Control of Pore Size of High Purity Nanoporous Silica Formed from Volcanic Ash Deposit Shirasu

Abstract

High purity nanoporous silica was fabricated using Shirasu volcanic ash as a starting material. The starting materials were placed into a platinum crucible and were melted at 1400°C. A mother glass was formed by quenching the melt in pure water. Leaching was performed by immersing the mother glass into an HCl solution. Nonsilica phases formed by phase separation in the mother glass were leached out with acid solution. The obtained porous silica was more than 99% pure and had pore size smaller than 2 nm. In order to control the pore size, post heat treatment was performed. The pore size could be controlled from 3.1 to 21.7 nm by changing the post treatment temperature.

Formation of Silicon from Shirasu Volcanic Ash Using Solar Furnace

“…Non-silica phases formed by phase separation in the mother glass were leached out with acid solution. The obtained porous silica was more than 99% pure [13], [14].…”

“…The material of the Fresnel lens was PMMA, and it had an area of 1.40 m × 1.05 m. (diameter: 20.3 cm, depth: 19.2 cm) and quartz glass plate functioning to guide the concentrated sunlight into the furnace, and we put a thermal insulation and crucible, at the Fresnel lens' focal point. The sample was made from a mixture of silica formed using Shirasu volcanic ash [13], [14] and SiC fabricated using silica and graphite [15], and placed in the carbon crucible inside the reacting furnace. The high purity nanoporous silica was fabricated using Shirasu volcanic ash as a starting material.…”

Formation of Silicon Carbide Using Volcanic Ash as Starting Material and Concentrated Sunlight as Energy Resource

“…Nonsilica phases formed by phase separation in the mother glass were leached out with acid solution. The obtained porous silica was more than 99% pure [9,10].…”

“…A kind of volcanic ashes called "Shirasu, " abundantly deposited due to a big pyroclastic flow in Southern Kyushu, Japan, is one of the unused natural resources. In our previous work, we have successfully formed high purity SiO 2 from Shirasu with a simple process [9,10].…”

Carbothermal reduction process of silica formed from shirasu volcanic ash using solar furnace

“…The sample was made from a mixture of silica formed using Shirasu volcanic ash [6,7] and carbon, and placed in the carbon crucible, as shown in Fig. 2, inside the reacting furnace.…”