Abstract
The dissolution behavior of α-SiC coated with amorphous SiO 2 films 0.67 ± 0.34 nm thick and the adsorption of Al ions onto SiC surface were studied in 1.0 vol.% solid suspensions containing 0.37 or 3.7 mM of Al(NO 3) 3 at pH 3–10. In the suspension at pH 3–7, the SiO 2 films and H 2O interacted to form soluble H 4SiO 4. The amount of SiO 2 dissolved in the SiC suspensions was dominated by the solubility limit of surface SiO 2 films and increased at pH 10 due to the formation of H 3SiO 4 − and H 2SiO 4 −2 ions. The addition of Al(NO 3) 3 to the neutral and basic suspensions suppressed the dissolution of the SiO 2 films. The neutral SiC surface near the isoelectric point (pH 3.1) adsorbed no Al 3+ ions or just a trace. The negatively charged SiC surface adsorbed 1.13 μmol of Al 3+ ions m −2 at pH 4. In the pH range 5–8, negatively charged SiC particles coexisted with positively charged Al(OH) 3 precipitate was charged negatively at pH 10 because its isoelectric point was pH 9.0 and some Al(OH) 3 dissolved as Al(OH) 4 − ions.
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