Studies on synthesis and densification of niobium diboride using carbothermic reduction and hot pressing

Niobium Diboride (NbB ₂ ) is a candidate refractory metal boride material for high - temperature structural applications as well as a neutron absorber material in the fourth-generation nuclear reactors. In the present investigation, the feasibility study on the synthesis of high purity NbB ₂ was carried out by reduction of Nb ₂O ₅ using B ₄C and C as reducing agents. The process parameters such as the feed composition, temperatures etc. were optimised to carry out the reduction in a vacuum atmosphere. The production of NbB ₂ powder was scaled up to a kilogram scale by using this method. The synthesized and mechanically milled powder was characterized using XRD, chemical analysis and laser particle size analyser. Single - phase NbB ₂ powder was produced successfully under optimum conditions. The milled synthesized powder was having an average particle size of 3.1 μm with oxygen and carbon contents of <0.5% each. Pellets with a high density of 93% of theoretical value were prepared by hot pressing at 1800 °C, after carrying out the detailed densification studies. Hardness and elastic modulus of hot press NbB ₂ were determined by using the nano-indentation technique and values found to be 27.9 GPa and 705 GPa respectively. Flexural strength of hot pressed NbB ₂ obtained from a three-point bend test was found to be 339 MPa.