高坝泄流溶解氧过饱和影响因子主成分分析

针对高坝泄洪可能造成大坝下游水体溶解氧过饱和给下游水生生物带来较大影响的问题,采用主成分分析法对三峡-葛洲坝坝下近坝区溶解氧过饱和主要影响因素的权重进行了分析,得出对坝下近坝区溶解氧饱和度影响最大的是泄洪方式、泄洪建筑物总泄洪量、坝上溶解氧饱和度、水电站泄流量、上下游水位.可为有效控制三峡-葛洲坝区域下游近坝区气体过饱和问题提供借鉴.     

曝气对过饱和总溶解气体传质系数计算与分析研究

过饱和总溶解气体(TDG)主要由高坝溢洪道泄流、植物光合作用产氧过剩和水温剧增等方式引起，这可能直接导致鱼类和水生生物患有“气泡病”(GBD)甚至死亡。为探索减缓过饱和TDG不利影响的措施，采用两种类型的漩混曝气盘对过饱和TDG释放进行试验。结果表明，在不同曝气条件下，漩混曝气方式对过饱和TDG释放有明显的促进作用，其作用效果略强于针孔曝气方式，且曝气速率对过饱和TDG传质系数影响最大，曝气深度次之，曝气直径最小，并获得了过饱和TDG传质系数与曝气速率、曝气直径和曝气深度的关系式，且其误差平均在±6.25%以内。研究结果为减缓过饱和TDG的不利影响提供了数据基础。     

溢洪道挑流坎对消力池内过饱和气体的影响分析

消力池中过饱和气体的浓度通常与包括溢洪道射流流态在内的多种影响因素有关。为了得到溢洪道射流流态与溢洪道结构之间的关系,在采用室内物理模型试验分析各种溢洪道流态的基础上,基于气体向气泡界面和水体表面传质的机理,通过建立三维两相流数学模型,模拟分析了不同溢洪道结构对消力池内饱和气体的影响。结果表明,溢洪道挑流坎可大幅降低消力池中的过饱和气体浓度。     

环境条件对上海蕴藻浜水体沉积物Ni释放影响的研究

通过改变环境条件(温度、pH、溶解氧),并采用Tessier五步连续提取法,研究了温度、pH和溶解氧对蕴藻浜沉积物中Ni的释放的影响,并对不同条件下的沉积物释放前后Ni的形态进行了对比分析.结果表明:随着温度的升高,沉积物对Ni的释放通量升高,可交换态、铁锰氧化物结合态以及有机物结合态在沉积物中所占百分比均上升;随着pH的增加,沉积物对Ni的释放通量下降,可交换态、碳酸盐结合态、铁锰氧化物结合态以及有机结合态所占百分比均有不同程度的增加;而溶解氧高的水体比溶解氧较低的水体更不容易释放Ni.     

松子壳基活性炭光催化剂的制备及其催化性能研究

为了提高TiO_2光催化剂对水体有机污染物的降解能力,将松子壳基活性炭作为载体负载TiO_2,研究载体比表面积、载体与TiO_2的复合比例以及煅烧温度对复合光催化剂降解水体有机污染物亚甲基蓝的影响。通过BET,XRD,FTIR和SEM分析方法对复合光催化剂的比表面积、晶体结构、有机官能团和表面形貌进行了表征。研究结果表明:适当的增加载体的比表面积,有利于Ti O2的负载和复合光催化剂催化活性的提高;当活化水量为1.5 mL/min时,在充分的水蒸气活化反应下,松子壳炭可制备成比表面积为634.65 m~2/g的活性炭,使其负载TiO_2后具有较好的亚甲基蓝吸附作用和光降解作用;当TiO_2与活性炭的质量比为0.8∶1时,复合光催化剂的催化效果较好;当煅烧温度为450℃时,复合光催化剂具有较优的催化效果,降解率可达77.10%。     

昆明市盘龙江流域水质的时空差异性分析

盘龙江下游区域自北向南纵贯昆明市区流入滇池,是地下水的重要径流和排泄地带,受人类活动影响较大,为探究盘龙江流域水环境特征,于2017、2018年12月采集18个采样点的水质数据,利用EXO多参数水质监测仪等测定水质参数,综合考虑各测点水质的pH值、溶解氧、电导率、总溶解固体等8种理化变量,通过调查监测、配对T检验分析其时空差异性。结果表明,2017、2018年盘龙江pH值偏弱碱性;浊度、盐度相对稳定;整个流域溶解氧量均超过10 mg/L,处于过饱和状态;蓝绿藻、叶绿素含量达到中富营养化程度;电导率、总溶解固体的空间差异明显;流域整体呈上段（瀑布公园—鱼龙桥）比下段（金家村—滇池入口）良好的空间分布特征。     

煤基颗粒活性炭(MJ-AC)对模拟燃煤烟气中Hg0吸附能力研究

在模拟烟气汞吸附机理研究实验台上对以煤为原料的颗粒活性炭(MJ-AC)吸附Hg~0的性能开展了实验研究,研究烟气成分对MJ-AC吸附过程的影响。研究表明MJ-AC在N_2气氛下对Hg~0的吸附不是简单的通过孔隙间范德华力作用的直接物理吸附过程,而是复杂的化学吸附过程。模拟气氛中,NO_2和NO酸性气氛对MJ-AC吸Hg~0有极大的促进作用。MJ-AC在模拟烟气下Hg~(2+)析出过程快于一般木制活性炭,主要是原因MJ-AC的比表面积,孔容积和微孔容积等物理特性参数均小于一般木质活性炭,影响了MJ-AC的饱和吸附性能。     

pH和溶解氧对上海蕴藻浜河道沉积物重金属的影响

通过改变上覆水体pH和溶解氧,并采用改进的由欧共标准测量与检测局(BCR)提出的连续提取法,研究pH和溶解氧对蕴藻浜沉积物中Cu、Cr释放的影响,以及沉积物释放前后Cu、Cr形态的变化,探索沉积物中重金属释放的机理.结果表明:随着pH增加,沉积物中重金属释放量下降,可还原态在沉积物中的含量上升,可氧化态与酸可提取态含量均有下降,这主要和H~+与重金属离子的竞争以及沉积物中自然胶体的吸附有关;随着溶解氧含量增加,沉积物中重金属释放量升高,可氧化态含量呈明显下降趋势,而可还原态含量略有上升趋势,这主要与沉积物的还原性、硫化物及铁锰氧化态重金属有关.     

橡木锯屑制备直接碳燃料电池活性炭

以橡木锯木屑为原料,K2CO3为研究活化剂,采用化学活化法制备DCFC用活性炭,着重考察了碱炭比、活化温度、活化时间对活性炭的比表面积、孔隙率的影响,同时采用HNO3浸渍对活性炭表面进行改性及镍负载对活性炭导电性能进行改善。研究结果表明:当碱炭比为1、活化温度为900℃、活化时间为120min时,活性炭比表面积达1240m2/g,孔容积为0.768m3/g;镍负载后的活性炭体积电阻率明显下降;HNO3浸渍后,活性炭表面含氧官能团增多,灰分明显减少,但比表面积有一定下降,而体积电阻率增加明显。     

管内湍流传热传质耦合对过饱和度的影响

为了探究湍流情况下水汽相变传热传质耦合对管道内过饱和度的影响,使用Fluent用户自定义标量(UDS)对传热传质耦合模型进行计算,研究了在不同径向位置、空气温度、壁面温度、空气流速及湿度等因素下耦合项对管道中过饱和度分布的影响。结果表明：沿径向不同位置处,耦合项对过饱和度的影响有所不同;随着温差的增大,耦合项对过饱和度的影响也会增大,当温差增大到一定程度时,耦合项的影响不可忽略;在不同的进口空气流速及湿度下,耦合项对过饱和度的影响基本相同,温差的大小直接决定了耦合项对过饱和环境的影响。     

Structure and hydrogen permeability of V–15Ni alloy

The structure of the V–15Ni at.% alloy before and after hydrogen permeability tests was investigated by means of XRD and SEM with EDS analysis. We have found that decomposition of supersaturated V-based solid solution with variable Ni content occurred during testing. The volume fraction of the solid solution decreased and the fraction of V₃Ni phase increased during permeability testing, thus bringing the alloy to nearly equilibrium. The membrane without Pd coating showed satisfactory hydrogen fluxes with a significant impact of the surface dissociation rate of hydrogen. The shape of hydrogen permeation curves at the downstream side of the membrane at various temperatures was unusual. We attribute it to the high concentration of dissolved hydrogen in the metal lattice and its effect on the hydrogen diffusivity and solubility. In addition, the multiphase structure with non-uniform distribution of nickel both between the phases and within the BCC solid solution (and, consequently, different hydrogen concentrations) may cause dilatation or compressing effect on neighbouring micro-volumes of the alloy.     

Suppression of hydrogen absorption into 304L austenitic stainless steel by surface low temperature gas carburizing treatment

Effect of low temperature gas carburizing (LTGC) on hydrogen absorption and hydrogen embrittlement (HE) susceptibility of 304L metastable austenitic stainless steel was investigated. The LTGC treatment imparted carburized layer on the steel surface with supersaturated solute carbon atoms (namely expanded austenite or S-phase) and more than 1 GPa surface compressive stress. Carburized layer thickness, carbon concentration level, residual compressive stress and hardness increased but hydrogen absorption decreased with increasing LTGC treatment time. Carburized surface layers had much higher austenite stability. The HE susceptibility of carburized steel was reduced due to the reduction of hydrogen absorption and the increment of austenite stability. The specimens whose residual compressive stresses were eliminated by tensile plastic straining also exhibited low hydrogen absorption during hydrogen charging, indicating that, besides the residual compressive stress, the supersaturated solute carbon atoms also have the ability to reduce hydrogen absorption. In addition, the results indicate that the supersaturated solute carbon atoms in the LTGC case can suppress hydrogen solubility without affecting diffusivity.     

Phosphorus and iron doped nitrogen-containing carbon derived from biomass for oxygen reduction under various pH conditions

Various catalysts were synthesized by incorporating phosphorus and iron into nitrogen-containing carbon derived from shrimp shell with pyrolysis. These catalysts had high specific surface area, uniform atomic doping and various active sites, which resulted in the high kinetics activity towards oxygen reduction reaction (ORR) under various pH conditions. Based on different doping sources to analyse ORR activity, phosphorus-doped catalyst was suitable for alkaline medium and iron doping for acidic medium, while their synergistic effect induced the highest ORR activity in neutral medium. Besides, the stability measurements investigated their abilities for application. Introducing iron into nitrogen-containing carbon could gradually strengthen the long-term stability for different catalysts in various pH conditions. Especially, phosphorus doping promoted the best ORR performance in alkaline condition with an extremely poor stability, which could be overcome by further adding iron. This work provides a strategy for the doped biomass-based carbon to accommodate different fuel cells.     

Studies on the mechanism and capacity of hydrogen uptake by physisorption-based materials

Nanostructure carbons are the most important physisorption-based hydrogen carriers. The mechanism of hydrogen uptake was studied based on the adsorption isotherms collected for a wide range of temperature and pressure. It was concluded that the hydrogen adsorbed is arranged on carbon surface monolayerly; therefore, the storage capacity depends only on the specific surface area of the carbon. This rule applies also for other organic/inorganic materials if the interaction between hydrogen and the solid surface remains the Van der Waals force. Carbon nanotubes cannot be good carriers of hydrogen due to the small surface area, but superactivated carbon is of great potential and a storage capacity over 10 wt% was proven for the condition of 77 K and 6 MPa.     

Effect of carbon coating on thermal stability of natural graphite spheres used as anode materials in lithium-ion batteries

To investigate the effect of non-graphitic carbon coatings on the thermal stability of spherical natural graphite at elevated temperature, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) measurements are performed. Data from DSC studies show that the thermal stability of the surface modified natural graphite electrode is improved. The surface modification results in a decrease in the BET surface specific area. An improvement in coulombic efficiency and a reduction in irreversible capacity are also observed for the carbon-coated natural graphite. X-ray diffraction analysis confirms that carbon coating alleviates the release of intercalated lithium from natural graphite at an elevated temperature and acts as a protective layer against electrolyte attack.     

Improvement in electrochemical capacitance of carbon materials by nitric acid treatment

Four commercial carbon materials, carbon nanotube, active carbon, acetylene black, and graphite, were treated by concentrated nitric acid. The surface properties and the electrochemical capacitance of the treated and the untreated carbon samples were studied by using scanning electron spectroscopy, BET surface analysis, constant current charge/discharge test, cyclic voltammetry, and alternative current impedance. It is found that the untreated samples have different specific capacitance and specific surface area, which are in the order from large to small: carbon nanotube, active carbon, acetylene black, and graphite. After treated with nitric acid, the specific surface area of these commercial carbon materials increases to different extents, and the specific capacitance of carbon nanotube, acetylene black and graphite increases proportionally to their specific surface area but the specific capacitance of active carbon decreases. The effect of acid treatment on the capacitance of the commercial carbon samples is related to their porosity structure and surface functional groups.     

H2 storage on single- and multi-walled carbon nanotubes

The adsorption of hydrogen on single-walled and multi-walled carbon nanotubes (CNTs) was investigated at 77 and 298 K, in the pressure range of 0–1000 Torr. The adsorption isotherms indicate that adsorption follows the Langmuir model. Hydrogen uptakes were found to depend strongly on the nature of the CNTs. Single-walled CNTs adsorb significantly higher quantities of hydrogen per unit mass of the solid, while the opposite is true on a per unit surface area basis. This observation implies that adsorption takes place selectively on specific sites on the surface. The hydrogen uptake capacity of CNTs was also found to be affected by the purity of the materials, increasing with increasing purity. Temperature programmed desorption indicated that relatively strong adsorption bonds develop between adsorbent and adsorbate and that a single type of adsorption site exists on the solid surface.     

Hydrogen adsorption in carbon nanostructures

Hydrogen adsorption, (BET) specific surface area and X-ray diffraction (XRD) measurements have been performed on carbon nanofibers, intercalated and exfoliated carbon materials. Excess adsorption capacity was evaluated at equilibrium pressures and temperatures ranging from 0.1 to 10.5MPa and 77 to 295K, respectively. We find that at room temperature, carbon nanofibers can adsorb up to 0.7wt% at 10.5MPa. We observed that the presence of different nickel–copper ratios in the catalyst particles leads to change in crystalline structure and specific surface area. Furthermore, we noted that the latter can be increased by the addition of hydrogen in the organic gas during the synthesis of the nanofibers. Finally, we will discuss the hydrogen coverage per unit surface area which is substantially larger on nanostructures than on activated carbon.     

影响煤焦比表面和孔隙特性因素的灰色关联分析

煤焦比表面积和孔隙特性直接决定着煤焦的反应性和煤焦的燃尽时间。影响煤焦比表面积和孔隙特性的因素很多,其关系也相当复杂。本文对实验测得的不同煤种煤焦的比表面积和平均孔径与各影响因素之间的关系进行了灰色关联分析。结果发现,水分、挥发分和矿物质对煤焦的比表面积影响较大,而镜质组含量、固定碳和灰分对煤焦的孔隙特性有较大影响。     

Enhanced hydrogen reversibility of nanoconfined LiBH4–Mg(BH4)2

This study shows the hydrogen desorption kinetics and reversible hydrogen storage properties of 0.55LiBH₄–0.45Mg(BH₄)₂ melt-infiltrated in different nanoporous carbon aerogels with different BET surface areas of 689 or 2660 m²/g and pore volumes of 1.21 or 3.13 mL/g. These investigations clearly show a significantly improved hydrogen storage capacity after four cycles of hydrogen release and uptake for bulk 0.55LiBH₄–0.45Mg(BH₄)₂ and infiltrated in carbon aerogel and the high surface area scaffold, where 22, 36 and 58% of the initial hydrogen content remain after four cycles of hydrogen release and uptake, respectively. Nanoconfinement in high surface area carbon aerogel appears to facilitate hydrogen release illustrated by release of 13.3 wt% H₂ (93%) and only 8.4 wt% H₂ (58%) from bulk hydride in the first cycle using the same physical condition. Notably, nanoconfinement also appear to have a beneficial effect on hydrogen uptake, since 8.3 wt% H₂ (58%) is released from the high surface area scaffold and only 3.1 wt% H₂ (22%) from the bulk sample during the fourth hydrogen release.