JPS6176663A - Graphite crucible for evaporating aluminum - Google Patents

Abstract

PURPOSE:To prolong considerably the life of a graphite crucible for evaporating Al by filling alumina and carbon into the pores in the graphite crucible and forming a layer of pyrolytic graphite on the surface of the graphite crucible. CONSTITUTION:A graphite crucible of artificial graphite having >=1.78 bulk specific gravity is immersed in a soln. of an Al compound which leaves alumina by thermal decomposition such as aluminum nitrate or aluminum hy droxychloride, and the crucible is immersed in a dispersion of fine carbon pow der in water or an org. solvent to fill alumina and carbon into the pores in the graphite crucible. A layer of pyrolytic graphite is then formed on the surface of the graphite crucible.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to improvement of graphite melt for aluminum deposition.

(Prior art) Vacuum deposition of aluminum is approximately 1500°C, io-3 ~
It is generally carried out under conditions of 10"-' mmHg, but in this case, molten aluminum has a greater permeability into the pores of the graphite crucible than other metals, and reacts with graphite to form aluminum carbide. The crucible may be destroyed after a small number of uses.

Various studies have been made to prevent this and increase the number of times graphite crucibles are used. For example, a method is used in which a graphite crucible is impregnated with an aqueous solution of aluminum nitrate or aluminum hydroxychloride and heat treated to coat the pores with alumina (A1203) A to prevent penetration of molten aluminum.

However, with this method, compared to the AJzOs production yield of aluminum nitrate or aluminum hydroxychloride, it is necessary to repeat the treatment 3 to 6 times to obtain the effect of preventing molten aluminum from penetrating into the graphite crucible. However, it is not always possible to completely prevent penetration.

On the other hand, there is a method of forming a layer of pyrolytic graphite on the surface of a graphite crucible in order to fill the pores on the surface of the graphite crucible. However, the thickness of the formation layer of pyrolytic graphite is limited to 0.00 mm due to production cost considerations.
01 = about 0.3rMn, which is sufficient to prevent penetration of molten aluminum when the graphite crucible is first used, but as the graphite crucible is used more times, it becomes worn out due to oxidation, etc., and the formation layer of pyrolytic graphite is formed. When it runs out, molten aluminum penetrates into the pores of the graphite crucible, greatly reducing the number of times it can be used thereafter. If the layer of pyrolytic graphite is formed thickly, the number of times the graphite crucible can be used can be increased, but this increases the production cost and is not practical.

(Objective of the Invention) An object of the present invention is to solve the above-mentioned problems and provide a long-life graphite crucible for aluminum deposition.

(Embodiment of the Invention) The present invention relates to a graphite crucible for aluminum deposition, in which a layer of pyrolytic graphite is formed on the surface of the graphite crucible after the pores of the graphite crucible are filled with alumina and carbon.

The material of the graphite crucible of the present invention is artificial graphite with a bulk specific gravity of 1.
78 or more is preferred. This is because if the bulk specific gravity is small, the porosity is large and a large amount of alumina and carbon are required to be filled.

Filling with alumina is performed by impregnating with a solution of an aluminum compound such as aluminum nitrate or aluminum hydroxychloride that leaves alumina after being thermally decomposed by a known vacuum pressure impregnation method, followed by M treatment, which is repeated several times. Filling with carbon is done to make the surface of the graphite crucible denser and make it easier for pyrolytic graphite to adhere to it.It is done by liquefying organic materials with a large amount of carbonization such as furan resin, phenol resin, and tar pinch. The material may be impregnated using a vacuum pressure impregnation method, followed by heat treatment and carbonized, or may be impregnated with a dispersion of finely powdered carbon, such as carbon black, dispersed in water or an organic solvent. From the viewpoint of ease of handling, it is preferable to impregnate and heat-treat the furan resin.

Formation of a layer of pyrolytic graphite on the surface of a graphite crucible.

Any known means for thermally decomposing hydrocarbons and precipitating graphite may be used.

(Function) When using a graphite crucible for aluminum evaporation obtained by K as described above, a layer of pyrolytic graphite initially blocks penetration of molten aluminum, and as the pyrolytic graphite is consumed, it fills the pores. Alumina prevents penetration of molten aluminum and reaction of molten aluminum with graphite.

(Example) Next, an example will be described.

Example A crucible made of artificial graphite with an inner diameter of 80 mm, an outer diameter of 100 mm, a height of 90 mm, and a bulk specific gravity of 1.78 was prepared, placed in an autoclave, and the pressure reduced to 100-3 o + Hg. After holding at this pressure for 30 minutes, aluminum nitrate (At N03)
A 5Qwt% aqueous solution of s-9H20) was injected and impregnated, and the pressure was further maintained at 5 atm for 30 minutes to return to atmospheric pressure.

Next, the graphite crucible was taken out and the temperature was gradually raised to 600° C. over 24 hours to fill and fix alumina into the pores. After performing the above impregnation and heat treatment operations twice, it was immersed in a 1 wt% methanol solution of para-toluene sulfone e for 1 hour, and after drying, para-toluene sulfonic acid ethyl ester i,
s wt % formulation 1. After impregnating fc furan resin under reduced pressure under the same conditions as aluminum nitrate impregnation, 7 kg/c
The pressure was increased to m2 for 30 minutes and the pressure was returned to atmospheric pressure.

Next, the graphite luribo was gradually heated to 900'C over 72 hours to carbonize the furan resin. After cleaning the surface of the graphite crucible, it was placed in a quartz reaction tube, heated to 900°C by high-frequency induction heating, and 2 g/m of trichloroethane with a concentration of 13 vo/% was added using N2 gas as a carrier gas.
The mixture was fed for 5 hours at a gas flow rate of 1.5 in. to form a layer of pyrolytic graphite of about 0.1 - to obtain a graphite crucible for deposition of aluminum.

The graphite crucibles for aluminum evaporation of the Examples and the Comparative Examples were treated as Comparative Examples in which the Example was filled with alumina, and the film material was polyester resin, the film winding speed was 200 m/min, and the purity of the deposited metal was 99.9. A%
Aluminum, evaporation film thickness 400λ, evaporation temperature 145
0°C, degree of vacuum 2 x 10-', nHg and evaporation length 2
As a result of testing under the condition of 500 m/time, the number of uses (life) was 25 times for the comparative example and 3 times for the example example.
It was 8 times.

(Effects of the Invention) According to the present invention, after filling the pores of a graphite crucible with alumina and carbon, a layer of pyrolytic graphite is formed on one surface, thereby greatly improving the life of the crucible for aluminum deposition.

Matatono

Claims (1)

[Claims] 1. A graphite crucible for aluminum evaporation, in which the pores of the graphite crucible are filled with alumina and carbon, and then a layer of pyrolytic graphite is formed on the surface of the graphite crucible.