surface activation

can anybody point me to some info on activating metal (and glass) surfaces?

i see virtually nothing online, this is all i found:



besides remembering don gelbarts video:

YouTube

scrubbing powder seems not to work (i tried three brands) and he doesns mention sanding, only sand blasting. what might be the difference?

are you trying to say "passivating"?

By looking at the chart I have to assume you are referring to passivation as in passivating SS. This removes a layer of oxidation on the surface and exposes the substrate beneath the oxidation. I would think that hydrofluoric acid would passivate glass. I am not sure if there is more to it then just removing a layer from the surface, but perhaps some of the chemistry oriented folks can elaborate on that.

he is looking for the exact opposite of passivation, passive layer is inert, it will not attract or react, activated surface on the other hand attracts other stuff, be it another metal - think plating, or as a preparation step for bonding with glues etc

I think the question in the original post is way to broad, you might get better suggestions if you describe what exactly are you trying to do, coat what surface with what, bond this to that etc, because the answers are very application specific as you can see from the etching examples table in the picture

yes, as i understand the expressions, passivating is the opposite of activating. passivating would be using a phosphocic acid solution to thicken the oxide layer on stainless. look at the video and the water test. if you want good adhesion of glue (and maybe other coatings?) you have to activate the surface. there is a bunch of appropriate products out there, mostly very specific and expensive (sika has about a dozen activators). im mainly interested in steel, zink/cadmium plated steel, stainless, aluminum (only this one is clear to me, use an alcalic media, but there probably are nuances as well), glass and plastics.

Here comes the freight train

Here comes the freight train of information, reader beware...

Most substances exist in nature in their lowest energy form, for example iron exists as oxide of iron.
The items we use in real life generally tend to be in a higher energy form, for example metallic iron, however this also means they want to go back to their low energy form like forming an oxide.

Activation of a surface means cleaning off the passive layer of oxides or other substances to expose the higher energy state material.

Passivation of a surface requires applying a layer of low reacting and stable material. This could be phosphate coating, black iron oxide coating or in case of stainless steel a thin layer of chromium oxide.
Side note: passivation of stainless steel is actually a 2 step process. he first step is pickling, which uses nitric acid to dissolve iron from the surface leaving mostly chromium. Second step is the actual passivation when the abundantly present chromium on the surface forms a stable layer of chromiium oxide, which is a passive layer since it is already is low energy state.

Just term activation could mean several things depending on application. In many cases removing protective coating or oils will expose the clean active substrate. In some other cases you may need to add certain elements to the surface to allow certain reaction to take place. In electro plating you may need to use a seeding bath which operates at lower concentration and higher voltage to allow deposition of the initial layer of metal to be plated with. Then a lower voltage, higher concentration bath can be used to do the bulk of plating. In other cases you may underplate with completely different metal. Often copper is plated onto steel before chrome is applied to copper. In some cases it is even a 3-step process involving copper, then nickel then chrome.

Generally, acid is a standard thing to use to dissolve top layer of the metal and metal oxides and expose underlying layer of active metal to achieve activation of said metal. Care must be taken as to which acid is used on which metal to prevent formation of metal salt deposit from the acid. for example, using high concentration phosphoric acid on iron will clean and activate it, but using low concentration phosphoric acid will deposit a layer or iron phosphate achieving opposite of activation.

Mostof the time surface activation is application specific, so this question cannot be accurately answered in general form.

i was not really looking for answers, just info on where to get info.

well, ill share some of my findings. aluminum is easy, dunk it in a warm lye solution, rinse with destilled water and it passes the water test. mild steeel: phosphoric acid works, vinegar works, borax works, sodium triphosphate doesnt. neither do any organic solvents like aetone, perchloretylene, trichloretylene or mek. sanding does work, but not very well. thats it so far, i have to get hold of some acids to experiment on other materials.

so dou you think the "water test" is a good one? for what, gluing, painting, parkerising, anodising, nickel plating? or is it not needed for some processes and would hurt other ones?

if you leave the part in phosphoric acid too long it develop a grey coating, phosphate i understand. while they say its good for painting i wonder what it does if you want to blue the part or use let say a zink coat. in vinegar steel also gets coated after a couple of days, i wonder what the coating is.

Re activating glass, how do you form an oxide coating on an oxide?

As to activation, it depends on the coating to be applied. For example, I silver plate beryllium copper by stripping the beryllium atoms off the surface, leaving pure copper, then go into a silver cyanide plating solution, full strength, no strike and get a bond that bead blasting will not peel.

See if you can find a Metal Finishing Guidebook and Directory. It has a couple hundred pages on this subject. This link will give you a lot of leads.

metal finishing guidebook and directory free download - Google Search

Bill

that looks promissing, thanks.

i fished out another piece of info: acid activation is beneficial when applying black oxide.

dian said:

i was not really looking for answers, just info on where to get info.

well, ill share some of my findings. aluminum is easy, dunk it in a warm lye solution, rinse with destilled water and it passes the water test. mild steeel: phosphoric acid works, vinegar works, borax works, sodium triphosphate doesnt. neither do any organic solvents like aetone, perchloretylene, trichloretylene or mek. sanding does work, but not very well. thats it so far, i have to get hold of some acids to experiment on other materials.

so dou you think the "water test" is a good one? for what, gluing, painting, parkerising, anodising, nickel plating? or is it not needed for some processes and would hurt other ones?

if you leave the part in phosphoric acid too long it develop a grey coating, phosphate i understand. while they say its good for painting i wonder what it does if you want to blue the part or use let say a zink coat. in vinegar steel also gets coated after a couple of days, i wonder what the coating is.

Click to expand...

Its not that easy. For most metals you have to use several steps, basically

1) remove grease
2) remove oxides and/or impurities

then the surface is active but how long, its another question. Aluminium develops new oxide fast. So

3) create new oxide layer which has known composition and is good surface for following process

I would recommend ASM handbooks but they have recipes which have bad ingredients like hydrofluoric acid and Cr VI compounds.

So, better sources are industrial suppliers, find someone who offers electroplating chemicals and use these.

P.S. Aluminium cleaning by lye is very bad but very common. Youre basically removing bare metal with lye. Its like removing scalp for better haircut.