Journal of Inorganic Materials

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Heterogeneous Photocatalytic Oxidation Removal of Gaseous Benzene over
TiO₂/ACF Composite Prepared by Improved Sol-Gel Method

LIU Shou-Xin,LIU Zheng-Feng 　
2009 Vol. 24 (2): 209–214

Abstract( 3268 )

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TiO₂/ACF composite was prepared by improved solgel method using Ti(OBu)₄ as titanium source. TiO₂ precursor was loaded on activated carbon fiber (ACF) by dip-coating method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and N₂ (77K) adsorption were used to characterize the obtained composite. High concentration gaseous benzene in a staticmode photocatalytic reactor was used as model compound for photocatalytic activity test. Gas chromatographmass spectrum (GC-MS) was used for intermediates identification. The results show that TiO₂ can form perfect thin film on ACF surface. With the increase of dipcoating times, surface area of TiO₂/ACF decrease, thickness of TiO₂ film increase, then split and even fall off. Complete anatase can be formed for the sample calcinated at 400℃ and phase transformation of anatase to rutile occurrs at 700℃. The crystal size of TiO₂ decrease with the increase of calcination temperature. The sample of TiO₂/ACF-400-2 calcinated at 400℃ and dip-coated twice exhibits the highest activity for benzene removal. Intermediate analysis result reveals that no toxic of phenol and quinine compound is detected.

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Preparation and Photo Absorption Property of Coupled Semiconductor NiO-TiO₂

WANG Xi-Tao,HE Zhong,ZHONG Shun-He 　
2009 Vol. 24 (2): 215–220

Abstract( 3052 )

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NiO-TiO₂ coupled semiconductors were synthesized by organic templates method．Their pore distribution, crystal structure，surface composition and photo absorption properties were investigated by techniques of N₂ adsorptiondesorption, XRD, TPR, TEM and UV-Vis DRS. The results show that the NiO-TiO₂ coupled semiconductors prepared by organic templates exist in nanotube or nanobelt with mesporous structure, and the BET surface area is higher than 100m²/g. The NiO particles disperse well on the surface of TiO₂, and the strong interaction between NiO and TiO₂ results in the formation of NiTiO₃. The p-n couple effect of NiO and TiO₂ extends distinctly the photo absorption field and decreases the Eg from 3.82eV to 3.49eV when the addition amout of NiO is increased from 2% to 10%.

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Thirdorder Nonlinear Optical Properties of TiO₂ Films

LONG Hua,CHEN Ai-Ping,YANG Guang,LI Yu-Hua,LU Pei-Xiang 　
2009 Vol. 24 (2): 221–224

Abstract( 3252 )

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Anatase TiO₂ films were fabricated on fused quartz by pulsed laser deposition （PLD） technique and the single-phase anatase films were obtained under the optimal conditions. The X-ray diffraction and atomic force microscope were used to investigate the structure and surface characters of the film. The third-order optical nonlinearities of the films were measured by Z-scan technique using a femtosecond laser (50fs) of 800nm. From the transmission spectra, the optical bandgap and linear refractive index of the TiO₂ film are determined to be 3.18eV and 2.1, respectively. The nonlinear absorption coefficient and nonlinear refractive index are determined to be -6.2×10^-11m/W and -6.32×10^-17m²/W, respectively.The real and imaginary parts of third-order nonlinear susceptibility χ(³) are determined to be -7.1×10^-11esu and -4.42×10^-12esu, respectively. And the following figure of merit T=βλ/n₂ is calculated to be 0.8 for the film, indicating that the anatase TiO₂ films have great potential applications to nonlinear optical devices.

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Synthesis of Ordered Mesoporous TiO₂ from Industrial Titanyl Sulfate
Solution and its Formation Mechanism

TIAN Cong-Xue,ZHANG Zhao 　
2009 Vol. 24 (2): 225–228

Abstract( 3657 )

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Using composite template (CTAB and P123) as structuredirecting agents, industrial titanyl sulfate as Ti source, the precursor of mesoporous TiO₂ was prepared via controlling the hydrolysis and condensation rate of industrial TiOSO₄, self-assembly rate of template and pH value of solution. The asprepared materials were characterized by XRD, HRTEM, SAED and nitrogen adsorptiondesorption.Ordered mesoporous anatase titania is obtained after template removal, with hexaganol mesopore, S_BET of 205.7m²/g，average pore diameter of 3.28nm. The formatiom process of mesopore belongs to cooperative formation mechanism, i.e. the hydrolysis colloid particles of titanium and composite template interact through static force and hydrogen bond on the interface, cooperating to form mesopore.

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Preparation of Porous SiO₂-TiO₂ Nanocomposites and Their Photocatalytic Activity

KANG Chuan-Hong,GUO Tong,JING Li-Qiang,CUI Hu-Cheng,ZHOU Jia,FU Hong-Gang 　
2009 Vol. 24 (2): 229–233

Abstract( 3167 )

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Porous SiO₂-TiO₂ nanocomposites were synthesized by utilizing TiO₂ nanopartilces obtained by a sol-gel method, followed by an impregnation process with F127 modified SiO₂ sol. The resulting samples were characterized by XRD, BET, TEM, N₂ adsorptiondesorption, UV-Vis DRS spectra and FT-IR spectra, and their photocatalytic activities were also evaluated by degrading RhB solution under illumination. The effects of the SiO₂ on the thermal stability and photocatalytic activity of anatase nanoparticles were mainly investigated. The results show that the SiO₂ can greatly enhance the thermal stability of TiO₂ crystallities, even having a principal anatase phase composition after heattreated at 900℃, and make TiO₂ maintain a small crystallite size. The large surface area of the resulting SiO₂-TiO₂ nanocomposites is attributed to the small crystallite size and porous SiO₂. During the processes of photocatalytic degradation RhB, all the asprepared SiO₂-TiO₂ nanocomposites by thermal treatment at high temperature exhibit higher activity than Degussa P-25 TiO₂. The high activity is attributed to the high anatase crystallinity and the large surface area.

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Analysis to Microstructure and PhotoLuminescent Properties of CuO/SiO₂ Composite Thin Films

SHI Feng,LI Yu-Guo,SUN Qin-Jun 　
2009 Vol. 24 (2): 234–238

Abstract( 3364 )

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Cu/SiO₂ composite thin films were deposited on n-type Si(111) substrates by radio frequency (RF) magnetron cosputtering method, annealed at high temperature in N₂ atmosphere, then cooling and oxidation in the air to fabricate low-dimensionality CuO nanostructure. The microstructure and photo luminescent properties were studied. The main phase of sample is cubic CuO(200) crystal face and sample forms nanoline structure with Cu, O elements as the main components to form CuO/SiO₂ composite thin film in the sample surface after annealing at 1100℃. The ultraviolet light and purplelight appear in photoluminescence (PL) spectra, which is abscribed to the electron transition from the defect level，resulting from the Cu vacancies to the conductor band of CuO composite thin films.

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Combustion Synthesis and Temperature Dependent Photoluminescence
of Nanocrystalline Y₂Zr₂O₇∶Eu³⁺

WANG Dian-Yuan,WANG Qing-Kai,CHANG Zhang-Yong,GUO Yan-Yan,WU Xing-Hua 　
2009 Vol. 24 (2): 239–242

Abstract( 3226 )

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Nanocrystal and bulk Y₂Zr₂O₇∶Eu³⁺ were prepared by combustion synthesis and solidstate reaction, respectively. By using X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM) and fluorescence spectrometer, the structural, morphological and temperature dependent spectroscopic properties of Y₂Zr₂O₇∶Eu³⁺ were investigated. The results show that the main emission peaks of Y₂Zr₂O₇∶Eu³⁺ nanocrystal are at 606nm and 628nm, which is attributed to ⁵D₀→⁷F₂ transition of Eu³⁺, the ratio of the intensity of 606nm and 590nm in Y₂Zr₂O₇∶Eu³⁺ nanocrystal increases 60% than that in bulk Y₂Zr₂O₇∶Eu³⁺, and all the intensities of ⁵D₀→⁷F_J(J=1,2,3,4) transitions change evidently with decreasing temperature. In addition, the fluorescence spectra of the Y₂Zr₂O₇∶Eu³⁺ nanoparticles which surface were treated by steeping in hydrochloric acid show that the ratio of the intensity of 606nm and 590nm in surface treated Y₂Zr₂O₇∶Eu³⁺ nanoparticles decreases 15% than that in surface untreated Y₂Zr₂O₇∶Eu³⁺ nanoparticles. A qualitative explanation and discussion on the above results is presented on base of surface effect and local structural environment of Eu³⁺ ions.

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OH^- Removal and its Effect on the Fluorescent Properties of
Er³⁺/Yb³⁺ Co-doped Barium Gallogermanate Glass

JIANG Xiao-Ping,YANG Zhong-Min,FENG Zhou-Ming 　
2009 Vol. 24 (2): 243–246

Abstract( 2558 )

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Barium gallogermanate glass is a good candidate material for infrared emission. However, the residual OH^- in the barium gallogermanate glass destroys the glass network and degrades its fluorescence emission properties. Two methods, introduction of fluoride into glass raw materials and Reaction Atmosphere Process (RAP) based on introducting fluoride into glass raw materials, were adopted to dehydrate and then the effects of OH^- concentration on the upconversion and 1.53μm luminescence emission were investigated. Energy transfer rate between Er³⁺ and OH^- is analyzed by a simple Forster-Dexter semi-empirical model. The results show that the RAP can reduce the OH^- concentration up to one eleventh of the original. Correspondingly, the intensity of 545nm upconversion emission increases 2.8 times, which is obviously larger than the increase of 1.53μm emission intensity. Energy transfer parameter between Er³⁺ and OH^- is 1.75×10^-19cm⁴/s,which is a little larger than that in phosphate glass.

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Preparation and Optical Properties of CdS∶Cu/CdS Nanocrystals

CAI Ke,WANG Hong-Zhe,SHEN Huai-Bin,TAO Xiao-Jun,LI Lin-Song,DU Zu-Liang 　
2009 Vol. 24 (2): 247–250

Abstract( 3083 )

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CdS cores were successfully synthesized in noncoordinating solvents. The composite structure of core/shell CdS∶Cu/CdS nanocrystals was obtained through the modification of as-prepared Cu²⁺ ions doped CdS cores using successive ion layer adsorption and reaction (SILAR) technique. The crystal structures, shapes and optical properties of as-synthesized nanocrystals were characterized by X-ray diffraction, transmission electron microscope, UV-Vis absorption and photoluminescence spectroscope. The results show that the crystal structure of asprepared CdS∶Cu/CdS nanocrystal is zinc blende. Compared with pure CdS nanocrystals, the Cu²⁺ dopant in CdS leads the surfacestate related emission peak shifting to longer wavelength. The surfacestate related emission of CdS∶Cu nanocrystal can also be adjusted consecutively from 570nm to 620nm by tuning the doping concentration of Cu²⁺ ions from 2% to 6%. The overcoating of CdS shell can increase the stability of surfacestate related emission of CdS∶Cu nanocrystals.

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Aqueous Phase Preparation of CdTe Nanorods and its Application
in Recognition of Cu²⁺ Ions

ZHENG Ai-Fang,CHEN Jin-Long 　
2009 Vol. 24 (2): 251–254

Abstract( 2959 )

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Opticaltunable CdTe nanorods were synthesized in aqueous solution using thioglycoclic acid and L-cysteine as co-stabilizing reagents. CdTe nanorods with dualwavelength emission was appreciated as a novel fluorescent probe for copper ions. Copper ions display a significant quenching effect on the nanorods trap emission at 645nm and no effect on band-edge emission at 535nm. In a slight basic medium, the surface trap emission intensity of nanorods is proportional to the concentration of Cu²⁺ ion in the range from 0 to 2.8×10^-6mol/L, and the corresponding limit of detection is 4.0×10^-9mol/L. The mechanism of reaction between CdTe nanorods and Cu²⁺ ions are discussed in further.

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Growth of α-Al₂O₃∶C Crystal by Edge-Defined, Film-Fed Growth Technique

YANG Xin-Bo,LI Hong-Jun,BI Qun-Yu,CHENG Yan,SU Liang-Bi,TANG Qiang,XU Jun 　
2009 Vol. 24 (2): 255–258

Abstract( 2839 )

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α-Al₂O₃∶C crystal was grown by Edge-Defined, Film-Fed Growth Technique (EFG) in which graphite heating unit and shield acted as the carbon source and high purity Al₂O₃ was used as the raw material. Thermoluminescence (TL) and optically stimulated luminescence (OSL) properties of as-grown crystal after annealing in H₂ were investigated. The crystal shows a single one-order kinetic glow peak at 460K and blue emission band at 415nm. OSL decay curve of α-Al₂O₃∶C crystal shows exponential characteristic. The decay curve is made up of two components, i.e. the faster component and the slower component. The TL and OSL responses of α-Al₂O₃∶C crystal show linearsublinearsaturation characteristics. The TL exhibits good linear dose response in the dose range from 5×10^-6 to 0.2Gy and saturation is about 10Gy. The OSL exhibits good linear dose response in the dose range from 5×10^-6 to 10Gy and saturation is about 30Gy.

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Synthesis and Stability of Lead-hydroxyapatite

ZHOU Ji-Zhi,XU Xia,ZHANG Yi,QIAN Guang-Ren 　
2009 Vol. 24 (2): 259–263

Abstract( 3495 )

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Lead-hydroxyapatite was a new mineral phase of leadbearing phosphate formed from the stabilization of fly ash treated by phosphate. The control conditions of the formation of various new phosphates from reaction between PO₄^3- and lead ions (X_Pb) in terms of different molar ratios were studied. The products’ characteristics, thermal behaviors and chemical stability were also discussed. It is indicated that Ca₈Pb₂(PO₄)₆(OH)₂, Ca_5.5Pb_4.5(PO₄)₆(OH)₂, Ca_2.12Pb_2.22(PO₄)₃(OH)_0.67, Ca₂Pb₈(PO₄)₆(OH)₂and Pb₁₀(PO₄)₆(OH)₂ are synthesised respectively with the increase of X_Pb at the pH value of 10. And the products are changed from clavate polymer, granulated aggregate to massive aggregate. Furthermore, they can exist stably below 400℃. The lead leached via TCLP are decreased with the increase of the pH value of leaching solution. When the X_Pbis in the range from 0.1 to 0.7, the products perform good chemical stability. However, the stability is weakened when the X_Pb is above 0.7.

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Study on Preparation of n-HA and Silk Fibroin Bio-mineral Material

WANG Jiang,ZUO Yi,YANG Wei-Hu,ZHOU Gang,ZHANG Li,LI Yu-Bao 　
2009 Vol. 24 (2): 264–268

Abstract( 3580 )

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A new hydroxyapatite (n-HA)Silk fibroin (SF) bio-mineral material was prepared by using a biomimetic method, with Ca(NO₃)₂ and Na₃PO₄ used as the starting reagent to synthesize the inorganic phase. In details, SF was dissolved in Ca(NO₃)₂ solution without desalting procedure, the compound solution was directly dropped into Na₃PO₄ solution. In this way, HA was synthesized at 37℃ by controlling Ca/P ratio, meanwhile the minerialized HA interacted with SF to form biomineral material. The morphology and structure of this n-HA-SF biomineral material were characterized by XRD, FTIR, XPS and SEM. The results show that there are strong chemical interaction between n-HA and SF. Moreover, in the biomineral material, the inorganic phase is calciumdeficient hydroxyapatite, containing a small amount of carbonated HA with an average crystal size of 37.6nm. In addition, The particle size of biomineral materials range from 50nm to 200nm.It can be deduced that silk fibroin chain can regulate the growth and morphology of HA crystals. The compressive strength of the biomineral material is 32.21MPa， which is a good potential material for bone tissue engineering and unloadedbearing bone defects repairing.

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Research on Adsorption Capacity for Ni²⁺ and Mechanism of Nano-hydroxyapatite

ZHANG Jun,WANG De-Ping,YAO Ai-Hua,HUANG Wen-Hai 　
2009 Vol. 24 (2): 269–274

Abstract( 3002 )

PDF(2136KB)( 1929 )

Nano-hydroxyapatite was prepared by chemical precipitation with Ca(NO₃)₂ and (NH₃)₂HPO₄ as reagent. The phase composition, crystal morphology and specific surface area were characterized by XRD,TEM and BET. The results indicate that n-HA synthesized shows needlelike morphology with uniform average size of 31.9nm×21.3nm, week crystallinity, high surface energy, and the specific surface area of 135m²/g. Ni²⁺ is selected as adsorption object ion, the Langmuir adsorption isotherm is applicable when Ni²⁺ initial concentration is lower than 0.1mol/L, whereas when Ni²⁺ initial concentration is higher than 0.1mol/L, Ni²⁺ substitutes Ca²⁺ and binds with atom O on the surface. The adsorption of Ni²⁺ on nHA concludes ion exchange, electrostatic adsorption and dissolution-precipitation processes, This result is proved by the change on surface potential, crystal phase composition and binding energy of surface elements of n-HA before and after adsorption, which are analyzed by Zeta potential, XRD and XPS.

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Restoration of Tooth Enamel Caries by Hydrolysis of α-TCP

MA Ying,LI Si-Wei,FENG Zu-De 　
2009 Vol. 24 (2): 275–279

Abstract( 3156 )

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A novel method was developed to grow hydroxyapatite (HA) coatings on the surface of enamel. The coatings were formed by hydrolysis of α-TCP for 6h at 37℃. The detailed characterizations of the microstructure and mechanical properties of the coatings, and cytotoxicity of α-TCP hydrolysis solution were performed. SEM and TEM analysis show that the HA coatings, approximate 20μm in thickness grow perpendicularly to the enamel surface, contacting well to the surface of enamel. Vickers microhardness and wearresistance tests indicate that there is no statistical significant difference of the hardeness and wearresistance between the coatings and healthy natural enamel. The grade of cytotoxicity of α-TCP hydrolysis solution is I grade, satisfying the relevant criterion on biomaterials. The study suggests that the hydrolysis of α-TCP is a promising method to effectively and conveniently restore and prevent early enamel caries.

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Study on Porous Bioglass Scaffold Prepared by Dipping with Polymer Foams

XIE Lin,CHEN Xiao-Feng,ZHAO Na-Ru,GUO Chang-Liang 　
2009 Vol. 24 (2): 280–284

Abstract( 3461 )

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The porous bioglass scaffolds with high porosity and interconnectivity and controllable pore size were prepared by using the powder of sol-gel derived bioactive glass-58S as the material and the pre-produced polymer foam as the template. The apparent porosity, crystalline phases, micromorphologies and bioactivity were investigated by using Archimedes drainage method, X-ray Diffraction (XRD), Scan emission Microscope (SEM) and Fourier Transform Infrared Spectroscope (FTIR) techniques. The results show that the apparent porosity of the porous scaffolds can reach about 93% when the materials are dipped once, while the apparent porosity decreases to 80% after dipped twice. The originally formed amorphousphosphorus compounds on the surface of samples are mineralized to hydroxyl-carbonate-apatite (HCA) with increasing dipping time in the SBF solution as the reaction progressed. So it can be concluded that this kind of material has good biomineralization property and bioactivity in SBF solution at the constant temperature of 37℃.

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Synthesis of SiC Nanoparticles by Template Confined Method

ZHANG Yong,CHEN Zhi-Zhan,SHI Er-Wei,YAN Cheng-Feng,LIU Xue-Chao 　
2009 Vol. 24 (2): 285–290

Abstract( 3404 )

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A template confined method was selected to synthesize silicon carbide (SiC) nanoparticles (NPs), where ordered mesoporous silica molecular sieve SBA-15 was chosen as the template and sucrose as the carbon source. Experimental results show that the carbothermal reduction temperature and heating rate are the key parameters on synthesizing SiC NPs. Lower temperature, higher heating rate and shorter reaction time are beneficial to SiC NPs formation, whereas higher temperature, lower heating rate and longer reaction time lead to the formation of SiC nanowires. SiC NPs are obtained at carbothermal reduction temperature of 1400℃ and 75℃/min heating rate. The unique property of SiC NP provides new opportunities for the exploitation of SiC materials. It might substitute the traditional material to work in the rigorous environments.

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Microstructure Evolution and Reaction Mechanism of Microporous Carbon Derived SiC Ceramic

XU Shun-Jian,QIAO Guan-Jun,WANG Hong-Jie,LI Di-Chen,LU Tian-Jian 　
2009 Vol. 24 (2): 291–296

Abstract( 3049 )

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The process of reaction of silicon carbide ceramics derived from microporous carbon was investigated. The reaction mechanism was also analyzed. The ultimate microstructure of SiC ceramics are affected by the mass ratio of C to Si and infiltration time. Composite materials, which consist of SiC, Si and a small fraction of unreacted C, are obtained when the mass ratio of C to Si is higher whereas partial infiltration occurs when the mass ratio of C to Si is lower. Composite materials demonstrates many uniformly distributed stripshaped SiC grains in certain region at transitional stage of reaction, and shows irregular SiC grains and an obvious bimodal distribution of grain size at terminal stage of reaction. The process of siliconcarbon reaction can be described as follows, melted Si ascends via capillary of micropore carbon and reacts with contacted carbon forming SiC. Size difference of pore and carbon wall induces difference of the infiltration deep of melted Si within micropore carbon and thicknesses of the dissolved carbon layer, respectively. As a result, some carbon particles are embedded in SiC grain and pore channel system is restructured. New pore channel with bigger pore size are formed, which accelerates infiltration rate of melted Si. Then the unreacted carbons embedded in SiC grain are firstly diffuse through the SiC layer and dissolved in the Si melt, and then deposits on the first SiC formed. Finally, liquid epitaxial growth of SiC causes coalescence of SiC grains and envelopment of some Si in SiC grains, resulting in change of microstructure of SiC ceramics.

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Joining Strength and Microstructure of Sintered SiC/SiC Joints Prepared by Active Brazing Process

LIU Yan,HUANG Zheng-Ren,LIU Xue-Jian,CHEN Jian 　
2009 Vol. 24 (2): 297–300

Abstract( 3637 )

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Sintered SiC ceramics were brazed with itself by ternary Ag-Cu-Ti filler metal foil. Effects of brazing parameters such as temperature, holding time on joining strength, together with interface microstructure and reaction products were investigated. Experimental results indicate that joining strength has peak value with the increasing of brazing temperature and holding time, and the max fourpoint bending strength of SiC/SiC joints reaches 342MPa. The joining strength increases first with the increasing of brazing temperature and holding time due to thickening of the reaction layer, then decreases due to evaporation of the filler metal. A uniform compact reaction layer of about 1μm thickness is found at the interface between SiC and filler metal, which is formed by the reaction of active element Ti of filler metal and SiC substrate. TiC and Ti₅Si₃ are confirmed as the reactive products by XRD and EDX.

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Effect of Grinding Induced Damage on Bending Strength of RBSiC

YAO Wang,ZHANG Yu-Min,HAN Jie-Cai,ZHA Yan-Feng，ZHOU Yu-Feng,HAN Yuan-Yuan,QU Wei 　
2009 Vol. 24 (2): 301–304

Abstract( 2996 )

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The effect of surface residual stress and crack on bending strength of reaction bonded silicon carbide (RBSiC) after grinding was investigated. The residual stress of the ground surfaces were determined using X-ray diffraction.The sizes of strength controlling cracks were assessed using fracture mechanics approach. The investigations show that mechanical load, which has relation with grinding direction, phays a dominateve role in the grinding processes. and the measured residual stresses have a direction dependency. With increase of down feed from 0.9μm/s to 1.35μm/s, the bending strength is reasonably correlated with the surface residual stress and crack size.

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Research of Oxidation Resistance of Short Carbon Fiber Reinforced SiC Composite by Hotpressing

ANG Han-Ling,ZENG Xie-Rong,XIONG Xin-Bo,LI Long,ZOU Ji-Zhao 　
2009 Vol. 24 (2): 305–309

Abstract( 3011 )

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Short carbon fiber reinforced SiC (C_sf/SiC) composite was prepared by hotpressing method. XRD, SEM and isothermal oxidation test were used to study the isothermal oxidation property of C_sf/SiC composite. The results show that the oxidation weight loss of the composite is the most at 900℃. The weight loss decreases with the oxidation temperatures rising. Below 900℃, the oxidation weight loss of the composites is caused by the carbon fibers oxidation. Above 1450℃, the composites gain weight. Between 900-1450℃, short carbon fibers on the composite surface are oxidized and the SiC matrix forms a protecting film. The inner short carbon fibers still have the strengthen effect for the oxidation layer and matrix protecting them from oxidation, and the composites have good self-resistance oxidation property. When the composites oxide at 1600℃, the composite surface is destroyed badly and lose the resistance oxidation capacity.

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Preparation and Properties of C/SiO₂ Coaxial Fibers

SUN Liang-Kui,CHENG Hai-Feng,CHU Zeng-Yong,ZHOU Yong-Jiang,SUN Guo-Liang 　
2009 Vol. 24 (2): 310–314

Abstract( 2973 )

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PAN/SiO₂ coaxial fibers were prepared firstly by coaxial electrospinning using PAN as the core and SiO₂ sol as shell, and then C/SiO₂ coaxial fibers were obtained with an outer diameter of 1μm after oxidation and pyrolysis of the eletrospun fibers. The structure and cross-section morphologies of the C/SiO₂ coaxial fibers were investigated by FTIR, XRD and SEM. The results show that SiO₂ coating with thickness of about 20nm is successfully prepared on the carbon fibers. Radar absorbing properties of the C/SiO₂ coaxial fibers are studied by voter network analyzer. Compared with uncoated carbon fibers, both the real part and the imaginary part of their permittivity decrease when the fiber mass fraction is 20%. The reflectivity is simulated using RAMCAD software which shows that the 3mmthick composites has an absorbing bandwidth of 3.3GHz below -10dB in the frequency range of 2-18GHz, and the lowest reflectivity is -17dB at 12GHz. DTA-TG analysis also indicates an increase in oxidation resistance of the coaxial fibers.

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Effect of Pre-oxidation on the Pore Structure and Foaming Mechanisms
of Mesophase Pitch Based Carbon Foam

LI Juan,WANG Can, ZHAN Liang,ZHANG Rui,QIAO Wen-Ming,LING Li-Cheng 　
2009 Vol. 24 (2): 315–319

Abstract( 2874 )

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The effects of pre-oxidation for naphthalene mesophase pitch on the surface chemical properties, component distribution as well as the foaming conditions, pore structures and microstructures of carbon foam were investigated. After the given mesophase pitch is oxidized at 210℃ for 2h in air, the composition of quinoline insoluble increases by 32.3% and the component distribution tends to narrower. The average pore size and compressive strength of the resultant graphitized foam are about 200μm and 2.8MPa, respectively, under the foaming condition of 600℃/3MPa.

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Radar Absorbing Properties of Light Radar Absorbing Materials Based on Hollowporous Carbon Fibers

XIE Wei,CHENG Hai-Feng,CHU Zeng-Yong,CHEN Zhao-Hui,ZHOU Yong-Jiang 　
2009 Vol. 24 (2): 320–324

Abstract( 3767 )

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A kind of lightweight and wideband radar absorbing materials were prepared based on resistance matching principles and electromagnetic wave propagation laws. These materials consist of two-layers, one made of PAN-derived hollowporous carbon fibers contributing to the low density, and the other made of carbon blacks, short carbon fibers or carbonyl iron powders acting as the matching layer. Their radar absorbing properties investigated show that the introduction of the matching layer, as well as the properties of the matching layer, plays an important role in improving the absorbing properties of the materials. Carbonyl iron powders are more suitable for the matching layer than the other two as the radar absorbing properties concerned. Thus obtained material has a bandwidth of 11.42GHz under -8dB, and a bandwidth of 10.90GHz under -10dB in the range of 4-18GHz, provided that the thickness and the density are 2.90mm and 1.28g/cm³, respectively.

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Synthesis of MCM-48/ZSM-5 Composite Molecular Sieve by Two-step Crystallization

ZHOU Zhi-Hua,LU Jin-Ming,WU Shu-Feng,ZHOU Jing-Lin,WANG Jin-Qu 　
2009 Vol. 24 (2): 325–329

Abstract( 3809 )

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Composite micro/mesoporous MCM-48/ZSM-5 materials were successfully prepared by using a twostep synthesis route. The different structures of composite materials compared with the mechanical mixture were characterized by powder XRD，IR spectroscope，SEM，TEM，N₂ adsorption and the influence of the crystallization time was investigated. The results show that the composite MCM-48/ZSM-5 materials possess mesoporous wall constructed by secondary building units characteristic of ZSM-5 and threedimensional pore structure with pore size of about 2.6nm. The mesoporous framework of MCM-48/ZSM-5 is still found to be somewhat preserved after treatment in boiling water for 6h. It is proved that the selfassemble is a competitive process and the ratio of mesopore to micropore has a close relationship with crystallization time. The optimum crystallization time under 150℃ is 8h.

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Oriented ZSM-5 Zeolite Membranes on Biomorphic SiSiC Ceramics for Microreactors

LUO Min,WANG Zheng,WANG Yan,LIANG Jun,FANG Jun-Zhuo 　
2009 Vol. 24 (2): 330–334

Abstract( 3231 )

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Oriented ZSM-5 zeolite membranes on the biomorphic porous SiSiC ceramics were successfully synthesized by in situ hydrothermal synthesis. The ZSM-5/ SiSiC composite materials were characterized by XRD, SEM-EDX and BET. The effects of synthesis time and surface pre-treatment of the beech-derived SiSiC monolith were systematically studied. It shows that a homogeneous coverage within the pores channel of SiSiC monolith by b-oriented ZSM-5 crystals with 1μm average size is formed after hydrothermal treatment at 150℃ for 15h. The structure composites exhibit a hierarchical pore structure with a BET specific surface area of 42.8m²/g and microporous volume of 0.015cm³/g. The weight percent of ZSM-5 in the final zeolite/SiSiC composites is about 8.6% after coating.

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Hydrothermal Synthesis of Yttrium Hydroxide Nanotubes

TIAN Li,CHEN Wen-Chun,CHEN Lin,LIANG En-Xiang,ZHANG Xin 　
2009 Vol. 24 (2): 335–339

Abstract( 3473 )

PDF(2467KB)( 1937 )

Yttrium hydroxide nanotubes were synthesized by hydrothermal method using Y₂O₃ as raw materials. And then yttrium hydroxide nanotubes were characterized by X-ray diffraction （XRD）,scan electron microscope （SEM）, energy-dispersive X-ray spectroscope (EDS) and thermogravimetry-differential thermal analysis（TG-DTA）to investigate the phase, morphology, composition and heat stability of the products. Effects of reaction temperature and hydrothermal time on the formation of hydroxide yttrium nanotubes were studied. The results indicate that the optimal reaction conditions of hydroxide yttrium nanotubes are as follows: T=220℃, pH=11-12 and t=24h. The formation mechanism of hydroxide yttrium nanotubes is suggested to be twostep process，the initiative production of yttrium precursor and the successional achievement of hydroxide yttrium nanotubes.

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Synthesis and Microwave Absorption of the Silica-coated Fe Nanocomposites

WANG Deng-Ke,HUANG Hao,YU Kuai,ZHANG Xue-Feng,DONG Xing-Long 　
2009 Vol. 24 (2): 340–344

Abstract( 2687 )

PDF(1592KB)( 1896 )

Silica-coated Fe nanocomposites were prepared by the DC arc plasma in a mixed atmosphere of hydrogen (H2) and argon (Ar). The phase structure, composition and morphology of silica-coated Fe nanocomposites were examined by X-ray diffraction(XRD), transmission electron microscope(TEM) and electron energy dispersive spectroscope(EDS). The results show that the mean size of silica-coated Fe nanocomposites is about 50nm, and the amorphous silica which cover BCC-Fe cores form nanorods with the length of 150-200nm. The growth mechanism of silicacoated Fe nanocomposites is governed by an extended vaporliquidsolid mechanism and Fe nanoparticles acted as a catalyst for the growth of the nanorods. Its electromagnetic parameters are measured in the range from 2GHz to 18GHz. It is calculated that the maximum reflection loss of silica-coated Fe nanocomposites can reach -14.5dB at 15.4GHz with 1.79mm in thickness, and the bandwidth with a reflection loss less than -10dB is from 8-18GHz. The indepth study of relative complex permittivity and permeability reveals that the excellent microwave absorption properties are the consequence of a proper EM match in microstructure. And the loss mechanism is natural resonance, as the consequence of the increased surface anisotropic energy for nanosized particles.

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Preparation and Characterization of α-Ni(OH)₂/SiO₂ Submicrosphere
and α-Ni(OH)₂ Hollow Submicrosphere

LOU Zai-Liang,LI Qun-Yan,WANG Zhi-Hong,WEI Qi,NIE Zuo-Ren 　
2009 Vol. 24 (2): 345–348

Abstract( 2937 )

PDF(1709KB)( 1893 )

The nearly monodisperse SiO₂ submicrospheres with uniform size (270nm) were prepared by the hydrolysis of TEOS. Then the SiO₂ submicrospheres were coated with α-Ni(OH)₂ nanoflakes by a new solution growth method. The Ni(OH)₂ nanoflakes were synthesized by a solution process using hydrofluoric acid solution as nickel ion ligand to form nickel-fluoro complex, NH₃ aqueous solution as OH^- supplier and also supplemental nickel ion ligand. The coating thickness is increased with coating times. It is only 35nm for coating once. After coating three times, the coating thickness is increased to about 100nm. The α-Ni(OH)₂ hollow submicrospheres are obtained after subsequent removal of the core particles by NaOH solution(20wt％) at 40℃ for 24h. BET calculation shows that the surface area of the Ni(OH)₂ hollow spheres is 141.06m²/g.

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Synthesis and Performance of Cathode Material Li₃V₂(PO₄)₃/C by Spray Drying and Carbothermal Method （SDATM）

YU Feng,ZHANG Jing-Jie,YANG Yan-Feng,SONG Guang-Zhi 　
2009 Vol. 24 (2): 349–352

Abstract( 2955 )

PDF(1564KB)( 1863 )

Li-ion battery cathode material Li₃V₂(PO₄)₃/C composite was successfully prepared by spray drying and carbothermal method(SDCTM). The effect of spray drying was carefully studied. The structural, morphological and electrochemical properties were investigated by means of XRD, SEM, TEM and constant current chargedischarge cycling. The results indicate that the sample prepared with spray drying twice at 260℃ and subsequent heat-treating at 750℃ for 12h has better performance. Its average particle size is under 0.5μm.It presents large reversible discharge capacity of 121.9, 114.6 and 104.6mAh·g^-1 and excellent capacity retention rate closed to 100% after 50 cycles at C/5, 1C and 5C rate, respectively at the room temperature.

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Coprecipitation Synthesis and Oxide Ionic Conductivities of Ce_0.8Sm_0.2O_1.9-based Nanocomposite Materials

ZHANG Hong,ZHANG Zhe,MA Guo-Qiang,ZHANG Yu-Xing,LI Zhi-Cheng 　
2009 Vol. 24 (2): 353–356

Abstract( 2820 )

PDF(1235KB)( 1735 )

Ce_0.8Sm_0.2O_1.9-La_9.33Si₆O₂₆ nanocomposite materials were prepared by a two-step coprecipitation synthesis process. Phases and microstructure were investigated by X-ray diffraction and transmission electron microscope. Conductivities were measured by an A.C. impedance measurement system. The results show that the calcined nanocomposites have average grain size of 20nm and the sintered bulks have average grain size of 44nm. The oxideion conductivity of the nanocomposite material is 0.25Ω/cm at 700℃.The conductivities of the nanocomposites are 3 orders higher than that of pure La_9.33Si₆O₂₆ ceramics, which are also higher than that of Ce_0.8Sm_0.2O_1.9 conductor in the test temperatures range. The conducting mechanisms for the nanocomposite ionic conductors are discussed.

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Electrospun Manganese Oxides Nanofibers Electrode for Lithium Ion Batteries

SUN Ke,LU Hai-Wei,LI Da,ZENG Wei,LI Yue-Sheng,FU Zheng-Wen 　
2009 Vol. 24 (2): 357–360

Abstract( 3838 )

PDF(1639KB)( 2855 )

Manganese oxides nanofibers were successfully fabricated by an electrospinning method and its electrochemical behavior was investigated as three-dimensional (3D) architecture of cathodic materials. Scanning electron microscope, X-ray diffraction and the discharge/charge curves were used to characterize their structures and electrochemical properties. Manganese oxides nanofibers are achieved after calcination at 450℃. The high reversible discharge capacity reaches 160mAh/g and the discharge capacity is about 132.5mAh/g with capacity loss less than 1.0% per cycle in 50 cycling. SEM observations show that the structure of manganese oxides nanofibers is stable without the mechanical destruction of nanofibers during the Li⁺ ion intercalation and deintercalation. The results demonstrate that manganese oxides nanofibers are promising cathodic materials for 3D lithium batteries.

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Preparation and Electrochemical Characteristics of MgNi-TiNi_0.56M_0.44（M=Al,Fe）Alloys

LIU Su-Qin,CHEN Dong-Yang,HUANG Ke-Long,HUANG Hong-Xia 　
2009 Vol. 24 (2): 361–366

Abstract( 4545 )

PDF(2027KB)( 1833 )

MgNi and MgNi-TiNi_0.56M_0.44（M=Al,Fe）alloys were successfully synthesized by mechanical alloying (MA) approach. The structure and the electrochemical characteristics of these Mg-based electrodes were studied. The results of X-ray diffraction and scanning electron microscope show that the alloys have amorphous structures. The chargedischarge cycle tests indicate that the cycle performance of these alloys are better than those of MgNi alloys, although the first discharge capacities are lower than that of the MgNi alloys. Among these alloys, the discharge capacity of MgNi-TiNi_0.56Al_0.44 is the highest, up to 380.64mAh/g，and the capacity maintaining rate is 48.97％ after 50 cycles. Potentiodynamic polarization curves prove that anti-corrosion performance of the electrodes become better. Cyclic voltammetry (CV) and electrochemical impedance spectroscope (EIS) tests show that the introduction of the TiNi_0.56M_0.44（M=Al,Fe）alloys decrease the charge-transfer reaction resistance and the H atom diffusion impedance, and improve the electrode catalytic activity significantly.

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Magnetoelectric Effect in Laminate Composites Tb_1-xDy_xFe_2-y-BaTi_0.99Cr_0.01O_3-δ

GAO Jian-Sen，ZHANG Ning 　
2009 Vol. 24 (2): 367–370

Abstract( 2886 )

PDF(1258KB)( 1879 )

Chromiun doped BaTiO₃ was synthesized with sol-gel technique. The Cr-doped BaTiO₃ was still in the structure of tetragonal perovskite by X-ray diffraction, and its transformation point of ferroelectric to paraelectric as well as the latent heat of the transformation were observed a little less than those of pure BaTiO₃, respectively, by the tests of differential scanning calorimetry. Layered composites Tb_1-xDy_xFe_2-y and BaTi_1-zCr_zO_3-δ were fabricated by bonding the discs of the doped BaTiO₃ and rare earth alloy Tb_1-xDy_xFe_2-y. The magnetoelectric (ME) effect of the layered samples was investigated. The transverse ME voltage coefficient for the bilayer Tb_1-xDy_xFe_2-y-BaTi_1-zCr_zO_3-δ and the trilayer Tb_1-xDy_xFe_2-y-BaTi_1-zCr_zO_3-δ-Tb_1-xDy_xFe_2-y reach 732.5 and 2753mV/A, respectively, under a bias magnetic field 28kA/m at room temperature, which are about 54% and 56% larger than those for the bilayer and trilayer composed by pure BaTiO₃, respectively. Since Cr-doped BaTiO₃ does not contain injurants, such as lead and zirconium, it can replace lead zirconium titanite as a “green” piezoelectric material for ME composites.

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Influence of Zn-Al Codoping on Dielectric Properties of 0.95MgTiO₃-0.05CaTiO₃ Ceramics

YANG Xiu-Ling,DING Shi-Hua,SONG Tian-Xiu,ZHANG Dong 　
2009 Vol. 24 (2): 371–373

Abstract( 2720 )

PDF(1344KB)( 1783 )

The dielectric properties of (Mg_0.95Ca_0.05Zn_0.02)(Ti_1-xAl_x)O₃ ceramics prepared by conventional solid-state route were investigated. The results show that MgTiO₃ and CaTiO₃ are the main phases of 95MCT ceramics with codoped Zn-Al, without second phase MgTi₂O₅ is observed but a new phase CaAl₂O₄. Zn-Al additive can lower the sintering temperature of 95MCT ceramics to 1300℃, and improve the dielectric properties. Moreover, it also effectively adjusts the temperature coefficient of dielectric constant. The 95MCT ceramics with x=0.02 possess excellent dielectric properties: dielectric constant ε_r of 20.35, dielectric loss tgδ of 2.0×106 and temperature coefficient of dielectric constant α_c value of 1.78×106.

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Effects of NiobiumDoping on the Structure and Electrical Properties of (Ba,Bi,Na)TiO₃-based PTCR Ceramics

LI Yan-Yan,LI Guo-Rong,WANG Tian-Bao,ZHENG Liao-Ying,LENG Sen-Lin,YIN Qing-Rui 　
2009 Vol. 24 (2): 374–378

Abstract( 2841 )

PDF(1724KB)( 2089 )

(Ba, Bi, Na)TiO₃-based PTCR Ceramics (BBNMT) doped with Nb₂O₅ (0.1mol%, 0.3 mol%, 0.5mol%, 0.7mol%) were prepared by the solid state reaction method and annealing in the reduction atmosphere. The microstructures and electrical properties of BBNMT were investigated. The results show that with the increase of Nb₂O₅ contents, the grain size increases firstly and then decreases, which indicates that there exists an optimal content of Nb₂O₅. The low resistivity PTC ceramic materials are obtained when the content of Nb₂O₅ is 0.5mol% with the room temperature resistivity(ρ₂₅) of 1.06×10³Ω·cm, the Curie temperature (T_c) of 183℃, and the resistivity jump (ρ_max/ρ_min) of 1.0×10⁴. By analyzing the impedance spectroscopy, the influence of the grain phase, grain boundary phase and “shell phase” on the resistivity are discussed, the interaction mechanism of Nb₂O₅ donor in PTCR ceramics are also studied.

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Influence of Ta₂O₅ Addition on the Properties of MnZn Power Ferrites

LI Le-Zhong,LAN Zhong-Wen,YU Zhong,SUN Ke,LUO Ming,JI Hai-Ning 　
2009 Vol. 24 (2): 379–382

Abstract( 3289 )

PDF(1736KB)( 1916 )

MnZn ferrites with the chemical formula Mn_0.68Zn_0.25Fe_2.07O₄ were prepared by conventional ceramic techniques. The influence of Ta₂O₅ addition on the microstructure and magnetic properties of MnZn ferrites was investigated. When the Ta₂O₅ addition is less than 0.04wt%, the grain size increases with the increase of Ta₂O₅ concentration, the initial permeability, saturation magnetic flux density and DC resistivity increase, the power losses and porosity decrease. However, excessive Ta₂O₅ addition (>0.04wt%) results in the exaggerated grain growth and porosity increase which make the initial permeability, saturation magnetic flux density and DC resistivity decrease, and the power losses increase. When the Ta₂O₅ addition is 0.04wt%, the initial permeability, saturation magnetic flux density and DC resistivity reach the maximum, the power losses and porosity reach the minimum.

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Study on Phase Structure, Dielectric and Magnetic Properties of BST/YIG Composites

LI Xiang,YAN Biao,DONG Gang,ZHAO Shen-Qiang,LIANG Xiao-Wei 　
2009 Vol. 24 (2): 383–386

Abstract( 3186 )

PDF(1997KB)( 2483 )

A series of composites were synthesized by solidstate reaction, with ferroelectric powder of BST and ferromagnetic powder of YIG as raw materials. Dielectric and magnetic properties of ferroelectricferromagnetic composites were tested. The results show that the ferroelectric/ferromagnetic composites sintered at proper temperature consist of ferroelectric phase and ferromagnetic phase. The composite materials xBST-(1-x)YIG(x=0，0.1，0.2，0.3，0.4，0.5，0.6，0.7，0.8，0.9，1.0) exhibit excellent dielectric and magnetic properties. Both ε′ and ε″ increase with the increase of BST content, and the dielectric resonant frequency shifts to a higher frequency with YIG content increasing. The permeability rises with BST content decreasing. The resonance frequency and high frequency characteristics of YIG are improved by adding BST.

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Surface Structures and Dielectric Properties of Yttrium-doped Barium
Strontium Titanate Films by Improved Sol-Gel method

LIAO Jia-Xuan,WANG Hong-Quan,PAN Xiao-Feng,FU Xiang-Jun,ZHANG Jia,TIAN Zhong 　
2009 Vol. 24 (2): 387–391

Abstract( 2919 )

PDF(2641KB)( 1873 )

Normal Sol-Gel method was improved by adding polyvinyl pyrrolidone to sol and forming seed layer on Pt electrode. Undoped and Yttrium (Y)-doped Ba_0.6Sr_0.4TiO₃ (BST) films were prepared on Pt/Ti/SiO₂/Si by the improved Sol-Gel method. The surface structures and dielectric tunable properties of the as-prepared BST films were investigated. X-ray photoelectron spectrum (XPS) shows that Ba3d, Sr3d, Ti2p or O1s on the surfaces of BST films displays two or three chemical states, and these chemical states correspond to perovskited structure and non-perovskited structure. Y doping has significant effect on the chemical states of Ba3d, Sr3d and O1s except those of Ti2p, and makes the contents of Ba, Sr and O atoms in non-perovskited structure decrease from 41% to 26%, from 33% to 29% and from 51% to 40%, respectively, thus results in large decrease of nonperovskited structure. Meanwhile, scanning electron microscope (SEM) and atomic force microscope (AFM) demonstrate that Y-doped BST films show prominent improvement in morphologies with smooth and compact surface with no crack or shrinkage cavity. Such morphologies visibly decrease the adsorption of gases and hydrocarbon contaminations and their diffusion passes, which is the probable reason for nonperovskited structure to be formed. Also, voltagecapacitance curves obtained at 40V and 100kHz illustrate that Y-doped BST films exhibit improved dielectric tunable properties with tunability of more than 43%, dielectric loss of 0.0216 and merit factor value of 20. Additionally, the improved mechanism of Y doping is discussed.

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Effect of Deposition Temperature on Microstructures and Properties of MoSi₂
Coatings Prepared by Low Pressure Chemical Vapor Deposition

WU Heng,LI He-Jun,WANG Yong-Jie,FU Qian-Gang,HE Zi-Bo,WEI Jian-Feng 　
2009 Vol. 24 (2): 392–396

Abstract( 3113 )

PDF(2255KB)( 1707 )

MoSi₂ coatings were prepared on Mo substrates by low pressure chemical vapor deposition（LPCVD）using SiCl₄ and H₂ as source gases, in the temperature range from 1000℃ to 1300℃. Effect of deposition temperature on the microstructures, phase composition, deposition process, deposition rates, hardness and the bonding strength between coatings and Mo matrix were studied. It is indicated that the MoSi₂ coatings deposited in the temperature range from 1100℃ to 1200℃ are compact consisting of single MoSi₂ phase. The deposition rates, hardness and the bonding strength increase with the increase of temperature；however above 1200℃, cracks and Si phase appear in the coating, the deposition rates, hardness and the bonding strength decrease. The deposition process is mainly controlled by the reaction between Si and Mo below 1100℃, while above 1100℃ the diffusion of Si in MoSi₂ coatings becomes the controlling step.

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Corrosion Behavior of AlPO₄ as Environmental Barrier Coating in Water Vapor Enviroment

CHEN Xian-Hong,CHENG Lai-Fei,WANG Yi-Guang,ZHANG Li-Tong,HONG Zhi-Liang,WU Ya-Hui 　
2009 Vol. 24 (2): 397–401

Abstract( 2836 )

PDF(2191KB)( 1871 )

AlPO₄ was synthesized by a Sol-Gel method. Its coefficient of thermal expansion (CTE) was measured by dilatometer. Its corrosion behavior was tested in an environment of 50vol%H₂O/50vol%O₂ with a flow rate of 0.085cm/s at 1350℃. The phases and composition of the samples were analyzed by X-ray diffraction and Energy Dispersive Spectroscope. The microstructures of AlPO₄ were characterized by Scanning Electron Microscope. The results indicate that the CTE of AlPO₄ matches with that of C/SiC composites and its corrosion resistance is much better than that of SiC. However, the decomposition of AlPO₄ at high temperatures is the main problem in the water vapor enviroment， which will be accelerated in combination with silica.

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Corrosion Behavior of Layered Ternary Carbide Ti₂AlC in Acidic Solution

WANG Jing-Ping,MEI Bing-Chu,ZHOU Wei-Bing,WANG Ping,YANG Shu-Xia 　
2009 Vol. 24 (2): 402–406

Abstract( 2790 )

PDF(3968KB)( 1777 )

High-purity, fully dense Ti₂AlC samples were synthesized by hot pressing process. Their corrosion rate and corrosion type after immersed in concentrated and dilute HNO₃, HCl and H₂SO₄ were obtained. The corrosion potential, corrosion current and potentiodynamic polarization curves were measured by electrochemical methods. Corrosion process is pitting at first, then intergranular corrosion, while exfoliation at last. The corrosion rate increases with time. The corrosion rate reaches the biggest in concentrated HNO₃ while reaches the slowest in dilute HCl. The corrosion rate in the concentrated solution is faster than that in dilute solution, except in H₂SO₄.Electrochemical test shows the corrosion current reaches the biggest in the dilute H₂SO₄ and reaches the smallest in dilute HNO₃. Ti₂AlC shows passive behavior in all acid solution, and the passivation interval is the widest in dilute H₂SO₄.

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Structural Design of Symmetric Laminated Ceramic Nozzle and Study on it’s Erosion Behavior

YUN Dong-Ling,DENG Jian-Xin,DUAN Zhen-Xing 　
2009 Vol. 24 (2): 407–412

Abstract( 2884 )

PDF(2795KB)( 1637 )

Al₂O₃+(W,Ti)C/Al₂O₃+TiC symmetric laminated ceramic materials and nozzles were produced by hot pressing in order to reduce the tensile stress at the entry and the exit region of nozzles and improve their erosion wear resistance. The test results show that both hardness and toughness of laminated ceramic materials are improved than the simple materials. Under same erosion conditions, the laminated ceramic nozzles have superior erosion wear resistance to that of the common ceramic nozzle; the experimental value of optimal layer thickness ratio is 2. In addition, the residual thermal stress generated in the preparation of laminated ceramic materials is analyzed by finite element method (FEM). Relationship between stress distribution and layer thickness ratio is obtained. It is suggested that the residual thermal stress lead to grain refining mechanical properties strengthening, and improve the erosion wear resistance of laminated ceramic nozzles improving. The theoretical value of optimal layer thickness ratio is 2, the experimental results are consistent with the theoretical prediction.

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Study on Dispersion Behavior of ZnO-Al₂O₃ Powders Aqueous Suspension

SUN Yi-Hua,XIONG Wei-Hao,LI Cheng-Hui 　
2009 Vol. 24 (2): 413–416

Abstract( 3382 )

PDF(1299KB)( 1861 )

The stability and fluidity of ZnO-Al₂O₃ mixed powders suspension in aqueous solution adding with polyacrylic acid and polyethylene glycol were investigated. The Zeta potential of ZnO and Al₂O₃ were measured respectively in absence and presence of polyacrylic acid and polyethylene glycol. The influences of milling time, pH value, mass fraction of the additive and solid volume fraction on the stability and fluidity of ZnO-Al₂O₃ powders aqueous suspension were investigated by experiments of viscosity and sedimentation etc. It is noted that ZnO and Al₂O₃ powders have absolute value of zeta potential bigger than 45mV in pH value from 8 to 10.3 with adding polyacrylic acid. It is found that the suspension has the lowest viscosity and the best stability when the pH value is around 9 and the additive amount of polyacrylic acid is about 0.2wt%, in which the 55vol% solids content of slurry is obtained with the apparent viscosity less than 400mPa·s. The saturation absorption amount of polyacrylic acid for ZnO-Al₂O₃ mixed powders could be 0.2wt% in which the apparent viscosity is lower and the suspension stability is good in the pH range from 9 to 10.3. With the additive amount of polyethylene glycol increasing, the viscosity of suspension increase and the stability of suspension decease. The optimized milling time is 40h.