My sample is copper, run under Nitrogen gas at 20ml/min. Temperature range is 30deg - 990deg. I already subtracted with blank curve which is I perform with the same parameter.However, the curve still shows weight gain. Is that it producing a new compound during the analysis? for example, Metal Nitride?
Usually, this happens due to reactions such as oxidation
I propose that nitrogen may contain an impurity (steam, oxygen) or the analyses camera is not very clean. In this case, perform some blank processes to 900 deg until the sample mass stabilize.
Good luck. V.Kozlov.
Residual humidity can be involved at a (seemingly) possible Cu oxidation. The purity of the nitrogen gas should be considered for its humidity content, since for higher purity gas the humidity content is significantly lower than for low purity grade. You may consider drying the nitrogen gas with CaH2, P2O5, or molecular sieve; and/or by using a vapour condensing trap cooled by liquid nitrogen or by a cryogenic mixture such as diethyl ether with dry ice (approx. -100 ºC). You may consider to previously dry the copper sample. Note that the TGA-DSC instrument should be calibrated at analogous experimental conditions; namely in terms of heating rate (or thermal schedule), type of pans, selected gas and flow rate.
I agree with the answer of Vladimir Kozlov. The possibility of forming some metal oxide during analysis under high temperature. Please make gas purity check.
Dear Fareezex. The gain in weight did not exceed 4% as I may see from the TG curve. It means that it is not stoichiometric with the amount of copper present. The most possible reaction is the oxidation of the surface material with the gaseous contaminants (mostly Oxygen) within the purge gas. For a reliable decontamination practice purify the purge gas by the use of multiple traps containing drying agent (Silica gel and CaCl2, an oxidizable species like some chromium compound in aqueous solution before letting the purge gas to fill the atmosphere of the TG pan. Copper oxides, Cu2O and CuO are thermodynamically stable than Cu metal and hence there was no decomposition of the formed oxides. Cu-N reaction is not possible with the open system involved. If it is not harmful for your system you may include very small amount of graphite (mixed with Cu powder). This will capture any oxygen from the atmosphere and further will reduce any possibly forme dCu oxides. You may refer to one of my publications dealy partly with this situation:
Thermal behaviour of copper oxides and copper sulphate in the presence of carbon.
M.M. Barbooti,
Solar Energy Materials, 10 (1984) 35.
Regards
Dear Fareezex, when I run into such problems I change my purge gas to Helium or Argon to further explain this anomaly. I've read somewhere that horizontal TGA's is more prone to this because of the buoyancy effect at elevated temperatures. What is the particle size and purity of your sample? Inherent inclusion within your sample can also cause anomalies.
sometimes you also tare the wrong pan, and then this happens. its a possibility too.
Basically, weight loss or weight gain depend on chemicals, however, when the laboratory instruments are not calibrated, experimental results might be changed.
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