Low-temperature Stage Research Articles

Major element and oxygen isotope geochemistry of vapour-phase garnet from the Topopah Spring Tuff at Yucca Mountain, Nevada, USA

AbstractTwenty vapour-phase garnets were studied in two samples of the Topopah Spring Tuff of the Paintbrush Group from Yucca Mountain, in southern Nevada. The Miocene-age Topopah Spring Tuff is a 350 m thick, devitrified, moderately to densely welded ash-flow tuff that is zoned compositionally from high-silica rhyolite to latite. During cooling of the tuff, escaping vapour produced lithophysae (former gas cavities) lined with an assemblage of tridymite (commonly inverted to cristobalite or quartz), sanidine and locally, hematite and/or garnet. Vapour-phase topaz and economic deposits associated commonly with topaz-bearing rhyolites (characteristically enriched in F) were not found in the Topopah Spring Tuff at Yucca Mountain. Based on their occurrence only in lithophysae, the garnets are not primary igneous phenocrysts, but rather crystals that grew from a F-poor magmaderived vapour trapped during and after emplacement of the tuff. The garnets are euhedral, vitreous, reddish brown, trapezohedral, as large as 2 mm in diameter and fractured. The garnets also contain inclusions of tridymite. Electron microprobe analyses of the garnets reveal that they are almandinespessartine (48.0 and 47.9 mol.%, respectively), have an average composition of (Fe1.46Mn1.45Mg0.03Ca0.10)(Al1.93Ti0.02)Si3.01O12and are comparatively homogeneous in Fe and Mn concentrations from core to rim. Composited garnets from each sample site have δ18O values of 7.2 and 7.4%. The associated quartz (after tridymite) has δ18O values of 17.4 and 17.6%, values indicative of reaction with later, low-temperature water. Unaltered tridymite from higher in the stratigraphic section has a δ18O of 11.1% which, when coupled with the garnet δ18O values in a quartz-garnet fractionation equation, indicates isotopic equilibration (vapour-phase crystallization) at temperatures of ∼600°C. This high-temperature mineralization, formed during cooling of the tuffs, is distinct from the later and commonly recognized low-temperature stage (generally 50−70°C) of calcite, quartz and opal secondary mineralization, formed from downward-percolating meteoric water, that locally coats fracture footwalls and lithophysal floors.

The role of cool-flame chemistry in quasi-steady combustion and extinction of n-heptane droplets

Experiments on the combustion of large n-heptane droplets, performed by the National Aeronautics and Space Administration in the International Space Station, revealed a second stage of continued quasi-steady burning, supported by low-temperature chemistry, that follows radiative extinction of the first stage of burning, which is supported by normal hot-flame chemistry. The second stage of combustion experienced diffusive extinction, after which a large vapour cloud was observed to form around the droplet. In the present work, a 770-step reduced chemical-kinetic mechanism and a new 62-step skeletal chemical-kinetic mechanism, developed as an extension of an earlier 56-step mechanism, are employed to calculate the droplet burning rates, flame structures, and extinction diameters for this cool-flame regime. The calculations are performed for quasi-steady burning with the mixture fraction as the independent variable, which is then related to the physical variables of droplet combustion. The predictions with the new mechanism, which agree well with measured autoignition times, reveal that, in decreasing order of abundance, H2O, CO, H2O2, CH2O, and C2H4 are the principal reaction products during the low-temperature stage and that, during this stage, there is substantial leakage of n-heptane and O2 through the flame, and very little production of CO2 with no soot in the mechanism. The fuel leakage has been suggested to be the source of the observed vapour cloud that forms after flame extinction. While the new skeletal chemical-kinetic mechanism facilitates understanding of the chemical kinetics and predicts ignition times well, its predicted droplet diameters at extinction are appreciably larger than observed experimentally, but predictions with the 770-step reduced chemical-kinetic mechanism are in reasonably good agreement with experiment. The computations show how the key ketohydroperoxide compounds control the diffusion-flame structure and its extinction.

The Nb3Sn layers formation at diffusion annealing of Ti-doped multifilamentary Nb/Cu–Sn composites

The structure and morphology of superconducting Nb3Sn layers in multifilamentary Nb–Ti/Cu–Sn and Nb/Cu–Sn–Ti composite wires after various regimes of the diffusion annealing have been studied by transmission and scanning electron microscopy. The effect of the doping mode and Ti concentration on the thickness, structure and morphology of Nb3Sn layers is pronounced even after the first (low-temperature) stage of the diffusion annealing. After various regimes of the annealing the wires with doped bronze matrix (Nb/Cu–Sn–0.24Ti) demonstrate wider zones of fine equiaxed Nb3Sn grains with narrow grain size distributions compared to those with Ti-doped Nb filaments, which is of great importance for an attainment of the highest critical current densities Jc.

A solid sorbent-based multi-stage fluidized bed process with inter-stage heat integration as an energy efficient carbon capture process

A thermally coupled multi-stage fluidized bed process was developed as a viable option for the carbon capture process with reduced energy consumption. The process is composed of multiple stages that operate at different temperature levels. Each stage consists of an absorber, a regenerator, and a heat exchanger for intra-stage heat recovery. Between adjacent stages, an absorber at a higher temperature stage is thermally integrated with a regenerator at a lower temperature stage to balance the supply and demand of thermal energy. A conceptual scheme of the process and an associated mathematical model was developed. Case studies of two- and three-stage fast fluidized bed processes are presented. For each stage, K2CO3, Na2CO3 promoted MgO, and Li4SiO4 are used as low-, medium-, and high-temperature solid sorbents which undergo independent gas-solid reaction pathways but with thermally coupled. The sorbents were chosen based on the availability of data on their kinetics and properties. A flow-sheet simulation of the developed process for a 500-MWe pulverized coal-based power plant was conducted using the Aspen Custom Modeler, to produce a process design study and a sensitivity analysis. Finally, the energy efficiency, including the net electrical efficiency, of the retrofitted power plant is compared with those of optimized MEA-based carbon capture processes and the calcium looping process.

Mineralogy and geochemistry of hydrothermal precipitates from Kairei hydrothermal field, Central Indian Ridge

The Kairei hydrothermal field was the first confirmed active submarine hydrothermal system on the Central Indian Ridge. It has been suggested to be related to mafic as well as ultramafic host rocks based on vent fluid composition and the presence of ultramafic rocks in its vicinity. In this study, detailed geochemical and mineralogical analyses have been carried out on the hydrothermal precipitates from the Kairei vent field in order to investigate the possible presence of indications for an ultramafic substrate at this vent site. The studied samples included fragments of sulfide chimneys, massive sulfides and talc-bearing and silicified breccias. Three mineralization stages were identified: (1) a high-temperature stage consisting largely of chalcopyrite, isocubanite, and pyrite; (2) a medium to low temperature stage characterized by the mineral assemblages of sphalerite and pyrite; and (3) a weathering stage characterized by secondary Cu-sulfides (bornite, digenite, covellite and idaite), Fe-oxihydroxides, Opal-A, and Cu-chloride (paratacamite and atacamite). The sulfide geochemistry is characterized by high concentrations of Cu and Zn (Cu + Zn up to 29.3 wt.%, n = 17) and Au (mean 5.28 ppm, n = 17), which is comparable to results from seafloor massive sulfides collected from ultramafic-hosted sites in the Atlantic Ocean, but differs from those of typical mafic-hosted deposits. The high concentrations of Cu and Au at the Kairei hydrothermal field could be an indication for the involvement of ultramafic rocks in the subseafloor. Ultramafic-hosted, Au-rich sulfide deposits may not be restricted to the Atlantic Ocean and may be common along all slow- and intermediate-spreading ridges.

Waxing and waning of dynamical heterogeneity in the superionic state

Using molecular dynamics simulations of UO2-a type II superionic conductor-we identify a well-defined onset of dynamic disorder (Tα), which is remarkably correlated to a nontrivial advance of dynamical heterogeneity (DH). Quantified by the correlations in the dynamic propensity and van Hove self-correlation function, the DH is shown to grow with increasing temperature from Tα, peak at an intermediate temperature between Tα and Tλ-the superionic transition temperature-and then recede. Surprisingly, the DH attributes are not uniform across the temperatures-our investigation shows a low temperature (αT) stage DH, which is characterized by weak correlations and a plateaulike period in the correlations of the propensity, and a high temperature (λT) stage DH with strong correlations that are analogous to those in typical supercooled liquids. Our work, which has rigorously identified the onset of superionicity, gives a different direction for interpreting scattering experiments on the basis of statistical, correlated dynamics.

空心莲子草叶甲对越冬保护的响应与控害效能比较

The alligator weed flea beetle,Agasicles hygrophila( Coleoptera: Chrysomelidae) is a biological control agent of the alligator weed Alternanthera philoxeroides( Amaranthacese: Alternanthera),a worldwide invading weed. Low temperature and frost stress in winter-spring seasons are the key factors that affect A. hygrophila. To explore whether the protections used in habitat could increase the population of overwintered A. hygrophila,we investigated and compared the populationnumber,structure,distributing characteristic in spatial niches of A. hygrophila and the controlling efficiency of A.hygrophila on A. philoxeroides in protected habitat( PH) with those in natural habitat( NH). The investigation was phased with the variation of air temperature and the elapse of time. Low temperature stage was from 21th,January to 9th,April,2009,followed by temperature rise period from 15th,April to 1st,May,and the third investigated period which was the first emergence time of beetle adults in NH from 1stto 29th,June. The protected habitat was constructed by covering plastic film on net room before low temperature and freezing came. The results showed that A. hygrophila could overwinter smoothly and no dormancy was observed in protected habitat at low temperature in winter-spring time. Adults gadded and fed on up-right stems of A. philoxeroides both in sunny and air temperature rising day in winter-spring time,but were inactive and stayed creep layer of weed or surface or crevice of soil at overcast,rainy or low temperature time. Beetle adults in protected habitat laid eggs in early April. There was a rapid increasing of the populationwhich played an important role in controlling the above ground parts of A. philoxeroides. Only a few beetle adults can be found in natural habitat even at the beginning of June. Consequently,the weed grew very well due to the low density of the beetle population which was difficult to play the role of a biocontrol factor. Comparing the results obtained in the first day with that in 15th,June,the increasing rate of stem height of A. philoxeroides in this interval of time were-13.91% in the protected habitat and-2.94% in the natural habitat,respectively. The stem height of A. philoxeroides in the natural habitat was significantly higher than that in the protected habitat. The control rate of a plant biomass of A. philoxeroides by A. hygrophila in the protected habitat was 47.56% which was significantly stronger comparing with the control rate of 4.89% in the natural habitat. The control effect to leaves of A.philoxeroides in the protected habitat was extremely better as compared with that in the natural habitat in the interval of time from 15thto 29th,June. There were no leaves left on stems of A. philoxeroides plants as leaves being either eaten up by A.hygrophila or withered after attacked by A. hygrophila in the protected habitat. The rate of damage stem,rate of stem bore hole and the number of stem bore hole per plant in the protected habitat were significantly higher than that in the natural habitat. These results suggested that the overwintered A. hygrophila population could be significantly increased by covering plastic film to protect the habitat. The beetle adults in protected habitat could lay eggs ahead of time compared to that in the natural one,thus could effectively control the growing of weed.

Study and Prediction for the Fire Resistance of Acid Corroded Intumescent Coating

Acid corrosion may cause the deterioration of the fire resistance of the intumescent fire retardant coatings, especially for the coatings used in the acid polluted environment. This paper reported the results of an experimental study of degradation in fire protection performance of intumescent coating for steel elements after different times of immersion in the hydrochloric acid solution. After acid erosion, the thickness of the coating thinned, the surface became rough and had cracks and broken holes. The size of the pores in the char layer was larger and uneven, and some ‘cement’ parts were formed in the char layer. The TG/DTG results showed in the low temperature stage the curve was relatively flat. In the medium temperature stage, the number of the weight loss troughs decreased; the shape of the troughs simplified; and the top weight loss rate increased. In the high temperature stage, the troughs near 593°C flattened gradually, and the top weight loss rate became smaller, while the top weight loss rate became larger around 674°C. And there were significant changes in the thermal dynamic parameters. A prediction method of remained fire resistance property for the acid erosion coatings was proposed, by comprehensively considering the physical and chemical characteristics change trends of the corroded coating. And this method can be a reference for the fire safety evaluation of the built protected steel structure.

Distribution, microfabric, and geochemical characteristics of siliceous rocks in central orogenic belt, China: implications for a hydrothermal sedimentation model.

Marine siliceous rocks are widely distributed in the central orogenic belt (COB) of China and have a close connection to the geological evolution and metallogenesis. They display periodic distributions from Mesoproterozoic to Jurassic with positive peaks in the Mesoproterozoic, Cambrian—Ordovician, and Carboniferous—Permian and their deposition is enhanced by the tensional geological settings. The compressional regimes during the Jinning, Caledonian, Hercynian, Indosinian, and Yanshanian orogenies resulted in sudden descent in their distribution. The siliceous rocks of the Bafangshan-Erlihe ore deposit include authigenic quartz, syn-depositional metal sulphides, and scattered carbonate minerals. Their SiO2 content (71.08–95.30%), Ba (42.45–503.0 ppm), and ΣREE (3.28–19.75 ppm) suggest a hydrothermal sedimentation origin. As evidenced by the Al/(Al + Fe + Mn), Sc/Th, (La/Yb)N, and (La/Ce)N ratios and δCe values, the studied siliceous rocks were deposited in a marginal sea basin of a limited ocean. We suggest that the Bafangshan-Erlihe area experienced high- and low-temperature stages of hydrothermal activities. The hydrothermal sediments of the former stage include metal sulphides and silica, while the latter was mainly composed of silica. Despite the hydrothermal sedimentation of the siliceous rocks, minor terrigenous input, magmatism, and biological activity partly contributed to geochemical features deviating from the typical hydrothermal characteristics.

Parametric and exergetic analysis of a two-stage transcritical combined organic Rankine cycle used for multiple grades waste heat recovery of diesel engine

Diesel engine has multiple grades of waste heat with different ratios of combustion heat, exhaust is 400 °C with the ratio of 21% and coolant is 90 °C with 19%. Few previous publications investigate the recovery of multiple grades waste heat together. In this paper, a two-stage transcritical combined organic rankine cycle (CORC) is presented and analyzed. In the combined system, the high and low temperature stages transcritical cycle recover the high grades waste heat, and medium to low grades waste heat respectively, and being combined efficiently. Meanwhile, the suitable working fluids for high stage are chosen and analyzed. The cycle parameters, including thermal efficiency (ηth), net power output (Pnet), energy efficiency (ηexg) and global thermal efficiency of DE-CORC(ηglo) have also been analyzed and optimized. The results indicate that this combined system could recover all the waste heat with a high recovery ratio (above 90%) and obtain a maximum power output of 37kW for a DE of 243kW. The global thermal efficiency of DE-CORC can get a max value of 46.2% compared with 40% for single DE. The results also indicate that all the energy conversion process have a high exergy efficiency.

Exploration of crystallization behavior of Cu<sub>36</sub>Zr<sub>48</sub>Al<sub>8</sub>Ag<sub>8</sub> amorphous alloy and melt overheating on its GFA and thermal stability by electrical resistivity measurement

The crystallization behavior of Cu36Zr48Al8Ag8 amorphous alloy and the melt overheating on its glass-forming ability(GFA) and thermal stability are explored by the high-temperature four-electrode electrical resistivity method. The results show that this amorphous alloy has a high-temperature crystallization stage which has not been revealed in the previous literatures besides the lowtemperature crystallization stage. The crystallization products of the first stage are AgZr and Cu10Zr7 metastable phases by using differential scanning calorimetry(DSC) and X-ray diffractometry(XRD). They transform into equilibrium phases CuZr2, AlCu2Zr and CuAl2 in the second stage crystallization. On one hand, when the overheating temperature is greater than 430 K, the thermal stability of Cu36Zr48Al8Ag8 amorphous alloy decreases significantly, and the first stage crystallization behavior changes and the quasicrystals precipitate firstly. On the other hand, its glass-forming ability firstly increases and then decreases with the melt overheat increasing.The effect of the melt overheating on the glass-forming ability and the thermal stability of amorphous are analyzed and discussed from two aspects of melt structure homogeneity and the degree of oxidation.

Thermo-Gravimetric Analysis and Kinetic Study of Biomass Pyrolysis

In order to realize the optimization of pyrolysis process, the pyrolysis characteristics and kinetics of common agriculture and forestry biomass were studied. Four kinds of biomass were chosen as experiment materials for thermo-gravimetric experiment. The Characteristics of biomass pyrolysis was studied by defining a new evaluation methodology. The method of Coats-Redfern was used to analyze pyrolysis kinetics of biomass pyrolysis process. The results of research show that the pyrolysis process of biomass can be divided into three stages, including drying and preheating, fast pyrolysis and slow decomposition of residue. The activation energy of pyrolysis reaction of biomass during the low temperature stage is higher than that of the high temperature stage. The values of the activation energy and pre-exponential factor are increasing with the increase of heating rate. The pyrolysis of biomass in the main pyrolysis zone can be effectively described by using the kinetic model n=2. The heating rate of 15K/min and temperature of 500°C can improve the reaction rate, and it helps to reduce energy consumption of the reaction.

Influence of structural and morphological characteristics on the hydrogen production and sodium recovery in the NaOH–MnO thermochemical cycle

The Na–Mn thermochemical cycle is a three step process that has recently attracted renewed attention due to its potential for efficient hydrogen production. In this study, the two low temperature stages have been investigated in order to establish the factors determining the efficiency of both hydrogen production and recyclability of the different solid phases involved. The obtained result reveal that the influence of MnO particle size distribution is crucial for the solid–liquid reaction with NaOH and, therefore, for hydrogen production. Lower particle size and relatively high crystallinity causes a two-fold increment of the conversion, with respect to commercial MnO with very large particles. On the other hand, the influence of reaction conditions on the hydrolysis step has been analyzed in this study. Na extraction from the sodium manganese oxide is favored by performing the process at temperatures around 100 °C, in excess of water; during relatively longer periods and in inert gas. Nevertheless, it has been observed that the structure of the mixed oxide formed during the hydrogen production stage is the most relevant factor determining the efficiency of the Na–Mn oxide hydrolysis. This work reveals that α-NaMnO2 presents the best ion exchange properties for the hydrolysis reaction, leading to more than 80% of Na recovery.

Preparation of high-quality AIN films by two-step method of radio frequency magnetron sputtering

The preparation of nanometer aluminum nitrogen (AlN) films with uniform lattice arrangement is of great significance for the manufacture of high-frequency surface acoustic wave (SAW) device. We put forward the two-step growth method and the annealing treatment method for the deposition of (100) AlN thin films. The results show that when the sputtering pressure is 1.2 Pa and the ratio between N2 and Ar is 12:8, the influence of lattice thermal mismatch and anti-phase is the smallest during the nucleation growth at low-temperature stage of (100) AlN/(100) Si films. The root-mean-square (RMS) surface roughness of AlN prepared by the two-step method is reduced from 6.4 nm to 2.1 nm compared with that by common deposition process.

A Study of Ore-Controlling Factors and Metallogenic Mechanism of Lead-Zinc Deposit in Luziyuan, Zhenkang, Yunnan

The lead-zinc ore in Luziyuan, Zhenkang Town, Yunnan Province is a large lead-zinc polymetallic deposit discovered in recent years. The ore body mainly occurs in the stratum of Shahechang Group of Upper Cambrian. Controlled by NE trending faults and its flanking associated structures, it features equal interval and lateral trending distribution in the spatial domain. The development and mineralization of wall-rock alteration experienced two stages, low medium temperature stage and medium-high temperature stage. Metallogenic materials are mainly from the ore-bearing stratum and deep concealed rock mass. Through the study of such geological features as lithology of ore-bearing stratum, structure of ore-controlling Faults, wall-rock alteration, and ore fabrics, the author believes that the formation of the deposit is closely related to the multi stages of tectonic movements and magmatic hydrothermal activities. It is a sedimentary-reworked type, and skarn-type lead-zinc-iron polymetallic deposit and it is of multiple mineralization stages and varieties of mineral sources.

Lorentz microscopy observation of vortices in high-Tcsuperconductors using a 1-MV field emission transmission electron microscope

Lorentz microscopy has opened the door to observing a single quantized magnetic flux line (i.e. a vortex) and its dynamic behavior inside a superconductor in real time. It resulted from the efforts of Dr Akira Tonomura and his collaborators, who developed a field emission electron microscope and advanced the technologies used for visualizing vortices (e.g. a low-temperature specimen stage and a magnetic-field application system). They used a 1-MV field emission transmission electron microscope with an electron beam that can penetrate thick specimens of high-temperature superconductors (Bi2Sr2CaCu2O8+δ and YB2C3O7-δ) to reveal the flux-line features inside materials and their interactions with defects. This memorial paper reviews the results of research in the area of vortex matter physics.

Effects of Aluminum Nanoparticles on Thermal Decomposition of Ammonium Perchlorate

The effects of aluminum nanoparticles (AlNs) on the thermal decomposition of ammonia perchlorate (AP) were investigated by DSC, TG-DSC and DSC-TG-MS-FTIR. Addition of AlNs resulted in an increase in the temperature of the first exothermic peak of AP and a decrease in the second. The processing of non-isothermal data at various heating rates with and without AlNs was performed using Netzsch Thermokinetics. The dependence of the activation energy calculated by Friedman's isoconversional method on the conversion degree indicated the decomposition process can be divided into three steps. They were C1/D1/D1 for neat AP, determined by Multivariate Non-linear Regression, and changed to C1/D1/F2 after addition of AlNs into AP. The isothermal curves showed that the thermal stability of AP in the low temperature stage was improved in the presence of AlNs.

Vortex Matter Research by Electron Microscopy – Memorial to Dr. Akira Tonomura –

Electron phase microscopy represented by electron holography and Lorentz microscopy, has opened the way to observing a single quantized magnetic flux-line – “vortex” – and its dynamical behavior inside superconductors. It was realized by Dr. Akira Tonomura and his collaborators by developing a field emission electron microscope and by advancing the technologies for visualizing the vortices, for example, low-temperature specimen stage and magnetic-field application system. Electron phase microscopy was clarified to be a powerful tool for investigating the flux-line features inside materials and their configurations with defects. This paper intends to give a review of the research results on vortex matter physics.

Study on Co-Combustion of Oil Shale Semi-Coke and Corn Stalk

Co-combustion experiment of oil shale semi-coke and corn stalk at different blend ratios was performed using thermogravimetric analyzer. The influence of different blend ratios has been studied. The combustion characteristics are obtained under the heating rates of 20oC/min and the experimental temperature range of 40-850oC. The combustion process of the blends is divided into three stages: low-temperature stage, transition stage and high-temperature stage. With the increasing of corn stalk in the blends, the reaction of combustion mainly shifts from high-temperature stage to low-temperature stage, and there is no obvious change for the ignition temperature, but the burn out temperature comes down. The combustion kinetics parameters of the blends were analyzed using Flynn-Wall-Ozawa model. The result shows that the activation energy of the volatile matter stage increases and the activation energy of semi-coke combustion stage decreases. The combustion characteristics of the oil shale semi-coke get improved significantly with the mixture of corn stalk.

Genetic overlap of QTL associated with low-temperature tolerance at germination and seedling stage using BILs in soybean

Zhang, W.-B., Jiang, H.-W., Qiu, P.-C., Liu, C.-Y., Chen, F.-L., Xin, D.-W., Li, C.-D., Hu, G.-H. and Chen, Q.-S. 2012. Genetic overlap of QTL associated with low-temperature tolerance at germination and seedling stage using BILs in soybean. Can. J. Plant Sci. 92: 1381–1388. Low temperature is one of the critical environmental factors that limit agricultural production worldwide. In northeast China soybean frequently suffers low temperature stress, especially at germination stage and seedling stage. The most effective way to solve this problem is to breed cultivars with low-temperature tolerance. A set of advanced backcross introgression lines was constructed with Hongfeng 11 as recurrent parent, which was a local variety in Heilongjiang province, and Harosoy as donor parent, which was introduced from Canada. Their BC2F4lines were screened in low-temperature condition at the two stages, and 41 transgressive lines were selected out at germination stage and 45 lines at seedling stage. Sixty-four and fifty-one pairs of simple sequence repeat primers with fine polymorphism were used for genotyping the selected population and random population at the two stages, respectively. Related quantitative trait loci (QTL) were obtained by chi-test and ANOVA analysis with genotypic and phenotypic data. Finally, 25 QTL at germination stage and 13 QTL at seedling stage were mapped. Among them, 10 QTL overlapped between two stages, which showed a partial genetic crossover on low-temperature tolerance stages in soybean. This would play an important role in marker-assisted selection for breeding elite variety with low-temperature tolerance at both stages.