TEXRAY LAB » 2014

Film effects on XRD data

Posted by: Ken Stauver In: Uncategorized 27 Nov 2014 0 comments Tags: Bruker D5000, D500, D5000, D5005, D8, Diffraction, Diffractometer, Energy-dispersive detector, film, Jade, Jade 2010, Kapton, KS Analytical, Materials Data Inc, MDI, Mylar, Polycarbonate, Polyimide, Prolene, PXRD, X-ray, XRD, XRD data collection

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.

Scotch “Magic” office tape. Adhesive side down.

Scotch “Heavy duty” packing tape. Adhesive side down.

Energy dispersive detectors for XRD systems

Posted by: Ken Stauver In: Uncategorized 20 Nov 2014 0 comments Tags: Bruker, D500, D5000, D5005, D8, Diffraction, Diffractometer, Energy-dispersive detector, KS Analytical, powder XRD, PXRD, X-ray, XRD, XRD data collection

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.

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.

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

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.

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

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.

Air-sensitive sample cells

Posted by: Ken Stauver In: Uncategorized 16 Nov 2014 0 comments Tags: Diffraction, Diffractometer, powder XRD, PXRD, reactive, sample preparation, X-ray diffraction

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.

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.

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.

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.

Sample holders for XRD analysis

Posted by: Ken Stauver In: Uncategorized 25 Aug 2014 0 comments Tags: D500, D5000, D5005, D8, Sample holder, XRD

The most common practice in powder XRD is to simply fill the recessed well of a sample holder with finely ground powder and start collecting data. That works for a great many users, but everyone is eventually faced with a more complicated situation at some point. At Texray, odd samples and special requirements are the norm. The photos below represent some of the common and not-so-common needs we’ve come across. Many of these are one-off designs fabricated by KS Analytical Systems.

The top row shows the three most common holders we see with various well depths. These are almost exclusively used for loose powders. The goal is to get the surface of the sample into the plane of diffraction with as little of the holder in the beam as possible. The plastic material has a very high scattering coefficient which creates a hump in the data around 13 degrees 2Theta. These are all designed for the 40-position sample changers from Siemens (now Bruker).

The second row gets more interesting with a special holder for high volume instruments. This was designed for magnetic handling and worked great as long as you don’t mind the low angle scatter problem of the plastic and aren’t working with ferrous powders.

The middle is one we use for collecting data from membrane filters. These are notoriously hard to hold down with any precision so they get mounted from the rear and held against a “lip” to keep them both flat, and in the plane of diffraction. They work wonderfully.

Next we have a simple side load sample holder. I’m a big fan of these and use them anytime I’m running loose powders on a single sample stage. It allows the user to load with a very smooth top surface that’s perfectly flat without creating any preferred orientation. Preferred orientation is frequently caused by pressure being applied to the basic top-load holders in an effort to get a flat surface. It is to be avoided whenever possible. Notice that the holders are all Aluminum at this point. Most custom holders are Al or a combination of Al and stainless steel depending upon the special properties desired.

The last row are good examples of odd-shaped sample holders. When you’ve got a rock with one flat surface or a little chip of some material, you still need to keep it in the plane of diffraction. The user simply places a ball of clay in the middle of the holder, the sample goes on top of that and then a glass plate is used to crush the clay (with the sample on top) down such that everything is in plane with the elevates posts. These posts interface with the machine to define the plane of diffraction right across their surface, thus the sample is right where it needs to be without any complicated engineering or microscopic adjustments.

Custom holders for a D500 user. Side load as well as top-load in Al.

Side load precision without the possibility of powder falling out at low angles.

Vacuum holding is common when working with semiconductors or other materials with very consistent thicknesses.

We needed to keep our standards in our desiccator cabinet as well as store membrane filters long-term. Custom laser-cut shelves make this easy.

A typical run of custom sample holders for a high volume XRD operation. This user actually has a custom loading tool that allows for multiple holders to be filled simultaneously.

$This is a completely custom stage designed to hold a large thrust bearing race such that the bottom of the groove is in the plane of diffraction for retained austenite and residual stress measurements. The bearing is held in place by magnets.$

This is a completely custom stage designed to hold a large thrust bearing race such that the bottom of the groove is in the plane of diffraction for retained austenite and residual stress measurements. The bearing is held in place by magnets.

OSHA Propose a Change in Crystalline Silica Rules

Posted by: Vallerie DeLeon In: Uncategorized 16 Apr 2014 0 comments Tags: cristobalite, free crystalline silica, industrial hygiene, NIOSH 7500, OSHA, quartz, respirable silica, X-ray diffraction, XRD

XRD is the preferred analytical method of testing free crystalline silica in workplace atmospheres. At Texray, we offer respirable silica testing using the NIOSH 7500 method, so we thought those of you in industries such as concrete, construction, glass, milling, mining, hydraulic fracking and sandblasting will find it important to know that OSHA has proposed an update to the current rules. The most notable change is a decrease in OSHA’s Permissible Exposure Limits (PEL) from 100 mg/m³ of air for general industries and 250 mg/m³ of air for construction industries to 50 mg/m³ of air for all industries. OSHA, along with other independent occupational health institutions, feel the current PELs are outdated and inadequate, and rightfully so, considering limits were last set in 1971 and based on 1960s research. However, most of these industries may not feel an impact from such as change, as many employers already use preventative measures to reduce dust exposure.

Would this rule change affect the analytical testing procedure?

Photo Courtesy of New Jersey Department of Health

No, XRD limits of detection (LOD) for NIOSH 7500 are 0.005 mg/m³ for an 800 L air sample. This rule change would not affect the testing method, since the LODs for silica in the form of quartz and cristobalite are well below the newly proposed PEL. However, the rule change may increase the number of industrial sites needing to test their work environments for respirable silica.

According to OSHA, “The proposed rule is expected to prevent thousands of deaths from silicosis, lung cancer, other respiratory diseases, and kidney disease. OSHA estimates that the proposed rule will save nearly 700 lives and prevent 1,600 new cases of silicosis per year once the full effects of the rule are realized.” The rule change was proposed last September and the hearing was recently concluded at the beginning of April. Final decision will be coming soon. We will keep you posted.

Free XRD/XRF Literature

Posted by: Vallerie DeLeon In: Uncategorized 27 Mar 2014 0 comments Tags: Advanced X-ray Analysis, crystallography, ICDD, International Centre of Diffraction Data, X-ray diffraction, X-ray Fluorescence Spectroscopy, XRD, XRF

In my last post, I hinted towards the importance of literature searches before attempting to analyze a new material, and then someone in one of my discussion groups posted a link to the 30 Most Downloaded Advanced X-ray Analysis Articles from the ICDD. I thought some of you might find this helpful, so I am reposting the link.

30 Most Downloaded AXA Publications

The articles are free to download and written by well-known, respected professionals that have been in the business of X-ray analysis for many years. The topics range from sample preparation to applications to instrumentation hardware. Enjoy!

Sample Preparation for XRD

Posted by: Vallerie DeLeon In: Uncategorized 14 Mar 2014 0 comments Tags: Bruker D5000, ICDD, McCrone Micronizing Mill, powder XRD, preferred orientation, quantitative XRD, Rietveld refinement, sample preparation, shale, X-ray diffraction

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

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.

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.