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991.
This article will review the development of the Fe–Ga (Galfenol) alloy system for magnetostriction applications including
work on substitutional ternary alloying additions for magnetic property enhancement. A majority of the alloying addition research
has focused on substitutional ternary elements in Bridgman grown single crystals with the intent of improving the magnetostrictive
capability of the Galfenol system. Single crystals provide the ideal vehicle to assess the effectiveness of the addition on
the magnetostrictive properties by eliminating grain boundary effects, orientation variations, and grain-to-grain interactions
that occur when polycrystals respond to applied magnetic fields. In almost all cases, ternary additions of transition metal
elements have decreased the magnetostriction values from the binary Fe–Ga alloy. Most of the ternary additions are known to
stabilize the D03 chemical order and could be a primary contribution to the observed reduction in magnetostriction. In contrast, both Sn and
Al are found to substitute chemically for Ga. For Sn additions, whose solubility is limited, no reduction in magnetostriction
strains are observed when compared to the equivalent binary alloy composition. Aluminum additions, whose effect on the magnetoelastic
coupling on Fe is similar to Ga, result in a rule of mixture relationship. The reviewed research suggests that phase stabilization
of the disordered bcc structure is a key component to increase the magnetostriction of Fe–Ga alloys. 相似文献
992.
Z. Ferhat-Hamida H. Phuong-Nguyen P. Bernazzani A. Haine G. Delmas 《Journal of Materials Science》2007,42(9):3138-3154
LLDPE samples synthesized with Ziegler–Natta (ZN) and Metallocene (MT) catalysts have been analyzed to investigate a potential
catalyst-dependent morphology and to find an explanation for the difficult processing of MT. Slow calorimetry at v = 0.02 K/min and IR at RT and in the melt are used. The differences between MT and ZN are assigned to their different composition,
MT not having the linear segments, which are present in ZN. Slow calorimetry is effectively a drawing process of the melt
with chain orientation followed by decay. The later event, characterized by an endotherm, ΔH
network, occurs at higher temperatures for MT, the presence of a regular distribution of methyl groups slowing down the process.
The rocking, gauche, bending and stretching regions of the IR spectra are analyzed. The nascent MT has more strained bands
in the rocking region. The wagging region reveals the more homogeneous environment of MT through the maximum absorbance at
1,368 cm−1. Decomposition of bands is made for the rocking and wagging regions. The orthorhombic crystallinity, αc (FTIR), measures the sum of long- and short-range orthorhombic order, the latter being obtained by αc (FTIR)-αc (X-rays). The values of αc (FTIR) for MT and ZN are very similar in conditions of equilibrium. The justifications for the molecular origin of ΔH
network are presented: (i) the slow relaxation of long chains strained and oriented in the melt measured by other techniques, (ii)
The correlation, for gels of a linear sample, made in different solvents, between the maximum drawability, λmax, and ΔH
network in a slow T-ramp. The range is 80–270 for λmax and 40–120 J/g for ΔH
network. (iii) The comparison of two traces of the same sample, between 140 °C and 270 °C, show that comparable events in the melt
appear in the integrated absorbance and in the slow calorimetry signal. Analysis on thin films of the little-studied CH2 stretching region reveals that their extinction coefficient, ε, and the shape of the bands are highly sensitive to the sample
history, ε diminishing by a large factor in slowly crystallized samples. Events in the slow T-ramp, followed by a fast crystallization, on the other hand, leads to materials with standard characteristics. Slow calorimetry
traces display more events (endothermic and exothermic) for MT than for ZN, a finding consistent with more flow irregularities
during processing. Equilibrium conditions and better processing could be reached for MT by extending time in the melt or using
higher temperatures. 相似文献
993.
Daniel X. Gouveia Odair P. Ferreira Antonio G. Souza Filho M. G. da Silva J. A. C. de Paiva Oswaldo L. Alves Josué Mendes Filho 《Journal of Materials Science》2007,42(2):534-538
The thermal decomposition properties of Mg–Fe hydrotalcites were studied through in situ 57Fe Mössbauer spectroscopy and in situ X-ray diffraction. Abrupt changes in the quadrupolar splitting measured in the Mössbauer spectra revealed a phase transition from the starting lamellar structure to a new crystalline arrangement. By analyzing the Mössbauer parameters we show that the material is highly disordered in the 300–400 °C temperature range. This hypothesis is confirmed by the X-ray results whose diffractograms indicated the collapse of the lamellar structure and the formation of a solid solution. 相似文献
994.
Modelling of effects of ultrastructural morphology on the hygroelastic properties of wood fibres 总被引:1,自引:0,他引:1
Wood fibres constitute the structural framework of e.g. wood, paper, board and composites, where stiffness and dimensional
stability are of importance. An analytical modelling approach has been used for prediction of hygroelastic response, and assessment
of the stresses in thick-walled cylinder models of wood fibres. A wood fibre was idealised as a multilayered hollow cylinder
made of orthotropic material with helical orientation. The hygroelastic response of the layered assembly due to axisymmetric
loading and moisture content changes was obtained by solving the corresponding boundary value problem of elasticity. A simple
solution scheme based on the state space approach and the transfer matrix method was employed. This was combined with an analytical
ultrastructural homogenisation method, used to link hygroelastic properties of constituent wood polymers to properties of
each layer. Predicted hygroelastic response captured experimentally measured behaviour. Fibres that were constrained not to
twist showed a stiffer response than fibres allowed twisting under uniaxial loading. It was also shown that the ultrastructure,
i.e. the microfibril angle, will control the hygroexpansion in the same way as it controls the compliance of the cell wall.
Qualitative failure trends comparable with experimental observations could be established with stress analysis and a simple
plane-stress failure criterion. 相似文献
995.
996.
997.
C. B. Winkelmann E. Collin Yu. M. Bunkov H. Godfrin 《Journal of Low Temperature Physics》2004,135(1-2):3-14
We report systematic measurements of the response of a Vibrating Wire Resonator (VWR) in normal and superfluid liquid 3He. Special attention has been paid to the hydrodynamic regime of the superfluid B-phase, where the response parameters of the VWR do not follow a simple law. We show that a simple interpolation between the region where first order slip-corrections can be applied and the ballistic regime is insufficient. Measuring an empirical effective viscosity, we propose a temperature calibration method which allows the use of VWRs as a secondary thermometer at intermediate and high pressures in the temperature range 0.2 T c < T < 50 mK. 相似文献
998.
Solubilization of the armchair, metallic (10,10) single-walled carbon nanotubes (SWCNTs) in toluene is modeled using molecular dynamics simulations. Inter- and intra-molecular atomic interactions in the SWCNT + toluene system are represented using COMPASS (Condensed-phased Optimized Molecular Potential for Atomistic Simulation Studies), the first ab initio forcefield that enables an accurate and simultaneous prediction of various gas-phase and condensed-phase properties of organic and inorganic materials.The results obtained show that due to a significant drop in the configurational entropy of toluene, the solvation Gibbs free energy for these nanotubes in toluene is small but positive suggesting that a suspension of these nanotubes in toluene is not stable and that the nanotubes would fall out of the solution. This prediction is consistent with experimental observations. 相似文献
999.
1000.