Alumina Oxide

[truk 57]

Hello All! First time on this site. It is Great. We are spraying a high purity Alumina Oxide, but we have some black spots I would call them that show up, we have done I believe all the obvuios things ,nozzles, powder ports etc,etc, I have been told this can from the way the Powder is processed. is this true? Thank You!

[Gordon]

Hi truk 57

to the Surface Engineering Forum.

Black spots in the coating can be from impurities in the supplied powder, so the only cure for this is to change grade or supplier.

More commonly this is due to contamination from powder feeders. Very stringent house keeping is required to avoid this problem. With mechanical powder feeders, complete strip downs and felt replacements will be required. Some go to the extreme of dedicating a feeder or hopper only to this type of powder.

Also the spraying environment needs to be clean, it only needs a tiny amount of dust entrained into the spray stream to produce black spots in a white coating.

On the whole a few black spots is not going to be detrimental to the coating other than spoiling the appearance.

[truk 57]

Thanks for your help!!!

[Stephen Booth]

we have seen the similar situation in spraying of high purity Y2O3 powders for very particular electronics companies.

Ended up changing the powder manufacturer, and even going as far as to package the powder in vacuum packs. I do not know how the vacuum packing helped?

The price ended up being about 3X greater than the standard hi-purity material