TiO_2-SnO_2纳米晶膜紫外光照下对臭氧气敏性能的研究

以低温水热法制备了TiO2-SnO2复合纳米晶粒,采用提拉法涂敷于带有金电极的氧化铝陶瓷管表面形成敏感薄膜,设计了一种新型薄膜式臭氧传感器。采用 X 射线衍射仪、热场发射扫描电子显微镜、能量色散X 射线谱仪和紫外-可见光谱能谱仪,表征了TiO2-SnO2纳米晶粒的晶体结构和微观形貌。采用紫外-可见吸收光谱法和电化学方法,讨论了TiO2-SnO2纳米晶粒对臭氧敏感机理与光电化学特性。在气体传感器静态测试系统上,采用XEDWS-60A型气敏元件分析仪测试了紫外光下臭氧传感器敏感特性、动态响应、抗干扰和稳定性。结果表明,以Ti与Sn摩尔比为6的TiO2-SnO2纳米晶粒为敏感薄膜的臭氧传感器,在相对湿度为40%和温度为25℃条件下,臭氧浓度为0.1~1.8μg/L时,有、无紫外光照射的臭氧传感器线性度分别为97.5%和78.5%,动态响应分别为2和9 s,恢复时间分别为5.5和15 s。此传感器对CO、NOx、甲醛、丙酮、丁醇和甲醇等气体具有良好的抗干扰性能。在汽车上连续使用12个月后,响应衰减了4.7%,响应正常时间为8.5个月。

Effect of nano TiN/Ti refiner on as-cast and hot-working microstructure of commercial purity aluminum

A novel type nano TiN/Ti composite grain refiner （TiN/Ti refiner） was prepared by high energy ball milling, and its effect on as-cast and hot-working microstructure of commercial purity aluminum （pure Al） was investigated. The results show that TiN/Ti refiner exhibits excellent grain refining performances on pure Al. With an addition of 0.2% TiN/Ti refiner, the average grain size of pure Al decreases to 82 μm, which is smaller than that of pure Ti and Al 5Ti 1B master alloy as refiners. The microstructure of weld joint of pure Al with 0.1% TiN/Ti refiner is fine equiaxed grains and the hardness of weld joint is higher than that of the base metal. For pure Al with 40% cold deformation and recrystallization at 250 °C for 1.0 h, the grains of the sample added 0.1% Ti powder have an obvious grain growth behavior. In contrast, oriented grains caused by deformation have been eliminated, and there is no obvious grain growth in pure Al refined with 0.1% TiN/Ti refiner, indicating that nano TiN in the refiner inhibits the growth of grain during recrystallization.

Strategies to suppress grain growth of nanocrystalline aluminum

The grain growth behaviors of nanocrystalline aluminum, alloy and composite are compared. First, nanocrystalline aluminum is fabricated by consolidation of ball-milled powder. Second, nanocrystalline aluminum alloy is designed to have elements such as Mn, Zr, and Misch metals, which can form thermally stable second phases at grain boundaries and also drag the movement of grain boundaries. Third, nanocrystalline aluminum-based composites containing multi-walled carbon nanotubes(MWCNTs) are also prepared because MWCNTs are expected to be located at grain boundaries and to suppress the grain growth of nanocrystalline aluminum. These three types of samples are annealed at 550 °C for up to 5 d and the effect of annealing time on Vickers hardness of the samples is compared. As a result, MWCNTs are found to be most effective to impede grain growth of nanocrystalline aluminum.

Fabrication and application of nano/microcrystalline composite diamond coated drawing dies using alternative carbon sources

Nano/microcrystalline composite diamond films were deposited on the holes of WC-6%Co drawing dies by a two-step procedure using alternative carbon sources, i.e., methane for the microcrystalline diamond（MCD） layer and acetone for the nanocrystalline diamond（NCD） layer. Moreover, the monolayer methane-MCD and acetone-NCD coated drawing dies were fabricated as comparisons. The adhesion and wear rates of the diamond coated drawing dies were also tested by an inner hole polishing apparatus. Compared with mono-layer diamond coated drawing die, the composite diamond coated one exhibits better comprehensive performance, including higher adhesive strength and better wear resistance than the NCD one, and smoother surface（Ra=65.3 nm） than the MCD one（Ra=95.6 nm） after polishing at the same time. Compared with the NCD coated drawing die, the working lifetime of the composite diamond coated one is increased by nearly 20 times.

Biomimetic Method Synthesis of HgS/Polyurethane Composite Film and Its Sensing Properties to Ba2＋

Polyurethane-conjugated HgS nanocrystals with tunable sizes prepared by using biomimetic method. The obtained HgS nanoparticles with good dispersibility were characterized by Fourier transform infrared. Scanning electron microscopy are used to envisage the binding of nanoparticles with functional groups. The polyurethane molecules can control nucleation and growth of HgS crystals by binding on the surface of nanocrystals to stabilize nanoparticles. Quantum confinement effect of polyurethane-conjugated HgS nanocrystals was confirmed by UV-Vis spectra. The nanoparticles exhibit a well-defined emission feature at about 291 nm. The fluorescence results reveal that the PU/HgS nanoparticles film is sensitive to Ba2＋, and a small amount of Ba2＋ makes the emissions increase rapidly. The emission is hardly affected by other common ions in water. The nanocomposite film is possible to become a special sensor material for Ba2＋.

A facile strategy for ultrasmall Pt NPs being partiallyembedded in N-doped carbon nanosheet structure for efficient electrocatalysis

A facile strategy is established for constructing composite nanostructure with ultrasmall Pt nanoparticles(NPs) of ~2 nm in diameter being homogeneously embedded in N-doped carbon nanosheets. The strong coordination between Pt atoms in cisplatin and N atoms in pyrrole contributes to the robust embedding of Pt NP into the N-doped carbon nanosheets after annealing. Such a unique partially-embedding structure facilitates the active site exposure while stabilizing the ultrasmall Pt NPs, leading to the comparable electrochemical activities for hydrogen evolution and oxygen reduction reactions, and substantially improves durability performance compared to that of the state-of-the-art Pt/C(20 wt%).