共查询到20条相似文献,搜索用时 31 毫秒
1.
A. Venkataraman Vijay A. Hiremath S. K. Date S. D. Kulkarni 《Bulletin of Materials Science》2001,24(6):617-621
A new combustion route for the synthesis of γ-Fe
2
O
3
is reported by employing purified a-Fe
2
O
3
as a precursor in the present investigation. This synthesis which is similar to a self propagation combustion reaction, involves
fewer steps, a shorter overall processing time, is a low energy reaction without the need of any explosives, and also the
reaction is completed in a single step yielding magnetic iron oxide i.e. γ-Fe
2
O
3
.The as synthesized γ-Fe
2
O
3
is characterized employing thermal, XRD, SEM, magnetic hysteresis, and density measurements. The effect of ball-milling on
magnetic properties is also presented. 相似文献
2.
P. K. Thiruvikraman 《Bulletin of Materials Science》2006,29(4):371-374
We propose a microscopic, phenomenological model for the decrease in the viscosity observed at glass transition. Our model
is primarily applicable to chalcogenide glasses. According to this model, the decrease in the viscosity at glass transition
is mainly due to the breaking of the Van der Waals bonds in the chalcogenides. Using this model, we derive a relationship
between the glass transition temperature,T
g
,and the molar volume
V
m.The validity of this relation is checked using experimental data available in the literature for two binary systems (Ge-Se
and As-S) and a pseudo-binary system (As
40
Se
x
Te
60-x
. 相似文献
3.
Sm-Ru intermetallic surface alloy films were prepared by vacuum deposition and annealing of rare earth Sm on single crystal
Ru(0001) surface. The Ru 3
d
and Sm 3
d
core level spectra clearly show the formation of surface alloy layers. XPS measurements on surface alloy film revealed an
induced peak in the Ru 3
d
region at lower binding energy by 1 eV compared to the bulk Ru (elemental) suggesting an electronic effect of alloying and
Sm-Ru bond formation. The Sm 3
d
5/2
photoemission peak of Sm film consists of strong features characteristic of Sm(II) with electron configuration 4
f
6
(5
d
6
s
)
2
and Sm(III) with electron configuration 4
f
5
(5
d
6
s
)
3
.It is observed that the Sm(II) feature decreases in intensity upon alloy formation with surface Ru atoms. Oxidation of these
films with carbon monoxide indicates alloy breakdown due to the oxidation of Sm atoms selectively. Alloy oxidation also shows
a clear shift of Sm 3
d
5/2
feature. 相似文献
4.
S. N. Ekbote G. K. Padam M. Sharma N. K. Arora B. S. Khurana R. C. Goel D. K. Suri N. Mehra B. K. Das 《Bulletin of Materials Science》2001,24(6):603-609
Bulk tube conductors of Bi
1.84
Pb
0.4
Sr
2
Ca
2.2
Cu
3
O
10+x
with addition of silver varying from 0 to 25 wt% (not reported earlier) were systematically studied using X-ray diffraction
(XRD), scanning electron microscopy (SEM), electrical transport and a.c. susceptibility techniques. The tube conductors formed
by cold isostatic pressing (CIP) of the powders obtained from spray drying method have been made successfully. It was found
that Ag addition has not only affected the formation of the desired Bi-2223 phase and the microstructure of these large bulk
tube samples thereby influencing on the critical current (
I
c
),it also reduces the contact resistance to minimize the cryogen losses. These variations have been found to be Ag content dependent.
An optimized value of 10 wt% Ag has been found to produce the best quality tubes showing reproducible
I
c
value > 120 Amp at 77 K which is in general a requirement to energies of the cryogen free conventional/HTSC superconducting
magnets below 20 K. 相似文献
5.
Effect of zirconium addition on the recrystallization behaviour of a commercial Al-Cu-Mg alloy 总被引:3,自引:0,他引:3
K. T. Kashyap 《Bulletin of Materials Science》2001,24(6):643-648
It is well known that the second phase particles have an effect on recrystallization and grain growth behaviour of an alloy.
Particularly the bimodal distribution of second phase particles has an effect which is opposite in sense where coarse second
phase particles (> 1 μm) stimulate nucleation while fine particles exhibit Zener drag.
In the literature, the effect of zirconium addition to aluminium alloys has been well documented in order to produce superplasticity
by giving ultra fine grain size to the alloy. Addition of zirconium produces Al
3
Zr particles which pin the grain boundaries during recrystallization and grain growth.
In the present work, zirconium was added to a commercial Al-Cu-Mg alloy and by heat treatment Al
3
Zr particles were precipitated and after forging, the grain size was an order of magnitude lower than the alloy without zirconium.
Transmission electron microscopy was employed to characterize the second phase particles, i.e. Al
3
Zr particles and found to be rod shaped and identified to be cubic ordered
L
1
2
phase with a lattice parameter of 0.408 nm. Further, it was observed that fine (100 nm) Al
3
Zr particles promote only continuous recrystallization which is polygonization of subgrains and subgrain growth.
It was found that the fine dispersion of Al
3
Zr particles inhibits both recrystallization and grain growth in the commercial Al-Cu-Mg alloy. 相似文献
6.
Ca
4
Mg
5
(PO
4
)
6
:Eu2+^{\boldsymbol{2+}} blue-emitting phosphor was synthesized by the combustion-assisted synthesis method under reductive atmosphere. The products
were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) spectrum.
XRD analysis confirmed the formation of Ca
4
Mg
5
(PO
4
)
6
pure phase. Photoluminescence results showed that the phosphor can be excited efficiently by UV light range from 230–400 nm,
and then exhibited bright blue light with peak wavelength at 431 nm. It is a very promising candidate as a blue-emitting phosphor
for potential applications in display devices. 相似文献
7.
T. C. T. Ting 《Acta Mechanica》2006,185(3-4):147-164
Summary It is shown that a necessary and sufficient condition for a longitudinal wave to propagate in the direction n in an anisotropic elastic material is that the elastic stiffness C
11 (n) is a stationary value (maximum, minimum or saddle point) at n. Explicit expressions of all n and the corresponding elastic stiffness C
11 (n) for which a longitudinal wave can propagate are presented for orthotropic, tetragonal, trigonal, hexagonal and cubic materials.
As to longitudinal waves in triclinic and monoclinic materials, only few explicit expressions are possible. We also present
necessary and sufficient conditions for a transverse wave to propagate in the direction n. As an illustration, explicit expressions of all n, the polarization vector a and the wave speed c for which a transverse wave can propagate in cubic and hexagonal materials are given. The search for n in hexagonal materials confirms the known fact that a transverse wave can propagate in any direction. A longitudinal wave
is necessarily accompanied by two transverse waves. However, a transverse wave can propagate without being accompanied by
a longitudinal wave. 相似文献
8.
9.
Synthesis of Hg(Tl)Ba
2
Ca
2
Cu
3
O
8+δ
superconducting tapes have been accomplished by annealing the precursor tape, Ba
2
Ca
2
Cu
3
O
y
(fabricated by doctor blade tape casting technique) in an environment of Hg(Tl) vapour. Characterization of superconducting
HTSC tape sample was carried out through XRD, TEM, SEM and R-T measurements. Surface morphological investigations of the as-synthesized
Hg(Tl)Ba
2
Ca
2
Cu
3
O
8+δ
HTSC tapes by scanning electron microscope have shown the occurrence of curious growth characteristics resembling spiral like
features. These growth spirals encompass nearly the whole grain suggesting that spiral growth led to the formation of small
crystal like grains of superconducting material Hg(Tl)Ba
2
Ca
2
Cu
2
O
8+δ
.The likely mechanism for the generation of these screw dislocations has been elucidated in terms of incoherent coalescence
of growth fronts formed from Hg(Tl):1223 and Hg(Tl):1234 nuclei. 相似文献
10.
Rare earth based materials have recently attracted considerable attention as potential ecofriendly colourants for low temperature
as well as high temperature applications. In the present study, we have synthesized a series of Ca-doped PrPO4 compounds with the general formula, Pr1-xCaxPO4 (x
= 0-0.4 in steps of 0.1) and characterized the compounds by powder X-ray diffraction. All the compositions show a monoclinic
monazite structure. The optical properties of the brilliantly coloured pigments [
L
(brightness),a*
(+ red- green),b*
(+ yellow - blue) have been examined. These materials can find application as potential green colourants. 相似文献
11.
A. I. Belogorokhov I. S. Zakharov A. F. Knyazev A. V. Kochura 《Inorganic Materials》2000,36(7):653-656
The spectral response of the photocurrent through Se-dopedCd
1.23
Zn
1.77
As
2
single crystals was studied. The results were used to determine the band gap at absolute zero (0.540 eV) and the temperature
coefficient of band gap (-0.39 meV/K). The photocurrent spectra were found to contain a photovoltaic peak attributable to
Schottky barriers at the interface between the semiconductor and the metallic contact. The heights of the barriers responsible
for residual conductivity were evaluated using a two-barrier model. Both surface and bulk inhomogeneities were shown to play
a significant part in residual conductivity. 相似文献
12.
Abstract We show that every Mueller matrix, that is a real 4 × 4 matrix M which transforms Stokes vectors into Stokes vectors, may be factored as M = L 2 KL 1 where L 1 and L 2 are orthochronous proper Lorentz matrices and K is a canonical Mueller matrix having only two different forms, namely a diagonal form for type-I Mueller matrices and a non-diagonal form (with only one non-zero off-diagonal element) for type-II Mueller matrices. Using the general forms of Mueller matrices so derived, we then obtain the necessary and sufficient conditions for a Mueller matrix M to be Jones derived. These conditions for Jones derivability, unlike the Cloude conditions which are expressed in terms of the eigenvalues of the Hermitian coherency matrix T associated with M, characterize a Jones-derived matrix M through the G eigenvalues and G eigenvectors of the real symmetric N matrix N = [Mtilde]GM associated with M. Appending the passivity conditions for a Mueller matrix onto these Jones-derivability conditions, we then arrive at an algebraic identification of the physically important class of passive Jones-derived Mueller matrices. 相似文献
13.
J. K. Radhakrishnan B. S. Sunderseshu Meenakshi Srivastava G. L. Seth R. Raman R. C. Narula R. K. Bagai 《Bulletin of Materials Science》2001,24(6):659-663
One of the most pressing issues in the growth of high quality single crystal Cd
0.96
Zn
0.04
Te material, is to achieve homogenization of the high axial variation of Zn concentration, caused by the larger than unity
segregation coefficient of Zn in CdTe. This is achieved in our crystals (i) by thermal annealing of the CdZnTe crystal, which
redistributes the as grown Zn distribution by solid state diffusion of Zn (this solid state diffusion of Zn occurs at three
stages (a) during the growth when the solidified crystal is near to the melting point temperature, (b) during the post growth
annealing of the crystal at a high temperature and (c) during the cooldown to room temperature) and (ii) by the reduction
of Zn segregation during the growth stage by enhanced convective mixing of the melt, through a proper choice of ampoule and
furnace dimensions. By adopting suitable growth parameters and sufficient post growth annealing it has been possible to grow
Cd
0.96
Zn
0.04
Te crystals, which have nearly 75% of their fraction within 1% Zn concentration variation. 相似文献
14.
Multivariate exponentially weighted moving average (MEWMA) control chart with five different estimators as population covariance matrix is rarely applied to monitor small fluctuations in the statistical process control. In this article, mathematical models of the five estimators (S1, S2, S3, S4, S5) are established, with which the relevant MEWMA control charts are obtained, respectively. Thereafter, the process monitoring performance of the five control charts is simulated. And the simulation results show that the S4 estimator-based MEWMA control chart is of the best performance both in step offset failure mode and ramp offset failure mode. Since the inline process monitoring of photovoltaic manufacturing is intended to be a problem of multivariate statistics process analysis, the feasibility and effectiveness of the proposed model are elaborated in the case study during the cell testing and sorting process control for the fabrication of multicrystalline silicon solar cells. 相似文献
15.
Seven samples of the polycrystalline, Ni1.25-xZnxPb0.25Fe1.5O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) ferrites, were prepared by usual double sintering ceramic method. X-ray diffraction
patterns of the samples revealed single-phase cubic spinel structure. The magnetic properties were investigated by means of
magnetization and a.c. susceptibility (χ) measurements. A.C. susceptibility was measured from room temperature to the Curie
temperatureT
C) of the samples. Variation of a.c. susceptibility (χ) with temperature showed that the samples withx
= 0.3 and 0.5 contain single-domain (SD) particles whereas the samples with
x
= 0.4 and 0.6 showed multi-domain (MD) nature. Values of Curie temperature (
T
C)as obtained from the study of variation of a.c. susceptibility with temperature were found to decrease with increase in the
Zn
2+ concentration (x bd. Magnetic measurements showed increase in magnetization as Zn2+ content was increased from 00 to 0.5. Further increase in Zn2+ contentx bd reduces the magnetization. 相似文献
16.
Silicate based bioceramics are promising candidates as biomaterials for tissue engineering. The combustion synthesis method
provides control on the morphology and particle size of the synthesised material. This paper discusses the combustion synthesis
of akermanite (Ca
2
MgSi
2
O
7
and Sr
2
MgSi
2
O
7
), which has been shown to have good in vitro and in vivo bioactivities by earlier studies. Both Ca
2
MgSi
2
O
7
and Sr
2
MgSi
2
O
7
have akermanite structure. Ca
2
MgSi
2
O
7
and Sr
2
MgSi
2
O
7
were prepared using urea and ammonium nitrate. The combustion synthesis using urea and ammonium nitrate was found to be cost
effective and efficient method of synthesis. The photoluminescence study of Ca
2
MgSi
2
O
7
: Eu2+^{\boldsymbol{2+}} and Sr
2
MgSi
2
O
7
: Eu2+^{\boldsymbol{2+}} shows host specific intense emission of Eu2+^{\boldsymbol{2+}}. 相似文献
17.
Roberto K?ferstein Lothar J?ger Stefan G. Ebbinghaus 《Journal of Materials Science》2010,45(23):6521-6527
The formation of BaCeO3 by a co-precipitation method is described herein. The co-precipitation route leads to an orange (BaCe)-precursor powder (1). To improve the sintering behaviour, a small amount of Ge4+ was incorporated, leading to a (BaCe0.95/Ge0.05)-precursor (2). Both precursor powders results in fine-grained preceramic powders (1A, 2A) after calcination. The shrinkage and sintering behaviour of resulting powder compacts were studied in comparison to a coarse-grained
mixed-oxide BaCeO3 powder (3). Compacts of 2A reach a relative density of 90% after sintering at 1350 °C with grain sizes between 0.9 and 3.2 μm. On the other hand ceramics
of 1A and 3 have, after sintering at 1500 °C (10 h), relative densities of 85 and 76%, respectively. Ceramic bodies of 1A consisted of phase-pure orthorhombic BaCeO3, whereas bodies of 2A show reflections of BaCeO3 and a Ba2GeO4 phase. DTA investigations of samples 1A and 2A reveal three phase transitions at 255 °C (1A) and 256 °C (2A) as well as 383 °C (1A) and 380 °C (2A). A very weak one can be obtained in the range 880–910 °C. 相似文献
18.
D BOZIC J STASIC B DIMCIC M VILOTIJEVIC V RAJKOVIC 《Bulletin of Materials Science》2011,34(2):217-226
The multiple hardening mechanisms of a copper matrix have been presented and discussed. The pre-alloyed ball milled Cu–3 wt.%Al
and the atomized Cu–0·6 wt.%Ti–2·5 wt.%TiB
2
powders have been used as starting materials. Dispersoid particles Al
2
O
3
and TiB
2\thinspace _{{\bf 2}\thinspace }were formed in situ. The powders have been hot consolidated. Optical microscopy, SEM, TEM, and X-ray diffraction analysis were performed for
microstructural characterization. Increase in microhardness of Cu–3 wt.%Al compacts is a consequence of the crystallite size
refinement and the presence of Al
2
O
3
particles. High hardening of Cu–0·6 wt.%Ti–2·5 wt.%TiB
2
is a consequence of the presence of modular structure, Cu
4
Ti(m), and TiB
2
particles. 相似文献
19.
Quadratic response surface methodology often focuses on finding the levels of some (coded) predictor variables x = (x 1, x 2,…, x k) that optimize the expected value of a response variable y. Typically the experimenter starts from some best guess or “control” combination of the predictors (usually coded to x = 0) and performs an experiment varying them in a region around this center point. The question of interest addressed here is whether any x in the experimental region provides a long-run mean response E(y) preferable to that of the control, and if so, by what amount? This article approaches this question via simultaneous confidence intervals for δ(x) = E(y|x) = E(y|0) for all x within a specified distance of 0. A new method for two or more predictors is introduced that gives sharper intervals than the Scheffé method and also the Sa and Edwards adaptation of the Casella and Strawderman method. The new method does not require a rotatable design and allows for one-sided simultaneous bounds for δ(x). Approximate sample-size savings of the improved method over the Sa and Edwards adaptation of the Casella and Strawderman method ranged from 12%–45% for two-sided intervals and 19%–40% for one-sided intervals for designs with two or three predictors. Approximate sample-size savings of the improved method over the Scheffe method ranged from 14%–47% for two-sided intervals and 22%–62% for one-sided intervals. 相似文献
20.
ANGELOS G KALAMPOUNIAS 《Bulletin of Materials Science》2011,34(2):299-303
IR and Raman spectroscopies have been utilized to study the structure and vibrational modes of sol–gel-derived binary silicate
glasses. The present study is motivated by the immense geological significance and focuses on the MO–SiO
2
(M = Ca, Mg) binary systems in an effort to unveil the role of the CaO and MgO modifiers when incorporated to the 3D silica
structure. Glasses in the composition range
x
=0, 0·1, 0·2, 0·3 and 0·4 prepared by the sol–gel method were compared with the corresponding glasses formed by appropriate
mixing of SiO
2
and MO powders through melting and fast cooling. The vibrational spectra of the sol–gel-derived glasses have revealed considerable
changes in relative intensities as a function of the MO mole fraction. These changes signify structural modifications on the
silica network. The population of the
Q
3
species was found to increase for both modified silicate systems. The rate of increase is more pronounced in the CaO–SiO
2
glasses. The extent of network depolymerization in the porous glass is higher at the same content of alkaline earth oxide
compared to the bulk glass. The results are indicative of a more ‘defective’ nature of the sol–gel glasses compared to the
corresponding melt-quenched ones. 相似文献