Sintering and Microstructural Modification of Seeded and Neodymium Doped Lanthanum Hexaaluminate

2016 ◽  
Vol 835 ◽  
pp. 237-250 ◽  
Author(s):  
P. Jana ◽  
P.S. Jayan ◽  
S. Mandal ◽  
Koushik Biswas
Keyword(s):  
Rare Earth ◽  
Heterogeneous Nucleation ◽  
Single Phase ◽  
Sol Gel ◽  
Phase Evolution ◽  
Neodymium Oxide ◽  
Lower Temperature ◽  
House Structure ◽  
Gel Processing ◽  
Lanthanum Hexaaluminate

The effect of (i) heterogeneous nucleation by seeding or (ii) doping with neodymium on the formation of lanthanum hexaaluminate was studied during sol to gel conversion. The resultant dried gels were calcined at various temperatures starting from 1100°C to 1600°C for 2 h to study the phase evolution and microstructure.The combined effects of advanced sol gel processing and heterogeneous nucleation promoted the formation of lanthanum hexaaluminate phase at lower temperature (1200°C) than the conventional routes (1300°C). Lanthanum hexaaluminate phase was detected at 1200°C and 1300°C in seeded gel (SG) and unseeded gel (UG), respectively. Heterogeneous nucleation of SG decreases the temperature of formation of lanthanum hexaaluminate by 100°C. Single phase lanthanum hexaaluminate was formed at 1600°C in seeded gel whereas trace of lanthanum monoaluminate phase was still present in UG even at 1600°C.On the doped ones, randomly grown platelets of lanthanum magnesium hexaaluminate form a porous interlocking structure. Presence of various percentages of neodymium oxide significantly modifies the porous interlocking microstructure into self-reinforced, card-house like microstructure. Platelets of rare earth rich magnesium hexaaluminate were grown preferentially more than the stoichiometric rare earth magnesium hexaaluminate at elevated temperature greater than 1450°C. Rare earth rich magnesium hexaaluminate platelets formed the skeleton of a card house structure and the tiny platelets of stoichiometric rare earth magnesium hexaaluminate fill the rest. Lattice parameters of the hexagonal unit cell (c and a) decrease, relative density increases and pore size distribution remained almost unaltered with the increment of doping concentration.

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.

AN INVESTIGATION INTO MECHANOCHEMICAL SYNTHESIS OF NANOCRYSTALLINE HEXAFERRITE POWDER

2011 ◽  
Vol 25 (07) ◽  
pp. 987-993
Author(s):  
S. SADEGHI-NIARAKI ◽  
S. A. SEYYED EBRAHIMI ◽  
SH. RAYGAN
Keyword(s):  
Crystallite Size ◽  
Single Phase ◽  
Sol Gel ◽  
Milled Powder ◽  
Particle Morphology ◽  
Average Crystallite Size ◽  
Phase Evolution ◽  
High Energy ◽  
Strontium Hexaferrite ◽  
Electron Microscopes

Nanocrystalline strontium hexaferrite powder has been prepared by a new mechanochemical method in which the single phase hexaferrite was obtained via a sol–gel autocombustion process followed by an intermediate high energy milling step and subsequent annealing. The effects of the intermediate milling on the phase evolution, crystallite size and annealing behavior of the final products were investigated using the X-ray diffraction (XRD) technique. The single phase strontium hexaferrite was obtained at an annealing temperature of 800°C, while this temperature was 1,000°C for the powder synthesized without milling. It could be seen that an intermediate milling accelerates the formation of strontium hexaferrite during the calcination process. The results showed that in the milled powder, the average crystallite size of the ferrite was about 40 nm and much smaller than that of the nonmilled powder. Magnetic properties were also measured by a vibrating sample magnetometer (VSM). The particle morphology was then studied by scanning and transmission electron microscopes (SEM and TEM).

scholarly journals Synthesis of Silicon Carbide Powders from Methyl-Modified Silica Aerogels

2020 ◽  
Vol 10 (18) ◽  
pp. 6161
Author(s):  
Kyoung-Jin Lee ◽  
Yanggu Kang ◽  
Young Hun Kim ◽  
Se Won Baek ◽  
Haejin Hwang
Keyword(s):  
Silicon Carbide ◽  
High Purity ◽  
Silica Aerogel ◽  
Carbothermal Reduction ◽  
Single Phase ◽  
Phase Evolution ◽  
Silica Aerogels ◽  
Methyl Groups ◽  
Modified Silica ◽  
Lower Temperature

β-silicon carbide (SiC) powders were synthesized by the carbothermal reduction of methyl-modified silica aerogel/carbon mixtures. The correlations between the phase evolution and morphologies of the SiC powders and the C/SiO2 ratio were investigated. At a C/SiO2 ratio of 3, β-SiC formed at 1425 °C and single-phase SiC powders were obtained at 1525 °C. The methyl groups (-CH3) on the silica aerogel surfaces played important roles in the formation of SiC during the carbothermal reduction. SiC could be synthesized from the silica aerogel/carbon mixtures under lower temperature and C/SiO2 ratios than those needed for quartz or hydrophilic silica. The morphology of the SiC powder depended on the C/SiO2 ratio. A low C/SiO2 ratio resulted in β-SiC powder with spherical morphology, while agglomerates consisting of fine SiC particles were obtained at the C/SiO2 ratio of 3. High-purity SiC powder (99.95%) could be obtained with C/SiO2 = 0.5 and 3 at 1525 °C for 5 h.

Synthesis and Characterization of Fe2O3 Prepared Via Sol-Gel Method

2012 ◽  
Vol 545 ◽  
pp. 410-413 ◽  
Author(s):  
Abdul Rahman Noor Azreen ◽  
Mustaffa Nur Amalina ◽  
Nor Diyana Abdul Aziz ◽  
Nurhanna Badar ◽  
Norlida Kamarulzaman
Keyword(s):  
Impedance Spectroscopy ◽  
Single Phase ◽  
Sol Gel ◽  
Synthesis And Characterization ◽  
Gel Method ◽  
Sol Gel Method ◽  
Lower Temperature

Fe2O3 was synthesized via a sol-gel method. Pure, single phase materials were obtained at 300 °C and 800 °C heated for 24 hours. The conductivies of the materials were investigated using a.c. impedance spectroscopy. It was found that the material annealed at a lower temperature gives better conductivity value of about two orders of magnitude higher.

Zirconia – A Ceramic for Excess weapons Plutonium Wastes

1999 ◽  
Vol 556 ◽  
Author(s):  
W. L. Gong ◽  
W. Lutze ◽  
R. C. Ewing
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Metal Oxides ◽  
Solid Solutions ◽  
Binary Systems ◽  
Single Phase ◽  
Sol Gel ◽  
Neutron Absorber ◽  
Cubic Zirconia

AbstractWe synthesized a ceramic containing simulated excess weapons plutonium waste in solidsolution with zirconia (ZrO2)ss. ZrO2 has a large solubility for other metal oxides. More thantwenty binary systems AxOy- ZrO2 have been reported in the literature, including PuG2, rare earth elements, and oxides of metals contained in weapons plutonium wastes. We show that significant amounts of gadolinium (neutron absorber) and yttrium (stabilizer of the cubic modification) can be dissolved in ZrO2, together with plutonium (simulated by Th4+, Ce4+, or U4+) and impurities (e.g., Ca Mg, Fe, Si). Sol-gel and powder methods were applied to make homogeneous, single phase zirconia solid solutions. Pu waste impurities were completely dissolved in the solid solutions. In contrast to other phases, e.g., zirconolite and pyrochlore, yttrium stabilized cubic zirconia does not undergo amorphization upon irradiation.

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.

Enhanced Tunability Properties of Pure (Ba,Sr)TiO3 Lead free Ferroelectric by Polar Nano-region Contributions

2021 ◽  
Author(s):  
Abdelrazek Mahmoud ◽  
Samar Moen ◽  
M.K. Gerges
Keyword(s):  
Electric Fields ◽  
Room Temperature ◽  
Single Phase ◽  
Domain Switching ◽  
Ferroelectric Properties ◽  
Sol Gel ◽  
Lead Free ◽  
Multiple Components ◽  
The Difference ◽  
Lower Temperature

Abstract In the present work, a series compositions of (Ba1-xSrx)TiO3 (0≤x≤0.4) lead-free ferroelectric (BST) were successfully prepared by sol-gel method. The effects of Sr2+ on the optical properties, crystal structure and morphology of BaTiO3 were systematically investigated. Compositions with x<0.4 exhibit single phase tetragonal perovskite at room temperature, while a cubic structure of BST has been detected in the ceramic with x=0.4. Phase transition temperature was shifted toward lower temperature by increasing Sr-doping. Moreover, detailed tunability analysis for the present ceramics confirmed an enhancement by Sr-addition and the maximum values were observed at Sr=0.2. The enhancement back to present multiple components contribute to the dc-field induced dielectric constant, where at low electric fields the Langevin theory indicate present polar nano-region (PNR) contributions into tunability data, however domain switching contributions at high electric field was described by Johnson equation. Ferroelectric properties appraised by P-E loop and positive up negative down (PUND) methods have been introduced. The results shown the remnant polarization appraised by PUND method is much lower than polarization estimated by P-E loop indicate the difference values of Pr is mostly owing to leakage current contribution in P-E method.

Hydrolysis of aluminium metal, synthesis of nano alumina and sol-gel processing of monoliths

2004 ◽  
Vol 848 ◽  
Author(s):  
M. Thiruchitrambalam ◽  
V.R. Palkar
Keyword(s):  
High Purity ◽  
Sol Gel ◽  
Purity Aluminium ◽  
Nano Alumina ◽  
High Purity Aluminium ◽  
Sol Gel Transition ◽  
Lower Temperature ◽  
Gel Processing ◽  
Hydrolysis Of ◽  
Aluminium Metal

ABSTRACTHigh purity alumina is usually prepared using various intermediate aluminium compounds such as aluminium nitrate, aluminium alkoxides etc., as precursors. In fact the above mentioned intermediate aluminium compounds themselves are produced from aluminium metal. The present investigation is concerned with examining the feasibility of using aluminium hydroxides prepared by hydrolyzing aluminium metal, for sol gel processing. The study assumes added significance in view of the claims of Alcoa that it is possible to produce high purity aluminium metal in large quantities economically.During the present investigation sols were prepared by using various hydroxides, ie., bayerite, gibbsite and boehmite. Sol gel transition was observed only in the case of boehmite sol and this was gelated by either forced gelation method to prepare powder or controlled gelation method to prepare monoliths.Transparent Xerogels (boehmite) could be prepared by controlled gelation method but the presence of a thin layer of bayerite often resulted in translucency. Crack free monoliths could be prepared by heating the xerogels at a low heating rate(< 1 °C/min). It was found that sol gel processed boehmite transformed to alpha alumina at a relatively lower temperature (∼ 1080 °C ) than the as prepared boehmite which transformed at about 1200 °C.

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