FLAME-DETECTING DEVICE

PURPOSE:To provide a flame-detecting device which is prevented from deterioration in insulation due to deterioration with age, by a method wherein the flame-detecting element of a flame detector is formed by a ZrO2 series material. CONSTITUTION:A change in expansion coefficient along with transformation from a single crystal A to a tetragonal system B during heating of ZrO2 and a change in thermal expansion coefficient during cooling are utilized for a flame-detecting element 10 detecting the presence of flame. When the high-temperature stable type tetragonal system B is migrated to the low-temperature stable type single crystal A, some of ZrO2 material is thermally expanded about 5%, the high the thereof expansion of the material of the flame-detecting element 10 is, the more preferably it is that the material as that of thermal expansion coefficient produced along with transformation is used. It is preferable in terms of strength that the ZrO2-based material, locally prevented from transformation, is used in the flame-detecting element 10. In the partially stabilized ZrO2 material, since thermal expansion coefficient during transformation is low, it is preferable that a material, to which SiO2 and Al2O3 are added in addition to ZrO2, is used in the flame detecting element 10, Further, it is desirable in terms of durability that a material, having residual thermal expansion coefficiency being as low as possible, is preferably used as the material of the flame-detecting element 10 on which thermal deformation is repeatedly exerted.