Spark plug
Disclosed is a spark plug capable of suppressing high-frequency noise by improving the material of an electrical connection part between a center electrode and a metal terminal within an axial hole of an insulator. A spark plug has an electrical connection part arranged in an axial hole of an insulator to establish electrical connection between a center electrode and a metal terminal. The electrical connection part includes a conductor having a first crystal phase formed of a Fe-containing oxide and a second crystal phase formed of a conductive metal oxide of perovskite crystal structure.
1. A spark plug, comprising:
an insulator having an axial hole formed in an axis direction of the spark plug;
a center electrode retained in one end side of the axial hole;
a metal terminal retained in the other end side of the axial hole;
an electrical connection part arranged in the axial hole to establish electrical connection between the center electrode and the metal terminal; and
a metal shell holding therein the insulator,
wherein the electrical connection part includes a conductor consisting of a first crystal phase formed of a Fe-containing oxide and a second crystal phase formed of a conductive metal oxide of perovskite crystal structure.
2. The spark plug according to claim 1 ,
wherein the conductor satisfies a relationship of 0.05≤S 2 /(S 1 +S 2 )≤0.60 where S 1 is an area occupied by the first crystal phase in a cross section of the conductor; and S 2 is an area occupied by the second crystal phase in the cross section of the conductor.
3. The spark plug according to claim 1 ,
wherein the conductive metal oxide of perovskite crystal structure is represented by the chemical formula: ABO 3 having, as an A-site element thereof, at least one of La, Nd, Pr, Y and Yb.
4. The spark plug according to claim 1 ,
wherein the Fe-containing oxide has an average grain size of 3.0 μm to 25.0 μm.
5. The spark plug according to claim 1 ,
wherein the Fe-containing oxide contains two or more kinds of ferrites.
6. The spark plug according to claim 1 ,
wherein the electrical connection part further includes a resistor containing a conductive material and a glass material; and
wherein a resistance between the metal terminal and the center electrode is in a range of 1 kΩ to 25 kΩ.