Effective Methods for Blackening Aluminum: Seeking Simple Solutions (Electronics Forum)

As in the topic. After 14 days of searching the Internet, I give up scientific chemistry. I need a simple but effective method.
Sorry that I am asking this topic on the electronic forum but I have not found a chemical one.

I heard that aluminum is heated and "thrown" into the oil. Hehe, but I don't know if it's true

This is how steel that actually takes a dark color is hardened.

then clean ALU to hot water and add Soda (one from the store, in plastic jars) and it turns black

Aluminum is dyed black with the usual fabric dyes.
Before that, the surface of the object must be free from scratches and scratches, and then. you have to clean it completely: nitric acid + water in a proportion of half to half; you immerse the object for 10 to 30 seconds. Then you cook the object in the dissolved dye for about 2 - 10 minutes (at about 80 degrees). In order for the surface to have a durable coating after dyeing, you need to cook the item for another hour. in pure water, preferably distilled.
Greetings

And you don't accidentally add vinegar during this cooking?

Seriously, .... it doesn't pour.
Greetings

Not all aluminum can be easily blackened at home. Effective and permanent blackening is achieved in the anodizing process. It is possible to obtain other colors, e.g. blue. I recommend taking this alu to the powder paint shop - they anodize there before painting. They blackened me a few elements for the brewery: sm21:

vinegar is added only when you want the takanine not to stain your skin after rinsing - I know from my own experience

Re. Gurgle
A minor correction, permanent electrolytic staining, is anodization (oxidation of the surface and its discoloration). Contrary to appearances, this particular process is easy to do at home. Anodizing, oxidation creates only a fairly resistant (colorless) layer on the Al surface, you can later color the surfaces, e.g. with varnishes. In fact, the trick is to make the paint coat stick permanently to Al.
Greetings

Do you know what black heat sinks are for? Just to increase the heat sink's contact area with the air, not to get some colors. I do not know how the heat sinks black out at the factory, but once I took a piece of aluminum, applying it to the grinder, I produced filings that just fell on the radiator underneath it, that it was covered with filings. If someone tried, the alu filings are invisible but very hot:?

Hello

"gzresiek", you kick something, by changing the color nothing in the world changes its surface.
And it is about a completely different phenomenon, the radiation of heat to the environment, which is, let's say, easier than black (I explain briefly).

In sum. Coloring of aluminum at home can be done as follows (from the book Electroplating at home):
An object made of aluminum is ground or polished. We degrease. Then we immerse for 15 (or 5) seconds in 20% nitric acid HNO3. Then rinse with cold water. The radiator connected with a thick aluminum wire is put into a solution of 20% sulfuric acid H2SO4. Inside the acid tub there must be either two aluminum objects or one lead Pb and the other aluminum. In the case of the Pb / Al system, we use direct current, a voltage of 16V and a current density of probably 2A / dm2. If we have an Al / Al system alternating current, it can be, for example, 20V and a similar density. The allodyning process (production of the Al2O3 aluminum oxide layer) is carried out for about 60 - 90 minutes. During operation, the acid must be cooled to below 18 ° C. The process does not work properly at higher temperatures. After finishing the allodyning, rinse the object and then put it in the dyeing bath. There are many recipes. The best are baths based on iron sulphides (black inorganic dye), because the color is the most durable and relatively resistant to temperature. Cook in a (acid) dye bath, then close the pores in hot water (about 40 minutes of cooking). And we have a heat sink.
This is more or less what it looks like. If you don't clean the item before allodyning, it will have smudges later on. Not mixing during staining will result in uneven color. A lot of work and ingredients in total. Better to rely on professionals - less fun, although it may be more expensive.
Sometimes you can buy heat sinks already blackened, but I only managed it twice.
Regards.

oldking, sometimes you can find blackened heat sinks with a light color, e.g. light green, but it is for better heat dissipation. Why is this happening? Well, because it's not about the color, but about the surface area, increased by obtaining many particles on the surface.

Black color facilitates heat dissipation - it absorbs faster, but also gives up faster. Other colors, e.g. green on heat sinks, are used only to protect their surface. Besides, blackening is not the easiest and not the cheapest. Maybe that's why some heat sinks are green. Sometimes it is for aesthetic reasons.
I recommend the publication on heat sinks in Polish Elektronik Elektorze no. 7/94.
Regards.

black makes it easier to dissipate heat, but it makes it difficult to receive from the transistor - I tested myself in an identical layout, blackened and white radiator cooled with a fan - with white, the system tended more slowly

because the transistors are screwed to the white polished aluminum, because there the heat exchange does not take place through radiation but through conductivity ...

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With the better heat dissipation through blackened heat sinks, someone has done a lot of harm to humanity ...; p

Certainly, he misunderstood the theories of black-body radiation, and neither aluminum nor any of its coatings are such; p ...

Quote:

Black color facilitates heat dissipation - it absorbs faster, but also gives up faster.

Nemo, bodies radiate heat in the infrared and not in the visible spectrum, so color has nothing to do with it In addition, the protective layer can absorb heat only at the rate at which aluminum will give it away, and on the way there will be other phenomena that obstruct the heat flow.

So black mainly improves aesthetic value and increases corrosion resistance. Perhaps blackened aluminum dissipates heat better than corroded ... but I do not know, maybe someone will comment?

PS In the past, all heat sinks for computers were blackened and now they are not ... I wonder why? I even have 2 graphics cards with a heatsink painted in black paint! (both from the same company in Taiwan )

Well, because decent blackening means increasing the surface of the heat sink's contact with the air and that's what it's all about, the color has nothing to do with it. Regards

Nice archeology. And about aluminum corrosion? ......I do not know.
Greetings

xys007 wrote:

Nemo, bodies radiate heat in the infrared and not in the visible spectrum, so color has nothing to do with it In addition, the protective layer can absorb heat only at the rate at which aluminum will give it away, and on the way there will be other phenomena that obstruct the heat flow.

I didn't make it up. See in Elektronik Elektor nr 7/1994 - "Radiators - when and how to use". It is about reducing the thermal resistance at the interface: heat sink - air. According to this article, blackened has 10% less Rth ha

Regards.

How long can one topic be reheated (this has been for 2 years). I think everything was written about it at that time, why the hell to fight it again, just because someone woke up with his hand in the potty. What does it matter, black or not black, is supposed to give off heat and that's it. As in the saying, it doesn't matter if the cat is white or black, it has to catch the mice.
Greetings

If it is connected with the fact that people living, for example, in Africa have dark skin and in Greenland light skin, you will know that black radiates warmth better, and light skin - much less. Blackened radiators are always smaller than non-blackened ones because they dissipate heat better.

Hello.
I have this type of question:
I recently bought heat sinks in a non-anodized option. Well, but their surface is as if covered with something (so that they do not tarnish) only in the place of cutting you can see clean alu. Is it possible to make such a coating on the cut places in some simple way? Of course, varnishing and anodizing are not included in the game.

I think that it is easier than varnishing it, it cannot be done anymore. And it is not easy, the varnish does not catch without oxides.

As for the color: A color that is bright in visible light can be dark in infrared, and vice versa.