Anisotropy of the Mechanical and Thermoelectric Properties of Hot-Pressed Single-Layer and Multilayer Thick Ca3Co4O9 Ceramics

Abstract

Ca3Co4O9 (349) thermoelectric (TE) ceramics were prepared by hot‐pressing (HP) process under various stress levels up to 30 MPa. Microstructure investigations have revealed strong enhancements of the bulk density and the texture strength, and a remarkable decrease of the in‐plane grain boundary density as the HP stress, σ, is increased. The mechanical properties obtained from nanoindentation and three‐point bending tests, and the TE properties were correlated to the microstructure. The influence of the HP stress level on these properties was examined in the parallel (c) and perpendicular (ab) directions to the pressing axis. Hardness (Hab and Hc ) and elastic modulus (Eab and Ec ) values were shown to increase remarkably with the HP stress level and the anisotropy ratio between out‐of‐plane and in‐plane resistivity values too. As ρab was considerably reduced and the Seebeck coefficient, Sab, remains constant when σ is raised, the power factor, PFab, was greatly improved for the higher stress values. and PFab900 K are 64 and 595 μW.m−1.K−2, respectively, for the HP samples processed under 30 MPa. Thick specimens usable in practical devices were obtained by HP stacked single layers. Their microstructure was investigated and correlated to the TE and mechanical properties.

Influência da composição e das variáveis de processamento deformulações à base de argilas - uso em materiais refratários

“…No presente trabalho foi avaliado um tempo de maturação de até quatro semanas e realizada uma análise estatística para verificar a significância desta variável nas propriedades físico-mecânicas. Além da composição e do tempo de maturação, a etapa de conformação é fundamental, uma vez que durante este processo o material adquire a forma e características estruturais pretendidas, podendo ser conformado via plástica, seca ou líquida, sendo os métodos de conformação mais comuns: prensagem [10,11], slip casting [12] e extrusão [13]; dentre estes, o processo de prensagem é bastante utilizado na cerâmica tradicional em virtude de sua elevada produtividade, fácil automatização e versatilidade, sendo possível a produção de peças de tamanhos e formas variadas. Além disso, permite a conformação de peças com baixa retração de secagem devido ao uso de baixos teores de umidade e, como consequência, apresentam estabilidade dimensional [14].…”

Anisotropic thermal conductivity of thin polycrystalline oxide samples

“…Effect of microstructure, grain size, pressure tuning, mineralogy and porosity and fluid control on thermal conductivity of anisotropic ceramics have been studied as relevant factors in earlier research. [10][11][12][13][14][15] The present work sets out to study the anisotropic thermal conductivity in polycrystalline oxide materials. Standard methods to measure the thermal conductivity using a heat flow technique and laser-flash technique have been used wherever sample sizes were suitable for these methods.…”

Influence of Ca substitution by Mg on the Ca₃Co₄O₉ performances

“…Such processes allow the alignment of the conducting planes producing macroscopic properties comparable to the obtained on single crystals, by decreasing electrical resistivity. Numerous methods have been reported to be efficient in producing well aligned bulk materials, in these or in similar anisotropic systems, such as hot uniaxial pressing [13], spark plasma sintering (SPS) [14], microwave texturing [15], laser floating zone melting (LFZ) [16,17], electrically asisted laser floating zone (EALFZ) [18,19], templated grain growth (TGG) [20], etc. The main advantage of these techniques is the production of materials with very low electrical resistivity values due to the preferential alignment of conducting planes with the current flow direction.…”