Preparing accurate and reproducible samples is key to obtaining high-quality results in IR and XRF spectroscopy. Whether you are making KBr pellets for FTIR or homogenizing rock powders for XRF, your choice of dies, mills, and presses can make a major difference in sample quality, analytical precision, and lab efficiency.
This guide will walk you through everything you need to know about selecting the right equipment for your spectroscopy lab. You will learn how to choose the best pellet dies for XRF analysis, when to use evacuable vs. non-evacuable dies, what kind of press you need for pelletizing, and how to use grinding mills for proper sample homogenization.
Pellet dies are an essential part of the sample preparation process in both IR and XRF spectroscopy. They are used to compress powders into solid pellets suitable for analysis. Choosing the right type of die ensures the production of dense, uniform pellets with minimal moisture content and air pockets.
XRF analysis typically requires very dense, uniform pellets with a smooth surface. Tungsten carbide dies are often preferred for this purpose due to their superior hardness, abrasion resistance, and ability to withstand the high pressures needed for XRF pelletizing.
FTIR analysis, on the other hand, often uses stainless steel dies for creating KBr pellets. These dies are more affordable and work well with softer materials like KBr or polymers.
Evacuable pellet dies can be connected to a vacuum pump to remove moisture and trapped air from the sample during compression. This is particularly useful when making pellets for FTIR, where air bubbles can interfere with light transmission. Non-evacuable dies are a simpler option and often used for XRF sample preparation where air content is less critical.
Here is a quick comparison of the two most common die materials:
| Feature | Stainless steel | Tungsten carbide |
|---|---|---|
| Maximum temperature | ~200°C | Up to 760°C |
| Abrasion resistance | Moderate | Excellent |
| Suitable for | KBr, organics, soft polymers | Hard minerals, abrasives |
| Cost | More affordable | Premium |
The amount of pressure you apply during pelletizing is just as important as your choice of die. The right lab press will help you achieve dense, durable pellets with consistent results.
Manual lab presses, such as 8-ton or 15-ton models, are an excellent choice for labs with limited budgets or lower sample volumes. Automatic lab presses, available in models up to 25 tons, are ideal for high-throughput labs that require consistent, repeatable pelletizing.
The best pellet press for spectroscopy depends on your lab’s needs. A 25-ton automatic press offers excellent versatility and consistency across a wide range of materials.
Grinding mills are essential for achieving uniform particle size in spectroscopy sample preparation. Proper homogenization helps ensure accurate and repeatable results.
The Wig-L-Bug grinding mill is one of the most popular tools for preparing spectroscopy samples. It quickly grinds powders to the fine particle size required for XRF and FTIR pelletizing.
When analyzing high-melting-point samples or performing spectroscopy at elevated temperatures, high-temperature tungsten carbide dies rated up to 760°C are essential.
Annulus dies produce thin, ring-shaped pellets that are ideal for diffuse reflectance spectroscopy or specialized transmission studies.
Evacuable dies allow moisture and trapped air to be removed using a vacuum, which is helpful for creating clearer FTIR pellets. Non-evacuable dies are simpler and often used for XRF analysis.
For FTIR, 8 to 15 tons is usually sufficient. For XRF, 15 to 25 tons may be required, depending on the material.
Tungsten carbide dies are typically the best option for XRF, due to their hardness and resistance to wear when working with abrasive samples.
