共查询到20条相似文献,搜索用时 31 毫秒
1.
Roberto Köferstein Florian Oehler Stefan G. Ebbinghaus 《Journal of Materials Science》2018,53(2):1024-1034
A one-pot polymerization method using citric acid and glucose for the synthesis of nano-crystalline BaFe0.5Nb0.5O3 is described. Phase evolution and the development of the crystallite size during decomposition of the (Ba,Fe,Nb)-gel were examined up to 1100 °C. Calcination at 850 °C of the gel leads to a phase-pure nano-crystalline BaFe0.5Nb0.5O3 powder with a crystallite size of 28 nm. The shrinkage of compacted powders starts at 900 °C. Dense ceramic bodies (relative density ≥ 90%) can be obtained either after conventional sintering above 1250 °C for 1 h or after two-step sintering at 1200 °C. Depending on the sintering regime, the ceramics have average grain sizes between 0.3 and 52 µm. The optical band gap of the nano-sized powder is 2.75(4) eV and decreases to 2.59(2) eV after sintering. Magnetic measurements of ceramics reveal a Néel temperature of about 23 K. A weak spontaneous magnetization might be due to the presence of a secondary phase not detectable by XRD. Dielectric measurements show that the permittivity values increase with decreasing frequency and rising temperature. The highest permittivity values of 10.6 × 104 (RT, 1 kHz) were reached after sintering at 1350 °C for 1 h. Tan δ values of all samples show a maximum at 1–2 MHz at RT. The frequency dependence of the impedance can be well described using a single RC-circuit. 相似文献
2.
A. A. Titov N. P. Sokolova M. V. Vorob’eva N. L. Opolchenova Z. V. Eremenko N. N. Stepareva 《Inorganic Materials》2009,45(8):884-888
Nanocrystalline ytterbia powders have been synthesized using different precursors prepared by precipitation from nitrate solutions: ytterbium carbonates, oxalates, and hydroxides. The powders have been characterized by X-ray diffraction and scanning electron microscopy. The nature of the precursor has no effect on the crystallization temperature of ytterbia but influences its microstructure. The particles range in shape from spherical to platelike. The average crystallite size of the Yb2O3 powders is 20–25 nm. Raising the heat-treatment temperature from 600 to 1000°C increases the crystallite size to 33–46 nm. The highest thermal stability is offered by the ytterbia powders prepared through carbonate decomposition. 相似文献
3.
J. Yu H. Wang J. Q. Li X. K. Cheng C. L. Chen Z. L. Huang 《Inorganic Materials》2010,46(11):1212-1219
Apatite-type La9.33(SiO4)6O2 powders have been prepared by urea-nitrates combustion at low temperature. Process parameters of combustion and characteristics
of electrolyte were studied and optimized. Gelation time of precursor has been shortened distinctly by introducing an appropriate
solvent system. Molar ratio of nitric acid to lanthanum oxide dependence of the nature of the phases has first been characterized.
Well-crystallized La9.33(SiO4)6O2 powders with an average size of 30.5 nm were obtained at a calcining temperature as low as 800°C for 12h. Dense ceramic with
a relative density of 96% was prepared by sintering the green compact of these nanopowders at 1400°C for 3 h. The sintering
body exhibited a high ionic conductivity of 4.38 × 10−3 S/cm at 700°C. 相似文献
4.
D. Bochenek P. Niemiec M. Adamczyk I. Szafraniak-Wiza 《Journal of Materials Science》2018,53(19):13501-13512
Modern electronics expect functional materials that are eco-friendly and are obtained with lower energy consumption technological processes. The multiferroic lead-free BaFe1/2Nb1/2O3 (BFN) ceramic powder has been prepared by mechanochemical synthesis from simple oxides at room temperature. The development of the synthesis has been monitored by XRD and SEM investigations, after different milling periods. The obtained powders contain large agglomerates built by crystals with an estimated size about 12–20 nm depending on the period of milling. From this powder, the multiferroic BFN ceramic samples have been prepared by uniaxial pressing and subsequent sintering pressureless method. The morphology of the BFN ceramic samples strongly depends on high-energy milling duration. The properties of the ceramic samples have been investigated by dielectric spectroscopy, in broad temperature and frequency ranges. The high-energy milling of the powders has strongly affected the dielectric permittivity and dielectric loss of the BaFe1/2Nb1/2O3 ceramic samples. The usage of the mechanochemical synthesis to obtain the multiferroic lead-free BFN materials reduces the required thermal treatment and simultaneously improves the parameters of the BFN ceramics. 相似文献
5.
A. P. Kazin M. N. Rumyantseva V. E. Prusakov I. P. Suzdalev Yu. V. Maksimov V. K. Imshennik S. V. Novochikhin A. M. Gaskov 《Inorganic Materials》2010,46(11):1254-1259
Nanocrystalline nickel ferrite with a crystallite size from 3 to 40 nm has been prepared by spray pyrolysis. The 57Fe Mössbauer spectrum of NiFe2O4 samples has been found to vary systematically with crystallite size. The sensing response of the nanocrystalline nickel ferrite to 50 ppm NH3 has been studied using in situ conductance measurements. NiFe2O4 offers a strong sensing response to ammonia at the level of its maximum concentration limit. The optimum nickel ferrite crystallite size and temperature for ammonia detection are determined. 相似文献
6.
Xiumin Yao Shouhong Tan Xiangyu Zhang Zhengren Huang Dongliang Jiang 《Journal of Materials Science》2007,42(13):4960-4966
SiC reticulated porous ceramics (SiC RPCs) was fabricated with polymer replicas method by using MgO–Al2O3–SiO2 additives as sintering aids at 1,000∼1,450 °C. The MgO–Al2O3–SiO2 additives were from alumina, kaolin and Talc powders. By employing various experimental techniques, zeta potential, viscosity
and rheological measurements, the dispersion of mixed powders (SiC, Al2O3, talc and kaolin) in aqueous media using silica sol as a binder was studied. The pH value of the optimum dispersion was found
to be around pH 10 for the mixtures. The optimum condition of the slurry suitable for impregnating the polymeric sponge was
obtained. At the same time, the influence of the sintering temperature and holding time on the properties of SiC RPCs was
investigated. According to the properties of SiC RPCs, the optimal sintering temperature was chosen at 1,300 °C, which was
lower than that with Al2O3–SiO2 additives as sintering aids. 相似文献
7.
Ceramic particle reinforced aluminum metal matrix composites (MMCs) have resulted in potential use in aerospace and automobile
industries. The composites have been processed by mechanical milling followed by traditional powder metallurgy route. The
Al crystallite size is reduced to 27 nm after 60 h of milling. Results of the corrosion tests, evaluated using the potentiodynamic
method in the NaCl solution, indicate that corrosion of the investigated composite materials depends on the weight fraction
of the reinforcing particles. It has been found out, based on the determined anode polarization curves, that the investigated
materials are susceptible to pitting corrosion. Moreover, experimental results suggest that the milled composite material
Al–Zn/Al2O3p has higher corrosion resistance in the selected environment compared to unmilled composite Al–Zn/Al2O3p. Polarization curves show that the milling procedure improves the composite corrosion resistance in passive conditions. This
is illustrated by the corrosion potential, which becomes nobler with milling. 相似文献
8.
LiSn2P3 − y
V
y
O12 powders with y = 0.2, 0.4, 0.6, and 0.8 are prepared by mechanochemical milling method. The pellets of the compounds are heat treated at
temperatures between 700 to 1,000 °C for sintering period of 8 h. X-ray diffraction analysis indicates that all samples consist
of rhombohedral crystalline LiSn2P3O12 phase. Energy dispersive X-ray analysis confirmed that V5+ has been successfully substituted into LiSn2P3O12 crystalline phase. The conductivities of the pellets are determined using impedance spectroscopy. Impedance analysis shows
enhancement in both bulk and grain boundary conductivities with increase in y. The enhancement in bulk conductivity is due to decrease in bulk activation energy reflecting an increase in ion mobility
as a result of an increase in bottleneck size. Enhancement in grain boundary conductivity is attributed to increase in the
number of conducting pathways due to an increase in crystallite homogeneity. 相似文献
9.
Qing Zhi Shi Ze Sheng Yan 《Journal of Materials Science: Materials in Electronics》2010,21(7):656-658
Bulk materials of MgB2 have been prepared with the stoichiometry of MgB2(Al2O3)
x
(x = 0, 2, 5, 10 and 20% nano-Al2O3 powders), by using solid-state reaction route. All samples were sintered at 750 °C for 30 min in a calorimeter to monitor
the sintering reaction process. It is found that the onset temperatures of reaction between Mg and B powders increase significantly
with increasing the amount of Al2O3. However, the reaction time is shortened for the nano-Al2O3 powders can effectively activate the reaction as a catalyst. The critical transition temperature decreases from 38.5 to 31.6 K,
and the corresponding temperature window becomes narrow (less than 2.6 K). Furthermore, the amount of MgO impurity was found
to increase with the increase of Al2O3, which probably indicates that partial Mg was replaced by Al. 相似文献
10.
M. R. Mohammadi M. Ghorbani M. C. Cordero-Cabrera D. J. Fray 《Journal of Materials Science》2007,42(13):4976-4986
Nanostructured and nanoporous TiO2–Ga2O3 films and powders with various Ti:Ga atomic ratios and high specific surface area (SSA) have been prepared by a new straightforward
particulate sol–gel route. Titanium isopropoxide and gallium (III) nitrate hydrate were used as precursors and hydroxypropyl
cellulose (HPC) was used as a polymeric fugitive agent (PFA) in order to increase the SSA. X-ray diffraction (XRD) and Fourier
transform infrared spectroscopy (FTIR) revealed that powders contained both rhombohedral α-Ga2O3 and monoclinic β-Ga2O3 phases, as well as anatase and rutile. It was observed that the Ga2O3 formed from the nitrate precursor retarded anatase-to-rutile transformation. Furthermore, transmission electron microscope
(TEM) analysis also showed that Ga2O3 hindered the crystallisation and crystal growth of powders. SSA of powders, as measured by Brunauer–Emmett–Teller (BET) analysis,
was enhanced by introducing Ga2O3. Ti:Ga = 50:50 (at%/at%) binary oxide annealed at 500 °C produced the smallest crystallite size (2 nm), the smallest grain
size (18 nm), the highest SSA (327.8 m2/g) and the highest roughness. Ti:Ga = 25:75 (at%/at%) annealed at 800 °C showed the smallest crystallite size (2.4 nm) with
32 nm average grain size and 40.8 m2/g surface area. Ti:Ga = 75:25 (at%/at%) annealed at 800 °C had the highest SSA (57.4 m2/g) with 4.4 nm average crystallite size and 32 nm average grain size. One of the smallest crystallite size and one of the
highest SSA reported in the literature is obtained, and they can be used in many applications in areas from optical electronics
to gas sensors. 相似文献
11.
Soumen Pal A. K. Bandyopadhyay S. Mukherjee B. N. Samaddar P. G. Pal 《Bulletin of Materials Science》2011,34(4):865-872
Although low temperature fast coprecipitation technique has been used to synthesize stoichiometric (MgO-nAl2O3, n = 1) MgAl2O4 spinel forming precursor, delayed spinellization has always been the concern in this process. In this article, the precursor
of this ‘fast technique’ has been used for bulk production by further processing by high speed mixing with solvents and mechanical
activation by attrition milling in terms of superior spinellization. At 1000°C, MgAl2O4 — γ-Al2O3 solid solution and MgO phases are formed (spinel formed by 1000°C is regarded as primary spinel). At higher temperatures,
due to large agglomerate size, MgO can not properly interact with the exsolved α-Al2O3 from spinel solid solution to form secondary spinel; and consequently spinellization gets affected. Solvent treatment and
attrition milling of the coprecipitated precursor disintegrate the larger agglomerates into smaller size (effect is more in
attrition). Then MgO comes in proper contact with exsolved alumina, and therefore total spinel formation (primary + secondary)
is enhanced. Extent of spinellization, for processed calcined samples where some alumina exists as solid solution with spinel,
can be determined from the percentage conversion of MgO. Analysis of the processed powders suggests that the 4 h attrited
precursor is most effective in terms of nano size (< 25 nm) stoichiometric spinel crystallite formation at ≤ 1100°C. 相似文献
12.
M. M. Kolte V. B. Pawade S. J. Dhoble 《Journal of Materials Science: Materials in Electronics》2018,29(2):906-913
This article present the reports on optical study of Eu2+ and Ce3+ doped SrMg2Al6Si9O30 phosphors, which has been synthesized by combustion method at 550 °C. Here SrMg2Al6Si9O30:Eu2+ emission band observed at 425 nm by keeping the excitation wavelength constant at 342 nm, whereas SrMg2Al6Si9O30:Ce3+ ions shows the broad emission band at 383 nm, under 321 nm excitation wavelength, both the emission bands are assigned due to 5d–4f transition respectively. Further, phase purity, morphology and crystallite size are confirmed by XRD, SEM and TEM analysis. However, the TGA analysis is carried out to know the amount of weight lost during the thermal processing. The CIE coordinates of SrMg2Al6Si9O30:Eu2+ phosphor is observed at x?=?0.160, y?=?0.102 respectively, which may be used as a blue component for NUV-WLEDs. The critical distance of energy transfer between Ce3+ ions and host lattice is found to be 10.65 Å. 相似文献
13.
Zheng Li Le Zhang Tianyuan Zhou Lixi Wang Ching Ping Wong Hao Yang Qitu Zhang 《Journal of Materials Science: Materials in Electronics》2017,28(6):4684-4689
A novel spray co-precipitation method was adopted to synthesize well dispersed nanocrystalline Y2O3 powders for transparent ceramics. Several analytic techniques such as XRD, SEM, BET and UV–Vis–NIR spectrophotometer were used to determine the properties of coprecipitated powders, and the microstructure and optical properties of as-fabricated ceramics. The influences of the aging time on powders and ceramics were systematically investigated. Precursors were completely reached to yield the Y2O3 phase after being calcined at 1250 °C in air. The calcined Y2O3 powders exhibited an approximately spherical morphology with narrow size distribution and weak agglomeration, with mean particle size of ~140 nm. The co-precipitated nanopowders with an aging time of 12 h exhibited the best sintering activity due to the low agglomeration, and the in-line transmittance of Y2O3 ceramic sintered at 1800 °C for 8 h in vacuum reached to 77.2% at 1064 nm (1 mm thickness). 相似文献
14.
Using electrophoretic deposition (EPD), we have produced YSZ individual ceramic coatings and YSZ/Al2O3 composite coatings for a wide range of applications in modern materials research. YSZ and Al2O3 nanopowders were prepared by high-energy physical dispersion techniques, namely, by a laser evaporation–condensation process and electroexplosion of wire, respectively. Stable nonaqueous suspensions for the EPD process have been prepared using YSZ and Al2O3 nanopowders with an average particle size of 11 and 22 nm, respectively. The YSZ/Al2O3 composite coating produced by sintering at 1200°C has been shown to have higher density in comparison with the YSZ individual coating produced at the same temperature. X-ray diffraction characterization showed that the YSZ/Al2O3 composite coating consisted of two crystalline phases: α-Al2O3 (corundum) (42 wt %) and cubic ZrO2〈Y2O3〉 (58 wt %). Quantitative analysis of electron micrographs of the surface of the films showed that the YSZ individual coating produced by sintering at 1200°C had a loose structure and contained pores (9%), as distinct from the composite coating, which had a dense, porefree grain structure. 相似文献
15.
Ni25Te75 nanocrystalline alloy containing trigonal NiTe2 and Te nanocrystals was prepared through mechanochemical processing of pure elemental tellurium and nickel powders in argon atmosphere. The Ni25Te75 samples processed from 3 h to 30 h milling times were characterized by X-ray powder diffraction, transmission electron microscopy, magnetization and Raman spectroscopy. Trigonal NiTe2 crystals with average size of 16 nm can be obtained after only 3 h of processing time. For longer milling times, the trigonal NiTe2 phase becomes majority (about 70% with 30% for nanometric Te and no pure Ni was detected) and its average crystallite size slightly increases to 20 nm. Transmission electron microscopy images and electron diffraction patterns confirm the nanometric size of the crystalline domains in the agglomerated particles. The magnetic properties of the Ni25Te75 powders are dependent on synthesis time, suggesting a paramagnetic behavior mainly associated with the NiTe2 nanophase. Raman spectra showed peaks that can be associated with unreacted Te and tellurium oxides modes, but it also showed several modes that can be attributed to trigonal NiTe2 nanophase. The high-pressure experiments showed no phase transitions for NiTe2 up to 17 GPa and Te phase transitions from form I to forms II and III occurred simultaneously at 4.5 GPa, remaining up to 12 GPa; after that, only reflections of Te-III and the NiTe2 were observed. All the phase transitions observed with pressure are reversible after decompression. The bulk modulus determined from the least-squares fit of first-order Murnaghan equation of states is 110 GPa for the NiTe2 nanophase and 28 GPa for Te-I. 相似文献
16.
Abdelmajid Lassoued Mohamed Saber Lassoued Brahim Dkhil Salah Ammar Abdellatif Gadri 《Journal of Materials Science: Materials in Electronics》2018,29(9):7057-7067
Nanoparticles of nickel ferrites (NiFe2O4) were synthesized at different temperature of synthesis (25, 50 and 80 °C) through the chemical co-precipitation method. The synthesized powders were characterized using X-ray diffraction for crystallite size and lattice parameter calculation. It reveals the presence of cubic spinel structure of ferrites with crystallite size between 29 and 41 nm. Transmission electron microscopy and scanning electron microscopy showed uniform distribution of ferrite particles with some agglomeration. The Fourier-transform infrared spectroscopy showed absorption bonds, which were assigned to the vibration of tetrahedral and octahedral complexes. Raman spectroscopy is used to verify that we have synthesized ferrite spinels and determines their phonon modes. The thermal decomposition of the NiFe2O4 was investigated by TGA/DTA. The optical study UV–visible is used to calculate the band gap energy. Magnetic measurements of the samples were carried out by means of vibrating sample magnetometer and these studies reveal that the formed nickel ferrite exhibits ferromagnetic behavior. Photoluminescence showed three bands of luminescence located at 420, 440 and 535 nm. The photocatalytic properties of nickel ferrite (NiFe2O4) nanoparticles were evaluated by studying the photodecomposition of methyl orange as organic pollutant models and showed a good photocatalytic activity. 相似文献
17.
Bi5Ti3FeO15 (BTFO), an Aurivillius compound, was synthesized via sintering the Bi2O3 and Fe2O3 mixture and TiO2 oxides. The precursor material was ground in a high-energy attritorial mill for (1, 3, 5, and 10) h. The orthorhombic system
Bi5Ti3FeO15 ceramics was obtained by a solid-state reaction process at 1313 K. Phase formation behavior was investigated using differential
thermal analysis (DTA), thermal gravimetric (TG), and X-ray diffraction (XRD) techniques. The frequency-dependent properties
of the material were investigated by impedance spectroscopy. The impedance spectroscopic method is widely used to characterize
electrical properties of materials and their interfaces with electronically conducting electrodes. These studies indicate
that 1h, 3h, and 5h primary high-energy ball milling followed by sintering is a promising technique for pure Bi5Ti3FeO15 ceramic preparation, whereas the ceramics obtained from the substrates after 10h milling is a two-phase material. As the
result of this investigation, the model of adjusting the Nyquist charts with a three-element R-CPE (constant phase element) series connection was proposed. It was found that the value of the dielectric constant at the
Curie temperature decreases when the milling time of the substrates increases. The decrease in the dielectric constant is
influenced by the great dispersion of the grains, their dense packing, and location of particular grains in relation to other
grains. Moreover, the change of resistivity with frequency indicates that relaxation processes take place in the material.
In conclusion, it was reported that the optimal milling time of precursor oxide powders for carrying out the sintering process
is equal to 5 h. Then the obtained ceramics contain one phase and exhibit the highest dielectric properties for practical
applications. 相似文献
18.
E. V. Dudnik V. V. Tsukrenko A. V. Shevchenko A. K. Ruban L. M. Lopato 《Inorganic Materials》2011,47(10):1107-1110
We have studied the properties of nanocrystalline ZrO2-Y2O3-CeO2-CoO-Al2O3 powders prepared via hydrothermal treatment of a mixture of coprecipitated hydroxides at 210°C. A number of general trends
are identified in the variation of the properties of the synthesized powders during heat treatment at temperatures from 500
to 1200°C. Our results demonstrate that the addition of 0.3 mol % CoO to nanocrystalline ZrO2-based powders containing 1 to 5 mol % Al2O3 allows one to obtain composites with good sinterability at a reduced temperature (1200°C). 相似文献
19.
Nopsiri Chaiyo Banjong Boonchom Naratip Vittayakorn 《Journal of Materials Science》2010,45(6):1443-1447
A modified solid-state reaction was applied to produce lead-free piezoelectric sodium niobate (NaNbO3) powders. The mixture of Na2C2O4 and Nb2O5 was identified by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). The powders were characterized
using a scanning electron microscope (SEM) and the X-ray diffraction technique (XRD). The SEM image suggested that the particle
size of the powders obtained ranged from 180 to 360 nm. The XRD pattern showed that the pure perovskite phase of NaNbO3 could be synthesized at the low temperature of 475 °C for 1 h, with an average crystallite size of 31.45 ± 5.28 nm. This
temperature was about 300 °C lower than that when using the conventional solid-state method with Na2CO3 as reactant, which resulted in a cost-, energy-, and time-saving method. 相似文献
20.
Guo-hua Chen Jun-tao Liu Hua-rui Xu Chang-rong Zhou Min-hong Jiang Xin-yu Liu 《Journal of Materials Science: Materials in Electronics》2011,22(8):915-919
Ultrafine strontium barium niobate (Sr0.3Ba0.7Nb2O6, SBN30) powders were prepared by urea method starting from a precursor solution constituting of Sr (NO3)2, Ba (NO3)2, NbF5, urea and polyvinyl alcohol (PVA) as surfactant. Their structural behavior and morphology were examined by means of X-ray
diffractometry (XRD) and Scanning electron microscopy (SEM). The results showed that the SBN30 powders crystallized to a pure
tetragonal phase at annealing temperatures as low as 750 °C. The average particle size of SBN powders subjected to 750 °C
was of the order of 150–300 nm. With increasing calcination temperature,however, the average particle size of the calcined
powders increased. The SBN30 ceramic prepared from urea method can be sintered at temperature as low as 1,225 °C. The transition
temperature from the ferroelectric phase to the paraelectric phase and the relative dielectric permittivity of the SBN30 powder
were less than the corresponding values of the bulk ceramic. The permittivity and loss tangent (tan δ) at room temperature
(1 kHz) was found to be 930 and below 0.025. 相似文献