How to make an aluminumoxide coating on an electrode? [duplicate]

The Questions is above. I am not a chemist but that is what I know:

• Aluminum has an Oxide Layer normally
• Aluminum-Oxide Layer can be broken down with NaOH
• Zink coatings are done by galvanic coating using a certain voltage

Another way to ask: Can I do this with Aluminum?

• Are you asking how to electroplate aluminum onto a substrate? Jun 21 '19 at 16:02
• yes essentially, And if thats possible without any further difficulties/ what i should consider when doing so Jun 21 '19 at 16:10
• It may be possible to electroplate , but I have only seen vapor deposition in vacuum or "flame"spray ( actually done like electric welding) which makes a relatively coating ( used for cathodic protection. ). and Alonizing , done at very high temperature. Jun 21 '19 at 16:51
• Alonizing , a proprietary process, deposits aluminum vapor on steel at about 1800 F. It is used to coat high temperature equipment ( eg. furnace tubes) for oxidation and sulfidation resistance. Not decorative. Jun 21 '19 at 16:57
• Does this answer your question? Can I anodize an aluminum coating on steel to have better corrosion inhibition for the steel? Jan 2 at 1:15

Yes, it is definitely possible, but also relatively difficult as compared to electroplating zinc onto another metal.

It is a significantly important industrial process. Although aluminium itself is reactive, it develops an impervious oxide layer that quite much renders it unreactive.

However, comparatively larger negative standard electrode potential of Al/Al(III) couple (− 1.67 V vs. SHE) precludes its deposition from the aqueous baths.

So it is usually considered impossible in aqueous (water-based) solution so is conducted in either organic liquids or fused (molten) state.

Fused: Usually a bath of an eutectic mixture of $$\ce{LiBr, KBr}$$ & $$\ce{CsBr}$$ is taken along with molten $$\ce{AlBr3}$$ (melts at about 94-98°C). A concentration of $$80\%$$ (by wt.) of $$\ce{AlBr3}$$ is reported to give a shiny finish.

Source $$1$$ reports that a satisfactory result was obtained with constant current of $$1-3$$ $$\pu{A}$$ passed for $$1$$ hour.

Non-aqueous solution:

From Source $$2$$ (emphasis mine)

..the commercial processes for electroplating of Al are based on organic solvents such as SIGAL (Siemens-Galvano-Aluminium) and REAL (Room-temperature Electroplated Aluminium) processes. In the SIGAL process which was developed in Siemens laboratories Al is electrodeposited at 100 °C from alkylaluminium compounds in toluene. In the REAL process which was developed in the laboratories of Philips $$\ce{Al}$$ is deposited at room temperature from $$\ce{AlCl3}$$ and $$\ce{LiAlH4}$$ in tetrahydrofurane.

The process must be conducted avoiding any traces of water, or the water would be electolysed first, leading to observable evolution of gas.

TL;DR: Electroplating aluminium is not something I would recommend trying at home.

References:

1. Aluminum electroplating on steel from a fused bromide electrolyte, P. K. Tripathy et al, Surf. Coat. Tech., Vol. 258, 15 Nov. 2014, 652-663. DOI:10.1016/j.surfcoat.2014.08.021
2. Electroplating of mild steel by aluminium in a first generation ionic liquid: A green alternative to commercial Al-plating in organic solvents, S. Zein El Abedin et al, Surf. Coat. Tech., Vol. 201, Issues 3–4, 5 Oct. 2006, 1352-1356. DOI:10.1016/j.surfcoat.2006.01.065
• Thank you very much. Very informative. I think i will then try some other material though. Thats too much of a hassle to homebrew. But I have one question left: Why do some people recommend using NaOH to destroy the oxide Layer and why isn't it possible form Al+1 or Al+2 to go into solution and then using a voltage to redirect the ions to flow to the other electrode? Jun 22 '19 at 8:44
• You're welcome. $\ce{NaOH}$ forms an aluminate complex, and hence dissolves $\ce{Al2O3}$ under moderate heat (read more here). And no, forming and stabilizing +1 or +2 states would be really challenging (and maybe impossible altogether) at room temperature. +1 state is rare but existent, while I don't believe the +2 state exists. If you've studied basic electronic configuration, you might know that Al prefers a +3 state. Jun 22 '19 at 9:53
• Yeah I had studied that, but its a while ago and i never considered one impossible. Thank you very much for the answers Jun 22 '19 at 12:27