Chuangchuang Ruan,Hongzhang Song,Mengmeng Fan,Haoshan Hao,Shaohui Liu
Misfit-layered oxides Ca 3 Co 4 O 9+δ + z wt% SiC ( z = 0.00, 0.025, 0.05, 0.1, 0.2) samples were synthesized using solid-state sintering method and the effects of SiC nanoparticles diapersion on the thermoelectric properties were investigated. Thermoelectric properties of Ca 3 Co 4 O 9+δ + z wt% SiC ( z = 0.00, 0.025, 0.05, 0.1, 0.2) were investigated up to 923 K. Compared with pure sample, the electrical resistivity of SiC-added samples reduces, for Ca 3 Co 4 O 9+δ + z wt% SiC ( z = 0.00, 0.025, 0.05, 0.1, 0.2) ceramic samples with x ≤ 0.05, the electrical resistivity decreases with increasing SiC nanoparticles adding amounts. And, the electrical resistivity exists transition from semiconductor to metal conduction mechanism. While, the thermal conductivity also decreases due to the addition of SiC nanoparticles . As a result, the Ca 3 Co 4 O 9+δ + 0.2 wt% SiC sample had the lowest thermal conductivity of 1.47 W/Km at 923 K, which was 18.4% lower than that of the Ca 3 Co 4 O 9+δ sample. The ZT value of Ca 3 Co 4 O 9+δ + 0.05 wt% SiC can reach 0.218, which is 40.9% higher than the pure Ca 3 Co 4 O 9+δ sample.
Songtong Xuan,Yuming Tian,Xiangchen Kong,Jianying Hao,Xiaojun Wang
The tuning of the properties of MgAl 2 O 4 -based materials has aroused great attention in the field of engineering technology. Along these lines, magnesia and alumina were used as raw materials to prepare spinel by the solid-phase sintering method at 1500–1600 °C. Particularly, the impacts of the different MgO/Al 2 O 3 molar ratios on the microstructural densification, sintering process and mechanical property of the fabricated materials were systematically studied. The results showed that the stoichiometric spinel with the highest concentration of ion diffusion possessed the best densification. And the magnesium-rich spinel displayed the better densification following with the formation of solid-solution, while the aluminum-rich spinel exhibited the worst ability in forming the solid-solution. Moreover, the different molar ratios changed the microstructure of the spinel, which induced the optimal sintering temperature of stoichiometric spinel to be at least 50 °C below that of the others. Specifically, in stoichiometric spinel, spinel grains grew up and formed obvious structure, which made the sintering process arrive at the end point and made the performance reach the best. Specifically, the flexural strength was 112.62 MPa and apparent porosity was 0.44%. However, no grown or developed spinel grains were observed for magnesium-rich/aluminum-rich spinels, which delayed the sintering process.
Porous gelcasted and solid-state-sintered SiC (S-SiC) ceramics with significantly improved connectivity were successfully prepared through the synergistic pore-forming mechanism of direct foaming and particle packing, using fine (D 50 = 0.5 μm) and coarse (D 50 = 5.0 μm) graded SiC powders as the main raw materials. As the proportion of coarse SiC powder increased, the viscosities of aqueous SiC-B 4 C-C slurries sharply decreased, which thus flourished foaming and enlarged bubble-derived-pore diameter in porous S-SiC ceramics, accompanied with the increased amount and size of window. Moreover, abundant particle-packing pores in struts of bubble-derived pores were also formed and even interconnected with each other at 60 wt% of coarse SiC powder. Besides, there was a remarkable increase in porosity from 61.0% to 81.7% and accordingly a significant decline in density from 1.24 g cm −3 to 0.58 g cm −3 as the content of coarse SiC powder increased. The optimized multiple pore microstructures resulted in an amazing nitrogen gas permeability of 1.78×10 −11 m 2 under the condition of an excellent compressive strength of 10.8 ± 2.7 MPa.
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