Thermodynamic and magnetic properties of surface Fe3+ species on quartz: effects of gamma-ray irradiation and implications for aerosol–radiation interactions

Abstract

Samples of a natural amethyst, pulverized in air, and irradiated for gamma-ray doses from 0.14 to 70 kGy, have been investigated by powder electron paramagnetic resonance (EPR) spectroscopy from 90 to 294 K. The powder EPR spectra show that the surface Fe 3? species on the gamma-ray-irradiated quartz differ from its counterpart without irradiation in both the effective g value and the observed line shape, suggesting marked radiation effects. This suggestion is supported by quantitatively determined thermodynamic properties, magnetic susceptibility, relaxation times, and geometrical radius. In particular, the surface Fe 3? species on gamma-ray-irradiated quartz has larger Gibbs and activation energies than its non-irradiated counterpart, suggesting radiation-induced chemical reactions. The shorter phase-memory time (T m ) but longer spin-lattice relaxation time (T 1 ) of the surface Fe 3? species on the gamma-ray-irradiated quartz than that without irradiation indicate stronger dipolar interactions in the former. Moreover, the calculated geometrical radius of the surface Fe 3? species on the gamma-ray-irradiated quartz is three orders of magnitude larger than that of its counterpart on the as-is sample. These results provide new insights into radiation-induced aerosol nucleation, with relevance to atmospheric cloud formation and global climate changes.

Electron Spin Resonance Study of E<SUB>1</SUB>' in Natural and #947;-ray-irradiated Amethyst

“…5(a) and 5(b) show that log 10 (N) of the E 1 ' center at g = 2.0 for natural and 10 kGy γ-ray-irradiated amethyst correlates linearly with the reciprocal of temperature (1/T). The slope of this correlation yields the activation energy Ea at -0.03 and -0.02 eV, for E 1 ' of natural and 10 kGy γ-ray-irradiated amethyst, which is consistent with those reported for Fe 3+ in amethysts (Sivaramaiah et al, 2011;Sivaramaiah and Pan, 2012). The pre-exponential coefficient (PEC) has been determined to be 56, 54 per second for E 1 ' in natural and 10 kGy γ-ray-irradiated amethyst from In the calculation of activation energy, we observed negative slope from origin programme and therefore the activation energy is negative.…”

“…Sivaramaiah et al (2011) studied the thermal properties of Fe 3+ center in natural amethyst. Sivaramaiah and Pan (2012) studied the thermal properties of Fe 3+ center in γ-ray-irradiated natural amethyst. To our best knowledge, there are no previous reports on thermal properties of E 1 ' in natural and γ-ray-irradiated amethyst.…”

Mineralogy and mineral chemistry of quartz: A review

“…Iron can be incorporated into quartz in three different valence states (Fe 2+ , Fe 3+ and Fe 4+ ; Cox, 1976Cox, , 1977Gressey et al, 1993;Weil, 1994;Schofield et al, 1995;Dedushenko et al, 2004;Di Benedetto et al, 2009;SivaRamaiah et al, 2011;SivaRamaiah and Pan, 2012), although colloidal clusters of metallic iron have been reported to occur in quartz as…”

“…well (Daniels and Morton, 1981;SivaRamaiah and Pan, 2012 S1; Scala and Hutton, 1976;Mombourqette et al, 1986Mombourqette et al, , 1989Halliburton et al, 1989;Minge et al, 1990;Weil, 1984Weil, , 1994. Because of the larger ionic radius of Fe 3+ (0.64 Ǻ) compared to Si 4+ (0.42 Ǻ), the tetrahedra will be distorted.…”

“…Iron can be incorporated into quartz in three different valence states (Fe 2+ , Fe 3+ and Fe 4+ ; Cox, 1976, 1977; Cohen, 1985; Cressey et al , 1993; Weil, 1994; Schofield et al , 1995; Dedushenko et al , 2004; Di Benedetto et al , 2009; SivaRamaiah et al , 2011; SivaRamaiah and Pan, 2012), in addition colloidal clusters of metallic iron have also been reported to occur in quartz (Daniels and Morton, 1981; SivaRamaiah and Pan, 2012). EPR studies have established at least six distinct Fe 3+ centres substituting for Si, as either the charge uncompensated [FeO 4 ] – centre or charge-compensated [FeO 4 /M + ] 0 centres (M + = Li + , H + , Na + , Table S1; Scala and Hutton, 1976; Mombourqette et al , 1986, 1989; Halliburton et al , 1989; Minge et al , 1989, 1990; Weil, 1984, 1994).…”