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Using Plasma for Surface Cleaning and Activation

Today’s blog post is the first of a two-part series focusing on plasma. In today’s post, with the help of Rose Roberts, Ph.D., Senior Custom Applications and Materials Engineer, we are going to review plasma basics and discuss how plasma can be used for both cleaning and surface activation. We will also touch upon the differences between atmospheric and vacuum plasma. Next week we will discuss how to optimize plasma use at your facility.

What Is Plasma?

Plasma is an ionized gas. It is the fourth state of matter — solids, liquids, and gas are the other states of matter. When energy is applied to matter, the form of matter may change. Applying heat to a solid can transform it into a liquid, heating a liquid can transform it into a gas, and adding energy to a gas can transform it into plasma.

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Using Plasma to Activate Your Surface

Although plasma can be used to remove soil contamination, it may not be the best option for achieving chemically clean surfaces. Watch Rose describe various factors that might affect your cleaning efforts including:

  • Identifying the chemical composition of the soil on the surface
  • Confirming that plasma has the capability to remove the particular contaminant from the surface
  • Match the amount of soil contamination on the surface with the duration and the power of the plasma treatment

 

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Using Plasma for Surface Activation

Highly engineered products across multiple industries including, aerospace, automotive, electronics, film & packaging, medical devices and consumer goods, are created by bonding dissimilar materials — like bonding a composite to a metal, a metal to a polymer, or bonding two polymers together when each polymer has a different chemical composition from the other.

Plasma treatment is used to alter the top few molecular layers of surfaces. When plasma is applied to the surface, the energy applied to the surface “activates” the surface. This freshly energized surface improves the adhesion characteristics of paints, coatings, and adhesives.

Atmospheric Plasma and Vacuum Plasma

Atmospheric plasma is applied to a surface using a nozzle to direct a stream of flowing gas to the surface. Atmospheric plasma treatment is well-suited for continuous processing applications and can easily be integrated into a manufacturing line.

Vacuum plasma, in contrast, requires that parts to be treated are placed in a chamber. The parts are typically placed in the chamber on racks and trays that are suspended between electrodes. A vacuum is created in the chamber when a pump pulls the gases out of the chamber. After a vacuum has been created, a small amount of the gas that has been identified for use in the plasma treatment is injected back into the chamber. Gases typically used for plasma treatment may include oxygen, argon, forming gas, or dry air. Once the small amount of gas has been injected back into the chamber, the electric field between electrodes accelerates electrons which then impact other gas molecules. These collisions create more free electrons and ions. As these free electrons and ions interact with the surfaces of parts in the chamber, the molecular bonds of the first 1 to 5 layers of surface molecules are broken. This process creates chemically reactive sites which improves the ability of parts to achieve effective bonding, coating, sealing, painting, or printing. 

Vacuum plasma is well-suited for treating parts with complex shapes and challenging geometries. In a vacuum, there are fewer molecules that can impede the diffusion of the plasma (relative to atmospheric plasma). Because the vacuum allows plasma molecules to diffuse further and more evenly through the chamber, it is easier for plasma to quickly reach and thoroughly access crevices, complex shapes and other challenging geometries. 

Let’s watch Rose describe atmospheric and vacuum plasma treatments:

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We hope you have enjoyed learning these plasma treatment basics — continue reading part II: How Manufacturers Can Optimize the Effectiveness of Plasma Activation.