Development course of sealing alloy

/kloc-at the beginning of the 0/9th century, platinum has been used as a sealing material for sealing soft glass. 1879, Edison invented incandescent light bulbs, as well as early electron tubes and x-ray tubes, all of which used platinum wires to pass through glass leads. French C.E.Guillaume made Invar alloy (36Ni-Fe) in 1896, and then derived 46Ni-Fe sealing alloy instead of platinum, which is the earliest sealing alloy. Later, this alloy was further improved and the surface was covered with a thin layer of copper. This copper-plated 42Ni-Fe wire (commonly known as Dumex wire) was also used as the lead-out wire for the sealing of mismatched soft glass until 1970s. With the development of electric vacuum technology, hard glass with high melting point, good thermal stability and low thermal expansion coefficient has appeared. Initially, molybdenum or tungsten was used to seal with hard glass. In 1930s, a kind of Fe-Ni-Co alloy-Kovar alloy sealed with hard glass appeared. In addition, sealing alloys such as Fe-Ni-Cr system, Fe-Cr system and Fe-Ni-Cu system have also appeared.

After World War II, with the development of ultra-high frequency and high power electric vacuum devices, ceramic sealing alloys such as alumina and beryllium oxide appeared. Expandable alloys need to have high thermal conductivity, high electrical conductivity and non-magnetism. To this end, composite expansion alloys (such as copper-clad kovar alloy strips and wires) and sealing alloys containing refractory metals (such as Ni-Mo, Ni-Mo-W system, etc.) are used. ) are used, but the dosage is not large.

In a certain temperature range, the sealing with the same thermal expansion coefficient between metal and glass is called matching sealing. The seal with large difference in thermal expansion coefficient between them is called mismatch seal. Matching seal is generally used to ensure the sealing quality. The attached table lists the brands, compositions, average thermal expansion coefficients and uses of some common sealing alloys. Figs. 2 and 3 show the expansion curves of alloys, glasses and ceramics, respectively.