焼成したカオリナイトおよびセリサイト中の鉄イオンのESRによる研究

抄録

The behavior of Fe ions contained in kaolinite and sericite during the firing at110-1300°C in air was studied mainly by ESR.
On increasing the firing temperature of kaolinite, the intensity of the signal due to (strongly) magnetic iron oxides grew to a maximum at 600°C and decreased above 600°C whereas that of isolated Fe³⁺ ion (g=4.25) increased above 600°C. The quantity of bulky iron oxides was roughly proportional to the intensity of the signal due to (strongly) magnetic iron oxides.
The percentage of the soluble Fe ions to the total Fe ions in the kaolinite body on the elution treatment with a dilute oxalic solution was also roughly proportional to the intensity of the signal due to (strongly) magnetic iron oxides. In the case of the fired sericite, ESR signal due to bulky iron oxides was comparatively weak and the percentage of the soluble Fe ions to the total Fe ions was found to be low on the elution treatment.
Chemical analyses of Fe²⁺ and Fe³⁺ in the sericite bodies fired at various temperatures and measurements of the intensities of the signal at g=4.25 in their spectra revealed that only a part of the isolated Fe³⁺ was observable by ESR. The presence of Fe³⁺ unable to observe by ESR indicates that ESR is generally inapplicable to the quantitative analysis of Fe³⁺ in clay.
The line width of the signal at g=4.25 observed in the kaolinite body decreased after the dehydration at 500°C and increased after the firing at 1000°C. Similar changes of this Fe³⁺ signal were also found in the case of the sericite body. Primitive speculations were made on the relations between structural changes of kaolinite and sericite and spectral changes of the isolated Fe³⁺ and bulky iron oxides.