Dear researchers,
I have some multiport extruded tubes with a certain white precipitate visible on the iner side of the tubes and would like to know a way to determine what that precipiate is.
During extrusion the aluminium multiport tubes are passed through a water quench to cool them down from an temperature in excess of 500°C to about 40°C. In some cases when the water enters into the ports of the MPE tube due to porosities a thin layer of white precipitate is observed which is mostly aluminium hydroxide. In severe cases a considerable amount of white powder can be detected. After performing an XRD on the white powder it was found to bayerite.
Also anodic dissolution of aluminium around the Al(Mn,Fe)/Al(Mn.Fe)Si precipitates was observed when some samples were analyzed under the SEM. Very minute quantities of oxygen could be detected with the EDX analysis on the SEM but these measurements cannot confirm the exact composition of the precipitates.
Is there a quick way to determine if the precipitate on the surface of the tube is Aluminium hydroxide?(without the need to perform XRD or any other time consuming analyses) And can any other type of precipitate that can form under these conditions?
Would be grateful for your inputs and suggestions.
Dear Amol Suresh Jadhav , The method consists in the formation of a colored complex compound by the reaction with aluminum ions pyrocatechol violet, followed by photometric determination in the wavelength range from 570 to 590 nm and calculating the mass of aluminum concentration in the sample being analyzed of water.
Why it should be aluminium hydroxide? It's almost certainly intermetallic phase, and EDS results confirm it.
Hello Vladimir, Yes it is an intermetallic phase but the black regions around the intermetallic is most probably the result of anodic dissolution in the presence of water combined with the high temperature of aluminium before quenching. Also the EDS results show a minute quantity of Oxygen which normally wont be detected on a normal sample.
You need to take pictures at higher magnifications and lower accelerating voltages to be sure you see cavities, not something like organic surface contamination.
There is only one way to be certain. Solve the structure of the material. Scrape the surface onto a carbon coated grid and use micro diffraction techniques in a tem or backscatter diffraction techniques in an sem. The material may be beam sensitive so good luck but there is only one way to be certain, solve the crystallography.
Or Even better, make an extractionreplika for the TEM diffraction
Vladimir Dusevich , I took your suggestion and reduced the accelerating voltage. Analysed a different sample with a similar looking white/grey color precipitate. It can be seen there is some kind of residue around some of the intermetallic particles. When I scan the region around the intermetallic the EDS results show significant presence of oxygen.
This most probably is oxidation/corrosion of some type. Has anyone seen something similar or can explain what this could be?
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