Use of Thermal Boron Technique to Determine Optimum Synthesis Parameters for Zirconium and Hafnium Diborides

Abstract

Zirconium and hafnium diborides were synthesized. The process of obtaining zirconium and hafnium diborides was carried out by reduction of zirconium and hafnium dioxides with amorphous boron at high temperature in a vacuum furnace with a residual pressure of 10 Pa. The synthesis of metal diborides included the following stages: preparation of charge, pressing, annealing of tablets, milling, and classification. The initial components were mixed in a drum-type apparatus; an aqueous solution of polyvinyl alcohol was used as a plasticizer. Tableting was performed on an OYSTAR Manesty FlexiTab tablet press with a punch diameter of 13 mm at a pressure of 218.7 MPa. The thickness of the obtained tablets was 3 mm. The obtained tablets were annealed in a Nabertherm VHT/GR vacuum furnace. A graphite crucible with zirconium oxide or hafnium oxide backfill, respectively, was used for annealing. The furnace was vacuumized with a forevacuum pump to a residual pressure of 10 Pa. The morphology of ZrB2 and HfB2 particles was investigated using the QUANTA 200 3D electron and focused-beam system. The phase composition and structural parameters of the samples were investigated on a Shimadzu XRD-6000 diffractometer with Cu Kα radiation. We determined the optimal parameters for the synthesis of zirconia and hafnium diborides: the optimal temperature for the synthesis of zirconia diboride was 1800 оС, for the synthesis of hafnium diboride — 1850 оС, the heating rate was 8.5 оС/min. The highest yield of zirconium and hafnium diborides was achieved in samples with a molar ratio of MeO2:B = = 1:6 at a synthesis time of 60 minutes. The yield of metal diborides was 99%.The authors who contributed to this paper include V. I. Sachkov, R. A. Nefedov, R. O. Medvedev, A. S. Sachkova, D. A. Biryukov.The authors would like to thank the Tomsk Regional Centre of Shared Knowledge for their support of this research work. This research was funded by the Ministry of Education and Science of the Russian Federation under the Governmental Assignment no. FSWM-2020-0028.