MgO

Gilman [124] and Westwood and Hitch [135] have applied the cleavage technique to a variety of crystals. The salts studied (with cleavage plane and best surface tension value in parentheses) were LiF (100, 340), MgO (100, 1200), CaFa (111, 450), BaFj (111, 280), CaCOa (001, 230), Si (111, 1240), Zn (0001, 105), Fe (3% Si) (100, about 1360), and NaCl (100, 110). Both authors note that their values are in much better agreement with a very simple estimate of surface energy by Bom and Stem in 1919, which used only Coulomb terms and a hard-sphere repulsion. In more recent work, however, Becher and Freiman [126] have reported distinctly higher values of y, the critical fracture energy. ... 

As a final example, similar spectroscopy was carried out for CO2 physisorbed on MgO(lOO) [99]. Temperatures were around 80 K and equilibrium pressures, as low as 10 atm (at higher temperatures, CO2 chemsorbs to give surface carbonate). Here, the variation of the absorbance of the infrared bands with the polarization of the probe beam indicated that the surface CO2 phase was highly oriented. 

Fig. XVll-19. Adsorption of CH4 on MgO(lOO) at 77.35 K. The vertical line locates each vertical step corresponds to the condensation of a monolayer. There was no hysteresis. Desorption points are shown as . (From Ref. 110.)...

Some general points are the following. One precondition for a vertical step in an isotherm is presumably that the surface be sufficiently uniform that the transition does not occur at different pressures on different portions, with a resulting smearing out of the step feature. It is partly on this basis that graphitized carbon, BN, MgO, and certain other adsorbents have been considered to have rather uniform surfaces. Sharp LEED patterns are another indication. 

The classic catalyst consists of Co-Th02-MgO mixtures supported on Kieselguhr (see Ref. 269) group VIII metals, especially Ni, generally are active,... 

MgO films have been grown on a Mo(lOO) substrate by depositing Mg onto a clean Mo(lOO) sample in O2 ambient at 300 K [39, 40]. LEED results indicated that MgO grows epitaxially at an opthnum O2 pressure of... 

Torr, with the (100) face of MgO parallel to the Mo(lOO) surface. Figure A3.10.13 shows a ball model... 

Figure A3.10.13 Ball model illustration of an epitaxial MgO overlayer on Mo(lOO) [38].

Wu M-C, Estrada C A, Corneille J S and Goodman D W 1996 Model surface studies of metal oxides adsorption of water and methanol on ultrathin MgO films on Mo(IOO) J. Chem. Phys. 96 3892... 

Grimes R W, Catlow C R A and Stoneham A M 1989 A oomparlson of defeot energies In MgO using Mott-LIttleton and quantum meohanloal prooedures J. Phys. Condens Matter 1 7367-84... 

Wu R and Freeman A J 1994 Magnetism at metal-ceramic interfaces effects of a Au overlayer on the magnetic properties of Fe/MgO(001) J. Magn. Magn. Mater. 137 127-33... 

Basic properties of product Be(OH)2 amphoteric MgO insoluble slightly MjOH), soluble... 

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