西藏昌果沟遗址粟碳化粒的发现

西藏昌果沟遗址粟（Ｓｅｔａｒｉａｉｔａｌｉｃａ）碳化粒的发现傅大雄（西南农业大学农学系麦类研究室／重庆市６３０７１６）ＤＩＳＣＯＶＥＲＹＯＦＴＨＥＣＡＲＢＯＮＩＺＥＤＭＩＬＩＥＴ（ＳＥＴＡＲＩＡＩＴＡＬＩＣＡ）ＫＥＲＮＥＬＩＮＣＨＡＮＧＧＵＯＧＯＵＡ...

Environmental Changes Analysis of Hongjiannao Lake During Recent Fifty Years——Based on the Data of Lake Sediments

Particle size, the contents of carbonate and TOC were analyzed on lake sediments from a short core in Hongjiannao Lake to discuss the environmental changes during the past decades. On the basis of the records in lake sediments and comparison with the meteorological data of Yulin region, the environmental changes in Hongjiannao Lake were approximately divided into two stages. In stage A （1957 -1996）, the lake evolution and the environmental change were mainly influenced by natural factors. It contains three sub-stages： A1 （1957-1969）, a period of lake expansion, A2 （1969-1990）, a stable period with high lake levels, and A3 （1990 -1996）, a period of gradual extraction of the lake. In stage B （1996 -2005）, the lake area still keeps diminishing. During this period, organic matter increased rapidly due to the input of nutrient elements in the catchment. The carbonate content, however, decreased. As the precipitation was decreasing and the temperature was increasing, the decrease of carbonate content could not be explained by either temperature or precipitation change.

Theoretical investigations on CO oxidation reaction catalyzed by gold nanoparticles

It is crucial to understand the mechanism of low temperature CO oxidation reaction catalyzed by gold nanoparticles so as to find out the origin of the high catalytic reactivity and extend the indus‐trialization applications of nano gold catalysts. In this work, some theoretical works on CO adsorp‐tion, O2 adsorption, atomic oxygen adsorption, formation of surface gold oxide films, reaction mechanisms of CO oxidation involving O2 reaction with CO and O2 dissociation before reacting with CO on gold surfaces and Au/metal oxide were summarized, and the influences of coordination number, charge transfer and relativity of gold on CO oxidation reaction were briefly reviewed. It was found that CO reaction mechanism depended on the systems with or without oxide and the strong relativistic effects might play an important role in CO oxidation reaction on gold catalysts. In particular, the relativistic effects are related to the unique behaviors of CO adsorption, O adsorption, O2 activation on gold surfaces, effects of coordination number and the wide gap between the chem‐ical inertness of bulk gold and high catalytic activity of nano gold. The present work helps us to understand the CO oxidation reaction mechanism on gold catalysts and the influence of relativistic effects on gold catalysis.

Effect of hot extrusion and heat treatment on microstructure of nickel-base superalloy

Effects of hot extrusion (HEX) and heat treatment on prior particle boundary (PPB), MC carbides,γ′precipitates and grain size of nickel-base FGH96 superalloy were studied. The results show that PPB consists of largeγ′, MC carbides enriched with Ti, Nb and a modicum of oxides. Thereafter, it can efficaciously tune γ′ precipitate size from micrometer down to nanometer region and simultaneously results in the annihilation of PPB by HEX process. The activation energy for grain growth of as-HEXed FGH96 superalloy was measured to be 402.6 kJ/mol, indicating that γ′ precipitate serves the critical role in inhibiting grain growth under sub-solvus heat treatment. Moreover, the results reveal that grain growth is primarily restrained by MC carbide in the case of super-solvus temperature.

Cathode made of compacted silver nanoparticles for electrocatalytic carboxylation of 1-phenethyl bromide with CO_2

Silver nanoparticles prepared by the direct reduction of AgNO3 in aqueous solution were compacted into coins and used as the cathode for the electrocatalytic carboxylation of 1-phenethyl bromide with CO2. The influences of the working electrode, charge, current density and temperature were investigated. Under optimized conditions, 98% yield of 2-phenylpropionic acid was obtained. The reaction was performed under very mild conditions and no added catalyst was required in the electrolyte. Yields that varied from moderate to excellent were also achieved with other benzyl bromides. This electrode has good stability and reusability, and the yield and selectivity of 2-phenylpropionic acid could be maintained during reuse for 10 times.

Calculation of Apparent Activation Energy of Coal Oxidation at Low Temperatures by Measuring CO Yield

By analyzing previous studies on activation energy of coal oxidation at low temperatures, a theoretical calculation model of apparent activation energy is established. Yield of CO is measured by using the characteristic detector of coal oxidation at 30-90 ℃. The impact of parameters, such as airflow and particle size, on activation energies is analyzed. Finally, agreement was obtained between activation energies and the dynamic oxygen absorbed in order to test the accuracy of the model. The results show that： 1） a positive exponential relation between concentration of CO and temperature in the process of the experiment is obtained： increases are almost identical and the initial CO is low; 2） the apparent activation energies increase gradually with the sizes of particle at the same airflow, but the gradients increase at a decreasing rate; 3） the apparent activation energies increase linearly with airflow. For the five coal particles, the differences among the energies are relatively high when the airflow was low, but the differences were low when the airflow was high; 4） the optimum sizes of particle, 0.125-0.25 ram, and the optimum volume of airflow, 100 mL/min, are determined from the model; 5） the apparent activation energies decrease with an increase in oxygen absorbed. A negative exponential relation between the two is obtained,

Comparison of wear behaviour of LM13 Al−Si alloy based composites reinforced with synthetic(B_(4)C)and natural(ilmenite)ceramic particles

Dry sliding wear behaviour of stir-cast aluminium matrix composites(AMCs)containing LM13 alloy as matrix and ceramic particles as reinforcement was investigated.Two different ceramic particle reinforcements were used separately:synthetic ceramic particles(B_(4)C),and natural ceramic particles(ilmenite).Optical micrographs showed uniform dispersion of reinforced particles in the matrix material.Reinforced particles refined the grain size of eutectic silicon and changed its morphology to globular type.B_(4)C reinforced composites(BRCs)showed maximum improvement in hardness of AMCs.Ilmenite reinforced composites(IRCs)showed maximum reduction in coefficient of friction values due to strong matrix−reinforcement interfacial bonding caused by the formation of interfacial compounds.Dry sliding wear behaviour of composites was significantly improved as compared to base alloy.The low density and high hardness of B_(4)C particles resulted in high dislocation density around filler particles in BRCs.On the other hand,the low thermal conductivity of ilmenite particles resulted in early oxidation and formation of a tribo-layer on surface of IRCs.So,both types of reinforcements led to the improvement in wear properties of AMCs,though the mechanisms involved were very different.Thus,the low-cost ilmenite particles can be used as alternative fillers to the high-cost B_(4)C particles for processing of wear resistant composites.

Carotenoids Particle Formation by Supercritical Fluid Technologies

Based on the solubility in supercritical CO2,two strategies in which CO2 plays different roles are used to make quercetine and astaxanthin particles by supercritical fluid technologies.The experimental results showed that micronized quercetine particles with mean particle size of 1.0-1.5 μm can be made via solution enhanced dispersion by supercritical fluids(SEDS) process,in which CO2 worked as turbulent anti-solvent;while for astaxanthin,micronized particles with mean particle size of 0.3-0.8 μm were also made successfully by rapid expansion supercritical solution(RESS) process.

Reduction and subsequent carburization of pre-oxidation magnetite pellets

Magnetite is a kind of iron ore that is difficult to carburize.In order to improve the carburizing performance of magnetite pellet,pre-oxidation treatment was carried out,and the oxidation,reduction and carburization behaviors of magnetite pellet were investigated in this study.The magnetite pellet was oxidized in the air and carburized in CO-CO_(2)-H_(2) gas mixtures,the oxidation,reduction and carburization behaviors were demonstrated by detecting phase change,microstructure,carburizing index via thermogravimetry,X-ray diffraction(XRD),infrared carbon-sulfur analyzer,and scanning electron microscope(SEM).The results show that the dense magnetite particles inside pellet are oxidized to porous hematite particles,and the Fe_(3)O_(4) transforms to Fe_(2)O_(3) with high lattice defect concentration during the pre-oxidation process.Then the porous hematite particles and newly formed Fe_(2)O_(3) significantly promote the reduction efficiency.Porous metallic iron particles are produced in the reduction process.Finally,both high reduction efficiency and the porous structure of metallic iron particles dramatically enhance the carburization efficiency of pellet.High preoxidation temperature favors to the carburization of magnetite pellet.However,the carburized index decreases due to the recrystallization of iron oxide when the temperature extends to 1000℃.The optimum pre-oxidation temperature for magnetite pellet carburization is 900℃.

Kinetic and Microstructure of SiC Deposited from SiCl_4-CH_4-H_2

Silicon carbide was prepared from SiCl4-CH4-H2 gaseous precursors by isothermal, isobaric chemical vapor deposition (CVD) at atmospheric pressure and temperatures ranging from 900°C to 1100°C. Kinetic studies showed that carbosilane of SiH2Cl2, SiHCl3 and SiCl2 formed from decomposition of SiCl4 and CH4 contributed to the deposition of hexangular facet and granular pebble structured SiC. An average apparent activation energy of 152 kJ·mol-1 was determined. The overall CVD process was controlled not only by the surface reactions but also by complex gas phase reactions. The as-deposited thin film was characterized using scanning electron microscopy, X-ray diffraction and transmission electron microscopy, these analysis showed that the deposited thin film consisted of pure phase of the β-SiC, the growth morphology of β-SiC differs from hexangular facet to granular pebble struc-tures, which varied with substrate length and CVD temperature.

Characterization of foreign grain on 6H-SiC facet

6H-SiC single crystals were grown by sublimation method. It is found that foreign grains occur frequently on the facets of the crystals. To characterize the foreign grain, a longitudinal and a sectional cut samples were prepared by standard mechanical processing method. Raman spectrum confirms that the foreign grain is actually a mis-oriented 6H-SiC grain. The surface structure of the foreign grain was studied by chemical etching and optical microscopy. It is shown that etch pits in foreign grain region take the shape of isosceles triangle, which are different from those in mono-crystalline region, and high density stacking faults are observed on the surface of the foreign grain. The orientation of foreign grain surface is determined to be （10]-4） plane by back-scattering X-ray Laue image. The X-ray powder diffraction reveals that the powder is partly graphitized after a long crystal growth rim. Therefore it is believed that the loss of Si results in the formation of C inclusions, which is responsible for the nucleation of foreign grain in the facet region.

Comparison of microstructural stability of IN939 superalloy with two different manufacturing routes during long-time aging

Microstructural stability of IN939 superalloy with two different manufacturing routes was investigated during long-term aging at elevated temperatures by light optical microscope（OM） and scanning electron microscope（SEM） equipped with an EDS system.The results show mat the coarsening behavior of γ＇ particles is primarily impacted by the initial heat treatment conditions,and the effect of the prior manufacturing route（casting or hot forming） is found to be insignificant,if any,on the γ＇ particles coarsening kinetics.In the temperature range of 790-827 ℃,IN939 cast/wrought-HT2 alloys have more microstructural stability,while in the temperature range of 827-910 ℃,the initial heat treatment marked as HT1 provides more stable microstructure for the cast or wrought IN939 superalloy.

Gold/monolayer graphitic carbon nitride plasmonic photocatalyst for ultrafast electron transfer in solar-to-hydrogen energy conversion

Gold(Au)plasmonic nanoparticles were grown evenly on monolayer graphitic carbon nitride(g‐C3N4)nanosheets via a facile oil‐bath method.The photocatalytic activity of the Au/monolayer g‐C3N4 composites under visible light was evaluated by photocatalytic hydrogen evolution and environmental treatment.All of the Au/monolayer g‐C3N4 composites showed better photocatalytic performance than that of monolayer g‐C3N4 and the 1%Au/monolayer g‐C3N4 composite displayed the highest photocatalytic hydrogen evolution rate of the samples.The remarkable photocatalytic activity was attributed largely to the successful introduction of Au plasmonic nanoparticles,which led to the surface plasmon resonance(SPR)effect.The SPR effect enhanced the efficiency of light harvesting and induced an efficient hot electron transfer process.The hot electrons were injected from the Au plasmonic nanoparticles into the conduction band of monolayer g‐C3N4.Thus,the Au/monolayer g‐C3N4 composites possessed higher migration and separation efficiencies and lower recombination probability of photogenerated electron‐hole pairs than those of monolayer g‐C3N4.A photocatalytic mechanism for the composites was also proposed.

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.

The Enhancement of CO2 Chemical Absorption by K2CO3 Aqueous Solution in the Presence of Activated Carbon Particles

The enhancement of chemical absorption of CO2 by K2CO3/H2O absorbents in the presence of activated carbon （AC） particles was investigated. The results show that the gas absorption rates can be enhanced significantly in the presence of AC particles, and the maximum enhancement factor 3.7 was observed at low stirring intensities. The enhancement factor increased rapidly with the solid loading during the initial period of absorption and then be- came mild gradually to a maximum value. Both the liquid-solid contact area and the probability of solid particles residing at the gas-liquid interface decreased with the increase of the particle size, leading to a negative effect on the enhancement of mass transfer. The influence of the particles on gas absorption decreased with the reaction rate. The stirring speed changed the interfacial coverage and mass transfer rate on the liquid side and consequently affected the mass transfer between the gas and liquid phases; the enhancement factor decreased with the stirring intensity. A heterogeneous two-zone model was proposed for predicting the enhancement factor and the calculated results agreed well with the experimental data.

Decomposition Kinetics for Formation of CO_2 Hydrates in Natural Silica Sands

The decomposition kinetics for formation of CO2 hydrates in 90 cm 3wet natural silica sands were studied systematically using the depressurization method at the temperatures ranging from 273.2 to 277.2 K and the pressures from 0.5 to 1.0 MPa.The effects of temperature,pressure,particle diameter,porosity,and salinity of formation water on the decomposition kinetics were investigated.The results show that the dissociation percentage increases as temperature increases or as the initial decomposition pressure decreases.An increase in porosity or a decrease in particle diameter of silica sands accelerates the decomposition.Increasing the salinity of the formation water gives rise to a faster decomposition.However,a combination of the present results with the observations in literature reveals that the effect of the coexisting ionic solute depends on its chemical structure.

Assessment of solidification characteristics of carbon-inoculated Mg-3%Al melt by thermal analysis

The Mg-3%Al melt was inoculated by carbon with different holding time.The effect of holding time on grain refining efficiency was evaluated.The solidification characteristics of the carbon-inoculated Mg-3%Al melt with different holding time were assessed by computer-aided cooling curve analysis.The results showed that Mg-3%Al alloy could be effectively refined by carbon inoculation.Slight fading phenomenon occurred with increasing the holding time to 60 min.Carbon inoculation could significantly influence the shape of cooling curves of Mg-3%Al melt.The nucleation starting and minimum temperatures increased.The recalescence undercooling and duration decreased to almost zero after carbon inoculation.The grain refining efficiency of carbon inoculation could be assessed by the shape of the cooling curve and solidification characteristic parameters including nucleation starting and minimum temperatures,recalescence undercooling and duration.

Enhanced Performance of Denitrifying Sulfide Removal Process by 1,2-Naphthoquinone-4-Sulphonate

The denitrifying sulfide removal(DSR) process with bio-granules comprising both heterotrophic and autotrophic denitrifiers can simultaneously convert nitrate, sulfide and acetate species into di-nitrogen gas, elemental sulfur and carbon dioxide, respectively, at high loading rates. This study has determined that the reaction rate of sulfide oxidized into sulfur could be enhanced in the presence of 1,2-naphthoquinone-4-sulphonate(NQS). The presence of NQS mitigated the inhibition effects of sulfide species on denitrification. Furthermore, the reaction rates of nitrate and acetate to nitrogen gas and CO_2, respectively, were also promoted in the presence of NQS, thereby enhancing the performance of DSR granules. The advantages and disadvantages of applying the NQS-DSR process are discussed.

Tailoring the surface structures of iron oxide nanorods to support Au nanoparticles for CO oxidation

Iron oxide supported Au nanomaterials are one of the most studied catalysts for low-temperature CO oxidation.Catalytic performance not only critically depends on the size of the supported Au nanoparticles(NPs)but also strongly on the chemical nature of the iron oxide.In this study,Au NPs supported on iron oxide nanorods with different surface properties throughβ-FeOOH annealing,at varying temperatures,were synthesized,and applied in the CO oxidation.Detailed characterizations of the interactions between Au NPs and iron oxides were obtained by X-ray diffraction,transmission electron microscopy(TEM),and X-ray photoelectron spectroscopy.The results indicate that the surface hydroxyl group on the Au/FeOOH catalyst,before calcination(Au/FeOOH-fresh),could facilitate the oxygen adsorption and dissociation on positively charged Au,thereby contributing to the low-temperature CO oxidation reactivity.After calcination at 200℃,under air exposure,the chemical state of the supported Au NP on varied iron oxides partly changed from metal cation to Au0,along with the disappearance of the surface OH species.Au/FeOOH with the highest Au0 content exhibits the highest activity in CO oxidation,among the as-synthesized catalysts.Furthermore,good durability in CO oxidation was achieved over the Au/FeOOH catalyst for 12 h without observable deactivation.In addition,the advanced identical-location TEM method was applied to the gas phase reaction to probe the structure evolution of the Au/iron oxide series of the catalysts and support structure.A Au NP size-dependent Ostwald ripening process mediated by the transport of Au(CO)x mobile species under certain reaction conditions is proposed,which offers a new insight into the validity of the structure-performance relationship.

Grinding Characteristics Of Directionally Aligned SiC Whisker Wheel - Comparison With A12O3 Fiber Wheel

A unique SiC whisker wheel was invented,in which the whiskers were aligned normally to the grinding wheel surface.In this paper,grindabilities of the SiC whisker wheel are investigated and compared with those of other wheels of SiC grains,Al2O3 grains,as well as Al2O3 long and short fibres which were also aligned normally to the grinding wheel surface,respectively.The main research contents concern grinding characteristics of a directionally aligned SiC whisker wheel such as material-removal volume,wheel-wear rates,integrity of the ground surfaces,grinding ratios and grinding efficiency.Furthermore,grinding wheels of whiskers and fibres have a common disadvantage:they tend to load easily.The authors have proposed a simple method of loading-free grinding to overcome this propensity and investigate some related grinding characteristics under loading-free grinding conditions.