Volatile metal beta-diketonates - new precursors for the sonochemical synthesis of nanosized materials - sonolysis of thorium(IV) beta-diketonates

Ultrasonic irradiation (22 kHz, Ar atmosphere) of Th(IV) beta-diketonates T h(HFAA)(4) and Th(DBM)(4), where HFAA and DBM are hexafluoroacetylacetone a nd dibenzoylmethane respectively, causes them to decompose in hexadecane so lutions, forming solid thorium compounds. The first-order rate constants fo r Th(IV) beta-diketonate degradation were found to be (9.3+/-0.8)x 10(-3) f or Th(HFAA)(4) and (3.8+/-0.4)x 10(-3) min(-1) for Th(DBM)(4), (T=92 degree s C, I=3 Wcm(-2)). The rate of the sonochemical reaction increased with the rising beta-diketonate volatility and decreased with the rising hydrocarbo n solvent vapor pressure. Solid sonication products consisted of a mixture of thorium carbide ThC2 and Th(IV) beta-diketonate partial degradation prod ucts. The average ThC2 particle size was estimated to be about 2 nm. ThC2 f ormation was attributed to the high-temperature reaction occurring within t he cavitating bubble. The thorium beta-diketonate partial degradation produ cts formed in the liquid reaction zones surrounding the cavitating bubbles. (C) 2000 Elsevier Science B.V. All rights reserved.