“…Some of these ''solid bubbles" were destroyed and the character of the damage looks like a crush under the action of high external pressure at the cooling stage of the process. As in early paper by Denham et al [79], the authors of [77,78] supposed that hollow particles are formed by evaporated water and expanded steam within molten droplets. The physical picture of possible penetration of small water jets or droplets into the melt drop is not quite clear at the moment, but one should recall the early paper [80] where the authors assumed that a micro-jet flow is generated during asymmetrical collapse of the steam bubble.…”