Synthesis of WO3 nanorods by the oxidation of bulk tungsten samples with supercritical water

Abstract

dT/dt = 2 K min -1 . A cell with a specified amount of water and a cell with the 〈W〉 sample were loaded in the reactor. In entries 2—4, only a cell with the 〈W〉 sample was loaded in the reactor and water at the supercritical parameters (Т > 647 K, P > 22.1 MPa) was sprayed in the preheated reactor through a highperformance gate from a prereac� tor. After water was sprayed, the temperature of the reac� tor was maintained constant. The volume of the prereac� tor is ∼20 times of the volume (VR) of the reactor occupied with water. The pressure (P) was measured by membrane tensiosensors, whose accuracy in the range from 1 to 40 MPa was 0.25%. The temperature regime of the reactor was established by a thermoregulator using ohmic heaters and chromel—alumel thermocouples. The temperature dependence of the hydrogen pressure was measured in en� try 1, and the time dependence of the hydrogen pressure was measured in entries 2—4. At the end of experiments the reactor was rapidly cooled. Water and Н 2 , which was formed upon oxidation, were collected in a collector cooled with liquid nitrogen. The amount of hydrogen NH2 was determined from the results of measurements of the H2 pressure in a volumetric cylinder of a known volume, and the gas composition in the cylinder was measured on a quadrupole mass spectrometer. 6 In addition, the weights m0 of the 〈W〉 samples were measured before and after oxidation, and the difference indicated the weight increase Δm. The values of the above parameters are given in Table 1