Effect of moisture on the adsorption of ammonia
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The effect of moisture on the adsorption of ammonia was systematically studied using different surface materials and humidity levels. The experimental water amount fractions varied between 6 and 18,000 µmol mol−1, and the ammonia amount fraction was 400 nmol mol−1. The investigated materials included plain 316L stainless steel and stainless steel cured with Dursan, SilcoNert 2000 and halocarbon wax coatings. Furthermore, Teflon (PTFE) and polyvinylidene difluoride (PVDF) polymer surfaces were studied. Dynamically diluted ammonia, test tubes prepared with the investigated materials, a commercial ammonia analyzer based on cavity ring-down spectroscopy, and a commercial dew-point transmitter were employed. The adsorption was assessed quantitatively using continuous flow conditions and real-time monitoring of the adsorption process. The ammonia adsorption was found to increase substantially in dry conditions for all the studied materials except PVDF. The increase was largest for plain stainless steel which was the most adsorbing material. The coatings applied on stainless steel decreased the adsorption significantly in dry conditions. Polymers PVDF and PTFE were the least-adsorbing materials. In water amount fractions between 1000 and 10,000 µmol mol−1, the ammonia adsorption was at its lowest. The adsorption increased again above 1% humidity levels.
This work is part of European Metrology Research Programme (EMRP) Joint Research Project (JRP) “Metrology for Ammonia in Ambient Air”—MetNH3 (http://www.metnh3.eu). O. V. was employed as a Research Excellency Grant (REG) beneficiary in the Project. The research was carried out with funding by EURAMET and the European Union. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. SilcoTek Corporation is thanked for supplying the SilcoNert 2000 and Dursan-coated stainless steel test tubes and for providing an additional information about the coatings. Dr. Hannu Sairanen from VTT MIKES Metrology is acknowledged for verifying the appropriate operation of the Vaisala dew-point transmitter. Dr Raimo Timonen is thanked for providing a prepared halocarbon wax solution. Funding was provided by European Association of National Metrology Institutes.
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