Characterization of Synthetic Nanocrystalline Mackinawite: Crystal Structure, Particle Size, And Specific Surface Area
Iron sulfide was synthesized by reacting aqueous solutions of sodium sulfide and ferrous chloride for 3 days. By X-ray powder diffraction (XRPD), the resultant phase was determined to be primarily nanocrystalline mackinawite (space group: P4/ nmm) with unit cell parameters a = b = 3.67 {angstrom} and c = 5.20 {angstrom}. Iron K-edge XAS analysis also indicated the dominance of mackinawite. Lattice expansion of synthetic mackinawite was observed along the c-axis relative to well-crystalline mackinawite. Compared with relatively short-aged phase, the mackinawite prepared here was composed of larger crystallites with less elongated lattice spacings. The direct observation of lattice fringes by HR-TEM verified the applicability of Bragg diffraction in determining the lattice parameters of nanocrystalline mackinawite from XRPD patterns. Estimated particle size and external specific surface area (SSA{sub ext}) of nanocrystalline mackinawite varied significantly with the methods used. The use of Scherrer equation for measuring crystallite size based on XRPD patterns is limited by uncertainty of the Scherrer constant (K) due to the presence of polydisperse particles. The presence of polycrystalline particles may also lead to inaccurate particle size estimation by Scherrer equation, given that crystallite and particle sizes are not equivalent. The TEM observation yielded the smallest SSA{sub ext} of 103 m{sup 2}/g. This measurement was not representative of dispersed particles due to particle aggregation from drying during sample preparation. In contrast, EGME method and PCS measurement yielded higher SSA{sub ext} (276-345 m{sup 2}/g by EGME and 424 {+-} 130 m{sup 2}/g by PCS). These were in reasonable agreement with those previously measured by the methods insensitive to particle aggregation.
- Research Organization:
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC02-76SF00515
- OSTI ID:
- 953131
- Report Number(s):
- SLAC-REPRINT-2009-153; GCACAK; TRN: US200914%%333
- Journal Information:
- Geochim. Cosmochim. Acta 72:493,2008, Vol. 72, Issue 2; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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