Zr-in-rutile thermometry in eclogite at Jinheqiao in the Dabie orogen and its geochemical implications

Trace element analysis was made by an electron microprobe on rutiles from ultrahigh-pressure ec-Iogite at Jinheqiao in the Dabie orogen. The results show Zr contents of 37 to 118 μg.g^-l, with signifi-cant variations between grains within the same thin section. Zr-in-rutile temperatures were calculated by the pressure-dependent thermometer, yielding 595 to 678℃ at 4.1 GPa for the upper limit of meta- morphic pressures. The temperatures are about 200 to 250℃ lower than temperatures of 846±70℃ calculated from garnet-omphacite Fe-Mg partition geothermometry, but 150 to 200℃ higher than -460℃ from quartz-ruUle O isotope temperatures and rutile Pb diffusion closure temperature for the same specimen. This indicates that the diffusion rate of Zr in ruUle is remarkably slower than that of Pb and O in rutile, and that the temperature of Zr-in-rutile is higher than the closure temperature corre-sponding to cooling age as dated by rutile U-Pb radiometric system. The latter is consistent with ex-perimental result of Zr diffusion in rutile. Diffusion and re-crystallization with intensive retrograde fluid during exhumation of UHP metamorphic rocks may be the major reason why the Zr contents in rutile decreased and thus did not provide the record of the peak metamorphic temperatures. The remarkable difference in Zr content between rutile grains suggests that the distribution of Zr in rutile was in the state of disequilibrium due to differential diffusion and retrograde resetting.     

Optical limiting of niobic tellurite glass induced by self-trapped exciton absorption of the AgCl nanocrystal dopant

Niobic tellurite glass doped by silver chloride nanocrystal was prepared with the melting-quenching and heat treatment method, and the self-trapped exciton absorption band of the silver chloride nanocrystal was observed at 532 nm in the UV-visible absorption spectrum. The glass structure characteristics were investigated by Raman spectroscopy, and the mechanism of self-trapped exciton was analyzed by Jahn-Teller model. Its optical limiting was measured with 532 nm picosecond laser pulses, and the corresponding nonlinear absorption coefficient was measured with open-aperture Z-scan. The experimental results showed that optical limiting at 532 nm was attributed to free carrier absorption between the self-trapped state and the continuum band. Supported by Shanghai Leading Academic Discipline Project (Grant No. B408), National Basic Research Program of China (Grant Nos. 2006CB806006, 2006CB921105), Program for Changjiang Scholars and Innovative Research Team in University, Doctoral Program of High Education (Grant No. 20050269011) and Project sponsored by Shanghai Science and Technology Committee (Grant Nos. 06DJ14008, 07dz22025, 06QH14003)     

Density functional study on mechanism of CO oxidation with activated water on O/Au （1 1 1 ） surface

With density functional theory, the mechanism of water-enhanced CO oxidation on oxygen pre-covered Au （111） surface is theoretically studied. First, water is activated by the pre-covered oxygen atom and dissociates to OHads group. Then, OHads reacts with COads to form chemisorbed HOCOads, Finally, with the aid of water, HOCOads dissociates to CO2. The whole process can be described as 1/2H2Oads ＋ H2Oads ＋ 1/2Oads＋ COads→H3Osds ＋ CO2, gas. One CO2 is formed with only 1/2 pre-covered oxygen atom. That is why more CO2 is observed when water is present on oxygen pre-covered Au （111） surface. Activation energy of each elementary step is low enough to allow the reaction to proceed at low temperature.     

Study of low-pressure premixed laminar n-heptane+propane/oxygen/nitrogen flames

Low-pressure premixed laminar n-heptane+propane/oxygen/nitrogen flames were investigated with tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam sampling mass spectrometry. Three flames with different mass percentage of propane in the fuel blends of 0%, 10%, and 20% were studied. The combustion intermediates were identified by comparing the measured IEs with those values in literatures. Mole fraction profiles of the main species were compared among the three flames. The experimental results provide detailed data in understanding the combustion of n-heptane and n-heptane/propane blends in engine. They are also helpful in establishing and verifying the kinetic models. Supported by the National Natural Science Foundation of China (Grant Nos. 50636040 and 50521604)     

Tribological properties of La2O3 and CeO2 doped CoCrW coatings deposited by supersonic plasma spraying

A novel supersonic plasma spraying was used to prepare rare earth oxides doped CoCrW coatings. X-ray diffractometer, contact surface profiler, hardness tester, micro-friction and -wear tester and en- vironmental scanning electron microscope equipped with energy dispersive X-ray spectroscopy were employed to investigate the phase structure, surface morphology, microhardness, friction and wear properties of the sprayed coatings. The results show that rare earth oxide doped coatings have high microhardness and excellent tribological properties. Furthermore, the friction and wear mechanisms of sprayed coatings are also discussed.     

Solidification characteristics of Pb-Sb hypereutectic alloy within ultrasonic field

The solidification of Pb-16%Sb hypereutectic alloy is investigated within ultrasonic field with a fre-quency of 15 kHz. It is found that the ultrasonic field promotes crystal nucleation and terminates the further bulk undercooling of the alloy melt. Theoretical analysis shows that the cavitation effect and the forced bulk vibration are the main factors that reduce the undercooling level. With the increase of ul-trasound intensity, the primary (Sb) phase experiences a growth mode transition from faceted to non-faceted branched growth, and the macrosegregation of primary (Sb) phase is gradually sup-pressed. In addition, the microstructures of Pb-Sb eutectic exhibit a conspicuous coarsening with in-creasing ultrasound intensity, and a structural transition of “lamellar eutectic—anomalous eutectic” occurs when ultrasound intensity rises up to 1.6 W/cm2. The ultrasonic field also changes the solute distribution adjacent to the solidification front, which lowers the Pb contents in primary (Sb) phase.     

北京城区土壤与灰尘中重金属的健康风险评价

选择北京市城区公园广场、大学校区、商业区和居民小区等市民日常活动区域,采集地表土壤及灰尘样品,分析重金属种类及其浓度。采用单因子指数法和Nemerrow指数法,研究了各功能区不同重金属的污染程度,并采用美国环保总署健康风险评价模型,计算北京市居民经呼吸途径和皮肤接触途径摄入重金属而引起的健康风险。研究结果表明,北京市城区人口活动密集区域地表灰尘重金属污染较为严重,Cu、Pb和Zn质量分数的平均值分别为北京市土壤背景值的2~3倍,其中西单灰尘中Zn的质量分数达528mg/kg,超过背景值9倍以上。健康风险评价模型计算结果表明,人体重金属摄入途径风险大小为：呼吸途径>皮肤接触途径;重金属对人体非致癌风险大小为 Pb>Cu>Zn;在不同功能区之间非致癌风险大小为公园广场>大学校区>居民区>商业区。因非致癌风险指数小于阈值1,所以北京市地表灰尘中的重金属,在目前尚不至引起严重的健康风险。