共查询到20条相似文献,搜索用时 15 毫秒
1.
Nada Marnada Hiroshi Miyahara Naoyoshi Ueda Keiichi Ikeda Nobuo Hayashi 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2002,480(2-3):591-597
Precise measurements of disintegration rates by using a 4πβ-γ coincidence apparatus have resulted in improved certainties of the principal γ-ray emission probabilities of 193Os. Most of the uncertainties are less than 1%, whereas the uncertainties of emission probabilities evaluated in the Nuclear Data Sheets (83 (1998) 921) are more than 6%. The precision is improved for the β-ray branching ratio for direct transition to the ground state and the value is larger than the evaluated value by about 6%. 相似文献
2.
-Al2O3 prepared by combustion technique was ball-billed in a planetary mill in toluene medium at 300 rpm in ZrO2 pot with a ball to powder ratio 10:1 for 1, 5, 10, 15, and 20 hours. X-ray diffraction pattern from the milled materials showed super-Lorentzian peak shapes for -Al2O3 peak profiles. The super-Lorentzian peak shape has been attributed to the bimodal size distribution of the -Al2O3 particles. Rietveld analysis using two different phase fractions of -Al2O3 with different microstructural features yielded a low goodness-of-fit of the x-ray data indicating the suitability of the assumed model. The phase fraction of -Al2O3 particles with smaller size increases with the milling time. Further the particles shapes were observed to be cylindrical in this case with the cylinder axis along the crystallographic c-axis. The cylinder diameter and the length were obtained to be 86 and 140 respectively after 20 hrs of milling. The -Al2O3 particles of larger size are isotropic. It is, thus, proposed that milling induces bimodal size distribution in the initial hours of milling. 相似文献
3.
M.A. Saettel A. Sellam A. Nourreddine A. Pape 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2008,590(1-3):151
The RaMsEs Group (Radioprotection et Mesures Environnementales) of the IPHC performs research and offers services mainly in the field of radioactivity measurements and sample analysis. This report will describe some of our recent experience using a semiautomatic evaporation system to prepare large area thin deposits for total α and β counting and gives experimental and simulated results for the autoabsorption coefficients. 相似文献
4.
Kousuke Morita Hiroshi Miyahara Yoshimune Ogata Keiji Katoh 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2005,540(2-3):324-327
105Rh becomes a stable 105Pd after β−-decay with a half-life of 35.36 h. The energies of especially strong γ-rays emitted from 105Rh are 306.1 and 318.9 keV, and the emission probabilities are evaluated to be 5.1±0.3% and 19.1±0.6% by de Frenne et al. To improve the certainty, the γ-ray emission probabilities were determined from the disintegration rate and absolute γ-ray intensities measured using a 4πβ(ppc)-γ(HPGe) coincidence apparatus with two-dimensional data-acquisition system. The results for the 306.1 and 318.9 keV γ-rays were 4.76±0.05% and 16.99±0.17%, respectively. 相似文献
5.
The studies of the (1 − x)Pb(Sc1/2Nb1/2)O3–xPbTiO3 (PSN–PT) single crystals reveal that the chemical and physical properties of the materials are affected by the growth conditions. By the measurements of the dielectric constant as a function of temperature upon cooling, it is found that crystals grown from the same charged stoichiometric composition (x = 0.425), but under different flux environments (i.e. the composition of flux and the flux to PSN–PT ratios are varied), show anomalies (i.e. phase transitions) at different temperatures. This phenomenon is attributed to the complex local chemical structure of the PSN–PT solid solution single crystals with B-site random occupancy of three different cations (Sc3+, Nb5+ and Ti4+). The dielectric and domain structure of the PSN–PT crystals with composition near the morphotropic phase boundary (MPB) are investigated, showing much more complex situations compared with Pb(Sc1/2Nb1/2)O3. 相似文献
6.
Okorn Mekasuwandumrong Nitikon Wongwaranon Joongjai Panpranot Piyasan Praserthdam 《Materials Chemistry and Physics》2008,111(2-3):431-437
In the present study, Ni-modified α-Al2O3 with Ni/Al ratios of 0.3 and 0.5 were prepared by sol–gel and solvothermal method and then were impregnated with 0.3 wt.% Pd. Due to different crystallization mechanism of the two preparation methods used, addition of nickel during preparation of α-Al2O3 resulted in various species such as NiAl2O4, mixed phases between NiAl2O4 and α-Al2O3, and mixed phases between NiAl2O4 and NiO. As revealed by NH3-temperature programmed desorption, formation of NiAl2O4 drastically reduced acidity of alumina, hence lower amounts of coke deposited during acetylene hydrogenation was found for the Ni-modified α-Al2O3 supported catalysts. For any given method, ethylene selectivity was improved in the order of Pd/Ni–Al2O3-0.5 > Pd/Ni–Al2O3-0.3 > Pd/Ni–Al2O3-0 Pd/α–Al2O3-commercial. When comparing the samples prepared by different techniques, the sol–gel-made samples showed better performances than the solvothermal-derived ones. 相似文献
7.
Transmission electron microscopy (TEM) of a bimodal near-α titanium alloy revealed the existence of retained β phase layers and silicide precipitates at the α platelet boundaries inside transformed β grains. The β to α phase transformation accompanied by the precipitation of silicide resulted in the formation of a large number of dislocations at α platelet boundaries. Orientation relationships between silicide, β phase and α phase were also identified. However high-resolution TEM (HRTEM) revealed crystal mismatches between these phases generating high strains at α platelet boundaries. The strengthening effects of the platelet boundaries are discussed in terms of dislocations slip across the boundaries. The mechanism that governs the β to α phase transformation is also discussed. 相似文献
8.
The effect of vacancies on structural properties of the perovskite-type oxide was studied using the full-potential linearized augmented plane wave (FP-LAPW) method, within the density functional theory. In this approach, the generalized gradient approximation was used for the exchange-correlation potential. The ground state properties such as lattice parameter, bulk modulus and inter-atomic distances of cubic Ba1−xZrO3 compounds (x = 0, 0.125 and 0.25) were calculated. Additionally, using a set of total energy versus volume obtained with the FP-LAPW method, the quasi-harmonic Debye model was applied to determine the thermal properties including temperature dependence of bulk modulus, thermal expansion coefficient, specific heats at constant volume and constant pressure. No experimental data are available and our results are considered as purely predictive. 相似文献
9.
Monodisperse α-Fe2O3 nanoparticles have been successfully prepared by hydrothermal synthetic route using FeCl3, CH3COONa as reagents and reacted at 200 °C for 12 h. The morphology and structure of products were characterized by powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the α-Fe2O3 nanoparticles were single-crystalline hexagonal structure and average diameters were about 80 nm. Magnetic properties have been detected by a vibrating sample magnetometer at room temperature. The nanoparticles exhibited a ferromagnetic behavior with the coercive force (Hc), saturation magnetization (Ms) and remanent magnetization (Mr) was 185.28 Oe and 0.494 emu/g, 0.077 emu/g. 相似文献
10.
Meili Zhang Lingzhi Ye Yuan Gao Xiqin Lv Jiang Chang 《Composites Science and Technology》2009,69(15-16):2547-2553
In this research, β-CaSiO3 particles were surface modified with dodecyl alcohol, and Poly-(DL-lactic acid) (PDLLA)/modified β-CaSiO3 composite films were fabricated with a homogenous dispersion of β-CaSiO3 particles in the PDLLA matrix. The aim of the study was to investigate the properties of the composite films before and after hydrolytic treatment. SEM images showed retained homogenous dispersion of β-CaSiO3 particles after hydrolysis and tensile test also showed maintained mechanical property. Simulated body fluid (SBF) incubation experiment suggested that hydrolytic treatment did not affect the formation of hydroxyapatite on the surface of the composite films. The hydrophilicity of the composites was greatly recovered (from 69.82° to 50.28°) after hydrolysis. In addition, cells cultured on composite films after hydrolysis presented the highest cell proliferation rate and differentiation level. All of these results suggested that the surface modification of silicate particles with dodecyl alcohol along with reversible hydrolytic treatment was an effective and feasible approach to fabricate polymer/silicate composite materials with improved properties. 相似文献
11.
Emin Bayraktar Claude Bathias Xue Hongquian Tao Hao 《International Journal of Fatigue》2004,26(12):1263-1275
Fatigue crack initiation behaviour is investigated at room temperature in the (α2-Ti3Al and γ-TiAl) alloy. High cycle fatigue tests ranging up to 1010 cycles are carried out on the powder metallurgy (P/M) bar specimens under different loading conditions with a stress ratio of R=0.1 and R=0.5. Microstructural characterization and fracture surface analysis are also investigated by optical (OM) and scanning electron microscopy (SEM). Ti–Al alloy studied here shows two phases in microstructure (nearly refined lamellar thickness) composed of α2-Ti3Al and γ-TiAl (hereafter called γ+α2 alloys) and fracture mechanism is explained with different plastic incompatibilities between the two phases. 相似文献
12.
Polar nanodomains and relaxor behaviour in (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 crystals with x = 0.3–0.5
Phase transitions and dielectric properties of the (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 crystals with x = 0.3–0.5 are studied. The solid solutions in this composition range are shown to be relaxor ferroelectrics. The crystals with low x demonstrate a diffused maximum in the temperature dependences of the dielectric permittivity at Tm. Tm varies with frequency according to the Vogel–Fulcher law. The polarizing microscopy investigations reveal a first-order phase transition from the relaxor phase to the low-temperature ferroelectric phase at TC, which is several degrees below Tm. The permittivity peak in the crystals with x = 0.5 is sharp, and Tm is equal to TC and does not depend on frequency, as is typical of the transition from a ferroelectric to an ordinary paraelectric phase. Nevertheless, the relaxor, but not the paraelectric, phase is observed at T > Tm. This conclusion is confirmed by the observation of the temperature behaviour of complex dielectric permittivity at T > Tm, which is typical of relaxors and related to the existence of polar nanodomains. 相似文献
13.
In this paper we compare the elastic energies obtained by tight-binding molecular dynamics simulations for several strained structures of β-FeSi2, corresponding to the most frequent epitaxial relationships ‘on’ and ‘in’ silicon. Our results confirm that, for coherent interfaces, the very common β-FeSi2(101) or (110)//Si(111) orientation generates a very large contribution to the elastic energy, due to the large misfit. Therefore, we suggest that the frequent nucleation of such epitaxial relationships in precipitates is provided by the correspondence of the two-dimensional crystal structure for the Si sites between Si(111) and β-FeSi2(101) or (110). We show it to be maintained even after misfit relaxation in the silicon matrix, as simulated by a large-scale molecular dynamics run. 相似文献
14.
In β1–Cu–Zn–Al single crystals the course of cyclic martensititic transformation ‘β1 parent phase↔γ′1 martensite’ induced by tensile stress were studied with use of X-ray topography, light microscopy and etch pits. Two groups of single crystals were studied. The first one (OR) contained single crystals of subgrain boundaries parallel to the direction of elongation [001], the second one (RA) consisted of single crystals of random subgrain boundaries orientations. Single crystals from the RA group cracked after about 300 cycles of martensitic transformation; single crystals from the OR group did not crack even after 1200 cycles. In OR single crystals changes of dislocation density inside the subgrains caused by cycling occurred much more slowly than in the RA single crystals. This has been related to the dislocation movement from inside the subgrains to their boundaries. 相似文献
15.
Dissolution of the γ′ phase in a PM superalloy Astroloy was studied at equilibrium and under rapid heating. The ‘solvus’ temperature of primary and secondary γ′ precipitates was determined experimentally. The most prominent feature concerns the large departure from equilibrium for the dissolution of the γ′ precipitates during rapid heating and this departure depends on the initial size of the precipitates. A model for γ′ dissolution during fast thermal cycling is proposed. 相似文献
16.
In Situ Encapsulating α‐MnS into N,S‐Codoped Nanotube‐Like Carbon as Advanced Anode Material: α → β Phase Transition Promoted Cycling Stability and Superior Li/Na‐Storage Performance in Half/Full Cells
下载免费PDF全文
![点击此处可从《Advanced materials (Deerfield Beach, Fla.)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dai‐Huo Liu Wen‐Hao Li Yan‐Ping Zheng Zheng Cui Xin Yan Dao‐Sheng Liu Jiawei Wang Yu Zhang Hong‐Yan Lü Feng‐Yang Bai Jin‐Zhi Guo Xing‐Long Wu 《Advanced materials (Deerfield Beach, Fla.)》2018,30(21)
Incorporation of N,S‐codoped nanotube‐like carbon (N,S‐NTC) can endow electrode materials with superior electrochemical properties owing to the unique nanoarchitecture and improved kinetics. Herein, α‐MnS nanoparticles (NPs) are in situ encapsulated into N,S‐NTC, preparing an advanced anode material (α‐MnS@N,S‐NTC) for lithium‐ion/sodium‐ion batteries (LIBs/SIBs). It is for the first time revealed that electrochemical α → β phase transition of MnS NPs during the 1st cycle effectively promotes Li‐storage properties, which is deduced by the studies of ex situ X‐ray diffraction/high‐resolution transmission electron microscopy and electrode kinetics. As a result, the optimized α‐MnS@N,S‐NTC electrode delivers a high Li‐storage capacity (1415 mA h g?1 at 50 mA g?1), excellent rate capability (430 mA h g?1 at 10 A g?1), and long‐term cycling stability (no obvious capacity decay over 5000 cycles at 1 A g?1) with retained morphology. In addition, the N,S‐NTC‐based encapsulation plays the key roles on enhancing the electrochemical properties due to its high conductivity and unique 1D nanoarchitecture with excellent protective effects to active MnS NPs. Furthermore, α‐MnS@N,S‐NTC also delivers high Na‐storage capacity (536 mA h g?1 at 50 mA g?1) without the occurrence of such α → β phase transition and excellent full‐cell performances as coupling with commercial LiFePO4 and LiNi0.6Co0.2Mn0.2O2 cathodes in LIBs as well as Na3V2(PO4)2O2F cathode in SIBs. 相似文献
17.
The effect of hollow structure on the optoelectronic properties of β-Fe2O3 hollow nanoparticles (HNPs) was determined. Spectrophotometry showed that the optical transmittance of the β-Fe2O3 HNPs was less than 40% in the visible-light region. This opaqueness was suggested to be an optical characteristic, commonly found in the authors' previous studies of TiO2 and δ-Al2O3 HNPs. In addition, β-Fe2O3 HNPs had a band gap (1.86 eV) between amorphous (1.73 eV) and polycrystalline (1.97 eV) β-Fe2O3 thin films, which was a 5–7 nm thick shell that embraced an intermediate volume of the crystal phase, in-between the two thin films. 相似文献
18.
Richard Akinyeye Mantoa Sekota Priscilla Baker Emmanuel Iwuoha 《Fullerenes, Nanotubes and Carbon Nanostructures》2006,14(1):49-55
A preliminary result of the morphology and yield of chemically synthesized polypyrrole (PPY) using β-naphthalene sulfonic acid (NSA) and ammonium peroxodisulphate (APS) in aqueous medium is presented. Various micro/nanotubes were obtained using different dopant/monomer (D/M) ratios and temperature settings. Similar but shorter and sheet-like nanostructures were obtained without the use of surfactant NSA; with a fibre-like, loose and admixed physical outlook. The percentage yield (m/v) of the doped PPY was greater than that from the undoped, being 27-44 and 18-20, respectively with higher values obtained from the low temperature synthesis. The highest percentage yield of 44 was obtained from a D/M ratio of 0.8. 相似文献
19.
20.
以共沉淀法、喷雾干燥法制备了三元正极材料LiNi_(1/3)Co_(1/3)Mn_(1/3)O_2,应用基于密度泛函理论的第一性原理计算方法,与实验制备的LiNi_(1/3)Co_(1/3)Mn_(1/3)O_2进行对比,对3种不同的预想结构模型(堆叠结构、随机排列结构、超晶格结构)进行研究。实验结果表明,两种方法制备的三元材料都具有良好的层状结构,其中共沉淀法制备的层状结构更加明显,而喷雾干燥法制备的材料中过渡金属元素比更接近LiNi_(1/3)Co_(1/3)Mn_(1/3)O_2的化学计量比。计算结果表明,随机排列的结构模型能量最低、最稳定,与实验制备的三元正极材料结构最为相似。 相似文献