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PLAINTIFF'S EXHIBIT
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FEB 11
RADIATION-INDUCED DAMAGE TO GASKET
R. C. HubexWDEXCD: B. W. Wilkinson NR-58016-1U May 5, 1958
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THIS REPORT IS THE PROPERTY OF THE DOW CHEMICAL COMPANY
1
RADIATION-INDUCED DAMAGE TO GASKET MATERIAL
SUMMARY
Materials of 5 compositions were irradiated to find a suitable 60
material for a Co reaction vessel. Materials tested wore-:
Rubber, cork, Teflon, fiber and asbestos. These were irradiated
for doses of 0, 10, 100, 500 and 1000 megaRads.
The asbestos materials stand up the best and Vellumoid tend to get brittle.
Rubber cork, Teflon
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INTRODUCTION: In reactions using Co 60 radiation, the gaskets on the reaction vessels often failed sooner than normally expected. This report covers 14 gasket materials that are in stock at Dow. Irradiation was done at the Radiation facility of the Nuclear and Basic
60 Research Laboratory using a Co radiation source. These mater ials were irradiated for doses of 0, 10, 100, 500 and 1000 mega Rads, and tested for Shore Durometer A Hardness and durometer elasticity.
EXPERIMENTAL PROCEDURE:
Samples of Saran rubber, Silastic 51, sponge rubber, Neoprene rubber, Red (rainbow) rubber, Red rubber, JM 60, JM 61, JM 83, Durabla, Garlock 7021, Vellumoid, Teflon and cork were obtained from the Dow gasket stockroom. See Table I for composition and supplier.
Three inch gaskets were cut out of these materials and divided into 5 sets. These sets were irradiated for 0, 10, 100, 500 and 1000 iviegarads at room temperature. The radiation intensity was 535,000 rads/hr. (measured by ferrous dosimetry).
After irradiation the gaskets were tested for hardness and elas ticity using a Durometer A Hardness tester and a durometer elas ticity tester in the Saran Development Laboratory.
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EXPERIMENTAL RESULTS: Table II gives the hardness and elasticity of the gasket materials tested. After 10 Megar.ads of radiation the Teflon gaskets became brittle and broke. After 100 ilegarads the Vellumoid began to turn a lighter color. After 500 uega ads the Silastic, sponge rubber and vellu moid became brittle and broke. After 1000 Megai ads the cork began to crumble. See Figures 1 and 2 for conditions of the gaskets at various dosages of radiation.
DISCUSSION OF RESULTS: The scission of the carbon-fluorine bond is believed to cause the degradiation of Teflon, as Teflon is a poly tetrafluoro ethylene polymer. The rubber gasket materials probably degrade because of the side chains splitting off. Most of the natural and synthetic rubbers have side chains or double bonds which tend to break under radi ation. These in turn can polymerize, crosslink or release HC1, forming a different molecular structure.
The cork and Vellumoid gasket materials are cellulose base. Cellulose degrades under radiation. The asbestos fiber, used in asbestos gasket materials is a mineral fiber. Minerals are inorganic and inorganic materials are usually more stable than organic materials under radiation. It is expected that if asbestos gaskets fail under radiation, the damage would be in the binder.
CONCLUSIONS: Asbestos gasket materials are more radiation resistant than rubber, cork, Teflon and Vellumoid.
Rubber gasket materials tend to harden as the amount of radiaticn increases, while Vellumoid, cork and Teflon get brittle.
3
NOTEBOOK REFERENCE: Nuclear Research Notebook Number 86, Page 19.
INDEX HEADINGS:
Radiation damage of Gaskets
Gamma Radiation;
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