JPS5844632B2 - Manufacturing method for corrosion-resistant, high-hardness ceramics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an industrially advantageous manufacturing method for corrosion-resistant, high-hardness ceramics containing sialon as a main component, and in particular uses acidic volcanic ejecta or its secondary deposits as a silicon source, and The present invention relates to a method for producing ceramics having excellent corrosion resistance, hardness and strength at firing temperatures.

Sialon is a ceramic that is composed of Si, Al, O, and N and has excellent high-temperature strength and high-temperature corrosion resistance, and is attracting attention and expectations as, for example, a component material for high-temperature heat engines or a corrosion-resistant heat-resistant material.

Sialon is generally Si3N4, AIN and Al
2O3 mixed powder or S i 02, S i
Mixed powder of 3N4 and AIN was heated at 1700℃ to 19℃.
It is manufactured by sintering and densifying it at a temperature of 00°C.

In the course of research on Sialon, the present inventors discovered that silicon oxide (8102) and aluminum (Al), or 5i
02, we discovered that Sialon could be effectively produced using Al and silicon (Si) as raw materials, and proposed it earlier (Japanese Patent Publication No. 5347245, Japanese Patent Application No. 55-88)
No. 614, Japanese Unexamined Patent Publication No. 53-3408).

According to this method, as with the general method, the final result is 1
By sintering at a high temperature of 700 to 1900°C, a densified sintered body with low porosity can be effectively produced.

Furthermore, the present inventors added a small amount of carbon powder to the starting materials 5i02 and A1, or SiO2, Al and Si.
is added to the mixed powder and finally heated to 1700℃~2000℃
He also proposed a method for improving the properties of sintered bodies, especially high-temperature strength, porosity, and oxidation resistance, by firing at a temperature of
No. 466).

However, these methods improve the densification and physical properties of the sintered body, and require firing at a high temperature of 1700°C or higher.
This does not relate to improvements in processing conditions.

In addition, regarding firing, it is possible to increase the atmospheric pressure in the furnace to prevent thermal decomposition of the sample that occurs in normal pressure firing, or to fire the sample in a closed container filled with powder of the starting material composition. A method for obtaining a sintered body by suppressing the thermal decomposition of is proposed.

However, in order to increase the pressure inside the furnace, a special firing furnace is required, and to suppress the thermal decomposition of the sample, a special sample arrangement is required, so there is no substantial improvement in the firing conditions. However, there is a problem in that a fusion phenomenon occurs between the fired body and the surrounding filler or between the graphite mold.

The present inventors have conducted further research on a method for relaxing the firing conditions for Sialon, particularly for reducing the firing temperature under normal pressure, and as a result, they have arrived at the present invention.

That is, the present invention uses 65 to 79.5% by weight of acidic volcanic ejecta or secondary deposits thereof, and 20 to 30% by weight of aluminum powder.
% by weight and 0.5 to 5% by weight of carbon powder are mixed and pulverized, then molded, and the molded product is heated under nitrogen atmosphere for 130 min
A method for producing corrosion-resistant, high-hardness ceramics, which comprises heating to a temperature of 0 to 1400°C to nitride, and then heating it to a temperature of 1500°C or more and less than 1700°C to sinter and densify it, and a powder having the above composition. The mixture was granulated into granules with a diameter of 3 mm or less, and the granules were heated at 1300 °C under a nitrogen atmosphere.
A method for producing corrosion-resistant, high-hardness ceramics, which comprises heating to a temperature of ~1,400°C, nitriding, pulverizing, molding it into a predetermined shape, and sintering the molded product at a temperature of 1,500°C or more and less than 1,700°C; The present invention provides a method for producing fine powder-like corrosion-resistant, high-hardness ceramics by firing the nitrided fine powder obtained by nitriding the above-mentioned granular material and pulverizing it at a temperature of 1500° C. or more and less than 1700° C. without molding.

In the method of the present invention, the acidic volcanic ejecta, deposits, or secondary deposits used as raw materials have 5i02 as its main constituent mineral, and contain several weight percent of various sub-constituent minerals such as feldspar and pyroxene. , contains various elements such as magnesium, calcium, and iron as metal components.

As a result of many experiments using a wide range of silicon sources as the raw material for producing Sialon, the present inventors found that acidic volcanic ejecta represented by Shirasu or its secondary deposits were found to contain aluminum and carbon in specific ranges. It was discovered that when combined with the same amount of heat, it is possible to produce ceramics with excellent corrosion resistance and high hardness that retain the excellent properties inherent in Sialon at a much lower firing temperature than conventional methods.

Although it is not yet clear which ingredients can achieve such a firing temperature reduction effect, it is possible to reduce the firing temperature compared to the conventional method that required a firing temperature of 1,700°C or higher to manufacture Sialon. was completely unthinkable.

According to the method of the present invention, firing can be performed at a temperature approximately 200° C. lower, which is completely unexpected from the conventional concept of conventional sialon firing technology.

The acidic volcanic ejecta or secondary deposits thereof used in the method of the present invention may be either one of them, but
In many cases, it is not possible to clearly distinguish between the two, and it goes without saying that a mixture of the two can be used.

A typical example is shirasu, but other materials such as rosinite and obsidian can also be used.

Further, in the method of the present invention, aluminum powder and carbon powder are used in combination with the above-mentioned acidic volcanic ejecta.

The aluminum powder is preferably in the form of fine pine dew, and for example, pine dew aluminum with a grain size of 50 μm or less can be suitably used.

Further, the carbon powder may be any type of carbon, such as carbon black or coke powder, but it is extremely preferable to use a fine powder that has been heat-treated in advance at a temperature of 1000 to 1400°C.

In the method of the present invention, 65 to 79.5% by weight of acidic volcanic ejecta and its secondary deposits, 20% by weight of aluminum powder,
-30% by weight of carbon powder and 0.5-5% by weight of carbon powder.

Since it is desirable to disperse the mixture as finely and uniformly as possible, a method in which pulverization and mixing are performed simultaneously is advantageously employed.

When the ratio of each component raw material deviates from the above-mentioned range, it is inconvenient that the above-mentioned excellent effects of the present invention cannot be obtained and the physical properties of the sialon are deteriorated.

In other words, if the amount of acidic volcanic ejecta or its secondary deposits is greater than the appropriate amount (when the amount of aluminum is low) or less than the appropriate amount (when the amount of aluminum is large), the amount of carbon is within the appropriate range. Even though
Densification does not proceed and a strong sintered body cannot be obtained.

Also acidic volcanic ejecta,! , 7) Or, even if both the secondary deposits and the amount of aluminum are within the appropriate range, if the amount of carbon deviates from the appropriate range, densification will not progress and the porosity will be significantly large. It becomes a body.

The pulverized fine powder mixture is then molded into a desired molded body or granular body with a diameter of 3N1L or less by compression molding or the like.

In that case, a small amount of a binder, such as a 10% starch solution, can be added to the raw powder mixture to facilitate shaping.

next. This molded product or granular material is placed in a nitriding furnace and heat-treated at a temperature of 1,300 to 1,400° C. for 5 to 6 hours in a nitrogen atmosphere to cause a nitriding reaction.

The nitrided molded product is directly subjected to the next high-temperature sintering process, but the nitrided granules are ground again, the crushed powder is molded into a molded product of the desired shape, and the product is sent to the next high-temperature sintering process. .

The molding of the powder mixture before the nitriding reaction is suitable for producing molded products with simple shapes, and the pulverized nitride film mixture is suitable for producing molded products with complex shapes.

Furthermore, when the powder obtained by crushing the nitrided granules is fired without being molded, it is possible to produce a powder material suitable as a raw material for abrasives and refractories with excellent oxidation resistance and heat resistance, for example.

The production of highly practical sialon powder from such an inorganic raw material powder mixture was completely unknown in the past, and the method of the present invention is groundbreaking in this respect as well.

The nitrided molded product, the powder obtained by crushing the nitrided granules, and the molded product are fired at a temperature of 1000° C. or more and less than 1700° C., which is lower than the conventional sintering temperature.

This high-temperature treatment yields a densified sialon sintered body and sialon powder having excellent corrosion resistance and hardness.

According to the method of the present invention, it is possible to effectively obtain a sialon sintered body at a low sintering temperature of less than 1700°C, which could not be adopted in the production of a sialon sintered body conventionally, and furthermore, the sialon sintered body A powder may be provided.

The method of the present invention is considerably lower than conventional methods that require high temperatures of 1,700 to 1,900 degrees Celsius.
Sialon sintered bodies can be produced at a firing temperature of less than 700°C, which is extremely advantageous industrially.Furthermore, in the conventional method, sufficient densification does not proceed unless aluminum is present in an amount of 30% by weight or more, but the method of the present invention In the method,
Since a densified sialon sintered body can be effectively obtained with an aluminum content of 30% by weight or less, costs can be reduced, and this method is also industrially superior.

Furthermore, the method of the present invention allows the use of a relatively low calcination temperature of less than 1700°C, which was taken to suppress thermal decomposition of the sample in the conventional method requiring a calcination temperature of 1700°C or higher. For example, by increasing the atmospheric pressure in the furnace and firing, or by filling the surrounding area of the sample with silicon nitride powder, which generates pyrolysis gas at high temperatures like the sample, or with powder having the same composition as the sample. There is no need to use a baking method, and the improvement effect can be evaluated.

As mentioned above, the method of the present invention can produce fired powder of Sialon, which has not been previously available, and this new powder ceramic can be used in various applications that take advantage of the characteristics of Sialon.

The sialon sintered body obtained by the method of the present invention has high density, high strength, high hardness, and excellent corrosion resistance, and can be used as a variety of heat-resistant and corrosion-resistant materials such as mechanical parts, protection tubes, and crucibles. The bodies are useful on their own as an abrasive or in combination with other ceramic powders as corrosion-resistant refractories.

EXAMPLES Below, the present invention will be explained in detail by way of examples so that it can be better understood.

Example 1 Shirasu was used as the acidic volcanic ejecta, 30% by weight of aluminum powder and 1% by weight of carbon powder were added thereto, and after thorough mixing, it was molded into a disc-shaped body with a diameter of 30 m, and this was placed in a nitrogen gas atmosphere. The temperature was raised to 1380° C. in the chamber, and nitriding was carried out at the same temperature for 5 hours.

Then, the temperature was kept at 1690℃ without cooling.
The temperature was further increased to 100.degree. C. and maintained for 1 hour to obtain a compact sintered body.

The sintered body is mainly composed of β-sialon and has an apparent specific gravity of 2.
．． 95, apparent porosity: 0.06%, water absorption: 0.05
%, Vickers hardness: 1000 Iy/m4, and room temperature bending strength: 24 kg/wait.

In addition, the sintered body was oxidized in air for 2 hours at 1200℃, molten aluminum was exposed to 700℃ for 1 hour, or molten copper was exposed to 1220℃ for 1 hour, but no change in the surface of the sintered body due to reaction with the molten metal was observed. There wasn't.

Example 2 Shirasu was used as the acidic volcanic ejecta, 20% by weight of aluminum powder and 3% by weight of carbon powder were added thereto, and after thorough mixing, it was made into granules with a diameter of 37IL7rL or less,
The temperature was raised to 1350℃ in a nitrogen gas atmosphere, and the temperature was increased to 6.
It was held for a time and nitrided.

Next, the nitride granules were finely pulverized, formed into a disk shape with a diameter of 30 mm, and fired at a temperature of 1550° C. for 1 hour under normal pressure without using nail powder or a closed container to obtain a sintered body.

The main component of the sintered body is β-sialon, and the apparent specific gravity is 2.
．． 8. Apparent porosity: 0.06%, water absorption: 0.02%
, Vickers hardness: 800 kg/mt? t, and room temperature bending strength of 20 kg/ma.

In addition, in an air oxidation experiment at 1000°C for 2 hours, all (
No change was observed.

In addition, molten aluminum at 700°C for 1 hour and molten steel at 12
Even in an erosion experiment conducted at 20° C. for 1 hour, no change in the contact surface due to reaction was observed.

Example 3 Shirasu was used as the acidic volcanic ejecta, and 30% by weight of aluminum powder and 1% by weight of carbon powder were added thereto, thoroughly mixed, and formed into a granular compact with a diameter of 1 to 3 mm using a granulator.

Next, the granules were placed in a firing furnace, heated to 1350° C. in a nitrogen gas atmosphere, and kept at the same temperature for 6 hours to nitride.

Next, this nitrided granular molded body was finely pulverized and formed into a disk shape with a diameter of 30 mm using a mold forming plate, and the molded body was baked at 1695°C under normal pressure for 1 hour without using powder or a closed container. ,
A sintered body was obtained.

The obtained sintered body has β-sialon as its main component, has an apparent specific gravity of 3.11, an apparent porosity of 0.05%, and a water absorption rate of 0.0.
2%, Vickers hardness was 1200 kg/myA, and room temperature bending strength was 3 kg/rm?t.

Furthermore, no change was observed in an air oxidation experiment at 1200°C for 2 hours.

Also, molten aluminum at 700°C for 1 hour and molten copper at 122°C.
No change due to reaction on the contact surface was observed in the 1-hour drop test at 0°C.

Example 4 A mixed powder of 78 parts by weight of acidic volcanic secondary pickle powder with a SiO2 composition of 70% by weight, 20 parts by weight of aluminum powder, and 2 parts by weight of carbon powder was granulated into granules with a particle size of 3 mm or less. The temperature was raised to 1300° C. in a nitrogen atmosphere, and the temperature was maintained for 5 hours to nitride.

Next, the nitrided granules were crushed into powder, placed in a graphite container, and fired in a nitrogen atmosphere at a temperature of 1500° C. for 1 hour to obtain a sialon-based powder.

Using this sialon powder as a raw material for refractories, we created a blended refractory material in place of the previously used raw material SiC, and conducted an air oxidation experiment at a temperature of 1650°C for 3 hours. No foaming or glass formation phenomena were observed.

Claims (1)

[Claims] 1. Acidic volcanic ejecta or secondary deposits thereof 65-79.
5% by weight, 20 to 30% by weight of aluminum powder, and 0.5 to 5% by weight of carbon powder are mixed and pulverized, then molded, and the molded body is heated at 1300 to 1400°C under a nitrogen atmosphere.
1. A method for producing a corrosion-resistant, high-hardness ceramic, which is characterized by heating to a temperature of 1,500° C. or higher to nitride it, and then heating it to a temperature of 1,500° C. or higher and lower than 1,700° C. to sinter and densify it. 2 Acidic volcanic ejecta or secondary deposits 65-79.
A mixed powder consisting of 5% by weight, 20 to 30% by weight of aluminum powder, and 0.5 to 5% by weight of carbon powder was granulated into granules with a diameter of 3 mm or less, and the granules were heated under a nitrogen atmosphere for 13 to 30 minutes.
After heating to a temperature of 00 to 1400°C and nitriding, it is pulverized, molded into a predetermined shape, and the molded product is heated to 150°C.
A method for producing corrosion-resistant, high-hardness ceramics, characterized by sintering at a temperature of 0°C or more and less than 1700°C. 3 Acidic volcanic ejecta or secondary deposits 65-79.
A mixed powder consisting of 5% by weight, 20 to 30% by weight of aluminum powder, and 0.5 to 5% by weight of carbon powder was granulated into granules with a diameter of 3 mm or less, and the granules were heated under a nitrogen atmosphere for 13 to 30 minutes.
A method for producing powdered corrosion-resistant, high-hardness ceramics, which comprises heating to a temperature of 00 to 1,400°C, nitriding, pulverizing, and firing the nitrided fine powder at a temperature of 1,500°C to 1,700°C.