KR100290565B1 - Chloride-based zinc-iron alloy plating solution - Google Patents

Abstract

PURPOSE: Provided is a chloride-based zinc-iron alloy plating solution, which has good stability in chloride bath. CONSTITUTION: In a chloride-based zinc-iron alloy plating solution of which pH is 2-3, iron particle having a diameter of 0.1-1mm and its weight is 1/2 to 2 times of the concentration of Fe ion in the chloride-based zinc-iron alloy plating solution is immersed in the zinc-iron alloy plating solution being put in an acid resistant bag, whereby inhibiting oxidation of Fe¬2+, which would cause iron sludge deposition as well as supplying a proper amount of Fe¬2+ ion.

Description

Highly stable zinc-iron alloy plating solution

The present invention relates to a zinc-iron alloy plating solution having excellent stability in a chloride bath, and more particularly, pure iron particles having a diameter of 0.1-1 mm in a zinc-iron alloy plating solution of chloride having a pH of 2-3. It is possible to supply the proper amount of iron ions to the solution as well as to prevent oxidation of the divalent iron ions by storing them in the acid-resistant bag that is free to go in and out of the solution at a weight ratio 1 / 2-2 times the concentration of iron ions in the solution. The present invention relates to a zinc-iron alloy plating solution having excellent stability.

When the zinc-iron alloy plating solution containing chloride ions and the pH of the solution is stored for a long time, the divalent iron ion is easily contacted with air as shown in equations (1)-(3) to easily trivalent iron ion. And trivalent iron ions again form solid suspended solids such as iron hydroxide or iron oxide. These suspended substances cause a load on wastewater treatment, reduce productivity, and cause stains on the surface of the plating. In a carousel plating bath, foreign matter enters between the conductive roll and the steel sheet, causing fatal defects such as arc spots. Decrease productivity.

1 shows the zinc-iron alloy plating solution containing zinc 60g / l, divalent iron ion 11g / l, trivalent ion 0.3g / l, pH 2.0 and temperature 55 ℃ In the graph of the analysis of trivalent iron ions in, as shown in Figure 1, when the zinc-iron alloy plating solution stored for about one month trivalent iron ions are 0.3g / l to 4-5g Significantly increases to / l, the pH of the solution drops from 2 to 1 and divalent iron decreases from 11g / l to 5g / l. The cause of such a phenomenon can be explained as follows.

Since the trivalent iron ions formed by the above formula (1) react with the hydroxide ions in the solution to form iron hydroxide, the pH of the solution drops and the divalent iron ions are oxidized to trivalent iron ions by dissolved oxygen. When the pH of the solution decreases by the amount, trivalent iron ions easily form hydroxides when the pH of the solution is about 1 or more, and changes to sludge as a solid suspended solid. Therefore, the total iron ion concentration is finally reduced by the difference between the oxidation rate of the divalent iron ion and the consumption rate of the trivalent iron ion formed into the sludge. That is, the total iron ion concentration is reduced by the concentration of trivalent iron ions participating in the sludge formation. As a result, the sludge amount increases, the pH decreases, and only the total iron ion concentration is lost. Therefore, there are the following conventional techniques used to prevent the oxidation of trivalent iron ions to trivalent or to prevent the trivalent iron ions from forming a sludge of the hydroxide or oxide.

First, the addition of a complexing agent such as citric acid, which can complex only iron ions, in the form of a salt can reduce the oxidation of divalent iron ions to trivalent iron, preventing the sludge formation of trivalent iron ions. The addition ultimately slows the activity of the iron ions, resulting in a reduction of the iron ion's reducing power during the plating reaction and a decrease in the iron content in the coating.The addition of a complexing agent such as sodium citrate, however weakly acid, reduces the pH of the solution. It is difficult to put a large amount at one time because the stability is slowed down and the dissolution speed is slowed down, and there are various problems such as high price.

Secondly, a zinc powder is added using a reducing device. When zinc powder is added to an acidic solution having a pH of 2, it is dissolved very quickly. In particular, when the particle size is small and the surface area is large, there is a risk of fire because it dissolves instantaneously while generating a large amount of hydrogen gas. Therefore, although the reducing power of reducing trivalent iron ions to divalent ions is high as the melting speed is high, the concentration of zinc ions is easily increased, and the amount of hydrogen gas is generated, which may cause a fire, and greatly increase the pH. There is a problem in terms of maintaining the stability of the solution.

Finally, inert gas is blown into the solution. Continuously blowing inert gas, such as argon or nitrogen, into the solution will prevent the dissolved oxygen from dissolving, thus preventing the oxidation of iron ions of bivalent iron ions. However, when the amount of the solution is large, the amount of gas to be blown must be large and the effect is not so large that there is a problem in that the blowing of the fluorinated gas in reality.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art described above, and has as a base to provide a chloride-based zinc-iron alloy plating solution having excellent stability, and in order to achieve the above object, it contains chloride ions and has a pH of 2 Pure iron particles with a diameter of 0.1-1mm in a zinc-iron alloy plating solution of -3 are stored in an acid-resistant bag at a weight ratio of 1 / 2-2 times the concentration of iron ions in the solution. It provides a zinc-iron alloy plating solution with excellent stability that can prevent a fire and provide an appropriate amount of divalent iron ions to the solution.

1 is a graph showing the change of the concentration of trivalent iron ion in the solution over time when the zinc-iron alloy plating solution containing 60 g / l zinc, 11 g / l divalent iron.

FIG. 2 is a graph showing the concentration of divalent iron ions analyzed over time while putting 20 g / l of iron powder having a diameter of 0.1 mm in a bag and storing it in a solution.

FIG. 3 is a graph showing the trivalent iron ion concentration obtained in the solution composition and conditions described in FIG.

In the zinc-iron alloy plating solution of the chloride bath, the iron powder corresponding to 1 / 2-2 times the iron ions in the solution to prevent oxidation of the divalent iron ions in the solution and to supply an appropriate amount of iron ions. It is characterized by hanging in an acid-resistant bag and kept in solution at all times.

Hereinafter, a zinc-iron alloy plating solution having excellent stability of the present invention will be described in detail.

The zinc-iron alloy plating solution using a chloride bath is carried out with the solution having a pH of about 2-3. The reason is that if the pH is lower than 2, the zinc anode has a large amount of chemical dissolution and the concentration balance is broken. When dissolved, the amount of hydrogen gas generated increases and there is a risk of fire. When the pH rises above 3, as shown in equations (1) and (2), trivalent iron ions form hydroxides or oxides to form sludge and various defects. Or waste water treatment load. In addition, as the plating proceeds, the insufficient metal ions are supplied as the soluble anode is electrochemically dissolved, and in case of shortage, the zinc chloride or ferric chloride stock solution is added at an appropriate time.

Therefore, in the present invention, the bag containing the pure iron powder is always stored in the solution to prevent oxidation of trivalent iron ions and serves to supplement the insufficient iron ions. When the iron powder is added to the solution, the trivalent ions cannot exist because the electrons emitted during the dissolution, that is, oxidized, are used to reduce the trivalent iron ions to the divalent ions. Therefore, since there is no trivalent iron ions, it is possible to always maintain a transparent solution without forming sludge. In addition, since iron powder is dissolved, it supplies a proper amount of divalent iron ions, so there is a great advantage of not having to separately add ferrous chloride plating stock solution.

Next, the reason for limitation of the numerical value suggested by the present invention will be described.

If the particle size of iron powder is smaller than 0.1mm, the surface area is large, so the dissolution rate is large at first but as dissolution progresses, the dissolution rate is large so that oxide forms on the surface of iron powder and is entangled with each other. Hardened and thus the dissolution does not proceed anymore. Therefore, if the size of the iron powder is less than 0.1mm at the time of long-term storage is not effective. In addition, if the size of the iron powder is larger than 1mm, the surface area is small and the dissolution rate is slowed down, so a large amount of iron powder is required, which is not practical, and it is impossible to reduce trivalent iron ions in a short time. Will result.

If the weight of the iron powder is 1/2 or less of the iron ion concentration in the solution, it is not sufficient to reduce trivalent iron ions, and if it is more than 2 times, it is the amount remaining after reducing trivalent iron ions. It is uneconomical and the concentration of divalent iron ions is so high that the ion balance of the solution is broken. And the bag containing the iron powder should be the size that the solution can penetrate freely, and the material may be any material that can withstand the long term in the acid solution.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

20 g of iron powder having a diameter of 0.1 mm was placed in a bag under the following solution composition and conditions, and the bivalent iron ion concentration was analyzed according to the storage days while the solution was slightly stirred for 7 days. Quantitative analysis of iron ions was carried out by a wet method. First, divalent iron ions were analyzed, and then, total iron ions were analyzed, and then trivalent iron ions were obtained by subtracting the concentration of divalent iron ions from the total iron ions.

end. Solution composition

Zinc chloride (ZnCl ₂ ): 128 g / l

Ferric Chloride (FeCl ₂ ): 58g / l

Potassium chloride (KCl): 340g / l

I. Solution condition

Temperature: 55 ℃

pH: 2.0

Figure 2 shows the results, the first 11g / l bivalent iron ion concentration gradually increased with the storage days, and after 7 days can be seen that about 1g / l increased. After all, if iron powder with the same weight ratio as the iron ion concentration in the solution is stored for one month, the bivalent iron ion, which was the first 11 g / l, can be increased by about 4 g / l, which is 15 g / l. Considering the fact that it is difficult to secure iron content in the coating film because it is plated with an increased iron ion concentration, it is a very desirable result.

FIG. 3 shows the trivalent iron ion concentration in the solution according to the storage days in this case. As shown in FIG. 1, when the pure zinc-iron alloy plating solution is stored for 7 days, the trivalent iron ion concentration increases by 1.7 g / l from 0.3 g / l to about 2 g / l, but as shown in FIG. If the iron powder is put in a pocket and stored in the solution, it can be seen that even after 7 days, the trivalent iron ion concentration remains as it is for the first time. Therefore, by storing the iron powder in the zinc-iron alloy plating solution in an appropriate amount in this way it is possible to completely prevent the formation of trivalent iron ions and to secure an appropriate amount of divalent iron temperature.

Example 2

Iron in a solution containing 60 g / l zinc, 11 g / l divalent iron ion, 0.22 g / l trivalent iron ion, and 340 g / l potassium chloride, which is a common zinc-iron alloy plating solution concentration, and has a temperature of 55 ° C. and a pH of 2.0 Table 1 shows the bivalent and trivalent iron ion concentrations and sludge amounts analyzed after storing them in a bag for 7 days while changing the size and amount of horses. The iron ion concentration was analyzed in the same manner as in Example 1, and the amount of sludge was measured by weight difference by weighing the filter paper after drying the solution by filtration with filter paper. As can be seen from the comparative examples, the addition of iron powder in any form reduces the concentration of trivalent iron ions and increases the amount of sludge. However, the iron powder size is within the limits set forth in the present invention, but only when the amount is more than twice the iron ion concentration in the solution, there is almost no trivalent iron ion and no sludge amount, but the divalent iron ion concentration is greatly increased. This increases the balance of iron ion concentration in the solution.

However, when the size of the iron powder proposed in the present invention is 0.1-1mm and the weight is added at 1 / 2-2 times the iron ion concentration in the solution, the trivalent iron ion concentration in the solution does not change as it was when the first solution was made. Since divalent iron increased by about 1 g / l after the maximum temperature of 7 days, there is no problem at all, and it can be seen that it is a stable solution that does not generate sludge at all.

According to the zinc-iron alloy plating solution excellent in the stability of the present invention described above, the iron powder in the zinc-iron alloy plating solution of the chloride bath has a particle size of 0.1-1mm and the addition amount is 1 / 2-2 times the iron ion concentration in the solution. It is stored in the bag for a long time in the solution to inhibit the oxidation of divalent iron ions to prevent sludge formation and supply the appropriate amount of iron ions to the solution, there is an effect.

Claims (1)

A zinc-iron alloy plating solution with a pH of 2-3 is 0.1-1mm in diameter and weighed 1 / 2-2 times the iron ion concentration in the solution. Zinc-iron alloy plating solution with excellent solution stability.