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Cyanide based electrolytes of silver and copper deposits possess excellent throwing power property.


None of the nickel or chromium electroplating electrolytes contain cyanide ions.


The paper discusses the polarization, coordination chemistry, and thermodynamic reasons for these phenomena.


Did you ever think about why nickel does not possess a simple cyanide-based plating electrolyte? Why can’t we electrolyze a nickel cyanide salt [Ni (CN2)] to get a deposit? Won’t a cyanide nickel electrolyte with a good active polarization and throwing power property be of use?

 

We will deliberate the evidences of asking these questions.

 

Cyanide based electrolytes such as silver and copper deposits possess excellent throwing power. Copper possesses good leveling characteristics, while nickel without organic molecules has negative throwing power. Bright nickel with class 1 and 2 brighteners can get a uniform deposit on the cathode, but it is not comparable with copper.

 

Coordination chemistry plays an important role in electrolysis. It is important to distinguish thermodynamic parameters such as stable and unstable, and kinetic parameters such as inert and labile. These terms refer to stability. Nickel and chromium cyanide complexes like [Ni (CN)4]2- and [Cr (CN)6]3- are (extremely) thermodynamically stable. Unlike kinetically inert compounds, thermodynamically stable coordination compounds become very difficult to break a bond or ligand during electrolysis.

 

cyanide copper plating

 

Silver and copper cyanide baths possess good throwing power because of the presence of simple cyanides like sodium or potassium cyanide. Cyanide ions during electrolysis effects total polarization. The concentration polarization increases at the cathode interface because electrolysis liberates cyanide ions. The concentration polarization and cathode current efficiency work in tandem and distribute electrodeposition based on primary and secondary current distributions factors. This behavior is a part of tertiary current distribution phenomenon.

 

Ni and Cr are not incomparable with their limitations. Platinum and gold have unique advantages and restrictions. Like Cu and Ag, brass plating containing cyanide ions produce beautiful deposit colour. In aqueous electrolysis Cu, Zn, Ag & Cd deposits differ from Ti, Zr, V & Nb. These points emphasize distinct properties and limitations of elements, chemicals and media (aqueous or ionic).

 

Purpose

The short paper does not offer a solution or recommend an alternate method. It explains the fundamental benefits of cyanide ions and distinguishes unique elements of the periodic table like Ni and generates an awareness on their chemical properties.

 

Understanding the characteristics of an element, position in the periodic table, and their chemical properties are important to research scientists and advanced engineers.

 

If you are a scientist formulating a bath recipe or a forward-thinking engineer choosing a process to meet deposit characteristics’ fundamental concepts, advantages and limitations are important to understand. This learning will take full advantage of the prospect or prevent an issue in the long-term.

 

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A profound analysis of periodic table will help ardent electroplating professionals understand the effectiveness of the deposition of elements from the outlook of electrode potential, current efficiency, and the deposit characteristics. Use of the table provides added knowledge and supports to decipher the precise information swiftly.


As we celebrate the 150th anniversary of periodic table, we will dedicate this short paper on the properties of elements and their position in the periodic table. Regarding electroplating of elements and alloys there are a few significant relationships with the groups and periods of the table. Though these are important for all plating specialists, it particularly interests those involved in research and formulation of an electrolyte and the alloy deposit.

 

Here are some properties:

 

Water:

The presence or absence of water affects the plateability and the current efficiency of the deposit. Chromium, the group 6 element of periodic table is a good example. Ability to plate Cr using the aqueous (presence of water) chromic acid-based electrolyte is an exception. Low current efficiency property of the electrolyte shows the reason for the struggle. On other hand, one can conveniently plate neighboring elements like Ti, Zr, Hf, V, Nb, Ta, Mo and W using ionic liquid (absence of water) electrolyte, with other challenges.

 

Position of elements:

The position of elements in the table and their properties are insightful. The position and proximity with each other can also help determine suitable alloying elements. On another point, let us look at indium, tungsten and boron. The relevant properties of this example are hardness and melting point. The position and the properties of these elements seen with their respective neighboring elements will show a trend.

 

Oxide (passive) layer:

The group of elements in the table say a lot about the oxide layer of the metal or the deposit. Examples are Ti, Ta, W and Cr. The formation of an oxide layer protects the metal from corrosion and make it tough to form an adherent deposit using the conventional electrolytes. Electrode and decomposition potentials of these elements also contribute significantly towards effective plating or the challenges thereof.

 

periodic table nickel electroplating

         

There are nearly 35 elements suitable for plating and their effective deposits offer a unique and superior properties. But aqueous electrolytes can conveniently plate only ≤ 20 elements (read metals) and alloys. Certain ionic liquid formulations can electroplate all or most of the 35 elements. We will discuss the reasons and mechanism of ionic plating in another short paper. Looking at the elements in groups and periods of the periodic table will offer unique understanding on plateability and desired functional properties such as corrosion resistance, tribology, and electrical conductivity.

 

Refractory elements, precious metals, sacrificial protection metals, and conductive ions (cations) are in proximity among their groups on the periodic table. They are in decreasing or increasing order within the groups or periods.

 

Summary:

Periodic review of the periodic table will enable electroplating professionals strengthen their understanding on the feasibility and properties of the deposit. Greater effort to interpret different properties are definitely worth it!


 

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