Method of synthesizing metal oxides

Details Method of synthesizing metal oxides Method of synthesizing metal oxides

2000-12-12

2004-03-02

Bos, Steven (Department: 1754)

Chemistry of inorganic compounds

Rare earth compound

C423S593100, C423S594800, C423S594150, C423S594160

Reexamination Certificate

active

06699449

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of synthesizing metal oxides usable as, for instance, superconductors, semiconductors, magnetic materials and catalysts.
2. Description of the Prior Art
It is known that synthesis of certain metal oxides requires the oxygen partial pressure to be controlled to an extremely low level. Regarding synthesis of Sr
2
MoO
4
, for example, Lindblom et al. estimated from the oxidation-reduction potential of the metal oxide that the oxygen partial pressure must be maintained at an extremely low 10
−21
atm. [B. Linblom and R. Rosen, Acta Chem Scand. A40, 452 (1986)]. Since such an extremely low oxygen partial pressure could not be achieved with an ordinary vacuum pump, they adopted a method comprising the steps of placing a mixture of Sr(OH)
2
and MoO
2
as a starting material and a mixture of SrO and Mo metallic powders as an oxygen partial pressure buffer side by side in a vacuum vessel and heating the vacuum vessel. They succeeded in obtaining Sr
2
MoO
4
by this method.
When the oxygen partial pressure is lowered too much, however, metals in the starting material precipitate as simple substances that constitute impurities. The foregoing prior art method of controlling oxygen partial pressure with a mixture of SrO and Mo metallic powders therefore has a major drawback in that precipitation of Mo metal, Sr
3
Mo
2
O
7
and other impurity phases on the starting material side makes production of a single-phase material impossible [U. Steiner and W. Reichelt, Z. Naturforsch. 53b, 110 (1998)].
An object of the present invention is to provide a method of synthesizing metal oxides that utilize a rationally selected oxygen partial pressure control agent to achieve oxygen partial pressure control even in an extremely low oxygen partial pressure region of 10
−21
atm. and thus to enable synthesis of a target metal oxide without precipitation of simple metal as impurity on the starting material side.
SUMMARY OF THE INVENTION
The present invention achieves this object by providing a method of synthesizing metal oxides that, when synthesizing an oxide of a metal A, controls oxygen partial pressure by using an oxygen partial pressure control agent containing an oxide of a metal B capable of assuming multiple valence numbers, which method satisfies an ionization tendency relationship of A
1+
<B
j+
<A
0
, where i is a valence number of the metal A and j is a valence number of the metal B.
An example of synthesizing Sr
2
MoO
4
using Ti
2
O
3
as the oxygen partial pressure control agent will be described. In this case, metal A=Mo, metal B=Ti, and the Ti
3+
(B
j+
) ions in the oxygen partial pressure control agent Ti
2
O
3
have an ionization tendency just midway between the Mo
4+
(A
1+
) ions as in Sr
2
MoO
4
and Mo (A
0
) simple metal, that is, the relationship of Mo
4+
<Ti
3+
<Mo holds. The first half of the relation, Mo
4+
<Ti
3+
, ensures that residual oxygen gas in the vacuum vessel is absorbed by Ti
2
O
3
to produce the extremely low oxygen partial pressure of 10
−21
atm. necessary for Sr
2
MoO
4
formation. At the same time, no liberation of Mo metal occurs since Ti
3+
<Mo. Pure Sr
2
MoO
4
can therefore be synthesized.
The above and other objects and features of the invention will become apparent from the description made with reference to the accompanying drawings.


REFERENCES:
patent: 6403053 (2002-06-01), Fang et al.
patent: 04-305020 (1992-10-01), None
Fotiev, et al., “Synthesis and study of solid solutions in strontium vanadate-strontium lanthanide vanadate systems,” Zhurnal Neorganicheskoi Khimii, 1981, no month, 26(4), pp. 881-883.*
Vinogradov, et al., “Synthesis and structural characteristics of calcium molybdenum oxide,” Doklady Akademii Nauk, 1991, no month, 320(6), pp. 1396-1399.*
U. Steiner, et al, “On the System Sr/Mo/O: Phase Diagram, Synthesis and Characterization of Ternary Compounds”, 1998, pp. 110-116, no month.
Bo Lindblom, et al., “Solid State emf Measurements and Phase Studies in the System SrO/Mo/O in the Temperature Range 1200-1600 K”, Department of Inorganic Chemistry, University of Umeá, pp. 452-458, 1986, no month.

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