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Summary of nine electroplating process characteristics

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Summary of nine electroplating process characteristics

作者: 烟台运通电镀有限公司点击: Release Date: 2019-11-19 Author: Plating Co., Ltd. Yantai Express Views:

Yantai electroplating process is a specific technical solution to realize the electroplating process. The same plating type can be obtained by different processes, and different Yantai electroplating processes have different characteristics.

1.galvanized

The appearance of the galvanized layer varies depending on the process, and is usually blue-white. The element symbol of zinc is Zn, and the standard electrode potential is -0.763V (Zn2 + / Zn).

Zinc is a typical amphoteric metal that is soluble in both acids and bases. Corrosion is easy to occur in a humid environment, but the corrosion resistance is greatly improved after passivation.

Generally, the galvanized layer after passivation treatment can withstand a neutral salt spray test for 48 hours; the galvanized layer treated with a high corrosion resistance film can withstand hundreds of hours of neutral salt spray. Because the galvanized layer has a lower potential than steel, zinc plating on steel parts is an anode coating, which has an electrochemical protective effect on the substrate.

The same is galvanizing process, which is divided into two categories: alkaline galvanizing and acid galvanizing.

Alkaline zinc plating has cyanide zinc plating, which can be divided into three types: high cyanide, medium cyanide, and low cyanide; there are zincate zinc plating, and zincate zinc plating is obtained by the different brighteners and additives The performance of the coating is different.

Acid galvanizing includes sulfate zinc plating, chloride galvanizing, etc. These different galvanizing processes vary depending on the additives and brighteners used.

The post-treatment after galvanizing is divided into color passivation, white passivation, blue-white passivation, army green passivation, yellow passivation, and black passivation due to different processes used. Hydrogen embrittlement sensitive steel parts should be dehydrogenated after galvanizing.

Galvanizing production can be rack plating production or barrel plating production.

2.Copper plating

Copper is a purplish red metal, which has good ductility and is easy to process and alloy. Its element symbol is Cu, atomic number 29, atomic weight 63.5, melting point 1083 ° C, boiling point 2595 ° C, relative density 8.9, valence is 1 or 2.

Standard electrode potentials are + 0.34V (Cu2 / 10 / Cu) and · + 0.52V (Cu2 + / Cu). Copper has good electrical and thermal conductivity. Stable in dry air, but susceptible to oxidation in humid air. Soluble in nitric acid and hot concentrated sulfuric acid, slightly soluble in hydrochloric acid and dilute sulfuric acid.

Copper plating can also be divided into two categories: alkaline copper plating and acid copper plating. Alkaline copper plating has cyanide copper plating, which is mainly used as a base plating layer for iron and steel or non-ferrous metal plating. It is also used for thickening electroplating, but additives need to be added.

There are also some basic copper plating which is cyanide-free copper plating, mainly pyrophosphate copper plating, citrate copper plating, HEDP (hydroxyethylene diphosphoric acid) copper plating, etc. The weak alkaline copper plating in these plating solutions, The dispersing ability is not as good as that of cyanide copper plating, but with a better brightener, a fine and bright crystal coating can be obtained.

Acid copper plating is mainly sulfate copper plating. Commercial brighteners are now commonly used to obtain high-brightness coatings, which are widely used in decorative plating and electronic plating.

3.Nickel plating

Nickel is a silvery white metal with a yellowish luster. The element symbol is Ni, the atomic number is 28, the atomic weight is 58.7, the relative density is 8.9, the valence is 2, and the standard electrode potential is -250V (Ni + / Ni). The melting point is 1453 ° C and the boiling point is 2732 ° C.

High hardness, but good plasticity, can be attracted by magnets, nickel has high chemical stability, is not easily oxidized in the air, resistant to strong alkalis, reacts slowly with hydrochloric acid and sulfuric acid, and is soluble in nitric acid.

In addition to the use of nickel as an alloy, stainless steel, coinage, electrodes and catalysts, an important application is nickel plating.

Whether in decorative plating, protective plating or functional plating, nickel occupies an important position and is the mainstream plating species in electroplating technology.

The current popular nickel plating process is based on a sulfate nickel plating solution called watt nickel.

Due to the different brighteners, it is divided into dark nickel, semi-bright nickel, bright nickel, and multilayer nickel (high sulfur nickel, nickel seal, etc.), as well as satin nickel, black nickel, etc. In addition to sulfate nickel plating, it is also useful Nickel plating of sulfamates, nickel plating of fluoroborate, etc. for electroforming.

4.Chrome plating

Chromium is a silver-white metal. Because its surface can produce a dense, transparent layer that is naturally dense, it can always maintain its bright white color and obtain a full-bright specular gloss.

This makes chrome plating widely used in decorative plating of all metals or non-metals such as machinery, electronics, and hardware for El.

The element symbol of chromium is Cr, atomic number 24, atomic weight 52, relative density 7.2, melting point 1890 ° C, and valences are 2, 4, and 6. The standard electrode potential is 0.74V (Cr shake / Cr), but the standard potential for reduction from hexavalent chromium to trivalent chromium is very positive, which is + 1.33V (Cr6 + / Cr3 +), because the electrochemical reduction of chromium plating is a stepwise The process that controls the speed is the process of reducing trivalent chromium to metallic chromium, so the standard potential of chromium plating takes the former.

Metal chromium is hard and brittle, but chemically stable. It is stable in the air, including in humid environments. Chromium is dissolved in hydrochloric acid. In addition to a large number of decorative plating and wear-resistant coatings, chromium is also used to make alloys, especially stainless steel.

Chrome plating is mainly carried out in a higher concentration of chromic acid solution. The standard chromium plating solution contains chromic acid 2509 / L and sulfuric acid 2.59 / L. Since chromic acid is a chemical that seriously pollutes the environment, its use has been severely restricted.

Therefore, some low-concentration chrome plating technology or chrome-plating technology came into being, but it will take time to replace the current chrome plating technology.

It is said that since the toxicity of trivalent chromium is only one percent of that of hexavalent chromium, trivalent chromium plating is now widely used. But currently it is mainly used for decorative plating, and the color is slightly different from the traditional hexavalent chromium plating.

The currently popular chromium-plated coating is ternary alloy chromium-plated. That is, tin drill zinc ternary alloy instead of chromium plating.

This process is also used as a decorative chromium substitute, which can obtain a coating very close to the chrome color. The chromium substitute 90 additive used in this process has been widely used in the plating of daily hardware.

5.Tinning

The element symbol of tin is Sn, the atomic weight is ll8.7, the relative density is 7.3, and the melting point is 232 ° C. The standard electrode potential for reduction of tetravalent tin is -0.25V (Sn4 + / Sn); the standard potential for reduction of divalent tin is + 0.14V ( Sn2X / Sn).

Tin is a silver-white metal with a very soft texture. Tin has high chemical stability and is almost insoluble in dilute solutions of sulfuric acid, nitric acid and hydrochloric acid, but tin is dissolved in hot concentrated acids and alkalis, and sulfides have no effect on tin.

Tin plating is the cathode plating for steel. However, it is relatively stable in organic acids, and the compound is non-toxic, so it can be used as a packaging container for the food industry. Tin has a good soldering property, so tin plating is widely used in connectors for aviation, marine and radio communication equipment.

Tin plating is also divided into two categories: alkaline tin plating and acid tin plating. Alkaline tin plating is tetravalent tin plating, and the temperature of the plating solution is relatively high. Acid tin plating is mainly sulfate tin plating and divalent tin plating. Bright additives for acid tin plating are important, without which it is impossible to obtain a qualified coating.

Other tin plating includes pyrophosphate tin plating and ammonia triacetic acid tin plating.

6.Silver plating

Silver is also a familiar noble metal. The element symbol is A9, atomic number 47, atomic weight 107.9, melting point 960.8 ° C, and boiling point 2212 ° C. The valence is l and the relative density is l0.5. The standard electrode potential of silver reduced in the form of cyanide is -0.31V (Ag + / Ag).

Silver is as malleable as gold and is a metal with excellent electrical and thermal conductivity, so it is widely used in the electronics industry, especially in connectors, printed boards and other products. Silver is easy to polish, has a beautiful silvery white, and is chemically stable, but its surface is very easy to react with the sulfides and chlorides in the atmosphere to change color. Metal silver particles are sensitive to light, so it is an important raw material for making photographic films.

The main process of silver plating is silver cyanide plating. Because the potential of silver is very positive, the bonding force between the plating layer and the substrate is affected by the replacement layer in the simple salt plating solution.

The quality of coatings in other cyanide-free silver plating solutions cannot be compared with silver cyanide plating. However, cyanide is limited due to its highly toxic nature, and the cyanide-free silver plating process still has important significance.

At present, the cyanide-free silver plating that has application value in industrial production is mainly thiosulfate silver plating. Others, such as sulfosalicylic acid silver plating and other non-cyanide plating. The silver process has not yet reached the scale of industrial production.

7, gold-plated

Gold is the most familiar precious metal, but not everyone knows its chemical properties and related parameters. The element symbol of gold is Au, atomic number 79, atomic weight l97, relative density 19.3, melting point 1063 ° C, boiling point 2860 ° C, and valence is 1 or 3.

The texture of gold is very soft and has very good ductility. It can process very fine wires and very thin pieces, so thin that it can transmit light.

Gold is stable in the air, does not dissolve in acids, does not react with sulfides, and is only soluble in aqua regia and alkali cyanide solutions. The standard electrode potential of gold is more positive in the acidic system, which is about + 1.5V (Au3 + / Au), but only 0.6V (Au2 + / Au) in the cyanide system.

The important position of gold in the national economy is not only a strong backing of currency, but also an important jewelry and decoration, and also plays an important role in the electronics industry. In order to save this precious resource, gold alloy is often used, which is usually called K gold.

The color of pure gold is golden yellow, and the color of gold alloys becomes lighter as the gold content decreases. But the gold powder is brown and green when transmitted.

When the electroplated gold is an alloy, various colors such as red gold, gold, cyan gold, and platinum can be plated according to the composition change. Among gold compounds, gold trichloride is yellow, sodium gold is yellow, and gold sulfide is black.

Gold plating, like silver plating, mainly uses various cyanide gold plating processes, but some cyanide-free or low-cyanide plating solutions are also useful, such as sulfite gold plating and citrate gold plating.

8.Plating alloy

For alloy plating, copper-tin alloys, copper-zinc alloys, and lead-tin alloys are used more in electroplating.

Some alternative coatings that have appeared in recent years are also alloy plating layers, which are mostly ternary alloys.

For example, copper-tin-zinc alloy, tin-cobalt-zinc alloy, and the like. There are also some corrosion-resistant coatings that are also binary alloys, such as nickel-iron alloys, zinc-nickel alloys, and the like. The application of alloy plating in electroplating production and processing is expected to increase.

9.Rare metal plating

Rare and precious metal plating is mostly used for special products or industries. Therefore, general electroplating companies do not have the level and ability of large-scale production, and some are only used for scientific research and trial production.

The plating types that can be plated include platinum, palladium, rhodium, titanium, indium, and rhenium.

The above is a summary of the characteristics of the 9 different plating types of Yantai electroplating . As a plating manager, you must understand, otherwise it is impossible to manage the plating production well.

烟台电镀

URL of this article: http://acwlkj.cn/news/461.html

Keywords: electroplating , Yantai electroplating , zinc-nickel alloy

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