Gordo, E., F. García-Carcedo, and J. M. Torralba. “Tantalum and Niobium Carbides Obtention by Carbothermic Reduction of Columbotantalite Ores”. Revista De Metalurgia, vol. 34, no. Extra, May 1998, pp. 395-9, doi:10.3989/revmetalm.1998.v34.iExtra.779.