Troubleshooting Salt Spray (ASTM B117)

kane

Registered
Hello all,

Recently our lab decided to start mixing our own 5% salt solution for our two salt fog chambers. We installed a DiH2O water system which uses mixed bed tanks and monitor the resistivity levels daily to make sure they are within the specs of ASTM D1193. We purchased Morton Culinox 999 salt because it gave us the purity required. After mixing solution, we check the specific gravity of the final product with a hydrometer to make sure it's within the 4-6% range outlined in B117 and I will use NaOH or HCl to target pH 6.8.

Now, mixing a 5% solution is simple enough on paper but we have run into a few issues that maybe someone can help us troubleshoot. We have seen the pH in our collection tubes fluctuate up and down and sometimes land below the 6.5-7.2 range. Currently the 5% solution in our tank is pH 6.8 and spec grav 1.034, but the collected solution is pH 6.5 and spec grav 1.039. Based on B117 I was under the impression that the pH should increase slightly after atomization. What can we do control the pH better? Is it normal to expect the values to fluctuate? Also, what could lead to the specific gravity changing that much? We have taken apart the atomizer to inspect/clean it and we have replaced the filters in the tower and the reservoir tank, but nothing changed.

We are still in the R&D phase of this process, so any insights or resources are welcomed and appreciated. Thanks in advance.


Regards,

Kane
 

Miner

Forum Moderator
Leader
Admin
I would start with verifying the R&R of your measurement instruments. Are you certain that the fluctuations aren't simply measurement error?
 

kane

Registered
We have been checking our pH probe against certified calibration fluids, so I generally feel good about the measurement reading. I had a technician use a second probe to compare the numbers and they were the same.
 
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