INSULATOR FOR SPARK PLUG AND SPARK PLUG

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PROBLEM TO BE SOLVED : To effectively suppress occurrence of channeling while achieving favorable withstand voltage characteristics. SOLUTION : A grain boundary phase 32 located between alumina particles 31 includes : an element selected from a 2A group element group consisting of Mg, Ca, Sr and Ba; an element selected from a rare earth element group consisting of La, Nd, Pr, Y, Yb and Ce; and an element selected form a first element group consisting of Zr, Ti, Cr, Nb, Mn and Fe. When a quantitative analysis in terms of oxide is performed by EPMA in a visual field of 180 μm×250 μm on a given cross section of an insulator 2, 0.40≤Y/X≤2.00 and 0.10≤Z/X≤0.40 are satisfied, where X (mass%) represents a total amount of elements selected from the rare earth element group, Y (mass%) represents a total amount of elements selected from the 2A group element group, and Z (mass%) represents a total amount of elements selected from the first element group. COPYRIGHT : (C)2015, JPO&INPIT