Ferrihydrite porosity

The small, spherical particles of ferrihydrite often pack together to form aggregates >0.1 pm across. The aggregated structure and interparticle porosity create difficulties in measurement of surface area because the internal area is not fully accessible to all measurement techniques. It is rare for more than two methods of area measurement to have been applied to the same sample. Pyman and Posner (1978) obtained an area of 250 m g" using both N2 and water BET measurements. With the EG ME method, however, the same sample had an area of 600 m g". These... 

Due to aggregation of particles, ferrihydrite is microporous, i. e. the porosity is interparticular. Ferrihydrite precipitated at pH 8 from Fe " solution displayed a type IV isotherm with type E hysteresis (Crosby et al., 1983). The freshly precipitated material contained ink bottle pores 2-5 nm in diameter. Larger pores (ca. 20 nm) developed over an 11 day period. Between 83 and 95% of the total pore volume of a 2-line ferrihydrite was found to be due to micropores (Weidler, 1995). 

GrefFie, C. Amouric, M. Parron, C. (2001) HRTEM study of freeze-dried and untreated synthetic ferrihydrites consequences of sample processing. Clay Min. 36 381-387 Gregg, S.J. Sing, K.S.W. (1991) Adsorption, surface area and porosity. 2"" ed.. Academic Press, London, 371 pp. 

Weidler, P.G. (1997) BET sample pretreatment of synthetic ferrihydrite and its influence on the determination of surface area and porosity. J. Porous Materials 4 165-169 Weidler, P.G. Degovics, G. Laggner, P. (1998) Surface roughness created by acidic dissolution of synthetic goethite monitored with SAXS and N2 adsorption isotherms. J. Colloid Interface Sd. 197 1-8... 

Weidler, P. G. (1997) BET sample pretreatment of synthetic ferrihydrite and its influence on the determination of surface area and porosity. J. Porous Mat. 4 165-169. 

Weidler, PG and Stanjek, H. (1998). The effect of dry heating of synthetic 2-line and 6-line ferrihydrite II. Surface area, porosity and fractal dimension. Clay Miner, 33, 277-284. 

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