JP7803233B2 - Hydrogen gas barrier film and hydrogen gas barrier structure - Google Patents

Description

The present invention relates to a hydrogen gas barrier film and a hydrogen gas barrier structure equipped with the same.

Many inorganic thin films, primarily made of SiON, have been proposed as gas barrier films, but they are ineffective against hydrogen. One known hydrogen gas barrier film is described in Patent Document 1. The hydrogen barrier film described in Patent Document 1 is a multilayer film in which first and second layers are alternately stacked. If the number of first layers is n and the number of second layers is m, the total number of first and second layers, i.e., n + m, is 10 to 1,000. This hydrogen barrier film has an overall thickness of 0.5 μm to 2 μm. The thicknesses of the first and second layers are each 5 nm to 10 nm. The first layer is made of an alloy nitrogen compound selected from TiSiNbN, TiMoN, TiAlN, and AlCrN, and the second layer is made of an alloy nitrogen compound selected from TiSiNbN, TiMoN, TiAlN, and AlCrN that is different from the first layer.

Japanese Patent Application Laid-Open No. 2021-139009

As mentioned above, simply using an amorphous film, like conventional gas barrier films, is not enough to function as a hydrogen gas barrier film. Furthermore, the range of application is limited, making it difficult to apply to complex shapes such as piping. Meanwhile, the hydrogen barrier function film described in Patent Document 1 is thick and expensive. Furthermore, nitride films tend to have high stress, and a thick film increases this stress even more. High stress can lead to cracking and peeling. Furthermore, cracks can occur at grain boundaries in crystalline films, which can act as pathways for hydrogen permeation and potentially reduce barrier performance. Meanwhile, a large crystal size is required to create a single-crystal film, which is practically impossible.

The present invention has been made in consideration of the circumstances exemplified above. That is, the present invention provides, for example, a hydrogen gas barrier film having better hydrogen gas barrier properties than conventional films, and a hydrogen gas barrier structure including the same.

The hydrogen gas barrier film according to the first aspect of the present invention is made of AlTiON, contains 32 to 42 at % of N, and is formed to a thickness of 200 nm or less.
The hydrogen gas barrier structure (1) according to claim 2 comprises:
A substrate (2),
a hydrogen gas barrier film (3) formed on the surface (21) of the substrate;
Equipped with
The hydrogen gas barrier film is made of AlTiON, contains 32 to 42 at % of N, and is formed to a thickness of 200 nm or less.

Note that in each section of the application documents, each element may be assigned a reference symbol in parentheses. In such cases, the reference symbol merely indicates an example of the correspondence between the element and the specific configuration described in the embodiment below. Therefore, the present invention is not limited in any way by the reference symbol.

1 is a cross-sectional view showing a schematic configuration of a hydrogen gas barrier structure according to one embodiment of the present invention. 2 is a table comparing the hydrogen gas barrier properties of the hydrogen gas barrier film shown in FIG. 1 with those of comparative examples. 2 is a graph showing the relationship between the nitrogen content and the hydrogen gas barrier properties in the hydrogen gas barrier film shown in FIG. 1 .

(Embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that various modifications applicable to one embodiment may be hindered from being understood if they are introduced in the middle of a series of explanations relating to the embodiment. Therefore, the modifications will not be introduced in the middle of a series of explanations relating to the embodiment, but will be explained together after the series of explanations.

(composition)
1 , the hydrogen gas barrier structure 1 according to this embodiment includes a substrate 2 and a hydrogen gas barrier film 3. The hydrogen gas barrier film 3 is formed on a surface 21 of the substrate 2. In other words, the hydrogen gas barrier structure 1 has a structure similar to a bonded body of the substrate 2 and the hydrogen gas barrier film 3.

The substrate 2 is formed of an iron-based material, for example, a chromium-containing steel material _, i.e., stainless steel. Specifically, the substrate 2 may be formed of an austenitic stainless steel such as SUS316L. The surface 21 of the substrate 2 is formed as an interface containing _Fe3O4 .

The hydrogen gas barrier film 3 is made of AlTiON and contains 30 at% or more of N. Specifically, the nitrogen content is, for example, 30 to 50 at%. If the nitrogen content is higher than 50 at%, the oxygen content becomes extremely low, resulting in a nitride film. Preferably, the hydrogen gas barrier film 3 contains 32 to 42% N. The hydrogen gas barrier film 3 may also contain 0.4 at% or more of Cl as an impurity. The hydrogen gas barrier film 3 is formed to a thickness of 200 nm or less (i.e., as a thin film). In this embodiment, the hydrogen gas barrier film 3 is provided as a single layer on the surface 21 of the substrate 2. The hydrogen gas barrier film 3 is formed so that AlO is the main component at the outermost surface 31 and the substrate interface 32. The outermost surface 31 is the surface of the hydrogen gas barrier film 3 opposite the substrate interface 32, which is the bonding interface with the substrate 2. The hydrogen gas barrier film 3 can be formed by a vapor phase deposition method (e.g., ALD). ALD is an abbreviation for atomic layer deposition.

(Manufacturing method)
The method for manufacturing the hydrogen gas barrier structure 1 and the hydrogen gas barrier film 3 according to this embodiment will be outlined below using a specific example in which a substrate 2 made of austenitic stainless steel such as SUS316L is used.

First, a substrate 2 made of austenitic stainless steel is prepared. The prepared substrate 2 is degreased with an organic solvent such as acetone, and then the surface 21 of the substrate 2 is treated with an alkaline chemical solution. This alkaline chemical treatment improves adhesion between the surface 21 of the substrate 2 and the hydrogen gas barrier film 3. A solution of a quaternary ammonium hydroxide is preferably used as the alkaline chemical solution. Specific examples of usable quaternary ammonium hydroxides include tetramethylammonium hydroxide (i.e., TMAH), tetraethylammonium hydroxide (i.e., TEAH), and tetrapropylammonium hydroxide, with TMAH being particularly preferred. One or more types of quaternary ammonium hydroxide may be used. The hydrogen gas barrier film 3 is formed on the surface 21 of the substrate 2 by vapor deposition (e.g., ALD), thereby obtaining the hydrogen gas barrier structure 1 shown in FIG. 1 . The oxygen content and nitrogen content can be controlled by pulses of H ₂ O or NH ₃ .

(effect)
Hereinafter, the hydrogen gas barrier performance exhibited by the hydrogen gas barrier structure 1 according to this embodiment, that is, the hydrogen gas barrier film 3, will be described using examples and comparative examples.

As mentioned above, the hydrogen barrier film made of nitride, as described in Patent Document 1, is thick (specifically, 0.5 μm to 2 μm). This results in high costs and high stress. High stress makes it more susceptible to cracks and peeling, reducing barrier performance. In particular, because it is a crystalline film, cracks are more likely to occur starting from grain boundaries.

In this regard, while AlTiO, an oxide film, has excellent barrier performance, when it is thinned (for example, to a thickness of 200 nm or less), sufficient barrier performance cannot be achieved. Therefore, after extensive research, the inventors discovered that by doping the AlTiO film with nitrogen, it is possible to achieve both a thin film and sufficient barrier performance. According to the inventors' investigations, nitrogen doping densifies the film, presumably making it more difficult for hydrogen to permeate. Furthermore, because of its amorphous structure, cracking is effectively suppressed and adhesion to the substrate 2 is improved.

Figure 2 shows the hydrogen gas barrier properties of the hydrogen gas barrier film 3 in the examples, compared with those of the comparative examples. The hydrogen gas barrier film 3 in Example 1 is an AlTiON thin film with a thickness of 175 nm, and has a nitrogen content of 42 at%, an aluminum content of 28 at%, a titanium content of 19 at%, and an oxygen content of 8 at%. Example 2 is an example of an AlTiON film with the same nitrogen content as Example 1, but with a thickness of 85 nm. Examples 3 and 4 are examples of an AlTiON film with the same thickness as Example 1, but with a different nitrogen content. Comparative Example 1 is an example of an AlTiO thin film with approximately the same thickness as Example 1, but with a nitrogen content of 0. Comparative Example 2 is an example of an AlO thin film with a thickness of 160 nm, approximately the same thickness as Comparative Example 1. Comparative Example 3 is an example of a TiO thin film with the same thickness as Comparative Example 2, 160 nm. Figure 3 is a graph plotting the relationship between nitrogen content and hydrogen permeability coefficient for Examples 1, 3, and 4, and Comparative Example 1, which have approximately the same film thickness.

As shown in Figure 2, very good hydrogen gas barrier performance was obtained in Example 1, where the nitrogen content was 42 at%. Furthermore, even when the nitrogen content was varied within the ranges of 40-44 at%, the aluminum content was varied within the ranges of 25-30 at%, the titanium content was varied within the ranges of 16-23 at%, and the oxygen content was varied within the ranges of 6-10 at%, similar hydrogen gas barrier performance was obtained. Furthermore, very good hydrogen gas barrier performance was also obtained in Example 2, where the thickness of the hydrogen gas barrier film 3 was reduced to a very thin 85 nm.

Note that Comparative Example 1, which is an AlTiO thin film, has higher hydrogen gas barrier performance than Comparative Example 2, which is an AlO thin film, and Comparative Example 3, which is a TiO thin film. However, the Examples, which are nitrogen-doped AlTiON thin films, have higher hydrogen gas barrier performance than Comparative Example 1, which is an oxide film not doped with nitrogen, i.e., an AlTiO thin film. In particular, very good hydrogen gas barrier performance was obtained in Examples 1 to 3, which had nitrogen contents of 32 to 42 at%. Referring to the graph in Figure 3, there is a large difference in hydrogen permeability coefficient between the example with a nitrogen content of 21% (i.e., Example 4) and the example with a nitrogen content of 32% (i.e., Example 3). From this graph, it can be estimated with high certainty that the hydrogen permeability coefficient decreases to the ^10-16 range by increasing the nitrogen content to at least 30% or more.

As such, the hydrogen gas barrier film 3, which is an AlTiON thin film according to this embodiment, can exhibit very good hydrogen gas barrier performance even when formed as a thin single layer. Therefore, this embodiment can simultaneously achieve excellent effects such as low cost, low stress, crack suppression, and improved adhesion.

(Modification)
The present invention is not limited to the above-described embodiment. Therefore, the above-described embodiment can be modified as appropriate. Representative modifications will be described below. In the following description of the modifications, differences from the above-described embodiment will be mainly described. Furthermore, the same reference numerals are used for parts that are identical or equivalent to each other in the above-described embodiment and the modifications. Therefore, in the following description of the modifications, the description of the above-described embodiment can be used as appropriate for components that have the same reference numerals as the above-described embodiment, unless there is a technical contradiction or special additional explanation.

The substrate 2 is not limited to austenitic stainless steel such as SUS316L. Furthermore, the method for forming the hydrogen gas barrier film 3 is not limited to ALD; general physical vapor deposition or chemical vapor deposition can also be used. There is also no particular limit to the number of layers in the hydrogen gas barrier film 3; for example, it may have a two-layer or three-layer structure.

It goes without saying that the elements constituting the above embodiments are not necessarily essential, except when expressly stated as essential or when they are clearly considered essential in principle. Furthermore, when numerical values such as the number, amount, range, etc. of components are mentioned, the present invention is not limited to those specific numerical values, except when expressly stated as essential or when they are clearly limited to specific numerical values in principle. Similarly, when the shape, direction, positional relationship, etc. of components are mentioned, the present invention is not limited to those shapes, directions, positional relationships, etc., except when expressly stated as essential or when they are clearly limited to specific shapes, directions, positional relationships, etc., in principle.

The modified examples are not limited to the examples above. That is, for example, in addition to the examples above, multiple embodiments may be combined with each other as long as there is no technical contradiction. Similarly, multiple modified examples may be combined with each other as long as there is no technical contradiction.

REFERENCE SIGNS LIST 1 Hydrogen gas barrier structure 2 Substrate 21 Surface 3 Hydrogen gas barrier film 31 Outermost surface 32 Substrate interface

Claims (4)

A hydrogen gas barrier film (3),
Made of AlTiON and containing 32 to 42 at% N,
Formed with a film thickness of 200 nm or less,
Hydrogen gas barrier film. A hydrogen gas barrier structure (1),
A substrate (2),
a hydrogen gas barrier film (3) formed on the surface (21) of the substrate;
Equipped with
The hydrogen gas barrier film is made of AlTiON, contains 32 to 42 at % N, and is formed to a film thickness of 200 nm or less.
Hydrogen gas barrier structure. The hydrogen gas barrier film is formed on the surface in a single layer or two layers.
The hydrogen gas barrier structure according to claim 2 . The substrate is made of an iron-based material.
The hydrogen gas barrier structure according to claim 2 or 3 .