Papers by Author: Dong Ming Zhang

Abstract: Self-assembled method for controllable fabrication of a hydrophobic triazine dithiol-silane composite film on 304 stainless steel (SS) is reported in this paper. Hierarchical structure composed of micro/nanofeatherlike surface was obtained by acid etching. After modification with 2-( Dibutylamino )-4,6-dimercapto-1,3,5-triazine ( DB ) and n-octadecyltrichlorosilane ( OTS ), the suface became hydrophobicity. By applying SEM, FTIR-RAS, and water contact angle analysis, the surface morphology and hydrophobicity of the as-prepared surfaces were studied in detailed. The results indicated that at the optimal condition, the surface showed a good hydrophobicity with a water contact angle as high as 152±3°. Possible growth mechanism of featherlike hierarchical structure was discussed. Additionally, the anticorrosion effect of the hydrophobic surface was studied by potentiodynamic polarization measurement. It showed that the surface covered with hydrophobic composite film was found to be more positive than bare and monolayer, the corrosion current was significantly lower to 1.68 nA/cm², and the corrosion potential shifted positively from-253 mV to-118 mV ( vs SEC ).

Abstract: Spark plasma sintering (SPS) is a newly developed technique that enables poorly sinterable tin oxide powder to be fully densified. Sintering without sintering aids is of great importance when SnO₂ ceramics are used as electrodes in the glass melting industry and aluminum electrometallurgy. Dense and good-conductive Antimony-doped SnO2 ceramics can be achieved by SPS at a lower sintering temperature and in a shorter time. When the Sb₂O₃ concentration is 1.0 mol%, the densities of the samples reach their maximum value, which is 98.2% of the theoretical value. When the content of Sb₂O₃ was 2.44mol%, SnO₂ ceramics with densities 97.6% can be obtained at 800°C-1000°C, and the resistivity was about 5.19×10^-2Ω.cm at the sintering temperature of 1000°C. Defined amount of Sb³⁺ used in our research are beneficial to low the sintering temperature and promote the densification of SnO₂ ceramics

Abstract: In the present study, we try to prepare hydrophobic film coated on stainless steel as the bipolar plate for polymer electrolyte membrane fuel cell (PEMFC). Magnetron sputtering (MS) was adoped to prepare the Cr3Ni2/Cr2N multi-layer coated on stainless steel. The corrosion resistance and electrical conductance of the coated substrate were tested. The water contact angles were measured. The film exhibits improved corrosion resistance and electrical conductance. The corrosion current is 0.58µA.cm-2 and the contact resistance at 240N.cm-2 is 8.5mΩ.cm2. Meanwhile, it is a kind of hydrophobic film with water contact angle of 107o. The performance shows strong dependance on microstructural characteristics. The nano-protrudes on the SS304/Cr3Ni2/Cr2N surface result in the film with hydrophobic property, just like the effect of lotus surface.

Abstract: In this study, SnO2-based ceramics, with CuO as sintering aid and Sb2O3 as activator of the electrical conductivity, was obtained by pressure-less sintering at 1100°C ~ 1470°C. Addition of antimony leads to a higher densification temperature. Densification behavior and microstructure development are strongly dependant on CuO and Sb2O3. CuO gives rise to a liquid phase; Sb2O3 retards the formation of liquid phase and hinders the growth of grain. The electrical resistivities of SnO2-based ceramics vary in a wide range from 10-2 to 107 Ω•cm, depending on starting compositions and processing conditions. The electrical resistivities of samples with different amounts of CuO and Sb2O3 show different trends with the increasing of sintering temperature. The addition of antimony rapidly promotes electrical conductivity of SnO2-based ceramics containing CuO as the solid solution reaction of Sb2O3-SnO2. As the additions of CuO and Sb2O3 are the same, the electrical resistivity arrives the minimal value of 4.72×10-2 Ω•cm for 99%SnO2+0.5%CuO +0.5%Sb2O3 at 1470°C. More content of Sb2O3 than CuO causes the degression of density and the rising of electrical resistivity of ceramics.

Abstract: In this paper, silicon nitride (Si3N4) ceramics by aligning α-Si3N4 whiskers were prepared via tape casting, hot-press sintering technique using Y2O3 and MgO as sintering additives. Aligned α-Si3N4 whiskers were realized by modifying the tape casting technique. After tape casting, Si3N4 tape with good flexibility and uniform pores can be obtained. Microstructures of the tape, green body and sintered sample were observed by SEM images. The results show α-Si3N4 whiskers in Si3N4 tape and green body were aligned preferentially along the tape casting direction. Si3N4 ceramics with aligned elongated grains are developed by hot-press sintering technique based on the reaction between Si3N4 and the sintering additives which lead to the liquid phase.

Abstract: Nano-scale 8mol% titania doped yttria stabilized zirconia (8TiYSZ) powders were prepared by coprecipitation combined with azeotropic distillation process. Powder X-ray diffraction, BET method and TEM were performed to characterize the powder properties. The relative density of 8TiYSZ sample sintered by spark plasma sintering technique at 1150°C for 3min reached 99%. The electrical conductivity of sintered pellet was much higher than the reported one.

Abstract: Dense SnO2 based ceramics are widely used. In this paper, 95SnO2-5MnO2 ceramics were prepared by pressureless sintering in air at different temperatures. Phase compositions and microstructures are examined by XRD, SEM and EDX, respectively. The SEM results show that different morphologies exist at the SnO2 grain boundary of ceramic, which compose of manganese oxidation, testified by EDX. The different manganese oxides phases, found by XRD, are the source of oxygen concentration at the grain boundary during heating and oxygen dissipation when cooling. However, solid solutions of Mn, Sn and O are not observed. The density of 95SnO2-5MnO2 ceramics decreases with increasing the sintering temperature, due to the evaporation of SnO and decreasing concentration of oxygen at grain boundary in the cooling process. Densification of the ceramic is promoted with inhibiting the decomposition of SnO2 by increasing oxygen concentration in the heating process, but it is limited by the dissipation of oxygen at the grain boundary in the cooling process.

Abstract: In this study, SnO2-based ceramics, with 0.5%CuO as sintering aid and Sb2O3 as activator of the electrical conductivity, was obtained by pressureless sintering at 1450°C for 5 h. Densification behavior and microstructure development strongly depend on Sb2O3. The characteristization of microstructures on Sb2O3 concentrations are analyzed by SEM. A small amount of CuO improves densification; Sb2O3 retards the densification of SnO2-based ceramic. The electrical resistivities of SnO2-based ceramics with different contents of Sb2O3 are measured by the standard four probe method and varied in a wide range. The electrical resistivity arrives the minimal value of 4.964×10-2 0·cm for 99%SnO2+0.5%CuO +0.5%Sb2O3. More content of Sb2O3 than that of CuO causes the degression of density and the increasing of electrical resistivity of ceramics.

Abstract: Nano-sized turbostritic-BN (t-BN) was fabricated through chemical process using boric acid and urea in this work. By the same method, the AlN powders coated with nano-BN were prepared too. The results of X-ray diffraction (XRD) and transmission electron microscope (TEM) revealed that nano-sized t-BN was synthesized at about 600°C in nitrogen gas and it surrounded the surface of AlN particles. High-density AlN/BN nano-composites were fabricated spark plasma sintering (SPS). Microstructure and properties of AlN/BN nano-composites (5~30vol% BN) were investigated. The h-BN flake particles were homogenously dispersed at AlN grain boundaries and within grains in the AlN/BN composites. A little nano-BN additions significantly improved the bending strength of the nano-composites. However, the bending strength was decreased with the BN content increasing. The thermal conductivity of AlN/BN nano-composites was investigated too.

Abstract: In the present study, Fe-Si sheets were formed by powder rolling of Fe-6.5wt%Si mixture powders, then were sintered in flowing Ar+5vol%H2 atmosphere. The changes in microstructure and density during the formation process were mainly discussed. The results show that Fe-Si mixture powders can be rolled into comparatively compact sheets. During subsequent sintering and re-rolling, the density of the sheet gradually increased and Si diffused into Fe lattice step by step with the increasing of temperature.