Importance

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Abstract

One embodiment of the present disclosure is directed to an insulator comprising a ceramic composition, wherein the ceramic composition comprises about 25-60% SiO₂; 15-35% R₂O₃, wherein the R₂O₃ is 3-15% B₂O₃ and 5-25% Al₂O₃; 4-25% MgO+0-7% Li₂O, wherein the total of MgO+Li₂O is between about 6-25%; 2-20% R₂O, wherein the R₂O is 0-15% Na₂O, 0-15% K₂O, 0-15% Rb₂O; 0-15% Rb₂O; 0-20% Cs₂O; and 4-20% F; crystalline grains, wherein the crystalline grains are substantially oriented to extend in a first direction to provide improved insulating properties in a direction perpendicular to the first direction, wherein the first direction is circumferential and the direction perpendicular to the first direction is radial; and a first zone and a second zone, wherein the first zone is in compression and the second zone is in tension.

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First Claim