The synthesis of nanocrystalline powders of zirconia often produces the tetragonal phase, which for coarse-grained powders is stable only at high temperatures and transforms into the monoclinic form on cooling. This stability reversal has been suggested to be due to differences in the surface energies of the monoclinic and tetragonal polymorphs. In the present study, we have used high-temperature oxide melt solution calorimetry to test this hypothesis directly. We measured the excess enthalpies of nanocrystalline tetragonal, monoclinic, and amorphous zirconia. Monoclinic ZrO 2 was found to have the largest surface enthalpy and amorphous zirconia the smallest. Stability crossovers with increasing surface area between monoclinic, tetragonal, and amorphous zirconia were confirmed. The surface enthalpy of amorphous zirconia was estimated to be 0.5 J/m 2 . The linear fit of excess enthalpies for nanocrystalline zirconia, as a function of area from nitrogen adsorption (BET) gave apparent surface enthalpies of 6.4 and 2.1 J/m 2 , for the monoclinic and tetragonal polymorphs, respectively. Due to aggregation, the surface areas calculated from crystallite size are larger than those measured by BET. The fit of enthalpy versus calculated total interface/ surface area gave surface enthalpies of 4.2 J/m 2 for the monoclinic form and 0.9 J/m 2 for the tetragonal polymorph. From solution calorimetry, the enthalpy of the monoclinic to tetragonal phase transition for ZrO 2 was estimated to be 1071 kJ/mol and amorphization enthalpy to be 3472 kJ/mol. J ournal

A new synthesis of the silicon‐network‐backbone polymer poly(methylsilyne) gives a material that is easily converted by pyrolysis to smooth continous films of stoichiometric silicon carbide (see Figure). The films are adherent to the silicon or alumina substrates, and show root mean square roughness of 169 Å over a 500 μm range. Applications in electronics are envisaged.

A simple demonstration of photocatalysis is presented. The demonstration is visual, simple to perform, and could easily be modified into a laboratory experiment. The mechanism of dye degradation by the photocatalyst is also discussed. In addition to illustrating a photocatalytic reaction, it is also an example of the reduction and oxidation of organic compounds and experimental design that link the catalysis to TiO 2 .

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