FeCrAl多孔材料烧结体表面球状物和结壳形成原因研究

以FeCrAl粉末为原料,采用粉末冶金法制备FeCrAl多孔材料,试样烧结后表面出现球状物和结壳现象。采用光学显微镜、扫描电子显微镜和X射线能谱仪等设备,对球状物和结壳进行表征,探讨其形成原因并提出预防措施。结果表明:烧结体表面产生球状物和结壳与材料增碳(C)有关。C来源于黏结剂和石墨发热体,在烧结过程中会促进样品表层烧结,形成壳层;C的进一步渗入会降低表层区域熔点,使表层熔化形成液相,冷却后形成球状物。采用硅钼发热体烧结炉可避免试样表面产生球状物和结壳。

RESEARCH ON IMPERFECTION SENSITIVE REGION OF SINGLE-LAYER LATTICED DOMES

The concept of the imperfection sensitive region is given. The advanced stochastic imperfection method is used to research the imperfection sensitive region of single-layer latticed domes. Taking a K6 single-layer latticed dome with a diameter of 50 m as an example, its imperfection sensitive region is made up of the first 12 kinds of joints. The influence of the imperfections of support joints on the stability of the K6 single-layer latticed dome is negligible. Influences of the joint imperfections of the main rib and the secondary rib on the structural stability are similar. The initial deviations of these joints all greatly lower the critical load of the dome. Results show that the method can analyze the structural imperfection sensitive region quantitatively and accurately.

Investigation on Chemical Components of Higher Fungus Phellinus rhabarbarinus(Berk.) G. Cunn.

Five compounds including 2 benzene derivatives, 2 terpenoids and 1 sterol were separated by various separation methods such as positive silica gel, Sephadex LH-20 and Rp-18 gel from higher fungi Phellinus rhabarbarinus （Berk.） G. Cunn. Their structures were elucidated on the basis of nuclear magnetic resonance （NMR） spectroscopy and other methods. All the compounds were separated from this higher fungus for the first time.

Reinforcement by polyurethane to stiffness of air-supported fabric formwork for concrete shell construction

By spraying concrete on inner surface,air-supported fabric structures can be used as formwork to construct reinforced concrete shell structures.The fabric formwork has the finished form of concrete structure.Large deviation from the desired shape of concrete shells still remains as central problem due to dead weight of concrete and less stiffness of fabric formwork.Polyurethane can be used not only as a bonding layer between fabrics and concrete but also as an additional stiffening layer.However,there is little research on mechanical behaviors of the polyurethane shell structure.This paper presents experimental studies on an inflated fabric model with and without polyurethane,including relief pressure tests,vertical loading tests and horizontal loading tests.Experimental results show that the additional polyurethane layer can significantly enhance the stiffness of the fabric formwork.Compared with the experiment,a numerical model using shell layered finite elements has a good prediction.The reinforcement by polyurethane to improve stiffness of air-supported fabric formwork is expected to be considered in the design and construction of the concrete shell,especially dealing with the advance of shape-control.

Exploration and Research of Deep Crustal Structures in the Zhangzhou Basin and Its Vicinity

The Zhangzhou basin is located at the middle section of the southeast coast seismic zone of the mainland of China. Using high-resolution refraction and wide-angle reflection/refraction seismic profiling of Zhangzhou basin and its vicinity, we have obtained the crustal geometric structure and velocity structure as well as the geometric configuration and structural relationship between the deep and shallow fractures. The results show that the crust in the region is divided into the upper crust and lower crust. The thickness of the upper crust is 16.5km- 18.8km, and that of the lower crust is 12.0km- 13.0km. The upper crust is further divided into an upper and lower section. In the lower section of the upper crust, there is a low-velocity layer with a velocity of about 6.00km/s; the depth of the top surface of the low-velocity layer is about 12.0km, and the thickness is about 5.0km. The lower crust is also divided into an upper and lower section. The depth of Moho is 29.0km- 31 .8km There are 6 normal faults in the shallow crust in this region, and most of them extend downwards to a depth of less than 4kin, the maximum depth is about 5km. Below the shallow normal faults, there is a conjectural high-dip angle deep fault zone. The fault zone extends downwards till the Moho and upwards into the low-velocity layer in lower section of the upper crust. The deep and shallow faults are not tectonically connected. The combination character of deep and shallow structures in the Zhangzhou basin indicates that the Jiulongjiang fault zone is a deep fault zone with distinct characteristics and a complex deep and shallow structure background. The acquisition of deep seismic exploration results obviously enhanced the reliability of explanation of deep-structural data and the exploration precision of the region. The combination of deep and shallow structures resulted in uniform explanation results. The delamination of the crust and the characteristic of the structures are more precise and explicit. We discovered for the first time the combination characteristics of extensional structures and listric faults in the upper crust. This is not only helpful to the integrative judgment of earthquake risk in Zhangzhou and its vicinity, but also of importance for deepening the knowledge of deep dynamic processes in the southeast coast seismic zone.

Recent Crustal Stress Field and Dislocation Along Seismic Faults in the East China Region

A statistic analysis of the characteristics of recent tectonic stress fields in the East China region was performed using 143 sets of data of single focal mechanical solutions of moderate and small earthquakes and 17 sets of data of composite focal mechanism solutions. The result shows that at present the East China region is controlled by an ENE-（ about 80°） oriented principal compressive and NNW-（about 350°） oriented principal tensile stress field. The effect mode of the principal stress is mainly horizontal and sub-horizontal. In a background of basic consistency of the direction and effect mode of stress field, the existence of different seismotectonic zones may be related to the distribution of major active faults in the relevant areas. It indicates the effect and control of the existing structures on the seismic dislocation. Analysis of focal mechanism solution data of recent moderate and small earthquakes and directions of long axes of isoseismal contours of historic moderate and strong earthquakes and recent felt earthquakes indicates that seismic rupture and dislocation in East China region occurred mainly along the faults in NE and NW directions, and sometimes in NNE, ENE, WNW or near-WE directions. Movement along the seismic faults is mainly strike-slip or nearstrike-slip, with a less oblique slip component. Regional difference in dislocation modes exist along the seismic faults. The historical moderate and strong earthquakes in East China produced mainly NE-trending ruptures and dislocations, while the recent earthquakes produced NW-SE ruptures and dislocations in the land region and NE and NW ones in the sea areas.

Coseismic slip distribution of 2009 L'Aquila earthquake derived from InSAR and GPS data

To better understand the mechanism of the Mw6.3 L＇Aquila （Central Italy） earthquake occurred in 2009, global positioning system （GPS） and interferometric synthetic aperture radar （InSAR） data were used to derive the coseismic slip distribution of the earthquake fault. Firstly, based on the homogeneous elastic half-space model, the fault geometric parameters were solved by the genetic algorithm. The best fitting model shows that the fault is a 13.7 km×14.1 km rectangular fault, in 139.3° strike direction and 50.2° southwest-dipping. Secondly, fixing the optimal fault geometric parameters, the fault plane was extended and discretized into 16× 16 patches, each with a size of 1 kmx 1 krn, and the non-uniform slip distribution of the fault was inverted by the steepest descent method with an appropriate smoothing ratio based on the layered crustal structure model. The preferred solution shows that the fault is mainly a normal fault with slight right-lateral strike slip, the maximum slip of 1.01 m is located in the depth of 8.28 km, the average rake is -100.9°, and the total geodetic moment is about 3.34× 1018 N.m （Mw 6.28）. The results are much closer than previous studies in comparison with the seismological estimation. These demonstrate that the coseismic fault slip distribution of the L＇Aauila earthauake inverted by the crustal model considering layered characters is reliable.

Electronic Stability of Bimetallic Au2@Cu6 Nanocluster:Closed-Shell Interaction and Multicenter Bonding

Metallophilic interaction is a unique type of weak intermolecular interaction,where the electronic configuration of two metal atoms is closed shell.Despite its significance in multidisciplinary fields,the nature of metallophilic interaction is still not well understood.In this work,we investigated the electronic structures and bonding characteristic of bimetallic Au2@Cu6 nanocluster through density functional theory method,which was reported in experiments recently[Angew.Chem.Int.Ed.55,3611(2016)].In general thinking,interaction between two moieties of(CuSH)6 ring and(Au2PH3)2 in the Au2@Cu6 nanocluster can be viewed as a d^10-σ closed-shell interaction.However,chemical bonding analysis shows that there is a ten center-two electron(10c-2e)multicenter bonding between two moieties.Further comparative studies on other bimetallic nanocluster M2@Cu6(M=Ag,Cu,Zn,Cd,Hg)also revealed that multicenter bonding is the origin of electronic stability of the complexes besides the d10-σclosed-shell interaction.This will provide valuable insights into the understanding of closed-shell interactions.

Healing Temperature of Hybrid Structures Based on Genetic Algorithm

The healing temperature of suspen-dome with stacked arches(SDSA)and arch-supported single-layer lattice shell structures was investigated based on the genetic algorithm. The temperature field of arch under solar radiation was derived by FLUENT to investigate the influence of solar radiation on the determination of the healing temperature. Moreover, a multi-scale model was established to apply the complex temperature field under solar radiation. The change in the mechanical response of these two kinds of structures with the healing temperature was discussed. It can be concluded that solar radiation has great influence on the healing temperature, and the genetic algorithm can be effectively used in the optimization of the healing temperature for hybrid structures.

Ni@RuM(M=Ni or Co) core@shell nanocrystals with high mass activity for overall water-splitting catalysis

Developing efficient water-splitting electrocatalysts with high mass activity is in urgent need for largescale sustainable production of hydrogen but,still remains as a big challenge.Herein,we report a one-pot method to fabricate a series of core@shell Ni@RuM(M=Ni or Co)nanocrystals(NCs)with Ni as the core and tunable RuM(M=Ni or Co)as the alloy shell for efficient water-splitting catalysis.Among these core@shell NCs,the obtained Ni@Ru Ni NCs exhibit the highest intrinsic activity for hydrogen evolution reaction(HER)and possess an outstanding mass activity of 1590 m A mgRu^-1 at 0.07 V vs.reversible hydrogen electrode(RHE),which is 1.7 times higher than that of commercial Pt/C(950 m A mgPt^-1).As for oxygen evolution reaction(OER),the prepared Ni@Ru0.4 Co0.6 NCs with optimized shell composition achieve more enhanced mass activity of 270 m A mgRu^-1 at1.56 V vs.RHE,approaching three times higher than that of commercial RuO2(89 m A mgRu^-1).The superb mass activity of these Ni@Ru M(M=Ni or Co)NCs can be attributed to their core@shell structure and modulated electronic structure through alloying with Ni or Co metal in the shell.

Crustal P-wave velocity structure of the Longmenshan region and its tectonic implications for the 2008 Wenchuan earthquake

The P-wave velocity structure of the crust in the Longmenshan region has been imaged by seismic travel time tomography us ing local and regional first P-wave arrivals recorded from 2000 to 2008. The tomographic model provides a way to analyze the deep tectonics of the Longmenshan fault belt and the tectonic implications for the 2008 Ms8.0 Wenchuan earthquake. The P-wave velocity images indicate that the initial rupture site and focal depth of the Wenchuan earthquake, together with the di rection of rupture propagation, closely relate to the crustal structure of the Longmenshan region. The Pengguan massif to the west of the Longmenshan fault belt is characterized by high velocity anomalies, suggesting that the crust has a strong strain strength that can accumulate large stresses over a long period. The Ms8.0 Wenchuan earthquake is located at the southwestern end of the Pengguan massif and the western edge of the Sichuan Basin. The collision between the Pengguan massif and the Sichuan Basin becomes the primary reason for the occurrence of the Ms8.0 Wenchuan earthquake. To the north of Wenchuan, the occurrence and propagation of rupture benefit from low velocity anomalies along the Longmenshan fault belt; whereas to the south of Wenchuan, the brittle rupture can occur with more difficulty in relatively weak crust with low velocities. This may be one of the reasons for the absence of aftershocks to the south of Wenchuan, and the rupture induced by the Ms8.0 Wenchuan earthquake propagating from the north to the south along the Longmenshan fault belt. The deep geodynamics of the Ms8.0 Wenchuan earthquake may occur due to the discrepancy of crustal structures on the two sides of the Longmenshan fault belt. Ductile deformation and crustal flow can easily occur in the weak middle-lower crust beneath the Songpan-Garze orogenic belt. The eastward movement of the Tibetan Plateau is obstructed by the rigid lithosphere of the Sichuan Basin, and then the thick ening of the middle-lower crust and vertical deformation occur in the crust of the Longmenshan fault belt. In addition, the down-warping of the Moho and the basement thrusting onto the range front induced crustal deformation and strain accumula tion, which provided the potential energy to trigger the occurrence of the Ms8.0 Wenchuan earthquake.

Nitrogen-doped iron for selective catalytic reduction of nitrate to dinitrogen

Nitrate is the leading cause of eutrophication worldwide and is one of the most challenging pollutants for restoration of polluted surface waters such as lakes, rivers and reservoirs. We report herein a new architecture of iron nanoparticles for high-efficiency denitrification by selective reduction of nitrate (NO3-) to dinitrogen (N2). The iron nanoparticles are doped with nitrogen (FeN) and encapsulated within a thin layer of nitride-carbon (NC). The nanoparticles have high pyrrolic N content (17.4 at.%) and large specific surface area (2040 m2/g). Laboratory experiments demonstrated high N2selectivity (91%) and nitrate removal capacity (6004 mg N/g Fe) for treatment of nitrate-containing water. This iron-based nanomaterial overcomes shortcomings of conventional catalysts by eliminating the use of precious and toxic heavy metals (e.g., Pd, Pt, Cu, Ni) and minimizing the generation of undesirable byproducts (e.g., ammonia) from the reactions with nanoscale zero-valent iron (n ZVI). The multiple electron transfers process from NO3- to N2can be fine-tuned by adjusting the NC shell thickness. Superior electrocatalytic perfor- mance, low cost and minimal environmental impact of the iron-derived nanocatalyst offer promising prospects for water purification, waste treatment and environmental remediation.

Node shift method for stiffness-based optimization of single-layer reticulated shells

This paper presents a node shift method to find the optimal distribution of nodes in single-layer reticulated shells. The optimization process searches for the minimum strain energy configuration and this leads to reduced sensitivity in initial imper- fections. Strain energy sensitivity numbers are derived for free shift and restricted shift where nodes can move freely in the 3D space or have to move within a predefmed surface respectively. Numerical examples demonstrate the efficiency of the proposed approach. It was found that optimized structures achieve higher ultimate load and are less sensitive to imperfections than the initial structure. The configuration of the final structure is closely related to factors like the initial structural configuration, spatial conditions, etc. Based on different initial conditions, architects can be provided with diverse reasonable structures. Furthermore, by amending the defined shapes and nodal distributions, it is possible to improve the mechanical behavior of the structures.

Crustal thickness and Poisson's ratio beneath the Yunnan region

A total of 1939 receiver functions were obtained from 732 teleseismic events （M〉5.0） recorded at 21 broadband portable seis- mic stations on the Tengchong, Baoshan and Simao blocks and Yangtze platform. These stations were installed by the Institute of Crustal Dynamics, China Earthquake Administration during 2010 and 2011. Using the H-x stacking and searching method, crustal thickness and velocity ratio beneath the stations are obtained. Results show that crustal thickness and Poisson＇s ratio in- ferred from the velocity ratio clearly vary, and they illustrate block features in deep structures. Except for the Tengchong block crustal thickness increases from south to north along the same block and from west to east across different blocks. In the Yangtze platform, Poisson＇s ratio and crustal thickness show a consistent and significant increasing trend from south to north, possibly indicating that crustal thickening is caused mainly by lower crustal variations. In contrast, Poisson＇s ratio has no sig- nificant change within the Baoshan and Simao blocks. Such differences demonstrate that the Jinshajiang-Red River fault is a southern boundary of the South China block. The H-κ results inferred from three portable stations on the Tengchong block show high Poisson＇s ratios, but they vary clearly with back-azimuth, implying the existence of strong anisotropy in the crustal medium beneath the stations.

Preparation and Characterization of Core-Shell MoSi_(2)@Nb Materials Sintered by SPS

Core-shell MoSi_(2)@Nb powder was prepared by electrostatic layer self-assembly method.The surfactants SDS(CHSO4Na)and CTAB(C19H42BrN)were used to modify the surface of the two particles to make them charged,and the Zeta potential of the suspension was tested by the Zeta potentiometer.Scanning electron microscope,transmission electron microscope and energy dispersive spectrometer were used to characterize the phase,morphology,microstructure and element distribution of synthetic materials.The results show that when the SDS concentration is 2 mmol/L,the CTAB concentration is 3mmol/L and the pH value of Nb suspension is 5,the coating effect is better after secondary cladding.NbSi_(2)phase is found at the interface between Nb and MoSi_(2)after calcination at 200℃ for 2 h in Ar atmosphere,indicating that Nb is highly active and reacts with Si.Core-shell structure is still retained in MoSi_(2)@Nb material after spark plasma sintering at 1450℃ for 2 h under uniaxial pressure of 40 MPa.However,it is found that Nb reacts strongly with MoSi_(2),and most of the Nb phase is reacted.This issue needs to be addressed in subsequent studies.The fracture toughness(K_(IC))of MoSi_(2)@Nb material is significantly improved to 5.75 MPa·m^(0.5)compared with that of MoSi_(2)material(3.32 MPa·m^(0.5)).