共查询到20条相似文献,搜索用时 31 毫秒
1.
M. I. B. Bernardi E. Antonelli A. B. Lourenço C. A. C. Feitosa L. J. Q. Maia A. C. Hernandes 《Journal of Thermal Analysis and Calorimetry》2007,87(3):725-730
The results reported here based on a study
of BaTi1–xZrxO3
(x=0, 0.2 and 1) nanometric powders prepared
by the modified Pechini method. The powder samples annealed from 600 to 1000°C/2
h were characterized by thermogravimetric analysis (TG), differential scanning
calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy
(SEM) techniques. The decomposition reactions of resins were studied using
thermal analysis measurements. The barium titanate zirconate system presented
just one orthorhombic phase. Furthermore, this study produced BaTiO3
powders with a tetragonal structure using shorter heat treatments and less
expensive precursor materials than those required by the traditional methods. 相似文献
2.
Elisa Mercadelli Carmen Galassi Anna Luisa Costa Stefania Albonetti Alessandra Sanson 《Journal of Sol-Gel Science and Technology》2008,46(1):39-45
Ba-modified bismuth sodium titanate with composition 0.94[(Bi0.5Na0.5)TiO3]-0.06BaTiO3 (BNBT) was prepared by a citrate nitrate sol–gel combustion method. The sol was obtained using barium acetate, bismuth nitrate,
sodium nitrate and a peroxo-citrate complex of titanium isopropoxide as starting precursors. Various molar ratios of citrate/nitrate
(C/N) were considered for the sol production. The corresponding gels were fired at different temperatures (300, 400, 500 °C)
in order to evaluate the conditions necessary to obtain the decomposition of the precursors and the formation of the pure
BNBT perovskitic phase in a single step. The best conditions to obtain the desired phase are: (C/N) = 0.2, and combustion
temperature of 500 °C. Ball milled powders were densified at a temperature 100 °C lower than the one generally used for powder
produced with the conventional mixed oxide route. The electrical properties are comparable to those reported for conventionally
prepared materials. 相似文献
3.
E. P. Simonenko N. A. Ignatov N. P. Simonenko Yu. S. Ezhov V. G. Sevastyanov N. T. Kuznetsov 《Russian Journal of Inorganic Chemistry》2011,56(11):1681-1687
Nanocrystalline powders of super-refractory complex carbides Ta4HfC5 and Ta4ZrC5 were synthesized using a hybrid method comprising sol-gel technology for preparing highly dispersed metal oxidescarbon starting
mixtures and a relatively low-temperature (1300–1500°C) carbothermal synthesis under a dynamic vacuum (P = 1 × 10−3 to 1 × 10−5 MPa). The elemental and phase compositions of the products and average crystallite sizes were determined. TEM was used to
study particle morphology and dispersion. Microstructures were observed by SEM. BET specific surface areas were determined
for powders prepared at 1400°C. 相似文献
4.
Eniko Berei Cornelia Muntean Oana Ştefănescu Mircea Niculescu Mircea Ştefănescu 《Journal of Thermal Analysis and Calorimetry》2018,131(1):137-144
CuCr2O4 spinel powders were synthesized starting from different chromium sources, namely (i) chromium oxide (α-Cr2O3) and (ii) ammonium dichromate ((NH4)2Cr2O7). The copper source was a Cu(II) carboxylate-type complex. The Cu(II) carboxylate complex was obtained by the redox reaction between Cu(NO3)2·3H2O and 1,3-propanediol (1,3PG) at 130 °C. In the first case (i), we have started from a mixture of α-Cr2O3, Cu(NO3)2·3H2O and 1,3PG that upon heating formed the copper malonate complex, which decomposed around 220 °C forming an oxide mixture (CuO + α-Cr2O3). In the second case (ii), (NH4)2Cr2O7, Cu(NO3)2·3H2O and 1,3PG were homogenously mixed. Heating this mixture at 130 °C resulted, in situ, in the Cu(II) complex. On controlled temperature increase, the violent decomposition of (NH4)2Cr2O7 took place at 180 °C along with the decomposition of the Cu(II) complex, leading to an amorphous oxide mixture of Cr2O3+x and CuO. By annealing the samples in the temperature range 400–1000 °C, the spinel phase (CuCr2O4) was obtained in both cases: (i) at 800 °C and (ii) at 600 °C as a result of the interactions between the precursors used, when the oxide system was amorphous and highly reactive. The presence of CuCr2O4 was highlighted by XRD and FTIR analyses. 相似文献
5.
This paper reports on a novel processing route for producing ZrO2/GrO nanocomposites by solid-state thermal decomposition of zirconium acetate nanostructures and graphene as starting reagents, powders were carried out in the temperature 200 °C for 2 h. In addition, nanocomposites of ZrO2/GrO were obtained by solid-state thermal decomposition of the as-synthesized graphene oxide and Zr(CH3COO)2·4H2O. The as-synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, atomic force microscope, photoluminescence spectroscopy and Thermogravimetric analysis. The sublimation process of the Zr(OAc)2 and GrO powder were carried out within the range of 210, 220 and 230 °C. The XRD studies indicated the production of pure ZrO2/GrO nanocomposites after thermal decomposition. 相似文献
6.
This study reports the synthesis of nickel titanate (NiTiO3) powders by using the modified sol‐gel method, with nickel acetate tetrahydrate as the nickel source, titanium isopropoxide as the titanium source, and 2‐methoxyethanol as the solvent, followed by post‐heat treatment in air at temperatures ranging from 500 °C to 900 °C. The characteristics of powders were determined by X‐ray diffraction (XRD), FT‐infrared spectroscopy (FT‐IR), ultraviolet/visible spectroscopy (UV/Vis), and Raman spectroscopy. The particle size and surface area of the powders were also measured. The results indicated that single‐phase NiTiO3 can be prepared using the modified sol‐gel method, followed by post‐heat treatment at the relatively low temperature of 550 °C. The crystallite sizes and particle sizes of NiTiO3 powders increase in conjunction with the post‐heat treatment temperatures. However, the surface area of the powders shrinks as the post‐heat treatment temperatures increase. The dielectric constants of NiTiO3 powders, based on the capacitance‐voltage analysis, are within a range of 13.2 to 17.8. 相似文献
7.
AgNbO3 powders and ceramics were prepared by aqueous solution-gel method. The phase evolution of the powders was investigated by
TG/DSC and XRD. The results showed that the pure AgNbO3 phase was obtained at 600 °C without special treatment. The sintering behavior and dielectric properties of the AgNbO3 ceramics were also investigated. It showed the dense ceramics were obtained as lower as 925 °C, which had the excellent dielectric
properties with the permittivity of 291 and dielectric loss of about 1.7% at 1 MHz. The coarse grains were observed for the
sample sintered over 975 °C, and then they decreased with the sintering temperature further increasing to 1,050 °C. 相似文献
8.
A facile synthesis of NaNbO3 powders was performed by solid-state reaction at low temperature. Stoichiometric ammonium niobium oxalate and Na2CO3 were mixed in water and then calcined at different temperatures for various times after drying. A combination of X-ray diffraction
(XRD), scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy and thermogravimetric (TG) analysis
was used to characterize the product and precursor compound. The XRD patterns show that single-phase NaNbO3 powders with high crystallinity can be synthesized at 425 °C for 15 min. The particle size from XRD data is found to be about
40 nm for NaNbO3 powders calcined at 500 °C for 3 h, which is in good agreement with SEM data. The SEM photograph shows that NaNbO3 powders are cuboid-like and well crystallized when calcination at 800 °C for 3 h. The product compositions prepared using
other sodium reactants, such as HCOONa and NaNO3, are also discussed. 相似文献
9.
A. Kirilin P. Mäki-Arvela K. Kordas A. -R. Leino A. Shchukarev D. Boström J. -P. Mikkola L. M. Kustov T. O. Salmi D. Yu. Murzin 《Kinetics and Catalysis》2011,52(1):72-76
One-pot synthesis of R-1-phenyethylacetate at 70°C was investigated using three different catalysts simultaneously, namely a bimetallic PdZn/Al2O3 as a hydrogenation catalyst, an immobilized lipase as an acylation catalyst and Ru/Al2O3 as a racemization catalyst. The most active bimetallic catalyst was PdZn/Al2O3 calcined at 300°C and reduced at 400°C, whereas the most selective although less active catalyst was the one being calcined
and reduced at 500°C. The highest selectivity to R-1-phenylethyl acetate over this catalyst was 32 at 48% conversion. Ru/Al2O3 was confirmed to have a positive effect on the formation of the desired product, although it was not very active in the racemization
during one-pot synthesis. 相似文献
10.
M. Yu. Smirnov A. V. Kalinkin A. A. Dubkov E. I. Vovk A. M. Sorokin A. I. Nizovskii B. Carberry V. I. Bukhtiyarov 《Kinetics and Catalysis》2011,52(4):595-604
Changes in the chemical composition of the surface of a Pt/(BaCO3 + CeO2) model NO x storage-reduction catalyst upon its interaction with SO x (SO2 (260 Pa) + O2 (2600 Pa) + H2O (525 Pa)) followed by regeneration in a mixture of CO (2100 Pa) with H2O (525 Pa) were studied by X-ray photoelectron spectroscopy (XPS). Model catalyst samples were prepared as a thin film (about several hundreds of angstrom units in thickness) on the surface of tantalum foil coated with a layer of aluminum oxide (~100 Å). It was found that the Pt/BaCO3 and Pt/CeO2 catalyst constituents acquired different surface charges (differential charging) in the course of photoelectron emission; because of this, it was possible to determine the nature of surface compounds formed as a result of the interaction of the catalyst with a reaction atmosphere. It was found that barium carbonate was converted into barium sulfate as a result of reaction with SO x on the surface of BaCO3 at 150°C. As the treatment temperature in SO x was increased to 300°C, the formation of sulfate on the surface of CeO2 was observed. The sulfatization of CeO2 was accompanied by the reduction of Ce(IV) to Ce(III). The regeneration reaction of the catalyst treated in SO x at 300°C resulted in the consecutive decomposition of cerium(III) sulfate at ≤500°C and then barium sulfate at 600–700°C. Upon the decomposition of BaSO4, a portion of sulfur was converted into a sulfide state, probably, because of the formation of BaS. 相似文献
11.
A. V. Loginov Yu. G. Mateyshina A. I. Aparnev N. F. Uvarov 《Russian Journal of Applied Chemistry》2018,91(10):1660-1664
Method of differential thermal analysis was used to study the thermolysis of a mixture of barium oxalate hydrate and α-SnO2·H2O, produced by precipitation from hydrochloric solutions. The methods of X-ray diffraction analysis, electron microscopy, and low-temperature nitrogen adsorption were used to examine the reaction products formed at various heating temperatures and determine their phase composition. The nanocomposite BaSnO3/SnO2 is the final product of thermolysis and subsequent heating to 950°C. The nanocomposite was used as a heterogeneous oxide additive for obtaining a CsNO2–BaSnO3/SnO2 composite solid electrolyte. The conductivity of the composite exceeds that of the starting salt by more than order of magnitude. 相似文献
12.
Ronaldo Santos da Silva Maria Inês Basso Bernardi Antonio Carlos Hernandes 《Journal of Sol-Gel Science and Technology》2007,42(2):173-179
In this work, we have studied the influence of the pH on the synthesis and structural properties of the Ba0.77Ca0.23TiO3 nanopowders synthesized by a modified polymeric precursor method, in order to achieve non-agglomerated powders. Synthesis,
morphology, thermal reactions, crystallite and average particle size of the synthesized powders were investigated through
thermal analysis (DTA/TG), X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and Infrared spectroscopy.
In summary, Ba0.77Ca0.23TiO3 nanopowders were synthesized for the first time at a relative low temperature (500 °C). It was also found that the alkalinity
and acidity of the solution presented a great influence on the powder properties. The best results were obtained from solutions
with pH = 8.5 and 11 whose nanopowders presented weakly agglomerate, with homogeneous particle size and a narrow size distribution
(30–40 nm). This behavior could be explained based on the FT-IR results in which it was possible to see the increased of the
chelation in higher pHs. 相似文献
13.
A. Kirilin P. Mäki-Arvela K. Kordas A. -R. Leino A. Shchukarev D. Boström J. -P. Mikkola L. M. Kustov T. O. Salmi D. Yu. Murzin 《Kinetics and Catalysis》2011,52(1):77-81
One-pot synthesis of R-1-phenyethylacetate at 70°C was investigated using three different catalysts simultaneously, namely a bimetallic PdZn/Al2O3 as a hydrogenation catalyst, an immobilized lipase as an acylation catalyst and Ru/Al2O3 as a racemization catalyst. The most active bimetallic catalyst was PdZn/Al2O3 calcined at 300°C and reduced at 400°C, whereas the most selective although less active catalyst was the one being calcined and reduced at 500°C. The highest selectivity to R-1-phenylethyl acetate over this catalyst was 32 at 48% conversion. Ru/Al2O3 was confirmed to have a positive effect on the formation of the desired product, although it was not very active in the racemization during one-pot synthesis. 相似文献
14.
Pinyang Fang Huiqing Fan Shaojun Qiu Liajun Liu Jin Chen 《Journal of Sol-Gel Science and Technology》2009,50(3):290-295
Lanthanum-modified bismuth titanate (Bi3.25La0.75Ti3O12, BLTO) powders were prepared by the complex polymerization method. The structure and morphology of BLTO powders were investigated
by X-ray diffraction and scanning electron microscopy. The complexation of citric acid with the metallic cations was detected
by Fourier transformed infrared (FT-IR). The thermal analyses of obtained gels were investigated by differential thermal gravimetric
(DTG). The pure and normally stoichiometric phase of BLTO powders could be obtained at relatively low temperature of 550–700 °C
even if the bismuth content is not excess in the starting precursors, while the secondary phase could be detected at lower
and higher calcination temperatures. The shape of the BLTO grains is similarly to platelet in Bi-layer structure and stoichiometry
BLTO was detected by the analysis of energy dispersive spectrometry. 相似文献
15.
Single-phase Ca3Al2O6 was prepared via polymeric precursor method. The influence of the reactants nature in the Ca3Al2O6 synthesis was investigated. For this purpose, citric acid and soluble salts of calcium (nitrate, chloride, carbonate) and
aluminium (nitrate, chloride, acetate) were used as starting materials, in the presence and, respectively, in the absence
of ethylene glycol. Ca3Al2O6 resulted as single-phase after annealing at 1050 °C for 1 h only starting from calcium nitrate or carbonate and aluminium
nitrate or acetate as salts precursor for Ca2+ and Al3+ cations. The formation of Ca3Al2O6 is not conditioned by the ethylene glycol presence in these mixtures. Using calcium and aluminium chlorides, the phases present
at 1050 °C are Ca12Al14O33 and unreacted CaO. 相似文献
16.
Nafise Modanlou Juibari Abbas Eslami 《Journal of Thermal Analysis and Calorimetry》2017,127(1):115-122
A new powder metallurgy technique was developed in order to increase the reinforcement proportion of aluminum with two different fractions of Al2O3. Aluminum powders were mixed with 20 % vol of alumina particles as primarily reinforcement, and additional alumina was produced in situ as a result of reaction between Al and additional 7.5 % vol of Fe2O3 powder. The three grades of powders were milled and hot-pressed into small preforms, and differential scanning analysis (DSC) was performed to determine the kinetics of microstructural transformations produced on heating. DSC curves were mathematically processed to separate the superposing effects of thermal reactions. Transformation points on resulting theoretical curves evidenced two distinct exothermal reaction peaks close to the melting point of aluminum that were correlated with formation of Fe–Al compounds and oxidation of aluminum. Microstructural investigations by means of SEM-EDX and XRD suggested that these exothermal reactions produced complete decomposition of iron (III) oxide and formation of Fe–Al compounds during sintering at 700 °C, and therefore, heating at higher temperatures would not be necessary. These results, along with calculation of activation energies, based on Kissinger’s method, could be used to optimize the fabrication of Al-Al2O3 composites by means of reactive sintering at moderate temperatures. 相似文献
17.
Glycine-nitrate combustion method was used to obtain powders based on CeFeO3 nanocrystals with average crystallite size in the range from 33 ± 3 to 51 ± 5 nm. The influence exerted by parameters of the glycine-nitrate combustion process and, in particular, by the glycine-nitrate ratio (G/N) on the composition and crystallite size of the synthesis products was determined. The optimal G/N ratio at which nanocrystalline cerium orthoferrite is formed with the minimum amount of impurity phases Fe2O3 and CeO2 was found to be 0.8. It was demonstrated that the composition of the starting solution affects the nature of the phase heterogeneity in the resulting product, crystallite size, and porosity of the nanocrystalline powders being formed. The patterns determined in the study make it possible to optimize the technology of nanocrystalline powders based on CeFeO3 in order to obtain powders with prescribed phase composition and crystallite sizes to enable their use as a basis for photocatalytic materials. 相似文献
18.
Wanquan Jiang Chuanxia Jiang Xinglong Gong Zhong Zhang 《Journal of Sol-Gel Science and Technology》2009,50(1):8-14
In this paper, a novel nanoporous barium titanate (BaTiO3) crystalline powder was synthesized by using triblock poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) based systems
(P-123) as the soft template via a sol–gel method and their structure-dependent electro rheological property was studied.
The pore diameter and specific surface area of BaTiO3 were precisely controlled by varing the calcined temperature. The chemical composition, structure and surface morphology
of BaTiO3 were characterized by X-ray diffraction (XRD), thermo gravimetric analysis (TGA), and nitrogen adsorption–desorption method,
scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The result revealed that the pore volume and
specific surface area of BaTiO3 decreased with the increment of calcined temperature. The electro rheological fluids (ERFs) were obtained by dispersing BaTiO3 crystallites in silicon oil and three kinds ERFs were fabricated by using three kinds of BaTiO3 which were prepared under different calcined temperature (550, 600 and 900 °C) as the precursors. The behaviors of the ERFs
were evaluated via a rotational rheometer fixed with electric field generator. The results showed that electro rheological
effect was related to the pore volume and specific surface area of BaTiO3. Due to the distinct advantage of sol–gel method for preparing nanoporous BaTiO3 without contamination of the materials, the markedly low current destiny of the ERFs was obtained. The yield stress of ERFs
with large specific surface area of BaTiO3 reached the maximum of 3 kPa, which is higher than that of ERFs using traditional pure BaTiO3 crystallites (lower than 1 kPa). 相似文献
19.
Sol-Gel Synthesis of Nano-Scaled BaTiO3, BaZrO3 and BaTi0.5Zr0.5O3 Oxides via Single-Source Alkoxide Precursors and Semi-Alkoxide Routes 总被引:2,自引:0,他引:2
Veith Michael Mathur Sanjay Lecerf Nicolas Huch Volker Decker Timo Beck Horst P. Eiser Wolfgang Haberkorn Robert 《Journal of Sol-Gel Science and Technology》2000,18(2):145-158
Sol-gel synthesis of nano-sized BaTiO3, BaZrO3 and BaTi0.5Zr0.5O3 ceramics using alkoxide and semi-alkoxide routes has been investigated and the pervoskites obtained have been compared with respect to crystallisation temperature, crystallite size and compositional purity. Heterometal alkoxides containing two (for BaTiO3 and BaZrO3) and three (for BaTi0.5Zr0.5O3) different metals were used as single-source precursors in the alkoxide route while semi-alkoxide synthesis was performed by reacting barium hydroxide or acetate with Ti and/or Zr alkoxides. Semi-alkoxide synthesis also produces stoichiometric and phase-pure oxides, however, at temperatures higher than 1000°C. At temperatures below 1000°C, BaCO3 and small amounts of other undesired phases (e.g., BaTi2O4) were present in the oxides derived from semi-alkoxide synthesis. Thermal behaviour, studied by TGA/DTA measurements, shows that thermal decomposition occurs in three major steps and depends on the educt composition and the synthesis route. Among alkoxide derived powders, crystalline BaTi0.5Zr0.5O3 phase is formed at 400°C while complete crystallisation of BaMO3 ceramics occurs around 600°C. The cubic to tetragonal phase transition for BaTiO3 is clearly observed at relatively low-temperature of 800°C. The stoichiometry and phase homogeneity of the obtained powders were demonstrated by energy dispersive X-ray analysis and powder diffractometry. The averaged crystallite size of the obtained nano-ceramics was evaluated using the FormFit programme. SEM and TEM observations revealed a high microstructural uniformity. 相似文献
20.
G. S. Zakharova I. V. Baklanova A. Yu. Suntsov Y. Liu Q. Zhu W. Chen 《Russian Journal of Inorganic Chemistry》2016,61(12):1584-1590
The effect of the method used for the synthesis of NH4V3O7 on its morphology, textural parameters, and optical properties was studied. Ammonium vanadate NH4V3O7 was prepared by treating NH4VO3 in the presence of citric acid under hydrothermal (4.0 ≤ pH ≤ 5.5, T = 180–200°C, 48 h) and microwave–hydrothermal (3.5 ≤ pH ≤ 5.0, T = 180–220°C, 20 min) conditions. Self-assembled NH4V3O7 microcrystals crystallizing in monoclinic system with unit cell parameters a = 12.247(5) Å, b = 3.4233(1) Å, c = 13.899(4) Å, β = 89.72(3)°, and V = 582.3(4) Å3 (space group P21) were shown to be formed independently of the method used to treat the reaction mixture. The morphology of NH4V3O7 particles was shown to depend on рН of the reaction mass and the method of synthesis. The structural features of NH4V3O7 were studied by IR, UV, and Vis spectroscopy, and the optical bandgap was determined. 相似文献