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《Journal of the European Ceramic Society》2014,34(12):2989-2995
New high temperature negative temperature coefficient (NTC) thermistor ceramics based on a xMgAl2O4–(1 − x)YCr0.5Mn0.5O3 (x = 0.1, 0.4, 0.6) composite system have been successfully fabricated through spark plasma sintering (SPS) with a low sintering temperature and a short sintering period. The X-ray diffraction analysis indicates that the SPS-sintered composite ceramics consist of a cubic spinel MgAl2O4 phase and an orthorhombic perovskite YCr0.5Mn0.5O3 phase isomorphic to YCrO3. The SPS-sintered composite ceramics have high relative density ranging from 94.1 to 97.4% of the theoretical density. X-ray photoelectron spectroscopy analysis corroborates the presence of Cr3+, Cr4+, Mn3+, and Mn4+ ions on lattice sites, which may result in the hopping conduction. The obtained ρ25, B25–150, and B700–1000 of the SPS-sintered composite NTC thermistors are in the range of 1.53 × 106–9.92 × 109 Ω cm, 3380–5172 K, and 7239–9543 K, respectively. These values can be tuned by adjusting the MgAl2O4 concentration. 相似文献
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Tsai-Ta Lai Chih-Cheng Chang Che-Yuan Yang Subrata Das Chung-Hsin Lu 《Ceramics International》2013,39(1):159-163
SrAl2O4:Eu2+ phosphors with various content of Bi2O3 flux were synthesized and analyzed. It was observed that the crystallinity and the particle size of the phosphors were increased with the addition of Bi2O3 flux. These phenomena are considered to be caused via the melting of the Bi2O3 flux particles during the synthesis of the phosphors. The melted Bi2O3 flux increased the mobility and homogeneity of solid reactants, thereby enhancing the photoluminescence intensity of the phosphors. SrAl2O4:Eu2+ phosphors with Bi2O3 as the flux exhibited a broad green emission with a peak at 520 nm. The highest photoluminescence emission intensity was observed when 5 mol% Bi2O3 flux was added into the phosphors. The emission is due to 4f65d→4f7 (8S7/2) transitions of the Eu2+ ions. Moreover, Bi2O3 flux extended the application of the ultraviolet excited phosphors toward the blue-light excited phosphors. Nevertheless, the influence of Bi2O3 on the afterglow and the emission color of SrAl2O4:Eu2+ phosphors were not significant. This research indicated that Bi2O3 flux is effective flux for synthesizing SrAl2O4:Eu2+ phosphors. 相似文献
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Mn掺杂BaTi4O9陶瓷结构和介电性能 总被引:7,自引:0,他引:7
用电子陶瓷工艺制备主晶相为BaTiO9(BT4)的介电陶瓷,研究用锰掺杂的BaTi4O9陶瓷的结构和介电性能。XRD研究表明BaTiO9属正交晶系,空间群Pmmn,晶格常数为a=1.453nm,b=0.379nm,c=0.629nm,每个原胞有两个分子,钛原子位于变形的氧八面体之中。这种氧八面体的极化类似于或大于在BaTiO3和PbTiO3铁电相观察到的极化。锰掺杂极大地增强了Q值,在1MHz下测得的Q值为12500。而没有掺杂的陶瓷有高的损耗,这可能是由于在空气中烧结时形成的Ti^3 ,显然锰的作用是在缺陷平衡中作为一种补偿剂,依据反应:Mn^3 Ti^3 →Mn^2 Ti^4 ,可能有助于Ti^4 的形成,BaTi4O9陶瓷具有优良的介电性能;低介质损耗、中等介电常数和介电常数温度系数。此种陶瓷造成多层陶瓷电容器开拓了一种新的应用领域。 相似文献
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用非均相沉淀法首次合成了名义化学式为Ba2.88MgSi2O8:0.02Eu2+,0.1Mn2+的Eu2+、Mn2+共掺杂Ba3MgSi2O8荧光粉.用XRD、SEM和荧光光谱进行表征,并与相同条件下用高温固相法合成的荧光粉作对比.研究沉淀反应温度、金属离子浓度对非均相沉淀法制备荧光粉相纯度和发光性能的影响.结果表明:相对于高温固相法,非均相沉淀法可在更低的温度下合成相纯度高的荧光粉,且粉末颗粒呈近球状,粒径均匀,粉末基本无团聚;沉淀反应温度为40℃,在此温度下,金属离子溶液滴加完毕后,继续搅拌2h,并在室温下陈化24h,金属离子浓度为0.30mol/L左右时为最宜. 相似文献
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The catalytic oxidation of CO over nanocrystallite Cu
x
Mn(1−x)Fe2O4 powders was studied using advanced quadruple mass gas analyzer system. The oxidation of CO to CO2 was investigated as a function of reactants ratio and firing temperature of ferrite powders. The maximum CO conversion was
observed for ferrite powders which have equal amount of Cu2+ and Mn2+ (Cu0.5Mn0.5Fe2O4). The high catalytic activity of Cu0.5Mn0.5Fe2O4 can be attributed to the changes of the valence state of catalytically active components of the ferrite powders. The firing
temperature plays insignificant role in the catalytic activity of CO over nanocrystallite copper manganese ferrites. The mechanism
of catalytic oxidation reactions was studied. It was found that the CO catalytic oxidation reactions on the surface of the
Cu
x
Mn1−x
Fe2O4 was done by the reduction of the ferrite by CO to the oxygen deficient lower oxide then re-oxidation of this phase to the
saturated oxygen metal ferrite again. 相似文献
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Manganese oxide catalyst was prepared by a novel dispersion–precipitation method, which involved synthesis of stable aqueous dispersion of manganese oxide nanoparticles and the subsequent precipitation by dilution-induced destabilization. The characterizations indicated that the thus prepared catalyst was composed of nanorod particles with a Hausmannite structure of Mn3O4, and had a high reducibility. In comparison to the catalysts prepared by alkaline-salt reaction or calcination of manganese acetate, this catalyst prepared by the new method showed much better performance in the catalytic complete oxidation of airborne carbon monoxide and toluene, which is possibly attributed to the smaller particle sizes and higher oxygen mobility. 相似文献
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Gao-Juan Cao Shou-Tian Zheng Wei-Hui Fang Guo-Yu Yang 《Inorganic chemistry communications》2010,13(7):834-836
An unexpected 3D manganese vanadate (en)Mn2(V2O7) (1) (en = ethylenediamine) has been hydrothermally obtained by H2E2Ge2O3 (E = ? CH2CH2COO?) ligands and well-prepared mixture of V–Mn-amine and characterized by IR spectroscopy, elemental analysis, thermal stability and powder X-ray diffraction. Single-crystal X-ray diffraction analysis reveals that the structure is a novel pillared-layer, in which MnO5N octahedra are corner-linked to form an infinite sheet with 4-membered rings (MRs) and further condensed to the 3D framework. The most prominent feature of 1 is the connection between the sheets via double bridges, namely, inorganic V2O7 dimeric units and organic en molecules. It is noteworthy that inorganic and organic double bridges between sheets have not been seen in manganese vanadates. 相似文献
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通过精确控制葡萄糖的摩尔反应比,采用水热结合低温烧结法制备了多孔球状黑锰矿结构Mn3O4.当高锰酸钾与葡萄糖比例为1∶3(MNO-3)时,具有最优性能.SEM结果显示最优样品具有多孔球状结构,粒径大小均匀,约为1 ~4 μm.运用恒流充放电、交流阻抗、循环伏安等电化学测试方法研究其电容特性和电化学性能.结果 表明:在6 mol·L-1KOH电解质溶液中,电流密度为1A·g-1的条件下MNO-3样品具有最高比容量321.7 F·g-1,循环400圈后,其比容量保持率为97.15%. 相似文献
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采用聚合物辅助方法合成了纳米级的LiNi0.5Mn1.5O4颗粒.通过XRD测试,扫描电镜观察和充放电测试表征了材料的晶体结构、形貌和电化学性能.结果表明烧结温度对于颗粒的尺寸形貌和结晶度具有重要的影响作用,并影响其放电能力,800℃烧结获得的LiNi0.5Mn15O4具有更好的结晶性并且展示出更好的电性能. 相似文献
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Ming Zhang Xinhai Li Zhixing Wang Huajun Guo Jinhui Li Wanrong Liu 《Powder Technology》2009,195(2):69-72
Spherical BaSO4 particles have been coated with Y2O3:Eu3+ phosphor layers (BaSO4/Y2O3:Eu3+) by the wet chemical method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dipersive spectroscopy (EDS), photoluminescence spectra were utilized to characterize the BaSO4/Y2O3:Eu3+ core–shell-structured phosphor particles. The obtained core–shell phosphors consist of well dispersed submicron spherical particles with narrow size distribution. XRD result shows that no reaction occurred between the BaSO4 cores and the Y2O3:Eu3+ shells even after annealing at 1400 °C. TEM and EDS results show that BaSO4 particles are well coated with the shell of Y2O3:Eu3+. The BaSO4/Y2O3:Eu3+ core–shell particles show a red emission corresponding to 5D0?7F2 of Eu3+ under the excitation of ultraviolet. 相似文献
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《Ceramics International》2017,43(11):7984-7991
Co-precipitated and 800 °C heat treated Ni-Cu-Zn nanoferrites with chemical formula NixCu0.1Zn0.9-xFe2O4 (x=0.5, 0.6, 0.7) were prepared because of their potential use as multilayer chip inductors in electromagnetic applications. Their structural, magnetic properties and phase formation were studied using X-ray diffractometer (XRD), field emission scanning electron microscope (FE–SEM), vibrating sample magnetometer (VSM), Mössbauer spectrometer, thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC). The XRD patterns confirm the cubic spinel structure of the ferrite phase belonging to Fd3m space group. Lattice parameters and cation distributions were obtained by Rietveld refinement of the XRD patterns. The lattice parameter decreases with increase in Ni2+ ion concentration. Rietveld analysis indicates that Cu2+ ions predominantly occupy the B-sites and Ni2+ ions partly going into B-sites but predominantly into A-sites. An excellent agreement is observed between the experimental lattice parameters and lattice parameters theoretically calculated using this cation redistribution. The inversion parameter (λ) observed for Fe3+ ions by Mössbauer spectroscopy is different from that of Rietveld analysis. Magnetization and Mössbauer spectroscopic measurements indicate that the ferrite nanoparticles are mostly superparamagnetic. The cation redistribution is supposed to alter the magnetocrystalline anisotropy which in turn affects the magnetic parameters of the present ferrite samples. The reduced magnetization is attributed to core-shell interactions and possible canting of A- and B-shell magnetizations. TGA-DSC studies indicate that ferrite formation in the 800 °C heat treated samples is completed but grain growth increases as the particles are subject to the increased temperature. 相似文献
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U. Kurtan Y. Junejo B. Ünal A. Baykal 《Journal of Inorganic and Organometallic Polymers and Materials》2013,23(5):1089-1096
Polyaniline (PANI)/cobalt-manganese ferrite, PANI/Co0.5Mn0.5Fe2O4, nanocomposite was synthesized by oxidative chemical polymerization of aniline in the presence of ammonium peroxydisulfate. Microwave assisted synthesis method was used for the fabrication of core Co0.5Mn0.5Fe2O4 nanoparticles. The presence of PANI on the surface of the Co0.5Mn0.5Fe2O4 NPs was confirmed by infrared spectroscopy and thermal gravimetric analysis. The crystallite size was calculated with line profile fitting method as 20 ± 9 nm. The spherical morphology of the product was presented by Scanning electron microscopy and transmission electron microscopy. The electrical characterizations showed that ac conductivity is found to be independent of frequency and increases with increase of temperatures. However, imaginary component of dielectric function obey the power law of frequency while it is almost independent of temperature. This can be attributed to the molecular interatomic interaction between Co0.5Mn0.5Fe2O4 nanoballs and PANI shells. 相似文献
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过碳酸钠是过氧化氢与碳酸钠的加成化合物,具有在存储、运输和使用过程中安全稳定的优点。本文采用共沉淀-高温煅烧法制备纳米片状Mn2O3@α-Fe3O4,活化过碳酸钠(SPC)产生自由基氧化降解偶氮染料活性黑5(RBK5)。采用透射电子显微镜(TEM)、X射线粉末衍射仪(XRD)、扫描电子显微镜(SEM)、傅里叶变换红外光谱仪(FTIR)、X射线光电子能谱(XPS)及比表面积测试(BET)表征制备的纳米片状Mn2O3@α-Fe3O4催化剂,分别探究催化剂投加量、过碳酸钠浓度、初始pH及RBK5溶液浓度对降解效率的影响。当催化剂投加量为0.3g/L、过碳酸钠浓度为1.0mmol/L、初始pH为3、反应时间为90min时,RBK5的降解效率达88%,反应过程符合拟一级动力学(R2>0.9)。Mn2O3@α-Fe3O4/过碳酸钠体系中起氧化降解作用的活性物种为·OH、CO ·、O ·和1O2,其中·OH占据主导地位,XPS反映了铁锰元素存在价态以及双金属间的协同作用,依据猝灭实验及XPS分析降解机理。 相似文献
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《Ceramics International》2015,41(8):9729-9733
CaBi4Ti4O15–Bi4Ti3O12 (CBT–BIT) ceramics were synthesized using a solid state reaction method. The X-ray diffraction (XRD) analysis revealed the existence of bismuth layered perovskite phase with orthorhombic crystal structure. High-resolution transmission electron microscopy (HRTEM) confirmed the alternate arrangement of CBT part and BIT part along c axis in the intergrowth structure. CBT–BIT ceramics showed excellent thermal stability of the dielectric loss (tan δ), but the relaxation of dielectric loss in the 100 Hz to 1 MHz frequency range had been observed. Meanwhile, an enhanced piezoelectric constant (d33) value of 15 pC/N was observed without degradation even the temperature up to 650 °C. The dc resistivity (ρdc) of CBT–BIT performed a high value of 5.68×1014 (Ω cm) at room temperature (RT). In addition, the ρdc values of CBT–BIT within the temperature range of 100–450 °C were close to those of CBT and kept almost one hundred times higher than those of BIT. 相似文献