JPS6240318B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved method of manufacturing a sialon sintered body. In detail, a molded product whose main components are a silicon compound and an aluminum compound is coated with powder whose main components are Si ₃ N ₄ and SiO ₂ and then fired to obtain the composition formula.
1500 when manufacturing a sialon sintered body represented by Si _6-z Al _z O _z N _8-z (where z is a positive number from 1.0 to 4.2)
The temperature increase rate [t (℃/min)] above ℃ is 6z≦t
≦9(z+2), and the amount of SiO ₂ [w (g/cm ² )] of the coating powder per unit surface area of the molded body is 0.005(t+10)/z≦w≦0.009(t+2).
This is a method for producing a sialon sintered body in which firing is performed in a nitrogen gas atmosphere within the range expressed by 0)/z. Sialon sintered body consists of four elements: Si, Al, O, and N, and its composition formula is Si _6-z Al _z O _z N _8-z (however, z
is a positive number from 0 to 4.2). Moreover, the applications of the sialon sintered body as a heat-resistant material are attracting attention in various fields. As a method for producing a sialon sintered body, raw material mixed powder such as Si ₃ N ₄ −Al ₂ O ₃ −AlN system or Si ₃ N ₄ −
A method of densifying SiO ₂ -AlN system by hot pressing method, or molding of raw material mixed powder.
A method of firing in an N ₂ gas atmosphere is known. The latter method is suitable for mass production of products with complex shapes, and is an industrially advantageous method. However, this method tends to cause thermal decomposition of the raw materials during firing, and simply firing in an _N2 gas atmosphere cannot prevent the weight loss of the sintered body and the resulting compositional deviation, so it is not sufficient. It has the disadvantage that it is difficult to obtain a dense sintered body. In addition, in order to prevent the above-mentioned thermal decomposition, a method in which the molded body is coated with powder mainly composed of Si ₃ N ₄ and SiO ₂ and then fired is described in the Journal of Materials Science (J.
materials science) 14 [10] 2309-2316
(1979). However, although this method is a method that has been significantly improved industrially, it is still not fully satisfactory industrially. As a result of extensive research into the production of sialon sintered bodies, the present inventor has determined that the composition, properties, etc. of the obtained sialon sintered bodies are similar to the temperature increase rate at 1500°C or higher in the production of sialon sintered bodies. It was also found that this was significantly affected by the amount of SiO ₂ coated on the molded body. Further, as a result of continuing research into these effects, the inventors discovered a correlation between the temperature increase rate and the amount of SiO ₂ and completed the present invention. That is, in the present invention, a molded article whose main components are a silicon compound and an aluminum compound is coated with a powder whose main components are Si ₃ N ₄ and SiO ₂ and then fired.
When manufacturing a sialon sintered body represented by Si _6-z Al _z O _z N _8-z (where z is a positive number from 1.0 to 4.2),
Temperature increase rate [t (°C/min)] at 1500°C or higher is 6z
≦t≦9(z+2) and the amount of SiO ₂ [w (g/cm ² )] of the coating powder per unit surface area of the molded body is 0.005(t+10)/z≦w≦0.009(t+2)
This is a method for producing a sialon sintered body in which firing is performed in a nitrogen gas atmosphere within the range expressed by 0)/z. The raw material for the Sialon sintered body in the present invention is not particularly limited, and known raw materials can be used. As is clear from the above general formula, the sialon sintered body is composed of Si,
It consists of four elements, AlO and N, but the raw materials that are generally preferably used are Si ₃ N ₄ - Al ₂ O ₃ or Si ₃ N ₄ -
It is a mixture of raw materials such as SiO ₂ -AlN. These raw materials are generally used in the form of fine powder for the purpose of speeding up the reaction. Therefore, it is suitable to use the powder as a powder with a diameter of usually 5 μm or less, preferably 1 μm or less. The raw material mixture composition is the composition of the target Sialon sintered body, that is, Si _6-z Al _z O _z N _8-z (however, z is 1.0 ~
4.2 positive number). These raw materials are first molded into the desired shape. Although the molding is not particularly limited, the density is generally 1.6 to 2.0.
It is preferable to mold to approximately g/cm ³ . The molded body is then coated with a powder whose main components are Si ₃ N ₄ and SiO ₂ . The coating means may be any known method without particular limitation, but generally alumina, silicon nitride,
A preferred method is to place the molded body in a container made of a heat-resistant material such as silicon carbide or sialon containing a mixed powder of Si ₃ N ₄ and SiO ₂ . Although the powder mixing ratio of Si ₃ N ₄ and SiO ₂ is not particularly limited, it is generally preferable to use a larger amount of Si ₃ N ₄ than SiO ₂ . For example, the mixing ratio of Si ₃ N ₄ and SiO ₂ is generally selected such that Si ₃ N ₄ is 20% by weight or more, and SiO ₂ is preferably 5 to 80% by weight.
It is preferable to select a proportion of 60% by weight.
The amount of SiO ₂ has a great influence on the properties of the obtained sialon sintered body, as described below, but if the SiO ₂ content in the above mixing ratio is less than 5% by weight, there is a tendency for weight loss to occur during firing, which will be described later. Not desirable. On the other hand, if the SiO ₂ mixing ratio exceeds 80% by weight, molten SiO ₂ will react with the molded body during firing, making post-treatment difficult, so it is generally preferable not to employ it. It is possible to coexist Al ₂ O ₃ , Si, SiC, Si ₃ N ₂ O, etc. in the powder mixture of Si ₃ N ₄ and SiO ₂ as necessary. As is clear from the above explanation, the reason why the molded body is coated with powder of Si ₃ N ₄ and SiO ₂ and fired is that SiO, which causes thermal decomposition of the sialon sintered body during production of the sialon sintered body, This is to prevent this and also to promote the sintering reaction and shrinkage of the molded body. The molded body coated with the powders of Si ₃ N ₄ and SiO ₂ is fired to become the desired sialon sintered body. The firing temperature is not particularly limited, and any known temperature may be selected. Generally 1700 or more preferably
Baking at 1750-1950°C for 30-120 minutes is sufficient. The greatest feature of the present invention is the rate of temperature increase at 1500°C or higher during firing of the molded body and the temperature increase in the coating powder.
The point is to control the amount of _SiO2 . That is,
The temperature increase rate [t (°C/min)] above 1500°C must be controlled within the range of the formula 6z≦t≦9(z+2) (1). Also, SiO ₂ of the coating powder per unit area of the molded body
The amount [w (g/cm ² )] is calculated using the formula 0.005(t+10)/z≦w≦0.009(t+
20) /z......It is necessary to control within the range of (2). The reason why the temperature increase rate above 1500° C. is important is not necessarily clear, but it is thought to be due to the following reason. The X phase (estimated composition
The formation of a reaction intermediate called Si ₉ Al ₇ O ₂₁ N ₅ ) is 1500
It is presumed that this is because the SiO partial pressure of the coating powder gradually increases from 1500°C or higher, and the effect of preventing thermal decomposition (SiO scattering) of the molded body begins. The conditions expressed by the above equations (1) and (2) were derived by the inventor based on numerous tests and evaluation of the results. When both the conditions of formula (1) and formula (2) are satisfied, the obtained sialon sintered body has high density and excellent strength with little change in strength at room temperature and high temperature. In order to explain the above conditions in more detail and in a simplified manner, a case where z in the compositional formula of the Sialon sintered body is 2 will be exemplified and explained below. Of course, values of z from 1.0 to 4.2 will be understood in the same manner as in the following explanation. In FIG. 1, the conditions for satisfying equations (1) and (2) in the case of z=2 are indicated by diagonal lines. The temperature increase rate is the first
If the temperature is below 12°C/min as shown by straight line a in the figure, even if the amount of SiO ₂ in the coated powder is an appropriate amount that satisfies formula (2) above, molding under high SiO gas pressure generated in the firing reaction The body is exposed for a long time. As a result, SiO
The gas permeates relatively deep into the molded body and reacts, producing a large amount of glass phase especially near the surface of the sialon sintered body. This glass phase softens at high temperatures, which causes the sintered body to have lower high-temperature strength. Therefore, it cannot be an excellent sialon sintered body. Furthermore, if the temperature increase rate is 36° C./min or higher, as indicated by straight line C in FIG. 1, the molded body will be exposed to high temperatures before the reaction to produce the sialon sintered body from the molded body has sufficiently progressed. As a result, a part of Si ₃ N ₄ becomes Si ₃ N ₄ →3Si+2N ₂
It decomposes due to the reaction, and metal Si tends to coexist in the sialon sintered body after firing. The coexistence of metal Si in a sialon sintered body has a negative effect on the high temperature strength of the sialon sintered body. Next, use straight lines b and d in Figure 1 to determine the appropriate temperature rise rate range.
The amount of SiO ₂ (per unit surface area of the molded body) is shown. If the amount of SiO ₂ is less than the value of b, even if heated at an appropriate temperature increase rate, it will not be possible to provide a sufficient amount of SiO into the atmosphere around the compact, resulting in a high density sintered compact. becomes difficult to do. In addition, if the amount of SiO ₂ is greater than the value of d, the shrinkage will proceed sufficiently and a high-density sialon sintered body will be formed.
The reaction between the SiO gas and the molded body progresses, and a large amount of glass phase accumulates in the Sialon sintered body. The amount and distribution of the glass phase in the sintered body explained above can be determined by etching the fractured surface of the sintered body with an appropriate treatment solution (e.g. HF + HNO ₃ ) and then observing it with a scanning electron microscope (SEM). You can know by this. For example, SiAlON with a composition of z = 2 (Si ₄ Al ₂ O ₂ N ₆ ) is heated at t = 25°C/min, w = 0.22 g/cm ²
(range above the straight line d in Figure 1) and t
= 25°C/min, w = 0.18g/ ^cm2 (within the shaded area in Figure 1), the fractured surfaces of each specimen were sintered for 90 minutes at 1800°C, and after etching, the results were observed using SEM. Shown in Figure 2 a and b. Both a and b are photographs taken 200 μm from the surface. In a, the space between the Sialon particles was considerably removed by etching, indicating that a large amount of glass phase existed at the grain boundaries. . On the other hand, in case b, although the pores that originally existed in the sintered body can be seen, the degree of etching between the particles is very small, indicating that there is little presence of the second phase at the grain boundaries. ing. It is clear that the difference between the two appears as a difference in the strength of the sintered body at high temperatures. Although the sialon sintered body having z=2, that is, the compositional formula Si ₄ Al ₂ O ₂ N ₆ has been described above, the same tendency exists for other compositions as well. Furthermore, as shown in equations (1) and (2) above, as the value of z increases, the sialon sintering reaction becomes faster, so the appropriate range of the temperature increase rate also shifts toward higher values as the value of z increases. Also, as the value of z above increases, it is expressed by the above equation (2).
The amount of SiO ₂ will shift to a smaller amount. this is,
It is thought that this is because as the value increases, the sialon sintering reaction becomes faster and the SiO decomposition pressure of sialon becomes lower, so that the required amount of SiO ₂ becomes smaller. As is clear from the above explanation, the above (1) of the present invention
An excellent sialon sintered body can be obtained by sintering the molded body under conditions that satisfy the conditions of formula and (2) and in a silicon gas atmosphere. Although the presence of nitrogen gas during the firing is an essential requirement in the present invention, the nitrogen gas atmosphere does not necessarily need to be in a pressurized state. Normally, atmospheric pressure is sufficient, but when the firing temperature is high, for example at 1800°C or higher, it is preferable to fire under nitrogen gas pressure of 2 to 10 atmospheres or more. EXAMPLES In order to explain the present invention more specifically, the present invention will be described below with reference to Examples, but the present invention is not limited to these Examples. Example 1 Highly purified Si ₃ N ₄ (average particle size 0.8 μm), Al ₂ O ₃ (average particle size 0.8 μm)
0.3μm) and AlN (same μm), Si ₄ Al ₂ O ₂ N ₆
(z=2) They were mixed using high-purity alumina balls. Mixing was performed in hexane, and the weight loss of the alumina balls during mixing was subtracted in advance as the amount of Al ₂ O ₃ when weighing. Approximately 2.3g of the mixed powder was first molded using a mold, then hydrostatically pressed (1000Kg/cm ² ) to form a powder with a density of 1.87g/cm ^{3 .}
A prismatic molded body measuring 0.5 x 0.6 x 4 cm was made. This molded body was covered almost uniformly with 3.8 g of mixed powder of Si ₃ N ₄ (70% by weight) and SiO ₂ (30% by weight),
It was placed in a crucible made of boron nitride (w = 0.18
g/ ^cm2 ). Next, the temperature of this crucible was raised to 1800°C at a temperature increase rate of 25°C/min over 1500°C in a N ₂ stream at 1 atm, and maintained at this temperature for 90 minutes. The weight loss after firing was in the range of 1.1 to 1.8% by weight, and the average density of the obtained sialon sintered body was 2.99 g/cm ³ (96% of theoretical ratio). The sample for bending strength measurement was prepared by polishing the surface of the sintered body (I2000SiC, final finish).
Three-degree bending strength was measured at 25°C and 1200°C with a span of 20 mm. The result is 44Kg/mm ² at 25℃, 1200
The strength was 42Kg/mm ² at ℃, and there was almost no decrease in strength. Examples 2 to 14 and Comparative Examples 1 to 19 Examples were carried out in the same manner as in Example 1, except that various conditions in Example 1 were changed as shown in Table 1. The results were as shown in Table 1. For comparison, various conditions other than the conditions of the present invention were selected, and experiments were carried out in the same manner as in Example 1 except for the conditions shown in Table 2. The results are shown in Table 2.

【table】

【table】 [Brief explanation of the drawing]

In FIG. 1, preferred firing conditions of the present invention when z=2 in the composition formula are indicated by diagonal lines. Figure 2 is a SEM photograph of the sialon sintered body carried out by a for comparison.
It is a SEM photograph of the sialon sintered compact obtained by implementing this invention of b.

Claims (1)

[Claims] 1. A molded body containing a silicon compound and an aluminum compound as its main components is coated with a powder containing Si ₃ N ₄ and SiO ₂ as its main components, and then fired to obtain a composition having the composition formula Si _6-z Al _z O _z N _8-z
(However, z is a positive number from 1.0 to 4.2) When manufacturing a sialon sintered body, the temperature increase rate [t (°C/min)] above 1500°C must be 6z≦t≦9 (z+
2), and the amount of SiO ₂ [w (g/cm ² )] of the coating powder per unit surface area of the molded body is 0.005 (t+
10) A method for producing a sialon sintered body, which comprises firing in a nitrogen gas atmosphere within the range expressed by /z≦w≦0.009(t+20)/z.