On Thu, 1 Aug 2002, Bill Johns wrote: >I'll butt in here again. First off, aluminum oxide is good hard stuff, but >sensitive to certain environments. For optimal performance, like the >really high-end aerospace stuff, the clean, freshly prepared aluminum oxide >layer is primed or painted with a non epoxy paint, typically a >phenolic. This protects the aluminum oxide layer from water and epoxy resin.
Do you have a brand name for a phenolic paint? -J > >I hate to say this, but epoxy resins are not that water resistant, there >are better resins for water durability out there. They can be made to be >good but it takes work. Many of the curing agents used to harden the epoxy >are amines, chemically identified with -NH and -NH2 groups. These react >with water to form strong alkaline materials which turn the aluminum oxide >(sapphire) into aluminum hydroxide, a material which has the mechanical >properties of wet corn flakes. So where does the water come from? Alas, >virtually every glue I know of is porous to different extents to >water. The water as a gas simply permeates through the epoxy layer and >attacks the surface. Life happens. Fortunately we don't let our planes >sit out on hot tarmacs in Houston or Miami after a rain. We don't have to >deal with some of the really ugly reactions that can go on with our >planes. Our planes don't have life expectancies of 20+ years and these >reactions do take a while to happen. > >And one more thing. If you want to "post cure" the epoxy, especially the >fast cure kind, first let the resin go to a complete cure at room >temperature before you hit it with heat. Don't hit it with heat right >after you lay up the glue joint. Certain reactions have to happen to form >the solid before you reheat. Yes, it will work if you heat it up >immediately, but you probably won't get the best strength that way. > >Cheers, > >Bill > >-- >The one good thing about repeating your mistakes is that you >know when to cringe. > >Bill Johns >Pullman, WA > >RCSE-List facilities provided by Model Airplane News. Send "subscribe" and >"unsubscribe" requests to [EMAIL PROTECTED] > RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
