JP4090335B2 - Corrosion resistant ceramics - Google Patents

Description

【００４８】
【表２】

【００４９】
本発明の試料Ｎｏ．１〜１５は熱衝撃試験による被覆層の剥離も無く曝露試験による減肉量も２μｍ以下であり、耐熱衝撃性、耐食性に優れていることがわかる。
また、表面層に安定化ＺｒＯ_２を用いていない試料Ｎｏ．１６〜１８はいずれも熱衝撃試験で被覆層にクラックが生じ、さらに減肉量が１００μｍ以上となった。
【００５０】
【発明の効果】
本発明の耐食性セラミックスでは、１０００℃以上、特に１０００〜１５００℃の燃焼ガス雰囲気中でも耐水蒸気腐食性が高く、寿命を改善して長時間使用が可能な耐食性セラミックスを実現できる。
【図面の簡単な説明】
【図１】本発明の耐食性セラミックスの断面構造の一例を示す図。
【符号の説明】
１：セラミック基体
２：耐食セラミック層
２ａ，２ｂ：ダイシリケート結晶層
３：表面保護層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a corrosion-resistant ceramic that is suitably used as a high-temperature member, particularly as a heat engine component such as a gas turbine engine component.
[0002]
[Prior art]
Silicon nitride, silicon carbide, and sialon, which are conventionally known as engineering ceramics, are excellent in heat resistance, thermal shock resistance, wear resistance, and oxidation resistance, so that they are particularly suitable for heat engine parts such as gas turbines and turbo rotors. Application is underway.
Such non-oxide ceramics containing silicon generally have high density and high strength properties by adding a sintering aid. For example, Y ₂ O ₃ , Al ₂ O _3, MgO, or the like is added to the silicon nitride powder as a sintering aid and fired to obtain a high-density and high-strength silicon nitride-based sintered body.
Such ceramics can be used in a high temperature range that cannot be used with a metal material of 1000 ° C. or higher. For example, it is possible to realize thermal efficiency that is impossible with a conventional metal material of 40% or higher. It is possible.
[0003]
When these ceramics are used in an internal combustion engine, particularly a gas turbine member, not only high strength but also other characteristics are required to be excellent in a severe environment of high temperature. For example, in a combustion engine such as a gas turbine engine, it is required to be resistant to corrosion by a high-temperature combustion gas stream, or it is necessary to improve wear resistance and impact resistance against collision of fine particles.
[0004]
However, non-oxide ceramics containing silicon react with high-temperature water vapor contained in the gas turbine combustion gas, and as a result, there is a problem that the ceramics are consumed by corrosion due to high-temperature water vapor and the life is short. In particular, parts such as combustor liners, transition ducts, and stationary blades used in gas turbines are exposed to high-temperature combustion gas containing water vapor, and the surface ceramics are significantly consumed.
[0005]
Thus, improvements have been made so far by making an oxidation protective film in addition to various improvements such as examination of sintering aids and grain boundary phases and improvement of firing conditions. For example, an attempt has been made to improve the resistance to high-temperature steam by coating the surface of a sintered body mainly composed of silicon nitride or sialon with a glass layer mainly composed of SiO ₂ (see, for example, Patent Document 1).
Attempts have also been made to improve oxidation resistance, erosion resistance, and corrosion resistance by coating a protective film with CVD, thermal spraying, etc. on alumina, mullite, zirconia, etc. with good oxidation resistance on a silicon nitride-based sintered body. ing.
[0006]
[Patent Document 1]
JP-A-9-183676 [0007]
[Problems to be solved by the invention]
However, as in Patent Document 1, the method of forming a glass layer on the surface has the effect of improving characteristics under static conditions without airflow, but is exposed to high-temperature, high-pressure, high-speed gas in an actual engine. Then, there was a problem that the surface coating layer was rapidly consumed due to the evaporation of the glass, and the life was short and the protective film was not used.
Alumina, mullite and the like have higher corrosion resistance than silicon nitride and the like, but there is a problem that the practicality is insufficient because the corrosion resistance is low and the durability is poor in an atmosphere having a high water vapor partial pressure. Furthermore, although zirconia has high resistance to high-temperature steam, there has been a problem that the surface coating layer peels off due to a difference in thermal expansion from the silicon nitride of the base material.
[0008]
Accordingly, an object of the present invention is to provide a corrosion-resistant ceramic having high corrosion resistance against high-temperature steam and a long life in a high temperature range of 1000 ° C. or higher.
[0009]
[Means for Solving the Problems]
According to the present invention, the ceramic substrate includes a ceramic substrate, a corrosion-resistant ceramic layer provided on the surface of the ceramic substrate, and a surface protective layer provided on the corrosion-resistant ceramic layer. Formed from a plurality of disilicate layers formed from disilicate crystals of Table 3a elements,
The surface protective layer is made of zirconium oxide stabilized with Group 3a element of the periodic table,
Corrosion-resistant ceramics characterized in that each of the thermal expansion coefficients of the ceramic base, the plurality of disilicate layers forming the corrosion-resistant ceramic layer, and the surface protective layer are arranged in an inclined manner from the ceramic base toward the surface protective layer. Provided.
[0010]
In the present invention, a surface protective layer made of stabilized zirconia is provided on the surface of a ceramic substrate via a corrosion-resistant ceramic layer, but a plurality of dies formed by different anti-corrosion ceramic layers formed of different disilicate crystals. It is an important feature that it is formed of a silicate crystal layer, and the thermal expansion coefficient of each layer is set so as to be inclined from the ceramic substrate toward the surface protective layer. That is, by arranging the layers so that the thermal expansion coefficient is inclined in this way, the thermal stress due to the thermal expansion difference between the surface protective layer and the ceramic substrate is effectively relieved, and the surface protective layer is effectively peeled off. As a result, corrosion resistant ceramics that can stably be used as a component that constitutes an internal combustion engine such as a gas turbine engine that operates at a high temperature, in which the characteristics of each layer are stably exhibited, the resistance to high-temperature steam is improved, and the resistance to high-temperature steam is improved. It has been realized.
[0011]
In the present invention, the thickness of the surface protective layer is preferably 5 to 200 μm. By setting the thickness of the surface protective layer within this range, peeling of the surface protective layer due to a difference in thermal expansion from the ceramic substrate can be effectively prevented.
[0012]
Moreover, it is preferable that content of Al and Si is suppressed to 1 mass% or less in the said surface protective layer in total. Stabilized zirconia, in which the content of Al and Si, which are highly consumed by reaction with high-temperature steam, is suppressed to a small amount (1% by mass or less) is resistant to high-temperature steam corrosion and protects the surface of a ceramic substrate such as silicon nitride. Ceramics suitable for gas turbine engine parts and the like can be provided.
[0013]
Furthermore, it is preferable that the surface protective layer is made of columnar crystals, and the major axis of the columnar crystals is substantially perpendicular to the surface of the ceramic substrate. That is, if it has a structure extending in a columnar shape in the surface direction from the interface with the corrosion-resistant ceramic layer, even if the surface protective layer cracks due to thermal stress, this crack occurs at the interface of the columnar crystals, This is because the surface protective layer is held in a state of being attached to the ceramic substrate without being peeled off from the ceramic substrate.
[0014]
The porosity of the surface protective layer described above is preferably 1 to 30%. This is because the stress due to the difference in thermal expansion between the ceramic substrate and the surface protective layer is further relaxed, and the effect of suppressing the peeling of the surface protective layer is enhanced.
[0015]
In the present invention, the porosity of each disilicate crystal layer forming the corrosion-resistant ceramic layer is preferably 5% or less. Thereby, even if the surface protective layer is cracked, the corrosion resistance of the corrosion resistant ceramic layer itself is high, and corrosion of the ceramic substrate can be suppressed.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
As shown in FIG. 1, the corrosion-resistant ceramic of the present invention comprises a ceramic substrate 1, a corrosion-resistant ceramic layer 2 provided on the surface of the ceramic substrate 1, and a surface protective layer 3 provided on the corrosion-resistant ceramic layer 2. It has become.
In the present invention, the group 3a element of the periodic table is used for forming the corrosion-resistant ceramic layer 2 and the surface protective layer 3 described below, and is used if necessary for producing the ceramic substrate 1. Although a compound of Group 3a element of the periodic table is used as a sintering aid, the Group 3a element of the periodic table (hereinafter sometimes referred to as RE) is a so-called rare earth element, Sc, Y, It is an element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
[0017]
(Ceramic substrate 1)
As the ceramic substrate 1, those formed from various ceramic sintered bodies are used. In the present invention, non-oxide ceramic sintered bodies such as metal carbides, nitrides, borides and silicides are used. In particular, a silicon nitride sintered body, a silicon carbide sintered body and a sialon sintered body are suitable.
[0018]
That is, the silicon nitride sintered body, the silicon carbide sintered body, and the sialon sintered body are all excellent in properties such as mechanical strength, but are inferior in corrosion resistance in a high-temperature combustion gas atmosphere. Therefore, by covering these surfaces with a corrosion-resistant ceramic layer 2 and a surface protective layer 3 to be described later, the corrosion resistance can be effectively improved and the life as a high-temperature structural component can be improved. In particular, the silicon nitride sintered body has a high strength from room temperature to high temperature, and is most advantageous for realizing a corrosion-resistant ceramic suitable as a member for a gas turbine.
[0019]
In the ceramic substrate 1, an oxide of a group 3a element of the periodic table (or carbonate, nitrate, etc. capable of forming an oxide by firing) or SiO ₂ is usually used as a sintering aid. You may contain in the quantity of the range which does not impair a characteristic.
[0020]
(Surface protective layer 3)
In the corrosion-resistant ceramic of the present invention, the surface protective layer 3 located on the outermost surface is formed from zirconium oxide (stabilized zirconia) stabilized with Group 3a element of the periodic table. In other words, zirconium oxide undergoes a phase transformation when a temperature change occurs, and at that time, a volume change occurs and a crack is generated. Therefore, stabilization can prevent the generation of a crack.
The surface protective layer 3 made of such stabilized zirconia has a larger coefficient of thermal expansion than the ceramic substrate 1 described above, and more than protective films such as SiO ₂ , Al ₂ O ₃ , mullite, cordierite, and YAG. It exhibits very high stability in an oxidizing atmosphere containing high-temperature steam, and as a result, it is possible to exhibit excellent oxidation resistance and corrosion resistance. In addition, since the melting point is high, there are also advantages of excellent heat resistance and long life at high temperatures.
[0021]
The group 3a element in the periodic table used for stabilizing zirconium oxide is not particularly limited, but is preferably at least one of Y, Er, Yb, and Lu. This is because these elements have small ionic radii, and by stabilizing with these elements, the thermal expansion coefficient becomes relatively small, and peeling of the surface protective layer 3 due to thermal stress can be effectively suppressed.
The content of the Group 3a element in the periodic table may be within a range that stabilizes zirconium oxide and does not significantly affect the corrosion resistance against water vapor, and is particularly 3 to 15 mol%, more preferably 5 to 12 mol%. It is good to be.
[0022]
In the present invention, the thickness of the surface protective layer 3 is preferably 5 to 200 μm, particularly 10 to 150 μm, and more preferably 30 to 100 μm. This is for reducing the difference in thermal expansion to prevent the protective layer 3 from peeling off and prolonging the life of the corrosion-resistant ceramic.
[0023]
Further, the Al and Si contents in the surface protective layer 3 are preferably controlled to be 1% by mass or less, particularly 0.1% by mass or less, and more preferably 0.01% by mass or less. That is, the stabilized zirconia forming the surface protective layer 3 may contain Al or Si, but if the total content exceeds 1% by mass, corrosion in high-temperature steam increases. This is because there is a tendency.
[0024]
Furthermore, the surface protective layer 3 is preferably formed from a columnar crystal of stabilized zirconia, and the long axis of the columnar crystal is preferably substantially perpendicular to the surface of the ceramic substrate. That is, even if a crack occurs in the surface protective layer 3 due to thermal stress, cracks are generated at the interface of the columnar crystals, so that the cracked surface protective layer 3 adhered to the ceramic substrate 1 without peeling off from the ceramic substrate 1. Because it will remain.
[0025]
Furthermore, the porosity of the surface protective layer 3 described above is preferably 1 to 30%, particularly preferably 2 to 15%. This is because even if the fine particles collide with the surface protective layer 3, the generation and progress of cracks are effectively suppressed, and chipping and peeling are suppressed.
[0026]
(Corrosion resistant ceramic layer 2)
In the present invention, the corrosion-resistant ceramic layer 2 formed as an intermediate layer between the ceramic substrate 1 and the surface protective layer 3 is formed of a plurality of layers 2a and 2b made of a disilicate crystal of group 3a element of the periodic table. The elements 3a of the periodic table of the disilicate forming the layers 2a and 2b are different from each other.
These disilicate crystals have the following formula: RE as a group 3a element in the periodic table.
RE ₂ Si ₂ O ₇
By providing a corrosion-resistant ceramic layer 2 made of such a disilicate crystal even if pinholes and cracks are present in the surface protective layer 3, the corrosion resistance against high-temperature water vapor is high and the melting point is high. The influence on the ceramic substrate 1 can be reduced.
[0027]
Moreover, in the present invention, the most important feature is that the corrosion-resistant ceramic layer 2 contains Group 3a elements of the periodic table whose disilicate crystals are different from each other, and heat from each layer toward the surface protective layer 3 from the ceramic substrate 1. The expansion coefficient is arranged so as to be inclined. That is, the thermal expansion coefficient gradually increases in the order of the ceramic substrate 1, the disilicate crystal layers 2a and 2b, and the surface protective layer 3.
Since the number of thermal expansions and slopes changes in an inclined manner as described above, the corrosion-resistant ceramic layer 2 effectively relieves the thermal stress caused by the thermal expansion difference between the ceramic base 1 and the surface protective layer 3. The peeling of the surface protective layer 3 can be effectively prevented, and the life at high temperatures can be extended.
[0028]
In the example shown in FIG. 1, the corrosion-resistant ceramic layer 2 is formed of two disilicate crystal layers 2a and 2b. However, as long as the thermal expansion coefficients are arranged in an inclined manner, three or more disilicate crystal layers are used. Of course, the corrosion-resistant ceramic layer 2 may be formed.
[0029]
In the present invention, the type of disilicate of each disilicate crystal layer 2a, 2b (type of group 3a element in the periodic table) is not particularly limited as long as the thermal expansion coefficient is arranged with an inclination. However, generally, at least one of the disilicate crystal layers 2a and 2b is Er ₂ Si ₂ O ₇ , Yb ₂ Si ₂ O ₇ or Lu ₂ Si ₂ O _{7 in} terms of water vapor resistance at high temperatures. It is preferable that it is formed.
[0030]
The thicknesses of the disilicate crystal layers 2a and 2b forming the corrosion-resistant ceramic layer 2 are 1 to 100 μm, particularly 10 to 70 μm, and 20 to 50 μm, respectively, for thermal stress relaxation, high reliability, and long life. The thickness of the corrosion-resistant ceramic layer 2 formed of a plurality of disilicate crystal layers is preferably in the range of 2 to 500 μm.
[0031]
Furthermore, the porosity of each disilicate crystal layer 2a, 2b is preferably 5% or less, particularly preferably 3% or less. This is because even if pinholes and cracks exist in the surface layer 3, the influence on the ceramic substrate 1 can be reduced.
[0032]
The corrosion-resistant ceramic of the present invention thus configured is particularly excellent in oxidation resistance and corrosion resistance against water vapor, and is suitable for internal combustion engine parts such as gas turbine engine parts such as turbine rotors, nozzles, combustor liners, and transition ducts. Preferably used.
[0033]
(Manufacture of corrosion-resistant ceramics)
The corrosion-resistant ceramics described above can be manufactured, for example, by the following method.
[0034]
First, a ceramic substrate made of silicon nitride ceramic or the like is prepared. The ceramic substrate is preferably a sintered body in terms of cost, and may contain a sintering aid as already described. A silicon nitride sintered body containing 5 to 10 mol% and 1 to 20 mol% of silicon dioxide can be used.
[0035]
A plurality of disilicate (RE ₂ Si ₂ O ₇ ) crystal layers containing Group 3a elements of the periodic table are provided on the surface of the ceramic substrate to form a corrosion-resistant ceramic layer.
For example, a slurry is prepared by dispersing a powder represented by RE ₂ Si ₂ O ₇ or a mixed powder obtained by mixing RE ₂ O ₃ powder and SiO ₂ powder in a predetermined ratio in a predetermined solvent or dispersant. Then, the slurry is sequentially applied to the surface of the ceramic substrate and heat-treated at a high temperature of 1400 ° C. or higher, whereby the corrosion-resistant ceramic layer composed of the plurality of disilicate crystal layers described above can be produced. For the application, a spray method in which slurry is sprayed, a dipping method in which the slurry is immersed in the slurry, or the like can be employed. In order to form the slurry uniformly on the surface of the ceramic substrate, the viscosity of the slurry is preferably 0.5 to 3.0 Pa · s.
[0036]
As described above, the corrosion-resistant ceramic layer can be formed inexpensively and with good adhesion by using a coating method in which slurry is sequentially applied to the surface of the ceramic substrate and heat-treated, but other methods such as plasma spraying, CVD, PVD, etc. It is also possible to form with the existing film-forming technique.
[0037]
Next, a surface protective layer made of stabilized zirconia is formed on the corrosion-resistant ceramic layer.
As starting materials for forming the surface protective layer, zirconium oxide powder of high purity (99.9% or more) and Group 3a element oxide (RE ₂ O ₃ ) powder of the periodic table are used. Moreover, you may use the stabilized zirconia powder already stabilized with the periodic table group 3a element oxide. In any case, the total content of Al and Si in the raw material powder is preferably 1% by mass or less.
[0038]
These raw material powders are mixed with a solvent and a dispersant to prepare a slurry. This slurry is applied to the surface of the ceramic substrate having the corrosion-resistant ceramic layer and dried to form a coating layer. As with the formation of the corrosion-resistant ceramic layer, a spray method, a dipping method, or the like can be employed for application. Moreover, in order to form a slurry uniformly on the surface of a corrosion-resistant ceramic layer, the viscosity of the slurry is preferably 0.5 to 3.0 Pa · s.
[0039]
Next, heat treatment can be performed to form a surface protective layer. The heat treatment temperature is desirably 1300 ° C. to 1600 ° C., particularly 1350 to 1550 ° C., more preferably 1400 to 1500 ° C., in order to sufficiently densify the surface protective layer.
[0040]
As described above, the surface protective layer can be formed at low cost and with good adhesion by slurry coating and heat treatment. In addition, the surface protective layer is formed by existing film forming techniques such as plasma spraying, CVD, and PVD. It is also possible to do.
In order to form a columnar crystal, it is preferable to use a CVD method and a PVD method, and it is particularly preferable to use an EB-PVD (Electron Beam Phisical Vapor Deposition) method.
Furthermore, in order to control the porosity to 1 to 30%, the heat treatment temperature may be controlled. For example, when the surface protective layer is formed by a coating method using a stabilized zirconia powder having an amount of Y ₂ O ₃ of 8% by mass, the heat treatment temperature may be adjusted in the range of 1300 to 1600 ° C. In addition, the porosity can be adjusted by changing the stabilizer content and the heat treatment time.
[0041]
By such a manufacturing method, surface protection with a low content of Al and Si, zirconium oxide stabilized with Group 3a element of the periodic table, especially porosity of 5-30% and thickness of 5-200 μm The corrosion-resistant ceramic of the present invention having a layer can be produced. Furthermore, it is possible to form a surface protective layer having columnar crystals whose major axis is substantially perpendicular to the surface of the ceramic substrate.
[0042]
【Example】
Experimental example 1
A silicon nitride sintered body was prepared as a ceramic substrate. The silicon nitride sintered body is fired by adding 3 mol% of lutetium oxide and 6 mol% of silicon dioxide as a sintering aid.
These ceramic substrates were processed into a shape having a length of 4 mm, a width of 40 mm, and a thickness of 3 mm.
[0043]
A corrosion-resistant ceramic layer was formed on the surface of the ceramic substrate. That is, a slurry made of a disilicate powder of a group 3a element of the periodic table having the smallest thermal expansion coefficient closest to the ceramic substrate is applied by spraying to the surface of the ceramic substrate with a spray gun, and after drying at a temperature of 1650 ° C. for 10 minutes. The first corrosion-resistant ceramic layer was formed by performing the heat treatment.
Next, a slurry made of a disilicate powder of Group 3a element of the periodic table having a thermal expansion coefficient lower than that of the first corrosion-resistant ceramic layer and higher than that of the surface protective layer to be formed below is sprayed. The surface of the ceramic substrate was sprayed and applied with a gun, and after drying, heat treatment was performed at a temperature of 1600 ° C. for 10 minutes to form a second corrosion-resistant ceramic layer. Further, a third corrosion-resistant ceramic layer was formed by the same method as desired.
[0044]
ZrO ₂ powder with a purity of 99.9%, Y ₂ O ₃ powder with a purity of 99.9%, Lu ₂ O ₃ powder, Yb ₂ O ₃ powder, Er ₂ O ₃ powder, Sm ₂ O ₃ powder and Sc ₂ O ₃ The powder was weighed so as to have the composition shown in Table 1, and water and a binder (PVA) were added thereto and mixed with a zirconium oxide ball for 24 hours by a rotary mill to prepare a slurry.
For comparison (Sample Nos. 16 to 18), a slurry was prepared in the same manner using 99.9% pure Al ₂ O ₃ powder, mullite (MU) powder, and cordierite (CJ) powder. did.
The obtained slurry was applied to the surface of the ceramic substrate by spraying with a spray gun and dried in a dryer at 120 ° C. The obtained sample was heat-treated in air under the conditions shown in Table 1 to prepare a surface protective layer.
[0045]
Sample No. No. 12 formed a surface layer made of stabilized zirconia by the EB-PVD method.
Sample No. For comparison, 19 was evaluated without forming a corrosion-resistant ceramic layer and a surface protective layer on a ceramic substrate made of a silicon nitride-based sintered body.
[0046]
The evaluation was conducted by a thermal shock test and an exposure test. In addition, the thermal shock test was carried out 100 cycles under the conditions of 1300 ° C. to 300 ° C., and the presence of cracks in the surface layer was observed using a fluorescent flaw detection liquid penetration method.
In the exposure test, a sample was placed on an exposure test apparatus, methane gas was combusted, and combustion gas was sprayed onto the sample at a flow rate shown in Table 2.
[0047]
[Table 1]

[0048]
[Table 2]

[0049]
Sample No. of the present invention. Nos. 1 to 15 show no exfoliation of the coating layer by the thermal shock test, and the amount of thinning by the exposure test is 2 μm or less, which indicates that the thermal shock resistance and corrosion resistance are excellent.
Sample No. which does not use stabilized ZrO ₂ for the surface layer. In all of Nos. 16 to 18, cracks were generated in the coating layer in the thermal shock test, and the thickness reduction was 100 μm or more.
[0050]
【The invention's effect】
With the corrosion-resistant ceramic of the present invention, it is possible to realize a corrosion-resistant ceramic that has high steam corrosion resistance even in a combustion gas atmosphere of 1000 ° C. or higher, particularly 1000 to 1500 ° C., and that can be used for a long time with improved life.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a cross-sectional structure of a corrosion-resistant ceramic according to the present invention.
[Explanation of symbols]
1: Ceramic substrate 2: Corrosion-resistant ceramic layers 2a, 2b: Disilicate crystal layer 3: Surface protective layer

Claims (9)

A ceramic base, a corrosion-resistant ceramic layer provided on the surface of the ceramic base, and a surface protective layer provided on the corrosion-resistant ceramic layer,
The corrosion-resistant ceramic layer is formed from a plurality of disilicate layers formed from disilicate crystals of Group 3a elements of the periodic table different from each other,
The surface protective layer is made of zirconium oxide stabilized with Group 3a element of the periodic table,
Corrosion-resistant ceramics characterized in that the thermal expansion coefficients of the ceramic substrate, the plurality of disilicate layers forming the corrosion-resistant ceramic layer, and the surface protective layer are arranged in an inclined manner from the ceramic substrate to the surface protective layer. The corrosion-resistant ceramic according to claim 1, wherein the surface protective layer has a thickness of 5 to 200 μm. The said surface protective layer is corrosion-resistant ceramics in any one of Claim 1 or 2 by which content of Al and Si is suppressed to 1 mass% or less in total. The corrosion-resistant ceramic according to any one of claims 1 to 3, wherein the surface protective layer is made of columnar crystals, and the major axis of the columnar crystals is substantially perpendicular to the surface of the ceramic substrate. The corrosion-resistant ceramic according to any one of claims 1 to 4, wherein the surface protective layer has a porosity of 1 to 30%. The corrosion-resistant ceramic according to any one of claims 1 to 5, wherein each of the disilicate layers forming the corrosion-resistant ceramic layer has a porosity of 5% or less. The corrosion-resistant ceramic according to any one of claims 1 to 6, wherein a thermal expansion coefficient of the surface protective layer is larger than a thermal expansion coefficient of the ceramic substrate. The corrosion-resistant ceramic according to any one of claims 1 to 7, wherein the ceramic base is a silicon nitride sintered body. The disilicate crystals _{Er 2 Si 2 O 7, Yb} 2 Si 2 O 7 or _Lu 2 _Si 2 _{O 7} a corrosion resistant ceramic according to any one of claims 1 to 8.

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