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(S) Redox c e l l performance: Performance i s determined dur1ng charge and d1scharge at several reactant and acid concentrations and operating temperatures. Solution crossm1xing and variation of res1stance with tlme are also monitored. In addition to these routine tests, membrane surface fouling measurements are made on selected samples. In these tests the area reslstiv1ty of each of several membrane samples 1S measured after presoak1ng in Solut10ns con- ta1n1ng various concentratlon ratios of FeC13 to FeC12 1n 2.0 NHC1. Resistances are measured with an ac bridge at 1000 Hz. Data are normal1zed by subtracting the resistance of the cell without a membrane. Addlt10nal 1nformation on screen1ng t e s t s and apparatuses 1nvolved can be found ln references Sand 6. Status. - Results of resistivity flow tests on various membrane formu- lations are presented 1n table 12. Included in this table are preliminary results of new thinner fabric-backed membranes produced durlng the present contract (DEN3-204). In general, O.S Mferr1c 1ron Solut10ns have a m1n1mal effect on membrane "fouling." Large resistance increases occur between 1.0 M and 1.S Mferr1C iron concentrations. Among membranes w1th acceptable select1v1ty, the new standard membrane formulations foul the least at ferric lon concentrat10ns above O.S M. The enhanced conductiv1ty lmparted by 2.0 N HCl is almost balanced by the increased fouling tendency caused by the higher chloride 10n content. Results shown are for samples from each type of vari- ation that was fabricated at Ionics, Inc. Membranes that perform wel~ 1n selectivity and res1st1vity screening tests are run 1n small (14.S cm ) laboratory-size Redox cells. Results of performance data are shown ln f1gure 14. The data are obtained by measuring cell voltage at various current densit1es during charge and discharge. These polarizat10n curves were taken at SO percent depth of discharge. It is 1nterestlng to note that the curves for the new standard membrane 1n 1.5 M solutions lle very close to the curves for the old standard membrane 1n 1.0 M solutions. The vert1cal d1stance between a charge and discharge curve indicates a measure of the cell voltage eff1ciency, and the slope of the discharge curve 1S the membrane resistance if there are no other significant polar1zat1ons or IR losses. The 1mprovement 1n d1scharge current dens1ty at 0.9 V, between the two membranes, in 1.0 Msolutions is about 43 percent. A slm1lar set of data was obta1ned for a cell w1th a new, th1n fabr1c membrane. The results shown in figure lS are compared with those for the new standard membrane. An improvement of about 16 percent 1S 1nd1cated. However, from table 12 it can be seen that the select1vity of the fabric C membrane i s not as good as t h a t of the new standard CD1L-AAS-0.062S. In add1t10n, the fabr1c C membrane has slightly higher area resist1vity ln 1.5 M1ron than does the new standard. Since it w1ll be des1rable 1n the near future to use 2.0 Msolutions (to decrease tank size), the behavior in 1.5 M1ron Solut1ons becomes very important in decldlng Wh1Ch membranes are super1or. Select1v1ty is also a very important criterion. More samples of this thin membrane are being prepared to try to improve selectivity and make the membrane surface more reslstant to fouling. 15PDF Image | NASA Redox Storage System Development Project 1980
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