Thermal Crystallization Kinetics of an Opal-like Biogenic Silica

Daglar S., Kahya N. D., Ustunisik G., Önal M., Sarikaya Y.

SILICON, cilt.14, sa.12, ss.7211-7217, 2022 (SCI-Expanded) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 14 Sayı: 12
  • Basım Tarihi: 2022
  • Doi Numarası: 10.1007/s12633-021-01498-2
  • Dergi Adı: SILICON
  • Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Chemical Abstracts Core, Compendex, INSPEC
  • Sayfa Sayıları: ss.7211-7217
  • Anahtar Kelimeler: Biogenic silica, Cristobalite, Kinetics, Opal, Thermal crystallization, X-RAY-DIFFRACTION, POROUS SILICA, ALPHA-CRISTOBALITE, CT, TRANSFORMATION, POLYMORPHS, BENTONITE, MODEL
  • Ankara Üniversitesi Adresli: Evet

Özet

A gray-colored sediment from Erzurum/Turkey zone was characterized by scanning election microscopy, X-ray diffraction, chemical analysis, and thermal analysis techniques. The raw sample contains mainly an amorphous biogenic opal-A as well as opal-CT, smectite, illite, and quartz as impurities. The XRD-pattcm of the heated samples at different temperatures ranging between 1050 and 1175 degrees C for durations from zero to 4 h was recorded. Consecutive increases in the intensity of the characteristic XRD-reflection at 2 theta = 22 degrees showed that the biogenic silica changed over paracrystalline opal-CT to crystalline alpha-cristobalite having the reflection with the maximum intensity (I-m). Its insolubility in orthophosphoric acid digestion proved this formation. The temperature and heating time dependent intensity (1) were used as kinetic variables and the ratio of I/I-m = alpha was defined as crystalline fraction. Using the differential rate law, d alpha/dt = k(1 - alpha)(n) and Arrhenius equation Ink = -E-#/RT + lnA, the order and activation energy for the crystallization were calculated as n = 1, and E-# = 202 kJmol(-1), respectively.