JP4172653B2 - Seawater protection method - Google Patents

Description

  The present invention relates to a seawater corrosion-resistant corrosion prevention method that can sufficiently prevent corrosion caused by seawater on a structural member made of an iron-based metal.

  Many steel materials used for bridges, steel structures for construction, etc. are damaged by red rust in the natural environment. In particular, it is known that steel structures constructed in marine meteorological areas are significantly worn by corrosion by seawater and sea salt particles. Therefore, these steel structures are usually devised to suppress corrosion by applying some anticorrosive surface treatment.

  As one of the anticorrosion surface treatments as described above, anticorrosion by a thermal spray technique may be performed. In this method, a metal film having a sacrificial anodic action such as aluminum or zinc is sprayed on the surface of the substrate to form a protective film. Such anticorrosion technology by thermal spraying using a metal material having a sacrificial anodic action is that the coating of aluminum, zinc and their alloys has excellent corrosion resistance in the first place, and a part of the coating is worn out to form a substrate. Even if is exposed, the remaining metal film has the property of electrochemically protecting the steel substrate, that is, has a sacrificial anodic action.

  A technique for forming a film containing almost no microdefects in the film by devising a thermal spraying method has been studied. However, it is considered difficult to perform thermal spraying work with almost no defects in construction on site for large structures such as actual ships and bridges.

As a result, there has not yet been a sufficient method for preventing corrosion caused by seawater on structural members made of iron-based metals. And development of the seawater-proof anticorrosion method which can fully prevent the corrosion by the seawater of the structural member which consists of an iron-type metal was desired.
On the other hand, it is said that the loss due to corrosion of steel materials in plants and structures in Japan will be about 4 trillion yen per year. In this regard, the problems of anticorrosion maintenance costs, power energy costs, environmental pollution problems due to corrosion inhibitors such as hydrazine and tar epoxy paint components, etc. have been pointed out, and an alternative anticorrosion technology that is environmentally friendly and does not require maintenance is desired. ing.

  The present invention has been made in view of the above-described problems, and provides a seawater corrosion-resistant corrosion-proof method that can sufficiently prevent corrosion caused by seawater on a structural member made of an iron-based metal. For the purpose.

  In order to solve the above-mentioned problem, a seawater corrosion-resistant method as a base of the present invention is a method for preventing corrosion caused by seawater on a structural member made of an iron-based metal, and a ceramic having a eutectic composition comprising at least a two-phase system The powder is sprayed on the surface of the member under the condition that an amorphous phase appears, and a network of the amorphous phase is formed in the through-holes in the sprayed coating, and iron ions are precipitated as iron oxide in the network. Let

  According to the above water-proofing and corrosion-proof method, the deposited iron oxide blocks the through-holes in the film, and when the structural member comes into contact with seawater, the seawater does not directly contact the structural member. Can be prevented from being corroded by seawater.

Also, the seawater corrosion resistance prevention method as a base of the present invention is a method for preventing corrosion caused by seawater on a structural member made of an iron-based metal. It sprays on the surface of the member under conditions.
In the water and corrosion resistant method of the present invention, spraying is performed under such conditions that when the powder is sprayed onto the surface of the member, the sprayed coating is sufficiently quenched to form an amorphous phase.
Seawater corrosion process of the present invention is a method of preventing corrosion by seawater for structural members formed of ferrous metal, to prepare a powder of 3Al _{2 O} 3 _· 2SiO 2, the powder, X-rays of the sprayed coating In the diffraction result, seawater anticorrosion protection method, characterized in that plasma spraying is performed on the surface of the member under the following conditions in which an amorphous phase is formed in which a line indicating the presence of a continuous amorphous phase appears;
The arc current is 500 to 750 A, the arc voltage is 33 to 45 V, the spraying distance (distance between the nozzle and the structure) is 10.0 to 12.5 cm,
Thermal spraying is performed in a mixed gas of argon, hydrogen and helium, and the mixing ratio (argon: hydrogen and helium) is set to 10: 1 to 10: 2.
Seawater corrosion structural member of the present invention, thermally sprayed coating surface of 3Al _{2 O} 3 _· 2SiO 2 of structural members made of an iron-based metal is formed, the X-ray diffraction results of the solution morphism coating, continuous amorphous An amorphous phase in which a line indicating the presence of a phase appears is formed.

  As is apparent from the above description, the present invention can sufficiently prevent the corrosion of the structural member made of an iron-based metal by seawater, and can provide a seawater-proof anticorrosion method that is environmentally friendly and does not require maintenance.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, it demonstrates, referring drawings.
In the water and corrosion resistance method of the present invention, the structural member to be prevented from corrosion by seawater is made of an iron-based metal. A typical material for large structures is JISG3101. Moreover, a structural member shall include all the structural members which may be exposed to seawater, for example, a ship, a bridge, a port cargo handling equipment, a seawall, etc. are mentioned.

FIG. 1 is a diagram schematically illustrating the structure of a plasma spraying apparatus used in the seawater corrosion resistance prevention method according to the embodiment of the present invention.
The plasma spraying apparatus 10 includes a plasma generation unit 15 that includes an annular positive electrode 11 and a negative electrode 13 disposed at the center of the positive electrode 11. The plasma generation unit 15 is provided with a nozzle 17. A structure (for example, a hull) on which a sprayed coating is formed is disposed at the tip of the nozzle 17. A gas inlet 19 is connected to the donut-shaped gap between the positive electrode 11 and the negative electrode 13. Plasma is generated when a plasma working gas is supplied from the inlet 19 to cause a DC arc discharge to ionize the gas. The plasma is ejected from the nozzle 17 as a plasma jet 21. A cooling water inlet 23 and a cooling water outlet 25 are connected to the plasma generator 15. The surroundings of the bipolar electrodes 11 and 13 and the nozzle 17 are cooled by the cooling water supplied from the cooling water inlet 23 and discharged from the cooling water outlet 25.

  The powder material is supplied to the plasma jet 21 almost vertically from a supply port 27 provided in the vicinity of the outlet of the nozzle 17. As a result, the powder raw material is melted in the plasma and ejected from the outlet of the nozzle 17 and deposited on the surface of the sprayed material to form a film made of the powder material.

As a powder material, for _example, using a powder 3Al ₂ O 3 · 2SiO _2. The conditions for plasma spraying are, for example, an arc current of 500 to 750 A and an arc voltage of 33 to 45V. Further, the spraying distance (distance between the nozzle and the structure) is set to 10.0 to 12.5 cm.
The thickness of the thermal spray coating is preferably about 200 to 300 μm. When the thickness of the sprayed coating is less than 100 μm, corrosion protection by the coating is insufficient, and when it is thicker than 400 μm, peeling between the coating and the sprayed material tends to occur.
By thermal spraying under such conditions, an amorphous phase network is formed in the through-holes in the thermal spray coating (details will be described later).

As the powder material, eutectic composition composed of at least two phases or eutectic composition composed of three or more phases can be used (for example, Y ₂ O ₃ .Al ₂ O ₃ system). , ZrO ₂ · SiO ₂ · Al ₂ O ₃ system, etc.). Moreover, there is no restriction | limiting in particular in the shape of ceramic powder, Although what kind of shape can be used, It is preferable to use a spherical thing. This is because when a spherical material is used, heat is easily transmitted to the inside of the powder, the melting in the thermal spraying process is good, and dense thermal spraying is generated. The magnitude | size (diameter) of ceramic powder becomes like this. Preferably it is about 10-60 micrometers, More preferably, it is about 20-40 micrometers.

  The plasma working gas for plasma spraying is preferably a mixed gas of argon, hydrogen and helium. By performing thermal spraying in a mixed gas of argon, hydrogen and helium, the ceramic powder is sufficiently dissolved, the heating effect of the material powder in the plasma is increased, and the formed film contains almost no crystals. .

  When thermal spraying is performed in a mixed gas of argon, hydrogen and helium, argon gas, hydrogen and helium gas can be mixed and used, and the mixing ratio (argon: hydrogen and helium) is preferably 10: 1-10: 2. As the ratio of argon gas increases, the amorphous phase decreases and the ratio of crystal parts due to unmelted particles increases. On the other hand, when the ratio of the argon gas is reduced, unmelted particles are not seen and a film structure mainly composed of an amorphous phase is obtained.

  In order to perform plasma spraying in a mixed gas of argon, hydrogen, and helium, for example, argon is used as the main gas, argon is flowed at 45 to 50 liters / minute, and a mixed gas of hydrogen and helium is used as the secondary gas. It is preferable to use a mixed gas of helium and helium at a flow rate of 5 to 15 liters / minute.

  Further, there is no particular limitation on the thermal spraying method used in the water-proof and corrosion-resistant method of the present invention, and plasma spraying, flame spraying, high-speed flame spraying, explosion spraying, arc spraying, RF plasma spraying, electromagnetic acceleration plasma spraying, and line explosion spraying. Any method such as electrothermal explosive powder spraying, laser spraying, laser / plasma composite spraying, and cold spraying may be used. However, in the water and corrosion resistance method of the present invention, the high melting point ceramic is sufficiently melted in flight. From the viewpoint of quenching the sprayed material to obtain an amorphous phase film, it is preferable to use plasma spraying.

  Further, when the ceramic powder is sprayed on the surface of the member, the spraying is performed under such a condition that the sprayed coating is sufficiently quenched to form an amorphous phase. Possible means for increasing the cooling rate of the sprayed coating include water cooling from the back surface of the sprayed object or cooling by compressed air from the front and back surfaces.

The anticorrosive action in the seawater resistant anticorrosion method of the present invention is considered as follows.
FIG. 2 is a diagram for explaining the anticorrosive action in the seawater-resistant anticorrosion method of the present invention.
As shown in FIG. 2A, the coating 51 formed on the substrate 50 by thermal spraying is composed of a plurality of layered flat particles 53. During thermal spraying, minute voids 55 are formed between adjacent flat particles 51. When the holes 55 for each layer are connected in the longitudinal direction of the film, a through-hole 57 penetrating the film 51 is formed (the left portion in the figure).

  When such a base material 50 is immersed in a saline solution (seawater) W, the salt solution W reaches the surface of the substrate 50 through the through-holes 57 as shown in FIG. Then, FeOOH 59 which is a source of rust is generated on the surface 50. When a certain amount of time elapses after immersion, the saline solution gradually permeates into the holes even when the positions of the holes are shifted as shown in the right part of the figure.

  When the seawater corrosion resistance prevention method of the present invention is not applied, rust 59 generated on the surface of the base material grows in the through-holes 57 and reaches the surface of the coating 51 as shown in FIG. At the same time, it spreads along the surface of the substrate 50. As the rust progresses, rust appears on the surface of the film 51, and the film 51 peels from the surface of the substrate 50. Even when the positions of the holes are displaced, the salt solution gradually permeates into the holes and reaches the substrate surface over time.

On the other hand, in the seawater corrosion resistance prevention method of the present invention, as described above, by spraying ceramic powder onto the surface of the base material under the condition that the amorphous phase appears, the network of the amorphous phase is formed in the through-holes 57 in the coating. Is formed. Then, as shown in FIG. 2C, in this network, the rust 59 changes to iron oxide (Fe ₃ O ₄ ) 59 ′. Since this iron oxide 59 ′ blocks the through-holes 57 in the film, the saline solution W does not come into contact with the base material 50. Thereby, the surface of the base material 50 becomes oxygen-deficient, and corrosion of the base material 50 made of an iron-based metal can be prevented. Further, once generated rust 59 does not grow any more and does not spread along the substrate 50 or along the coating 51, it is possible to prevent the progress of rust.
Whether or not an amorphous phase is formed by thermal spraying can be examined using an X-ray diffractometer (details will be described later).

Hereinafter, the present invention will be described in more detail with reference to examples.
(Example)
3Al ₂ O ₃ · 2SiO ₂ ceramic powder (shape: sphere, diameter: 10～45Myuemu, mp (MP): 2010K) and diameter: 28mm, thickness: mild steel plate sample (material, JISG3101) of 2mm into the atmosphere Thermal spraying was performed to form a film on the surface of the mild steel. Table 1 shows typical spraying conditions.

At the time of thermal spraying, the sample to be sprayed was cooled by spraying compressed air from the back surface. And in order to prevent salt water from penetrating into the sprayed coating from the portion not covered with the sprayed coating of the sample, the periphery of the sprayed portion was covered with a thermosetting resin (black bakelite).
Next, this mild steel was immersed in a 3% by mass aqueous sodium chloride solution and left in that state for 30 days.

(Comparative example)
A film was formed by thermal spraying on a mild steel plate under the same conditions as in Example except that Al ₂ O ₃ powder (shape: spherical, diameter: 40 μm, melting point (MP): 2320K) was used as the ceramic powder. And like the Example, the mild steel plate was immersed in 3 mass% salt solution for 30 days.

  After 30 days, the surfaces of the mild steels of Examples and Comparative Examples were observed. The observation was performed with the naked eye and with an optical microscope and a scanning electron microscope. The phase change was also examined using an X-ray diffractometer.

FIG. 3 is an optical micrograph of the entire surface of the sprayed coating after the corrosion test of Examples and Comparative Examples. FIG. 3 (A) is a photograph showing the surface state of the mild steel of the example, and FIG. 3 (B) is a photograph showing the surface state of the mild steel of the comparative example.
As apparent from FIG. 3 (A), in the mild steel plate of the example, the surface keeps the color almost immediately after thermal spraying, and no rust is observed by visual observation. On the other hand, as is clear from FIG. 3B, it can be visually observed that the brown rust appears on the surface of the mild steel plate of the comparative example.

FIG. 4 is an optical micrograph in which the surface of the sprayed coating after the corrosion test of Examples and Comparative Examples is enlarged. FIG. 4A shows an example, and FIG. 4B shows a comparative example.
As is clear from FIG. 4A, in the example, a small amount of rust was confirmed on the surface of the film, but the rust did not spread greatly from the portion to the surface. In contrast, as is clear from FIG. 4B, in the comparative example, a large amount of rust was confirmed on the surface of the film. In the example, rust appeared from one point, whereas in the comparative example, it was confirmed that rust appeared so as to blur from the whole.

FIG. 5 is an optical micrograph of the cross section of the sprayed coating after the corrosion test of Examples and Comparative Examples. FIG. 5A shows an example, and FIG. 5B shows a comparative example.
As is clear from FIG. 5A, in the example, rust is generated at the interface between the mild steel sheet and the film, but does not reach the surface of the film. On the other hand, as is clear from FIG. 5B, in the comparative example, rust generated at the interface between the mild steel sheet and the coating reaches the surface through the inner hole in the coating and proceeds so as to spread along the surface. You can see that

As a result of observation with a scanning electron microscope, no significant difference could be confirmed between the example and the comparative example. Since 3Al ₂ O ₃ .2SiO ₂ has a relatively lower melting point than Al ₂ O ₃ , it is considered that a film having a few pores is generated to some extent. In addition, since Al ₂ O ₃ is spherical, heat is easily transmitted to the inside of the powder, and it is expected that it will melt well in the thermal spraying process to form a dense film.

FIG. 6 is a diagram showing X-ray diffraction results of the coating formed on the ceramic powder used in the example and the mild steel prepared in the example. The lower side shows powder and the upper side shows a film.
As is apparent from the upper chart, the film contains a little crystalline phase, but it can be confirmed that the film is almost amorphous (amorphous phase). This is because a substantially continuous mountain-shaped line 94 appears at a portion other than the two sharp peaks 90 and 92, and this line 94 indicates the presence of an amorphous phase. On the other hand, the chart of the lower powder consists of only a clear peak, indicating that it is a crystalline phase with almost no amorphous phase. In the diffraction line of the film, the large peak 92 that appears in the vicinity of 46 ° may be γ-Al ₂ O ₃ or Al-Si Spinel.

As described above, when spraying powder 3Al _{2 O} 3 _· 2SiO 2 mild steel surface, that amorphous phase is formed in the film was confirmed. And as shown in the Example, when the sprayed steel plate sample was immersed in a saline solution, it was found that the generation of rust was reduced and the growth of rust was prevented, and there was an anticorrosive property of seawater resistance. In addition, it is expected that the seawater corrosion protection method of the present invention is almost permanently effective and does not require maintenance. Furthermore, it is not necessary to use substances that adversely affect the environment, such as corrosion inhibitors and tar epoxy paints, to prevent corrosion.

It is a figure which illustrates typically the structure of the plasma spraying apparatus used for the seawater-proof corrosion-proof method which concerns on embodiment of this invention. It is a figure for demonstrating the anti-corrosion action in the seawater-proof anti-corrosion method of this invention. It is an optical microscope photograph of the whole sprayed coating surface after the corrosion test of an Example and a comparative example. It is the optical microscope photograph which expanded the thermal spray coating surface after the corrosion test of an Example and a comparative example. It is an optical microscope photograph of the sprayed coating cross section after the corrosion test of an Example and a comparative example. It is a figure which shows the X-ray-diffraction result of the membrane | film | coat formed on the ceramic powder used in Example 1, and the mild steel created in Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Plasma spraying apparatus 11 Positive electrode 13 Negative electrode 15 Plasma generating part 17 Nozzle 19 Gas inlet 21 Plasma jet 23 Cooling water inlet 25 Cooling water outlet 50 Base material 51 Film | membrane 53 Molten flat particle 55 Hole 57 Through-hole 59 FeOOOH
90, 92 Peak 94 line

Claims (3)

A method for preventing corrosion caused by seawater on a structural member made of iron-based metal,
Prepare a powder of 3Al ₂ O ₃ · 2SiO _2,
The powder is subjected to plasma spraying on the surface of the member under the following conditions in which an amorphous phase in which a line indicating the presence of a continuous amorphous phase appears in the X-ray diffraction result of the thermal spray coating is characterized by anti-seawater protection Method;
The arc current is 500 to 750 A, the arc voltage is 33 to 45 V, the spraying distance (distance between the nozzle and the structure) is 10.0 to 12.5 cm,
Thermal spraying is performed in a mixed gas of argon, hydrogen and helium, and the mixing ratio (argon: hydrogen and helium) is set to 10: 1 to 10: 2. The seawater corrosion-resistant method according to claim 1, wherein the powder has a size (diameter) of 10 to 60 μm. Sprayed coating surface of _{3Al 2 O} 3 · 2SiO 2 of structural members made of an iron-based metal are formed,
A seawater-resistant anticorrosion structure member, wherein an amorphous phase in which a line indicating the presence of a continuous amorphous phase appears in the X-ray diffraction result of the sprayed coating.