bob330
Materials
- May 2, 2007
- 44
Greetings,
Recently, I was asked to examine some near pure (1XXX) series aluminum cooling fins that were reportedly not conducting heat very well. The fins (on 304SS tubes) have plant environment air blown on them by a large fan and this air is suspected to have a significant amount of ammonium sulfate in it released from a nearby stack. When I went to touch some of these thin fins (which still looked perfectly intact and in proper dimensions despite having a light brownish color), they literally turned to a very fine (like talcum powder) dust in my fingers. I collected a sample of the dust and noticed that some very small slivers of metal were left within the hyper-fine light brown powder. I sent the powder off for analysis including X-ray fluorescence, ion chormatography, and diffractometry which that the bulk of the fins had now become calcium sulfate hydrate or gypsum which not surprisingly is known to have the same color as the powder we had. Some un-hydrated calcium sulfate was also found along with FCC aluminum (uncorroded aluminum). No oxides of aluminum were found nor was any aluminum sulfate as I expected to find. A relatively high amount of chloride ions were also found by the ion chromatography and fluoresence tests. I discovered that for some time years ago, the tubes were often sprayed in the summer with chloride and calcium bearing semi-brackish river water to aid in cooling. Can anybody explain how this aluminum turned to gypsum and if this is to be expected given the information above? Does the above evidence prove that ammonium sulfate was the key culprit here or not?
Thanks,
bob
Recently, I was asked to examine some near pure (1XXX) series aluminum cooling fins that were reportedly not conducting heat very well. The fins (on 304SS tubes) have plant environment air blown on them by a large fan and this air is suspected to have a significant amount of ammonium sulfate in it released from a nearby stack. When I went to touch some of these thin fins (which still looked perfectly intact and in proper dimensions despite having a light brownish color), they literally turned to a very fine (like talcum powder) dust in my fingers. I collected a sample of the dust and noticed that some very small slivers of metal were left within the hyper-fine light brown powder. I sent the powder off for analysis including X-ray fluorescence, ion chormatography, and diffractometry which that the bulk of the fins had now become calcium sulfate hydrate or gypsum which not surprisingly is known to have the same color as the powder we had. Some un-hydrated calcium sulfate was also found along with FCC aluminum (uncorroded aluminum). No oxides of aluminum were found nor was any aluminum sulfate as I expected to find. A relatively high amount of chloride ions were also found by the ion chromatography and fluoresence tests. I discovered that for some time years ago, the tubes were often sprayed in the summer with chloride and calcium bearing semi-brackish river water to aid in cooling. Can anybody explain how this aluminum turned to gypsum and if this is to be expected given the information above? Does the above evidence prove that ammonium sulfate was the key culprit here or not?
Thanks,
bob
