Abstract: A spark plug exhibits a satisfactory withstand voltage characteristic and sufficient mechanical strength in a high temperature environment exceeding 700° C. The spark plug has a center electrode, an insulator, and a ground electrode, characterized in that the insulator is formed of an alumina-based sintered material containing an Si component, a Group 2 element (2A) component, and a rare earth element (RE) component; that the alumina-based sintered material has an RE-?-alumina crystal phase; and that the mean crystal grain size DA(RE) of the RE-?-alumina crystal phase and that of alumina DA(Al) satisfy the following relationship (1): 0.2?DA(RE)/DA(Al)?3.0.

Abstract: There is provided a gas sensor element for detecting the concentration of a specific gas component in gas under measurement, which includes a plate-shaped element body and a porous protection layer. The element body has, at one end portion thereof, a gas sensing portion formed with a solid electrolyte substrate and a pair of electrodes. The porous protection layer has a porous structure formed of ceramic particles and surrounds at least the circumference of the one end portion of the element body. In the present invention, the porous protection layer has an inner region, an intermediate region and an outer region laminated together in order of mention from the element body toward the outside. The intermediate region has a porosity lower than those of the inner and outer regions. There is also provided a gas sensor with such a gas sensor element.

Abstract: A spark plug exhibits a satisfactory withstand voltage characteristic and sufficient mechanical strength in a high temperature environment exceeding 700° C. The spark plug has a center electrode, an insulator, and a ground electrode, characterized in that the insulator is formed of an alumina-based sintered material containing an Si component, a Group 2 element (2A) component, and a rare earth element (RE) component; that the alumina-based sintered material has an RE-?-alumina crystal phase; and that the mean crystal grain size DA(RE) of the RE-?-alumina crystal phase and that of alumina DA(Al) satisfy the following relationship (1): 0.2?DA(RE)/DA(Al)?3.0.

Abstract: An object of the invention is to provide a spark plug including an insulator which is difficult to cause breakdown and exhibits higher withstand voltage characteristics. This invention relates to a spark plug 1 including a center electrode 2, an insulator 3 and a grounding electrode 6, wherein the insulator is formed by an alumina-based sintered body which has a theoretical density ratio of 95.

Abstract: This invention has an object to provide a spark plug exhibiting high withstand voltage characteristics and high strength at high temperature, formed by an alumina-based sintered body prepared with excellent processability and high productivity, and a method for manufacturing the spark plug. This invention relates to a spark plug 1 including an insulator 3, wherein the insulator 3 includes a dense alumina-based sintered body having an average crystal particle diameter of 1.50 ?m or more, and the alumina-based sintered body contains Si, a Group 2 element component containing Ba and a Group 2 element other than those, and a rare earth element component, such that a ratio of a content S of the Si component to a total content of the content S and a content A of the Group 2 element component is 0.60 or more, and a method for manufacturing the spark plug 1 prepared through a grinding-shaping process in which the insulator 3 is ground before burning to shape the same.

Abstract: An object of the invention is to provide a spark plug including an insulator which is difficult to cause breakdown and exhibits higher withstand voltage characteristics. This invention relates to a spark plug 1 including a center electrode 2, an insulator 3 and a grounding electrode 6, wherein the insulator is formed by an alumina-based sintered body which has a theoretical density ratio of 95.

Abstract: A ceramic-metal assembly including: a ceramic base; an electrode pad provided on a surface of the ceramic base; a connection terminal for external electrical connection; and a joining portion which joins the connection terminal to the electrode pad. The electrode pad has a first layer which is in contact with the ceramic base and a second layer which is in contact with the joining portion. The first layer contains 20 to 50 vol % of a ceramic component, and the second layer contains a component of the joining portion.

Abstract: A ceramic-metal assembly including: a ceramic base; an electrode pad provided on a surface of the ceramic base; a connection terminal for external electrical connection; and a joining portion which joins the connection terminal to the electrode pad. The electrode pad has a first layer which is in contact with the ceramic base and a second layer which is in contact with the joining portion. The first layer contains 20 to 50 vol % of a ceramic component, and the second layer contains a component of the joining portion.

Abstract: An insulator for spark plug comprises an alumina-based sintered body comprising: Al2O3 as a main component; and at least one component (hereinafter referred to as “&bgr; component”) selected from the group consisting of Ca component, Sr component and Ba component, wherein the alumina-based sintered body comprises particles comprising a compound comprising the &bgr; component and Al component, the compound having a molar ratio of the Al component to the &bgr; component of 4.5 to 6.7 as calculated in terms of oxides thereof, and has a relative density of 90% or more.

Abstract: An insulator for spark plug comprises an alumina-based sintered body comprising: Al2O3 (alumina) as a main component; and at least one component (hereinafter referred to as “E. component”) selected from the group consisting of Ca (calcium) component, Sr (strontium) component and Ba (barium) component, wherein the alumina-based sintered body comprises particles comprising a compound comprising the E. component and Al (aluminum) component, the compound having a molar ratio of the Al component to the E. component of 4.5 to 6.7 as calculated in terms of oxides thereof, and has a relative density of 90% or more.