Hematite particles

The adhesion between two solid particles has been treated. In addition to van der Waals forces, there can be an important electrostatic contribution due to charging of the particles on separation [76]. The adhesion of hematite particles to stainless steel in aqueous media increased with increasing ionic strength, contrary to intuition for like-charged surfaces, but explainable in terms of electrical double-layer theory [77,78]. Hematite particles appear to form physical bonds with glass surfaces and chemical bonds when adhering to gelatin [79]. 

As a result, nanometer-sized metallic Au particles were selectively deposited onto monodispersed polycrystalline ellipsoidal hematite particles without addition of any specific reducing agent, as shown in Figure 5. 

It seems that Au ions of Au(OH) Cl4 complex, formed by the first aging at room temperature, are reduced to Au particles by electron transfer from the coordinated OH ions on the surface of hematite as a catalyst of the electron transfer. As a consequence, the essential reducing agent is water. The optimum pH to yield the maximum quantity of Au particles was ca. pH 5.9, as measured at room temperature, corresponding to the pH of the above standard system. Au ions are reduced to metallic Au by electron transfer from coordinated OH ions on the surfaces of hematite particles through their catalytic action. 

Figure 6 shows transmission electron micrographs of Au particles supported by (a) monocrystalline ellipsoidal (B), (b) monocrystalline pseudocubic, and (c) monocrystalline platelet-type hematite particles (see also Figure 5 for Au particles on polycrystalline ellipsoidal (A) particles). Figure 7 shows Au particles deposited on (a) a-FeOOH, (b) P-FeOOH, (c) ZrOj (A), (d) ZrOj (B), and (e) Ti02 (anatase). 

Figure 5. Transmission electron micrographs of Au nanoclusters deposited on the surfaces of the polycrystalline ellipsoidal hematite particles. The left photograph is a close-up view of the right one.

Figure 6. Au particles deposited on monodispersed hematite particles different in size and structure (a) monocrystalline ellipsoid, (b) monocrystalline pseudocube, and (c) monocrystalline platelet. Flematite particles were also prepared by the authors.

The liquid-phase reduction method was applied to the preparation of the supported catalyst [27]. Virtually, Muramatsu et al. reported the controlled formation of ultrafine Ni particles on hematite particles with different shapes. The Ni particles were selectively deposited on these hematite particles by the liquid-phase reduction with NaBFl4. For the concrete manner, see the following process. Nickel acetylacetonate (Ni(AA)2) and zinc acetylacetonate (Zn(AA)2) were codissolved in 40 ml of 2-propanol with a Zn/Ni ratio of 0-1.0, where the concentration of Ni was 5.0 X lO mol/dm. 0.125 g of Ti02... 

The catalyst, composite of crystalline hematite particles embedded into a mesopor-ous silica SBA-15 matrix was used. They accounted the following reactions for ultrasound coupled with Fenton-like reagent ... 

In Situ Mossbauer Measurement on Hematite/Divalent Co-57. The adsorption behavior of cobaltous ions on hematite surfaces was essentially the same as that on silica reported by James and Healy (12). Appreciable adsorption begins at about pH 4 followed by an abrupt increase in adsorption between pH 6 and 8. Beyond pH 9, adsorption is practically complete. Emission Mossbauer spectra of Fe-57 arising from the divalent Co-57 ions at the interface between hematite particles and the 0.1 mol/dm3 NaCl solutions of different pH at room temperature are shown in Figure 3 The emission spectra show a marked dependence on the pH of the aqueous phase. No emission lines ascribable to paramagnetic iron species are recognized in... 

Particle mobility and zeta potential can now be measured by more sophisticated techniques. With photoelectrophoresis, particle mobility is measured as a function of pH under the influence of ultraviolet radiation. At pH < 8, the electrophoretic mobility of irradiated hematite particles (A = 520 nm) was markedly different from that measured in the absence of UV irradiation. This was attributed to the development of a positive surface charge induced by photo-oxidation of the surface Fe-OH° sites to (Fe-OH) sites (Zhang et al., 1993). The electroacoustic technique involves generation of sound waves by the particles in the colloidal dispersion and from this data. 

Fig. 10.8 Electrophoretic mobilities of spherical hematite particles in the absence and presence of EDTA (1.3 10 M,...

Fig. 10.13 Fraction of hematite particles deposited on steel as a function of pH at 25°C (solid line). For each point 50 cm of the hematite sol (dmodai = 170 nm and 10 particles cm ) was passed through the bed at a flow rate of one cm min Dashed lines represent the electrophoretic mobilities of the hematite and of the steel particles (Matijevic, 1980, with permission).

Kanai, H., Navarrete, R.C., Macisko, C.W. Scriven, L.E. (1992) Rheol. Acta 31 333 Kandori, K. Ishikawa,T. (1991) Selective adsorption of water on amorphous ferric oxide hydroxide. Langmuir 7 2213-2218 Kandori, K. Aoki,Y. Yasukawa, A. Ishikawa, T. (1998) Effects of metal ions on the morphology and structure of hematite particles produced from forced hydrolysis reaction. 

Characterization of monodispersed hematite particles by gas adsorption and Fourier transform infrared spectroscopy. 

Kandori, K. Ohkoshi, N. Yasukawa, A. Ishikawa, T. (1998 a) Morphology control and texture of hematite particles by dimethylforma-... 

Kandori, K. Tamura, S. Ishikawa.T. (1994) Inner structure and properties of diamondshaped and spherical a-Fe203 particles. Colloid Polym. Sci. 272 812-819 Kandori, K. Uchida, S. Kataoka, S. Ishikawa, T. (1992) Effects of silicate and phosphate on the formation of ferric oxide hydroxide particles. J. Mater Sci. 27 719-728 Kandori, K. Yasukawa, A. Ishikawa,T. (1996) Influence of amines on formation and texture of uniform hematite particles. J. Colloid Interface Sci. 180 446-452 Kaneko, K. Inouye, K. (1974) Electrical properties of ferric oxyhydroxides. Bull. Chem. 

Muramatsu, A., Ishikawa, S. Sugimoto.T. (1994) Controlled formation of ultrafme nickel particles on well-defined hematite particles. Coll. Surf. A 82, 29-35... 

Ozaki, M. Krathovil, S. Matijevic, E. (1984) Eormation of monodispersed spindle type hematite particles. J. Colloid Interface Sci. 102 146-151... 

Shindo, D. Murakami,Y. Hirayama,T. (1998) Application of electron hologram to morphological analysis of spindle-type hematite particles, Mater. Transact. JIM 39 322-324 Shindo, H. Huang, P.M. (1984) Catalytic effects of manganese (IV), iron(III), aluminum, and silicon oxides on the formation of... 

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