Sachiko Furuta

Porous hydroxyapatite monoliths from gypsum waste

Porous hydroxyapatite (HAp) monoliths were synthesized from gypsum mold waste with diammonium hydrogen phosphate solution by hydrothermal treatment at 50-190°C and their properties studied. Gypsum waste samples could be completely converted to HAp with 0.5 mol dm –3 (NH 4 ) 2 HPO 4 at 50°C in 15 days and 100°C in 2 days. This paper describes the effect of hydrothermal reaction conditions such as reaction temperature, time and concentration of (NH 4 ) 2 HPO 4 on the formation of new HAp monoliths and their porous properties.

Microwave Versus Conventional-Hydrothermal Synthesis of NaY Zeolite

This paper focuses on the synthesis of NaY zeolite crystals by using microwave-hydrothermal (M-H) processing. NaY zeolites were synthesized from colloidal silica, sodium aluminate, sodium hydroxide and deionized water at 100°C, and some properties were studied. NaY zeolite crystals with high surface area, in the range of 439 to 716 m2/g, have been prepared at 100°C for 1 to 3 hrs. Compared to the formation of NaY zeolite via conventional-hydrothermal (C-H) treatment, the M-H treatment led to increased rate of formation by 3 to 4 times.

Porous mullite honeycomb by hydrothermal treatment of fired kaolin bodies in NaOH

A conventional hydrothermal treatment with various concentrations of NaOH was used at 150° and 190°C to dissolve excess silica glass and thus make porous mullite ceramics from a fired New Zealand kaolin body. The effect of hydrothermal treatment time on the dissolution of the glass was examined. At 150°C, the dissolution of glass was almost complete after treatment for 8 hrs in 5N-NaOH solution and about 40–43 wt% of the glass was removed from the fired kaolin body leading to porous mullite. However, when the fired kaolin body was treated for more than 5 hrs in 5N-NaOH at 190°C, a composite of mullite and a nonporous crystalline phase of unknown symmetry resulted. These crystals formed from the dissolution and recrystallization of the glass. After the dissolution of glass in 2N-NaOH solution at 190°C for 5 hrs, a porous mullite body of 52.8% porosity with an average pore diameter of 0.57 μm could be obtained, and this was only composed of mullite whiskers. Growth of unidentified nonporous crystals in the body which was treated in 5N-NaOH solution at 190°C led to a decrease in specific surface area and therefore, these crystals should be avoided.

Modification of Porous Silica with Activated Carbon and its Application for Fixation of Yeasts

Mixtures of small silica particles and activated carbon were heated at 1250–1450°C in an inert atmosphere to make nano- and macro-sized porous silica for incorporating yeast in the porous strucrure. Without activated carbon, porous silica of 45–60% porosity and 15–30 μm pore diameter was produced with a specific surface area below 1 m2/g. By the addition of 8 wt% of activated carbon granules, the surface area of porous silica increased to 100 m2/g at 1250°C. It was confirmed that there were micropores(1.2 nm) and mesopores(4.0 nm) due to activated carbon granules in porous silica when granule type activated carbon was used. However, in the case of activated carbon fiber, its micro- and mesoporous structure was destroyed in the firing process. The fixation of Z. rouxii yeasts was promoted on the porous silica with activated carbon.

Conventional- versus microwave-hydrothermal leaching of glass from sintered kaolinite to make porous mullite

A microwave-hydrothermal treatment with 1 and 5N-NaOH solution was used at 150°C and 190°C to dissolve excess silica glass and thus make porous mullite ceramics from a fired New Zealand kaolin honeycomb. The effect of microwave-hydrothermal (M-H) treatment time on the dissolution of the glass was examined and compared to the result of conventional-hydrothermal (C-H) treatment. As expected, the rate of the dissolution of glass was faster with M-H treatment compared to C-H treatment. The dissolution of 40–43% glass was almost complete after M-H treatment in 1N-NaOH for 6 hrs at 150°C, in1N-NaOH for 3 hrs at 190°C, in5N-NaOH for 1.5 hrs at 150°C, and in 5N-NaOH for 35 minutes at 190°C. When the M-H treatment in 5N-NaOH solution at 190°C was more than 45 minutes, nonporous prismatic crystals were formed on the honeycomb and these crystals decreased the specific surface area. There were no changes in the morphology of mullite whiskers or in the structure of porous mullite body after M-H treatments in NaOH solutions compared to that of C-H treatment. The M-H treatment has been shown to be a rapid technique to prepare porous mullite ceramics from fired kaolin honey comb.