Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2001-08-08
2004-05-11
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C423S263000
Reexamination Certificate
active
06733882
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a rare earth hydroxide and a method for the preparation thereof. More particularly, the invention relates to a rare earth hydroxide powder characterized by unique properties and having usefulness as a base ingredient or as an adjuvant in various ceramic dielectric materials and other sintered ceramic materials as well as to a novel method for the preparation of such a rare earth hydroxide powder from a corresponding rare earth oxide.
It is a well known and established technology to employ a rare earth compound as an adjuvant in the preparation of a variety of ceramic materials including those in electronic or dielectric devices such as dielectric filters and ceramic capacitors and ceramic structural bodies of silicon nitride, aluminum nitride and the like. When a compound of lanthanum or neodymium is used as an adjuvant in ceramic compositions, it is usual that the rare earth compound is an oxide of the respective rare earth element. A problem encountered in the use of lanthanum oxide or neodymium oxide is the strong hygroscopicity of these rare earth oxides. Namely, these rare earth oxides readily absorb moisture from the ambient atmosphere and are rapidly converted at least partly into the hydroxide of the respective rare earth element resulting in an uncontrollable changes in the compounding amount of the rare earth oxide with other base ingredients of the ceramic compositions under preparation from time to time.
As a means for solving the problem due to moisture absorption of a rare earth oxide to cause a weight change with time, a method sometimes undertaken is the use of a rare earth hydroxide in place of the corresponding rare earth oxide. Rare earth hydroxides are usually prepared by a wet-process method. Namely, an aqueous solution of a rare earth salt such as a nitrate and chloride is admixed with an aqueous alkaline solution such as ammonia water and an aqueous solution of sodium hydroxide at a temperature from room temperature up to about 80° C. to effect precipitation of the rare earth hydroxide precipitates having good filtrability which are collected by filtration, washed thoroughly with water and finally dried at a temperature not exceeding 200° C. (see Japanese Patent Kokai 62-65928 and 09-188515). The crystallites as the primary particles forming the rare earth hydroxide particles obtained in this wet-process method, however, have irregular configurations so that the particle diameter thereof cannot be determined by the X-ray diffractometric method.
In addition, the secondary particles have a needle-formed configuration and exhibit strong agglomeration to form agglomerates of a relatively large particle diameter. The above named Japanese patent documents disclose that the secondary particles have a particle diameter of 2 to 100 &mgr;m or 5 to 100 &mgr;m, respectively. As a consequence of such a relatively large particle size, the hydroxide precipitates have good filtrability from the aqueous precipitation medium. The thus obtained rare earth hydroxide particles, however, are too coarse for some applications necessitating further comminution by using a grinding mill, jet mill and the like. The rare earth hydroxide powder after further comminution in this way is still not quite satisfactory as an adjuvant to a base ingredient of a ceramic composition because of the poor dispersibility due to strong agglomeration.
Another problem encountered in the wet-process preparation of rare earth hydroxide particles is the poor washability of the precipitates as a consequence of the irregular configuration of the primary particles. Namely, it is an extremely difficult matter to completely wash away the residual ions such as nitrate ions, chloride ions, sodium ions ammonium ions and others strongly adsorbed from the precipitation medium onto the irregular primary particles. If a rare earth hydroxide powder containing a substantial amount of these adsorbed ions is used as an adjuvant in ceramic materials, noxious gases such as Nox and chlorine are eventually generated from the ceramic body under sintering to cause damages on the furnace linings and environmental pollution.
Japanese Patent Kokai 11-349376 recommends samarium oxide having hydroxyl groups on the particle surface as a base material for the preparation of a filter device in a microwave resonator. This is because, although the problem of hygroscopicity is solved at least partly in commercially available rare earth hydroxides prepared by wet-process ball-milling in an aqueous medium, the above mentioned problems cannot still be solved therewith and, when rare earth oxide particles are ball-milled in an aqueous medium, oxide particles having hydroxyl groups on the particle surface only can be obtained, which, however, are still not quite satisfactory in respect of physical properties.
SUMMARY OF THE INVENTION
In view of the above described problems and disadvantages in the prior art, the present invention has a primary object to provide a novel rare earth compound which is free from uncontrollable changes with time in the rare earth content due to moisture absorption unnecessitating precise determination of the rare earth content in each time of compounding with the base ingredients of the ceramic material, which exhibits good dispersibility to the base ingredient of the ceramic materials and which can be used as an adjuvant even in a ceramic material, in which moisture should be avoided, because of the very low content of water of crystallization or adherent water.
The rare earth compound provided by the present invention to accomplish the above described primary object of the invention is a rare earth hydroxide characterized by the parameters;
that the crystallites have a particle diameter not exceeding 40 nm as measured by the X-ray diffractometric method;
that the content of impurities does not exceed 300 ppm for chlorine and 100 ppm for nitrate ions;
that the weight loss by ignition for 1 hour at 1000° C. is not larger or not smaller by more than 2% by weight than the theoretical value for the conversion of the rare earth hydroxide to the rare earth oxide; and
that the secondary particles as an agglomerate of the crystallites have an average particle diameter in the range from 0.1 &mgr;m to 2 &mgr;m.
When the rare earth hydroxide is neodymium hydroxide, in particular, it is preferable that, in addition to the above given characterizing parameters, the hydroxide has a color difference value L*a*b* of which L* does not exceed 95, a* is in the range from 3 to 6 and b* is in the range from −10 to −5.
The present invention also provides a method for the preparation of the above defined specific rare earth hydroxide, which comprises the steps of:
(a) bringing a powder of a rare earth oxide into contact with water either in the liquid form or in the vapor form in an amount of from 1.5 moles to 3.0 moles per mole of the rare earth oxide; and
(b) keeping the rare earth oxide powder in contact with water at a temperature in the range from 30° C. to 200° C.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The rare earth hydroxide as the subject matter of the present invention is a compound represented by the general formula R(OH)
3
, in which R is a rare earth element selected from the group consisting of yttrium and the elements having an atomic number in the range from 57 to 71. The present invention is of course applicable when the rare earth hydroxide is derived from a combination of two kinds or more of these rare earth elements.
When the rare earth hydroxide of the present invention is used as an adjuvant in various electronic ceramic materials as in dielectric filters and ceramic capacitors, of which the base ingredient of the ceramic material is assumed to be barium titanate, for example, the rare earth adjuvant is admixed with the base ingredient in the form of a rare earth titanate which is a reaction product prepared in advance from titanium dioxide and the rare earth hydroxide.
Commercially available products of barium titanate and tita
Takai Yasushi
Tsukatani Toshihiko
Le H. Thi
Shin-Etsu Chemical Co. , Ltd.
Wenderoth Lind & Ponack LLP
LandOfFree
Rare earth hydroxide and method for the preparation thereof does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Rare earth hydroxide and method for the preparation thereof, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Rare earth hydroxide and method for the preparation thereof will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3268501