Electroplating - Chemistry LibreTexts

Understanding Electroplating

Electroplating, a fascinating process in the realm of chemistry, involves layering one metal onto another through the method of hydrolysis. This technique is commonly applied for aesthetic purposes or as a means to prevent the corrosion of metals. There are various specific forms of electroplating including copper, silver, and chromium plating. By utilizing electroplating, manufacturers can opt for lower-cost metals such as steel or zinc for their core products while applying more desirable metals to the exterior, enhancing appearance, safeguarding against damage, and imparting additional desirable characteristics. Importantly, electroplating can be applied to both metal and even plastic surfaces.

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Overview of Electroplating

In many instances, electroplating serves a purely decorative role, particularly in products intended for indoor use or environments with minimal exposure to corrosion factors. Such items often feature a thin layer of gold or silver to enhance their visual appeal. Industries that leverage the advantages of electroplating encompass a wide range, including automobiles, aircraft, electronics, jewelry, and toys. The electroplating process is conducted within an electrolytic cell, where a negatively charged metal is submerged in a solution containing metal salts (which act as electrolytes) with positively charged metal ions. This creates a magnetic attraction between the two metals due to their opposing charges.

The Objectives of Electroplating

1. Enhancing Appearance
2. Providing Protection
3. Imparting Unique Surface Properties
4. Improving Engineering or Mechanical Properties

Historical Context of Electroplating

The origins of electroplating can be traced back to Luigi Brugnatelli, who first discovered the electrodeposition technique to deposit gold onto surfaces. Unfortunately, his groundbreaking work went largely unrecognized by the French Academy of Science and Napoleon Bonaparte. It wasn't until decades later that John Wright successfully applied potassium cyanide as an electrolyte for gold and silver, demonstrating its effectiveness. Subsequent innovations by the Elkington cousins established a practical electroplating method using potassium cyanide, leading to its widespread adoption from England. Over time, electroplating has progressed thanks to advancements in eco-friendly formulations and the use of direct current power supplies.

Selecting the Right Electrolytes

Choosing the appropriate electrolyte is crucial for achieving high-quality plating, as various metals can be utilized in the process. Electrolytes can take the form of acids, bases, metal salts, or molten salts. Considerations when selecting an electrolyte include factors such as corrosion resistance, brightness, hardness, mechanical strength, and wear resistance.

Surface Preparation

Before electroplating, it is essential to ensure that the surface is clean and devoid of contaminants that could hinder the bonding process. Contaminants often lead to poor deposition and lack of adhesion. The preparation typically occurs in three main steps: cleaning, treatment, and rinsing. Cleaning involves the use of specific solvents, such as alkaline solutions, water, or acidic cleansers to eliminate oil and grime from the surface. Treatment encompasses surface modifications to harden components and apply metal layers. Rinsing is the final step that leads to the completed electroplating. Two prominent techniques in surface preparation are physical cleaning and chemical cleaning, each employing different methods to ensure cleanliness.

Methods of Electroplating

Multiple processes exist for applying electroplating, which include mass plating (or barrel plating), rack plating, continuous plating, and line plating. Each method has unique procedures suited for optimal plating outcomes.

Identifying Plating Metals

The majority of electroplating coatings can be classified into the following categories:

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• Sacrificial Coating: Primarily offers protection using metals that are consumed in the reaction. Common examples are zinc and cadmium (now prohibited in several countries).
• Decorative Coating: Applied for visual enhancement, utilizing metals like copper, nickel, chromium, zinc, and tin.
• Functional Coatings: Selected for their essential properties, including metals such as gold, silver, platinum, and others.
• Minor Metals: Includes easier-to-plate metals like iron, cobalt, and indium, though they are infrequently used.
• Unusual Metal Coating: Comprises rarely plated metals like As, Sb, Bi, Mn, and others.
• Alloy Coatings: Involve coatings made from two or more metals plated simultaneously, forming substances like brass and bronze.

Key Points for Review

1. What purposes does electroplating serve?
2. What are the operational principles of electroplating?
3. Why is surface preparation a critical step in electroplating?
4. What are the various methods of electroplating?
5. Can you name five metals suitable for electroplating?

Final Notes

1. The primary uses of electroplating are typically for aesthetic improvement or to protect metals from corrosion.
2. The process is governed by an electrolytic cell, which includes a cathode that requires plating.
3. Surface preparation is crucial as contaminants can negatively impact the electroplating process.
4. The main electroplating methods include mass plating, rack plating, continuous plating, and line plating.
5. Examples of metals used in electroplating include zinc, cobalt, iron, tin, and platinum.

Acknowledgments

• Vaishali Mittal (UC Davis)

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