碳颗粒尺寸对自发渗透原位制备TiCp/Mg微观组织的影响

利用原位反应自发渗透技术制备了组织均匀且致密度高的TiCp/Mg复合材料,研究了原位反应温度以及碳颗粒尺寸对制备的TiCp/Mg复合材料微观组织的影响。结果表明:当使用大尺寸碳粒子(≤100μm)时,随着反应温度的提高,原位生成物TiCp的含量增加,但有残留反应物Ti和C的存在;碳粒子尺寸减小(≤30μm)时,原位反应较完全,不再有残留物存在;原位反应产物组织中,增强相TiCp主要呈互穿网络状、颗粒状以及片状等形态;增强相的尺寸随碳粒子尺寸的减小而减小,在碳颗粒尺寸为1.5μm时TiC更易呈现等轴颗粒状,尺寸约为0.5～2.0μm。

电极制备工艺对褐藻多孔碳双电层电容性能的影响

为探究电极制备过程对材料双电层电容可能带来的变化,以褐藻为前驱体制备多孔碳,研究了电容测试过程中碳颗粒尺寸和电极制片压力两种工艺参数对其双电层电容性能的影响规律.通过将多孔碳粉末严格筛分成5组不同的尺寸,分别制成电极并测试其充放电性能和循环伏安曲线,得到比电容随颗粒尺寸变化的规律;再选取优化尺寸的多孔碳,在4种不同的压力下制成电极片,进而研究了不同制片压力对电极电容的影响规律.研究表明,在微米级,所制电极的比电容随碳颗粒尺寸的减小显著增加,同时随制片压力的增大,比电容先增大后减小.本实验条件下,碳颗粒尺寸小于25μm、制片压力为10 MPa(对应电极片所受真实压强约619 MPa)时,得到的电极片具有最高的比电容值.

Size-control growth of thermally stable Au nanoparticles encapsulated within ordered mesoporous carbon framework

Simultaneously controlling the size of Au nanoparticles and immobilizing their location to specific active sites while hindering migration and sintering at elevated temperatures is a current challenge within materials chemistry.Typical methods require the use of protecting agents to control the properties of Au nanoparticles and therefore it is difficult to decouple the influence of the protecting agent and the support material.By functionalizing the internal surface area of mesoporous carbon supports with thiol groups and implementing a simple acid extraction step,we are able to design the resulting materials with precise control over the Au nanoparticle size without the need for the presence of any protecting group,whilst simultaneously confining the nanoparticles to within the internal porous network.Monodispersed Au nanoparticles in the absence of protecting agents were encapsulated into ordered mesoporous carbon at various loading levels via a coordination-assisted self-assembly approach.The X-ray diffractograms and transmission electron microscopy micrographs show that the particles have controlled and well-defined diameters between 3 and 18 nm at concentrations between 1.1 and 9.0 wt%.The Au nanoparticles are intercalated into the pore matrix to different degrees depending on the synthesis conditions and are stable after high temperature treatment at 600 °C.N2 adsorption-desorption isotherms show that the Au functionalized mesoporous carbon catalysts possess high surface areas（1269–1743 m^2/g）,large pore volumes（0.78–1.38 cm^3/g）and interpenetrated,uniform bimodal mesopores with the primary larger mesopore lying in the range of 3.4–5.7 nm and the smaller secondary mesopore having a diameter close to 2 nm.X-ray absorption near extended spectroscopy analysis reveals changes to the electronic properties of the Au nanoparticles as a function of reduced particle size.The predominant factors that significantly determine the end Au nanoparticle size is both the thiol group concentration and subjecting the as-made materials to an additional concentrated sulfuric acid extraction step.

RELATIVE BRIGHTNESS INDEX AND IT'S CLIMATIC SIGNIFICANCE FROM LACUSTRINE SEDIM ENT OF NAPAHAI LAKE,NORTHWESTERN YUNNAN PLATEAU,CHINA

Information on the palaeoenvironm ent from Late Pleistocene to Holocen e in northwestern Yannan Plateau has been deduced from a study of a 28.81m-long core taken from Napahai Lake.The results from Relative Brightness In-dex(RBI )as well as those from the lithological analyses of bulk sediments,total organic carbon and granulometric analy-ses have been used to reconstruct the environmental and climatic evoluti on of the area.The ages were provided by three 14 C datings.The record suggested a climate fluctuation between warm-dry a nd cool-wet from ca.57to 32ka B.P.,which led a shallowing and swamping of the l ake.The water level again increased quickly at ca.32ka B.P.,reached it’ s peak during LGM(Last Glacial Maximum,ca.18-20ka B.P.)and remained relative high until ca.15ka B.P.The high wa-ter level at LGM is attributed to cold-wet conditions.The area experienced an abrupt and unstable climatic ch anges dur-ing the transition period from15to 10ka B.P.with a dominated littoral en vironment.Awarm-dry climate led to the contrac-tion of the lake during the Holocene a nd reed-swamps became dominant.After a minor wet-cool pulse during the L ate Holocene,the modern climate became to be established.

High-temperature creep properties of uranium dioxide pellet

High-temperature creep properties of sintered uranium dioxide pellets with two grain sizes （9.0 μm and 23.8μm） were studied. The results indicate that the creep rate becomes a little faster with the reduction of the uranium dioxide grain size at the same temperature and the same load. At the same temperature, the logarithmic value of the steady creep rate vs stress has linear relation, and with increasing load, the steady creep rate of the sintered uranium dioxide pellet increases. Under the same load, the steady creep rate of the sintered uranium dioxide pellet increases with increasing temperature; and the creep rates of sintered uranium dioxide pellet with the grain size of 9.0 μm and 23.8 μm under 10 MPa are almost the same. The creep process is controlled both by Nabarro--Herring creep and Hamper-Dorn creep for uranium dioxide pellet with grain size of 9.0 μm, while Hamper---Dora creep is the dominantmechanism for uranium dioxide with grain size of 23.8 μm.

Experimental Study on the Characteristics of CO_2 Hydrate Formation in Porous Media below Freezing Point

Porous medium has an obvious effect on the formation of carbon dioxide hydrate. In order to study the characteristics of CO2 hydrate formation in porous medium below the freezing point, the experiment of CO2 hydrate formation was conducted in a high-pressure 1.8-L cell in the presence of porous media with a particle size of 380 μm, 500 μm and 700 μm, respectively. The test results showed that the porous medium had an important influence on the process of CO2 hydrate formation below the freezing point. Compared with porous media with a particle size of 500 μm and 700 μm, respectively, the average hydrate formation rate and gas storage capacity of carbon dioxide hydrate in the porous medium with a particle size of 380 μm attained 0.016 14 mol/h and 65.094 L/L, respectively. The results also indicated that, within a certain range of particle sizes, the smaller the particle size of porous medium was, the larger the average hydrate formation rate and the gas storage capacity of CO2 hydrate during the process of hydrate formation would be.