Method of preparing coprecipitated inorganic particles

Details Method of preparing coprecipitated inorganic particles Method of preparing coprecipitated inorganic particles

2000-11-29

2003-01-14

Koslow, C. Melissa (Department: 1755)

Compositions

Inorganic luminescent compositions

Compositions containing halogen; e.g., halides and oxyhalides

C423S263000

Reexamination Certificate

active

06506320

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a method of preparing coprecipitated inorganic particles, to calcined particles obtained from the coprecipitated inorganic particles, and to an inorganic phosphor containing the calcined particles.
There are many inorganic compounds containing rare earth element ions having peculiar characteristics. Such compounds are used as functional materials in a wide variety of fields such as electronics field. In order for the inorganic compounds to efficiently exhibit their effects, powder of such compounds is desired to have specifically controlled shape and particle distribution.
U.S. Pat. No. 5,413,736 discloses a fluorescent material of spherical particles of Y
2
O
3
and Eu
2
O
3
and having an average particle diameter of 0.09-0.21 &mgr;m. The fluorescent material is produced by heating an aqueous solution having a pH of 3 or less and containing a yttrium salt, a europium salt and urea at a temperature of at least 90° C. to coprecipitate particles, followed by calcination. Such small diameter particles, however, have problems with respect to the service life and handling.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a simple method which can produce coprecipitated particles having controlled particle diameter and shape and which have solved the above problems of the prior art.
It is a special object of the present invention to provide a method which can produce a phosphor of Eu
3+
-doped yttrium oxide spherical particles having a weight average particle diameter of 0.3-10 &mgr;m.
In accordance with one aspect of the present invention, there is provided a method of preparing coprecipitated inorganic particles, comprising the steps of:
(a) preparing an aqueous solution containing two or more metal ions;
(b) dividing said aqueous solution into first and second portions;
(c) subjecting said first portion to a coprecipitation reaction to form a liquid containing nucleus particles;
(d) mixing said nucleus particles-containing liquid with said second portion to form a mixture; and
(e) subjecting said mixture to a coprecipitation reaction to produce coprecipitated inorganic particles.
In another aspect, the present invention provides a method of preparing coprecipitated inorganic particles, comprising the steps of:
(a) subjecting a first aqueous solution containing two or more metal ions to a coprecipitation reaction to form a liquid containing nucleus particles;
(b) mixing said nucleus particles-containing liquid with a second aqueous solution to form a mixture, said second solution containing the same metal ions as those of said first solution, wherein the relative amounts of said metal ions in said first and second solutions are substantially equal to each other; and
(c) subjecting said mixture to a coprecipitation reaction to produce coprecipitated inorganic particles.
The present invention also provides calcined inorganic particles obtained by calcining coprecipitated inorganic particles obtained by the above methods. The calcined inorganic particles have an average particle diameter of 0.3-10 &mgr;m.
The present invention further provides a phosphor including the above calcined inorganic particles.
Other objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments of the invention to follow.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
In one embodiment according to the present invention, coprecipitated inorganic particles are prepared from an aqueous solution containing two or more metal ions. Any metal or metalloid ions capable of being coprecipitated can be used for the purpose of the present invention. Examples of metals of the metal ions include Group Ib metals such as Cu, Ag and Au; Group IIa and IIb metals such as Mg, Ca, Sr, Ba, Zn, Cd and Hg; Group IIIa and IIIb metals such as Al, Ga, In, Tl, Sc and Y; Group IVa and IVb metals such as Si, Ge, Sn, Pb, Ti, Zr and Hf; Group Va and Vb metals such as as, Sb, Bi, V, Nb and Ta; Group VIa and VIb metals such as Cr, Mo, W and Se; Group VIIa metals such as Mn, Tc and Re, Group VIII metals such as Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt; lanthanide elements such as La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; and actinium elements such as Ac, Th, Pa, U, Np, Pu and Am.
The aqueous solution containing the metal ions (stock solution) may be obtained by dissolving salts of the metal ions in water. The relative amounts of the metal ions are the same as those of the relative amounts of the metals of the desired coprecipitated particles. A total concentration of the metal ions in the aqueous solution is generally 0.0005 to 0.5 mole/L, preferably 0.001-0.1 mole/L, more preferably 0.005-0.05 mole/L, most preferably 0.01-0.02 mole/L.
The aqueous solution is divided into first and second portions. The amount of the second portion is generally 1-50 parts, preferably 1-10 parts, more preferably 2-5 parts, per part of the first portion.
The first portion is subjected to a coprecipitation reaction to form a liquid containing nucleus particles. The coprecipitation reaction can be carried out in any known manner depending upon the metal ions used. It is preferred that urea be used as a precipitant. The amount of urea is generally 5-100 moles, preferably 20-80 moles, per mole of a total of the metal ions. Urea may be previously added to the stock solution or, if desired, to the first and/or second portions after separation from the stock solution.
The liquid containing nucleus particles thus produced is then mixed with the second portion. The mixture is subjected to a coprecipitation reaction to produce coprecipitated inorganic particles. If desired, the thus obtained reaction mixture is mixed with a third portion of the stock solution to further perform the coprecipitation reaction.
The coprecipitated particles are separated by, for example, filtration or centrifuge, dried and calcined. While the drying and calcining conditions may vary with the kind of the metal ions and the desired size of the particles, the drying temperature may be generally 40-150° C., preferably 60-100° C. and the calcination temperature may be generally at least 600° C., preferably 600-1500° C., more preferably 1000-1400° C. The calcination may be performed in an oxidating atmosphere such as air, an inert atmosphere such as nitrogen or argon or a reducing atmosphere such as hydrogen, depending upon the kind of the coprecipitated particles.
The process according to the present invention can produce calcined coprecipitated particles having a weight average particle diameter of 0.3-10 &mgr;m, especially 0.5-3 &mgr;m. The particle diameter can be changed by the coprecipitation conditions and number of repetition of the coprecipitation reaction. The calcined coprecipitated particles are generally spheres.
The present invention will now be described in detail with regard to the preparation of Eu
3+
-doped yttrium oxide. First, an aqueous solution containing a yttrium salt, and a europium salt is prepared. As the yttrium salt, a yttrium halide, such as yttrium chloride (YCl
3
), yttrium nitrate (Y(NO
3
)
3
) or a hydrate thereof is preferably used. As the europium salt, a europium halide, such as europium chloride (EuCl
3
), europium nitrate (Eu(NO
3
)
3
) or a hydrate thereof is preferably used. Other salts may be used as long as they are soluble in water at a pH of 3 or less.
The amount of the yttrium compound relative to that of the europium compound is not specifically limited and is suitably selected according to the end use. Generally, the yttrium and europium compounds are used in such an amount as to provide an atomic ratio Y/Eu of 9.5:0.5 to 0.5:9.5, namely such an amount that the fluorescent material produced has a composition of (Y
1−x
, EU
x
)
2
O
3
wherein x is a number of between 0.05 and 0.95. The pH of the aqueous solution is generally adjusted to 3 or less, preferably 2-3, by addition of an acid such as hydrochloric acid, nitric acid, sulfu

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