Adding a New Dimension to Analysis

Dr. Oleg Lourie, Regional Manager A/P, EDAX

With every dimension, we add to the volume of data, we believe that we add a new perspective in our understanding and interpretation of the data. In microanalysis adding space or time dimensionality has led to the development of 3D compositional tomography and dynamic or in situ compositional experiments. 3D compositional tomography or 3D EDS is developing rapidly and getting wider acceptance, although it still presents challenges such as the photon absorption, associated with sample thickness and time consuming acquisition process, which requires a high level of stability, especially for TEM microscopes. After setting up a multi hour experiment in a TEM to gain a 3D compositional EDS map, one may wonder Is there any shortcut to getting a ‘quick’ glimpse into 3-dimensional elemental distribution? The good news is that there is one and compared to tilt series tomography, it can be a ‘snapshot’ type of the 3D EDS map.

3D distribution of Nd in steel.

3D distribution of Nd in steel.

To enable such 3D EDS mapping on the conceptual level we would need at least two identical 2D TEM EDS maps acquired with photons having different energy – so you can slide along the energy axis (adding a new dimension?) and use photon absorption as a natural yardstick to probe the element distribution along the X-ray path. Since the characteristic X-rays have discrete energies (K, L, M lines), it might work if you subtract the K line map from the L line or M line map to see an element distribution based on different absorption between K and L or M line maps. Ideally, one of EDS maps should be acquired with high energy X-rays, such as K lines for high atomic number elements, and another with low energy X-rays where the absorption has a significant effect, such as for example M lines. Indeed, in the case of elements with a high atomic number, the energies for K lines area ranged in tens of keV having virtually 0 absorption even in a thick TEM sample.

So, it all looks quite promising except for one important detail – current SDDs have the absorption efficiency for high energy photons close to actual 0. Even if you made your SDD sensor as large 150 mm2 it would still be 0. Increasing it to 200 mm2 would keep it steady close to 0. So, having a large silicon sensor for EDS does not seem to matter, what matters is the absorption properties of the sensor material. Here we add a material selection dimension to generate a new perspective for 3D EDS. And indeed, when we selected a CdTe EDS sensor we would able to acquire X-rays with the energies up to 100 keV or more.

To summarize, using a CdTe sensor will open an opportunity for a ‘snapshot’ 3D EDS technique, which can add more insight about elemental volume distribution, sample topography and will not be limited by a sample thickness. It would clearly be more practical for elements with high atomic numbers. Although it might be utilized for a wide yet selected range of samples, this concept could be a complementary and fast (!) alternative to 3D EDS tomography.

Rotary Engines Go “Round and Round”

Dr. Bruce Scruggs, XRF Product Manager EDAX

Growing up outside of Detroit, MI, automobiles were ingrained in the culture, particularly American muscle cars. I was never a car buff but if I said little and nodded knowingly during these car discussions, I could at least survive. Engine displacement? Transmission? Gear ratios? Yep, just nod your head and grunt a little bit. Well, it turns out working at EDAX that I’ve run into a couple of serious car restoration experts. There always seems to be a common theme with these guys: how do I get more power out of this engine?

Recently, one of these restoration experts brought in a small section of the rotor housing of a Mazda engine circa early ‘80s. Turns out, this guy likes to rebuild Mazda engines, tweak the turbocharging and race them. As we all know, Mazda was famous for commercializing the Wankel engine, aka the rotary engine, to power their cars. Rotary engines are famous for their simplicity and the power one can generate from a relatively small engine displacement. These engines are also infamous (i.e. poor fuel consumption and emissions) as well which has led Mazda to end general production in roughly 2012 with the last of the production RX-8s.

Now, one of the questions in rebuilding these engines is how to repair and resurface the oblong rotor housing. In older engines of this type, the surface of the rotor housing can suffer deep gouges. The gouges can be filled and then need to be resurfaced. Initially, we imaged the cross-section of the rotor housing block in an Orbis PC micro-XRF spectrometer to determine what was used to surface coat the rotor housing. If you read up on this engine, (it’s a 12A variant), the block is aluminum with a cast iron liner and a hard chromium plating. The internet buzz claims the liner is installed via a “sheet metal insert process”. And when I google “sheet metal insert process” all I get are links to sheet metal forming and links referring to webpages which have copied the original reference to “sheet metal insert process”.

In the following Orbis micro-XRF maps (Figures 1a and 1b), you can see the aluminum rotor housing block and the cast iron liner. Each row of the map is about 100 µm wide with the iron liner being about 1.5 mm thick. If you look carefully, you can also see the chrome coating on the surface of the iron liner. On the cross-section, which was done with a band saw cut, the chrome coating is about one map pixel across. So, it’s less than 100 µm thick. From web searches, hard chrome plating for high wear applications start at around 25 µm thick and range up to hundreds of microns thick. For very thick coatings, they are ground or polished down after the plating process to achieve more uniform application. So, what is found in the elemental map is consistent with the lower end of web-based information for a hard chrome coating, bearing in mind that the coating measured had well over 150k miles of wear and tear. If we had a rotor housing with less wear and tear, we could use XRF to make a more proper measurement of the chrome plating thickness and provide a better estimate of the original manufacturer’s specification on the hard chrome thickness.

Figure 2: Orbis PC elemental map

Figure 1a: Orbis PC elemental map

Overlay of 4 elements:
Fe: Blue (from the cast iron liner)
Al: Green (from the aluminum rotor housing block)
Cr: Yellow (coating on the cast iron liner)
Red: Zinc (use unknown)

Figure 3: Total counts map: Lighter elements such as Al generate fewer X-ray counts and appear darker than the brighter, heavy Fe containing components.

Figure 1b: Total counts map: Lighter elements such as Al generate fewer X-ray counts and appear darker than the brighter, heavy Fe containing components.

We did have a look at the chrome coating by direct measurement with both XRF, looking for alloying elements such as Ti, Ni, W and Mo, as well as SEM-EDS looking for carbides and nitrides. We found that it’s simply a nominally, pure chrome coating with no significant alloying elements. We did see some oxygen using SEM-EDS, but that would be expected on a surface that has been exposed to high heat and combustion for thousands of operating hours. Again, these findings are consistent with a hard chrome coating.

In some on-line forum discussions, there was even speculation that the chrome coating was micro-porous to hold lubricant. So, we also looked at the chrome surface under high SEM magnification (Figure 2). There are indeed some voids in the coating, but it doesn’t appear that they are there by design, but rather that they are simply voids associated with the metal grain structure of the coating or perhaps from wear. We specifically targeted a shallow scratch in the coating, looking for indications of sub-surface porosity. The trough of the scratch shows a smearing of the chrome metal grains but nothing indicating designed micro-porosity.

Figure 4: SEM image of chrome plated surface of rotor housing liner. The scratch running vertically in the image is about 120 µm thick.

Figure 2: SEM image of chrome plated surface of rotor housing liner. The scratch running vertically in the image is about 120 µm thick.

The XRF maps in Figure 1 also provides some insight into the sheet metal insert process. The cast iron liner appears to be wrapped in ribbons of aluminum alloy and iron. The composition of the iron ribbon (approximately 1 wt% Mn) is about the same as the liner. But, the aluminum alloy ribbon is higher in copper content than the housing block. This can be seen in the elemental map (Figure 1a) where the aluminum ribbon is a little darker green, lower Al signal intensity, than the housing block itself. The map also shows a thread of some zinc bearing component running through (what we speculate are) the wrappings around the liner. My best guess here is that it is some sort of joining compound. Ultimately, the sheet metal insert process involves a bit more than a simple press or shrink fit of a cylinder sleeve in a piston engine block. Nod knowingly and grunt a little.

My Turn

Dr. Stuart Wright, Senior Scientist, EDAX

One of the first scientific conferences I had the good fortune of attending was the Eighth International Conference on Textures of Materials (ICOTOM 8) held in 1987 in Santa Fe, New Mexico. I was an undergraduate student at the time and had recently joined Professor Brent Adams’ research group at Brigham Young University (BYU) in Provo, Utah. It was quite an introduction to texture analysis. Most of the talks went right over my head but the conference would affect the direction my educational and professional life would take.

Logos of the ICOTOMs I've attended

Logos of the ICOTOMs I’ve attended

Professor Adams’ research at the time was focused on orientation correlation functions. While his formulation of the equations used to describe these correlations was coming along nicely, the experimental side was quite challenging. One of my tasks for the research group was to explore using etch pits to measure orientations on a grain-by-grain basis. It was a daunting proposition for an inexperienced student. At the ICOTOM in Santa Fe, Brent happened to catch a talk by a Professor from the University of Bristol named David Dingley. David introduced the ICOTOM community to Electron Backscatter Diffraction (EBSD) in the SEM. Brent immediately saw this as a potential experimental solution to his vision for a statistical description of the spatial arrangement of grain orientations in polycrystalline microstructures.

At ICOTOMs through the years

At ICOTOMs through the years

After returning to BYU, Brent quickly went about preparing to get David to BYU to install the first EBSD system in North America. Instead of etch pits, my Master’s degree became comparing textures measured by EBSD and those measured with traditional X-Ray Pole Figures. I had the opportunity to make some of the first EBSD measurements with David’s system. From those early beginnings, Brent’s group moved to Yale University where we successfully built an automated EBSD system laying the groundwork for the commercial EBSD systems we use today.

I’ve had the good fortune to attend every ICOTOM since that one in Santa Fe over 30 years ago now. The ICOTOM community has helped germinate and incubate EBSD and continues to be a strong supporter of the technique. This is evident in the immediate rise in the number of texture studies undertaken using EBSD immediately after EBSD was introduced to the ICOTOM community.

The growth in EBSD in terms of the percentage of EBSD related papers at the ICOTOMs

The growth in EBSD in terms of the percentage of EBSD related papers at the ICOTOMs

Things have a way of coming full circle and now I am part of a group of three (with David Fullwood of BYU and my colleague Matt Nowell of EDAX) whose turn it is to host the next ICOTOM in St George Utah in November 2017. The ICOTOM meetings are held every three years and generally rotate between Europe, the Americas and Asia. At ICOTOM 18 we will be celebrating 25 years since our first papers were published using OIM.
icotom-2017
It is a humbling opportunity to pay back the texture community, in just a small measure, for the impact my friends and colleagues within this community have had both on EBSD and on me personally. It is exciting to consider what new technologies and scientific advances will be germinated by the interaction of scientists and engineers in the ICOTOM environment. All EBSD users would benefit from attending ICOTOM and I invite you all to join us next year in Utah’s southwest red rock country for ICOTOM 18! (http://event.registerat.com/site/icotom2017/)

Some of the spectacular scenery in southwest Utah (Zion National Park)

Some of the spectacular scenery in southwest Utah (Zion National Park)

With Great Data Comes Great Responsibility

Matt Nowell, EBSD Product Manager, EDAX

First, I have to acknowledge that I stole the title above from a tweet by Dr. Ben Britton (@BMatB), but I think it applies perfectly to the topic at hand. This blog post has been inspired by a few recent events around the lab. First, our data server drives suffered from multiple simultaneous hard drive failures. Nothing makes you appreciate your data more than no longer having access to it. Second, my colleague and friend Rene de Kloe wrote the preceding article in this blog, and if you haven’t had the opportunity to read it, I highly recommended it. Having been involved with EBSD sample analysis for over 20 years, I have drawers and drawers full of samples. Some of these are very clearly labeled. Some of these are not labeled, or the label has worn off, or the label has fallen off. One of these we believe is one of Rene’s missing samples, although both of us have spent time trying to find it. Some I can recognize just by looking, others need a sheet of paper with descriptions and details. Some are just sitting on my desk, either waiting for analysis or around for visual props during a talk. Here is a picture of some of these desk samples including a golf club with a sample extracted from the face, a piece of a Gibeon meteorite that has been shaped into a guitar pick, a wafer I fabricated myself in school, a rod of tin I can bend and work harden, and then hand to someone else to try, and a sample of a friction stir weld that I’ve used as a fine grained aluminum standard.

fig-1_modified
Each sample leads to data. With high speed cameras, it’s easier to collect more data in a shorter period of time. With simultaneous EDS collection, it’s more data still. With things like NPAR™, PRIAS™, HR-EBSD, and with OIM Analysis™ v8 reindexing functionality, there is also a driving force to save EBSD patterns for each scan. With 3D EBSD and in-situ heating and deformation experiments, there are multiple scans per sample. Over the years, we have archived data with Zip drives, CDs, DVDs, and portable hard drives. Fortunately, the cost for storage has dramatically decreased in the last 20+ years. I remember buying my first USB storage stick in 2003, with 256 MB of storage. Now I routinely carry around multiple TBs of data full of different examples for whatever questions might pop up.

cost-per-gigabyte-large_modified
How do we organize this plethora of data?
Personally, I sometimes struggle with this problem. My desk and office are often a messy conglomerate of different samples, golf training aids (they help me think), papers to read, brochures to edit, and other work to do. I’m often asked if I have an example of one material or another, so there is a strong driving force to be able to find this quickly. Previously I’ve used a database we wrote internally, which was nice but required all of us to enter accurate data into the database. I also used photo management software and the batch processor in OIM Analysis™ to create a visual database of microstructures, which I could quickly review and recognize examples. Often however, I ended up needing multiple pictures to express all the information I wanted in order to use this collection.

blog-fig-3_modified

To help with this problem, the OIM Data Miner function was implemented into OIM Analysis™. This tool will index the data on any given hard drive, and provide a list of all the OIM scan files present. A screenshot using the Data Miner on one of my drives is shown above. The Data Miner is accessed through this icon on the OIM Analysis™ toolbar. I can see the scan name, where it is located, the date associated with the file, what phases were used, the number of points, the step size, the average confidence index, and the elements associated with any simultaneous EDS collection. From this tool, I can open a file of interest, or I can delete a file I no longer need. I can search by name, by phase, or by element, and I can display duplicate files. I have found this to be extremely useful in finding datasets, and wanted to write a little bit about it in case you may also have some use for this functionality.

Help!

Dr. René de Kloe, Applications Specialist EDS, EBSD, EDAX

The job of an applications engineer is to help people. Help sales people to explain to customers what a system can do. Help customers to get the most out of their system and help them to understand their materials better. Help the marketing group with nice examples. And help the development team to devise applications that have not been tried before.

One thing you need in order to be able to help is knowing the EDAX analysis systems inside-out. But the other thing you need is samples. Lots of samples. Every function or analysis tool in the software, regardless if it is for EDS, EBSD, WDS, or XRF is best shown with a specific material or combination of elements or phases. Some of these, like chemical standards with known composition, you have to make or perhaps buy. Others you have to collect yourselves, but from where? A great source for new materials are our customers. People often send me materials to evaluate our systems, or for help on how to best analyse their samples. When I then get permission to keep a bit of the material it goes directly into my collection, together with valuable information on the current analysis requirements in different scientific disciplines.

Eight phase FeSi alloy Brass with NiMnSi particles 

This goes a long way in getting good example materials, but I always keep my eyes open for new interesting things. When I see a metal strip in an anti-theft label in clothing I keep it (after buying the item of course), when a droplet of lead-tin solder falls on the floor, I stick it in the microscope to see if it looks good. I also scrutinize things that get thrown away, ranging from the lid of a vegetable jar to a damaged bellows of an EBSD system. That has given me beautiful cast aluminium samples for EDS mapping, multiphase brass alloys for ChI-Scan EDS-EBSD analysis, and recently an unexpected copper-plated zinc-aluminium-silicon alloy for EBSD phase identification from a broken belt buckle.

Grain structure of a staple Grain structure of a key ring 

Luckily I don’t always have to go dumpster diving to get my example materials. One of my favorite sample mounts contains different types of heavily deformed ferrite, duplex stainless steel, and also martensitic structures. That sounds perhaps complicated, but on the outside the same sample just looks like staples, a paperclip, a key ring, and a screw.

The screw, for example, I polished after doing some DIY work at home and because a certain type of screw kept breaking off when I tightened it, I wanted to take a close look why that happened. It turned out that there were lots of small cracks along the thread, which then also lined up with trails of carbides further inside the screw. That turned out to be a really bad combination and when you tighten the screw, the cracks propagate, connect with the carbide trails and the screw head snaps off. The replacement screws that I used instead had a much finer structure without any cracks and that is what is still holding things together in the house. This shows how microstructures literally shape our daily life. And it also provides a beautiful example to help illustrate the importance of microstructural characterization to new EBSD users.

Weak screw Strong screw

The huge variation in materials and microstructures makes the collection of demonstration samples the most important tool for an application scientist and from this place I hereby want to thank all people who have given me a piece of some material during my years at EDAX to use to help others.

By the way, I would appreciate it very much if the person who briefly “borrowed” my marble sample last year gives it back soon …

Don’t Beam Me Up Yet!

Sia Afshari, Global Marketing Manager, EDAX
enterprise
This September is the 50th anniversary of the airing the Star Trek series and if you live around New York City, where this year’s convention is being held, you cannot help running into some of the characters walking around in the Star Fleet uniforms or some alien costumes.

The Star Trek series left its mark on the psyche of many especially those who grew up in that era. Many inventions from the Motorola flip phone, tablets, flat screens, hypospray, stun guns, universal translator, all the way to the concept of a retractor beam that is being used as an optical tweezer to trap and remove bacteria by a focused laser beam have been inspired or attributed to this series.

The most intriguing device in the series was the Tricorder concept. It performed medical, biological, geological, physical, and chemical analyses along with detecting spatial anomalies and alien life forms all in one handheld device!

2e0a28b400000578-0-image-a-34_1446467985814

Mr. Spock used his Tricorder to deliver results with an unquestionable degree of accuracy and confidence level that covered analytical capabilities of the following techniques in one package:
IR, entire photon spectrum detection, colorimetry, pressure sensor, humidity gauge, ultrasonic, particle analyses (e-, e+, n, p, ν, HP), XRF, XRD, ICP, AA, HPLC, medical X-rays, MRI, CAT-scan, PET-scan, Electron Microscopy, EDS, EBSD, Raman, to name a few.

And, Tricorder did them all apparently remotely, without any interaction with its subject matter that as we know is the fundamental rule of a measurement.

As has been reported in the media this week, some of the Tricorder functionalities have come to fruition. NASA’s handheld device called LOCAD, measures microorganisms such as E. coli, fungi and salmonella onboard the International Space Station. Two handheld medical devices are on their way to help doctors examine blood flow and check for cancer, diabetes or bacterial infection. Loughborough University in England announced a photo-plethysmography technology in a handheld device that can monitor the heart function and at Harvard Medical School a small device that utilizes a similar technology as MRI that can non-invasively inspect the body. China’s version of the Tricorder health monitor is reported to have cleared FDA approval for the US market!

Regardless of the validity of the Star Trek inspired inventions as being real or nostalgic, one cannot deny the everlasting impact that the series has had on the imaginations of those who saw the achievable possibilities through science and technology in the future. At least it allowed our imaginations to go wild for that one hour.

220px-locad-pts

In insomniac moments, besides the whereabouts of the Orion planet one may wonder, is there a signature force for matter that has not been discovered yet that can be used for the design of a true Tricorder? Until that time, focusing on EDS miniaturization for the next generation portable electron microscope is on my mind with the hope that I will not be beamed up until the realization of the concept! You hear that Scotty?

Browsing for the Trekkies:
http://www.tricorderproject.org/tricorder-mark2.html
http://www.nature.com/nphoton/journal/v6/n2/full/nphoton.2011.322.html
https://spie.org/membership/spie-professional-magazine/spie-professional-archives-and-special-content/2016_january_archive/the-photonics-of-star-trek?WT.mc_id=ZTWZ
China’s Version Of A ‘Star Trek’ Tricorder Has Just Been Approved By The FDA
http://spectrum.ieee.org/biomedical/diagnostics/the-race-to-build-a-reallife-version-of-the-star-trek-tricorder

Metals, Minerals and Gunshot Residue

Dr. Jens Rafaelsen, Applications Engineer EDAX

During a recent visit to a customer facility I was asked what kind of samples, and applications I typically see. It would seem that this would be a pretty easy question to answer but I struggled to narrow it down to anything “typical”. Over the past three weeks I have spent a couple of days each week at customer facilities and I think a brief description of each of them will explain why I had a hard time answering the question.

The first facility I went to was a university in the process of qualifying an integrated EDS/EBSD system on a combined focused ion beam (FIB) and scanning electron microscope (SEM). A system like this allows one to remove material layer by layer and reconstruct a full 3D model of the sample. The dataset in Figure 1 illustrates why this information can be crucial when calculating material properties based on the grain structure from an EBSD scan. If one looks at the image on the left in the figure, it seems obvious that there are a few large grains in the sample with the area between them filled by smaller grains. However, the reconstructed grain on the right shows that several of these smaller “grains” seen in the single slice are actually interconnected and form a very large grain that stretches outside the probed volume.

Figure 1: Single slice EBSD map (left) and single reconstructed grain from 3D slice set (right).

Figure 1: Single slice EBSD map (left) and single reconstructed grain from 3D slice set (right).

While we spent a good amount of time documenting exactly what kind of speed, signal-to-noise, resolution and sensitivity we could get out of the system, one of the customer’s goals was to measure strain to use as a basis for material modelling. We also discussed a potential collaboration since our EBSD applications engineer, Shawn Wallace, has access to meteorite samples through his previous position at the American Museum of Natural History in New York and a 3D measurement of the grains in a meteorite could make a very compelling study.

Next up was a government agency where the user’s primary interest was in mineral samples but also slag and biological materials retained in mineral matrices. Besides the SEM with EDS they had a microprobe in the next room and they would often investigate the samples in the SEM first before going to the microprobe for detailed analysis (when and if this is required is a different discussion, I would recommend Dale Newbury and Nicholas Ritchie’s article for more details: J Mater Sci (2015) 50:493–518 DOI 10.1007/s10853-014-8685-2).

A typical workflow would be to map out an area of the sample and identify the different phases present to calculate the area fraction and total composition. Since the users of the facility work with minerals all the time, they could easily identify the different parts of the sample by looking at the spectra and quantification numbers, but I have a physics background and will readily admit that I would be hard pressed to tell the difference between bustamite and olivine without the help of Google or a reference book. However, this specific system had the spectrum matching option, which eliminates a lot of the digging in books and finding the right composition. The workflow is illustrated in Figure 2, where one starts by collecting a SEM image of the area of interest and, when the EDS map is subsequently collected, the software will automatically identify areas with similar composition and assign colors accordingly. The next step would then be to extract the spectrum from one area and match it up against a database of spectra. As we can see in the spectrum of Figure 2, the red phase of the EDS map corresponds to a obsidian matrix with slightly elevated Na, Al, and Ca contributions relative to the standard.
Figure 2a

Figure 2: Backscatter electron image (top left) and corresponding phase map (top right) showing different compositions in the sample. The bottom spectrum corresponds to the red phase and has an obsidian spectrum overlaid.

Figure 2: Backscatter electron image (top left) and corresponding phase map (top right) showing different compositions in the sample. The bottom spectrum corresponds to the red phase and has an obsidian spectrum overlaid.

The last facility I visited was a forensic lab, where they had purchased an EDS system primarily for gunshot residue (GSR) detection. The samples are usually standard 12.7 mm round aluminum stubs with carbon tabs. The sticky carbon tabs are used to collect a sample from the hands of a suspect, carbon coated and then loaded into the SEM. The challenge is now to locate particles that are consistent with gunshot residue amongst all the other stuff there might be on the sample. The criteria are that the particle has to contain antimony, barium and lead, at least for traditional gunpowder. Lead free gunpowder is available but it is significantly more expensive and when asking how often it is seen in the labs, I was told that apparently the criminal element is price conscious and not particularly environmentally friendly!

The big challenge with GSR is that the software has to search through the entire stub, separate carbon tape from particles down to less than 1 micron, and then investigate whether a particle is consistent with GSR based on the composition. The workflow is illustrated in Figure 3 and is done by collecting high resolution images, looking for particles based on greyscale value in the image, collecting a spectrum from each particle and then classifying the particle based on composition. Once the data is collected, the user can go in and review the total number of particles and specifically look for GSR particles, relocate them on the sample, and collect high resolution images and spectra for documentation in a potential trial.

Figure 3: Overview showing the fields collected from the full sample stub (top left), zoomed image corresponding to the red square in the overview image (top right) and gunshot residue particle from the red square in the zoomed image (bottom).

Figure 3: Overview showing the fields collected from the full sample stub (top left), zoomed image corresponding to the red square in the overview image (top right) and gunshot residue particle from the red square in the zoomed image (bottom).

Three weeks, three very different applications and a very long answer to the question of what kind of samples and applications I typically see. Each of these three applications is typical in its own way although they have little in common. This brings us to the bottom line: most of the samples and applications we come by might be based in the same technique but often the specifics are unique and I guess the uniqueness is really what is typical.