JPS6133912B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention is used to prevent corrosion caused by aqueous solutions in stainless steel and steel machine parts, particularly crevice corrosion that occurs in minute gaps in shaft seals and sealing parts by sealing materials, etc., and to enhance the sealing effect. This relates to an effective crevice corrosion inhibitor.For example, when applied to bolts, it prevents corrosion of the bolt itself, and when applied to O-type seal rings, it suppresses crevice corrosion that occurs at the seal ring and metal interface. At the same time, the sealing performance is also improved. [Background of the Invention] Conventionally, these minute gaps have been filled with a sealing material made of natural rubber, vulcanized synthetic rubber, or synthetic resin material having a planar or spherical curvature surface.
It has a sealed structure (hereinafter referred to as a seal). However, even if it is sealed with a sealant like this,
If there is a very fine gap between the metal surface under the sealing surface and the interface of the sealing material, and if liquid such as water molecules penetrates and diffuses, this will cause the metal to dissolve on the metal surface within the gap. A reaction occurs and crevice corrosion occurs. For example, if the metal surface is steel, an anode reaction as shown in equation (1) and a cathode reaction of reduction and consumption of oxygen as shown in equation (2) occur. Fe→Fe ²⁺ +2e …(1) O ₂ +2H ₂ O+4e→4OH ^- …(2) However, since material movement is difficult to occur in these minute crevices, the amount of dissolved oxygen in the liquid in the crevices decreases from offshore to As a result, active dissolution reactions are more likely to occur on the metal surface within the crevice, and in addition, the pH of the liquid in the crevice decreases and becomes acidic, causing further corrosion of the metal surface within the crevice. do. Such crevice corrosion phenomena could not be avoided by conventional sealing techniques. [Object of the Invention] An object of the present invention is to provide a crevice corrosion inhibitor that prevents such crevice corrosion. [Summary of the Invention] The main composition of the crevice corrosion inhibitor of the present invention consists of zinc, borate, SiO ₂ fine powder, polybutene, dioctyl sebacate, and molten polystyrene. To explain the role of these compositions in preventing crevice corrosion, zinc easily dissolves in an aqueous solution when liquid enters the crevice, and as a result of the dissolution reaction, the pH of the liquid in the crevice shifts to the alkaline side. At the same time, amorphous hydroxide is formed. This hydroxide diffuses into the gap and renders the metal surface within the gap passivated to the liquid. Borate is necessary to prevent the pH of the interstitial fluid from becoming acidic. SiO ₂ fine powder is necessary to uniformly disperse zinc powder and borate. Polybutene is necessary to impart a certain viscosity to molten polystyrene. A liquid consisting of molten polystyrene (approximately 50 to 10 parts by weight of polystyrene resin, 50 to 90 parts by weight of ethyl acetate solvent, specific examples of ethyl acetate solvent: 35 parts by weight of methyl isobutyl ketone,
(30 parts by weight of xylene, 35 parts by weight of K solvent) is used to apply the zinc and borate to the metal in a uniformly dispersed state, and these become amorphous hydroxides that flow out of the gap. This is necessary to prevent corrosion and maintain its anticorrosion effect for a long time. Next, regarding the relationship between these composition ratios and anticorrosion properties, SiO ₂ fine powder has a primary particle size of 10 to 100 mμ, which is good for sealing properties.
If it is less than this, the dispersibility will be poor, and if it is more than this, the sealing property will be poor. The amount is molten polystyrene
If it is less than 0.5 parts by weight per 100 parts by weight, there is no effect of uniformly dispersing the zinc particles, and if it is more than 4.0 parts by weight,
0.5 to 4.0 due to poor sealing and corrosion resistance.
Limited to parts by weight. If polybutene is less than 0.1 part by weight per 100 parts by weight of molten polystyrene, it will not have the effect of imparting the required viscosity, and if it is more than 5 parts by weight, the viscosity will be high and it will not be possible to uniformly disperse zinc and borate particles. Limited to 0.1-5.0 parts by weight. The amount of dioctyl sebacate to be added is often determined in consideration of the amount of polybutene, and 0.1 to 5.0 parts by weight is appropriate. The primary particle size of the zinc particles is desirably 10 mμ to 50 μm, and is limited to 10 mμ to 50 μm because it becomes uneconomical if it is less than 10 mμ and the sealing performance deteriorates if it is more than 50 μm. The amount is molten polystyrene, polybutene,
For 100 parts by weight of SiO ₂ fine powder and dioctylesebacate added, if it is less than 10 parts by weight, there will be no stable and lasting effect, and if it is more than 300 parts by weight, the applicability to metal surfaces will be poor and the sealing properties will be poor. It also deteriorates, so it is limited to 10 to 300 parts by weight. Borate is Na ₂ B ₄ O ₇・H ₂ O, Na ₂ B ₄ O ₇・
It is effective to select and add one or more of 10H ₂ O, NaBO ₃ .4H ₂ O, and (NH ₄ ) ₂ B ₄ O _{7.4H 2} O. If the amount added is less than 0.001 parts by weight per 100 parts by weight of polybutene, SiO ₂ fine powder, and dioctyl sebacate added to molten polystyrene, it will not be effective in increasing the pH of the liquid in the crevice, and it will be 1.0% by weight. 0.001 or more because the sealing performance deteriorates.
Limited to ~1.0% by weight. Next, embodiments of the invention will be described. As shown in Fig. 1, test specimens 1 and 2 were made of stainless steel (SUS304) having the chemical composition shown in Table 1, and they were combined with anticorrosion agent 3 and placed in 3% saline solution at 25°C. The potential was measured by immersing it in water. In addition, immersion 720, 1440, 500Hr
(hours) later, the test piece 1 was pulled out, the pH of the liquid in the liquid pool 4 was measured, and the presence or absence of crevice corrosion was observed. In the figure, a stainless steel wire 5 is connected to a potentiometer, and a cotton thread 7 covered with a pipe 6 is connected to a reference electrode. The measurement results are shown in Figure 2. Table 2 also shows the pH and presence or absence of crevice corrosion.

【table】

[Table] Values indicate maximum erosion depth.
Inhibitor 1 in Table 2 was prepared by adding 1.5 parts by weight of polybutene, 1.0 parts by weight of dioctyl sebacate, and 1.0% by weight of SiO ₂ fine powder to 100 parts by weight of molten polystyrene (A). 10 _{parts by} weight of zinc powder and _0.003 parts by weight of _{Na2B4O7.10H2O} were added. Inhibitor 2 is 40 parts by weight of zinc powder per 100 parts by weight of the above A.
% by weight, and 0.003 parts by weight of Na ₂ B ₄ O ₇ .10H ₂ O was added. Inhibitor 3 was prepared by adding 100 parts by weight of zinc powder and 0.003 parts by weight of Na ₂ B ₄ O ₇ .10H ₂ O to 100 parts by weight of the above A. Inhibitor 4 was prepared by adding 3.2 parts by weight of polybutene, 1.5 parts by weight of dioctyl sebacate, and 2.5 parts by weight of SiO ₂ fine powder (B), and 5 parts by weight of zinc powder.
parts by weight, and 0.003 parts by weight of Na ₂ B ₄ O ₇ ·10H ₂ O were added. Inhibitor 5 is 100 parts by weight of the above B and 100 parts by weight of zinc powder.
parts by weight, and 0.003 parts by weight of Na ₂ B ₄ O ₇ ·10H ₂ O were added. Inhibitor 6 was obtained by adding 300 parts by weight of zinc powder to 100 parts by weight of the above B. In FIG. 2, the solid line 7 is the potential when no inhibitor is applied at all. corresponds to inhibitor 2, and similarly solid line 6 below.
(corresponding to Inhibitor 6) was located on the more base potential side by 400 mV or more compared to the case where it was not applied at all, and it was confirmed that the stainless steel was sufficiently cathodically polarized. Furthermore, as is clear from Table 2, the liquid quality in the crevices was maintained at pH 10 to 11, and crevice corrosion did not occur at all, giving good results. As explained above, according to the present invention, a crevice corrosion inhibitor that is effective in preventing crevice corrosion of mechanical parts made of stainless steel, steel, etc. can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a method for measuring the effect of the crevice corrosion inhibitor of the present invention, and FIG. 2 is a diagram showing the relationship between the potential of the metal surface in the crevice and time when the crevice corrosion inhibitor is used. 1, 2...Test piece, 3...Crevice corrosion inhibitor.

Claims (1)

[Claims] 1. 0.1 to 5.0 parts by weight of polybutene and SiO ₂ with a primary particle size of 10 to 100 mμ to 100 parts by weight of molten polystyrene obtained by dissolving polystyrene resin in an ethyl acetate solvent.
Fine powder 0.5-4.0 parts by weight, dioctyl sebacate 0.1
A crevice corrosion inhibitor characterized by further adding 10 to 300 parts by weight of zinc powder with a primary particle size of 10 mμ to 50 μ and 0.001 to 1.0 parts by weight of borate to 100 parts by weight of the additive containing ~5.0 parts by weight. . 2 As borates, Na ₂ B ₄ O ₇・10H ₂ O, Na ₂ B ₄ O ₇・
Claim 1, characterized in that one or more are selected from the group consisting of H ₂ O, NaBO ₃ 4H ₂ O, (NH ₄ ) ₂ B ₄ O ₇ 4H ₂ O. Crevice corrosion inhibitor as listed.