Aluminium Pigments in Paints

Thermal conductivity. Al is a good heat conductor.

Since you don't give any useful information, I'd say go to the individual who makes the final material decisions and ask them. I hope that person isn't you.

What additional info would you like?

First, answer this. Do you know why you are painting whatever it is that you are painting? You didn't say what that was. What is the purpose of the paint?

What is the substrate? clean, bare metal? What kind? Is it primed?

How's the paint applied?

Little things like these help make INFORMED decisions. We don't read minds here.

Didn't I read somewhere that there was aluminum in the Hindenburg's paint?

!

Isn't powdered aluminum a component of rocket fuel?

Just asking......

Wow Lyn wake up on the wrong side of the cave?

Aluminum powder filled two component epoxy does have higher temperature tolerance than unfilled versions. Might be suitable for the specified application. Can you not coat a coupon with this and validate in an air oven?

Dear fawagy, in order to understand the reason(s) behind the selection of this particular coating, you should understand the function of the various components.

Firstly, the 'Binder', which is the resin, has been specified as an epoxy two pack, with a temperature resistance of 140 celsius, this could be Amine Adduct Epoxy, Epoxy Polyamide, or more likely in your case, Epoxy Novolac resins. This latter has higher temperature resistance. The physical property that makes the material 'surface tolerant' is its ability to thoroughly 'wet out' the surface it is being applied to, (surfactant effect) and thus is more tolerant of lower standard of surface preparation. This coating is generally specified as the 'Primer' coat in a coating system, so it must provide compatability with, and adhesion to the substrate, it should also provide a suitable compatable base for any subsequent coatings.

Secondly, the main reason for the choice of Aluminium pigment is that the form of Aluminium used is 'Leafing' aluminium, this is 'Lamellar' or platelet like structure, which creates a 'Labrinthine' path through the coating film, which slows down the transmission of moisture vapour through the coating film, thus extending the service life of the coating system quite considerably. ( It is not the same physical form as 'Powdered Aluminium' which is the type used in rocket fuel.)

As stated above, the coating is normally used as a system primer, but occasionally may be used as a finish coat to reflect UV, which causes degradation of the epoxy binder.

Hope this helps, for what it is worth, I would stick with the materials as specified.

George,

The use of the word "Pigment" denotes the use of the oxide of Aluminium. The use of Aluminum (in powder form) in paints and epoxies is generally there for strength. The Aluminum oxide (Alumina) is generally associated with high temperature or directly as a colorant (white) in chimerical paint. Aluminum added to paints also will provide some galvanic protection to carbon steel, provided that the volume of Aluminum itself is extremely high. I have experimented with some diffusion coatings, where the part being sprayed is steel and is heat treated allowing the Aluminum to melt and diffuse into the surface of the part. Note, that a controlled furnace atmosphere is required here. You need to offer up more information about your application in order to answer the question with better detail.

Only two pigments resist high heat, one is aluminum and the other is carbon black. I don't think it is a good choice to select two component Epoxy/polyamide system for heat resistance, the better choice would be a baking system based on silicone resin.

Hi arup01,

Let me say Welcome to you.

You have joined a great site with some very intellectual Members and very kind ones as well.

You mention "a baking system" as a type of system paint.

It may be that the application does not suite a 'Baked finish"?

Anyway, this was the 2 Part Type of paint or perhaps 'more correctly' finish was specified.

Take care and enjoy your Membership.

Thank you all for your good responses and apologies for not posting more information earlier. The paint is supposed to be applied on a new flanged connection that is to be installed in a fume treatment plant. The environment in the plant is hot (140oC) and is highly dusty with aluminium oxide (alumina). A 2-layer/coat paint is to be applied on a primed steel by air spray. The main purpose is to withstand high heat and provide UV protection.

"Good Answer" to arup01 (post 10)... the first post to mention silicone based systems as being well-suited to high temp applications.

NACE offers some fantastic training in the realm of Protective Coatings --- as well as "paints" (reserved for "cosmetic" applications) and Linings (for immersion-duty).

Silicone systems are popular on exhaust stacks where temps can be extraordinarily high. A point that is stressed , with respect to their application is:

They must be brought-up to a "cure" temperature and HELD there for a specific time... otherwise disaster is guaranteed...! One plant experienced complete blistering and sloughing-off of a Big-$$ job on a stack, because they didn't hold the cure temp. [...went straight on up to full operating temp, and in "no time", saw the coating falling away]

"PS"~ the previous comments regarding Al -vs- Al oxide and "powder" vs "plate" shape were well-put too... not all pigments are created equal...

Best wishes to you in all endeavors ~ !