共查询到20条相似文献,搜索用时 31 毫秒
1.
V. I. Vettegren A. Ya. Bashkarev G. I. Morozov A. A. Lebedev E. Yu. Nefed’ev M. A. Kryuchkov 《Physics of the Solid State》2005,47(10):1869-1871
The amplitude distributions of acoustic emission signals generated during the formation of corrosion microcracks in loaded welded joints connecting two corrosion-resistant steel tubes are studied. For acoustic emission signal amplitudes of less than 0.6 mV and a microcrack concentration of ~10 mm?3, the distribution density of the signal amplitudes is described by a gamma function. For acoustic emission signal amplitudes exceeding 1.0 mV and a microcrack concentration of greater than or equal to 102 mm?3, the distribution density of the amplitudes exhibits two maxima, whose shape is described by a Gaussian function. The mean amplitudes of acoustic emission signals differ by a factor of 3. The change in the amplitude distribution of acoustic emission signals is explained by the effect exerted by the weld-metal interface on the microcrack formation. 相似文献
2.
A. Peterlin 《Journal of Macromolecular Science: Physics》2013,52(3):401-419
In the creep experiment the brittle fracture of the unoriented semicrystalline polymers at very small and very high tensile load with the intermediate ductile region may be explained by the competition between crazing and shear band formation during the microcrack growth phase. The former type of microcrack growth leads to brittle fracture while the latter type yields necking which transforms the original lamellar structure into the final fibrous structure. The actual fate of the strained sample depends on the growth time of the craze, tg, and of the shear band formation time, ts. If tg<ts, the material will break in a brittle manner, and if tg > ts, the material will deform plastically. The failure of the fibrous material seems to occur when the ratio between the average distance and diameter of the microcracks reaches a value about 3. The microcracks seem to form primarily at defects of the microfibrillar structure, i.e., at the ends of microfibrils where the axial connection of subsequent crystal blocks through the amorphous layers by a great many taut tie molecules is either completely interrupted or at least drastically reduced. The stress concentration resulting from the opening of these defects into microcracks may rupture also some of the adjacent microfibrils. Such nucleation and subsequent lateral growth of the microcrack ruptures the taut tie molecules in its path. The ruptured molecules yield free radicals which can be monitored by electron spin resonance. 相似文献
3.
Xinwei Lu 《辐射效应与固体损伤》2013,168(6):455-462
The activity concentrations of 226Ra, 232Th and 40K in commercial marble materials have been determined using a NaI(Tl) γ-ray spectrometer with a matrix-inversion-based spectral stripping technique. Knowledge of radioactivity present in marble materials enables one to assess any possible radiological risks to human health. The concentrations of 226Ra, 232Th and 40K in Chinese commercial marble range from 8.4 to 157.4, 5.6 to 165.5 and 44.1 to 1352.7 Bq kg?1, respectively. The natural radionuclide concentration varied with color and production site of commercial marble. The activity concentrations of 226Ra, 232Th and 40K in white, gray, black, green and yellow marble samples are comparatively smaller than those in brown and red marble samples. The radium equivalent activity (Raeq), the external hazard index (H ex), the internal hazard index (H in) and the annual gonadal dose equivalent were also calculated and compared with the internationally recommended values. One type of brown commercial marble (TSB) of China does not satisfy the universal standards. 相似文献
4.
Reactions between superdislocations involved in deformation in the basal, prismatic, and type-I and II pyramidal planes in single-crystal Ti3Al are considered. The types of dislocation interactions are established that result in the formation dislocation barriers (microcrack nuclei). The force and energy conditions for microcracks to arise are found. The interaction between a and 2c + a superdislocations results in microcracks with the plane of opening lying in basal and pyramidal planes; the interaction of 2c + a superdislocations in different pyramidal planes results in the formation of microcracks in prismatic and pyramidal planes; and the interaction of a superdislocations in basal and/or pyramidal planes does not cause the formation of dislocation barriers. The types of microcracks are classified in terms of the orientation of deformation axes of single crystals, and the regions of the stereographic triangle are determined characterized by a preferential type of crack opening. 相似文献
5.
L. E. Kar’kina O. A. Elkina L. I. Yakovenkova 《Bulletin of the Russian Academy of Sciences: Physics》2007,71(5):618-620
Microcracks in the Ti3Al alloy indented at room temperature have been analyzed by electron microscopy. Analysis of the microstructure has revealed that microcracks propagate in the {0\(\overline 1 \)11} pyramidal planes and in the slip bands of the 2c + a superdislocations in the {20\(\overline 2 \)1} and {11\(\overline 2 \)1} pyramidal planes. It is found that the formation of a slip band in the basal plane at the microcrack tip leads to a change in the character of microcrack propagation from straight-line to steplike. 相似文献
6.
Microcracks in a Ti3 Al alloy subjected to indentation at room temperature were studied by transmission electron microscopy. The microcracks are shown to grow on \(\{ 0\overline 1 11\} \) pyramidal planes and in the slip bands of 2c + a superdislocations on \(\{ 20\overline 2 1\} \) and \(\{ 11\overline 2 1\} \) pyramidal planes. It is found that, due to the formation of a slip band in the basal plane at a microcrack tip, the propagating microcrack becomes steplike rather than straight. It is shown that a microcrack can nucleate at the line of intersection of \(\{ 11\overline 2 1\} \) pyramidal and \(\{ 0\overline 1 10\} \) prismatic planes. 相似文献
7.
Morphological defects in β-barium borate (β-BBO) thin films grown on Sr2+-doped α-BBO substrates by liquid phase epitaxy (LPE) technique were studied by scanning electron micrograph (SEM), atomic force microscopy (AFM) and optical spectroscopy. The present results indicate that the main defects exit in β-BBO thin films are microcracks and hollow structure. The formation of microcrack is due to the lattice mismatch and the difference of thermal expansion coefficients between substrate and film. The hollow structure might be caused during the combination of islands, which formed in the initial stage. 相似文献
8.
This paper gives a quantitative analysis of the effect of near-tip microcracks on electric-field-induced stress intensity factors in isotropic elastic dielectrics. Nucleation of the microcracks is assumed to be governed by the electric-field-induced mean stress or the maximum normal stress. Based on the solutions for the effect of a single microcrack on the local electric field at the main crack, simple formulae are derived for the electric-field-induced stress intensity factors in the presence of the microcracks. It is found that the relative change in the stress intensity factor due to the microcracks for a conducting crack is equal and opposite to that for an insulating crack provided that the distribution of microcrack orientations is random. In particular, the microcracking zone is found to amplify the electric-field-induced stress intensity factor in some cases, especially for stationary insulating cracks, while the microcracking zone wake has an antishielding effect for sufficiently grown conducting cracks. These results are in sharp contrast with the well-known toughening effects of microcracks in elastic media under pure mechanical loads. This is attributed to the fact that the interaction between the microcracks and the main crack in elastic dielectrics under electrical loading is governed essentially by electrostatics, while the shape of the microcracking zone is determined by the electric field induced elastic stress field. 相似文献
9.
Thin polycrystalline films of SnO2 and antimony doped SnO2 have been prepared by simple economic electroless deposition technique. The transmittance in the visible range and the reflectance in the i.r. range for SnO2 films are ~80% and ~70%, respectively, with resistivity ~10?2 Ω cm. On the other hand, antimony doped SnO2 films have transmittance in the visible range and reflectance in the i.r. range, as good as ~86% and ~83%, respectively, with resistivity as low as ~10?3Ω cm. By vacuum annealing, the resistivity of both types of films has been brought down as low as ~10?3 and ~10?4 Ω cm, respectively. 相似文献
10.
Silver-clad tapes of highT
c Bi-Pb-Sr-Ca-Cu-O superconductors have been fabricated through the powder-in-tube method. The critical current density, J
c
, of a thick tape was 534 A.cm−2 (77 K, 0 T). Subsequent rolling and sintering of the tapes led to a gradual decrease inJ
c, instead of the expected increase. This was caused by the microcracks developed in the core material by a rather drastic
reduction during the rolling of the tapes. A modified and well controlled rolling technique, on the other hand, resulted in
much improvedJ
c values. Repeated rolling and sintering resulted in a good grain alignment and no microcracks were observed. In the present
studies, maximumJ
c of 1846 A.cm−2 (77 K, 0 T) and 2.43 × 104 A.cm−2 (4.2 K, 0 T) have been obtained Optimization of the processing and sintering parameters are expected to lead to still higherJ
c values. 相似文献
11.
Zai-Chun Xu Mei-Feng Liu Lin Lin Huimei Liu Zhi-Bo Yan Jun-Ming Liu 《Frontiers of Physics》2014,9(1):82-89
Double pyrochlore Dy2Ru207 is synthesized and its magnetism and ferroelectricity below the Ru4+ spin ordering temperature (NI00 K) are investigated. The ferroelectric transition appears at -18 K, much higher than the Dy3+ spin ordering point at -1.8 K and lower than the Ru4+ spin ordering point at -100 K. The measured electric polarization at ,-2 K is as big as 145℃/m2 in the polycrystalline samples. It is argued that the ferroelectricity is possibly ascribed to the electric dipole ordering arising from the collective monopole excitations in the Dy3+ tetrahedrons in prior to the Dy3+ spin ordering into spin-ice like state below -1.8 K. 相似文献
12.
A. M. Kalashnikova V. V. Pavlov R. V. Pisarev L. N. Bezmaternykh M. Bayer Th. Rasing 《JETP Letters》2004,80(5):293-297
The optical spectra and the second-harmonic generation (SHG) are studied in a noncentrosymmetric GdFe3(BO3)4 magnet. In the region of weak absorption (α~20–400 cm?1) below ~3 eV, three absorption bands are distinguished, which can be unambiguously assigned to forbidden electronic transitions from the ground 6A1 state of the Fe3+ ion to its excited states 4T1(~1.4 eV), 4T2(~2 eV), and 4A1, 4E(~2.8 eV). Intense absorption begins in the region above 3 eV (α~2–4×105 cm?1), where two bands at ~4.0 and 4.8 eV are observed, which are caused by allowed electric dipole charge-transfer transitions. The spectral features of SHG in the 1.2–3.0-eV region are explained by a change in the SHG efficiency caused by a change in the phase mismatch. It is shown that in the weak absorption region, phase matching can be achieved for SHG. 相似文献
13.
The prevailing opinion is that excess Cd in CdI2 produces diamagnetic Cd22+ ions. 113Cd relaxation data indicates that ~1% of added atoms produce paramagnetic Cd+ ions with lifetime ~ 10 ps. The concentration of Cd+ ions is depressed by excess iodine. 相似文献
14.
Vijay Singh Vineet Kumar Rai Katharina Al-Shamery Markus Haase Sang Hwan Kim 《Applied Physics A: Materials Science & Processing》2013,113(3):747-753
The ZrO2:Er3+ codoped with Yb3+ phosphor powders have been prepared by the urea combustion route. Formation of the compounds ZrO2:Er3+ and ZrO2:Er3+, Yb3+ was confirmed by XRD. The frequency upconversion emissions in the green and red regions upon excitation with a CW diode laser at ~978 nm are reported. Codoping with Yb3+ enhances the emission intensities of the triply ionized erbium in the green and red spectral regions by about ~130 and ~820 times respectively. The emission properties of the ZrO2:Er3+ phosphor powders are discussed on the basis of excited state absorption, energy transfer, and cross-relaxation energy transfer mechanisms. 相似文献
15.
D. Ghosh B. Ghosh S. Hussain R. Bhar A. K. Pal 《Applied Physics A: Materials Science & Processing》2014,115(4):1251-1261
Gallium antimonide (GaSb) films were deposited onto fused silica and n-Si (100) substrates by coevaporating Ga and Sb from appropriate evaporation sources. The films were polycrystalline in nature. The size and the shape of the grains varied with the change in the substrate temperature during deposition. The average surface roughness of the films was estimated to be 10 nm. Grain boundary trap states varied between 2×1012 and 2.2×1012 cm?2 while barrier height at the grain boundaries varied between 0.09 eV and 0.10 eV for films deposited at higher temperatures. Stress in the films decreased for films deposited at higher temperatures. XPS studies indicated two strong peaks located at ~543 eV and ~1121 eV for Sb 3d3/2 and Ga 2p3/2 core-level spectra, respectively. The PL spectra measured at 300 K was dominated by a strong peak located ~0.55 eV followed by two low intensity peaks ~0.63 eV and 0.67 eV. A typical n-Si/GaSb photovoltaic cell fabricated here indicated V oc~311 mV and J~29.45 mA/cm2, the density of donors (N d)~3.87×1015 cm?3, built in potential (V bi)~0.48 V and carrier life time (τ)~28.5 ms. Impedance spectroscopy measurements indicated a dielectric relaxation time ~100 μs. 相似文献
16.
V. S. Kovivchak T. V. Panova 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2016,10(6):1226-1230
The influence of a high-power ion beam on polycrystalline oxides (V2O5, MoO3, and WO3) is investigated. Oxide irradiation with ion beams with current densities of greater than ~30 A/cm2 is established to initiate changes in the color of irradiated layers and lead to surface-layer particle melting. It is demonstrated that a distinctive feature of the interaction between a high-power ion beam and V2O5 is the formation of surface nanosheets and nanowires whose characteristic cross-sectional size and thickness are ~1 μm and up to ~40 nm, respectively. The nanosheets are generated near emerging surface cracks if the beam current density is ~100 A/cm2. Possible mechanisms of surface nanostructures formation under the action of pulsed ion beams are discussed. 相似文献
17.
C. Klee Dipl.-Phys. T. K. McNab Dr. F. J. Litterst Dr. H. Micklitz 《Zeitschrift für Physik A Hadrons and Nuclei》1974,270(1):31-36
The Mössbauer absorption spectra of matrix isolated57Fe atoms have been measured in the inert matrices CH4 and CO2 with matrix temperatures between ~3.3 and ~46 K. The isomer shift of the observed resonances is (?0.79±0.02) mm/s and (?0.76±0.05) mm/s with respect to iron metal at 300 K for57Fe in CH4 and for CO2 respectively. This is within the experimental errors the same isomer shift as that of rare-gas matrix isolated57Fe atoms. All spectra show quadrupole doublets due to the noncubic point symmetry of the lattice site occupied by the57Fe atoms. The effective Debye temperatures as obtained from the temperature dependence of the resonance absorption areas are (46±4) K for the CH4 matrix and (121±6) K for the CO2 matrix annealed at ~20 K. 相似文献
18.
用高温熔融法制备了相同质量百分比浓度4%Tm2O3掺杂浓度下(90-x)GeO2-xNb2O5-10Na2O(其中数字为摩尔百分比x=1,2,4,6,8)以及Tm2O3掺杂浓度分别为质量百分比1%,2%,3%,4%下86GeO2-4Nb2O5-10Na2O(其中数字为摩尔分数)系列玻璃.研究了Nb2O5组分对玻璃热稳定性,荧光强度和J-O参数的影响.应用Judd-Ofelt理论,计算了Tm3+离子在Nb2O5浓度不同时的J-O强度参数(Ω2,Ω4,Ω6)及Tm3+离子各激发态能级的自发跃迁概率、荧光分支比以及辐射寿命等光谱参量.根据McCumber理论,计算了Tm3+离子能级3F4→3H6(1.8 μm)跃迁的吸收截面和受激发射截面.从获得的吸收截面、发射截面与离子掺杂浓度计算了1.8 μm荧光波段的增益截面曲线.在808 nm波长光的激发下,研究了Tm3+掺杂玻璃在1.47与1.8 μm附近的荧光特性.发现当Tm2O3掺杂浓度为质量百分比3%时,在1.8 μm处的荧光强度达最大,然后随着掺杂浓度的增大,其荧光强度反而降低;当Nb2O5摩尔分数含量大约在2%时,Tm3+在1.8 μm处的荧光强度最强.并讨论了Nb2O5组分变化对玻璃结构与光谱特性的影响情况.
关键词:
3+掺杂锗铌酸盐玻璃')" href="#">Tm3+掺杂锗铌酸盐玻璃
红外光谱性质
交叉弛豫
2O5')" href="#">Nb2O5 相似文献
19.
When Ho3+:Yb3+:CaF2 crystalline powders prepared by combustion synthesis were exposed to near-infrared (λ ~ 975 nm) radiation, intense photon up-conversion (UC) was observed at the visible with emission bands peaked at ~ 545, ~650 and ~750 nm identified as 4f-4f transitions from higher levels (5F4, 5S2) and 5F5 to lower levels 5I8 and 5I7 of Ho3+. The emission bands at the green and red, in particular, have been demonstrated to be useful for temperature sensing based on luminescence intensity ratio technique. However, no model is available in literature to explain the change of the electronic populations of states (5F4, 5S2) and 5F5 with temperature. The UC phenomenon was studied from both theoretical and experimental points of view. A rate equation model with temperature dependent parameters for Ho3+ and Yb3+ electronic populations considering a high sensitization of Ho3+ ions by Yb3+ ions was used. High Yb3+ → Ho3+ energy transfer efficiency was found (~88% at room temperature). The change with temperature predicted by the model for the luminescence intensity ratio of the UC green and red emission lines agrees well with the experimental data. 相似文献
20.
A steel striker impacting the surface of single-crystalline quartz generates strain waves and their related acoustic and electromagnetic
emissions. Simultaneously, microcracks with free excited SiO• radicals at their edges appear in the single crystal. The relaxation
of the electronic excitation causes bursts of fractoluminescence. The intensity of the bursts is proportional to the microcrack
surface area. It is found that the linear sizes of microcracks vary from 15 to 70 μm. Cracking changes the slope of the time
dependences of the acoustic and electromagnetic emission intensities. The microcrack size distribution obeys a power law with
an exponent of about two. 相似文献