原位合成Si3N4／BN纤维独石陶瓷高温强度的研究

本实验对原位合成的Si3N4/BN纤维独石高温强度的力学性能进行了研究,实验结果表明：Si3N4/BN纤维独石陶瓷具有优异的高温力学性能。单轴排布的纤维独石陶瓷随温度的升高,直至1000℃,抗弯强度基本没有下降。到1200℃,强度还保持在600MPa以上,为室温强度的85％,实验通过扫描电镜SEM观察了材料的显微以及断口形貌,并对此材料具有优异的高温抗弯强度的机理进行了探索。     

不同结构的Si_3N_4/BN纤维独石陶瓷的力学性能

通过实验对两种不同结构在不同温度下的Si3N4/BN纤维独石陶瓷力学性能进行了研究。实验结果表明 :单轴排布的纤维独石陶瓷具有明显的各向异性。 0 0 /90 0 /0 0 排布的纤维独石陶瓷宏观上各向异性不明显。单轴排布的纤维独石陶瓷随温度的升高 ,强度下降幅度较小 ,具有优异的高温力学性能。而按 0 0 /90 0 /0 0 排布的纤维独石陶瓷随温度的升高 ,表现为层状结构特征 ,容易开裂。实验通过扫描电镜SEM观察了材料的显微结构以及断口形貌 ,并探索了结构对性能影响的机理。     

不同结构的Si3N4／BN纤维独石陶瓷的力学性能

通过实验对两种不同结构在不同温度下的Si3N4/BN纤维独石陶瓷力学性能进行了研究。实验结果表明：单轴排布的纤维独石陶瓷具有明显的各向异性,0^0/90^0/0^0排布的纤维独石陶瓷宏观上各向异性不明显,单轴排布的纤维独石陶瓷随温度的升高,强度下降幅度较小,具有优异的高温力学性能,而按0^0/90^0/0^0排布的纤维独石陶瓷随温度的升高,表现为层状结构特征,容易开裂,实验通过扫描电镜SEM观察了材料的显微结构以及断口形貌,并探索了结构对性能影响的机理。     

烧结助剂含量对多孔Si3N4/BN复合陶瓷力学性能和介电性能的影响

以Si3N4和BN为原料,叔丁醇为溶剂,SiO2、Y2O3和Al2O3为烧结助剂,采用凝胶注模成型工艺制备具有高强度、低介电常数多孔Si3N4/BN复合陶瓷。研究了Y2O3和Al2O3含量对多孔陶瓷气孔率、孔径分布、物相组成、显微结构、抗弯强度和介电常数的影响。结果表明:通过调节Y2O3和Al2O3含量,多孔Si3N4/BN复合陶瓷的气孔率由55%增加到68%,气孔尺寸呈单峰分布,平均孔径为0.89～1.02μm;抗弯强度和相对介电常数随Y2O3和Al2O3含量的增加而单调增大,抗弯强度和相对介电常数的变化范围分别为29.9～60.9 MPa和2.30～2.85;通过调节Y2O3和Al2O3含量调控气孔率,能够获得介电性能和力学性能可调的高性能透波材料。     

氟化钙对常压烧结Si3N4/BN复相陶瓷结构与性能的影响

以微米级Si3N4和h-BN粉末为原料,CaF2–Al2O3–Y2O3为烧结助剂,采用常压烧结工艺制备了BN体积含量为25%的Si3N4/BN复相陶瓷。研究了CaF2添加量对Si3N4/BN复相陶瓷材料力学性能的影响,并通过X射线衍射和场发射扫描电镜分析了复相陶瓷的物相组成和显微组织。结果表明：随着CaF2添加量增加,制备的Si3N4/BN复相陶瓷材料气孔率逐渐增大,收缩率变小,相对密度减小。添加量为2%（质量分数）时,Si3N4/BN复相陶瓷的室温抗弯强度达145.5MPa。添加适量的CaF2可在Si3N4/BN复相陶瓷材料常压烧结过程中较大程度地破坏h-BN的卡片房式结构,将微米级的h-BN颗粒变成纳米级颗粒。     

稀土氧化物对Si3N4陶瓷力学性能和显微组织的影响

采用常压烧结工艺制备了Si3N4-Y2O3-La2O3陶瓷,并对Si3N4陶瓷的力学性能、相组成和显微组织进行了分析和讨论。结果表明:添加4%Y2O3～4%La2O3的复合稀土氧化物后,Si3N4陶瓷呈长柱状的β-Si3N4晶粒,抗弯强度为960MPa,断裂韧性为7.5MPa.m1/2,具有较好的力学性能。     

BN纤维织物增强陶瓷透波材料的制备及其力学性能初探

以全氢聚硅氮烷(PHPS)为先驱体,采用聚合物浸渍裂解工艺制备BN纤维织物增强陶瓷透波材料,研究了复合材料的致密化工艺和力学性能。结果表明:先驱体PHPS在1637℃裂解产物主晶相为α-Si3N4。以PIP工艺制备BNf/Si3N4复合材料,经过4个浸渍裂解周期密度达到1·5g/cm3,复合材料的室温弯曲强度达到39·6MPa。裂解过程中,PHPS与BN纤维发生了强界面反应,导致复合材料力学性能不高。     

国内外信息

含SiC片晶的Si3N4复合陶瓷的显微组织与力学性能哈尔滨工业大学的WeiTao等人，用热压法制成St。N。HIC复合陶瓷，并研究了其显微组织和力学性能。结果表明，在S江含量低于20V01％时，随着S记片晶含量的增加，维氏硬度、弹性模量和断裂韧性提高，而室温时，抗弯强度略有下降。高温时（ifs℃、125o℃和1350℃）测试抗弯强度，发现高温范围内，抗弯强度仍然随温度升高而下降，当S记片晶含量为10V01％时，这种下降趋势较平缓；试验结果还表明，加入SIC片晶对提高高温强度有益处。他们还研究了S记片晶的增韧作用。多层St。N。／BN陶瓷…     

氧化锆纤维对氮化物复合材料性能的影响

在Si3N4、BN陶瓷中加入涂层处理后的ZrO2纤维对其进行复合,研究ZrO2纤维对氮化物复合材料部分性能的影响.结果表明:ZrO2纤维的引入能降低材料的抗弯强度,但是加入适量的ZrO2纤维后材料的热学性能可得到较大的改善.     

反应烧结制备轻质高强Si3N4/SiC材料

采用反应烧结制备轻质高强Si3N4/SiC材料.分析了烧成制度对氮化合成Si3N4结合相的影响,研究了Si3N4结合相、SiC骨料粒径大小以及级配对试样性能的影响.通过X射线衍射仪、扫描电子显微镜、Archimedes排水法以及万能试验机分别表征材料的物相组成、微观结构、体积密度和力学性能.实验结果表明:坯料中添加大粒径SiC(D50=150μm)会增加试样的体积密度,降低试样的抗弯强度;试样中加入大粒径SiC会减少氮化增重,阻碍氮化反应;试样分别在1350℃/1450℃保温2h,生成α-Si3N4和β-Si3N4的量基本相等,性能最佳,抗弯强度达到125MPa,(弯曲)比强度达到5.4×104N·m/kg.     

Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3–BaTiO3–SrTiO3陶瓷的准同型相界与电性能

采用固相法制备了 Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3–BaTiO3–SrTiO3（NBT–KBT–BT–ST）陶瓷,该体系是按（1–2x）（0.8NBT–0.2KBT）–x（0.94NBT–0.06BT）–x（0.74NBT–0.26ST） （x = 0.10、0.20、0.25、0.30、0.35、0.40、0.45）组合而成的,研究了该系陶瓷的结构与电性能。结果表明：所有样品都处于三方–四方准同型相界区域。该系陶瓷在准同型相界附近表现出了优异的压电性能,压电常数 d33、机电耦合系数 kp和剩余极化强度 Pr随 x 的增加先升高后降低,其中 x=0.35 陶瓷的电性能最佳：d33= 210 pC/N,kp= 0.319,Pr= 39.3 μC/cm2,Ec= 20.2 kV/cm,是一种良好的无铅压电陶瓷候选材料。依据准同型相界组成的线性组合规律来寻找具有优异压电性能的 NBT–KBT–BT–ST 陶瓷准同型相界组成是可行的。     

Graphite trifluoromethylsulfate C12+SO3CF3−

Graphite trifluoromethylsulfate C₁₂SO₃CF₃, a new binary graphite salt is formed by the irreversible solvolysis of C₈SO₃F in a large excess of trifluoromethylsulfuric acid. The salt is identified as a stage one intercalation compound with a C₀ value of 8.12 Å and characterised by microanalysis, epr and ¹⁹F NMR spectroscopy. Both Raman spectra, in the back scattering configuration, and IR spectra, in transmission as well as reflection geometries, are used to support an ionic formulation as C₁₂⁺SO₃CF₃^?.     

Composite cathodes of La0.9Ca0.1Ni0.5Co0.5O3-Ce0.8Sm0.2O1.9 for solid oxide fuel cells

The mixed ionic and electronic conductors of La_0.9Ca_0.1Ni_0.5Co_0.5O₃-Ce_0.8Sm_0.2O_1.9 (LCNC-SDC) are investigated systematically for potential application as a cathode for solid oxide fuel cells based on a Ce_0.8Sm_0.2O_1.9 (SDC) electrolyte. The electrochemical impedance spectroscopy (EIS) measurements are performed in air over the temperature range of 600-850 °C to determine the cathode polarization resistance. The exchange current densities for oxygen reduction reaction (ORR), determined from the low-field cyclic voltammetry, high-field cyclic voltammetry, and EIS data are systematically investigated. The activation energies (E_a) for ORR determined from the slope of Arrhenius plots are in the range of 102.33-150.73 kJ mol⁻¹ for LCNC-SDC composite cathodes. The experimental results found that LCNC-SDC (70:30) composite cathode has a maximum exchange current density and a minimum polarization resistance of 0.30 Ω cm² for 850 °C among LCNC-SDC composite cathodes.     

Dielectric relaxation and resistive switching of Bi0.96Sr0.04Fe0.98Co0.02O3/CoFe2O4 thin films with different thicknesses of the Bi0.96Sr0.04Fe0.98Co0.02O3 layer

Bi_0.96Sr_0.04Fe_0.98Co_0.02O₃/CoFe₂O₄(BSFCO/CFO) bilayered thin films with different thicknesses of the BSFCO layer are synthesized on FTO/glass substrates by chemical solution deposition method (CSD). The influence of BSFCO thickness on the microstructure, dielectric relaxation, ferroelectric properties and resistive switching (RS) of the thin films are researched. Strain exists in the prepared thin films and gives rise to structural distortion, which has an effect on charged defects and ferroelectric polarization. Dielectric relaxation that is closely related to the interfacial polarization at the BSFCO/CFO interface is observed, and the dielectric loss peaks along with decreasing intensity shift to high frequency with decreasing strain. The Maxwell-Wagner two-layer model is adopted to investigate the mechanism of dielectric relaxation, and the relaxation time τ is calculated and it shown to be directly proportional to the strain. It is found that the dielectric properties, including low dielectric loss, can be improved by controlling the BSFCO layer thickness. The ferroelectric properties improve with the decreasing strain, the 12-BSFCO/CFO thin film possesses a large P_r ~ 102.9?μC/cm² at 660?kV/cm. The observed resistive switching (RS) behavior is attributed to the interfacial conduction mechanism, it is found that strain-dependent the ferroelectric polarization switching modulates the width of depletion layer and the height of potential barrier at the interface, resulting in the different resistance states.     

High piezoelectric coefficient of Pr2O3-doped Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics

Pr₂O₃-doped Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ (BCTZ-xPr) ceramics were prepared by the conventional solid-state method. A tetragonal phase is only observed in these ceramics, and the introduction of Pr₂O₃ decreases their sintering temperature without affecting negatively the piezoelectric constant. Enhanced ferroelectric properties were obtained in these BCTZ-xPr ceramics. The ceramic with x=0.06 wt% exhibits a good electrical behavior of d₃₃∼460 pC/N, k_p∼47.6%, ε_r∼4638, and tan δ∼0.015 when sintered at a low temperature of ∼1400 °C. As a result, the BCTZ-xPr ceramic is a promising candidate for lead-free piezoelectric ceramics.     

Preparation and characterization of Cr2O3-TiO2-Al2O3-V2O5 green pigment

Green pigments with high near infrared reflectance based on a Cr₂O₃-TiO₂-Al₂O₃-V₂O₅ composition have been synthesized. Cr₂O₃ was used as the host component and mixtures of TiO₂, Al₂O₃ and V₂O₅ were used as the guest components. TiO₂, Al₂O₃, and V₂O₅ were mixed into 39 different compositions. The spectral reflectance and the distribution of pigment powder were determined using a spectrophotometer and a scanning electron microscope, respectively. It was found that a pigment powder sample S9 with a Cr₂O₃-TiO₂-Al₂O₃-V₂O₅ composition of 80, 4, 14 and 2 wt%, respectively, gives a maximum near infrared solar reflectance of 82.8% compared with 49.0% for pure Cr₂O₃. The dispersion of pigment powders in a ceramic glaze was also studied. The results show that the pigment powder sample S9 is suitable for use as a coating material for ceramic-based roofs.     

ZrO2/SiO2- and La2O3/Al2O3-supported platinum catalysts for CH4/CO2 reforming

Surface-phase ZrO₂ on SiO₂ (SZrOs) and surface-phase La₂O₃ on Al₂O₃ (SLaOs) were prepared with various loadings of ZrO₂ and La₂O₃, characterized and used as supports for preparing Pt/SZrOs and Pt/SLaOs catalysts. CH₄/CO₂ reforming over the Pt/SZrOs and Pt/SLaOs catalysts was examined and compared with Pt/Al₂O₃ and Pt/SiO₂ catalysts. CO₂ or CH₄ pulse reaction/adsorption analysis was employed to elucidate the effects of these surface-phase oxides.

The zirconia can be homogeneously dispersed on SiO₂ to form a stable surface-phase oxide. The lanthana cannot be spread well on Al₂O₃, but it forms a stable amorphous oxide with Al₂O₃. The Pt/SZrOs and Pt/SLaOs catalysts showed higher steady activity than did Pt/SiO₂ and Pt/Al₂O₃ by a factor of three to four. The Pt/SZrOs and Pt/SLaOs catalysts were also much more stable than the Pt/SiO₂ and Pt/Al₂O₃ catalysts for long stream time and for reforming temperatures above 700 °C. These findings were attributed to the activation of CO₂ adsorbed on the basic sites of SZrOs and SLaOs.     

Photocatalytic activity of Cu2O/TiO2, Bi2O3/TiO2 and ZnMn2O4/TiO2 heterojunctions

Cu₂O/TiO₂, Bi₂O₃/TiO₂ and ZnMn₂O₄/TiO₂ heterojunctions were studied for potential applications in water decontamination technology and their capacity to induce an oxidation process under VIS light. UV–vis spectroscopy analysis showed that the junctions-based Cu₂O, Bi₂O₃ and ZnMn₂O₄ are able to absorb a large part of visible light (respectively, up to 650, 460 and 1000 nm). This fact was confirmed in the case of Cu₂O/TiO₂ and Bi₂O₃/TiO₂ by photocatalytic experiments performed under visible light. A part of the charge recombination that can take place when both semiconductors are excited was observed when a photocatalytic experiment was performed under UV–vis illumination. Orange II, 4-hydroxybenzoic and benzamide were used as pollutants in the experiment. Photoactivity of the junctions was found to be strongly dependent on the substrate. The different phenomena that were observed in each case are discussed.     

Ni~(2+)-Fe~(3+)-C_7H_7SO_3~--LDHs催化剂的制备

以尿素为沉淀剂,柠檬酸钠为络合剂,采用均相沉淀法制备Ni~(2+)-Fe~(3+)-CO_3~(2-)-LDHs。以制备的Ni~(2+)-Fe~(3+)-CO_3~(2-)-LDHs为前驱体,分别与Na Cl和对甲苯磺酸钠进行离子交换反应得到Ni~(2+)-Fe~(3+)-C_7H_7SO_3~--LDHs新型催化剂,成功实现对甲苯磺酸根负载Ni~(2+)-Fe~(3+)-LDHs。研究表明,Ni~(2+)-Fe~(3+)-C_7H_7SO_3~--LDHs为介孔材料,比表面积为165.6 m~2·g~(-1),平均孔径为14.7 nm,较大比表面积和空隙结构增强了其吸附性能和催化活性。