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1.
Suchitra Rajput Sujeet Chaudhary Subhash C. Kashyap Pankaj Srivastava 《Bulletin of Materials Science》2006,29(3):207-211
Superconducting bulk MgB2 samples have been synthesized by employing sintering technique without using any additional process steps, generally undertaken
in view of the substantial loss of magnesium, during heat treatment. Starting with Mg rich powders having different atomic
ratios of Mg : B, as against the nominally required Mg : B = 1:2 ratio, we have obtained superconducting MgB2 samples of different characteristics. The effect of excess Mg in the starting mixture and processing temperature on the phase-formation,
transition temperature (T
C) and critical current density (J
C) have been investigated by electrical transport and a.c. susceptibility measurements. The X-ray diffraction and X-ray photoelectron
spectroscopic analyses of MgB2 bulk samples have been carried out to understand the role of excess Mg and the effect of processing temperature. It is established
that MgB2 samples with high critical current density can be synthesized from a Mg rich powder having Mg : B in 2:2 ratio, at temperatures
around 790°C. Critical current density has been found to vary systematically with processing temperature. 相似文献
2.
Someswar Datta 《Bulletin of Materials Science》2001,24(6):569-577
The corrosion resistant oxide coatings, developed and applied by the conventional vitreous enamelling techniques, showed superior
resistance to a range of mineral acids at various strengths and temperatures, alkaline solutions, boiling water and chrome
plating solutions. These coatings possess considerable abrasion and impact resistance as well as high thermal shock resistance.
The properties of the coating system have been studied in detail and found to be strongly dependent on composition and processing
parameters. These coatings have been characterized by X-ray diffraction analysis and SEM studies. Some of the coating materials
have been found to be biocompatible. 相似文献
3.
M. P. Mahabole R. C. Aiyer C. V. Ramakrishna B. Sreedhar R. S. Khairnar 《Bulletin of Materials Science》2005,28(6):535-545
Hydroxyapatite (HAp) biomaterial ceramic was synthesized by three different processing routes viz. wet chemical process, microwave
irradiation process, and hydrothermal technique. The synthesized ceramic powders were characterized by SEM, XRD, FTIR and
XPS techniques. The dielectric measurements were carried out as a function of frequency at room temperature and the preliminary
study on CO gas sensing property of hydroxyapatite was investigated. The XRD pattern of the hydroxyapatite biomaterial revealed
that hydroxyapatite ceramic has hexagonal structure. The average crystallite size was found to be in the range 31–54 nm. Absorption
bands corresponding to phosphate and hydroxyl functional groups, which are characteristic of hydroxyapatite, were confirmed
by FTIR. The dielectric constant was found to vary in the range 9–13 at room temperature. Hydroxyapatite can be used as CO
gas sensor at an optimum temperature near 125°C. X-ray photoelectron spectroscopic studies showed the Ca/P ratio of 1.63 for
the HAp sample prepared by chemical process. The microwave irradiation technique yielded calcium rich HAp whereas calcium
deficient HAp was obtained by hydrothermal method. 相似文献
4.
AbstractThe retention of nanocrystallinity in dense ceramic materials is still a challenge, even with the application of external pressure during sintering. The compaction behavior of high purity and acetate enriched zinc oxide (ZnO) nano-powders was investigated. It was found that acetate in combination with water plays a key role during the compaction into green bodies at moderate temperatures. Application of constant pressure resulted in a homogeneous green body with superior packing density (86% of theoretical value) at moderate temperature (85 °C) in the presence of water. In contrast, no improvement in density could be achieved if pure ZnO powder was used. This compaction behavior offers superior packing of the particles, resulting in a high relative density of the consolidated compact with negligible coarsening. Dissolution accompanying creep diffusion based matter transport is suggested to strongly support reorientation of ZnO particles towards densities beyond the theoretical limit for packing of ideal monosized spheres. Finally, the sintering trajectory reveals that grain growth is retarded compared to conventional processing up to 90% of theoretical density. Moreover, nearly no radial shrinkage was observed after sinter-forging for bodies performed with this advanced processing method. 相似文献
5.
P. N. Vishwakarma V. Prasad S. V. Subramanyam V. Ganesan 《Bulletin of Materials Science》2005,28(6):609-615
Amorphous conducting carbon films deposited over quartz substrates were analysed using X-ray diffraction and AFM technique.
X-ray diffraction data reveal disorder and roughness in the plane of graphene sheet as compared to that of graphite. This
roughness increases with decrease in preparation temperature. The AFM data shows surface roughness of carbon films depending
on preparation temperatures. The surface roughness increases with decrease in preparation temperature. Also some nucleating
islands were seen on the samples prepared at 900°C, which are not present on the films prepared at 700°C. Detailed analysis
of these islands reveals distorted graphitic lattice arrangement. So we believe these islands to be nucleating graphitic.
Power spectrum density (PSD) analysis of the carbon surface indicates a transition from the nonlinear growth mode to linear
surface-diffusion dominated growth mode resulting in a relatively smoother surface as one moves from low preparation temperature
to high preparation temperature. The amorphous carbon films deposited over a rough quartz substrate reveal nucleating diamond
like structures. The density of these nucleating diamond like structures was found to be independent of substrate temperature
(700–900° C). 相似文献
6.
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
7.
Certain processing-related flaws in cold isostatically pressed ceramic powder compacts may arise from the delayed burn-out of organic binders until the sintering temperature is approached, although the isostatic compaction technique usually gives a higher and much more uniform green density than the conventional die compaction technique. For the 3 mol% Y2O3-doped zirconia powder in which 3 wt% PEG 1500 was introduced, the sintered density and sintering shrinkage were found to decrease in a near linear manner with increasing isostatic compaction pressure. The processing-related defects were identified as intergranular pores (1–5 m). It is considered that these processing-related defects are a consequence of incomplete organic burn-out at low and intermediate temperatures in the heating-up period and the swelling of intergranular pores associated with the burn-out of residual organic binders at temperatures close to the sintering temperature. A higher calcination temperature and an extended calcination dwell time may be required to eliminate the organic residuals in the isostatically pressed ceramic powder compacts than in the conventional die-pressed samples. 相似文献
8.
External stimuli response on a novel chitosan hydrogel crosslinked with formaldehyde 总被引:1,自引:0,他引:1
Keeping in mind the significance of hydrogels as an external stimuli sensitive super absorbing material, some transparent
covalent hydrogels of chitosan were prepared by crosslinking with varying amounts of formaldehyde solution used as crosslinking
agent. The characteristics of hydrogels were investigated by Fourier transform infrared (FT-IR) spectroscopy and swelling
experiments. The effect of crosslinking agent on water absorbency has been investigated. The hydrogels exhibited a relatively
higher swelling ratio in the range of 2066–3306% and equilibrium water content (EWC) in the range of 95-38–97 06% at pH 7
and 35°C temperature. The influence of external stimuli such as pH, temperature, and ionic strength of the swelling media
on equilibrium swelling properties has been observed. Hydrogels showed a typical pH and temperature responsive behaviour such
as low pH and high temperature has maximum swelling while high pH and low temperature show minimum swelling. An increase in
the ionic strength of swelling media caused a continuous decrease in the swelling of hydrogels at both acidic and basic pH. 相似文献
9.
Several applications of iron tartrate and manganese tartrate compounds are reported in the literature. In the present investigation,
we have grown pure and mixed iron (II)-manganese levo-tartrate crystals by single diffusion gel growth technique. Crystals
with spherulitic morphology were harvested. The colouration of the crystals changed from black to pinkish brown upon increasing
the content of manganese in the crystals. The crystals were characterized by FTIR spectroscopy, powder XRD, TGA, VSM and dielectric
study. Crystal structures of different mixed crystals were studied. From TGA it was observed that on heating the hydrated
crystals became anhydrous and then converted into oxides. Paramagnetic nature of the crystals was revealed from VSM study.
The variation of the dielectric constant with frequency was studied. The results are discussed. 相似文献
10.
Manjunath B. Bellakki A. S. Prakash C. Shivakumara M. S. Hegde A. K. Shukla 《Bulletin of Materials Science》2006,29(4):339-345
Cubic fluorite related Bi1−x
LnxO1.5 (Ln = Y and LaYb) phases are synthesized by solution-combustion method using glycine as the fuel. The cubic fluorite
phase is stabilized with 25 mole% of rare earth cations. The lattice parameter of cubic phase increases linearly with size
of the lanthanide ion. The synthesized powders are nano-metric in size and exhibit excellent compactability and reach 98%
densification even on short period of sintering. The oxides with relatively larger cations Nd, Sm, Eu, Pr and Gd with 25 mole%
composition transform to rhombohedral structure while others retain cubic upon sintering. All the phases show high oxide-ion
conductivity and the values obtained are in good agreement with the reported values. 相似文献
11.
We discuss the high pressure behaviour of zinc as an interesting example of controversy, and of extensive interplay between
theory and experiment. We present its room temperature electronic structure calculations to study the temperature effect on
the occurrence of its controversial axial ratio (c/a) anomaly under pressure, and the related electronic topological transition (ETT). We have employed a dense 63 X 63 X 29 k-point
sampling of the Brillouin zone and find that the small (c/a) anomaly near 10 GPa pressure persists at room temperature. A weak signature of the anomaly can be seen in the pressure-volume
curve, which gets enhanced in the universal equation of state, along with that of K-point ETTs. We attribute the change of
slope in the universal equation of state near 10 GPa pressure, mainly to hybridization effects. The temperature effect in
fact enhances the possibility of L-point ETT. We find that the L-point ETT is very sensitive to exchange correlation terms,
and hence we suggest that further refinements in the theoretical techniques are needed to resolve the controversies on the
ETT in Zn. 相似文献
12.
Cells of lithium ion conducting glassy electrolyte Li
2SO4-Li2O-B2O3 with different combinations of electrodes (stainless steel blocking electrode, lithium non-blocking electrode and TiS2 electrode) have been prepared. The a.c. impedance measurements of the cells have been studied at elevated temperature as
a function of time. The circuit elements such as bulk resistance, double layer capacitance and charge transfer resistance
have been inferred and their time dependence studied. The results show that the electrolyte and the interface are chemically
very stable with the different types of electrodes studied here. 相似文献
13.
P. D. Gaikwad D. J. Shirale V. K. Gade P. A. Savale K. P. Kakde H. J. Kharat M. D. Shirsat 《Bulletin of Materials Science》2006,29(4):417-420
The potentiometric study of polyaniline (PANI) film synthesized with dopants viz. polyvinyl sulfonic acid (PVS),p-toluene sulfonic acid (p
TS), dodecyl benzene sulfonic acid (DBS) and composite-dopants viz. PVS-p
TS and PVS-DBS, has been carried out. The synthesized PANI films were characterized by electrochemical technique, UV-visible
spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and conductivity measurement.
It was found that the PANI doped with PVS gives good electrochemical properties, conductivity as well as surface morphology
as compared to
p
TS and DBS, whereas in composite dopants the PANI doped with PVS-pTS gives good polymer matrix as compared to PVS-DBS. 相似文献
14.
Four different varieties of class F fly ashes, collected from different sources from the state of West Bengal (India) were
mixed with lime in 9 : 1 wt ratio, followed by compaction of the mixes. The compacts were subjected to steam curing to develop
an optimum strength by the reaction between fly ash and lime. The steam cured compacts were heated at different elevated temperatures
and free lime content, compressive strength, bulk density and water absorption tendency of these compacts were measured and
FTIR spectral changes were studied as a function of the heating temperatures. Kinetics of thermal dehydration of the compacts
was also studied from thermogravimetric measurements under non-isothermal condition to ascertain the order of dehydration
process and the associated activation energy. 相似文献
15.
S. R. Murthy 《Bulletin of Materials Science》2001,24(6):611-616
Polycrystalline NiZn ferrites with different grain sizes (1.2 (Am to 10.2 (Am) were prepared by the usual ceramic method.
The magnetic properties were measured at room temperature. The ultrasonic velocity and attenuation were measured on Ni-Zn
ferrite by using the pulse transmission method at 1 MHz, in the temperature range 300–600 K. The velocity was found to be
slightly sample dependent at room temperature and decreased with increasing temperature, except near the Curie temperature,
T
c
,where a small anomaly was observed. The longitudinal attenuation (α
1
)at room temperature was found to be more sample dependent. The temperature variation of ultrasonic longitudinal attenuation
exhibited a broad maximum around 400 K and a sharp maximum just below Curie temperature (
T
c
).The above observations were carried out in the demagnetized state. The application of a 380 mT magnetic field allowed us to
reach the saturated state of the sample at all the measuring temperatures. The anomaly observed in the thermal variation of
velocities (longitudinal and transverse) and attenuation has been qualitatively explained with the help of the temperature
variation of the magneto-crystalline anisotropy constant. 相似文献
16.
Preparation of Porous Ceramics from Nanocrystalline Zirconia and Their Microstructure 总被引:1,自引:0,他引:1
D. S. Nikitin V. A. Zhukov V. V. Perkov S. P. Buyakova S. N. Kul'kov 《Inorganic Materials》2004,40(7):760-763
Data are presented on the compaction behavior of nanocrystalline yttria partially stabilized zirconia powder and the effects of compaction pressure, sintering temperature, and sintering time on the microstructure of the resultant ceramics. It is shown that even relatively low (50 MPa) compaction pressures lead to the disintegration of powder particles and aggregates. The compaction behavior of the powder points to changes in the densification mechanism: from quasi-liquid sliding of powder particles at the beginning of the process to the breakdown of large microstructural constituents at the end. In the initial stages of sintering, a robust skeleton forms, which plays a key role in determining the pore structure of the ceramic. 相似文献
17.
H. C. Pant M. K. Patra S. C. Negi A. Bhatia S. R. Vadera N. Kumar 《Bulletin of Materials Science》2006,29(4):379-384
In the present paper, we report electrical conductivity and dielectric studies on the composites of conducting polyaniline
(PANI) with crystalline semiconducting ZnS powder, wherein PANI has been taken as inclusion and ZnS crystallites as the host
matrix. From the studies, it has been observed that the value of room temperature d.c. conductivity of the composites with
volume fraction of PANI > 0.65 shows an unusual behaviour wherein, conductivity values of the composites exceed that of PANI
itself with maximum value as high as 6 times that of PANI at the volume fraction of 0.85. A similar trend has also been observed
for the real and imaginary parts of complex dielectric constant values of the composites. This unusual behaviour in the d.c.
conductivity and dielectric properties has been attributed to the enhancement in the degree of crystallinity of PANI as a
consequence of its interfacial interaction with ZnS matrix. The results of optical microscopy show coating of PANI all around
the ZnS particles. The temperature dependent conductivity studies suggest the quasi one-dimensional VRH conduction in PANI
as well as its composites with ZnS. FTIR and XRD studies have also been reported. 相似文献
18.
A series of calcium substituted polycrystalline ferrite ceramics with magnetoplumbite structures were synthesized using perfect
stoichiometric mixtures of oxides with chemical composition, CaAlxCoxFe12−2xO19 (x = 2−5), by standard ceramic technique. The variation in the values ofH
candM
s,which depends on the additive content and the temperature, was studied by means of a vibration magnetometer. The strong variation
observed in coercivity, saturation magnetization and Curie temperature with chemical composition give rise to the possibility
of controlling these properties and hence applying these compounds in the millimeter— microwave range. 相似文献
19.
Matrix assisted laser desorption ionization mass spectroscopy (MALDI MS) is a technique which allows the measurement of molecular
mass > 200,000 Daltons by ionization and vapourization without degradation. This technique is useful for the mass analysis
of synthetic polymers, which have very low volatility. The basic principles of and its applications for polymer characterization
have been discussed in this paper. In addition, the possibilities of combining MALDI MS with chromatographic and other analytical
techniques have also been discussed. 相似文献
20.
A new high temperature and abrasion resistant glass-ceramic coating system (based on MgO-Al2O3-TiO2 and ZnO-Al2O3-SiO2 based glass systems) for gas turbine engine components has been developed. Thermal shock resistance, adherence at 90°-bend
test and static oxidation resistance at the required working temperature (1000°C) for continuous service and abrasion resistance
are evaluated using suitable standard methods. The coating materials and the resultant coatings are characterized using differential
thermal analysis, differential thermogravimetric analysis, X-ray diffraction analysis, optical microscopy and scanning electron
microscopy. The properties evaluated clearly showed the suitability of these coatings for protection of different hot zone
components in different types of engines. XRD analysis of the coating materials and the resultant coatings showed presence
of a number of microcrystalline phases. SEM micrographs indicate strong chemical bonding at the metal-ceramic interface. Optical
micrographs showed smooth glossy impervious defect free surface finish. 相似文献