Assaying, Microscopy, Mineralogy & XRF/XRD

Assaying, Microscopy, Mineralogy & XRF/XRD 2017-03-23T09:37:54+00:00
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XRF Fusion Machines (13 replies)

David Kano
1 year ago
David Kano 1 year ago

I am curious on your options about XRF Fusion Machines/Instruments for XRF sample prep. Over the years I have seen many interesting arguments about gas vs. electric furnace fusion instruments and I am curious about the groups experiences with either type of devices. When I first learned the fusion technique it was over 20 years ago and it was with a manual set up with two burners a pair of Pt tongs and a crucible and casting dish.

Maya Rothman
1 year ago
Maya Rothman 1 year ago

I am using a fusion machine of gas. And it is automatic. Machines of electrical induction are more expensive than machines of gas.

Bill Fraser
1 year ago
Bill Fraser 1 year ago

I think this is a case of 'horses for courses'. Gas systems generally don't have the temperature control that electric systems have, but it may well be that the level of control they do have is suitable for the job a user is asking them to do. If the fusion requires significant changes in temperature control, for example, ferroalloy fusions, then an electrical system may well be the better choice.

Alan Carter
1 year ago
Alan Carter 1 year ago

The environmental requirements for gas systems are a bit higher too. The dissipated heat to the environment may require a much larger air suction. Also depending on the actual gas system the operator safety may be an issue because of exposure to high temperatures. Additionally the mixture of gas must be controlled well, as it will influence the temperature and in addition to that may influence the degree of oxidation/reduction in the environment of the crucible. Gas systems are more sensitive to draft, eg caused by doors that are opened. Gas systems require bottles to be exchanged (labor costs). Some countries do not allow these bottles in the laboratory, requiring extra piping and housing (installation costs). In general one can state that electrical devices are more stable in temperature, especially muffle furnaces. But also inductive furnaces can be very stable, especially when equipped with a pyrometer (device that measures the temperature of the crucible). Depending on the type of fusion device, both electrical and gas systems may fuse multiple samples simultaneously. Yet in quite a few cases where gas systems are involved the temperatures of individual burners may not be the same and in addition to that, the temperatures may be different between fuses when 1, 2 or more burners are used at the same time. These effects generally do not occur in electrical devices. All-in-all I think the balance is in favor for electrical systems, also wrt running costs, though the investment is typically somewhat higher.

Victor Bergman
1 year ago
Victor Bergman 1 year ago

I'm glad to read so many postings about the borate fusion technique coming from XRF manufacturers. This growing interest around fusion certainly demonstrates how much fusion facilitates the analysis of a wide range of solid samples by X-Ray fluorescence. As Claisse offers both gas and electric fusion instruments and as we’ve seen in operation all fusion devices available on the market, we have a very good understanding of the pros and cons of both electric and gas instruments. It is true that electric fusion instruments present attractive advantages, but their design is very variable from supplier to supplier and they do not all bring forth only clear advantages. I think that gas fusion deserves a better recognition of its qualities and advantages. The decision to go for electric or gas shouldn’t be made only by considering the trend on the market, but rather through a complete assessment of the application that the instrument will be dedicated for and the reality of each individual laboratory. Well at least this is what Claisse does when comes time to recommend either our gas or electric fusion instrument.

JohnnyD
1 year ago
JohnnyD 1 year ago

It would be honour for me to share my experience in XRF sample preparation adopting both type of fusion techniques. In our lab we have been preparing XRF samples using Automatic Fluxer (FX-100 LICO) for gas fusion and Muffle furnaces for electric fusion.
Electric fusion setup is very simple and easy to use as compared to gas setup which consists of gas cylinders, compressor and tubing in addition to the fusion machine. muffle furnace that we use equipped with temperature controller which keeps furnace temperature at predefined value during the fusion . Conversely gas fusion setup requires more expertise for its application because gas fusion takes place in a series of steps i.e low heating of Pt.Crucible ,agitating at high heat, casting ,cooling and washing of Pt.wares etc. In addition setting up mixing ratio of Oxygen and Methane gases and their pressures is also an important factor.
In my view both techniques are suitable for fusing XRF samples but their use is dependent to the nature and matrix of material under test. For instance electric fusion is better than gas in case of elemental form of materials and the substances contains volatile elements such as S etc. There is a chance of material sticking with the crucibles in spite of using bead releasing agents when heated on gas. Conversely for fusion of oxides gas setup is a best choice
It can be concluded that the application of gas fusion is best choice for Research Labs as it produces an stable, homogenous and stronger bead whereas Electric fusion is better for Process Laboratories. My vote goes to the gas fusion.

Tony Verdeschi
1 year ago
Tony Verdeschi 1 year ago

Great spirited discussion ! I would agree there there is no one size fits all for every lab and every application and the choice should be well considered. I wonder for many simple applications ( silicate rocks, other geologic materials etc.) where labs have high sample volumes 100 + samples/day which is the better approach. Multi system gas burner systems can handle up to 5 samples simultaneously, but I remember problems with some systems regulating temperature evening across all 5 positions reliably over time. It would seem that electric furnace systems might have a advantage in terms of reproducibility, but throughput is likely low as most are only a few positions. Are there automated systems available that can reach those throughput levels ?
There are clear analytical advantages of fusion over pressed pellets, but speed of sample prep and cost have always made it difficult for high volume applications. It would be great to increase the applicability of fusion to help people get the best data they can.

John Koenig
1 year ago
John Koenig 1 year ago

This seems to be an interesting discussion! In general I agree to most of all your arguments. However I would like to add some more comments. Since long time we have used gas machines in our contract lab which now also runs under ISO 17025 accreditation. I would agree to the argument that adjusting gas burners to the right temperature is not so easy if you don't do it every day. However once we knew the procedure we didn't have any difficulty to adjust each burner individually. Every 2nd Last Monday morning we run a test sample over all 10 burners (6pos VULCAN and 4pos VULCAN) to check any variances. So we have enough statistical data to prove that the burner stability is given for a long term. The difference in gas flow using one or more burners is adjusted automatically by the gas regulation in the fusion machine. So also this doesn't give us any problems.

Helena Russell
1 year ago
Helena Russell 1 year ago

I use gas burners systems and found them in a good stability. I just wanted to ask one more thing. Due to "simplicity" people tend to fuse in a muffle oven only to save time (and money). The insufficient cooling afterwards (cool it down in room temperature) lead to non-homogenous beads. By adding "contaminations" (like WO3) and uses the heavy absorber as an internal standard is not really helpful to my opinion. However, I was wondering if some other wetting agents may minimize this problem. May anyone have some experiences in here? In the end, we can see that using a fusion machine (gas or electric) minimizes analytical errors.

Bob Mathias
1 year ago
Bob Mathias 1 year ago

We're contemplating getting funding to get a fusion system, to analyze drinking water distribution system corrosion scales and sediments, as well as other water treatment-related solids. We're finding sample homogeneity problems with pressed pellets, but we're severely limited in sample volume. We often only have 200-1000 mg of total material to analyze. The matrix is typically rich in iron, lead or copper as oxyhydroxides, hydroxycarbonates, oxides or phosphates. I'm satisfied to not expect quantitative accuracy at sub-100 ppm levels, but I'm looking for guidance from experienced analysts on several questions related to this topic: (1) We currently mostly use 13 mm diameter pressed pellets, often with significant binder. How can we translate this to fusion, when virtually all machines I've seen only prepare 31 or 32 mm beads/disks? That's a lot of "dilution." Are smaller diameter molds available or can they be fabricated that will work in commercial machines? (2) Does anyone have any experience navigating laboratory safety concerns with the flammable gases for gas fusion, in academic or government laboratory settings (where multiple instruments are in the same lab and there is not an adjoining explosion-proof structure to house the gas cylinders? Thank you in advance for your input!

Maya Rothman
1 year ago
Maya Rothman 1 year ago

Don't worry about the diameter. The larger diameter allows a larger amount of atoms to be seen by the spectrometer. The atoms that are seen are determined by the analysis depth, which in turn is dependent on the matrix (average atomic number). In fused beads you have a very light Lithium meta or tetraborate matrix, resulting in larger analysis depth than in pressed powder, partly compensating for the loss caused by the dilution. For heavier elements one will use L-lines or constant weights for the fused beads. Wrt to use of gas, in case of an electrical furnace there is no need for gas, so that problem is overcome as well. Depending on the dilution and element, LLD's can be obtained that are well below 100ppm. With 200mg your dilution will be no more than a factor 30 at 32mm fused beads, at 1000mg it is only a factor 6, which even allows traces to be measured. Should the Cu level become very high then you may need a relatively large dilution as Cu does not dissolve very well. For the other elements there is no problem at all.

Bill Fraser
1 year ago
Bill Fraser 1 year ago

Having between 200 to 1000 mg for Fusion will be more than good enough. Depending on your sample composition we can probably develop a Fusion Recipe with a ratio somewhere between 1/20 to 1/5. It really depends on your sample composition. You would have to tell me more about this in order to get a complete answer to that question.

Also you probably already know Claisse manufactures Gas and Electric Fluxers. We recommend the instrument as per the applications you are running in your laboratory, and also depending on the sample volume. In writting it would take a while to make a long story short but here is what I can tell you. In the past 3 years I've helped other people, in the same situation as you, asking question about safety and Gas Fluxer. Almost all the time, the concerns are coming from the Safety Department which has no experience with the reality of what is going on in the lab. Almost all of them ended-up with a Gas Fluxer, only a few changed their mind to an Electric Fluxer. Like with any piece of equipment, you have to follow the Pre-Installation Requirements.

Alan Carter
1 year ago
Alan Carter 1 year ago

Actually, 30 mm beads can be made with 1:4 dilution as well (I am talking about 12:22 flux) , so 1000 mg sample will give you quite nice LLD, even 200 mg will give you only 20x dilution, which will be enough for most elements. If your samples are high on copper, you would like to have oxidizing atmosphere as well - copper just loves to turn in monovalent or elemental copper, which do not dissolve well.

Bob Mathias
1 year ago
Bob Mathias 1 year ago

A lot of interesting comments! As for selecting between Gas and Electric machines, one comment XRF Scientific are increasingly hearing from customers is the concern about the costs associated with spare parts, in some cases it can be as much as 50% of the original purchase price on an annual basis.  Customers who have gas machines tend to like the fact that they can see the reaction evolve and choose the various process parameters accordingly. Issues with burner stability by position and with time are usually solved with the right laboratory procedure. Oxygen enriched gas machines typically allow a larger temperature range and have fewer heat dissipation issues.

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