FAQ

Characteristics of Trivalent Chromium Plating

1. The color of the chromium coating obtained from the trivalent chromium bath is slightly different from that obtained from the hexavalent chromium bath. The coatings obtained with trivalent chromium tend to be of a dark yellow color, while those with hexavalent chromium tend to be of a white-blue color.
2. The deposition rate, cover ing power, and throw power of the trivalent chromium bath are better than that of the hexavalent chromium bath
The trivalent chromium plating bath of the sulfate system requires a platinum-coated titanium mesh as an anode, while the trivalent chromium plating bath of the chloride system requires graphite as an anode.
3. Trivalent chromium bath is highly corrosive, especially in the low current density area of the parts.
4. Low tolerance of metal and organic impurities in the trivalent chromium bath.
5. Similarly to hexavalent chromium plating, trivalent chromium plating baths also require heating and cooling equipment, usually with titanium as the heating and cooling tube.

The difference between electrolytic silver stripping and electroless silver stripping?

1. Electrolytes are treated only by immersion and do not require electrification.
2. Thin silver with no distinct high and low areas is suitable for electrostatics.
3. Strong depth power of electrolysis.
4. Electrolytic stripping is faster and has a longer lifetime.
5. Electroless silver stripping is suitable for thin, electroless silver..
6. Electrolytic silver is suitable for thic k silver, distinct high and low areas, or deep silver coatings.

Protection of Anode Coating and Cathode Coating on Substrate Metals

The protection principle of the anode coating is based on the fact that the potential of the coating is negative compared to the substrate metal and the electro-dissolution pressure is large, so that it acts as an anode in the corroded cell, thus delaying the corrosion of the substrate metal. Even when the substrate metal is slightly exposed, the coating can still be protective. Therefore, the number of pores on the anode coating has little effect on the protective performance. In terms of thickness, the thicker the coating, the more protective it is.

The cathodic coating only has a purely mechanical isolation effect on the substrate metal and does not have the electrochemical protection effect as the anode coating does. Therefore, it must have a protective effect when the porosity of the coating is small. Otherwise, in the presence of a pore or damage to the coating, the substrate metal will act as an anode for the corroded cell, which accelerates the corrosion of the substrate metal. In general, the porosity of the coating decreases with the thickness of the coating, so the larger the thickness, the stronger the protection of the cathode coating.

Why Do Cyanide Silver Plating Use Potassium Salt Instead of Sodium Salt ?

Long-term experiments have shown that potassium salts have many unique properties than sodium salts.

The conductivity of the potassium electrolyte is higher than that of the sodium electrolyte, as is the limiting current density, and the whole range of current densities is higher than that of the sodium electrolyte.

1. Potassium carbonate produced in electrolytes prepared with potassium salts is highly solvable. When sodium salts were used to prepare the electrolyte, the sodium carbonate in the bath exceeded 609/L, which would rough up the crystallization of the silver coating, and potassium salts were used to prepare the electrolyte. Potassium carbonate concentrations can rise as high as 909/L without harmful effects.

2. The potassium electrolyte has slightly higher cathodic polarization than the sodium electrolyte, strong throwing power, and a fine-grained coating crystal.

3. The purity and physical properties of the silver coating obtained from the potassium salt electrolyte are superior to those obtained from the sodium salt electrolyte.

4. The sulfur content of potassium salt is less than that of sodium salt (infinitesimal), and the sulfur content of silver plating is relatively reduced, which improves the anti-tarnishing ability.

For example, when sodium salts of general purity are used, it is difficult to dissolve the anode lightly, and the sulphur in the sodium salts interacts with the silver in the bath , rendering the whole electrolyte grayish-black and giving rise to anomalous electroplating. As a result, potassium salts are often used to prepare electrolytes when plating precious metals.

What are the common methods of degreasing before electroplating?

After each process, the metal will produce grease that covers the surface layer of the metal. Therefore, in electroplating, anti-tarnish and other processes, degreasing is required to increase the adhesion between the coating and the oxide layer of the workpiece.

Degeasing methods	Features	Application
Organic solvent	Both saponified and non-saponified grease can be dissolved and generally do not corrode workpieces. The degreasing is quick, but not complete, and requires degreasing again by an electroless or electrolytic method. In addition, organic solvents are flammable; toxic and costly.	It can preliminarily degrease small workpieces with complex shape (juncture, blind hole ), non-ferrous metal parts, workpieces with serious grease and workpieces easily corroded by alkali bath.
Electroless degreasing	Simple method, simple equipment, low cost, but long degreasing time	General parts
Electrolytic degreasing	High degreasing efficiency, which removes the mechanical impurities such as floating ash and corrosion residue from the surface of the part. However, the cathodic electrolytic degreasing part is prone to hydrogen permeation, and the degreasing is slow in the deep holes and a DC power supply is required.	General parts or anodes remove etching residues
Wipe degreasing	Operations are flexible and convenient, not limited by parts, but labor intensive and inefficient.	Large and medium parts or parts that cannot be degreased by other methods
Barrel degreasing	High efficiency, good quality, but not suitable for large and easily deformed parts.	Small parts with low precision
Ultrasonic degreasing	It has small corrosion to the substrate, high degreasing efficiency, and good purification performance. The corners, holes, blind holes, and inner walls of complex parts can be completely degreased.	Complex shape of special parts

After the foregoing introduction, it is believed that every one knows how to select the right product in the process of degreasing. A product of No. 1 is recommended here: RC-DCR degreasing-dewaxing bath

It has excellent water solubility and washability. It can replace organic solvents for degreasing ( such as gasoline, trichloroethylene, etc.), avoiding the toxicity and flammability of organic solvents. It is suitable for dewaxing from a variety of metals such as zinc alloys, copper and copper alloys, aluminum and aluminum alloys, stainless steel, precious metals and steel. After dewaxing, it maintains the surface finish of the work piece, and after treatment , the surface of the work piece is coated with an anti-water coating , which gives the workpiece a certain self-protection performance .

The Causes and Removal of Carbonate in Cyanide Copper Plating Bath

CAUSES
Any cyanide plating bath will gradually accumulate carbonate during its use. This is due to the decomposition of cyanide and the dissolution of carbon dioxide from the air into the bath.
2NaCN+2H2O+2NaOH+O2( air )→2Na2CO3+2NH3
2NaCN+H2O+CO2( air )→Na2CO3+2HCN

METHODS
Cooling----sodium carbonate can be removed by crystallization from the bath when cooling the cyanide bath, the temperature should be about 0 and for more than 8 hours. Natural cooling can be applied in winter. The use of cooling will reduce the loss of metal salts by around 10%, and it ’ s not for the removal of potassium carbonate because of the large solubility of potassium salt.

Chemical precipitation----calcium sulfate, calcium hydroxide and barium hydroxide can be used, the reaction is as follows:
CaSO4+Na2CO3→CaCO3↓+Na2SO4
Ca(OH)2+Na2CO3→CaCO3↓+2NaOH
Ba(OH)2+Na2CO3→BaCO3↓+2NaOH
Sodium sulfate is used to precipitate sodium carbonate into calcium carbonate, and the resulting calcium sulfate is less harmful than sodium carbonate as a result of this reaction. The presence of sulfate is beneficial in the tartrate baths. In addition, the sulfate can be removed by cooling, which removes the potassium carbonate.
The advantage of using calcium hydroxide or barium hydroxide is that the sodium hydroxide produced after the reaction is required in general bath. If alkali is not required, it can be treated with insoluble anode electrolysis or adding organic acids (such as tartaric acid) after treatment.

Acidizing----the principle of acid-carbonate reaction into CO2 gas
2H++Na2CO3→ 2Na++H2O+CO2 ↑

Dilution----this dilutes the bath to reduce the concentration of carbonate, which loses a portion of the bath, and is therefore only used in cases of necessity.

The Role of Sulfuric Acid in Sulfuric Acid Copper Plating Bath and The Effect of Content On The Coating

-Prevent the hydrolysis of copper to form cuprous oxide or other basic salt precipitate.
-Reducing the effective concentration of copper ions results in a fine-grained crystallization of the copper coat.
-The bath resistance and power consumption are reduced and the conductivity of the bath is improved.
-Prevent rough or dendritic coating at high current densities.
The sulfuric acid content of the bath is generally 60-80 g/l. Coating can be brittle, and the solubility of copper sulfate decreases when sulfuric acid is applied in excess. On the contrary, it can lead to coating roughness, anode passivation, and a reduction in the throwing power of the bath.

Impact of Excess Carbonate in the Cyanide Bath

- Anodic polarization increased.
- The efficiency of the cathode is decreased.
- The conductivity of the bath is reduced.
- Reduction of the gloss range.
- The coating is easy to exuded stains.
- The coating is easily spongy (especially in gold or silver plating bath).
- Bath viscosity increases and drag-out losses increase.