溶液から調製したK-Al含有ケイ酸塩ゲルの合成と特性に及ぼすpHの影響

概要

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Silicate gels were prepared by mixing K_2O・3.9SiO_2 (0.3 mol/L) and Al (NO_3)_3・9H_2O (1 mol/L) solutions in various ratios, using potassium hydroxide solution (1 mol/L) to regulate the pH. Nine gel samples were thus prepared at a range of pH conditions, filtered, washed and air-dried. About 1 mol% of potassium was incorporated into the gels at low pH, but up to 20 mol% was incorporated under high pH conditions. On heating, characteristic DTA exotherms were observed at higher temperatures, possibly providing an indication of the degree of polymerization of the gels. The low-potassium gels exhibited a sharp exothermic peak at about 1000℃ corresponding to mullite formation, whereas the high-potassium gels exhibited a small, gentle exotherm at about 1000-1100℃ corresponding to the formation of KAlSiO_4 (PAS, considered to be one of the modifications of kalsilite) and/or KAlSi_2O_6 (leucite), depending on the gel composition. The ^<29>Si and ^<27>Al MAS-NMR spectra showed that the potassium-poor gels contain predominantly tetrahedral Si (1-2Al) and Q1 silicate units, and both tetrahedral and octahedral Al^<3+>, whereas the potassium-rich gels contain predominantly Si (4Al) units and solely tetrahedral Al^<3+>. The implications of these results for the formation of potassium geopolymers are discussed.
社団法人日本セラミックス協会の論文
2006-07-01