Patent ID: 6258233
Filing Date: 2001-07-10
Classification: G01N

Abstract:
A multilayered air-fuel ratio sensing element comprising a zirconic solid electrolytic body and a heat-generating portion equipped with a heater, whereinsaid zirconic solid electrolytic body is made of a partially stabilized zirconia containing 5 to 7 mol % yttria and having a mixed phase structure including a cubic phase, monoclinic phase and a tetragonal phase,said zirconic solid electrolytic body has a relative density of 94 to 100% with a mean sintered grain size of 0.5 to 3.0 .mu.m,said heat-generating portion includes an alumina substrate which is located adjacent to said zirconic solid electrolytic body and has a relative density of 95 to 100% with a mean sintered grain size of 0.5 to 4.0 .mu.m, andsaid partially stabilized zirconia has an M/C ratio in a range from 0.05 to 0.25, the M/C ratio being defined by the following equation: ##EQU5##wherein M(111) represents a reflective integrated intensity of a monoclinic phase (111), M(111) represents a reflective integrated intensity of a monoclinic phase (111), and C(111) represents a reflective integrated intensity of a cubic phase (111),wherein a thermal expansion difference A between said alumina substrate and said partially stabilized zirconia is in a range from 0 to 0.2, said thermal expansion difference .DELTA. being defined by the following equation: ##EQU6##wherein C.sub.ZR represents a thermal expansion coefficient of the partially stabilized zirconia in a temperature range from room temperature to 1,000.degree. C.; C.sub.AL represents a thermal expansion coefficient of the alumina in a temperature range from room temperature to 1,000.degree. C.; and T represents the temperature variation from room temperature to 1,000.degree. C., andwherein a ratio of the mean sintered grain size of said alumina substrate to the mean sintered grain size of said zirconic solid electrolytic body is in a range from 0.33 to 4.00.