AN ANALYTICAL XRAY SERVICES LABORATORY
Feel free to call us: 940-784-3002

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.

 

XRD work is categorized into two major groups. Single crystal and powder analysis. While single crystal work is usually highly customized to particular applications and involves a largely unique hardware set, powder (PXRD) work covers a broad range of applications. Many of which can be performed without any special hardware at all. Perhaps it would be more accurate to call it “Randomly oriented small particle” diffraction. Somehow I think “ROSPXRD” would be slow to catch on. At the risk of oversimplifying the options, I’d like to take a few posts to showcase some of the more common analyses which can be performed with a basic PXRD system and perhaps wholesale nfl jerseys a few that require minimal additional attachments.

This is an example of a Bruker D8 Advance configured in its most basic PXRD state with only a scintillation counter, sample stage and source.

This is an example of a Bruker D8 Advance configured in its most basic PXRD state with only a scintillation counter, sample stage and source.

This is the same D8 base instrument configured for single crystal XRD. Note the Chi, phi, XYZ stage, area detector (2D) and Goebel focusing mirrors.

This is the same D8 base instrument configured for single Damen crystal XRD. Note the Chi, phi, XYZ stage, area detector (2D) and Goebel focusing mirrors.

 

 

 

 

 

 

 

 

 

 

 

My last post involved a basic phase identification and this seemed like a great place to start. Most PXRD users are asked to identify some unknown bit of скачать corrosion, rock or contaminant at some point. I once took a shot at something which later turned out to be sewage sludge ash. I have no idea what they hoped to find in that. Exotic, mundane or distasteful, the most basic XRD can collect the necessary data to perform this analysis. Phase ID is usually the first step most users take toward more advanced software. In addition to the simple pattern analysis features that usually come standard, you’ll need an engine designed to search one of the many commercial or open-source databases available. The ICDD, NIST and wholesale mlb jerseys AMCSD are probably the most popular with several others on the fringe. There are even user-developed databases which are usually compiled in a particular lab to cover the range of phases they expect to see based on their product or application.

Limiting the search to categories of phases which are likely to be present Broker greatly improves the relevance of the results list. There’s obviously no reason to search through a huge list of minerals when trying to identify a metallic oxide coating. Hit lists can also be refined based on data from other sources such as qualitative elemental analysis. We use our WDXRF systems and the built in elemental filter in Jade to trim the options substantially.

Any good search/Match engine will have support not only for multiple databases, but also offer the option to limit your search to certain subfiles which are group my material categories.

Any good search/Match engine will have support not only for multiple databases, but also offer the option to limit your search to certain subfiles which are group my material categories.

Semi-quantitative or simple qualitative elemental data can be used to eliminate a large percentage of erroneous hits so the analyst can focus on only pertinent options. We prefer to bundle an XRF scan with any Phase ID project.

Semi-quantitative or simple qualitative elemental data can be used to eliminate a large percentage of erroneous hits so the analyst can focus on only pertinent options. We prefer to bundle an XRF scan with any Phase ID project.

 

 

 

 

 

 

 

 

 

 

Isolating the valid hits from erroneous is where experience comes into play. Non-ideal particle size, preferred orientation and crystallographic imperfections can make the process quite difficult. Relative peak intensity ratios, peak width and sometimes even the complete absence of ID a particular peak which would theoretically be present all present opportunities to gain additional insight. Sometimes this is relatively easy as in the case I presented in the previous post, wholesale nba jerseys but other situations are not so simple. These difficulties are amplified in the case of low concentrations and complex mixtures.

This is  a great example of Phase ID the way we all wish it came out. The peaks are sharp, intense and located right on their theoretical angle.

This is a great example of Phase ID the way we all wish it came out. The peaks are sharp, intense and located right on their theoretical angle.

This is an example of something a little harder to nail down. Overlapping peaks, several additional phases and a highly imperfect sample. Refining the options based on external measurements and in depth sample prep make the difference between success and failure in cases like this.

This is an example of something Texray a little harder to nail down. Overlapping peaks, several additional phases and a highly imperfect sample. Refining the options based on external measurements and in depth sample prep make the difference between success and failure in cases like this.

 

 

 

 

 

 

 

 

 

 

XRD pattern analysis has come along way in the last 40 years and most of the major improvements have come on the heels of increased computing capability which enables us to perform exhaustive iterative calculations on complex patterns quickly and at comparatively low cost. However, there is nothing on the market as of now which has made an experienced analyst obsolete.

 

I stumbled into Dondero’s Rock Shop a few weeks ago and struck up a conversation with the owner. He had been interested in geology all his life and was now operating a very nice shop in North Conway, NH with just about every type of mineral one could imagine on display. It was a great opportunity to have an expert identify a few specimens my boys had collected the previous day and he was more than happy to help. These were very large single crystals of relatively common minerals, but it was obvious that experience makes all the difference when one is trying to identify them by sight. I offered to return the favor by collecting XRD data on anything that ever managed to stump his well cheap MLB jerseys trained eye and he immediately brought out an interesting sedimentary formation which he’d sliced into cross to sections. He had been very curious about its composition and I brought home a sample. My wholesale MLB jerseys technical expertise is primarily in the hardware we use at Texray while the real science is handled by other, more highly skilled hands, but this seemed like a fun little project and good practice if nothing else.

Geological samples are particularly difficult to analyze by XRD as they contain various defects which are difficult if not impossible to model based on theoretical data. Our precious Rietveld refinements roll off of this type of data like water off a ducks back all too often and we’re left wondering how on earth this mud could be mistaken for moon rocks. As wonderful as Erlebnis Rietveld is in well-trained hands, we tend to rely much more on comparative data when we’re working with this type of sample. We can thank Dennis Eberl of USGS in Boulder, CO for bringing RockJock into the world to solve exactly these types of problems. RockJock is relies on what’s called RIR. That is Relative Intensity Ratio analysis to cheap nfl jerseys provide both qualitative and quantitative results. The  algorithm has been massaged into a number of commercial products in an effort to improve the user interface and add additional functionality, but the core of all that is still readily available on the internet for anyone interested to download. If you’re interested in something a little more user friendly, we offer ClaySim from MDI.

To the left you can see the data I collected after mild grinding. It’s not uncommon to spend several hours collecting data before it’s adequate for quantification or other advance analysis, but as we’re only interested in qualitative phase Program ID, this will more than suffice. I was quite surprised to find only two major phases present since the sample clearly shows four distinct layers with completely different coloration. The scan actually ran all the way to 120°2Θ, but the “action” is mostly concentrated at the lower angles. Hardcore geologist actually push the lower limit all the way down to 2.5°2Θ in an effort to catch a few illusive peaks. The analysis program you see here is MDI Jade 2010. It’s their flagship product and for good reason. Almost all of our users are running some form of Jade for their wholesale NFL jerseys analysis and all have had nothing but glowing praise for it.

So it appears that the mystery rock was actually little more than Quartz and Dickite. It’s possible that there’s a bit of Kaolinite mixed in there as well, particularly because Dickite and Kaolinite share a chemical composition. The real fun started when I let Jade loose using a feature called “One Click Analysis”. This is as close to a “black box” as XRD analysis will ever get. With good data collected on a solid, well-aligned XRD, this little button can provide impressive results with no user input at all. It’s not the magic bullet for every situation, but in Face this case, it recommended yet another phase with the same chemical composition as Kaolinite and Dickite. Nacrite. Adding this into our phase list improved the difference pattern and cheap NBA jerseys allowed Jade to model nearly every bump in the pattern.