共查询到20条相似文献,搜索用时 31 毫秒
1.
Titanium metal bodies have been prepared from the sintered powder compacts of TiO2 by a novel molten salt electrochemical approach, known as FFC Cambridge process. The phase and compositional characterizations
of both Ti and TiO2 have been carried out by X-ray diffraction. The pore morphologies of sintered TiO2 pellet and the metallic Ti pellet, obtained after electrochemical reduction have been studied by SANS over a scattering wave
vector q range of 0.003–3.5 nm−1 using a double crystal diffractometer and a pin-hole collimated SANS instrument. In the case of reduced metal pellet, average
pore size was found to be larger than that of the oxide pellet as the voids left behind after the oxygen atoms left the oxide
matrix, could not coalesce.
相似文献
2.
Effect of porosity and pore size distribution on the low-frequency dielectric response, in the range 0.01–100 kHz, in sintered
ZrO2—8 mol% Y2O3 ceramic compacts have been investigated. Small-angle neutron scattering (SANS) technique has been employed to obtain the
pore characteristics like pore size distribution, specific surface area etc. It has been observed that the real and the imaginary
parts of the complex dielectric permittivity, for the specimens, depend not only on the porosity but also on the pore size
distribution and pore morphology significantly. Unlike normal Debye relaxation process, where the loss tangent vis-à-vis the
imaginary part of the dielectric constant shows a pronounced peak, in the present case the same increases at lower frequency
region and an anomalous non-Debye type relaxation process manifests. 相似文献
3.
Mesoscopic density fluctuations in liquid phase sintered silicon carbide have been investigated using small angle neutron
scattering (SANS). The increase in the additives results in the modification in the pore size distribution and to some extent
the total porosity. SANS revealed a mass fractal nature of the agglomerated matrix microstructure. The fractal dimension of
the matrix does not change appreciably with the additives although the upper cut-off value of the fractal decreases significantly
with the increase in the additives. The liquid phase sintering due to the presence of additives helps to achieve higher level
of densification. However, the agglomeration hinders achievement of the fully dense pellets.
相似文献
4.
We report a combined use of small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) to the study of
counterion condensation in ionic micelles. Small-angle neutron and X-ray scattering measurements have been carried out on
two surfactants cetyltrimethylammonium bromide (CTABr) and cetyltrimethylammonium chloride (CTACl), which are similar but
having different counterions. SANS measurements show that CTABr surfactant forms much larger micelles than CTACl. This is
explained in terms of higher condensation of Br− counterions than Cl− counterions. SAXS data on these systems suggest that the Br− counterions are condensed around the micelles over smaller thickness than those of Cl− counterions. 相似文献
5.
Chivalrat Masingboon Prasit Thongbai Santi Maensiri Teerapon Yamwong 《Applied Physics A: Materials Science & Processing》2009,96(3):595-602
Nanocrystalline CaCu3Ti4O12 powders were synthesized by a simple PVA sol–gel route and calcined at 700 and 800°C in air for 8 h. The diameter of the
powders ranges from 40–100 nm. The calcined CaCu3Ti4O12 powders were characterized by TG-DTA, XRD, FTIR, SEM, and TEM. Sintering of the powders was conducted in air at 1100°C for
16 h. The XRD results indicated that all sintered samples had a typical perovskite CaCu3Ti4O12 structure although the sintered samples contained some amount of CaTiO3. SEM of the sintered CaCu3Ti4O12 ceramics showed the average grain sizes of 13–15 μm. The samples exhibit a giant dielectric constant, ε′∼105 at 150 to 200°C with weak temperature dependence below 1 kHz in the sample sintered using the powders calcined at 700°C.
The Maxwell–Wagner polarization mechanism is used to explain the high permittivity in these ceramics. It is also found that
all sintered samples have the same activation energy of grains, which is ∼0.122 eV. 相似文献
6.
Nanocrystalline nickel oxide powders were calcined at 300, 600 and 900°C and pore structure evolution was followed by small
angle neutron scattering (SANS). Pore size distributions at two widely separated size ranges have been revealed. Shrinkage
of larger-sized pore with reduction in polydispersity has been observed with increasing heat treatment temperature. The pore
structures at various heat treatment temperatures do not scale. This has been attributed to the grain boundary diffusion leading
to an asymmetric shrinkage of the pores.
相似文献
7.
The morphology of carbon nanofoam samples comprising platinum nanoparticles dispersed in the matrix was characterized by small
angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) techniques. Results show that the structure of pores
of carbon matrix exhibits a mass (pore) fractal nature and the average radius of the platinum particles is about 2.5 nm. The
fractal dimension as well as the size distribution parameters of platinum particles varies markedly with the platinum content
and annealing temperature. Transmission electron micrographs of the samples corroborate the SANS and SAXS results.
相似文献
8.
J. Bahadur D. Sen S. Mazumder V. K. Aswal V. Bedekar R. Shukla A. K. Tyagi 《Pramana》2008,71(5):959-963
Effects of sintering on pore morphology and dielectric response have been investigated. Pore structure has been probed by
small angle neutron scattering (SANS). It has been observed that the size distribution becomes less polydisperse with a slight
modification in the distribution as sintering temperature is increased. Dielectric response in the frequency range 0.02–1000
kHz is significantly altered by modification of pore structure because of sintering. A transition from non-Debye type to near-Debye
type response has been observed as the sintering temperature is increased.
相似文献
9.
An analytical approach has been taken for analyzing the multiple scattering effects in small angle scattering (SAS) from both
monodisperse and polydisperse systems. Two limiting regions, viz the Guinier region and the Porod region have been studied.
A modified form of Guinier law has been deduced for the scattered intensity distribution in the region of small wave vector
transfer, q. In the regionq(=|q|)→∞, it is shown that the effect of multiple scattering does not alter the Porod (q
−4) law. In the case of polydisperse systems, a correlation has been established between the size distribution of the inhomogeneities
and the experimentally extractable parameters. The validity of the formalism has been examined by reinterpretation of the
multiple SANS data (Hardman-Rhyne and Berk 1985) on polydisperse Al2O3 samples. This formalism is useful in characterizing the inhomogeneities from SAS measurements, particularly when thick samples
are used. 相似文献
10.
R. Neffati J. Rault 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(2):205-210
By differential Scanning Calorimetry (DSC), at low heating rate and using a technique of fractionation, we have measured the
equilibrium DSC signal (heat flow) J
q
0 of two families of porous glass saturated with water. The shape of the DSC peak obtained by these techniques is dependent
on the sizes distribution of the pores. For porous glass with large pore size distribution, obtained by sol-gel technology,
we show that in the domain of ice melting, the heat flow Jq is related to the melting temperature depression of the solvent, ΔT
m , by the scaling law: J
q
0∼ΔT
m
- (1 + D). We suggest that the exponent D is of the order of the fractal dimension of the backbone of the pore network and we discuss the influence of the variation
of the melting enthalpy with the temperature on the value of this exponent. Similar D values were obtained from small angle neutron scattering and electronic energy transfer measurements on similar porous glass.
The proposed scaling law is explained if one assumes that the pore size distribution is self similar. In porous glass obtained
from mesomorphic copolymers, the pore size distribution is very sharp and therefore this law is not observed. One concludes
that DSC, at low heating rate ( q? 2°C/min) is the most rapid and less expensive method for determining the pore distribution and the fractal exponent of a porous
material.
Received 23 July 1999 and Received in final form 16 February 2001 相似文献
11.
Precipitates of ceria were synthesized by homogeneous precipitation method using cerium nitrate and hexamethylenetetramine
at 80°C. The precipitates were ground to fine particles of average size ∼0.7 μm. Circular disks with 10 mm diameter, 2 and
3 mm thickness were prepared from the green compacts by sintering at 1300° C for three different sintering times. Evolution
of the pore structures in these specimens with sintering time was investigated by small-angle neutron scattering (SANS). The
results show that the peak of the pore size distribution shifts towards the larger size with increasing sintering time although
the extent of porosity decreases. This indicates that finer pores are eliminated from the system at a faster rate than the
coarser ones as sintering proceeds and some of the finer pores coalesce to form bigger ones. 相似文献
12.
H. Tietze-Jaensch D. Sieger R. Geick W. Zulehner A. de Geyer 《Applied Physics A: Materials Science & Processing》1992,54(1):19-21
The formation of silicon oxide precipitates from Czochralski grown silicon depends on the time and temperature of the heat treatment as well as on the initial content of interstitially dissolved oxygen. Samples containing between 5×1017 Oi/cm3 and 13×1017 Oi/cm3 have been heated at 750° C for 96 h. SiO2 precipitates of various shape and size have been obtained and investigated by means of small angle neutron scattering (SANS) in the Q-range 0.05 Å–1<Q<0.2 Å–1. The obtained SANS patterns reveal a typical anisotropy of their intensity distribution, which splits into a central peak at Q<0.1 Å–1 due to the shape of the individual particles and a number of weak intensities for large Q-values, originating from a correlation between defects, possibly between the precipitates. While these correlation peaks in the SANS patterns are seen best for rather low values of about (5–7)×1017 Oi/cm3 oxygen content, the central peak anisotropy is most pronounced for higher values of ca 10×1017 Oi/cm3. The integrated intensity of the central peak increases with increasing initial oxygen content. For comparison, untreated samples of the same initial oxygen content do not reveal any anisotropic SAN scattering or a broadened central peak beam. 相似文献
13.
Aqueous solutions of a well-defined poly(N-isopropylacrylamide-co-sodium 2-acrylamido-methylpropanesulfonate) (NIPAM/NaAMPS in a 95/5 molar ratio) have been investigated by means of small-angle
neutron scattering (SANS) and rheological experiments as a function of temperature ( 25°
C
T
60°
C) and polymer concentration ( 0.5wt%
C
12wt%). The solutions remain optically transparent and isotropic over the whole temperature range, in contrast with the homopolyNIPAM
which precipitates above its lower critical solution temperature (LCST = 32°
C). Upon addition of salt, the systems undergo a micro-macrophase separation. At temperatures above 45°
C, the SANS spectra exhibit a sharp peak at a scattering wave vector, q
max, which increases slightly with temperature. At high temperature ( T∼ 60°
C), the scattered intensity follows a power law I(q) ∼q
-4 in the asymptotic regime, characteristic of two-density media with sharp interfaces, and q
max is found to vary with polymer concentration as q
max∼C
0.22. Estimates of the typical sizes give values between 40 ? and 200 ?. These results provide a strong evidence of a thermally
induced microphase separation, which is corroborated by the very sharp increases of the viscosity (over 2 decades) and of
the stress relaxation time of the solutions, occurring in the temperature range where the scattering peak is observed. The
results are discussed and compared with the theoretical models proposed for weakly charged polyelectrolytes in a poor solvent.
Received 1 October 2001 相似文献
14.
D. Sieger H. Tietze-Jaensch R. Geick W. Zulehner A. F. Wright A. de Geyer 《Applied Physics A: Materials Science & Processing》1991,53(5):422-425
Czochralski grown silicon crystals contain interstitially dissolved oxygen which diffuses on heating to form precipitates of silica. We have examined these precipitates by small angle neutron scattering (SANS) in the Q-range 0.05 Å–1<Q<0.4 Å–1. The obtained SANS patterns reveal pronounced anisotropic intensity distributions which resemble the symmetry of the host crystal. The SANS spectra show an anisotropic central peak at Q<0.1 Å–1 due to the single particle shape and a number of weak intensities for larger Q-values. These weak side maxima are considered correlation peaks or quasi-elastic interference peaks. They show, however, an unexpected and distinct temperature dependence: with decreasing temperature below values of 220 K their intensity is lost slowly, but reversibly. At T = 50 K only the central peak from the single-particle scattering remains unchanged. Upon heating, the correlation peaks regain their former value of intensity and Q-position without any evidence of thermal hysteresis. 相似文献
15.
Eunjoo Shin Shi-Hoon Choi Baek-Seok Seong Hu-Chul Lee Kye Hong Lee 《Applied Physics A: Materials Science & Processing》2010,99(3):621-625
The effect of cold rolling on the small-angle neutron scattering (SANS) pattern was investigated for low-carbon steels. Several
cold rolled steel samples with different reduction ratios and annealed samples after cold rolling were respectively measured
by SANS. The cold rolled samples presented anisotropic two-dimensional (2D) SANS patterns. From the 2D SANS patterns two kinds
of 1D pattern were calculated: one was for the Q⊥RD (rolling direction), the other for the Q//RD. The scatterer sizes calculated from the 1D patterns by using a model fitting
increased with the reduction ratio, for the Q⊥RD section only. The annealed sample presented an isotropic SANS pattern. It can be concluded that the dislocations produced
during the cold rolling process accumulated around the precipitates and then caused anisotropic 2D SANS patterns. 相似文献
16.
Takenao Shinohara Jun-ichi Suzuki Takayuki Oku Shin-ichi Takata Hiroshi Kira Kentaro Suzuya Kazuya Aizawa Masatoshi Arai Toshiya Otomo Masaaki Sugiyama 《Physica B: Condensed Matter》2009,404(17):2640-2642
Small-angle neutron scattering technique using polarized neutrons is powerful for studying structures in the range between nm and μm of magnetic materials. In addition, they have been used for the incident beam of focusing-geometry SANS instruments using a magnetic neutron lens, where a high polarization degree of about 99.9% is necessary because the imperfectness of the neutron polarization increases the background level. We are going to install such a magnetic focusing system on the new time-of-flight SANS (TOF-SANS) instrument at the J-PARC so as to make qmin smaller than 10−3 Å−1 and improve the resolution of the conventional TOF-SANS at low q. As a polarizing device of the instrument, two V-shaped polarizing super mirrors arranged in crossed geometry to enhance the polarization degree has been considered. In this paper, we present the concept and the detailed design of this device and its performance estimated by Monte Carlo simulations. 相似文献
17.
The double perovskite Sr2NiMoO6 powders and ceramics were prepared by two different (conventional and precursor) solid-state reaction methods. The phase
structure was characterized by XRD and TEM techniques. It has been indicated that single-phase perovskite powders were obtained
when calcined in air at 1300°C. However, nano-particles of the size 30–60 nm have been found in powders prepared with the
precursor method, while those from the conventional route exhibit large irregular shaped particles with aggregation. The dielectric
properties (ε
r
and tanδ) were also examined in the sintered ceramics. The results showed the transition point at 280°C for conventional route, while
no clear phase change was observed in ceramics from the precursor route. These observations clearly indicate that the different
starting processes affected the phase formation behavior and the electrical properties of Sr2NiMoO6 ceramics. 相似文献
18.
A. Kotani 《The European physical journal. Special topics》2009,169(1):191-197
We examine the structure of aggregates formed due to DNA
interaction with dipalmitoylphosphatidylcholine (DPPC) in presence of Ca2+ and Zn2+ using small-angle synchrotron X-ray diffraction (SAXD)
and neutron scattering (SANS). SAXD shows structural heterogeneity as a
function of the cation concentration and temperature: At low cation
concentration (∼1 mM), aggregates show two DPPC phases, one with a
lateral segregation of DNA and cation, while higher cation concentration
improves the DNA packing and the condensed lamellar phase is observed in
DNA+DPPC+20mMion2+ aggregates. The SANS detected the dissolution of
the condensed lamellar phase into unilamellar DPPC+Zn2+ vesicles due
to gel ↦ liquid-crystal phase transition in DNA+DPPC+20mM Zn2+ aggregates with the short fragmented salmon sperm DNA. 相似文献
19.
The equation describing the distribution of energy losses of a particle propagating in a fractal medium with quenched and
dynamic heterogeneities has been derived. It has been shown that in the case of the medium with fractal dimension 2 < D < 3, the losses Δ are characterized by the sublinear anomalous dependence Δ ∼ x
α with a power-law dependence on the distance x from the surface and exponent α = D − 2. 相似文献
20.
C. Masingboon S. Maensiri T. Yamwong P.L. Anderson S. Seraphin 《Applied Physics A: Materials Science & Processing》2008,91(1):87-95
Nanocrystalline CaCu3Ti4O12 powders with particle sizes of 50–90 nm were synthesized by a simple method using Ca(NO3)2·4H2O, Cu(NO3)2·4H2O, titanium(diisoproproxide) bis(2,4-pentanedionate) and freshly extracted egg white (ovalbumin) in aqueous medium. The synthesized
precursor was characterized by TG-DTA to determine the thermal decomposition and crystallization temperature which was found
to be at above 400 °C. The precursor was calcined at 700 and 800 °C in air for 8 h to obtain nanocrystalline powders of CaCu3Ti4O12. The calcined CaCu3Ti4O12 powders were characterized by XRD, FTIR, SEM and TEM. Sintering of the powders was conducted in air at 1100 °C for 16 h.
The XRD results indicated that all sintered samples have a typical perovskite CaCu3Ti4O12 structure and a small amount of CuO, although the sintered sample of the 700 °C calcined powders contained some amount of
CaTiO3. SEM micrographs showed the average grain sizes of 12.0±7.8 and 15.5±8.9 μm for the sintered CaCu3Ti4O12 ceramics prepared using the CaCu3Ti4O12 powders calcined at 700 and 800 °C, respectively. The sintered samples exhibit a giant dielectric constant, ε′ of ∼ 1.5–5×104. The dielectric behavior of both samples exhibits Debye-like relaxation, and can be explained based on a Maxwell–Wagner model.
PACS 77.22.Gm; 81.05.Je; 81.07.Wx; 81.20.Ev 相似文献