共查询到20条相似文献,搜索用时 15 毫秒
1.
F. J. Gotor P. Odier M. Gervais J. Choisnet 《Journal of Sol-Gel Science and Technology》1994,2(1-3):427-430
High T
c
-superconducting powders of the Y-Ba-Cu-O system are prepared by a solution-polyacrylamide gel using citric acid as a complexing agent. This method provides an easy way to prepare reactive YBaCuO powders by sol-gel synthesis. However this synthesis involves intermediate phases formation which impedes the obtention of the pure phase at low temperature. An intermediate oxycarbonate phase forms between 800° and 850°C in flowing oxygen. From powder X-ray diffraction, thermal analysis and IR spectroscopy, it is concluded that the intermediate oxycarbonate has an average tetragonal structure—SG P4/mmm—similar to that of the parent oxide with a stoichiometry close to YBa2Cu2.95(CO3)0.35O6.6. The carbonate group is located in the center of the basal CuO square. This compound has superconducting properties. A pure 123 phase is obtained when the xerogel precursor is annealed at 925°C in O2 or at 800°C in Ar, then in O2. The grain growth and microstructure development of YBaCuO have also been investigated and compared using two different powders, i.e. sol-gel route and commercial powder from Hoechst. 相似文献
2.
We report the antibacterial efficacies of silver and/or silver chloride containing titania xerogels synthesized with modified
single step sol-gel methods against Escherichia coli bacteria. As the silver loading in TiO2 increases, the amount of the xerogel required to inhibit the growth of the bacteria decreases and also we found that pure
TiO2 was not bactericidal. Among modified single step sol-gel methods used in this study, the additional HCl treatment sol-gel
route III was very effective to obtain only AgCl crystallites in TiO2. Based on viable cell count method, 0.125 g/L of 29%Ag/TiO2 (made with HNO3 sol-gel route I) was enough to inhibit the growth of E. coli whereas 0.6 g/L of 29%Ag/TiO2 (made with the additional HCl treatment sol-gel route III) was required. However, antibacterial activity of 29%Ag/TiO2 (made with HNO3 sol-gel route I) after 6 usages was the same as 29%Ag/TiO2 (made with the additional HCl treatment sol-gel route III). 相似文献
3.
Rutile Ni
x
Ti1-3x
Sb2x
O2 solid solution nanoparticles were synthesized by a sol-gel route using propylene oxide as a gelation agent. Titanium oxide
nanopowder and 12% TiCl3 solution were used as the source for titanium to investigate the influence of the titanium precursors on the formation of
the target materials. It was found that the nanoparticles prepared using 12% TiCl3 solution showed a much lower phase formation temperature (700°C) as compared to those prepared from TiO2 nanoparticles (1000°C). This lower phase formation temperature allowed a substantial reduction of the aggregation of the
particles during calcination leading to the formation of nearly mono-dispersed nanoparticles of about 20 nm. The results of
this work show that the epoxide assisted sol-gel method is capable to produce titanium-based ternary oxide solid solution
nanoparticles, owing to the formation of a highly homogeneous precursor gel intermediate. 相似文献
4.
Mathur S. Shen H. Lecerf N. Jilavi M.H. Cauniene V. Jørgensen J-E. Kareiva A. 《Journal of Sol-Gel Science and Technology》2002,24(1):57-68
Superconducting oxide ceramics of composition Y(Ba1–x
Sr
x
)2Cu4O8 (x = 0.00, 0.10, and 0.20) have been prepared by a simple sol-gel method based on the complexation of metal ions in aqueous medium, by chelating acetate and tartarate ligands. Homogeneous sols were obtained by complexing copper ions with tartaric acid, which prevented the flocculation of copper acetate during the gelation process. Single-phase bulk samples were obtained after firing the mixed-metal polymeric acetate-tartarate precursor to 835°C for 70 h in flowing oxygen atmosphere. Thermal decomposition of the gels was studied by thermogravimetry. Effect of strontium substitution on the properties of the compounds was studied by X-ray powder diffraction, electron microscopy, X-ray photoemission spectroscopy and resistivity measurements. These data indicate that nearly monophasic Y(Ba1–x
Sr
x
)2Cu4O8 superconducting samples were obtained for x < 0.30. The Sr-doping in the YBa2Cu4O8 (Y-124) phase shows a pronounced effect on the superconducting properties enhancing the critical temperature from 78 K (for the non-substituted sample) to 88 K (for Y(Ba1–x
Sr
x
)2Cu4O8). 相似文献
5.
Tran Thi Thuy S. Hoste G. G. Herman K. De Buysser P. Lommens J. Feys D. Vandeput I. Van Driessche 《Journal of Sol-Gel Science and Technology》2009,52(1):124-133
A water based YBa2Cu3O7−x
(YBCO) precursor using a triethanolamine (TEA)/acetic acid complexing method to obtain YBCO thin films is described in detail.
The influence of complexation behavior in the formation of transparent and homogenous sols and gels after the combination
of Y, Ba and Cu—acetates, acetic acid and TEA has been studied by potentiometric titration and the results are compared with
analytical simulations. The decomposition of the gel was studied by IR (infrared) and Thermal Gravimetric Analysis/Differential
Thermal Analysis (TGA/DTA). The results in sol-gel chemistry can be used to decide on the necessities in the preparation of
stable sol–gel precursors with a minimum amount of organic compounds. The sol–gel system was also used for the deposition
of high textured superconducting thin films on STO substrates by dip coating. The synthesized YBCO showed a superconducting
transition temperature of 90.95 K with narrow ΔT (2 K) for thin films. The results from X-ray diffraction show that the single
phase YBCO was obtained. SEM pictures also indicate that the properties of the surface thin films are good. 相似文献
6.
Valerie Briois Christine Giorgetti Elisabeth Dartyge Francois Baudelet Miriam S. Tokumoto Sandra H. Pulcinelli Celso V. Santilli 《Journal of Sol-Gel Science and Technology》2006,39(1):25-36
The simultaneous formation of nanometer sized zinc oxide (ZnO), and acetate zinc hydroxide double salt (Zn-HDS) is described.
These phases, obtained using the sol-gel synthesis route based on zinc acetate salt in alcoholic media, were identified by
direct characterization of the reaction products in solution using complementary techniques: nephelometry, in situ Small-Angle X-ray Scattering (SAXS), UV-Vis spectroscopy and Extended X-ray Absorption Fine Structures (EXAFS). In particular,
the hydrolytic pathway of ethanolic zinc acetate precursor solutions promoted by addition of water with the molar ratio N=[H2O]/[Zn2+] = 0.05 was investigated in this paper. The aim was to understand the formation mechanism of ZnO colloidal suspension and
to reveal the factors responsible for the formation of Zn-HDS in the final precipitates. The growth mechanism of ZnO nanoparticles
is based on primary particle (radius ≈ 1.5 nm) rotation inside the primary aggregate (radius <3.5 nm) giving rise to an epitaxial
attachment of particles and then subsequent coalescence. The growth of second ZnO aggregates is not associated with the Otswald
ripening, and could be associated with changes in equilibrium between solute species induced by the superficial etching of
Zn-HDS particles at the advanced stage of kinetic. 相似文献
7.
G. Nenartaviciene K. Tõnsuaadu D. Jasaitis A. Beganskiene A. Kareiva 《Journal of Thermal Analysis and Calorimetry》2007,90(1):173-178
In this study the formation of chromium substituted YBa2Cu4O8 (Y-124) superconductors has been investigated by TG/DTA measurements. The YBa2(Cu1−xCrx)4O8 ceramics with nominal compositions of x=0.01, 0.03, 0.05, 0.10 and 0.20 have been prepared by an aqueous sol-gel method using aqueous mixtures of the corresponding
metal acetates and nitrates. Homogeneous precursor gels were obtained by complexing metal ions with tartaric acid. To assist
the interpretation of the results obtained the synthesis products were additionally characterized by X-ray powder diffraction
(XRD) and resistivity measurements. It was determined that doping the YBa2Cu4O8 phase with chromium has a strong effect on the phase purity and superconducting properties of the synthesis products. 相似文献
8.
采用溶胶-凝胶法、水热法和溶胶-凝胶-水热法三种化学方法合成K0.5Bi0.5TiO3 (KBT)无铅压电陶瓷粉体. 用X射线衍射(XRD)分析产物的结构, 用扫描电镜(SEM)和透射电镜(TEM)观察产物的形貌. 实验结果表明, 三种化学方法均可获得纯钙钛矿相KBT粉体, 但不同工艺获得的粉体在形貌和生成机制上有很大的不同. 溶胶-凝胶法属高温固相扩散机制, 需要700 ℃以上温度煅烧才可获得KBT纯相, 且粉体颗粒度大、团聚严重. 水热法符合溶解-结晶机制, 生长出四方形的KBT纳米片. 溶胶-凝胶-水热法利用了凝胶团聚体空间链状结构的模板作用, 通过原位结晶机制生长出KBT纳米线. 相似文献
9.
G. V. Rama Rao U. V. Varadaraju S. Venkadesan S. L. Mannan 《Journal of Thermal Analysis and Calorimetry》1997,48(5):1051-1067
The high temperature superconducting compound YBa2Cu3O72212; (Y-123) is synthesised by sol-gel process using various precursors viz., acetate, acetate-citrate, nitrate-citrate and acrylamide. The phase purity of the final product depends on the homogeneity of the gels which intern depends on the bonding of the metal ions in the gels. The samples prepared by acrylamide and nitrate-citrate gel routes yielded phase pure Y-123 compound with better superconducting properties. The mechanism of formation of Y-123 in all these four gel routes is established by characterising the gels and intermediate phases using TG, DTA and XRD techniques. Kinetic analysis is carried out on the mass loss data using the method proposed by Phadni's and Deshpande. Avrami-Erofeev nuclei growth in case of acrylamide, diffusion controlled process in nitrate-citrate and phase boundary reaction mechanisms in case of acetate-citrate gels are found to be responsible for the formation of Y-123 phase.The authors are grateful to Dr. Baldev Raj, Director, Metals and Materials Group, for his constant encouragement and support. We thank Prof. G. V. Subba Rao, Director, Central Electrochemical Research Institute, Karaikudi for his keen interest in this work. Thanks are also due to Dr. Sundaram, CECRI, Karaikudi for his help in thermal analysis experiments. 相似文献
10.
Soraru Gian Domenico Babonneau Florence Gervais Christel Dallabona Nicola 《Journal of Sol-Gel Science and Technology》2000,18(1):11-19
A new sol-gel route, without any external water addition, for the preparation of hybrid RSiO1.5/B2O3 gels (R = Me, Et, Vi) is reported. The gels are easily synthesized by reacting B(OH)3 with the liquid silicon alkoxide. The gels have been characterized mainly by FT-IR and 11B MAS NMR spectroscopy. The results show that this new sol-gel process allows the formation of a homogeneous borosilicate gel in which trigonal BO3 units are incorporated into the siloxane network via B—O—Si bonds. 相似文献
11.
L. Marta C. Sarbu L. Zador M. Zaharescu D. Crisan 《Journal of Sol-Gel Science and Technology》1997,8(1-3):681-684
Metal acetates represent suitable precursors in the sol-gel method. Generally, acetates are used in multicomponent systems
with alkoxides or other carboxylic salts. However, Bi−Sr−Ca−Cu−O superconductors have been obtained by the sol-gel method
starting only from acetate mixture. This work was intended to study the gelling process of acetates involved in the formation
of bismuth-based superconducting phases, both individually and in the bi-and multicomponent systems. Probably, copper acetate
is mainly responsible for the gel formation in these systems. The gelling process was monitored by measuring the pH, density
and viscosity changes. The gels obtained were characterized by UV-VIS and IR spectra, DTA/TGA and powder X-ray diffraction. 相似文献
12.
A. Vadivel Murugan B. B. Kale Lalita B. Kunde Aarti V. Kulkarni 《Journal of Solid State Electrochemistry》2006,10(2):104-109
A comparative study of nanocrystalline spinel LiMn2O4 powders prepared by two different soft chemical routes such as solution and sol-gel methods using lithium and manganese acetates
are the precursors under different calcination temperatures. The dependence of the physicochemical properties of the spinel
LiMn2O4 powder has been extensively investigated by using thermal analysis (TGA/DTA), FTIR, X-ray diffraction studies, SEM, specific
surface area (BET) and electrical conductivity measurements. The results show that pure LiMn2O4 can be prepared from acetate precursors as starting materials at a low temperature of 600°C from solution route and 500°C
from sol-gel method. The charge-discharge characteristics and the cycling behavior of Li/1M LiBF4-EC/DEC electrolyte / LiMn2O4cells revealed that LiMn2O4 calcined at higher temperatures showed a high initial capacity, while the LiMn2O4calcined at lower temperatures exhibited a good cycling behavior. 相似文献
13.
K. Przybylski T. Brylewski M. Bućko 《Journal of Thermal Analysis and Calorimetry》1995,45(5):1099-1108
Calcination conditions of the precursor powders, i.e. temperature, type of atmosphere and duration, were determined with a view to obtain superconducting powders with the most advantageous physico-chemical properties. Investigated were powders in the Y?Ba?Cu?O system prepared by the sol-gel method. Thermogravimetric examinations of the powders have revealed that the decomposition kinetics of BaCO3 determines the formation rate of the superconducting YBa2Cu3O7?x (‘123’) phase. It follows from the decomposition kinetics of BaCO3 that the process is the most intensive in argon, whereas in static air and oxygen it is the slowest. The phase composition analysis (XRD) and low-temperature magnetic susceptibility measurements of the calcinated powders, confirm the above mentioned changes in the decomposition kinetics. The reaction of barium carbonate can be completed if the calcination process is conducted at the temperature of 850°C for 25 h, yielding easily sinterable powders for obtaining single-phase superconducting bulk samples with advantageous functional parameters. 相似文献
14.
Comparative study of sol-gel-hydrothermal and sol-gel synthesis of titania-silica composite nanoparticles 总被引:2,自引:0,他引:2
Titania-silica composite nanoparticles were prepared by sol-gel-hydrothermal and sol-gel routes, respectively, and their physico-chemical and photocatalytic properties were compared. The results of XRD, TEM and BET surface areas showed that sol-gel-hydrothermal route led to anatase titania-silica composite nanoparticles with large specific surface area, but the sol-gel route tended to form mixture of anatase and rutile. The composite nanoparticles prepared by sol-gel-hydrothermal route had better thermal stability against phase transformation from anatase to rutile, agglomeration and particle growth than those prepared by sol-gel route. On the basis of XRD, FT-IR, XPS and 29Si MAS-NMR, a strong interaction was found between SiO2 and TiO2, and Ti-O-Si bonds formed during both the two routes. But more Ti-O-Si bonds formed in the composite nanoparticles prepared by sol-gel-hydrothermal route than those prepared by sol-gel route. As a result, the titania-silica composite nanoparticles prepared by sol-gel-hydrothermal route exhibited higher photocatalytic activity in decomposition of methylene blue than that prepared by sol-gel route, and it had excellent photocatalytic activity even after calcined at 1000 °C. 相似文献
15.
Laila Čakare Marija Kosec Barbara Malič 《Journal of Sol-Gel Science and Technology》2000,19(1-3):603-606
PbZrO3 (PZ) thin films have been prepared by 2-methoxyethanol route from lead oxide or lead acetate and zirconium n-butoxide. The use of lead oxide as lead source and the seeding layer of TiO2 on Pt/TiO2/SiO2/Si substrate facilitate the formation of the perovskite phase. 相似文献
16.
The bulk superconducting YCa2Cu3O7−δ compounds are prepared at an ordinary pressure of oxygen by conventional solid-state reaction method. The formation of sample is tested by means of XRD and is studied for their ac susceptibility below room temperature up to 77.5 K. The samples are found single-phase orthorhombic structure and found superconducting at 83.5 K. It is shown that the analysis is consistent with published data on YBa2Cu3O7−δ oxide superconductor. 相似文献
17.
Olivine-type Co2SiO4 ultrafine particles were synthesized by a sol-gel method using propylene oxide as a gelation agent. Owing to the high homogeneity
of the intermediate gel precursor, the usage of this epoxide method results in a substantial reduction of calcination temperature
and time as compared with the solid-state route, and a great reduction of calcination time as compared with other wet-chemistry
routes. This high homogeneity is obtained by the usage of an appropriate amount of HCl, as a catalyst that matches the rate
of hydrolysis of TEOS and the metal ions, allowing the formation of Si–O–Co bonds. 相似文献
18.
Lachezar Radev Katia Hristova Valery Jordanov Maria Helena V. Fernandes Isabel Margarida M. Salvado 《Central European Journal of Chemistry》2012,10(1):137-145
The 70SiO2-30CaO (wt.%) sol-gel glasses doped with 1, 3 and 5 NbF5 (wt.%) were prepared via polystep sol-gel route. The synthesized glasses were characterized by XRD, FTIR and SEM. Changes in 1.5 SBF solutions were
measured by ICP-AES. XRD of the glasses stabilized at 700°C for 6 hours proved the presence of niocalite. FTIR was consistent
with XRD data. The in vitro bioactivity study of all glasses prepared were carried out by soaking in 1.5 simulated body fluid (1.5 SBF) at 37°C for 6
and 12 days in static conditions. The FTIR reveals the formation of A-type and B-type carbonate containing hydroxyapatite
(CO3HA) layer. Changes in 1.5 SBF solutions, after 6 days of soaking, show that the Ca concentration increased significantly,
compared to the initial Ca content in the 1.5 SBF solution before in vitro test. After 12 days of immersion, the Ca concentration decreased, i.e., the formation of HA phase consumed Ca from 1.5 SBF solution. For all soaking times, the concentration of P is much lower
than that the used 1.5 SBF. Based on these results we suggest that Ca and P play an active role in the future of the glasses.
SEM depicts that the different morphology of hydroxyapatite can be formed as a function of soaking time. 相似文献
19.
TiO2 nanoparticles with different shapes and sizes were synthesised by the sol-gel route in Water/Brij78/Hexane reverse microemulsions.
The aqueous cores of these microemulsions were used as nanoreactors to control sol-gel reactions. We studied the effect of
water/surfactant mole ratio (W
0) on the morphology, and textural properties of the final products. The materials thus obtained were characterised by different
techniques. Thermogravimetric and differential thermal analysis (TG-DTA) was used to study the thermal behaviour of the products
and X-ray diffraction (XRD) to identify the crystalline phases. The morphological and textural properties of the products
were determined by scattering electron microscopy (SEM) and the Brunauer-Emmett-Teller (BET) method, respectively. We also
studied the influence of thermal treatment on the structure and size of the TiO2 particles. The effect of W
0 on the anatase-rutile phase transition temperature was investigated. 相似文献
20.
Acosta Gloria Chapela Víctor Manuel 《Journal of inclusion phenomena and macrocyclic chemistry》1985,3(1):9-12
It was hypothesized that the formation of polypeptide bonds inside a lamellar superconducting compound such as 2H-TaS2 could enhance the superconducting transition temperature. The preparation of tantalum disulfide intercalated with polyglycine is described. The intercalated systems were characterized by powder X-ray diffraction and thermogravimetric analysis. Superconducting transition temperatures were also measured. The results show that the system 2H-TaS2/polyglycine does not have a more favourableT
cvalue than 2H-TaS2/glycine. 相似文献