Prismatic ceramic heater for heating gas sensor element, prismatic gas sensor element in multilayered structure including the prismatic ceramic heater, and method for manufacturing the prismatic ceramic heater and prismatic gas sensor element

摘要

A prismatic ceramic heater for heating a gas sensor element includes a heating resistor embedded in ceramic, and has a substantially rectangular cross section. At least part of a longitudinally extending edge portion of the prismatic ceramic heater is located in the vicinity of the heating resistor. This part of the longitudinally extending edge portion is coated with a porous protective layer. The protective layer has a thickness not less than 20 mum and a curved surface of a curvature radius not less than 10 mum. The protective layer prevents cracking induced by contact with water.