By a News Reporter-Staff News Editor at Life Science Weekly — Hitachi Metals, Ltd. (Tokyo, JP) has been issued patent number 8766145, according to news reporting originating out of Alexandria, Virginia, by NewsRx editors (see also Hitachi Metals, Ltd.).
The patent’s inventors are Shimada, Takeshi (Osaka, JP); Ino, Kentaro (Osaka, JP); Kida, Toshiki (Tottori, JP).
This patent was filed on March 12, 2009 and was published online on July 1, 2014.
From the background information supplied by the inventors, news correspondents obtained the following quote: “The present invention relates to a process for producing a semiconductive porcelain composition having a positive temperature coefficient of resistance (PTC), and a heater employing the semiconductive porcelain composition.
“BaTiO.sub.3 semiconductive porcelain composition has been known as a material showing a positive resistance temperature characteristic. When SrTiO.sub.3 or PbTiO.sub.3 is added to the BaTiO.sub.3 semiconductive porcelain composition, a Curie temperature can be shifted, but only PbTiO.sub.3 is an additive material that enables shifting in a positive direction. However, since PbTiO.sub.3 contains an element causing environmental pollution, a material using no PbTiO.sub.3 as an additive material has been desired. Consequently, a semiconductive porcelain composition in which a part of Ba in BaTiO.sub.3 is substituted with Bi–Na was proposed (see Patent Document 1).
“Where a BaTiO.sub.3-based material is treated by, for example, sintering in a reducing atmosphere so as to decrease room temperature resistivity, there is a problem that a temperature coefficient of resistance (jump characteristic) is decreased. When the jump characteristic is decreased, there is a problem that switching does not occur at the objective temperature. Therefore, to improve the jump characteristic, it is proposed to conduct a heat treatment at high temperature exceeding 1,100.degree. C. (Patent Document 2). Patent Document 1: WO 2006/106910 Patent Document 2: JP-A-56-169301”
Supplementing the background information on this patent, NewsRx reporters also obtained the inventors’ summary information for this patent: “In recent years, PTC material is frequently used in high temperature environment in view of improvement in heat resistance characteristic thereof. However, further improvement in jump characteristic has been desired to enable the material to be used in higher temperature environment. BaTiO.sub.3–(Bi.sub.1/2Na.sub.1/2)TiO.sub.3-based material, which is free of Pb and in which a part of Ba is substituted with Bi–Na, has sufficient jump characteristic by itself, but it is necessary to improve the jump characteristic in view of the above-mentioned demand. Although the above-described heat treatment may be considered to improve the jump characteristic thereof, it could be confirmed that even though the heat treatment as applied to a BaTiO.sub.3-based material containing Pb is merely applied as it is, the jump characteristic is not improved.
“Aspects of the present invention has been made in view of the above circumstances, and has an object to improve a jump characteristic of a semiconductive porcelain composition in which a part of Ba of BaTiO.sub.3 in BaTiO.sub.3–(Bi.sub.1/2Na.sub.1/2)TiO.sub.3-based material and the like is substituted with Bi–Na.
“As a result that the present inventors have conducted heat treatment to a BaTiO.sub.3–(Bi.sub.1/2Na.sub.1/2)TiO.sub.3-based material, it was confirmed that PTC characteristics are impaired by high heat temperature treatment such that an element becomes an insulator at the treatment temperature of 1,280.degree. C. The reason therefor is considered that trivalent Ti formed by valence control is oxidized into tetravalent Ti, whereby a carrier is reduced.
“Furthermore, since the jump characteristic of a BaTiO.sub.3-based material containing Pb depends on an oxygen amount of grain boundary, it is necessary to introduce oxygen into the grain boundary after reducing oxygen defect caused during sintering. Therefore, unless the heat treatment is conducted at 800.degree. C. or higher that recovers oxygen defect, the practicable jump characteristic cannot be obtained. On the other hand, in the BaTiO.sub.3–(Bi.sub.1/2Na.sub.1/2)TiO.sub.3-based material, not only oxygen amount of grain boundary but also component distribution of a material affect the jump characteristic. Therefore, it is possible to improve the jump characteristic only by introducing oxygen into the grain boundary without restoring oxygen defect. Consequently, it has been found that the jump characteristic can be improved even when heat treatment is conducted at 600.degree. C. or lower.
“Based on the above finding, aspects of the present invention are to improve a jump characteristic by heat-treating a semiconductive porcelain composition in which a part of Ba is replaced with Bi–Na at 600.degree. C. or lower. The heat treatment may be conducted in the air, but is preferably conducted in an atmosphere containing oxygen. More quickly, heat treatment in an oxygen atmosphere is preferred.
“Furthermore, aspects of the present invention are to improve a jump characteristic by forming an electrode to a semiconductive porcelain composition in which a part of Ba is substituted with Bi–Na, followed by heat-treating the same at 600.degree. C. or lower in the air. In the case of forming an electrode, heat treatment in the air is preferred in order to avoid deterioration of the electrode.
“The semiconductive porcelain composition produced by aspects of the present invention has a jump characteristic that is not appeared in the conventional semiconductive porcelain composition in which a part of Ba of BaTiO.sub.3 is substituted with Bi–Na. Therefore, a heater employing a heating element comprising the semiconductive porcelain composition produced by aspects of the present invention is suitable for use in higher temperature environment.
“According to aspects of the present invention, a jump characteristic of a semiconductive porcelain composition in which a part of Ba is substituted with Bi–Na can be improved.
“Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.”
For the URL and additional information on this patent, see: Shimada, Takeshi; Ino, Kentaro; Kida, Toshiki. Process for Producing Semiconductive Porcelain Composition and Heater Employing Semiconductive Porcelain Composition. U.S. Patent Number 8766145, filed March 12, 2009, and published online on July 1, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8766145.PN.&OS=PN/8766145RS=PN/8766145
Keywords for this news article include: Chalcogens, Hitachi Metals Ltd.
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