Materials Science Forum Vols. 809-810

Abstract: In order to increase the electrical conductivity greatly but maintain a large Seebeck coefficient and a low thermal conductivity simultaneously, the binary-phased LaCeFe₃CoSb₁₂-Sb nanocomposites composed of LaCeFe₃CoSb₁₂ skutterudite nanospheres and semimetal Sb microsized ribbons were fabricated via a hydro/solvo thermal route. The results suggest that the Sb powders result in a disordered structure during a hot-press process at its melting-point temperature and the disordered structure has been partly preserved into the room-temperature materials successfully. The Sb microsized ribbons enhance the electrical conductivity of the binary-phased materials largely, meanwhile the disordered structure increases the Seebeck coefficient obviously even though the thermal conductivity is also increased slightly. Consequently, the figure of merit of the binary-phased materials is improved significantly and the maximum value of 1.54 at 773 K has been realized for the LaCeFe₃CoSb₁₅ material.

Abstract: Monodispersed magnetic SmCo nanoparticles have been prepared by polyol synthesis using non-toxic inorganic precursors (nitrates). The effect of the additives of NaOH, HNO₃, CH₃COOH and poly vinyl pyrrolidone (PVP) on the formation of SmCo nanoparticles is studied in this paper. The results indicate that base solution can boost the reduction of Co while acid solution is helpful for the formation of SmCo due to decreasing the reduction velocity of Co. CH₃COOH is appropriate additive for the synthesis of SmCo nanoparticles, but more addition of CH₃COOH will result in the emergence of CoC₂ phase and decrease the coercivity of the resultants. The additive of PVP not only is a dispersing agent, but can prevent them from oxidating during preparation process. The SmCo nanoparticles with a size of 5-8 nm have the ferromagnetic properties of high coercivity (>1000 Oe).

Abstract: Barium titanate (BaTiO₃) used a strong dielectric materials, piezoelectric materials and ferroelectric materials, which is a kind of important electronic ceramic materials. With the miniaturization of electronic components, miniaturization, thin layer, nanosized barium titanate powder become an inevitable developing trend of barium titanate dielectric ceramics material. Some recent new progress for synthesis of barium titanate at home and abroad are summarized, the commentaries are made on the preparation process about advantages or disadvantages. Meanwhile, the analysis is made on the developing trend. Supercritical fluid extraction method have simple process, high extraction efficiency, no organic solvent residual, products of good quality, no environmental pollution, and so on. Research of BaTiO₃ nanopower may become an important direction of the field in the future.

Abstract: PbS nanocrystals was synthesized by a heterogeneous reaction of hydrogen sulfide gas and lead nitrate solution containing EDTA in ethanol. The influenceof initial molar concentration ratio of EDTA/Pb (NO₃)₂ (C_EDTA/C_{Pb (NO3)2}), volume ratio of ethanol/water (V_ethanol/V_H2O), pH value and flux of H₂S on the particle size of PbS were investigated. The structure, morphology, particle size, and particle size distribution ranges of PbS were characterized by XRD, FE-SEM, and laser particle size analyzer, respectively. Increasing C_EDTA/C_{Pb (NO3)2}, V_ethanol/V_H2O, and pH value, as well as decreasing the flux of H₂S decrease the particle size of PbS. PbS nanocrystals have an average particle size of 69 nm, a narrow size distribution, and a quasi-spherical shape when C_EDTA/C_{Pb (NO3)2} is 1, V_ethanol/V_H2O is 1, pH is 3.5, and the flux of H₂S is 20 ml/min.

Abstract: Effect of nanoparticles to improve the lubrication load capacity and resistance to extreme pressure of water-based rolling liquid was studied by four-ball tester. Compression experiments were conducted in different lubrication conditions with nanoparticles using Gleeble hot compression simulation machine. Then the residual nanoparticles characteristics and the surface morphology of the compressed sample were analyzed by SEM and EDS. The results show that water-based nanoTiO₂ lubricant can efficiently reduce the friction during metal deformation. nanoZnO is preferred to adhere to metal surfaces and employed to isolate the surfaces. A new lubricating mechanism of nanoparticles in metal hot deformation named convex peak extreme pressure buffering mechanism is thereby proposed, which is verified by the surface morphology of compressed sample.

Abstract: In this paper, Ag₂S nanomaterials with good morphology and crystalline have been prepared successfully by a hydrothermal method with AgNO₃ and (CH₂)₂CS as raw materials, SUDEI and PVP as surfactant, respectively. The photo-thermal transformation performance of the nanomaterials was studied. It was found that the Ag₂S nanomaterials had a good photo-thermal property and the corresponding photo-thermal transformation efficiency could reach up to 63%.

Abstract: Multiwalled carbon nanotubes (MWCNTs) as an excellent supporter covered with a thick layer of cobalt phthalocyanine (CoPc) were prepared by in-situ synthesis. Platinum particles were adopted to enhance the conductivity of CoPc-MWCNTs. The final nanocomposite Pt-CoPc-MWCNTs was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Strong aromatic π-π stacking between MWCNTs and CoPc made CoPc in-situ forming on MWCNTs. With homogeneous thickness of CoPc covered on the MWCNTs and Pt particles equally distributed, the nanocomposite was used as electrocatalyst. The electrochemical properties of the composite got researched by casting the dispersion of Pt-CoPc-MWCNTs on the glassy carbon electrode. Compared with other modified electrodes, Pt-CoPc-MWCNTs/GC electrode exhibited excellent electrochemical activity towards dopamine (DA) and uric acid (UA). Linear responses for DA and UA were obtained in the ranges of 5 to 170 μM and 5 to 100 μM, and limits of detection were 2.6 and 1.4 μM (S/N = 3), respectively. Simultaneous detection of DA and UA in the presence of ascorbic acid (AA) also displayed selective property, with no interference to each other.

Abstract: A mild synthetic process using formic acid as the reduction agent was applied to prepare 40 wt% Pt/carbon aerogel (CA) electrocatalyst. The as-prepared sample was characterized by transmission electron microscopy (TEM) and electrochemical measurements. The results exhibit Pt nanoparticles with narrow particle size distribution are dispersed throughout carbon aerogel structure. Moreover, the Pt/CA catalyst has smaller Pt nanoparticle mean size than Johnson Matthey HiSpec^TM 4000 (JM4000). The electrochemical measurement results indicate that the Pt/CA catalyst with Pt loading of 40 wt% possesses similar electrochemical surface area (ESA) value and oxygen reduction reaction (ORR) activity as JM4000.

Abstract: A novel kind of AgNPs catalyst was synthesized by in-situ reduction method using poly(2-acrylamido-2-methyl propyl sulfonic acid-co-2-hydroxyethyl methclate) [short as P(AMPS-co-HEMA)] hydrogel as matrices and AgNO₃ as a metal precursor. The structure of the composite hydrogel was characterized by Scan Electrical Microscope (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). The results showed that AgNPs were binded with end group and most of the particles were isolated and uniformly distributed on the P(AMPS-co-HEMA). The catalytic properties in the reduction reaction of 4-nitrophenol(shorted as 4-NP) to 4-aminophenol(shorted as 4-AP) were studied in detail, and the result showed that conversion rate and conversion efficiency attained 97.56% and 0.9671 mmol/g·min when the amount of AgNPs was 9mg, [NaBH₄] was 2.0×10⁻¹ mol/L, [4-NP] was 2.0×10⁻² mol/L and the total volume of solution was 50 mL, respectively.