JPH0791109B2 - Silicon nitride SiC refractory and method for manufacturing the same - Google Patents

Description

The present invention relates to a silicon nitride SiC refractory having excellent thermal shock resistance and a method for producing the same.

[Prior Art and Problems to be Solved by the Invention] Silicon carbide (SiC) refractory occupies an important industrial position due to its excellent heat resistance and fire resistance. For example, shelf boards for firing ceramics, etc. It is often used for firing jigs and sheaths.

As a method for producing such SiC refractories, conventionally, SiC particles are mixed with about 10% by weight of clay, and the mixture is kneaded, molded and fired, and the SiC particles are combined with a silicate mineral, for example, a clay mineral to form a SiC refractory material. Methods of manufacturing things are known. However, since the SiC refractory manufactured by this method uses a clay mineral having a low refractory degree as a grain boundary bonding portion, there is a problem that soft deformation and oxidation easily occur at high temperatures.

Further, in U.S. Pat.No. 2752258, a silicon nitride SiC refractory is manufactured by mixing Si in SiC particles, molding, and then firing the molded body in a non-oxidizing nitrogen-containing atmosphere. Is disclosed. This SiC refractory is S
The iC particles are bonded by a binder made of silicon nitride, and the purpose is to improve mechanical strength and thermal shock resistance at high temperatures.

However, even in the SiC refractory produced by the method described in US Pat.No. 2752258, deformation or swelling of the SiC refractory occurs during long-time use at high temperature, or cracks, etc. It was found that coloring of the object occurs.

[Means for Solving the Problems] Therefore, the present invention solves the problems of the conventional SiC refractories described above, and suppresses deformation and swelling during high temperature use as much as possible, and SiC refractories that do not cause cracks and the like. It is intended to provide a manufacturing method.

And, according to the present invention, the purpose is to obtain SiC aggregate particles of 60
If the main phase of the grain boundary bonding portion is Si ₃ N ₄ or Si ₂ ON ₂ quality SiC refractory, the cristobalite existing as a sub phase in the SiC grain boundary bonding portion is more than X% by weight. Line peak ratio 21.
Silicon nitride SiC refractory which is contained in the range of 0.2 to 0.3 at 9 ° (peak of cristobalite) /34.1° (peak of SiC) and has a bending strength of 610 kg / cm ² or more, and After mixing metal Si with SiC aggregate particles and molding this, the molded body is fired in a nitrogen-containing atmosphere, and then oxidized at a temperature of 1300 to 1500 ° C. to produce the above SiC refractory. And a silicon nitride SiC refractory manufacturing method.

[Operation] The SiC refractory of the present invention is produced by firing a molded body composed of SiC aggregate particles and metallic Si in a nitrogen-containing atmosphere, and then subjecting it to an oxidation treatment at a predetermined temperature.

The SiC refractory produced by this method has extremely excellent thermal shock resistance, that is, even when it is used at high temperature for a long time, there is almost no deformation or swelling, and cracks do not occur. No coloring occurs.

In the conventional method, the molded body is fired in a nitrogen-containing atmosphere and is not subjected to the subsequent oxidation treatment as in the present invention. The present inventor has found that further performing an oxidation treatment after firing in a nitrogen atmosphere improves the thermal shock resistance and the like of the SiC refractory as described above.

The SiC refractory of the present invention comprises SiC aggregate particles, mainly Si ₃ N ₄
Alternatively, it is composed of a grain boundary bonding part made of Si ₂ ON ₂ .

SiC aggregate particles are more than 60% by weight, preferably 65-80% by weight
As described above, the remaining grain boundary bonding portion is composed of Si ₃ N ₄ or Si ₂ ON ₂ and the glassy or crystalline phase.

Cristobalite, which is a polymorph of silica (SiO ₂ ), has an X-ray peak height ratio of 21.9 ° (cristobalite peak) /34.1° (SiC peak) of 0.2 with respect to SiC.
To 0.3, preferably 0.1 to 0.25. Here, the X-ray peak is a 2θ value using Kα of Cu. If the ratio of cristobalite to SiC is out of the above range, the SiC refractory may be deformed, swollen, cracked, or the like when it is used at high temperature for a long time, and coloring of the object to be fired may occur.

The SiC refractory material of the present invention is manufactured as follows.

That is, metallic Ag is mixed with SiC aggregate particles, and this is molded into a desired shape. The mixing ratio is usually SiC aggregate particles 6
Metallic 8 to 35% by weight, preferably 0 to 90% by weight, preferably Si
C 19 to 24% by weight of metal Si with respect to 65 to 75% by weight of aggregate particles.

The size of the SiC aggregate particles is 5 mesh or less (4000μ
m or less), 6 mesh or less (3360 μm)
It is more preferable to use the following).

The particle size of metallic Si is preferably 350 μm or less.

In addition to SiC aggregate particles and metallic Si, bentonite,
It is also possible to mix clay minerals such as kaolin,
A small amount of CaO or the like can be added.

Next, the obtained molded body is fired in a nitrogen-containing atmosphere. Here, the content ratio of nitrogen in the nitrogen-containing atmosphere is preferably 90% by volume or more, and more preferably 99% by volume or more. When the content ratio of nitrogen is less than 90% by volume, there is a problem that the nitriding rate is delayed and a part of oxygen causes an unnitriding phenomenon.

The firing temperature is such that the maximum holding temperature is usually in the range of 1100 to 1500 ° C, preferably 1300 to 1450 ° C, and the firing time is suitably 1 to 30 hours.

Then, the fired body thus obtained, 1300 ~ 1500
Oxidize at a temperature of ℃. If the oxidation treatment temperature is lower than 1300 ° C, a SiC refractory having improved thermal shock resistance cannot be obtained or the bending strength becomes low. Further, when the oxidation treatment temperature exceeds 1500 ° C., although the thermal shock resistance is good, the bending strength is somewhat lowered. The oxidation treatment time is usually 1 to 30 hours.

In addition, in order to favor the formation of silica glass, which is the source of cristobalite, the temperature may be kept several times before reaching the maximum temperature, or the CO, CO ₂ , and O ₂ concentrations may be controlled.

[Examples] Hereinafter, the present invention will be described in more detail with reference to Examples.
The invention is not limited to these examples.

(Example 1) 75% by weight of SiC aggregate particles having a particle size of 6 mesh or less, 15% by weight of metallic Si having a particle size of 10 μm or less, 9.5% by weight of bentonite, and 0.5% by weight of CaO were mixed. 8% by weight of water was added and kneaded, and the mixture was molded into 400 × 350 × 10 mm (thickness). This molded body was placed in a nitrogen gas atmosphere at 1400
It was baked at 10 ° C. for 10 hours. The heating rate and the cooling rate were 100 ° C./hr.

Next, the obtained fired body was subjected to oxidation treatment under various conditions as shown in Table 1.

The strength (flexural strength), thermal shock resistance, and presence / absence of coloring of the obtained fired body after the oxidation treatment were measured and shown in Table 1.

Moreover, the composition of the fired body after the oxidation treatment was measured, and the X-ray peak height ratio of cristobalite and SiC was calculated to be 21.9 ° (cristobalite peak height) /34.1° (SiC peak height), and the results are shown in Table 1. Indicated.

Here, the production amount of cristobalite is slightly different between the surface layer and the inner layer of the sample. In particular, if the sample is thick (about 50 mm thick), it often happens that cristobalite is hardly generated in the inner layer. However, if the cristobalite within the scope of the present invention is near the surface layer (surface layer to 5 mm inside), the object of the present invention can be achieved. Here, 10
Since a plate with a thickness of mm was used, the amount of cristobalite shown in Table 1 was examined by sampling from any part of the plate.

The thermal shock resistance (ΔT _700-RT ) was shown by the occurrence of cracks when the fired body was repeatedly placed between 700 ° C and room temperature.
In addition, the pottery was placed on the fired body, and the presence or absence of coloration on the pottery when used for the first time at 1200 ° C was determined. Furthermore, 90
The degree of tearing and swelling when exposed for 500 hours at 1150 ° C. in an atmosphere of wt% H ₂ O was measured.

As is clear from the results shown in Table 1, the fired body obtained by subjecting it to oxidation treatment at 1300 to 1500 ° C. after firing in a nitrogen atmosphere has higher bending strength than a fired body not subjected to oxidation treatment, It can be seen that there is no coloration, and the thermal shock resistance is extremely excellent.

[Effects of the Invention] As described above, according to the present invention, mechanical strength such as bending strength is large, and even when used at high temperature for a long time, there is almost no deformation or swelling, and cracks or the like occur. It has excellent thermal shock resistance, that is, it does not occur, and it does not cause coloring of the fired product.
A refractory material and a manufacturing method thereof can be provided.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyuki Ito 81, 5668 Asahigaoka, Asahigaoka-cho, Owariasahi-shi, Aichi 81 (72) Inventor, Masaru Hasegawa 65, Ijiri, Mitake-cho, Kani-gun, Gifu (56) References JP 63 -69757 (JP, A)

Claims (2)

[Claims] 1. A SiC refractory material containing 60% by weight or more of SiC aggregate particles and a main phase of a grain boundary bonding part being Si ₃ N ₄ or Si ₂ ON ₂
The cristobalite existing as a sub-phase in the C grain boundary joint is S
It is characterized in that it is contained in the range of 0.2 to 0.3 at an X-ray peak ratio of 21.9 ° (cristobalite peak) /34.1° (SiC peak) with respect to iC and has a bending strength of 610 kg / cm ² or more. Silicon nitride SiC refractory. 2. A method in which SiC aggregate particles are mixed with metallic Si, formed into a compact, and the compact is fired in a nitrogen-containing atmosphere and then subjected to an oxidation treatment at a temperature of 1300 to 1500 ° C. 1. A method for producing a silicon nitride SiC refractory, which comprises producing the SiC refractory according to 1.