DSA

Ruthenium will be dissolved by oxygen evolution (volatile RUO4). Coatings based on iridium/tantalum oxides are stabile for oxygen evolving anodes, even with simultaneous chlorine evolution in the presence of chlorides. 

The application of a DSA for electroorganic oxidations [39] may possibly be disturbed because of corrosion of the active layer and/or the titanium carrier by organic reactants and products. If significant advantages using a DSA are expected, stabihty tests of the DSA under the special conditions have to be performed. 

Analogous to the DSA manufacture, a pure htanium dioxide coating can be prepared, which shows a high activity and stabihty (also against titanium hydride formation), for electroorganic cathodic reductions (e.g. [40], see Chapter 7). 

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Figure 25 shows the results of the 2 distortion induced by a degenerate e 2 vibration that removes the Dsa degeneracy (compare Fig. 23). By symmetry, five...

Fig. 9. Dow diaphragm cell, section view a, perforated steel back plate b, cathode pocket c, asbestos diaphragm d, DSA anode e, copper back plate f,...

Data, for a 32% caustic concentration at 90°C and a current efficiency of 96.0%, obtained in laboratory cells using a DSA anode and an activated cathode, where the membrane is against the anode at a 3-mm gap. 

Fig. 16. Performance data obtained ia laboratory cells using Nafion NX-961, DSA anode, activated cathode, narrow gap, at 90°C. Energy consumption is...

Success in the chlorine industry led to the incorporation of DSA in sodium chlorate [7775-09-9] NaClO, manufacture. The unique stmctural characteristics of the anode allowed for innovative designs in ceU hardware, which in turn contributed to the extensive worldwide expansion of the sodium chlorate industry in the 1980s. 

Several more traditional materials have found specific though limited commercial apphcation as metal anodes. Examples are lead [7439-92-1] and ziac [7440-66-6] ia the electrogalvaniziag practice. Lead dioxide [1309-60-0] and manganese dioxide [1313-13-9] anode technologies have also been pursued. Two iadustrial electrolytic iadustries, aluminum [7429-90-5] and electric arc steel, stiU use graphite anodes. Heavy investment has been devoted to research and development to bring the advantages of DSA to these operations, but commercialization has not been achieved. 

DSA, lead, platinized titanium platinized titanium or niobium... 

Fig. 1. Scanning electron microscope photograph of DSA mthenium oxide coating, showing typical cracked surface.

Platinum—Iridium. There are two distinct forms of 70/30 wt % platinum—iridium coatings. The first, prepared as prescribed in British patents (3—5), consists of platinum and iridium metal. X-ray diffraction shows shifted Pt peaks and no oxide species. The iridium [7439-88-5] is thus present in its metallic form, either as a separate phase or as a platinum—iridium intermetallic. The surface morphology of a platinum—iridium metal coating shown in Figure 2 is cracked, but not in the regular networked pattern typical of the DSA oxide materials. 

The most common oxidation states and the corresponding electronic configuration of mthenium are +2 and +3 (t5 ). Compounds are usually octahedral. Compounds in oxidations states from —2 and 0 (t5 ) to +8 have various coordination geometries. Important appHcations of mthenium compounds include oxidation of organic compounds and use in dimensionally stable anodes (DSA). 

Miscellaneous. Iridium dioxide, like RUO2, is useful as an electrode material for dimensionally stable anodes (DSA) (189). SoHd-state pH sensors employing Ir02 electrode material are considered promising for measuring pH of geochemical fluids in nuclear waste repository sites (190). Thin films (qv) ofIr02 ate stable electrochromic materials (191). 

Anode Applications. Graphite has been used as the primary material for electrolysis of brine (aqueous) and fused-salt electrolytes, both as anode and cathode. Technological advances, however, have resulted in a dimensionally stable anode (DSA) consisting of precious metal oxides deposited on a titanium substrate that has replaced graphite as the primary anode (38—41) (see Alkali and chlorine products). 

Diaphrag m Cell Technology. Diaphragm cells feature a porous diaphragm that separates anode and cathode compartments of the cell. Diaphragms should provide resistance to Hquid flow, requite minimum space between anode and cathode, produce minimum electrical resistance, and be durable. At the anode, which is generally a DSA, chloride ions are oxidized to chlorine (see eq. 1) and at the cathode, which is usually a woven steel wine mesh, water is reduced to hydrogen. 

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