JPH03115170A - Refractory material - Google Patents

Abstract

PURPOSE:To obtain refractory material having high corrosion resistance in the case of melting active metal by forming the surface of material of either cerium oxide or cerium oxide mixed with the specified metallic oxide. CONSTITUTION:Refractory material is obtained by forming the surface of either at least cerium oxide or the substance mixed with <=20mol% at least one kind selected from among alumina, magnesia and calcia in addition to cerium oxide. Therein the utilized corrosion resistant material is limited to cerium oxide selected from among the rare earth metallic oxides because the oxides of the rare earth elements cause change in a crystalline structure in the interval to ordinary temp. from m.p. or are expensive and unsuitable to industrial applications. Al2O3, MgO and CaO are preferably added to cerium oxide in order to enhance sinterability, bonding property and adhesive property to the material of a substrate sticking a film and consistency of thermal expansion coefficient. However when these oxides deteriorated in corrosion resistance are mixed at large amounts, corrosion resistance of the material itself is remarkably impaired. Therefore it is necessary that the mixed amount thereof be regulated to 20mol%.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a method for melting active metals such as rare earth metals and alloys containing the same, the surface of which is made of a corrosion-resistant material. Regarding fireproof materials.

Rare earth metals such as T1 and V are important as raw materials for various new materials such as magnetic materials and special alloys. In applications involving these new materials, trace amounts of impurities often significantly impair the quality of the materials, so care must be taken to prevent contamination during the production and processing of these active metals and their alloys. There is a need.

However, these metals are generally highly active and react with the crucible material during the process of melting and casting the metal, eroding the crucible and contaminating the crucible itself.
Conventionally, oxides that are difficult to reduce, such as MgO5Cab, Al, and O, have been used as materials for melting these highly corrosive metals.

However, even with these materials, it was not possible to sufficiently prevent corrosion by rare earth metals, etc., and high-quality products could not be obtained because oxygen mixed in with the refined or melted metals.

As a method for solving the above problems, the following invention has been made.

That is, the present invention provides (1) a surface of at least cerium oxide or alumina having a molar ratio of up to 20% to cerium oxide;
A refractory material consisting of a mixture of one or more of magnesia and calcia, and characterized by having extremely high corrosion resistance when melting active metals and alloys containing the same, and (2) the above (1). ) relates to a refractory material characterized in that the material is a film of the substance described in item 1 formed on the surface of a general-purpose material using a plasma spraying method.

To make a point The invention will be described in detail below.

The active metals targeted by the present invention include Ti-V, rare earth metals, and alloys thereof (including Mitsushi metal).

As a method to solve the above problem, the inventor used cerium oxide, which is believed to have corrosion resistance against active metals. Since cerium oxide itself is an oxide of an element that has a strong affinity for oxygen, it is thought that its reactivity with active metals is extremely low, and the results obtained were extremely favorable. This corrosion-resistant material can be used on its own as a processing vessel for active metals, or it can be replaced with commonly used easily moldable and inexpensive ceramic materials such as AI,
A film is formed on the surface of a container made of O, MgO, etc. to provide corrosion resistance to the container material.

Furthermore, the reason why the corrosion-resistant material to be used is limited to cerium oxide among rare earth oxides is because the crystal structure of other rare earth element oxides changes between the melting point and room temperature, or because they are expensive and cannot be used for industrial purposes. This is because it is not suitable. Cerium oxide has the above-mentioned A in order to improve its sinterability, adhesion with the underlying material to which the film is attached, and consistency in thermal expansion coefficient.
I, 0. , MgO, and CaO are preferably added. However, if a large amount of these oxides with poor corrosion resistance are mixed, the corrosion resistance of the material itself will be significantly impaired, so the amount of these mixed should be kept at 20 mo1%. In addition, there are other oxides that improve sinterability, but
It is unsuitable in terms of corrosion resistance, price, etc.

Here, the case where a single sintered body is used will be described in detail below.

When using a sintered body, in order to produce a dense sintered body, it is preferable to use a fine powder with an average particle size of 10 μm or less, preferably 1 μm or less. The powder is compression molded by conventional pressure molding or cold isostatic pressing. The sintering temperature varies depending on the type and amount of the auxiliary agent added to the rare earth oxide, but is at least 1400°C or higher, preferably 1700°C or higher.
℃ or higher. Further, in the case of film formation, the procedure is as follows.

Possible methods for forming a ceramic film include (1) sputtering, (2) CVD, (2) sintering after application of slurry, and (2) plasma spraying. However, among these methods, methods (1) to (2) have problems such as difficulty in forming a thick and strong film, difficulty in attaching it to the inner surface of the crucible, slow film formation speed, and low slurry adhesion strength.

In this invention, a method is used in which a film of the above-mentioned corrosion-resistant material is formed by plasma spraying on the inner surface of a crucible made of a relatively heat-resistant general-purpose ceramic material such as alumina. Here, the advantages of using plasma spraying are: ■
Possible to attach a film to the surface of a container with a somewhat complex shape, ■ Capable of increasing the size, ■ High-speed film formation, ■ Applying a film of sufficient thickness, ■ High adhesion strength, ■ Can be applied to high melting point ceramics, etc. It will be done.

The average particle size of the powder to be plasma sprayed is 100 μm.
A material with good fluidity consisting of nearly spherical particles with a diameter of less than 5 μm, preferably in the range of 50 to 5 μm is used. The material for the base material to be thermally sprayed is not limited as long as it can withstand the temperature and thermal shock of thermal spraying and treatment of active metals, but materials that can withstand the active metal to some extent even if the corrosion-resistant film peels off, such as A
I.

0, MgO is good. The thickness of the film is suitably in the range of 50 μm to IM, preferably 200 to 300 μm.

If it is less than 50 μm, the film strength will be low, and if it exceeds lllll11, it will take an extremely long time to form the film, which is not practical.

<Example 1> 4 wt% (approximately 12 mo
le%) of AI, O, and powder were added and sintered at 1,700°C for 3 hours to obtain an inner diameter of 30 m with 92% of the assumed density (d = 6.76).
A +n cylindrical crucible-shaped sintered body was made.

This was used to melt Mitsushi metal and Ti alloys, but as shown in Table 1.2, the increase in oxygen content relative to the raw materials was small.

<Example 2> CeO was applied to the inner surface of an MgO cylindrical crucible with an inner diameter of 35 mm.
, was sprayed with Ar plasma to form a film with a thickness of 0.2 m+e. This was used to melt Mitsushi metal and Ti alloy, but as shown in Tables 1 and 2, the oxygen content increased only slightly compared to the raw materials.

<Comparative example> Inner diameter 3 C) ~ 35 mm (7) Made of MgO and AI, O
However, as shown in Table 1.2, the oxygen content of the raw materials increased significantly when Mitsushi metal and Ti alloy were melted using an inner cylindrical crucible.

Table 1. Differences in oxygen content in Mitshu metal during vacuum heat treatment depending on crucible material (after heating at 1100°C for 1 hour) Table 2 Difference in oxygen content in Ti-6AI-4V alloy during vacuum melting depending on crucible material (1600°C (After heating for 20 minutes) (1) According to the present invention, it is possible to prevent oxygen from being mixed into the processed material during the melting or purification treatment of active metals.

(2) By using a film formed, the above (
The effect of 1) can be obtained.

(3) For example, if a low-oxygen metal treated according to the present invention is used in the production of a rare earth-based hydrogen storage alloy, favorable characteristics can be obtained by suppressing the generation of moisture.

Claims (2)

[Claims] (1) The surface is made of at least cerium oxide or a substance mixed with cerium oxide and one or more of alumina, magnesia, and calcia in a molar ratio of up to 20%,
A refractory material characterized by extremely high corrosion resistance when melting active metals and alloys containing the same. (2) A refractory material according to item 1, characterized in that the material is a film of the substance described in item 1 formed on the surface of a general-purpose material using a plasma spraying method.