Patent GB-1391625-A (GB)
Title: Electrolysis of aqueous alkali metal chloride solution
Inventor: ANTHONY PAUL P
IPC: C25B11/06
Filed: 1972-03-07
Abstract: 1391625 Anode metal chloride electrolysis PPG INDUSTRIES Inc 7 March 1972 [8 March 1971] 10559/72 Heading C1A [Also in Division C7] An anode, used in the electrolysis of aqueous alkali metal chloride solution, comprises an electroconductive perovskite "bronze" oxide selected from the tantalates, tungstates, molybdates, niobates, titanates, vanadates, iron (III) compounds and chromium III compounds. The term "bronze" signifies a non- stoichiometric compound. The perovskite bronze oxide may have the formula C x DO y  where DO y  represents any of the groups mentioned above, C represents Na, K, Ba, Sr, Ca, Mg, Be, Cu, Ag, Au, Ge, Sn, Pb, Tl, or any of the lanthanides,  x  is between 0À00 and 1À00 and y is from 2À25 to 3À00. Mixed perovskite bronze oxides may also be used such as Sr x8  La x2  WO 3  where x 1  + x 2  totals between 0À00 and 1À00. The perovskite bronze may be disposed on an electroconductive substrate such as Ti, Ta, W, Hf, Zr, Al, Nb, C, graphite, titanium hydride or steel clad with Ti. The substrate may be an imperforate plate of a foraminous mesh. The perovskite bronze may include an inorganic binder to make it adhere to the substrate. Suitable binders are a glass frit; an oxide, sulphide, nitride, boride or carbide of Ti, Ta, Nb, Al, Bi, W, Zr, Hf, V, Cr or Si. There may be an intermediate layer between the substrate and the perovskite bronze which is more reistant to oxidation and more electroconductive than the substrate. The inter-layer may be selected from Pt group metals, their oxides and sulphides; mixtures of Pt group metals and their oxides; an alloy of the metal used in fabricating the substrate with a Pt group metal; alloys of Pt, Ir or Os with Cr, Ni or Co; Pt group metals mixed with oxides of Ti, Si, W, Cr, Ni, Co, or V; calcium ruthenate; Ti hydride or Zr hydride; metallic Ni, Co or Cr. In the examples, the perovskite bronzes are applied to an etched Ti substrate with an inter-layer (except for Example II) of a Pt group metal or an oxide thereof. In Examples I, II and IV to VII the perovskite bronze is La x WO 3  where x is from 0À05 to 0À20. This is prepared by heating ground lanthanum oxide, WO 3  and metallic W in an evacuated sealed silica capsule to 1050‹ C. for 120 hours. The product is formed into a slurry with toluene and Ti resinate, brushed on to platinised Ti and heated. In Example III, SrNb perovskite bronze is prepared by grinding a mixture of strontium oxide, NbO 2  and Nb 2 O 5 , compressing the resulting powders into pellets, sealing them in an evacuated silica capsule and heating to 1200‹ C. for 48 hours. The product is formed into a slurry with toluene and Ti resinate brushed on to platinized Ti and heated. In Examples I, III and IV the inter-layer is prepared by heating Pt resinate. The interlayer is prepared by electrolysis in the following examples as indicated: V, deposition of Pd from an aqueous solution of PdCl 2 , NH 4 Cl and HCl with subsequent heating in air to form Pd oxide; VI, deposition of Pd from an aqueous solution of PdCl 2  and KOH with subsequent oxidizing of the Pd; and VII; deposition of Ru from an aqueous solution of ruthenium nitroso chloride and H 2 SO 4 . In each example, NaCl solution is electrolysed to produce NaOH, in a cell having an iron screen cathode with a diaphragm thereon. Electrolysis of brine using a mercury cell is referred to.