ButylFill Conductive Elastomers

1. Ja-Bar Series Silver-plated Aluminum & Butyl Rubber 8B5-51 and 8B5-78 ButylFill Conductive Elastomers M83528 Mil-Spec Performance Low Permeability, Butyl Rubber Copolymer Silver-plated Aluminum for Military Applications Ja-Bar Silicone Corporation — Shielding Division 252 Brighton Rd., Andover, NJ 07821 ph. 973-786-5000 www.ja-bar.com

2. ButylFill Elastomers ButylFill Elastomers are Ja-Bar's new grade of conductive shielding gaskets designed specifically to combat field performance degradation due to corrosion. Our extremely low-permeability formulation of butyl rubber is combined with uniquely treated, silver-plated aluminum, conductive particles; providing a sealing system unmatched in performance. While newly developed competitive products boast a 20–50 percent reduction in flange pitting, ButylFill outperforms competitor's formulations by blocking water vaporthroughoutthe width of the seal, while maintaining electrical conductivity and dramatically reducing corrosive degradation.

3. As seen below, on both 8B5-78 and 8B5-51, the protective chem-film treatment on the aluminum test coupon remains intact throughout the gasket interface, while the passivated silver-aluminum fluorosilicone test coupon reveals that the salt spray vapor is able to penetrate the gasket width and propagate corrosion. 500 Hr Salt Spray Resistivity Silver-plated aluminum in butyl rubber 85B-78 after salt spray test Chem-filmed aluminum disk Silver-plated aluminum in butyl rubber 85B-51 after salt spray test Passivated, silver-plated aluminum in fluorosilicone after salt spray test

4. All silicone- and fluorosilicone-based shielding materials tested largely portrayed this phenomena, due in part to the high level of water vapor permeability of polysiloxane elastomers.

5. Theory Behind Our Product Development GALVANIC CORROSION Galvanic corrosion and it’s containment has been succinctly explained by Kennedy Space Center’s Corrosion Control and Treatment Manual (TM-584C): “3.2.1 CONDITIONS NECESSARY FOR CORROSION. For the purpose of this manual, electrochemical corrosion is the most important classification of corrosion. Four conditions must exist before electrochemical corrosion can proceed: (1) there must be something that corrodes (the metal anode), (2) there must be a cathode, (3) there must be continuous conductive liquid path (electrolyte, usually condensate and salt or other contaminations), and (4) there must be a conductor to carry the flow of electrons from the anode to the cathode. This conductor is usually in the form of metal-to-metal contact such as in bolted or riveted joints. The elimination of any one of the four conditions will stop corrosion.”

6. Galvanic corrosion potential has plagued the RF Shielding community for decades. Particles conductive enough to meet demanding shielding applications are silver-coated, and most often having an electrode potential different than the mating structure, causing corrosion potential. Alternatively offered nickel and nickel-plated particles—while achieving less corrosion—often fail in meeting the shielding and/or electrical bonding required in more rigorous applications. Since the premise of a shielding elastomer is to provide electrical conductivity between two electrically conductive surfaces, Ja-Bar has focused our resolve on number (3) of the four conditions (as explained by TM-584C)—elimination of the electrolyte. Published corrosion testing of silicone-based shielding elastomers show varying levels of corrosion throughout the width of the test specimen, indicating the migration of the electrolyte through the gasket width. Our product focus was to prevent this migration from happening. ButylFill 8B5-51 and 8B5-78 achieved this objective through the use of low-permeability butyl rubber.

7. Elastomer Technology The most common conductive elastomers for both military and commercial applications incorporate silicone or fluorosilicone (polysiloxanes) as the base elastomer. The molecular structure of silicone—which provides such properties as extreme temperature range, high degree of flexibility, low chemical reactivity, and formulation adaptability—is also attributable for silicones high permeability of water vapor and gasses. While there have been several attempts to modify the molecular structure of silicone to reduce permeability through the use of phenyls and other additives, the resulting formulations still maintain a high level of permeability when compared to the “Best in Class”­— butyl rubber. The permeation rates of silicones still remain nearly 100 to 400 times higher than that of butyl rubber as seen in the table on the following page.

8. [Cm 3*cm]/[cm2*{s*cm2* cmHg}] Oxygen = 1.2 Moisture = 110 Elastomer Permeability To some degree ALL elastomers are permeable to gases. The rate of gas permeation varies by material compounding, material hardness, degree of compression, presence or absence of lubrication, temperature, and type of gas being sealed. Typically, harder compounds containing more carbon black feature lower diffusion rates. Of analyzed elastomers, butyl rubber was chosen due to both its permeability performance and excellent physical characteristics.

9. Test Method Ja-Bar’s ButylFill elastomers are engineered to eliminate one of the key elements necessary for galvanic corrosion to exist—the liquid electrolyte path. Silver-plated aluminum in butyl rubber ButylFill 85B-78 Competitor’s passivated, silver-plated aluminum- filled fluorosilicone Type D Silver-plated aluminum in butyl rubber ButylFill 85B-51

10. Galvanic corrosion of aluminum disks was tested by exposure to salt spray according to MIS-47057 and ASTM B117. Samples were evaluated after 500 hours. The aluminum disks were treated with a hexavalent chromate conversion coating to meet MIL-C-5441 Class 1a. This chemical film treatment corroded away on the passivated “TYPE D” material.

11. The dimensional change and hardness of the gasket was related to the edge of the gasket swelling and creating a lip. The powder-filled silicone and fluorosilicone gaskets consistently had about an 11% increase in thickness on the edge due to swelling, whereas the gaskets containing butyl rubber showed 3% or less. The hardness of the gaskets changed very little from the salt spray exposure. The passivated Type D gasket became slightly softer after salt spray—about 3 points on the Shore A scale. The silver/aluminum butyl rubber gasket also lost about 2 points in hardness.

12. Conclusion The dimensional change and hardness of the gasket was related to the edge of the gasket swelling and creating a lip. The powder-filled silicone and fluorosilicone gaskets consistently had about an 11% increase in thickness on the edge due to swelling, whereas the gaskets containing butyl rubber showed 3% or less.

13. Chemical Compatibility The hardness of the gaskets changed very little from the salt spray exposure. The passivated Type D gasket became slightly softer after salt spray—about 3 points on the Shore A scale. The silver/aluminum butyl rubber gasket also lost about 2 points in hardness. As is the case with all conductive elastomers, ButylFill 8B5-51 and 8B5-78 are compatible with an array of chemicals and media and are used in a wide range of environmental conditions. The most common end use is where fluid, fuel, oil, and/or chemical resistance is required. See the chart on the next slide for the most common chemical compatibilities. For a more extensive click here for a downloadable, interactive, excel spreadsheet.

14. Chemical Compatibility Chart Key 1 Very good; 2 Good; 3 Fair; 4 Not Recommended

15. Shielding Effectiveness Test Report

16. Batch Test Results

17. For more information Ja-Bar Silicone Corporation — Shielding Division Applications Engineers Mark A Derr Scott Ackerman mderr@ja-bar.comsackerman@ja-bar.com 252 Brighton Rd., Andover, NJ 07821 ph. 973-786-5000 fax 973-786-5546 www.ja-bar.com