Crystallization of Perovskites from Solutions

1996 ◽  
Vol 453 ◽  
Author(s):  
I. Maurin ◽  
P. Barboux ◽  
J. P. Boilot
Keyword(s):  
Phase Separation ◽  
Heating Rate ◽  
Perovskite Structure ◽  
Reaction Rate ◽  
Sol Gel ◽  
Diffusion Limited ◽  
History Of

AbstractLaMnO3 and PbZrO3 perovskites have been synthesized through coprecipitation and sol-gel techniques. After the drying and calcination steps, amorphous mixtures of oxides have been obtained. They are unstable towards phase separation. Therefore, their homogeneity and reactivity strongly depend on the parameters of the calcination, such as the temperature and heating rate. In all cases, the perovskite structure crystallizes around 600°C through nucleation- or diffusion-limited kinetics. The reaction rate depends on the history of the material. A mechanistic interpretation of the reaction, based on the similarity between the structures of PbO, ZrO2, Mn2O3 and La2O3 is proposed.

Phase separation in sol gel-derived ceramic films of silica-zirconia, alumina-zirconia, and titania-zirconia system

1994 ◽  
Vol 52 ◽  
pp. 646-647
Author(s):  
J. Tong ◽  
L. Eyring
Keyword(s):  
Fracture Toughness ◽  
Phase Separation ◽  
Sol Gel ◽  
Great Influence ◽  
High Strength ◽  
Chemical Durability ◽  
Separation Method ◽  
Toughening Mechanism ◽  
Ceramic Films ◽  
Zirconia Toughened Alumina

There is increasing interest in composites containing zirconia because of their high strength, fracture toughness, and its great influence on the chemical durability in glass. For the zirconia-silica system, monolithic glasses, fibers and coatings have been obtained. There is currently a great interest in designing zirconia-toughened alumina including exploration of the processing methods and the toughening mechanism.The possibility of forming nanocrystal composites by a phase separation method has been investigated in three systems: zirconia-alumina, zirconia-silica and zirconia-titania using HREM. The morphological observations initially suggest that the formation of nanocrystal composites by a phase separation method is possible in the zirconia-alumina and zirconia-silica systems, but impossible in the zirconia-titania system. The separation-produced grain size in silica-zirconia system is around 5 nm and is more uniform than that in the alumina-zirconia system in which the sizes of the small polyhedron grains are around 10 nm. In the titania-zirconia system, there is no obvious separation as was observed in die alumina-zirconia and silica-zirconia system.

Porous Gel Coatings Obtained by Phase Separation in ORMOSIL System

2000 ◽  
Vol 628 ◽  
Author(s):  
Kazuki Nakanishi ◽  
Souichi Kumon ◽  
Kazuyuki Hirao ◽  
Hiroshi Jinnai
Keyword(s):  
Phase Separation ◽  
Reaction Time ◽  
Volume Fraction ◽  
Sol Gel ◽  
Reaction Times ◽  
Dip Coating ◽  
Coating Solution ◽  
Coating Method ◽  
Gel Phase ◽  
Dip Coating Method

ABSTRACTMacroporous silicate thick films were prepared by a sol-gel dip-coating method accompanied by the phase separation using methyl-trimethoxysilane (MTMS), nitric acid and dimethylformamide (DMF) as starting components. The morphology of the film varied to a large extent depending on the time elapsed after the hydrolysis until the dipping of the coating solution. On a glass substrate, the films prepared by early dipping had inhomogeneous submicrometer-sized pores on the surface of the film. At increased reaction times, relatively narrow sized isolated macropores were observed and their size gradually decreased with the increase of reaction time. On a polyester substrate, in contrast, micrometer-sized isolated spherical gel domains were homogeneously deposited by earlier dippings. With an increase of reaction time, the volume fraction of the gel phase increased, then the morphology of the coating transformed into co-continuous gel domains and macropores, and finally inverted into the continuous gel domains with isolated macropores. The overall morphological variation with the reaction time was explained in terms of the phase separation and the structure freezing by the forced gelation, both of which were induced by the evaporation of methanol during the dipping operation.

Preparation of Macroprous C12A7 Mayenite Monoliths via a Sol-Gel Process with Nitrates as Precursors

2018 ◽  
Vol 768 ◽  
pp. 211-217 ◽  
Author(s):  
Rui Wang ◽  
Yu Kun Sun ◽  
Bao Jia Qi Jiang ◽  
Hui Yang ◽  
Xing Zhong Guo
Keyword(s):  
Heat Treatment ◽  
Phase Separation ◽  
Binary System ◽  
Propylene Oxide ◽  
Crystalline Phase ◽  
Sol Gel ◽  
Single Crystalline ◽  
Sol Gel Process

Macroporous Ca12Al14O33(C12A7) mayenite monoliths have been successfully prepared via a sol-gel process in the presence of propylene oxide (PO) and poly (ethyleneoxide) (PEO). Gelation of CaO-Al2O3binary system with nitrates salts as additional precursors is accelerated by PO as an acid scavenger, while PEO works as a phase separation inducer to mediate the phase separation of the system. Appropriate PO and PEO amounts allow the formation of monolithic xerogel with interconnected macropores and co-continuous skeletons. The resultant dried gels are amorphous and the single crystalline phase Ca12Al14O33mayenite forms after heat-treatment at 1100 °C in air, while the macrostructure is preserved with a porosity as high as 78% and smoother and denser skeletons.

Sol–gel chemistry in molten Brønsted acids towards “activated” carbons and beyond

Nanoscale ◽  
2019 ◽  
Vol 11 (27) ◽  
pp. 13154-13160
Author(s):  
Burak Koyutürk ◽  
Josh Evans ◽  
Hendrik Multhaupt ◽  
Sören Selve ◽  
Jan Ron Justin Simke ◽  
...  
Keyword(s):  
Phase Separation ◽  
High Temperature ◽  
Activated Carbons ◽  
Chemical Activation ◽  
Sol Gel ◽  
Bronsted Acids ◽  
Carbon Phase

Chemical activation of carbons is usually assigned to an oxidative and dehydrating nature of activating agents. We herein suggest that activating agents rather act as high temperature solvents and the porosity is developed by carbon phase separation.

Facile preparation of macro-mesoporous zirconium titanate monoliths via a sol–gel reaction accompanied by phase separation

2019 ◽  
Vol 34 (24) ◽  
pp. 4066-4075
Author(s):  
Mingliang Sun ◽  
Tianbo Zhao ◽  
Zhaofei Ma ◽  
Zunfeng Li
Keyword(s):  
Phase Separation ◽  
Sol Gel ◽  
Zirconium Titanate ◽  
Facile Preparation ◽  
Image Position

Abstract

Multiscale-structured superhydrophobic/superoleophilic SiO2 composite poly(ether sulfone) membranes with high efficiency and flux for water-in-oil emulsions separation under harsh conditions

2020 ◽  
Vol 44 (10) ◽  
pp. 3824-3827
Author(s):  
Rui Chen ◽  
Jiuduo Xu ◽  
Shu Li ◽  
Qiang Li ◽  
Han Wu ◽  
...  
Keyword(s):  
Phase Separation ◽  
High Efficiency ◽  
Sol Gel ◽  
Oil Emulsions ◽  
Harsh Conditions

Multiscale-structured SiO2 composite poly(ether sulfone) membranes (MSiCPESMs) are facilely prepared via the methods of nonsolvent induced phase separation and sol–gel.

scholarly journals In situ SAXS observation on metal–salt-derived alumina sol–gel system accompanied by phase separation

2010 ◽  
Vol 352 (2) ◽  
pp. 303-308 ◽  
Author(s):  
Yasuaki Tokudome ◽  
Kazuki Nakanishi ◽  
Kazuyoshi Kanamori ◽  
Teiichi Hanada
Keyword(s):  
Phase Separation ◽  
Metal Salt ◽  
Sol Gel ◽  
Alumina Sol ◽  
Gel System
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