Since the surface of the molten aluminum is always covered by a layer of slag during the aluminum smelting process, there is little possibility of any gas being directly discharged automatically, and it can only escape by floating up after generating bubbles. However, the precipitation pressure of hydrogen and nitrogen in the aluminum liquid is very small, and the bubble core cannot be formed independently. The Nitrogen Degassing Aluminum is the most effective way of degassing.
The gas must rely on the ready-made bubbles in the aluminum liquid or the help of other bubble-forming reactions, such as the carbon-oxygen reaction in the molten pool or blowing into the aluminum ladle. It can be removed from the molten aluminum only after entering argon. Because the nascent argon bubbles are equivalent to a vacuum chamber for hydrogen and nitrogen, that is, the partial pressure of hydrogen and nitrogen in the bubbles are zero, so that the hydrogen and nitrogen in the molten aluminum will diffuse into these bubbles.
As the volume of the bubble continues to increase during the rapid ascent, the actual partial pressure of hydrogen and nitrogen in the bubble is continuously reduced. Therefore, during the entire decarburization process or the argon bubble floating process, the hydrogen and nitrogen in the aluminum will continue to diffuse into these bubbles, and was finally taken out of molten aluminum. This shows that the boiling of molten aluminum is a very effective means of Hydrogen Degassing.
Steps of Nitrogen Degassing Aluminum
The Nitrogen Degassing Aluminum process of gas dissolved in molten steel to gas phase consists of the following steps:
- Through diffusion or convection, gas atoms dissolved in molten steel migrate to the gas-liquid interface:
- The gas atom changes from the dissolved state to the surface adsorption state;
- The gas atoms adsorbed on the surface interact with each other to generate gas molecules;
- Desorption of gas molecules from the surface of molten steel;
- The gas molecules diffuse into the gas phase and are drawn out by the vacuum pump.