Thermochemical stability of zirconia-titanium nitride as mixed ionic-electronic composites

Submitted by Marco Antonio Oliveira da Silva ([email protected]) on 2018-07-31T16:34:13Z No. of bitstreams: 1 24797.pdf: 1218080 bytes, checksum: 809ce282cc353a847cc89476da445e01 (MD5)Made available in DSpace on 2018-07-31T16:34:13Z (GMT). No. of bitstreams: 1 24797.pdf: 1218080 bytes, checksum: 809ce282cc353a847cc89476da445e01 (MD5)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Dense zirconia (8% molar yttria-stabilized ZrO2)-titanium nitride (TiN) composites are fabricated to obtain mixed ionic-electronic conducting ceramic systems with high degree of electronic and thermal conductivity. The composites are consolidated by spark plasma sintering (SPS), starting from pure powders of the pristine phases mixed in different ratios (TiN = 25, 50, 75 wt%). A careful optimization of the SPS conditions allows producing highly dense samples with no reaction between the phases or degradation by oxidation, thus maintaining the chemical integrity of the two phases. For all the composites, high electrical conductivity is attained. Samples exhibit metallic behavior, showing an unexpected percolation of TiN in the YSZ matrix for volume fraction ≤ 25 wt% (27 vol%). Chemical degradation and electrical properties of the compounds were monitored under oxidative (air) and inert (Ar) atmosphere at high temperatures. The oxidation kinetics of the nitride phase was inhibited by the microstructure of the composite. The electrical properties of such composites were explored at high temperature to evaluate its application in electrochemical devices. As results, it is shown that electrical transport properties of the composite can be tuned by both the relative volume fraction of phases and controlled oxidative treatments. Adjusting such parameters different electric behaviors were observed ranging from predominant electronic conductors, to temperature-independent resistivity, and semiconducting.CNPq: 447813/2014-5; 401218/2014-7FAPESP: 15/20434-0; 14/09087-4; 14/50279-