Ultra high vacuum high precision low background setup with temperature control for thermal desorption mass spectroscopy (TDA-MS) of hydrogen in metals.

In this work, a newly developed UHV-based high precision low background setup for hydrogen thermal desorption analysis (TDA) of metallic samples is presented. Using an infrared heating with a low thermal capacity enables a precise control of the temperature and rapid cool down of the measurement chamber. This novel TDA-set up is superior in sensitivity to almost every standard hydrogen analyzer available commercially due to the special design of the measurement chamber, resulting in a very low hydrogen background. No effects of background drift characteristic as for carrier gas based TDA instruments were observed, ensuring linearity and reproducibility of the analysis. This setup will prove to be valuable for detailed investigations of hydrogen trapping sites in steels and other alloys. With a determined limit of detection of 5.9×10(-3)µg g(-1) hydrogen the developed instrument is able to determine extremely low hydrogen amounts even at very low hydrogen desorption rates. This work clearly demonstrates the great potential of ultra-high vacuum thermal desorption mass spectroscopy instrumentation.

An electrochemical calibration unit for hydrogen analysers.

Determination of hydrogen in solids such as high strength steels or other metals in the ppb or ppm range requires hot-extraction or melt-extraction. Calibration of commercially available hydrogen analysers is performed either by certified reference materials CRMs, often having limited availability and reliability or by gas dosing for which the determined value significantly depends on atmospheric pressure and the construction of the gas dosing valve. The sharp and sudden appearance of very high gas concentrations from gas dosing is very different from real effusion transients and is therefore another source of errors. To overcome these limitations, an electrochemical calibration method for hydrogen analysers was developed and employed in this work. Exactly quantifiable, faradaic amounts of hydrogen can be produced in an electrochemical reaction and detected by the hydrogen analyser. The amount of hydrogen is exactly known from the transferred charge in the reaction following Faradays law; and the current time program determines the apparent hydrogen effusion transient. Random effusion transient shaping becomes possible to fully comply with real samples. Evolution time and current were varied for determining a quantitative relationship. The device was used to produce either diprotium (H2) or dideuterium (D2) from the corresponding electrolytes. The functional principle is electrochemical in nature and thus an automation is straightforward, can be easily implemented at an affordable price of 1-5% of the hydrogen analysers price.