JP3524177B2 - Method for producing metal plate coated with zeolite - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a zeolite layer having pores at the molecular level on the surface of a metal plate by the sol-gel method.

[0002]

Zeolites are crystalline aluminosilicates of alkali or alkaline earth metals. SiO ₄
All of the oxygen atoms at the four vertices of the tetrahedron are shared, and they have a three-dimensional skeleton structure containing pores at the molecular level. Since some of the silicon atoms constituting the skeleton are replaced with aluminum atoms, and the oxidation number of the aluminum atoms is one lower than the oxidation number of the silicon atoms, it has a negative charge to be electrically neutralized and stabilized. It has the property of compensating for and absorbing an equivalent amount of cations. Further, in addition to being ceramic, it has a large number of pores, so it is also excellent in heat resistance and heat insulation. Utilizing the properties of zeolite, it has begun to be used in various fields. Under normal hydrothermal synthesis conditions, zeolite is obtained as a powder. In order to form a film that is easy to handle, a method of dispersing zeolite in a polymer or crystallizing the zeolite on the surface of an inorganic porous material is adopted. Recently, a thin film made of zeolite crystals alone has been developed. For example, when an aqueous gel mixture containing colloidal silica, aluminum nitrate, sodium hydroxide, a crystallization modifier, etc. is brought into contact with an appropriate substrate and hydrothermally treated, a zeolite film is formed on the substrate surface (Nippon Kagaku Magazine 1992). Year No. 877
~ Page 880).

[0003]

[Problems to be Solved by the Invention] In conventional hydrothermal synthesis,
Since the solution does not hydrolyze at room temperature and atmospheric pressure, zeolite solids are not generated and film formation is impossible, etc.
High temperature heating using an autoclave requires long-term treatment. However, by using an autoclave,
The manufacturing process is batch type, making it unsuitable for continuous manufacturing. Also, manufacturing of large products is difficult. When crystallization of zeolite becomes possible by heating at a relatively low temperature, a functional material utilizing the characteristics of zeolite can be obtained in various fields.
For example, zeolite formed on the surface of a metal plate such as a steel plate acts as a heat insulating layer and improves the fire resistance of the metal plate. Further, a functional material having a catalytic activity, a selective separation property, an antibacterial property, etc. can be obtained according to the selection of the substance to be supported on the zeolite layer. The present invention has been devised to meet such a demand, and utilizes the fact that the solubility of aluminum alkoxide in alcohol is remarkably improved by the alkoxide of an alkali metal or an alkaline earth metal, and a transparent stabilizing bath is used. The purpose of this is to form a zeolite membrane that can be synthesized by heating at low temperature on the surface of a metal plate by preparing.

[0004]

According to the production method of the present invention, a sol-gel bath is prepared by adding an alcohol in which an alkali metal or alkaline earth metal alkoxide is dissolved to a mixed solution of aluminum alkoxide, alcohol and alkoxysilane. The method is characterized in that a metal plate is immersed or spray-coated using the sol-gel bath, dried and then fired. After calcination, when the coated metal plate is immersed in a metal salt-containing solution to introduce metal ions into the zeolite layer, the metal supported can impart a given function to the zeolite layer.

[0005]

Function: Aluminum alkoxides and aluminum salts have low solubility in alcohol. Although it is possible to dissolve an aluminum alkoxide or an aluminum salt by adding an acid, the solution immediately becomes cloudy when an alkali metal or alkaline earth metal alkoxide or salt is added to the solution. Then, as a result of various studies on compounds containing elements constituting zeolite, it was found that aluminum alkoxide was easily dissolved in alkoxysilane. When aluminum alkoxide, ethanol and alkoxysilane are mixed, a mixed solution in which aluminum alkoxide is dissolved is obtained. However, the solubility at this time is insufficient, and a long time is required to obtain a complete solution. Also, the solubility is low.

In the present invention, the solubility of aluminum alkoxide is improved by the alkali metal or alkaline earth metal alkoxide. That is, when an alcohol in which an alkoxide of an alkali metal or an alkaline earth metal is dissolved is added to the aluminum alkoxide mixed solution, a transparent liquid is promptly obtained. The sol-gel bath used in the present invention is a transparent solution in which, for example, sodium alkoxide, alkoxysilane, aluminum alkoxide and the like are dissolved in an organic solvent and which contains water, a catalyst and a stabilizer. An acid added as a stabilizer in a usual sol-gel coating is not preferable because it has the opposite effect of making the liquid cloudy in the subsequent step. On the other hand, diethanolamine or the like is effective as a stabilizer. It is also possible to add an equivalent amount of water to all the alkoxides.

When the metal plate is immersed in the sol-gel bath, hydrolyzed hydroxide such as alkoxysilane, aluminum alkoxide, alkoxide of alkali metal or alkaline earth metal adheres to the surface of the metal plate. When this metal plate is heated, a synthetic reaction proceeds and a zeolite film having a predetermined crystal structure is formed on the surface of the metal plate. At this time, the mixed alkoxide is hydrolyzed, and the produced inorganic polymer undergoes further polycondensation as the solvent evaporates or the like to form a continuous network structure and gel. Therefore, 5
The film formation of the zeolite precursor sufficiently proceeds even at a low temperature of 0 ° C. or lower. The zeolite precursor membrane synthesized at low temperature is
A uniform zeolite thin film is formed by firing at 400 ° C. or higher. The thickness of the obtained film is 1 μm or less, but it is a dense film and has excellent adhesion to the substrate. When the zeolite layer has a predetermined function, the coated metal plate is immersed in the displacement solution after firing. For example,
When immersed in a silver nitrate solution, silver is introduced into the zeolite by ion exchange, and the zeolite layer is provided with antibacterial properties.

[0008]

EXAMPLE In a sol-gel bath containing only Al ₂ O ₃ , the stability was changed as shown in Table 1 depending on the solvent and catalyst used. That is, Al ₂ O ₃ has low solubility in various solvents, and a transparent liquid is obtained by adding HNO ₃ or HCl as a catalyst. With SiO ₂ alone, a stable sol-gel bath was obtained when using the solvents and catalyst HNO ₃ shown in Table 2. The stability of Tables 1 and 2 is
The transparency of the sol-gel bath was investigated, and those with high transparency were marked with ○,
The case where the transparency was low and cloudiness was observed was evaluated as x.

[0009]

[Table 1]

[0010]

[Table 2]

As shown in Tables 1 and 2, since the transparency of the sol-gel bath and the homogeneity of the Al ₂ O ₃ or SiO ₂ film were confirmed by the addition of acid, sodium methoxide was subsequently added. At this time, the sol-gel bath became cloudy due to the addition of sodium methoxide, and a transparent bath could not be prepared. As a result of examining the cause of cloudiness, it was found that the acid contained in the sol-gel bath was the cause. Therefore, when a system in which a transparent bath was prepared even in the absence of an acid was investigated, when alcohol was added to a mixed solution containing aluminum isopropoxide, alkoxysilane and sodium methoxide, stability as shown in Table 3 was obtained. A high transparent sol-gel bath was obtained. SU using this sol-gel bath
When the S430 substrate was dip coated, a homogeneous film was obtained after firing.

[0012]

[Table 3]

Observation of the obtained zeolite membrane by SEM revealed that it had a homogeneous zeolite skeleton structure although microscopically fine cracks were formed. Further, when the influence of the calcination temperature on the zeolite membrane was investigated, as shown in FIG. 1 showing the X-ray diffraction pattern, the formation of zeolite was confirmed even at the low temperature calcination of 400 to 600 ° C. Further, as seen in FIG. 2 showing the ESCA analysis result, peaks of Al, Si, Na and O were detected. Moreover, looking at the analysis results of Al2p and Si2p, Al and Si are Al ₂ O ₃ and Si, respectively.
It was deviated from the peak position of O ₂ and almost coincided with the peak of zeolite. This also supports the formation of the zeolite membrane. In the above examples, the application of the coating having the zeolite structure has been described. When various metals are supported by utilizing this zeolite structure, it is possible to form a coating layer having a predetermined function.
For the metal loading, conventionally used dipping treatment, contact treatment, or the like can be employed. For example, when immersed in a solution in silver nitrate, Ag ions were taken into the zeolite skeleton by ion exchange, and a ceramic layer exhibiting antibacterial properties could be obtained.

[0014]

As described above, in the present invention, the fact that the solubility of aluminum alkoxide and alkoxysilane is improved by the alkoxide of the alkali metal or the alkaline earth metal is used to cause the sol-gel solution to become cloudy. A highly transparent sol-gel liquid having excellent stability is prepared without adding an acid that becomes When this sol-gel solution is used to dip-coat a metal plate such as a steel plate, a ceramic layer having a zeolite skeleton structure is formed on the surface of the metal plate. Since this ceramic layer has a stable zeolite structure by low temperature firing, it is possible to impart various functions without adversely affecting the metal plate.

[Brief description of drawings]

FIG. 1 X-ray diffraction of a zeolite membrane obtained in an example of the present invention

FIG. 2 ESCA analysis result of the zeolite membrane

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-7-330326 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C01B 39/02 JSTPlus (JOIS)

Claims (2)

(57) [Claims] 1. A sol-gel bath is prepared by adding an alcohol in which an alkali metal or alkaline earth metal alkoxide is dissolved to a mixture of aluminum alkoxide, alcohol and alkoxysilane, and the sol-gel bath is used to prepare a metal plate. A method for producing a zeolite-coated metal plate, which comprises dipping or spray coating, drying, and then firing. 2. A method for producing a metal plate coated with zeolite, which comprises immersing the metal plate coated with the coating according to claim 1 in a solution containing a metal salt to introduce metal ions into the zeolite layer.