Stable metal-oxide surfaces

All boiler system waterside surfaces need the protection given by the smooth, hard, tenaciously adherent magnetite layer. The magnetite film sometimes may sparkle because of the precipitation of fine magnetite crystals onto the metal-oxide surface. Magnetite film formation is best achieved under stable, low-oxygen content operating conditions at a pH level of 10.5 to 11.5 (possibly up to 12.0). 

The arrows show the isotherm evolution for continual addition of dissolved Me. The initial isotherm with the slope of 1 (in the double logaritmic plot) corresponds to a Langmuir isotherm (surface complex formation equilibrium). [Me]S0 = solubility concentration of Me for the stable metal oxide [Me]p = solubility concentration of Me for a metastable precursor (e.g., a hydrated Me oxide phase). 

These stable DIP concentrations are believed to be controlled by a buffering of DIP through the adsorption and desorption onto metal oxide surfaces. This P buffering is believed to balance the low availability of SRP in higher-salinity waters, which occurs from phytoplankton uptake and anionic competition for surface adsorption sites. 

Figure 13.29. Schematic sorption isotherms of a metal ion (Me) on an oxide (XO ) at constant pH (a) adsorption only (H) adsorption and surface precipitation via ideal solid solution (c) adsorption and heterogeneous nucleation in the absence of a free energy nucleation barrier (AG 0) adsorption and heterogeneous nucleation of a metastable precursor (e) same as in (3) but with transformation of the precursor into the stable phase. The arrows show the isotherm evolution for continual addition of dissolved Me. The initial isotherm with the slope of 1 (in the double logarithmic plot) corresponds to a Langmuir isotherm (surface complex formation equilibrium). [Me]s , = solubility concentration of Me for the stable metal oxide [Me]p = solubility concentration of Me for a metastable precursor (e.g., a hydrated Me oxide phase). (From Van Cappellen, 1991.)...

Shohat and Mandler (37), and more recently Turyan et al. (33), have reported additional studies of patterning inorganic materials. The goal of the first report was to develop an approach for driving local acid-base reactions on surfaces. The motivation stems from previous work in which stable metal oxides, e.g., nickel hydroxide, served as an anchor for attaching organic and biological molecules onto surfaces in specific patterns. 

Different crystallographic planes of a semiconductor electrode usually exhibit different reaction kinetics. It was found in III-V compounds in indifferent electrolytes that the (lll)B face terminated with the anion plane (P, As) etched faster than the (lll)A face containing the cations (Ga, In) [47]. The planes composed entirely of metal atoms react more slowly than any other crystal plane because of the stable metal oxide layer, which can be formed on such planes. Consequently on these planes termed etch stop planes, provision of reactants (diffusion control) is not rate-limiting. In Si, the (100) planes are known to etch faster than (111) planes in alkaline solutions. This property is at the origin of various apphcations, such as texturization of silicon surface [formation of pyramids on (100) planes], which allows reduction of reflectivity of the front surface of solar cells and Si micromachining [48]. The semiconductor surface may be shaped during the anodic dissolution... 

Quantum chemical calculations have mostly been limited to small adsorbates such as formic acid (HCOOH) on different ZnO surfaces [449, 450]. Three structures have been suggested for the formate anion adsorbed on metal oxide surfaces bridging, bidentate, and unidentate structures as shown in Fig. 5. The energy difference between bridging structure and unidentate structure in interactions with the surface OH species was calculated to be very small [449]. Thus, theoretical studies of the adsorption of HCOOH on ZnO surface energetically favor a bridging structure, which is also found to be the most stable adsorption mode [449]. However, the results also indicate that the bonding mode of HCOOH on ZnO is sensitive to the... 

The patterned structures resulting from etching are continuous and electrically conductive within each pattern, and separated patterns are electrically isolated. Using pCP, Schottky diodes of aluminum have been prepared on p-type Si(lOO). Octadecanephosphonic acids are air stable compounds that are known to form stable, ordered monolayers on metal oxide surfaces [298,435]. SAMs on the native oxides of aluminum [435, 472, 473] and copper or iron [435, 473] have been formed from alkanephosphonic acids. 

---