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Ar-Ar Lab
1) Furnace and first getter

The stepwise heating technic implies that we heat a sample to analyse (mineral or rock chip) by temperature steps in a vacuum system (at least 10-7 mbar at room temperature) to extract gas and volatile particles. The sample to analyse is contained in a mobylden tube, inside a furnace we heat from 20 to more than 1500°C. The whole is isolated and a cold water system allow to cool down the furnace. Before starting an analysis, furnace is preheated (for micas) at ca. 400°C, while pumping system is always active. A sample, mineral separate or rock chips, is then introduced into furnace for pre-cleaning (illustration of sample holder, see next page). A large part of adsorbed impurities (essentially water and some hydrocarbons) and some fluid inclusions are degassing at this stage. This avoid a large contamination of the line without affecting the analysis (no argon mineral extracted at this "low" temperature). These impurities are directly thrown away to avoid a too large contamination inside the line, and this, without affecting the analysis (analysed minerals degas argon at temperature higher than 500-700°C).

After this pre-cleaning, pumping system of furnace and getter is closed (for the whole analysis time) and the furnace temperature is set to value of the first step of analysis. Gas is thus extracted and cleaned through a first "getter". This "getter" is a sponge of Zirconium-Vanadium-Titanium alloy, which will trap on its surface all reactant gases when it is heated at a temperature of ca. 200°C ("gettering" process). Argon beeing a noble gas, it cannot be trapped in this alloy. After at least 15 minutes, gas is moved to purification line where a second getter is awaiting it. At the end of this transfer (see next page) we start the next step of analysis by increasing the furnace temperature to liberate the second step. The total number of steps is determined in function of various parameters, notably personnal experience (:-D) irradiation time and chemical composition of the sample.

Towards sample holder & purification line Next1
Towards laser extraction line Next2

ArFurnace
Fig. 1, First getter and furnace of argon extraction line of Berne.

ArInsideFurnace
Fig. 2, View from above of the furnace, when it is heated at more than 1500°C (final stage, cleaning of the furnace). Samples are thrown inside a Mobylden tube. Only the last centimeters of this tube are heated (glowing dots on this figure).

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