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Electroless nickel plating (ENP) is a technique for protecting materials from corrosion, wear and abrasion.

It is widely used across a range of industries, including:

  • Engineering
  • Construction
  • Aerospace
  • Electronics

A crucial part of the ENP process is the accurate measurement of thickness and composition. The perfect technique for this is x-ray fluorescence (XRF).

What is ENP?

ENP is an alternative to nickel-coating using electroplating, or coating with hard chrome. It provides a less porous coating, and the process itself uses no electricity and requires fewer coats to achieve a strong, high-quality finish.

With ENP, there’s considerable scope for flexibility in plating thickness and volume, and the technique fills in surface recesses and pits smoothly.

ENP applies a nickel phosphorus deposit, containing between 2% and 14% phosphorus. The higher the phosphorus content, the greater corrosion resistance the part will have, once its applied.

  • High phosphorus nickel alloys have a phosphorus content of around 10–13%
  • For medium alloys it’s 6–9%, and
  • Low phosphorus alloys usually have under 5% phosphorus content.

The most common of these is the medium alloy, also known as MPEN.

The ENP process works by reducing nickel ions to metallic nickel using a chemical agent such as sodium hypophosphite.

What are the Uses of ENP?

You can apply electroless nickel plating to these substrates:

  • Iron
  • Steel
  • Stainless steel
  • Aluminium
  • Copper
  • Brass

ENP protects parts and surfaces, and is used in these industries:

  • Aviation
  • Agriculture
  • Engineering
  • Construction
  • Chemical
  • Oil and gas
  • Food processing and handling
  • Textiles
  • Paper and pulp manufacturing

Industries where moving parts require protection from constant wear, abrasion and friction, or from harsh external elements, can all benefit from electroless nickel plating coatings.

What are the Benefits of Using Electroless Nickel Plating?

Along with being less porous than electroplated nickel, and offering a high degree of uniform coverage, ENP also offers an excellent degree of flexibility in both plating thickness and volume.

It will fill recesses, pits and other surface imperfections. This makes it suitable for coating a wide range of industrial parts and engineering equipment, including valves, pumps, shafts and mechanical tools.

ENP provides a uniformly thick finish, even in holes, slots or the inner walls of tubing and pipework.

It provides a protective barrier against corrosion, and you can apply it with little or no compressive stress. Higher phosphorus-content coatings are used in applications such as oil drilling, where high levels of corrosion resistance are essential.

Where you want a product to look brighter, certain ENP coatings will also give a cosmetic as well as resilient finish.

As a coating method, ENP is cost-effective, requiring no electricity and fewer coats to achieve good levels of thickness.

On the Rockwell Hardness scale, electro nickel plating has a hardness of 68–72.

How Does XRF Support ENP Coating Quality?

If you are applying ENP to a surface or part, how do you accurately and conveniently measure the coating thickness you wish to achieve?

A method that has proven effectiveness and reliability in measuring the thickness of plated layers is x-ray fluorescence (XRF).

This technique analyses materials by directing an x-ray beam at them. Certain substances produce secondary x-rays in response to receiving the initial x-ray beam. This is what the term fluorescence refers to.

The x-rays will provide different readings depending on the nature of the material the technique is analysing.

Applying XRF to substrates coated with ENP provides accurate measurements of plating thicknesses and composition.

What are the Advantages of Advanced XRF Instruments?

Traditional XRF instruments measure plating thickness using gas-filled proportional detectors. The big disadvantage these devices had concerning ENP was their inability to measure phosphorus.

A significant development in the technology of XRF instruments has been the introduction of solid-state detectors. Typically, these are silicon PIN diodes or silicon drift detectors (SDD).

These solid-state detectors can analyse light elements, providing the necessary sensitivity to measure phosphorus.

The Bowman XRF series is perfect for measuring ENP coatings. These instruments perform three key functions:

  • Measurement of deposit thickness – simultaneously measuring up to five coating layers
  • Elemental analysis
  • Plating solution analysis.
  • The ability to pin-point the x-ray beam on to the specific part or parts of the component that needs to me measured.

Advanced software powers Bowman XRF plating measurement systems, combining intuitive controls with streamlined performance and time-saving shortcuts for users.

They save all readings to a database, enabling you to store and analyse coating readings for future reference.

The Bowman range of x-ray fluorescence instruments can be used to measure the thickness and quality of electroless nickel plating coatings, which provides an accurate indication if a coating is meeting its requirements. For more information on the XRF instruments we provide, please contact us today.

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