the specified range of 0.1 to 2 μm, so that the adhesion to the titanium metal electrode substrate is further improved.

[0024] A mesh-shaped electrode substrate can be used as the electrode substrate, and such a mesh-shaped electrode substrate may be, for example, a mesh-shaped electrode substrate woven with fine wires having a wire diameter of 0.2 mm or less.

[0025] To efficiently produce such mesh-like or other forms of corrosion-resistant titanium electrodes, it is preferable to employ a method for producing a corrosion-resistant titanium electrode that includes the following essential steps: blasting the surface of a titanium electrode substrate to a surface roughness of Ra 0.1 to 1.0 μm; then chemically or electrolytically polishing the surface to remove any titanium oxide coating; and forming a conductive and corrosion-resistant coating consisting of a glassy carbon layer on the surface of the titanium electrode substrate that has been left unoxidized through the above steps by plasma vapor deposition (CVD). [Effects of the Invention]

[0026] This invention provides a corrosion-resistant titanium metal electrode in which a coating made of a glassy carbon layer is provided on the surface of an electrode substrate made of unoxidized titanium metal, which is formed with a specified surface roughness.As a result, the glassy carbon layer at corners and edges where flat and curved surfaces intersect provides a corrosion-resistant titanium metal electrode with a glassy carbon layer that has strong adhesion and can withstand bending deformation.

[0027] In particular, there is an advantage that the glassy carbon layer does not crack or peel off from the titanium electrode substrate even when the titanium electrode substrate is bent into a flat plate or mesh shape or deformed into a curved shape.

[0028] By employing the above-described essential steps as a method for producing such titanium corrosion-resistant electrodes, titanium corrosion-resistant electrodes having the above-described advantages can be efficiently produced with stable quality through the predetermined essential steps. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 is a perspective view schematically illustrating a first embodiment. [Figure 2] FIG. 10 is an enlarged plan view showing a main part of an electrode base material according to a second embodiment. [Figure 3] FIG. 10 is an enlarged cross-sectional view showing a main part of a second embodiment. [Figure 4] Illustrative diagram of bending test for Examples 1-3 and Comparative Examples 1 and 2 [Figure 5] Plan view of the electrode substrate of Examples 1-3 [Figure 6] Stereomicroscope photograph of the area around the indentation after the Rockwell hardness test in Example 4 [Figure 7] Stereomicroscope photograph of the area around the indentation after the Rockwell hardness test of Comparative Example 3 DETAILED DESCRIPTION OF THE INVENTION

[0030] An embodiment of the present invention will be described below with reference to the accompanying drawings. As shown in FIG. 1, the first embodiment is a corrosion-resistant titanium metal electrode having a sheet (thin plate) electrode substrate 1 made of non-oxidized titanium metal and a conductive and corrosion-resistant coating of a glassy carbon layer 2 having a thickness of 0.1 to 2 μm provided on the surface thereof. The surface roughness of the sheet-like electrode substrate is Ra 0.1 to 1.0 μm, and the surface of the electrode substrate is a chemically polished or electrolytically polished surface that does not have a titanium oxide coating.

[0031] The electrode substrate 1, with a surface roughness of Ra 0.1 to 1.0 μm, is made by blasting the surface of a thin titanium metal plate to form a finely textured surface. The media used for such blasting are glass beads or alumina powder, and favorable results have been obtained.

[0032] If the surface roughness of the electrode substrate 1 is Ra 0.1 μm or less, the anchor effect when coated with glassy carbon will not be obtained, resulting in insufficient adhesion. In addition, to achieve Ra 1.0 μm or more, the media must be strongly impacted, and such blasting treatment may damage the titanium metal mesh.

[0033] In view of this tendency, the electrode substrate 1 preferably has a surface roughness Ra of 0.2 to 0.9 μm, more preferably 0.3 to 0.8 μm, and even more preferably 0.4 to 0.7 μm.

[0034] The second embodiment shown in FIGS. 2 to 5 employs a mesh-like titanium electrode substrate 3 made of plain-woven titanium thin wires 3a, 3b instead of the sheet-like titanium electrode substrate 1 of the first embodiment, and provides a glassy carbon layer 2 on the surface of the non-oxidized electrode substrate 3, and the manufacturing process is the same as that of the first embodiment.

[0035] Although not shown in the figures, the shape of the electrode substrate may be any well-known shape such as a rod, plate, column, polygonal prism, cylinder, or square tube, or may be a composite shape in which multiple of these are stacked together, such as an electrode substrate in the shape of a disk or square plate with a columnar or square prism portion stacked on top of it, or an electrode substrate in a disk-like base with a circular or polygonal hole. Any electrode substrate may have the shape required depending on the purpose of the product form.

[0036] The blasting treatment employed in this invention selectively employs air blasting, wet blasting, or shot blasting, and is carried out so as to form fine irregularities with a surface roughness Ra of 0.1 to 1.0 μm on the surface of the titanium metal electrode substrate.

[0037] The media used for blasting, particularly when the object to be treated is an extremely fine mesh, is preferably fine glass beads with a particle size of less than 1 mm, preferably less than 500 μm, or fine alumina powder, since the blasting process is likely to cause deformation or damage to the mesh.

[0038] In addition, it is preferable to use propane gas or acetylene gas as the hydrocarbon gas used in the plasma chemical vapor deposition (CVD) process when coating glassy carbon, as these gases are prone to carbon dissociation due to the action of plasma and therefore prone to the production of glassy carbon.

[0039] The pressure of the process gas using hydrocarbon gas is preferably 80 Pa to 1000 Pa, at which point glassy carbon is easily deposited.

[0040] The processing temperature during plasma vapor deposition (CVD) processing is preferably 600°C or higher to ensure strong adhesion of the glassy carbon, and 760°C or lower to prevent deterioration of the strength of the spot welds and to prevent thermal deformation of the ultra-fine titanium mesh.

[0041] Immediately after this blasting process, plasma vapor deposition (CVD) processing is carried out, but beforehand, the titanium metal surface must be made non-oxidized by sufficiently removing the titanium oxide film through chemical polishing or electrolytic polishing, etc. If physical polishing using an abrasive or grinding stone is used, it is appropriate to perform the polishing process in a non-oxidizing atmosphere such as an inert gas.

[0042] For chemical polishing, it is appropriate to prepare a polishing solution that is corrosive to titanium metal and immerse the workpiece in, for example, a 10 to 30% aqueous solution of fluoronitric acid at room temperature for several seconds to several minutes.For electrolytic polishing, it is desirable to apply a voltage for several seconds in an ethylene glycol-based solution to activate the outermost surface and remove titanium oxide.

[0043] As described above, if the immersion time in the chemical polishing treatment solution is within a few minutes, the fine irregularities on the surface will remain as they are, and only the oxide film on the very outermost surface will be removed.

[0044] By chemically polishing or electrolytically polishing the surface in this manner, the titanium oxide film is thoroughly removed, and the surface of the electrode substrate made of unoxidized titanium metal with a surface roughness Ra of 0.1 to 1.0 μm is coated with a conductive and corrosion-resistant film made of a glassy carbon layer.

[0045] As described in Patent Document 1, the glassy carbon layer can be formed by using a known technique, for example, by plasma carburization treatment using a hydrocarbon gas at a pressure of 100 to 2666 Pa and an atmospheric gas temperature range of 500 to 700°C.

[0046] However, when the glassy carbon layer is coated, the surface of the titanium metal electrode substrate is in a non-oxidized state. As described above, the electrode substrate is preferably chemically polished or electrolytically polished, and is stored in an atmosphere of an oxygen-free hydrocarbon gas and an inert gas, and a conductive and corrosion-resistant coating made of a glassy carbon layer is formed in that state by a plasma vapor deposition (CVD) method. [Example]

[0047] [Examples 1-3] As shown in Figure 2-3, a plain-woven rectangular mesh (wire diameter 0.1 mm, mesh size 0.154 mm, width approximately 15 mm, length approximately 20 mm) was fabricated using titanium fine wires with a diameter of 0.2 mm or less.

[0048] The longitudinal ends of this mesh were bent as shown by the chain lines in Figure 4 and wrapped around the outer surface of the tip of a titanium round bar (length: 6 cm) 4 with a diameter of 0.8 mm, making approximately one full turn, as shown in Figure 5. The mesh was then spot-welded locally at multiple locations indicated by the dashed lines in Figure 5, to produce an electrode substrate 3 made of titanium mesh.

[0049] The electrode substrate was subjected to blasting treatment using alumina fine powder media, and the surface roughness was adjusted to Ra 0.1 μm (Example 1), 0.3 μm (Example 2), and 1.0 μm (Example 3), as shown in Table 1.

[0050] The electrode substrates used in Examples 1-3 were then chemically polished by immersing them in a 10% aqueous solution of nitric acid and hydrofluoric acid at room temperature for several seconds to remove the titanium oxide coating from the surface and to clean and remove impurities. Immediately thereafter, the electrode substrates were placed in a processing tank containing 100% propane gas and subjected to plasma vapor deposition (CVD) at a gas pressure of 200 Pa and a processing temperature of 700°C to coat the surface with a glassy carbon (GLC) layer 0.1-2 μm thick, producing corrosion-resistant titanium metal electrodes.

[0051] [Comparative Example 1] A corrosion-resistant platinum electrode was obtained by coating with a glassy carbon layer in the same manner as in Example 2, except that a platinum mesh electrode (commercially available) was used instead of the titanium metal electrode substrate in Example 2, and the surface roughness Ra was set to 0.08 μm.

[0052] Comparative Example 2 A corrosion-resistant titanium electrode was obtained by carrying out plasma vapor deposition (CVD) treatment in exactly the same manner as in Example 2, except that chemical polishing of the electrode substrate was not carried out.

[0053] The obtained titanium metal corrosion-resistant electrodes were subjected to a bending deformation test in which the end was bent twice consecutively along the cylindrical surface to a predetermined angle θ (0 to 90°) as shown in Figure 4, and the presence or absence of "cracks" and "peeling" of the GLC layer was visually inspected. The results are shown in Table 1. The evaluation in the table is shown on a three-point scale: ○ for no cracks or peeling, △ for cracks, and × for both cracks and peeling.

[0054] [Table 1]

[0055] As is clear from the results shown in Table 1, cracks and peeling occurred in the bending deformation test in Comparative Example 1, in which the platinum mesh was coated with GLC. In Comparative Example 2, cracks occurred in the bending deformation test because the titanium oxide coating of the titanium metal mesh was coated with GLC.

[0056] On the other hand, it was found that the corrosion-resistant titanium metal electrode mesh of Example 1-3 had a glassy carbon layer with sufficient adhesion to the corners where the curved surfaces intersect, and was provided with a glassy carbon layer with such strong adhesion that it could withstand bending deformation without cracking or peeling.

[0057] It was also found that such titanium corrosion-resistant electrodes can be efficiently manufactured with stable quality by depositing glassy carbon onto the surface of a non-oxidized titanium metal electrode substrate using a plasma vapor deposition (CVD) method, after the process of removing the titanium oxide coating.

[0058] [Example 4] A titanium metal plate with a thickness of 2 mm was used as the electrode substrate, and was subjected to blasting treatment using alumina fine powder media to adjust the surface roughness to Ra 0.3 μm.

[0059] Thereafter, in the same manner as in Examples 1-3, the electrode was subjected to chemical polishing by immersion in a 10% aqueous solution of nitric acid and fluorocarbons at room temperature for several seconds, and immediately thereafter, plasma vapor deposition (CVD) treatment was carried out using propane gas at a gas pressure of 200 Pa and a treatment temperature of 700°C, yielding a titanium metal corrosion-resistant electrode of Example 4 coated with a glassy carbon (GLC) layer having a thickness of 1.0 μm.

[0060] Comparative Example 3 The same titanium metal flat plate electrode substrate as in Example 4, 2 mm thick, was used. The surface was ground with a grindstone or the like and then buffed to form a mirror finish (Ra 0.1 μm or less). A titanium oxide coating was then formed on this mirror finish, and then plasma vapor deposition (CVD) treatment was carried out in the same manner as in Example 4 at a gas pressure of 200 Pa and a treatment temperature of 700°C to form a 1.0 μm thick glassy carbon (GLC) layer, thereby obtaining a titanium metal corrosion-resistant electrode for Comparative Example 3.

[0061] The obtained titanium metal corrosion-resistant electrodes of Example 4 and Comparative Example 3 were subjected to an "adhesion test (ISO26443)" of the coating using the Rockwell hardness C scale. The adhesion test was evaluated by pressing a diamond indenter into the surface of the glassy carbon layer with a load of 981 N, observing under a microscope whether or not the coating around the indentation had peeled off, and classifying the state of damage according to the test criteria. The results, which were evaluated into predetermined ranks, are shown in the "Rockwell hardness C scale" column in Table 2, and micrographs of each example are shown in Figure 6 (Example 4) and Figure 7 (Comparative Example 3).

[0062] Incidentally, the ISO26443 evaluation criteria for each rank are: Class 0 (no cracks in the coating, no delamination), Class 1 (cracks in the coating, no delamination), Class 2 (partial delamination regardless of whether cracks in the coating exist), and Class 3 (complete delamination).

[0063] [Table 2]

[0064] As is clear from the results shown in Table 2 and FIG. 7, the flat titanium corrosion-resistant electrode of Comparative Example 3 was found to have partial delamination in the glassy carbon coating around the indentation when evaluated in the adhesion test.

[0065] On the other hand, as is clear from the results shown in Table 2 and FIG. 6, the flat titanium corrosion-resistant electrode of Example 4 was evaluated in the coating adhesion test and showed no damage such as cracks in the glassy carbon coating around the indentation, demonstrating excellent coating adhesion. [Industrial Applicability]

[0066] The corrosion-resistant titanium metal electrode of the present invention can be used as a current collector for storage batteries, an insoluble electrode widely used in electrochemical reaction devices such as electrolysis of electrolytes such as salt water, and the like. [Explanation of symbols]

[0067] 1, 3 Electrode base material 2. Glassy carbon layer 3a, 3b Titanium metal thin wire 4 round bars

Claims

1. A corrosion-resistant titanium metal electrode, which has a surface roughness Ra of 0.1 to 1.0 μm and is made of non-oxidized titanium metal, and has a conductive and corrosion-resistant coating made of a glassy carbon layer formed on the surface of the electrode base material.

2. 2. The corrosion-resistant electrode made of titanium metal according to claim 1, wherein said surface is a chemically polished or electrolytically polished surface free of a titanium oxide coating.

3. 3. The corrosion-resistant electrode made of titanium metal according to claim 1, wherein said glassy carbon layer has a thickness of 0.1 to 2 μm.

4. 3. The corrosion-resistant electrode made of titanium metal according to claim 1, wherein the electrode substrate is a mesh electrode substrate.

5. 4. The corrosion-resistant electrode made of titanium metal according to claim 3, wherein said electrode substrate is a mesh-type electrode substrate.

6. 5. The corrosion-resistant electrode made of titanium metal according to claim 4, wherein the mesh electrode substrate is a mesh electrode substrate woven with fine wires having a wire diameter of 0.2 mm or less.

7. 6. The corrosion-resistant electrode made of titanium metal according to claim 5, wherein the mesh electrode substrate is a mesh electrode substrate woven with fine wires having a wire diameter of 0.2 mm or less.

8. a step of processing the surface of the titanium metal electrode substrate by blasting to a surface roughness Ra of 0.1 to 1.0 μm; Thereafter, chemically or electrolytically polishing the surface to remove the titanium oxide coating; a step of forming a conductive and corrosion-resistant coating made of a glassy carbon layer on the surface of the electrode substrate made of non-oxidized titanium metal through the above steps by plasma chemical vapor deposition (CVD); A method for manufacturing corrosion-resistant electrodes made of titanium metal, which requires the following steps:

9. 9. The method for producing a corrosion-resistant titanium electrode according to claim 8, wherein the titanium electrode substrate is a mesh-shaped titanium electrode substrate.

Images