Determination of effects of sulphation on lead-acid batteries

[isaaclimdc]

Hi all,

I'm doing this project entitled "determining the effects of Sulphation on lead-acid batteries", and what it essentially is, is the reason why these batteries lose their effectiveness after being left in a discharged state for a period of time. What happens is lead sulphate is formed from the discharge redox reactions of the lead electrodes in sulphuric acid electrolyte. This lead sulphate crystallises after awhile, and is very insoluble and a nonconductor. These crystallise around the electrodes, hence hindering the flow of electricity.

For my experiment, I have a cell up and running, and I need to find a way to determine whether or not lead sulphate crystallises, and use the "Nernst Equation" to calculate the actual voltage. Can this be done by determining the concentration (by standardisation with borax) of the sulphuric acid before and after the cell activity, and say that if a decrease in concentration is observed, then this amount of sulphate ions were converted to lead sulphate?

Sorry for the long explanation, but this is a really important project for me, so any help is much appreciated.

Thank you,
Isaac.

 

[Borek]

Determining acid concentration should be more or less enough. Depending on the accuracy you may either use titration or just check acid density with hydrometer. As checking battery charge level is (or at least was) quite popular thing to do there were hydrometers already scaled in the sulfuric acid concentration.

 

[isaaclimdc]

Does the design of my experiment sound feasible to you? It was all made up in my head without expert help, so I was wondering whether everything is valid?

 

[Borek]

This is more complicated. PbSO₄ is always present in the battery and its presence is absolutely normal. However, usually it is in amorphous form, which can be easily dissolved. Sulfation refers to the process of crystallization - where amorphous lead sulfate is converted into crystalline lead sulfate. Just measuring amount of sulfuric acid you will be not able to tell what kind of sulfate is present on the electrodes. If you will compare concentration of sulfuric acid in fully charged batteries (otherwise identical, but one already broken) you will see the difference in acid concentration - but you will be not able to tell "why". That requires some crystallographic method.

 

[isaaclimdc]

Thanks for your replies. I understand what you're saying. However now, is there an alternative way for me to show the effects of sulphation in this manner, without the use of complex analytic methods? My teacher suggested the use of nitric acid. How does this work?

 

[Borek]

No idea what s/he aims at. Perhaps determination of just lead left?

 

[isaaclimdc]

Is there really no way else around this.. I really need this experiment to work..

 

[Borek]

Could be that "simple" comparison of electrodes from the new and dead battery will work. Just charge the battery and compare the surface. You may try microscope. You may try to scratch some precipitate that covers electrode and analyse it.

 

[chemisttree]

What color is your fresh electrode? It should be red. What color is lead sulfate?