Several attempted syntheses of Ti-TMS1, a hexagonal mesoporous TiO2 reported by Antonelli and Ying, have resulted in a lamellar structure as determined by two-dimensional powder X-ray diffraction and transmission electron microscopy (TEM). Regions of partially calcined lamellar materials, when observed by TEM can be mistaken for hexagonal material. In no cases are specimens produced that were unambiguously hexagonal. It is concluded that the hexagonal material exists, if at all, only as a minor component of a larger lamellar structure when phosphate surfactants are used. Ti-TMS1 therefore remains elusive.
The X-ray powder diffraction pattern for the title compound is reported in the range 5 ≤ 2 θ ≤ 125°. The sample was prepared through solid-state reaction of BaCO 3 , CuO, and Pr 6 O 11 , and characterized with respect to oxygen content through iodometric titration. Refined parameters for the orthorhombic (space group Pmmm ) unit cell are a = 3.8587(2) Å; b = 3.9302(1) Å; c = 11.7126(3) Å; a/b = 0.98181(6); a/c = 0.32945(2); b/c = 0.33555(1); Z = 1; D x = 6.705(2) Mg m −3 ; V = 177.62(1) Å 3 ; formula wt. = 717.48(16) g mol −1 ; SS/FOM: F 30 = 48(0.005,127).
A consistent methodology for obtaining the enthalpy of formation of Fe2+-containing binary and multicomponent oxides using high-temperature oxide melt solution calorimetry has been developed. The enthalpies of wüstite (FeO) and magnetite (Fe3O4) oxidation to hematite (Fe2O3) were measured using oxidative drop solution calorimetry in which the final product is dissolved ferric oxide. Two methods were applied: drop solution calorimetry at 1073 K in lead borate solvent and at 973 K in sodium molybdate, each under both oxygen flowing over and bubbling through the solvent, giving consistent results in agreement with literature values. The enthalpies of formation of all three iron oxides from the elements were obtained using a thermodynamic cycle involving the directly measured oxidative dissolution enthalpy of iron metal in sodium molybdate at 973 K and gave excellent consistency with literature data.
Nanocrystalline BaTiO 3 particles are synthesized under hydrothermal conditions by the reaction of nanosized TiO 2 colloids with aqueous solutions of Ba(OH) 2 at 80°C. A dissolution-precipitation mechanism is proposed for the formation of BaTiOs by this route, because suspended TiO 2 nano-particles dissolve into Ba(OH) 2 solution, supersaturate the solution phase, and subsequently precipitate BaTiO s particles. The origin of the rough "raspberry-like" BaTiOs particles during growth stages can be explained by one of two mechanisms: (i) the morphological instability at the growth front during continuous growth, or (ii) aggregation of colloidal particles by multiple clustering. Our TEM studies on samples prepared by controlled seeding experiments show that a multiplicity of low or high angle grain boundaries occur during growth, supporting the aggregation growth. In order to separate the nucleation step from the growth step more efficiently, seed BaTiO 3 particles were prepared by adding TiO 2 colloids (Degussa, P-25) to 2.23 M Ba(OH) 2 solution and hydrothermally reacting at 80°C under atmospheric pressure for 48 hours in polyethylene bottles. The resulting seed particles were recovered by centrifugation, rinsed with C02-free deionized water and freeze-dried.
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