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2008年  第15卷  第6期

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Mineral
New development of hydraulic fracturing technique for in-situ stress measurement at great depth of mines
Meifeng Cai, Hua Peng, Hongguang Ji
2008, 15(6): 665-670. doi: 10.1016/S1005-8850(08)60268-6
中文摘要(227) PDF(15) SpringerLink
摘要:
In-situ stress measurement using the hydraulic fracturing technique was made at Wanfu Coal Mine in Shandong Province, China. To solve problems caused by great measuring depth and extra thick overburden soil layers in the mine, a series of improved techniques were developed for the traditional hydraulic fracturing technique and equipment to increase their pressure-enduring ability and to ensure safe and flexible removal of the sealing packers with other experimental apparatus. Successful in-situ stress measurement at 37 points within 7 boreholes, which were mostly over 1000 m deep, was completed. Through the measurement, detailed information of in-situ stress state has been provided for mining design of the mine. The improved hydraulic fracturing technique and equipment also provide reliable tools for in-situ stress measurement at great depth of other mines.
Metallurgy
Vaporization behavior of lead from the FeO-CaO-SiO2-Al2O3 slag system
Yanling Zhang, Rui Zhang, Eiki Kasai, Shiqi Li
2008, 15(6): 671-677. doi: 10.1016/S1005-8850(08)60269-8
中文摘要(208) PDF(8) SpringerLink
摘要:
Vaporization behavior (1163-1463 K) of lead in the slag system of FeO-CaO-SiO2-Al2O3 with CaC% was examined. A thermodynamic estimation with the principle of Gibbs free energy minimization showed that the major vapor species from the sample of the FeO-CaO-SiO2-Al2O3 system+PbO+CaCl2 were metallic Pb, PbCl, PbCl2, and FeCl2, at the experimental temperature range. The experimental results show that the mole ratio of vaporized Cl in lead chlorides to vaporized Pb, simply expressed as Cl/Pb decreases with increasing temperature. The larger Cl/Pb means a larger ratio of gaseous PbCl2, since metallic Pb and PbCl vapors are formed in a similar reduction atmosphere. The evaporation is initially rapid and becomes steady after holding for 10 min. Gaseous PbCl2 is mainly formed during the heating period, and at the holding stage, it reacts with FeO to produce gaseous FeCl2 With regard to slag composition, FeO content and basicity significantly affect the evaporation of lead. High FeO content and high basicity promotes the formation of metallic Pb and PbCI, whereas, it prohibits PbCl2 evaporation.
Metallurgy
Microstructure of AISI 304 stainless steel strips produced by a twin-roll caster
Chenxi Ji, Jiongming Zhang, Fuxiang Huang, Xinhua Wang, Yuan Fang, Yan Yu
2008, 15(6): 678-682. doi: 10.1016/S1005-8850(08)60270-4
中文摘要(194) PDF(12) SpringerLink
摘要:
By optical inspection of macro-etched metallography and electron back-scattered diffraction (EBSD) mapping, this paper analyzed the microstructure of austenitic stainless steel strips produced with an equal-diameter twin-roll strip caster. The results indicate that the microstructure of the strips includes two columnar zones with highly compact dendrites and one equiaxed zone. The characteristics, such as grain size and growing direction of columnar grains and equiaxed grains, were investigated. An additional transitional area with many finer grains between the columnar zone and the equiaxed zone was found. As shown in EBSD analysis, small angle boundaries exist both in the columnar zone and the equiaxed zone, although they are especially more in the transitional area. Additionally, some <111> twin boundaries were found in the microstructure of the strips.
Materials
Influences of microstructure and texture on crack propagation path of X70 acicular ferrite pipeline steel
Hao Yu
2008, 15(6): 683-687. doi: 10.1016/S1005-8850(08)60271-6
中文摘要(296) PDF(13) SpringerLink
摘要:
The aspects of two pipeline steels with different technologies were investigated by using transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD). The microstructure presents a typical acicular ferrite characteristic with fine particles of martensite/austenite (M/A) constituent, which distributes in grains and at grain boundaries. The bulk textures of the pipeline steel plate are {112}<110> and <111> fibers, respectively, and the {112}<110> component is the favorable texture benefiting for drop weight tear test. Moreover, low angle boundaries and low coincidence site lattice boundaries are inactive and more resistant to fracture than high energy random boundaries.
Materials
Effect of zirconium addition on the austenite grain coarsening behavior and mechanical properties of 900 MPa low carbon bainite steel
Jia Guo, Aimin Guo, Hui Guo, Ying Wang, Jing Li, Xinlai He
2008, 15(6): 688-695. doi: 10.1016/S1005-8850(08)60272-8
中文摘要(237) PDF(9) SpringerLink
摘要:
The ultra-fine bainitic microstructure of a 900 MPa low carbon bainitic Cu-Ni-Mo-B steel was obtained by a newly developed relaxation precipitation control (RPC) phase transformation processing. In a pan-cake like prior-austenite grain, the micro- structure consisted of lath bainite, a little of abnormal granular bainite, and acicular ferrite. The effect of zirconium carbonitrides on the austenite graincoarsening behavior was studied by transmission electron microscopy (TEM). The results show that, the lath is narrower with increasing cooling rate. The ratio of all kinds of bainitic microstructure is proper with the intermediate cooling rate; and Zr-containing precipitates distribute uniformly, which restrains austenite grain growing in heat-affected welding zone.
Materials
Modeling texture development during cold rolling of IF steel by crystal plasticity finite element method
Hejie Li, Jingtao Han, Huachun Pi, Zhengyi Jiang, Dongbin Wei, A. Kiet Tieu
2008, 15(6): 696-701. doi: 10.1016/S1005-8850(08)60273-X
中文摘要(219) PDF(10) SpringerLink
摘要:
With the consideration of slip deformation mechanism and various slip systems of body centered cubic (BCC) metals, Taylor-type and finite element polycrystal models were embedded into the commercial finite element code ABAQUS to realize crystal plasticity finite element modeling, based on the rate dependent crystal constitutive equations. Initial orientations measured by electron backscatter diffraction (EBSD) were directly input into the crystal plasticity finite element model to simulate the development of rolling texture of interstitial-free steel (IF steel) at various reductions. The modeled results show a good agreement with the experimental results. With increasing reduction, the predicted and experimental rolling textures tend to sharper, and the results simulated by the Taylor-type model are stronger than those simulated by finite element model.'Conclusions are obtained that rolling textures calculated with 48 {110} <111>+ {112} <111>+ {123} <111> slip systems are more approximate to EBSD results.
Materials
Mechanism of protective film formation during CO2 corrosion of X65 pipeline steel
Tong Li, Yongjin Yang, Kewei Gao, Minxu Lu
2008, 15(6): 702-706. doi: 10.1016/S1005-8850(08)60274-1
中文摘要(285) PDF(13) SpringerLink
摘要:
Electrochemical techniques, X-ray diffraction (XRD), and scanning electron microscopy (SEM) were applied to study the corrosion behaviors of X65 steel in static solution with carbon dioxide (CO2) at 65℃. The results show that iron carbonate (FeCO3) deposits on the steel surface as a corrosion product scale. This iron carbonate scale acts as a barrier to CO2 corrosion, and can reduce the general corrosion rate. The protection ability of the scale is closely related to the scale morphological characteristics.
Materials
Effect of deteriorated microstructures on stress corrosion cracking of X70 pipeline steel in acidic soil environment
Zhiyong Liu, Guoli Zhai, Xiaogang Li, Cuiwei Du
2008, 15(6): 707-713. doi: 10.1016/S1005-8850(08)60275-3
中文摘要(209) PDF(12) SpringerLink
摘要:
In order to investigate stress corrosion cracking (SCC) of X70 pipeline steel and its weld joint area in acidic soil environment in China, two simulating methods were used:one was to obtain bad microstructures in heat affected zone by annealing at 1300℃ for 10 min and then, quenching in water; the other was to get different simulating solutions of acidic soil in Yingtan in south-east China. The SCC susceptibilities of X70 pipeline steel before and after quenching in the simulating solutions were analyzed using slow stain rate test (SSRT) and potentiodynamic polarization technique to investigate the SCC electrochemical mechanism of different microstructures further. The results show that SCC appears in the original microstructure and the quenched microstructure as the polarization potential decreases. Hydrogen revolution accelerates SCC of the two tested materials within the range of -850 mV to -1200 mV vs. SCE. Microstructural hardening and grain coarsening also increase SCC. The SCC mechanisms are different, anodic dissolution is the key of causing SCC as the polarization potential is higher than the null current potential, and hydrogen embrittlement will play a more important role to SCC as the polarization potential lower than the null current potential.
Materials
Optimizing SUS 304 wire drawing process by grey relational analysis utilizing Taguchi method
Al-Refaie Abbas, Ming-Hsien Li, Kuo-Cheng Tai
2008, 15(6): 714-722. doi: 10.1016/S1005-8850(08)60276-5
中文摘要(260) PDF(8) SpringerLink
摘要:
In the stainless steel 304 (SUS 304) wire drawing process, optimizing the die life and wire tensile strength, which are the larger-the-better quality characteristics (QCH) types, is of main interest. Three control factors, involving reduction ratio, lubricant temperature, and drawing speed, were investigated utilizing L9(34) orthogonal array (OA). The grey relational analysis was conducted for the normalized signal-to-noise (S/N) ratios. The ordinal value of the grey grade was then used to decide optimal factor levels. The anticipated improvements in die life and wire tensile strength were estimated 25.31 h and 22.50 kg/mm2, respectively. To decide the significant factor which had effect on each QCH and predict the average value of each QCH, analysis of variance (ANOVA) was performed for S/N ratio and QCH. Confirmation experiments were then conducted, where a good overlap was noticed between the predicted and confirnation intervals for each QCH. The Hotelling T2 and the sample generalized variance control charts were finally utilized in controlling and monitoring future production. In conclusion, the grey relational analysis utilizing Taguchi method is an effective approach for optimizing the die life and wire tensile strength for SUS wire drawing process. 2008 University of Science and Technology Beijing. All rights reserved.
Materials
HSM strategy study for hardened die and mold steels manufacturing based on the mechanical and thermal load reduction strategy
Ying Tang, Hongsheng Guo
2008, 15(6): 723-728. doi: 10.1016/S1005-8850(08)60277-7
中文摘要(197) PDF(9) SpringerLink
摘要:
The paper discussed cutter-work engagement situation hidden behind the mechanical and thermal load effect on cutting edges during high speed hard machining process. The engagement situation was investigated in great detail using experimental and geometrical analytic measures. Experiments were conducted using AlTiN-coated micro-grain carbide end mill cutters to cut hardened die steel. On the basis, a general high speed hard machining strategy, which aimed at eliminating excessive engagement situation during high-speed machining (HSM) hard machining, was proposed. The strategy includes the procedures to identify prone-to-overload areas where excessive engagement situation occurs and then to create a reliable tool path, which has the effect of cutting load reduction to remove the prone-to-overload areas.
Materials
Effect of solution cooling rate on the γ′ precipitation behaviors of a Ni-base P/M superalloy
Gaofeng Tian, Chengchang Jia, Ying Wen, Benfu Hu
2008, 15(6): 729-734. doi: 10.1016/S1005-8850(08)60278-9
中文摘要(214) PDF(9) SpringerLink
摘要:
The effect of cooling rate on the cooling γ' precipitation behaviors was investigated in a Ni-base powder/metallurgy (P/M) superalloy (FGH4096). The empirical equations were established between the cooling rate and the average sizes of secondary and tertiary γ' precipitates within grains and tertiary γ' precipitates at grain boundaries, as well as the apparent width of grain boundaries. The results show that the average sizes of secondary or tertiary γ' precipitates are inversely correlated with the cooling rate. The shape of secondary γ' precipitates within grains changes from butterfly-like to spherical with the increase of cooling rate, but all the tertiaryγ' precipitates formed are spherical in shape. It is also found that tertiary γ' may be precipitated in the latter part of the cooling cycle only if the cooling rate is not faster than 4.3℃/s, and the apparent width of grain boundaries decreases linearly with the increase of cooling rate.
Materials
Novel foaming agent used in preparation process of aluminum foams
Xiangyang Zhou, Xiquan Liu, Jie Li, Hongzhuan Liu
2008, 15(6): 735-739. doi: 10.1016/S1005-8850(08)60279-0
中文摘要(251) PDF(10) SpringerLink
摘要:
The performances of a novel foaming agent used in the preparation process of aluminum foams were investigated, and the effects of some factors, such as addition of the foaming agent, foaming temperature on the porosity, and appearance of aluminum foams were also discussed. Experimental results show that the novel foaming agent has a wide decomposition temperature range and a mild decomposed rate; the foaming agent has the ability to enhance the viscosity of aluminum melt, as a result, an extra viscosifier such as Ca or SiCp is unnecessary while using this foaming agent; the bubble-free zone in material decreases and the foaming efficiency increases with the increase of foaming agent; the bubble-free zone disappears and the foaming efficiency is near 100% when the addition of foaming agent is more than 1.4wt%; the porosity of the aluminum foam increases with the increase of foaming agent when the addition of foaming agent is less than 2.2wt%.
Materials
Characterization of microstructure evolution and mechanical properties of the spray-deposited AZ31 magnesium alloy
Yongbing Li, Jinfeng Huang, Hua Cui, kai Tao, Kui Zhang, Jishan Zhang
2008, 15(6): 740-746. doi: 10.1016/S1005-8850(08)60280-7
中文摘要(216) PDF(8) SpringerLink
摘要:
The cylindrical billets of a Mg-3Al-1Zn (AZ31) alloy were synthesized by spray deposition processing. The microstructure evolution and mechanical properties of the alloy were investigated. The results reveal that the microstructure of the AZ31 alloy is refined significantly by spray deposition processing. A homogeneous and equiaxial-grain structure with an average grain size of 17 μm is obtained. Further grain refinement with an average grain size of 5 μm is attributed to dynamic recrystallization during extrusion processing. The great increase in the density of grain boundary nucleation sites by the finer initial grain sizes makes the dislocation pile-ups near subgrain boundaries being absorbed easily by the boundaries, resulting in an accelerated recrystallization process. The average tensile ultimate and yield strengths of the extruded rods are 321 MPa and 237 MPa, respectively, with an elongation of 15.2% at room temperature, which are remarkably higher than those of the conventional as-cast AZ31 alloy.
Materials
Effects of heat treatment on the microstructure and mechanical properties of ZA84 magnesium alloy
Mingbo Yang, Liang Bai, Fusheng Pan, Hongjun Hu
2008, 15(6): 747-752. doi: 10.1016/S1005-8850(08)60281-9
中文摘要(288) PDF(10) SpringerLink
摘要:
The effects of heat treatment on the microstructure and mechanical properties of ZA84 (Mg-8Zn-4Al-0.25Mn) alloy were investigated. The results indicate that the as-cast microstructure of the alloy is mainly composed of α-Mg matrix and two different morphologies of precipitates (continuous and quasi-continuous Mg32(Al,Zn)49 phases and isolated Mg5Al2Zn2 phases). After solid solution treatment at 345℃, the Mg32(Al,Zn)49 phases change from continuous and quasi-continuous net to disconnected acute angle shape, and parts of second phases sphericize. The optimum heat treatment condition for the alloy is solution treatment at 345℃ for 48 h and water quenching, then aging treatment at 200℃ for 12 h and atmosphere cooling. Under the optimum condition, the ultimate tensile strength and yield strength of the alloy can be imoroved, but the elongation is not effected much bv heat treatment.
Materials
Effect of Cu doping and annealing treatment on the microstructure and mag-netic properties of nanocrystalline single-phase Nd-Fe-B alloys
Xiaoqian Bao, Xuexu Gao, Maocai Zhang, Yi Qiao, Xiaoyan Guo, Jie Zhu, Shouzeng Zhou
2008, 15(6): 753-757. doi: 10.1016/S1005-8850(08)60282-0
中文摘要(212) PDF(6) SpringerLink
摘要:
The effects of Cu addition and annealing treatment on the magnetic properties and microstructure of Nd12.3Fe81.7-xCuxB6 (x=0-1.2) ribbons melt-spun and annealed were systematically investigated by the methods of vibrating sample magnetometer (VSM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Optimum magnetic properties were achieved by annealing melt-spun Nd12.3Fe81.5Cu0.2B6 ribbons at 550℃ for 15 min, which only contained Nd2Fe14B phase. The remanence, coercive force, and maximum energy product increase by 18.4%, 36.2%, and 49% respectively compared with those of Cu-free samples. The significant improvement in magnetic properties originates from the freer grains of the samples by introducing Cu, which leads to the stronger exchange-coupling between neighboring grains.
Materials
Particle erosion of infrared materials
Qi He, Fanxiu Lv, Fenglei Zhang, Huibin Guo, Junjun Wei
2008, 15(6): 758-763. doi: 10.1016/S1005-8850(08)60283-2
中文摘要(188) PDF(8) SpringerLink
摘要:
Erosion test of some infrared (IR) optical crystals (Ge, ZnS, MgF2, and quartz) was conducted with a number of different erodents (glass bead, and angular SiC, SiO2, Al2O3) by a homemade gas-blasting erosion tester. The influence of impact angle, impact velocity, erodent, and erosion time on the erosion rate and the effect of erosion on their IR transmittance were studied. The dam- aged surface morphology was characterized by scanning electron microscopy, and the erosion mechanism was explored. All of the materials show the maximum in wear versus impact angle at 90°, confirming their brittle failure behavior. It is found that the erosion rate is dependent on the erodent velocity by a power law, and it is highly correlated to the hardness of the erodent. The erosion rate-time curves do not show an incubation state, but an accelerated erosion period followed a maximum erosion (steady state). The decrease of IR transmittance is direct proportion to the erosion rate. Although the material loss occurs primarily by brittle process, ductile behavior is clearly an important feature, especially for MgF2 and ZnS.
Materials
Preparation and properties of dental zirconia ceramics
Xinjie Liang, Yuexiu Qiu, Shaoxiong Zhou, Xiaoyang Hu, Guangyan Yu, Xuliang Deng
2008, 15(6): 764-768. doi: 10.1016/S1005-8850(08)60284-4
中文摘要(301) PDF(18) SpringerLink
摘要:
Y2O3-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramics with high-performance were prepared for dental application by use of the micro-emulsion and two-step sintering method. The crystal phase, morphology, and microstructure of the reaction products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD results show that the ceramics mainly consist of tetragonal zirconia. Physical and mechanical properties test results show that the bending strength, fracture toughness, and the density of full sintered Y-TZP ceramics are 1150 MPa, 5.53 MPa·m1/2, and 6.08 g/cm3, respectively, which suggest that the material is relatively suitable for dental restoration. The dental base crown machined with this material by CAD/CAM system exhibits a verisimilitude configuration and the material's expansion coefficient well matches that of the glaze. These results further indicate that the product can be used as a promising new ceramic material to fabricate dental base crowns and bridges.
Materials
Microstructure and wear properties of the electroslag remelting layer reinforced by TiC particles
Qianlin Wu, Yangshan Sun, Guoqing Li
2008, 15(6): 769-774. doi: 10.1016/S1005-8850(08)60285-6
中文摘要(204) PDF(8) SpringerLink
摘要:
The electroslag remelting (ESR) layer reinforced by TiC particles was obtained by electroslag remelting. The microstructure and wear properties of the ESR layer were studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), and wear test. The results indicate that TiC particles are synthesized by self-propagating high-temperature synthesis (SHS) reaction during the electroslag remelting process. The size of TiC particles is in the range of 1-10 μm, and the distribution of TiC particles is uniform, from outside to inside of the ESR layer, and the volume fraction and the size of TiC particles decrease gradually. Molten iron and slag flow into porosity due to the SHS process leading to rapid densification and the elimination of porosity in the ESR layer during the ESR process. TiC particles enhance the wear resistance of the ESR layer, whereas CaF2 can improve the high temperature lubricating property of the ESR layer.
Materials
Influence and determinative factors of ion-to-atom arrival ratio in unbalanced magnetron sputtering systems
Jun Zhou, Zhe Wu, Zhanhe Liu
2008, 15(6): 775-781. doi: 10.1016/S1005-8850(08)60286-8
中文摘要(279) PDF(14) SpringerLink
摘要:
Low pressure sputtering with a controlled ratio of ion flux to deposited atom flux at the condensing surface is one of the main directions of development of magnetron sputtering methods. Unbalanced magnetron sputtering, by producing dense secondary plasma around the substrate, provides a high ion current density. The closed-field unbalanced magnetron sputtering system (CFUBMS) has been established as a versatile technique for high-rate deposition high-quality metal, alloy, and ceramic thin films. The'key factor in the CFUBMS system is the ability to transport high ion currents to the substrate, which can enhance the formation of full dense coatings at relatively low value homologous temperature. The investigation shows that the energy of ions incidenced at the substrate and the ratio of the flux of these ions to the flux of condensing atoms are the fundamental parameters in determining the structure and properties of films produced by ion-assisted deposition processes. Increasing ion bombardment during deposition combined with increasing mobility of the condensing atoms favors the formation of a dense microstructure and a smooth surface.
Materials
Comparison of room-temperature multiferroics in Bi4Fe2TiO12 film and bulk
Jun Lu, Lijie Qiao, Wuyang Chu
2008, 15(6): 782-785. doi: 10.1016/S1005-8850(08)60287-X
中文摘要(235) PDF(7) SpringerLink
摘要:
It was reported that both dielectricity and magnetism at room temperature were appreciably improved in Bi4Fe2TiO12 film compared with Bi4Fe2TiO12 bulk. X-ray diffraction profiles reveal similar crystalline nature and random orientation of the two, but X-ray photoelectron spectroscopy (XPS) experiments indicate that it is 1.4 eV lower binding energy of core-state Ols in the film relative to that of the bulk, so the improvement of multiferroics in the film is attributed to oxygen vacancies and high fraction of interface. The results have promising applications in multifunctional integrated devices.
Materials
Effect of different additives on the properties of lithium alanate
Xueping Zheng, Ping Li, Xuanhui Qu, I. S. Humail, Yanghuan Zhang, Guoqing Wang
2008, 15(6): 786-790. doi: 10.1016/S1005-8850(08)60288-1
中文摘要(184) PDF(6) SpringerLink
摘要:
LiAIH4 doped with Ni and Ce(SO4)2 additives and the effect of doping on temperature and hydrogen release were studied by pressure-content-temperature (PCT) experiment and X-ray diffraction (XRD) analysis. It is indicated that doping with Ni induces a significant decrease in temperature in the first step and LiAlH4 doped with 1mol% Ni presents the most absorption of hydrogen. Doping with Ce(SO4)2 also causes a marked decrease, while the amount of hydrogen release changes only slightly. The results from X-ray diffraction analysis show that doping does not cause any structural change; Ni and Ce-containing phases are not observed at room temoerature or even at 250℃.
Materials
Thermal conductivity measurements on xonotlite-type calcium silicate by the transient hot-strip method
Gaosheng Wei, Xinxin Zhang, Fan Yu
2008, 15(6): 791-795. doi: 10.1016/S1005-8850(08)60289-3
中文摘要(253) PDF(8) SpringerLink
摘要:
The experimental results of the thermal conductivities of xonotlite-type calcium silicate insulation materials were presented at different temperatures and pressures. Two appropriative surroundings, i.e. an elevated temperature surrounding from ambient temperature to 1450 K and a vacuum surrounding from atmosphere pressure to 10-3 Pa, were designed for the transient hot-strip (THS) method. The thermal conductivities of xonotlite-type calcium silicate with four densities from ambient temperature to 1000 K and 0.045 Pa to atmospheric pressure were measured. The results show that the thermal conductivity of xonotlite-type calcium silicate decreases apparently with the fall of density, and decreases apparently with the drop of pressure, and reaches the least value at about 100 Pa. The thermal conductivity of xonotlite-type calcium silicate increases almost linearly with T3, and increases more abundantly with low density than with high density. The thermal conductivity measurement uncertainty is estimated to be approximately 3% at ambient temperature, and 6% at 800 K.
Materials
Effect of alkali-activation on aluminosilicate-based cementitious materials
Xiaoguang Yang, Wen Ni, Xufang Zhang, Yali Wang
2008, 15(6): 796-801. doi: 10.1016/S1005-8850(08)60290-X
中文摘要(202) PDF(9) SpringerLink
摘要:
High-performance aluminosilicate-based cementitious materials were produced with fly ash from a coal power plant as one of the major raw materials. The structures of fly ash containing aluminosilicate-based cementitious materials were compared before and after treatment by the methods of nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). During the 28 d curing time, the compressive strength of water glass and fly ash samples increased from 9.08 MPa to 26.75 MPa. The results show that most of the stiff shells are destroyed after mechanical grinding and chemical activation. Magic angle spinning (MAS) NMR of 27Al shows that the wide peak becomes narrow and the main peak shifts to the direction of low field, indicating the decrease of polymerization degree, the enhancing of activity, the decrease of six-coordination structure, and the increase of small and symmetrical four-coordination polyhedron structure within the aluminum-oxygen polyhedron network. Comparisons between MAS NMR of 29Si with different treatments suggest that Q0 disappears, the quantity of Q2 increases, and the quantity of Q4 decreases. The polymerization degree of silicon-oxygen is reduced, and the potential activity of fly ash is increased.
Materials
Effects of different iron sources on the performance of LiFePO4/C composite cathode materials
Fei Gao, Zhiyuan Tang, Jianjun Xue
2008, 15(6): 802-807. doi: 10.1016/S1005-8850(08)60291-1
中文摘要(258) PDF(9) SpringerLink
摘要:
Olivine LiFePO4/C composite cathode materials were synthesized by a solid state method in N2 + 5vol% H2 atmosphere. The effects of different iron sources, including Fe(OH)3 and FeC2O4·2H2O, on the performance of as-synthesized cathode materials were investigated and the causes were also analyzed. The crystal structure, the morphology, and the electrochemical performance of the prepared samples were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), laser particle-size distribution measurement, and other electrochemical techniques. The results demonstrate that the LiFePO4/C materials obtained from Fe(OH)3 at 800℃ and FeC2O4·2H2O at 700℃ have the similar electrochemical performances. The initial discharge capacities of LiFePO4/C synthesized from Fe(OH)3 and FeC2O4·2H2O are 134.5 mAh.g-1 and 137.4 mAh.g-1 at the C/5 rate, respectively. However, the tap density of the LiFePO4/C materials obtained from Fe(OH)3 are higher, which is significant for the improvement of the capacity of the battery.
Materials
Effect of chemical vapor infiltration treatment on the wave-absorbing performance of carbon fiber/cement composites
Kezhi Li, Chuang Wang, Hejun Li, Lingjun Guo, Jihua Lu
2008, 15(6): 808-815. doi: 10.1016/S1005-8850(08)60292-3
中文摘要(215) PDF(6) SpringerLink
摘要:
Short carbon fibers were treated at high temperatures around 1100℃ through chemical vapor infiltration technology. A thinner layer ofpyrocarbon was deposited on the fiber surface. The dispersion of carbon fibers in a cement matrix and the mechanical properties of carbon fiber/cement composites were investigated by scanning electron microscopy (SEM) and other tests. The reflec- tivity of electromagnetic waves by the composites was measured in the frequency range of 8.0-18 GHz for different carbon fiber contents of 0.2wt%, 0.4wt%, 0.6wt%, and 1.0wt%. The results show that the reflectivity tends to increase with the increase of fiber content above 0.4wt%. The minimum reflectivity is -19.3 dB and the composites exhibit wave-absorbing performances. After pyrocarbon is deposited on the fiber, all the refiectivity data are far greater. They are all above -10 dB and display mainly wave-reflecting performances.
Materials
Pseudo-capacitance of ruthenium oxide/carbon black composites for electrochemical capacitors
Xiaofeng Wang, Dianbo Ruan, Peng Wang, Yiqiang Lu
2008, 15(6): 816-821. doi: 10.1016/S1005-8850(08)60293-5
中文摘要(205) PDF(9) SpringerLink
摘要:
Hydrous ruthenium oxide was formed by a new process. The precursor was obtained by mixing the aqueous solutions of RuCl3·xH2O and NaHCO3. The addition of NaHCO3 led to the formation of an oxide with extremely fine RuO2 particles forming a porous network structure in the oxide electrode. Polyethylene glycol was added as a controller to partly inhibit the sol-gel reaction. The rate capacitance of 530 F·g-1 was measured for the powder formed at an optimal annealing temperature of 210℃. Several details concerning this new material, including crystal structure, particle size as a function of temperature, and electrochemical properties, were also reported. In addition, the rate capacitance of the composite electrode reached 800 F·g-1 after carbon black was added. By using the modified electrode of a RuO2/carbon black composite electrode, the electrochemical capacitor exhibits high energy density and stable power characteristics. The values of specific energy and maximum specific power of 24 Wh·kg-1 and 4 kW·kg-1, respectively, are demonstrated for a cell voltage between 0 and 1 V.
Materials
SiC/Si-W-Mo coating for protection of C/C composites at 1873 K
Dangshe Hou, Kezhi Li, Hejun Li, Qiangang Fu, Yulei Zhang
2008, 15(6): 822-826. doi: 10.1016/S1005-8850(08)60294-7
中文摘要(330) PDF(12) SpringerLink
摘要:
In order to prevent carbon/carbon composites from oxidation at 1873 K, an efficient oxidation protective SiC/Si-W-Mo coating was prepared by a two-step pack cementation technique. The microstructures and the phase composition of the as-received multi-coating were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). It is seen that the compact multi-coating is composed of α-SiC, Si, and (WxMO1-x)Si2. Oxidation test shows that, after oxidation at 1873 K in air for 102 h and thermal cycling between 1873 K and room temperature for 10 times, the weight loss of the SiC/Si-W-Mo coated C/C composites is only 0.26%. The invalidation of the multi-coating is attributed to the formation of penetrable cracks in the coating. 2008 University of Science and Technology Beijing. All rights reserved.
Materials
Monitor automatic gauge control strategy with a Smith predictor for steel strip rolling
Dianhua Zhang, Hao Zhang, Tao Sun, Xu Li
2008, 15(6): 827-832. doi: 10.1016/S1005-8850(08)60295-9
中文摘要(211) PDF(9) SpringerLink
摘要:
The simplified transfer function diagram block for a monitor automatic gauge control (Mon-AGC) system of strip steel rolling process was investigated. The new notion of strip sample length was given. In this way, the delay time varying with the rolling speed was evaded. After a Smith predictor was used to monitor the AGC system, the control laws were deduced for both proportional and integral regulators. The control strategies showed that by choosing the controller parameter P=∞ for both control algorithms each regulator could compensate the whole strip gage error in the first control step. The result shows that the integral algorithm is more controllable for the system regulating process and has a better steady-state precision than the proportional regulator. Compared with the traditional control strategy, the new control laws have a faster response speed and a hieher steadv-state precision.

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