Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Reexamination Certificate
1995-10-12
2002-01-15
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
C423S066000
Reexamination Certificate
active
06338832
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improved process for producing valve metal compounds, such as niobium (columbium) compounds including niobium oxides and niobium hydrates, and tantalum compounds including tantalum oxides and tantalum hydrates. The present invention also relates to novel valve metal compounds, in particular to novel niobium oxides, niobium hydrates, tantalum oxides and tantalum hydrates.
BACKGROUND OF THE INVENTION
The term “valve metal” refers to metals such as vanadium, tantalum and niobium that are often utilized in valves, such as the intake/exhaust valves in engines. A commercially valuable form of a valve metal is a valve metal oxide such as a tantalum pentoxide, (Ta
2
O
5
) or a niobium pentoxide (Nb
2
O
5
) which are produced from mineral ores.
Minerals of concentrates containing tantalum and niobium are conventionally extracted with hydrofluoric acid (HF) or mixtures of hydrofluoric acid and sulfuric acid (HF/H
2
SO
4
). The tantalum and niobium heptafluoro complexes formed are typically separated by solvent extraction.
In a conventional process for producing tantalum pentoxide (Ta
2
O
5
), the tantalum fraction from the ore and solvent extraction is stripped into the aqueous phase, and tantalum pentoxide is precipitated using ammonia and recovered by filtration. Niobium pentoxide may be produced in a similar fashion.
Typical conventional processes for producing niobium pentoxides/hydrates and tantalum pentoxides/hydrates are batch processes. Disadvantages inherent with batch processes include the need to clean and reload processing vessels, that batch size is limited to the size of the processing equipment, and that the production of large quantities of material requires multiple batch runs.
In addition, in conventional processes for producing tantalum pentoxides/hydrates and niobium pentoxides/hydrates it is difficult to control the particle size, and the particle size distribution of the pentoxides and hydrates produced.
For many applications, it is desirable to have a tantalum pentoxide, or niobium pentoxide, product with a consistent particle size (i.e. a narrow particle size distribution). In addition, for many applications it is desirable to have a tantalum pentoxide, or niobium pentoxide, having large dense spherical particles (a particle size greater than or equal to 5 micrometers (&mgr;m)) and a bulk density of 2.0 g/cc or greater for Ta
2
O
5
and 1.2 g/cc or greater for Nb
2
O
5
. For other applications low bulk density fine particle sizes are preferred (a particle size less than or equal to 5 &mgr;m) and a bulk density of less than 2.0 for Ta
2
O
5
and less than 1.2 for Nb
2
O
5
. The present invention advantageously allows the production of tantalum pentoxide, or niobium pentoxide, products with narrow particle size distributions within a desired particle size range.
SUMMARY OF THE INVENTION
The present invention provides a process for producing valve metal pentoxides, such as tantalum pentoxide or niobium pentoxide, with a narrow particle size distribution within a desired particle size range.
According to the present invention a process for producing valve metal pentoxides comprises:
reacting an aqueous solution comprising a valve metal compound with a base solution under controlled temperature, pH and residence time conditions to precipitate valve metal pentoxide precursor;
converting the valve metal pentoxide precursor to valve metal pentoxide; and
separating and recovering the valve metal pentoxide. Among the valve metal compounds suitable for use in the process of the present invention are included the valve-metal compounds found in naturally occurring ores and valve metal compounds produced as products or by-products in industrial processes.
In a preferred embodiment of the process of the present invention, the aqueous solution comprises a valve-metal fluoro compound such as those formed during digestion of naturally occurring tantalum and niobium containing ores. The aqueous solution in this preferred embodiment of the present invention will be an aqueous-flouro solution. According to the process of the present invention a valve metal-fluoro compound material is processed under controlled temperature, pH and residence time conditions to produce the valve metal pentoxide. In particular, according to the present invention, a process for producing a valve metal pentoxide comprises:
reacting an aqueous fluoro-solution comprising a valve metal-fluoro compound with an ammonia containing solution under controlled temperature, pH and residence time conditions to precipitate valve metal pentoxide precursor;
converting the valve metal pentoxide precursor to valve metal pentoxide; and
separating and recovering the valve metal pentoxide.
Further details relating to the process of the present invention are set forth below in the
DETAILED DESCRIPTION OF THE INVENTION SECTION
The present invention also provides new valve metal pentoxide products, in particular new niobium pentoxide products and new tantalum pentoxide products.
A first embodiment of calcined niobium pentoxide powders of the present invention may be characterized by having a BET surface area of less than or equal to 6 square meters per gram (m
2
/g), preferably less than or equal to 3 m
2
/g, more preferably less than or equal to 0.5 m
2
/g; and a packed bulk density of greater than 1.8 grams per cubic centimeter (g/cc), preferably greater than or equal to 2.1 g/cc. The first embodiment of calcined niobium pentoxide powders may be further characterized as comprising substantially spherical particles.
A second embodiment of calcined niobium pentoxide powders of the present invention may be characterized by having a BET surface area of greater than or equal to 2 m
2
/g, preferably greater than or equal to 4 m
2
/g, more preferably greater than or equal to 6 m
2
/g; and a packed bulk density of less than or equal to 1.8 g/cc, preferably less than or equal to 1.0 g/cc, more preferably less than or equal to 0.75 g/cc.
A first embodiment of calcined tantalum pentoxide powders of the present invention may be characterized by having a BET surface area of less than or equal to 3 m
2
/g, preferably less than or equal to 0.75 m
2
/g, more preferably less than or equal to 0.4 m
2
/g; and a packed bulk density of greater than 3.0 g/cc, preferably greater than or equal to 3.8 g/cc, more preferably greater than or equal to 4.0 g/cc. The first embodiment of calcined tantalum pentoxide powders may be further characterized as comprising substantially spherical particles.
A second embodiment of calcined tantalum pentoxide powders of the present invention may be characterized by having a BET surface area of greater than or equal to 3 m
2
/g, preferably greater than or equal to 7 m
2
/g, more preferably greater than or equal to 11 m
2
/g; and a packed bulk density of less than or equal to 3.0, preferably less than or equal to 1.1 g/cc, more preferably less than or equal to 0.75 g/cc.
Further details relating to the products of the present invention are also set forth in the following Detailed Description of the Invention section.
In addition, the present invention provides new valve metal pentoxide precursors, in particular new niobium pentoxide precursors and new tantalum pentoxide precursors. The valve metal pentoxide precursors of the present invention may be processed to produce advantageous valve metal pentoxide products.
The valve metal pentoxide precursors of the present invention are characterized by having a line broadened d-value under x-ray analysis at:
6±0.3;
3±0.2; and
1.8±1.
A first embodiment of niobium pentoxide precursors of the present invention may be further characterized by having a BET surface area of less than or equal to 3 m
2
/g, preferably less than or equal to 0.5 m
2
/g; and a Fluoride content of less than or equal to 500 parts per million (ppm), preferably less than or equal to 150 ppm.
A second embodiment of niobium pentoxide precursors of the present invention may be further characterized by having a BET surface area of gr
Brown Patrick M.
Madara Michael G.
Pedicone Raymond C.
Wu Rong-Chein R.
Bos Steven
Cabot Corporation
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