Central Glass Company, Limited

Takamitsu Enomoto

Noboru Murata

Hiromi Kawamoto

Naoki Okada

Tetsuhiro Ono

Tamotsu Mizuno

Masao Fujinaga

Hiroshi Ueda

Midori Kawahara

Kyoji Tanaka

Motoshige Ogura

To produce a modified barium titanate ceramic which is semiconductive and sufficiently high in breakdown voltage and has a low specific resistance at room temperature and a high positive temperature coefficient (PTC) of resistance, the invention provides a powder composition comprising (A) a basic mixture consisting of 45-85 mol % of BaTiO.sub.3 powder, 1-20 mol % of SrTiO.sub.3 powder, 5-20 mol % of CaTiO.sub.3 powder and 1-20 mol % of PbTiO.sub.3 powder, (B) a source of a dopant element such as Nb, Sb, Y, La or Ce to render the ceramic semiconductive, (C) a source of Mn such as MnC.sub.2 O.sub.4 and/or a source of Cu such as CuO added such that the total amount of Mn and Cu is not more than 0.06 mol % on the basis of the quantity of the mixture (A) with proviso that the amount of Mn is not more than 0.025 mol % and (D) SiO.sub.2 amounting to 0.1-2.0 mol % on the basis of the quantity of the mixture (A). The BaTiO.sub.3 powder and the SrTiO.sub.3 powder are produced by calcining BaTiO(C.sub.2 O.sub.4).sub.2 and SrTiO(C.sub.2 O.sub.4).sub.2, respectively, and in each of these powders very fine primary particles agglomerate to constitute porous and coarse secondary particles (about 100-200 .mu.m). The PbTiO.sub.3 powder may be produced by calcining PbTiO(C.sub.2 O.sub.4).sub.2 so as to have nearly the same structure as the BaTiO.sub.3 and SrTiO.sub.3 powders. The aimed ceramic is produced by compacting the powder composition into a green body and sintering it at 1300.degree.-1400.degree. C.

Powder composition for sintering into modified barium titanate

A process of preparing calcium hydrogen phosphate anhydride suitable as a raw material for phosphate phosphors, wherein CaHPO.sub.4.2H.sub.2 O is precipitated by mixing aqueous solutions of NaNH.sub.4 HPO.sub.4.4H.sub.2 O and CaCl.sub.2.6H.sub.2 O at 5.degree.-40.degree. C. An entire quantity of CaHPO.sub.4.2H.sub.2 O to be converted to CaHPO.sub.4 in one batch is put into an acidified water maintained above 80.degree. C. all at once. Crystalline CaHPO.sub.4 is obtained through agitation of a resultant hot slurry for a few minutes. Crystal habit of the product depends on the pH of the hot water: lozenge-shaped plates when the pH is below 3.4, parallelogram plates in the pH range of 3.4-4.4, and square or rectangular plates when the pH is above 4.4. The particle size of CaHPO.sub.4 depends on the water temperature and the degree of agitation. To precipitate CaHPO.sub.4.2H.sub.2 O in the presence of suitable quantity of seed crystals is effective for minimizing the Na content of CaHPO.sub.4.

Process of preparing calcium hydrogen phosphate anhydride suitable as

An aqueous slurry of CaHPO.sub.4.2H.sub.2 O in a 5-20 Wt% concentration is prepared by the use of the phosphate dihydrate obtained by reaction of NaNH.sub.4 HPO.sub.4.4H.sub.2 O with CaCl.sub.2 in water. After adjustment of the pH of the slurry to 4.5-5.5, the slurry is rapidly heated to 85.degree.-97.degree. C by contact with steam to convert the dihydrate to the anhydride, which is suitable for use in the preparation of fluorescent materials due to its high purity, platy and square crystal shape and uniform particle size.

Process for preparation of calcium hydrogen phosphate anhydride

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Ube, Japan

Takamitsu Enomoto