Setter for vacuum firing furnace and vacuum firing method using the same

Abstract

The present invention provides a firing setter that does not affect the workpiece being fired and has little impact on the durability of the fixing jig for the workpiece used in a vacuum furnace, and a vacuum firing method using the same. [Solution] A firing setter that is placed on a carbon jig positioned in a vacuum chamber for firing an object to be fired in a vacuum furnace, and on which the object to be fired is placed, wherein a zirconia layer is laminated on one side of a plate-shaped alumina substrate with an alumina purity of 95% by weight or more. In a vacuum firing method in which an object to be fired is heat-treated at 1300°C or higher using a carbon jig in a vacuum furnace that can be reduced to a vacuum state, the firing setter of the present invention is placed on the carbon jig so that the zirconia layer is in contact with the carbon jig, and the object to be fired is placed on the firing setter and fired.

Description

Technical Field

[0001] The present invention relates to a firing setter used for placing a fired object fired in a vacuum furnace or a vacuum atmosphere furnace into which an inert gas is blown after evacuation, and a vacuum firing method using the same.

Background Art

[0002] Complex-shaped metal parts used in precision machinery, electrical equipment, automotive parts, etc. are usually manufactured by powder metallurgy or metal injection molding (MIM) techniques that mold fine metal powders into a desired shape as raw materials. Powder metallurgy and metal injection molding (MIM) use, as a raw material, a mixture of fine metal powders mixed with a small amount of a resin binder, mold it into a predetermined shape, then degrease it, and fire or sinter it in a vacuum or an inert gas.

[0003] A vacuum furnace used for firing and heat treatment of various alloy products forms a processing chamber (vacuum chamber) surrounded by a heat-resistant insulating wall inside a furnace body having a pressure-resistant and airtight structure, and is configured to heat the fired object loaded into the processing chamber using a heater (for example, JP-A-7-20887). In addition, a vacuum pump for evacuating the inside of the chamber is connected to the processing chamber, and in a vacuum degreasing furnace that also performs a degreasing process, an exhaust pipe for exhausting the internal air is connected.

[0004] From the viewpoint of facilitating the loading and unloading of the fired object into and out of the furnace, it is generally known to place the fired object on a fixed jig such as a mounting table or a setter inside the processing chamber and fire it (for example, JP-A-2001-263957). As the above-mentioned fixed jig, from the viewpoint of being lightweight and excellent in strength and heat resistance, carbon-made fixed jigs such as graphite and carbon fiber reinforced carbon composite materials (C / C composites), mounting shelves, etc. are used.

[0005] On the other hand, when the workpiece is placed directly on a graphite mounting base, high-temperature heating can cause elements in the workpiece (such as nickel and chromium) to react with carbon at the contact points between the mounting base and the workpiece, potentially forming carbides. Fluctuations in the carbon content of the workpiece can affect the quality of the product, such as its strength and hardness.

[0006] To prevent reaction between the fixing jig and the workpiece to be fired, a method is known in which the surface of the fixing jig is coated with zirconia (ZrO2), yttria (Y2O3), or alumina (Al2O3). For example, a firing jig for firing ceramic electronic components fired in an atmospheric furnace is known, which consists of a jig body made of alumina with a bulk density of 1.5 or less, using alumina or mullite fibers, and its surface coated with zirconia stabilized by the addition of yttria (Japanese Patent Publication No. 2-89989). Regarding carbon jigs, a setter for MIM (Metal Injection Molding) has been proposed that is coated with an inorganic coating containing 10% or more by weight of zirconia and a mixture of zirconia-based material and a binder (Japanese Patent Publication No. 6-256078). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 7-20887 [Patent Document 2] Japanese Patent Publication No. 2001-263957 [Patent Document 3] Japanese Patent Publication No. 2-89989 [Patent Document 4] Japanese Patent Publication No. Hei 6-256078 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] While zirconia boasts excellent chemical stability, its coefficient of thermal expansion is greater than that of graphite. This can lead to problems such as cracking or peeling of the coating film in environments where heating and cooling are repeatedly performed. Furthermore, while the effect on the workpiece can be suppressed, it is known that the zirconia coating film itself reacts with workpieces containing transition metals, limiting the repeated use of setters or fixing jigs coated with zirconia (for example, Japanese Patent Application Publication No. 6-219873). For these reasons, there is a need to improve the durability of graphite jigs, mounting bases, and fixing jigs coated with zirconia.

[0009] This invention has been made in view of these circumstances, and its purpose is to provide a firing setter that does not affect the workpiece to be fired and has little impact on the durability of the fixing jig for the workpiece used in a vacuum furnace, and a vacuum firing method using the same. [Means for solving the problem]

[0010] As a fixing jig for firing objects, a mounting platform (mounting shelf) with excellent strength, durability, and heat resistance, and a setter on which the objects to be fired are directly placed, are constructed as separate components. By using these in combination, the graphite mounting platform can be used continuously.

[0011] As a setter material, it is being considered to use an alumina setter, which has excellent heat resistance and chemical stability. Alumina has poor reactivity with the material to be fired and is therefore thought to have no effect on the quality of the fired material during firing. Furthermore, alumina has a higher specific gravity than carbon materials, limiting its use as a fixing jig such as a mounting base. However, when combined with a carbon mounting base, it can be used as a setter for materials several millimeters thick.

[0012] However, a new problem has been pointed out: when an alumina setter is placed on a carbon base, and the object to be fired is placed on top of that, and degreasing and firing are performed in a vacuum furnace, the vacuum furnace becomes more susceptible to contamination, leading to more frequent maintenance.

[0013] The inventors of this invention have conducted various studies on the effects on the furnace when using an alumina setter during degreasing and firing in a vacuum furnace. As a result of our investigation, we found that when the material to be fired was placed on an alumina setter placed on a carbon mounting base and heated to over 1500°C, maintenance problems for the firing furnace (furnace wall, exhaust pipe) arose. Since these problems were not observed when the alumina setter was used in an atmospheric furnace or an inert gas furnace without a carbon mounting base, we concluded that the furnace contamination problem was caused by the combined use of a carbon mounting base and alumina setter in a vacuum furnace, and thus completed the present invention.

[0014] In other words, the alumina setter for vacuum firing furnaces of the present invention has the following configuration. (1) A firing setter which is placed on a carbon jig positioned in a vacuum chamber for firing an object to be fired in a vacuum furnace, and which is used to place the object to be fired on, wherein a zirconia layer is laminated on one side of a plate-shaped alumina substrate with an alumina purity of 95% by weight or more.

[0015] (2) A setter for firing in form (1), wherein the zirconia layer is stabilized zirconia containing at least 3 to 20% by weight of yttria, calcia, magnesia, or ceria, or a mixture of two or more of these, in zirconia. (3) The plate-shaped alumina substrate is a firing setter in form (1) or (2) having a thickness of 0.1 to 8 mm. (4) The plate-shaped alumina substrate is a firing setter of any one of the forms (1) to (3) having a porosity of 0 to 70%. (5) A firing setter of any one of the forms (1) to (4) wherein the zirconia layer has a thickness of 300 μm or less.

[0016] The present invention also includes a vacuum firing method using the firing setter of the present invention. That is, the vacuum firing method of the present invention is a vacuum firing method in which an object to be fired is fired at 1300 ° C or higher using a carbon fixture in a vacuum furnace that can be depressurized to a vacuum state. On the carbon fixture, a firing setter in which a zirconia layer is laminated on one side of a plate-shaped alumina substrate with an alumina purity of 95% by weight or more is placed so that the zirconia layer contacts the carbon fixture, and the object to be fired is placed on the firing setter. And a firing step.

[0017] As a result of various studies on the cause of contamination that occurs when an alumina setter is used in a vacuum furnace, the present inventors considered as follows and completed the above invention.

[0018] When alumina is exposed to a high temperature of 1500 ° C or higher in a vacuum, the following reduction reaction can occur at the contact surface with the carbon mounting table. (1) Al2O3 + C → Al2O2 + CO (2) Al2O3 + 2C → Al2O + 2CO (3) Al2O3 + 3C → Al2 + 3CO

[0019] Since aluminum produced by reduction has a boiling point of about 700 ° C under vacuum, it can evaporate from the alumina setter as aluminum gas in an atmosphere under heating at 1000 ° C or higher under reduced pressure. It was considered that the evaporated aluminum gas adhered to the wall surface of the processing chamber and the wall surface of the exhaust pipe, and became aluminum by cooling and adhered to the wall surface.

[0020] [[ID=es22]]And it was considered that the reduction reaction of alumina can be prevented by coating the contact surface of the alumina setter with the carbon mounting table with stabilized zirconia.

Effect of the Invention

[0021] The firing setter of the present invention can have a stabilized zirconia layer on the contact surface with the carbon mounting base, thus preventing the reduction reaction of alumina even when exposed to a heating atmosphere of 1000°C or higher under reduced pressure. Therefore, the firing setter of the present invention is lightweight, has no effect on the workpiece being fired, and can avoid affecting the vacuum furnace even when used in vacuum firing. [Brief explanation of the drawing]

[0022] [Figure 1] This is a schematic cross-sectional view showing the configuration of a firing setter for one embodiment of the present invention. [Figure 2] This is a schematic diagram illustrating the method of using the firing setter of the present invention. [Figure 3] This is a schematic diagram showing an example of a vacuum furnace configuration. [Figure 4] This is a schematic diagram showing other configuration examples of a vacuum furnace. [Modes for carrying out the invention]

[0023] [Setter for firing] The firing setter according to the present invention is a firing setter that is placed on a carbon jig positioned in a vacuum chamber for firing an object to be fired in a vacuum furnace, and is used by placing the object to be fired on it, and is a firing setter in which a zirconia layer is laminated on one side of a plate-shaped alumina substrate with an alumina purity of 95% by weight or more.

[0024] Figure 1 shows the configuration of a firing setter according to one embodiment of the present invention. The firing setter 10 shown in Figure 1 has a zirconia layer 2 laminated on one side of a plate-shaped alumina substrate 1.

[0025] (1) Alumina substrate The alumina substrate 1 is high-purity alumina (Al2O3) containing 95% or more by weight, preferably 99% or more by weight, and more preferably a sintered body of high-purity alumina containing 99.5% or more by weight, in terms of oxide. From the viewpoint of not reacting with the material to be fired and suppressing its influence on the material to be fired, it is preferable that it does not contain any components other than alumina.

[0026] The size of the alumina substrate 1 depends on the size of the object to be fired, but its thickness is approximately 0.1 to 8 mm, preferably 0.5 to 5 mm. This thickness is sufficient to prevent the carbon fixing jig from affecting the object to be fired. On the other hand, if it becomes too thick, the weight of the firing setter increases, reducing its handling and the ease of loading and unloading the carbon mounting platform.

[0027] Alumina substrate 1 can range from dense (0% porosity) to approximately 70% porosity. It should be selected appropriately depending on the type of material to be fired. If the porosity exceeds 70%, the strength of the alumina substrate 1 itself decreases, and its handling properties deteriorate. The porosity measurement referred to here will be conducted in accordance with JIS R2205.

[0028] Although the alumina substrate 1 was plate-shaped in Figure 1, the present invention is not limited to this. Any shape that can support the object to be fired is acceptable, and it may be a tray-like shape with a surrounding wall around the edge of the plate-like body.

[0029] (2) Zirconia layer The zirconia constituting zirconia layer 2 is obtained by mixing it with stabilizers such as yttria (Y2O3), calcia (CaO), magnesia (MgO), or ceria (CeO2), and causing the zirconia crystal to undergo a phase transition from monoclinic to tetragonal or cubic.

[0030] Zirconia, when used alone, undergoes a phase transition from monoclinic to tetragonal at around 1100°C. This phase transition results in an extremely large volume change of approximately 7%, making its use on its own difficult. However, stabilized zirconia, which is ZrO2 with Y2O3 added as a stabilizer, prevents this volume change and retains zirconia's inherent properties of high melting point, chemical stability, corrosion resistance to metals, and wear resistance.

[0031] Specifically, the material contains 80-97% by weight of zirconia, and at least 3-20% by weight of yttria, calcia (CaO), magnesia (MgO), or ceria (CeO2), and is stabilized by a phase transition. Two or more of the above stabilizing components may be included.

[0032] The zirconia raw material used to form zirconia layer 2 has an average particle size (D 50 Preferably, the stabilized zirconia particles have the above composition and are 1 to 50 μm in size.

[0033] The thickness of the zirconia layer 2 is 300 μm or less, preferably 200 μm or less. If it is too thick, the zirconia layer will be prone to peeling due to repeated firing.

[0034] The zirconia layer 2 described above can be formed by thermal spraying, sputtering, or vapor deposition (CVD, PVD) of zirconia powder; or by applying, drying, or firing a coating agent containing a binder made of zirconia particles and an inorganic polymer. As for the coating method, a zirconia layer can be formed by applying the coating agent onto an alumina substrate using methods such as spraying, dipping, or screen printing, drying it at 200°C, and then firing it at 1500°C.

[0035] The zirconia layer 2 described above is laminated on only one side of the alumina substrate 1. That is, only the contact surface with the carbon jig (described later) becomes a zirconia layer, and no zirconia layer is laminated on the surface on which the workpiece is placed. In other words, the surface on which the workpiece is placed becomes alumina, so it can be used, for example, for vacuum firing of steel, alloys, etc. containing transition metals.

[0036] (3) How to use The firing setter 10 having the above configuration (a firing setter in which a zirconia layer is laminated on one side of an alumina substrate) is used in combination with a carbon fixing jig, as shown in Figure 2. Specifically, the firing setter 10 is placed on the carbon fixing jig 20. At this time, it is placed so that the zirconia layer 2 is in contact with the carbon jig 20. The object to be fired 30 is placed on the side of the firing setter that is not in contact with the carbon jig.

[0037] According to the above method of use, it is believed that the reduction of the alumina setter by carbon at the contact surface with the carbon jig can be suppressed. Specifically, with the firing setter of the present invention, when the firing setter is placed on a carbon fixing jig so that the zirconia layer is in contact with it, and the thermal history of heating at 1400°C for 1 hour under reduced pressure of 200 Pa or less, returning to room temperature and atmospheric pressure, and then heating again at 200 Pa or less and 1400°C for 1 hour is repeated 50 times, the weight loss rate can be suppressed to about 1 / 4 compared to when there is no zirconia layer. For dense materials, it can be suppressed to about 0.1%. Furthermore, while the weight loss rate tends to increase with higher porosity, when the porosity is similar, the presence of a zirconia layer can suppress the weight loss rate to about one-quarter.

[0038] [Carbon fiber fixing jig] The carbon fixing jig 20, used in combination with the firing setter described above, is set inside the vacuum chamber and used as a jig for placing and fixing the object to be fired. In addition to being used as a mounting platform or shelf, it may also be used as a tray for loading and unloading. The shape, size, and structure can be appropriately selected according to the configuration of the firing furnace.

[0039] The carbon material referred to here is lightweight, has excellent heat resistance, mechanical strength, and dimensional stability, and possesses semi-permanent durability against repeated heating and cooling. Specifically, examples include graphite, C / C composite, glassy carbon (non-graphitized carbon obtained by carbonizing thermosetting resin), and porous carbon (porous carbon graphite), of which graphite and C / C composite are preferred.

[0040] [Vacuum firing method] The vacuum firing method of the present invention is a vacuum firing method in which an object to be fired is fired at 1300°C or higher using a carbon jig in a vacuum furnace that can be reduced to a vacuum state, and the method includes the step of placing the aforementioned firing setter of the present invention on the carbon jig so that the zirconia layer is in contact with the carbon jig, and firing the object to be fired with the object placed on the firing setter.

[0041] (1) Vacuum furnace Examples of vacuum furnaces to which the vacuum firing method of the present invention can be applied include conventionally used vacuum furnaces. Figure 3 shows the configuration of an example of a vacuum furnace.

[0042] The vacuum furnace 40 shown in Figure 3 has a double-walled structure consisting of a cylindrical outer cylinder 41 and an inner cylinder 42 made of insulating material, with the inside of the inner cylinder 42 serving as the firing area (processing chamber) 40A. A heater 43 is installed in the inner cylinder 42, and a refrigerant passage 44 is piped between the outer cylinder 41 and the inner cylinder 42. In the vacuum furnace 40 shown in Figure 3, the inner cylinder 42 is composed of double insulating walls 42a and 42b, and the heater 43 is sandwiched between the insulating walls 42a and 42b.

[0043] A carbon fiber fixing jig 21 or a carbon fiber shelf is set in the firing area 40A. The carbon fiber fixing jig 21 may be fixed inside the processing chamber 40A, or it may be configured to be moved in and out. A firing setter 11 is placed on the carbon fiber fixing jig 21, and the object to be fired 31 is placed on top of that.

[0044] An exhaust pipe 45 for exhausting the internal air is connected to the inner cylinder 42 that constitutes the firing area 40A, and is connected to a vacuum pump, thereby allowing the processing chamber to be reduced in pressure or to a vacuum state (1000 Pa or less). Any heater capable of heating to over 2000°C will suffice for heater 43, and carbon heaters are commonly used.

[0045] The vacuum furnace to which the present invention is applied is not limited to a cylindrical processing chamber as shown in Figure 3. For example, a vacuum furnace 50 equipped with a box-shaped processing chamber 50A as shown in Figure 4 may also be used. Furthermore, the carbon fixing jig may be a shelf-type fixing jig 22 equipped with multiple mounting stages.

[0046] In the vacuum furnace 50 shown in Figure 4, an insulating wall 52, formed in a box shape by arranging an insulating material 51a on a retaining material 51 made of metal, is housed within, and the processing chamber 50A is internally defined by being surrounded by the insulating wall 52. In addition, a door 56 that can be opened and closed is provided on one of the side walls of the insulating wall 52. Inside the processing chamber 50A, carbon fiber shelves (three shelves in Figure 4) 22 are arranged as carbon fiber fixing fixtures, which can be moved in and out through the door 56 of the processing chamber 50A. A firing setter 12 is placed on each shelf, and the object to be fired 32 is placed on the firing setter 12. The processing chamber 50A, which is constructed with box-shaped insulated walls, is connected to an exhaust pipe 55 to which a vacuum pump is connected, and is configured to create a vacuum atmosphere inside the processing chamber 50A.

[0047] The vacuum furnace to which the present invention is applied may also be used for heating under an inert gas atmosphere. In this case, an inert gas supply device is connected to the processing chamber. The inert gas supplied by the inert gas supply device may be used as a cooling medium for cooling the workpiece W to be fired. Examples of inert gases include nitrogen (N2) gas, argon (Ar) gas, helium (He) gas, or mixtures thereof.

[0048] Furthermore, the vacuum furnace may also be used as a degreasing furnace. In this case, the exhaust pipe may also be used as a degreasing exhaust pipe if the furnace performs both the degreasing and firing processes in the same furnace.

[0049] (2) Vacuum firing method Next, we will explain a method of vacuum firing using the vacuum furnace described above. First, the processing chamber in the vacuum furnace is opened and the object to be fired is placed in the insulated container. Then, the vacuum furnace is closed to create a vacuum inside. Once a vacuum is reached, the heater is activated to heat the object to be fired. After firing, the object to be fired placed inside the processing chamber can be cooled by flowing a cooling medium between the insulated walls, or by opening the processing chamber and introducing a cooling medium into the processing chamber after a predetermined time has elapsed.

[0050] Heat treatments include firing and sintering. Of these, vacuum firing is particularly suitable. The firing temperature is appropriately selected depending on the type and purpose of the material to be fired.

[0051] The contact surface with the workpiece is a chemically stable alumina sintered body with a high melting point (alumina melting point: 2073°C), and can withstand firing at 1600°C under vacuum. On the other hand, the zirconia coating on the contact surface with the carbon fixing jig has an even higher melting point than alumina, and under reduced pressure, firing at around 2000°C results in almost no reaction with carbon (graphite, C / C composite). Therefore, repeated firing and cooling have little effect on the durability of the carbon fixing jig.

[0052] The vacuum firing method of the present invention can be applied to any workpiece to which vacuum firing is applicable, but it is preferably applied to workpieces made of metal or alloy. In the case of metals (steel) or alloys, the influence of carbon in the fixing jig material tends to be a problem, and furthermore, the degradation of the zirconia film due to trace amounts of transition metals contained in steel or alloys tends to be a problem. However, these problems can be solved by using the firing setter of the present invention.

[0053] The vacuum firing method of the present invention can be used as part of powder metallurgy or MIM (Metal Injection Molding) methods. The Metal Injection Molding (MIM) method is effective for firing metallic materials, particularly stainless steel, where carbon can affect the firing process, and also for firing materials containing trace amounts of transition metals that react with zirconia.

[0054] The firing setter of the present invention, even when used in combination with a carbon fixing jig, can prevent the reduction of alumina due to high-temperature firing, thereby suppressing contamination of the processing chamber and even vacuum piping by aluminum gas in the vacuum furnace. Therefore, when the alumina setter is used as a setter for vacuum furnace firing, the maintenance problems of the equipment caused by the alumina setter can be solved. [Examples]

[0055] [Measurement and evaluation methods] (1) Bulk density of the setter for firing (g / cm³) 3 ), porosity (%) Bulk density and porosity were measured in accordance with JIS R2205. Specifically, a test specimen (sintered body) with a width of 5 mm and a thickness of 2 mm was used as the measurement sample. After being submerged in a water bath and boiled for more than 3 hours, it was allowed to cool to room temperature and was used as the saturated water sample. This saturated water sample was measured while suspended in water by wire, and the value corrected for the mass of the jig was taken as the water mass W2. The saturated water sample was removed from the water, the surface was quickly wiped with damp gauze to remove water droplets, and then measured to obtain the saturated water mass W3. The saturated water sample was dried in a constant temperature oven set to 130°C, allowed to cool to room temperature, and the mass measurement procedure was repeated until a constant weight was reached, which was taken as the dry mass W1.

[0056] Bulk specific gravity (ρ(g / cm³) 3 )) and porosity (P b The percentage (%) was calculated using the following formula. In the formula below, ρ1 is the density of water.

[0057]

number

[0058] (2) Weight reduction rate (%) The prepared firing setter was placed on a carbon graphite tray (300mm x 300mm x 10mm thick) with the zirconia layer facing the carbon tray. In this state, it was placed in a vacuum furnace and heated at 1400°C for 1 hour under reduced pressure of 200 Pa. After returning to room temperature and atmospheric pressure, it was heated again at 1400°C for 1 hour under reduced pressure of 200 Pa. After repeating this heat treatment 50 times, the weight of the firing setter was measured, and the percentage decrease relative to the weight before heating was calculated according to the following formula. Reduction rate (%) = (Weight before heating - Weight after heating) ÷ Weight before heating × 100

[0059] [Preparation and evaluation of firing setters] Example 1: A zirconia layer was formed on one side of a plate-shaped alumina sintered body (60mm x 30mm x 2mm thick, bulk density 3.9) with an alumina purity of 99.8% and 0% porosity, as described below, to create a setter for firing. The zirconia layer is a zirconia-yttria-based zirconia powder containing 92% zirconia by weight, 7.9% yttria by weight, and the remainder being calcia (average particle size D 50 A coating solution containing an inorganic binder (5-6 μm thick) was sprayed onto the surface of an alumina substrate and fired at 1500°C to form a zirconia layer with a thickness of 120 μm. When the weight loss rate due to firing was measured according to the method described above, the weight loss rate was found to be 0.12%.

[0060] Comparative Examples 1-4 The alumina substrate shown in Table 1 was used without forming a zirconia coating. For each firing setter, a heating test similar to that in Example 1 was performed, and the weight loss rate was measured. The results are shown in Table 1.

[0061] [Table 1]

[0062] In firing setters without a zirconia layer, the weight loss rate exceeded 0.4%. Furthermore, the weight loss rate tended to increase with increasing porosity. On the other hand, in the firing setter having a zirconia layer (Example 1), the weight loss rate was reduced to about 1 / 4 compared to the case without a zirconia layer (Comparative Examples 1 and 2). Therefore, it is considered that the impact on the vacuum furnace caused by the firing setter of the present invention can be avoided. [Industrial applicability]

[0063] By using the firing setter of the present invention, it is possible to avoid affecting the workpiece while continuing to use conventionally used vacuum furnaces and carbon fixing jigs, and moreover, it does not introduce new troubles such as contamination of the vacuum furnace or maintenance, making it useful. [Explanation of Symbols]

[0064] 1. Alumina substrate 2 Zirconia layer 10, 11, 12 Setters for vacuum furnace firing 20, 21, 22 Carbon fiber fixing fixtures 30, 31, 32 Object to be fired 40, 50 vacuum furnace 40A, 50A Vacuum Chamber (Processing Chamber)

Claims

1. A firing setter is used by placing the object to be fired on a carbon jig placed inside a vacuum chamber in a vacuum furnace, and the object to be fired is placed on the jig. A firing setter in which a zirconia layer is laminated on one side of a plate-shaped alumina substrate with an alumina purity of 95% by weight or more.

2. The firing setter according to claim 1, wherein the zirconia layer is stabilized zirconia containing at least 3 to 20% by weight of yttria, calcia, magnesia, or ceria, or a mixture of two or more of these.

3. The firing setter according to claim 1, wherein the plate-shaped alumina substrate has a thickness of 0.1 to 8 mm.

4. The firing setter according to claim 1, wherein the plate-shaped alumina substrate has a porosity of 0 to 70%.

5. The firing setter according to claim 1, wherein the zirconia layer has a thickness of 300 μm or less.

6. In a vacuum firing method in which a workpiece is fired at 1300°C or higher using a carbon jig in a vacuum furnace that can be reduced to a vacuum state, A vacuum firing method comprising the step of firing a firing setter, which has a zirconia layer laminated on one side of a plate-shaped alumina substrate with an alumina purity of 95% by weight or more, on a carbon jig, with the zirconia layer in contact with the carbon jig, and firing the object to be fired while it is placed on the firing setter.

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