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.
Dispersion of Graphene in water is conducive to their practical applications as lubricating additive in water-based fluids due to their safety, low cost and environmental-friendliness. But owing to its hydrophobicity , it is difficult to achieve stable aqueous graphene suspension. Here, we use the Toluene-2,4-diisocyanate as bridging agent between hydrophilic Poly (ethylene glycol) (PEG) and ethanolamine to prepare the amino-containing PEG (PEG-NH 2 ), followed by covalently grafting PEG-NH 2 onto the surface of carboxylaed graphene (G-COOH) nanosheets to synthesize the PEGlated graphene (PEG-G) via facile amidation under mild conditions. The physical, chemical properties of product were characterized by Fourier transformed infrared spectra (FTIR), Raman spectra , X-ray photo electron spectroscopy (XPS) and so on. Transmission electron microscopy (TEM) and scanning probe microscope (SPM) were utilized to observed the morphology of G-COOH and PEG-G. The frictional properties of PEG-G as nanoadditive of water-based lubricant were characterized by UMT-3 tribometer, following with analyzes on wear surfaces by 3D laser scanning confocal microscopy . Based on the results of characterization, the PEG-G was prepared successfully and the dispersion shows superior friction-reducing and anti-wear properties owing to the formation of fluid adhesive film and carbon protective film, especially the concentration of PEG-G in water is 0.05 wt%.
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