Chemistry: physical processes – Physical processes – Crystallization
Patent
1996-11-14
1998-11-03
Straub, Gary P.
Chemistry: physical processes
Physical processes
Crystallization
23305RE, 423263, 423608, C01F 1700, C01G 2502, C01G 2507
Patent
active
058302425
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a process for producing rare earth oxide precipitates, more specifically to a process for producing precipitates of a metal oxide comprising a rare earth oxide, a mutual solid solution of rare earth oxides, or a solid solution containing a rare earth oxide as a main component, from an aqueous solution, for example, a process for forming the precipitates as a thin film on the surface of a substrate or precipitating said rare earth oxide in a liquid.
Also, this invention relates to a process for producing precipitates comprising crystals of zirconium oxide and/or hafnium oxide, more specifically to a process for producing crystal precipitates of a metal oxide comprising zirconium oxide and/or hafnium oxide, a mutual solid solution of both oxides, or a solid solution containing them as a main component in the presence of seed crystal(s) from an aqueous solution, for example, a process for forming a crystal thin film on the surface of a substrate or precipitating said metal oxide crystals in a liquid.
BACKGROUND ART
Zirconium oxide, hafnium oxide and a solid solution thereof, particularly crystals thereof are excellent in heat resistance and corrosion resistance and also have high oxide ion conductivities and electronic conductivities so that they have been used as an electrolyte and an electrode of a fuel cell, an oxygen sensor, an oxygen-enrich membrane, a heating element, a catalyst, etc. Particularly in these uses, in order to make moving distances of electrons and ions smaller to heighten electric conductivity and sensitivity or heighten a gas permeation amount; or in order to obtain a wide surface area or contact area, or in order to save weight, it has been desired to form a thin uniform crystal film or, depending on the use, crystal precipitates existing dispersedly on the surface of a substrate, easily on the surfaces of various substrates. On the other hand, zirconium oxide has been also used as a surface-protecting film of a metal, a semiconductor, ceramics, etc.
Among these uses, when the case of zirconium oxide is taken, when it is used at a high temperature region of 1,100.degree. C. or higher, further 2,370.degree. C. or higher, a zirconium oxide layer may be broken due to change in volume accompanied with phase transition during raising temperature from ordinary temperature to use temperature or cooling. In order to solve this problem, a thin film of a solid solution having the same cubic fluorite type structure even at ordinary temperature as that at the time of high temperature, obtained by dissolving a rare earth oxide such as yttrium oxide, or calcium oxide, etc. in zirconium oxide in a solid state is used as an electrolyte and an electrode of a fuel cell, an oxygen sensor, an oxygen-enrich membrane, a heating element, a catalyst, a surface-protecting film, etc. Further, by dissolving a metal oxide having a valence lower than that of a metal oxide which is a main component, in a solid state, there can be obtained an electrolyte, an electrode, a sensor, an oxygen-enrich membrane, a heating element, etc. in which ionic conductivity and a mobility of oxide ion are heightened.
On the other hand, a rare earth oxide and a solid solution containing it have been used as a catalyst of a decomposition reaction or an oxidation reaction of hydrocarbon and also used as a sensor and a solid electrolyte by utilizing high oxide ion conductivity, and among these uses, utilization as precipitates such as a thin uniform thin film, etc. is advantageous.
As a method for forming such a metal oxide thin film, there may be mentioned methods such as CVD, ion plating, sputtering, etc. However, in these methods, not only a special expensive apparatus is required, but also formation of a thin film having a large area and formation of a thin film on the surface of a substrate having a complicated shape are difficult, in particular, a thin film required for a large fuel cell cannot be obtained easily.
On the other hand, there is a method in which an admixture obtained by kne
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patent: 5026421 (1991-06-01), Le Loarer et al.
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Database WPI, Section CH, Week 8937, Derwent Publications Ltd., AN 89-266641 of JP 01 192 707 A (1989).
Hoya Corporation
Straub Gary P.
Yao Takeshi
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