Fire-resistant heat-insulating film and method for manufacturing the same

Abstract

To provide a fire-resistant heat insulation film comparatively inexpensive and excellent in fire-resistant heat insulation, and a method for manufacturing the same.SOLUTION: A fire-resistant heat insulation film including magnesium oxide has a porosity of 50% or more. A method for manufacturing the fire-resistant heat insulation film including magnesium oxide and having a porosity of 50% or more comprises the step of introducing magnesium chelate complex particles into a thermal fluid to hit them on a base material.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a fire-resistant and heat-insulating film that is relatively inexpensive and has excellent fire resistance and heat insulation properties, and to a method for manufacturing the same. [Background technology]

[0002] In a typical internal combustion engine, the cycle of fuel intake, compression, combustion, and exhaust of fuel gases is repeated, converting thermal energy into mechanical energy to generate power. Inside the internal combustion engine, especially in the combustion chamber, high temperatures are reached due to fuel compression and combustion, sometimes reaching approximately 3000°C. Therefore, the materials that make up the internal combustion engine are coated with a fire-resistant and heat-insulating film.

[0003] For example, Patent Document 1 discloses a multilayer coated aluminum substrate in which an anodized layer and a ceramic layer are sequentially formed on a substrate made of aluminum or an aluminum alloy, for use as an engine component or other component requiring thermal insulation performance. Examples of materials for forming the ceramic layer include alumina, zirconia, yttria, calcia, magnesia, ceria, and hafnia, and in the embodiment, SiO2-TiO2 glass is used as the ceramic layer material.

[0004] Furthermore, Patent Document 2 discloses a thermal insulation coating system composed of yttria-stabilized zirconia.

[0005] Incidentally, the present inventors have developed a method for easily forming a yttrium oxide film with high density, transparency, and adhesion on a silicon oxide substrate, which is used as a composite material for parts of semiconductor manufacturing equipment that require plasma resistance, by introducing non-vaporizing yttrium chelate complex particles into a thermal fluid and applying it to the silicon oxide substrate (Patent Document 3). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2015-166484 [Patent Document 2] Japanese Patent Publication No. 2000-119869 [Patent Document 3] Japanese Patent Publication No. 2018-140913 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] As mentioned above, various refractory and heat insulating films have been considered, but silica and alumina have low melting points and are therefore unsuitable as materials for refractory and heat insulating films, especially in combustion chambers where temperatures are high. Furthermore, the only materials actually put into practical use are zirconia and yttria-stabilized zirconia, which have low thermal conductivity, but zirconia and yttria-stabilized zirconia are relatively expensive. On the other hand, magnesium oxide (magnesia) has the problem of high thermal conductivity. For example, according to one technical document, the thermal conductivity of zirconia at 400°C is 3 W / (m·K), while that of magnesium oxide is 15 W / (m·K). However, magnesium oxide has the advantage of being relatively inexpensive. In addition, the specific heat capacity of magnesia is 0.879 kJ / (kg·K) at 298 K, which is higher than the specific heat capacity of zirconia (0.47 kJ / (kg·K)) and silica (0.75 kJ / (kg·K)), giving it the advantage of not rising easily when heated. Therefore, the present invention aims to provide a fire-resistant and heat-insulating film that is relatively inexpensive and has excellent fire resistance and heat insulation properties, and a method for manufacturing the same. [Means for solving the problem]

[0008] The inventors focused on magnesium oxide, which has a high heat capacity, because the refractory insulating film of an internal combustion engine is not constantly heated, but only becomes hot during fuel combustion, is only slightly heated during fuel compression, and actually decreases during fuel intake and gas exhaust. In other words, materials with a low heat capacity, such as zirconia, experience significant temperature fluctuations with intermittent heating, altering the temperature environment of the combustion chamber. However, magnesium oxide, with its high heat capacity, is difficult to heat up and difficult to cool down, and therefore has little impact on the temperature environment of the combustion chamber. Furthermore, the inventors considered that since the thermal conductivity of air is extremely low compared to metal oxides, the problem of magnesium oxide having a relatively high thermal conductivity could be solved by making the film porous. Furthermore, it has been revealed that porous magnesium oxide films can be easily formed using a thermal spraying method employing a chelating agent and thermal spray gun developed by the present inventors. Specifically, when forming zirconia films and the like by thermal spraying, the mass of zirconium and other metal oxide particles is relatively large, so when the high-temperature metal oxide particles collide with the substrate, they are crushed by kinetic energy, forming a dense film. On the other hand, since the mass of magnesium is relatively small, the chelating component of magnesium chelating particles is thermally decomposed and removed in the thermal spray flame, and the remaining magnesium oxide particles do not completely collapse when they collide with the substrate, thus forming a porous film. The present invention is described below.

[0009] [1] A fire-resistant and heat-insulating film characterized by containing magnesium oxide and having a porosity of 50% or more. [2] The fire-resistant heat-insulating film according to [1], wherein the porosity is 70% or less. [3] The fire-resistant heat-insulating film according to [1] or [2], wherein the average thickness is 20 μm or more and 100 μm or less. [4] A method for manufacturing a fire-resistant heat-insulating film, The aforementioned fire-resistant heat-insulating film contains magnesium oxide and has a porosity of 50% or more. A method characterized by including the step of introducing magnesium chelate complex particles into a thermal fluid and applying it to a substrate. [5] The method according to [4], wherein the molecular weight of the chelating agent contained in the magnesium chelate complex particles is 200 or less. [6] The method according to [4] or [5], wherein the chelating agent contained in the magnesium chelate complex particles has a valence of 2. [7] The method according to any one of the above [4] to [6], wherein the chelating agent contained in the magnesium chelate complex particles is hydroxyethyliminodiacetic acid. [Effects of the Invention]

[0010] The magnesium oxide constituting the refractory heat-insulating film according to the present invention can be manufactured at a lower cost compared to zirconia, yttria-stabilized zirconia, and other materials that constitute conventional refractory heat-insulating films. Furthermore, while the internal temperature of an internal combustion engine is not constantly high, and the temperature changes during one cycle are relatively large, magnesium oxide has a relatively large heat capacity, making it difficult to heat up and difficult to cool down, thus having little impact on the temperature environment of the combustion chamber. In addition, although magnesium oxide has a relatively high thermal conductivity, the refractory heat-insulating film according to the present invention is porous, so the overall thermal conductivity of the film is low and at a practical level. Furthermore, according to the method of the present invention, a porous fire-resistant and heat-insulating film can be easily manufactured. Specifically, in conventional physical vapor deposition (PVD) methods, particles in the atomic or molecular state are attached and deposited on the substrate, making it impossible to form a porous film. Also, in methods where a metal oxide slurry is applied to a substrate and then fired, the metal oxide crystal particles grow and sinter with each other during firing, resulting in a dense film. In contrast, in the method of the present invention, the atomic weight of magnesium is relatively low, and the molecular weight of magnesium oxide is also relatively small, resulting in low kinetic energy. Therefore, even if magnesium oxide particles collide with the substrate due to the thermal fluid, they are less likely to be crushed, and as a result, the formed film is porous. Therefore, the present invention is extremely useful in industry as a technology that enables the easy formation of a fire-resistant and heat-insulating film on a substrate at a relatively low cost and with excellent fire resistance and heat insulation properties. [Brief explanation of the drawing]

[0011] [Figure 1]Shows an example of a thermal spraying gun used in the flame spraying method and represents a cross-sectional view of the thermal spraying gun.

Mode for Carrying Out the Invention

[0012] The refractory heat-insulating film according to the present invention contains magnesium oxide (MgO) and has a porosity of 50% or more.

[0013] The refractory heat-insulating film according to the present invention contains magnesium oxide, and for the purpose of improving the characteristics of the refractory heat-insulating film, a metal element other than magnesium may be added. For example, for the purpose of improving the adhesion strength between stacked magnesium oxide particles, it is also possible to intentionally add a metal element such as aluminum that lowers the melting point of magnesium oxide. Further, the refractory heat-insulating film according to the present invention may be substantially composed of only magnesium oxide except having pores. Substantially consisting of only magnesium oxide means that the refractory heat-insulating film is composed of magnesium oxide except for inevitable impurities and inevitable contaminants. As the inevitable impurities and inevitable contaminants, organic components derived from a chelating agent that could not be completely decomposed by heating and remained may be considered.

[0014] Since magnesium oxide has a relatively large heat capacity, it is difficult to be heated and cooled, and it can be said that it is difficult to affect the temperature environment of the combustion chamber. Therefore, magnesium oxide is very suitable as a material for the inner film of an internal combustion engine that is intermittently heated. Further, since magnesium oxide has a high melting point of 3250 °C, it can be said that it has excellent fire resistance.

[0015] The porosity of the refractory heat-insulating film according to the present invention is 50% or more. Although the thermal conductivity of magnesium oxide constituting the refractory heat-insulating film according to the present invention is relatively high, due to the high porosity, the thermal conductivity of the refractory heat-insulating film becomes low.

[0016] The porosity can be determined by a conventional method. For example, the volume and mass of the refractory heat-insulating film are measured to calculate the bulk density, and the bulk density and the theoretical density of magnesium oxide 3.58 g / cm 3The volume of stomata can be calculated from the ratio, and the porosity can be determined as the ratio of the volume of stomata to the total volume.

[0017] The porosity is 50% or more, preferably 55% or more, and more preferably 60% or more. Since the thermal conductivity of air is very low, the higher the porosity, the lower the thermal conductivity of the fire-resistant heat-insulating film. On the other hand, the higher the porosity, the lower the strength of the fire-resistant heat-insulating film, so the porosity is preferably 80% or less, more preferably 75% or less, and even more preferably 70% or less. It should be noted that even a fire-resistant heat-insulating film with slightly lower strength can be formed on the inner surface of the internal combustion engine, except for parts where components come into contact, such as sliding parts.

[0018] The average thickness of the fire-resistant heat-insulating film according to the present invention is not particularly limited, but is preferably 20 μm or more and 500 μm or less. If the thickness is 20 μm or more, the heat-insulating performance can be more reliably exhibited, and if it is 500 μm or less, cracking and peeling due to excessive thickness can be more reliably suppressed. The thickness is more preferably 40 μm or less, even more preferably 30 μm or less, even more preferably 400 μm or less or 200 μm or less, and even more preferably 100 μm or less, 70 μm or less or 50 μm or less.

[0019] The average thickness of a fire-resistant insulation film can be measured by conventional methods. For example, a cross-section of the fire-resistant insulation film can be photographed with an electron microscope, the thickness can be measured at four or more points on the photograph, and the average value can be calculated. Alternatively, a film thickness gauge can be used, or the above measurement method can be used in combination with measurement using a film thickness gauge.

[0020] The fire-resistant and heat-insulating film according to the present invention is not particularly limited, but can be manufactured, for example, by thermal spraying. More specifically, it can be formed by introducing magnesium chelate complex particles into a thermal fluid and applying it to a substrate.

[0021] Magnesium chelate complex particles are complexes formed from magnesium and a chelating agent, and can be used without particular limitations. It is preferable that the magnesium chelate complex particles are non-vaporous. If the magnesium chelate complex particles are non-vaporous, the chelating agent portion will decompose thermally before vaporization occurs when introduced into a thermal fluid. Furthermore, if the magnesium chelate complex is present, the chelating agent portion will decompose rapidly even with a short residence time in the thermal fluid. The magnesium component remaining after thermal decomposition is oxidized in the thermal fluid to magnesium oxide, which then collides with the surface of the substrate, causing the magnesium oxide to deposit on the substrate and forming a magnesium oxide film. Therefore, a magnesium oxide film can be efficiently formed on the substrate. In this process, because the atomic weight of magnesium is relatively small and the energy of the collision with the substrate is small, the particles are less likely to be crushed, and the particle shape is maintained as they deposit on the substrate, thus forming a porous film.

[0022] The decomposition temperature of the magnesium chelate complex should be lower than the boiling point of the complex, preferably between 250°C and 400°C.

[0023] Magnesium chelate complex particles can be obtained by reacting a magnesium compound with a chelating agent. Specifically, a magnesium compound and a chelating agent are reacted in an aqueous solvent to obtain an aqueous magnesium chelate solution. Solid magnesium chelate complex particles can then be obtained by removing the solvent from this solution or by precipitating the magnesium chelate complex.

[0024] The magnesium compound used as the raw material for magnesium chelate complex particles is not particularly limited as long as it becomes a magnesium ion in an aqueous solvent and forms a complex with the chelating agent. Examples of magnesium compounds that can be used include oxides, hydroxides, halide salts such as chloride salts and bromide salts, carbonates, nitrates, and sulfates.

[0025] Examples of chelating agents include dihydroxyethylglycine, hydroxyethyliminodiacetic acid (HIDA), ethylenediaminediacetic acid, ethylenediaminedi(o-hydroxyphenyl)acetic acid, ethylenediaminedipropionic acid, iminodiacetic acid, methylglycinediacetic acid, ethylenediaminedisuccinic acid, 1,3-diaminopropanedisuccinic acid, glutamic acid-N,N-diacetic acid, aspartic acid-N,N-diacetic acid, hydroxyethylenediaminetriacetic acid, nitrilotriacetic acid, nitrilotripropionic acid, ethylenediaminetetraacetic acid (EDTA), 1,2-cyclohexanediaminetetraacetic acid, diaminopropanoltetraacetic acid, glycol A Aminocarboxylic acid chelating agents such as terdiaminetetraacetic acid, hexamethylenediaminetetraacetic acid, 1,3-diaminopropanetetraacetic acid, 1,2-diaminopropanetetraacetic acid, diethylenetriaminepentaacetic acid, and triethylenetetraminehexaacetic acid; phosphonic acid chelating agents such as hydroxyethylidenediphosphonic acid; aminophosphonic acid chelating agents such as nitrilotris(methylenephosphonic acid) and ethylenediaminetetra(methylenephosphonic acid); carboxylic acid-phosphonic acid chelating agents such as phosphonovutanetricarboxylic acid; and hydroxycarboxylic acid chelating agents such as gluconic acid, citric acid, tartaric acid, and malic acid can be used. These chelating agents are preferably water-soluble. Using such chelating agents makes it easy to obtain non-vaporizing magnesium complex particles, and also facilitates the reaction in which the chelating agent portion of the magnesium chelate complex decomposes to produce magnesium oxide, even at temperatures of 500°C or higher, for example, even if the temperature of the thermal fluid is not very high.

[0026] As a chelating agent, aminocarboxylic acid-based chelating agents are preferably used. Aminocarboxylic acid-based chelating agents are preferred because they readily bind with magnesium ions to form magnesium chelate complexes, and these complexes can be easily isolated as crystals and purified. Furthermore, when magnesium chelate complexes obtained from aminocarboxylic acid-based chelating agents are introduced into a thermal fluid, they decompose before vaporizing and are readily converted to magnesium oxide.

[0027] The molecular weight of the chelating agent is preferably 200 or less. Because the atomic weight of magnesium is relatively small, using a chelating agent with a large molecular weight may result in a small relative amount of magnesium in the magnesium chelate complex particles, potentially making it difficult to form a refractory and heat-insulating film by thermal spraying. However, using a chelating agent with a molecular weight of 200 or less makes it easier to form a refractory and heat-insulating film more effectively. There is no particular lower limit to the molecular weight of the chelating agent, but for example, it can be 100 or more.

[0028] Furthermore, chelating agents with a valency of 2 are preferred, such as diacetic acid compounds having two carboxyl groups in one molecule. For example, if the chelating agent has a valency of 3, one molecule of the chelating agent can only chelate one magnesium ion, and ammonium ions or the like are used to neutralize the remaining anion. As a result, the hydrophilicity of the magnesium chelate complex particles increases, which may make them sticky and difficult to supply to the thermal spray gun. Tetravalent chelating agents generally cannot chelate two magnesium ions per molecule, and similarly, this may make it difficult to supply the magnesium chelate complex particles to the thermal spray gun. In contrast, a divalent chelating agent chelates one magnesium ion per molecule, and electrically neutral magnesium chelate complex particles can be obtained without using ammonium ions or the like.

[0029] The reaction conditions between the magnesium compound and the chelating agent should be set appropriately to efficiently obtain a magnesium chelate complex. For example, the amounts of magnesium compound and chelating agent used should be set appropriately based on the stoichiometric ratio, and it is preferable to adjust the molar ratio of the magnesium compound to the chelating agent to 0.8 or more and 1.2 or less. The total concentration of the magnesium compound and chelating agent in the reaction solution should be, for example, 5% by mass or more and 50% by mass or less. The reaction temperature and reaction time can also be adjusted appropriately and should be determined by preliminary experiments, but for example, the reaction should be carried out at 10°C or higher and below the boiling point of the solvent for 1 minute or more and 10 hours or less.

[0030] As the solvent for the reaction between the magnesium compound and the chelating agent, an aqueous solvent that has excellent solubility in the starting compound is preferred. An aqueous solvent is a solvent mainly composed of water, or a mixed solvent of water and a water-miscible organic solvent. A water-miscible organic solvent is an organic solvent that is miscible with water without restriction, and examples include alcohol solvents such as methanol, ethanol, and 2-propanol. The proportion of water in the mixed solvent is preferably more than 50% by mass, more preferably 60% by mass or more, 70% by mass or more, or 80% by mass or more, and even more preferably 90% by mass or more, 95% by mass or more, or 98% by mass or more.

[0031] After the reaction is complete, magnesium chelate complex particles can be obtained by concentrating the reaction solution, adding a poor solvent miscible with the aqueous solvent used, or cooling the reaction solution. Furthermore, if necessary, the magnesium chelate complex particles may be further processed by filtering, drying, washing, or recrystallization.

[0032] The resulting magnesium chelate complex particles may be processed to adjust their particle size. For example, the resulting magnesium chelate complex particles may be finened by grinding them using a ball mill, rod mill, hammer mill, etc. Alternatively, coarse particles or excessively fine particles may be removed by sieving, etc., to obtain particles with a narrow particle size distribution and uniform particle size. The magnesium chelate complex particles are preferably spherical or nearly spherical in shape, and preferably have a small aspect ratio. The aspect ratio is preferably 3 or less, and more preferably 2 or less. The aspect ratio can be determined by taking a microscopic photograph of the magnesium chelate complex particles and measuring the ratio of the length in the longitudinal axis direction to the length in the axial direction perpendicular to it.

[0033] The magnesium chelate complex particles introduced into the thermal fluid have a volume-based median diameter (D) determined by laser diffraction and scattering. 50The particle size of the magnesium chelate complex particles is preferably 10 μm or larger, more preferably 15 μm or larger, more preferably 150 μm or smaller, more preferably 100 μm or smaller, and even more preferably 80 μm or smaller. By adjusting the particle size of the magnesium chelate complex particles in this way, blockage in the powder hose that transports the particles becomes less likely, making it easier to stably supply the magnesium chelate complex particles into the thermal fluid, and also allowing the thermal decomposition reaction of the magnesium chelate complex in the thermal fluid to proceed favorably. The magnesium chelate complex particles introduced into the thermal fluid preferably have a certain degree of uniform particle size, and as an indicator of the variation in particle size distribution, the volume-based median diameter is D 50 , cumulative 10% diameter D 10 , cumulative 90% diameter D 90 When that happens, (D 90 -D 10 ) / D 50 The index (coefficient of variation) represented by is preferably 400% or less, more preferably 300% or less, and even more preferably 250% or less.

[0034] In the method for producing a fire-resistant and heat-insulating film according to the present invention, magnesium chelate complex particles are introduced into a thermal fluid and brought into contact with a substrate. The magnesium chelate complex particles introduced into the thermal fluid have their organic chelating agent components removed by thermal decomposition, and the magnesium components remaining after thermal decomposition are oxidized to magnesium oxide. The generated magnesium oxide is then transported by the thermal fluid and collides with the surface of the substrate, causing the magnesium oxide to deposit on the substrate and forming a magnesium oxide film.

[0035] The thermal fluid is not particularly limited as long as it has the temperature necessary for the thermal decomposition and oxidation reactions of the magnesium chelate complex to occur and for magnesium oxide to be produced, and a flow toward the substrate is formed. Preferably, a combustion flame or plasma flame is used as the thermal fluid, which allows for the easy production of magnesium oxide from the magnesium chelate complex and the easy formation of a flow toward the substrate. From the viewpoint of forming the thermal fluid more easily, it is preferable to use a combustion flame as the thermal fluid, and as the combustion flame, it is preferable to use a gas flame formed by the combustion of a combustible gas. The flow of the thermal fluid toward the substrate can be appropriately controlled, for example, by appropriately setting the ejection direction of the combustion gas such as combustible gas, oxygen gas, or air, or plasma, or by appropriately setting the flow of the transport gas for the magnesium chelate complex particles.

[0036] The temperature of the thermal fluid should be at least high enough to thermally decompose the magnesium chelate complex, for example, 500°C or higher. The upper limit of the thermal fluid temperature is not particularly limited, but for example, it can be 5000°C or lower, preferably 3500°C or lower, and more preferably 3000°C or lower. According to the manufacturing method of the present invention, a magnesium oxide film can be formed on the substrate at a lower temperature compared to the case in which magnesium oxide is used as a thermal spray material and heated before thermal spraying.

[0037] The method and apparatus for generating the thermal fluid are not particularly limited as long as they can generate a thermal fluid at the temperature necessary to produce magnesium oxide from the magnesium chelate complex. For example, commonly used thermal spraying methods and thermal fluid generators for thermal spraying apparatuses can be used. That is, it is sufficient that the magnesium chelate complex particles, which are the raw material, can be thermally decomposed by the thermal energy of the thermal spray flame as a thermal fluid. As long as it is possible to heat the magnesium chelate complex to the temperature at which it decomposes, the thermal spraying method and thermal spraying conditions are not particularly limited. Specifically, examples include flame spraying and high-speed gas flame spraying, which form a thermal spray flame as a thermal fluid by burning a gas; plasma spraying and arc spraying, which form a thermal spray flame as a thermal fluid by electrical discharge; and cold spraying, which sprays using a high-speed working gas as a thermal fluid. Among these, flame spraying, which can be implemented at low cost, is more preferred.

[0038] When using flame spraying, the maximum temperature reached by the flame (combustion flame) is approximately 3200°C for acetylene flames and approximately 2700°C for hydrogen flames, which is a sufficient temperature, for example, above 400°C, to decompose the magnesium chelate complex. Furthermore, the flame temperatures for other spraying methods are said to be approximately 2700°C for high-velocity gas flame spraying and approximately 10000°C for plasma spraying, and the magnesium chelate complex can be decomposed by any of these spraying methods. Therefore, by using magnesium chelate complex as a spraying material, the magnesium chelate complex can be easily heated to its decomposition temperature using conventional general spraying methods and conditions, causing thermal decomposition and oxidation to obtain magnesium oxide, which can then be applied to the substrate along the flow of thermal fluid to form a magnesium oxide film on the substrate.

[0039] Figure 1 shows an example of a thermal spray gun that can be used in flame spraying. The thermal spray gun 100 has an oxygen-combustible gas supply channel 1 for supplying oxygen-combustible gas, a transport gas supply channel 2 for supplying a raw material transport gas for transporting magnesium chelate complex particles, a raw material supply channel 3 for supplying magnesium chelate complex particles, and a nozzle 4. The raw material supplied from the raw material supply channel 3 is ejected by the transport gas and introduced into a cylindrical thermal spray flame (flame) 5. The magnesium chelate complex is heated in the thermal spray flame 5, undergoing thermal decomposition and oxidation to produce magnesium oxide. Then, the magnesium oxide particles accelerated by the thermal spray flame 5 collide with the substrate 6 and deposit, forming a magnesium oxide film 7.

[0040] The thermal spray flame is preferably sprayed onto the substrate in the areas where a fire-resistant and heat-insulating film should be formed, so that the film is formed as uniformly as possible. For example, the thermal spray flame can be moved across the substrate at a speed of approximately 1 cm / second or more and 100 cm / second or less. The thermal spray flame may also be sprayed onto the substrate multiple times. For example, the thermal spray flame may be sprayed onto the substrate one to five times.

[0041] When adding metal elements other than magnesium to the refractory heat insulating film according to the present invention, for example, magnesium chelate complex particles may be mixed with complex particles of other metals or organic acid metal salts and subjected to thermal spraying. Alternatively, a porous magnesium oxide film obtained by subjecting magnesium chelate complex particles to thermal spraying may be coated with a liquid containing other metal elements, dried, and then fired. It is preferable to adjust the concentration and amount of such liquid containing other metal elements so as not to reduce the porosity of the porous magnesium oxide film more than necessary.

[0042] The base material is not particularly limited as long as it is a material that constitutes equipment or components exposed to high temperatures, such as internal combustion engines, and on which a fire-resistant and heat-insulating film should be formed. Examples of such materials include aluminum alloys and cast iron. The shape of the base material is also not particularly limited and can be appropriately selected according to the application, such as flat plates, curved plates, tubular shapes, cylindrical shapes, columnar shapes, or spherical shapes.

[0043] In general, in ceramic surface coatings, chemical treatments using acids or alkalis, or surface roughening treatments such as laser processing, electrical discharge machining, or blasting are sometimes performed on the substrate surface as a pretreatment to improve the adhesion between the substrate and the coating film. In the present invention, one or more substrate surface pretreatments may be performed to improve the adhesion between the material surface and the fire-resistant heat-insulating film. [Examples]

[0044] The present invention will be described in more detail below with reference to examples, but the present invention is not limited by the following examples, and it is certainly possible to implement it with appropriate modifications within the scope that is consistent with the spirit of the preceding and following descriptions, and all such modifications are included within the technical scope of the present invention.

[0045] Example 1 (1) Preparation of magnesium chelate complex particles Hydroxyethyliminodiacetic acid (HIDA) was added to water, and then magnesium oxide was added and the mixture was stirred. The precipitated crystals were filtered off and dried at 60°C for 12 hours to obtain Mg-HIDA complex particles.

[0046] (2) Formation of a refractory and heat insulating film by flame spraying Mg-HIDA complex particles were introduced into the flame of a thermal spray gun schematically shown in Figure 1 under the conditions described below. A refractory and heat-insulating film was formed by moving the thermal spray gun back and forth once at a speed of 5 cm / min in the plane perpendicular to the surface, starting from a position where the distance between the blast-processed 5 cm × 5 cm × 10 mm thick Al-Mg aluminum alloy (A5052) substrate and the nozzle tip of the thermal spray gun was 130 mm. Thermal sprayer: "6P-II" manufactured by Sulzer Metco. Raw material powder feeder: "5MP" manufactured by Sulzer Metco. Carrier gas (O2) flow rate: 7.1 L / min Combustion gas (H2) flow rate: 32.5 L / min Combustion gas (O2) flow rate: 43.0 L / min Spraying distance: 130 mm Raw material supply rate: 3 g / min

[0047] (3) Measurement of the average thickness of the refractory heat-insulating film The magnesia-coated substrate obtained in (2) above was cut with a sample cutting machine (“Fine Cut N-7 type” manufactured by Heiwa Kikai Co., Ltd.). The cut surface was polished flat with a cross-section ion polisher (“SM-09010” manufactured by JEOL Ltd.) and observed with a scanning electron microscope (“Hitachi FlexSEM 1000 II” manufactured by Hitachi, Ltd.). The thickness was determined by double-checking using a method of applying a micrometer to four or more locations on the sample and measuring the average, and a method of measuring using a digital film thickness gauge. As a result, the average thickness of the refractory heat-insulating film was 24.3 μm.

[0048] (4) Measurement of the bulk density of the refractory heat-insulating film The volume of the refractory heat-insulating film (5 cm × 5 cm × 24.3 μm) was calculated from the average thickness obtained in (3) above. Also, the mass of the refractory heat-insulating film was 0.0717 g. When the bulk density of the refractory heat-insulating film was determined from the volume and mass, it was 1.18 g / cm 3 .

[0049] (5) Measurement of the porosity of the refractory heat-insulating film Since the theoretical density of magnesia is 3.58 g / cm 3 , the volume of pores in the coating film was calculated from the ratio with the bulk density obtained in (4) above, and the porosity was calculated as the ratio of the pore volume to the volume of the refractory heat-insulating film, and it was 67.0%.

[0050] (6) Measurement of the thermal conductivity On the rotary jig, with the side of the refractory heat-insulating film facing the front side, the aluminum alloy substrate on which the refractory heat-insulating film was formed was fixed, and K-type thermocouples were fixed on the refractory heat-insulating film and the back side of the substrate, respectively. While rotating the jig at a rotational speed of 60 rpm, a flame was emitted from a position where the distance between the substrate and the nozzle tip of the thermal spray gun was 130 mm, under the conditions described below. The temperature on the refractory insulation film and the back side of the substrate was recorded at 10 ms intervals using a high-speed thermocouple temperature logger ("SHTDL4-HiSpeed," manufactured by Syscom). Thermal sprayer: "6P-II" manufactured by Sulzer Metco. Combustion gas (H2) flow rate: 32.5 L / min Combustion gas (O2) flow rate: 43.0 L / min Thermal spray distance: 130mm The temperature on the refractory insulation film rises when a flame is emitted and decreases over time when no flame is emitted. The temperature on the back of the substrate also changes periodically due to the rotation of the rotating jig, but there is a time difference in the temperature change between the refractory insulation film and the back of the substrate. The thermal conductivity was calculated from the measured temperature changes on the refractory insulation film and the back of the substrate using the following formula. For comparison, the aluminum alloy substrate itself, without the refractory insulation film, was also measured in the same way. The thermal conductivity of the refractory insulation film was obtained by dividing the thermal conductivity of the substrate itself by the overall thermal conductivity. The results are shown in Table 1. φ = (Q / P) × 2π α=(d 2 ×f × π) / φ 2 Thermal conductivity k = α × ρ × c [In the formula, φ represents the phase difference between the temperature change on the fire-resistant insulating film and the back of the substrate, Q represents the time difference (s) between the temperature change on the fire-resistant insulating film and the back of the substrate, P represents the period (s) of the temperature change on the fire-resistant insulating film and the back of the substrate, and α is the thermal diffusivity (mm²). 2 ρ represents the sample density (g / cm³), d represents the sample thickness (mm), f represents the frequency (Hz), and ρ represents the sample density (g / cm³). 3 The formula shows the specific heat of the sample [J / (g×K)], and the unit of thermal conductivity k is W / (m·K).

[0051] [Table 1]

[0052] As shown in Table 1, the formation of the fire-resistant heat-insulating film according to the present invention significantly reduced the thermal conductivity. Furthermore, the thermal conductivity of the fire-resistant and heat-insulating film according to the present invention is also very low. For example, the thermal conductivity of magnesium oxide itself at 500°C is 17.68 W / (m·K), but the measured values ​​shown in Table 1 are clearly lower. This is thought to be due to the porous nature of the fire-resistant and heat-insulating film according to the present invention. From the above, it has been revealed that the fire-resistant and heat-insulating film according to the present invention is extremely excellent for being formed on the surface of materials such as internal combustion engines, due to its low conductivity. [Explanation of symbols]

[0053] 1: Oxygen-flammable gas supply line 2: Raw material (magnesium chelate complex particles) transport gas supply path 3: Raw material (magnesium chelate complex particles) supply route 4: Nozzle 5: Thermal spray flame 6: Base material 7: Magnesium oxide film 100: Thermal spray gun

Claims

1. A component in which a fire-resistant and heat-insulating film is formed on the surface of the base material. The aforementioned base material is made of aluminum or an aluminum alloy. The member is characterized in that the fire-resistant heat-insulating film consists solely of magnesium oxide, and the porosity of the fire-resistant heat-insulating film is 50% or more.

2. The member according to claim 1, wherein the porosity is 70% or less.

3. The member according to claim 1 or 2, wherein the average thickness of the fire-resistant heat-insulating film is 20 μm or more and 100 μm or less.

4. A method for manufacturing a fire-resistant and heat-insulating film, The aforementioned fire-resistant heat-insulating film contains magnesium oxide and has a porosity of 50% or more. A method characterized by including the step of introducing magnesium chelate complex particles into a thermal fluid of a hydrogen flame or acetylene flame and applying it to a substrate.

5. The method according to claim 4, wherein the molecular weight of the chelating agent contained in the magnesium chelate complex particles is 200 or less.

6. The method according to claim 4 or 5, wherein the valency of the chelating agent contained in the magnesium chelate complex particles is 2.

7. The method according to any one of claims 4 to 6, wherein the chelating agent contained in the magnesium chelate complex particles is hydroxyethyliminodiacetic acid.

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