Ngk Insulators, Inc.

Ritsu Sato

Osamu Imai

Kunio Ohira

Method and apparatus for quickly drying shaped ceramic bodies (3) having a complex surface (3a, 4a) with enriched unevenness, and a simple surface (3b, 4b) which is less uneven as compared to the complex surface (3a, 4a), without causing drying cracks and within a shortened time. The shaped ceramic body (3) within a drying chamber (1) is primarily heated from the simple surface (3b, 4b) by a main infrared heater (6), which is arranged on the simple surface side. Preferably, the ceramic body (3) is also heated by an auxiliary infrared heater (7) of a relatively low temperature, which is arranged on the side of the complex surface (3a, 4a), or dried while admitting a hot air into the drying chamber (1) with a low speed.

Method of, and apparatus for drying shaped ceramic bodies

An object of the present invention is to shorten the working time for high pressure slip casting. There is provided a composition for high pressure casting slip including a first starting powder forming a frame of a mold body and second starting powder forming the frame of the mold body and acting as a plastic agent, wherein the first and second starting powders are uniformly mixed in a dry condition. 'Slip' of a minimum water content is easily prepared by the composition to effect optimal fluidity of the slip so that the water is removed from the slip in a short time during a casting process.

Composition for high pressure casting slip, high pressure casting slip

A ZnO.sub.2 voltage non-linear resistor excellent in all characteristics of life under electrical stress, current impulse withstandability, discharge voltage ratio, change rate of discharge voltage after application of current impulse and moisture absorbency contains, as additive ingredients: 0.4-1.5 mol. % bismuth oxides as Bi.sub.2 O.sub.3, 0.3-1.5 mol. % cobalt oxides as Co.sub.2 O.sub.3, 0.2-1.0 mol. % manganese oxides as MnO.sub.2, 0.5-1.5 mol. % antimony oxides as Sb.sub.2 O.sub.3, 0.1-1.5 mol. % chromium oxides as Cr.sub.2 O.sub.3, 0.4-3.0 mol. % silicon oxides as SiO.sub.2, 0.5-2.5 mol. % nickel oxides as NiO, 0.001-0.05 mol. % aluminum oxides as Al.sub.2 O.sub.3, 0.0001-0.05 mol. % boron oxides as B.sub.2 O.sub.3, 0.0001-0.05 mol. % silver oxides as Ag.sub.2 O, and 0.0005-0.1 mol. % zirconium oxides as ZrO.sub.2, which bismuth oxides contain 30 wt. % of a .gamma.-type crystalline phase. A small-sizable ZnO.sub.2 voltage non-linear resistor having a higher varistor voltage in addition to the above characteristics contains, as additive ingredients: 0.3-1.5 mol. % bismuth oxides as Bi.sub.2 O.sub.3, 0.3-1.5 mol. % cobalt oxides as Co.sub.2 O.sub.3, 0.2-1.5 mol. % manganese oxides as MnO.sub.2, 0.5-1.5 mol. % antimony oxides as Sb.sub.2 O.sub.3, 0.1-1.5 mol. % chromium oxides as Cr.sub.2 O.sub.3, 4.0-10.0 mol. % silicon oxides as SiO.sub.2, 0.5-2.5 mol. % nickel oxides as NiO, 0.001-0.05 mol. % aluminum oxides as Al.sub.2 O.sub.3, 0.0001-0.05 mol. % boron oxides as B.sub.2 O.sub.3, 0.0001-0.05 mol. % silver oxides as Ag.sub.2 O, and 0.0005-0.1 mol % zirconium oxides as ZrO.sub.2, which bismuth oxides contain 30 wt. % of a crystalline .gamma.-type phase.

Voltage non-linear resistor

A voltage non-linear resistor element mainly including ZnO, substantially free from internal defects, exhibiting an excellent current impulse withstand capability, can be manufactured by a process wherein an SiC inclusion in the starting ZnO powder is restricted to at most 10 ppm, preferably at most 0.1 ppm, by weight, whereby formation of closed pores in the element is prevented, which is otherwise caused by decomposition of considerable amount of SiC during firing. The starting ZnO powder has an average particle diameter (R) of 0.1-2.0 .mu.m, preferably 0.3-0.8 .mu.m, a particle size distribution within the range of between 0.5R and 2R, of at least 70%, preferably 80%, by weight, needle-like crystals of at most 20%, preferably at most 10%, by weight, and an SiC content as an impurity of at most 10 ppm, preferably at most 0.1 ppm, by weight.

Starting material for use in manufacturing a voltage non-linear resistor

A voltage non-linear resistor element mainly comprising ZnO, substantially free from internal defects, exhibiting an excellent current impulse withstand capability, can be manufactured by a process wherein an SiC inclusion in the starting ZnO powder is restricted to at most 10 ppm, preferably at most 0.1 ppm, by weight, whereby formation of closed pores in the element is prevented, which is otherwise caused by decomposition of considerable amount of SiC during firing. The starting ZnO powder has an average particle diameter (R) of 0.1-2.0 .mu.m, preferably 0.3-0.8 .mu.m, a particle size distribution within the range of between 0.5R and 2R, of at least 70%, preferably 80%, by weight, needle-like crystals of at most 20%, preferably at most 10%, by weight, and an SiC content as an impurity of at most 10 ppm, preferably at most 0.1 ppm, by weight.

Process for manufacturing a voltage non-linear resistor and a zinc oxide

Process for manufacturing a voltage non-linear resistor

An excellent voltage non-linear resistor for use in a gapped lightning arrestor having a composition containing 1 0.5-1.2 mole % of bismuth oxide calculated as Bi.sub.2 O.sub.3, 2 0.3-1.5 mole % of cobalt oxide calculated as Co.sub.2 O.sub.3, 3 0.2-0.8 mole % of manganese oxide calculated as MnO.sub.2, 4 0.5-1.5 mole % of antimony oxide calculated as Sb.sub.2 O.sub.3, 5 0.1-1.5 mole % of chromium oxide calculated as Cr.sub.2 O.sub.3, 6 0.6-2.0 mole % of silicon oxide calculated as SiO.sub.2, 7 0.8-2.5 mole % of nickel oxide calculated as NiO, 8 0.004-0.04 mole % of aluminum oxide calculated as Al.sub.2 O.sub.3, 0.0001-0.05 mole % of boron oxide calculated as B.sub.2 O.sub.3 , 10.circle.  0.001-0.05 mole % of silver oxide calculated as Ag.sub.2 O, and 11.circle.  the rest of zinc oxide, 12.circle.  a limited current of 250-350 V/mm at a current density of 0.1 A/cm.sup.2 calculated per unit thickness of the sintered resistor, 13.circle.  a limited current ratio of V.sub.0.1A /V.sub.0.1mA of 1.2-1.7 at current densities of 0.1 A/cm.sup.2 and 0.1 mA/cm.sup.2, and 14.circle.  a deterioration rate of limited current of not more than 3% at a current density of 0.1 A/cm.sup.2 before and after applying twice a lightning surge current (4/10 .mu.s wave form) of 5 KA/cm.sup.2 per unit surface area.

Voltage non-linear resistor for gapped lightning arrestors and method of

A voltage non-linear resistor, composed mainly of zinc oxide and contains at least bismuth oxide, antimony oxide, and silicon oxide as additives, wherein crystalline phases of bismuth oxide includes at least two kinds of .beta. and .delta. satisfying the following inequalities: ##EQU1## in which .beta. and .delta. are contents of the .beta. type crystalline phase and the .delta. type crystalline phase, respectively. A voltage non-linear resistor is also provided, wherein bismuth oxide further includes an .alpha. type crystalline phase, and .alpha., .beta. and .delta. satisfy the following inequalities: ##EQU2## in which .alpha. is a content of the .alpha. type crystalline phase. A voltage non-linear resistor is further provided, wherein the resistor contains at least .delta. type crystalline phase of bismuth oxide and an amorphous phase containing bismuth, and a content of bismuth in each of the phases satisfies the following inequalities:

Voltage non-linear type resistors

An improved voltage non-linear sintered resistor which includes zinc oxide, bismuth oxide and at least one metal oxide additive selected from the group consisting of antimony oxide, silicon oxide, and mixtures thereof. The sintered resistor includes at least two crystalline phases including .alpha. and .delta. crystalline phases of bismuth oxide and has a quantity ratio of .alpha./.delta. crystalline phases of bismuth oxide of about 0.1-0.8.

Growing community of inventors

Iwakura, Japan

Ritsu Sato