• Coelho, Rodrigo

Abstract

Ni and Mn doped tetrahedrites synthesized by solid state reaction and densified by hot-pressing were coated with boron nitride and two refractory silicon pastes. The coated materials were exposed to air for 1000 h and 500 h, while heated at 648 K to test the protection efficiency of the coatings. Trough X-Ray Diffraction (XRD) analysis and Scanning Electron Microscopy conjugated with Energy dispersive spectroscopy (SEM-EDS), phases of antimony oxide and dicopper sulfide were detected in the materials coated with boron nitride. Similar secondary phases were also detected on the Cu10.5Ni1.5Sb4S13 tetrahedrites while using the silicon paste coatings, whereas on Cu11Mn1Sb4S13 no traces of oxidation or degradation were observed. However, measurements of the Seebeck coefficient made on the manganese material indicate a reduction from 127 µV/K to 85 µV/K for the coated and aged materials, respectively. A deeper analysis made by optical and electronic microscopy, revealed the presence of a MnSO4 interlayer that affects the stoichiometry of the materials and, consequently, changes the Seebeck coefficient.

Topics

• phase
• scanning electron microscopy
• x-ray diffraction
• nitride
• Silicon
• Boron
• Energy-dispersive X-ray spectroscopy
• refractory
• Manganese
• Antimony