Cover gas composition, cover gas mixture, method for suppressing oxidation or combustion of molten metal, cover gas supply device, and method for supplying cover gas composition

Abstract

Provided is a cover gas composition for suppressing oxidation or combustion of molten metal: the cover gas composition comprising a halogenated olefin having 2 carbon atoms and carbon dioxide, wherein the content of the carbon dioxide is 76.4 mass% or more with respect to the total amount of the halogenated olefin having 2 carbon atoms and the carbon dioxide; the cover gas composition comprising a halogenated olefin having 2 carbon atoms and nitrogen, wherein the content of the nitrogen is 77.6 mass% or more with respect to the total amount of the halogenated olefin having 2 carbon atoms and the nitrogen; or the cover gas composition comprising a halogenated olefin having 2 carbon atoms and argon, wherein the content of the argon is 89.9 mass% or more with respect to the total amount of the halogenated olefin having 2 carbon atoms and the argon. Also provided are a cover gas mixture using said cover gas composition, a method for suppressing oxidation or combustion of molten metal, a cover gas supply device, and a method for supplying the cover gas composition.

Description

Cover gas composition, cover gas mixture, method for inhibiting oxidation or combustion of molten metal, cover gas supply device, and method for supplying cover gas composition

[0001] The present disclosure relates to cover gas compositions, cover gas mixtures, methods for inhibiting oxidation or combustion of molten metal, cover gas delivery devices, and methods for delivering cover gas compositions.

[0002] Conventionally, sulfur dioxide (SO ) has been used as a cover gas (protective gas) in the manufacturing process of metals such as magnesium and magnesium alloys. ２ Although sulfur dioxide is inexpensive, its use is limited due to its odor and relatively high toxicity. Instead, sulfur hexafluoride (SF) is used because it is relatively non-toxic, easy to use, and safe. ６ ) has been widely used.

[0003] For example, the protective mechanism for molten magnesium or molten magnesium alloy when sulfur hexafluoride is used as a cover gas is not clear, but it is believed to proceed through the following reaction: In this case, magnesium oxide (MgO) is first formed as a protective film, which then reacts with sulfur hexafluoride to form magnesium fluoride (MgF ２ ) Here, fluorine atoms play an important role in protecting the molten magnesium or molten magnesium alloy, and a larger fluorine content in the cover gas molecules is thought to be advantageous for forming a protective film, and sulfur hexafluoride has been widely used.

[0004] 2Mg (liquid) + O ２ →2MgO (solid) (1) 2Mg (liquid) + O ２ +SF ６ →2MgF ２ (Solid) + SO ２ F ２ (2) 2MgO (solid) + SF ６ →2MgF ２ +SO ２ F ２ (3)

[0005] However, sulfur hexafluoride has a global warming potential (GWP) lower than that of carbon dioxide (CO２ ), and its atmospheric lifetime is extremely long at 3,200 years, so its emissions are regulated by the Kyoto Protocol. As a cover gas to replace sulfur hexafluoride, various fluorine-containing compounds have been proposed based on the above-mentioned fluorine content. For example, Patent Document 1 describes a composition containing a fluorinated olefin. Patent Document 2 describes a cover gas composition containing a cover gas component including a hydrochlorofluoroolefin.

[0006] JP 2009-255136 A JP 2020-075260 A

[0007] Fluorinated olefins have low GWP and low toxicity to humans and animals, making them promising compounds to replace sulfur hexafluoride. However, fluorinated olefins such as (E)-1,3,3,3-tetrafluoropropene and 1,1-difluoroethylene have the problem of being flammable. Furthermore, (E)-1,3,3,3-tetrafluoropropene, for example, has a relatively high boiling point and is easily liquefied, which poses a problem in terms of handling.

[0008] The present disclosure relates to a cover gas composition for suppressing oxidation or combustion of molten metal, which has a low GWP and a low boiling point, making it easy to handle and reducing flammability; and to a cover gas mixture using the same, a method for suppressing oxidation or combustion of molten metal, a cover gas supply device, and a method for supplying the cover gas composition.

[0009] Means for solving the above problems include the following aspects. <1> A cover gas composition for suppressing oxidation or combustion of molten metal, comprising: a halogenated olefin having two carbon atoms and carbon dioxide, wherein the content of the carbon dioxide relative to the total amount of the halogenated olefin having two carbon atoms and the carbon dioxide is 76.4% by mass or more; a halogenated olefin having two carbon atoms and nitrogen, wherein the content of the nitrogen relative to the total amount of the halogenated olefin having two carbon atoms and the nitrogen is 77.6% by mass or more; or a halogenated olefin having two carbon atoms and argon, wherein the content of the argon relative to the total amount of the halogenated olefin having two carbon atoms and the argon is 89.9% by mass or more. <2> The cover gas composition according to <1>, comprising a halogenated olefin having two carbon atoms and carbon dioxide, wherein the content of the carbon dioxide relative to the total amount of the halogenated olefin having two carbon atoms and the carbon dioxide is 79.5% by mass or more; or a halogenated olefin having two carbon atoms and nitrogen, wherein the content of the nitrogen relative to the total amount of the halogenated olefin having two carbon atoms and the nitrogen is 81.5% by mass or more. <3> The cover gas composition according to <1>, comprising a halogenated olefin having two carbon atoms and argon, wherein the content of the argon relative to the total amount of the halogenated olefin having two carbon atoms and the argon is 90.3 mass% or more. <4> The cover gas composition according to any one of <1> to <3>, wherein the halogenated olefin having two carbon atoms comprises at least one selected from the group consisting of 1,1-difluoroethylene, (E)-1,2-difluoroethylene, (Z)-1,2-difluoroethylene, and trifluoroethylene. <5> The cover gas composition according to any one of <1> to <4>, wherein the halogenated olefin having two carbon atoms is 1,1-difluoroethylene.<6> The cover gas composition according to any one of <1> to <5>, wherein the total content of the C2 halogenated olefin and carbon dioxide relative to the total amount of the cover gas composition is 99.0% by volume or more, the total content of the C2 halogenated olefin and nitrogen relative to the total amount of the cover gas composition is 99.0% by volume or more, or the total content of the C2 halogenated olefin and argon relative to the total amount of the cover gas composition is 99.0% by volume or more. <7> The cover gas composition according to any one of <1> to <6>, wherein the metal is any one selected from the group consisting of magnesium, aluminum, lithium, and alloys thereof. <8> A cover gas mixture comprising the cover gas composition according to any one of <1> to <7> and oxygen. <9> The cover gas mixture according to <8>, wherein the amount of oxygen is 2.5 times or more by volume relative to the amount of the C2 halogenated olefin. <10> The cover gas mixture according to <8>, comprising the cover gas composition and air. <11> The cover gas mixture according to <10>, wherein the amount of air is 12.0 times or more by volume relative to the amount of the halogenated olefin having two carbon atoms. <12> A method for suppressing oxidation or combustion of molten metal, comprising supplying the cover gas composition according to any one of <1> to <7> or the cover gas mixture according to any one of <8> to <11> to the surface of molten metal. <13> A method for suppressing oxidation or combustion of molten metal, comprising supplying the cover gas mixture according to any one of <8> to <11> to the surface of molten metal. <14> A cover gas supply device comprising: a halogenated olefin having two carbon atoms; a container for storing the halogenated olefin having two carbon atoms; a flow meter for adjusting the flow rate of the halogenated olefin having two carbon atoms; carbon dioxide, nitrogen, or argon; a container for storing the carbon dioxide, nitrogen, or argon; and a flow meter for adjusting the flow rate of the carbon dioxide, nitrogen, or argon. <15> A cover gas supply device comprising: the cover gas composition according to any one of <1> to <7>; a container for storing the cover gas composition; and a flow meter for adjusting a flow rate of the cover gas composition.<16> A method for supplying the cover gas composition from the container in the cover gas supply apparatus according to <15> to a metal melting furnace, wherein the cover gas composition in the container is maintained in a single-phase state from the start of supply to the end of supply. <17> The method according to <16>, wherein the single-phase state is a supercritical state. <18> The method according to <16> or <17>, wherein the cover gas composition in the container is heated, pressurized, or cooled from the start of supply to the end of supply. <19> A method for supplying a cover gas composition according to any one of <1> to <7> and air to the surface of molten metal, wherein the amount of air supplied is 12.0 times or more by volume relative to the amount of the halogenated olefin having two carbon atoms supplied. <20> A method for supplying a cover gas composition according to any one of <1> to <7> and oxygen to a surface of a molten metal, wherein the amount of oxygen supplied is 2.5 times or more by volume relative to the amount of the halogenated olefin having two carbon atoms supplied.

[0010] According to the present disclosure, there are provided a cover gas composition for suppressing oxidation or combustion of molten metal, which has a low GWP and a low boiling point, making it easy to handle, and has suppressed flammability; as well as a method for suppressing oxidation or combustion of molten metal using the same, a cover gas supply device, and a method for supplying the cover gas composition.

[0011] FIG. 1 is a schematic diagram of a cover gas supply device according to one embodiment. FIG. 2 is a schematic diagram of a cover gas supply device according to one embodiment. FIG. 3 is a schematic diagram of a cover gas supply device according to one embodiment. FIG. 4 is a schematic diagram of a cover gas supply device according to one embodiment. In the examples, the results of the comparison of HFO-1132a and CO when the test temperature was 20°C ± 5°C are shown. ２ CO relative to the total amount ２ The horizontal axis represents the content of HFO-1132a and CO ２ , and HFO-1132a and CO relative to the total amount of air ２ In the examples, the total content of HFO-1132a and CO was plotted on the vertical axis. ２CO relative to the total amount ２ The horizontal axis represents the content of HFO-1132a and CO ２ , and HFO-1132a and CO relative to the total amount of air ２ In the examples, the total content of HFO-1132a and N was plotted on the vertical axis. ２ N relative to the total amount of ２ The horizontal axis represents the content of HFO-1132a, N ２ , and HFO-1132a and N relative to the total amount of air ２ In the examples, the total content of HFO-1132a and N was plotted on the vertical axis. ２ N relative to the total amount of ２ The horizontal axis represents the content of HFO-1132a, N ２ , and HFO-1132a and N relative to the total amount of air ２ This is a graph plotting the total content of HFO-1132a and Ar relative to the total amount of HFO-1132a, Ar, and air on the vertical axis when the test temperature in the examples was 20°C ± 5°C, with the content of Ar relative to the total amount of HFO-1132a and Ar on the horizontal axis and the total content of HFO-1132a and Ar relative to the total amount of HFO-1132a, Ar, and air on the vertical axis. This is a graph plotting the total content of Ar relative to the total amount of HFO-1132a and Ar relative to the total amount of HFO-1132a, Ar, and air on the horizontal axis when the test temperature in the examples was 60°C ± 5°C.

[0012] Hereinafter, modes for carrying out embodiments of the present disclosure will be described in detail. However, the embodiments of the present disclosure are not limited to the following embodiments. In the following embodiments, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and they do not limit the embodiments of the present disclosure.

[0013] In the present disclosure, the term "process" includes not only processes that are independent of other processes, but also processes that cannot be clearly distinguished from other processes as long as the purpose of the process is achieved. In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another staged numerical range. Furthermore, in numerical ranges described in the present disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, each component may contain multiple corresponding substances. When multiple substances corresponding to each component are present in a composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, even when an element is described in the singular, this does not exclude the presence of multiple substances unless technical contradiction arises, unless otherwise specified. In the present disclosure, the ratio of each component in the cover gas composition represents the ratio of each component when the cover gas composition is in a gaseous state. When embodiments are described with reference to the drawings in the present disclosure, the configuration of the embodiment is not limited to the configuration shown in the drawings. In addition, the size of each component in each drawing is conceptual, and the relative size relationship between the components is not limited thereto.

[0014] In this disclosure, fluoroolefin refers to an unsaturated hydrocarbon compound having a carbon-carbon double bond that contains fluorine atoms as halogen atoms but no chlorine atoms in the molecule. Fluoroolefins may or may not contain hydrogen atoms in the molecule. In this disclosure, chloroolefins refer to unsaturated hydrocarbon compounds having a carbon-carbon double bond that contains chlorine atoms as halogen atoms but no fluorine atoms in the molecule. Chloroolefins may or may not contain hydrogen atoms in the molecule. In this disclosure, chlorofluoroolefins refer to unsaturated hydrocarbon compounds having a carbon-carbon double bond that contain fluorine atoms and chlorine atoms as halogen atoms in the molecule. Chlorofluoroolefins may or may not contain hydrogen atoms in the molecule. In this disclosure, fluorocarbons refer to saturated hydrocarbon compounds that contain fluorine atoms as halogen atoms but no chlorine atoms in the molecule. Fluorocarbons may or may not contain hydrogen atoms in the molecule. In this disclosure, chlorofluorocarbons refer to saturated hydrocarbon compounds that contain fluorine atoms and chlorine atoms as halogen atoms in the molecule. Chlorofluorocarbons may or may not contain hydrogen atoms in the molecule. In this disclosure, chlorofluoroalkyne refers to an acetylenic hydrocarbon compound containing fluorine and chlorine atoms as halogen atoms in the molecule. Chlorofluoroalkyne may or may not contain hydrogen atoms in the molecule. In this disclosure, hydrofluoroolefin refers to an unsaturated hydrocarbon compound having a carbon-carbon double bond that contains fluorine atoms as halogen atoms but no chlorine atoms in the molecule, and that contains hydrogen atoms. In this disclosure, hydrochlorofluoroolefin refers to an unsaturated hydrocarbon compound having a carbon-carbon double bond that contains fluorine and chlorine atoms as halogen atoms and that contains hydrogen atoms in the molecule. In this disclosure, hydrofluorocarbon refers to a saturated hydrocarbon compound that contains fluorine atoms as halogen atoms but no chlorine atoms, and that contains hydrogen atoms in the molecule. In this disclosure, hydrofluoroether refers to an ether compound that contains fluorine atoms as halogen atoms but no chlorine atoms, and that contains hydrogen atoms in the molecule.

[0015] <Cover Gas Composition> The cover gas composition of the present disclosure is a cover gas composition for suppressing oxidation or combustion of molten metal, comprising a halogenated olefin having two carbon atoms and carbon dioxide, wherein the carbon dioxide content relative to the total amount of the halogenated olefin having two carbon atoms and the carbon dioxide is 76.4% by mass or more; a halogenated olefin having two carbon atoms and nitrogen, wherein the nitrogen content relative to the total amount of the halogenated olefin having two carbon atoms and the nitrogen is 77.6% by mass or more; or a halogenated olefin having two carbon atoms and argon, wherein the argon content relative to the total amount of the halogenated olefin having two carbon atoms and the argon is 89.9% by mass or more. Hereinafter, the halogenated olefin having two carbon atoms is also referred to as "specific olefin." The cover gas composition of the present disclosure has a low GWP and a low boiling point, making it easy to handle and suppressing flammability. For example, the cover gas composition of the present disclosure is resistant to combustion at 20°C, even when leaked into air, regardless of the amount of air.

[0016] In one embodiment, the cover gas composition contains a specific olefin and carbon dioxide, and the content of the carbon dioxide relative to the total amount of the specific olefin and the carbon dioxide is 79.5 mass% or more, or contains a specific olefin and nitrogen, and the content of the nitrogen relative to the total amount of the specific olefin and the nitrogen is 81.5 mass% or more. The cover gas composition of this embodiment is difficult to combust even when leaked into air in a higher temperature environment, for example, at 60°C, regardless of the amount of air.

[0017] In one embodiment, the cover gas composition contains a specific olefin and argon, and the argon content is 90.3 mass% or more relative to the total amount of the specific olefin and the argon. The cover gas composition of this embodiment is difficult to combust even when leaked into air, for example, at 60°C, regardless of the amount of air.

[0018] Patent Document 1 specifically describes that fluorinated olefins such as 1,1,3,3,3-pentafluoropropene and 1,2,3,3,3-pentafluoropropene are preferably used. However, fluorinated olefins with three carbon atoms have relatively high boiling points, and therefore have issues with handling, such as being prone to liquefaction at low operating temperatures. In contrast, specific olefins have relatively low boiling points, which are advantageous in terms of handling. Meanwhile, although some specific olefins are flammable, in the cover gas composition of the present disclosure, flammability can be suppressed by using carbon dioxide, nitrogen, or argon in combination.

[0019] Hereinafter, an embodiment of a cover gas composition containing a specific olefin and carbon dioxide, wherein the carbon dioxide content relative to the total amount of the specific olefin and carbon dioxide is 76.4% by mass or more, will be referred to as the "first embodiment." Furthermore, an embodiment of a cover gas composition containing a specific olefin and nitrogen, wherein the nitrogen content relative to the total amount of the specific olefin and nitrogen is 77.6% by mass or more, will be referred to as the "second embodiment." Furthermore, an embodiment of a cover gas composition containing a specific olefin and argon, wherein the argon content relative to the total amount of the specific olefin and argon is 89.9% by mass or more, will be referred to as the "third embodiment." The cover gas compositions of the first to third embodiments will be collectively referred to as the "cover gas composition of the present disclosure" or simply as the "cover gas composition." Below, each component contained in the cover gas composition of the present disclosure will be described in detail.

[0020] (Specific Olefin) The cover gas composition contains a specific olefin as a cover gas component. In the present disclosure, the cover gas component refers to a gas component capable of forming a protective film on the surface of molten metal in the presence of oxygen. The specific olefin is not particularly limited as long as it is an olefin having two carbon atoms and containing at least one halogen atom. From the viewpoints of low environmental impact and suppression of flammability, it is preferable that the specific olefin contains a fluorine atom. The number of halogen atoms in the specific olefin is preferably 2 to 4, more preferably 2 or 3. In addition, generally, the fewer the number of hydrogen atoms in an olefin, the lower the flammability tends to be. From this viewpoint, the number of hydrogen atoms in the specific olefin is preferably 2 or less, and may be 1 or less. One specific olefin may be used alone, or two or more specific olefins may be used in combination.

[0021] The GWP of the specific olefin is preferably 500 or less, more preferably 200 or less, even more preferably 150 or less, particularly preferably 100 or less, even more preferably 50 or less, even more preferably 20 or less, even more preferably 15 or less, even more preferably 10 or less, even more preferably 7 or less, even more preferably 5 or less, even more preferably 4 or less, and even more preferably 3 or less. Unless otherwise specified, the GWP is the 100-year value from the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6).

[0022] From the viewpoint of ease of handling, the boiling point of the specific olefin is preferably −25° C. or lower, more preferably −30° C. or lower, even more preferably −35° C. or lower, particularly preferably −40° C. or lower, and extremely preferably −45° C. or lower. The boiling point of the specific olefin may be −100° C. or higher. From this viewpoint, the boiling point of the specific olefin is preferably −100 to −25° C., more preferably −100 to −30° C., even more preferably −100 to −35° C., particularly preferably −100 to −40° C., and extremely preferably −100 to −45° C.

[0023] Examples of the specific olefin include 1,1-difluoroethylene, (E)-1,2-difluoroethylene, (Z)-1,2-difluoroethylene, vinyl fluoride, tetrafluoroethylene, trifluoroethylene, etc. Among these, 1,1-difluoroethylene, (E)-1,2-difluoroethylene, (Z)-1,2-difluoroethylene, and trifluoroethylene are preferred, and from the viewpoint of ease of handling due to their low boiling points, 1,1-difluoroethylene, (E)-1,2-difluoroethylene, and trifluoroethylene are more preferred, and 1,1-difluoroethylene is even more preferred.

[0024] The boiling points and GWPs of specific olefins used in the cover gas compositions of the present disclosure, as well as other compounds used as cover gas components, are listed in the table below, in comparison with those of carbon dioxide. In the table below, "N.D." indicates that the boiling point and GWP are not listed in the IPCC Sixth Assessment Report (AR6), and are presumed to be 10 or less due to the structure of the compound.

[0025]

[0026] In the first embodiment, the content of the specific olefin relative to the total amount of the cover gas composition is preferably 15.05% by volume or less, more preferably 14.5% by volume or less, and even more preferably 14.0% by volume or less, from the viewpoint of suppressing flammability. From the viewpoint of performance as a cover gas, the content is preferably 0.1% by volume or more, more preferably 0.5% by volume or more, and even more preferably 1.0% by volume or more. From such a viewpoint, the content is preferably 0.1 to 15.05% by volume, more preferably 0.5 to 14.5% by volume, and even more preferably 1.0 to 14.0% by volume. Among these, it is preferable that the specific olefin is 1,1-difluoroethylene, and the content of 1,1-difluoroethylene is in the above range.

[0027] In the second embodiment, the content of the specific olefin relative to the total amount of the cover gas composition is preferably 9.0% by volume or less, more preferably 8.5% by volume or less, and even more preferably 8.0% by volume or less, from the viewpoint of suppressing flammability. From the viewpoint of performance as a cover gas, the content is preferably 0.1% by volume or more, more preferably 0.5% by volume or more, and even more preferably 1.0% by volume or more. From such a viewpoint, the content is preferably 0.1 to 9.0% by volume, more preferably 0.5 to 8.5% by volume, and even more preferably 1.0 to 8.0% by volume. Among these, it is preferable that the specific olefin is 1,1-difluoroethylene, and the content of 1,1-difluoroethylene is in the above range.

[0028] In the third embodiment, the content of the specific olefin relative to the total amount of the cover gas composition is preferably 6.2% by volume or less, more preferably 6.0% by volume or less, and even more preferably 5.5% by volume or less, from the viewpoint of suppressing flammability. From the viewpoint of performance as a cover gas, the content is preferably 0.1% by volume or more, more preferably 0.5% by volume or more, and even more preferably 1.0% by volume or more. From such a viewpoint, the content is preferably 0.1 to 6.2% by volume, more preferably 0.5 to 6.0% by volume, and even more preferably 1.0 to 5.5% by volume. Among these, it is preferable that the specific olefin is 1,1-difluoroethylene, and the content of 1,1-difluoroethylene is in the above range.

[0029] (Carbon dioxide) In the first embodiment, the cover gas composition contains carbon dioxide. The carbon dioxide content relative to the total amount of the specific olefin and carbon dioxide is 76.4% by mass or more. From the viewpoint of reducing flammability, it is preferably 79.5% by mass or more, more preferably 80.0% by mass or more, and even more preferably 80.5% by mass or more. From the viewpoint of better exhibiting the function of the specific olefin, the content is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and even more preferably 99.0% by mass or less. From this viewpoint, the content is preferably 76.4 to 99.9% by mass, more preferably 79.5 to 99.9% by mass, even more preferably 80.0 to 99.5% by mass, and particularly preferably 80.5 to 99.0% by mass.

[0030] In the first embodiment, when the specific olefin is 1,1-difluoroethylene, the content of carbon dioxide relative to the total amount of 1,1-difluoroethylene and carbon dioxide is 76.4% by mass or more, and from the viewpoint of reducing flammability, it is preferably 79.5% by mass or more, more preferably 80.0% by mass or more, and even more preferably 80.5% by mass or more. From the viewpoint of better exhibiting the functions of 1,1-difluoroethylene, the content is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and even more preferably 99.0% by mass or less. From such viewpoints, the content is preferably 76.4 to 99.9% by mass, more preferably 79.5 to 99.9% by mass, even more preferably 80.0 to 99.5% by mass, and particularly preferably 80.5 to 99.0% by mass.

[0031] In the first embodiment, the carbon dioxide content of the entire cover gas composition is preferably 76.4% by mass or more, more preferably 79.5% by mass or more, even more preferably 80.0% by mass or more, and particularly preferably 80.5% by mass or more, from the viewpoint of reducing flammability. From the viewpoint of better exerting the function of the specific olefin, the content is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and even more preferably 99.0% by mass or less. From this viewpoint, the content is preferably 76.4 to 99.9% by mass, more preferably 79.5 to 99.9% by mass, even more preferably 80.0 to 99.5% by mass, and particularly preferably 80.5 to 99.0% by mass.

[0032] (Nitrogen) In a second embodiment, the cover gas composition contains nitrogen. The nitrogen content relative to the total amount of the specific olefin and nitrogen is 77.6% by mass or more, and from the viewpoint of further reducing flammability, it is preferably 81.5% by mass or more, more preferably 82.0% by mass or more, and even more preferably 82.5% by mass or more. From the viewpoint of better exhibiting the function of the specific olefin, the content is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and even more preferably 99.0% by mass or less. From this viewpoint, the content is preferably 77.6 to 99.9% by mass, more preferably 81.5 to 99.9% by mass, even more preferably 82.0 to 99.5% by mass, and particularly preferably 82.5 to 99.0% by mass.

[0033] In the second embodiment, when the specific olefin is 1,1-difluoroethylene, the nitrogen content relative to the total amount of 1,1-difluoroethylene and nitrogen is 77.6% by mass or more. From the viewpoint of further reducing flammability, it is preferably 81.5% by mass or more, more preferably 82.0% by mass or more, and even more preferably 82.5% by mass or more. From the viewpoint of better exhibiting the functions of 1,1-difluoroethylene, the content is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and even more preferably 99.0% by mass or less. From such viewpoints, the content is preferably 77.6 to 99.9% by mass, more preferably 81.5 to 99.9% by mass, even more preferably 82.0 to 99.5% by mass, and particularly preferably 82.5 to 99.0% by mass.

[0034] In the second embodiment, the nitrogen content of the entire cover gas composition is preferably 77.6% by mass or more, more preferably 81.5% by mass or more, even more preferably 82.0% by mass or more, and particularly preferably 82.5% by mass or more, from the viewpoint of reducing flammability. From the viewpoint of better exerting the function of the specific olefin, the content is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and even more preferably 99.0% by mass or less. From this viewpoint, the content is preferably 77.6 to 99.9% by mass, more preferably 81.5 to 99.9% by mass, even more preferably 82.0 to 99.5% by mass, and particularly preferably 82.5 to 99.0% by mass.

[0035] (Argon) In a third embodiment, the cover gas composition contains argon. The argon content relative to the total amount of the specific olefin and argon is 89.9% by mass or more. From the viewpoint of reducing flammability, it is preferably 90.3% by mass or more, more preferably 91.0% by mass or more, and even more preferably 92.0% by mass or more. From the viewpoint of better exhibiting the function of the specific olefin, the content is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and even more preferably 99.0% by mass or less. From this viewpoint, the content is preferably 89.9 to 99.9% by mass, more preferably 90.3 to 99.9% by mass, even more preferably 91.0 to 99.5% by mass, and particularly preferably 92.0 to 99.0% by mass.

[0036] In a third embodiment, when the specific olefin is 1,1-difluoroethylene, the content of argon relative to the total amount of 1,1-difluoroethylene and argon is 89.9% by mass or more. From the viewpoint of reducing flammability, it is preferably 90.3% by mass or more, more preferably 91.0% by mass or more, and even more preferably 92.0% by mass or more. From the viewpoint of better exhibiting the functions of 1,1-difluoroethylene, the content is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and even more preferably 99.0% by mass or less. From such viewpoints, the content is preferably 89.9 to 99.9% by mass, more preferably 90.3 to 99.9% by mass, even more preferably 91.0 to 99.5% by mass, and particularly preferably 92.0 to 99.0% by mass.

[0037] In the third embodiment, the argon content of the entire cover gas composition is preferably 89.9% by mass or more, more preferably 90.3% by mass or more, even more preferably 91.0% by mass or more, and particularly preferably 92.0% by mass or more, from the viewpoint of reducing flammability. From the viewpoint of better exerting the function of the specific olefin, the content is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and even more preferably 99.0% by mass or less. From this viewpoint, the content is preferably 89.9 to 99.9% by mass, more preferably 90.3 to 99.9% by mass, even more preferably 91.0 to 99.5% by mass, and particularly preferably 92.0 to 99.0% by mass.

[0038] (Oxygen) The amount of oxygen in the cover gas composition is preferably 1.0 vol% or less, more preferably 0.5 vol% or less, even more preferably 0.1 vol% or less, and particularly preferably 0.06 vol% or less. The cover gas composition does not necessarily contain oxygen.

[0039] (Other Components) In a first embodiment, the cover gas composition may or may not contain components other than the specific olefin and carbon dioxide. In a second embodiment, the cover gas composition may or may not contain components other than the specific olefin and nitrogen. In a third embodiment, the cover gas composition may or may not contain components other than the specific olefin and argon.

[0040] In the first or third embodiment, the cover gas composition may or may not further contain nitrogen. When the cover gas composition in the first or third embodiment further contains nitrogen, the nitrogen content relative to the total amount of the cover gas composition is preferably 2.0 vol% or less, more preferably 1.0 vol% or less, and even more preferably 0.5 vol% or less. In the second or third embodiment, the cover gas composition may or may not further contain carbon dioxide. When the cover gas composition in the second or third embodiment further contains carbon dioxide, the carbon dioxide content relative to the total amount of the cover gas composition is preferably 2.0 vol% or less, more preferably 1.0 vol% or less, and even more preferably 0.5 vol% or less. In the first or second embodiment, the cover gas composition may or may not further contain argon. When the cover gas composition in the first or second embodiment further contains argon, the argon content relative to the total amount of the cover gas composition is preferably 2.0 vol% or less, more preferably 1.0 vol% or less, and even more preferably 0.5 vol% or less.

[0041] The cover gas composition may or may not contain components other than the specific olefin, carbon dioxide, nitrogen, and argon. Examples of components other than the specific olefin, carbon dioxide, nitrogen, and argon include cover gas components other than the specific olefin, and gases other than carbon dioxide, nitrogen, and argon that are inactive to the molten metal or that cannot by themselves form a protective film that prevents oxidation of the molten metal even if they react with the molten metal.

[0042] Examples of cover gas components other than the specific olefin include hydrofluoroolefins (HFOs), hydrochlorofluoroolefins (HCFOs), hydrofluorocarbons (HFCs), and hydrofluoroethers (HFEs) other than the specific olefins. From the viewpoint of better demonstrating the function of the specific olefins, the total content of cover gas components other than the specific olefins relative to the total amount of cover gas components is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less.

[0043] Examples of HFOs other than specific olefins include 2,3,3,3-tetrafluoropropene (HFO-1234yf), 2-fluoropropene (HFO-1261yf), 1,1,2-trifluoropropene (HFO-1243yc), (E)-1,2,3,3,3-pentafluoropropene (HFO-1225ye(E)), (Z)-1,2,3,3,3-pentafluoropropene (HFO-1225ye(Z)), (E)-1,3,3, Examples of fluorofluoropropene include 3-tetrafluoropropene (HFO-1234ze(E)), (Z)-1,3,3,3-tetrafluoropropene (HFO-1234ze(Z)), 3,3,3-trifluoropropene (HFO-1243zf), (E)-1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz(E)), and (Z)-1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz(Z)).

[0044] As HFOs other than the specific olefins, HFO-1234yf, HFO-1234ze(E), HFO-1234ze(Z), HFO-1336mzz(Z), and HFO-1243zf are preferred, and HFO-1234yf, HFO-1234ze(E), HFO-1234ze(Z), and HFO-1336mzz(Z) are more preferred. One HFO may be used alone, or two or more HFOs may be used in combination.

[0045] The content of HFOs other than the specific olefins relative to the total amount of cover gas components is preferably 30 mass% or less, more preferably 20 mass% or less, and even more preferably 10 mass% or less, from the viewpoint of better exhibiting the function of the specific olefins.

[0046] Examples of HCFOs include HCFOs having 2 to 5 carbon atoms. Specifically, HCFOs include 1,1,2-trichloro-3,3-difluoropropene (1222xa), 1,2,3-trichloro-3,3-difluoropropene (1222xd), 1,1,3-trichloro-2,3-difluoropropene (1222ya), 1,3,3-trichloro-1,2-difluoropropene (1222yb), 1,3,3-trichloro-2,3-difluoropropene (1222yd), 1,2-dichloro-1,3,3-trifluoropropene (1223xb), and 1,2-dichloro-3,3,3-trifluoropropene. 1,1-dichloro-2,3,3-trifluoropropene (1223xd), 2,3-dichloro-1,3,3-trifluoropropene (1223xe), 1,1-dichloro-2,3,3-trifluoropropene (1223ya), 1,3-dichloro-1,2,3-trifluoropropene (1223yb), 3,3-dichloro-1,1,2-trifluoropropene (1223yc), 1,3-dichloro-2,3,3-trifluoropropene (1223yd), 3,3-dichloro-1,2,3-trifluoropropene (1223ye), 1,1-dichloro-3,3,3-trifluoro Propene (1223za), 2-chloro-1,1,3,3-tetrafluoropropene (1224xc), 2-chloro-1,3,3,3-tetrafluoropropene (1224xe), 1-chloro-1,2,3,3-tetrafluoropropene (1224yb), 3-chloro-1,1,2,3-tetrafluoropropene (1224yc), 1-chloro-2,3,3,3-tetrafluoropropene (1224yd), 3-chloro-1,2,3,3-tetrafluoropropene (1224ye), 1-chloro-1,3,3,3-tetrafluoropropene propene (1224zb), 1,2-dichloro-3,3-difluoropropene (1232xd), 1,3-dichloro-1,2-difluoropropene (1232yb), 1,3-dichloro-2,3-difluoropropene (1232yd), 3,3-dichloro-2,3-difluoropropene (1232yf), 2-chloro-1,1,3-trifluoropropene (1233xc), 2-chloro-1,3,3-trifluoropropene (1233xe), 2-chloro-3,3,3-trifluoropropene (1233xf), 1-chloro-1,2,3-trifluoropropene (1233yb), 3-chloro-1,1,2-trifluoropropene (1233yc), 1-chloro-2,3,3-trifluoropropene (1233yd), 3-chloro-1,2,3-trifluoropropene (1233ye), 3-chloro-2,3,3-trifluoropropene (1233yf), 1-chloro-3,3,3-trifluoropropene (1233zd ), 1-chloro-2,3,3,4,4,5,5,5-octafluoropentene (1428yd), 1-chloro-2,3,3,4,4,5,5-heptafluoropentene (1437dycc), 1-chloro-3,3,4,4,5,5,5-heptafluoropentene (1437zd), and 1-chloro-3,3,4,4,5,5-hexafluoropentene (1446dzcc).

[0047] The content of HCFO relative to the total amount of cover gas components is preferably 30 mass % or less, more preferably 20 mass % or less, and even more preferably 10 mass % or less, from the viewpoint of better exerting the function of the specific olefin.

[0048] Examples of HFCs include HFCs having 1 to 5 carbon atoms, which may be linear, branched, or cyclic. Specific examples of HFCs include difluoromethane, difluoroethane, trifluoroethane, tetrafluoroethane, pentafluoroethane, pentafluoropropane, hexafluoropropane, heptafluoropropane, pentafluorobutane, heptafluorocyclopentane, and dihydrodecafluoropentane.

[0049] As the HFC, from the viewpoints of having little effect on the ozone layer and having excellent performance as a cover gas component, HFC-32, 1,1,2,2-tetrafluoroethane (HFC-134), HFC-134a, HFC-125, HFC-152a, HFC-227ea, and HFC-43-10mee are preferred. One HFC may be used alone, or two or more HFCs may be used in combination.

[0050] The content of HFC relative to the total amount of cover gas components is preferably 0.5 mass % or less, and more preferably 0.1 mass % or less, from the viewpoint of maintaining a low GWP and allowing the specific olefin to exhibit its function better.

[0051] Examples of HFEs include methoxynonafluorobutane (HFE-7100), 1,1-difluoroethyl-2,2,2-trifluoroethyl ether (HFE-365mf-c), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (HFE-347pc-f), 1,1-difluoroethyl-2,2,3,3,3-pentafluoropropyl ether (HFE-467sc-f), ethoxynonafluorobutane (HFE-569s1), 1,1,2,3,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether (HFE-449mec-f), and 1,1,2,2-tetrafluoroethyl-2,2,3,3,3-pentafluoropropyl ether. ether (HFE-449pc-f), 1,1-difluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE-476pcf-c), 1,1,2,3,3,3-hexafluoropropyl-2,2,3,3,3-pentafluoropropyl ether (HFE-54-11mec-f), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE-458pc-fc), 1,1,2,3,3,3-hexafluoropropyl-2,2,3,3-tetrafluoropropyl ether (HFE-55-10mec-fc), and 3-methoxy-4-trifluoromethyl-1,1,1,2,2,3,4,5,5,5-decafluoropentane (C ２ F ５ CF (OCH ３ )CF(CF ３ )CF ３ ) etc.

[0052] As the HFE, from the viewpoint of low GWP and relatively low boiling point, HFE-7100 and HFE-7200 are preferred. One HFE may be used alone, or two or more HFEs may be used in combination.

[0053] The content of HFE relative to the total amount of cover gas components is preferably 0.5 mass % or less, and more preferably 0.1 mass % or less, from the viewpoint of maintaining a low GWP and better exhibiting the function of the specific olefin.

[0054] The cover gas composition may or may not contain at least one component selected from the group consisting of halogenated olefins other than the specific olefins (fluoroolefins other than the specific olefins, chloroolefins other than the specific olefins, chlorofluoroolefins other than the specific olefins, etc.), fluorocarbons, chlorofluorocarbons, chlorofluoroalkynes, methanol, ethanol, acetone, hexane, ethylene, methane, chloromethane, dichloroethane, acetylene, 2-methyl-2-propanol, β-pinene, pentafluoroiodoethane, and carbon monoxide (hereinafter also referred to as the "first specific trace component"). Although the reason for this is unclear, it is believed that these components have the function of suppressing and stabilizing the decomposition of the specific olefins. The first specific trace component is preferably non-flammable. Specifically, the first specific trace component is preferably Class 1 according to ASHRAE Standard 34 Refrigerant Safety Classification.

[0055] The first specific trace component may contain a fluoroolefin other than the specific olefin. Examples of the fluoroolefin other than the specific olefin include (E)-1,1,1,4,4,4-hexafluorobut-2-ene, (Z)-1,1,1,4,4,4-hexafluorobut-2-ene, 2,3,3,3-tetrafluoro-1-propene, (E)-1,3,3,3-tetrafluoropropene, (Z)-1,3,3,3-tetrafluoropropene, hexafluoropropene, and C ４ H ４ F ４ Examples of fluorinated hydrocarbons include those represented by the following formula: ４ H ４ F ４Examples of the fluorohydrocarbon represented by the formula (I) include 1,3,4,4-tetrafluoro-1-butene, 3,4,4,4-tetrafluoro-1-butene, 1,1,2,3-tetrafluoro-1-butene, and 2,4,4,4-tetrafluoro-1-butene.

[0056] The first specific trace component may contain a chloroolefin other than the specific olefin. Examples of the chloroolefin other than the specific olefin include chloroethylene, 1,1-dichloroethylene, 1,2-dichloroethylene, 1,1,2-trichloroethylene, and 1,1,2,2-tetrachloroethylene.

[0057] The first specific minor component may contain a chlorofluoroolefin other than the specific olefin. Examples of the chlorofluoroolefin other than the specific olefin include (E)-1-chloro-2,3,3,3-tetrafluoropropene, (Z)-1-chloro-2,3,3,3-tetrafluoropropene, (E)-1-chloro-3,3,3-trifluoropropene, (Z)-1-chloro-3,3,3-trifluoropropene, 1,1-dichloro-2,3,3,3-tetrafluoropropene, (Z)-2-chloro-1,3,3,3-tetrafluoropropene, (E)-2-chloro-1,3,3,3-tetrafluoropropene, 2-chloro-1,1,3,3,3-pentafluoro-1-propene, 2-chloro-3,3,3-trifluoropropene, 1,2-dichloro-1-fluoroethene, and 1,1,2-trichloro-2-fluoroethene.

[0058] The first specific trace component may contain a fluorocarbon. Examples of the fluorocarbon include monofluoromethane, difluoromethane, trifluoromethane, tetrafluoromethane, fluoroethane, 1,1-difluoroethane, 1,2-difluoroethane, 1,1,1-trifluoroethane, 1,1,2-trifluoroethane, 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane, 1,1,1,2,2-pentafluoroethane, 1,1,1,2-tetrafluoropropane, 1,1,1,3,3-pentafluoropropane, 1,1,1,2,2,3,3-heptafluoropropane, C ４ H６ F ４ and octafluorocyclobutane. ４ H ６ F ４ Examples of the fluorohydrocarbon represented by the formula include 1,1,2,3-tetrafluorobutane.

[0059] The first specific trace component may include a chlorofluorocarbon, such as chlorodifluoromethane, chlorotrifluoromethane, 1-chloro-1,1-difluoroethane, 1-chloro-1,2-difluoroethane, 1-chloro-2,2-difluoroethane, 1,1-dichloro-1-fluoroethane, 1,1-dichloro-2-fluoroethane, 1,2-dichloro-2-fluoroethane, 2-chloro-1,1,1,2-tetrafluoropropane, 1,3-dichloro-1,1,2,2,3-pentafluoropropane, and 3,3-dichloro-1,1,1,2,2-pentafluoropropane.

[0060] The first specific trace component may include a chlorofluoroalkyne, such as 1-chloro-3,3,3-trifluoro-1-propyne.

[0061] In a first embodiment, the total content of the specific olefin and carbon dioxide relative to the total amount of the cover gas composition is preferably 99.0% by volume or more, more preferably 99.5% by volume or more, or even 100% by volume. In a second embodiment, the total content of the specific olefin and nitrogen relative to the total amount of the cover gas composition is preferably 99.0% by volume or more, more preferably 99.5% by volume or more, or even 100% by volume. In a third embodiment, the total content of the specific olefin and argon relative to the total amount of the cover gas composition is preferably 99.0% by volume or more, more preferably 99.5% by volume or more, or even 100% by volume.

[0062] In a first embodiment, when the specific olefin is 1,1-difluoroethylene, the total content of 1,1-difluoroethylene and carbon dioxide relative to the total amount of the cover gas composition is preferably 98.0% by volume or more, more preferably 99.0% by volume or more, even more preferably 99.5% by volume or more, and may be 100% by volume. In a second embodiment, when the specific olefin is 1,1-difluoroethylene, the total content of 1,1-difluoroethylene and nitrogen relative to the total amount of the cover gas composition is preferably 98.0% by volume or more, more preferably 99.0% by volume or more, even more preferably 99.5% by volume or more, and may be 100% by volume. In a third embodiment, when the specific olefin is 1,1-difluoroethylene, the total content of 1,1-difluoroethylene and argon relative to the total amount of the cover gas composition is preferably 98.0% by volume or more, more preferably 99.0% by volume or more, even more preferably 99.5% by volume or more, and may be 100% by volume.

[0063] Among the cover gas compositions according to the first to third embodiments, the cover gas composition according to the first embodiment is particularly preferred. In particular, when the specific olefin is 1,1-difluoroethylene, 1,1-difluoroethylene and carbon dioxide form an azeotropic mixture, which results in little compositional variation due to temperature changes and excellent handleability.

[0064] (Characteristics and Usage of Cover Gas Composition) The cover gas composition of the present disclosure may be in a gaseous state or a state in which gas and liquid coexist at 25° C. The cover gas composition is preferably in a gaseous state in a melting furnace when supplied to the surface of the molten metal as a cover gas.

[0065] The cover gas composition may be mixed in advance with the content ratio of each component adjusted and then circulated above the molten metal, or the flow rate of each component may be adjusted individually to achieve the desired content ratio and then circulated continuously above the molten metal.

[0066] The cover gas composition of the present disclosure is used to suppress oxidation or combustion of molten metal. Specifically, the cover gas composition is used to suppress oxidation or combustion of the surface of molten metal that comes into contact with air during the manufacturing process of metals or metal alloys. Metals include magnesium, aluminum, lithium, and alloys thereof (i.e., magnesium alloys, aluminum alloys, and lithium alloys). The cover gas composition of the present disclosure is particularly useful for magnesium and magnesium alloys.

[0067] Examples of magnesium alloys include Mg—Al alloys, Mg—Al—Zn alloys, Mg—Al—Mn alloys, Mg—Zn—Zr alloys, Mg-rare earth element alloys, Mg—Zn-rare earth element alloys, etc. Examples of aluminum alloys include Al—Zr alloys, Al—Ni—Zr alloys, Al—Co—Zr alloys, Al—Fe—Zr alloys, Al—Mg—Si alloys, Al—Zn—Mg alloys, etc. Examples of lithium alloys include Li—Cu alloys, Li—Al alloys, Li—Mg alloys, Li—Zn alloys, Li—Sn alloys, Li—Pb alloys, Li—Si alloys, etc.

[0068] The temperature of the melting furnace depends on the melting temperature of the metal to be melted, which in turn depends on the type of metal: for magnesium or magnesium alloys, the melting furnace temperature is about 650 to 900°C; for aluminum or aluminum alloys, the melting furnace temperature is about 660 to 900°C; and for lithium or lithium alloys, the melting furnace temperature is about 185 to 430°C.

[0069] <Cover Gas Mixture> The cover gas mixture of the present disclosure contains the cover gas composition of the present disclosure described above and oxygen. If the balance between the combustion of the cover gas components and the protection of the molten metal is lost during casting, black smoke may be observed. This occurs when the ratio of metal oxide to metal fluoride (e.g., MgO / MgF) is appropriate for forming a protective film on the surface of the molten metal. ２This is thought to be due in part to the inability to maintain the ratio of oxygen to carbon dioxide, resulting in an unstable protective film structure. Therefore, by mixing oxygen into the cover gas composition to form a cover gas mixture, the oxygen concentration in the furnace can be maintained at an appropriate concentration, making it easier to suppress the generation of black smoke.

[0070] For example, when the metal is Mg and the specific olefin is 1,1-difluoroethylene, assuming that the organic matter is completely decomposed, the reaction proceeds as shown in the following formula: (1) 2Mg + 2C ２ F ２ H ２ → 4C + 2MgF ２ +2H ２ (2) 2Mg + O ２ →2MgO (3)2MgO+2C ２ F ２ H ２ → 4C + 2MgF ２ +2H ２ +O ２ (4) 8C + 8O ２ →8CO ２ (5) 4H ２ +20 ２ →4H ２ O In this case, from the above formulas (1), (3), (4), and (5), it is found that 2.5 times as much oxygen is consumed as 1,1-difluoroethylene in terms of volume ratio. Furthermore, when reaction (2) is taken into consideration, 2.5 times or more as much oxygen is consumed as 1,1-difluoroethylene in terms of volume ratio. The same can be said for the case where the metal is Li or Al, and assuming that the organic matter is completely decomposed, the same proportion of oxygen is consumed as 1,1-difluoroethylene.

[0071] From this viewpoint, the amount of oxygen in the cover gas mixture is preferably 2.5 times or more, more preferably 3.0 times or more, and even more preferably 3.5 times or more, by volume, relative to the specific olefin. From the viewpoint of forming a suitable protective film, the amount of oxygen is preferably 10.5 times or less, more preferably 9.5 times or less, and even more preferably 8.5 times or less, by volume, relative to the specific olefin. From this viewpoint, the amount of oxygen is preferably 2.5 to 10.5 times, more preferably 3.0 to 9.5 times, and even more preferably 3.5 to 8.5 times, by volume, relative to the specific olefin. When the specific olefin is 1,1-difluoroethylene, the amount of oxygen relative to 1,1-difluoroethylene is preferably in the above ratio.

[0072] The oxygen may be oxygen in air. In one embodiment, the cover gas mixture may contain the cover gas composition of the present disclosure and air. From the above viewpoint, the amount of air is preferably 12.0 times or more, more preferably 12.5 times or more, and even more preferably 13.0 times or more, by volume, relative to the specific olefin. From the viewpoint of forming a suitable protective film, the amount of air is preferably 50.0 times or less, more preferably 45.0 times or less, and even more preferably 40.0 times or less, by volume, relative to the specific olefin. From this viewpoint, the amount of air is preferably 12.0 to 50.0 times, more preferably 12.5 to 45.0 times, and even more preferably 13.0 to 40.0 times, by volume, relative to the specific olefin. When the specific olefin is 1,1-difluoroethylene, the amount of air relative to 1,1-difluoroethylene is preferably the above ratio.

[0073] The cover gas composition and oxygen, or the cover gas composition and air, may be contained in separate containers and supplied to the melting furnace, respectively. By adjusting the flow rate of each component with a flow meter, the ratio of the components when the cover gas mixture is formed in the furnace can be adjusted.

[0074] <Method for Suppressing Oxidation or Combustion of Molten Metal> The method for suppressing oxidation or combustion of molten metal of the present disclosure includes supplying the cover gas composition or cover gas mixture of the present disclosure described above to the surface of the molten metal.

[0075] Melting of metals, such as magnesium, aluminum, lithium, and alloys of these metals, is typically carried out in a melting furnace. In the melting furnace, the surfaces of these molten metals are exposed to air. In the method for suppressing oxidation or combustion of molten metal disclosed herein, a cover gas composition or cover gas mixture is supplied to prevent air from contacting the surface of the molten metal and causing oxidation or combustion. Examples of methods for supplying the cover gas composition or cover gas mixture include providing a cover gas composition inlet for introducing the cover gas composition or cover gas mixture into the melting furnace, and spraying the cover gas composition or cover gas mixture from the inlet into the melting furnace containing the molten metal.

[0076] As for the method of supplying the cover gas composition or cover gas mixture, as described below, a previously prepared cover gas composition or cover gas mixture may be supplied to the surface of the molten metal, or each or some of the components contained in the cover gas composition or cover gas mixture may be supplied separately to the surface of the molten metal. In other words, the supply method is not limited as long as the cover gas composition or cover gas mixture is brought into contact with the molten metal.

[0077] The amount of cover gas composition or cover gas mixture supplied into the melting furnace is appropriately adjusted depending on the surface area of ​​the molten metal that comes into contact with air, the shape and size of the melting furnace, etc., so that the protective film formed sufficiently covers the surface of the molten metal that comes into contact with air. For example, when supply is by spraying, the spray speed and angle are appropriately adjusted.

[0078] The cover gas composition or cover gas mixture of the present disclosure can effectively prevent the surface of the molten metal from coming into contact with air and from oxidizing or burning, and has a small GWP and low flammability. According to the method of the present disclosure, by using such a cover gas composition of the present disclosure, the oxidation or combustion of the molten metal can be prevented safely and effectively while reducing the environmental load.

[0079] <Cover Gas Supply Apparatus> In one embodiment, the cover gas supply apparatus comprises a specific olefin, a container for storing the specific olefin, a flow meter for adjusting the flow rate of the specific olefin, carbon dioxide, nitrogen, or argon, a container for storing the carbon dioxide, nitrogen, or argon, and a flow meter for adjusting the flow rate of the carbon dioxide, nitrogen, or argon. Details of the specific olefin, carbon dioxide, nitrogen, and argon are as described above in the section on the cover gas composition. In this embodiment, the container is not particularly limited as long as it can store each component. When the cover gas composition is supplied to a sealed container, it may be filled as a cover gas composition, or the specific olefin and carbon dioxide, nitrogen, or argon may be filled separately. By configuring the flow meters to independently adjust the flow rates of the specific olefin and carbon dioxide, nitrogen, or argon, the ratio of the specific olefin to carbon dioxide, nitrogen, or argon can be adjusted as desired, which is advantageous in terms of versatility. The cover gas supply apparatus may or may not further comprise a flow meter for adjusting the flow rate of the cover gas composition containing the specific olefin and carbon dioxide, nitrogen, or argon.

[0080] In a further aspect, a cover gas supply device includes the cover gas composition of the present disclosure, a container for storing the cover gas composition, and a flow meter for adjusting the flow rate of the cover gas composition. The cover gas supply device of this aspect can supply a prepared cover gas composition containing a specific olefin and carbon dioxide, nitrogen, or argon. Details of the specific olefin, carbon dioxide, nitrogen, and argon are as described above in the section on the cover gas composition. In this aspect, the container is not particularly limited as long as it can store the cover gas composition. In this aspect, the flow meter adjusts the flow rate of the cover gas composition containing the specific olefin and carbon dioxide, nitrogen, or argon.

[0081] In one embodiment, the cover gas supply device may further include a container for storing oxygen or air and a flow meter for adjusting the flow rate of the oxygen or air. By supplying a cover gas mixture obtained by mixing the cover gas composition and air, it becomes easier to properly form a protective film on the surface of the molten metal.

[0082] A schematic diagram of a cover gas supply apparatus according to one embodiment is shown in Figure 1. The cover gas supply apparatus 1 includes a cover gas composition, a container 10 for storing the cover gas composition, a pressure regulator 12, and a flow meter 14 for adjusting the flow rate of the cover gas composition, and supplies the cover gas composition to a metal melting furnace 16.

[0083] 2 shows a schematic diagram of a cover gas supply apparatus according to a further embodiment. The cover gas supply apparatus 2 includes a cover gas composition, a container 20 for storing the cover gas composition, a pressure regulator 22a, and a flow meter 24a for adjusting the flow rate of the cover gas composition. The cover gas supply apparatus 2 further includes oxygen or air, a container 28 for storing the oxygen or air, a pressure regulator 22b, and a flow meter 24b for adjusting the flow rate of the oxygen or air. By adjusting the flow rates of the cover gas composition and oxygen or air using the flow meters 24a and 24b, the ratio of each component supplied to the metal melting furnace 26 can be adjusted.

[0084] 3 shows a schematic diagram of a cover gas supply apparatus according to a further embodiment. The cover gas supply apparatus 3 includes a specific olefin, a container 30 for storing the specific olefin, a pressure regulator 32a, and a flow meter 34a for adjusting the flow rate of the specific olefin. The cover gas supply apparatus 3 further includes a container 38 for storing carbon dioxide, nitrogen, or argon, the carbon dioxide, nitrogen, or argon, a pressure regulator 32b, and a flow meter 34b for adjusting the flow rates of the carbon dioxide, nitrogen, or argon. By adjusting the flow rates of the specific olefin and the carbon dioxide, nitrogen, or argon using the flow meters 34a and 34b, the ratio of each component supplied to the metal melting furnace 36 can be adjusted. By using such a supply apparatus, the ratio of each component can be easily adjusted, and therefore the cover gas composition of the first, second, or third embodiment can be easily supplied to the metal melting furnace 36.

[0085] 4 shows a schematic diagram of a cover gas supply apparatus in a further embodiment. The cover gas supply apparatus 4 includes a specific olefin, a container 40 for storing the specific olefin, a pressure regulator 42a, and a flow meter 44a for adjusting the flow rate of the specific olefin. The cover gas supply apparatus 4 further includes a container 48 for storing carbon dioxide, nitrogen, or argon, the carbon dioxide, nitrogen, or argon, a pressure regulator 42b, and a flow meter 44b for adjusting the flow rates of the carbon dioxide, nitrogen, or argon. The cover gas supply apparatus 4 further includes a container 50 for storing oxygen or air, a pressure regulator 42c, and a flow meter 44c for adjusting the flow rate of the oxygen or air. The ratio of each component supplied to the metal melting furnace 46 can be adjusted by adjusting the flow rates of the specific olefin; carbon dioxide, nitrogen, or argon; and oxygen or air using the flow meters 44a to 44c. By using such a supply device, the ratio of each component can be easily adjusted, and therefore a cover gas mixture containing the cover gas composition of the first, second, or third embodiment and oxygen or air can be easily supplied to the metal melting furnace 46. Note that the electric device of the present disclosure is not limited to the embodiments shown in FIGS.

[0086] <Method for Supplying a Cover Gas Composition> The method for supplying a cover gas composition according to the present disclosure is a method for supplying a cover gas composition from the container in the cover gas supply device described above, the method including the cover gas composition according to the present disclosure, a container for storing the cover gas composition, and a flow meter for adjusting the flow rate of the cover gas composition, to a metal melting furnace, wherein the cover gas composition in the container is maintained in a single-phase state from the start of supply to the end of supply. The single-phase state refers to the entire amount of the cover gas composition in the storage container being in the same phase. The state of the cover gas composition in the storage container when supplying the cover gas composition is preferably a gaseous state or a supercritical state, more preferably a supercritical state. When the cover gas composition is in a supercritical state in the storage container, changes in the component ratio of the specific olefin to carbon dioxide, nitrogen, or argon in the cover gas composition in the storage container can be suppressed from the start of supply to the end of supply.

[0087] In one embodiment, the cover gas composition in the container is heated, pressurized, or cooled between the start and end of the supply of the cover gas composition. Here, "heating, pressurizing, or cooling" means performing at least one of heating, pressurizing, and cooling, and two or more of these, such as heating and heating, may be performed. By heating and / or pressurizing, the cover gas composition can be brought into a supercritical state. Furthermore, by cooling, the supercritical state can be returned to a subcritical state (i.e., a state in which a gas phase and a liquid phase coexist).

[0088] In a further aspect of the present disclosure, a method for supplying a cover gas composition includes supplying the cover gas composition of the present disclosure and air to the surface of molten metal, wherein the amount of air supplied is 12.0 times or more by volume relative to the amount of the halogenated olefin having 2 carbon atoms supplied. The ratio of the amount of the cover gas composition to the amount of air supplied is the same as the ratio of the two in the description of the cover gas mixture of the present disclosure above.

[0089] Next, embodiments of the present disclosure will be described in detail using examples, but the embodiments of the present disclosure are not limited to these examples.

[0090] <Combustion Test> In the following examples, the flammability of the cover gas composition was evaluated by a combustion test. The combustion test was carried out by measuring the temperature rise inside the test container before and after ignition using a measuring device based on the Explosion Limit Measurement Method A of Article 2, Paragraph 1, A and B of the General High-Pressure Gas Safety Regulations. Ignition was carried out by discharge from an electrode installed in the center of the container. The discharge was carried out under ignition conditions of 16 kV, 50 mA, and 0.23 seconds. The details of the test conditions and the evaluation criteria are as follows.

[0091] (Test conditions) Test vessel: 2L capacity spherical stainless steel vessel Test gas: cover gas composition, dry air, and moisture Test temperature: 20°C ± 5°C or 60°C ± 5°C Test pressure: 101.3 kPa ± 0.7 kPa (absolute pressure) Moisture: 0.0088 g ± 0.0005 g per 1 g of dry air (moisture content at 50% relative humidity at 23°C) Ignition method: AC discharge, voltage 16 kV, current 50 mA, 0.23 seconds Electrode position: center of vessel, electrode spacing 4.0 mm Stirring conditions: 300 rpm, 10 minutes

[0092] (Evaluation criteria) - If the temperature rise in the test container before and after ignition is 50°C or more: Flame spread (flammable: A) - If the temperature rise in the test container before and after ignition is less than 50°C: Flame does not spread (non-flammable: B)

[0093] 1. CO to HFO-1132a ２ , N ２ The effect of adding Ar is to convert flammable HFO-1132a into non-flammable CO ２ , N ２ After preparing the cover gas composition by adding HFO-1132a or Ar, water and dry air were further mixed to obtain air with a relative humidity of 50% at 23°C, and the temperature rise in the test vessel before and after discharge ignition under the above test conditions (test temperature: 60°C ± 5°C) was observed. Note that in this test, HFO-1132a alone (Nos. 1 to 3), HFO-1132a and CO ２ Mixture of HFO-1132a and N ２ The mixtures of HFO-1132a and Ar (Nos. 7 to 9) and HFO-1132a and Ar (Nos. 10 to 12) were regarded as cover gas compositions, and evaluations were performed by mixing dry air and air containing water to confirm that flammability would be suppressed if each cover gas composition leaked into the air.

[0094] The mass ratio and volume ratio of each component and the test results are shown in the table below. In the table below, "mass ratio / cover gas composition" refers to the total amount of the cover gas composition (i.e., HFO-1132a, CO ２ , N ２ The "volume ratio / (cover gas composition + air)" represents the mass ratio of each component when the total amount of the cover gas composition and air is taken as 100% by volume. From Nos. 4 to 12, it can be seen that the cover gas composition contains CO ２ , N ２ It was confirmed that the temperature rise inside the test vessel can be suppressed by adding argon or Ar.

[0095]

[0096] 2. CO of HFO-1132a ２ Non-flammable by mixing HFO-1132a with CO ２After preparing the cover gas composition by adding HFO-1132a and CO, water and dry air were further mixed to obtain air with a relative humidity of 50% at 23°C, and the temperature rise in the test vessel before and after discharge ignition under the above test conditions was observed. ２ The mixture was regarded as a cover gas composition, and in order to confirm that each cover gas composition could be guaranteed to be non-flammable even if it leaked into the air, it was mixed with air at a specified ratio and evaluated.

[0097] The mass ratio, molar ratio, and volume ratio of each component, as well as the test results, are shown in Table 3 (test temperature: 20°C ± 5°C) and Table 4 (test temperature: 60°C ± 5°C). In the tables below, "mass ratio / cover gas composition" refers to the total amount of cover gas composition (i.e., HFO-1132a and CO ２ The "molar ratio / cover gas composition" represents the mass ratio of each component when the total amount of the cover gas composition (i.e., the total amount of HFO-1132a and CO ２ The "volume ratio / (cover gas composition + air)" represents the volume ratio of each component when the total amount of the cover gas composition and air is taken as 100 vol%.

[0098]

[0099] Based on the results in Table 3, HFO-1132a and CO ２ CO relative to the total amount ２ The horizontal axis represents the content (mass%) of HFO-1132a and CO ２ , and HFO-1132a and CO relative to the total amount of air ２ The total content (volume %) of HFO-1132a and CO is plotted on the vertical axis in a graph shown in Figure 5. ２ It was confirmed that the flammable range was suppressed by adding HFO-1132a and CO. ２ CO ２ By making the amount of HFO-1132a and CO ２ It was found that cover gas compositions containing HFO-1132a and CO are non-flammable regardless of the ratio of HFO-1132a and CO２ Contains HFO-1132a and CO ２ CO relative to the total amount ２ 5 shows that a cover gas composition containing 76.4 mass % or more of HFO-1132a and CO can be guaranteed to be non-flammable even when leaked into the air. ２ CO relative to the total amount ２ The right side of the dashed line (indicated as "non-combustible"; including 76.4% by mass) represents the range of the Examples, and the left side of the dashed line (indicated as "combustible"; not including 76.4% by mass) represents the range of the Comparative Examples.

[0100]

[0101] Based on the results in Table 4, HFO-1132a and CO ２ CO relative to the total amount ２ The horizontal axis represents the content (mass%) of HFO-1132a and CO ２ , and HFO-1132a and CO relative to the total amount of air ２ The total content (volume %) of HFO-1132a and CO is plotted on the vertical axis in a graph shown in Figure 6. ２ It was confirmed that the flammable range was suppressed by adding HFO-1132a and CO. ２ CO ２ By making the amount of HFO-1132a and CO 79.5 mass % or more, ２ It was found that cover gas compositions containing HFO-1132a and CO are non-flammable regardless of the ratio of HFO-1132a and CO ２ Contains HFO-1132a and CO ２ CO relative to the total amount ２ 6 indicates that a cover gas composition containing 79.5 mass % or more of HFO-1132a and CO can be guaranteed to be non-flammable even when leaked into the air. ２ CO relative to the total amount ２ This indicates that the content of

[0102] 3. N in HFO-1132a ２Non-flammable by mixing HFO-1132a with N ２ After preparing the cover gas composition by adding HFO-1132a and N, water and dry air were further mixed to obtain air with a relative humidity of 50% at 23°C, and the temperature rise inside the test vessel was observed before and after discharge ignition under the above test conditions. ２ The mixture was regarded as a cover gas composition, and in order to confirm that each cover gas composition could be guaranteed to be non-flammable even if it leaked into the air, it was mixed with air at a specified ratio and evaluated.

[0103] The mass ratio, molar ratio, and volume ratio of each component, as well as the test results, are shown in Table 5 (test temperature: 20°C ± 5°C) and Table 6 (test temperature: 60°C ± 5°C). In the tables below, "mass ratio / cover gas composition" refers to the total amount of cover gas composition (i.e., HFO-1132a and N ２ The "molar ratio / cover gas composition" represents the mass ratio of each component when the total amount of the cover gas composition (i.e., the total amount of HFO-1132a and N ２ The "volume ratio / (cover gas composition + air)" represents the volume ratio of each component when the total amount of the cover gas composition and air is taken as 100 vol%.

[0104]

[0105] Based on the results in Table 5, HFO-1132a and N ２ N relative to the total amount of ２ The horizontal axis represents the content (mass%) of HFO-1132a, N ２ , and HFO-1132a and N relative to the total amount of air ２ The total content (volume %) of HFO-1132a is plotted on the vertical axis in Figure 7. ２ It was confirmed that the flammable range was suppressed by adding HFO-1132a and N. ２ For the total amount of ２ By making the amount of HFO-1132a and N ２It was found that cover gas compositions containing HFO-1132a and N are non-flammable regardless of the ratio of HFO-1132a and N ２ Contains HFO-1132a and N ２ N for the total amount of ２ 7 indicates that a cover gas composition containing 77.6 mass % or more of HFO-1132a and N can be guaranteed to be non-flammable even when leaked into the air. ２ N relative to the total amount of ２ The right side of the dashed line (indicated as "non-combustible"; including 77.6% by mass) represents the range of the Examples, and the left side of the dashed line (indicated as "combustible"; not including 77.6% by mass) represents the range of the Comparative Examples.

[0106]

[0107] Based on the results in Table 6, HFO-1132a and N ２ N relative to the total amount of ２ The horizontal axis represents the content (mass%) of HFO-1132a, N ２ , and HFO-1132a and N relative to the total amount of air ２ The total content (volume %) of HFO-1132a is plotted on the vertical axis in Figure 8. ２ It was confirmed that the flammable range was suppressed by adding HFO-1132a and N ２ For the total amount of ２ By making the amount of HFO-1132a and N ２ It was found that cover gas compositions containing HFO-1132a and N are non-flammable regardless of the ratio of HFO-1132a and N ２ Contains HFO-1132a and N ２ N for the total amount of ２ 8 indicates that a cover gas composition containing 81.5 mass % or more of HFO-1132a and N can be guaranteed to be non-flammable even when leaked into the air. ２ N relative to the total amount of ２ This indicates that the content of

[0108] In addition, when a similar test was carried out using HFO-1123 instead of HFO-1132a, the boundary value of the carbon dioxide or nitrogen content at which the cover gas composition became non-flammable was lowered.

[0109] 4. Making HFO-1132a Nonflammable by Mixing with Ar After Ar was added to HFO-1132a to prepare a cover gas composition, water and dry air were further mixed to obtain air with a relative humidity of 50% at 23°C, and the temperature rise inside the test vessel was observed before and after discharge ignition under the above test conditions. In this test, a mixture of HFO-1132a and Ar was regarded as the cover gas composition, and air was mixed in at a predetermined ratio to confirm that nonflammability could be ensured even if each cover gas composition leaked into the air.

[0110] The mass ratio, molar ratio, and volume ratio of each component, as well as the test results, are shown in Table 7 (test temperature: 20°C ± 5°C) and Table 8 (test temperature: 60°C ± 5°C). In the tables below, "mass ratio / cover gas composition" represents the mass ratio of each component when the total amount of the cover gas composition (i.e., the total amount of HFO-1132a and Ar) is taken as 100 mass%. "molar ratio / cover gas composition" represents the molar ratio of each component when the total amount of the cover gas composition (i.e., the total amount of HFO-1132a and Ar) is taken as 100 mol%. Furthermore, "volume ratio / (cover gas composition + air)" represents the volume ratio of each component when the total amount of the cover gas composition and air is taken as 100 vol%.

[0111]

[0112] Based on the results of Table 7, a graph is shown in Figure 9, in which the content (mass%) of Ar relative to the total amount of HFO-1132a and Ar is plotted on the horizontal axis, and the total content (volume%) of HFO-1132a and Ar relative to the total amount of HFO-1132a, Ar, and air is plotted on the vertical axis. It was confirmed that the flammable range was suppressed by adding Ar to HFO-1132a. Furthermore, when the test temperature was 20 ° C, it was found that by making Ar 89.9 mass% or more relative to the total amount of HFO-1132a and Ar, the cover gas composition containing HFO-1132a and Ar became non-flammable regardless of the ratio present in the air. This indicates that non-flammability can be ensured even when a cover gas composition containing HFO-1132a and Ar and having an Ar content of 89.9 mass% or more relative to the total amount of HFO-1132a and Ar leaks into the air. In FIG. 9 , the dashed line indicates that the content of Ar relative to the total amount of HFO-1132a and Ar is 89.9% by mass, with the right side of the dashed line (indicated as "non-combustible"; including 89.9% by mass) representing the range of the Examples and the left side of the dashed line (indicated as "combustible"; not including 89.9% by mass) representing the range of the Comparative Examples.

[0113]

[0114] Based on the results of Table 8, a graph is shown in Figure 10, in which the content (mass%) of Ar relative to the total amount of HFO-1132a and Ar is plotted on the horizontal axis, and the total content (volume%) of HFO-1132a and Ar relative to the total amount of HFO-1132a, Ar, and air is plotted on the vertical axis. It was confirmed that the flammable range was suppressed by adding Ar to HFO-1132a. Furthermore, when the test temperature was 60 ° C, it was found that by making Ar 90.3 mass % or more relative to the total amount of HFO-1132a and Ar, the cover gas composition containing HFO-1132a and Ar became non-flammable regardless of the ratio present in the air. This indicates that non-flammability can be ensured even when a cover gas composition containing HFO-1132a and Ar and having an Ar content of 90.3 mass % or more relative to the total amount of HFO-1132a and Ar leaks into the air. In FIG. 10, the dashed line indicates that the content of Ar relative to the total amount of HFO-1132a and Ar is 90.3 mass %.

[0115] As shown above, a cover gas composition with low flammability was obtained using HFO-1132a, which has a low GWP and a low boiling point.

[0116] (Additional Notes) The present disclosure includes the following aspects. <1> A cover gas composition for suppressing oxidation or combustion of molten metal, comprising a halogenated olefin having two carbon atoms and carbon dioxide, wherein the content of the carbon dioxide relative to the total amount of the halogenated olefin having two carbon atoms and the carbon dioxide is 79.5 mass% or more, or a halogenated olefin having two carbon atoms and nitrogen, wherein the content of the nitrogen relative to the total amount of the halogenated olefin having two carbon atoms and the nitrogen is 81.5 mass% or more. <2> The cover gas composition according to <1>, wherein the halogenated olefin having two carbon atoms comprises at least one selected from the group consisting of 1,1-difluoroethylene, (E)-1,2-difluoroethylene, (Z)-1,2-difluoroethylene, and trifluoroethylene. <3> The cover gas composition according to <1> or <2>, wherein the halogenated olefin having two carbon atoms is 1,1-difluoroethylene. <4> The cover gas composition according to <1>, wherein the total content of the halogenated olefin having two carbon atoms and carbon dioxide relative to the total amount of the cover gas composition is 99.0% by volume or more, or the total content of the halogenated olefin having two carbon atoms and nitrogen relative to the total amount of the cover gas composition is 99.0% by volume or more. <5> The cover gas composition according to any one of <1> to <4>, wherein the metal is any one selected from the group consisting of magnesium, aluminum, lithium, and alloys thereof. <6> A cover gas mixture comprising the cover gas composition according to any one of <1> to <5> and oxygen. <7> The cover gas mixture according to <6>, wherein the amount of oxygen is 2.5 times or more by volume relative to the halogenated olefin having two carbon atoms. <8> The cover gas mixture according to <6>, comprising the cover gas composition and air. <9> The cover gas mixture according to <8>, wherein the amount of air is 12.0 times or more by volume relative to the halogenated olefin having two carbon atoms. <10> A method for suppressing oxidation or combustion of molten metal, comprising supplying the cover gas composition according to any one of <1> to <5> or the cover gas mixture according to any one of <6> to <9> to a surface of the molten metal.<11> A method for suppressing oxidation or combustion of molten metal, comprising supplying the cover gas mixture according to any one of <6> to <9> to the surface of the molten metal. <12> A cover gas supply device comprising: a halogenated olefin having two carbon atoms; a container for storing the halogenated olefin having two carbon atoms; a flow meter for adjusting the flow rate of the halogenated olefin having two carbon atoms; carbon dioxide or nitrogen; a container for storing the carbon dioxide or the nitrogen; and a flow meter for adjusting the flow rate of the carbon dioxide or nitrogen. <13> A cover gas supply device comprising: the cover gas composition according to any one of <1> to <5>; a container for storing the cover gas composition; and a flow meter for adjusting the flow rate of the cover gas composition. <14> A method for supplying the cover gas composition from the container in the cover gas supply device according to <13> to a metal melting furnace, wherein the cover gas composition in the container is maintained in a one-phase state from the start of supply to the end of supply. <15> The supply method according to <14>, wherein the one-phase state is a supercritical state. <16> The method according to <14> or <15>, wherein the cover gas composition in the container is heated, pressurized, or cooled between the start and end of the supply. <17> A method for supplying a cover gas composition according to any one of <1> to <5> and air to the surface of molten metal, wherein the amount of air supplied is 12.0 times or more, by volume, the amount of the halogenated olefin having two carbon atoms supplied. <18> A method for supplying a cover gas composition according to any one of <1> to <5> and oxygen to the surface of molten metal, wherein the amount of oxygen supplied is 2.5 times or more, by volume, the amount of the halogenated olefin having two carbon atoms supplied.

[0117] The disclosure of Japanese Patent Application No. 2024-129227, filed on August 5, 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

[0118] 1, 2, 3, 4 Cover gas supply device 10, 20 Container for storing cover gas composition 28, 50 Container for storing oxygen or air 30, 40 Container for storing specific olefin 38, 48 CO ２ , N ２ , or a container for storing Ar 12, 22a, 22b, 32a, 32b, 42a, 42b, 42c Pressure regulator 14, 24a, 24b, 34a, 34b, 44a, 44b, 44c Flow meter 16, 26, 36, 46 Metal melting furnace

Claims

1. A cover gas composition for suppressing oxidation or combustion of molten metal, comprising: a halogenated olefin having two carbon atoms and carbon dioxide, wherein the content of the carbon dioxide relative to the total amount of the halogenated olefin having two carbon atoms and the carbon dioxide is 76.4 mass% or more; a halogenated olefin having two carbon atoms and nitrogen, wherein the content of the nitrogen relative to the total amount of the halogenated olefin having two carbon atoms and the nitrogen is 77.6 mass% or more; or a halogenated olefin having two carbon atoms and argon, wherein the content of the argon relative to the total amount of the halogenated olefin having two carbon atoms and the argon is 89.9 mass% or more.

2. The cover gas composition according to claim 1, comprising a halogenated olefin having two carbon atoms and carbon dioxide, wherein the content of the carbon dioxide relative to the total amount of the halogenated olefin having two carbon atoms and the carbon dioxide is 79.5 mass% or more, or a halogenated olefin having two carbon atoms and nitrogen, wherein the content of the nitrogen relative to the total amount of the halogenated olefin having two carbon atoms and the nitrogen is 81.5 mass% or more.

3. The cover gas composition according to claim 1, comprising a halogenated olefin having two carbon atoms and argon, wherein the content of the argon relative to the total amount of the halogenated olefin having two carbon atoms and the argon is 90.3 mass% or more.

4. The cover gas composition of claim 1, wherein the halogenated olefin having two carbon atoms comprises at least one selected from the group consisting of 1,1-difluoroethylene, (E)-1,2-difluoroethylene, (Z)-1,2-difluoroethylene, and trifluoroethylene.

5. The cover gas composition of claim 1, wherein the halogenated olefin having two carbon atoms is 1,1-difluoroethylene.

6. The cover gas composition of claim 1, wherein the total content of the halogenated olefin having two carbon atoms and carbon dioxide relative to the total amount of the cover gas composition is 99.0% by volume or more, the total content of the halogenated olefin having two carbon atoms and nitrogen relative to the total amount of the cover gas composition is 99.0% by volume or more, or the total content of the halogenated olefin having two carbon atoms and argon relative to the total amount of the cover gas composition is 99.0% by volume or more.

7. The cover gas composition of claim 1, wherein the metal is any one selected from the group consisting of magnesium, aluminum, lithium, and alloys thereof.

8. A cover gas mixture comprising the cover gas composition of any one of claims 1 to 7 and oxygen.

9. The cover gas mixture of claim 8, wherein the amount of oxygen is at least 2.5 times by volume the amount of the halogenated olefin having two carbon atoms.

10. The cover gas mixture of claim 8, comprising the cover gas composition and air.

11. The cover gas mixture of claim 10, wherein the amount of air is 12.0 times or more by volume relative to the amount of the halogenated olefin having two carbon atoms.

12. A method for inhibiting oxidation or combustion of molten metal, which comprises supplying the cover gas composition according to any one of claims 1 to 7 to the surface of the molten metal.

13. A method for inhibiting oxidation or combustion of molten metal, comprising supplying the cover gas mixture of claim 8 to the surface of the molten metal.

14. A cover gas supply device comprising: a halogenated olefin having a carbon number of 2; a container for storing the halogenated olefin having a carbon number of 2; a flow meter for adjusting the flow rate of the halogenated olefin having a carbon number of 2; carbon dioxide, nitrogen, or argon; a container for storing the carbon dioxide, nitrogen, or argon; and a flow meter for adjusting the flow rate of the carbon dioxide, nitrogen, or argon.

15. A cover gas supply device comprising: a cover gas composition according to any one of claims 1 to 7; a container for storing the cover gas composition; and a flow meter for adjusting the flow rate of the cover gas composition.

16. A method for supplying a cover gas composition from the container in the cover gas supply device of claim 15 to a metal melting furnace, wherein the cover gas composition in the container is maintained in a single-phase state from the start of supply to the end of supply.

17. The method of claim 16, wherein the one-phase state is a supercritical state.

18. The supply method according to claim 16, wherein the cover gas composition in the container is heated, pressurized, or cooled during the period from the start of supply to the end of supply.

19. A method for supplying a cover gas composition, comprising supplying the cover gas composition according to any one of claims 1 to 7 and air to the surface of molten metal, wherein the amount of air supplied is 12.0 times or more by volume relative to the amount of the halogenated olefin having two carbon atoms supplied.

20. A method for supplying a cover gas composition according to any one of claims 1 to 7 and oxygen to the surface of molten metal, wherein the amount of oxygen supplied is at least 2.5 times the volumetric amount of the halogenated olefin having two carbon atoms supplied.

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