Gas sensor element, gas sensor, and method of manufacturing gas sensor element

A method of manufacturing a gas sensor element which comprises an element body having a substantially rectangular-parallelepiped shape extending along a longitudinal axis, a forward end surface through which the longitudinal axis extends, and four side surfaces adjacent to the forward end surface so as to define four vertexes, and including a detecting section for detecting a particular gas, and a protection layer located on the forward end surface and four side surfaces of the element body in such a manner as to cover at least the detecting section, the protection layer having a largest thickness perpendicular to the element body at a place on the side surfaces of the element body and formed in a porous manner,

• the element body and the protection layer defining at least one space therebetween in a forward region located entirely forward of the place of the largest thickness of the protection layer;
• the space being positioned over at least one of the four vertexes such that the space extends over three surfaces of the element body which define the one of the four vertexes;
• and
• the protection layer being in contact with at least a portion of the forward end surface and being in contact with at least a portion of the four side surfaces in the forward region,
• the method comprising:
• a solvent disposing step of disposing a volatile solvent on an outer surface of the element body in a region where the space is to be formed,
• a protection layer forming step of forming, on the element body on which the volatile solvent remains, a green protection layer which is to become the protection layer through heat treatment, in such a manner as to cover at least the detecting section, and
• a heat treatment step of performing heat treatment on the element body on which the green protection layer is formed, thereby forming the protection layer,
• wherein the volatile solvent is volatilized in a period from start of the solvent disposing step to end of the heat treatment step, thereby forming the space.