Thermal spray powder

Abstract

To provide a technique to improve the uniformity of components in thermal spray coatings.SOLUTION: Powder for thermal spraying is used to form electrodes for solid oxide fuel cells or solid oxide electrolysis cells. The powder for thermal spraying has a peak in a range of 0.15 μm or more and 1 μm or less in a log differential pore volume distribution with a pore diameter of 1 μm or less obtained by a mercury intrusion method.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] This disclosure relates to powders for thermal spraying. [Background technology]

[0002] Solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs) comprise an air electrode, a fuel electrode, and a solid electrolyte layer. In this regard, the fuel electrode for a solid oxide fuel cell disclosed in Patent Document 1 is a particle mixture of electrolyte material particles with an average particle size D50 of 0.1 to 0.6 μm and nickel oxide particles with an average particle size D50 of 0.5 to 1.5 μm, and is characterized by being obtained by calcining a particle mixture in which the mass ratio of the electrolyte material particles to the nickel oxide particles is 35:65 to 50:50. The same document states that the interfacial resistance between the fuel electrode and the electrolyte can be reduced by the above configuration.

[0003] Furthermore, Patent Document 2 discloses a nickel-ion-conducting ceramic mixed powder used in fuel electrodes. This mixed powder contains metallic nickel particles (A) with a median diameter of 10 nm to 200 nm and ion-conducting ceramic particles (B) with a median diameter of 10 nm to 200 nm. This mixed powder is characterized by a volume ratio of nickel element content to ion-conducting ceramic particle content of [nickel element] / [ion-conducting ceramic particles] = 20 / 80 to 80 / 20. The same document states that it is possible to achieve both high catalytic activity and high conductivity, reduce internal resistance, and improve the operational efficiency as a functional material. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2009-266713 [Patent Document 2] Japanese Patent Publication No. 2021-28417 [Overview of the project] [Problems that the invention aims to solve]

[0005] Incidentally, the fuel electrode is a porous membrane containing ion-conductive ceramic particles and metal particles, with voids formed between the particles (see Patent Documents 1 and 2). In such a fuel electrode, it is required that the ceramic particles, metal particles, and voids be uniformly dispersed.

[0006] In view of these circumstances, the present invention aims to provide a technology for improving the uniformity of components in thermal spray coatings. [Means for solving the problem]

[0007] The thermal spray powder disclosed herein is for forming electrodes for solid oxide fuel cells or solid oxide electrolytic cells. The thermal spray powder has a peak in the range of 0.15 μm to 1 μm in the log differential pore volume distribution obtained by the mercury intrusion method for pores with a diameter of 1 μm or less. By using thermal spray powder with such a configuration, the uniformity of the components in the thermal spray coating can be improved.

[0008] Furthermore, in one preferred embodiment of the thermal spray powder disclosed herein, the thermal spray powder includes composite particles comprising ion-conductive ceramic particles and transition metal compound particles. By using a thermal spray powder with such a configuration, the uniformity of the components in the thermal spray coating can be improved, and conductivity can be imparted to the thermal spray coating.

[0009] In one preferred embodiment of the thermal spray powder disclosed herein, the composite particles have regions where primary particles are in contact with each other and there are no particle interfaces at the contact points. This configuration makes it easier to achieve a desired pore size distribution in the thermal spray powder. As a result, the uniformity of the components in the thermal spray coating can be further improved.

[0010] Furthermore, in another preferred embodiment of the thermal spray powder disclosed herein, the ratio of ceramic particles to transition metal compound particles (ceramic particles:transition metal compound particles) is 60:40 to 20:80. With such a configuration, it is possible to improve the ionic conductivity of the formed thermal spray coating while suppressing the decrease in electrode conductivity. This makes it possible to increase the operating efficiency of SOFC or SOEC.

[0011] Furthermore, in another preferred embodiment of the thermal spray powder disclosed herein, the median diameter (D) based on laser diffraction scattering is used. 50 The particle size is between 10 μm and 100 μm. This configuration can improve the fluidity of the thermal spray powder.

[0012] In another preferred embodiment of the thermal spray powder disclosed herein, the ceramic particles are zirconia particles containing rare earth metal oxides. Such ceramic particles are suitable for realizing the effects of the technology disclosed herein. Alternatively, the transition metal compound particles may be nickel oxide particles. Such transition metal compound particles are suitable for realizing the effects of the technology disclosed herein.

[0013] Furthermore, in another preferred embodiment of the thermal spray powder disclosed herein, when thermal spray powder subjected to a reduction treatment at a processing temperature of 800°C for 2 hours in a hydrogen gas atmosphere is heated from room temperature to 1200°C in an air atmosphere at a heating rate of 10 K / min and thermogravimetric analysis is performed, the temperature at which a 3% weight increase occurs is between 470°C and 570°C. With this configuration, when a thermal spray coating formed from this thermal spray powder is used to form an electrode, the conductivity of the electrode can be increased.

[0014] Furthermore, in another preferred embodiment of the thermal spray powder disclosed herein, the peak is in the range of 0.15 μm to 0.23 μm. With such a configuration, the uniformity of the components in the thermal spray coating can be further improved. [Brief explanation of the drawing]

[0015] [Figure 1] Fig. 1 is a cross-sectional view of SOFC 10. [Figure 2] Fig. 2 is a top-view image of the thermal spraying powder of Example 3. [Figure 3] Fig. 3 is an enlarged image of Fig. 2. [Figure 4] Fig. 4 is a cross-sectional view of the thermal spraying powder of Example 3. [Figure 5] Fig. 5 is a top-view image of the thermal spraying powder of Example 4. [Figure 6] Fig. 6 is an enlarged image of Fig. 5. [Figure 7] Fig. 7 is a cross-sectional view of the thermal spraying powder of Example 4. [Figure 8] Fig. 8 is a top-view image of the thermal spraying powder of the comparative example. [Figure 9] Fig. 9 is an enlarged view of Fig. 8. [Figure 10] Fig. 10 is a cross-sectional view of the thermal spraying powder of the comparative example. [Figure 11] Fig. 11 is a graph showing the log differential pore volume distribution of each example. [Figure 12] Fig. 12 is a graph showing the log differential pore volume distribution of each example. MODE FOR CARRYING OUT THE INVENTION

[0016] Hereinafter, preferred embodiments of the technology disclosed herein will be described. Matters necessary for carrying out the present invention other than those specifically mentioned in the present specification can be understood as design matters for those skilled in the art based on prior art in the relevant field. The technology disclosed herein can be implemented based on the contents disclosed in the present specification and common general technical knowledge in the relevant field. In the specification, unless otherwise specified, the notation "X to Y" indicating a numerical range means "X or more and Y or less", and also means the range of "more than X and less than Y", the range of "more than X and Y or less", and the range of "X or more and less than Y".

[0017] <Definition> In this specification, "thermal spray powder" refers to powdered material used for thermal spraying. In this specification, "composite particle" refers to a particulate matter (a particle in the form of a particle) composed of multiple materials that are mutually bonded together and behave as a single particle. Examples of composite particles include granulated particles and granulated sintered particles composed of at least two or more materials. In this specification, "primary particle" refers to the smallest unit of morphological components constituting the thermal spray powder that can be identified as granular material from its appearance. Therefore, if the composite particles constituting the thermal spray powder disclosed herein include secondary particles, for example, the particles constituting the secondary particles are referred to as primary particles. Here, "secondary particle" refers to a particulate matter in which primary particles are three-dimensionally bonded together and behave as a single particle. Examples of "secondary particles" here include granulated particles and particles that have been sintered after granulation (granulated sintered particles).

[0018] In this specification, "bonding" refers to the direct or indirect bonding of two or more primary particles. Examples of "bonding" include bonding of primary particles by chemical reactions, bonding of primary particles by simple adsorption, bonding utilizing the anchoring effect by embedding adhesives into the irregularities on the surface of primary particles, bonding of primary particles utilizing the attractive effect of static electricity, and bonding in which the surfaces of primary particles melt and become one. Furthermore, with respect to secondary particles composed of two or more materials, "bonding" includes bonding in which one material constitutes a primary particle and the other material melts to fuse the primary particles together. In this specification, "raw material particles" refers to particles that constitute the raw material powder used to produce the thermal spray powder disclosed herein.

[0019] <Method for measuring median diameter> In this specification, "median diameter" with respect to thermal spray powder and primary particles constituting secondary particles (thermal spray powder) refers to the median diameter (D) at 50% of the cumulative value in the volume-based particle size distribution measured by a particle size distribution analyzer based on the laser scattering and diffraction method. 50This refers to the median diameter. For measuring the median diameter, commercially available measuring devices are used, for example.

[0020] Patent documents 1 and 2, mentioned above, list methods such as screen printing and doctor blade methods as means for applying a paste (slurry) containing powder material for electrode formation to a substrate. On the other hand, the inventors wanted to form electrodes by thermal spraying powder material. Thermal spraying is a process in which powder material is melted or semi-molten and sprayed onto the surface of a substrate to form a film, and is completely different from processes such as screen printing and doctor blade methods. For this reason, the inventors investigated the composition of a powder material (thermal spray powder) that is suitable for forming electrodes by thermal spraying and can improve the uniformity of the components in the thermal sprayed film.

[0021] <Composition of thermal spray powder> The thermal spray powder disclosed herein may include, for example, composite particles containing ceramic particles and transition metal compound particles. While the thermal spray powder preferably consists of composite particles containing ceramic particles and transition metal compound particles, it may contain unavoidable impurities originating from the manufacturing process of the ceramic particles, transition metal compound particles, or the composite particles. The proportion of unavoidable impurities relative to the total thermal spray powder is generally 5% by mass or less, preferably 3% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, particularly preferably 0.1% by mass or less, and the closer to 0% by mass, the better.

[0022] Ceramic particles, for example, possess ionic conductivity. In this case, it is preferable that the ceramic particles possess oxide ion conductivity. As the ceramic constituting the ceramic particles, ceramics suitable for this type of application are appropriately selected. Examples of such ceramics include metal oxides. As metal oxides, zirconium oxide (zirconia) and cerium oxide (ceria) are preferably used.

[0023] The zirconium oxide in this context is preferably stabilized zirconia in which one or more stabilizers are dissolved. Note that zirconia in which stabilizers are dissolved means zirconia containing stabilizers. Examples of stabilizers include rare earth metal oxides such as scandium oxide (scandia; Sc2O3), yttrium oxide (yttria; Y2O3), cerium oxide (ceO2), gadolinium oxide (gadolinia; Gd2O3), and ytterbium oxide (Yb2O3); and alkaline earth metal oxides such as calcium oxide (calcia; CaO) and magnesium oxide (magnesia; MgO). Preferably, the ceramic particles are zirconia particles containing rare earth metal oxides. The effects of the technology disclosed herein are better realized when manufacturing electrodes (in this case, fuel electrodes) containing zirconia particles containing rare earth metal oxides as ceramic particles. In particular, scandia-stabilized zirconia particles and yttria-stabilized zirconia can be preferably used.

[0024] In this context, cerium oxide can be doped ceria. Doped ceria are ceria doped with rare earth metal oxides such as yttrium oxide (yttria; Y2O3), samarium oxide (samaria; Sm2O3), and gadolinium oxide (gadolinia; Gd2O3).

[0025] The median diameter of the ceramic particles is not limited as long as the effects of the technology disclosed herein are realized. The median diameter is, for example, 0.01 μm to 5 μm, preferably 0.05 μm to 2.5 μm, more preferably 0.1 μm to 1 μm, and even more preferably 0.1 μm to 0.5 μm. By setting the median diameter of the ceramic particles within the above range, the dispersibility of the ceramic particles in the composite particles can be improved, and consequently, the uniformity of the components in the thermal spray coating can be improved. This can improve the operating efficiency of the SOFC or SOEC.

[0026] Transition metal compounds include substances exhibiting metallic properties, such as alloys, solid solutions, and intermetallic compounds, which consist of a transition metal element with at least one other metallic element or metalloid element, as well as compounds of a transition metal element with a nonmetallic element (e.g., oxides). Examples of transition metal compounds include 3d transition elements such as titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu); metals such as ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), and silver (Ag); alloys such as platinum-palladium alloys and platinum-rhodium alloys; and oxides (transition metal oxides). Other examples include oxides (transition metal oxides) such as cobalt oxide (CoO, Co2O3, Co3O4), copper oxide (CuO, Cu2O), silver oxide (AgO, Ag2O), and tungsten oxide (WO, W2O3, WO3, WO6). Among these, nickel oxide is preferred. Transition metal compound particles become transition metal particles by reduction, for example. Therefore, during the operation of SOFC or SOEC, transition metal compound particles become transition metal particles and exhibit catalytic activity and electronic conductivity. For this reason, it is preferable that the transition metal compound particles are larger than the ceramic particles. For example, the median diameter of the transition metal compound particles should be larger than the median diameter of the ceramic particles. The median diameter of the transition metal compound particles is not limited as long as the effects of the technology disclosed herein are realized. The median diameter is, for example, approximately 0.01 μm to 10 μm, preferably 0.05 μm to 5 μm, more preferably 0.1 μm to 2 μm, and even more preferably 0.1 μm to 1 μm. By setting the median diameter of the transition metal compound particles within the above range, the dispersibility of the transition metal compound particles in the composite particles can be improved, and consequently, the uniformity of the components in the thermal spray coating can be improved. This can improve the conductivity of the electrodes of SOFC or SOEC.

[0027] The mixing ratio (here, mass ratio) of ceramic particles and transition metal compound particles in thermal spray powder can be a factor that affects the performance of SOFC or SOEC, the uniformity of components in the thermal spray coating, etc. From this viewpoint, the mass ratio (ceramic particles:transition metal compound particles) of ceramic particles to transition metal compound particles is preferably, for example, 80:20 to 20:80, or 70:30 to 30:70. In one preferred embodiment, the mass ratio (ceramic particles:transition metal compound particles) is 60:40 to 20:80. When the mass ratio (ceramic particles:transition metal compound particles) of ceramic particles to transition metal compound particles is 80:20 to 20:80, or 70:30 to 30:70, it is possible to improve the conductivity of the electrodes in the formed thermal spray coating while suppressing a decrease in ionic conductivity.

[0028] Composite particles can be particles created by mixing, for example, ceramic particles and transition metal compound particles. Although composite particles contain mutually different materials, the ceramic particles and transition metal compound particles are integrated with each other and behave as a single particle. Therefore, for example, if the ceramic particles and transition metal compound particles are well dispersed in the composite particles, the uniformity of the components in the thermal spray coating can be increased.

[0029] The morphology of the composite particles is not limited as long as the ceramic particles and transition metal compound particles are integrated and the effects of the technology disclosed herein can be realized. The composite particles may be, for example, granulated particles. In this case, granulated particles (secondary particles) can be produced, for example, by mixing ceramic particles (primary particles) and transition metal compound particles (primary particles) with any other component (e.g., binder, solvent, etc.) and granulating the mixture.

[0030] The composite particles are preferably particles in which primary particles are in contact with each other and have regions at the contact points where there are no particle interfaces. The composite particles are preferably sintered particles. Sintered particles can be produced by first creating granulated particles from ceramic particles and transition metal compound particles as described above, and then sintering the granulated particles (such particles are sometimes called granulated sintered particles). In sintered particles, a neck is formed at the contact point between the primary particles of the ceramic particles and the transition metal compound particles by sintering, and the neck grows as solid-phase diffusion progresses at the neck, resulting in a bond that changes from point contact to surface contact. Such a bond is achieved, for example, by the diffusion of at least a portion of the ceramic particles or transition metal compound particles. Preferably, the ceramic particles and transition metal compound particles, which are primary particles, are bonded in a state where there are regions at the contact points where there are no particle interfaces. This, for example, enhances the conductivity of the electrode. Granulated sintered particles have higher strength than granulated particles before sintering. Therefore, by the composite particles being granulated sintered particles, the desired pore size distribution in the thermal spray powder can be realized and maintained more easily. Therefore, by using such granulated sintered particles, it is possible to produce a thermal spray coating with improved uniformity of components.

[0031] The median diameter (D) at 50% integration in the volume-based particle size distribution of the thermal spray powder disclosed herein, based on laser diffraction scattering method. 50 The median diameter is not particularly limited and can be set to a size suitable for the specifications of the equipment used. The median diameter is, for example, 1 μm or more. The larger the median diameter, the better the handling and fluidity of the thermal spray material can be. From this viewpoint, a median diameter of 3 μm or more is appropriate, preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. On the other hand, if the median diameter is too large, there is a concern that the thermal spray powder will not melt sufficiently during thermal spraying. From this viewpoint, the median diameter is, for example, 300 μm or less, preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less.

[0032] Incidentally, when measuring thermal spray powder using the mercury intrusion method, for example, in the log differential pore volume distribution in the range of pore diameters of 1 μm or less, the pore diameter originating from the voids between primary particles (i.e., voids within the composite particles) can be measured. On the other hand, in the log differential pore volume distribution in the range of pore diameters larger than 1 μm, the pore diameter originating from the voids between secondary particles can be measured. Therefore, by analyzing the log differential pore volume distribution in the range of pore diameters of 1 μm or less, it is possible to understand the bonding state (necking state) between ceramic particles and transition metal compound particles in thermal spray powder and the degree of void formation within the composite particles.

[0033] The thermal spray powder disclosed herein preferably has a peak in the range of 0.15 μm to 1 μm in the log differential pore volume distribution for pores with a diameter of 1 μm or less, obtained by the mercury intrusion method. This indicates that the bonding state (necking state) between the ceramic particles and the transition metal compound particles in the composite particles is in a favorable state, and that appropriate voids are formed within the composite particles. Therefore, by thermal spraying the thermal spray powder described above, it is possible to form a thermal spray coating with improved uniformity of components. From this viewpoint, the thermal spray powder preferably has a peak in the range of, for example, 0.15 μm to 0.5 μm, more preferably 0.15 μm to 0.3 μm, and even more preferably 0.15 μm to 0.23 μm, in the log differential pore volume distribution for pores with a diameter of 1 μm or less, obtained by the mercury intrusion method. In this context, "peak" refers to a region in the log differential pore volume distribution (curve) that protrudes and has a high height (a region with high frequency) (see Figure 11). In other words, a "peak" can also be described as the point in the log differential pore volume distribution (curve) where the sign of the slope of the tangent line changes from "+" to "-".

[0034] The mercury intrusion method is a method for determining the pore size distribution of powder by examining the relationship between the pressure applied to infiltrate mercury into the pores of the powder and the amount of mercury injected into the pores. Pore distribution measurement based on the mercury intrusion method is performed, for example, according to JIS R1655:2003 (Test method for pore size distribution of molded fine ceramics by mercury intrusion method). Furthermore, the "log differential pore volume distribution" in this specification is also called the log differential pore size frequency distribution, dV / d(logD) (where D is the diameter of the pore and V is the volume of that pore), and is a commonly used representation of pore distribution for a relatively wide range of pore sizes.

[0035] The log differential pore volume distribution can be constructed from the relationship between the amount of mercury injected (i.e., pore volume) and the change in unit pore diameter (which may be a change in unit pressure) obtained by measuring the pore diameter distribution based on the mercury intrusion method. Specifically, the log differential pore volume distribution can be constructed by dividing the differential pore volume (dV), which is the increase in pore volume, by the difference value d(logD) of the pore diameter treated as a logarithm, and plotting this value against the average pore diameter in each pore diameter region (see Figure 11). In this specification, the peak peaks and other characteristics are determined based on the pore diameter distribution characteristics obtained by measuring the pore diameter distribution by the mercury intrusion method with a measurement range of 0.0036 nm to 1 μm. For example, in the log differential pore volume distribution for thermal spray powder (here, composite particles) disclosed herein, two peaks may be obtained (see Figure 11). The larger diameter peak of the two peaks may be a peak originating from the pores between the composite particles contained in the thermal spray powder. On the other hand, the smaller of the two peaks may be a peak originating from pores in the composite particles. Furthermore, the "peak" in this specification refers to a peak originating from pores in the composite particles, not a peak originating from the gaps between composite particles, and may be the peak with the highest height in the log differential pore volume distribution (curve) for pore diameters of 1 μm or less.

[0036] After the thermal spray powder is sprayed and a thermal spray coating is formed, the thermal spray coating can be subjected to a reduction treatment and used as an electrode for SOFC or SOEC. In this reduction treatment, the transition metal compound components derived from the transition metal compound particles in the thermal spray coating are reduced to transition metal components. Since the transition metal components are the main components that make the electrode conductive, it is preferable that they are not easily oxidized. From this viewpoint, it is preferable that the thermal spray powder disclosed herein is subjected to a reduction treatment in a hydrogen gas atmosphere at a treatment temperature of 800°C for 2 hours, and then heated in an air atmosphere from room temperature (30°C) to 1200°C at a heating rate of 10K / min, and that the temperature at which the weight increases by 3% is 470°C or more and 570°C or less when thermogravimetric analysis is performed. Alternatively, from the viewpoint of realizing the effects of the technology disclosed herein, it is more preferable that the temperature at which the weight increases by 3% is 470°C or more and 520°C or less. Note that "temperature at which the weight increases by 3%" is defined as "3% weight change point" in the test examples described later.

[0037] Here, when the thermal spray powder is subjected to a predetermined reduction treatment, the transition metal compound particles in the thermal spray powder are reduced to transition metal particles. In the thermogravimetric analysis described above, the transition metal particles are oxidized when the thermal spray powder, after the reduction treatment, is heated in an atmospheric environment. This causes an increase in the weight of the thermal spray powder. The fact that the temperature at which the weight of the reduced thermal spray powder increases by 3% in thermogravimetric analysis satisfies the above range indicates that when the thermal spray coating obtained by thermal spraying the thermal spray powder is reduced to become an electrode, the transition metal components in the thermal spray coating are less likely to be oxidized. By using thermal spray powder with this characteristic, the conductivity of the electrode can be further improved.

[0038] <Method for manufacturing thermal spray powder> The thermal spray powder disclosed herein can be prepared, for example, by mixing and compounding ceramic particles and transition metal compound particles as raw material particles with other optional components. In particular, the thermal spray powder is preferably composed of granulated sintered particles in which ceramic particles and transition metal compound particles are mixed. The thermal spray powder is preferably composed of granulated sintered particles as secondary particles, which are formed by mixing, granulating, and further sintering each raw material particle (primary particle), and in which each primary particle is three-dimensionally bonded with gaps between them.

[0039] Granulation and sintering is a method in which raw material particles are granulated into secondary particles, and then sintered to bond (sinter) the raw material particles together. In granulation and sintering, granulation can be carried out by methods such as dry granulation or wet granulation. Examples of granulation methods include rolling granulation, fluidized bed granulation, agitation granulation, crushing granulation, melt granulation, spray granulation, and microemulsion granulation. Among these, spray granulation is considered a preferred granulation method.

[0040] According to the spray granulation method, powder materials can be manufactured, for example, by the following procedure. First, raw material particles containing ceramic particles and transition metal compound particles are prepared, and their surfaces are stabilized with a protective agent or the like as needed. Then, for example, the stabilized raw material particles, along with organic materials such as binders and spacer particles as optional components, are dispersed in a suitable solvent to prepare a spray solution. Here, the raw material particles are dispersed in the solvent using a mixer, disperser, etc., such as a homogenizer or a blade agitator. Then, droplets are formed from the spray solution using an ultrasonic atomizer or the like. The droplets are carried by the airflow and passed through a spray dryer to form granulated particles. The granulated particles thus obtained are introduced into a predetermined firing furnace and fired. This makes it possible to produce a thermal spray material consisting of granulated sintered particles in the form of secondary particles in which primary particles are bonded together with gaps (sintered). Here, the primary particles may have approximately the same dimensions and shape as the raw material particles, or they may be bonded together in a state where they have grown through firing.

[0041] In the above manufacturing process, once the droplets are dry, the raw material particles and binder are in a uniformly mixed state. The raw material particles are bound together by the binder to form mixed particles. When spacer particles are used, the raw material particles and spacer particles are bound together by the binder in a uniformly mixed state to form mixed particles. When these mixed particles are fired, the binder (and spacer particles) disappear (burn through) and the raw material particles are sintered. This forms secondary particles in which primary particles are bonded (sintered) with gaps between them. During sintering, depending on their composition and size, some of the raw material particles may become liquid and contribute to bonding with other particles. Therefore, the median diameter of the primary particles may be larger than that of the starting material particles. The median diameter of the secondary particles, the median diameter of the primary particles, and the size and proportion of the gaps formed between the primary particles can be designed according to the desired form of the secondary particles.

[0042] Furthermore, the concentration of raw material particles in the spray solution is preferably, for example, 10% to 80% by mass. Examples of binders to be added include polyvinyl alcohol (PVA) and carboxymethylcellulose (CMC). Water can be used as the solvent. The amount of binder added is preferably adjusted to a ratio of 0.05% to 10% by mass (for example, 1% to 5% by mass) relative to the mass of the raw material particles.

[0043] Furthermore, in the sintering of granulated particles, the granulated particles are heat-treated (fired) for 1 to 10 hours at a predetermined temperature (generally 600°C to 1600°C (preferably 700°C to 1500°C, more preferably 800°C to 1400°C, and even more preferably 1000°C to 1300°C)) in an air atmosphere; an inert atmosphere such as a nitrogen atmosphere or a noble gas atmosphere; or in a vacuum. The predetermined temperature may be, for example, the set temperature of the firing furnace. The temperature and time when heat-treating the granulated particles can be appropriately set to produce a sprayable powder having the desired pore size distribution. The firing temperature and time can also be appropriately set to achieve the desired median diameter of the sprayable powder, the temperature at which the weight increases by 3% in thermogravimetric analysis in an air atmosphere, etc. Furthermore, after heat treatment, the obtained granulated sintered particles may be crushed and classified as needed.

[0044] <Applications of thermal spray powder> The sprayable powder disclosed herein can be used to produce sprayed coatings on various substrates by spraying it using various spraying methods. The sprayable powder is particularly suitable for producing sprayed coatings using plasma spraying methods such as atmospheric plasma spraying (APS), low-pressure plasma spraying (LPS), and high-pressure plasma spraying. The sprayable powder can also be suitably used in high-velocity flame spraying methods such as high-velocity oxygen flame (HVOF) spraying, warm spray spraying, and high-velocity air flame (HVAF) spraying. The sprayable powder may be supplied to the spraying apparatus in powder form, or in slurry form dispersed in a suitable dispersion medium.

[0045] The sprayable powders disclosed herein are used, for example, to form electrodes for solid oxide fuel cells (SOFCs) or solid oxide electrolytic cells (SOECs). The sprayable powders are preferably used as materials for forming fuel electrodes of SOFCs or SOECs. SOFCs can, for example, extract electricity (electrical energy) from the chemical energy produced by the combustion reaction of hydrogen and oxygen. SOECs can, for example, induce a chemical reaction that produces hydrogen and oxygen from water by applying electrical energy to water (e.g., steam).

[0046] Figure 1 is a cross-sectional view of SOFC10. Figure 1 shows the layered structure of the electrode and solid electrolyte layer in SOFC10. As shown in Figure 1, SOFC10 comprises a fuel electrode 1, an air electrode 2, and a solid electrolyte layer 3. In SOFC10, the fuel electrode 1 is the anode, and the air electrode 2 is the cathode. In this specification, "anode" refers to the electrode from which electrons flow out to the external circuit, and "cathode" refers to the electrode into which electrons flow from the external circuit.

[0047] The fuel electrode 1 is, in this embodiment, an electrode where hydrogen reacts with oxide ions. In this embodiment, the reaction between hydrogen and oxide ions produces water and releases electrons. These electrons generate electricity. As shown in Figure 1, the fuel electrode 1 is provided on one side of the solid electrolyte layer 3. In this embodiment, the fuel electrode 1 is formed by using the thermal spray powder disclosed herein.

[0048] The air electrode 2 is an electrode in which oxygen in the air accepts electrons. In this embodiment, at the air electrode, oxygen in the supplied air accepts electrons released from the fuel electrode 1, and oxide ions are generated. As shown in Figure 1, the air electrode 2 is provided on the other side of the solid electrolyte layer 3 (in Figure 1, the side opposite the forming surface of the fuel electrode 1). Various air electrodes that have been proposed to date may be used as the air electrode 2 without particular limitation. For this reason, the description of the configuration of the air electrode 2 is omitted here.

[0049] The solid electrolyte layer 3 in this embodiment is a layer that has the function of conducting oxide ions. In this embodiment, oxide ions generated at the air electrode 2 are supplied to the fuel electrode 1 by passing through the solid electrolyte layer 3. As shown in Figure 1, the solid electrolyte layer 3 is sandwiched between the fuel electrode 1 and the air electrode 2. Various solid electrolyte layers that have been proposed to date may be used as the solid electrolyte layer 3 without any particular limitations. For this reason, the description of the configuration of the solid electrolyte layer 3 is omitted here.

[0050] A method for manufacturing SOFC10 may include, for example, a preparation step, a lamination step, a thermal spraying step, and a firing step. The preparation step is, for example, a step of preparing a green sheet of the solid electrolyte layer 3. In this step, for example, a green sheet of the solid electrolyte layer 3 may be prepared by coating a slurry for forming the fixed electrolyte layer 3 onto a carrier sheet, molding it to a predetermined shape and dimensions, and drying it. The method of coating the carrier sheet with the slurry for forming the fixed electrolyte layer 3 is not particularly limited, and conventional coating methods such as screen printing and doctor blade methods may be employed.

[0051] The lamination process involves, for example, laminating the green sheet of the air electrode 2 onto one surface of the green sheet of the solid electrolyte layer 3. In this process, for example, a slurry for forming the air electrode 2 is applied to one surface of the green sheet of the solid electrolyte layer 3 (in this case, the surface opposite to the carrier sheet), molded to a predetermined shape and dimensions, and dried, thereby laminating the green sheet of the air electrode 2 onto the green sheet of the solid electrolyte layer 3. Subsequently, the carrier sheet is preferably removed from the green sheet of the solid electrolyte layer 3. The method for applying the slurry for forming the air electrode 2 to the green sheet of the solid electrolyte layer 3 is not particularly limited, and conventional coating methods such as screen printing and doctor blade methods can be employed.

[0052] The thermal spraying process involves, for example, spraying the thermal spraying powder disclosed herein onto the other surface of the green sheet of the solid electrolyte layer 3. In this process, for example, the thermal spraying powder is sprayed onto the green sheet of the solid electrolyte layer 3 on the side opposite to the laminated surface of the green sheet of the air electrode 2. This forms a thermal spray coating of the thermal spraying powder disclosed herein, which will serve as a precursor for the fuel electrode 1.

[0053] The firing process involves firing a laminate of a green sheet of the solid electrolyte layer 3 and a green sheet of the air electrode 2, which are coated with a thermal spray film. This process causes the fuel electrode 1, the air electrode 2, and the solid electrolyte layer 3 to sinter with each other, forming the laminated structure of the fuel electrode 1, the air electrode 2, and the solid electrolyte layer 3 in the SOFC 10.

[0054] As described above, the thermal spray powder disclosed herein is a thermal spray powder for forming electrodes of SOFC or SOEC. The thermal spray powder preferably contains composite particles of ion-conductive ceramic particles and transition metal compound particles. The thermal spray powder preferably has a peak in the range of 0.15 μm to 1 μm in the log differential pore volume distribution obtained by the mercury intrusion method for pores with a diameter of 1 μm or less.

[0055] The thermal spray powder contains ceramic particles and transition metal compound particles in a composite particle state. Therefore, when the thermal spray powder is sprayed, it is possible to suppress the uneven distribution of ceramic components derived from ceramic particles and transition metal compound components derived from transition metal compound particles in the sprayed coating. Furthermore, in the thermal spray powder, a log differential pore volume distribution with a pore diameter of 1 μm or less, obtained by the mercury intrusion method, has a peak in the range of 0.15 μm to 1 μm, thereby achieving a favorable bonding state (necking state) between the ceramic particles and transition metal compound particles. Therefore, by using the thermal spray powder disclosed herein, the uniformity of the components of the thermal spray coating can be improved. In addition, it is thought that by achieving a favorable bonding state within the granules, bonding occurs between the transition metal compound particles, creating a good contact state between the transition metals after reduction treatment. Therefore, it is possible to improve the conductivity of the electrode by efficiently forming electron paths between the transition metals.

[0056] Furthermore, by using the thermal spray powder disclosed herein, it is possible to improve the uniformity of the components in the thermal spray coating, and it is expected that the three-phase interface between the voids, ceramic components (ceramic particles), and transition metal compound components (transition metal compound particles) will be more uniformly dispersed. By forming electrodes (e.g., fuel electrodes) of SOFCs or SOECs from such a thermal spray coating, it is expected that both the power generation efficiency in SOFCs and the hydrogen production efficiency in SOECs will be improved.

[0057] The following describes test examples relating to the present invention, but it is not intended to limit the present invention to those shown in the following test examples. In the following description, unless otherwise specified, the "%" notation refers to a mass basis.

[0058] <Manufacturing example> (Example 1) A starting material was prepared containing yttria-stabilized zirconia (YSZ) particles as ceramic particles, nickel oxide (NiO) particles as transition metal compound particles, polyvinyl alcohol (PVA) as a binder, and water (ion-exchanged water) as a solvent. The median diameter of the YSZ particles was 0.2 μm. The median diameter of the NiO particles was 0.7 μm. The median diameters of the YSZ particles and the NiO particles were determined based on the volume-based particle size distribution measured using a laser diffraction particle size distribution analyzer (Malvern Panalytical, Mastersizer 3000). 50 This refers to the diameter. The median diameter of the YSZ particles and NiO particles was measured under wet dispersion conditions using water, taking into account the dispersion state during particle size distribution measurement of each powder. Furthermore, when the total of YSZ particles and NiO particles was set to 100%, the proportion of YSZ particles was 40%, and the proportion of NiO particles was 60%. Also, when the entire starting material was set to 100%, PVA was 2% and water was 50%.

[0059] Next, a slurry was prepared by mixing and dispersing the starting materials. Granulated particles were produced by spraying this slurry into an airflow using a spray granulator and drying it. Next, the granulated particles were placed in an alumina sagger and fired in an air atmosphere to produce sintered granulated particles. In this firing, the sagger containing the granulated particles was held at a temperature of 950°C for 4 hours. Next, the sintered granulated particles were crushed and classified to obtain a spray powder having a predetermined particle size distribution. This spray powder is referred to as the spray powder of this example.

[0060] (Example 2) The firing temperature for the granulated particles was set to 1040°C. Aside from this, the same materials and procedures as in Example 1 were used to prepare the thermal spray powder for this example.

[0061] (Example 3) The firing temperature for the granulated particles was set to 1200°C. Aside from this, the same materials and procedures as in Example 1 were used to prepare the thermal spray powder for this example.

[0062] (Example 4) The firing temperature for the granulated particles was set to 1300°C. Aside from this, the same materials and procedures as in Example 1 were used to prepare the thermal spray powder for this example.

[0063] (Comparative example) The firing temperature for the granulated particles was set to 200°C. Aside from this, the same materials and procedures as in Example 1 were used to prepare the thermal spray powder for this example.

[0064] [SEM observation] Cross-sectional and plan views were obtained for the thermal spray powders of Examples 1 to 4 and the thermal spray powder of the comparative example using a benchtop SEM (Phenom-World, Phenom ProX). For reference, Figures 2 to 10 show the cross-sectional and plan views of the thermal spray powders as follows. Figure 2 is a plan view of the thermal spray powder of Example 3. Figure 3 is a magnified image of Figure 2. Figure 4 is a cross-sectional view of the thermal spray powder of Example 3. Figure 5 is a plan view of the thermal spray powder of Example 4. Figure 6 is a magnified image of Figure 5. Figure 7 is a cross-sectional view of the thermal spray powder of Example 4. Figure 8 is a plan view of the thermal spray powder of the comparative example. Figure 9 is a magnified view of Figure 8. Figure 10 is a cross-sectional view of the thermal spray powder of the comparative example.

[0065] [Measuring the median diameter] For the thermal spray powders of Examples 1 to 4 and the thermal spray powder of the comparative example, the volume-based particle size distribution was measured using a laser diffraction particle size distribution analyzer (Malvern Panalytical, Mastersizer 3000), and the median diameter was obtained. The results are shown in the "Median Diameter (μm)" column of Table 1. The median diameter of the thermal spray powders was measured under dry dispersion using compressed air, taking into account the dispersion state during particle size distribution measurement of each powder.

[0066] [Pore volume] The pore volume of the thermal spray powders from Examples 1 to 4 and the thermal spray powder from the comparative example was measured using a mercury intrusion porosimeter (Quantachrome, POREMASTER-60). Specifically, the mercury contact angle was 140° and the surface tension was 480 erg / cm². 2 Measurements were performed under the condition of (0.480 N / m). Here, the cumulative pore volume (cc / g) was measured for pores with a diameter of 1 μm or less (specifically, in the range of 0.0036 μm to 0.98 μm). The measurement results are shown in the "Pore Volume (cc / g)" column of Table 1.

[0067] As described above, the cumulative pore volume of pores with a diameter of 1 μm or less was defined as the "pore volume" of each thermal spray powder. Furthermore, the mode diameter (peak top position) of the log differential pore volume distribution was measured within the range of the "pore volume" defined above. The measurement results are shown in the "Peak Top Position (μm)" column of Table 1. Figures 11 and 12 are graphs showing the log differential pore volume distribution for each example. Figure 12 shows an enlarged view of the graph in Figure 11, specifically the range for pores with a diameter of 1 μm or less. In Figures 11 and 12, the X-axis represents "pore diameter (μm)" and the Y-axis represents "Log differential pore volume (cc / g)". The reason why the cumulative pore volume of each thermal spray powder with a pore diameter of 1 μm or less is defined as the "pore volume" is that the pore volume measured in the range of pore diameters larger than 1 μm includes a large amount of voids between particles of the thermal spray powder (in this case, voids between secondary particles).

[0068] [Thermogravimetric analysis] The thermal spray powders of Examples 1 to 4 and the thermal spray powder of the comparative example were subjected to reduction treatment. Thermogravimetric analysis was performed on each thermal spray powder after reduction treatment using a thermogravimetric differential thermal analyzer (Netzsch STA2500 Regulus). Specifically, 37.5 mg ± 2.5 mg of each thermal spray powder that had undergone reduction treatment was placed in an alumina pan, and the weight change of each thermal spray powder was measured when the temperature was raised from room temperature (30°C) to 1200°C at a heating rate of 10 K / min under an atmospheric atmosphere. The temperature at which the weight increased by 3% was defined as the "3% weight change point". The results are shown in Table 1 under "3% weight change point (°C)". In the above reduction treatment, each thermal spray powder was held at a temperature of 800°C for 2 hours under a reducing atmosphere (hydrogen gas atmosphere).

[0069] <Fabrication of thermal spray coatings> Thermal spray coatings were fabricated by atmospheric pressure plasma spraying using the thermal spray powders from Examples 1 to 4 and the thermal spray powder from the comparative example. An aluminum substrate was used as the base material. The thermal spraying conditions were as follows. Thermal sprayer: SG-100 (manufactured by Praxair) Powder dispenser: Model 1264 (Praxair) Plasma working gas: Argon (Ar) gas (50 psi (0.34 MPa)); and, Helium (He) gas (50 psi (0.34 MPa)) Plasma output: 34kW Plasma generation voltage: 37V Plasma generation current: 900A Supply rate of thermal spray powder: 17.5 ± 5 g / min Thermal spray distance (distance from thermal spray gun to substrate): 120 mm Thermal spray gun traverse speed: 400 mm / s

[0070] [Evaluation of component uniformity in thermal spray coatings] The thermal spray coatings prepared as described above were subjected to compositional analysis using SEM and energy-dispersive X-ray spectroscopy (EDS) (Phenom ProX, Phenom-World). Specifically, the following procedures (1) to (7) were performed. (1) A composite of an aluminum substrate and a thermal spray coating was cut to obtain a thermal spray coating of a predetermined size, and a test specimen was obtained. (2) The test specimen was immersed in an aqueous sodium hydroxide solution to dissolve the aluminum substrate and isolate the thermal spray coating. (3) The isolated thermal spray coatings were subjected to a reduction treatment. The conditions for the reduction treatment here are the same as those described in the [Thermogravimetric Analysis] section above. (4) The thermal spray coating after reduction treatment was embedded in epoxy resin, and mechanical polishing and cross-section polishing were performed. (5)(4) The cross-sectional structure of the thermal spray coating was observed and analyzed using SEM and EDS at an observation magnification of 10,000x, within an observation field of view (approximately 27 μm × 27 μm). In addition, one field of view was divided into 16 sections, and the composition of the thermal spray coating in each section was quantified using a Phenom ProX from Phenom-World. Here, the field of view was selected at an arbitrary position in the cross-sectional structure of the thermal spray coating, but the field of view was not selected from the surface side of the thermal spray coating or from the 20 μm region from the substrate side. The procedure in (6)(5) was repeated a total of five times to quantify the composition of the thermal spray coating in an 80-section field of view. (7) The coefficient of variation (standard deviation / mean) was calculated for the quantitative value of Ni atoms in the 80-resolved field of view. The results are shown in the "Coefficient of Variation" column of Table 1. The coefficient of variation is an indicator for evaluating the uniformity of the components in the thermal spray coating. Here, the smaller the coefficient of variation, the better the uniformity of the components.

[0071] [Measurement of electrical conductivity of thermal spray coating] The conductivity of the thermal spray coatings of Examples 1-4 and the comparative example was measured using a low resistivity meter (Loresta GP MCP-T610, manufactured by Mitsubishi Analytec). Specifically, the following procedures (1) to (3) were performed. (1) The thermal spraying powder of each example was thermally sprayed onto an alumina substrate (30 mm × 30 mm × 5 mm) to prepare a thermal sprayed coating of each example. The thermal spraying conditions herein are the same as those described in the above item <Preparation of Thermal Sprayed Coating>. (2) A reduction treatment was performed on the thermal sprayed coating to obtain a measurement sample. The reduction treatment conditions herein are the same as those described in the above item [Thermogravimetric Analysis]. (3) In an environment with an air temperature of 21°C and a relative humidity of 37%, a measurement probe was brought into contact with the sample to measure the electrical conductivity of the sample. The electrical conductivity was measured at three positions for one sample, and the average value was calculated. The results are shown in the "Electrical Conductivity (×10 2 S / cm)" column of Table 1. [Application Characteristics] For the thermal sprayed coatings of Examples 1 to 4 and the thermal sprayed coating of the comparative example, the application characteristics were evaluated. Specifically, a rating of "◎" is given when the value of the coefficient of variation is less than 0.09 and the electrical conductivity value is 3×10 2 S / cm or more, a rating of "〇" is given when the value of the coefficient of variation is 0.09 or more and the electrical conductivity value is 3×10 2 S / cm or more, and a rating of "×" is given when the value of the coefficient of variation is 0.09 or more and the electrical conductivity value is less than 3×10 2 S / cm to evaluate the overall application characteristics.

[0072]

Table 1

[0073] As shown in Table 1, the thermal spray powders of Examples 1 to 4 have a peak in the range of 0.15 μm to 1 μm in the log differential pore volume distribution obtained by the mercury intrusion method for pores with a diameter of 1 μm or less. It was found that using the thermal spray powders of Examples 1 to 4, as shown in Table 1, allows for the production of thermal spray coatings with a smaller coefficient of variation than the thermal spray coatings of the comparative examples (i.e., thermal spray coatings with improved compositional uniformity). Furthermore, the thermal spray coatings produced using the thermal spray powders of Examples 1 to 4 had higher conductivity and superior applicability compared to the thermal spray coatings of the comparative examples. From these findings, it was found that the thermal spray powders of Examples 1 to 4 are suitable as thermal spray powders for forming electrodes (in this case, fuel electrodes) of SOFCs or SOECs.

[0074] The above describes specific examples of the technology disclosed herein, but these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples described above.

[0075] The technologies disclosed herein encompass the inventions relating to items 1 through 9 below. [Item 1] A powder for thermal spraying to form electrodes for solid oxide fuel cells or solid oxide electrolytic cells, A powder for thermal spraying, obtained by mercury intrusion, having a peak in the range of 0.15 μm to 1 μm in the log differential pore volume distribution for pores with a diameter of 1 μm or less. [Item 2] Ion-conducting ceramic particles, Transition metal compound particles and A thermal spray powder as described in item 1, containing composite particles including the above. [Item 3] The composite particles are the thermal spray powder described in item 2, wherein primary particles are in contact with each other and the contact area has a region without a particle interface. [Item 4] The thermal spray powder according to item 2 or 3, wherein the mass ratio of the ceramic particles to the transition metal compound particles (ceramic particles:transition metal compound particles) is 60:40 to 20:80. [Item 5] Median diameter (D) based on laser diffraction scattering method 50 A thermal spray powder described in any one of items 1 to 4, wherein the particle size is between 10 μm and 100 μm. [Item 6] The thermal spray powder according to any one of items 2 to 4, wherein the ceramic particles are zirconia particles containing rare earth metal oxides. [Item 7] The transition metal compound particles are nickel oxide particles, as described in any one of items 2 to 4, for thermal spraying powder. [Item 8] The thermal spray powder described in any one of items 1 to 7, wherein the thermal spray powder, which has been subjected to a reduction treatment at a processing temperature of 800°C for 2 hours in a hydrogen gas atmosphere, is heated from room temperature to 1200°C in an air atmosphere at a heating rate of 10 K / min, and when thermogravimetric analysis is performed, the temperature at which a 3% weight increase occurs is between 470°C and 570°C. [Item 9] The aforementioned peak is in the range of 0.15 μm to 0.23 μm, and is a thermal spray powder according to any one of items 1 to 8. [Explanation of Symbols]

[0076] 1 Fuel electrode 2 Air poles 3 Solid electrolyte layer 10 SOFC

Claims

1. A powder for thermal spraying to form electrodes for solid oxide fuel cells or solid oxide electrolytic cells, In the log differential pore volume distribution obtained by the mercury intrusion method, where the pore diameter is 1 μm or less, there is a peak in the range of 0.15 μm to 1 μm. Ion-conducting ceramic particles, Transition metal compound particles and Includes composite particles containing, A thermal spray powder wherein the mass ratio of the ceramic particles to the transition metal compound particles (ceramic particles:transition metal compound particles) is 60:40 to 20:

80.

2. The thermal spray powder according to claim 1, wherein the composite particles have a region where primary particles are in contact with each other and there is no particle interface at the contact point.

3. Median diameter (D) based on laser diffraction scattering method ５０ The thermal spray powder according to claim 1 or 2, wherein the particle size is 10 μm or more and 100 μm or less.

4. The thermal spray powder according to claim 1 or 2, wherein the ceramic particles are zirconia particles containing rare earth metal oxides.

5. The thermal spray powder according to claim 1 or 2, wherein the transition metal compound particles are nickel oxide particles.

6. The thermal spray powder according to claim 1 or 2, wherein the thermal spray powder, which has been subjected to a reduction treatment at a processing temperature of 800°C for 2 hours in a hydrogen gas atmosphere, is heated from room temperature to 1200°C in an air atmosphere at a heating rate of 10 K / min, and when thermogravimetric analysis is performed, the temperature at which the weight increases by 3% is 470°C or more and 570°C or less.

7. The thermal spray powder according to claim 1 or 2, wherein the peak is in the range of 0.15 μm or more and 0.23 μm or less.

Images