JPS6230681A - Non-gas-permeable ceramic sintered body and manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is directed to Si 3N which is used by being immersed in molten Al.
The present invention relates to a reaction sintered compact made of a SiC material and/or a SiC material, and a method for producing the same.

(Prior Art) Conventionally, ceramic-coated cast iron has been used as a material for protection tubes for immersion heaters for molten Al, hot water supply pipes for low-pressure casting machines for molten Al (hereinafter referred to as "stalks"), and the like.

However, during use, the coating part of the cast iron may be damaged or peeled off, and the iron content in the cast iron may mix into the M molten metal.
Recently, SiO quality + Si3N4 quality.

Ceramic materials such as ZrO2 are used.

By the way, reaction sintering, normal pressure sintering, and hot pressing are known as methods for obtaining molded bodies of Si3N4 + SiC, but the above-mentioned normal pressure sintering and hot pressing methods have poor formability and It has drawbacks such as poor workability and difficulty in achieving dimensional accuracy. Furthermore, it is known that a sintered compact having a complicated shape can be obtained by the reaction sintering method.

However, the reaction sintered compact has a large open porosity, and in particular, the Si3N4 and/or SiO reaction sintered compact has an open porosity of 10 to 15%. The following methods have been proposed to reduce the open porosity.

According to the invention described in Japanese Patent Publication No. 38-145 and Japanese Patent Publication No. 41-4961, the surface of a carbide product such as 5iCi + TiCI ZrO is coated with alkali silicate, or mixed with an organic or inorganic acid such as borax or boric acid. After applying the material, heat treatment is performed to form a glassy base layer, and then A120 S T Z r O2rz is applied to the base layer.
Heat-resistant materials such as rSi04 and 0r203 are flame sprayed to form an intermediate layer, and the top layer is Si02 + Ca.
A method of forming an oxide layer such as O+ZnO+BeO is known.

JP-A-54-142219 and JP-A-56-9217
According to the invention described in No. 0, a method is known in which a solution of an inorganic salt or an organic salt such as Si r Alt Mg + Zr' is impregnated into the voids of a reaction-sintered Si3N4 molded body, and then firing is performed. There is.

In accordance with the invention described in JP-A-58-130175, porous SiO+si3N, Al2O in the pores of the porous molded body.
,.

A corrosion-resistant material for immersion in molten metal has been proposed, which is impregnated with fine powder of Si3N4 and SiC and then coated with a BN-based coating material.

According to the invention described in JP-A No. 55-22424, U203 quality + ZrO2 quality + 5i (by impregnating the surface of the three types of refractory material with one or more of carbonaceous materials and inorganic materials, firing and glazing) A stalk subjected to one or more types of treatments has been proposed.

(Problems to be Solved by the Present Invention) However, according to the conventionally known inventions described in JP-A No. 38-145 and JP-B No. 41-4961, the coating is formed into a base layer, an intermediate layer, and an upper layer. Therefore, when a product coated with such a coating is immersed in molten metal, the coating layer has the disadvantage of peeling off due to thermal shock.

Also, JP-A-54-142219 and JP-A-56-9
According to the invention described in No. 2170, reaction sintered Si3N
It is not easy to impregnate 4 with a solution of inorganic or organic salts such as Si + Kl + Mg + Zr, so it has almost no effect on improving airtightness, and if impregnated However, since the coefficient of thermal expansion is different from that of Si and the tJ4 sintered body, it has the disadvantage that it easily peels off due to thermal shock.

Furthermore, the material of the invention described in JP-A No. 58-130175 does not sufficiently impregnate pores as described above.
Further, even if a ceramic foot material such as a BN type ceramic foot material is coated, the airtightness is significantly reduced during use.

Furthermore, the stalk for low-pressure casting equipment according to the invention described in JP-A No. 55-22424 is impregnated with a carbonaceous material such as tar or a colloidal inorganic material on its surface, fired, or glazed. It is a stalk that has been subjected to two or more types of treatments, and the surface coating of the obtained stalk is made of two layers when a glaze is applied and fired, and the two layers have different coefficients of thermal expansion. On the other hand, impregnating only colloidal or doped inorganic materials is not easy and has little effect on improving airtightness, and materials impregnated with carbon materials are easily separated from each other. It has the disadvantage that it is oxidized and the airtightness is impaired.

(Means for Solving the Problems) The present invention aims to eliminate and improve the drawbacks of the prior art. By providing a method, the above object can be achieved.

In other words, 5i5N used in contact with molten At
In an impermeable ceramic sintered body made of at least one of the four materials and the SiC material and covered with a vitreous silicate film, the film contains a ceramic powder having low wettability with respect to the molten metal. The present invention relates to an air-impermeable ceramic sintered body characterized in that the present invention is dispersed in a non-porous ceramic sintered body, and a method for manufacturing the same.

The present invention will be explained in detail below.

The present inventors first discovered that 5i5N4 and/or SiC
In order to eliminate the air permeability of the reactive sintered compact, we investigated a method of covering the surface of the reactive sintered compact with a conventionally known silicate glass film.

In other words, the basic components in the glass (Na201 K2O
A slurry of mixed powder containing various amounts of rCaO, Mg0-), acidic components (Si02) + amphoteric components (ht2o, IB2O5) was applied to the reaction sintered compact, and then fired. When we observed the condition, we found that there were few alkaline components and boric acid (B2).
0. ) was found to form an intermediate layer with the reactive sintered compact to provide a strong bond. However, according to this method of vitrifying and simultaneously applying a film, the B10° component, which has a low melting temperature and low viscosity, in the mixed powder can be melted before eutectic with other mixed powder components during firing. It has been found that it melts in its own state and seeps into the pores of the molded body, lowering the thermal shock resistance of the molded body itself and making cracks more likely to occur due to thermal shock. Therefore, by using borosilicate glass powder prepared by melting and fritting these components in advance, we newly discovered that it is possible to apply a coating with strong adhesion without impairing the thermal shock resistance of the molded body.

Furthermore, the present inventors discovered that Si 3 of the borosilicate glass powder
The thermal expansion coefficient is 1.5X for N4 molded bodies.
10-' ~3.5 X 10-'/'CI SiG
The coefficient of thermal expansion is 2.5 x 1 for molded products.
It has been found that a borosilicate-glass powder having a composition of 0-6 to 4.5 x 1 o-'/°C is most preferred as a coating for a reaction-sintered compact. The reason for this is that if the thermal expansion coefficient of the borosilicate glass powder is significantly different from the thermal expansion coefficient of the reaction sintered compact, there is a problem that the coating will peel off. It is preferable that the coefficient of thermal expansion be the same or slightly smaller so that appropriate compressive stress is applied to the molded body.If the coefficient of thermal expansion is increased, cracks may occur on the surface of the coating during firing, and the molten aluminum may This is not preferable because the film peels off during immersion, and also among borosilicate powders, the softening point generally increases as the coefficient of thermal expansion becomes smaller, so from this point of view as well, borosilicate powders with a slightly smaller coefficient of thermal expansion are used. This is because it is desirable to apply the coating using the same method.

The softening temperature of the borosilicate glass needs to be higher than the temperature of the At molten metal, and is preferably at least 700°C or higher, preferably 800°C or higher.

Based on the above results, we repeatedly conducted tests in which a reactive sintered molded body coated with borosilicate glass of a specific composition was immersed in molten Al, and as a result, there was no peeling or cracking of the coating. It was observed that upon immersion, the molten metal 1 reacts with the borosilicate glass, precipitates free silicon, and elutes the borosilicate glass coating.

Therefore, the present inventors further studied a method of making the borosilicate glass film difficult to wet with At molten metal, that is, a method of preventing the borosilicate glass film from eluting. This result A
5i5N4t BN p Ti with low wettability to molten metal
It has been found that a ceramic powder such as B2p T1Cr Zr02r Zr5iO suspended in a borosilicate glass coating is the most difficult to wet with molten Al. At this time, the ceramic powder with low wettability to the At molten metal (hereinafter referred to as ceramic powder) is a vitreous silicate powder of 100%
It has been found that it is preferable to mix 2ON parts by weight or less. The reason for limiting the amount of ceramic powder blended is that if the amount of ceramic powder blended is more than 20 parts by weight, the heat resistance of the coating will improve, but the airtightness will deteriorate and the coating will peel easily. must be 20 parts by weight or less.

Next, a method for manufacturing the non-porous ceramic sintered body of the present invention will be explained.

A method for blending and mixing ceramic powder with a borosilicate glassy coating is to MQ the ceramic powder and borosilicate glassy powder in a solvent such as aqueous alcohol, and then apply this to the surface of the reaction sintered body with a brush.

It can be obtained by applying by spraying, dipping, etc., and baking. According to another method of the present invention, borosilicate glass powder of a specific component is first applied to the surface of the reaction-sintered compact with water! A slurry of ceramic powder suspended in a solvent such as alcohol was applied, and then a slurry of ceramic powder suspended in a solvent such as water or alcohol, or a mixture of the ceramic powder and borosilicate glass powder was suspended in a solvent. The slurry is further applied on top of the layer coated with the vitreous silicate powder, and then fired.

According to the above method, the ceramic powder is present relatively on the surface of the siliceous glass coating, and not only the wettability is further improved, but also the part of the coating near the reaction sintered body has There is no ceramic powder present, and the surface of SiC, Si, or N4, which is the base material of the reaction sintered compact, reacts with the borosilicate glass to form an intermediate compound, resulting in a very strong bond and no peeling due to thermal shock. It disappears.

According to the method of the present invention, the surface of the reaction-sintered compact is made of thin Si.
Although it is covered with a film, before applying the borosilicate glass film, the reaction sintered compact is fired in an oxidizing atmosphere to further grow the 5in2 film, and then the borosilicate glass film is applied. By applying this, a very strong film can be formed.

According to the present invention, the particle size of the ceramic powder to be mixed with the borosilicate glass powder is preferably 20 μm or less, because if the particle size is larger than 20 μm, it will not be sufficiently uniform even when mixed with the borosilicate glass powder. It is.

According to the present invention, the firing temperature is generally 300 to 300° below the softening point, as long as the temperature is sufficient to melt the borosilicate glass powder.
A temperature 400°C higher is sufficient. If the atmosphere during firing is oxidizing, it is not preferable because firing at high temperature or for a long time will cause a foaming phenomenon, and it is preferable to perform firing in a non-oxidizing atmosphere.

When firing in an oxidizing atmosphere, the above foaming phenomenon can be suppressed by first firing the reaction sintered compact in an oxidizing atmosphere, then applying a slurry mixture of vitreous silicate powder and ceramic powder and firing. It can be prevented.

Examples of the present invention will be described below.

Example 1 Borosilicate glass powder adjusted to a particle size of 200 mesh or less (thermal expansion coefficient 2.3 x 1 o-', /'c, softening temperature 830°C2 composition 5i0280.2%lB2031
7.9%1K201.9%) and 5fold N% BN powder (
average particle size 10.5 μ) and 5 wt% ZrO□ powder (
Si 31J produced by reaction sintering was prepared by creating a 40-layer mixed fire-water solution slurry containing an average particle size of 2.7μ).
, spray applied to the outer surface of the stalk to a thickness of approximately 2 coats.

After drying this, it was fired in a N2 atmosphere under conditions of holding at 1200° C. for 1 hour to obtain a stalk for aluminum low pressure casting. When this was subjected to a pressure leakage test under the pressurizing condition of IKty/cm2, the stroke without coating was 1.7
X l O”” (cm2-cm/H2Q cm・
The stalk of the present invention had an air permeability of 8.8 x 10-' (cm2.cm).
/H20cm, cm2.3), and it was found that there was no problem at all in actual use. It was also found that this stalk was difficult to wet with molten A/, and could be used continuously even after one month had passed after use.

Example 2 A slurry of a 40% by weight aqueous solution of borosilicate glass powder of the same quality as in Example 1 was prepared, and this was mixed with Si produced by reaction sintering.
3N, was spray applied to the protective tube to a thickness of approximately 2 coats. Next, about 1 f! Spray coated to a thickness of m. After drying, it was fired at 950° C. for 30 minutes to obtain a heater protection tube for immersion in molten Al. An air permeability test confirmed that this protective tube had almost no air permeability, and when it was immersed in A7 molten metal 5N9 heated to 750°C in a graphite crucible to examine its corrosion resistance, it was found that after 3 months had passed. Almost no change was observed.

For comparison, when a protective tube glazed only with borosilicate glass powder was immersed in molten Al, Al was observed to adhere to the surface of the protective tube shortly after immersion.

Example 3 The same mixed slurry as in Example 1 was applied to the outer surface of a reactive sintered 5i5N pipe that had been heat-treated in an oxidizing atmosphere.
It was spray coated thickly, and after drying, it was fired in an air atmosphere at 1100° C. for 1 hour. Almost no foaming phenomenon was observed in the resulting coating, but when a coating and baking was performed on a coating that had not undergone oxidation treatment for comparison, significant foaming was observed in the glassy coating.

(Effects of the present invention) The reaction sintered compact of the present invention has no air permeability, the film does not peel off even when repeatedly immersed in molten Al, and its wettability with molten metal is extremely low, so it has excellent corrosion resistance. Significantly improved.

Claims (1)

[Claims] 1. Si_3N_ used in contact with molten Al
In the non-porous ceramic sintered body made of at least one of the four materials and the SiC material and covered with a vitreous silicate film, a ceramic powder having low wettability with respect to the molten Al is dispersed in the film. A breathable ceramic sintered body characterized by: 2. The ceramic powder dispersed in the coating is S
i_3N_4, BN, TiB_2, TiC, ZrO_2
, ZrSiO_4, or two or more thereof. 3. The impermeable ceramic sintered body according to claim 1 or 2, wherein the ceramic powder dispersed in the coating has a particle size of 0.1 to 20 μm. 4. Claims 1 to 3, characterized in that the content of the ceramic powder dispersed in the coating is 20 parts by weight or less per 100 parts by weight of silicate glass in the coating.
The impermeable ceramic sintered body according to any one of paragraphs. 5. The silicate glass coating has a thermal expansion coefficient of 1.5.
x10^-^6 to 4.5 x 10^-^6/℃, and the softening temperature is 700℃ or higher. The impermeable ceramic sintered body according to any one of the above. 6. Si_3N_ used in contact with molten Al
A method for manufacturing an impermeable ceramic sintered body made of at least one of four materials and a SiC material and coated with a vitreous silicate film, wherein the surface of the ceramic sintered body is coated with the molten Al metal. A method for manufacturing a non-porous ceramic sintered body, which comprises applying a slurry of a ceramic powder with low wettability and a vitreous silicate powder suspended in a solvent, and then firing the slurry. 7. The ceramic powder dispersed in the coating is S
i_3N_4, BN, TiB_2, TiC, ZrO_2
, ZrSiO_4, or ZrSiO_4. 8. The method for producing a non-porous ceramic sintered body according to claim 6 or 7, wherein the particle size of the ceramic powder dispersed in the coating is 0.1 to 20 μm. . 9. Claims 6 to 8, characterized in that the content of the ceramic powder dispersed in the vitreous silicate film is 20 parts by weight or less per 100 parts by weight of the vitreous silicate powder. A method for producing a non-porous ceramic sintered body according to any one of the above. 10. The silicate glass powder has a coefficient of thermal expansion of 1.
Claims 6 to 9 are characterized in that the powder is a borosilicate glassy powder having a softening temperature of 5×10^-^6 to 4.5×10^-^6/℃ and a softening temperature of 700℃ or higher. A method for producing a non-porous ceramic sintered body according to any one of the above. 11. Si_3N used in contact with molten Al
A method for manufacturing an impermeable ceramic sintered body made of at least one of the following materials: After applying the slurry suspended in Al,
A non-porous ceramic sintered body characterized by applying a slurry of a ceramic powder having low wettability to molten metal or a mixture thereof with a silicate glass powder suspended in a solvent and firing it. Production method. 12. The ceramic powder dispersed in the coating is
Si_3N_4, BN, TiB_2, TiC, ZrO_
2. The method for producing a non-porous ceramic sintered body according to claim 11, characterized in that the material is one or more of ZrSiO_4. 13. Ceramic powder dispersed in the coating,
13. The method for producing a non-porous ceramic sintered body according to claim 10 or 12, wherein the particle size is 0.1 to 20 μm. 14. The content of the ceramic powder dispersed in the coating is 20 parts by weight or less per 100 parts by weight of the vitreous silicate powder. A method for producing a non-porous ceramic sintered body according to any one of the above. 15. The vitreous silicate powder has a coefficient of thermal expansion of 1.
Claims 11 to 14, characterized in that the powder is a borosilicate glassy powder having a softening temperature of 5×10^-^6 to 4.5×10^-^6/℃ and a softening temperature of 700℃ or higher. A method for producing a non-porous ceramic sintered body according to any one of the above.