Background of Non-sag Tungsten Wire

Non-sag tungsten wire background, it was initially developed prior to 1920 and the introduction of the non-sag tungsten wire had a great impact on the incandescent lamp industry.In explanation of the term "non-sag," if a tungsten wire elongates when it is operated, and thus sags, the individual turns between wire coils will tend to contact one another and short out, thereby shortening the life of the wire. In the practices of the prior art, non-sag tungsten has been fabricated by including therein a very small amount of so-called "dopant," which dopant is added in the form of alkali silicates. Because of this dopant addition, when the wire is initially incandesced, the crystals or grains which are formed therein are elongated and interlocking and generally disposed along the axial dimension of the wire. Within recent years, it has been discovered that the non-sag characteristic which is imparted by the alkali silicate doping is due to the formation of very minute potassium particles, which form potassium bubbles when the wire is incandesced. A substantial portion of these bubbles are generally aligned along the axial dimension of the wire and serve to inhibit the recrystallization and control the grain growth of the wire due to dislocation and grain boundary pinning by the potassium bubbles.

These potassium-formed bubbles are generally submicroscopic in nature and a representative diameter of same is in the order of 100 to 500A. While the performance of such a wire is generally satisfactory, a major problem in the manufacture of the tungsten is the uniform incorporation of the doping impurity into the metal, and the attainment of the consistency of the required concentration, in order to produce the best wire material. 

 

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