JPH06179960A - Production of spinel film and transmissive aluminaspinel composite and spinel body obtained by using the same - Google Patents

Abstract

PURPOSE:To simply and stably form a spinel film by keeping a closed space, in which a member to be coated and a spinel material are arranged, at a prescribed spinel vapor pressure by heating in a reducing atmosphere or in an evacuating atmosphere. CONSTITUTION:The member to be coated and the spinel material such as MgAl3 O4 powder are adjacently arranged in the closed space. The member to be coated has a smaller evaporative factor than that of the spinel material and an optional shape. The spinel vapor is generated and kept by heating the space in a reducing atmosphere of gaseous hydrogen or in evacuating atmosphere at 1500-1900 deg.C. As a result, the spinel film is vapor deposited on the member to be coated. By using this method, the transmissive alumina-spinel composite is formed by forming a spinel coating film on the transmissive dense alumina and the spinel body is formed by forming the spinel coating film on a combustible material before burning the combustible material.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a spinel film which is stable against erosion of acids, alkalis, molten metals, etc., has excellent heat resistance and chemical resistance, and has translucency. The present invention relates to a translucent alumina-spinel composite and a spinel body to be obtained.

[0002]

2. Description of the Related Art The so-called spinel magnesium aluminate (MgA ₁₂ O ₄ ) has excellent heat resistance and corrosion resistance and is used in coating films for various materials. It is expected to be used as a coating film for ceramic members that require remarkable light-transmitting properties and optoelectronic members such as optical display devices and optical storage devices. Conventionally, as a method of forming a spinel film, hydrogen chloride (HCl), along with a mixed gas stream of hydrogen (H ₂₎ and carbon dioxide (CO _2), and magnesium chloride (MgCl2) and aluminum vapor onto the film substrate A method of forming a spinel CVD film by circulating it to form a spinel CVD film is known.

[0003]

However, in the above method, it takes a long time to form a film, a complicated apparatus is required, and the reaction conditions such as atmospheric gas and temperature must be strictly controlled. It has been pointed out that the facility cost must be increased and the operation is complicated, and a method for easily forming a spinel film is desired. The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for forming a spinel film that is simpler and more stable than conventional methods.

[0004]

According to the present invention, a member to be coated and a spinel material are arranged in close proximity in a closed space, and the space is heated to 1500 to 1900 ° C under a reducing atmosphere or reduced pressure. Provided is a method for producing a spinel film, which comprises heating and maintaining a predetermined spinel vapor pressure.

Further, according to the above method for producing a spinel film,
Provided is a translucent alumina-spinel composite in which a spinel film is formed on translucent dense alumina.

Furthermore, the above spinel film manufacturing method provides a spinel body formed by forming a spinel film on a combustible material and then burning the combustible material.

[0007]

According to the present invention, the spinel material having the above-mentioned structure and arranged in the closed space is heated to generate the spinel-forming vapor, and the member to be coated is brought into proximity with the spinel material in the same space. With this arrangement, the surface to be coated and the spinel-forming vapor can be brought into contact with each other to deposit the spinel film. The present invention is 1
Although it is a kind of vapor deposition operation, no report has been known up to now that spinel film formation was carried out by the method of the present invention. The present invention has found that a spinel film can be formed easily and stably.

Further, by forming a spinel film on a translucent alumina member by using the above-described simple method for producing a spinel film, a translucent alumina-spinel composite can be formed as a whole. it can. Furthermore, the substrate on which the spinel film is formed is composed of a flammable material such as carbon material,
After the spinel film is formed, the substrate is burnt and lost, so that a spinel body having an arbitrary shape can be easily obtained.

The present invention will be described in detail below. In the present invention, as the spinel material, spinel powder or a molded body using spinel powder can be used. The particle size and the like of the spinel powder are not particularly limited, and commercially available MgA ₁₂ O ₄ powder can be used.

The member to be coated according to the present invention may have any size, shape and the like, and it is applicable even if it has a complicated shape having irregularities. The material forming the member to be coated is not particularly limited as long as its evaporation coefficient is smaller than that of spinel. Examples thereof include alumina material and carbon material, which may be dense or porous. The material of the coated material is
It can be appropriately selected depending on the purpose of forming the spinel film. For example, when a porous member to be coated is used, the spinel film is formed not only on the surface of the member but also on the inner surface of the porous hole. In this case, the thickness of the spinel film formed on the inner surface of the hole gradually decreases from the surface portion toward the inside. Further, the spinel film is translucent, and by forming the spinel film on a relatively thin translucent dense alumina coated member, a member of the same thickness formed only by the translucent dense alumina is formed. A highly translucent member can be obtained. Furthermore, a spinel film can be formed on a flammable member to be coated, and then the member to be coated can be burned to easily form a spinel body having an arbitrary shape.

In the present invention, when the member to be coated and the spinel material are arranged in the same space, they are arranged close to each other. The term "proximity" as used in the present invention means that they are installed apart from each other without making them contact with each other, and the separation may be planar or three-dimensional. When the member to be coated and the spinel material are placed in contact with each other, the formed spinel film is connected to a part of the placed spinel powder or spinel compact, and the surface condition of the formed film deteriorates, which is not preferable. The separation distance is not particularly limited as long as it is not in contact, and can be appropriately selected depending on the size of the material to be coated and the size of the closed space area. Usually, for example, in coating a member to be coated having a size of 50 mmφ, the spinel materials can be arranged at a distance of about 10 mm.

In the present invention, in the closed space, for example, the spinel material is arranged in the crucible and the upper lid is left stationary so that the spinel vapor generated by heating the arranged spinel material maintains a predetermined vapor pressure. As in the above state, the inside and the outside of the space may be separated and blocked so that the gas in the space is surrounded and held so as not to leak. In this case, it is preferable that the space surrounding wall is made of a material to be coated and the spinel material is arranged inside the wall. In the present invention,
This is because the inner wall of the space holding the spinel vapor comes into contact with the spinel vapor and a spinel film is formed. For example, it is possible to obtain a dome body having a spinel film formed on the inner wall by allowing the dome-shaped material to be coated to stand still while placing the spinel material in the dome shape and heating.

In the present invention, the closed space in which the material to be coated and the spinel material are arranged is 1500 to 1900 ° C. under a reducing atmosphere such as hydrogen gas or a reduced pressure such as vacuum.
It is heated to generate and retain spinel vapor. The reason why the space is under reducing gas or under reduced pressure is to form the spinel film while maintaining the MgA ₁₂ O ₄ structure. If the heating temperature is less than 1500 ° C, magnesium gas (Mg
(G)), MgA such as aluminum gas (Al (g))
The formation gas of the ₁₂ O ₄ film is small and the film formation is not sufficient. On the other hand, when the temperature exceeds 1900 ° C., Mg (g) is preferentially generated, and magnesium oxide (Mg
O) (second phase) is generated, and the formed MgA
It is not preferable because the ₁₂ O ₄ film itself is decomposed and the film is damaged.

[0014]

EXAMPLES The present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples. Example 1 A 50 cc alumina crucible was filled with about 50% by volume of spinel powder from the bottom, and the top was covered with a dense alumina plate. The crucible was left to stand in an electric furnace under a hydrogen gas atmosphere, heated and kept at 1830 ° C. for 8 hours. After cooling, the upper lid was removed, and the back side of the lid and the portion of the crucible that did not come into contact with the spinel powder were observed. As a result, a facet-like coating having a developed crystal face was formed on each of them. Further, the film formed on the lid was observed by X-ray diffraction, and as a result, it was found to be a single MgA ₁₂ O ₄ phase having a uniform thickness of 200 μm.

Examples 2 to 4 and Comparative Examples 1 and 2 The same operation as in Example 1 was conducted except that the heating temperature was set to 1400 to 2000 ° C., and the crystals of the formed film were observed in the same manner. The results are shown in Table 1. From Table 1, 15
It can be seen that in the temperature range of 00 to 1900 ° C., the film thickness formed increases as the temperature rises. Also 1400 ° C
However, the film was not formed, and a part of the particles considered to be crystal nuclei were formed. Further, at a temperature of 2000 ° C., a MgO phase was recognized.

[0016]

[Table 1]

Example 5 Except that the upper lid was made of a porous alumina plate having a porosity of 80%,
The same operation as in Example 1 was performed, and the crystals of the formed film were observed in the same manner. As a result, a 200 μm thick MgA ₁₂ O ₄ film was formed on the surface of the porous alumina plate, and the MgA ₁₂ O ₄ film was thinned from the surface layer toward the inside in the internal porous skeleton.

Example 6 A 50 cc carbon crucible was filled with spinel powder from the bottom in an amount of about half by volume, and the carbon crucible was turned down. The distribution of gas between the inside and outside of the crucible was not completely cut off. The crucible was allowed to stand in an electric furnace under a hydrogen gas atmosphere and heated and held at 1800 ° C. for 8 hours. After cooling, the crucible was taken out and the carbon crucible was oxidized and consumed to obtain a crucible-type spinel body. The spinel body thus formed has a thickness of 190 μm and has a uniform MgAl ₂ O content.
_{There were 4} monolayers.

[0019]

According to the method of the present invention, the spinel film can be easily formed and manufactured, and the thickness of the spinel film can be controlled by the operating temperature.

Claims (3)

[Claims] 1. A member to be coated and a spinel material are arranged close to each other in a closed space, and the space is heated to 1500 to 1900 ° C. in a reducing atmosphere or under reduced pressure,
A method for producing a spinel film, characterized in that the spinel vapor pressure is maintained at a predetermined value. 2. A translucent alumina-spinel composite body obtained by forming a spinel coating film on translucent dense alumina by the method according to claim 1. 3. A spinel body formed by forming a spinel coating film on a combustible material by the method according to claim 1, and then burning off the combustible material.