JP3445345B2 - High heat-resistant water sialon-based sintered body - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to relates to a high withstand heat water of the sialon-based sintered body, especially at high temperatures, harsh that can be used in environments high resistance to heat water resistance Sialon based heat in water under high pressure Regarding a sintered body.

[0002]

2. Description of the Related Art Silicon nitride sintered bodies, which are promising as high-temperature structural materials, are difficult to sinter, and it has been common to use oxides such as Y ₂ O ₃ and Al ₂ O ₃ as sintering aids. Target. By using these sintering aids, densification by atmospheric pressure sintering has been achieved, and application to complex shaped parts is possible. On the other hand, when the sintering aid is not used, a dense sintered body can be obtained by the glass capsule HIP method.

By the way, when such a sintering aid is used in such a silicon nitride sintered body, they often remain in the sintered body as a grain boundary phase. The presence of these grain boundary phases is one of the factors that cause deterioration of strength characteristics at high temperatures and deterioration of corrosion resistance such as oxidation resistance and hot water resistance.

In order to solve the problem, the reduction of the amount of the sintering aid to be added and the crystallization treatment of grain boundaries have been studied. Attempts have also been made to reduce the grain boundary phase and improve the properties by using sialon-based sintered bodies such as α-sialon and β-sialon.

Further, it has been reported that the corrosion resistance is improved by adding various compounds. For example, JP-A-62
-128969 discloses that a silicon nitride sintered body containing Y ₂ O ₃ , B, B ₄ C, BN and a group IIIa boride has excellent oxidation resistance at high temperatures. There is. Further, Japanese Patent Application Laid-Open No. 62-252388 discloses a silicon nitride sintered body having excellent oxidation resistance, which is formed by the surface of the silicon nitride sintered body being composed of a surface layer containing borosilicate. Has been done.

[0006]

However, in spite of the above-mentioned conventional studies, the corrosion resistance of silicon nitride-based sintered bodies is still insufficient. In particular, the corrosion resistance in hot water or in a solution containing alkali or acid is not high in the sintered body to which the sintering aid is added, and even in the sintered body without the sintering aid, hot water Corrosion is remarkable inside.

In recent years, there has been an increasing demand for ceramics for members used under high temperature and high pressure, such as hot water valves in thermal power plants. Sialon-based ceramic materials that can withstand such demands. The fact is that there is no.

The present invention has been made in view of this point, and an object thereof is to provide a sialon-based sintered body which meets the above-mentioned requirements, and particularly hot water under high temperature and high pressure.
And to provide a medium frustrated high withstand hot water can withstand the use under severe environment <br/> of Sialon-based sintered body.

[0009]

Means for Solving the Problems] high resistance to heat water resistance sialon-based sintered body of the present invention, alpha-sialon and / or compositions that produce a β- sialon and a predetermined proportion of the boron oxide (or even predetermined amount of _{CeO 2, HfO 2, ZrO 2} , B 4 C, molding a mixture of the compound of SiC), a sintered body obtained by sintering, sintered body, especially a high temperature, under high pressure a harsh that can be used in environments high resistance to heat water resistance sialon-based sintered body of the heat in the water.

That is, the present invention relates to "M _X (Si, Al) ₁₂ (O, N)"
₁₆ (0 <x ≦ 2, M is Li, Ca, Mg, Y and lanthanum-based elements excluding La and Ce) and a composition having a ratio of producing α-sialon and / or Si _{6 -Z} Al _Z O _Z N _8-Z (0 <
z ≦ 4.2), a composition comprising a β-sialon-producing ratio, and 0.1 to 5.0% by weight of boron oxide (or further 0.1 to 10.0% by weight of CeO ₂ , HfO ₂ , ZrO ₂ , B ₄ C, SiC
Each compound) and molding the mixture consisting, sintered, characterized in that it is obtained by a high resistance to heat water resistance sialon-based sintered body. Is the gist.

The present invention will be described in detail below. As a result of intensive studies conducted by the present inventors on a sialon-based sintered body having high corrosion resistance, it was found that boron oxide in the mixture was 0.1 to 5.0.
Wt% (or further CeO ₂ , HfO ₂ , ZrO ₂ , B ₄ C, SiC
0.1 to 10.0% by weight of at least one compound of)),
The present invention has been completed by finding that a sialon-based sintered body obtained by molding and sintering the mixture is very excellent in corrosion resistance, particularly in hot water.

The sialon-based sintered body referred to here is M _X (S
i, Al) ₁₂ (O, N) ₁₆ (0 <x ≦ 2, M is Li, Ca, Mg, Y and La, C
lanthanides other than e) and / or β-sialon represented by the composition formula of Si _6-Z Al _Z O _Z N _8-Z (0 <z ≦ 4.2) .

By the way, when the silicon nitride sintered body is stored in hot water under high temperature and high pressure, for example, when it is exposed to equilibrium vapor pressure (8.6 MPa) at 300 ° C. for a long time in an autoclave, The weight of the sintered body is reduced and the structure of the sintered body is changed from the surface to lower the strength. Corrosion due to such hot water is caused by the compound (Y ₂ O) added as a sintering aid.
₃ and compounds such as Al ₂ O ₃ ) and the elution of SiO ₂ and the dropping of silicon nitride particles due to the elution of these grain boundary phases.

The elution of such a grain boundary phase brings about a change in the surface structure, promotes the generation of defects that serve as the starting point of fracture, and the strength of the sintered body decreases. Regarding the degree of elution, the type of sintering aid, the structure of the sintered body,
Although it varies depending on the SiO ₂ content and the like, in any case, the weight loss and strength decrease of the sample due to the elution of the grain boundary phase are large.

According to the present invention, the boron oxide in the mixture is 0.1 to 5.0.
% By weight with the balance M _X (Si, Al) ₁₂ (O, N) ₁₆ (0 <x ≦ 2, M
Is a composition for producing α-sialon represented by Li, Ca, Mg, Y and lanthanum elements other than La and Ce, and / or Si _{6 -Z}
Characterized by a sialon-based sintered body obtained by molding and sintering a mixture composed of a composition that produces β-sialon represented by Al _Z O _Z N _8-Z (0 <z ≦ 4.2), The body is corrosion resistant,
In particular, it has excellent corrosion resistance to hot water.

The present invention also further provides boron oxide in a mixture.
0.1 to 5.0% by weight and CeO₂, HfO₂, ZrO₂, B_Four
Contains 0.1 to 10.0% by weight of at least one of C and SiC, and
Department is M_X(Si, Al)₁₂(O, N)₁₆(0 <x ≤ 2, M is Li, Ca, Mg, Y
And lanthanides other than La and Ce).
A composition and / or Si composed of a proportion that produces Aron_6-ZA
l _ZO_ZN_8-ZGenerates β-sialon represented by (0 <z ≦ 4.2)
A composition comprising a mixture of
Characterized by the sialon-based sintered body obtained by
The body is even more heat-resistant than adding boron oxide alone
The water content is improved.

In the present invention, the added boron oxide is
Although it exists as a grain boundary phase in the sintered body, when this sintered body containing boron oxide is treated in hot water, a reaction layer containing boron is formed on the surface of the sintered body. Is believed to have the function (role) of preventing the subsequent reaction with hot water, which suppresses the elution of other grain boundary phase components and the drop-off of sialon particles, thereby improving the hot water resistance. Further, the added boron oxide forms a liquid phase at a low temperature in the sintering process, promotes densification, and diffuses uniformly in the sintered body. Therefore, the reaction with hot water occurs uniformly, and this point is also considered to be a factor for improving hot water resistance.

In the present invention, when CeO ₂ , HfO ₂ , ZrO ₂ , B ₄ C or SiC is used as the additive compound other than boron oxide, the reason why the hot water resistance is further improved is
Each oxide of O ₂ and HfO ₂ forms a liquid phase during sintering, and exists as a grain boundary phase containing these oxides.
It is considered that the grain boundary phase containing CeO ₂ , HfO ₂ , and ZrO ₂ has a particularly low elution rate into hot water, which is a factor. It
> In addition, ZrO ₂ , SiC, and B ₄ C are originally materials that are excellent in hot water resistance by themselves, and it is considered that the addition of these materials exhibits excellent properties in synergy with the effect of adding boron oxide. .

By the way, in the sialon-based sintered body, since the compound added for its formation is finally dissolved in the grains as a solid solution element, the grain boundary phase is small, and therefore, the oxidation resistance and the resistance are high. It is characterized by relatively excellent corrosion resistance such as chemical properties. In the present invention, the main constituent phase is sialon, therefore, when a predetermined amount of a compound such as boron oxide or HfO ₂ , CeO ₂ is added, the effect of adding those compounds becomes clear, and sialon having more excellent properties is obtained. It is considered that the base sintered body has been obtained.

Further, in the sialon-based sintered body, the content ratio of α-sialon and β-sialon can be adjusted by changing the compounding composition. In the present invention, it has been found that the following characteristics are obtained when the ratio of α-sialon and β-sialon in the sintered body is changed.

One is that the sialon phase in the sintered body is α-
In the case of sialon single phase, it is particularly excellent in hot water resistance. Another point is that the combination of the two-phase sialon of α-sialon and β-sialon is excellent in mechanical properties such as bending strength and toughness as well as hot water resistance.

This is because the crystal grains of β-sialon form a long columnar structure in the sintering process and form a composite structure in combination with the granular structure of α-sialon.
It is considered that such an α-, β-composite sialon-based sintered body can be preferably used for application to a member that requires corrosion resistance and mechanical properties.

Regarding the amount of the compound added in the present invention, boron oxide is preferably in the range of 0.1 to 5.0% by weight. 0.
If it is less than 1% by weight, the effect of improving corrosion resistance (hot water resistance) is weak,
On the other hand, if it exceeds 5.0% by weight, densification is hindered and corrosion resistance (hot water resistance) becomes poor. CeO ₂ , HfO ₂ , Si
C and the like are preferably in the range of 0.1 to 10.0% by weight, and particularly preferably 0.1 to 5.0% by weight. If it is less than 0.1% by weight, the effect on the chemical resistance is weak, and if it exceeds 10.0% by weight, the corrosion resistance (hot water resistance) and strength properties are deteriorated.

[0024] High resistance to heat water resistance sialon-based sintered body of the present invention can be manufactured, for example, as follows. First, M _X (Si, Al) ₁₂ (O, N) ₁₆ (0 <x ≦ 2, M is Li, Ca, M
Predetermined ratio of α-sialon represented by g, Y and lanthanum elements other than La and Ce) and β-sialon represented by Si _6-Z Al _Z O _Z N _8-Z (0 <z ≦ 4.2) Of silicon nitride,
Boron oxide is mixed with aluminum nitride, Y ₂ O ₃ , Al ₂ O _{3 and the} like. Moreover, each compound such as CeO ₂ , HfO ₂ , and SiC is added and mixed at this stage.

As a mixing means, a ball mill, a vibration mill or the like can be used in water or an organic solvent, and at this time, an organic compound such as a binder or a dispersant can be added. The compound as a solid solution element of boron oxide or sialon to be mixed is not particularly limited in the present invention, and it can be used in the form of a powder or in the form of a liquid phase, and it is decomposed during sintering and those It is also possible to use a compound.

The obtained mixture is dried and granulated using a spray dryer or the like to obtain a raw material for molding. Molding methods include die molding, hydrostatic press molding, injection molding,
Cast molding or the like can be used. Since the obtained molded body usually contains an organic component such as a binder, it is degreased.

Next, the compact is sintered in a non-oxidizing atmosphere. Although firing shrinkage occurs at about 1200 ° C or higher, it is preferable to sinter at a temperature of 1600 ° C or higher in order to obtain a dense sintered body. The sintering time is usually in the range of 30 minutes to 10 hours. As for sintering, a sufficiently dense sintered body can be obtained by pressureless sintering, but a method such as HIP or hot pressing can be used if necessary.

The sialon-based oxide sintered in the present invention thus obtained has a high temperature, corrosion resistance against the hot water under high pressure is very good. Further, it is sufficiently excellent in mechanical properties such as bending strength and fracture toughness, and is suitable for use as a structural material.

[0029]

EXAMPLES Next, the present invention will be described in detail by giving examples of the present invention together with corresponding comparative examples.

(Example 1, Comparative Example 1) Raw material powders of silicon nitride, aluminum oxide, yttrium oxide, and aluminum nitride were blended so as to obtain a sialon-based sintered body, and boron oxide is shown in Table 1. Added in proportion. In addition, formulation Nos. 1 to 8 in Table 1 are Examples 1 of the present invention, and formulation Nos. 9 to 12 are Comparative Example 1 corresponding to Example 1.

The raw material powders were mixed using a resin pot and a silicon nitride cobblestone in an ethanol mill for 20 hours. The resulting mixture was vacuum-dried and then molded in a cold isostatic press at a pressure of 1.5 t / cm ² , and then this molded body was fired in a nitrogen atmosphere at 1700 ° C. for 5 hours under atmospheric pressure to produce a sialon-based material. A sintered body was obtained.

A 3 × 4 × 20 (mm) test piece was prepared from the obtained sintered body and used as an evaluation sample. After measuring the size and weight of this test piece after drying, a part of the test piece was put in a Teflon container, and distilled water was further put in the container to cover it. At this time, B / A = 10
cm (where A is the surface area of the test piece (cm ² ) and B is the amount of distilled water (c
m ³ ). The amount of distilled water was set so that One test piece was placed in one Teflon container.

This Teflon container was placed in an autoclave (autoclave filled with about 60% by volume of distilled water therein), heated to 300 ° C., under equilibrium vapor pressure of 300 ° C. (8.6 MPa). )
Hold for 100 hours. After cooling, take out the sample and
After drying for an hour, the weight of the test piece was measured to determine the weight reduction amount. The measurement results are shown in Table 1.

[0034]

[Table 1]

From Table 1, the sialon-based sintered body of Example 1
(Compound No. 1 to 8) has a weight loss of 3 mg after treatment in hot water.
/ Cm ² or less and small, it can be understood that show excellent resistance to heat water resistance. On the other hand, as shown in Comparative Example 1,
Without the addition of boron oxide (compounding Nanba9～11) and if this was excessively added (formulation No.12), both weight loss is large, inferior in resistance to heat water resistance was obtained.

(Example 2, Comparative Example 2) Raw material powders of silicon nitride, aluminum oxide, yttrium oxide, and aluminum nitride were blended so as to obtain a sialon-based sintered body, and boron oxide, cerium oxide, and hafnium oxide were mixed. , Zirconium oxide, boron carbide, and silicon carbide were added at the ratios shown in Table 2 (Example 2) and Table 3 (Comparative Example 2).

The formulations No. 1 to 23 in Table 2 are the second embodiment of the present invention, and the formulations No. 25 to 29 in Table 3 are the same as this Example 2.
Comparative Example 2 corresponding to, and in Example 2 and Comparative Example 2, the addition amount of boron oxide was 1.0 wt% in all the formulations. The composition of No. 24 in Table 2 is
This is a No. 2 formulation example of Example 1 (an example in which boron oxide: 1.0 wt% was added singly), and is shown for reference. That is,
Boron oxide of Example 2 and CeO ₂ , HfO ₂ , ZrO ₂ , B ₄ C, SiC
In order to clarify the effect of addition by the combined use of each of the above compounds, the compounding example of No. 2 in Table 1 above is transcribed.

These raw material powders were mixed, molded and fired in the same manner as in Example 1 to obtain a sintered body.
In the second embodiment, the sialon phase in the sintered body is α-
It consists of two phases, Sialon and β-Sialon,
The amount of boron oxide added was 1.0% by weight.

A test piece of 3 × 4 × 20 (mm) was prepared from the obtained sintered body and used as an evaluation sample. After measuring the size and dry weight of the test piece, it was treated in hot water in the same manner as in Example 1. After the treatment was completed, the sample was taken out and dried at 120 ° C. for 5 hours, and then the weight of the sample was measured to obtain the weight reduction amount. The measurement results are shown in Table 2 (Example 2) and Table 3 (Comparative Example 2).
Shown in.

[0040]

[Table 2]

[0041]

[Table 3]

[0042] From Table 2, the weight loss of sialon-based sintered body of the present embodiment 2 are both 3.3 mg / cm ² or less and small, it can be understood that show excellent resistance to heat water resistance. On the other hand, CeO ₂ , HfO ₂ , ZrO ₂ and B specified in the present invention
₄ C, when added in excess addition of more than the range (0.1 to 10.0 wt%) of each compound of SiC, as is clear from Comparative Example 2 in Table 3, a large weight loss, poor in resistance to heat water resistance It was confirmed that the effect of addition on hot water was lost.

In addition, in the sialon-based sintered body of Example 2, CeO ₂ , HfO ₂ , ZrO ₂ , B ₄ C and SiC specified in the present invention were used.
If a small amount is added even within the range of each compound
(Compound No. 1 to 14), reference example of Table 2 (Composition No. 24: Example 1)
As is clear from the comparison with the above, it was confirmed that the weight reduction amount was smaller than that of the case where boron oxide was added alone.

(Example 3, Comparative Example 3) Raw material powders of silicon nitride, aluminum oxide, yttrium oxide, and aluminum nitride were blended so as to obtain a sialon-based sintered body, and 1.0 wt% of boron oxide and CeO were added. 3.0 to ₂ % by weight
These raw material powders were added and mixed, molded and sintered in the same manner as in Example 1 to obtain a sintered body.

The composition ratio of the sialon phase in the sintered bodies obtained in Example 3 and Comparative Example 3 is as shown in Table 4. The composition ratio of the sialon phase in the sintered body was determined by X-ray diffraction.

From the thus obtained sintered body, 3 × 4 ×
A test piece having a bending test piece shape of 40 (mm) was produced and used as an evaluation sample. Three-point bending strength of each manufactured test piece
Ten points (three-point bending strength at a span of 30 mm) were measured for each composition to determine the initial strength characteristics. Further, as a corrosion resistance test in hot water, three test pieces were used for each composition, and the same method as in Example 1 was performed. Table 4 shows the measurement results.
Shown in.

[0047]

[Table 4]

From Table 4, it was found that the weight loss of the sialon phase consisting of the α-sialon single phase (formulation No. 1 of Example 3) was smaller than that of the other examples. It was confirmed that the composite sialon composed of α-sialon and β-sialon had a high initial strength of 1000 MPa or more and a small rate of strength reduction due to hot water treatment. The formulations No. 6 and 7 of Comparative Example 3 are examples corresponding to the results of evaluation using the samples of the formulations No. 9 and 10 containing no boron oxide prepared in Example 1 above. It was confirmed that the amount was large and the rate of strength reduction was also large.

[0049]

As described in detail above, the present invention provides a composition for producing α-sialon and / or β-sialon, a predetermined proportion of boron oxide (or a predetermined amount of CeO ₂ , Hf).
O ₂ , ZrO ₂ , B ₄ C, SiC compound) and a mixture,
A high resistance to heat water resistance sialon-based sintered body obtained by sintering, flexural strength and with an excellent fracture toughness and mechanical properties, in particular high-temperature, high corrosion resistance excellent against the hot water under high pressure < It has the effect of providing br /> heat resistance water resistance sialon-based sintered body.

[0050] Then, the present invention can provide a suitable material as a structural material, also for hot water valve or the like in a thermal power plant, in particular a high temperature, can be used in harsh environment of the heat in the water under high pressure We can provide various materials.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-61-209956 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C04B 35/599

Claims (2)

(57) [Claims] 1. M _X (Si, Al) ₁₂ (O, N) ₁₆ (0 <x ≦ 2, M
Is a lanthanum element other than Li, Ca, Mg, Y and La, Ce) and / or Si _6-Z Al _Z O _Z N _8-Z (0 < z ≦ 4.2), a composition comprising a proportion of β-sialon producing 0.1,
5.0% of the mold with a mixture consisting of boron oxide, sintering, characterized in that it is obtained by a high resistance to heat water resistance sialon-based sintered body. 2. Boron oxide in the mixture is 0.1 to 5.0% by weight,
At least one of CeO ₂ , HfO ₂ , ZrO ₂ , B ₄ C, and SiC is used.
1 to 10.0 containing by weight%, the balance _{M X (Si, Al) 12} (O, N) 16
Α-sialon and / or Si _{6-Z represented by} (0 <x ≦ 2, M is a lanthanum element other than Li, Ca, Mg, Y and La and Ce)
A composition comprising a proportion that forms β-sialon represented by Al _Z O _Z N _8-Z (0 <z ≦ 4.2), which is obtained by molding and sintering the mixture. heat resistance water resistance sialon-based sintered body.