Sol-gel processing of cordierite: Effect of seeding and optimization of heat treatment

1990 ◽  
Vol 5 (5) ◽  
pp. 1095-1103 ◽  
Author(s):  
Ann M. Kazakos ◽  
Sridhar Komarneni ◽  
Rustum Roy
Keyword(s):  
Heat Treatment ◽  
Single Phase ◽  
Excess Free Energy ◽  
Sol Gel ◽  
Nucleating Agents ◽  
Optimum Conditions ◽  
Nanosized Powders ◽  
Nanocomposite Gels ◽  
Powder Compacts ◽  
Gel Processing

Three series of cordierite powders were prepared by the sol-gel route: a single phase (monophasic) gel prepared from alkoxides, a nominally triphasic nanocomposite gel made with two nanosized powders and one solution phase, and a truly compositionally triphasic nanocomposite gel prepared from three nanosized powders. Crystalline α-cordierite seeds were also incorporated with the gels and their effectiveness as nucleating agents was investigated and found to lower the crystallization temperature of α-cordierite by 125–150°C. The densification behavior of powder compacts was examined and alterations made to the heat treatment until optimum conditions were found. The truly triphasic compact sintered at 1300°C for 2 h resulted in 100% of theoretical density whereas the nominally triphasic and monophasis pellets densified to 96% and 80%, respectively. The enhanced densification achieved with powder compacct prepared for triphasic nanocomposite gels is due to part to the excess free energy of the three components.

Effect of MCl (M = Na, K) addition on microstructure and electrical conductivity of forsterite

2020 ◽  
Vol 92 (1) ◽  
pp. 10901
Author(s):  
Saloua El Asri ◽  
Hamid Ahamdane ◽  
Lahoucine Hajji ◽  
Mohamed El Hadri ◽  
Moulay Ahmed El Idrissi Raghni ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Electrical Conductivity ◽  
Single Phase ◽  
Sol Gel ◽  
Complex Impedance ◽  
Transmission Spectra ◽  
Electrical Measurements ◽  
Cation Type ◽  
Edx Analyses ◽  
The Fourier Transform

Forsterite single phase powder Mg2SiO4 was synthesized by sol–gel method alongside with heat treatment, using two different cation alkaline salts MCl as mineralizers (M = Na, K) with various mass percentages (2.5, 5, 7.5, and 10 wt.%). In this work, we report on the effect of the cation type and the added amount of used mineralizer on microstructure and electrical conductivity of Mg2SiO4. The formation of forsterite started at 680–740  °C and at 630–700  °C with KCl and NaCl respectively, as shown by TG-DTA and confirmed by XRD. Furthermore, the Fourier transform infrared (FTIR) transmission spectra indicated bands corresponding to vibrations of forsterite structure. The morphology and elemental composition of sintered ceramics were examined by SEM-EDX analyses, while their densities, which were measured by Archimedes method, increased with addition of both alkaline salts. The electrical measurements were performed by Complex Impedance Spectroscopy. The results showed that electrical conductivity increased with the addition of both mineralizers, which was higher for samples prepared with NaCl than those prepared with KCl.

Synthesis and Dielectric Properties of SrBi2Nb2O9 Layered Perovskite by Sol-Gel Processing

1998 ◽  
Vol 541 ◽  
Author(s):  
Y. Wu ◽  
F. S. Ohuchi ◽  
G. Z. Cao
Keyword(s):  
Heat Treatment ◽  
Sol Gel ◽  
Dip Coating ◽  
Dielectric Constants ◽  
Layered Perovskite ◽  
Condensation Process ◽  
Complexing Agent ◽  
Low Dielectric ◽  
Gel Processing ◽  
Multiple Step

AbstractFerroelectric layered perovskite strontium bismuth niobium oxide SrBi2Nb2O9(SBN) ceramics and films were made by sol-gel processing. A multiple step hydrolysis-condensation process was applied to the synthesis of the SBN sol by using inorganic salts as precursors with citric acid as a complexing agent. Single phase polycrystalline SBN was obtained after heat-treatment at 650°C. It was found that the dielectric constants of SBN ceramics were dependent on heat-treatment. SEM, XPS, TGA/DTA and XRD analyses indicated that bismuth-deficiency may contribute to the relatively low dielectric constants. While a prolonged firing time at high temperatures may lead to a lattice expansion resulting in a significant decrease of the dielectric constant. C-oriented SBN films were obtained by dip-coating onto SrTiO3 substrates and the films are dense and crack-free with a thickness of 900 nm.

Evolution Of Molecular Structure In Alkoxide-Derived Lithium Niobate

1990 ◽  
Vol 180 ◽  
Author(s):  
Dennis J. Eichorst ◽  
D. A. Payne
Keyword(s):  
Heat Treatment ◽  
Lithium Niobate ◽  
Structural Changes ◽  
Sol Gel ◽  
Lithium Oxide ◽  
Structural Rearrangements ◽  
Raman Spectroscopic ◽  
Amorphous Network ◽  
Niobium Ethoxide ◽  
Gel Processing

ABSTRACTStructural rearrangements during the sol-gel processing of lithium niobate were investigated by FTlR and Raman spectroscopic methods. The reaction of lithium ethoxide with niobium ethoxide resulted in the formation of a bimetallic alkoxide, LiNb(OEt)6 , which could be crystallized from solution. Single crystals were comprised of helical polymeric units consisting of niobium octahedra linked by lithium in tetrahedral (distorted) coordination. Successive crystallizations from solution allowed for the enhanced purification of the alkoxide precursor. Hydrolysis of the bimetallic alkoxide resulted in the formation of an amorphous network structure, which contained niobium-oxygen octahedral units modified by lithium. Heat-treatment facilitated structural rearrangements for the niobium environment, which allowed for the formation of the lithium niobate crystal structure. Further heat-treatment above 700°C resulted in structural changes associated with lithium oxide volatility.

Sol-gel processing of PbTiO3 and Pb(Zr0.52Ti0.48)O3 fibers

1992 ◽  
Vol 7 (4) ◽  
pp. 992-996 ◽  
Author(s):  
Ulagaraj Selvaraj ◽  
A.V. Prasadarao ◽  
Sridhar Komarneni ◽  
Keith Brooks ◽  
Stewart Kurtz
Keyword(s):  
Heat Treatment ◽  
Sol Gel ◽  
Dielectric Constants ◽  
Heat Treated ◽  
Viscous Solutions ◽  
Gel Processing ◽  
Alkoxide Precursors

Homogeneous and stoichiometric PbTiO3 and PbZr0.52Ti0.48O3 gel fibers were drawn from viscous solutions prepared by sol-gel processing of alkoxide precursors. The fibrous gels on heating at 450 and 600 °C, respectively, formed the well-crystallized phases of PbTiO3 and PbZr0.52Ti0.48O3. Fibers heat treated at 700 °C are a few centimeters long and 50 to 150 μm in diameter. PbZr0.52Ti0.48O3 fibers subjected to heat treatment at 700 °C for 1 h consisted of fully dense submicron grains (0.15 to 0.2 μm). However, PbTiO3 fibers under analogous conditions showed a few micropores with grains of ∼0.1 μm. Dielectric constants of these PbTiO3 and PbZr0.52Ti0.48O3 fibers were approximately 300 and 800, respectively.

Preparation of La2(CexZr1-x)2O7 Nano-Porous Powders via Citric Acid Derived Sol-Gel Processing

2013 ◽  
Vol 833 ◽  
pp. 197-201
Author(s):  
Lu Zheng ◽  
Jian Qiu Guo ◽  
Liang Bin Liu ◽  
Yin Xin Tang ◽  
Yu Zhong Guo
Keyword(s):  
Citric Acid ◽  
High Efficiency ◽  
Sol Gel ◽  
Chelating Agent ◽  
Fluorite Phase ◽  
Ce Substitution ◽  
Powder Compacts ◽  
Gel Processing ◽  
Nanoporous Structures ◽  
Crystal Bulk

La2(CexZr1-x)2O7 powders were synthesized by the Pechini routine with citric acid as a chelating agent. TG-DTA, XRD and SEM were used to characterize as-prepared powders. Experimental results show that the crystalline structures of La2(CexZr1-x)2O7 transform to cubic fluorite phase with Ce substitution for Zr from x=0.1 to 1.0, no longer keeps the cubic pyrochlorite structure of La2Zr2O7. La2(CexZr1-x)2O7 powders present nanoporous low-density microstructurally, and successively lump-like, fluff-like and cotton-like morphologically with the increase of citric acid addition, this typical nanoporous microstructure results from a pore-crating mechanism initiated by self-propagation reactions between citric acids and nitrates. It is shown that the thermal conductivity k of powder compacts decreases sharply down from 1/10 to 1/32 of that of its single crystal bulk. as compact porosity increases from 60% to 95%. Therefore thermal barrier coatings (TBCs) of La2(CexZr1-x)2O7 with such nanoporous structures by an appropriate processing may work with quite a high insulative performance and very promising for TBC applications of high-efficiency and large propulsion engines.

Epitaxial Growth of (110) KnbO3 Films on (100) MgO Substrates via Sol-Gel Processing

1994 ◽  
Vol 341 ◽  
Author(s):  
Garo J. Derderian ◽  
James D. Barrie ◽  
Kenneth A. Aitchison ◽  
Martha L. Mecartney
Keyword(s):  
Surface Layer ◽  
Epitaxial Growth ◽  
Interfacial Layer ◽  
Single Phase ◽  
Annealing Temperature ◽  
Sol Gel ◽  
Sol Gel Process ◽  
Defective Surface ◽  
Gel Processing

AbstractEpitaxial, single phase (110) KnbO3 films were grown on (100) MgO substrates using a sol-gel process employing ethoxide precursors in methanol. The degree of epitaxy was dependent on both the annealing temperature and the amount of potassium in the film. Excess potassium in the sol-gel solution (K/Nb = 1.2) was necessary to produce single phase films. An amorphous or polycrystalline MgO interfacial layer was observed in some films, postulated to have developed after nucleation of KnbO3 and due to a highly defective surface layer.

Luminescent Properties of Ce Doped LuAG Thin Films Prepared by Pechini Sol–Gel Method

2012 ◽  
Vol 512-515 ◽  
pp. 1516-1519
Author(s):  
Qing Ma ◽  
Si Qing Shen ◽  
Jian Jun Xie ◽  
Fei Zhong Ma ◽  
Ying Shi ◽  
...  
Keyword(s):  
Single Phase ◽  
Sol Gel ◽  
Luminescent Properties ◽  
X Ray Diffraction ◽  
Low Loss ◽  
X Ray ◽  
Display Devices ◽  
Pl Spectra ◽  
Xrd Patterns ◽  
Gel Processing

Compared to phosphors, scintillating films are shown as a better feature for high–resolution display devices with low loss diffusion. Ce 3+ doped lutetium aluminum garnet (Lu3Al5O12, LuAG) scintillating films with different Ce 3+ concentration have been fabricated by Pechini sol–gel processing combined with the spin–coating technique and characterized by X–ray diffraction (XRD) and photoluminescence (PL) under excitation of UV–VIS light. The results of XRD patterns indicated that the specimen under study is a well–crystallized single–phase of cubic structure. Under an excitation of 442nm , it was found that the PL spectra was the typical Ce 3+ emissions located in the 460–650 nm consisting of two emission bands due to the transitions from the lowest 5d excited state (2D) to the 4f ground state of Ce 3+ , which matches well with the sensitivity curve of the Si–photodiode . The luminescent intensity of LuAG: Ce 3+ films varies with the Ce 3+ contents and reaches the maximum at 1.0 mol% doped. With the increase of calcining temperature, the luminescence intensity in the PL spectra of LuAG:Ce 3+ films was found to increased accordingly due to the improved crystallization.

Synthesis of silicon carbide powders from fumed silica powder and phenolic resin

2006 ◽  
Vol 21 (5) ◽  
pp. 1167-1174 ◽  
Author(s):  
Satoru Ishihara ◽  
Hidehiko Tanaka ◽  
Toshiyuki Nishimura
Keyword(s):  
Silicon Carbide ◽  
Fumed Silica ◽  
Single Phase ◽  
Phenolic Resin ◽  
Sol Gel ◽  
Molar Ratio ◽  
Homogeneous Distribution ◽  
Mixing Ratio ◽  
Silica Powder ◽  
Gel Processing

Silicon carbide powders were synthesized by application of sol-gel processing. Fumed silica powder was used as the starting material for the silicon source, and phenolic resin was used for the carbon source. The effects of mixing ratio and difference between hydrophilic and hydrophobic types of fumed silica powders were investigated. The stirred mixtures of fumed silica powders and phenolic resin became apparent sol states owing to homogeneous distribution. SiC powders were formed derived from both the types of fumed silica powders after the gelation and pyrolysis up to 1800 °C. The hydrophilic silica powder was effective to synthesize more homogeneous SiC powders than the hydrophobic type. Single-phase SiC was obtained in the C/Si (molar ratio after pyrolysis at 1000 °C) range between 1.0 and 2.5, while free carbon was contained in the obtained powders of C/Si > 2.5. In contrast, formation of SiC was insufficient, and SiO2 was retained at ratios of C/Si < 1.0.

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