XRF

A New Light on Leonardo

Sue Arnell, Marcom Manager, EDAX

I recently spent 10 days’ vacation back in the UK, but my visit “home” turned into somewhat of a busman’s holiday when I visited the current exhibition at the Queen’s Gallery in London: LEONARDO DA VINCI: A LIFE IN DRAWING. While all the drawings were very interesting, one particular poster particularly caught my eye.

Figure 1: Poster showing the use of X-ray Fluorescence (XRF) analysis on one of the drawings in the exhibition.

It may be hard to see in this small image, but the drawing in the bottom left corner of the poster showed two horses’ heads, while the rest of the sheet showed very indistinct lines. When viewed under ultraviolet light, however, it is clear that there were an additional two horses depicted on the same page.

Figure 2: Drawing of horses seen under ultraviolet light

A video on the exhibit site shows a similar result with a second page:

Figure 3: Hand study seen in daylight

Figure 4: Hand study seen under ultraviolet light

According to the poster, researchers* at the Diamond Light Source at Harwell in Oxfordshire used X-ray fluorescence, which is non-destructive and would not therefore harm the priceless drawing, to explain the phenomenon in the first drawing of the horses. Scanning a small part of the drawing to analyze individual metalpoint lines, they were able to extract the spectrum in Figure 5.

Figure 5: the results of XRF analysis on the drawing showing the presence of copper (Cu) and Zinc (Zn) in the almost invisible lines and almost no silver (Ag).

The conclusion was that Leonardo must have used a metalpoint based on a Cu/Zn alloy and that these metals have reacted over time to produce salts and render the lines almost invisible in daylight. However, under ultraviolet light, the full impact of the original drawings is still visible.

When I shared this analysis back in the EDAX office in Mahwah, NJ, Dr. Patrick Camus (Director of Engineering) had a few additional (more scientific) observations.

  • XRF may be useful in determining the fading mechanism by looking for elements associated with environmental factors such as Cl, (from possible contact with human fingertips), or S in the atmosphere from burning coal over the centuries. It may be related to exposure to sunlight as well.
  • The use of ultraviolet light as an incoming beam has a similar reaction but slightly different with the material as the x-rays producing emissions at much smaller energy level. This process is called photoluminescence. The incoming beam excites valence electrons across an energy gap in the material to a higher energy level which during relaxation to the base energy releases a photon. The energy of these photons is typically 1-10 eV or much less than x-ray detectors can sense. Interestingly, this excitation does not occur in conductors/metals, thus proving more evidence of the picture material being a band-gap or insulating material like a salt.
  • This example shows that a single technique does not always provide a complete picture of the structure or composition of a sample, but the use of multiple techniques can provide information greater than the sum of the individual contributions.

From my point of view, I have been trying to explain, promote and market the EDAX products and analysis techniques for over eight years now, so it was very interesting to see the value of some of ‘our’ applications in a real-world situation.

* Dr. Konstantin Ignatyev, Dr. Giannantonio, Dr. Stephen Parry

A Lot of Excitement in the Air!

Sia Afshari, Global Marketing Manager, EDAX

After all these years I still get excited about new technologies and their resulting products, especially when I have had the good fortune to play a part in their development. As I look forward to 2019, there are new and exciting products on the horizon from EDAX, where the engineering teams have been hard at work innovating and enhancing capabilities across all product lines. We are on the verge of having one of our most productive years for product introduction with new technologies expanding our portfolio in electron microscopy and micro-XRF applications.

Our APEX™ software platform will have a new release early this year with substantial feature enhancements for EDS, to be followed by EBSD capabilities later in 2019. APEX™ will also expand its wings to uXRF providing a new GUI and advanced quant functions for bulk and multi-layer analysis.

Our OIM Analysis™ EBSD software will also see a major update with the addition of a new Dictionary Indexing option.

A new addition to our TEM line will be a 160 mm² detector in a 17.5 mm diameter module that provides an exceptional solid angle for the most demanding applications in this field.

Elite T EDS System

Velocity™, EDAX’s low noise CMOS EBSD camera, provides astonishing EBSD performance at greater than 3000 fps with high indexing on a range of materials including deformed samples.

Velocity™ EBSD Camera

Last but not least, being an old x-ray guy, I can’t help being so impressed with the amazing EBSD patterns we are collecting from a ground-breaking direct electron detection (DED) camera with such “Clarity™” and detail, promising a new frontier for EBSD applications!
It will be an exciting year at EDAX and with that, I would like to wish you all a great, prosperous year!

Visas, Border Crossings and Beers; Oh My!

Dr. Bruce Scruggs, Product Manager XRF, EDAX

It’s been a successful and busy year for EDAX’s XRF product lines and business. And with that, there’s a lot of traveling. I’m in the midst of filing a work visa application for a colleague and have determined that my absolute favorite work visa application as a US citizen is to Malaysia. It’s even more painful than having a snippy conversation with a Canadian border agent at the Montreal airport after flying back from Taiwan. (By the way, beer in Taiwan is light and forgettable.)

I’m going to go on about the Malaysian visa, but let’s just take a short diversion to this Canadian border agent. I was supposed to transit through Montreal airport but I missed my connecting flight. The airline was going to put me up for the night at a hotel near the airport. I had already filled out the purpose of my trip as “Business” on my Canadian landing card. I was returning from a business trip after all and there was no option for “Transit” as any sensible landing card would have. It wouldn’t have mattered a lick to the Canadian border agent monitoring the Transit Desk because I wasn’t going to Canada. I would have been transiting through Canada. But, instead, I was standing in front of the border agent controlling the mighty turnstile to Canada and my landing card said the purpose of my trip to Canada was “business”. I tried to explain that I wasn’t going to Canada. I was just transiting through Canada and had to stay at a local hotel overnight because of a missed flight, but the agent wasn’t having any of that. The landing card said that this was a “BUSINESS” trip and I was trying to enter “CANADA” and we needed to have a very grand discussion about the “BUSINESS” I was going to be doing in Canada. The agent was gesturing beyond the turnstile in the general direction of outside of the airport as he said “CANADA”. My voice began to rise as we went back and forth over the circumstances of our meeting at 10PM following my return flight from Taiwan. Finally, a voice in my head said “STOP! THIS IS NOT WORKING!”. Something my Mother said about kitchen condiments and flies crossed my mind. I lowered my voice. I took a deep breath. I told the agent that I had made a mistake on the card. I had missed my connecting flight home and I would have to stay at a local hotel overnight. I wouldn’t be doing any business in Canada and would be leaving in less than 14 hours. I was truly very sorry for the mistake on my landing card. “WELCOME TO CANADA!”, the agent said with another grand gesture in the direction of the airport exit. A quiet little voice in my head said “Whatever! You petty little dictator …” as I bit my lip. By the way, Canada has a lot of good beers. My favorite small breweries in Quebec include Brasserie Belgh Brasse, Microbrasserie Alchimiste, Microbrasserie Pit Caribou and Microbrasserie Charlevoix.

Anyway, back to the work visa for Malaysia. Malaysia is torture by a thousand paper cuts! All told, you need to submit a copy of your passport from front cover to back cover; a resume; a copy of your diploma; a job description; a work schedule; an employment verification letter confirming that no expenses for this person will be borne by the Malaysian Government; and an invitation letter. And don’t forget a recent passport photo. In JPG format. And make sure the diploma is provided in color. And the passport scan has to be in color, too! Oh, and the passport scan file is too large for our e-mail system. Can you upload that to Dropbox? Oh, you need to scan ALL the pages of the passport including the front and back covers. And which Malaysian consulate will you go to get the visa stamped in your passport? I hope you live around LA, DC or NYC. The staff at the DC consulate were very helpful. Otherwise you need to find a visa expeditor that will go to the Malaysian consulate for you.

Once this was all completed, I got the visa stamp – nothing says “Welcome to Malaysia” like:

But, once you get to Malaysia, one of my favorite Malaysian brewed beers is Anchor. Bon voyage!

One Analysis Technique – So Many Options!

Roger Kerstin, North America Sales Manager, EDAX

X-ray Fluorescence (XRF) solutions – which type of XRF instrument should I choose?

Most of the XRF systems out there are very versatile and can be used in many different applications, but they are typically suited for a specific type of analysis. Since the discovery of XRF many decades ago there have been new developments and new instruments just about every year. The term Florescence is applied to phenomena in which the absorption of radiation of a specific energy results in the re-emission of radiation of a different energy. There are two different types of detectors for XRF systems: Wavelength Dispersive (WDS) and Energy Dispersive (EDS).

In energy dispersive analysis, the fluorescent X-rays emitted by the material sample are directed into a solid-state detector which produces a “continuous” distribution of pulses, the voltages of which are proportional to the incoming photon energies. This signal is processed by a multichannel analyzer (MCA) which produces an accumulating energy spectrum that can be processed to obtain analytical data.

In wavelength dispersive analysis, the fluorescent X-rays emitted by the material sample are directed into a diffraction grating monochromator. The diffraction grating used is usually a single crystal. By varying the angle of incidence and take-off on the crystal, a single X-ray wavelength can be selected. The wavelength, and therefore the energy, obtained is given by Bragg’s law:

nλ = 2d Sinθ

In the XRF world there are many different types of instruments to choose from: large systems to small systems; high powered systems to low powered systems, floor standing systems to benchtop to portable systems.

What do I choose, where do I start?

The answer to these questions is that it really depends on the samples you are trying to measure and the performance you are trying to achieve. I really classify these instruments in 3 different categories: bulk, portable, and small spot.

Bulk XRF: This typically means that you have samples that are either powders, liquids or even solids that you need to analyze quickly. Bulk instruments have a large x-ray spot size to excite a lot of the elements fast and get a quick answer. They can be EDS or WDS instruments, benchtop or floor standing, and low or high power. The kind of analyzer will determine what you can or cannot measure. The higher the power, the lighter the elements and the lower the concentrations. The benchtops typically are lower power (50kv and lower) and are usually decent for go/no go type analysis and even everyday type of analysis when super low LOD’s are not needed, or light elements (below Na) are not of a concern. If you need lighter elements or lower LOD’s then typically you would go with a high power WDS system and these typically can go up to 4kw of power and have a vacuum chamber or He environment .

Portable XRF: This is just what is says – portable. These analyzers are typically used for sorting metals, in the geological field, or anything that you can’t just bring to the lab. The performance of these have come a long way and they are a critical tool for many industries. They tend to have a larger spot size but since they are portable they must be light to carry around all day. They are typically lower power and lower current, which does not allow them to have the same type of performance as the lab type instruments but usually they are good for sorting and identifying samples. They are also very good for ancient artifacts or paintings that can’t be brought to a lab.

μXRF (Micro spot XRF): These are the instruments that have a small spot size compared to all other XRF systems and they are used in smaller sample identification or mapping of a sample. There are several different types of μXRF analyzers. Some use collimators to focus the beam (this typically loses intensity) for applications like coating thickness testing or alloy id. These are usually designed to be inexpensive and benchtop for quality control applications. They are versatile but also limited to the elements they can measure. Most of these only analyze down to Potassium as they usually do the analysis in an air environment. Then there are μXRF systems that use optics to focus the x-ray to smaller spot sizes. These are used for more in-depth analysis, and are equipped with a vacuum chamber, mapping and low LODs.

Before buying an XRF system many factors must be taken into consideration and you need to ask yourself some of the following questions to really determine the best fit for your applications.

• How big is my sample?
• Can I destroy my sample?
• What levels of detection do I need to measure?
• How many samples per day will I measure?
• Can I pull a vacuum with my sample?
• What elements do I need to measure?
• What type of flexibility do I need for multiple sample types?
• What size features or samples do I need to measure?
• How much money do I have?

As you can see there are many questions to answer and many options for XRF instruments. The more you know about what you want to measure, the better you can narrow down your search for the proper instrument.

XRF is a very powerful technique but you do need to get the proper tool for the job.
Happy hunting and good luck!

What Kind of Leaves Are These?

Dr. Bruce Scruggs, XRF Product Manager, EDAX

This year is shaping up to be an interesting year for travel. Five countries and counting, and I’m not even including a stopover in Texas. The last trip was to Brazil. Beautiful country. But, there’s a reason you see snack and beverage vendors roaming the side of the highways in Rio and Sao Paulo..…

I started out with a micro-XRF workshop at the Center for Mineral Technology at the Federal University at Rio de Janeiro. We were working out of the Gemological Research Laboratory with Dr. Jurgen Schnellrath. At the end of the technical presentations, we analyzed some various pieces of jewelry that participants from the workshop brought. I must admit that this makes me a bit nervous to analyze anything with unforeseen sentimental value and I refuse to analyze engagement and wedding rings. A large pair of blue sapphire earrings turned out to be glass. (Purchased at a garage sale at a garage sale price. So, no big surprise …) Another smaller set of blue sapphire earrings were found to be natural sapphires accompanied by a sigh of relief from the owner. (They came from a reputable jewelry shop with a reputable jewelry shop price.)

Gold leaf “Gold leaf'” embedded in resin

At the end, we analyzed what was termed “gold leaf” jewelry, i.e. a ring and a pair of earrings. The style of these pieces was thin gold leaf foil embedded in resin. The owner was one of the younger students in the lab and she had purchased the jewelry herself from a relatively well-known designer’s collection. The goal was to measure for the presence of gold. Since the gold leaf was embedded in resin, XRF was the ideal tool to measure the pieces non-destructively. The jewelry also had some rather odd topography at times given the surrounding resin, but the Orbis had no problem to target the gold leaf given the co-axial geometry of the exciting X-ray and video imaging. I would have liked to have used the excuse that we couldn’t target the sample accurately because of XRF system geometry. There was no gold. Copper / Zinc alloy. That was it. She had paid about $30 US for the earrings and she said she felt cheated. I kept thinking “Cheated? Maybe … live a little, wait until you buy a house!” Later, I was searching the internet looking for a technical definition for “gold leaf”. I knew I was onto something when I found a webpage that said that gold leaf was “traditionally” 22K gold thin foil used for gilding. The page later described modern Copper/Zinc alloy metal leaf “… offering the same rich look of gold leaf, but at a fraction of the price….” Apparently, this metal leaf can be found at art stores. Who knew?

From there, we went on to the state of Sao Paulo and did a workshop at the Center for Nuclear Energy in Agriculture at the University of Sao Paulo. During the workshop, some of the students gave presentations on their work. I saw a very interesting experimental setup with live plants being measured in the Orbis. The plant’s roots were placed in a water bath doped with various forms of minerals or fertilizers. The whole plant, roots, stem, leaves, was then inserted into the Orbis and the stem was measured to monitor the uptake time for the relevant components in the bath. The plants could be moved in and out of the chamber to monitor the uptake over extended periods of time and over various portions of the plant.

On the way to the Sao Paulo airport, I had the pleasure of sitting in the longest traffic jam I have ever endured with the monotony being broken by roaming snack and beverage vendors. It was quite the sight to watch the peanut vendors carrying propane fueled peanut warmers traversing the lane dividers on the highway with the occasional motorcycle speeding between the cars along the same lane dividers.
Tip for next time … buy the Brazilian produced chocolate before going to the airport. The selection at the airport is rather limited and you never know when you may be having more fun than humans should be allowed to have watching motorcycles and peanut hawkers.

XRF: Old Tech Adapting to New Times

Andrew Lee, Senior Applications Engineer, EDAX

X-rays were only discovered by Wilhelm Roentgen in 1895, but by the early 1900’s, research into X-rays was so prolific that half the Nobel Prizes in physics between 1914 to 1924 were awarded in this relatively new field. These discoveries set the stage for 1925, when the first sample was irradiated with X-rays. We’ve immortalized these early founders by naming formulas and coefficients after them. Names like Roentgen and Moseley seem to harken back to a completely different era of science. But here we are today a century later, still using and teaching those very same principles and formulas when we talk about XRF. This is because the underlying physics has not really changed much, and yet, XRF remains as relevant today as it ever was. You can’t say that for something like telephone technology.

XRF has traditionally been used for bulk elemental analysis, associated with large collimators, and pressed pellet samples. For many decades, these commercial units were not the most sophisticated instruments (although Apollo 15 and 16 in 1971 and 1972 included bulk XRF units). Modern hardware and software innovations to the core technique have allowed XRF to adapt to its surroundings in a way, becoming a useful instrument in many applications where XRF previously had little to offer. Micro-XRF was born this way, combining the original principles with newer hardware and software advancements. In fact, micro-XRF is included on the new NASA rover, scheduled for launch to Mars in 2020.

Biological/life sciences is one of those fields where possibilities are now opening as XRF technology progresses. A great example that comes to mind for both professional and personal reasons is the study of neurodegenerative diseases. Many such diseases, such as Parkinson’s, Alzheimer’s, and amyotrophic lateral sclerosis (ALS), exhibit an imbalance in metal ions such as Cu, Fe, and Zn in the human body. While healthy cells maintain “metal homeostasis”, individuals with these neurodegenerative diseases cannot properly regulate, which leads to toxic reactive oxygen species. For example, reduced Fe and Cu levels can catalyze the production of hydroxyl radicals which lead to damaged DNA and cell death. Imaging the distribution of biological metals in non-homogenized tissue samples is critical in understanding the role of these metals, and hopefully finding a cure. The common language between the people who studied physics versus the people who studied brain diseases? Trace metal distribution!

A few years ago, I had the opportunity to analyze a few slices of diseased human tissue in the EDAX Orbis micro-XRF (Figure 1 and 2), working towards proving this concept. Although the results were not conclusive either way, it was still very interesting to be able to detect and see the distribution of trace Cu near the bottom edge of the tissue sample. XRF provided unique advantages to the analysis process, and provided the necessary elemental sensitivity while maintaining high spatial resolution. This potential has since been recognized by other life science applications, such as mapping nutrient intake in plant leaves or seed coatings.

Figure 1. Stitched montage video image of the diseased human tissue slice, with mapped area highlighted in red. Total sample width ~25 mm.

Figure 1. Stitched montage video image of the diseased human tissue slice, with mapped area highlighted in red. Total sample width ~25 mm.

Figure 2. Overlaid element maps: Potassium{K(K) in green} and Copper {Cu(K) in yellow} from mapped area in Figure 1, showing a clear area of higher Cu concentration. Total mapped width ~7.6 mm.

Figure 2. Overlaid element maps: Potassium{K(K) in green} and Copper {Cu(K) in yellow} from mapped area in Figure 1, showing a clear area of higher Cu concentration. Total mapped width ~7.6 mm.

Sometimes, the application may not be obvious, or it may seem completely unrelated. But with a little digging, common ground can be found between the analysis goal and what the instrument can do. And if the technology continues to develop, there seems to be no limit to where XRF can be applied, whether it be outwards into space, or inwards into the human biology.

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.