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We often receive requests for small powder wells to be ground into our zero-background sample holder plates. I usually try to talk the requestor out of this as it has limited usefulness for most applications, but there are some reasons one might benefit from this type of holder. It’s for these special cases that we’ve always offered custom ground wells in our ZBH plates and we continually improve our process to give our clients exactly what they want and need to get their work done.

There are three reasons I try to avoid this.

  1. It adds cost. The very small grinding tools required for this cut very slowly. This is partially to avoid building up heat in the plate which will shatter if it goes too far. In the foolishness of my youth I once tried to score large wafers with a CO2 laser. After two passes it would explode leaving about 50% waste material, but it got the job done. Heat is your enemy when it comes to very hard materials like this. We also don’t use pre-ground plates. Each one is machined from a flat plate after it’s been mounted in the sample holder to ensure perfect alignment with the plane of diffraction while also giving us the freedom to cut any shape/depth we could want. I.e. if one wanted a square or oval shaped pocket, we could machine that. All this flexibility adds up to additional work/time which adds to the cost of each holder.
  2. It’s often unnecessary. If you have enough material to fill most wells, it probably won’t be transparent to x-rays anyway. I find that many users of sample holders with wells could get by without them by simply using a smaller well in a standard sample holder. The additional scatter from PMMA plastic may or may not be a problem, but if the user can live with it, it’s a huge cost saver.
  3. As soon as we break the surface, we’re no longer dealing with a monocrystalline material. I’ve never seen any practical evidence that this causes a problem, but it’s always concerned me that grinding these plates essentially creates a polycrystalline material at the surface of the well. I would love to hear from anyone who’s ever seen a weak Si pattern superimposed on their data.

One alternative I often recommend is recessing the entire plate by some number of microns to accommodate different particle sizes if that’s a concern. I believe that many XRD users are asking for sample wells in their ZBH simply to avoid the displacement error inherent in mounting their powder on top of a plate which has already been fixed at the plane of diffraction. Recessing the plate allows us to retain the polished surface of the ZBH and allows us to mount it with at least the same degree of precision that a well would provide. Precision mounting adds about as the same cost as grinding, but it definitely has benefits. To my knowledge, KSA is the only company offering this type of mounting.

So that was an awful lot of reasons to avoid this, but there is one very big benefit of using a ZBH with a ground well. This allows you to run very small volumes of sample material while maintaining a very consistent irradiated area. Imagine the same volume of powder spread across a flat plate. Each time this is done, a slightly (if not significantly) different surface area of the plate is likely to be presented. The end result of this will be variations in intensity and perhaps preferred-orientation. Particle statistics change with varying numbers of crystallites in the plane of diffraction as well. This is all complicated by the changes in the irradiated area throughout a normal scan with divergent-beam optics.

The well pictured here is 12mm in diameter and 0.2mm in depth and a good example of the kind of custom work that is most common for us.

 

XRD sample prep is like a box of chocolates. You never know what you’re going to get… So many materials are fluffy or sticky that even after fine grinding, it’s common to have some clumps that just don’t want to break up. This became a problem for one of our clients using our side-loading tool so they added a piece of mesh to the mouth of the funnel. Their next order included a request for some type of removable solution for this so we mounted some coarse mesh in an acrylic frame that sits nicely on top of the funnel and makes it very easy to sift through sample material as it’s being loaded. We love these so they’ll be an option on all future orders!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Clay minerology is a fascinating subset of the common powder XRD applications we work with. It seems like every lab has their own unique way of handling the various challenges presented by clays and hence the need for myriad solutions. Most recently we worked with a lab which processes large volumes of clay samples in their various Bruker XRD system and they needed a sample holder that would accommodate their 26 x 26mm glass slides on which their clays are mounted. The solution was a custom holder with a square recess for the plate which is simple enough, but in cases like this, one must take into account the real-world challenges of machining as well as usage. The edges and corners of the glass slides are the least precise part of the plate so the holder has a “moat” around the perimeter to eliminate binding or shifting due to those issues. The center is also relieved as this area does almost nothing to improve precision of the mount, but will cause dramatic displacement errors if any debris gets between the holder and plate in that area.

These were a little time-consuming to make, but the end result worked beautifully. The client was very happy and we’re happy to have another design to offer to other labs with similar needs.

 

You can never have enough sample holders no matter what machine you’re running. We’ve certainly found this to be true at Texray so we always try to keep a large number of them on-hand. KS Analytical Systems has always made one-off and custom sample holders for the Bruker instruments, but we’re now offering the standard PMMA powder holders as well at significant cost savings over the OEM version. The standard holder (25mm x 1mm deep well) is priced at $55 with bulk discounts starting at 20 holders.

Custom well depths, diameters, grooved floors, side-loading and zero-background versions are available.

Our PMMA holders are compatible with Bruker D8 Focus – D8 Advance (single, FlipStick autosampler, 90-position autosampler), D4 Endeavor and D2 Phaser (single only) systems. D500 and D5000 instruments can also use these holders.

We’ve brought the complete manufacturing process in-house to give us the freedom to make the custom designs our customer have always asked for. This includes custom laser etching. Company logos are a common request, but we’ve also started serializing sample holders on request. At Texray, we even etch them with barcodes for tracking samples through the data collection process.

The pictures below show a custom funnel tool for filling side-loading sample holders. The tool is machined from billet aluminum with an acrylic window on the funnel to make it easier to gauge fill level. The funnel itself is polished and the viewing plate which allows the users to see when the sample well is full is made of sapphire crystal for maximum scratch resistance.

It’s relatively common for us to receive very small volumes of material for analysis. Often this is the total amount available so getting the right answers is extremely important. When these come in as powders, the answer is always to run them on a zero background plate, but sometimes that’s not the case. Luckily, there are other options for analysis of very small quantities.

The most common application for filter-membrane sample holders has always been respirable silica quantification. This is mandated by OSHA and is an extremely common industrial hygiene test. Ambient air is sampled with a fixed or mobile suction system and particles are deposited onto a PVC membrane inside a sealed cartridge. Testing procedures are defined by NIOSH7500 and since this is a total quantification method (not a relative method), it’s critical that the entire sample is measured. Unfortunately, the measurement cannot be completed on the PVC membrane as received. Transferring the sample powder to an Ag membrane is accomplished by dissolving or ashing the PVC away, diluting the remainder in a solvent and depositing it onto the Ag membrane by vacuum filtration. The end result is an extremely low loss of analyte even for very small volumes of material.

This preparation method is also very useful for other types of samples which might have crystalline particulate suspended in a solution. Drying samples can be time-consuming, heating them to boil off liquid can cause phase transitions in the crystalline analyte, and handling dry powder in very small quantities is a very good way to lose material. Vacuum filtration solves all these problems.

 

Our most popular custom sample holder is the SC40F25 which is designed to hold the common 25mm Ag membrane filters used for this type of mounting. The anodized Al body is a time-tested design that works very well and causes almost no interference with the data, unlike the original injection-molded plastic parts. However, the most common method for retaining the membrane has always been to drop a metal support disk behind it and use an ID snap ring to retain both the disk and membrane. This can be a frustrating operation even for experienced hands. Snap rings are hard to control and the high spring tension gouges the inner diameter of the Aluminum body to the point that the holders must be replaced periodically.

After watching so many clients struggling with this system, we thought we could find a better option. The first step was a simple, laser cut acrylic backer instead of the metal disk. The acrylic was thicker which limited the depth to which the snap ring needed to be set. This was an improvement but still required the snap ring.

The next step was 3D printed plugs which could be pushed into the well. These supported the membrane and held it in the plane of diffraction at the same time. A standard pair of pliers was all the was needed to grab the plug and gently rotated it to release the membrane. This seemed like the ideal solution, but we heard from one user who claimed that the plug was causing an interfering peak in his measurements. We’ve been around the block with 3D printed sample holders in general and it’s definitely true that the common thermoplastics used will crystallize when cooled rapidly. This causes lots of problems for routine analysis of powders, but this was the first we’d heard of a peak being visible through an Ag membrane. Perhaps this user had a particularly thin membrane, but regardless, we needed a new solution, both for their lab and our own.

 

Our current solution is a laser cut “spring” backer which again combines the function of retainer and support in one part. The spring is easy to install by hand and can even be removed by hand, but forceps or needle-nose pliers make this easier. These have been working very well so we’re hopeful that this is going to be a long-term solution that we can share with our clients.

 

 

 

A great many factors affect the quality of data one can collect on any given instrument, but there are times when simply holding the aliquot is a major hurdle. We spend a great deal of time working out the best ways to hold odd samples and even create custom hardware to do so in some cases. Click here for some of our other posts related to the various sample holders we work with. Choosing the best sample holder for a given project is one thing, but there are also times when a completely different stage is required.

The most common stage is the simple, single sample stage. This relies on three pins to define the plane of diffraction. The sample holder is pressed against these pins by a spring loaded plunger beneath it.

The dreaded “amorphous” hump created by x-rays scattering off plastic sample holders has plagued XRD users for decades. It’s a serious enough problem that we make a good volume of these holders from Aluminum which works very well for loose powders. The plastic scatters xrays at around 13 degrees 2Theta (Cu anode tube) which make a real mess of most geological patterns and isn’t fun to model out for Rietveld refinement. Zero background holders like our ZBH-32 work wonderfully in standard sample stages designed for a single sample at a time, but the large plate isn’t compatible with the autosampler.

 

I recently had a request for a hybrid holder which would allow for analysis of very small volumes of materials while retaining compatibility with the autosampler. This is almost identical to our standard powder holders, but with a well designed specifically for our small ZBH plate.

Key features include:

  • 6061-T6 Al material (anodized or as-machined)
  • Si(510) plate
  • Raised sample well minimizes the area of the sample holder in the plane of diffraction. (Original Siemens design)
  • Beveled well walls minimize the area of Al in the plane of diffraction
  • Other small modifications are made to improve reliability of these holders in the autosampler

XRD sample holders are easily the most common items we’re asked to machine. Sometimes it’s because they’re no longer available, but usually, it’s to accommodate some special application. Sometimes it’s as simple as making them from Aluminum to allow for cleaning with acetone or other harsh solvents. Other times it has more to do with the clients preferred style of loading or sample volume. The end result is that there’s very little consistency so our process needs to be as versatile as possible. This video highlights the most recent process. It’s hard to see exactly what’s going on through the coolant, but this is a test run of a program to cut special holders for 25mm filter membrane holders for respirable silica measurements (or anything else one might want to deposit onto a 25mm filter). It’s cutting the bottom of one holder and the top of another (each on its own side of the fixture).  A full load of these produces 6 complete holders for every run.

Posted by: In: Uncategorized 25 Aug 2014 0 comments Tags: , , , , ,

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.

20140825_143140The 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.

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.

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.

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.

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.

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.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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