How to improve paint and coating formulations: Elemental analysis

par Patricia Kidd, Friday, 1st July 2022

In this first blog post in a series of five, we take a look at the analytical approaches that can be used to help drive better understanding of paints and coatings at a nanostructural level. First up is one that lies at the heart of understanding the constituents of a coating – elemental analysis.

What’s it made of? It’s a simple question, but one that doesn’t often have a straightforward answer, at least when it comes to paints and coatings. Complex chemistry is involved in the advanced coatings applied to the surfaces of everything from buildings to baby toys – and this demands advanced analytical methods able to provide details not just on the identity of the elements present, but their amounts too.

Comparing XRF and ICP-MS for elemental analysis

Before we look at the applications of elemental analysis, let’s get one thing straight – the best method for carrying out elemental analysis in the coatings industry.

For many decades, a popular method has been inductively coupled plasma–mass spectrometry (ICP-MS), which was one of the earliest methods to measure elemental composition. This involves digesting the sample in dilute acid, exposing it to an argon-derived plasma, and running it through a mass spectrometer to pick over the ions produced.

If that sounds fairly intensive, then you’d be right – and so in recent years X-ray fluorescence (XRF) has gained ground in many applications. This is largely because:

It’s inherently non-destructive because the X-rays used are low-power, and so are unlikely to compromise the sample’s integrity. This is in contrast to ICP-MS, which as you’ll have gathered is a destructive technique.
Sample preparation is quick and easy, and the method can work for any type of sample. This is unlike ICP-MS, which requires a rather complex and time-consuming sample preparation procedure.

So although ICP-MS remains useful for particular applications, XRF is being increasingly seen as a good way to make time and cost savings when carrying out elemental analysis, at a number of points in the paints and coatings value chain.

Applications of elemental analysis for paints and coatings

So, having established XRF as a modern ‘go-to’ method for elemental analysis in many stages within the coatings industry, what would you use it for?

Checking chemical purity

Perhaps the most widespread application is to ascertain the chemical purity of raw materials, especially the titanium dioxide (TiO₂) commonly used as a white pigment. Knowing exactly what’s in a supplied material is vital for meeting the specification, but most paint manufacturers simply rely on the raw material certifications provided by their suppliers. And as many will know to their cost, these may not always be accurate enough!

So XRF is a valuable tool here, and one that is a nice complement to more in-depth crystal phase analysis carried out using X-ray diffraction (more about that in the next blog post in the series).

Detecting residual lead in raw materials and in finished coatings

Another key application relates to the detection of residual lead, because some of the mineral-based constituents of paint can still contain traces of lead, despite the best efforts of suppliers. This is important largely because young children love to put painted toys (and, come to think of it, just about everything else) in their mouths. This may be a great way of exploring their environment, but it means that we need to strive to eliminate lead from any coatings used on these products.

So spurred on by increasingly stringent regulations on lead in paints and coatings, manufacturers have been tightening the acceptable limits on lead in their products. And for that, they need to routinely quantify lead in incoming supplies and their own final products, which is where XRF comes in.

Checking film thickness and integrity

A final and particularly interesting application of XRF in the coatings sector is to assess the film thickness and elemental composition of coatings. An obvious approach is to use the data to determine the composition of the applied product, and see if that’s within expectations – or indeed whether it shifts as the product cures and ages.

But a clever way of using the same data is to compare the intensities of elemental peaks against a simulation model. This can then give you information about the thickness of the film, and even whether constituents have ‘bled’ from one layer to another.

XRF – A valuable tool for elemental analysis

From this brief summary, it should be clear that elemental analysis has a useful role to play in the paints and coatings sector. But to take advantage of everything that elemental analysis can offer, it’s important to ensure you’re using the latest methods, and at the same time make your processes as cost-effective as possible.

Interested in finding out more about the role of analytical methods to characterize paints and coatings? Then check out our white paper: “Improving paint and coating formulations: Using nanostructural analysis to understand macroscopic properties”.