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1.
Two types of secondary emitter materials, the rare earth oxides (RE2O3) doped Mo cermet cathodes and the Y2O3-W matrix pressed cathode, are introduced in this paper. According to the calculation results, Y2O3 exhibits the best secondary emission property among Y2O3, La2O3, CeO2 and Lu2O3. The rare earth oxides co-doped Mo cathodes in which Y2O3 is the main active substance exhibit better secondary emission property than single RE2O3 doped Mo cathode. The results obtained by the Monte-Carlo calculation method show that the secondary electron emission property is strongly related to the grain size of the cathode. The decreasing of the grain size reduces the positive charge effect of the rare earth oxide due to the electrons supplement from the metal to the rare earth oxide, whereby the secondary electrons are easier to escape into the vacuum. Y2O3 is introduced into Ba-W cathode to fabricate a pressed Y2O3-W matrix dispenser cathode. The result indicates that the secondary emission yield of the Ba-W cathode increases from 2.13 to 3.51 by adding Y2O3, and the thermionic emission current density (J 0) could reach 4.18 A/cm2 at 1050 °Cb. 相似文献
2.
王衍行 《武汉理工大学学报(材料科学英文版)》2016,31(5):961-964
The effect of Ga2O3 on the structure and properties of calcium aluminate glasses fabricated by vacuum melting process was investigated by Raman spectrum, differential scanning calorimeter (DSC), and infrared spectrum methods. The results show that calcium aluminate glass network only consists of [AlO4] tetrahedral units. With the gradual addition of Ga2O3, the quantity of [GaO4] tetrahedral units increases. Substitution of Ga2O3 for Al2O3 results in a decrease in T g T x, and T p, and an increase in the thermal stable index ΔT. Similarly, the absorption band around 3.0 μm obviously reduces and the transparency in 4.0-6.0 μm rapidly increases with increasing Ga2O3 content. However, the chemical stability of calcium aluminate glasses decreases if Ga2O3 is introduced due to the increasing of [GaO4] units in the glass network. 相似文献
3.
殷海荣 《武汉理工大学学报(材料科学英文版)》2014,29(4):684-687
In order to increase the content of rare-earth oxides in magneto-optical glass and improve the Verdet constant, the rare-earth doped ternary Ga2O3-B2O3-SiO2(GBS) system magneto-optical glasses were prepared by the melt quenching technique. The infl uence of Tb3+ and Dy3+ ions on the structure of GBS glasses was investigated using FTIR, DSC and Faraday rotations. The experimental results showed that the content of rare-earth oxides in the glasses with the double incorporation of Tb2O3 and Dy2O3 was higher. The crystallization parameter β achieved the maximum 0.48 with Tb3+/Dy3+ content of 35mol%. Terbium oxide existed mainly in [TbO3] units in the glasses and [TbO4] units were converted into [TbO3] with increasing Tb2O3 content. As Ga3+ ion is larger than B3+ ion in radius, leading to an increasing of the glass network gap and improvement in the ability of accommodating rare earth ions, Verdet constant increased. 相似文献
4.
黄学辉 《武汉理工大学学报(材料科学英文版)》2018,33(1):23-29
Mesoporous La0.8Sr0.2MnO3+σ/z SBA-15 (z = 1, 2, 4) perovskite oxides were synthesized via hard-templating with ordered mesoporous silica SBA-15 as the template. The as-prepared samples were characterized by XRD, SEM, AFM, BET, and XPS and the catalytic activity was tested for CO oxidation. The wide-angle XRD patterns showed that La0.8Sr0.2MnO3+σ perovskite was formed. The SEM and AFM analyses exhibited that La0.8Sr0.2MnO3+σ by hard-templating method had much smaller particle size (18 nm) than that (40 nm) by the sol-gel method. The perovskite-type oxides La0.8Sr0.2MnO3+σ/z SBA-15 (z = 1, 2, 4) also displayed a higher BET surface area from 70 to 143.7 m2/g and a disordered mesostructure from nitrogen sorption analysis, as well as a small-angle XRD pattern. Moreover, the La0.8Sr0.2MnO3+σ/z SBA-15 (z = 1, 2, 4) perovskite exhibited a much higher activity in CO oxidation than the conventional La0.8Sr0.2MnO3+σ perovskite. Further analysis by the means of XPS techniques indicated that the existence of high content of Oads/Olatt species contributed to the high activity. 相似文献
5.
By introducing other oxide materials (SiO2, Al2O3, CaO) into the red mud, all materials were melted into aluminosilicate glasses. On the basis of 17.2Fe2O3-5.7CaO-18.2Al2O3-50SiO2-5.9Na2O-3TiO2 system glasses, [Al2O3]/[CaO] mass ratio changed further. For each sample, the assignment of IR absorption bands for aluminosilicate glasses was investigated by Fourier transform infrared spectroscopy and the glasstransition temperature and high temperature molten state were studied by differential scanning calorimetry. According to X-Ray diffraction and differential scanning calorimetry, the behavior of crystallization was analyzed. The results show that the glass structures of three-dimensional network are depolymerized and the amount of non-bridging oxygens increases gradually with network modifier CaO replacing network intermediate Al2O3 when [Al2O3]/[CaO] ratio of aluminosilicate glass decreases from 4.05 to 0.66, resulting in decreasing density, melting temperature, crystallization peak temperature and glass-transition temperature. As [Al2O3]/[CaO] mass ratio decreases, the concentration of crystallized phase maghemite (γ-Fe2O3) will increase which provides the possibility for production of black glass-ceramic further. 相似文献
6.
张光富 《武汉理工大学学报(材料科学英文版)》2018,33(3):566-570
The spontaneous magnetic transitions and corresponding magnetoelastic properties of intermetallic compounds RMn2Ge2 (R=Gd, Tb and Dy) were investigated by using the X-ray diffraction method and magnetic measurement. The results showed that the compounds experience two magnetic transitions, namely the second-order paramagnetic to antiferromagnetic transition at temperature TN (TN=368, 423 and 443 K for GdMn2Ge2, TbMn2Ge2 and DyMn2Ge2, respectively) and the first-order antiferromagnetic - ferrimagnetic transition at temperature Tt (Tt=96, 80 and 40 K for GdMn2Ge2, TbMn2Ge2 and DyMn2Ge2, respectively) as the temperature decreases. The temperature dependence of the lattice constant a(T) displays a negative magnetoelastic anomaly at the second-order transition point TN and, at the first-order transition Tt, a increases abruptly for GdMn2Ge2 and TbMn2Ge2, Δa/a about 10-3. Nevertheless, the lattice constant c almost does not change at these transition points indicating that such magnetoelastic anomalies are mainly contributed by the Mn-sublattice. The transitions of the magnetoelastic properties are also evidenced on the temperature dependence of magnetic susceptibility χ. The first-order transition behavior at Tt is explained by the Kittel mode of exchange inversion. 相似文献
7.
Hairong Yin Chunxiang Zhang Liying Liu Guoping Chen Baojun Tang 《武汉理工大学学报(材料科学英文版)》2009,24(4):640-643
The glass-forming region of B2O3-Al2O3-SiO2 (BAS) glass heavily doped with rare earth oxides was investigated by an effective method, and the chemical stability was
investigated by powder method. Influences of rare earth oxides on the glass-forming ability and the chemical stability of
the BAS glass were also discussed. The experimental results show that the BAS glass-forming region expands firstly with the
increase of the Tb2O3 content up to 30mol% and then shrinks. The acid-resistant capacity of the BAS glass doped with rare earth oxides is the lowest,
the water-resistant capacity is secondary, and the alkali-resistant capacity is the best. Besides, the glass chemical stability
can be improved by doping appropriate amount of rare earth oxides. Moreover, the stronger the ionic polarization ability of
the rare earth ions is, the better the chemical stability of the BAS glass will be. 相似文献
8.
Formation and thermal stability of Cu-Zr-Al-Er bulk metallic glasses with high glass-forming ability
《北京科技大学学报(英文版)》2007
The formation and thermal stabilities of Cu46.25Zr46.25-xAl7.5Erx, (x=0 to 8) bulk metallic glasses (BMGs) were investigated. The addition of a small amount of Er (2at%) for replacing Zr effectively improves the glass-forming ability of Cu46.25Zr46.25Al7.5 alloy, and the glassy rod with a diameter of at least 12 mm can be formed. The glass transition temperature (Tg), temperature interval of supercooled liquid region ΔTx (= Tx − Tg, and reduced glass transition temperature Trg (=Tg/T1) of Cu46.25Zr44.25Al7.5Er2 glassy alloy are 699 K, 62 K and 0.607, respectively. 相似文献
9.
c-axis-oriented SmBa_2Cu_3O_7(SmBCO) films have been deposited on(100)- LaA1O_3(LAO)substrate by metal organic chemical vapor deposition(MOCVD) technique.The effects of deposition temperature(T_(dep)) and total pressure(P_(tot)) on the orientation and microstructure of SmBCO films were investigated.The orientation of SmBCO films transformed from α-axis to c-axis with increasing of T_(dep) from 900 to 1 100℃.At T_(dep)=1 050℃,SmBCO films had c-axis orientation and tetragon surface.At P_(tot)~(dep)=400-800 Pa and T_(dep)=1 050 ℃,totally c-axis-oriented SmBCO films were obtained.The R_(dep) of SmBCO films increased firstly and then decreased with increasing P_(tot).The surface of SmBCO films exhibited tetragon morphology at 1 050 ℃ and400 Pa.Maximum thickness of SmBCO film deposited was 1.2μm at P_(tot)= 600 Pa,and the corresponding R_(dep)was 7.2 μm·h~(-1). 相似文献
10.
赖昌 《武汉理工大学学报(材料科学英文版)》2012,27(3):523-525
Glasses are prepared by sintering P2O5, ZnO and Ce2(C2O4)3 10H2O mixtures at 1 100 ℃ in air and then annealed at 400 ℃ for 10 hours. The obtained glasses are homogeneous, transparent and colorless. Emission and excitation spectra are measured for the samples and the results show that the glasses contain Ce3+ trivalent cerium ions. The parameters of glass preparation obtained here may be adapted to preparing this type of glasses doped with other lanthanide ions, so as to study energy transfer phenomena and variation of radiative lifetime with refractive index due to local field effect. 相似文献
11.
Luminescent properties of BaO-La2O3-B2O3 glasses with dopant 总被引:4,自引:0,他引:4
The luminescent properties of glasses synthesized in air atmosphere by conventional high temperature process were stud{ed. The emissions spectra of Eu^2 and Eu^3 were observed in BaO-La2O3-B2O3-Eu2O3 glasses.The results show that the broad emission peaks at 430 nm correspond to 5d→4f emission transition of Eu^2 , the sharp emission peaks at 592, 616, 650 and 250 nm correspond to 5^D0→1Fj(j=1--4) emission transition of Eu^3 ,respectively, which indicates that the BaO-La2O3a-B2O3-Eu2O3 glass can convert ultraviolet and green omponents of sunlight into blue and red light so as to increase the intensity of blue and red light, respectively. The luminescent in--tensity of Eu^2 increases with increasing the molar ratio of Tb^3 in BaO-La2O3-B2O3-Eu2O3a-Tb4O3 glasses, whereas the luminescent intensity of Eua^3 decreases. So the luminescent intensity of Eu(Ⅲ,Ⅱ) is influenced by Tb^3 .These phenomena can be explained by electron transfer mechanism; Eu^3 (4f6) Tb^3 (4f^8)→Eu^2 (4f′) Tb^4 (4f′). Taking advantage of the luminescent properties of BaO-La2O3-B2O3-Eu2O3 glasses, light-conversion glass for agriculture can be produced. 相似文献
12.
The energy transfer and upconversion of Er^3+/Yb^3+ co-doped TeO2-TiO2-K2O glasses upon excitation with 976 nm lasers diode were studied. The tellurite glasses were prepared by conventional melting methods. Their optical properties and sensitization upconversion spectra were performed. The dependence of green upconversion lu- minescence intensity on the mole ratio of Yb^3+ to Er^3+ and Er^3+ concentration were discussed in detail. When the mole ratio of Yb^3+ to Er^3+ is 25/1 and Er^3+ concentration is 0.1% (mole fraction), or when the mole ratio of Yb^3+ to Er^3+ is 10/1 and Er^3+ concentration is 0.15 %, the optimal upconversion luminescence intensity is obtained. The obtained glasses can be one of the potential candidates for lasers-diode pumping microchip solid-state lasers. 相似文献
13.
Crystal growth,structure and properties of bismuth triborate BiB<Subscript>3</Subscript>O<Subscript>6</Subscript> crystal 总被引:1,自引:0,他引:1
BiB3O6 (BIBO) single crystals with size of 46×23×10 mm3 and weight of 26.0 g have been successfully grown by top-seeded method. Problems encountered in the growth process of this crystal have been discussed in detail, and the methods of growing high-quality large crystals have been put forward. The relationship between their structure and properties is studied. The space group of monoclinic BiB3O6 is C2 and the cell parameters are a=7.1203(7) Å, b=4.9948(7) Å, c=6.5077(7) Å, β=105.586(8)″, and V=222.93(5) Å3. The density of BIBO is 4.8965 g/cm3. The Mohs’s scale of hardness is 5.5–6. There is no cleavage face in the crystal. The transmittance of BIBO is about 80 percent in the range from visible coherent light to near-infrared light. The ultraviolet cutoff wavelength is at 276 nm. BiB3O6 is a biaxial crystal and has two sets of axes, and the relative orientation of (X, Y, Z) with regard to (a, b, c) is: X//b, (Y, c)=47.2°, (Z, a)=31.6°, determined by X-ray analysis combined with polarized microscopy. Second-harmonic-generation (SHG) experiments were carried out for the first time. In type I phase-matching (PM) directions (11.1°, 90°) and (168.9°, 90°), SHG conversion efficiencies of two directions for 1.064 μm light are up to 67.7% and 58%, respectively. We have also obtained the third-harmonic-generation (THG) of 1.064 μm. The comparative experiments between BIBO and KTP were carried out on conversion efficiency, transmittance and hardness. All the above results indicate that BiB3O6 is a kind of excellent nonlinear optical (NLO) crystal. 相似文献
14.
The conversion of CO_2 to liquid hydrocarbon fuels using solar energy is gaining attraction as a means to deal with climate change and energy depletion,and assessment for related thermochemical cycles has attracted great interests in recent years.Here,we perform the thermodynamical analysis on solar-aided CO_2 conversion reactions based on Tin oxides.The equilibrium compositions,production purity and CO_2 conversion are obtained.Also,the variations of conversion efficiency with respect to temperature,normal beam solar insolation,mean flux concentration ratio,initial CO_2 to SnO ratio and heat recuperation percentage are revealed.Our results indicate the initial CO_2 to SnO ratio,χ_(ini),has an evident impact on conversion efficiency andχ_(ini)=0.5,T=700 K andχ_(ini)=1,T=950 K,are favourable for solid C and gaseous CO production,respectively.The calculated maximum cycle efficiency with direct work production is 0.340 at T=950 K andχ_(ini)=1,demonstrating the high conversion efficiency of the proposed system. 相似文献
15.
The effects of Al2O3 addition on both the sintering behavior and microwave dielectric properties of PbO-B2O3-SiO2 glass ceramics were investigated by Fourier transform infrared spectroscope (FTIR), differential thermal analysis (DTA),
X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that with the increase of Al2O3 content the bands assigned to [SiO4] nearly disappear. Aluminum replaces silicon in the glass network, which is helpful for the formation of boron-oxygen rings.
The increase of the transition temperature T
g and softening temperature T
f of PbO-B2O3-SiO2 glass ceramics leads to the increase of liquid phase precipitation temperature and promotes the structure stability in the
glasses, and consequently contributes to the decreasing trend of crystallization. Densification and dielectric constants increase
with the increase of Al2O3 content, but the dielectric loss is worsened. By contrast, the 3% (mass fraction) Al2O3-doped glass ceramics sintered at 725 °C have better properties of density ρ=2.72 g/cm3, dielectric constant ɛ
r
=6.78, dielectric loss tan δ=2.6×10−3 (measured at 9.8 GHz), which suggest that the glass ceramics can be applied in multilayer microwave devices requiring low
sintering temperatures. 相似文献
16.
徐晓虹 《武汉理工大学学报(材料科学英文版)》2010,25(3):370-374
A series of nanometer TiO2 photocatalysts co-doped respectively with rare earth Er3+-Ce3+ and La3+-Fe3+ were prepared by sol-gel method,and the photocatalytic activity under ultra-violet light was evaluated by photocatalytic degradation of methyl blue.The crystallographic forms,particles size,and morphology were characterized by XRD and TEM.The results showed that the optimum heat temperature of co-doped TiO2 was 550 ℃,and the co-doped TiO2 kept anatase.The anatase crystal had the average size of 20 nm.The ... 相似文献
17.
刘浩 《武汉理工大学学报(材料科学英文版)》2012,27(1):58-62
Structure, crystallization and dissolution properties of CaO-MgO-SiO2 inorganic glass fiber in the presence of additives (Al2O3, Y2O3) were investigated by DTA, XRD, FTIR and ICP-AES techniques. The results show that with the addition of Al2O3 and Y2O3, the glass network structure is strengthened and the precipitation of crystals is inhibited for heat-treated fibers. Compared with Y2O3 doped fibers, Al2O3 presents more significant effects on the enhancement of silica network and the inhibition of crystallization in fibers. As for dissolution properties in physiological fluids, though the weight losses, changes of pH values and leached ions concentration lower slightly with the addition of Al2O3 and Y2O3 for the intensified network structure, and fibers still present high dissolution rates. 相似文献
18.
High performance piezoelectric ceramics with high Curie temperatures(TC) are the bottle necks of relevant high temperature devices. In this study, the electrical performance and microstructure of Li and Mn codoped Aurivillius-type composite ceramics with a composition Ca_(0.99-x_Bi_(6.99+x)(Li Mn)_(0.01) Nb Ti_5O_(24)(x = 0–0.8) were systematically investigated. The results indicated that uniform intergrowth structure with a lattice similar to that of the end member CBT could be formed at a low x value(x 0.4). Phase separation occurred when more A-site Ca~(2+) ions were replaced by Bi~(3+) ions. Nevertheless, all composite samples showed d_(33) values about 2 to 3 times of that of the constituent phase Ca Bi_4Ti_4O_(15) and Bi_3 Ti NbO_9 with still a high depolarization temperature. The performance of the samples was found to be related to the density and larger lattice distortion along the polarization a axis. The results also demonstrated that formation of the compound system was an effective way in improving the performance of Aurivillius-type high TC piezoelectric ceramics. 相似文献
19.
王华 《武汉理工大学学报(材料科学英文版)》2016,31(6):1230-1234
ZnMn2O4 films for resistance random access memory (RRAM) were fabricated with different device structures by magnetron sputtering. The effects of electrode on I-V characteristics, resistance switching behavior, endurance and retention characteristics of ZnMn2O4 films were investigated. The ZnMn2O4 films, using p-Si and Pt as bottom electrode, exhibit bipolar resistive switching (BRS) behavior dominated by the space-charge-limited conduction (SCLC) mechanism in the high resistance state (HRS) and the filament conduction mechanism in the low resistance state (LRS), but the ZnMn2O4 films using n-Si as bottom electrodes exhibit both bipolar and unipolar resistive switching behaviors controlled by the Poole-Frenkel (P-F) conduction mechanism in both HRS and LRS. Ag/ZnMn2O4/p-Si device possesses the best endurance and retention characteristics, in which the number of stable repetition switching cycle is over 1000 and the retention time is longer than 106 seconds. However, the highest R HRS/R LRS ratio of 104 and the lowest V ON and V OFF of 3.0 V have been observed in Ag/ZnMn2O4/Pt device. Though the Ag/ZnMn2O4/n-Si device also possesses the highest R HRS/R LRS ratio of 104, but the highest values of V ON,V OFF, R HRS and R LRS, as well as the poor endurance and retention characteristics. 相似文献
20.
YU Chunlei DAI Shixun ZHOU Gang ZHANG Junjie HU Lili & JIANG Zhonghong . Shanghai Institute of Optics Fine Mechanics Chinese Academy of Sciences Shanghai China . Graduate School of the Chinese Academy of Sciences Beijing China 《中国科学E辑(英文版)》2005,48(6):638-647
With the rapid development of computer networks and other data-transmitting ser-vices, the demand for the increase of transmission capacity of the long distance trans-mission system is urgent. However, the conventional SiO2-based EDFA is limited for its small bandwidth. The Er3+-doped tellurite glass exhibits a larger stimulated-emission cross section and a broader emission bandwidth at the third communication window (1.55 μm) than that of silicate, phosphate, and germanate glasses, which c… 相似文献