A portable analyzer for real-time measurement and control of dissolved hydrogen in liquid aluminum alloys. The control of dissolved hydrogen in liquid aluminum alloys is a critical requirement for the aluminum industry.
If the hydrogen level is too high, during solidification, there is the potential for the formation of cavities / pores. Conversely, a moderate hydrogen level may be desirable under certain conditions, in order to combat shrinkage porosity. As such, there is an optimum hydrogen level which ideally should be established and controlled during casting. Although dissolved hydrogen is critical, pore formation is also influenced by several other factors, the most significant being melt cleanliness i.e. the level of inclusions such as metal oxides.
Hydrogen measurement techniques such as the ‘reduced pressure test’ provide an indication of the combined effect of both the hydrogen content and the metal cleanliness. However, in order to be able to analyze the hydrogen content specifically, it is necessary to measure it directly. Furthermore, in order to control the hydrogen content, it is necessary to measure it accurately in real-time.
The technology is based on a novel ceramic material (CaZrO3-In) which, at an elevated temperature, is able to conduct hydrogen ions. The principle behind how this material can be used to measure hydrogen concentration is shown in figure:
Above, an impervious section of hydrogen ion conducting ceramic (green) is coated with metal electrodes on both faces. The concentration of electrons is higher on the right side than on the left due to the greater hydrogen concentration. This results in the right side becoming negatively charged with respect to the left. If the voltage across the ceramic is known and the hydrogen concentration on one side is known (the “reference” hydrogen concentration), then the hydrogen concentration on the other side can be calculated. This type of arrangement is called a “hydrogen concentration cell”.