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Progress in Research on BiAlO3-based High Temperature
Leadfree Piezoelectric Ceramics
HOU Yu-Dong,CUI Lei,WANG Sai,WANG Chao,ZHU Man-Kang,YAN Hui
2010 Vol. 25 (3): 225–229
Abstract(
3395 )
PDF(935KB)(
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The bismuth aluminate (BiAlO3) is a new developed leadfree piezoelectric material with perovskite structure. BiAlO3 has no structural phase transitions between -133℃ and 550℃, which indicates that it is suitable to be applied in high temperature piezoelectric device. In this paper, the research progress and trends on BiAlO3 based ceramics are reviewed with emphases on the theoretical calculation, high pressure synthetic technology and the addition of the second compound. The limitation and problems in the recent works are discussed, and some ideas for further development of BiAlO3 based ceramics are suggested.
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Synthesis and Electrochemical Properties of LiFeP0.95B0.05O4-δ/C Cathode Materials
REN Zhao-Gang,QU Mei-Zhen,YU Zu-Long
2010 Vol. 25 (3): 230–234
Abstract(
3123 )
PDF(1714KB)(
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B-doped LiFePO4 in P-site, LiFeP0.95B0.05O4-δ/C composite materials were synthesized in flowing Ar atmosphere by solgel method, using citric acid as chelating agent and carbon source. Samples were characterized by X-ray diffraction and cyclic voltammetry, and their electrochemical performances were investigated by galvanostatic charge/discharge tests in terms of cycling performance and rate capability．The results show that the samples have wellregulated olivinetype structures without any impurity peaks while B-doping improves the conductivity of composite materials and decreases the polarization of electrode, and enhances the cycling performance and rate capability effectively. The discharge capacities of LiFeP0.95B0.05O4-δ/C synthesized at 650℃ are 149.3, 123.4 and 112.1 mAh/g at the rates of 0.2C, 5C and 10C, with retention ratio of 99.3% after 20 cycles at the rate of 0.2C, 91.65% after 150 cycles at the rate of 5C and 92.9% after 150 cycles at the rate of 10C, respectively. After continuous 30 cycles at different rates of 0.2, 1, 3, 5 and 10C, the discharge capacity of 0.2C can reconvert to the previous value.
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Synthesis and Electrochemical Properties of Highly Dispersed Li4Ti5O12
Nanocrystalline as Anode Material for Lithium Secondary Batteries
WANG Jin,CHENG Xue-Lian,WANG Zi-Gang,YANG Hui
2010 Vol. 25 (3): 235–241
Abstract(
3361 )
PDF(2801KB)(
2154
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Nano-sized Li4Ti5O12 powder with high dispersivity was prepared by a novel solgel route using lauric acid as surfactant. The crystal structure, microstructure and the electrochemical properties of samples were characterized by XRD, FESEM, TGDSC, laser particle size analysis, A.C. impedance and galvanostatically chargedischarge experiments. The results demonstrated that the crystallization, microstructure and electrochemical properties were influenced significantly by heattreatment temperature. Li4Ti5O12 powders calcined at 800℃ for 10h were comprised of crystallites with the particle size in the range of 120-275nm, revealing high dispersivity almost without any agglomerates, and exhibiting an excellent electrochemical performance. Its discharge capacities at 0.5C and 1C rates were 174.7mAh/g and 163.3mAh/g, respectively. After 50 cycles, fairly stable cycling performance was achieved without obvious capacity fading. Electrochemical impedance spectroscopy tests demonstrated that the surface reaction kinetics of Li4Ti5O12 was improved significantly from the state of the complete charge to the state of the complete discharge. The charge and discharge results of samples demonstrated that the route to synthesis highly dispersed nanocrystalline was appropriate for preparing Li4Ti5O12 with high electrochemical performance.
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Investigation of Structural and Physical Properties of Pt/Pb(Zr 0.4 Ti 0.6 )O3/ITO Capacitors Fabricated on Glass Substrate
ZHOU Yang,CHENG Chun-Sheng,ZHAO Jing-Wei,ZHENG Hong-Fang,ZHAO Qing-Xun,PENG Ying-Cai,LIU Bao-Ting
2010 Vol. 25 (3): 242–246
Abstract(
3316 )
PDF(1534KB)(
1580
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Pt/Pb(Zr0.4Ti0.6)O3 (PZT)/ITO capacitors were fabricated on glass substrate, where PZT film was prepared by solgel method. The structural and physical properties of Pt/PZT/ITO capacitors were investigated. The microstructural, electrical and optical properties of Pt/PZT/ITO capacitors were characterized by Xray diffraction (XRD), ferroelectric tester, UVspectrophotometer, respectively. It is found that PZT is highly (101) oriented and well crystallized. Ferroelectric measurements indicate that Pt/PZT/ITO capacitor, measured at 5V, possesses good ferroelectric properties, such as fatiguefree characteristics, retention characteristics, large remnant polarization (41.7μC/cm2 ) and high resistivity (2.5×109Ω·cm). The analysis of the leakage current mechanism indicates that Pt/PZT/ITO capacitor showes Ohmiclike behaviour at low voltages (<0.8V) and Schottky emission at high voltages (>0.8V). From the optical measurement, stronger absorption in shortwave and stronger transmission in longwave range are observed. The maximum value of transmission reaches 95%.
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Structure and Properties of BST/BZT/BST Multilayer Film
QIN Wen-Feng,XIONG Jie,LI Yan-Rong
2010 Vol. 25 (3): 247–250
Abstract(
3097 )
PDF(1521KB)(
1413
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Ba 0.6 Sr 0.4 TiO3（BST） thin film, Ba(Zr 0.2 Ti 0.8 )O3（BZT）thin film and Ba 0.6 Sr 0.4 TiO3（BST）/Ba(Zr 0.2 Ti 0.8 )O3（BZT）/Ba 0.6 Sr 0.4 TiO3（BST） (BST/BZT/BST) multilayer thin film were prepared by pulsed laser deposition (PLD) on the LaNiO3 (LNO) coated LaAlO3 (LAO) substrate. All the three kinds of films were characterized by XRD and atomic force microscope (AFM). XRD tests reveal that highquality ［00l］oriented films are obtained.AFM results show that the grain size and root mean square (RMS) roughness of BST/BZT/BST sandwich film are similar to that of BST film and BZT film. Compared with BST and BZT film, the BST/BZT/BST film posses the highest figure of merit FOM (42.07), indicating the highly promising potential of BST/BZT/BST film for the application in tunable microwave device.
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Synthesis of BiFeO3 Nanoparticles by a Polyacrylamide Gel Route
XIAN Tao,YANG Hua,SHEN Xi,FENG You-Cai,ZHANG HaiMin2,FENG Wang-Jun
2010 Vol. 25 (3): 251–254
Abstract(
3510 )
PDF(1845KB)(
2616
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A new polyacrylamide gel route was used to prepare BiFeO3 nanoparticles. In this route, the solution containing the required cations was gelled by using acrylamide; during the gelation process, acrylamide was polymerized to form a polymer network, which provided a structural framework for the growth of particles. It is demonstrated that highpurity BiFeO3 powders can be prepared using ethylenediaminetetraacetic acid (EDTA) as the chelating agent. On the other hand, it is found that adding an appropriate amount of glucose to the precursor solution can effectively suppress the gel shrinkage during drying, and consequently lead to a significant improvement of powder quality. Scanning electron microscope (SEM) observation reveals that the asprepared BiFeO3 powder has a uniform particle size, and the particles are almost spherical without any agglomeration or adhesion. Differential scanning calorimetry (DSC) analysis reveals that the product has an antiferromagnetic phase transition at about 370℃ and a ferroelectric phase transition at about 830℃. Ferroelectric and magnetic hysteresis loop measurements show that the product exhibits clear ferroelectric property and weak ferromagnetism.
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Investigation of Microwave Dielectric Properties of (Mg1-xZnx)2SiO4 (0≤x≤1) Ceramics
SONG Kai-Xin,YING Zhi-Hua,SHAO Li-Huan,ZHENG Liang,XU Jun-Ming,QIN Hui-Bin
2010 Vol. 25 (3): 255–258
Abstract(
3036 )
PDF(2198KB)(
1401
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The phase evolutions, microstructures, and microwave dielectric properties of (Mg 1-x Znx)2 SiO4 (0≤x≤1) ceramics were investigated. The XRD results show that Mg2SiO4 and Zn2SiO4 are partly limited solid solution in the systems of (Mg 1-x Znx)2 SiO4 ceramics, due to the large differences between their crystal structures. BESEM images show that with the increases of x, the second phase of MgSiO3 will be suppressed, and the occurrence of liquid phase sintering accelerates the growth of crystal grain and aggradations of glass phase in the boundary of grain. The dielectric constants of (Mg 1-x Znx)2 SiO4 ceramics gradually increase because of the polarization of Zn 2+ ion is larger than that of Mg 2+ ion. The microwave properties of (Mg 1-x Znx)2 SiO4 ceramics change with the variant of x value, together with external factors of the secondary phase, porosity and grain size of(Mg 1-x Znx)2 SiO4 ceramics. When x is equal to 0.6, the optimum microwave dielectric properties of (Mg 0.4 Zn 0.6 )2 SiO 4 ceramics is obtained：εr=6.6, Qf=95650GHz, τf=-60×10-6 /℃.
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Electrorheological Behavior of Ni/（TiO2+Urea）Core-shell Nano Particles
YANG Jian-Guo,JI Song,MENG Qing-Wei,TAN Suo-Kui,GUO Hong-Yan,ZHAO Hong
2010 Vol. 25 (3): 259–264
Abstract(
2917 )
PDF(1794KB)(
1419
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The Ni/（TiO2+Urea）coreshell nano particles composed of nano Ni particles and ureadoped TiO2 coating, were synthesized by using SolGel method, and their electrorheological (ER) behaviors were investigated. The results show that ER activity of the particles are closely associated with heattreatment temperature and urea content. The shear stress decreases when the particles is heattreated above 320℃. When the mass ratio of urea to Ti is 30%, the shear stress of the ER fluid made from Ni/(TiO2+Urea) particles reaches 40kPa (the DC electric field is 4kV/mm), which is 10 times as high as that made from particles without urea. However, the shear stress decreases when excessive urea is added. The microstructure observation of the ER fluids under DC electric field shows that the particles aggregate to form thicker and dense column structure when the mass ratio of urea to Ti is 30%, while the column structure is broken when excessive urea (>30%) is added. A thin and loose column structure is formed in ER fluid without urea added. It is suggested that the ER behaviors is substantially correlated with the polar molecules in urea.
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Preparation and Characterization of Co/Co9S8/ZnO Coreshell Nanoshperes
LAI Wen-Zhong,DONG Xiao-Jie,HUANG Jing,LENG Yong-Hua,LI Xing-Guo
2010 Vol. 25 (3): 265–271
Abstract(
3929 )
PDF(3197KB)(
1627
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Co/Co9S8/ZnO coreshell nanoshperes were successfully prepared via a thermal decomposition in the water and oxygenfree environmert. The latticematch between Co9S8 and ZnO played a significant role on the layerbylayer selfassembly of the coreshell nanospheres. The assynthesized nanospheres were characterized by XRD, TEM, SQUID and Photoluminescence Spectra. By controlling the reaction parameters, the coreshell nanostructure with uniform size of about 60 nm and shell thickness of 13.6nm was obtained. The effects on the shape control of the product were further investigated, and a proper formation mechanism of the Co/Co9S8/ZnO coreshell nanostructures was presumed. The results show that the favorable procedure to obtain the coreshell nanostructure shape is as follows, the reactants of OLA as solution and TOPO as surfactant, and the optimal temperature and quantity for precursor Zn(acac)2 is 70℃ and 1mmol, respectively. In additon, the sulfidation reaction time for Co is 5 min. The products show ferromagnetism at room temperature with a coercive force of 18.7kA/m. In the photoluminescence measurement, the strongest peak at 460nm which is attributed to oxygen defects can be obtained, while the band edge transitions of ZnO between 380nm and 390nm can hardly be observed.
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Synthesis and Catalytic Performance of Mesoporous Material by Twostep Crystallization
LIU Wei-Qiao,SHANG Tong-Ming,LI Gong,WU Fei-Ke,TONG Hui-Juan,SUN Yu-Han
2010 Vol. 25 (3): 272–278
Abstract(
3393 )
PDF(2216KB)(
1703
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A mesoporous material was synthesized by using the precursor of MCM22 zeolite through a twostep synthesis route, and characterized by XRD, N2 physical adsorptiondesorption, TEM, 27Al MAS NMR, IR spectra of pyridine adsorbed methods and so on. It was found that the synthesized sample was not a mixture of microporous zeolite and mesoporous material but a new mesoporous molecular sieve with strong acid sites and good thermal stability. The acid catalytic activity for macromolecules was evaluated and compared with conventional mesoporous material MCM-41 through the cracking reaction of cumene and alkylation reaction of benzene with 1dodecen. The results show that the conversions of cumene cracking at 350℃ over the new mesoporous material and MCM-41 are 68.98% and 48.80%, respectively. For the alkylation reaction of benzene with 1dodecen at 210℃, the conversions of 1dodecen over the new mesoporous materials and MCM-41 are around 95.20% and 86.89%, respectively. The selectivities of linear alkylbenzene over the new mesoporous materials and MCM-41 are around 88.11% and 90.06%, respectively. The results show that the catalytic property of the new mesoporous materials for macromolecules is superior to that of MCM-41.
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Influence of Carrier on Catalytic Activity of Platinum Based Hydrophobic Catalysts
XIONG Liang-Ping,HU Sheng,REN Xing-Bi,LUO Yang-Ming
2010 Vol. 25 (3): 279–284
Abstract(
3206 )
PDF(2450KB)(
1458
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In order to study the influence of carriers on platinum(Pt) based hydrophobic catalysts’ activity, and explore the practicability of applying silicon carbide and ceriumzirconium composite oxides as carriers of hydrophobic catalysts, Pt based catalysts were prepared by microwave heating method, with carbon black, nanometer SiC and Ce 0.4 Zr 0.6 O2-γ-Al2O3 as carriers, respectively. Then Pt based catalysts were loaded on foam nickel (FN) with polytetrafluoroethylene latex, and hydrophobic catalysts were obtained. Structure of catalysts was analyzed by XRD, TEM, XPS, SEM, etc, moreover, their catalytic activity for recombination of H2-O2 and hydrogen-water liquid catalytic exchange was tested. Results show that Pt particles are evenly distributed on carriers’ surface, and average size of Pt particles in Pt/C, Pt/SiC and Pt/Ce 0.4 Zr 0.6 O2-γ-Al2O3are 4.46, 1.67 and 1.77nm, respectively. Three valences, Pt (0), Pt (Ⅱ) and Pt (Ⅳ) exist in Pt/C and Pt/SiC catalysts. Pt/C and Pt/SiC catalyst particles are evenly distributed on the surface of foam nickel, but it is not the case for Pt/Ce 0.4 Zr 0.6 O2-γ-Al2O3. The catalytic activity of Pt/C/FN is quite high for both recombination of H2-O2 and hydrogenwater liquid catalytic exchange. The catalytic activities of Pt/SiC/FN and Pt/Ce 0.4 Zr 0.6 O2-γ-Al2O3/FN are high for recombination of H2-O2, however, they are quite low for hydrogen-water liquid catalytic exchange.
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Photoelectrocatalytic Performance of Ag/TiO2-xNx Nanotube
WAN Bin,CHEN Ming-Bo,ZHOU Xi-Ying,WANG Wei,LI Wen-Ge
2010 Vol. 25 (3): 285–288
Abstract(
3511 )
PDF(1612KB)(
1431
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High density, well ordered,vertically aligned and uniform titanium oxide nanotube arrays were fabricated on the surface of pure titanium sheet by direct electrochemical anodic oxidation under 20V in electrolyte of 0.5wt％NaF +1mol/L Na2SO4. Then TiO2 nano-tube array were annealed in ammonia for 2h, Ag nano-particles were deposited photocatalytically on the N-doped TiO2 nanotube surface. XRD, SEM and XPS techniques were used to characterize titanium oxide nanotube arrays. Results show that photoelectrondegradation efficiency of Ag/TiO 2-x Nx nano-tubes under UV-light is about 39.68% higher than that of TiO2 nanotubes; and photoelectrodegradation efficiency of Ag/TiO 2-x Nx nano-tubes under visible light is 12% higher than that of TiO2 nano-tubes. After photoelectrondegradation under visible hight for 16h, the degradation rate of mathylene blue with initial concentration of 10×10-6 mol/L is 50.53%.
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Studies of Two-photon Absorption in Heavy Metal Oxide Based Glasses
CHEN Fei-Fei,XU Tie-Feng,DAI Shi-Xun,NIE Qiu-Hua,SHEN Xiang,WANG Xun-Si
2010 Vol. 25 (3): 289–292
Abstract(
2735 )
PDF(1252KB)(
1516
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A serial of glass samples in Bi2O3-B2O3-SiO2 ternary system with high heavy metal oxide (Bi2O3) content were prepared by using conventional melting technique. Their linear refractive indexes n at 632.8nm were measured by prismcoupler, it showed that the n values were ranged from 1.9 to 2.1, and increased with increasing Bi2O3 content which was due to the high polarizability of Bi 3+ ions; their linear absorption spectra were depicted by spectrophotometer, and the optical band gaps Eopg were in the range from 2.229eV to 2.268eV while exhibited decreasing tendency with increasing Bi2O3 content. By employing open apertured Z-scan measurements at various wavelengths (770, 800, and 850nm), nonlinear absorption coefficients β which were due to twophoton absorption (TPA) since the incident photon energy hv (1.61, 1.55, and 1.46eV) of measured wavelengths were between Eopg/2 and Eopg of all samples studied were obtained. The results showed that the glass sample with lowest Bi2O3 content exhibited highest TPA coefficients ((3.6~6.1)×10 -12 m/W) which indicated as resonatetype induced by gap state at all measured wavelengths, demonstrating the sample can be applied in optical limiter. On the other hand, glass samples with higher Bi2O3 content showed offresonatetype TPA only at low wavelength of 770nm, and their TPA coefficients β increased with Bi2O3 content leading to the great potentials in all-optical switching (AOS).
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Borate Bioglass Based Drug Delivery of Teicoplanin for Treating Osteomyelitis
ZHANG Xin,JIA Wei-Tao,GU Yi-Fei,ZHANG Chang-Qing,HUANG Wen-Hai,WANG De-Ping
2010 Vol. 25 (3): 293–298
Abstract(
3424 )
PDF(2070KB)(
1418
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A drug delivery system which contains antibiotics for treating osteomyelitis based on a borate bioactive glass was developed. The system was consisted of the borate bioactive glass6Na2O-8K2O-8MgO-22CaO-54B2O3-2P2O5(mol%) as the solid phase, the solution of chitosan, critic acid and glucose as the liquid phase and carried watersoluble teicoplanin as the antibiotics. In vitro test, the drug release behavior, the mechanical properties and the biocompatibility of the drug delivery system were investigated, when the drug delivery device was immersed in phosphate buffer solution (PBS). The drug concentration in PBS were tested by HPLC(High Performance Liquid Chromatography). The drug releasing process could last as long as 30d and 72% of the drug content was released within the first week. The mechanism for the drug releasing from the devices was in accordance with Fick’s diffusion law, when the process was simulated in the Peppas model. The XRD results proved that the bioactive glass material converted into hydroapatite (HA) during the drug release process, indicating that the system had bioactivity in vitro. In vivo test on rabbits, the drug delivery system cured the osteomyelitis in tibial bone, and stimulated the regeneration of tibial bone. The above results proved that the borate bioactive glass was a suitable material for carrying antibiotics to cure osteomyelitis, and for stimulating bone regeneration.
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Preparation and Antibacterial Property of Copper-loaded
Activated Carbon Microspheres
TAN San-Xiang,TAN Shao-Zao,LIU Ying-Liang,JIANG Feng-Ping,YUAN Ding-Sheng
2010 Vol. 25 (3): 299–305
Abstract(
3319 )
PDF(2000KB)(
1381
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Carbon microspheres (CMs) were prepared via
a hydrothermal method, and then activated with KOH to form activated carbon microspheres (ACMs). Copperloaded activated carbon microspheres (CuACMs) were obtained by the direct immersion in CuCl2 aqueous solution. The structure and morphology of ACMs and Cu-ACMs were characterized by XRD, SEM, TEM, EDS, XPS and N2 adsorptiondesorption isotherms. The experimental results show that the copper valence state of Cu-ACMs samples is Cu 2+ ion, and the amount of absorbed copper increases with the increase of copper ion concentration in solution. The addition of ammonia can significantly improve the amount of absorbed copper. The antibacterial activities of asprepared materials measured indicate that the Cu-ACMs have the good activities to kill E. coli and S. aureus. Therefore, Cu-ACMs is a potential candidate as the antibacterial materials in some applications, such as water treatment, gas filtration and microbial contamination, etc.
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Thermal Decomposition Mechanism of MgCl 2·6H2O
HUANG Qiong-Zhu,LU Gui-Min,WANG Jin,YU Jian-Guo
2010 Vol. 25 (3): 306–310
Abstract(
3413 )
PDF(2186KB)(
1926
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The thermal decomposition mechanism and the intermediate morphology of MgCl2·6H2O before and after calcination by a resistance furnace, were studied using integrated thermal analysis, X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectrum and chemical analysis. The results showed that there were six steps in the thermal decomposition of MgCl2·6H2O, producing MgCl2·4H2O at 69℃, MgCl2·2H2O at 129℃, MgCl2·nH2O(1≤n≤2) and MgOHCl at 167℃, and the MgCl2·nH2O(1≤n≤2) converted to Mg(OH)Cl·0.3H2O with dehydration and hydrolysis simultaneously at 203℃, Mg(OH)Cl·0.3H2O dehydrated to MgOHCl at 235℃, MgOHCl directly converted to MgO at 415℃. The MgOHCl particle was irregular with porous structure, while Mg(OH)Cl·0.3H2O particle had relatively flat surface.
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Damage Behavior of 2D C/SiC Composites under Low Velocity Impact
YAO Lei-Jiang,LI Zi-Shan,CHENG Qi-You,TONG Xiao-Yan
2010 Vol. 25 (3): 311–314
Abstract(
2879 )
PDF(2077KB)(
1554
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Low velocity impact (LVI) damage behavior of 2D C/SiC composite was experimentally investigated. C/SiC laminates were impacted under various energy levels ranging from 1.5J to 9J by a dropping hammer. Impact damages were characterized by surface measurement and two nondestructive test (NDT) methods, which were ultrasonic C-scan and infrared thermal wave. The effect of impact energy on post-impact compressive performance was studied by static compress test. The results indicate that C/SiC behaves in a damage tolerant manner. While damage is produced under very low energy, but it is bounded in a limited area and no catastrophic failure occurs under all energy levels. LVI damage area increases with the impact energy. After impact of 1.5J, nearly no visible damage is found. When the impact energy increases to 9J, the specimen is nearly penetrated. LVI is a great threaten to the loading capacity of C/SiC, since the nominal compressive strength and modulus decreases maximum to 44.7% and 16.9%, respectively.
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Effect of Heattreatment Temperature on Mechanical Properties of
Pyrocarbon and Carbon/Carbon Composites
YU Shou-uan,ZHANG Wei-Gang
2010 Vol. 25 (3): 315–320
Abstract(
3520 )
PDF(3404KB)(
1871
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Carbon/carbon composites were infiltrated by isobaric, isothermal chemical vapor infiltration using propane as the carbon source. Effects of heattreatment temperature up to 2500℃ on the microstructure and the mechanical properties of pyrocarbon and carbon/carbon composites were investigated by X-ay diffractometry, polarized light microscope, scanning electron microscope, nanoindentation, and three points bending tests. The microstructural investigations of samples reveal a pronounced decreased of the interlayer spacing with a simultaneous enhance of the graphitization degree, and polarized light microscope results exhibit distinct concentric cracks due to local stress induced graphitization, the number and width of cracks increase with the increase of heattreatment temperature. Nanoindentation carried out on the pyrocarbon shows the indentation behavior is purely elastic, but the curves of loading and unloading do not overlap with significant amount of energy dissipation, the elastic modulus of pyrocarbon increases with the increase of heat-reatment temperature. On the other hand, with the decrease of fiber strength and the debonding of fiber/matrix interface after heattreatment, the flexural strength and modulus of the carbon/carbon composites decrease.
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Effects of Carbonization Pressure on Microstructure
of Graphitized Pitch-derived Carbons
HUANG Jian,HAO Zhi-Biao,ZOU Wu,WANG Kun-Jie,CHENG Wen
2010 Vol. 25 (3): 321–326
Abstract(
2935 )
PDF(2197KB)(
1493
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Graphitized pitchderived carbons were prepared under carbonization pressures of 30MPa and 60MPa respectively, using high temperature pitch as raw material. Microstructure of the samples were investigated by SEM and TEM. Results indicate that the samples prepared at 30MPa and 60MPa are dominated by easy graphitized flow/flow domain type texture and nongraphitized mosaic/domain type texture, respectively. Nucleation, growth and amalgamation of carbonaceous mesophase spherule as well as microstructures of as-prepared materials are influenced by carbonization pressures. Carbonaceous mesophase spherule can amalgamate completely to form anisotropic flow type texture at the carbonization pressure of 30MPa, while amalgamation of carbonaceous mesophase spherule is blocked to form mosaic type texture at the carbonization pressure of 60MPa. TEM and SAED results show that main texture of the sample prepared at 30MPa is flow type texture, some isotropic textures exist at the rim of lamellar structures or among them. Samples prepared at 60MPa exhibit nonhomogeneous microstructure where (002) rings distribute by spotted state. It can be concluded that uniformity and orientation of the sample prepared at 30MPa are better than those of the sample prepared at 60MPa.
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Effect of Heattreatment Temperature on the Electrochemical Performances of the Li2MnSiO4/C Composite Prepared through Polyol Process
LIU Wen-Gang,XU Yun-Hua,YANG Rong,HOJAMBERDIEV Mirabbos,ZHOU Zhi-Bin
2010 Vol. 25 (3): 327–331
Abstract(
3035 )
PDF(1669KB)(
1528
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The Li2MnSiO4/C composite was synthesized through a polyol process following by heattreatment at intermediate temperatures. The precursors were precipitated from Si(OC2H5)4, LiAc·2H2O and Mn(Ac)2·4H2O in ethylene glycol by refluxing at 196℃ for 16h, the dried powders were milled, pressed and heat-treated at 500℃, 600℃ and 700℃ for 10h. The obtained samples were characterized by X-ray diffraction, automatic elemental analyzer, field emission scanning electron microscope (FESEM), energy dispersive spectroscope (EDS), and high resolution transmission electron microscope (HRTEM). As a result of the Rietveld refinement, two possible Li2MnSiO4 forms crystallizing in Pmn21 and P121/n1 space groups, respectively, are considered as the major phases, and Li2SiO3 is identified as the impurity phase. According to the FESEM observation, the mean particle size increases from 5-20nm to 20-40nm as the heattreatment temperature increasing from 500℃ to 700℃. Carbon is homogenously distributed on the prepared Li2MnSiO4/C composites. The HRTEM examination confirms that the Li2MnSiO4 particles are surrounded by a very thin amorphous carbon layer. The electrochemical experiments reveal that the Li2MnSiO4/C composite heat-treated at 600℃ for 10h has the higher electrochemical performance with an initial discharge capacity of 132.4mAh/g and a capacity retention ratio of 80% at the tenth cycle.
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Study on the (1-x)(Mg0.7Zn0.3)TiO3－x(Ca0.61Nd0.26)TiO3 Microwave Dielectric Ceramics
LU Zheng-Dong,SHEN Chun-Ying,LI Liang，YANG Jian,QIU Tai
2010 Vol. 25 (3): 332–336
Abstract(
2664 )
PDF(1595KB)(
1227
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The microwave dielectric properties of the (1-x)(Mg0.7Zn0.3)TiO3－x(Ca0.61Nd0.26)TiO3(MZCNT) system were investigated. The system was prepared using a conventional solidstate ceramic route. The objective of the present work is to compensate for the negative temperature coefficient of resonant frequency (τf) of (Mg0.7Zn0.3)TiO3 by the addition of (Ca0.61Nd0.26)TiO3. The microwave dielectric properties are strongly correlated with the sintering temperature and the composition. Very dense MZCNT ceramics were synthesized by sintering at 1250℃, when sintered at temperatures above 1300℃, the decomposition of (Ca0.61Nd0.26)TiO3 and evaporation of Zn resulted the decrease in density and degradation in dielectric properties. With increasing (Ca0.61Nd0.26)TiO3, the dielectric constant (εr) increased and the quality factor Q×f decreased. For practical application, 0.87(Mg0.7Zn0.3)TiO3－0.13(Ca0.61Nd0.26)TiO3 ceramics sintered at 1250℃ with a dielectric constant εr～24.3, a Q×f value of 34000GHz and a temperature coefficient of resonance frequency (τf) of -9×10-6/℃ is proposed in this paper.
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