Ar-Ar Lab
2a) Sample holder and purification line

Back to furnace and first getter...
Back to laser extraction line...

The glass sample holder is directly connected above the furnace entry. During sample heating in furnace, some gaz are extracted from sample and cleaned by the first getter on the bottom-left (see also previous page). A quantity of gas liberated at a certain temperature represent one "step".

After a while, extracted gas is transfered into the purification line. To drive the gas, an active coal trap is used (cooled by liquid nitrogen at -196°C, see figure 2 and 3 below). The valve is then closed and the active coal heated. This liberate the gas in the "cube" and to clean it again with the second getters situated aside. After another gettering time, spectrometer valve is opened and gaz is analysed by spectrometer (see also scheme of extraction line). Gettering time is depending of gas purity. If too much impurities are present (generally at "low" temperature, i.e. 400-700°C), the measurement of argon peaks is perturbed by interferences with other peaks or by an increase of spectrometer background. Generally, the extracted gas of mineral is very dirty during first steps of analysis: impurities situated in cristal network (notably in hydrated phase = "open" structure), fluid or other mineral inclusions... Moreover, hydrated phases are often more dirty and need a longer gettering time up to one hour of gettering.

Towards spectrometer

Fig. 1, General view on "Sample holder" and "Purification line" of argon extraction system ("Helium part" not discussed here...).

Fig. 2, Detail view of the "Dewar" (isothermic recipient) containing liquid nitrogen at a temperature of -196°C (boiling point of nitrogen). At this extremely low temperature, any gas present in the furnace will be trapped in the active coal, including our precious Argon!

Fig. 3, View of cube and its connection with furnace (on the left), active coal and getter, and the spectrometer (on the right). After withdrawal of liquid nitrogen and re-heating of active coal, gas is liberated and cleaned by the getter: any reactive gaz will be trapped or adsorbed in this getter (sponge made of a Zr, V and Ti alloy); argon beeing a noble gaz (non reactive, very stable), it will not be trapped.