Author: Ken Stauver

One of the fundamental facts of lab-based X-ray production is that our x-ray tubes emit much more than the pure KA1 lines we rely on for material characterization and quantification. Most XRD users are familiar with techniques and hardware for the reduction or elimination of KB1, W LA1 and Bremsstrahlung, but take for granted the inseparable pair of KA1 and KA2 (referred to as the “doublet”). Luckily for us, these energies are present in strict proportion such that we can factor their paired presence into most XRD analysis to the point that one might barely notice their effect. However, the fact remains that we will see peak broadening at lower angles and completely independent additional peaks at higher angles due to this superfluous discrete emission.

Separating the doublet cannot be accomplished electronically or through absorption/attenuation such as might be effective for KB1 energies. It must be done in the primary-beam with an additional diffraction event. Primary-beam monochromators are generally classified by the number of diffraction events required for a photon to pass completely through the device. Single-bounce, 2-bounce and 4-bounce geometries are common with the latter providing the best energy resolution allbeit the lowest intensity (photon flux). My limited experience suggests that while the single-bounce models retain enough intensity to have some application in powder XRD, the others are relegated to HR-XRD applications such as XRR.

The alignment for any of this hardware is not for the faint of heart as it begins with coarse adjustments using fluorescent screens in the beam path. This was essential for us given how dramatically misaligned the monochromator had become after so many attempts to bring it back into operation. We actually needed our SDD system to verify that we were tuning for Cu KA1 energy rather than the KB1 emissions because some of the most basic aspects of the alignment had pushed way beyond their intended position.

Along the way we built ourselves a motorized remote adjustment tool which we’ll return to the user as small adjustments are required on a regular basis with this kind of monochromator to retain maximum intensity. It’s quite useful and even versatile enough to allow for the adjustment of multiple control knobs.

One final note regarding intensity. It’s easy to get excited about energy resolution like this, but bear in mind that we’re looking at ~20x reduction in intensity due to the inherent losses involved in the primary diffraction event. This data was collected at 10x the normal speed and at half the normal 2Theta step increment so it looks very good, but one would need a compelling reason to slow their data collection this much.

Another side effect of performing your energy discrimination in the primary beampath is that other issues such as fluorescence effects (incident x-rays exciting elements in the sample causing high background intensities) are harder to avoid than they would be with a diffracted-beam monochromator. The 4x reduction in intensity inherent in the diffracted-beam monochromatization makes it a poor choice to eliminate these effects when the incident intensities are already so low. We recommend energy-dispersive detectors such as our SDD-150 to eliminate extraneous energies without sacrificing net intensity. We’ve also worked with the Bruker LynxEye XE-T detector which has a very high energy resolution compared to other position sensitive detectors (PSD). Contact KS Analytical Systems for more information on these options.

Revisiting an experiment from 2014

I still reference this post on our laboratory site often so it seems like it deserves a place on the main blog for KS Analytical Systems. Enjoy

Our recent sealed sample cell project required a thin covering film to be applied over loose powder before analysis by XRD. We tested a few options for this film as part of the design process and the results were interesting enough that we thought it would be worth dedicating a full post to that data and expanding the range of materials a bit to satisfy our curiosity.

All data was collected on our primary powder system. This is a Siemens D5000 configured with a theta/theta goniometer, automatic anti-scatter and divergence slits, a standard sealed Cu tube (LFF) and our new KSA-XRD-150 detector system. We alternate between a digital phi stage, 40-position autosampler and the standard, single sample stage which was used in these experiments. I had a spare sealed-sample cell available which made it easy to exchange the films without disturbing the sample surface. The design of these stretches the film taught each time the cell is assembled. I’d originally tried to simply lay the film over a side-load holder, but without being tightly held, it would buckle enough that results at low angles were probably affected. A NiO standard powder was used due to its high purity and compositional difference from any of the film materials.

The data clearly shows that polyimide was the best choice for this application as it resulted in very limited attenuation as well as an extremely minimal increase in background intensity/amorphous scatter. Some of the other patterns were very interesting though.

These are probably the smallest parts we make in-house, but they’re critical to the proper function of about half of the instruments we support. These little bushings support the impeller of the water flow sensor in many Siemens and some Bruker XRF and XRD machines. They last for several years in most cases, but we replace them during most PM service visits because they’re easy to keep on-hand and very inexpensive.

This is a great example of a part that would force any machine into obsolescence if it were not available. Having the ability to rebuild these sensors gives them a lifespan measured in decades and while they are prone to sticking during periods of downtime, they can almost always be cleaned up and put back into service.

The Siemens D5000 and Bruker D8 systems we work with have an optional phi-stage that is very useful. It looks and moves like any other rotation stage, but it’s driven by a stepper motor which actually makes it an additional degree of freedom. The user can rotate the sample at a specified rate, position it at a specified angle, or even perform a scan in the phi axis.

We have a client who just took delivery of their D5000 and needed to analyze samples deposited on 25mm Ag filter membranes. Other users have tried a variety of solutions with varying degrees of success so this seemed like a good opportunity to create something that worked better was easier to use.

These stages use a ring of magnets to hold either a cup, transmission attachment, or a dedicated sample holder with a ferrous ring. None of these are a good solution for filters on their own. The prototype shown here uses a steel ring with an Aluminum body. Making the entire holder from steel would be easier, but the Fe in the beam would fluoresce. The filter is held in place from the bottom of the holder to keep it in the plane of diffraction while sacrificing only a small amount of surface area and shadowing at extremely low angled.

We’ve used snap rings with disks, 3D printed plastic, and now these laser-cut acrylic springs to support the membranes. The acrylic springs have made loading and unloading much easier and from what we have seen, they hold up very well through repeated use.

Much of the material we receive is already finely ground and ready for XRD or XRF analysis, but sometimes we receive bulk material which must be homogenized before we can take a representative split for analysis. This is one of the most frustrating parts of working with samples and very time-consuming as we’ve historically done it by hand. This usually means splitting out a large fraction of the material and breaking up larger rocks, etc by hand, sieving, then breaking again, then sieving, etc until we have a somewhat uniform particle size that can be split with some confidence that it is homogenous.

Looking at coarse crushers brings us into the world of large-scale mining exploration even on the laboratory side. These machines are designed to process a very large amount of material and contamination is not a primary concern. Fabricating our own tool was definitely a possibility, but we recently came across the OLESI orbital crusher. It’s small, inexpensive, and while it’s still designed for more material than we would generally use, it seems very capable of running small batches of a few kg.

The unit is designed to sit on top of a 5-gallon bucket, but it’s likely that we’ll fabricate a small base with a pull-out drawer to retrieve the material. We specified the AC motor-driven version, but there is also a 12V version for fieldwork. The first test was a batch of bauxite ore we received a few months ago. This material had sandy components, but also hard rocks of a different mineralogical makeup. Everything needed to be homogenized before we could hope to take a representative split. The OLESI 4 crushed all but the largest pieces which were easy enough to break up with a hammer before feeding. I attached a plastic bag to the bottom (inside the bucket) to catch the product.

The OLESI line is sold by Goldbelt Global which sounds like it would be an imported product, but it turns out that this is made in the USA. Support, spare parts, etc is all domestic.

https://www.goldbeltglobal.com/product-page/olesi-4-sample-crusher

Your little scientist will love the realistic lights and sounds of their very own X-ray diffraction system. At KSA we are firm believers that kids learn best by “doing”. There’s no better way to bring the next generation of bright thinkers into the lab. Now they can analyze real materials just like Mom and Dad!

There’s a simple and inverse relationship between the average atomic number of a given matrix and the efficiency with which it scatters X-rays. The effect isn’t all that much different from shining a flashlight on a white piece of paper. While it’s nothing like a mirror, you’ll definitely get light scattering off of it to some degree. This effect has strong effects on most XRD and XRF applications in that the additional photons must be dealt with somehow. This post addresses plastic sample holders and their effects on XRD data specifically.

Click on the scan images for full size versions:

Smaller anti-scatter and divergence slits work well as you can see in these scans, however, the intensity we lose throughout the remainder of the scan makes this an undesirable approach.

Automatic anti-scatter and divergence slits allow the irradiated area to be held constant throughout the scan which gives us the best of both worlds. These are not terribly common though and the data must be corrected as the intensities will vary dramatically from theoretical and historic data.

Perhaps the easiest way to deal with this effect is to simply change the sample holder material. While we make a large number of standard PMMA sample holders for Bruker XRD systems, the scatter from the plastic material is an undeniable problem. For that reason, we have also made Aluminum bodied holders for quite a while. Even steel holders are used, but usually not with Cu incident x-rays as Fe fluoresces strongly under Cu excitation.

While this works for most users, those using a FlipStick autosampler are in a difficult position. Due to the way this autosampler positions and rotates the sample holder during data collection, the only viable options for the body have been PMMA plastic or steel. Both of which handle the pressure well, but between the scatter off the plastic and the Fe fluorescence from the steel, we’re left without an ideal solution.

We make some very large zero background sample holders which are really the perfect solution in that there is near zero scatter or any effect from the sample holder itself. It’s like the sample material is floating in space. These are incredibly powerful, but not inexpensive so their use is usually limited to cases where they are required.

Recently, we decided to try an experiment with an outer edge of PMMA plastic surrounding an inner body and sample well made of Aluminum. Al will still scatter a bit, but it’s much better than plastic. We’re hopeful that this will be a useful solution for many XRD users who struggle with scatter in the 5-13 degree 2Theta range. Contact us if you’re interested in a solution like this.