Mechanism of Bubble Formation

Abstract

In the previous chapter, we learned that, for bubble generation, a supersaturated state is required. So, how do bubbles actually form in a supersaturated liquid? How do these bubbles grow to bubbles that we can see? To answer these questions and understand bubble formation, it is absolutely necessary for us to consider the meaning of the size and number of bubbles present in highly vesiculated volcanic rocks such as pumice and scoria, described in Chap. 1. These concepts are necessary for us to understand the dominant factors controlling eruption styles and intensity from the bubble texture in highly vesiculated volcanic rocks. In this chapter, we will understand the mechanisms of such bubble formation and behavior of bubbles in liquids based on both theories and experiments. Energetics of Bubble NucleationIn liquids that are supersaturated with a component that can vesiculate (a volatile component), nucleation is the process by which bubbles form embryos. In supersaturated liquids, nucleation does not always occur even if they are slightly supersaturated. Moreover, we already experience it at the table . When you open a bottle or a can of carbonated drinks that are gently carried, you will hear a soft pop and will not see active bubble formation. However, if you open a bottle or a can of the same drink that was subject to impact before opening, you know well that the results will be disastrous when you open it. As shown in Chap. 2, an opened bottle of beer is in supersaturation; however, it seems to require some special energy to vesiculate. In other words, an opened bottle of beer containing carbon dioxide can be stable because it is in supersaturation without work corresponding to the special energy. 1 If we assume that disturbance such as shock does work and gives the special energy required for vesiculation, we will realize what has happened. 1 The word stable used in this sentence actually means metastable. Water can be stable as liquid water even if it is cooled down to 0 • C, i.e., the freezing point. This state is a metastable state and such water is sometimes called supercooled water. Let us consider a metastable state from a point of view of energy under gravity as an analogy. When you place a cuboid on a horizontal plane, you can do it in two ways: where the longest sides are perpendicular to the horizontal plane and where the longest sides are parallel to the horizontal plane. Although the latter has lower potential energy and is stable, the former is stable unless pressed by an external force that is larger than a certain degree of force.