Potassium chloride zinc plating can stabilize the pH value of the plating solution to stabilize production!

In the acid potassium chloride zinc plating process, the maintenance and adjustment of the pH of the plating solution is an important link.

It is ideal to control the pH between 5 and 6. Too high or too low will adversely affect production.

When the pH is <5, the surface of the coating is foggy, and the dispersing ability and covering ability of the electrolyte are reduced;

When pH>6, the brightness of the coating decreases, the coating is rough, and the corners are easy to burn. The plating solution is turbid, and even hydroxide precipitates appear, and the performance of the plating solution deteriorates.

In production practice, the rapid rise of pH is a common phenomenon. In order to stabilize production, HCl must be added in time to make adjustments.

1

Causes of pH increase

Statistics show that the amount of HCl consumed in production is relatively large, which is higher than the theoretical calculation value. The reasons for the increase in pH are:

1) Hydrogen evolution at the cathode during electrodeposition is the main reason.

Although the ηκ of potassium chloride zinc plating is more than 95%, part of the current is still consumed in the side reaction. Elevated;

2) Potassium chloride zinc plating electrolyte is weakly acidic and has the ability to dissolve iron and steel metals.

When the part enters the plating solution and no current is applied, or the concave part (low current density area) of the geometrically complicated part cannot be coated with the zinc layer in time, chemical dissolution will occur. In addition, the parts dropped from the plating bath during production can also cause the chemical dissolution of iron and zinc.

In the comprehensive treatment of the electroplating solution, it can be seen that the parts removed from the bottom of the tank have been severely corroded, causing a large amount of zinc and iron ions to enter the plating solution, which is also an important reason for the increase in pH;

3) In the barrel plating production, the barrel loading quality is too large, the initial current is small, and the outer layer of the parts deposits the coating faster, and most of the parts are buried inside, and the coating cannot be deposited quickly, which also causes iron Chemical dissolution promotes pH increase;

4) After stopping production, observe that there are still bubbles near the anode plate, indicating that the zinc anode is undergoing chemical dissolution.

From this, it is inferred that the zinc anode in the production is electrochemically dissolved and there is also chemical dissolution, which also causes the pH to rise, and it is difficult to avoid;

5) When the content of H3BO4 in the electrolyte is too low, and the hydrogen ions dissociated step by step are not enough to supplement the amount of hydrogen ions consumed in the bath, the buffer function is lost, and the pH of the bath will naturally rise.

2

Control of bath pH

Through the above analysis, in order to effectively control the pH of the plating solution, in addition to adding dilute HCl in time for adjustment, the influence of the above factors should also be considered, and the following measures should be taken:

1) According to the chemical analysis results of ρ(H3BO3) solution, add H3BO4 in time to control ρ(H3BO3) at 35-40g/L to ensure the buffering effect on the plating solution;

2) The anode plate should be taken out in time during production shutdown or intermittent operation to reduce the chemical dissolution of zinc anode in the plating solution;

3) Reasonably design the mounting method of the hanger and the parts, and strive to cover the surface of the parts as soon as possible by the zinc layer at the beginning of the electroplating process.

During production, it is also necessary to prevent the plated parts from falling into the tank, and to remove the parts that fall into the tank in time to reduce the dissolution of iron and zinc;

4) In barrel plating production, a reasonable load quality is calculated, and a larger impulse current is initially applied to electroplating, so that all the plating parts are deposited on the zinc layer as soon as possible.