Compare the Difference Between Similar Terms

Difference Between

Home / Science & Nature / Science / Chemistry / Industrial Chemistry / Difference Between Electropolishing and Passivation

Difference Between Electropolishing and Passivation

May 28, 2019 Posted by Madhu

The key difference between electropolishing and passivation is that electropolishing gives a superior finish and removes discolouration that passivation would leave behind.

Electropolishing is an electrochemical process that removes material from a metallic surface in order to reduce surface roughness while passivation is the process of coating a surface of a metal in order to reduce the chemical reactivity. Compared to passivation, electropolishing ultimately creates long-lasting results. That means; electropolishing results in a long-lasting coat on the surface of the substrate.

CONTENTS

1. Overview and Key Difference
2. What is Electropolishing 
3. What is Passivation
4. Side by Side Comparison – Electropolishing vs Passivation in Tabular Form
5. Summary

What is Electropolishing?

Electropolishing is the process of removing material from a metal surface to reduce surface roughness. We can do this by levelling micro-peaks and valleys. Thus, this process improves the surface finish. Moreover, electropolishing is useful for polishing, passivation and deburring metal parts. It is often described as the reverse of the electroplating.

Difference Between Electropolishing and Passivation

Figure 01: Method of electropolishing (1. Electrolyte 2. Cathode 3. Work-piece to polish (Anode) 4. Particle moving from the work-piece to the cathode 5. Surface before polishing 6. Surface after polishing)

In the mechanism of electropolishing, the substrate (the material on which the electropolishing is required) is immersed in an electrolyte as the anode. The electrolyte should be a temperature-controlled bath. Since this substrate is the anode, it is connected to the positive end of the DC power supply. The cathode is generally stainless steel, copper or lead. Moreover, the current passing through the anode oxidizes the metal on the surface of the substrate and dissolve the metal ions in the electrolytic bath. Then, these ions reach the cathode, and the reduction reaction occurs. Thus, this is how the surface roughness of the substrate is reduced in electropolishing.

The following section discusses the pros and cons of electropolishing:

Pros

  • Easy operation and aesthetically pleasing finish
  • Effective in polishing irregularly-shaped objects
  • Useful to the sterile substrate
  • Improves corrosion resistance
  • Removes native oxide layers from metal surfaces; ex: TiO2 layer on Ti metal

Cons

  • Cannot remove very rough defects
  • Electropolishing multiphase alloys may cause roughening

What is Passivation?

Passivation is the process of coating a surface of a metal in order to reduce the chemical reactivity. Therefore, a substrate that undergoes passivation is less affected by corrosion by the environment. In fact, a passivated surface can survive for a long time without undergoing metal leaching. Moreover, a passivation layer can be organic or inorganic in nature. The major use of this process is the restoration of the corrosion resistance of a contaminated stainless steel part.

Key Difference - Electropolishing vs Passivation

Figure 2: Passivated Fitting (right) vs Normal Fitting (left)

Furthermore, the two major methods of passivation are nitric acid passivation and citric acid passivation. Earlier, nitric acid was used to passivate stainless steel. However, citric acid is the chemical we now use for this process since it is safer and more effective.

The following section discusses the pros and cons of both nitric acid passivation and citric acid passivation:

Pros and Cons of Nitric Acid Treatment Method

Pros: Low cost, require less contact time, the same nitric acid solution can be used several times,

Cons:  Hazardous effects of nitric acid, can dissolve heavy metals, which are toxic

Pros and Cons of Citric Acid Treatment Method

Pros: Not hazardous, dissolves only iron (does not dissolve heavy metals), keep the iron dissolved after neutralization, biodegradable end product, etc.

Cons: Expensive, if the solution has a low concentration, we need to heat it up to 80°C.

What is the Difference Between Electropolishing and Passivation?

Electropolishing is the removal of material from a metal surface to reduce the surface roughness while passivation is the process of coating a surface of a metal in order to reduce the chemical reactivity. Furthermore, the key difference between electropolishing and passivation is that electropolishing gives a superior finish and removes discolouration, which passivation would leave behind.

Moreover, electropolishing mainly includes immersing the substrate as the anode in an electrolytic solution and passing a DC current while passivation process includes steps such as alkaline cleaning, sanitization (strong oxidation), rinsing, drying and preservation. Moreover, another significant difference between electropolishing and passivation is that electropolishing is mainly done on nickel, tin and other metal alloys, whereas passivation is mainly used for stainless steel.

The following infographic summarizes the difference between electropolishing and passivation:

Difference Between Electropolishing and Passivation in Tabular Form

Summary – Electropolishing vs Passivation

Electropolishing is an electrochemical process that removes material from a metallic surface in order to reduce surface roughness while passivation is the process of coating a surface of a metal in order to reduce the chemical reactivity. In conclusion, the key difference between electropolishing and passivation is that electropolishing gives a superior finish and removes discolouration that passivation would leave behind.

Reference:

1. P. Allain, M. Echeverry-Rendón, in Hemocompatibility of Biomaterials for Clinical Applications, 2018.
2. Qing-Hua Lu, Feng Zheng, in Advanced Polyimide Materials, 2018.

Image Courtesy:

1. “Electropolishing principle” By LaurensvanLieshout – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Pre and post passivation” By Kees08 – Own work (CC BY-SA 4.0) via Commons Wikimedia

Related posts:

Key Difference Between Gas and PetrolDifference Between Gas and Petrol Difference Between Acid Zinc and Alkaline Zinc PlatingDifference Between Acid Zinc and Alkaline Zinc Plating Difference Between Inconel 625 and 825Difference Between Inconel 625 and 825 Difference Between Azeotropic and Extractive DistillationDifference Between Azeotropic and Extractive Distillation Difference Between Polyester Resin and Epoxy ResinDifference Between Polyester Resin and Epoxy Resin

Filed Under: Industrial Chemistry

About the Author: Madhu

Madhu is a graduate in Biological Sciences with BSc (Honours) Degree and currently persuing a Masters Degree in Industrial and Environmental Chemistry. With a mind rooted firmly to basic principals of chemistry and passion for ever evolving field of industrial chemistry, she is keenly interested to be a true companion for those who seek knowledge in the subject of chemistry.

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Request Article

Featured Posts

Difference Between Coronavirus and Cold Symptoms

Difference Between Coronavirus and Cold Symptoms

Difference Between Coronavirus and SARS

Difference Between Coronavirus and SARS

Difference Between Coronavirus and Influenza

Difference Between Coronavirus and Influenza

Difference Between Coronavirus and Covid 19

Difference Between Coronavirus and Covid 19

You May Like

What is the Difference Between Diffuser and Humidifier

What is the Difference Between Diffuser and Humidifier

Difference Between Procedures and Functions in Programming

What is the Difference Between Artificial Natural and Phylogenetic System of Classification

What is the Difference Between Artificial Natural and Phylogenetic System of Classification

Difference Between HTC Vivid and iPhone 4S

Difference Between Rhombic and Monoclinic Sulphur

Difference Between Rhombic and Monoclinic Sulphur

Latest Posts

  • What is the Difference Between Patent Ductus Arteriosus and Truncus Arteriosus
  • What is the Difference Between Lagophthalmos and Ptosis
  • What is the Difference Between Anesthesia and Paresthesia
  • What is the Difference Between Voice Over and Dubbing
  • What is the Difference Between Centric Occlusion and Centric Relation
  • What is the Difference Between Foundation and BB Cream
  • Home
  • Vacancies
  • About
  • Request Article
  • Contact Us

Copyright © 2010-2018 Difference Between. All rights reserved. Terms of Use and Privacy Policy: Legal.