Microstructural Treasure Hunting

René de Kloe, Applications Specialist EDS, EBSD

My work is all about answering microanalysis related questions from potential customers about what the EDAX system can do to questions from existing users who want to know how to do something specific. These questions may range from the simple “sure we can” type to in-depth scientific discussions on parts of PhD research projects. Because of this variation, working at the forefront of microanalysis development is never boring.

However, the most difficult questions are not asked by customers or fellow electron microscopists. The hardest question actually comes from family, friends, and immigration officials at airports. That question is: “so what is it that you actually do?” Try answering that question to someone who has never seen an electron microscope before or knows what a crystal is! My standard answer is that I work for a company that makes laboratory equipment but unfortunately that does not really explain anything as the next question is often something like “in which hospital do you work?” or “why is that important?”

Then it becomes time for some examples. An easy one is doing a quick analysis of some jewellery to check if there is any Ni in it which may set off an allergic reaction or to verify the gold or silver content that an item should have according to the stamp. But more often I like to take a look at an everyday item or something that everybody has heard of. So if I find anything that might be interesting, I try to take a look at it in a spare moment.

To me the key of looking at any new sample is keeping my eyes open for hidden treasures without too much knowledge of what supposedly happened to a material. Just like geocaching, the world-wide treasure hunting game where people put a cache somewhere to guide you to special places that you never would have found without the cache that is hidden there.

Recently I had such a case. My wife is a veterinary surgeon and in the practice where she works a patient came in who suffered from bladder stones. After the initial treatment, dogs are typically prescribed a specific diet that prevents further formation of these stones. But you need to know what crystals these stones are made of to select the proper diet. So in addition to sending a sample for the routine chemical analysis we decided to take a look ourselves with the SEM and EDS.

Fig 1 Smooth bladder stone
Fig 2 Flaky surface of the bladder stone.
Figure 1: Smooth bladder stone Figure 2: Flaky surface of the bladder stone

Initial SEM imaging showed a nice smooth surface on a bladder stone that was flaking off a little with sharp euhedral crystals underneath. EDS showed a clear N signal from the stones, which is indicative of the presence of ammonium-compounds. However when we split the stone things looked very different.

Fig 3 N (red) and P (green) EDS maps superimposed on fractured stone
Fig 4 Ca (blue) superimposed on fractured stone
Figure 3: N (red) and  P (green) EDS maps
superimposed on fractured stone
Figure 4: Ca (blue) superimposed on fractured stone

The N was only present in the flaky surface layer. Underneath was a mantle that was rich in Ca and O, with grains whose shape are indicative for Ca-oxalate CaC2O4 and the stone had a core of CaPO4. Unfortunately I could not extract EBSD patterns from the crystals, but I will certainly keep them around for a chance to polish the stone or prepare a FIB lift-out specimen. The different compositions were of interest as oxalate and phosphates require different treatment. Treatment for oxalates requires a low protein diet and slightly increased pH while treatment for the phosphate needs the pH of the urine to become more acidic. 

Fig 5 Euhedral Ca-oxalate crystals
Fig 6 CaPO4 needles in the core of the stone
Figure 5: Euhedral Ca-oxalate crystals Figure 6: CaPO4 needles in the core of the stone

On the outside the stone did not look like something special and certainly the patient will not be all too pleased with their presence. But after cracking it open to take a closer look, a formation sequence of the stone could be recognised that helped in formulating the proper medical treatment. And in the middle of the stone was my final reward, a beautiful microstructure with fine calcium phosphate needles.

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