N-doped SiC-MoSi 2 ceramics were successfully fabricated by hot pressing in N 2 using Y(NO 3 ) 3 .6 H 2 O as both sintering aids and additional N sources. The impact of Y(NO 3 ) 3 .6 H 2 O content on the densification, electrical properties, and infrared emission performance of the resulting ceramics were investigated. The distribution of Y-based sintering aid is improved by melting of Y(NO 3 ) 3 .6 H 2 O during slurry drying, enabling the relative density to increase up to 97.4%. Y(NO 3 ) 3 .6 H 2 O subsequently decomposes during sintering and allows the substitution of atomic N for the C sites in SiC lattice and production of the N-derived donor level. A larger amount of N dopant elevates the carrier density up to 1.90 × 10 16 cm -3 . Remarkably, The SiC − 10 wt% MoSi 2 ceramics sintered with 16.9 wt% Y(NO 3 ) 3 .6 H 2 O exhibits the lowest electrical resistivity (0.791 Ω·cm at room temperature) and highest infrared emissivity (0.913 at 800 ℃), the latter of which may also be attributed to lattice distortion induced by N doping . This work demonstrates N doping as a prospective strategy for synergistically optimizing the electrical conduction and infrared emission performance of SiC-based ceramics for infrared source applications.
Ya-nan Li,Ping Wu,Shiping Zhang,Yili Pei,Jinguang Yang,Sen Chen,Li Wang
Adding nanoparticles is a method to regulate the performance of thermoelectric materials. Ca 3 Co 4 O 9 /x MoSi 2 (x = 0, 0.05, 0.10, 0.13, and 0.16) was synthesized by a wet chemical method combined with atmospheric pressure sintering. The XRD and SEM results reveal that there are no other reaction in the samples. The grain size of all samples decrease with increasing MoSi 2 content, and all presented a similar flake morphology. The influence of MoSi 2 on the thermoelectric performance of Ca 3 Co 4 O 9 is systematically analysed. The appropriate addition of nano-MoSi 2 particles can increase the carrier concentration and enhance conductivity of Ca 3 Co 4 O 9 . The electrical conductivity of Ca 3 Co 4 O 9 /0.05 MoSi 2 is 83.16 Scm −1 , which is 49.2% higher than that of Ca 3 Co 4 O 9 at 1080 K. The Seebeck coefficient of the Ca 3 Co 4 O 9 /0.16 MoSi 2 sample reaches 197.56 μVK −1 at 980 K, which is significantly better than that of previously reported samples prepared by the same method. Moreover, combined with the experimental results and the analysis of the effective medium theory model, the addition of MoSi 2 can effectively debase the thermal conductivity of Ca 3 Co 4 O 9 . The thermal conductivity of Ca 3 Co 4 O 9 /0.16 MoSi 2 (∼1.26 Wm −1 K −1 , 1080 K) samples decrease greatly, which is attributed to the influence of interfacial thermal resistance and pores in the Ca 3 Co 4 O 9 /MoSi 2 . The ZT value of the Ca 3 Co 4 O 9 /0.05 MoSi 2 sample increases by 44.4% compare with that of Ca 3 Co 4 O 9 and reaches 0.26 at 1080 K. These results demonstrate that adding an appropriate amount of MoSi 2 particles is one of the methods to enhance the thermoelectric performance of Ca 3 Co 4 O 9 ceramic samples.
Lu Zhu,Yousen Zhu,Xuanru Ren,Ping Zhang,Jianghao Qiao,Peizhong Feng
MoSi 2 -MoB-ZrO 2 composite powders are one-step synthesized prepared by self-propagating high-temperature synthesis (SHS), which are further utilized to prepare the oxidation protective coatings by spark plasma sintering (SPS) method on molybdenum substrate. Microstructure and properties of the coatings were investigated and determined. Oxidation behavior of the coatings at high temperature was also studied. The results showed that the composite coating is dense and crack-free due to the addition of ZrO 2 , which is beneficial for the decrease of mismatch in coefficient of thermal expansion, and no void exists in the diffusion layer owing to the diffusion of Si, which is inhibited by adding MoB. Compared with the pure MoSi2 coating, the high hardness of the composite coating is enhanced by about 20% while the fracture toughness of the composite coating is improved by about 25%, which makes the occurrence of intergranular fracture , crack deflection and crack bridging. After oxidation at 1400 °C for 80 h, MoSi 2 coating failed while xMoSi 2 -MoB-3ZrO 2 (x = 3, 4, 5) composite coating still kept its protective effect. Only a little substrate is consumed during oxidation and improved oxidation resistance is gained by MoSi 2 -MoB-ZrO 2 composite coating. 3MoSi 2 -MoB-3ZrO 2 coating shows the relatively best oxidation resistance due to the formation of crack-free oxide film on the surface of the coating.
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