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  -  System to determine and evaluate the Hydrogen content of AL alloys
The measurement of hydrogen in aluminium melt is based on the prinziple of the "first bubble" according to Y. Dardel 1948.

The sample is filled in a evacuable crucible, with an appropriate temperature. As soon as the surrounding pressure is lower or equal to the partial pressure in the melt, the gas comes out of the melt, following the rule of nature. This is visible by bubbles at the surface of the metal.

Hydrogen is the only dissolved gas in aluminium, therefor this is the way the partial pressure of hydrogen is determined. The real "first bubble" is that one, which is followed by several further bubbles shortly after.

The concentration of hydrogen is calculated from the hydrogen partial pressure, the simultaneous melt temperatur, the time of solidifcation and the constants according to alloying elements. The calculation is made according to the "Sieverts rule".

This is shown in the following calculation:

log CH = 0,5 * log pH - A / T + B

CH concentration of the hydrogen dissolved in the aluminium in cm³/100g
pH partial pressure of hydrogen in mbar
T temperatur of the melt in K
A,B constants according to the effect of several alloying elements

The constants consider e.g. solubility of the element like Si, Mg, Cu, Mn. Further alloying elements can not be rated, because of missing research results.

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