Variation of the Surface Properties of Hematite upon Heat Treatment Evidenced by Inverse Gas Chromatography and Temperature Programmed Desorption Techniques: Influence of Surface Impurities and Surface Reconstruction
✍ Scribed by Eric Brendlé; Joseph Dentzer; Eugene Papirer
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 308 KB
- Volume
- 199
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
rate of release of volatile surface thermal decomposition
The influence of heat treatment on the surface properties of products.
hematite samples of different origins was examined by inverse gas
Information on the surface properties, especially the surchromatography (IGC) and temperature programmed desorption face energy of hematite, is rather scarce in the literature. (TPD) techniques. Comparison of the curve relating the evolution Two methods have so far been applied to the evaluation of of the free energy of adsorption of a methylene group, DG a (CH 2 ), the dispersive component of the surface energy ( g D s ): wettameasured by IGC using a homologous series of n-alkanes, and the bility based on the measurement of liquid contact angles and TPD curve reveals similarities. In particular, the increase either of gas adsorption. Van Oss et al. (3) used the capillary ascenthe rate of departure of impurities (SO 2 from a polluted hematite sion phenomenon of selected liquids in capillary tubes filled sample) or the rate of water release upon heating a pure hematite sample is accompanied by a significant increase of DG a (CH 2 ). with hematite particles having a diameter of about 1 mm.
Rehydration experiments of heat-treated hematite samples show
The liquid contact angle is calculated by application of that restoring the characteristics of the initial, nonheated oxide Washburn's equation that relates the rate of liquid ascension surface becomes quasi-impossible for samples treated at above to the liquid-solid contact angle. The g D s value obtained 350ЊC. This points to reconstruction or relaxation of the surface through this procedure is equal to 46 mJ/m 2 . This is a relalayer upon heat treatment. Determination of the changes in nanotively low value for an ionic oxide and probably corresponds morphology and acid/base properties complements this study. A to an iron oxide surface that is partially covered by adsorbed layer of oxyhydroxide possibly exists on hematite surfaces. ᭧ 1998 water molecules. Fowkes (4) calculated the spreading pres-Academic Press sure of n-heptane from the adsorption isotherm and then Key Words: hematite; heat treatment; inverse gas chromatogracomputed a g D s value for an oxidized iron powder sample phy; temperature programmed desorption; surface rehydration; acid/base properties.
that amounts to 107-108 mJ/m 2 . In all cases, sufficient information concerning the chemical origin and purity of the samples is lacking. That such information is of fundamental importance will be demonstrated in this paper by looking