Abstract: There is provided a cyanide-free immersion type electroless gold plating liquid that is low in toxicity, can be used near a neutral ph, and has a good solder adhesion and plating film adhesion. The electroless gold plating liquid contains a cyanide-free water-soluble gold compound and a pyrosulfurous acid compound. The plating liquid may further contain a sulfurous acid compound and an aminocarboxylic acid compound. Pyrosulfurous acid or an alkali metal, alkaline earth metal, ammonium, or another such salt thereof can be used as the pyrosulfurous acid compound.

Abstract: The invention provides a displacement electroless gold plating solution that is low in toxicity, can be used at a pH near to neutrality, and affords good solder adhesion and film adhesion. The displacement electroless gold plating solution contains a non-cyanide water-soluble gold compound and a hydrogensulfite compound. Preferably, the plating solution further contains a thiosulfuric acid compound or an aminocarboxylic acid compound. Sodium hydrogensulfite, potassium hydrogensulfite, ammonium hydrogensulfite or the like can be used as the hydrogensulfite compound.

Abstract: A cyanide-free immersion type electroless gold plating solution that is less toxic can be used at near neutrality and gives an excellent and improved solder adhesion and plated film adhesion is provided. The electroless gold plating solution contains a cyanide-free water-soluble gold compound, a pyrosulfurous acid compound and a thiosulfuric acid compound. This plating solution preferably further contains a sulfurous acid compound and an aminocarboxylic acid compound. Pyrosulfurous acid and alkali metal salts, alkaline-earth metal salts, ammonium salts and other salts thereof can be used as the pyrosulfurous acid compound.

Abstract: The invention provides a displacement electroless gold plating solution that is low in toxicity, can be used at a pH near to neutrality, and affords good solder adhesion and film adhesion. The displacement electroless gold plating solution contains a non-cyanide water-soluble gold compound and a hydrogensulfite compound. Preferably, the plating solution further contains a thiosulfuric acid compound or an aminocarboxylic acid compound. Sodium hydrogensulfite, potassium hydrogensulfite, ammonium hydrogensulfite or the like can be used as the hydrogensulfite compound.

Abstract: A cyanide-free immersion type electroless gold plating solution that is less toxic, that can be used at near neutrality, and that gives an excellent and improved solder adhesion and plated film adhesion is provided. An electroless gold plating solution, comprising a cyanide-free water-soluble gold compound, a pyrosulfurous acid compound and a thiosulfuric acid compound. This plating solution preferably further contains a sulfurous acid compound and an aminocarboxylic acid compound. Pyrosulfurous acid and alkali metal salts, alkaline-earth metal salts, ammonium salts and other salts thereof can be used as the pyrosulfurous acid compound.

Abstract: There is provided a cyanide-free immersion type electroless gold plating liquid that is low in toxicity, can be used near neutral, and has good solder adhesion and plating film adhesion. An electroless gold plating liquid containing a cyanide-free water-soluble gold compound and a pyrosulfurous acid compound. The plating liquid may further contain a sulfurous acid compound and an aminocarboxylic acid compound. Pyrosulfurous acid or an alkali metal, alkaline earth metal, ammonium, or other such salt thereof can be used as the pyrosulfurous acid compound.

Abstract: A method of making a spark plug having a noble metal chip joined to an electrode main body of a ground electrode by interposing therebetween an intermediate member. The method comprises the steps of prior to joining the noble metal chip to the electrode main body, joining the intermediate member and the noble metal chip together, placing a noble metal chip and intermediate member assembly on the electrode main body in a way as to allow the intermediate member to contact the electrode main body, and welding the electrode main body and the intermediate member together while restricting relative movement of the electrode main body and the intermediate member without applying an urging force to a joint between the intermediate member and the noble metal chip.

Abstract: A spark plug has a central electrode, an insulator surrounding the central electrode and a metallic shell retaining therein the insulator and provided with no thread thereon. The spark plug is clearance fitted in a plug hole of a cylinder head, without being screwed into the plug hole, in such a manner that a front end portion of the metallic shell is accommodated in a front end section of the plug hole with a clearance therebetween provided with a sealant so as to transmit heat from the spark plug to the cylinder head. The clearance is preferably given by the following expression: 0.005≦D−d1≦0.05, where D is an inner diameter (mm) of the front end section and d1 is an outer diameter (mm) of the front end portion. By this, the spark plug can be easily attached to the cylinder head and attain improved heat resistance.

Abstract: Provided is a method of making a spark plug having a noble metal chip joined to an electrode main body of a ground electrode by interposing therebetween an intermediate member. The method comprises the steps of prior to joining the noble metal chip to the electrode main body, joining the intermediate member and the noble metal chip together, placing a noble metal chip and intermediate member assembly on the electrode main body in a way as to allow the intermediate member to contact the electrode main body, and welding the electrode main body and the intermediate member together while restricting relative movement of the electrode main body and the intermediate member without applying an urging force to a joint between the intermediate member and the noble metal chip.

Abstract: A spark plug has a central electrode, an insulator surrounding the central electrode and a metallic shell retaining therein the insulator and provided with no thread thereon. The spark plug is clearance fitted in a plug hole of a cylinder head, without being screwed into the plug hole, in such a manner that a front end portion of the metallic shell is accommodated in a front end section of the plug hole with a clearance therebetween provided with a sealant so as to transmit heat from the spark plug to the cylinder head. The clearance is preferably given by the following expression: 0.005≦D−d1≦0.05, where D is an inner diameter (mm) of the front end section and d1 is an outer diameter (mm) of the front end portion. By this, the spark plug can be easily attached to the cylinder head and attain improved heat resistance.

Abstract: In a spark plug for a gas engine including a ground electrode (4) whose front end is to be placed in a combustion chamber of a gas engine which is driven by gaseous fuel, a metallic shell (3) enclosing a center electrode (5) which has a noble metal tip (18) superior in spark-erosion resistance at a firing portion in which a spark discharge occurs against the ground electrode (4). A resistor (10) is provided within the spark plug or a spark plug cap so as to be included in a spark plug voltage circuit which applies a high voltage to the center electrode. It is preferable that the noble metal tip (18) has a diameter in a range of 0.5.about.1.5 mm, and that the resistor has an electrical resistance greater than or equal to 50 k.OMEGA..

Abstract: A spark plug for an internal combustion engine with both sides of a surface, on a center electrode side, of an outer electrode and/or both side portions, on the top surface of the center electrode, form wedge-shaped projections. At least one surface having the wedge-shaped projection has no plane surface but is arcuate.