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Kovar 4J29 Precision Nickel Alloy Bar Strip Plate for Hard Glass Sealing Matching
kovar properties
Kovar is a nickelobalt ferrous alloy compositionally identical to
Fernico, designed to be compatible with the thermal expansion
characteristics of borosilicate glass ( /K between 30 and 200 C, to
~10 10 /K at 800 C) in order to allow direct mechanical connections
over a range of temperatures. It finds application in electroplated
conductors entering glass envelopes of electronic parts such as
vacuum tubes (valves), X-ray and microwave tubes and some
lightbulbs.
The name Kovar is often used as a general term for Fei alloys with
these particular thermal expansion properties. Note the related
particular Fei alloy Invar which exhibits minimum thermal
expansion.
OhmAlloy-4J29was invented to meet the need for a reliable
glass-to-metal seal, which is required in electronic devices such
as light bulbs, vacuum tubes, cathode ray tubes, and in vacuum
systems in chemistry and other scientific research. Most metals
cannot seal to glass because their coefficient of thermal expansion
is not the same as glass, so as the joint cools after fabrication
the stresses due to the differential expansion rates of the glass
and metal cause the joint to crack.
OhmAlloy-4J29 not only has thermal expansion similar to glass, but
its nonlinear thermal expansion curve can often be made to match a
glass, thus allowing the joint to tolerate a wide temperature
range. Chemically, it bonds to glass via the intermediate oxide
layer of nickel oxide and cobalt oxide; the proportion of iron
oxide is low due to its reduction with cobalt. The bond strength is
highly dependent on the oxide layer thickness and character. The
presence of cobalt makes the oxide layer easier to melt and
dissolve in the molten glass. A grey, grey-blue or grey-brown color
indicates a good seal. A metallic color indicates lack of oxide,
while black color indicates overly oxidized metal, in both cases
leading to a weak joint.
Mainly used in electric vacuum components and emission control,
shock tube, igniting tube, glass magnetron, transistors, seal plug,
relay, integrated circuits lead, chassis, brackets and other
housing sealing.
Chemical Composition
Grade | C% | P% | S% | Mn% | Si% | Cu% | Cr% | Mo% | Ni% | Co% | Fe% |
Kovar | Max 0.03 | Max 0.020 | Max 0.020 | Max 0.50 | Max 0.30 | Max 0.20 | Max 0.20 | Max 0.20 | 28.5-29.5 | 16.8-17.8 | Bal. |
Specifications
Grade | UNS | Werkstoff Nr. |
Kovar | K94610 | 1.3981 |
Physical Properties
Grade | Density | Melting Point |
Kovar | 8.17 g/cm3 | 1449°C |
Mechanical Properties
Grade | Tensile Strength N/mm² | ||||
Soft | 1/4 Hard | 1/2 Hard | 3/4 Hard | Full Hard | |
Kovar Strip | <570 | 520-630 | 590-700 | 600-770 | >700 |
Kovar Wire | <585 | 585-725 | 655-795 | 725-860 | >860 |
Coefficient of Expansion
Alloy | Linear Coefficient of Thermal Expansion a,10-6/°C | |||||||
20-200°C | 20-300°C | 20-400°C | 20-450°C | 20-500°C | 20-600°C | 20-700°C | 20-800°C | |
Kovar | 5.9 | 5.3 | 5.1 | 5.3 | 6.2 | 7.8 | 9.2 | 10.2 |
Package