I am currently running all my experiments in the DSC in Argon atmosphere, but I am thinking about switching to Nitrogen. The main difference between the two are (to my knowledge):
Argon: more expensive, but definitely inert in almost any circumstances, displaces the atmosphere in the chamber more successfully because it's much heavier (at least in our dsc which is filled from the bottom during the evacuation cycles).
Nitrogen: Cheaper, has a higher heat conductivity and thus heat in the sample chamber is more evenly distributed.
Did I miss something? Thank you very much for your help.
For most of the samples Nitrogen is inert and can be used without any problem. At least in my experience I have not found any problem with using nitrogen.
Nitrogen is used as a DSC standard purge gas due to its better heat conductivity. The only advantage of using Argon would be for measurements at very high temperatures, where the thermal properties of Ar become better than those of N2.
great! thank you! What are very high temperatures for you? We're usually working at around 400-1200°C.
That is already high - your instrument is probably rather DTA measuring in a DSC mode then. Normally, I would recommend the switch somewhere around 600°C but since most of your measurements are around or above this temperature, argon is most probably the best choice for you. Note that if you would like to switch between the two gases, you need to recalibrate the instrument - it is therefore better to choose only one of these gases as a permanent purge/atmosphere, if you want to do some consistent research or series of measurements.
I do agree with Roman. It is very high temperature. You should use Argon.
The two aspects mentioned by my predecessors have to be treated separately: From the point of heat transport, the lighter gas N2 is better, for sure. And now the point of "inertness": There will only be a very few materials (e.g. light metals such as Al) that behave in 100% pure N2 less inert compared to 100% pure Ar. This means from the chemical point of view there is no good argument for Ar. And now the BUT's: 1) Some furnaces (e.g. a noble metal furnace from NETZSCH) run better if the furnace itself (not necessarily the sample) is purged by Ar. In this case you need it anyhow. 2) No real gas is 100% pure, and the trace impurities in your purge gas can do the harm. Thus you should check which gas (Ar or N2) is purer. 2 examples for this: In J. Crystal Growth 275 (2005) e849–e854 (Fig. 4 there) we showed that the rest O2 impurities in 99.999% pure Ar are sufficient to oxidize FeO to Fe3O4. And if I try to melt Ni in my "inert" gases I always get "kinky" melt peaks, and the metal is partially oxidized. I have to put a oxygen getter metal ring (called "OTS" by NETZSCH) on top of the radiation shield, close to the sample. Only then I get a good Ni melting peak. "Inertness" means that it keeps the sample chemically unchanged - and this has to be checked before thoroughly. Some oxides even are stable if heated in air, but loose oxygen upon heating in Ar or N2. Then both gases are not really inert.
I carry out high temperature differential scanning calorimetry (up to 1500°C) since about 20 years. The DSCs used in this temperature range are all heat flux DSCs. I generally use Argon in most of my tests. The main reason is the lower thermal conductivity as it increases the sensitivity in the low temperature range by about 20%. Regarding inertness, there might not be such a big difference between Nitrogen and Argon. However, for some materials (some steels or other alloys) you might face nitrification. This will not happen in Argon. Price might be an issue but when you sue conventional flow rates (50 ml/min) you can work months with one bottle. Helium as the high thermal conductivity generates a very nice baseline but a low sensitivity of the DSC sensor heads. I hope my five cents are helpful.
In my opinion nitrogen of 99% purity is best. It creates an inert environment in the heating chamber. Of course this is true if your measuring temperatures are below 500C
Thank you all for your answers! This has been really helpful and I am now fully convinced that research gate actually is pretty cool! I will stick with Ar for now as most of our experiments are indeed above 500ºC and a lot of other labs working on similar topics use Ar as well. I am definitely thinking about getting that Oxygen getter ring though, I have definitely seen some slight oxidation in my samples during the experiments, so maybe that would help!
cheers,
Felix
I am measuring a lot of silicate glasses and use argon because it is less soluble than nitrogen in most silicate glasses.
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