AN ANALYTICAL XRAY SERVICES LABORATORY
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I spend a great deal of time meeting with XRD and XRF users throughout the year, but usually in the context of some problem or time-sensitive project. Luckily I’ve been able to attend the Denver X-ray Conference fairly consistently over the last few years. It’s a great time to catch up with other users who are as deeply invested in X-ray spectroscopy and crystallographic analysis as we are. The vendors always put on a great show in the exhibit hall and poster sessions.

The first three days of the week are filled with technical workshops focused on an array of topics. There are always some introductory classes for both XRD and XRF for new users to attend and then there will be additional topics which are usually more advanced. The educational opportunities alone are well worth the attendance fee. Each session is run by an expert in the field and questions, even from industrial users, are welcomed. The sessions are strictly non-sales oriented as well which lends the event a very egalitarian feeling. See the full program here.

Plenary sessions and more sales-oriented meetings occur later in the week and are a great way to get a feel for the cutting edge technology being released by the various vendors. The exhibit hall opens a few days into the conference so everyone has a few days to see all the different booths. We always spend a great deal of time at the Materials Data, Inc and Bruker-AXS booths in particular.

The conference moves between Westminster, CO just North of Denver, Chicago, IL and Big Sky, MO. I’ve never made the trek up to Big Sky, but I hear it’s beautiful. Some attendees only come when it’s up there.

I’d love to connect with as many of our readers as possible so contact us if you’ll be there and I’ll be sure to see you while I’m at DXC-Big Sky!

A great many factors affect the quality of data one can collect on any given instrument, but there are times when simply holding the aliquot is a major hurdle. We spend a great deal of time working out the best ways to hold odd samples and even create custom hardware to do so in some cases. Click here for some of our other posts related to the various sample holders we work with. Choosing the best sample holder for a given project is one thing, but there are also times when a completely different stage is required.

The most common stage is the simple, single sample stage. This relies on three pins to define the plane of diffraction. The sample holder is pressed against these pins by a spring loaded plunger beneath it.

The dreaded “amorphous” hump created by x-rays scattering off plastic sample holders has plagued XRD users for decades. It’s a serious enough problem that we make a good volume of these holders from Aluminum which works very well for loose powders. The plastic scatters xrays at around 13 degrees 2Theta (Cu anode tube) which make a real mess of most geological patterns and isn’t fun to model out for Rietveld refinement. Zero background holders like our ZBH-32 work wonderfully in standard sample stages designed for a single sample at a time, but the large plate isn’t compatible with the autosampler.

I recently had a request for a hybrid holder which would allow for analysis of very small volumes of materials while retaining compatibility with the autosampler. This is almost identical to our standard powder holders, but with a well designed specifically for our small ZBH plate.

Key features include:

  • 6061-T6 Al material (anodized or as-machined)
  • Si(510) plate
  • Raised sample well minimizes the area of the sample holder in the plane of diffraction. (Original Siemens design)
  • Beveled well walls minimize the area of Al in the plane of diffraction
  • Other small modifications are made to improve reliability of these holders in the autosampler

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.

Energy-dispersive detectors have been in use on XRD systems for decades, but have always come with caveats. Low energy resolution, Liquid nitrogen cooling, slow start-up and tedious/cryptic tuning controls have limited their popularity in many applications. Silicon Drift technology solves most of these issues and modern electronics covers the rest. The new KSA-SDD system for X-ray diffraction utilizes a full spectrum EDXRF detector which is fully software tuned. The result is a detection system with high enough energy resolution to match the performance of the traditional diffracted-beam monochromator/scintillation counter combination without the inherent 75% intensity drop. The increased countrate allows for much faster data collection speeds with the same counting statistics. We’ve been using this technology at our in-house testing lab (Texray Laboratory Services) for several months to great effect while we refined the system and are now ready to open it up to all XRD users. Contact us to discuss options for integration into your diffractometer.

SDD-XRD-150 installed on a Siemends D5000TT PXRD system. This is one of the powder systems we operate at Texray-Lab.

SDD-XRD-150 installed on a Siemends D5000TT PXRD system. This is one of the powder systems we operate at Texray-Lab.

The detector mounts directly in place of the original scintillation counter.

The detector mounts directly in place of the original scintillation counter.

 

 

 

 

 

 

 

 

 

 

 

Speed

  • Scanning 3-4 times as fast as the traditional scintillation counter/diffracted beam monochromator yields nearly identical results.
  • Scanning at the same rate results in much smoother scans, greatly improved statistical data and lower limits of detection/quantification.
Novaculite SDD vs SC

Complete scan of Novaculite Quartz with a diffracted beam monochromator and scintillation counter vs the new KSA-SDD-150.

Novaculite SDD vs SC 5 fingers

5-fingers of Quartz scan of Novaculite Quartz with a diffracted beam monochromator and scintillation counter vs the new KSA-SDD-150.

 

 

 

 

 

 

 

 

 

Energy resolution

  • 140eV under ideal conditions.
  • All KB peaks eliminated electronically.
  • W LA1 (8.40 KeV) lines eliminated from Cu KA1,2 (8.04 KeV) scans even with thoroughly contaminated tubes.
  • Common fluorescence energies (i.e. Fe when Cu tube anodes are used) are greatly reduced. (Bremsstrahlung effects are impossible to remove completely)
  • Most PSD detectors offer no better than 650eV. This allows for a great deal of fluorescence energy to pass as well as W LA1 from older Cu tubes.

Low angle scatter

  • The detector mounts in place of the traditional scintillation counter allowing for use of automated variable (motorized) or interchangeable aperture slits to control angular resolution. Scans starting from 0.5 degrees 2? are possible with the proper slit arrangement just as they are with the scintillation counter. The user controls the intensity vs angular resolution of the scan based upon the ideal conditions for their work rather than the limitations of the hardware.
  • Position sensitive detectors are wide open by design which necessitates knife edges over the sample and additional mechanical aperture plates to block air scatter at low angles. Closing off the detector limits the useable channels and reduces the benefit of these detectors dramatically.
Novaculite SDD vs SC low angle

Minimal low angle scatter due to the use of standard aperture slits.

Novaculite SDD vs SC Cu KB1 and W LA1

Cu KB1 and W LA1 energies diffract from the 100% peak of Novaculite in between the two primary peaks shown here. Tests with a severely contaminated tube showed no W LA1 passing through the discriminator.

 

 

 

 

 

 

 

 

 

Truly zero maintenance design

  • No delays – The detector is ready to collect data almost as soon as power is applied.
  • No external cooling – Air backed Peltier cooling eliminates the need for water circulation and/or liquid nitrogen.
  • Zero maintenance vacuum design eliminates reliance on an ion pump/backup battery.
  • 12 month warranty against hardware failure under normal use.

Versatility

  • The Digital Pulse Processor (DPP) includes a usb interface allowing for adjustment and refinement should they be necessary for a particular application. With optional software, full quantitative EDXRF analysis can be performed.
  • Compatibility with grazing-incidence attachments and parallel beam optics for analysis of thin films.

 

The detector can be set for any common XRD anode (energy) easily. Multiple energies may even be configured to allow for use with various anodes without the need for additional hardware. We specialize in Siemens (now Bruker) XRD and WD-XRF instrumention and have installation kits ready for the D500, D5000 and D5005. The output is a standard BNC cable with a 5V square pulse output which is standard across every manufacturer we’ve worked with. Kevex and Thermo Si(Li) detectors used this same output.

Please contact KS Analytical Systems for a quote.

 

Some months ago we had a pair of scientists visit our space to look over a refurbished Siemens D5000. Interestingly enough, they’d planned to use the system for some basic XRD, but mainly for the development of polycapillary optics. This is a fascinating new technology that’s gaining steam out in the R&D centers around the world and merits a full post dedicated to it ASAP. This is the type of “game changing” innovation which hasn’t come along in XRD in decades. They took delivery of their machine a few weeks ago, but while on-site they asked about another project. All that’s really needed is simple phase analysis by XRD with one complication, the material reacts violently when exposed to air.

We roughed out a basic design the same day, but that was only the beginning. Dealing with materials like this necessitates careful consideration of all material and procedures involved in getting it from the lab where it’s synthesized to ours and back. The final design involved billet Aluminum, BUNA rubber o-rings and polyimide (Kapton) film and took quite a while to flesh out. The end result is a complete system which allows the customer to load the samples into individual cells inside their own glove box. The individual cells can be loaded into the case inside the glove box as well. The outer o-rings on the cells seal against chamfered edges on the pockets of the case creating a second sealed area above and below the sample. It’s unlikely that the inner cell would ever rupture, but this protects the polyimide film and adds a substantial extra level of safety.

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This is the complete case as it will ship. The flat-head bolts hold everything together and provide the necessary force to seal the chambers.

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With the case open, you can see the individual cells along with the top and bottom of the case. The labeling shouldn’t be necessary since there are strict protocols in place for transportation of this material, but it never hurts to be cautious.

DSC_0331

The original design called for a slightly more secure seal, but when we started working up the procedure to assemble them, it became clear that something simpler was needed, particularly considering that these will be loaded in a glove-box. An 11th hour rehash necessitated new o-rings, modification of the outer cell rings and complete redesign and fabrication of the cell center sections. I think this was well worth the effort though as they’re much easier to assemble now. There’s even a nice little tool to make it easier to open them back up for disposal or reloading. The original design would have been essential disposable.

DSC_0331 (2)

 

 

 

 

 

 

 

 

Over the past 15 years, Barnett Shale has become a major resource for natural gas in Texas.  Being located in the North Texas region, it is easy to see the boom of drilling rigs and wells popping up in the suburban and rural areas between Ft. Worth and Denton.  Collaborations between Geologists at universities and major oil companies have put a large amount of research into characterizing shale.  In 2001, Środoń et al. published a journal article in Clays and Clay Minerals that discussed the importance of sample preparation for sediments, such as shale, to be analyzed using X-ray diffraction.

Powder X-ray diffraction is the preferred and best technique to identify and quantify mineral compositions in geological materials such as rocks, sediments, and soils.  Sample preparation and loading are two important factors for accurate quantitative XRD analysis using Rietveld refinement.  Proper sample grinding and using a side-loader or backside loader are common practices to avoid preferred orientation.  At Texray, we have a variety of sample holders for different applications, and we can even custom build holders for those random parts.  However, in this study we wanted to see for ourselves the effect of sample grinding and particle size, and also we wanted to test out our new McCrone Micronizing Mill.  We already knew what the results would be from experience and previous work by Środoń et al., 2001 and Klug and Alexander, 1974, but this was a fun experiment to try with shale.

Shale rock from the North Texas region

Shale Rock from the North Texas region

The rocks (pictured above) were broken up into smaller pieces using a mortar and pestle, and then half was transferred to the McCrone mill for wet grinding and the other half we continued to grind manually using the mortar and pestle.  By the way if you are running out of bench space in the laboratory and are looking for a mill, I highly recommend the McCrone Micronizing Mill because it takes up very the little space and it’s capable of grinding below 10 μm in less than 10 minutes.  After grinding, we loaded the powder samples into a backside loader and analyzed them using a Bruker D5000 X-ray Diffractometer.

Shale XRD Pattern

XRD pattern of Mortar & Pestle Ground Shale (blue) vs McCrone Mill Ground Shale (red)

In the XRD pattern shown above the main differences you will notice between the two grinding methods are peak intensities and a small 2-theta peak shift.  Both of these differences are effects related to particle size distribution and sample loading.  Wet grinding the shale in a McCrone Mill creates smaller uniform particles (~5μm), therefore when loading the sample into holders the powders pack easier and tighter creating a denser layer of material for the X-rays to penetrate, hence higher peak intensities compared to manual grinding.  Sample preparation is one of the most important aspects to quantitative XRD because of preferred orientation and sample displacement.  In order to reduce user error such as, induced preferred orientation, it is essential we learn from previous research and take the proper steps to prepare samples.  The ICDD is a great source for free literature on applications involving XRD and XRF.  We will be posting more discussions on sample preparation and applications in the future.