Title: Micro-Shirasuballoons (Hollow Glass Microspheres) from the Milled Shirasu Refined by Hydrothermal Treatment
Abstract:The hollow glass microspheres named “Shirasuballoons” can be produced from Shirasu, a kind of acidic volcanic ejecta. Weathered surface layers of the Shirasu particles have several good properties, ke...The hollow glass microspheres named “Shirasuballoons” can be produced from Shirasu, a kind of acidic volcanic ejecta. Weathered surface layers of the Shirasu particles have several good properties, keeping the shape of the Shirasuballoons and preventing sticking each other during heat treatment. However, they can not be produced from the particles milled under 10μm, because of the insufficient amount of water for foaming; ground particles have no weathered surface layer. This paper describes the hydrothermal treatment of milled particles to form the surface layer having the same properties as weathered one and to increase structural water. The results obtained are as follows: (1) The weathered surface layer of the Shirasu particles milled under 10μm is destroyed almost completely by milling process. (2) Sodium and potassium ions are replaced with H+ by the treatment in 2wt% HCl solution at 200°C and about 15atm. The structural water increased with increasing volume of the solution, pressure, and time. Other ions such as Ca++ and Fe++ were removed also. (3) The highest yield of the micro-Shirasuballoons obtained by hydrothermal treatment in HCl solution was 10 times than without treatment. Even if heat treatment is performed in oxidizing atmospheres, whiteness of the micro-Shirasuballoons was more than 85.Read More