JPH01176289A - Member for molten aluminum and production thereof - Google Patents

Abstract

PURPOSE:To enable formation of members for molten aluminum capable of withstanding use for a long period without causing fracture, cracking, fusion, corrosion, etc., by covering an inner layer consisting of silicon nitride or sialon based ceramics with an outer layer consisting essentially of boron nitride. CONSTITUTION:This member is constituted of an inner layer consisting of silicon nitride or sialon based ceramics and an outer layer consisting essentially of boron nitride (BN). The above-mentioned member for molten aluminum is produced by coating a compact of silicon nitride or sialon based ceramics with ceramics powder (preferably containing 40-60wt.% BN and 40-60wt.% SiO2) containing BN and SiO2 and then calcining the coated compact at 1,600-1,900 deg.C. The afore-mentioned silicon nitride or sialon base ceramics contain >=70wt.% Si3N4, <=20wt.% one or two or more oxides (e.g., Y2O3, La2O3 or ClO2) of group IIIa elements of the periodic table and <=20wt.% Al2O3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a member having good corrosion resistance against molten aluminum, high mechanical strength and thermal shock resistance, and a method for manufacturing the same.

[Prior art] Corrosion-resistant ceramics have been used for Stokes, ladle, immersion heater protection tube, gas blowing parts, molten metal pump parts, molten metal stirring parts, molten metal stoppers and seats, toys, etc. that handle molten aluminum. Powder-coated cast iron components were widely used. However, the metallic materials of such parts tend to dissolve in the molten aluminum with which they come into contact, thereby reducing the quality of the molten aluminum. Another problem is that corrosion-resistant ceramic coatings do not have sufficient adhesion to metal materials and are easily peeled off, requiring daily application. Furthermore, since it is made of metal such as cast iron, it is relatively heavy and difficult to handle.

Therefore, recently, ceramic members made of silicon nitride or silicon carbide for molten aluminum have been used instead of metal members.

[Problems to be Solved by the Invention] However, these ceramic members for molten aluminum have conventionally been manufactured by a reaction sintering method in which silicon metal is nitrided or carbonized, and therefore have a bending strength of only about 30/-. As expected, it was unable to withstand mechanical stress and shock during use. Furthermore, since these ceramic members have a relatively low density, their surfaces are rough and molten aluminum is easily welded to them. Moreover, even those with relatively good bending strength do not have sufficient thermal shock resistance, and are therefore prone to breakage due to thermal shock.

Ceramics with sufficient strength and thermal shock resistance, such as Si3N4 ceramics, sialon, and silicon carbide, have poor wettability with molten aluminum, but as the time of use increases, aluminum will gradually adhere to them. In particular, the number of aluminum deposits increases near the surface of the molten metal.

Therefore, the object of the present invention is to provide a member for molten aluminum in which an inner layer having high bending strength, good corrosion resistance against molten aluminum, high density, and high thermal shock resistance is coated with an outer layer mainly composed of BN to which aluminum does not easily adhere. It is to provide.

Another object of the present invention is to provide a method for manufacturing such a member for molten aluminum.

[Means for solving the problem] In view of the above objectives, as a result of intensive research, it was found that by forming an outer layer mainly composed of BN on silicon nitride or sialon ceramics, adhesion of molten aluminum can be suppressed, and aluminum The inventors have discovered that the lifespan of molten metal members can be significantly extended, and have come up with the present invention.

That is, the member for molten aluminum according to the present invention is characterized by comprising an inner layer made of silicon nitride-based or sialon-based ceramics, and an outer layer mainly composed of boron nitride.

Further, the method for manufacturing a member for molten aluminum of the present invention includes coating a molded body of silicon nitride or sialon ceramics with ceramic powder containing BN and SiO2,
It is characterized by being sintered at a temperature of 00 to 1900°C.

The above silicon nitride or sialon ceramic is 5i3N
70% by weight or more of a, one or more oxides of Group IIIIa elements of the periodic table and 20% or less of oxides, and Al20
320% by weight or less.

Regarding S i 3N4, it should contain more than 65% by weight of α phase. If the α phase is less than 65%, the sinterability is low and the sintered density is low, resulting in low mechanical strength.

The content of α phase is preferably 85% by weight or more.

The oxide of the first group a element that can be used in the present invention is Y2O3
, Lag'3, Cede, etc. These oxides primarily act as sintering aids. Y2O3 is most preferable, and when performing normal pressure sintering or gas pressure sintering, Y2O3 is 3 to 3.
The content is preferably 10% by weight. If Y2O3 is less than 3% by weight, the sintered density will not be sufficient, and if Y2O3 is more than 10% by weight, the high temperature strength of the obtained sintered body will be significantly reduced.

In order to perform pressureless sintering or gas pressure sintering in this way, a relatively large amount of Y 203 is required. A more preferred range of Y2O3 is 5 to 7% by weight.

As for Al2O3, it is preferable that the weight is in the range of 3 to 7 weights. If it is less than 3% by weight, sinterability is low and the sintered density is low. On the other hand, if it exceeds 7% by weight, the resulting sintered body will have significantly low high temperature strength.

More preferable Al2O3 content Φ is 3 to 5% by weight.

The silicon nitride or sialon ceramics of the present invention may further contain AIN or a solid solution thereof in an amount of 15% by weight or less. Here, the AIN solid solution can also be referred to as an AIN polytype and contains AIN, Si3N4 and Al2O3, and the content of AIN is about 68% by weight. AIN or A
The preferred content of IN solid solution is 1 to 9% by weight. 1
If it is less than 9% by weight, the sintered body will turn blue and have extremely low high temperature strength, and if it exceeds 9% by weight, sufficient sinterability will not be obtained and the strength of the sintered body will decrease. A more preferred content of AIN or AIN solid solution is 2 to 9 weights.

The ceramic powder having the above composition is mixed in a ball mill using ethyl alcohol, methyl alcohol, etc. as a solvent. A binder such as polyvinyl alcohol or polyvinyl butanol is added to the obtained powder mixture in a proportion of 0.5 to 1% by weight based on the ceramic component, and the mixture is spray-dried and granulated to a desired size.

After the ceramic granules are sieved to a particle size of 200 to 60 mesh, they are molded by cold isostatic pressing (CIP) at a pressure of about 700 to 1500 kg/cjI.

The molded body obtained by the CIP method is degreased by heating, its outer shape is adjusted, polished with sandpaper, and cut into a desired length.

Before sintering, the molded body is BN and S! Coating with ceramic powder containing 02. In a preferred IL1 embodiment, BN is 40-60% by weight and SiO2 is 40-60% by weight.
in weight. The coating layer can be formed by spraying or brushing. For application, alcohol, ether,
Organic solvents such as ketones, alkanes, aromatic hydrocarbons, etc. are used with organic binders. This ceramic powder coating layer should be at least 0.0% in order to obtain a sufficient effect.
It is necessary to have a thickness of 5rR1n.

The molded body of silicon nitride or sialon ceramics coated with ceramic powder according to the present invention is 30 (ly/-
Sintering is carried out in a nitrogen atmosphere at a gas pressure of: Both pressureless sintering and gas pressure sintering can be used.

The term ``normal pressure sintering'' used in Water Quantity A sintering refers to sintering performed under atmospheric pressure without pressing, and the term ``gas pressure sintering'' refers to sintering performed under gas pressure without pressing. means.

Pressureless sintering requires complicated sintering equipment and is therefore more preferred. In this sintering method, the nitrogen gas is usually 2 to 9 /
less than ci. As the pressure of nitrogen gas increases, the density of the sintered body also increases.

In the present invention, the sintering temperature is 1600 to 1900°C.

If it is less than 1600℃, sufficient sintered density cannot be obtained, and 190℃
If the temperature exceeds 0°C, 513Na may be decomposed.

The preferred sintering temperature is 1700-1800°C.

Furthermore, a sintered body of silicon nitride or sialon ceramics can also be coated with ceramic powder containing BN and Si02 to form an outer layer mainly composed of BN. In that case as well, the coating liquid for forming the coating layer is the same as that described above, and the sintering conditions are also the same. However, since it is a sintered body, the preferred sintering temperature is 1600°C to 1700°C.
It is ℃.

The sintered body of silicon nitride or sialon ceramics is A
When the IN or AIN solid solution is contained in an amount of 15 weight or less, it has a composition represented by the following general formula: % formula % (where Q<z≦4.2).

In addition, 5i3N450% by weight or more, li, Na.

Ca, M (1, Y and one or two oxides of rare earth elements
When containing 20% by weight or more of species or more, 20% by weight or less of Al203, and 15% by weight or less of AIN or AIN solid solution, the following general formula: % formula %) (Tatashi, Mashishii, Na, It has a composition represented by one or more of Ca, Mg, Y, and rare earth elements (O<X≦2). Sialon with this composition is α-phase sialon, and α-sialon has 10 to 70% by weight of α phase and β phase.
It consists of 20-90% by weight of a phase and 0.1-10% by weight of a glassy phase.

Sintered bodies of silicon nitride or sialon ceramics are so
It has a bending strength of at least /Wt, a density of at least 90% of the theoretical value, and a thermal shock temperature ΔT of at least 400°C.

80-90 wt% 513Na, 5-10 wt% Yt
03.3-7% by weight A l l! In the case of a sintered body made of 03 and 2 to 9 heavy weight AIN or AIN solid solution, the bending strength is 70 Ky/g or more, and the density is 95 to 99%.
The thermal shock temperature ΔT is 450° C. or higher.

When a molded body of silicon nitride or sialon ceramics seeded with ceramic powder containing BN and 5i02 is sintered, a sintered body having a two-layer structure is obtained, with the outer layer containing B.
N is the main component, mainly BN-81o2-AI 20
Consists of 3-Y2O3.

The inner layer has substantially the same composition as the ceramic starting powder. The thickness of the outer layer is 5 to 50 μm, and because of the presence of BN in the outer layer, the member has extremely good resistance to molten aluminum welding and also improves oxidation resistance. The formation of this outer layer is thought to occur through the following mechanism.

That is, due to the presence of SiO2 on the surface, the glass layer at the grain boundaries rises to the surface, allowing BN to sinter on the surface. Al2O3 and Y2O3 drawn from the silicon nitride or sialon ceramic layer act to enable sintering of the BN.

As described above, the member for molten aluminum of the present invention has a two-layer structure, the inner layer is made of silicon nitride or sialon ceramics having high mechanical strength and impact resistance, and the outer layer is mainly made of BN-8!02-AI 203. Since it is made of -Y2O3, it has good welding resistance to aluminum melt fields. This component is therefore highly resistant to impact loads, thermal shocks and welding. Furthermore, it has sufficient corrosion resistance against aluminum. Therefore, the member for molten aluminum of the present invention has an extremely long life.

[Example] The present invention will be explained in further detail by the following examples.

Example 1 85.6% by weight Si 3Na powder (particle size 0.8um
) with 6.5 wt% Y2O3 powder (particle size 1.0 μm)
, 2.9% AIN polytype (solid solution) powder (particle size 0.8 μm) and 4.811% AlO3 powder (particle size 0.1 μm) were added and mixed by a ball mill in isopropyl alcohol. After drying, a 10% polyvinyl alcohol solution with a 5% concentration was added to the powder mixture, placed in a rubber press, and subjected to cold isostatic pressing (CIP) using a hydrostatic pressure of 1 ton/Cl11 to form a compact. . 40 parts by weight of BN powder and 40 parts by weight of Si
O2 powder, 50 parts by weight of collodion and 4-methyl-2
- coated with a ceramic powder paste consisting of pentanone. The thickness of the coating layer after drying is approximately 1m#! Met. Then, it was sintered in a nitrogen atmosphere at 1750° C. and 1 atm for 5 hours. After sintering, the ceramic powder remaining on the surface was removed. The obtained sialon sintered member had the following characteristics.

Relative Density 99.0% Bending Strength* (Temperature) 80 to 9/C
) 80/(y/m” Thermal shock temperature T600°C Note*: Based on 4-point bending test (lower span 30ffi11 upper span 10M).

This member was cut and its cross section was examined using a scanning electron microscope (SEM).
) was measured. Figure 1 is a SEM photo, and it is clear that 2
The layered structure (the gray part is the inner layer of Sialon, and the white part is the outer layer) is shown. Infrared analysis shows that the outer layer is 8N.
It was confirmed that it contains Furthermore, the presence of A1 and Si in the outer layer was confirmed by electron probe micropart analysis (EPMA). Since Y2O3 is an essential component for sintering, it is considered certain that Y2O3 also exists in the sintered outer layer. This Y2O3 is sucked from the underlying silicon nitride or sialon ceramic layer.

This part was immersed in molten aluminum. the result,
It was found that even after six months of immersion, there was virtually no corrosion or welding caused by the molten aluminum. It was also able to withstand mechanical shock during immersion and thermal shock due to loading and unloading. Therefore, it can be seen that it can be used for more than one year without requiring repair.

Example 2 82.7% by weight of S! 3Na, 5.8% by weight Y2O3
, 3.8% by weight Al2O2 and 7.7% by weight AIN
Example 1 was repeated except that polytype was used as the ceramic material.

The obtained member was immersed in molten aluminum.

As a result, as in Example 1, even after being immersed for 6 months, the member was hardly dissolved in the molten aluminum.

Example 3 A molded body was formed using the same ceramic material as in Example 1 and the same method. Around the molded body, 80% by weight of 3
A powder consisting of i3N4 powder and 20% by weight BN powder was filled and sintered at 1750° C. and 1 atm in a nitrogen atmosphere for 5 hours. Next, the surface of the obtained sintered body was coated with the same ceramic powder paste as in Example 1, and heated at 1650°C.
, sintered in a nitrogen atmosphere at 1 atm for 3 hours.

The obtained member was immersed in molten aluminum.

As a result, the members were hardly dissolved in the molten aluminum even after being immersed for 6 months as in Examples 1 and 2.

[Effects of the Invention] As described above, the member for molten aluminum of the present invention has a two-layer structure, the inner layer is made of sintered silicon nitride or sialon ceramics, and the outer layer is mainly made of BN-3! 02
-AI 203-Y2O3, it can withstand long-term use without breaking, cracking, welding, corrosion, etc. Furthermore, since cast iron pipes are not used, it is lightweight and does not dissolve into molten aluminum. Therefore, deterioration in the quality of molten aluminum can be prevented.

The members for molten aluminum of the present invention having such features are suitable for Stokes, ladle, immersion heater protection tube, gas blowing member, molten metal pump member, molten metal stirring member, molten metal stopper and seat, toys, etc. It can be suitably used.

[Brief explanation of the drawing]

FIG. 1 is a scanning micrograph showing the crystal structure of the cross section of the member of Example 1. Agent Patent Attorney Takaishi Tachibana Ma Diagram 1 15kV DIJ

Claims (11)

[Claims] (1) A member for molten aluminum comprising an inner layer made of silicon nitride-based or sialon-based ceramics and an outer layer mainly composed of boron nitride. (2) In the member for molten aluminum according to claim 1, the silicon nitride or sialon ceramic has a bending strength of 50 kg/mm^2 or more, a density of 90% or more of the theoretical value, and a temperature of 400°C or more. A member for molten aluminum characterized by having a thermal shock temperature ΔT. (3) In the member for molten aluminum according to claim 1 or 2, the silicon nitride or sialon ceramic is Si_3N_470% by weight or more;
A member for molten aluminum, comprising 20% by weight or less of one or more oxides of Group IIIa elements of the periodic table and 20% by weight or less of Al_2O_3. (4) In the member for molten aluminum according to claim 1, the silicon nitride or sialon ceramic is β-sialon having the general formula: Si_6_-_zAl_zO_zN_8_-_z (0<z≦4.2). And,
Si_3N_470% by weight or more and III of the periodic table
20% by weight or less of one or more oxides of group a elements, 20% by weight or less of Al_2O_3, and AlN or AlN
A member for molten aluminum, characterized in that it contains 15% by weight or less of a solid solution. (5) In the member for molten aluminum according to claim 1, the silicon nitride or sialon ceramic has the general formula: M_x(Si,Al)_1_2(O,N)_1_6 (where 0<x≦ 2, M represents one or more of Li, Na, Ca, Mg, Y, and a rare earth element), which is an α-sialon having an α-phase sialon 10 to 7.
Si_3N_450
% by weight or more, one or more oxides of Li, Na, Ca, Mg, Y and rare earth elements and 20% by weight or less of A
A member for molten aluminum, characterized in that it contains 15% by weight or less of IN or AlN solid solution. (6) In the member for molten aluminum according to any one of claims 1 to 5, the outer layer has a
A member for molten aluminum, characterized in that it has a thickness of 50 μm. (7) In the member for molten aluminum according to any one of claims 1 to 6, the member includes a Stokes, a ladle, an immersion heater protection tube, a gas blowing member, a molten metal pump member, and a molten metal stirring member. A member for molten aluminum, characterized in that it is any one of a member for use with molten metal, a molten metal stopper and seat, and a toy. (8) In a method for producing a member for molten aluminum comprising an inner layer made of silicon nitride or sialon ceramics and an outer layer mainly composed of boron nitride, the molded body of silicon nitride or sialon ceramics is made of BN and S.
Coated with ceramic powder containing iO_2, 160
A method characterized by sintering at 0 to 1900°C. (9) The method according to claim 8, wherein the ceramic powder coating has a thickness of 0.5 mm or more. (10) In the method according to claim 8,
A method characterized in that the sintered body of silicon nitride or sialon ceramics is coated with ceramic powder containing BN and SiO_2 and sintered at 1600 to 1900°C. (11) The method according to claim 10, wherein the ceramic powder coating has a thickness of 0.5 mm or more.