Abstract
South America and particularly Colombia, has niobium and tantalum deposits, which can be used as a carbon steel protective agent. A preliminary step is the raw material characterization. Fresh and calcinated samples of niobium mineral in ores and sand were analyzed through optic microscopy, laser-Raman spectroscopy, DRX and textural aspects. The main components of the ore and alluvial sand were Ferrotapiolite and ferrocolumbite with chemical formula (Fe,Mn)•(Ta,Nb)2O6 and associated oxides like Fe2O3, SiO2. In the shape of Tectosilicates, Mn-Tantalite, Nb=O terminal and polyatomic octahedral structures of NbO6, highly distorted, susceptible to form carbides. Ferrocolumbite synthetic (FeNb50) was used as precursor of NbC coating for the surfaces protection of AISI 1020 steel samples having dimensions of 3/8 inch diameter and 1/2 inch length. The film was obtained by thermoreactive deposition at atmospheric pressure. The anticorrosive effectiveness of 9 thermic treatments was tested through accelerated corrosion tests and verified by Raman spectroscopy. The formation of a hard coating of NbC was identified using Energy Dispersive X-ray Spectroscopy (EDS), in a very small range between 950°C for 2.5h and 1000°C for 1.5h, in presence of Fe3C, corresponding with the lowest oxidation percentages. SEM microscopy shows a rough and uneven surface. The intervals of thickness of 4 µm to 137.2 µm, measured with a MCT-300. Bonds between Nb-C and Fe-C, Nb2O5 and NbO6 species were appreciated with the Laser-Raman spectroscopy after the oxidation process.
