Had a thought.

I ordered some anodised aluminium. Does that mean that the aluminium comes coated in a giant gemstone? Corundum/ruby/sapphire = Al2O3.

In my case a gemstone 6.5 metres long, 0.2 metres wide and up to 0.1 mm thick?

Or to put it another way, what is the hardness (Mohs, Brinnell or Vickers) of anodised aluminium?

mollwollfumble said:

Had a thought.

I ordered some anodised aluminium. Does that mean that the aluminium comes coated in a giant gemstone? Corundum/ruby/sapphire = Al2O3.

In my case a gemstone 6.5 metres long, 0.2 metres wide and up to 0.1 mm thick?

Or to put it another way, what is the hardness (Mohs, Brinnell or Vickers) of anodised aluminium?

What you are going to get is a translucent film of aluminium oxide wich becomes integral to the structure.

roughbarked said:

mollwollfumble said:

Had a thought.

I ordered some anodised aluminium. Does that mean that the aluminium comes coated in a giant gemstone? Corundum/ruby/sapphire = Al2O3.

In my case a gemstone 6.5 metres long, 0.2 metres wide and up to 0.1 mm thick?

Or to put it another way, what is the hardness (Mohs, Brinnell or Vickers) of anodised aluminium?

What you are going to get is a translucent film of aluminium oxide wich becomes integral to the structure.

Yes, but which aluminium oxide.

mollwollfumble said:

roughbarked said:

mollwollfumble said:

Had a thought.

I ordered some anodised aluminium. Does that mean that the aluminium comes coated in a giant gemstone? Corundum/ruby/sapphire = Al2O3.

In my case a gemstone 6.5 metres long, 0.2 metres wide and up to 0.1 mm thick?

Or to put it another way, what is the hardness (Mohs, Brinnell or Vickers) of anodised aluminium?

What you are going to get is a translucent film of aluminium oxide wich becomes integral to the structure.

Yes, but which aluminium oxide.

If you mean corundum, take your pick. ;) At least they call themselves https://www.sapphirealuminium.com.au/about-anodised-aluminium.html

mollwollfumble said:

roughbarked said:

mollwollfumble said:

Had a thought.

I ordered some anodised aluminium. Does that mean that the aluminium comes coated in a giant gemstone? Corundum/ruby/sapphire = Al2O3.

In my case a gemstone 6.5 metres long, 0.2 metres wide and up to 0.1 mm thick?

Or to put it another way, what is the hardness (Mohs, Brinnell or Vickers) of anodised aluminium?

What you are going to get is a translucent film of aluminium oxide wich becomes integral to the structure.

Yes, but which aluminium oxide.

As far as I am aware there is only one aluminium oxide: Al2O3.

IIRC anodising is only one to a few molecules thick.

Al2O3 is corundum. It is hard but brittle, and importantly, under most normal environmental conditions is completely unreactive.

Aluminium on the other hand, is so reactive that after any surface damage (eg cutting, hammering, machining, deforming etc) immediately self-heals by reacting with atmospheric oxygen forming Al2O3 on the surface.

So yes, your piece of anodised aluminium is coated with a thin layer of corundum.

Note that corundum is not a gemstone without other qualities that make it into sapphires or rubies etc. Colour, clarity and size are some of those qualities.

Michael V said:

mollwollfumble said:

roughbarked said:

What you are going to get is a translucent film of aluminium oxide wich becomes integral to the structure.

Yes, but which aluminium oxide.

As far as I am aware there is only one aluminium oxide: Al2O3.

IIRC anodising is only one to a few molecules thick.

Al2O3 is corundum. It is hard but brittle, and importantly, under most normal environmental conditions is completely unreactive.

Aluminium on the other hand, is so reactive that after any surface damage (eg cutting, hammering, machining, deforming etc) immediately self-heals by reacting with atmospheric oxygen forming Al2O3 on the surface.

So yes, your piece of anodised aluminium is coated with a thin layer of corundum.

Note that corundum is not a gemstone without other qualities that make it into sapphires or rubies etc. Colour, clarity and size are some of those qualities.

:)

Michael V said:

mollwollfumble said:

roughbarked said:

What you are going to get is a translucent film of aluminium oxide wich becomes integral to the structure.

Yes, but which aluminium oxide.

As far as I am aware there is only one aluminium oxide: Al2O3.

IIRC anodising is only one to a few molecules thick.

Al2O3 is corundum. It is hard but brittle, and importantly, under most normal environmental conditions is completely unreactive.

Aluminium on the other hand, is so reactive that after any surface damage (eg cutting, hammering, machining, deforming etc) immediately self-heals by reacting with atmospheric oxygen forming Al2O3 on the surface.

So yes, your piece of anodised aluminium is coated with a thin layer of corundum.

Note that corundum is not a gemstone without other qualities that make it into sapphires or rubies etc. Colour, clarity and size are some of those qualities.

> As far as I am aware there is only one aluminium oxide: Al2O3.

Thanks. Didn’t know that.
There may still be a difference between a crystal corundum and an amorphous glass? Like between silica and glass.

> IIRC anodising is only one to a few molecules thick.

(from wikipedia)
Without anodising, the surface layer of oxide is only a few molecules thick. Of order 2-3 nm for pure aluminium and 5-15 nm for alloys.
Anodising coatings of moderate thickness are 1.8 μm to 25 μm.
Hard anodizing, also called engineered anodising, can be made between 13 and 150 μm thick.

150 μm = 0.15 mm is really quite thick, thick enough to be seen by the naked eye.

mollwollfumble said:

Michael V said:

mollwollfumble said:

Yes, but which aluminium oxide.

As far as I am aware there is only one aluminium oxide: Al2O3.

IIRC anodising is only one to a few molecules thick.

Al2O3 is corundum. It is hard but brittle, and importantly, under most normal environmental conditions is completely unreactive.

Aluminium on the other hand, is so reactive that after any surface damage (eg cutting, hammering, machining, deforming etc) immediately self-heals by reacting with atmospheric oxygen forming Al2O3 on the surface.

So yes, your piece of anodised aluminium is coated with a thin layer of corundum.

Note that corundum is not a gemstone without other qualities that make it into sapphires or rubies etc. Colour, clarity and size are some of those qualities.

> As far as I am aware there is only one aluminium oxide: Al2O3.

Thanks. Didn’t know that.
There may still be a difference between a crystal corundum and an amorphous glass? Like between silica and glass.

There could be a difference between normal anodising and hard anodising here. Normal anodising may be amorphous and hard anodising crystalline.

> IIRC anodising is only one to a few molecules thick.

(from wikipedia)
Without anodising, the surface layer of oxide is only a few molecules thick. Of order 2-3 nm for pure aluminium and 5-15 nm for alloys.
Normal anodising coatings of moderate thickness are 1.8 μm to 25 μm.
Hard anodizing, also called engineered anodising, can be made between 13 and 150 μm thick.

150 μm = 0.15 mm is really quite thick, thick enough to be seen by the naked eye.

Variable hardness. Said to be above Mohs 6.8 and below Mohs 9.
(Rockwell C hardness quoted is useless as a guide)
Vickers VPN hardness of 800 to 1000.

A message to engineers out there. Yes, there is a conversion from Vickers, Rockwell, Brinnell to Mohs. It doesn’t take a genius to run a Vickers test on a Mohs mineral standard and record the result.

Michael V said:

mollwollfumble said:

roughbarked said:

What you are going to get is a translucent film of aluminium oxide wich becomes integral to the structure.

Yes, but which aluminium oxide.

As far as I am aware there is only one aluminium oxide: Al2O3.

IIRC anodising is only one to a few molecules thick.

Al2O3 is corundum. It is hard but brittle, and importantly, under most normal environmental conditions is completely unreactive.

Aluminium on the other hand, is so reactive that after any surface damage (eg cutting, hammering, machining, deforming etc) immediately self-heals by reacting with atmospheric oxygen forming Al2O3 on the surface.

So yes, your piece of anodised aluminium is coated with a thin layer of corundum.

Note that corundum is not a gemstone without other qualities that make it into sapphires or rubies etc. Colour, clarity and size are some of those qualities.

the lack of a formal crystal structure is also kinda key to be a gemstone

diddly-squat said:

Michael V said:

mollwollfumble said:

Yes, but which aluminium oxide.

As far as I am aware there is only one aluminium oxide: Al2O3.

IIRC anodising is only one to a few molecules thick.

Al2O3 is corundum. It is hard but brittle, and importantly, under most normal environmental conditions is completely unreactive.

Aluminium on the other hand, is so reactive that after any surface damage (eg cutting, hammering, machining, deforming etc) immediately self-heals by reacting with atmospheric oxygen forming Al2O3 on the surface.

So yes, your piece of anodised aluminium is coated with a thin layer of corundum.

Note that corundum is not a gemstone without other qualities that make it into sapphires or rubies etc. Colour, clarity and size are some of those qualities.

the lack of a formal crystal structure is also kinda key to be a gemstone

I am unsure of why it took this long to state that obvious, other than that it isn’t the main requirement.

I did point to the business name in the link I put up. and waited.