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Journal of Materials Science & Technology
Current Issue
2005, Vol.21 No.01
Online: 2005-01-28

Research Articles
 
 
Research Articles
1 Hongyang JING, Lianyong XU, Lixing HUO, Fumiyoshi Minami
Transferability of Charpy Absorbed Energy to Fracture Toughness Based on Weibull Stress Criterion
The relationship between Charpy absorbed energy and the fracture toughness by means of the (crack tip opening displacement (CTOD)) method was analyzed based on the Weibull stress criterion. The Charpy absorbed energy and the fracture toughness were measured for the SN490B steel under the ductile-brittle transition temperature region. For the instrumented Charpy impact test, the curves between the loading point displacement and the load against time were recorded. The critical Weibull stress was taken as a fracture controlled parameter, and it could not be affected by the specimen configuration and the loading pattern based on the local approach. The parameters controlled brittle fracture are obtained from the Charpy absorbed energy results, then the fracture toughness for the compact tension (CT) specimen is predicted. It is found that the results predicted are in good agreement with the experimental. The fracture toughness could be evaluated by the Charpy absorbed energy, because the local approach gives a good description for the brittle fracture even though the Charpy impact specimen or the CT specimen is used for the given material.
2005 Vol. 21 (01): 1-4 [Abstract] ( 602 ) [HTML 1KB] [PDF 277KB] ( 667 )
5 Guozheng KANG, Qianhua KAN, Juan ZHANG
Experimental Study on the Uniaxial Cyclic Deformation of 25CDV4.11 Steel
The strain cyclic characteristics and ratcheting behavior of 25CDV4.11 steel were studied by the experiments under uniaxial cyclic loading with relatively high cyclic number and at room temperature. The cyclic hardening/softening feature of the material was first observed under the uniaxial strain cycling with various strain amplitudes. Then, the ratcheting behavior of the material was researched in detail, and the effects of stress amplitude and mean stress on the ratcheting were discussed under uniaxial asymmetrical stress cycling. Comparing with the experimental results of SS316L stainless steel, it is concluded that the material exhibits remarkable cyclic softening feature, and then a special ratcheting behavior is caused. Some conclusions useful to establish corresponding constitutive model are obtained.
2005 Vol. 21 (01): 5-9 [Abstract] ( 545 ) [HTML 1KB] [PDF 702KB] ( 651 )
10 Ruijie ZHANG, Lei LI, Zhongwei CHEN, Zhi HE, Wanqi JIE
Calculation of Phase Equilibria Based on the Levenberg-Marquardt Method
The Levenberg-Marquardt method, the best algorithm to obtain the least-square solution of nonlinear equations, is applied to calculate the stable phase equilibria. It can get the best combination between robustness and speed of the calculations. Its application to ternary Al-Si-Mg system is executed in detail. The calculated phase equilibria agree well with the experimental results. Furthermore, the Levenberg-Marquardt method is not sensitive to the initial values.
2005 Vol. 21 (01): 10-12 [Abstract] ( 520 ) [HTML 1KB] [PDF 270KB] ( 572 )
13 Yunbo XU, Yongmei YU, Xianghua LIU, Guodong WANG
Modeling of Microstructure Evolution and Mechanical Properties of Steel Plates Produced by Thermo-Mechanical Control Process and Its On-line Application
An integrated metallurgical model was developed to predict microstructure evolution and mechanical properties of low-carbon steel plates produced by TMCP. The metallurgical phenomena occurring during TMCP and mechanical properties were predicted for different process parameters. In the later passes full recrystallization becomes difficult to occur and higher residual strain remains in austenite after rolling. For the reasonable temperature and cooling schedule, yield strength of 30 mm plain carbon steel plate can reach 310 MPa. The first on-line application of prediction and control of microstructure and properties (PCMP) in the medium plate production was achieved. The predictions of the system are in good agreement with measurements.
2005 Vol. 21 (01): 13-16 [Abstract] ( 491 ) [HTML 1KB] [PDF 393KB] ( 599 )
17 Shengquan CAO, Jinxu ZHANG, Jiansheng WU, Jiaguang CHEN
Analysis of Orange Peel Defect in St14 Steel Sheet by Electron Backscattered Diffraction (EBSD)
In this paper, the orange peel defect in the surface range of the st14 steel sheet has been investigated using the electron backscattered diffraction (EBSD) technique. It has been found that the orange peel defect in the st14 steel sheet was resulted from the local coarse grains which were produced during hot-rolling due to the critical deformation in dual-phase zone. During deep drawing, the coarse grains with {100}<001> microtexture can slip on the {112}<111> slip system to form bulging and yields orange peel defects, while the coarse grains with {112}<110> orientation do not form the defect as the Schmid factor of {112}<111> slip system in it equals zero.
2005 Vol. 21 (01): 17-20 [Abstract] ( 726 ) [HTML 1KB] [PDF 784KB] ( 842 )
21 Hao YU, Hao REN, Yonglin KANG, Kelu WANG
Carbon Diffusion in Hot Strips of Low Carbon Steel Produced by CSP Line under Different Thermal Histories
Two experiments were carried out on the same compact strip production (CSP) line, which differs in that one of them experienced γ→α→γ﹡thermal history. The differences in microstructure, precipitation, misorientation etc between two experiments were investigated by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron back-scattered diffraction (EBSD) and positron annihilation technique (PAT). The carbon concentration in matrix is more inhomogeneous in the experiment than that withγ→α→γ﹡ thermal history. The specific precipitation characteristic in the experiment withoutγ→α→γ﹡ thermal history is discussed on the basis of different carbon diffusion behavior and interaction between dislocation and excess carbon.
2005 Vol. 21 (01): 21-24 [Abstract] ( 580 ) [HTML 1KB] [PDF 684KB] ( 616 )
25 Wantang FU, Yi XIONG, Jun ZHAO, Yong LI, T.Furuhara, T.Maki
Microstructural Evolution of Pearlite in Eutectoid Fe-C Alloys during Severe Cold Rolling
The microstructural evolution of pearlite during severe cold rolling in Fe-0.8C binary alloy and Fe-1Mn-0.8C ternary alloys was investigated by using SEM, TEM and XRD etc. The results show that the deformed pearlite consists of irregularly bent lamella, coarse lamella with shear-band and fine lamella. As the rolling reduction increases, the proportion of fine lamella increases. The strong plastic deformation, amorphization and dissolution of cementite take place during the severe cold rolling. The maximum carbon content in ferrite reaches 0.15 mass% after 90% cold rolling.
2005 Vol. 21 (01): 25-27 [Abstract] ( 583 ) [HTML 1KB] [PDF 534KB] ( 675 )
28 Junwei WU, Xiaogang LI, Cuiwei DU, Song WANG, Yiquan SONG
Effects of Cl- and SO-42- Ions on Corrosion Behavior of X70 Steel
Corrosion behaviors of X70 steel were studied by means of electrochemical experiments and morphology observation. First, through potentiodynamic polarization in solution of various Cl- ions concentration, it was found that Epit began to appear in solution of Cl¬- concentration above 0.1 mol/L, and there was a critical point of Cl- concentration between 0.05 mol/L and 0.1 mol/L, below which the extent of pitting and general corrosion were trivial, while in solution of Cl- concentration above 0.1 mol/L, general and pitting corrosion became greater as the increasing of Cl- concentration. All of them were confirmed by the SEM observations after anodic polarization. Second, via the potentiodynamic polarization curves of X70 steel in 0.5 mol/L Cl-solution with 0, 0.05, 0.5 and 1 mol/L SO¬42- ions, it was found SO¬42- ions were able to inhibit corrosion aroused from Cl-1 ions, accordingly a model was set up to describe the process. In addition, to further explore the inhibited effect of SO¬42- ions, EIS was used in solutions of different Cl- and SO¬42- concentrations, the results revealed that the electrochemical resistance has a relation with the [SO42-]/[Cl-], that was, the bigger the value of [SO42-]/[Cl-], the greater the electrochemical resistance.
2005 Vol. 21 (01): 28-32 [Abstract] ( 617 ) [HTML 1KB] [PDF 450KB] ( 498 )
33 Hao GUO, Guangfu LI, Xun CAI, Jianjiang ZHOU, Wu YANG
SCC Behaviour of X-70 Pipeline Steel in Near-Neutral pH Solutions
The stress corrosion cracking (SCC) behaviour of X-70 pipeline steel in near-neutral pH solutions was studied $via$ slow strain rate testing (SSRT). The results showed that the cracking mode of X-70 pipeline steel in near-neutral pH solutions was transgranular at different temperatures and applied potentials with the feature of quasi-cleavage. The pH value of the solution decreased with increasing the addition of CO¬2, which increased the susceptibility to SCC. SCC susceptibility increased as the applied potential moved towards the cathodic direction, suggesting that hydrogen induced cracking (HIC) dominated the cracking process at cathodic potentials. The slight decrease of pH values with decreasing temperature of the solution increased the susceptibility to SCC, which attributed to the change of solubility of CO¬2 in the solution at different temperatures. The propagating directions of SCC cracks were different at different potentials. At rather negative cathodic potentials, the cracks were almost perpendicular to the tensile axis, while at free corrosion potential and near anodic potentials, cracks were nearly at 45 degree, and in the range of moderate cathodic potentials both propagating directions could be observed.
2005 Vol. 21 (01): 33-38 [Abstract] ( 572 ) [HTML 1KB] [PDF 736KB] ( 492 )
39 Senlin WANG
Electroless Plating of Ni-Fe-P Alloy and Corrosion Resistance of the Deposit
Electroless Ni-Fe-P alloys in an alkaline bath were plated. The effects of deposition parameters on the plating rate and the coating composition were examined. The weight loss test and the anodic polarization measurement of the deposits in 3.5 wt pct NaCl solution (pH7.0) showed that the deposits with the mole ratio of NiSO¬4/FeSO¬4 being 0.07:0.03, pH8.0 and 7.5 possess better corrosion resistance than that of the other deposits and the Ni-Fe-P deposits did not form passive films in this environment. In 5.0 wt pct NaOH solution, the Ni-Fe-P deposits have better corrosion resistance and formed passive films.
2005 Vol. 21 (01): 39-42 [Abstract] ( 595 ) [HTML 1KB] [PDF 616KB] ( 544 )
43 Weimin MAO, Heng JIANG, Ping YANG, Huiping FENG, Yongning YU
Distribution of Microelements and Their Influence on the Corrosion Behavior of Aluminum Foil
The distribution of microelement Fe, Si, Cu and Mg in the surface layer of aluminum foil annealed at 300℃ and 500℃ were determined by secondary ion mass spectrometer. The corrosion structure produced by electrochemical etching was also observed. It was found that the Mg concentration at external surface was increased exponentially over the fourth degree and promoted by higher annealing temperature, which will increase the number of corrosion pits inside the large grains, and therefore the specific capacity of the foils for electrolytic capacitors. The similar effects of microelement Fe, Si and Cu were not so strong.
2005 Vol. 21 (01): 43-46 [Abstract] ( 570 ) [HTML 1KB] [PDF 389KB] ( 447 )
47 Junwen LI, Tadashi MOMONO
Effect of Ultrasonic Output Power on Refining the Crystal Structures of Ingots and Its Experimental Simulation
In this study, a series of tests were conducted by using aluminum-based alloy to determine the formation of grain refining structure based on the ultrasonic vibration (UV). Furthermore, the simulation test and effect of ultrasonic output power were studied using ammonium chloride. Finally, the mechanism of grain refinement was investigated. The results show that: (1) By applying the UV to aluminum-base alloy, the grain refining rate of ingots tended to increase with the increase of the output value of UV. (2) It was confirmed that time from after the pour to the beginning of crystallization as well as cloudiness tended to decrease with increasing the ultrasonic power value of UV. Moreover, it can be seen from each cooling curve that a uniform temperature gradient existed in the melt as the power of UV increased, that made the melt strongly stirred. (3) It was also considered that the grain refining effect of ingots, which was observed from the simulation tests, resulted from nucleation action and stirring division action by applying the UV.
2005 Vol. 21 (01): 47-52 [Abstract] ( 561 ) [HTML 1KB] [PDF 770KB] ( 590 )
53 Ning LIU, Minghai CHEN, Yudong XU, Jie ZHOU, Min SHI
Wettability and Bonding between Ni and Ti(C, N) with Multiple Carbide Additions
The wettability and bonding in Ni/Ti(C, N) systems with multiple carbide additions were studied by sessile drop technique and vacuum brazing technique, respectively. The phase characterizations of substrates and fracture surfaces were conducted by XRD. The microstructures at metal/ceramic interfaces and fracture surfaces were observed via SEM in back scattered mode and second electron mode, respectively. Furthermore, an X-ray energy-dispersive spectrometer (EDS) attached to SEM was used to study the elements diffusion in interfacial regions. The results reveal that diffusion and dissolution mechanism controlled reactive wetting takes place in the system in high temperature wetting. Results also show that the contact angles decrease with multiple carbide additions, and the effect of multiple carbide additions is stronger than that of single additions. The contact angle reaches the lowest value in the lowest TiC content case. The enhancement of the wettability is due to alloying procedure during high temperature wetting when metallic atoms diffuse into Ni phase, which decreases the interfacial energy of Ni/Ti(C, N) systems. The bonding results show that the interfacial bonding strength is higher than that of solid solutions, that makes most of the specimens fail in ceramics matrix.
2005 Vol. 21 (01): 53-59 [Abstract] ( 573 ) [HTML 1KB] [PDF 1082KB] ( 685 )
57 X.Yao, C.Z.Wu, H.Wang, H.M.Cheng, G.Q.Max Lu
Hydrogen Storage of Magnesium-Based Nanocomposites System
Hydrogen storage in traditional metallic hydrides can deliver about 1.5 to 2.0 wt pct hydrogen but magnesium hydrides can achieve more than 7 wt pct. However, these systems suffer from high temperature release drawback and chemical instability problems. Recently, big improvements of reducing temperature and increasing kinetics of hydrogenation have been made in nanostructured Mg-based composites. This paper aims to provide an overview of the science and engineering of Mg materials and their nanosized composites with nanostructured carbon for hydrogen storage. The needs in research including preparation of the materials, processing and characterisation and basic mechanisms will be explored. The preliminary experimental results indicated a promising future for chemically stable hydrogen storage using carbon nanotubes modified metal hydrides under lower temperatures.
2005 Vol. 21 (01): 57-60 [Abstract] ( 877 ) [HTML 1KB] [PDF 308KB] ( 454 )
60 Wenbo HAN, Kaifeng ZHANG, Guofeng WANG, Xiaojun ZHANG
Superplastic Forming and Diffusion Bonding for Sandwich Structure of Ti-6Al-4V Alloy
Superplastic forming and diffusion bonding (SPF/DB) is a well-established process for the manufacture of components almost exclusively from Ti-6Al-4V sheet material. The sandwich structure of Ti-6Al-4V alloy is investigated. The effects of the microstructure on the SPF/DB process were discussed. The microstructure at the interfaces and the distribution of thickness were researched.
2005 Vol. 21 (01): 60-62 [Abstract] ( 597 ) [HTML 1KB] [PDF 311KB] ( 658 )
63 Mingyu LI, Chunqing WANG
Simulative Design of Pad Structure for High Density Electronic Interconnection
Solder bridge is a serious defect of solder joints in ultrafine pitch electronic device assemblies. Generation of the solder bridge is closely related to forming process of the solder joints. A three-dimensional model to simulate the formation of the solder bridge of QFP256 (quad flat packaging with 256 leads) is established and numerically calculated to predict the formation shape of the solder joints using surface evolver program. Based on the model, influence of structure of pads printed on circuit board on solder bridging is ivestigated. The results show that there is a critical solder volume Vc for solder joints to avoid solder bridging, and parameters of the pad size influence the critical solder volume.
2005 Vol. 21 (01): 63-67 [Abstract] ( 543 ) [HTML 1KB] [PDF 551KB] ( 533 )
68 Zhiqiang YU, Gaohui WU, Longtao JIANG, Dongli SUN
Microstructure and Tensile Properties of Yttria Coated-Alumina Particulates Reinforced Aluminum Matrix Composites
The liquid-phase coating method was used to deposit Y2O3 ceramic on the surface of α-Al¬2O3. The coated-Al2O3p/6061Al composites were produced using squeeze casting technology. The microstructure and tensile properties of the composites were analysed and studied. The results showed that the coated Al2O3 particles are able to disperse homogeneously in the aluminum liquid. The microstructure of the composites is more even in comparison with that of as-received powders. The tensile testing indicated that mechanical properties of the coated-Al2O3p/6061Al composites are better than those of uncoated particles. In the composite with 30% volume fraction, the tensile strength, yield strength as well as elongation is increased by 29.8%, 38.4% and 10.3%, respectively. The SEM analysis of fracture indicated that the dimples of the coated-Al2O3p /6061Al composites are more even.
2005 Vol. 21 (01): 68-70 [Abstract] ( 579 ) [HTML 1KB] [PDF 438KB] ( 585 )
71 Yinong WANG, J.C.Huang
Superplasticity Enhanced by Two-stage Deformation in a Hot-extruded AZ61 Magnesium Alloy
A two-stage strain rate deformation method is proposed to enhance the superplasticity in a hot extruded AZ61 alloy. In the stage-one of deformation, a relatively high strain rate was applied in order to obtain fine grains through dynamic recrystallization. The optimum strain rate for DRX at 300℃ was identified as ～5×10-3 s-1. Stage-two is conducted at relatively low strain rate in order to utilize the fine grains refined by DRX during stage-one to make the grain boundary sliding operate more smoothly, which resulting in enhanced superplastic elongation from 350% to 440%.
2005 Vol. 21 (01): 71-74 [Abstract] ( 598 ) [HTML 1KB] [PDF 445KB] ( 488 )
75 Zhihao ZHAO, Jianzhong CUI, Jie DONG, Beijiang ZHANG
Effect of Low Frequency Electromagnetic Field on Macrosegregation of Horizontal Direct Chill Casting Aluminum Alloys
The horizontal direct chill (HDC) casting process is a well-established production route for aluminum alloy ingot but the ingot may suffer from macrosegregation sometimes. In order to control the defect, a low frequency electromagnetic field has been applied in HDC casting process and the relevant influence has been studied. The results show that application of low frequency electromagnetic field can reduce macrosegregation in HDC casting process; and two main parameters of electromagnetic field density and frequency, have great influences on the solution distribution along the diameter of ingot. Moreover, the mechanisms of reduction of macrosegregation by electromagnetic field have been discussed.
2005 Vol. 21 (01): 75-78 [Abstract] ( 525 ) [HTML 1KB] [PDF 332KB] ( 595 )
79 Guoqing CHEN, Kaifeng ZHANG, Wenbo HAN, Junting LUO
Synthesis and Enhanced Superplasticity of the Zirconia-dispersed Alumina Nanocomposite
A series of alumina-zirconia composites with various grain sizes were prepared from the nano-sized powders with different agglomerations. Microstructural analysis of the sintered compacts indicates that the as-sintered material is a typical intra/inter granular nanocomposite with uniform distribution of the zirconia grains in the alumina matrix. Superplastic deep drawing test under different conditions demonstrates that dense Al2O3/ZrO2 samples with average grain size of 230 nm can be elongated to a dome height of at least 12 mm at the punch rate of 0.6 mm•min-1 at 1400℃. Further drawing tests show that for the composites with larger grain size, such elongation cannot be achieved at such a strain rate.
2005 Vol. 21 (01): 79-82 [Abstract] ( 592 ) [HTML 1KB] [PDF 304KB] ( 496 )
83 Ling ZHENG, Yinong LI
Sol-Gel Preparation of Graphite/TiO2 Composite Particles and Their Electrorheological Effect
Graphite/TiO¬2 composite particles were obtained by sol-gel technique in this paper. The structure and characteristic of the composite particles are analyzed by XRD, SEM and TG-DTA. The electrorheological properties of the ER fluid containing the particles were measured by a Couette-type rheometer under shear rates of 1～136 s-1 and AC electric fields of 0～3 kV/mm. The experimental results show that the leaking current density of the ER fluid is higher than that of pure titanium dioxide particles dispersed in damping oil. The shear yield stress of the ER fluid increases with increasing electric field and exhibits a typical Bingham flow behavior. The suspension demonstrates an excellent ER performance (τ/τ0=1200) compared with conventional ER fluids (τ/τ0≤500). The sedimentation of the ER fluid is improved obviously due to the coating effect of the particles.
2005 Vol. 21 (01): 83-86 [Abstract] ( 628 ) [HTML 1KB] [PDF 306KB] ( 603 )
87 Ling LIU, Boming ZHANG, Zhanjun WU, Dianfu WANG
Effects of Cure Pressure Induced Voids on the Mechanical Strength of Carbon/Epoxy Laminates
This work aims at designing a set of curing pressure routes to produce laminates with various void contents. The effects of various consolidation pressures resulting in different void contents on mechanical strength of carbon/epoxy laminates have been examined. Characterization of the voids, in terms of void volume fraction, void distribution, size, and shape, was performed by standard test, ultrasonic inspection and metallographic analysis. The interlaminar shear strength was measured by the short-beam method. An empirical model was used to predict the strength vs porosity. The predicted strengths conform well with the experimental data and voids were found to be uniformly distributed throughout the laminate.
2005 Vol. 21 (01): 87-91 [Abstract] ( 498 ) [HTML 1KB] [PDF 400KB] ( 680 )
92 Jun QIU, Xiaoming CAO, Chong TIAN, Jinsong ZHANG
Ablation Property of Ceramics/Carbon Fibers/Resin Novel Super-hybrid Composite
A novel super-hybrid composite (NSHC) is prepared with three-dimension reticulated SiC ceramic (3DRC), high performance carbon fibers and modified phenolic resin (BPR) in this paper. Ablation performance of super-hybrid composite is studied. The results show that the NSHC has less linear ablation rate compared with pure BPR and CF/BPR composite, for example, its linear ablation rate is 50% of CF/BPR at the same fiber content. Mass ablation rate of the NSHC is slightly lower than that of pure BPR and CF/BPR composite because of their difference in the density. Scanning electron microscopic analysis indicates that 3DRC can increase anti-erosion capacity of materials because its special reticulated structure can control the deformation of materials and strengthen the stability of integral structure.
2005 Vol. 21 (01): 92-94 [Abstract] ( 590 ) [HTML 1KB] [PDF 322KB] ( 536 )
95 Baowei QIAO, Yunfeng LAI, Jie FENG, Yun LING, Yinyin LIN, TingAo TANG, Bingchu CAI, Bomy CHEN
Study of Ge2Sb2Te5 Film for Nonvolatile Memory Medium
The amorphous Ge2Sb2Te5 film with stoichiometric compositions was deposited by co-sputtering of separate Ge, Sb, and Te targets on SiO2/Si (100) wafer in ultrahigh vacuum magnetron sputtering apparatus. The crystallization behavior of amorphous Ge2Sb2Te5 film was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and differential scanning calorimetry (DSC). With an increase of annealing temperature, the amorphous Ge2Sb2Te5 film undergoes a two-step crystallization process that it first crystallizes in face-centered-cubic (fcc) crystal structure and finally fcc structure changes to hexagonal (hex) structure. Activation energy values of 3.636±0.137 and 1.579±0.005 eV correspond to the crystallization and structural transformation processes, respectively. From annealing temperature dependence of the film resistivity, it is determined that the first steep decrease of the resistivity corresponds to crystallization while the second one is primarily caused by structural transformation from "fcc" to ``hex" and growth of the crystal grains. Current-voltage (I-V) characteristics of the device with 40~nm-thick Ge2Sb2Te5 film show that the Ge2Sb2Te5 film with nanometer order thickness is still applicable for memory medium of nonvolatile phase change memory.
2005 Vol. 21 (01): 95-99 [Abstract] ( 579 ) [HTML 1KB] [PDF 469KB] ( 550 )
100 Lingzhong DU, Binshi XU, Shiyun DONG, Xin LI, Hua YANG, Weiyi TU, Zixin ZHU
Friction and Wear Characteristics of Brush Plating Ni/nano-Al2O3 Composite Coating under Sand-Containing Oil
Ni-matrix composite coating containing Al2O3 nano-particles is prepared by brush plating. The effects of the nano-particles on the microstructure, microhardness and tribological properties of the composite coating under the lubrication of a diesel oil containing sand are investigated. The results show that the microstructure of the composite coating is finer than that of the pure nickel coating due to the codeposition of the nano-particles. When the nano-particle concentration in the electroplating bath reaches 20 g/L, the microhardness, and wear resistance of the composite coating is as much as 1.6 times and 1.3～2.5 times of those of the pure nickel coating respectively. The main hardening mechanism of the composite coating is superfine crystal grain strengthening and dispersion strengthening. The composite coating is characterized by scuffing as it slides against Si3N4 under the present test conditions.
2005 Vol. 21 (01): 100-104 [Abstract] ( 577 ) [HTML 1KB] [PDF 716KB] ( 629 )
109 Xiangyang XU, Yongwei ZHU, Baichun WANG, Zhiming YU, Shengzhong XIE
Mechanochemical Dispersion of Nanodiamond Aggregates in Aqueous Media
A technology of mechanochemical treatment (MCT) is introduced to modify nanodiamond (ND) surface aiming to obtaining a stable suspension with well-dispersed ND particles in aqueous medium. ND investigated in this paper is a purified product of nanometer-sized diamond synthesized by explosive detonation. As obvious aggregation and sediment were observed when the sample was added into deionized water, it is crucial to conduct deaggregation and dispersion investigations. Amid a series of mechanical treatments, i.e. grinding, stirring, ultrasonic and classification, some reagents are introduced to modify the newly created surface during aggregates comminution. For the co-effects of mechanical forces and surfactants, the mean size of particles was reduced and a stable system containing ND with narrow size distribution was prepared. Mechanism of surface reaction and modification are discussed, while AFM, Zetasizer3000HS, XRD, XPS and FTIR are utilized for the analysis. The functional chemical structure of ND particle surface and surface electrical property changed during the modification processes, and the dispersion character and stability of suspension can consequently be improved.
2005 Vol. 21 (01): 109-112 [Abstract] ( 569 ) [HTML 1KB] [PDF 494KB] ( 634 )
113 Zuquan TANG, Zhuoqiu LI, Jueshi QIAN, Kejin WANG
Experimental Study on Deicing Performance of Carbon Fiber Reinforced Conductive Concrete
Carbon fiber reinforced concrete (CFRC) is a kind of good electrothermal material. When connected to an external power supply, stable and uniform heat suitable for deicing application is generated in the CFRC slab. Electric heating and deicing experiments of carbon fiber reinforced concrete slab were carried out in laboratory, and the effect of the temperature and thickness of ice, the thermal conductivity of CFRC, and power output on deicing performance and energy consumption were investigated. The experimental results indicate that it is an effective method to utilize the thermal energy produced by CFRC slab to deice. The time to melt the ice completely decreases with increasing power output and ice temperature, and increases with increasing thickness of the ice. The energy consumption to melt 2 mm thickness of ice varies approximately linearly from 0.556 to 0.846 kW•h/m2 as the initial temperature ranges from -3℃ to -18℃. CFRC with good thermal conduction can reduce temperature difference in CFRC slab effectively.
2005 Vol. 21 (01): 113-117 [Abstract] ( 586 ) [HTML 1KB] [PDF 215KB] ( 516 )
118 Gaifei PENG Sammy Yin Nin CHAN, Jianhua YAN, Yefeng LIU, Quanxin YI
Characteristics of Crack Growth in High Performance Concrete Subjected to Fire
An experimental investigation was conducted to identify the characteristics of crack growth in high performance concrete (HPC) subjected to fire, including two parts of work, i.e. crack growth resistance determinations and cracking observations, using concrete of three strength grades 40 MPa, 70 MPa, and 110 MPa. The crack growth resistance curves (R-curves ) of HPC subjected to high temperatures were determined using notched three-point bend beam specimens of 100 mm×100 mm×300 mm. The R-curve (crack growth resistance curve) flattening shows that the crack growth resistance has been significantly reduced by elevated temperature. Concrete with a higher strength grade has a steeper R -curve, with a higher fracture toughness but a shorter critical crack growth. The shorter critical crack growth means that concrete of a higher strength grade has a more brittle behavior. The concrete cracking observations reveal that the consequences of rapid heating are quite different from those of slow heating. For slow heating at a rate of 0.5℃/min, HPC suffered no obvious cracking below 600℃ even if it had a high moisture content. Explosive spalling is an extreme case of the internal cracking driven mainly by vapor pressure. All these results confirmed the vapor pressure mechanism for spalling behavior which should be more significant for denser concrete. The crack growth ranges obtained from the R -curve determination results are in good agreement with those measured in the concrete cracking observations.
2005 Vol. 21 (01): 118-122 [Abstract] ( 632 ) [HTML 1KB] [PDF 392KB] ( 530 )
123 Lianquan GUO, Changxiang MA, Shuai WANG, He MA, Xin LI
Molecular Simulation of Hydrogen Adsorption Density in Single-Walled Carbon Nanotubes and Multilayer Adsorption Mechanism
The adsorption of hydrogen onto single-walled carbon nanotubes (SWCNTs) was studied by molecular dynamics (MD) simulation. It was found that the hydrogen molecules distribute regularly inside and outside of the tube. Density distribution was computed for H2 molecule. Theoretical analysis of the result showed the multilayer adsorption mechanism of SWCNTs. The storage of H2 in SWCNTs is computed, which provides essential theoretical reference for further study of hydrogen adsorption in SWCNTs.
2005 Vol. 21 (01): 123-127 [Abstract] ( 700 ) [HTML 1KB] [PDF 708KB] ( 505 )
128 Jiang ZHANG, Zongquan LI, Jin XU
Formation and Structure of Boron Nitride Nanotubes
Boron nitride (BN) nanotubes were simply synthesized by heating well-mixed boric acid, urea and iron nitrate powders at 1000℃. A small amount of BN nanowires was also obtained in the resultants. The morphological and structural characters of the BN nanostructures were studied using transmission electron microscopy. Other novel BN nanostructures, such as Y-junction nanotubes and bamboo-like nanotubes, were simultaneously observed. The growth mechanism of the BN nanotubes was discussed briefly.
2005 Vol. 21 (01): 128-130 [Abstract] ( 514 ) [HTML 1KB] [PDF 223KB] ( 666 )
131 Xiwen SONG, Yongwang ZHAO, Zhefeng WANG, Jun PENG, Wenguang ZHAO, Shengli AN
Synthesis and Characterization of SmxGdyCe1-x-yO2-δ Nanopowders
SmxGdyCe1-x-yO2-δ (x+y=0.2 and x=0, 0.04, 0.08, 0.12, 0.16, 0.2) nanopowders were prepared by a coprecipitation method. The zeta potential and sedimentation volume of Ce(OH)4 aqueous dispersions at different pH values were measured. The isoelectric point (IEP) of Ce(OH)4 suspensions is 7.0. The maximum potential value of -18.5 mV and maximum sedimentation volume of 19 ml are reached at pH=10. The evolution behaviors of the xSm(OH)3•yGd(OH)3•(1-x-y)Ce(OH)4 dried powders in the heating process was characterized by DTA/TG and XRD. The powders decompose to ceria based solid solution at a temperature below 300℃ and forms cubic fluorite structure ceria at about 650℃. The properties of SmxGdyCe1-x-yO2-δ solid solutions were characterized by XRD, TEM and BET. The lattice parameter of doped CeO2 increases linearly with increasing Sm3+ substitution (or decreasing Gd3+ substitution). The particle size of the doped ceria powders is from 5 nm to 10 nm
2005 Vol. 21 (01): 131-134 [Abstract] ( 571 ) [HTML 1KB] [PDF 593KB] ( 575 )
135 Chengdong LI, Xuelei TIAN, Xichen CHEN, A.G.Ilinsky, Likai SHI
Crystallization Behavior of C-containing FINEMET Amorphous Alloy Melt-spun Ribbon
The crystallization kinetics of amorphous Fe¬¬68.5Si¬13.5B¬9Cu¬1Nb¬3C¬5 (at. pct) melt-spun ribbons were studied by the DSC method in the mode of continuous heating. The apparent activation energy Ep1 and Ep2 (373.07±7.92 and 518.75±21.35 kJ/mol, respectively) derived from the Kissinger plots were calculated by the peak temperatures Tp1, Tp2, which display a strong dependence on the heating rates. The crystallization behavior during isothermal annealing at 823 K for 1, 5, 10 h and 973 K for 5 h were investigated using XRD and TEM. The results show that crystallization behavior becomes completely different from that of FINEMET. It is not bcc α-Fe (Si) but metastable fcc γ-Fe (Si) that participates in the first crystallization step combining the appearance of Fe23B6 and Nb2B. Therefore, the addition of C promotes the combination of Fe and B. Fe3.5B is participated in the second step together with the disappearing of Fe23B6, which indicates that transition Fe23B6→Fe3.5B+Fe2B presumably happens. γ-Fe (Si) with peculiar stability cannot transform into nano-sized α-Fe (Si) crystals until the amorphous ribbons were annealed for 5 h at 973 K.
2005 Vol. 21 (01): 135-139 [Abstract] ( 636 ) [HTML 1KB] [PDF 354KB] ( 526 )
140 M.G.Abd El Wahed, S.Abd El Wanees, M.El Gamel, S.Abd El Haleem
Physical Studies of Some Hydrazinobenzoic Acid Complexes
The stability constants of complexes of 2-hydrazinobenzoic acid and 4-hydrazinobenzoic acid with Ni (II), Cu (II), Zn (II), Cd (II), and Hg (II) were determined potentiometrically at different temperatures. The thermodynamic parameters, △G0, △H0, and △S0 were calculated and proved that the complexation process is spontaneous and endothermic. The thermodynamic functions were analyzed in terms of electrostatic and non-electrostatic components and the results reveal that ionic bonds are formed between the studied ligands and metal ions. Conductometric titration was shown that the stoichiometry of the formed complexes are M:L and M:2L. The structure of the prepared solid complexes was characterized using IR, 1H NMR, 13C NMR spectroscopies as well as X-ray diffraction technique. Finally electrical conductivity of the ligands and their copper complexes was measured and shown that the ligands have a semiconductor behaviour.
2005 Vol. 21 (01): 140-144 [Abstract] ( 549 ) [HTML 1KB] [PDF 247KB] ( 558 )

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