For corrosion protection I need to waterproof the junction where a nickel and a titanium sheet are bolted together (for an electrical connection). Part of the titanium sheet will be exposed to sea water and sunlight. The nickel will need to be fully insulated from the sea water.
I don't have access to any special chemicals for surface preparation other that those you can get in a supermarket.
Mike B wrote in news: email@example.com:
Get some G4 pond sealer (a moisture cured polyurethane). Solvent clean the surfaces, apply G4 and wet sand it into the surfaces to be bonded, wipe off the grit and debris with a lint free rag wetted with more G4 leaving a thin film behind then apply any marine polyurethane sealant sold for below waterline use while the G4 is still tacky.
I wouldn't expect silicone to adhere well to titanium unless the surface is chemically cleaned so dont use it! Also many silicones give off acetic acid when they cure and actually make the corrosion worse.
Ian Malcolm fired this volley in news:XnsA31DBF53F52B40xDEADBEEF@188.8.131.52:
Not "many"; type I silicones evolve acetic acid. Type II silicones evolve methanol instead of acetic acid. That's not entirely harmless to some base metals like cast zinc alloys, but a lot more innocuous than acetic acid.
My best guess on a sealant for that purpose would be a polyacrylic co- polymer rubber sealant like Sashco's LEXEL. You'd still need to mechanically prep the surface but the stuff sticks to virtually anything, including polyethylene.
And fingers , it's tough to get off even when uncured . This stuff smells a lot like the GOOP line of products , are they the same base formula or similar ? I used the Lexel to caulk a leaky chimney boot on a steel roof , worked just swell !
"Snag's Shop" fired this volley in news:Vsy7v.589346$ firstname.lastname@example.org:
Some of the GOOPs are acrylic-vinyl, some are straight acrylic resins, and some are polyacrylate co-polymer rubbers. The GOOP E6000 is a poly- resin, and approximately equal in character to the Lexel. However, the Lexel (to its advantage) contains more solvent (perchlorethylene), so it flows better, and intrudes into roughed-up surfaces better, yielding a stronger bond.
Both, if they penetrate equally, are tougher than a wild boar's nuts, and will stick to damned near anything they come into contact with.
They do shrink upon drying, because they're solvent-based. So far, that's not been a problem for me. I've put the Lexel on glossy MIC-6 aluminum sheet with no surface prep, and had to use mechanical means to get it off. It doesn't like greasy fingerprints. Solvent-wipe any surface to which you wish it to adhere.
I used a GOOP product once to glue the sole back on a W/m work boot . That sole was so thin I could step on a dime and tell you not only heads or tails , but what year and the goop was still hangin'on . I think I'll use part of the rest of that tube of Lexel on the currently de-soled pair . -- Snag In Memphis visitin' Grandkids
If the only results is to seal a joint then Gunner recommended 3M
5200. Having used the stuff for years I can second his suggestion but you do need to use it correctly. 3M recommends that you coat the mating surfaces and then tighten the clamping nuts/bolts so that the mating surfaces are parallel but not tightly fastened. Leave for at least 24 hours and then tighten firmly. You are, in essence, making a gasket.
It does work and it does last and once you open the tube it also hardens in the tube but taping the nozzle and storing the opened tube in the fridge will significantly lengthen it's life. Most shops here keep unopened, unsold tubes of "5200" in a fridge.
I'm in Australia so finding these brand names or equivalents is a challenge. Even 3M is poorly represented - buying from ebay sellers in the US is cheaper than buying locally, even with the $20 postage.
There are two major brands in local hardware stores, Selleys and Sikaflex. The documentation for both is lacking in detail. Often all you get is the material safety data sheet which may give a clue as to polyurethane/silicone/acrylic base or whether it contains organic solvents. Sikaflex products may (it's difficult to tell) need a primer which is 3 times the price of the sealant.
So far I've tested 'Selleys Urethane Bond' which is sold as a general adhesive. This was better than expected but could still be peeled off with a finger nail. I'm now testing 'Selleys Ultra Repair' which is some kind of modified semi flexible cyanoacrylate and 'Selleys Aqua Repair' which is some kind of modified epoxy/acrylic and 'Selleys All Clear' which as far as I can tell is synthetic rubber dissolved in toluene - I think there's a US brand equivalent but I cannot remember the name.
I'll wait a couple of days for these to cure fully before testing the adhesion. If none work then I'll buy some 3M 5200.
Your problem is first eliminating unsuitable sealents for marine immersed applications, and I would immediately rule out most cyanoacrylates (poor water resistance) ans silicones (difficult to get reliable adhesion). Marine epoxies are generally suitable, and can be used as their own sand- through primer, but may be too rigid and brittle for your application and also have poor UV resistance.
Next you have the surface preparation issue - both materials need to be extremely clean and totally degreased and as they are generally known to be difficult, if you cant etch the area to be bonded to condition or convert the oxide coating, you need to remove it mechanically while excluding air, hence priming the surface by sanding through a pool of catalysed or activated resin chemically compatible with the adhesive system to be used and applying the final adhesive or sealent while the priming resin is still tacky.
Due to the need to sand through it without entraining significant air bubbles, you need a liquid resin for the primer and some sort of paste or gel for the sealent so it stays where you put it. Apart from marine epoxy which can be thickened with collodial silica, this means you need a seperate primer.
N.B. I am assuming the the Nickel surface is NOT a cupronickel alloy as they are notoriously difficult (near impossible) to get long term adhesion to in a marine enviroment.
Look for Sikaflex. Apparently common in your part of the world, or at least all the Aussie sailors I've met recommended it :-)
Do a google search for Sikaflex+marine+sealant+bonding. You can find their "Sikaflex Marine Handbook", download that as it has explicit instructions for using their products.
You'll probably come up with Sikaflex-291, or 292, but they make some specialized bonding sealants, for example Sikaflex - 295 UV, formalized to bond plastic windows into a fiberglass or wooden boat where exposed to abundant UV.