Comparative study of β-Si3N4 powders prepared by SHS sintered by spark plasma sintering and hot pressing

β-Si3N4 powders prepared by self-propagating high-temperature synthesis (SHS) with additions of Y2O3 and Al2O3 were sintered by spark plasma sintering (SPS). The densification, microstructure, and mechanical properties of Si3N4 ceramics prepared using this method were compared with those obtained by hot pressing process. Well densified Si3N4 ceramics with finer and homo- geneous microstructure and better mechanical properties were obtained in the case of the SPS technique at 200°C lower than that of hot pressing. The microhardness is 15.72 GPa, the bending strength is 716.46 MPa, and the fracture toughness is 7.03 MPa?m1/2.     

Influence of pH on the property of apatite-type lanthanum silicates prepared by sol-gel process

The apatite-type lanthanum silicates with formula La9.33Si6O26 are prepared by sol-gel process. The homogeneity of the sol affected by pH value of the solution is investigated. The viscosity of the sols slightly increases first and then increases abruptly because the predominant reaction mechanism changes from hydrolysis reaction to condensation reaction. In addition, the onset time of the increase for the viscosity shortens from pH 1 to pH 4. The gelation time decreases with increasing pH of the solution. Therefore, the pH of the sols should be less than 4 to form gel. The sol with initial pH 2 shows maximum value of zeta potential and maximum stability. For the sample with initial pH 2, pure apatite-type lanthanum silicates La9.33Si6O26 have been successfully prepared after the dried gel is calcined at 1 000 ℃. In addition, this sample sintered at 1 550 ℃ exhibits the highest ionic conductivity. The activation energies are all less than 0.90 eV.     

Preparation and sintering of nano Fe coated Si3N4 composite powders

Fe/Si₃N₄ composite powder was synthesized by the heterogeneous precipitation-thermal reduction process, and then pressed into flakes under a pressure of 10 MPa. Flakes were sintered by pressureless and hot-pressing at 1 600 °C under 0.1 MPa N₂. The chemical composition, phases and microstructure of composite powder and sintered flakes were investigated by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the structure of composite powders is Si₃N₄ coated by nano Fe. The crystal phases of sintered flakes by pressureless are Fe(Si) compound, SiC and Si₃N₄. The crystal phases of the sintered samples by hot-pressing are Fe, Fe(Si) compound and Si₃N₄. It is found that crystal phases flakes obtained by pressureless and hot-pressing are very different. Foundation item: Project(50804016) supported by the National Natural Science Foundation of China     

Properties of plasma sprayed NiCrAlY+(ZrO2+Y2O3) coating on refractory steel surface

NiCrAlY+(ZrO₂+Y₂O₃) thermal barrier coating was prepared on the surface of refractory steel 1Cr18Ni9Ti with plasma spraying technique. The phases and microstructure of the thermal barrier coating were determined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the bonding between thermal barrier coating and substrate is sound. The surface hardness of 1Cr18Ni9Ti reaches up to 1 000 HV, but that of substrate is only 300 HV. The patterns sprayed with CoNiCrAlY+(ZrO₂+Y₂O₃) ceramic coating have a good heat insulation effect at 800 °C for heat insulation temperature difference reaches 54 °C, which increases the operating temperature and service life of refractory steel. Foundation item: Project (5040202140) supported by Scientific Research Common Program of Beijing Municipal Commission of Education     

Solid Solution Characteristics of Pb（B1/3Nb2/3）O3-bascd Composite Ceramics

The solid solution characteristics of Pb（B1/3Nb2/3）O3-based （B=Zn^2＋, Mg^2＋, Ni^2＋） composite ceramics prepared by two-phase mixed-sintering method were developed based on dielectric measurements. Results show that there are double dielectric peaks for PZN-based composite ceramic, implying two phases coexist. However single dielectric peak was presented in PMN- and PNN-based composite ceramics, respectively. It is indicated that obvious solid solution reaction exists during the sintering process of these two systems. The effects of B-site ion difference on the solid solution characteristics were discussed by crystal chemistry. SEM was employed to investigated the microstructures of composite ceramics. The influences of solid solution reaction on grain growth were discussed.     

Microstructures and characteristics of deep trap levels in ZnO varistors doped with Y2O3

In this paper discussions on ZnO based varistor ceramics doped with different ratios of Y₂O₃ are presented. Analysis on the phase and microstructures of the samples indicates that an additional phase is detected in the samples doped with Y₂O₃, and the average grain size of the specimens decreases from about 9.2 μm to 4.5 μm, with an increase in the addition of Y₂O₃ from 0 mol% to 3 mol%. The corresponding varistor’s voltage gradient markedly increases from 462 V/mm to 2340 V/mm, while the nonlinear coefficient decreases from 22.3 to 11.5, respectively. Furthermore, the characteristics of deep trap levels in these ZnO samples are investigated by measuring their dielectric spectroscopies. The trap energy level and capture cross section evaluated by relaxation peak of the Cole-Cole plot vary slightly as the addition of Y₂O₃ increases. These traps may be ascribed to the intrinsic defects of ZnO lattice.     

Mn_2O_3/PANI的制备及其防腐性能研究

采用溶剂热法制备Mn_2O_3微球,与化学氧化法制备的聚苯胺按不同比例混合,制得Mn_2O_3/PANI,将其涂覆于Q235碳钢表面制备复合涂层.采用扫描电镜(SEM)、原子力显微镜(AFM)、X射线衍射(XRD)和红外光谱(FTIR)表征Mn_2O_3/PANI的表面形貌和结构,利用动电位极化和电化学阻抗谱研究复合涂层的耐蚀性能.结果表明,当Mn_2O_3在复合材料中的质量分数为10%时,防腐性能最优.在3.5%NaCl溶液中浸泡7天后,相较于Q235裸钢,其自腐蚀电位正移约380 mV,自腐蚀电流密度降低约3个数量级;浸泡37天后,其仍有良好的稳定性和耐蚀性.     

Effect of catalyst on structure of （PEO）8LiClO4-SiO2 composite polymer electrolyte films

（PEO）8LiClO4-SiO2 composite polymer electrolytes（CPEs） were prepared by in-situ reaction, in which ethyl-orthosilicate （TEOS） was catalyzed by HCl and NH3·H2O, respectively. The ionic conductivity, the contact angle and the morphology of inorganic particles in the CPEs were investigated by AC impedance spectra, contact angle method and TEM. The conductivities of acid-catalyzed CPE and alkali-catalyzed CPE are 2.2×10^-5 and 1.1×10^-5 S/cm respectively at 30 ℃. The results imply that the catalyst plays an important role in the structure of in-situ preparation of SiO2, and influences the surface energy and conductivity of CPE films directly. Meanwhile, the ionic conductivity is related to the surface energy.     

Thermoelectric properties of Ca3Co4O9 ceramics

Ca₃Co₄O₉ ceramics were prepared using the sol-gel process with ordinary pressing sintering and their thermoelectric properties were measured from room temperature to 673 K. The experimental results show that single phase Ca₃Co₄O₉ can be fabricated at 750–900 °C in different citrate acid molar proportions for 0.2–1.0. For all the oxides, both the Seebeck coefficients S and the electrical conductivities κ increase with the increasing temperature. The Seebeck coefficients S are all positive. The thermal conductivities k increase with the increasing temperature also and the lattice thermal conductivity κ _l plays an important role to the thermal conductivity κ. The citrate acid molar proportions have a large influence on the particle sizes, which influences the thermoelectric properties of the ceramics. The figure of merit increases with the increasing temperature and reaches 4.5×10⁻⁵ K⁻¹ at 573 K for the sample in the citrate acid molar proportion of 0.46.     

BaZr0.9Y0.1O2.95/Na2SO4 composite with enhanced protonic conductivity

Heterogeneous composite BaZr_0.1Y_0.9O_2.95/Na₂SO₄ was designed and fabricated with Y-doped BaZrO₃ as matrix and Na₂SO₄ as dispersant by conventional powder processing to improve the total conductivity of barium zirconate. The electrical conduction of the composite was studied by electrical and electrochemical methods. Microstructure of the heterogeneous composite was examined by SEM. The experimewtal results show that the protonic conductivity of Y-doped BaZrO₃ is greatly improved upon incorporating Na₂SO₄ in the material. Microstructure observation indicates that a multiphase structure with Na₂SO₄ disperses at the grain boundaries of BaZr_0.1Y_0.9O_2.95. Electromotive force (EMF) measurements under fuel cell conditions reveal that the total ionic transport number of the composite is more than 0.9 at 750 °C. Funded by the National natural Science Foundation of China(No. 50872090)     

Manufacture Process of 8Y2O3 Stabilized ZrO2 from Nano Powders

The manufacture process of 8 mol% Y2O3 stabilized ZrO2 ( YSZ ) from nano powders, including the forming and sintering stages, was studied. During the forming process of YSZ powders, the relative density of YSZ increases lineally with the forming press, and the sintering linear shrinkage of YSZ to the forming press compiles to the parabola trend. When the forming press exceeding 500MPa, the samples with lower shrinkage and high density were obtained. The sintering temperature of YSZ decreases greatly because of the small size and high active surface of YSZ powders. As a result, the beginning sintering temperature of YSZ made in the experiment is as low as 825℃, and the end sintering temperature is 1300-1350℃ . The relative density of YSZ ceramic by solid sintering at 1300-1350℃ is more than 97% , with little and small pores in the uniform microstructure.     

球形LiMn1.5Ni0.5O4材料的嵌脱动力学

为明晰Li Mn1.5Ni0.5O4正极材料的动力学性能,采用水热辅助共沉淀法合成了尖晶石Li Mn1.5Ni0.5O4正极材料,并采用扫描电镜(SEM)、X射线粉末衍射(XRD)和电化学阻抗(EIS)研究了材料的结构和锂离子嵌脱动力学.实验结果表明:共沉淀法制备的Li Ni0.5Mn1.5O4材料颗粒呈均匀球形,且平均粒径较小,粒度分布较窄.在循环过程中,Li Ni0.5Mn1.5O4的电荷转移电阻增大,锂离子扩散系数减小,进而电子电导率和离子电导率下降.温度升高后,Li Ni0.5Mn1.5O4材料的溶液电阻变化不大,但是电荷转移电阻逐渐增大,锂离子扩散系数逐渐减小;此外,随着温度的升高,Li Ni0.5Mn1.5O4材料的溶解速度加快,从而导致SEI膜的厚度增大.Li Ni0.5Mn1.5O4材料的嵌脱锂动力学与温度和循环次数有密切关系.     

Morphology and conductivity of in-situ PEO-LiClO4-TiO2 composite polymer electrolyte

PEO-LiClO4-TiO2 composite polymer electrolyte films were prepared. TiO2 was formed directly in matrix by hydrolysis and condensation reaction of tetrabutyl titanate. The crystallinity, morphology and ionic conductivity of composite polymer electrolyte films were examined by differential scanning calorimetry, scanning electron microscopy, atom force microscopy and alternating current impedance spectroscopy, respectively. The glass transition temperature and the crystallinity of composite polymer electrolytes are decreased compared with those of PEO-LiClO4 polymer electrolyte film. The results show that TiO2 particles are uniformly dispersed in PEO-LiClO4-5%TiO2 composite polymer electrolyte film. The maximal conductivity of 5.5×10^-5 S/cm at 20℃ of PEO-LiClO4-TiO2 film is obtained at 5% mass fraction of TiO2.     

Effect of nano-ZrO2 on microstructure and thermal shock behaviour of Al2O3/SiC composite ceramics used in solar thermal power

The Al2O3-ZrO2(3Y)-SiC composite ceramics used in solar thermal power were prepared by micrometric Al2O3,nano-ZrO2 and SiC powders under the condition of pressureless sintering.The bulk density and bending strength of samples with 10vol% nano-ZrO2 sintered at 1480℃ were 3.222 g/cm3 and 160.4MPa,respectively.The bending strength of samples after 7 times thermal shock tests (quenching from 1000℃ to 25℃ in air medium) is 132.0MPa,loss rate of bending strength is only 17%.The effect of nano-ZrO2 content on the microstructure and performance of Al2O3-ZrO2(3Y)-SiC composite ceramic was investigated.The experimental results show that the bending strength of samples with above 10vol% nano-ZrO2 content has decreased,because the volume expansion resulting from t-ZrO2 to m-ZrO2 phase transformation is excessive;Adding proper nano-ZrO2 would be contributed to improve the thermal shock resistance of the composite ceramics.The Al2O3-ZrO2(3Y)-SiC composite ceramic has promising potential application in solar thermal power.     

Electrical conductivity of Cu/（10NiO-NiFe2O4） cermet inert anode for aluminum electrolysis

Cu/(10NiO-NiFe2O4) cermets containing mass fractions of Cu of 5%, 10%, 15% and 20% were prepared, and their electrical conductivities were measured at different temperatures. The effects of temperature and content of metal Cu on the electrical conductivity were investigated especially. The results indicate that the metallic phase Cu distributes evenly in 10NiO-NiFe2O4 ceramic matrix. The mechanism of electrical conductivity of Cu/(10NiO-NiFe2O4) cermets obeys the rule of electrical mechanism of semiconductor, the electrical conductivity for cermet containing 5% Cu increases from 2.70 to 20.41 S/cm with temperature increasing from 200 to 900 ℃. The change trend of electrical conductivity with temperature is similar with each other and it increases with increasing temperature and content of metal Cu. At 960 ℃, the electrical conductivity of cermet increases from 2.88 to 82.65 S/cm with the content of metal Cu increasing from 0 to 20%.     

Phase Evolution and Oxidation Resistance of YSZ/(Ni,Al) Composite Coatings in CH<Subscript>4</Subscript> Atmosphere

YSZ/(Ni, Al) composite coatings with different Ni:Al mole ratios were deposited on superalloy Inconel 600 by electrophoretic deposition (EPD) technique, followed by sintering in CH₄ atmosphere at 1 100 °C for 2 h and isothermally oxidation at 1000 °C for 50 h. After sintering at 1100 °C for 2 h in CH₄ atmosphere, besides ZrC and t-ZrO₂ phases, the phase constitutes of Ni:Al mole ratios with 1:3, 1:2, and 1:1 were (Zr, Al)C, AlNi₃ and Ni phases, respectively. A remarkable difference in the oxidation behaviors of YSZ/(Ni, Al) composite coatings with different Ni:Al mole ratios was observed. For YSZ(Ni:Al=1:3) coated sample, oxidation at 1000 °C causes decomposition of the (Zr,Al)C solid solution to metallic Al, and then most of the Al is oxidized to Al₂O₃. For the YSZ(Ni:Al=1:2) coated sample, oxidation at 1000 °C mainly causes decomposition of the AlNi₃ phase. For YSZ(Ni:Al=1:1) coated sample, after oxidation at 1000 °C, most of the Ni is oxidized to NiO phase, and tolerated 50 h of oxidation and finally cracked and spalled from the specimen. YSZ(Ni:Al=1:3) and YSZ(Ni:Al=1:2) coated samples show superior oxidation resistance than that of YSZ coating. The different oxidation resistance mechanisms of YSZ/(Ni, Al) composite coatings sintered in CH₄ atmosphere were discussed.     

Effects of carbon sources on electrochemical performance of Li4Ti5O12/C composite anode materials

Li₄Ti₅O₁₂/C composite materials were synthesized by two-step solid state reaction method with glucose, sucrose, and starch as carbon sources, respectively. The effects of carbon sources on the structure, morphology, and electrochemical performance of Li₄Ti₅O₁₂/C composite materials were investigated by SEM, XRD and electrochemical tests. The results indicate that carbon sources have almost no effect on the structure of Li₄Ti₅O₁₂/C composite materials. The initial discharge capacities of the Li₄Ti₅O₁₂/C composite materials are slightly lower than those of as-synthesized Li₄Ti₅O₁₂. However, Li₄Ti₅O₁₂/C composite materials show better electrochemical rate performance than the as-synthesized Li₄Ti₅O₁₂. The capacity retention (79%) of the Li₄Ti₅O₁₂/C composite materials with starch as carbon source, is higher than that of Li₄Ti₅O₁₂/C composite materials with glucose and sucrose as carbon source at current rate of 2.0C.     

Low-temperature sintering and microwave dielectric properties of Li2MgTi3O8 ceramics doped with BaCu（B2O5）

The influences of BaCu(B₂O₅) (BCB) addition on sintering, microstructure and microwave dielectric properties of Li₂MgTi₃O₈ ceramics were investigated using X-ray diffractometry, scanning electron microscopy and microwave dielectric measurements. The experimental results show that a small amount of BaCu(B₂O₅) addition can effectively reduce the sintering temperature to 900 °C, and induce only a limited degradation of the microwave dielectric properties. Typically, the best microwave dielectric properties of ɛ _r=24.5, Q×f =24 622 GHz, τ _f=4.2×10⁻⁶ °C⁻¹ are obtained for 1.0% BCB-doped Li₂MgTi₃O₈ ceramics sintered at 900 °C for 3 h. The BCB-doped Li₂MgTi₃O₈ ceramics can be compatible with Ag electrode, which may be a strong candidate for low temperature co-fired ceramics applications.     

Dielectric properties and electrical conductivity of CaCu3Ti4O12 ceramics doped with Zr4+

CaCu₃Ti₄O₁₂ (CCTO) ceramics doped with Zr⁴⁺ were prepared. Effects of Zr⁴⁺ on microstructure, dielectric properties and conduction behavior of CaCu₃Ti_4?x Zr _x O₁₂ (x=0, 0.05, 0.10, 0.20) ceramics were studied in the frequency range of 10–10⁶ Hz. Grain size and dielectric loss of Zr⁴⁺-doped CCTO ceramic decreased compared with pure CCTO. The loss tangent (tanδ) of CaCu₃Ti_4?x Zr _x O₁₂ (x=0.20) ceramic droped to 0.05 at a frequency of 1 kHz, which was reduced by 55% compared with pure CCTO ceramic. The mechanism effect of electrical conductivity on dielectric loss of Zr⁴⁺-doping CCTO ceramics was also discussed.     

Preparation and anti-oxidation mechanism of mullite/yttrium silicate coatings on C/SiC composites

In order to enhance the oxidation resistance of C/Si C composites, mullite/yttrium silicate coatings were fabricated on C/Si C composites through dip-coating route. Al_2O_3-SiO_2 sol with high solid content was selected as the raw material for mullite and "silicone resin + Y_2O_3 powder" slurry was used to synthesize yttrium silicate. The microstructure and phase composition of coatings were characterized, and the investigation on oxidation resistance and anti-oxidation mechanism was emphasized. The as-fabricated coatings consisting of SiO_2-rich mullite phase and Y_2Si_2O_7 phase show high density and favorable bonding to C/Si C composites. After oxidized at 1 400 ℃ and 1 500 ℃ for 30 min in static air, the coating-containing C/Si C composites possess 91.9% and 102.4% of the original flexural strength, respectively. The desirable thermal stability of coatings and the further densification of coatings due to viscous flow of rich SiO_2 and Y-Si-Al-O glass are responsible for the excellent oxidation resistance. In addition, the coating-containing composites retain 99.0% of the original flexural strength and the coatings exhibit no cracking and desquamation after 12 times of thermal shock from 1 400 ℃ to room temperature, which are ascribed to the combination of anti-oxidation mechanism and preferable physical and chemical compatibility among C/Si C composites, mullite and Y_2Si_2O_7. The carbothermal reaction at 1 600 ℃ between free carbon in C/Si C substrate and rich SiO_2 in mullite results in severe frothing and desquamation of coatings and obvious degradation in oxidation resistance.