AOliveira Posted May 2, 2011 Share Posted May 2, 2011 HI, i am having problems with some calculations in react, I am making a pH sliding of Zn++, i put the calculations with charge balance of Cl- and without charge balance. I get error for the charge balance, and the calculations stop for the pH of ~8.5 "Caution: molality of Cl- component forced negative by charge balance: -2.782e-007 *N-R didn't converge after 400 its., maximum residual = 4.83e+121, Xi = 0.5800 Cutting step size to find solution Residuals too large, 662-th interation -- Didn't wake up, abandoning path" For the sliding without the balance using react and even SpecE8 it can't compute from pH ~12.5 to ~13.8 but can compute for pH of 14. Why is that? I also find out that if i change the delxi from 0.01 to 0.001, making more dots the programs crushs and stops the compute arouth pH ~3.5 - ~6. Why is that? shouldn't it calculate the same for all? with_CB.rea without_CB.rea Quote Link to comment Share on other sites More sharing options...
Tom Meuzelaar Posted May 2, 2011 Share Posted May 2, 2011 Hi: Please attach the script you are working with, and I'd be happy to take a look. Regards, Tom Meuzelaar RockWare, Inc. Quote Link to comment Share on other sites More sharing options...
AOliveira Posted May 2, 2011 Author Share Posted May 2, 2011 They are here! with_CB.rea without_CB.rea Quote Link to comment Share on other sites More sharing options...
Tom Meuzelaar Posted May 9, 2011 Share Posted May 9, 2011 Hi: Apologies for the delay. In your first script, as the error message indicates, you run out of Cl- for charge balance, and it is forced to negative concentrations. You can remedy this by either beginning with a higher anion concentration, or better yet, consider a base titration (NaOH for example), rather than a pH slide, as this avoids negative concentration issues. Unless this is a pure solution, it's a good idea to have some background electrolytes (Na, Cl). The issue with the smaller reaction path steps occurs right when Zincite reaches saturation- you are essentially removing 1/10th the proton mass at each step, and this creates an unstable matrix when Zincite becomes supersaturated and React attempts to swap it in for the Zn++ matrix component. I'm not sure exactly why this happens, but this model is being run with a large charge imbalance- I recommend fixing the first model, with charge balance, as this should result in a model that is more stable overall. The same goes for the non-convergence issue at high pH. I hope that helps, Tom Meuzelaar RockWare, Inc. RockWare, Inc. Quote Link to comment Share on other sites More sharing options...
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