Aluminium vs. Aluminia

[MikeS]

Hi all

I've seen several discussions reguarding aluminium and the use or artificial live rock....

Aluminium has been suggested as a photoinhibitor in corals...the majority of aluminium in typical portland cement is in the form of aluminium oxide, or aluminia...

I'm wondering how aluminium would differ from aluminia in its effects...is it less harmfull in that form, or less likey to end up in the water, or a combo of both?

As long as we are on the topic...those of you well versed in chemistry can maybe help...this is a breakdown of portland cement...what do you think?

Calcium oxide, CaO 62-67%
Tricalcium silicate C3S 45-65%
Silicon oxide, SiO2 20-25%
Dicalcium silicate C2S 15-30%
Tetracalcium aluminoferrite C4AF 8-15%
Aluminium oxide, Al2O3 3-7% -
Tricalcium aluminate C3A 1-8%
Ferro oxide, Fe2O3 2-5%
Gypsum 1-3% Sulfate

thanks all...

MikeS

 

[liveforphysics]

Aluminum oxide is bonded with a bond so strong, no possible process that occurs in a fish tank is ever going to be able to permit any of the aluminum to become ions that the coral could possibily know exists.

General
Other names Alumina
Molecular formula Al2O3
Molar mass 101.96 g/mol
CAS number [1344-28-1]
Properties
Density and phase 3.97 g/cm3, solid
Solubility in water insoluble
Melting point 2054 °C
Boiling point ~3000 °C
Thermal Conductivity 18 W/m·K
Structure
Coordination
geometry octahedral
Crystal structure cubic ?
Thermodynamic data
Standard enthalpy
of formation ΔfHosolid -1675.7 kJ/mol
Standard molar entropy
Sosolid 50.92 J/(mol K)
Heat capacity Cp 79.04 J/(mol K)


Now, see that -1675.7 kJ/mol enthalpy of formation? That means its going to take some increadible energy to get that Aluminum away from its very very strong bond with Oxygen. I dont know what could occur in our tanks to liberate this bond. This means since its insoluable, and has a 2000deg C boiling point, no corals in the tank should ever be able to know that its in the tank, and because they wouldnt be able to strip an Al ion off it to save there lives, I would imagine they could grow directly on it just the same as the glass or acrilic in the tank.

 

[Llarian]

http://www.advancedaquarist.com/issues/july2003/chem.htm

This seems to suggest that the presence of Aluminum Oxide has caused issues with corals, particularly when used as a phosphate binder before people started using Ferrous Oxide. However, it doesn't seem to explain much as to why.

-Dylan

 

[dnjan]

Hi all
As long as we are on the topic...those of you well versed in chemistry can maybe help...this is a breakdown of portland cement...what do you think?

Calcium oxide, CaO 62-67%
Tricalcium silicate C3S 45-65%
Silicon oxide, SiO2 20-25%
Dicalcium silicate C2S 15-30%
Tetracalcium aluminoferrite C4AF 8-15%
Aluminium oxide, Al2O3 3-7% -
Tricalcium aluminate C3A 1-8%
Ferro oxide, Fe2O3 2-5%
Gypsum 1-3% Sulfate

thanks all...

MikeS

You should be aware that the above analysis is a mixture of two different things. Basic chemical analysis of portland cement is generally in terms of the metal oxides - calcium oxide, aluminum oxide, etc.
However, the actual chemicals in portland cement (the minerals, for those of a geological background) are primarily tri-calcium silicate (a combination of calcium oxide and silicon oxide), di-calcium silicate (also a combination of calcium oxide and silicon oxide, but in different proportions), tricalcium aluminate (a combination of calcium oxide and aluminum oxide) and calcium ferro-aluminate (a combination of calcium oxide, aluminum oxide and iron oxide). In addition, there is some added calcium oxide, as well as calcium sulfate, potassium oxide and sodium oxide. The various compounds are very stable in a basic solution.
These compounds form hydrates when combined with water. The chemical equations are rather complex, but again very stable in a basic solution.

 

[Boomer]

the minerals, for those of a geological background

Yes, one needs to be careful when reading assays. In the field of mineralogy and petrology it is quite common to list things as metal oxides, which they have done here. Even look a the Gypsum listed as Sulfate, when in fact it is a Calcium Sulfate. An example of where Don is going is this; Ca2(Al,Fe)8SiO16. Ca(Al,Fe)12O19. Ca(Al,Fe)6O10. Ca(Al,Fe)4O7. Ca(Al,Fe)2O4. Ca2(Al,Fe)2O5. Ca3(Al,Fe)2O6, where all are calcium ferro-aluminate.

http://www.crct.polymtl.ca/FACT/documentation/FToxid/FToxid_documentation.htm

 

[dnjan]

And those aren't even the hydrated forms! (which would be produced after the portland cement combined with water)