Hayato Nanri

Mineralizing action of iron in amorphous silica

Abstract The mineralizing action of iron in amorphous silica was investigated by firing mixtures of silica gel and iron oxides at 1100 and 1150°C. Silica gel did not crystallize in the absence of ferrous ion below 1200°C. When silica gel mixed with ferrous oxalate was heated at 1100°C in a mildly reducing atmosphere(N2, CO2, CO), quartz, cristobalite and ferrous silicate (Fe2SiO4) were formed. Application of the reducing atmosphere from room temperature promoted the crystallization to quartz, while that from the soaking temperature after heating in N2 accelerated the formation of cristobalite. Chemical analysis revealed that the N2 atmosphere acted as a mildly oxidizing atmosphere to FeO possibly due to the coexistence of water vapor released from silica gel and impurity O2. Furthermore, tentative crystallization mechanism is proposed where mildly reduced and mildly oxidized Fe2SiO4 produced nuclei for quartz and cristobalite, respectively.

Conversion of silica gel and silica glass mixed with various metal oxides into quartz

Mixtures of silica gel and various metal oxides were heated at temperatures within the range of 500 to 1200°C for 1 h. When mixtures of silica gel and intentional additives such as Li 2 CO 3 , MgO, CaCO 3 , SrO, Ba(CH 3 COO) 2 , and ZnO were heated at temperatures from 700 to 1050°C, quartz phases formed. Similarly, heating a mixture of powdered silica glass and Li 2 CO 3 yielded quartz. In all cases the formation of quartz phases always accompanied the formation of silicate minerals. When a mixture of silica gel and 1 wt% Li 2 CO 3 was heated at 900°C, quartz phases and a very small amount of Li 2 Si 2 O 5 (hereafter denoted as Q-S mixture) were formed. Silica gel mixed with 10 wt% of Q-S mixture was transformed almost completely into quartz phases at 1000°C. The Q-S mixture consisted of only quartz phases after washing with hot H 2 SO 4 . Silica gel mixed with 10 wt% of the washed Q-S mixture was not transformed into quartz, but rather into cristobalite above 1200°C. This fact also indicates that the formation of the silicate mineral is a necessary precursor to the conversion of silica gel and silica glass into quartz.