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Journal of Materials Sciences & Technology
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1997, Vol.13 No.3
Online: 1997-05-28
Articles
 
Articles
161 J.D.Hunt; Q.Hant and X.Wan(Dept. of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, U.K.)
Growth of a Cellular/Dendritic Array
This paper describes a time dependent numerical model for the steady and non-steady growthof a cellular/dendritic array in a moving linear temperature field. The model gives fully selfconsistent solutions for axisymmetric interface shapes, predicts cellular and dendritic spacings,undercoolings and the transition between structures. An important feature of the model is thatthe spacing selection mechanism has been treated. The model predicts two different dendriticgrowth regions. One occurs at low dimensionless velocities where the dendrite array is uniform:a small stable range of spacings is predicted and the prediction agrees very well with existing experiments. The other occurs at high dimensionless velocities where the dendrite array is irregular, its minimum spacing is inversely proportional to velocity Experiment was carried out to verify the prediction. The irregular dendrite array was observed and the measured minimum spacing fitted extremely well with the prediction. By fitting the numerical results. Relatively simple analytic expressions are obtained which provide an insight into the cellular and dendritic growth processes and are useful for comparing theory with experiment.
1997 Vol. 13 (3): 161-172 [Abstract] ( 238 ) [HTML 1KB] [PDF 1429KB] ( 296 )
173 Yanruo HONG(National Lab. on Solid Electrolytes and Metallurgical Testing Techniques, University of Science and Technology Beijing,Beijing 100083, China)
Progress of Solid Electrolytes and the Electrochemical Sensors
Four types of solid state electrochemical sensors and their general principles are introduced in the paper. The novel type-IV sensors developed in the last few years are emphasized to study hereafter. The ways to design new electrochemical sensors and the directions to develop new solid electrolytes for new electrochemical sensors are also discussed.
1997 Vol. 13 (3): 173-178 [Abstract] ( 257 ) [HTML 1KB] [PDF 740KB] ( 370 )
179 Qiqing ZHANG; Lei REN and Lingrong LIU(Institute of Biomedical Engineering, Chinese Academy of Medical Sciences, Tianjin 300192, China)Chun WANG(CCCD, University of Utah, Salt Lake City, UT84112, USA)
Structure Investigation of Poly(vinyl alcohol)-Collagen Composite
Naturally derived collagen protein was mixed thoroughly with medical grade poly (vinyl alcohol)(PVA) at the ratio of 90:10 (w/w) and was crosslinked by formaldehyde to form a homogeneous composite membrane. The buIk structure of the membrane was characterized ly means of Xray diffraction (XRD) and transmission electron microscoor (TEM). The membrane surface Structure was investigated using Fourier transform-infrared spectroscopy (attenuated totalrefraction) (FTIR-ATR), electron spectroscopy for chemical analysis (ESCA) and contact angle measurement. lt was found that collagen and PVA can remain Stable. This was supported by the fact that no sign of phase separation had been observed. The use of crosslinking agent can Substantially influence the Structure of the composite. It is suggested that this new compositedeserves further investigation and is potentially usable as a biomedical material.
1997 Vol. 13 (3): 179-183 [Abstract] ( 247 ) [HTML 1KB] [PDF 1234KB] ( 707 )
184 Shengmai ZHOU; Jintong XIA and Lianchen YAN(Dept. of Chemistry & Chemical Engineering, Hunan University, Changsha 410082, China)
Binderless Carbon/Graphite Materials
High performance binderless carbon bodies can be mamufactured from the mesophase raw material derived from petroleum pitch, which is ground into fine powders less than 10μm, and directly moulded, then sintered at 1000℃ without any kind of binder. The sintered bodies have a bulk density of 1.69 g/cm3, bending strength of 91.2 MPa. Shore hardness of 100. Porosity of only 7.2%. and electrical resistivity of 60x10-6 m. The bodies graphitized at 2800℃ have a bulk density of 1.88 g/cm3, bending Strength of 82 MPa. Shore hardness of 85, porosityof 5.4%, and electrical resistivity Of 12x10-6 nm. The scanning electron micrographs of thesection show that the bodies possess an extremely dense and homogeneous structure. lnfra-redspectrum analysis shows that carbonyls introduced when ground or activated are one of the keyfactors determining the selfbinding and self sintering properties of the mesophase fine powders,and the Structure and strength of the sintered bodies.
1997 Vol. 13 (3): 184-188 [Abstract] ( 262 ) [HTML 1KB] [PDF 3089KB] ( 480 )
189 S.F.Yoon and J.Ahn(School of Electrical and Electronic Engineering, Nanyang Technological University Nanyang Avenue, Singapore 639798,Rep. of Singapore)
Electron Cyclotron Resonance Deposition of Wide Bandgap a-SiC:HFilms Using Acetylene under High Hydrogen Dilution
The deposition of hydrogenated amorphous silicon carbide (a-SiC.H) films from a mixture of silane, acetylene and hydrogen gas using the electron cyclotron resonance chemical vapour deposition (ECR-CVD) process is reported. The variation of the deposition and film characteristics such as the deposition rate- optical bandgap, photoluminescence and the infra-red (IR) absorption as a function of the hydrogen dilution is investigated. The deposition rate increases to a maximum value of ~25 nm/min at a moderate hydrogen diIution ratio of ~20 [hydrogenflow (sccm)/acetylene+silane flow (sccm)], and decreases in response to a further increase in the hydrogen dilution. There is no strong dependence of the optical bandgap on the hydrogen dilution within the dilution range investigated (10 to 60), and the optical bandgap calculated from the E04 method varied marginally from ~2.85 eV to ~3.17 eV. The room temperaturephotoluminescence (PL) peak energy and intensity shows a prominent shift to a maximum value of ~2.17 eV corresponding to maximum PL intensity at a moderate hydrogen diIution of ~30.The PL intensity shows a strong dependence on the hydrogen dilution variation. IR absorption results show that films deposited at higher hydrogen dilution have more Si-C bonding.
1997 Vol. 13 (3): 189-193 [Abstract] ( 290 ) [HTML 1KB] [PDF 583KB] ( 311 )
194 A.Tawansi; H.I.Abdel-Kader and E.M.Abdel-Razek(Dept. of Physics, Faculty of Science, Mansoura University, 35516, Egypt)M I Ayad(Dept. of Chemistry Almonofeya University, Shebeen E1-Koam, Egypt)
Electron Spin Resonance of FeCl_3-filled Polyvinylidene Fluoride
Electron spin resonance (ESR) measurements were carried out at room temperature (=294 K),for FeCl3-filled polyvinylidene fluoride (PVDF) films, over the filling mass fraction range of 0
1997 Vol. 13 (3): 194-198 [Abstract] ( 258 ) [HTML 1KB] [PDF 459KB] ( 253 )
199 K.H.W.Seah and X.Li(Dept. of Mechanical and Production Engineering, National University of Singapore, 10 Kent Ridge Crescent,Singapore 119260)
Influence of Coolant on Cutting Tool Performance
This paper reports a Study carried out to substantiate or refute the belief that when coolant is applied, the cutting performance is actually improved. Experiments on cutting forces and chip geometry were conducted in which AISI 1050 Steel was machined by turning using P30 uncoated tungsten carbide tools. Experiments were performed on a CNC Okuma LH35-N lathe undermachining conditions commonly used in workshops in Singapore and many other parts of the world.
1997 Vol. 13 (3): 199-205 [Abstract] ( 222 ) [HTML 1KB] [PDF 2526KB] ( 648 )
206 Huibin XU and Shengkai GONG(Dept. of Materials Science and Engineering, Beijing University of Aeronautics and Astronautics, Beijing 100083, China)
Internal States of Temperature Hysteresis in Shape Memory Alloys
We propose a thermodynamic theory that permits us to connect the size of the temperature hysteresis loop to the interfacial energy between martensite and austenite. The free energy is a function of four variables, viz. deformation of austenite, deformation of martensite, phase fraction and temperature. A diagonal line inside the hysteresis loop in the deformation-temperaturediagram is identified as the line of unstable phase equilibrium. Upon reaching this line the phasemixture loses its (meta-)stability and the transformation from one phase to the other shouldoccur. The theoretical results are supported by experiments on NiTi and CuAINi specimens.
1997 Vol. 13 (3): 206-210 [Abstract] ( 224 ) [HTML 1KB] [PDF 481KB] ( 299 )
211 Xifeng YU and Zhuangi HU(State Key Lab. of RSA, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015, China)Xiang LIU and Lizhi CHENG(Northeastern University, Shenyang 110006, China)
Production of Nanometer Powders with an Electrohydrodynamic Technique
The principle of producing nanometer powders with the electrohydrodynamic technique and the apparatus were described. The effects of the geometry and size of the cathode and anode. and the applied voltage on the emitted current and the mean size of the nanometer powders were Studied.Experimental results show that with the decreasing in the diameter of the cylindrical cathode and in the calibre of the spiral cathode, the mean size of the nanometer powders decreases. The effect of the calibre of the spiral cathode is more remarkable. In addition, the mean size of the nanometer powders decreases with decrease in the internal and external diameter of the anode and the increase in the applied voltage.
1997 Vol. 13 (3): 211-214 [Abstract] ( 225 ) [HTML 1KB] [PDF 779KB] ( 240 )
215 Kezheng CHEN; Zhikun ZHANG and Zuolin CUI (Institute of Nanostructured Materials, Qingdao Institute of Chemical Technology Qingdao 266042, China)Dazhi YANG(Dept. of Materials Science and Technology Dalian University of Technology Dalian 116024, China)
Thin-shell Structure and Reactivity of Nanostructured NiPdCe Particles
Nanostructured NiPdCe particles be arc plasma method in Ar+H2 atmosphere were characterized by TEM, HRTEM and XRD. The results show that nanostructured NiPdCe particles possess the special Structure consisting of the thin-shell layer composed of a series of CeNi phases, Pd and CeO2 and the core composed of Ni and Pd. The thickness of the shell layer is 2~3 nm. The reactivity of nano-NiPdCe particles was measured in the gas-phase hydrogenation of toluene. The results show that nano-NiPdCe particles possess high reactivity above 325℃ and the product selectivity is 100%. The reactivity of nano-NiPdCe particles depends on the synergistic effects of CeNi phases, Ni and Pd as well as the hydrogen storage property.
1997 Vol. 13 (3): 215-218 [Abstract] ( 298 ) [HTML 1KB] [PDF 912KB] ( 244 )
219 Jianqiang ZHANG and Bingyao WU(Dept. of Mechanical Engineering, Southeast University Nanjing 210096, China)Zheng HU(Dept. of Chemistry Nanjing University, Nanjing 210008, China)Guiqin WHNG(Dept of Physics, Nanjing University, Nanjing 210008, China)
Mechanical Alloying Effect on the Structure of Fe-Al-(Si) Alloy
The mechanical alloying effects on the structures of Fe71.3AI28.4(CeO2)0.3 and Fe73.3AI9.8-Si,e.e(CeO2)0.3 samples have been investigated mainly by Mossbauer spectroscopy and X-ray diffraction. It is found that with the increase of milling time, a substituting disordered a-Fe solution is formed gradually and almost completed after milled for 72 h. Further increasing milling time causes the atomic rearrangement within the powders. Correspondingly' the average lattice parameter and average crystalline size change until 72 h and remain constant after 72 h. The addition of Si leads to the higher disordered degree reflected in the smaller average hyperfine field and larger mean Square deviation.
1997 Vol. 13 (3): 219-222 [Abstract] ( 210 ) [HTML 1KB] [PDF 390KB] ( 334 )
223 Qingquan LEI;Yong FAN;Xuan WANG;Jiaqi LIN and Yanling XIONG(Dept. of Electrical Materials Engineering, Harbin University of Science and Technology Harbin 150040, China)
Effect of Inorganic Filler on Thermally StimulatedCurrent in Low-density Polyethylene
By measuring the thermally stimulated current (TSC) spectra at various fields in low-density polyethylene with inorganlc filler (f LDPE) and comparing with those in LDPE, we found that thelr TSC spectra shew slgnificant distinction. in virtue of analysing change of peak current,peak temperature and activation enew with pollng field, it can be depicted that the TSC in f-LDPE specimen comes from dipole relaxation of residual silanol groups on surface of filler, but the injected electrons in very high 6elds, no doubt, are captured in deeper traps, and they can not be released even near 100"C. The filler (kaolin) plays a key role in changing the TSC spectra through deep and interfacial traps existing between the filler and the polymer matrix. Whereas,the TSC spectra of LDPE specimen possess marked characteristics of electron release from traps in amorphous-crystalline or crystalline region.
1997 Vol. 13 (3): 223-226 [Abstract] ( 236 ) [HTML 1KB] [PDF 412KB] ( 268 )
227
1997 Vol. 13 (3): 227-229 [Abstract] ( 223 ) [HTML 1KB] [PDF 1192KB] ( 239 )
230 Lizhi CHENG; Wei FENG; Xinquan DONG; Kuichang BAI and Kaiyuan HE (Dept. of Materials Science and Engineering, Northeastern University Shenyang 110006, China)
Mechanical Alloying of Fe_(100-x) B_x
The formation of nonequilibrium phase by mechanical alloying (MA) of Fe and B powders in a high energy vibration ball mill has been made for Fe100-xBx system with x=15. 30, 35, 45,55 and 70. By using the X-ray diffraction, magnetic measurement and M6ssbauer spectrummethods, it was revealed that the structure of the MA product varies with milling time and B contents.
1997 Vol. 13 (3): 230-232 [Abstract] ( 238 ) [HTML 1KB] [PDF 286KB] ( 208 )
233 Wenming ZENG; Nianyi CHEN and Guofang QIU(Shanghai Institute of Metallurgy Chinese Academy of Sciences, Shanghai 200050, China)
Calculation of Thermodynamic Properties from Phase Diagram of the Pb-Zn System
The formulas for obtaining the interaction parameters of the liquid solution were first deduced from the immiscible phase diagram of binary system. Then. the relationships between activity coefficients and interaction parameters of the binary system were also deduced. Finally, thermodynamic properties of the Pb-Zn system were calculated by using these formulas.
1997 Vol. 13 (3): 233-234 [Abstract] ( 228 ) [HTML 1KB] [PDF 173KB] ( 373 )
235 Xiyan ZHANG; Tianxin TAN; Wenyi PENG and Qing GAO (Southwest Jiaotong University, Chengdu 610031, China)
Cracking Behaviour of Al_2O_3 Short Fibre/Al-5.5Zn Composite in TEM
The micromechanical behaviour of Al2O3 short fibre reinforced Al-5.5Zn matrix composite has been in-situ studied by using TEM. The results show that in the composite the nucleation and propagation of cracks take place mainly in the matrix, as well as in the region near the fibre/matrix interface. It has been also observed that the microcracks can close during unloading.So the fracture property can be characterized by crack open displacement (COD). The cracking characteristic may result from the large strength difference between the matrix and fibre.
1997 Vol. 13 (3): 235-237 [Abstract] ( 210 ) [HTML 1KB] [PDF 1342KB] ( 218 )
238 Jiafeng LEP; Yuyin LIU ;Shaoxuan GUAN; Qingjiang WANG; Zhongguang WANG;Dong LI and Zhuangqi HU(State Key Lab. for Fatigue and Fracture of Materials, Institute of Metal Research, Chinese Academy of Sciences,Shenyan 110015, China)
Characteristics of Faigue Crack Initiation inTi-5Al-4Sn-2Zr-1Mo-0.7Nd-0.25Si Alloy
The characteristics of fatigue crack initiation in Ti-5AI-4Sn-2Zr1Mo-O.7Nd-O.25Si alloy wereStudied. Two modes Of fatigue crack initiation were found. The Nd-rich phase particles displaybetter resistance to fatigue crack initiation than the matrix at lower stress.
1997 Vol. 13 (3): 238-240 [Abstract] ( 213 ) [HTML 1KB] [PDF 1836KB] ( 234 )

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