Enhanced BaZrO3 mechanosynthesis by the use of metastable ZrO2 precursors.

The current work assesses the impact of structural differences between stable and metastable ZrO2 precursors on the mechanochemical preparation of BaZrO3. Monoclinic (m-ZrO2) and tetragonal (t-ZrO2) zirconia polymorphs were prepared without stabilizing additives by slow alkaline precipitation. High-energy milling of the individual ZrO2 precursors induced different partial transformations in each case. The as-synthesized m-ZrO2 powders showed partial conversion to the tetragonal polymorph on mechanical activation, reaching about 10% t-ZrO2 after 420 min accompanied by increases in strain. In contrast, the as synthesized t-ZrO2 powders underwent the inverse transformation to the monoclinic phase, producing about 50% m-ZrO2 after 120 min with the liberation of strain. The t-ZrO2 precursor was shown to exhibit the higher reactivity with barium peroxide, yielding significantly earlier formation of barium zirconate under room-temperature mechanosynthesis. The progress of the mechanochemical formation of BaZrO3 has been discussed with respect to the differing behaviour of the ZrO2 precursors upon mechanical activation and associated thermodynamic perspectives.

Pulmonary arteriovenous fistulas. Case presentations and clinical recognition.

This report describes characteristic features and clinical presentation of six young patients (ranging in age from five to 25 years) with various congenital forms of pulmonary arteriovenous fistulas as well as one 21-year old patient with traumatic intrapulmonary arteriovenous fistula. The former six patients were cyanotic, had clubbing of the digits and exertional dyspnea; two, additionally, had telangiectasia. All patients underwent cardiac catheterization and pulmonary angiography. None had pulmonary hypertension. Angiographically, four had diffuse arteriovenous fistulas in both lungs (Figures 1 and 3 to 5) and two had arteriovenous fistulas localized in one pulmonary segment. Four patients were additionally studied with radionuclide angiography and pulmonary perfusion scintigraphy. In three of these, substantial right-to-left shunt in the region of the lungs was detected; the diagnosis could not be established in only one of the latter with a small traumatic intrapulmonary arteriovenous shunt of less than 10%. While noninvasive methods provide adjunctive diagnostic support, pulmonary angiography is still required to assess, with certainty, the nature and localization of the lesion. In cyanotic patients with no evidence of cardiac disease, differential diagnostic consideration should be given to pulmonary arteriovenous fistulas.