JPH03177589A - Corrosion inhibitor - Google Patents

Abstract

PURPOSE:To satisfactorily prevent the corrosion of structural materials by using sodium silicate, nitrite and sodium molybdate as the effective components of a corrosion inhibitor and incorporating aminosilane as required. CONSTITUTION:Sodium silicate, nitrite and sodium molybdate are used as the effective components of a corrosion inhibitor to be added to water brought into contact with apparatus using ferrous metals as structural material, and aminosilane is incorporated as required. The concn. of the nitrite is regulated to >=5ppm, that of the sodium silicate to 5-100ppm (expressed in terms of SiO2) and that of the sodium molybdate to >=5ppm. The aminosilane is N-phenyl-gamma- aminopropyltrimethoxysilane or N-beta-aminoethyl-gamma-aminophopyltriethoxysilane. The corrosion inhibitor is suitable for use on an industrial scale.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a corrosion inhibitor used for example in circulating water for a cooling system, and more particularly to a corrosion inhibitor for general structural ferrous metals such as steel materials, particularly rolled steel materials. The present invention relates to corrosion inhibitors used to prevent corrosion of equipment constructed using the present invention.

(Prior Art) In industrial facilities and equipment such as various plants, temperature control is often performed as needed to ensure smooth reaction, and for this purpose, a cooling circulation device is used to adjust the temperature of the reaction system. It is also often attached.

In the above-mentioned cooling water system, the ffI of the cooling water or impurities present in the circulating water may gradually accumulate, creating an environment where the constituent materials are likely to corrode. Appropriate corrosion inhibitors are often added. For example, when iron-based materials are used as constituent materials, chromate has been used frequently and effectively as a corrosion inhibitor in the past. However, although this chromate-based corrosion inhibitor has excellent effects, it is known that there is a problem in that care must be taken when handling and using it because it is toxic due to its extremely strong oxidizing power.

In addition to the above methods, there are also known methods that use phosphoric acid and zinc salts to prevent corrosion with a zinc phosphate film, and methods that use organic corrosion inhibitors such as phosphonic acids or carboxylic acids. In the latter case, its use is restricted due to the problem of COD, and in the latter case, there are many problems that require countermeasures, such as the required amount of addition and the generation of slime.

It has also been known to prevent corrosion of mild steel by adding sodium silicate (Na, 0 . There are limits to its use at high concentrations. However, for example, if the concentration when added to cooling water is set to a low value of about 15pp11 calculated by 5tChtX, corrosion tends to decrease as shown in Table 3 below, but the corrosion protection rate is only about 50% at most. Even if the concentration is increased to about 38 ppm, the corrosion protection rate remains below 80%, and it is actually not appropriate to use this sodium silicate alone for corrosion protection.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned difficulties in using conventional corrosion inhibitors, and provides excellent corrosion protection for industrial equipment made of iron-based constituent materials against cooling water, etc. The purpose of the present invention is to provide a corrosion inhibitor that is inexpensive and does not cause pollution problems due to drainage.

[Means to solve the problem]

The corrosion inhibitor according to the present invention, which has been made to achieve the above object, is typically used for circulating water for cooling equipment, and in particular for cooling water for equipment made of mild steel. , sodium silicate, and sodium molybdate are used as active ingredients, and aminosilanes are added as needed.

The reason why the above components are necessary in the present invention is as follows. That is, when a nitrite salt represented by sodium nitrite (hereinafter referred to as sodium nitrite) is added, an active region is no longer observed in mild steel, and when it is used as an anode, it immediately becomes passivated. It is found from Table 4 and FIG. 5 below that the corrosion protection rate of mild steel can be maintained at 90% or more by adding nitrite alone at a concentration of about 5 ppm or more.

However, this addition of sodium nitrite is a problem for mild steel in industrial practice. ill! ! ! The present inventors have found that it is not always easy to obtain and maintain a concentration suitable for production. In other words, from Table 4 of the corrosion test results, considering the safety factor, it is preferable to maintain the added concentration of sodium nitrite at a level of at least 10 ppm or more for corrosion protection of mild steel. Considering the usage conditions, it is not easy to maintain the concentration of the added corrosion inhibitor at a constant level, considering its consumption, as some of it evaporates through the heat exchange process and other processes is replaced and replenished. On an actual industrial scale, it is inevitable that the passivation of mild steel will be incomplete at low additive levels, and there is a concern that localized corrosion or pitting will progress rapidly.

Furthermore, another problem when using this sodium nitrite as the above-mentioned corrosion inhibitor is that when the added concentration of sodium nitrite fluctuates and decreases, as can be seen from Table 4 and Figure 5, the corrosion protection rate decreases. The decline is significant. If the anticorrosive effect varies greatly due to changes in additive concentration, care must be taken when using it in industrial equipment.
This cannot be said to be appropriate.

Therefore, using sodium nitrite to passivate the surface of mild steel,
According to the inventor's intensive research with the aim of achieving the desired effect by adding other components, it was found that along with this sodium nitrite, sodium silicate, which has the effect of reducing corrosion through polarization, was added to the cooling water at the same time. Also, sodium molybdate, which passivates mild steel, is added to make the passivity more stable. Preferably, aminosilanes are further added as a component that improves the action of sodium nitrite on the surface of mild steel through adsorption. They recognized that the various problems mentioned above could be solved, and came up with the present invention.

From the above, in the present invention, the concentration of sodium nitrite added to circulating water for temperature adjustment such as cooling water is 5 ppm or more,
Preferably 5ppm to 1100pp, optimally 15pp
It is preferable to set the concentration to m~30ppm, and sodium nitrite is 5p.
Nitrite salts may be potassium salts, lithium salts, etc., which are not suitable at concentrations below pm as they may cause local corrosion.

Sodium silicate concentration is 5 ppm to 10 based on 5102
0pp111. Preferably 10ppn+ to 75ppm
, most preferably 30 ppm to 40 ppm I11. If it is more than 1100 ppm, the pH will increase, which is not preferable, and if it is less than 5 ppm, there is a problem that the effect of its addition is small.

Furthermore, sodium molybdate (Na, MoO4.2H), which has a passivating effect together with the above sodium nitrite and sodium silicate,
It is preferable to add 20), which facilitates the passivation of mild steel due to the joint effect with sodium nitrite and makes it stable up to high potentials (Figures 1 to 4).The addition concentration is 5 ppm or more. , preferably 5 ppm to 1100 ppm
, it is best to set it at 15 ppm to 30 ppm.
Passivation is insufficient at 5 ppm or less, and 1100 p
If it is more than p, it is unnecessary and economically disadvantageous.

Next, the corrosion inhibitor is expected to have an anticorrosive effect due to adsorption by adding aminosilanes.

Such aminosilanes include N-phenyl-γaminopropyltrimethoxysilane.

N-β-aminoethyl (γ-aminopropyltriethoxysilane) (hereinafter abbreviated as ^PES) can be mentioned, but APES is particularly preferred from the cost standpoint. Its concentration is lppmxloppm, preferably 2ppm
The content is preferably about 5 ppm. Generally, this additive is expensive, and even if it exceeds IQppm, it is not expected to improve the effect much, so it is set within the above range.

A typical device material for a cooling circulating water system to which the corrosion inhibitor of the present invention is applied is a ferrous metal material, specifically, a material made of steel. The cooling water to which this corrosion inhibitor is added is not particularly limited as long as it is fresh water, but generally natural water or natural ice that has not undergone special ess removal treatment is used as industrial cooling water. The present invention is suitable for such cooling water.

〔Effect of the invention〕

The corrosion inhibitor of the present invention effectively exhibits passivation when added to cooling water, and the polarization effect of the other component, sodium silicate, is mutually enhanced, making it a material for equipment that circulates a large amount of cooling water. This has the effect of providing good corrosion protection for the constituent materials in, etc.

In addition, the addition of aminosilanes enhances the adsorption effect and improves the corrosion inhibiting effect.
Since the amounts of sodium nitrite and sodium molybdate added can be reduced, there is an effect that use on an industrial scale can be suitably realized.

〔Example〕

The present invention will be described below based on Examples, but it goes without saying that the present invention is not limited only to the Examples.

The material used in the following examples is general structural rolled steel (
JIS symbol SS41).

The cooling water used in the test was the following natural ice (Yamaguchi Prefecture Kanno Water System) that had not been subjected to SS removal treatment.

Considering the components of the cooling water used and the case where it becomes concentrated,
C! Mainly involved in corrosion! - and 5042- ions added to the cooling water were also tested. For convenience, the former will be hereinafter referred to as Liquid S-1 and the latter as Liquid S-2, and their components are shown in the table below.

In the immersion test, the specimen was polished, degreased, weighed, and crushed in a test liquid for 3 days, and the liquid was maintained at 50° C. while stirring with a magnetic stirrer during the test.

(Polarization test) 1 crt in the test liquid made by adding corrosion inhibitor to cooling water? A test piece having a constant surface area was crushed, and a polarization curve was measured using a potentiostat (potential measuring device; manufactured by Hokuto Denko Co., Ltd.) at a sweep rate of 2 mV/sec.

(Degree of erosion and corrosion protection rate) The degree of erosion was determined from the change in weight before and after the test. Using this, the corrosion protection rate was calculated from the following formula.

-Y Corrosion protection rate ÷ 0100% Table 1 shows the test results in which the samples were added to cooling water at the concentrations shown in Table 1 and the test pieces were immersed in the test liquid as described above.

As can be seen from the graph, in liquid S-1, even with the addition of a small amount of the inhibitor shown in symbol 1, the degree of corrosion is low, and on the contrary, the corrosion protection rate is as high as 98.2%. When it is added at a level of 4 or above, no corrosion is observed at all, and it is clear that the effect is great.

Next is S-2, which has many C2- ions and 504'- ions.
In liquids, the degree of erosion gradually decreases as the amount added increases. In the case of C composition, it increases to 84%. When the amount added was further increased, the corrosion protection rate reached 99% or more.

As described above, the corrosion inhibitor of this example containing the three components has a corrosion protection rate of 98% or more even with composition 1, which is excellent. Also S
It can be seen that even in a corrosive environment containing a large amount of C1- ions and 5o42- ions in the -2 solution, it has very excellent performance showing a corrosion protection rate of 99% or more when added to D composition or higher.

Figure 1 shows various concentrations of 5IOz, NaN0z and Na2MoO4.2H2 with symbols 1 to 6 in Table 1.
The polarization curves of mild steel in S-1 liquid containing 0 are summarized. Even when composition 1 is added in a small amount, the polarization is significant, and when composition 2 is added, the polarization becomes even larger. From this, the results in Table 1, where the corrosion protection rate exceeded 98%, can be clearly understood. If the added concentration is higher than this, there is no active dissolution and the substance is in an inactive state from the beginning, so the corrosion protection rate is 100%.

The larger the amount added, the wider the passive region becomes, and the more stable it becomes.

Next, FIG. 2 shows a polarization curve of mild steel in liquid S-2.

There is polarization from composition A to C, but the degree of polarization is small.
The effect of high abundance of ions and S04'-ions is evident. Even in the D composition, the passive current is very large compared to the S-1 liquid of the 4 compositions.

Furthermore, even with compositions E and F, the passive state current is large and the passive state region is narrow. It is not good if the composition is more than that! lI worsens, so
The corrosion protection rate is a high value of 99% or more.

Example 2 Table 2 shows the results for a four-component system in which 8PES having an adsorption effect was added to the sodium silicate, sodium nitrite, and sodium molybdate of Example 1 above. As is clear from this, when a small amount of 8 PES is added to the S-1 solution, the corrosion protection rate of the solution with the symbol 1 becomes 99%. However, with the 3rd solution, there is almost no corrosion. Also, S-2 liquid can also be used for AP.
By adding ES, the C° composition solution has a corrosion protection rate of 98% or more.

As mentioned above, by comparing with the example work, it can be seen that the addition of APES makes corrosion prevention more effective.

Figure 3 shows 5in2°NaNO of various concentrations in Table 2.
2, S-1 containing NaJOO4'2H20 and APES
It is a polarization curve of mild steel in a composition liquid with a symbol of 1° to 6° in the liquid. Compared to FIG. 1, the polarizability at low concentrations increases increasingly. If the concentration increases further, it becomes passivated immediately when used as an anode, and the passivation region becomes wider. For example, the 6゛ composition liquid maintains a passive state up to +〇, 8V, but this is - level compared to +〇, 65V for the composition of symbol 6 in Example 1, which indicates that it has become more stable. .

FIG. 4 shows the same results for S-2 liquid, 0 polarizability, and it is clear when compared with FIG. 2 that the stability of the passive state increases with the addition of APES.

Comparative Example 1 Same as Example 1 except that sodium silicate was added alone to the 5-1 solution.
Corrosion tests were conducted in the same manner as above, and the results are shown in Table 3.

As seen from the table, when adding sodium silicate alone, 38
Even when ppm was added, the degree of corrosion was 0.48 mm/y, and the corrosion prevention rate was only 72.8%, which was insufficient as a suppressive effect.

Comparative Example 2 Table 4 shows the results of a corrosion test carried out in the same manner as in Example 1, except that sodium nitrite was added alone to liquid S-1. The polarization curve is shown in FIG.

When adding sodium nitrite alone, 0.9 mm at 3 ppm
The corrosion protection rate is about 50% at an erosion degree of about /y.

However, when 5 ppm or more is added, the corrosion protection rate increases to 90% or more. However, since pitting occurs on the mild steel surface after the test, its use alone is not preferred.

Comparative Example 3 Table 5 shows the test results when sodium molybdate was added alone.

When adding 2.5 ppm, the degree of corrosion is 0.45a+n/y, and the corrosion protection rate is about 74%, which is not sufficient.

However, when the content exceeds 5 ppm, the corrosion protection rate exceeds 90%. However, even if a large amount of 50 ppm is added, the
．． The corrosion protection rate is about 5%, and local corrosion is also observed, so its use alone is not preferable.

Table 6 Comparative Example 4 Table 6 shows the results of a similar test in which various concentrations of sodium nitrite and sodium silicate were added to liquid S-1 and used as the test liquid.

As can be seen from the table, when NaN0z is 5 ppm or more,
Even if the concentration of sodium silicate is around 7.2 ppm, the degree of corrosion is less than 0.1 mm/y, and the corrosion protection rate is 95%.
That was it. However, if the NaNo2 content is 1 to 2 ppm, corrosion will be extremely severe, and especially if the content is less than ippm, pitting will occur, making it unusable.

Comparative Example 5 Table 7 shows the results of a corrosion test of S- containing sodium silicate and sodium molybdate in a liquid.

14.4ppm as SiO□, as Na2M0
When 10 ppm of 04.2H20 is present, the corrosion protection rate is 99% or more. If more than that amount is contained, corrosion will hardly occur and the anticorrosive effect will be very large. However, as shown in Table 2, when NaNO2 and APES are further added, the corrosion protection rate exceeds 99% even in small amounts.

[Brief explanation of drawings]

Figure 1 is a diagram showing the polarization curve in the case of liquid S-1 containing the corrosion inhibitor of Example 1 of the present invention, and Figure 2 is the same.
2 is a polarization curve in liquid S-2 to which the corrosion inhibitor of Example 1 was added. Figure 3 shows the polarization curve in liquid S-1 containing the corrosion inhibitor of Example 2, and Figure 4 shows the polarization curve in liquid S-2 containing the corrosion inhibitor of Example 2. This is what is shown. FIG. 5 is a polarization curve in Comparative Example 2 in S-1 solution to which NaNO2 was added alone. Other 4 current density. μA/afl Current density μA/c Current density μA/cTj Current density. μA/C1 current density. μA/d 2゜flat r! 3rd patent application in t/year? ? 3rd month is also 1L years old (p. Date of current correction instruction: μA/c4 Current density: μA/c

Claims (1)

[Scope of Claims] 1. Corrosion treatment that contains sodium silicate, nitrite, and sodium molybdate as active ingredients, further contains aminosilanes as necessary, and is added to water that comes into contact with equipment made of iron-based metals. Suppressant. 2. The corrosion inhibitor according to claim 1, wherein the concentration of nitrite is 5 ppm or more. 3. In claim 1 or 2, the concentration of sodium silicate is Si
A corrosion inhibitor characterized by having a concentration of 5 ppm to 100 ppm in terms of O_2. 4. The corrosion inhibitor according to claim 1, wherein the sodium molybdate concentration is 5 ppm or more. 5. Corrosion according to any one of claims 1 to 4, characterized in that the aminosilane is either N-phenyl-γ-aminopropyltrimethoxysilane or N-β-aminoethyl (γ-aminopropyltriethoxysilane). Suppressant. 6. The corrosion inhibitor according to claim 1, wherein the water added is circulating water of a circulating water system for cooling equipment. 7. A corrosion suppression method characterized by using water to which sodium silicate, nitrite, sodium molybdate, and further aminosilanes are added as necessary, as cooling water for equipment made of iron-based metals.