Synthesis And Charaterization Of Yttrium Oxide Nanowires And Sub-micrometer Sized Fibers

Yttrium oxide （Y₂O₃） is one of the most important rare-earth compounds andhas been extensively applied to optics, functional ceramics, optoelectronics, catalyticreactions and high-efficient additives for functional composite materials. With respectto the physical properties, yttrium oxide has a high melting temperature （Tm=2430°C）, which is higher than that of a number of other well-known oxides, such asalumina, zirconia, YAG, and spinel. Yttrium oxide normally exists as a cubic phaseand is stable up to melting point without phase transformation. Many methods, suchas solid-state method, sol–gel processing, gas-phase condensation, precipitation,hydrothermal synthesis, and so on, have been developed to prepare yttrium oxide withdifferent morphology. Compared with other methods，hydrothermal synthesis iswidely accepted as a better and simple method to prepare materials with controlledmorphology and particle size. So in this paper we used hydrothermal synthesis toprepare yttrium oxide micro/nanometer materials.Here, we successfully synthesized yttrium oxide nanowires in nitric acid system.First，Y₄O（OH）₉（NO₃） nanowires were synthesized through a facile hydrothermalreaction, followed by a subsequent heat treatment obtained yttrium oxide nanowires.The diameter of the nanowires ranged from20to35nm, while the length was0.6-2 μm, with aspect ratio of20-50. XRD and TG-DTA charaterizations show that theobtained Y₂O₃is pure phase. TEM and N₂adsorption characterizations show theobtained yttrium oxide nanowires were porous, with pore size of5-15nm. It has beenshowed that the hydrothermal temperature and pH value play crucial roles indetermining morphology of the products. It is found that increasing reactiontemperature would increase the aspect ratio of nanowires as well as improving thedistributing uniformity on diameters. Smaller nanowires could be obtained byincreasing pH value. By controlled the hydrothermal reaction temperature and pHvalue, the optimal experimental reaction conditions of formation the best morphologyfor the nanowires have been obtained:200°C for the hydrothermal temperature,13for pH value. The pores were originated from the decomposition of the hydrothermalprecursor Y₄O（OH）₉（NO₃） during the heat treatment to form yttrium oxide. Yttriumoxide formed porous structure in thermodynamics after calcining perhaps due toforming a more stable structure in the process of heat treatment. And the porous Y₂O₃nanowires will be of interest in optics and catalysis fields.Yttrium oxide ceramic fibers are attractive as reinforcements for high-temperaturematerials due to the combination of high strength and excellent high-temperaturestability in air. We successfully synthesized yttrium oxide sub-micrometer sized fibersin hydrochloric acid system in this paper. In this experimentmt, yttrium oxidesub-micrometer sized fibers have been synthesized via hydrothermal reaction andsubsequent thermal treatment using yttrium compound for Y（OH）₃（NO₃）_3-x·yH₂Osub-micrometer sized fibers as precursor. The fiber diameter ranged from100to300nm, while the length was up to tens of microns. The products before and after thethermal treatment were characterized by powder X-ray diffractions （XRD）, scanningelectron microscopy （SEM）, ion chromatograph analysis, and thermogravimetry anddifferential thermal analysis （TG-DTA）. It was found that the chemical composition,structure, and morphology of the products were closely related to the pH value ofreaction solution, and fibrous products could be obtained at pH9.5-10.25. Theexperiment results show that hydrothermal temperature, pH value and yttriumconcentration play important roles in determining particle size of the products. It is found that increasing reaction temperature and decreasing pH value, would obtainebetter morphology of the fibers. By controlled the hydrothermal reaction temperatureand pH value, the optimal experimental reaction conditions of formation the bestmorphology for the fibers have been obtained:200°C for the hydrothermaltemperature,9.5for pH value. These oxide fibers exhibited outstandinghigh-temperature stability, which maintained their morphology at temperature up to1400°C. Consequently, these fibers would be promising materials for refractoryapplications, such as refractory insulation and high temperature gas filtration.