HEAT-RESISTANT ELEMENT

Abstract

Heat-resistant element, comprising: Aluminum oxide as a main component, Magnesium aluminate and Boron, where In a case where a surface layer area of ​​the heat-resistant element is a region from a surface of the heat-resistant element to a depth of 0.5 mm and a region deeper than the surface layer area is an inner section, both the surface layer area and the inner section contain the aluminum oxide and the magnesium aluminate, a boron content in the form of B2O3 in the surface layer area is lower than the boron content in the inner section and The percentage of magnesium aluminate at the surface is greater than the percentage of magnesium aluminate in the surface layer area located directly below the surface.

Description

TECHNICAL AREA

[0001] The present disclosure relates to a heat-resistant element. BACKGROUND OF THE INVENTION

[0002] For reasons of insulating properties and heat resistance, ceramics are widely used in heat-resistant elements (see, for example, Patent Document 1). Patent Document 2 discloses a corrosion-resistant element comprising an alumina ceramic containing α-alumina and anorthite. The alumina ceramic contains a total of 0.4 wt% or more Ca and Si, expressed as CaO and SiO₂ respectively, and the mass ratio of CaO / SiO₂ is in the range of 0.5–2. Furthermore, the ratio B / A of the peak strength B of X-ray diffraction at the (004) plane of the anorthite to the peak strength A of the X-ray diffraction at the (104) plane of the α-alumina is 0.01 or more at the surface of the alumina ceramic. QUOTE LIST PATENT LITERATURE

[0003] Patent Document 1: JP 04-132657 A; Patent document 2: WO 2018 / 124024 A1 SUMMARY

[0004] The present invention provides a heat-resistant element according to claim 1 and a heat-resistant element according to claim 3.

[0005] Further embodiments are described in the dependent claims. BRIEF DESCRIPTION OF THE FIGURES Fig. Figure 1 is a schematic perspective view of a heat-resistant element according to one embodiment. Fig. Figure 2 is a table which presents measurement results obtained by X-ray diffraction of a heat-resistant element according to embodiments. Fig. Figure 3 is a SEM image of a surface layer area of ​​part L2. Fig. 4 is an ESMA image in the same position as the REM photo in Fig. 3. Fig. Table 5 is a table which presents ICP analysis results of the surface layer area and an internal section of each air-fired product and reduction-fired product from parts L1 to L4. Fig. Figure 6 is a graph showing a relationship between the bonded boron content and the boron content in a sintered molded part, based on the ICP analysis results presented in Fig. 5 are shown. Fig. Figure 7 is a graph showing a relationship between the surface zone ratio of an AIMg-coexisting-particle section and the associated boron content. Fig. Figure 8 is a graph showing a relationship between the average equivalent circular diameter of the Al-Mg coexisting particles and the associated boron content. Fig. Figure 9 is a graph showing a relationship between the average distance between the gravitational centers of the AlMg-coexisting particles and the bonded boron content. DESCRIPTION OF EXECUTION FORMS

[0006] Modalities (hereinafter referred to as "embodiments") for carrying out a heat-resistant element according to the present disclosure are described in detail with reference to the figures. It should be noted that the embodiments described below are not intended to limit the heat-resistant element according to the present disclosure. Embodiments may be appropriately combined so as not to contradict each other with respect to the scope of work. In the following embodiments, identical sections are designated with the same reference numerals, and duplicate explanations are omitted.

[0007] In the embodiments described below, terms such as "constant," "orthogonal," "vertical," and "parallel" may be used, but these terms need not be exactly "constant," "orthogonal," "vertical," and "parallel." In other words, it is assumed that the above terms allow for variations in manufacturing accuracy, installation accuracy, or the like.

[0008] Fig. Figure 1 is a schematic perspective view of a heat-resistant element according to one embodiment. As shown in Fig. As shown in Figure 1, the heat-resistant element 1 according to the embodiment is, for example, a container which may be hermetically sealed. The shape of the heat-resistant element 1 is not limited to the present example, but can be any shape, such as a plate, a frame, or a column.

[0009] Ceramics are widely used in heat-resistant components for their insulating properties and heat resistance. In some cases, a ceramic heat-resistant component with excellent thermal shock resistance is desirable, such as a ceramic component exposed to high-temperature molten metal, or a component used in the combustion chamber wall of an internal combustion engine or in a fuel injector.

[0010] The heat-resistant element 1 according to one embodiment is made of alumina-based ceramic. When the heat-resistant element 1 is made of an alumina-based ceramic, compared to other ceramics, it exhibits excellent mechanical properties while being relatively inexpensive in terms of both raw material costs and manufacturing costs. An alumina-based ceramic is a material that contains 70 wt.% or more alumina (Al₂O₃) by weight of 100 wt.% of all components that make up the ceramic.

[0011] The material of heat-resistant element 1 can be confirmed, for example, using the following procedure. First, a heat-resistant element 1 to be confirmed is measured using an X-ray diffractometer (XRD), and the obtained value of 2θ (where 2θ represents a diffraction angle) is matched with a JCPDS chart. Next, a quantitative analysis of aluminum (Al) is performed using an intracranial pressure (ICP) emission spectrophotometer or an X-ray fluorescence (XRF) analyzer. Then, if the percentage of aluminum oxide (Al₂O₃), as calculated from the Al percentage measured by ICP or XRF, is 70 wt% or greater, the heat-resistant element 1 is an aluminum oxide-based ceramic.

[0012] The heat-resistant element 1 according to one embodiment contains magnesium aluminate and boron (B).

[0013] Magnesium aluminate is, for example, spinel (MgAl₂O₄). Therefore, magnesium aluminate can have a composition in which the ratios of Mg, Al, and O deviate from the stoichiometric ratios indicated by the chemical formula of spinel (MgAl₂O₄). This means that the composition of magnesium aluminate does not have to perfectly match the stoichiometric ratios given by the chemical formula of spinel, and, for example, unavoidable variations in the ratios of each element can be tolerated. Magnesium aluminate will be referred to simply as "spinel" below.

[0014] In the heat-resistant element 1 according to one embodiment, the percentage of spinel on the surface of the heat-resistant element 1 is greater than the percentage of spinel in the surface layer region located directly beneath the surface. As a result, the heat-resistant element 1 according to this embodiment has excellent thermal shock resistance.

[0015] In the heat-resistant element 1 according to one embodiment, the percentage of spinel in the surface layer region of the heat-resistant element 1 is greater than the percentage of spinel in an inner section. As a result, the heat-resistant element 1 according to this embodiment is further characterized by thermal shock resistance.

[0016] Here, the surface layer region of the heat-resistant element 1 extends from an outer surface of the heat-resistant element 1 to a depth encompassing the surface of the heat-resistant element 1. For example, the surface layer region of the heat-resistant element 1 extends from the outer surface (outermost surface) of the heat-resistant element 1 to a depth of 0.5 mm. The inner section of the heat-resistant element 1 comprises a region described above that is deeper than the surface layer region in the depth direction. For example, the inner section of the heat-resistant element 1 is a region that extends beyond a depth of 0.5 mm from the outer surface of the heat-resistant element 1. Preferably, the inner section of the heat-resistant element 1 is a central region in the depth direction of the heat-resistant element 1.The surface of the heat-resistant element 1 is a region extending from the outermost surface of the heat-resistant element 1 to a depth of a few micrometers. The outer surface of the heat-resistant element 1 is, from the surface of the heat-resistant element 1, a surface in contact with the external atmosphere (that is, an interface with the external atmosphere).

[0017] The reason why the heat-resistant element 1, according to the present embodiment, has superior thermal shock resistance is assumed to be as follows. That is, the thermal conductivity of spinel is lower than that of aluminum oxide. Thus, if the percentage of spinel in the surface layer region of the heat-resistant element 1 is greater than the percentage of spinel in the inner section, the thermal conductivity from the surface layer region of the heat-resistant element 1 to its inner section is suppressed, and therefore an increase in the temperature of the inner section of the heat-resistant element 1 can be suppressed. If the heat-resistant element 1 fractures due to thermal shock, the inner section of the heat-resistant element 1 is likely to be a source of fracture.Therefore, breakage of the heat-resistant element 1 due to thermal shock can be suppressed by suppressing a temperature increase of the inner section of the heat-resistant element 1. In other words, the thermal shock resistance of the heat-resistant element 1 can be improved.

[0018] If the percentage of spinel on the surface of the heat-resistant element 1 is greater than the percentage of spinel in the surface layer region, thermal conductivity from the surface of the heat-resistant element 1 to the surface layer region is suppressed, and thus an increase in the temperature of the surface layer region of the heat-resistant element 1 can be suppressed. A temperature increase in the inner section of the heat-resistant element 1 is also suppressed by suppressing a temperature increase in the surface layer region of the heat-resistant element 1, and therefore fracture of the heat-resistant element 1 due to thermal shock is suppressed. As a result, the thermal shock resistance of the heat-resistant element 1 can be improved.

[0019] The fracture toughness of aluminum oxide is greater than that of spinel, and therefore the mechanical strength of aluminum oxide is high. Accordingly, the mechanical strength of the inner section, which becomes a source of fracture, can be improved by adjusting the percentage of spinel in the inner section of the heat-resistant element 1 to be lower than the percentage of spinel in the surface layer region, or in other words, by adjusting the percentage of aluminum oxide in the inner section of the heat-resistant element 1 to be relatively high. The thermal shock resistance of the heat-resistant element 1 improves when its mechanical strength is increased. Therefore, the heat-resistant element 1 of the embodiment can improve the thermal shock resistance of the heat-resistant element 1.

[0020] Furthermore, the mechanical strength of the inner section, which becomes a source of fracture, can be improved by adjusting the percentage of spinel in the surface layer region of the heat-resistant element 1 to be lower than the percentage of spinel at the surface, or in other words, by increasing the percentage of aluminum oxide in a surface layer region closer to the inner section than at the surface. Therefore, the heat-resistant element 1 of this embodiment can improve the thermal shock resistance of the heat-resistant element 1.

[0021] The correlation between the percentage contents of spinel on the surface, in the surface layer region, and in the inner section of the heat-resistant element 1 can be confirmed, for example, using the following method. First, the surface, the surface layer region, and the inner section of the heat-resistant element 1 are measured using an X-ray diffractometer (XRD).Then, a value A1 / B1 is obtained by dividing an X-ray diffraction maximum intensity A1, which can be assigned to a (311) plane of the spinel in the surface layer region of the heat-resistant element 1, by an X-ray diffraction maximum intensity B1, which can be assigned to a (113) plane of aluminium oxide in the surface layer region of the heat-resistant element 1, and a value A2 / B2 is obtained by dividing an X-ray diffraction maximum intensity A2, which can be assigned to the (311) plane of the spinel in the inner section of the heat-resistant element 1, by an X-ray diffraction maximum intensity B2, which can be assigned to the (113) plane of aluminium oxide in the inner section of the heat-resistant element 1, and the value A1 / B1 is compared with the value A2 / B2.If the comparison result shows that A1 / B1 is greater than A2 / B2, it can be said that the percentage of spinel in the surface layer region of the heat-resistant element 1 is greater than the percentage of spinel in the inner section. A value A3 / B3 is also obtained by dividing an X-ray diffraction maximum intensity A3, which is attributable to the (311) plane of spinel on the surface of the heat-resistant element 1, by an X-ray diffraction maximum intensity B3, which is attributable to the (133) plane of aluminum oxide on the surface of the heat-resistant element 1, and the value A3 / B3 is compared with the value A1 / B1 described above. If the comparison result shows that A3 / B3 is larger than A1 / B1, it can be said that the percentage of spinel on the surface of the heat-resistant element 1 is greater than the percentage of spinel in the surface layer area.

[0022] According to one embodiment, the heat-resistant element 1 also contains anorthite (CaAl₂Si₂O₈). The coefficient of thermal expansion of anorthite is lower than that of aluminum oxide. Therefore, the coefficient of thermal expansion of the heat-resistant element 1 according to this embodiment can be improved by including anorthite.

[0023] The anorthite contained in the element can also improve the corrosion resistance of the heat-resistant element 1 according to the embodiment. During use, the heat-resistant element 1 can be exposed to a corrosive environment, such as nitrous oxide gas, ozone, fluorine-containing gases, and an acidic solution. However, the heat-resistant element 1 of the embodiment remains effective even when used in such corrosive environments.

[0024] The mechanical strength of anorthite is lower than that of aluminum oxide. Therefore, if a large amount of anorthite is contained in the inner section of the heat-resistant element 1, the thermal shock resistance cannot be sufficiently increased. For this reason, the percentage of anorthite is preferably higher in the surface layer region of the heat-resistant element 1 than in the inner section. Thus, in a heat-resistant element 1 according to one embodiment, the percentage of anorthite in the surface layer region is higher than the percentage of anorthite in the inner section.

[0025] For similar reasons to those described above, the percentage of anorthite is preferably higher on the surface of the heat-resistant element 1 than in the surface layer region of the heat-resistant element 1. Thus, in a heat-resistant element 1 according to one embodiment, the percentage of anorthite on the surface of the heat-resistant element 1 is higher than the percentage of anorthite in the surface layer region. Experimental data and analysis methods

[0026] The presence of spinel (MgAl2O4) can be confirmed, for example, by X-ray diffraction analysis. Furthermore, the percentage of spinel in the surface layer region of the heat-resistant element 1, which is greater than the percentage of spinel in the inner section of the heat-resistant element 1, can be analyzed, for example, using the two methods described below. First analytical method: X-ray diffraction

[0027] The first analytical method uses X-ray diffraction to confirm that a value obtained by dividing the maximum intensity of the spinel by the maximum intensity of aluminum oxide is greater at the surface of the heat-resistant element 1 than in the surface layer region of the heat-resistant element 1, and that the value of this is greater at the surface layer region of the heat-resistant element 1 than at the inner section of the heat-resistant element 1.

[0028] Fig. Figure 2 is a table presenting measurement results obtained by X-ray diffraction of the heat-resistant element 1 according to embodiments. In particular, it presents Fig. Figure 2 shows the maximum intensity ratio of anorthite based on aluminum oxide ((maximum intensity of anorthite) / (maximum intensity of aluminum oxide) (%)) and the maximum intensity ratio of spinel based on aluminum oxide ((maximum intensity of spinel) / (maximum intensity of aluminum oxide) (%)) for four types of parts L1 to L4 with different amounts of bonded boron (content in the form of boron trioxide (B₂O₃)). The bonded boron amounts of parts L1 to L4 were 0.4 wt%, 0.9 wt%, 1.5 wt%, and 2.5 wt%, respectively.

[0029] Parts L1 to L4 were fired in a reduction atmosphere. Specifically, the firing duration for parts L1 to L4 was 2 hours. The firing temperature of parts L1 to L4 was 1410°C for part L1, 1390°C for part L2, 1370°C for part L3, and 1350°C for part L4.

[0030] ICP analysis results of the boron amounts in the surface layer region and inner section of parts L1 to L4 are also combined in Fig. Figure 2 illustrates this. Specifically, the boron content in part L1 was 0.15 wt% in the surface layer region and 0.26 wt% in the inner section. The boron content in part L2 was 0.38 wt% in the surface layer region and 0.65 wt% in the inner section. The boron content in part L3 was 0.88 wt% in the surface layer region and 1.31 wt% in the inner section. The boron content in part L4 was 1.70 wt% in the surface layer region and 2.30 wt% in the inner section.

[0031] The shape of the test piece of heat-resistant element 1 was 3 mm x 4 mm x 50 mm after firing. In the XRD measurements, the surface layer of heat-resistant element 1 (an area encompassing the outer surface after firing; only a section of this outer surface down to a depth of 0.5 mm was sampled, collected, and crushed) and the inner section of heat-resistant element 1 (only an inner section deeper than 0.5 mm from the outer surface after firing was sampled, collected, and crushed) were taken as samples. The surface of each test piece was also subjected to XRD measurements. These XRD measurements were performed by irradiating the outer surface of the uncrushed test piece with X-rays.The X-rays shone onto the outer surface of the uncrushed test piece penetrated the test piece to a depth of approximately a few micrometers from its outer surface. Therefore, it can be said that the results obtained through XRD measurements of the test pieces' surfaces reflect a region extending from the outer surface of the test piece to a depth of a few micrometers.

[0032] As in Fig. As shown in Figure 2, the maximum intensity ratio of spinel ((maximum intensity of spinel) / (maximum intensity of aluminum oxide)) was 20 / 100 = 0.20 (-) at the surface, 16 / 100 = 0.16 (-) in the surface layer region, and 13 / 100 = 0.13 (-) in the inner section. From these results, it is clear that the percentage of spinel at the surface is greater than the percentage of spinel in the surface layer region, and that the percentage of spinel in the surface layer region is greater than the percentage of spinel in the inner section. It should be noted that the maximum of aluminum oxide occurs at the (113) plane and the maximum of spinel occurs at the (311) plane.

[0033] The maximum intensity ratio of anorthite ((maximum intensity of anorthite) / (maximum intensity of aluminum oxide)) was 32 / 100 = 0.32 (-) at the surface, 14 / 100 = 0.14 (-) in the surface layer region, and 13 / 100 = 0.13 (-) in the inner section. From these results, it is clear that the percentage of anorthite at the surface is greater than the percentage of anorthite in the surface layer region, and that the percentage of anorthite in the surface layer region is greater than the percentage of anorthite in the inner section. It should be noted that the maximum of aluminum oxide occurs at the (113) level and the maximum of anorthite occurs at the (-204) level.

[0034] It should also be noted that in cases where it is difficult to separate the surface layer region and the inner section of the heat-resistant element 1, a cross-section in a direction perpendicular to the outer surface of the heat-resistant element 1 can be measured using micro-X-ray diffraction. In this case, for the surface layer region, a section of the cross-section extending from the outer surface to a depth of 0.5 mm is measured. For the inner section, a section of the cross-section separated from the outer surface by more than 0.5 mm in the depth direction is measured. The inner section is preferably a section of the cross-section that is furthest from the outer surface in the depth direction. Second analysis method: REM and ESMA

[0035] The second analytical method uses a scanning electron microscope (SEM) and an electron beam microanalyzer (ESMA). This method measures the equivalent circular diameter, the percentage content, and the distance between the gravitational centers of the spinel. It is important to note that the equivalent circular diameter is specifically the equivalent circular diameter of the spinel present in the cross-section of the heat-resistant element 1.

[0036] Fig. Figure 3 is a SEM photograph of a surface layer area of ​​part L2 (bonded boron amount of 0.9 wt.%). Fig. 4 is an ESMA image at the same position as in the SEM photo of Fig. 3 is recorded.

[0037] SEM and ESMA imaging was performed at 3000x magnification using a mirror surface as the viewing surface, the edge of which was polished with a cross-sectional polisher (CP). The ESMA image of Fig. Figure 4 is a composite image showing regions with an abundance of both Al and Mg. In this composite image, the regions with an abundance of both Al and Mg are shown in white.

[0038] Image analysis of the ESMA image shown in FIG. 4 was performed using the image analysis software “A zou kun” (trademark name, available from Asahi Kasei Engineering Corporation; hereafter, the mention of the image analysis software “A zou kun” refers to the image analysis software available from Asahi Kasei Engineering Corporation).

[0039] A technique called "particle analysis" is used to determine the overall proportion of the surface area occupied by individual particles (surface area ratio (%)). In this case, a particle is actually a spinel crystal (MgAl2O4:Al2O3·MgO) within the total measured surface area. A technique called dispersion degree measurement is used to determine the distance between the gravitational centers of the particles.The analysis conditions used in the image analysis software "A zou kun" only require that, for example, the brightness of the particles is set to "bright" (in the case of the ESMA image) or "dark" (in the case of a trace image), the binarization method is set to "automatic", the small-figure removal zone is set to 0.1 µm, the noise removal filter is set to "yes", the binary image correction is set to "linear separation", and the display method is set to "superposition".

[0040] Fig. Table 5 presents ICP analysis results of the surface layer area and the inner section of each air-fired product and reduction-fired product from parts L1 to L4. Fig. Figure 6 is a graph that shows a relationship between the amount of bonded boron and the amount of boron in a sintered molded part based on the values ​​in Fig. The 5 ICP analysis results shown.

[0041] As in Fig. 5 and Fig. As shown in Figure 6, it is clear that the boron content is higher in the surface layer than in the inner section. A value obtained by subtracting the amount of ICP-boron in the surface layer from the amount of ICP-boron in the inner section is 0.1 wt.% or greater. Furthermore, the upper limit of the value obtained by subtracting the amount of ICP-boron in the surface layer from the amount of ICP-boron in the inner section is 0.6 wt.%. If this value is too high, the residual stress within the sintered part can increase and the mechanical strength can decrease.

[0042] If the boron content in the surface layer is equal to or greater than the boron content in the inner section, cracking occurs from the surface layer due to thermal shock applied to the heat-resistant element 1, and the resulting crack propagates easily into the inner section. Conversely, if the boron content in the surface layer is lower than in the inner section, the crack is more likely to originate in the inner section than in the surface layer. Therefore, the thermal impact resistance of the heat-resistant element 1 can be improved by adjusting the boron content in the surface layer to be lower than in the inner section.

[0043] Fig. Figure 7 is a graph showing a relationship between the surface zone ratio (surface zone percent) of the AlMg coexisting particle section and the amount of bonded boron (wt%) based on the ESMA image.

[0044] As in Fig. As shown in Figure 7, it is clear that the surface area ratio of the AlMg coexisting particles, i.e., spinel, in the surface layer region is greater than the surface area ratio of the spinel in the inner section of the heat-resistant element 1. Preferably, the surface area ratio of the spinel is from 9% to 14% in the surface layer region and from 3% to 8% in the inner section. Note that the surface area percentage refers to a volume percent.

[0045] In this way, the occurrence of cracking in the surface layer region can be suppressed by adjusting the surface area ratio of the spinel in the surface layer region to be greater than the surface area ratio of the spinel in the inner section. Therefore, the heat-resistant element 1 can further improve thermal shock resistance.

[0046] Fig. Figure 8 is a graph showing a relationship between the average circular diameter (µm) of AlMg-coexisting particles and the amount of bonded boron (wt%) based on the ESMA image.

[0047] As in Fig. As shown in Figure 8, with the reduction-fired product, the average equivalent circular diameter of the AlMg coexisting particles, or in other words, the average equivalent circular diameter of the spinel, is larger in the surface layer region than the average equivalent circular diameter of the spinel in the inner section. Preferably, the average equivalent circular diameter of the spinel is from 0.8 µm to 2 µm in the surface layer region and from 0.3 µm to 1 µm in the inner section.

[0048] If spinel crystals smaller than those of the surface layer region are present in the inner section, even when a thermal shock is applied to the heat-resistant element 1, the occurrence of cracking from the surface layer region to the inner section can be prevented by the small spinel crystals of the inner section. Therefore, the thermal shock resistance of the heat-resistant element 1 can be further improved by adjusting the average equivalent circular diameter of spinel in the surface layer region to be smaller than the average equivalent circular diameter of spinel in the inner section.

[0049] Fig. Figure 9 is a graph showing a relationship between an average distance (µm) between gravitational centers of the AlMg-coexisting particles and the amount of bonded boron (wt%) based on the ESMA image.

[0050] As in Fig. As shown in Figure 9, the average distance between the gravitational centers of the AlMg coexisting particles, or in other words, the average distance between the gravitational centers of the spinel in the surface layer region, is greater than the average distance between the gravitational centers of the spinel in the inner section. Preferably, the average distance between the gravitational centers of the spinel is between 3 µm and 8 µm. This can further improve the thermal shock resistance. Method for manufacturing heat-resistant element 1

[0051] Next, a method for manufacturing the heat-resistant element 1 is described below. Here, a case is described as an example in which the heat-resistant element 1 is formed from an aluminum oxide-based ceramic.

[0052] Aluminum oxide (Al2O3) powder is prepared as a primary raw material. Silicon oxide (SiO2) powder, calcium carbonate (CaCO3) powder, magnesium carbonate (MgCO3) powder, and boron trioxide (B2O3) powder are prepared as sintering aids.

[0053] The Al₂O₃ powder, the SiO₂ powder, the CaCO₃ powder, and the MgCO₃ powder are mixed so that the Al content in the form of Al₂O₃ ranges from 70 wt% to 92 wt%. The mixing ratio at this time results in the following composition. That is, the Al contained in a temperature shock-resistant container is present in the form of Al₂O₃ from 70 wt% to 92 wt%, and the sum of the values ​​of Si in the form of SiO₂, Ca in the form of CaO, and Mg in the form of MgO ranges from 8.5 wt% to 29 wt%.

[0054] The silicon content in the form of SiO₂ ranges from 4.5 wt% to 17 wt%, the calcium content in the form of CaO ranges from 1 wt% to 9 wt%, and the magnesium content in the form of MgO ranges from 1 wt% to 5 wt%. Furthermore, the borosilicate content in the form of B₂O₃ ranges from 0.5 wt% to 2.5 wt%.

[0055] A first suspension is prepared by adding ion-exchanged water and a dispersing agent to a mixed powder of Al₂O₃ powder, SiO₂ powder, CaCO₃ powder, and MgCO₃ powder, and subjecting the mixture to wet milling using a known method, such as ball milling. The particle size of the powder in the primary suspension is from 1 µm to 3 µm. This particle size is the particle size (D). 50), where, when laser diffraction is used and the volume ratio of particles is summed from the particle size of small particles to the particle size of large particles, the ratio of the cumulative volume of all particles is equal to 50 vol-%.

[0056] A binder is then added to the primary suspension in an amount of 6 parts by weight to 10 parts by weight per 100 parts by weight of a solid content, and the materials are mixed to prepare a secondary suspension.

[0057] The secondary suspension is then spray-dried to produce granules. Subsequently, the produced granules are uniaxially press-molded into a container or similar form to create a compressed powder body.

[0058] The powdered compact is then fired in a hydrogen atmosphere or in a reducing gas containing hydrogen in an amount of 5 to 95 vol%. The firing temperature is such that the maximum temperature is in the range of 1250°C to less than 1500°C, and the firing duration at the maximum temperature is from 10 minutes to 4 hours. The hydrogen-containing gas is preferably an ammonia decomposition gas consisting of 75% hydrogen and 25% nitrogen, because the heat-resistant element 1 is readily produced using such a gas. The boron content in the form of B₂O₃ in the surface layer region of the heat-resistant element 1 can be reduced to less than the boron content in the form of B₂O₃ in the inner section by firing in the reducing gas. At the same time, the spinel content in the surface layer region of the heat-resistant element 1 can be increased to be greater than the spinel content in the inner section.

[0059] The composition after firing is the same as the mixed composition with the exception of B2O3. The B2O3 evaporates during firing (see the graph of the bonded boron content and the ICP boron content: B2O3 (wt%), the data are an average of the entire sintered part).

[0060] As is clear from the manufacturing process described above, the heat-resistant element 1 has an outer surface after firing. However, the entire outer surface of the heat-resistant element 1 need not necessarily be the outer surface after firing. A portion of the outer surface of the heat-resistant element 1 can be treated by polishing or the like. Thermal shock resistance can be improved if at least 80% of the outer surface of the heat-resistant element 1 is configured as the outer surface after firing.

[0061] To produce a heat-resistant element 1 in which the percentage of spinel in the surface layer region is greater than the percentage of spinel in the inner section, the maximum temperature is preferably in the range of 1280°C to less than 1480°C and the firing time at the maximum temperature is from 10 minutes to 2 hours. The same applies to the production of a heat-resistant element 1 in which the percentage of spinel on the surface is greater than the percentage of spinel in the surface layer region.

[0062] To produce a heat-resistant element 1, for which a value A1 / B1 is from 0.1 to 0.22, wherein the value A1 / B1 is obtained by dividing an X-ray diffraction maximum intensity A1, which can be assigned to a (311) plane of the spinel in the surface layer region, by an X-ray diffraction maximum intensity B1, which can be assigned to a (113) plane of aluminum oxide in the surface layer region, and for which a value A2 / B2 is from 0.05 to 0.18, wherein the value A2 / B2 is obtained by dividing an X-ray diffraction maximum intensity A2, which can be assigned to the (311) plane of the spinel in the inner section, by an X-ray diffraction maximum intensity B2, which can be assigned to the (113) plane of aluminum oxide in the inner section, the maximum temperature is in a range from 1330°C to less The temperature is set to 1450°C and the firing duration at the maximum temperature is set from 10 minutes to 2 hours.

[0063] Similarly, in a method for producing a heat-resistant element 1, for which the boron content in the surface layer region of the heat-resistant element 1 is lower by an amount of 0.1 wt.% to 0.8 wt.% than the boron content in the inner section, the maximum temperature is preferably set in a range of 1280°C to less than 1480°C and the firing duration at the maximum temperature is set from 10 minutes to 2 hours.

[0064] Similarly, in a process for producing a heat-resistant element 1, in which the percentage of spinel in the surface layer region of the heat-resistant element 1 is greater than the percentage of spinel in the inner section, and the percentage of spinel in the surface layer region is set from 9 surface zone % to 14 surface zone % and in the inner section from 3 surface zone % to 8 surface zone %, the maximum temperature is set in a range from 1330°C to less than 1420°C, and the firing duration at the maximum temperature is set from 10 minutes to 2 hours.

[0065] In order to obtain an average equivalent circle diameter of the spinel in the inner section of the heat-resistant element 1, which is smaller than the average equivalent circle diameter of the spinel in the surface layer region, wherein the average equivalent circle diameter is from 0.8 µm to 2 µm in the surface layer region and from 0.3 µm to 1 µm in the inner section, the temperature reduction rate during firing is preferably set from 200°C / hour to 800°C / hour.

[0066] To adjust the average distance between gravitational centers of spinel in the surface layer region to a range of 3 µm to 8 µm, the particle size of the powder in the primary suspension is preferably such that the particle size at a cumulative volume ratio of 50%, as measured by laser diffraction, is from 0.7 µm to 1.2 µm.

[0067] To cause the heat-resistant element to contain anorthite, the temperature is preferably maintained at the maximum temperature during firing, after which the temperature is maintained at a constant temperature between 1100°C and 1200°C inclusive for 10 hours or more.

[0068] To increase the percentage of anorthite in the surface layer to a higher level than the percentage of anorthite in the inner section, the temperature is preferably maintained at the maximum temperature and then held at a constant temperature between 1100°C and 1200°C for 20 hours or more. The same applies if the percentage of anorthite at the surface is set to be higher than the percentage of anorthite in the surface layer. EXAMPLES Example 1

[0069] The mixture compositions of parts L2 to L4 described above were as follows. Al2O3: 80 wt.% SiO2: 12.1 wt.%, (B2O3 = 0.9 wt.%) CaO: 5 wt.% MgO: 2 wt.% B2O3: 0.9 wt.%, 1.5 wt.%, 2.5 wt.%

[0070] When the B₂O₃ quantity was increased or decreased by more than 0.9 wt%, the quantities of SiO₂, CaO, and MgO were increased or decreased while maintaining a constant SiO₂ : CaO : MgO ratio. The maximum firing temperature was 1400°C and the firing duration was 2 hours. The reduction atmosphere was N₂ : H₂ = 3 : 1. Temperature shock resistance test

[0071] The sample was a 3 mm x 4 mm x 50 mm sintered part. The sintered part was unpolished, and the sample was used in the test as it was after firing.

[0072] The sample was heated and held at a constant temperature (designated T2 (°C)) for 10 minutes. After being held at T2 (°C), the sample was dropped into water at a temperature of T1 = 25°C. Upon being dropped into the water, the sample was subjected to thermal shock. The dropped sample was then collected and dried, after which the three-point bending strength was measured. At that time, the procedure for measuring the three-point bending strength was the same as the procedure for measuring the three-point bending strength at room temperature (25°C) according to JIS R1601-2008, except that the sample was a 3 mm x 4 mm x 50 mm sintered part (an unpolished, post-firing sample was used as is in the test).The temperature T2 (°C) was increased and a temperature difference (T2 - T1 (°C)) just before the three-point bending strength began to decrease rapidly was used as a temperature with thermal shock resistance.

[0073] The results of the temperature shock resistance test were as follows. Part L2 (compound boron amount of 0.9 wt.%): Temperature shock resistance temperature of 285 °C Part L3 (bonded boron amount of 1.5 wt.%): Temperature shock resistance temperature of 250 °C Part L4 (bonded boron amount of 2.5 wt.%): Temperature shock resistance temperature of 200 °C Example 2

[0074] The mixture composition was modified as follows, and a temperature shock resistance test similar to the one described above was performed. Conditions other than the mixture composition were the same as in Example 1. Al2O3: 89 wt.%, SiO2: 7 wt.% CaO: 1 wt.%, MgO: 2 wt.% B2O3: 1 wt.% Temperature shock resistance temperature: 200°C Example 3

[0075] The mixture composition was modified as follows, the firing temperature was changed to 1450°C, and a temperature shock resistance test similar to the one described above was performed. The other conditions were the same as in Example 1. Al2O3: 92 wt.%, SiO2: 5.5 wt.% CaO: 1.5 wt.%, MgO: 1 wt.% B2O3: 0.5 wt.% Temperature shock resistance temperature: 240°C Example 4

[0076] The mixture composition was modified as follows, the firing temperature was changed to 1350°C, and a temperature shock resistance test similar to the one described above was performed. The other conditions were the same as in Example 1. Al2O3: 77 wt.%, SiO2: 15 wt.% CaO: 4.5 wt.%, MgO: 3 wt.% B2O3: 0.5 wt.% Temperature shock resistance temperature: 200°C Comparative example 1

[0077] The mixture composition of part L1 was as follows. Conditions other than the mixture composition were the same as in Example 1. Al2O3: 80 wt.%, SiO2: 12.6 wt.% CaO: 5 wt.%, MgO: 2 wt.% B2O3: 0.4 wt.% Temperature shock resistance temperature: 193°C Comparative example 2

[0078] The analysis results for part 4, which was produced using air firing, were as follows. Intensity ratio of spinel in the surface layer region ((maximum intensity of spinel) / (maximum intensity of aluminum oxide) (%)): 4.1 Intensity ratio of spinel in the inner section: 8.7 Temperature shock resistance temperature: 193°C

[0079] From the results of Examples 1 to 4 and Comparative Examples 1 and 2, it is clear that the heat-resistant element 1 is preferably produced under at least one condition in which the thermal shock resistance temperature is 200°C or higher.

[0080] As described above, the heat-resistant element according to one embodiment (for example, heat-resistant element 1) contains aluminum oxide as a main component, as well as magnesium aluminate and boron. Additionally, in the heat-resistant element according to this embodiment, the percentage of magnesium aluminate in the surface layer region, which encompasses the surface, is greater than the percentage of magnesium aluminate in an internal section located deeper than the surface layer region. Therefore, the heat-resistant element according to this embodiment exhibits excellent thermal shock resistance. REFERENCE MARK 1 Heat-resistant element

Claims

[1] Heat-resistant element comprising: Aluminum oxide as a main component, Magnesium aluminate and Boron, where In a case where a surface layer area of ​​the heat-resistant element is a region from a surface of the heat-resistant element to a depth of 0.5 mm and a region deeper than the surface layer area is an inner section, both the surface layer area and the inner section contain the aluminum oxide and the magnesium aluminate, a boron content in the form of B2O3 in the surface layer area is lower than the boron content in the inner section and The percentage of magnesium aluminate at the surface is greater than the percentage of magnesium aluminate in the surface layer area located directly below the surface. [2] Heat-resistant element according to claim 1, wherein the percentage of magnesium aluminate in the surface layer area is greater than the percentage of magnesium aluminate in the inner section. [3] Heat-resistant element comprising: Aluminum oxide as a main component, Magnesium aluminate and Boron, where In a case where a surface layer area of ​​the heat-resistant element is a region from a surface of the heat-resistant element to a depth of 0.5 mm and a region deeper than the surface layer area is an inner section, both the surface layer area and the inner section contain the aluminum oxide and the magnesium aluminate, a boron content in the form of B2O3 in the surface layer area is lower than the boron content in the inner section and a percentage of magnesium aluminate in the surface layer area which includes the surface is greater than a percentage of magnesium aluminate in the inner section which is deeper in a depth direction from the surface than the surface layer area. [4] Heat-resistant element according to claim 3, wherein the magnesium aluminate content on the surface of the heat-resistant element is greater than the magnesium aluminate content in the surface layer area. [5] Heat-resistant element according to claim 1 or 2, further comprising anorthite. [6] Heat-resistant element according to claim 5, wherein the percentage of anorthite in the surface layer area is greater than the percentage of anorthite in the inner section. [7] Heat-resistant element according to claim 5 or 6, wherein the percentage of anorthite on the surface of the heat-resistant element is greater than the percentage of anorthite in the surface layer area. [8] Heat-resistant element according to any one of claims 1 to 4, wherein an average equivalent circular diameter of the magnesium aluminate in the surface layer region is larger than an average equivalent circular diameter of the magnesium aluminate at the inner section. [9] Heat-resistant element according to any one of claims 1 to 4, wherein the distance between gravitational centers of the magnesium aluminate in the surface layer region is greater than the distance between gravitational centers of the magnesium aluminate in the inner section. [10] Heat-resistant element according to any one of claims 1 to 5, wherein the magnesium aluminate is spinel (MgAl2O4).

Images