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this study was intended only as an lnitlal lnvestigatlon to determine if a thorough market penetration study was warranted. As such, this study was based on several arbitrary assumptlons and was limited ln scope. ELEMENT 4 . 0 - SUPPORTING TECHNOLOGY Membrane Development Background Membranes used in Redox flow cells consist of ion-exchange resins that are fabricated lnto thln sheets relnforced by a thin layer of woven fabrlc. The resin, at present, is a copolymer of vinylbenzyl chlorlde and dimethyl- aminoethyl methacrylate, WhlCh form the crosslink and backbone components, respectively. The followlng parameters determine the properties of ion- exchange membranes: (1) Backbone monomer type (2) Crossllnk monomer density and type (3) Fract10n of nonpolymerizable material (NP content) in the membrane precursor (4) Amount of polymerizlng catalyst (catalyst level) (5) Total membrane thickness (different substrate backing or backing processing) (6) Amount of functional1ty (add1tion of funct10nal groups and sltes to polymer structure) By incorporat1ng varlat10ns into these parameters, a w1de selection of mem- brane characterlst1cs 1S poss1ble. The membranes are given an ion-exchange character to take advantage of Donnan exclus10n and to prohibit cations from passlng through the membrane by having cat10n charge sltes lncorporated into its structure. The more numerous these sites, the more selective the mem- brane would be. To further exclude cat10n passage, the effective pore size must be as small as pos1ble, yet not hinder the passage of anions. (Because of the very small Slze of the hydrogen ion, it 1S 1mposs1ble to prevent its passage through the membrane.) Amembrane's success in excluding cation passage 1S referred to as 1tS "selectlvity." The selectiv1ty and the con- duct1Vity of a membrane are of great importance. Consequently efforts to optim1ze the membrane are evaluated by measur1ng both factors. The dens1ty of charge sltes that are incorporated within the membrane structure is measured 1n terms of its lon-exchange capac1ty (IEC) in milli- equivalents per dry gram of mater1al (meq/dry g). In more recent membranes only a very th1n layer of resin is required to accompl1sh the exclusion of ions, allowing a reduct10n 1n substrate th1ckness and a slight reduct10n in res1stance to anion passage. The membrane eng1neer1ng that 1S applied to adJust pore Slze 1S not well understood but is affected by polymerization cond1t1ons, 1ncluding such th1ngs as the solvent used and the NP content. Contained 1n the following sections are hlghllghts of contract work performed, results of contract and 1n-house testing programs, and concluslons to be drawn from these evalut1ons. 13PDF Image | NASA Redox Storage System Development Project 1980
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