Mechanochemical Synthesis of Novel Sensor Materials
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1226-II04-05
Mechanochemical Synthesis of Novel Sensor Materials Monica Sorescu1, L. Diamandescu2 and A. Tomescu2 1 Duquesne University, Department of Physics, Pittsburgh, PA 15282-0321, U.S.A. 2 National Institute of Materials Physics, 77125 Bucharest, Romania ABSTRACT The xZnO-(1-x)α-Fe2O3 and xZrO2-(1-x)α-Fe2O3 nanoparticles systems have been obtained by mechanochemical activation for x=0.1, 0.3 and 0.5 and for ball milling times ranging from 2 to 24 hours. Structural and magnetic characteristics of the zinc and zirconium-doped hematite systems were investigated by X-ray diffraction (XRD), Mössbauer spectroscopy and conductivity measurements. Using the dual absorber method, the recoilless fraction was derived as function of ball milling time for each value of the molar concentration involved. As ZnO is not soluble in hematite in the bulk form, the present study clearly illustrates that the solubility limits of an immiscible system can be extended beyond the limits in the solid state by mechanochemical activation. Moreover, this synthetic route allowed us to reach nanometric particle dimensions, which makes these materials very important for gas sensing applications. INTRODUCTION Research studies of semiconducting oxides have become increasingly important due to their catalytic applications as well as their sensing properties in the detection of toxic gases, such as carbon monoxide or methane [1-3]. Metal oxides are semiconductor materials best suited for gas sensing. In contradistinction to other semiconductors, which suffer irreversible chemical transformations at the surface and progressive oxidation due to prolonged and repeated heating in air, metal oxides absorb the oxygen on their surface reversible. The sensing properties are expected to be enhanced for nanostructured semiconducting oxides due to the great surface area and subsequent great surface activity [4-14]. We recently synthesized xSnO2-(1-x)α-Fe2O3 system using the hydrothermal method [15] and characterized its structural and magnetic properties using several techniques. Our main finding was that the solubility limits of tin oxide in the hematite lattice are increased compared with the bulk values. A similar conclusion was obtained for the xIn2O3-(1-x)α-Fe2O3 system synthesized under hydrothermal supercritical conditions [16]. We propose to investigate if ball milling can increase even more the range of solubilities for this type of systems. As described in this paper, we designed an experiment to study the solubility limits in hematite of ZnO, which is known to be immiscible in the bulk configuration. We used high-energy ball milling to obtain the xZnO-(1-x)α-Fe2O3 system and XRD and Mössbauer spectroscopy to characterize the properties. One success of this route is the occurrence of particles at the nanoscale. To compare and contrast these results, we also synthesized xZrO2-(1-x)α-Fe2O3 nanoparticles system in order to decide whether the valence of the metal in the oxide (bivalent Zn over tetravalent Zr) plays a role in selecting the occurrence
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