Aluminum Oxide and NaOH

[schick]

I am working on a food processing piece of equipment which is cleaned fairly regularly with a heated solution of either NaOH or Cl.

We have tried different metal combinations in the past and have found that only stainless steel will have any kind of staying power on the metal side.

I am planning to introduce a flow meter into the machine. The contact material for the meter is Aluminum oxide.

My questions:
1.) Does anyone know of any kind of chemical reaction(s) I can expect?

2.) Would you eat/drink something after it went through this reaction?

Thanks in advance for all the responses

 

[Ceramicguy]

Hello,

I have some corrosion data dating from the early to mid nineties that may shed some light for you. Aluminum oxide exposed to a 50% (by weight) sol'n of NaOH at 100 C will have a corrosion rate on the order of 75 mg/sq cm/yr. This rate of corrosion will probably require replacement of the component on a yearly basis. For comparison, a high purity alpha phase SiC will have a corrosion rate of about 2.5 mg/sq cm/yr and can be recommended for long term service. Be sure it is a high purity alpha phase material and not a reaction bonded material.

As to whether I would eat or drink anything going through the flow meter I personally would have no problem with either material but I am not the person to make a professional recommendation here.

 

[tomwalz]

Only thing I can add is that galvanic reaction can accelerate the etching.

When I worked for Swanson foods we cleaned with a boiling NaOH solution followed by an acid neutralizer, then a lot of rinse water and finally a steilizing solution.

I wpouldn't think there would be any traces of the alumina left after that.

 

[Bugman]

You may find some intersting information at

http://www.azom.com/details.asp?ArticleID=52,

there is a link to a property table in the top right which may help you out.