JPS5947026B2 - galvanizing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a completely new galvanizing method for zinc and alloys whose main components are metals nobler than zinc.

In recent years, various plating methods have been proposed as the demand for plating powder has increased, and among these, the plating method based on the substitution method is widely used because of its ease of operation. The displacement plating method, which is conventionally known as a powder plating method, involves adding a plating metal-containing solution to a mixed powder of a powder to be plated and a reducing metal powder, or to the mixing process thereof, while stirring the mixed powder. Alternatively, the powder to be plated and the reducing metal powder are added together or separately into a solution containing the plating metal under stirring.

However, in the plating method using the above-mentioned substitution method, the basic reaction is to reduce the metal to be plated with a more base metal powder, so Au, Pt,
Powder plating for metals with very noble standard electrode potentials, such as Pd and Ag, has good reduction efficiency and finish, but for metals with base electrode potentials such as Zn, Sn, Ni, and Co. When plating powder, both the reduction efficiency and the plating finish are poor, making it impractical.

Recently, however, as a countermeasure for this problem, in the plating of Ni, Co, Zn, etc., the process of mixing the reducing metal powder such as Mg, At, etc., with the powder to be plated, or the process of mixing the powder to be plated with the powder to be plated, or adding chloride crystals of the plating metal to the mixture of both. A plating method has been proposed in which powder is added and some water and/or hydrochloric acid are added after the reaction has started.

However, in any of the above-mentioned plating methods, since the reducing metal powder must be more base than the plating metal, the two metals are necessarily different types, and therefore, the liquid after plating is Processing becomes a problem. For example, when galvanizing copper powder, if a zinc chloride solution is added to a mixture of copper powder and aluminum powder as a reducing metal powder, a solution containing aluminum chloride and zinc chloride will form according to the reaction equation below. It will be obtained as a liquid after plating treatment.

Cu+AtfZnCι2→CU−Zn+AUt3fZn
Ct2 That is, the solution after the plating treatment cannot be reused as it is as a solution for galvanizing copper powder, so the treatment is problematic and there are drawbacks such as a low reduction rate of zinc. The inventors of the present invention have conducted various studies on galvanizing powders whose main components are zinc and metals other than zinc, and as a result, they have discovered a completely new method different from conventional substitution methods.

That is, the present invention uses a metal of the same type as the plating metal as a metal powder for plating medium (because plating progresses by adding metal powder, metal powder of the same type as the metal ion component in the plating solution is referred to as metal powder for plating medium). The object is to provide a completely new and advantageous galvanizing method using powder.

The present invention will be explained in detail below.

The objects to be plated in the present invention include alloys of zinc and metals having a nobler ionization tendency than zinc, such as copper-zinc, lead-zinc, tin-zinc, silver-zinc, and the like.

There are no particular restrictions on the shape of these bodies to be plated, and powders, wires, plates, etc. may be used as appropriate depending on the purpose and use. The particle size of the zinc powder used as the metal powder for plating media in the present invention can be selected in consideration of the type and size of the object to be plated, as well as the thickness of plating for the object.

For example, when a copper-zinc alloy powder with an average particle diameter of 40 microns is used as the object to be plated, and plating is applied to the powder at a concentration of 28% by weight, the particle size of the zinc is suitably on the order of several microns. The amount of zinc powder used may be 1.0 to 1.05 times (by weight) the amount required for plating.
The aqueous solution containing zinc ions used in the present invention is preferably an aqueous solution of hydrochloric acid, sulfuric acid or nitric acid, such as an aqueous zinc chloride solution with a pH of 2 to 3. It is best to adjust it until it becomes excessive.

In the present invention, galvanizing is carried out by heat-treating the object to be plated as described above in the presence of an aqueous solution containing zinc powder and zinc ions. For example, when using powder as the object to be plated, It is preferable to add the above aqueous solution during the process of mixing the zinc powder to the plating powder or after mixing the zinc powder to the powder to be plated, and heat it while stirring to uniformly perform the plating reaction.

The plating reaction is completed by adding an aqueous solution containing zinc ions and heating for several minutes.

In addition, heating may be about 80-100 degreeC. After the reaction has been completed, the plating product is filtered to remove the liquid, and then washed to recover the galvanized powder.

Since the liquid obtained by the above-mentioned filtration is an aqueous solution containing zinc ions as metal ions, it can be directly recycled to the plating process and reused.

According to the present invention, the zinc plating powder obtained as described above does not deposit zinc on the powder to be plated in the form of particles.
A coating of substantially uniform thickness and relatively large thickness is formed.

Although the case where the object to be plated has a powder shape has been described above, the same can be said of the object to be plated if the object is a wire or a plate.

However, in the case of a plate, the plated body is different from the case of a powder in that before the heat treatment, the body to be plated is immersed in an aqueous solution containing zinc ions in which zinc powder is suspended, and that filtration is not necessary after the reaction is completed. Although the reaction mechanism in the plating method of the present invention is not yet clear, it is presumed that the zinc powder is dissolved during the reaction process, and the zinc ions in the aqueous solution are precipitated on the surface of the object to be plated.
As described above, according to the present invention, the liquid after plating can be directly recycled to the plating process and reused, so the above-mentioned problems found in the conventional method are solved.

The present invention will be explained in more detail below by way of examples.

Example 1 140f of 325 mesh under-sized brass powder (Cu8O%, Zn2O%) was added as the object to be plated to 400me of zinc sulfate aqueous solution containing 150f/t of zinc, and zinc powder with an average particle size of several microns was added. Add 60f and heat to 80°C while stirring.
The mixture was allowed to react for 5 minutes.

The obtained reaction product was washed with P and then dried. As a result, 199 tons of brass powder coated with zinc was obtained. This zinc plating powder exhibited a beautiful zinc color with no brass color even under a microscope, and the powder shape was similar to that of the brass powder before plating. Furthermore, since the slurry obtained by the above-mentioned filtration is an aqueous zinc sulfate solution, it is recycled to the above-mentioned plating step and reused. Example 2 2V of zinc powder with an average particle diameter of several μm was added to a zinc chloride aqueous solution containing 50 f/t of zinc, and after heating to 80°C, a bronze plate (Cu
85%, Snl5(:fl)) for 5 minutes to perform galvanizing.

The resulting galvanized bronze plate had a uniformly plated surface, and no bronze base surface was observed even under a microscope.

Claims (1)

[Claims] 1. A galvanizing method characterized by heat-treating an object to be plated made of zinc and an alloy whose main component is a metal nobler than zinc in the presence of an aqueous solution containing zinc powder and zinc ions.