Does the protective layer Al2O3 form on the surface of aluminium alloys (such as Al-Zr) like pure aluminium
Zr will form oxide preferably in this case because it has more affinity towards oxygen
The oxide on the surface of Al-Zr is going to be Al2O3 unless the Zr content is large enough that the amount of beta phase AlZr becomes quite large. Even though the Zr forms a stronger bond to oxides, for Zr dissolved in the Al phase, the Zr content is too dilute to form a continuous phase. For larger Zr concentrations, the Zr is tied up as an AlZr intermetallic which due to its stability will also reduce the availability of Zr to form an oxide.
Yes the oxide will form and it the it depends on the amount and type of the alloy used.
The solubility of oxygen in alpha-Zr (bcc) is very high up to 31 at%, depending upon the temperature range(863o C- 2129oC). Zr O2-x only known oxide, which has a very small deviation from stoichiometric composition.
On the hand the solubility of oxygen in aluminum (fcc) almost nil in solid state. There is one Al and O compound, which is trigonal Al oxide alpha Al2 O3 (alpha-alumina, sapphire, or corundum), for which deviations from stoichiometric are unknown but small.
There are numerous zirconium-aluminum intermetallic compounds starting Zr Al3...ZrAl...Zr5Al3. The solid solubility of Zr in aluminum is almost zero, on the hand terminal solid solution of alpha Zr has large domain, and the boundary of which increases with temperature.
As Dr. Jeenager mentioned properly one should know what intermetallic compound of Zr-Al one has in mind in order to make speculations about the reaction products form when that compound exposed to oxygen environment for given temperature and pressure.
One guest I have for tetragonal ZrAl3 intermetallic, which is stoichiometric and melts congruently at 1580Ci and it is in equilibrium with the fcc terminal solid solution of aluminum of 0.083 Zr at.% at its peritectic temperature of 660C. It has a superstructure derived from the cubic closed packed structure of Al (fcc).
In this system ZrAl3/Al two oxide layers form if its exposed to oxidizing atmosphere. ZrO2-x/Al2O3/ZrAl/Al, where x indicates rhe vacant sublattice sides of Oxigen! Happy New Year every Body
First we need to know if the Zr remains as Zr in equilibrium conditions. If an intermetallic is formed we cannot expect the Zr contained intermetallic to partake in any reaction at room temperature to form oxides rather we will have the alpha aluminium phase to react with oxygen to form the coating. The Al-Zr phase diagram is an important point to start looking at.
- Badges
- Science topic
- Similar topics
- Engineering
- Materials Engineering