Central Glass Company, Limited

Hiroshi Ueda

Noboru Murata

Naoki Okada

Midori Kawahara

Hiromi Sasaki

Takamitsu Enomoto

Sunao Yamamoto

Hirokazu Kusunoki

Yasushi Muneno

Takamitsu Eonomoto

A process of continuously crystalizing sodium percarbonate by the reaction of sodium carbonate with hydrogen peroxide using first and second reaction vessels includes the steps of: (a) continuously feeding a first feed solution containing sodium carbonate and a second feed solution containing hydrogen peroxide into the first reaction vessel, thereby to form therein a first slurry containing seed crystals of sodium percarbonate; (b) continuously discharging the first slurry from the first reaction vessel into the second reaction vessel while step (a) is performed; (c) continuously feeding at least one of hydrogen peroxide and sodium carbonate into the second reaction vessel while steps (a) and (b) are performed thereby to form therein a second slurry containing final sodium percarbonate crystals grown from the seed crystals; (d) continuously discharging the second slurry from the second reaction vessel while steps (a), (b) and (c) are performed; (e) continuously separating the second slurry into the final sodium percarbonate crystals and a mother liquor while steps (a), (b), (c) and (d) are performed; and (f) granulating the final sodium percarbonate crystals thereby to form a final product of sodium percarbonate. According to the process, it is possible to maintain particle size of the final sodium percarbonate crystals not larger than 100 .mu.m, thereby to efficiently produce sodium percarbonate granules having a satisfactory strength.

Continuous process for preparing sodium percarbonate

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 modified lead barium titanate ceramic which has a fundamental composition of (Ba.sub.1-x-y Sb.sub.y Pb.sub.x)TiO.sub.3, where x is not greater than 0.9 and usually not smaller than 0.6 and y is from 0.001 to 0.1, and has a high positive temperature coefficient of resistivity (PTCR) over a range of temperature higher than about 350.degree. C. at the lower boundary, is produced by using a metal salt of an organic acid such as lead titanate salt of oxalic acid as the source of Pb and by adding at least one of BaCO.sub.3, SiO.sub.2, BN and TiO.sub.2 to the raw materials of the above fundamental composition. After thermally decomposing the organic acid metal salt the mixture of the raw materials including the additive(s) is compacted and sintered. By this method the sintering is achieved with good reproducibility and with little dissipation of lead, and the obtained titanate ceramic is good and durable in the PTCR characteristics and hence is useful as the material of a PTC thermistor functioning at medium-to-high temperatures.

Method of producing modified lead barium titanate ceramic useful as PTC

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Ube, Japan

Hiroshi Ueda