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1.
X-ray diffraction, Mössbauer spectroscopy and magnetization measurements were used to study the structure and some magnetic properties of Fe 50Ge 50 and Fe 62Ge 38 prepared by mechanical alloying from the elemental powders. In both cases in the early stages of milling the intermediate paramagnetic FeGe 2 phase was formed. The mechanical alloying process of Fe 50Ge 50 resulted in the formation of the paramagnetic FeGe (B20) phase with an average crystallite size of about 15 nm. In the case of the Fe 62Ge 38, the ferromagnetic Fe 5Ge 3 (β) phase with a Curie temperature of about 430 K was obtained. The average crystallite size was about 9 nm. The average hyperfine magnetic field of about 16 T allowed it to determine that more than four germanium atoms exist in the nearest environment of the 57Fe isotopes in the Fe 5Ge 3 phase. 相似文献
2.
Infrared brazing of Ti 50Ni 50 using two brazing filler metals was investigated in the study. Three phases, including Cu-rich, CuNiTi (Δ) and Ti(Ni,Cu), were observed in the Ti 50Ni 50/Cu/Ti 50Ni 50 joint after brazing at 1150 °C. The Cu-rich phase was rapidly consumed in the first 10 s of brazing, and the eutectic mixture of CuNiTi and Ti(Ni,Cu) phases were subsequently observed in the joint. Samples brazed for longer time resulted in less CuNiTi and more Ti(Ni,Cu) phases in the joint. The existence of CuNiTi phase deteriorated the shape memory effect of the joint, but Ti(Ni,Cu) could still preserve shape memory behavior even alloyed with a large number of Cu. Therefore, higher shape recovery ratio was observed for specimens brazed for a longer time period. Extensive presence of Ti 2(Ni,Cu) phase was observed in Ti 50Ni 50/Ticuni ®/Ti 50Ni 50 joint upon brazing the specimens up to 1150 °C. The bending test could not be performed due to the inherent brittleness of Ti 2(Ni,Cu) matrix. Moreover, the stable Ti 2(Ni,Cu) phase was difficult to be removed completely by increasing either brazing time and/or temperature. 相似文献
3.
Fe 7S 8 nanorods and nanosheets were synthesized in large scale by a novel flux method. The starting materials are Fe, S powder and KI flux. XRD patterns demonstrated the as-prepared products were Fe 7S 8. The morphology could be controlled by the synthetic temperature easily. Nanorods and nanosheets were synthesized at 750 and 850 °C, respectively. The thickness of synthesized nanosheets was smaller than 100 nm. The nanorod diameter was about 200 nm, its length was about 2 μm, and the growth direction of nanorod was [0 1 2]. The growth mechanism for Fe 7S 8 nanorods and nanosheets are discussed in detail. 相似文献
4.
Li(Co xNi 1 − x)O 2 (0 ≤ x ≤ 1) cathode powders were prepared by solid state reaction method using Co 3O 4/NiO precursor powders obtained by spray pyrolysis. The effect of the ratios of cobalt and nickel components on the characteristics of Co 3O 4/NiO precursor and Li(Co xNi 1 − x)O 2 cathode powders were investigated. The Co 3O 4/NiO precursor powders with the ratios of cobalt and nickel components as 1/0, 0.75/0.25 and 0.5/0.5 had submicron size and regular morphologies. On the other hand, the Co 3O 4/NiO powders with the high contents of nickel component had aggregated morphologies of submicron size primary powders. The fine-sized precursor powders formed the fine-sized LiCoO 2 and Li(Co 0.75Ni 0.25)O 2 cathode powders by solid state reaction with LiOH powders. However, the high contents of the nickel component of the Co 3O 4/NiO precursor powders formed the Li(Co xNi 1 − x)O 2 (0 ≤ x ≤ 0.5) cathode powders with aggregated morphologies and large sizes. The discharge capacities of the powders increased with increasing the nickel content into the Li(Co xNi 1 − x)O 2 cathode powders up to 188 mAh/g. 相似文献
5.
After the reverse thermal induced martensitic transformation process of shape memory alloy is arrested at a temperature between the reverse transformation start and finish temperatures ( As and Af), and then cooled to a temperature below Mf, a kinetic stop will occur in the next heat flow curve during the heating process. The kinetic stop is closely related to the arrested temperature. This phenomenon is called temperature memory effect (TME). TME of Ti 50Ni 30Cu 20 (at.%) shape memory alloy with phase transformation between B2 austenite and B19 martensite has been investigated by differential scanning calorimeter in this paper. The results indicate that TME of Ti 50Ni 30Cu 20 alloy only exists in the heating process. 相似文献
6.
Isothermal d.c. magnetization measurements were performed for (R χY 1-χ)Fe 2 (RDy, Er, 0<χ<1) at several temperatures. The observed pronounced decay of the coercive field Hc with temperature was fitted with an exponential curve at low temperatures for concentrations near 30%. The coercive field Hc and the propagation field Hp showed maximum values in the concentration range 30%–40% for Dy or Er. These results can be explained by intrinsic domain wall pinning. Time relaxation effects of the remanent magnetization were detected and attributed to domain wall surface deformations. 相似文献
7.
We have investigated the alloy ZrV 1.5Ni 1.5 by means of scanning electron microscopy (SEM) with electron probe X-ray microanalysis (EPMA), X-ray diffraction (XRD), in situ STM (scanning tunnelling microscopy in an electrolyte under controlled electrochemical potential) and electrochemical charge discharge measurements. By means of EPMA we found that the alloy is composed of three different crystallographic phases. The main phase (≈75 vol.%) is ZrV 0.81Ni 1.47, the second phase (≈20 vol.%) is V 92Ni 8 and the third (≈5 vol.%) is a ZrNi based phase. Using in situ STM we investigated the different corrosion behaviour of the phases. At a potential of −600 mV versus the Hg/HgO reference electrode we observed the corrosion of the vanadium rich phase while the other two phases passivated. 相似文献
8.
Superplastic deformation and crystallization behavior of a Cu 54Ni 6Zr 22Ti 18 metallic glass were investigated. A maximum elongation of 650% was obtained at 733 K at 1 × 10 −2 s −1 from the sheet fabricated by squeeze copper-mold casting method. At low strain rates, the strain-rate-sensitivity exponent value was close to 1, suggesting that Newtonian-like behavior governed the plastic flow. At a high strain rate around 10 −2 s −1, a transition from Newtonian to non-Newtonian behavior took place with decrease in m value. Large strain hardening by crystallization occurred during the course of deformation. The strain hardening was found to be caused by crystallization according to the analyses of the relation of true stress vs. testing time, T-T-T diagram and DSC characteristics. The time periods up to the strain before strain hardening at 733 K for the Cu 54Ni 6Zr 22Ti 18 metallic glass were similar to that of the Zr 65Al 10Ni 10Cu 15 metallic glass at 696 K as 180–300 s (3–5 min). This coincidence could be explained by comparison of their T-T-T diagrams showing that the incubation times for crystallization of the Cu BMG at 733 K and for Zr BMG at 696 K are similar. 相似文献
9.
The crystal structure of iron(III) selenate(IV) trihydrate, Fe 2(SeO 3) 3 • 3H 2O, space group R3c, a = 9.360(1) Å, C = 20.297(2) Å, V = 1539.98 Å 3, Z = 6, was determined by single-crytal X-ray diffraction methods, 926 unique data, measured up to 2θ = 70° (Mo K radiation); R, R(I)w = 0.034, 0.088. Fe 2(SeO 3) 3 • 3H 2O is isotypic with the analogues Al, Ga and Cr compounds and was synthesized under moderate hydrothermal conditions. 相似文献
10.
The n-type Co-doped β-FeSi 2 (Fe 0.98Co 0.02Si 2) with dispersion of several oxides, such as ZrO 2 or several rare-earth oxides (Y 2O 3, Nd 2O 3, Sm 2O 3 and Gd 2O 3), was synthesized by mechanical alloying and subsequent hot pressing. The effects of these oxide dispersions on the thermoelectric properties of Fe 0.98Co 0.02Si 2 were investigated. ZrO 2 was decomposed in the β phase, and the ZrSi and -FeSi phases, which are metallic phases, were formed in the samples with ZrO 2 addition. The Seebeck coefficient and the electrical resistivity were significantly decreased with increasing amount of ZrO 2, indicating that a part of the Zr atoms was substituted for Fe atoms in the β phase. In the case of the samples with rare-earth oxide addition, a decomposition of a large amount of these added oxides did not occur. However, the rare-earth oxide addition caused a slight increase in the amount of the phase. The Seebeck coefficient was significantly enhanced by the rare-earth oxide addition especially in the low temperature range. These facts indicated that a small amount of rare-earth oxides was decomposed in the β phase, and rare-earth elements were substituted for Fe atoms as a p-type dopant, resulting in the decrease in the carrier concentration. The rare-earth oxide addition was also effective in reducing the thermal conductivity. 相似文献
11.
An experimental investigation of the hydrogen absorption rate in the two-phase (–β) region of La 1.5Ni 0.5Mg 17 powder under the condition of various pressures and temperatures is presented. The results are well interpreted using the Jander diffusion model, [1−(1−ξ) 1/3] 2= k( T, P) t, which suggests that the rate-controlling step of hydrogen absorption in La 1.5Ni 0.5Mg 17 is three-dimensional diffusion. An apparent activation energy for such diffusion process of 90±1 kJ/mol H 2 has been obtained from the absorption data. 相似文献
12.
Structure relaxation and crystallization of Al 83Ni 10Ce 7 metallic glass were studied by different scanning calorimetry (DSC) and X-ray diffraction (XRD). According to the DSC scan, it is interesting to find that the second exothermic peak changes with pre-annealing temperatures (below glass transition temperature), suggesting a change in the amorphous structure upon relaxation. Continuous heating crystallization and isothermal crystallization exhibit different crystallization mechanism of the present alloy. fcc-Al and a metastable phase precipitate simultaneously in the first stage crystallization during continuous heating; however, only a metastable phase precipitates during isothermal annealing below glass transition temperature ( Tg). 相似文献
13.
The micro-defects of Fe 81Ga 19 ribbons have been investigated by the positron annihilation technique. It has been found that the defects of mono-vacancies and vacancy-clusters exist in the melt-spun ribbons of Fe 81Ga 19 alloy and the relative concentrations of them may be changed by heat treatment. The heat treatment leads to variations of magnetostrictive strains. As high as −3000 ppm strains have been obtained in the ribbons annealed at 700 °C, surpass the strain values of Tb–Dy–Fe alloys. Experimental results prove that magnetostrictive strains of Fe 81Ga 19 ribbons are related to the atomic vacancies and vacancy-clusters. 相似文献
14.
The effects of Cu addition on the β phase formation rate and the thermoelectric power in various FeSi 2 and Fe 2Si 5 based alloys was examined. The peritectoid reaction ( a+→β) in FeSi 2 alloys was initially enhanced by the addition of Cu but it became slower for longer annealing times. The retained metallic ε was harmful for the thermoelectric power. The inherent thermoelectric properties of (FeSi 2) 99−XMn 1Cu X ( X=0–1. O at.%), (FeSi 2) 99−X Co 1Cu X ( X=0–1.0 at.%) alloys were attained after the elimination of ε. In the case of eutectoid reaction (→β+Si). Differential thermal analysis, X-ray diffraction and microscopic observation clearly confirmed that the eutectoid reaction rate was drastically enhanced by the addition of a small amount of Cu and its rate decreased with decreasing Cu content. The rate also depends on the annealing temperature and reached a maximum at about 1073 K for most alloys. The addition of only 0.1 at.% Cu was still very effective even in Mn or Co doped alloys. The thermoelectric power of these alloys increased very quickly with annealing time. Their final values decreased with Cu content and saturated at 0.2 at.% Cu. The value of the 0.1 at.% Cu added alloy was higher than that of both the conventional p- and a-type FeSi 2 based alloys. These results suggest that the Fe 2Si 5 alloys with a small amount of Cu may be attractive as new thermoelectric materials. 相似文献
15.
Measurements of magnetic properties, X-ray diffraction and magnetostriction were made on Tb 0.27Dy 0.73(Fe 1 − xAl x) 2 ( x = 0.1, 0.2, …, 0.7) compounds. It was found that the system has the cubic MgCu 2 structure over almost the whole (Fe,Al) concentration range investigated, except for a narrow intermediate range ( x = 0.4–0.6) where the hexagonal MgZn 2 structure appears. With increasing Al content x, the lattice constant a increases linearly with x. The first replacement of Fe results in a marked decrease in the Curie temperature, which is followed by a slight decrease in TC with x. A linear decrease in magnetostriction of |λ | − λ | at room temperature with x was also observed from 1530 × 10 −6 for x=0 to 36×10 −6 for x=0.3. The saturation magnetization σ s exhibits a complex concentration dependence in the Tb 0.27Dy 0.73(Fe) 1 − xAl x) 2 system: in the range x < 0.5, σ s increases linearly with x and, for x = 0.5–0.6, σ s decreases and then increases again. An enhancement of the magnetic ‘hardness’ in this system was also observed at low temperature. 相似文献
16.
The ternary phase Yb 4Ni 10+xGa 21−x has been synthesised from the elements by high frequency melting in argon atmosphere. The homogeneity region has been established from X-ray powder data and confirmed by EDX analysis for 0.3≤ x≤1. The crystal structure of Yb 4Ni 10+xGa 21−x has been estimated from X-ray single crystal data: space group C2/ m (no. 12), Z=2, a=20.6815(9) Å, b=4.0560(4) Å, c=15.3520(7) Å, β=124.800(3)°, R( F)=0.023 for 1701 symmetry independent reflections with F( hkl)>4σ( F). A special feature of the structure is the local disorder within the gallium/nickel network. Neglecting atomic disorder in the region of the Ga9 and Ga11 positions, the Yb 4Ni 10+xGa 21−x structure is an occupation variant of the Ho 4Ni 10Ga 21 type with nickel atoms partially replacing the Ga atoms in the 2 d sites at the centers of distorted icosahedra. From magnetic susceptibility and from L III-XAS spectra, the valence state of ytterbium is near 3+. 相似文献
17.
A partially crystallized amorphous Ti 50Ni 25Cu 25 melt-spun ribbon showing spherical particles in martensite has been investigated. Microstructural observations support the hindering of the martensitic transformation as well as the production of additional autoaccommodated structures nearby the interface compared with the ones used inwards. 相似文献
18.
Ferrites have been studied for several years due to their wide use as magnetic materials for telecommunications, audio and video, power transformers and many other applications. Equimolar mixtures of Fe2O3 and TiO2 were fired in a muffle furnace at 1200 °C for 4 h. Mixed samples were prepared by replacing TiO2 with calculated amounts of CuO (x = 0.2, 0.4, 0.6, 0.8 and 1 mol). The synthesized samples were characterized with X-ray diffraction and their magnetic properties were measured using vibrating-sample magnetometer. The microstructure of the sample was examined using reflected light microscope and scanning electron microscope. The formation of Fe2TiO5, Fe5CuO8, Cu2TiO3 and CuFeO2 phases were detected whereas their magnetic properties increased with increasing the added mole ratio of Cu2+ ions. The isothermal reduction kinetics of synthesized nanocrystallites Ti–Cu mixed ferrite compacts were studied at 500 °C using hydrogen gas. It was found that the reduction rate and the reduction extent increased with increasing the extent of Cu2+ (0.2–1) whereas the maximum reduction extent (100%) was detected for pure Cu ferrite (Cu2+) while the minimum reduction extent (12%) was detected for pure iron titanate (Cu2+ = 0). The magnetic properties showed a drastic improvement upon reduction with hydrogen gas. 相似文献
19.
Stoichiometric Nd 2(Fe 1−xCo x) 14B alloys ( x=0, 0.25, 0.5, 0.75 and 1) have been disproportionated into NdH 2+δ and bcc–(Fe,Co) (0≤ x≤0.75) or fcc–Co ( x=1), respectively, by milling in hydrogen at enhanced temperatures. Reactive milling leads to the disproportionation of the thermodynamically very stable Nd 2Co 14B alloy. This reaction is not possible via the conventional hydrogenation disproportionation desorption and recombination (HDDR) process. Grain sizes of disproportionated and recombined Nd 2(Fe,Co) 14B materials were found to be <10 nm and 40–50 nm, respectively — approximately an order of magnitude smaller than those of conventional-HDDR processed alloys. The recombined Nd 2Co 14B alloy shows on average slightly smaller grain sizes than the Nd 2Fe 14B compound. A more effective exchange coupling leading to enhanced remanences, possibly due to the slightly smaller grain size, has been observed for Nd 2Co 14B powders recombined at 600–700°C. 相似文献
20.
The effect of Co substitution for Fe in Nd 3(Fe 1−xCo x) 27.7Ti 1.3N y (0 ≤ x ≤ 0.4) compounds on the magnetocrystalline anisotropy has been investigated. The anisotropy constants K's and the anisotropy field HA have been deduced from the magnetization curves measured on magnetically aligned powder (4–7 μm) samples. The obtained results show that at RT the anisotropy is uniaxial and HA (about 10 T) does not change substantially upon the substitution. At 5 K the results for K's give evidence for the presence of easy-cone-type anisotropy. The cone angle as well as the anisotropy field decrease upon the substitution from 21.6° to 11.8° and from 22.8 to 18.6 T, respectively. 相似文献
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