Korea Advanced Institute of Science and Technology

Agency for Defense Development

Suk-Joong L Kang

Duk Y Yoon

Sung Min Lee

Sung Yoon Chung

Sung-Yoon Chung

Yong Kee Baek

Byung Kee Lee

Woon-Hyung Baek

Ho Yong Lee

Seong-hyeon Hong

Seung Su Baek

Deug J Kim

Nong M Whang

Beoung D You

Jae H Jeon

Young A Jee

Jeong-Hun Suh

Joo Sun Kim

Sang Yoon Koo

Seong-Min Wang

Yang Il Jung

Yu S Shin

The present invention relates to a method for manufacturing a SrTiOseries varistor using grain boundary segregation, and more particularly, to a method for manufacturing a SrTiOseries varistor by sintering a powdered composition in which acceptors such as Al and Fe are added in powdered form and then sintered under a reducing atmosphere and heat-treated them in the air to selectively form electrical conduction barriers at grain boundaries in a process for manufacturing SrTiOseries varistor having an excellent non-linear coefficient and a breakdown voltage suitable for use.

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A method for making a BaTiO -based dielectric having a high dielectric constant and a low dielectric loss wherein, a BaTiO -based body is subjected to a pre-heat treatment in a hydrogen (H ) atmosphere or a reducing atmosphere containing mixed gas of hydrogen and nitrogen in a ratio of hydrogen:nitrogen&equals;5 to 100%:0 to 95% prior to a sintering process in the manufacture of dielectrics, in order to obtain a reduced average grain size of BaTiO . By virtue of the reducing average grain size of BaTiO , a BaTiO -based dielectric having a high dielectric constant and a low dielectric loss is obtained. This method provides an advantage in that it is possible to make a BaTiO -based dielectric having a very small average grain size while having a high relative density in accordance with a simple heat treatment conducted for pure BaTiO or even for BaTiO added with an additive in a reducing atmosphere at a temperature less than a liquid phase forming temperature, prior to a sintering process for sintering the BaTiO .

Method for making BaTiO3-based dielectric

Disclosed is an SrTiO,-based grain boundary barrier layer capacitor which is superb in dielectric constant and temperature characteristics. It is prepared by infiltrating a liquid-phase oxide mixture into a donor-doped SrTiO,matrix to form second-phase dielectric layers at the grain boundaries of the matrix. The liquid-phase oxide mixture comprises CaO and BaO in a particular molar ratio. The SrTiO,-based grain boundary barrier capacitor exhibits a high dielectric constant and a low dieletric loss with stable temperature characteristics.

SrTiO3-based grain boundary barrier layer capacitor

A sialon composite and fabrication method thereof in which the phase of a surface layer thereof is modified differently from that of the bulk. The surface layer is modified to .alpha.-sialon or .alpha.-.beta. sialon composite but the bulk is .beta.-sialon. Also, the surface layer is modified to .beta.-sialon or .alpha.-.beta. sialon composite but the bulk is .alpha.-sialon.

Method of producing a surface modified sialon composite

There is a method for making a strontium titanate based Grain-Boundary Barrier Layer Capacitors (GBBLC) with improved dielectric properties by introducing an intermediate step of heat-treatment in an oxidizing atmosphere between sintering of a strontium titanate based powder in a reducing atmosphere and an infiltration of the obtained sintered body with a metal oxide.

Method for making strontium titanate based grain-boundary barrier layer

The present invention provides a process for the preparation of YBa.sub.2 Cu.sub.3 O.sub.7-x superconductor which comprises surrounding a sintered material in which the molar ratio of Y:Ba:Cu is 2:1:1 with liquid-forming powder and subjecting the powder compact to isothermal heat-treatment at a temperature below the peritectic temperature of YBa.sub.2 Cu.sub.3 O.sub.7-x. The YBa.sub.2 Cu.sub.3 O.sub.7-x superconductors prepared according to the present invention have aligned grain structure in one direction and thus exhibit a high critical current density.

Process for preparing YBa.sub.2 Cu.sub.3 O.sub.7-x superconductors

MoO.sub.2 is used as an accelerant for transformation of zirconia (ZrO.sub.2) from a tetragonal to a monoclinic crystal phase. A ZrO.sub.2 -MoO.sub.2 alloy having an increased content of monoclinic ZrO.sub.2 is prepared by mixing MoO.sub.2 with ZrO.sub.2 followed by heat treatment. In another aspect of the invention, the surface of an alumina-zirconia composite is strengthened by heating the composite in the presence of MoO.sub.2 -ZrO.sub.2 mixed powder.

Method of surface strengthening alumina-zirconia composites using MoO.sub.2

A tungsten based heavy alloy having a W--Ni--Fe based composition containing traces of lanthanum or calcium, thereby capable of exhibiting high toughness, irrespective of the content of impurities such as phosphorous and sulfur contained therein, the cooling rate after the sintering treatment and the re-heating treatment. The present invention provides a method for making the high toughness tungsten based heavy alloy. The tungsten based heavy alloy of the present invention is useful to manufacture warheads for breaking armor plates, which require high toughness.

High toughness tungsten based heavy alloy containing La and Ca.

Growing community of inventors

Taijeon, South Korea

Suk-Joong L Kang