The D4 Endeavor fits in a unique niche in the XRD world. It’s basically the same thing as a Bruker D8, but built into a very compact cabinet with a large autosampler on top. These machines see heavy use in the cement, pharmaceuticals, and aluminum industries among others. Today we have one headed out to a new home. It started life in the pharmaceutical world, but had light use so it was a great candidate for refurbishment.
Tag: bruker
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NIST 1976c custom mount
It’s easy to forget how much of our scientific work hinges upon comparative data. The entire field of metrology is concerned with the verification and maintenance of “standard reference materials” (SRMs). Creating a perfect reference standard essentially involves proving a negative. In the XRD world, we need to prove that there are no impurities, no crystalline defects, no unaccounted for thermal variations, no stress/strain effects present, and above all, that the first unit produced is effectively identical to the last and all between.
There really isn’t any one material that checks all the boxes, but the NIST gets very close thanks to the efforts of Mr. Jim Cline and his associates. The hardware they’re using is completely custom to the point that it bares no resemblance to the instrumentation we normally work with. There’s a great page on their divergent-beam lab here.
The NIST 1976 material has been a mainstay in regular monitoring and certification of XRD system performance for many years and is now on its third (c) generation. With this most recent revision the shape of the standard has been changed from a flat plate to a round disk. This allows for much greater compatibility across the range of sample holders in the market.
This week we made a custom mount for a company using a Siemens D5005 with a 40-position autosampler. It’s common to mount these, but this is the first time I can recall doing so for this particular autosampler so I thought it was worth sharing a little about the material and a picture of the finished product.
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PMMA vs Aluminum sample holders
Plastic sample holders have been the default option XRD for decades. They’re inexpensive to make, good enough for most purposes, and very resistant to a wide range of chemicals. Seems like a “win” all around right? As long as they’re made correctly and from the proper materials, these work just fine. Spoiler alert: 3D printed thermoplastics have a distinct structure so if you try making your own, be sure they’re well out of the irradiated area.
Comparison of the same powder in an aluminum holder vs a standard PMMA holder. Click the image for a full view of the scan. We’ve seen a big move toward more zero-background holders in the last few years and they’re definitely incredible, but many XRD users aren’t concerned with running extremely small volumes as much as they are eliminating or minimizing the scattering of x-ray by the plastic at low angles. As a general rule for polycrystalline materials, the lower the average atomic number of the material, the more efficiently it scatters x-rays. We’re not talking about Bragg diffraction. More like shining a flashlight on a white sheet of paper. Compton and Raleigh scattering are the two effects at work here.
We use this effect to great advantage in the XRF world when we want to check out the emission spectrum of the x-ray tube. Running a piece of graphite as the sample allows us to collect a scan which shows all the different energies in the emission spectra. Unfortunately, scatter is highly problematic in XRD.
This is why we supply aluminum holders with our refurbished systems and why we use mostly aluminum holders at Texray. Different plastics can perform differently, but the problem is characterized by a wide, low hump centered around 10 degrees 2Theta and with a width of about 10 degrees. This is a key area in many materials so anything we can do to clean up the background is usually beneficial.
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What’s really coming out of my XRD tube?
We’ve been experimenting with better ways to quantify the quality of XRD tubes in the shop. We use these tests on new and used tubes to monitor performance in two key areas. 1) Intensity 2) Spectral purity.
What we’ve settled on is a test that involves a wavelength-dispersive approach which gives us a lot of intensity to work with while eliminating background scatter and fluorescence effects. Basically, we’re able to extract more information from the data because the “noise” is almost zero.
We used Jade Pro to evaluate the scans, but they’re not D-spacing vs intensity as one would normally expect. This scan represents Wavelength vs intensity more like one would see in a WDXRF spectrometer. Cu KA1 and 2 are obvious, as is Cu KB1. Many of the current generation of XRD users have never seen a W LA1 peak in their data, but it’s clearly visible here as this is an older tube. What I’ve never been able to see before is the W La2 peak in the green scan. You’re looking at a peak that is ~62eV separated from W La1. No XRD detector on the market has energy resolution like that so these would always be lumped together so you’d see a series of additional peaks from every d-spacing in the sample in the diffractogram. Only a handful of detectors (our SDD-150 for example) could even separate the W La from the Cu K lines. That’s the power of wavelength-dispersive techniques. Incidentally, the most common device for cleaning up superfluous energy emissions in XRD data is a diffracted-beam monochromator and they eliminate all the W La through a secondary diffraction event much like what we’re doing.
Characterizing emissions is nothing new. In fact, I started wanting to improve this after listening to a talk at DXC about Jim Cline’s famous XRD system which is used at NIST to perform the primary data collection on the CRMs we all use. To paraphrase Sir Arthur Conan Doyle, “When you explain every extraneous data point, the remaining information is the pure truth of the sample”.
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Fully digital autosampler install
Another fully-rebuilt, digital autosampler out in the wild. This one is on a system that already has one of our Si-Drift Detectors and an awesome ICDD Jade Pro/PDF-4+ software package. We’ve got all the fancy new hardware at our in-house lab, but when we need the absolute best data, this is our goto configuration.
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Energy-dispersive detector systems for XRD applications
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. (Brehmstralung 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.
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.
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 instrumentation 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.
