JP3224034B2 - Corrosion resistant film and its formation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a corrosion-resistant coating,
Pipes for water supply or drainage of water pipes, sewer pipes, etc., water heater pipes, hot water pipes, circulating pipes for cooling / heating water systems for cooling and heating, water storage tanks for hot water supply equipment, etc. The present invention relates to a corrosion-resistant film formed on the surface of an exterior steel plate such as a roof and a roof material, and a method for forming the same.

[0002]

2. Description of the Related Art It is said that tap water in Japan has less hardness and is more susceptible to corrosion than those in Europe and the United States. In addition, in recent years, water sources have become increasingly polluted in large urban areas. Corrosive environments in water pipe systems are becoming increasingly severe due to increasing chlorine inputs. On the other hand, with the aging of buildings in urban areas, poor water discharge due to rust clogging of water supply pipes in buildings, generation of red water, and water leakage have become social problems.

In view of this situation, the inventor of the present application has studied the corrosion mechanism of galvanized steel pipe, which has been most commonly used as a conventional water supply pipe for water supply, and has developed two types of corrosion prevention, namely, formation of a corrosion-resistant film of zinc and a sacrificial anode. The two-sided action was announced in 1989 in "Corrosion and Corrosion Protection '89", and revealed that the corrosion resistance of galvanized steel pipes was significantly dependent on water quality. In particular, he mentioned the distribution of hemimorphite as a corrosion product of zinc in the cross section of corroded pipes.Hemimorphite was found to be uniformly corroded on the inner surface of corroded water pipes except for the locally corroded rust bumps. It was noted that there were many, and that there was no corrosion below this layer.

The present invention has been studied with a focus on this phenomenon, and has conceived an active use of hemimorphite as an anticorrosive film. This hemimorphite is also called hemimorphite, and according to the Geological Dictionary, Zn ₄ (OH) ₂
Has a Si ₂ O ₇ · H ₂ O in the formula, a orthorhombic crystal is assumed to show a clear hemimorphic.

[0005] From the viewpoint of the corrosion resistance of such water system piping, there has been no publication on the anti-corrosion function of hemimorphite. Kaisho 61-86
No. 284, JP-A-61-173984, etc., as well as fillers for thermal paper, fillers for various resins, rubbers, fillers for agriculture, and as a carrier for catalysts limited.

[0006]

The problem to be solved in the present invention is to utilize the corrosion resistance of hemimorphite in a water supply system and to use it positively for improving the corrosion resistance of a water treatment system or a water utilization device. It is to provide a measure.

[0007]

SUMMARY OF THE INVENTION The present invention provides a method for producing Zn ₄ (O
The object has been achieved by uniformly forming a zinc silicate compound film mainly composed of a synthetic hemimorphite crystal having a chemical formula of H) ₂ Si ₂ O ₇ .H ₂ O on the liquid contact surface of a substrate.

[0008] As a substrate to which the present invention can be applied, a substrate having at least a zinc layer on its surface can be suitably applied.
Here, the zinc layer can be applied in any form as long as it contains a zinc component on the surface of the substrate, for example, a zinc substrate itself or a substrate containing zinc as an alloy material, It can be applied to a substrate having a zinc or zinc alloy plating layer or an alloyed hot-dip galvanized layer.

The uniform layer of the synthetic hemimorphite can be suitably obtained by subjecting the surface having the zinc-containing layer to a hydrothermal treatment using an aqueous silicate solution. In performing the hydrothermal treatment, after degrease the metal material containing zinc in the surface layer, perform a pretreatment by an oxidation treatment or a hydroxylation treatment,
A relatively active ZnO layer or Zn (OH) ₂ layer is formed as a base material for forming synthetic hemimorphite.

The formation of the active ZnO layer by the oxidation treatment as a pretreatment is performed at 100 to 400 ° C. in air at 1 to 3 ° C.
This indicates that heating is performed for an hour. For example, in the case of zinc, heating at 300 to 350 ° C. for 1 to 2 hours can be suitably applied. If the temperature is too low, the oxidation rate is slow, and it takes time to form an oxide film on the surface. If the temperature is too high, the temperature approaches the melting point of zinc, which softens the zinc and adversely affects the formation of the active ZnO layer.

The formation of the active Zn (OH) ₂ layer by the hydroxylation method is carried out at pH 7 to 13, preferably at pH 8.
80-95 in sodium hydroxide solution of 5-10.5
A stable hydroxide film is formed by boiling at 1 ° C. for 1 to 60 minutes. In addition, by performing the hydroxylation treatment, the surface is moderately roughened, the surface area is increased, and the silicic acid is adsorbed and easily reacted. By these pretreatments, an active ZnO or Zn (OH) ₂ layer is continuously formed on the substrate surface in the substrate structure.

Further, after the pretreatment, the substrate is made of SiO
₂ Converted to a concentration, dipped or coated in an aqueous solution of silicic acid or silicate having a concentration of 50 to 15000 ppm, preferably 300 to 3000 ppm, and saturated steam at each temperature at 110 to 210 ° C., preferably 150 to 190 ° C. for 1 hour or more. Hydrothermal synthesis is performed under the condition of a pressure or higher to produce a synthetic hemimorphite film having a final film thickness of 0.5 to 50 μm. As shown in FIG. 2, the surface of the film covered with hemimorphite crystals has a three-dimensional structure in which plate-like or columnar single crystals are woven, and if it is too thin, the film lacks uniformity and is too thick. In some cases, cracks may occur in the coating due to the difference in thermal expansion between the base metal and the base metal.

As the silicic acid raw material, silicates having a M ₂ O / SiO ₂ ratio of 0 to 2 can be used. Here, M is a monovalent alkali metal such as Li, Na, K,
Cs or ammonium and amine. The treatment with the aqueous solution of silicic acid or silicate can be performed by means such as immersion or application by a roll or spray.

[0014]

The synthetic hemimorphite formed continuously on ZnO or the zinc-containing surface pretreated with zinc such as zinc plating has a continuous structure with ZnO, and has a high bondability with the base material. It has mechanical peel strength.

The formation of such synthetic hemimorphite is carried out by dipping or coating in an aqueous solution of silicic acid or silicate, followed by hydrothermal synthesis. As for the hydrothermal synthesis temperature, a film cannot be formed at a temperature lower than 110 ° C., and at 210 ° C. or more, the zinc layer is peeled off. Therefore, a preferable temperature range is 110 to 210 ° C. for 1 hour or more, and a saturated vapor pressure of each temperature or more. Under the condition,
Hydrothermal synthesis is performed to form a zinc silicate compound film having a final film thickness of 0.5 to 50 μm.

The synthetic hemimorphite layer itself is:
ZnO layer or Zn (OH) formed above zinc layer
_{It has} a form that is continuous with the _two layers in crystal structure, and has a thickness of 0.1 mm.
If it is 5 μm or more, sufficient corrosion resistance can be maintained for a long time even in heated sewage.

[0017]

EXAMPLE A synthetic hemimorphite corrosion-resistant film according to the present invention was formed using an electrogalvanized steel sheet, and its corrosion resistance was confirmed.

The surface of a sample having a surface area of 50 mm × 30 mm, a galvanized layer having a thickness of 10 μm and a steel plate having a thickness of 1 mm was degreased with acetone, and then oxidized in air at 350 ° C. for 2 hours to obtain zinc oxide. Was boiled in an aqueous sodium hydroxide solution having a pH of 9.7 for 30 minutes to form a zinc hydroxide film. Next, the galvanized steel plate was subjected to SiO ₂ concentration of 300 ppm or 1000 ppm.
ppm in an aqueous sodium metasilicate solution at 125 ° C.
Hydrothermal treatment was performed for 20 hours or 20 hours.

FIG. 1 is a model diagram showing the formation process of crystallized hemimorphite. FIG. 3A shows the molecular state several minutes after the treatment, and shows the process in which silicate and silicate ions in the solution are adsorbed on the surface of zinc oxide or zinc hydroxide. FIG. 2B shows the molecular state several tens of minutes after the start of the synthesis, in which zinc oxide or zinc hydroxide has reacted to produce a precursor amorphous substance of hemimorphite. FIG. 3C shows the molecular state several hundred minutes after the start of the treatment. The precursory amorphous substance of hemimorphite shown in FIG. This shows a state in which free water is taken into the crystal lattice space as crystal water. In this state, the crystallized hemimorphite has an integrated crystal structure with zinc oxide on the substrate surface.

FIG. 2 shows the surface morphology of the synthesized film observed by a scanning electron microscope (SEM). It can be seen that the substrate surface is covered with plate-like hemimorphite crystals.

FIG. 3 shows the result of identification of the film product by X-ray diffraction in comparison with the diffraction pattern of a natural mineral. The corrosion resistance of these hemimorphite synthetic films was evaluated by measuring the rusting area of each sample surface immersed in tap water at 85 ° C. for one week. The determination is as follows.

Table 1 shows the results of the heat resistance test of the samples prepared under the respective conditions.

[Table 1]

From these results, the hemimorphite film formed according to the present invention was compared with a sample not subjected to the treatment (Example 5) and other anticorrosion-treated materials (Example 6).
It can be seen that all Examples (1 to 4) have excellent heat resistance and have an anticorrosion effect. Furthermore, in order to examine the acid resistance and alkali resistance of the hemimorphite film, the hemimorphite crystals were immersed in a sulfuric acid solution of pH 3 and a caustic soda solution of pH 12 for 24 hours. I understood. Therefore, the hemimorphite film can be expected to function as a stable protective film in an alkaline solution. Further, since the hemimorphite film can be expected to be stable against rainwater, salt water, and the like, it is a suitable material as a protective film for exterior steel plates such as automobiles and roofing materials.

[0024]

According to the present invention, the following effects can be obtained. (1) The uniform film of synthetic hemimorphite formed on the base material has a sufficient barrier effect between the base material and the humid atmosphere or tap water or sewage, and has almost semi-permanent durability. (2) The maintenance work for corrosion can be extremely reduced by applying the corrosion-resistant film according to the present invention to household water-use products. (3) Corrosion of piping and tank inner surface can be almost permanently protected.
The device is freed from the maintenance design and the design tolerance can be expanded.

[Brief description of the drawings]

FIG. 1 is a model diagram showing a process of forming crystallized hemimorphite when a treatment in an autoclave is performed at 180 ° C.

FIG. 2 shows the crystal structure of a film synthesized on a galvanized steel sheet, as measured by a scanning electron microscope (SEM).

FIG. 3 shows identification results of a film product by X-ray diffraction.

Continuation of the front page (56) References JP-A-54-2945 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 22/00-22/86

Claims (8)

(57) [Claims] 1. A formed on the surface of the substrate having a zinc layer on the surface, essentially Zn 4 _(OH) zinc silicate consisting mainly of synthetic hemi molar Fight having _{2 Si 2 O 7 · H 2} O in the formula Corrosion resistant film composed of compound film. 2. A zinc oxide layer or a hydroxide layer on a surface of zinc or a zinc-containing alloy and Zn ₄ (OH) ₂ Si ₂ O
_7. A corrosion-resistant film formed by continuously forming a zinc silicate compound film mainly composed of synthetic hemimorphite having a chemical formula of ₇ · H ₂ O. 3. A corrosion-resistant film comprising a synthetic hemimorphite obtained by crystallizing a zinc silicate compound film mainly comprising synthetic hemimorphite according to claim 1. 4. A metal substrate having at least a zinc or zinc alloy layer on its surface is pre-treated to form an active ZnO or Zn (OH) ₂ film on the surface, and then dipped or coated in a silicic acid or silicate aqueous solution. For forming a corrosion-resistant film of a zinc silicate compound mainly composed of synthetic hemimorphite which is heat-treated in the presence of water or water vapor. 5. The corrosion-resistant film of a zinc silicate compound mainly composed of synthetic hemimorphite, according to claim 4, wherein the pretreatment is an oxidation treatment in which the pretreatment is performed at a heating temperature of 100 to 400 ° C. for 1 to 3 hours. Formation method. 6. The method according to claim 4, wherein the preliminary processing is p
80-95 ° C in sodium hydroxide solution of H7-13
Forming a corrosion-resistant film of a zinc silicate compound mainly composed of synthetic hemimorphite which is a hydroxylation treatment of boiling for 1 to 60 minutes. 7. The device according to claim 4, the concentration of silicic acid or silicate aqueous solution, 50～15000P in terms of SiO ₂
pm and a hydrothermal treatment at 110 to 210 ° C. for 1 hour or more under the condition that the heat treatment method is at or above the saturated vapor pressure, and wherein the zinc silicate compound is mainly composed of synthetic hemimorphite. 8. The method according to claim 7, wherein the raw material of silicic acid or silicate is Li, wherein M is a monovalent alkali metal.
A method for forming a corrosion-resistant film of synthetic hemimorphite, which is a silicate having a ratio of M ₂ O / SiO ₂ of 2 or less when Na, K, Cs or ammonium or amine is used.