热分析及其联用技术在纳米碳材料性能评价中的应用

热分析技术是在程序控温和一定气氛下,测量物质的某种物理性质与温度或时间变化等关系的一种方法技术手段,能够准确、快速的测量物质的变化,在纳米碳材料表征中有重要的应用。本文将简要阐述热分析及其联用技术在纳米碳材料表征方面的应用进展和研究成果,结果表明它们为纳米碳材料的耐氧化性、热稳定性、表面氧化度、不同形态碳含量、热分解机理等分析的探索提出了切实可行的研究途径,同时结合笔者在这方面的一些工作对热分析技术的具体应用进行了详述,最后对热分析及其联用技术在纳米碳材料表征中的应用做了重要的前景展望。

Preparation of gradient wettability surface by anodization depositing copper hydroxide on copper surface

A facile route for preparation of gradient wettability surface on copper substrate with contact angle changing from 90.3°to4.2°was developed.The Cu（OH）2 nanoribbon arrays were electrochemically deposited on copper foil via a modified anodization technology,and the growth degree and density of the Cu（OH）2 arrays may be controlled varying with position along the substrate by slowly adding aqueous solution of KOH into the two-electrode cell of an anodization system to form the gradient surface.The prepared surface was water resistant and thermal stable,which could keep its gradient wetting property after being immersed in water bath at 100℃ for 10 h.The results of scanning electron microscopy（SEM）,X-ray diffraction（XRD） and X-ray photoelectron spectroscopy（XPS） demonstrate that the distribution of Cu（OH）2 nanoribbon arrays on copper surface are responsible for the gradient wettability.

Effect of Calcination Temperature on Surface Oxygen Vacancies and Catalytic Performance Towards CO Oxidation of Co3O4 Nanoparticles Supported on SiO2

Co3O4/SiO2 catalysts for CO oxidation were prepared by conventional incipient wetness impregnation followed by calcination at various temperatures. Their structures were char- acterized with X-ray diffraction （XRD）, laser Raman spectroscopy, X-ray photoelectron spectroscopy （XPS）, temperature-programmed reduction （TPR） and X-ray absorption fine structure （XAFS） spectroscopy. Both XRD and Raman spectroscopy only detect the existence of Co3O4 crystallites in all catalysts. However, XPS results indicate that excess Co2＋ ions are present on the surface of Co3O4 in Co3O4（200）/Si02 as compared with bulk Co3O4. Meanwhile, TPR results suggest the presence of surface oxygen vacancies on Co3O4 in Co3O4（200）/SiO2, and XAFS results demonstrate that Co3O4 in Co3O4（200）/SIO2 contains excess Co2＋. Increasing calcination temperature results in oxidation of excess Co2＋ and the decrease of the concentration of surface oxygen vacancies, consequently the for- mation of stoichiometric Co3O4 on supported catalysts. Among all Co3O4/SiO2 catalysts, Co3O4（200）/SiO2 exhibits the best catalytic performance towards CO oxidation, demonstrating that excess Co2＋ and surface oxygen vacancies can enhance the catalytic activity of Co3O4 towards CO oxidation. These results nicely demonstrate the effect of calcination temperature on the structure and catalytic performance towards CO oxidation of silicasupported Co3O4 catalysts and highlight the important role of surface oxygen vacancies on Co3O4.

Enhanced oxygen reduction reaction performance over Pd catalysts by oxygen-surface-modified SiC

Obtaining a detailed understanding of the surface modification of supports is crucial;however,it is a challenging task for the development and large-scale fabrication of supported electrocatalysts that can be used as alternatives to Pt-based catalysts for the oxygen reduction reaction(ORR).In this study,commercial silicon carbide(SiC)was modified through surface oxidization(O-SiC)to support the use of Pd nanoparticles(Pd NPs)as electrocatalysts for ORR.The obtained Pd/O-SiC catalysts exhibited better ORR activity,stronger durability,and higher resistance to methanol poisoning than that exhibited by commercial Pt/C.The role of the support in enhancing the ORR performance,especially the oxidization of SiC surfaces,was discussed in detail based on the experimental characterizations and density functional theory calculations.The underlying mechanism of the superior ORR performance of Pd/O-SiC catalysts was attributed to the charge transfer from SiC_(x)O_(y)to Pd NPs on the surfaces of SiC and the strong metal–support interactions(SMSIs)between Pd and SiC_(x)O_(y).The charge transfer enhanced the ORR activity by inducing electron-rich Pd,increased the adsorption of the key intermediate OOH,and decreased the Gibbs free energy of the critical ORR step.Furthermore,SMSIs enhanced the ORR stability of the Pd/O-SiC catalyst.This study provided a facile route for designing and developing highly active Pd-based ORR electrocatalysts.

Surface finish effect on dry sliding wear behavior of thermally oxidized commercially pure zirconium

The effect of surface polishing on the wear behavior of thermally oxidized commercial pure zirconium (CP-Zr) under dry sliding conditions was investigated. Surface ground CP-Zr with a roughness of 0.21 μm (Ra) was thermally oxidized (TO) at 650 °C for 6 h. After TO, some samples were polished to smoothen the surface with a finish of 0.04 μm (Ra). The response of the polished and unpolished TO samples to dry sliding wear was investigated under unidirectional sliding conditions. The results show that surface polishing after TO affects the dry sliding wear behavior of TO CP-Zr in several aspects, including coefficient of friction, wear rate, crack formation and oxide layer breakdown. In particular, it is found that smoothening the TO surface favors the formation of semi-circular cracks in the wear track and accelerates oxide layer breakdown during dry sliding. A slightly rough TO surface helps to reduce the tendency of the oxide layer towards cracking and to increase the wear resistance at high contact loads. The mechanisms involved are discussed in terms of asperity contacts, crack formation, propagation and final fracture.

Influence of surface finish and annealing treatment on oxidation behavior of Ti-48Al-8Cr-2Ag alloy

The effect of surface finish and annealing treatment on the oxidation behavior of Ti-48Al-8Cr-2Ag (molar fraction, %) alloy was investigated at 900 and 1 000 ℃, respectively in air. Thermal gravimetric analysis (TGA) was conducted for the characterization of oxidation kinetics. The microstructures of oxide scales were studied by scanning electron microscopy (SEM) and transmission election microscopy (TEM) techniques. Unfavorable effect of the annealing treatment on the oxidation behavior of the coating was also investigated. The results indicate that the oxidation behavior of the alloy is influenced by surface finish and annealing treatment. The oxidation rate of ground sample is lower than that of the polished alloy at 1 000 ℃ in air. The former forms a scale of merely Al2O3, and the latter forms a scale of the mixture of Al2O3 and TiO2. Annealing can improve the formation of TiO2.

Insights into Syngas to Methanol Conversion on Cr_(2)O_(3) Oxide from First-Principles-based Microkinetic Simulations

Cr_(2)O_(3) has been recognized as a key oxide component in bifunctional catalysts to produce bridging intermediate,e.g.,methanol,from syngas.By combining density functional theory calculations and microkinetic modeling,we computationally studied the surface structures and catalytic activities of bare Cr_(2)O_(3)(001)and(012)surfaces,and two reduced(012)surfaces covered with dissociative hydrogens or oxygen vacancies.The reduction of(001)surface is much more difficult than that of(012)surface.The stepwise or the concerted reaction pathways were explored for the syngas to methanol conversion,and the hydrogenation of CO or CHO is identified as rate-determining step.Microkinetic modeling reveals that(001)surface is inactive for the reaction,and the rates of both reduced(012)surfaces(25−28 s^(-1))are about five times higher than bare(012)surface(4.3 s^(-1))at 673 K.These theoretical results highlight the importance of surface reducibility on the reaction and may provide some implications on the design of individual component in bifunctional catalysis.

HIGH EMISSION PERFORMANCE IMPREGNATED DISPENSER CATHODE

In order to obtain higher emission performance than that of a traditional M-type cathode, we have developed a new type impregnated dispenser cathode. The new cathode is impregnated with a new active substance with molar ratio of 26BaO·29SrO·8Sc2O3 ·7CaO·Al2O3 . This paper introduces the emission performance, surface active material, and work function of the new cathode. At 1100℃B , the DC current density and pulse current density are 30.6±1.0 A/cm2 and 171.6±2.8 A/cm2 , respectively, 2.1 and 5.4 times of that of an M-type cathode. The work function of the new cathode is 1.668± 0.002 eV. High concentration O-Al-Sc-Sr-Ba and O-Al-Sc-Ba are found in the pores and at pore edges, respectively. By comparing the emission performances and surface characteristics of as-polished and as-cleaned cathodes, it is proposed that, the emission around pore ends forms the major part of the total emission for the new cathodes.

Supercapacitors based on high-surface-area graphene

Exfoliated graphite oxide was prepared by an improved Hummers method and was then reduced to graphene with hydrazine in the presence of ammonium hydroxide.N2adsorption–desorption measurement showed that graphene so obtained had a specific surface area as high as 818 m2/g.Galvanostatic charge/discharge curves demonstrated that the as-prepared graphene exhibited a specific capacitance of 186.9 F/g at a current density of 0.1 A/g and that about 96%of the specific capacitance was retained after 2000 cycles at a current density of 5 A/g.

Molecular biomarker record of paleooceanographic environment in the East China Sea during the last 35000 years

By reference of the δ18O and δ13C isotopic compositions of G.sacculifer and accelerator mass spectrometry (AMS)14C dates, the U K 37 , ∑C – 21 /∑C +- 22 and Pr/Pn in core DGKS9603 have been used to characterize the changes of paleooceanographic environment occurring in the East China Sea (ECS) during the last 35000 years. The stratigraphic records of these proxies have shown that during the last 35 ka the Okinawa Trough has gone through 7 stronger cold-climate events (C1–C7) and 9 terrigenous matter-decreasing events (e2–e9), of which, the C1 corresponds to the cold episode occurring in the middle late Holocene, C2–C4 and C7 correspond to the H1–H4 events, respectively. e1 and e3–e8 correspond to the decrease of sea surface temperature (SST), respectively. The terrigenous inputs increased when Heinrich events occurred. Climate colding resulted in the decrease of terrigenous matter transported by rivers, and the increase of that transported by winter monsoon. Heinrich events are closely related to East Asia monsoon. During the Last Glacial Maximum (LGM, 15.5–25.8 Cal ka BP), reduction environment fluctuated strongly, bringing forth three stronger reduction events (R1–R3) and one weaker reduction event (O), of which, R1–R3 correspond to the decrease of SST and increase of terrigenous nutrient and O corresponds to the decrease of terrigenous nutrient. The fluctuation of reduction condition must be related to the change of sea surface productivity.

Atmospheric pressure and CO_2 concentration of potential habitable planet HD40307g

HD40307g is the closest potentially habitable planet discovered today orbiting a K2V star and will be a prime target for future TPF-like missions if its existence is confirmed.Although the atmosphere of HD40307g should be denser and contain more CO2 judging from the amount of radiation it receives from its star,it is unknown how dense and how much CO2 the planetary atmosphere should have.Thus more knowledge on its atmosphere is useful.For HD40307g to have Earth-like climate(288 K global mean surface temperature),we obtain the following combination of atmospheric pressure and CO2 mixing ratio:(1)10-bar+3%CO2;(2)5-bar+10%CO2;(3)3-bar+30%CO2.

Investigation of the interfacial properties for CO_2-methanol and CO_2-ethanol mixtures

An equation of state (EOS) applicable for the interfacial properties of CO2-methanol and CO2-ethanol mixtures was established by combining the cross-association EOS and the density gradient theory (DGT). The correlated surface tensions of CO2-ethanol mixtures agreed well with the experimental data. The results illustrated the temperature and pressure dependence of the cross-association between CO2 and alcohol hydroxyls in the whole vapor-liquid surface,and the influence of the cross-association on the calculation of the surface tensions of binary mixtures.

Theoretical study of propene oxidation on Bi_2O_3 surfaces

The role of bismuth in the selective oxidation of propene has long been debated. We performed density functional calculations to study the dehydrogenation reaction of propene on Bi203 surfaces. Our calculated thermodynamic data reveal that the first dehydrogenation of propene on the most stable （010） surface and the （100） surface are difficult. Our calculations indicate that the barrier of the first hydrogen abstraction on the high Miller index surface （211） is much lower than those on the （100） and （010） surfaces, and is close to the experimental one. Further dehydrogenation is shown to be difficult and production of 1,5-hexadiene through dimerization of allyl is likely, in agreement with the experimental observations.

Simulation of tin penetration process in the surface layer of soda-lime-silica float glass

Based on the analysis of tin penetration mechanism in the float glass process, the oxidation model of stannous ion is constructed considering the oxygen activity and the redox reaction in the glass surface layer. The calculation of stannous ion's oxidation rate makes it possible to predict both stannous and stannic ion's concentrations independently. And it is also the necessary precondition for the numerical verification of tin penetration mechanism. Coupled diffusion simulation method is established to simulate the penetration process of both stannous and stannic ions simultaneously. The result shows that when the green glass is formed in the reducing atmosphere in tin bath, the stannic ion is accumulated at the position where oxygen activity changes sharply. Satellite peak (internal local concentration maximum) occurs in the tin concentration profile of green glass, which is quite different from that in low iron glass. Compared with gradually cooling temperature regulation, the tin penetrated shifts to greater depth and the depth and magnitude of the satellite peak also increase when reheating temperature regulation is applied. In order to reduce the amount of penetrated tin, the residual time in the high temperature region should be shortened.

Experimental investigation of anodized/spray pyrolysed nanoporous structure on heat transfer augmentation

This paper analyzes the effects of nanoporous surface on heat transfer temperaments of assorted thermal conductingmaterials. A phenomenal proposal of wielding the surface roughness to ameliorate the heat transfer ratehas been discovered. The maximum increase of heat transfer rate procured by nanoporous layers is 133.3% higherthan the polished bare metals of surface roughness 0.2μm. This plays an imperative role in designing compact refrigerationsystems, chemical and thermal power plants. Experimental results picture a formidable upswing of58.3% heat transfer in chemically etched metals of surface roughness 3 μm, 133.3% in nanoporous surface of porosity75-95 nm formed by electrochemical anodization, and porosity of 40-50 nm formed by spray pyrolysis increasesthe heat transfer by 130%. Effects of porosity, flow velocity and scaling on the energy transfer are alsoscrutinized. This paper also analyzes the multifarious modes of nanoporous fabrication, to contrive both prodigiousand provident system.

Seasonally evolving dominant interannual variability mode of air-sea CO2 flux over the western North Pacific simulated by CESM1-BGC

We applied a season-reliant empirical orthogonal function(S-EOF) analysis based on the results of the Community Earth System Model, version 1-Biogeochemistry, to seasonal mean air-sea CO_2 flux over the western North Pacific(WNP)(0°–35°N, 110°E–150°E). The first leading mode accounts for 29% of the total interannual variance, corresponding to the evolution of the El Ni-Southern Oscillation(ENSO) from its developing to decaying phases. During the ENSO developing phase in the summer and fall, the contribution of surface seawater CO_2 partial pressure anomalies is greater than that of gas transfer/solubility anomalies, which contribute to increasing oceanic CO_2 uptake over the WNP. During the ENSO mature phase in the winter, the anomalous southwesterly northwest of the western North Pacific anticyclone(WNPAC) reduces the surface wind speed in the China marginal sea and thus decreases oceanic CO_2 uptake by reducing the gas transfer coefficient. In the subsequent spring, the WNPAC maintains with an eastward shift in position. The anomalous southwesterly warms sea surface temperatures in the China marginal sea by reducing evaporation and thus decreases oceanic CO_2 uptake by enhancing surface seawater CO_2 partial pressure. This process, rather than the effect of decreasing gas transfer coefficient, dominates CO_2 flux anomalies in the spring.

Improved picoliter-sized micro-reactors for high-throughput biological analysis

High-throughput pyrosequencing,carried out in millions of picoliter-sized reactors on a fiber-optic slide,is known for its longer read length.However,both optical crosstalk(which reduces the signal-to-noise ratio of CCD images)and chemical retention adversely affect the accuracy of chemiluminescence determination,and ultimately decrease the read length and the accuracy of pyrosequencing results.In this study,both titanium and oxidized aluminum films were deposited on the side walls and upper faces of micro-reactor slides to enhance optical isolation;the films reduced the inter-well crosstalk by one order of magnitude.Subsequently,chemical retention was shown to be caused by the lower diffusion coefficient of the side walls of the picolitersized reactors because of surface roughness and random pores.Optically isolated fiber-optic slides over-coated with silicon oxide showed smoother surface morphology,resulting in little chemical retention;this was further confirmed with theoretical calculations.Picoliter-sized micro-reactors coated with titanium-silicon oxide films showed the least inter-well optical crosstalk and chemical retention;these properties are expected to greatly improve the high-throughput pyrosequencing performance.