Anode for oxygen evolution in electrolytes containing fluorides or fluoride-complex anions

DESCRIPTION OF THE INVENTION
In the electrometallurgical field, the use of activated titanium anodes, made of a titanium substrate provided with a suitable electrocatalytic coating, is presently limited to a few specific applications such as chromium plating from conventional baths and gold plating.
The active coating may be alternatively based on:
a) platinum (mainly obtained by galvanic deposition)
b) noble metal oxides (mainly obtained by thermal treatment).
Both coatings are satisfactorily performing in sulphuric acid or similar solutions, provided that no fluorides or fluoride-containing anions are present, as it happens with the chromium deposition from conventional electrolytes, where the anodic lifetime reaches three years or more with electrode potentials 0.5 to 1.5 V lower than those typical of lead anodes. Conversely, they find no industrial application in electrolytes containing fluorides. In fact, even small contents of fluorides, in the range of one part per million (hereinafter ppm), irreversibly de-stabilize the anode (maximum lifetime of a few weeks only). It must be noted that the average concentration in industrial electrolytes may vary from some tens of parts per million (ppm) to some grams per liter (g/l). The destabilization of the anode is substantially due to the corrosion of the titanium substrate caused by the fluorides or fluoride-complex anions which make the titanium oxides soluble.
The complexing action of fluorides and fluoride-containing anions, which takes place according to an increasing order as follows: AlF.sub.6.sup.3-, FeF.sub.6.sup.3-, <SiF.sub.6.sup.2- <BF.sub.4.sup.- <HF.sub.2.sup.- <F.sup.-, is accelerated by acidity and temperature.
The presence of fluorides or fluoride-containing anions is normal in electrolytes of many industrial processes, where they are either added to, with the aim of obtaining particular characteristics of the deposited metal, as well as improving deposition speed and penetrating power, or released by the leached minerals.
It has been found that the use of titanium as a substrate for anodes suitable for electrolytes containing fluorides is possible if titanium is subjected, prior to the application of the electrocatalytic coating, to a pre-treatment comprising applying on its surface an interlayer made of elements or compounds potentially stable under the required operating conditions.
The selection criteria for the interlayer characteristics, (components and percentages) and the coating application or formation methods are reported in Tables 1 and 2.
TABLE 1__________________________________________________________________________Interlayer selection criteria__________________________________________________________________________1. Fluoride-resistant metals, alloys or oxides thereof, e.g. noble metals(Pt, Pd etc.), mixtures or alloys thereof (Pt--Ir, Pt--Pd ,etc.) and tungsten2. Oxides or metals convertible to insoluble fluorides or oxyfluorides,e.g. CeO.sub.2, Cr.sub.2 O.sub.3.3. Oxides resistant to fluorides or convertible to stable fluorides oroxyfluorides, containing definite quantities of noble metals, optionally as mixtures,to enhance electroconductivity.4. Metallo-ceramic compounds, both electroconductive, due to the metal component, and resistant to fluorides, due to the ceramic part, such as chromium - chromium oxide.5. Electroconductive and fluoride-resistant intermetallic compounds, suchas titanium nitride (TiN), titanium nitride (TiN) + titanium carbide(TiC), tungsten silicide, titanium silicide.__________________________________________________________________________
TABLE 2__________________________________________________________________________Method of production of the interlayerType Composition Deposition procedure__________________________________________________________________________Noble Pt 100% Thermal decomposition ofmetals, Pd 100% precursor salts based on chlorineoptionally as Pt--Ir (10-30-50%) complexes soluble in dilutedmixed Pt--Pd aqueous hydrochloric acidoxides or as Pt--Ir 30% Thermal decomposition ofalloys Pt--Pd 70% isomorphous precursor salts such as (NH.sub.4).sub.2 Pt(Ir)Cl.sub.6, (NH.sub.3).sub.2 Pt(Pd)(NO.sub.2).sub.2Oxides Cr.sub.2 O.sub.3 Plasma jet deposition of preformed oxide powderComposite TiO.sub.2 --Ta.sub.2 O.sub.5 --NbO.sub.2 (Molar Thermal decomposition ofoxides ratio: Ti 75, Ta 20, Nb 5); precursor salts based on TiO.sub.2 --Ta.sub.2 O.sub.5 --CeO.sub.2 (Molar chlorometallates soluble in a ratio: Ti 75,Ta 20 ,Ce 5); concentrated hydrochloric solution TiO.sub.2 --Ta.sub.2 O.sub.5 --Cr.sub.2 O.sub.3 (HCl .gtoreq. 10%) ratio: Ti 75, Ta 20, Cr 5)Composite TiO.sub.2 --Ta.sub.2 O.sub.5 --IrO.sub.2 (Molar Thermal decomposition ofoxides with ratio: Ti 75, Ta 20, Ir 5; precursor salts based onlow content Ti 70, Ta 20, Ir 10); TiO.sub.2 -- chlorocomplexes soluble inof noble Ta.sub.2 O.sub.5 --Nb.sub.2 O.sub.5 --IrO.sub.2 aqueous hydrochloric acid (.gtoreq.10%)metal ratio: Ti 70, Ta 20, Nb5, Ir 5)Metallo- Cr (2 microns) - Cr.sub.2 O.sub.3 Galvanic chromium depositionceramic Cr (20 microns) - Cr.sub.2 O.sub.3 from a conventional sulphate bathcompounds and thermal post-oxidation in air (450.degree. C. - 1 hour).Simple TiN Plasma jet deposition from a pre-intermetallic formed powdercompounds TiN Ionic nitridization TiN Nitridization in ammonia (600.degree. C., 3 hours, 10 atm)Composite TiN + TiC Carbo-nitridization from moltenintermetallic saltscompounds__________________________________________________________________________
The invention will be better illustrated by means of some examples wherein samples having the dimensions of 40 mm.times.40 mm.times.2 mm, made of titanium grade 2, have been prepared as follows:
a) Surface pretreatment by sandblasting with aluminum oxide powder+pickling in 20% HCl, 30 minutes;
b) application of the protective interlayer;
application of the electrocatalytic coating for oxygen evolution. The samples have been characterized by means of measurement of the electrochemical potential when used as anodes in electrolytes simulating the same operating conditions as in industrial processes and comparison of the results with reference samples prepared according to the prior art teachings.

EXAMPLE 1
No. 64 reference titanium samples, prepared according to the prior art teachings, dimensions 40 mm.times.40 mm.times.2 mm each, were subjected to a surface pre-treatment following the procedures mentioned above in item a).
Then, 32 samples, identified by A, were directly activated with an electrocatalytic coating made of Ta--Ir (Ir 64% molar and about the same by weight) and 32 samples, identified by B, were provided with an interlayer based on Ti--Ta (Ta 20% molar) and then with an electrocatalytic coating made of Ta--Ir (Ir 64% molar).
The compositions of the paints are reported in the following table:
__________________________________________________________________________Paint characteristics Interlayer Electrocatalytic coating__________________________________________________________________________Component TiCl.sub.3 TaCl.sub.5 HCl (20%) TaCl.sub.5 IrCl.sub.3.3H.sub.2 O HCl (20%)Content - mg/cc 5.33 (Ti) 5.03 (Ta) 50 (Ta) 90 (Ir)as metal__________________________________________________________________________
The composition of the layers is described in the following table:
__________________________________________________________________________Characteristics Stabilizing interlayer Electrocatalytic coating__________________________________________________________________________Components Ta.sub.2 O.sub.5 --TiO.sub.2 Ta.sub.2 O.sub.5 IrO.sub.2% molar as metal 20 80 36 64g/m.sup.2 as metal or noble metal .SIGMA.1.0 10__________________________________________________________________________
The interlayer was applied by brushing the paint. The application was repeated until the desired load was obtained (1.0 g/m.sup.2 total metal). Between one application and the subsequent one the paint is subjected to drying at 150.degree. C., followed by thermal decomposition in oven under forced air circulation at 500.degree. C. for 10-15 minutes and subsequent natural cooling.
On the protective interlayer the electrocatalytic coating is applied, also by brushing or equivalent technique. The application is repeated until the desired final load is obtained (10 g/m.sup.2 as noble metal). Between one application and the subsequent one the paint is subjected to drying at 150.degree. C., followed by thermal decomposition in oven under forced air circulation at 500.degree. C. for 10-15 minutes and subsequent natural cooling.
EXAMPLE 2
16 electrode samples having the same dimensions as those of Example 1 were prepared according to the present invention, applying various interlayers based on mixed oxides belonging to the transition metals and lanthanides. The samples were pre-treated (sandblasting+pickling) as described in Example 1. The samples were prepared according to the following procedure
a) application of the interlayer based on mixed oxides belonging to groups IIIB, IVB, VB, VIB, VIIB and lanthanides, by thermal decomposition of solutions containing the precursor salts of the selected elements.
b) application of the electrocatalytic coating based on tantalum and iridium oxides by thermal decomposition of solutions containing the precursor salts of the selected elements as summarized in Table 2.1
TABLE 2.1__________________________________________________________________________Interlayer Electrocatalytic coatingSample Components ComponentsNo. Type and %(*) g/m.sup.2 (**) Method Type, %(*) Method__________________________________________________________________________2.1 Ti--Ta--Y 1.0 Thermal Ta--Ir (64) thermal de-a, b, (75)-(20)-(5) decomposition compositionc, d from salts from same based on precursor chlorides or salts as in chlorocomplex Example 1 anions2.2 Ti--Ta--Cr 1.0 Thermal Ta--Ir (64)a, b, (75)-(20)-(5) decompositionc, d from salts based on chlorides or chlorocomplex anions2.3 Ti--Ta--Ce 1.0 Thermal Ta--Ir (64)a, b, (75)-(20)-(5) decompositionc, d from salts based on chlorides or chlorocomplex anions2.4 Ti--Ta--Nb 1.0 Thermal Ta--Ir (64)a, b, (75)-(20)-(5) decompositionc, d from salts based on chlorides or chlorocomplex anions2.5 Ti--Ta--Cr-- 1.0 Thermal Ta--Ir (64)a, b, Nb decompositionc, d (70)-(20)-(3)- from salts (7) based on chlorides or chlorocomplex anions__________________________________________________________________________ (*) % molar referred to the elements at the metallic state (**) (g/m.sup.2) total quantity of the metals applied
The paints are described in Table 2.2.
TABLE 2.2______________________________________Description of the paintsInterlayer Electrocatalytic coatingSample % as % asNo. components metal mg/cc components metal mg/cc______________________________________2.1 TaCl.sub.5 20 5.54 TaCl.sub.5 36 50a, b, c, d TiCl.sub.4 75 5.50 IrCl.sub.3 64 90 YCl.sub.3 5 0.68 HCl // 110 HCl // 1102.2 TaCl.sub.5 20 5.54 TaCl.sub.5 36 50a, b, c, d TiCl.sub.4 75 5.50 IrCl.sub.3 64 90 CrO.sub.3 5 0.40 HCl // 110 HCl // 1102.3 TaCl.sub.5 20 5.03 TaCl.sub.5 36 50a, b, c, d TiCl.sub.4 75 5.00 IrCl.sub.3 64 90 CeCl.sub.3 5 0.97 HCl // 110 HCl // 1102.4 TaCl.sub.5 20 5.03 TaCl.sub.5 36 50a, b, c, d TiCl.sub.4 75 5.00 IrCl.sub.3 64 90 NbCl.sub.5 5 0.65 HCl // 110 HCl // 1102.5 TaCl.sub.5 20 5.40 TaCl.sub.5 36 50a, b, c, d TiCl.sub.4 70 5.00 IrCl.sub.3 64 90 CrO.sub.3 3 0.24 HCl // 110 NbCl.sub.5 7 0.97 HCl // 110______________________________________
The method of preparation of the interlayer is described in Table 2.3.
TABLE 2.3__________________________________________________________________________Preparation of the interlayer__________________________________________________________________________ application of the paint containing the precursor salts by brushing orequivalent technique drying at 150.degree. C. and thermal decomposition of the paint at500.degree. C. for 10-15 minutes in oven under forced air circulation and subsequent naturalcooling repeating the application as many times as necessary to obtain thedesired load (1.0 g/m.sup.2).__________________________________________________________________________
The method for applying the electrocatalytic coating was the same as described in Example 1.
The samples thus prepared were subjected to electrochemical characterization as anodes in four types of electrolytes simulating the industrial operating conditions as shown in Table 2.4. For each type of operating conditions a comparison was made using reference samples prepared as described in Example 1.
TABLE 2.4__________________________________________________________________________Electrochemical characterizationSamples Operating conditions SimulatedSeries No. Electrolyte Parameters industrial process__________________________________________________________________________M Present invention H.sub.2 SO.sub.4 150 g/l 500 A/m.sup.2 Secondary zinc from 2.1a.fwdarw.2.5a HF 50 ppm and copper reference samples: 40.degree. C. electrometallurgy A1,B1N Present invention: H.sub.2 SO.sub.4 150 g/l 500 A/m.sup.2 Primary copper from 2.1b.fwdarw.2.5b HF 300 ppm electrometallurgy reference samples: 40.degree. C. A2,B2O Present invention: H.sub.2 SO.sub.4 150 g/l 1000 A/m.sup.2 Chromium plating from 2.1c.fwdarw.2.5c H.sub.2 SiF.sub.6 1000 reference samples: ppm 60.degree. C. A3,B3P Present invention: H.sub.2 SO.sub.4 150 g/l 5000 A/m.sup.2 High speed from 2.1d.fwdarw.2.5d H.sub.2 SiF.sub.6 1500 chromium plating reference samples: ppm 60.degree. C. A4,B4__________________________________________________________________________
The characterization comprised:
detecting the electrode potential as a function of the operating time
detecting the possible noble metal loss at the end of the test
visual inspection.
The results are summarized in Table 2.5.
TABLE 2.5______________________________________Results of the electrochemical characterization Potential V(NHE)Electrolyte Samples initial 100 h 1000 h 3000 h Morphology______________________________________M 2.1a 1.62 1.68 1.80 2.01 No variation 2.2a 1.60 1.70 1.80 1.80 " 2.3a 1.56 1.65 1.70 1.75 " 2.4a 1.58 1.64 1.70 1.69 " 2.5a 1.58 1.65 1.68 1.70 " A1 1.63 2.81 Corrosion B1 1.67 2.61 CorrosionN 2.1b 1.60 1.70 1.90 2.40 Corrosion 2.2b 1.58 1.60 1.85 1.95 No variation 2.3b 1.62 1.65 1.75 1.85 " 2.4b 1.63 1.70 1.83 1.90 " 2.5b 1.61 1.65 1.70 1.75 " A2 1.69 2.81 Corrosion B2 1.67 2.61 CorrosionO 2.1c 1.78 1.84 2.03 >2.6 Corrosion 2.2c 1.75 1.80 1.85 1.90 No variation 2.3c 1.65 1.65 1.75 1.75 " 2.4c 1.60 1.70 1.72 1.80 " 2.5c 1.65 1.64 1.65 1.67 " A3 1.65 3.22 Corrosion B3 1.72 3.47 CorrosionP 2.1d 1.85 1.90 2.15 4.50 Corrosion 2.2d 1.80 1.85 2.00 3.50 " 2.3d 1.78 1.85 1.90 2.20 Initial Corrosion 2.4d 1.75 1.77 1.84 2.00 " 2.5d 1.84 1.85 1.97 2.20 " A4 1.87 >6.0 Corrosion B4 1.92 >4.5 Corrosion______________________________________
The results reported in Table 2.5 point out that the presence of small quantities of metal oxides, which form insoluble compounds in the electrolyte containing fluorides or fluoride-complex anions, increases the lifetime of the electrode of the invention in any operating condition.
EXAMPLE 3
24 samples, same as those of Example 2 with the only exception that the interlayers contained minor amounts of noble metals, after sandblasting and pickling, were prepared according to the following procedure:
a) application of the interlayer based on valve metal oxides containing minor amounts of noble metals, by thermal decomposition of aqueous solutions containing the precursor salts of the selected elements.
b) application of the electrocatalytic coating based on tantalum and iridium oxides applied by thermal decomposition of solutions containing the precursor salts of said elements as summarized in Table 3.1.
TABLE 3.1__________________________________________________________________________Interlayer Electrocatalytic coatingComponents Components g/m.sup.2 Type andSamples No. Type and %(*) (**) Method %(*) Method__________________________________________________________________________3.1 a, b, c, d Ta--Ti--Ir 2.0 thermal Ta--Ir (64%) Thermal (20)-(77.5)-(2.5) decomposition decomposition of precursors in from precursor hydrochloric salt paints, solution same as in Example 132 a, b, c, d Ta--Ti--Ir 2.0 thermal (20)-(75)-(5) decomposition or precursors in hydrochloric solution3.3 a, b, c, d Ta--Ti--Ir 2.0 thermal (20)-(70)-(10) decomposition or precursors in hydrochloric solution3.4 a, b, c, d Ta--Ti--Pd 2.0 thermal (15)-(80)-(5) decomposition or precursors in hydrochloric solution3.5 a, b, c, d Ta--Ti--Ir--Pd 2.0 thermal (20)-(75)-(2.5) decomposition (2.5) or precursors in hydrochloric solution3.6 a, b, c, d Ta--Ti--Nb--Ir 2.0 thermal (20)-(70)-(5)-(5) decomposition or precursors in hydrochloric solution__________________________________________________________________________ (*) % molar referred to the elements at the metallic state (**) (g/m.sup.2) total quantity of the metals applied
The paints are described in Table 3.2.
TABLE 3.2______________________________________12/21 Paint characteristicsInterlayer Electrocatalytic coatingSample % as % asNo. Components metal mg/cc Components metal mg/cc______________________________________3.1 TaCl.sub.5 20 5.30 TaCl.sub.5 36 50a, b, c, d TiCl.sub.4 77.5 5.50 IrCl.sub.3 64 90 IrCl.sub.3 2.5 0.70 HCl // 110 HCl // 1103.2 TaCl.sub.5 20 5.54 TaCl.sub.5 36 50a, b, c, d TiCl.sub.4 75 5.50 IrCl.sub.3 64 90 IrCl.sub.3 5.0 1.47 HCl // 110 HCl // 1103.3 TaCl.sub.5 20 5.94 TaCl.sub.5 36 50a, b, c, d TiCl.sub.4 70 5.50 IrCl.sub.3 64 90 IrCl.sub.3 10.0 3.15 HCl // 110 HCl // 1103.4 TaCl.sub.5 20 3.54 TaCl.sub.5 36 50a, b, c, d TiCl.sub.4 70 5.00 IrCl.sub.3 64 90 PdCl.sub.2 10 0.69 HCl // 110 HCl // 1103.5 TaCl.sub.5 20 5.54 TaCl.sub.5 36 50a, b, c, d TiCl.sub.4 75 5.50 IrCl.sub.3 64 90 IrCl.sub.3 2.5 0.67 HCl // 110 PdCl.sub.2 2.5 0.37 HCl // 1103.6 TaCl.sub.5 20 5.40 TaCl.sub.5 36 50a, b, c, d TiCl.sub.4 70 5.00 IrCl.sub.3 64 90 NbCl.sub.5 5 0.69 HCl // 110 IrCl.sub.3 5 1.43 HCl // 110______________________________________
The method of preparation of the interlayer is described in Table 3.3.
TABLE 3.3__________________________________________________________________________Preparation of the interlayer__________________________________________________________________________ application of the paint containing the precursor salts by brushing orequivalent technique drying at 150.degree. C. and thermal decomposition of the paint at500.degree. C. for 10-15 minutes in oven under forced air circulation and subsequent naturalcooling repeating the application as many times as necessary to obtain thedesired load (2 g/m.sup.2).__________________________________________________________________________
The method for applying the electrocatalytic coating was the same as described in Example 1.
The samples thus prepared were subjected to electrochemical characterization as anodes in four types of electrolytes simulating the industrial operating conditions as shown in Table 3.4. For each type of operating conditions a comparison was made using reference samples prepared as described in Example 1. In particular, in addition to the reference electrodes as described in Example 1, also the best electrode sample of Example 2 (namely sample 2.4) was compared with the present samples.
TABLE 3.4__________________________________________________________________________Electrochemical characterizationSample Operating conditions SimulatedSeries No. Electrolyte Parameters industrial process__________________________________________________________________________M Present invention: H.sub.2 SO.sub.4 150 g/l 500 A/m.sup.2 Secondary zinc and from 3.1a .fwdarw. 3.6a HF 50 ppm 40.degree. C. copper reference samples: electrometallurgy A5, B5, 2.4N Present invention: H.sub.2 SO.sub.4 150 g/l 500 A/m.sup.2 Primary copper from 3.1b .fwdarw. 3.6b HF 300 ppm 40.degree. C. electrometallurgy reference samples: A6, B6, 2.4O Present invention: H.sub.2 SO.sub.4 150 g/l 1000 A/m.sup.2 Conventional from 3.1c .fwdarw. 3.6c H.sub.2 SiF.sub.6 1000 60.degree. C. chromium plating reference samples: ppm A7, B7, 2.4P Present invention: H.sub.2 SO.sub.4 150 g/l 5000 A/m.sup.2 High speed from 3.1d .fwdarw. 3.6d H.sub.2 SiF.sub.6 1500 60.degree. C. chromium plating reference samples: ppm A8, B8, 2.4__________________________________________________________________________
The characterization comprised detecting the electrode potential as a function of the operating time, detecting the possible noble metal loss at the end of the test and visual inspection.
The results are summarized in Table 3.5.
TABLE 3.5______________________________________Results of the electrochemical characterization Potential V(NHE)Electrolyte Samples initial 100 h 1000 h 3000 h Morphology______________________________________M 3.1a 1.60 1.78 1.83 2.12 No variation 3.2a 1.69 1.70 1.72 1.73 " 3.3a 1.60 1.71 1.70 1.70 " 3.4a 1.58 1.65 1.66 1.67 " 3.5a 1.60 1.61 1.64 1.64 " 3.6a 1.64 1.63 1.65 1.70 " 2.4 1.58 1.64 1.70 1.69 " A5 1.63 3.15 Corrosion B5 1.66 2.19 CorrosionN 3.1b 1.64 1.79 1.98 2.35 Corrosion 3.2b 1.63 1.74 1.78 1.79 No variation 3.3b 1.64 1.70 1.75 1.74 " 3.4b 1.62 1.68 1.68 1.72 " 3.5b 1.62 1.64 1.65 1.69 " 3.6b 1.66 1.71 1.75 1.80 " 2.4 1.63 1.70 1.83 1.90 " A6 1.63 2.75 Corrosion B6 1.67 2.31 CorrosionO 3.1c 1.77 1.83 1.97 >2.5 Corrosion 3.2c 1.75 1.75 1.83 1.91 No variation 3.3c 1.76 1.75 1.78 1.82 " 3.4c 1.74 1.75 1.75 1.80 " 3.5c 1.75 1.76 1.75 1.76 " 3.6c 1.81 1.87 1.89 1.91 " 2.4 1.60 1.70 1.72 1.80 " A7 1.68 3.19 Corrosion B7 1.79 2.66 CorrosionP 3.1d 1.86 1.89 2.12 4.6 Corrosion 3.2d 1.81 1.85 1.97 2.9 " 3.3d 1.80 1.82 1.94 2.15 Initial corrosion 3.4d 1.79 1.79 1.87 2.10 " 3.5d 1.78 1.79 1.83 2.06 " 3.6d 1.89 1.95 1.99 2.18 " 2.4 1.75 1.77 1.84 2.00 A8 1.90 >6.0 Corrosion B8 1.92 >5.0 Corrosion______________________________________
The analysis of the results reported in Table 3.5 leads to the conclusion that the presence of noble metals in the interlayer, mainly consisting of transition metal oxides, increases the lifetime of the electrodes of the invention in any type of solutions.
EXAMPLE 4
16 electrode samples having the same dimensions as those of Example 1 were prepared according to the present invention, comprising various metallo-ceramic (cermet) interlayers based on chromium and chromium oxide. The samples were prepared according to the following procedure:
galvanic chromium deposition
controlled oxidation with formation of a protective metallo-ceramic interlayer
subsequent application of the electrocatalytic coating based on tantalum and iridium.
The method of preparation and the characteristics of the samples are described in Table 4.1.
TABLE 4.1______________________________________Interlayer AverageSample thickness Air oxidation ElectrocatalyticNo. Method (micron) (hours) (.degree. C.) coating______________________________________4.1 H.sub.2 SO.sub.4 3.5 1 // // Ta--Ir (64%) bya, b, c, d g/l thermal CrO.sub.3 300 g/l decomposition 65.degree. C. from precursor 1000 A/m.sup.2 salt paints, as in Example 14.2 H.sub.2 SO.sub.4 3.5 1 1/2 400 Ta--Ir (64%) bya, b, c, d g/l thermal CrO.sub.3 300 g/l decomposition 65.degree. C. from precursor 1000 A/m.sup.2 salt paints, as in Example 14.3 H.sub.2 SO.sub.4 3.5 1 1/2 450 Ta--Ir (64%) bya, b, c, d g/l thermal CrO.sub.3 300 g/l decomposition 65.degree. C. from precursor 1000 A/m.sup.2 salt paints, as in Example 14.4 H.sub.2 SO.sub.4 3.5 3 1/2 450 Ta--Ir (64%) bya, b, c, d g/l thermal CrO.sub.3 300 g/l decomposition 65.degree. C. from precursor 1000 A/m.sup.2 salt paints, as in Example 1______________________________________
The samples thus prepared were subjected to anodic electrochemical characterization in four types of electrolytes simulating the industrial operating conditions as shown in Table 4.2. For each type of operating conditions a comparison was made using reference samples prepared according to the prior art teachings as described in Example 1.
TABLE 4.2______________________________________Electrochemical characterization OperatingSeries Sample No. Electrolyte conditions______________________________________M Present invention: from H.sub.2 SO.sub.4 150 g/l 500 A/m.sup.2 4.1a.fwdarw.4.4a, HF 50 ppm 40.degree. C. reference samples: A9, B9N Present invention: from H.sub.2 SO.sub.4 150 g/l 500 A/m.sup.2 4.1b.fwdarw.4.4b, HF 300 ppm 50.degree. C. reference samples: A10, B10O Present invention: from H.sub.2 SO.sub.4 150 g/l 1000 A/m.sup.2 4.1c.fwdarw.4.4c, H.sub.2 SiF.sub.6 1000 ppm 60.degree. C. reference samples: A11. B11P Present invention: from H.sub.2 SO.sub.4 150 g/l 5000 A/m.sup.2 4.1d.fwdarw.4.4d, H.sub.2 SiF.sub.6 1000 ppm 60.degree. C. reference samples A12, B12______________________________________
The characterization comprised detecting the electrode potential as a function of the operating time, detecting the possible noble metal loss at the end of the test and visual inspection.
The results are summarized in Table 4.3.
TABLE 4.3______________________________________Results of the electrochemical characterization Potential (V(NHE)Electrolyte Samples initial 100 h 1000 h 3000 h Morphology______________________________________M 4.1a 1.81 >3.0 Corrosion 4.2a 1.75 1.75 >3.0 Corrosion 4.3a 1.74 1.74 1.75 1.89 No variation 4.4a 1.78 1.76 1.76 1.79 " A9 1.62 2.90 Corrosion B9 1.65 2.31 CorrosionN 4.1b 1.83 >4.0 Corrosion 4.2b 1.77 1.98 >3.6 Corrosion 4.3b 1.75 1.77 1.78 1.89 No variation 4.4b 1.78 1.79 1.82 1.83 " A10 1.63 2.98 Corrosion B10 1.67 2.22 CorrosionO 4.1c 1.89 >5.0 Corrosion 4.2c 1.86 1.86 >2.5 Corrosion 4.3c 1.83 1.84 1.85 1.91 No variation 4.4c 1.82 1.84 1.85 1.86 " A11 1.68 3.12 Corrosion B11 1.75 2.55 CorrosionP 4.1d 1.93 >5.0 Corrosion 4.2d 1.90 1.92 >2.5 Corrosion 4.3d 1.88 1.88 1.89 1.94 No variation 4.4d 1.87 1.87 1.87 1.90 " A12 1.84 >5.5 Corrosion B12 1.89 >4.0 Corrosion______________________________________
The analysis of the results leads to the conclusion that the electrodes of the invention obtained by galvanic deposition and thermal oxidation are more stable than those of the prior art. In particular this stability (corrosion resistance, weight loss and potential with time) increases according to the following order, depending on the type of substrate:
__________________________________________________________________________Cr < Cr + oxidation < Cr + oxidation < Cr + oxidation1 micron 1 micron 400.degree. C. 1 micron 450.degree. C. 3 micron 450.degree. C.__________________________________________________________________________
EXAMPLE 5
12 electrode samples comprising various interlayers based on titanium nitride and having the same dimensions as those of Example 1 were prepared following the same pretreatment procedure described in Example 1. Nitridization was subsequently carried out by in-situ formation of a protective titanium nitride interlayer and the electrocatalytic coating was then applied (Table 5.1). The in situ formation was obtained by the conventional thermal decomposition technique of reactant gases or by ionic gas deposition.
TABLE 5.1______________________________________Method of forming the interlayer and the electrocatalytic coatingInterlayerSample Compo- Thickness ElectrocatalyticNo. sition (micron) Method coating______________________________________5.1a,b,c,d TiN 3-3.1 Plasma jet deposition Ta--Ir (64%), of TiN powder (0.5- Thermal 1.0 micron) decomposition from precursor salt paints, as in Example 15.2a,b,c,d TiN 2.9-3.0 "in situ" formation Ta--Ir (64%), by ionic nitridization: Thermal gas: N.sub.2 decomposition pressure: 3-10 millibar from precursor temperature: 580.degree. C. salt paints, as in Example 15.3a,b,c,d TiN 2.9-3.1 "in situ" formation by Ta--Ir (64%), gas nitridization: Thermal gas: NH.sub.3 decomposition catalyst: palladiate from precursor carbon salt paints, as pressure: 3-4 atm in Example 1 temperature: 580.degree. C.______________________________________
The samples thus prepared were subjected to electrochemical characterizations anodes in four types of electrolytes simulating the industrial operating conditions as shown in Table 5.2. For each type of operating conditions a comparison was made using reference samples prepared according to the prior art teachings as described in Example 1.
TABLE 5.2______________________________________Electrochemical characterization OperatingSeries Sample No. Electrolyte Conditions______________________________________M Present invention: from H.sub.2 SO.sub.4 150 g/l 500 A/m.sup.2 5.1a.fwdarw.5.3a, HF 50 ppm 40.degree. C. reference samples: A13, B13N Present invention: from H.sub.2 SO.sub.4 150 g/l 500 A/m.sup.2 5.1b.fwdarw.5.3b, HF 300 ppm 50.degree. C. reference samples: A14, B14O Present invention: from H.sub.2 SO.sub.4 150 g/l 1000 A/m.sup.2 5.1c.fwdarw.5.3c, H.sub.2 SiF.sub.6 1000 ppm 60.degree. C. reference samples: A15, B15P Present invention: from H.sub.2 SO.sub.4 150 g/l 5000 A/m.sup.2 5.1d.fwdarw.5.3d H.sub.2 SiF.sub.6 1000 ppm 60.degree. C. reference samples: A16, B16______________________________________
The characterization comprised:
detecting the electrode potential as a function of the operating time
detecting the possible noble metal loss at the end of the test
visual inspection.
The results are summarized in Table 5.3.
TABLE 5.3______________________________________Results of the characterization Potential (V(NHE)Electrolyte Samples initial 100 h 1000 h 3000 h morphology______________________________________M 5.1a 1.8 1.81 1.81 1.84 No variation 5.2a 1.78 1.79 1.79 1.81 " 5.3a 1.83 1.84 1.88 1.85 " A13 1.63 3.05 Corrosion B13 1.66 2.44 CorrosionN 5.1b 1.83 1.83 1.86 1.89 No variation 5.2b 1.79 1.82 1.84 1.86 " 5.3b 1.85 1.85 1.91 1.95 " A14 1.62 2.87 Corrosion B14 1.68 2.25 CorrosionO 5.1c 1.87 1.87 1.89 1.93 No variation 5.2c 1.85 1.84 1.85 1.90 " 5.3c 1.91 1.93 1.98 2.08 Initial corrosion A15 1.65 3.23 Corrosion B15 1.73 2.57 CorrosionP 5.1d 1.90 1.91 1.92 1.95 No variation 5.2d 1.88 1.88 1.89 1.90 Initial corrosion 5.3d 1.93 1.98 2.05 2.12 Initial corrosion A16 1.82 >5.5 Corrosion B16 1.92 >4.5 Corrosion______________________________________
The analysis of the results leads to the following conclusions:
the electrodes of the invention are more stable than those of the prior art;
the electrodes with a TiN interlayer obtained both by plasma jet deposition and by ionic nitridization are more stable in all operating conditions;
the electrodes with a TiN interlayer obtained by gas (NH.sub.3) nitridization are stable in those operating conditions where the fluoride content remains below 1000 ppm.
EXAMPLE 6
12 electrode samples comprising various interlayers based on intermetallic compounds comprising titanium nitrides (major component) and titanium carides (minor component) and having the same dimensions as those of Example 1 were prepared following the same pre-treatment procedure described in Example 1. Activation was subsequently carried out by
carbonitridization of the samples by thermal treatment in molten salts (in situ formation of the protective interlayer of titanium nitrides and carbides)
application of the electrocatalytic coating as described in Table. 6.1.
TABLE 6.1______________________________________Method of forming the interlayer and the electrocatalytic coatingInterlayerSample Composition Thickness ElectrocatalyticNo. % by weight (micron) Method coating______________________________________6.1 TiN .ltoreq. 80 0.8-1.5 Immersion in Ta--Ir (64%), bya,b,c,d TiC .gtoreq. 20 molten salts: from precursor NaCN + salt paints as in Na.sub.2 CO.sub.3 + Example 1 Li.sub.2 CO.sub.3 (550.degree. C.) for 30 minutes6.2 TiN .gtoreq. 90 3-3.5 Immersion in Ta--Ir (64%), bya,b,c,d TiC .ltoreq. 10 molten salts: from precursor NaCN + salt paints as in Na.sub.2 CO.sub.3 + Example 1 Li.sub.2 CO.sub.3 (550.degree. C.) for 90 minutes6.3 TiN .gtoreq. 90 5-5.3 Immersion in Ta--Ir (64%), bya,b,c,d TiC .ltoreq. 10 molten salts: from precursor NaCN + salt paints as in Na.sub.2 CO.sub.3 + Example 1 Li.sub.2 CO.sub.3 (550.degree. C.) for 120 minutes______________________________________
The samples thus prepared were subjected to electrochemical characterization as anodes in four types of electrolytes simulating the industrial operating conditions as shown in Table 6.2. For each type of operating conditions a comparison was made using reference samples prepared according to the prior art teachings as described in Example 1.
TABLE 6.2______________________________________Electrochemical characterization OperatingSeries Sample No. Electrolyte conditions______________________________________M Present invention: from H.sub.2 SO.sub.4 150 g/l 500 A/m.sup.2 6.1a.fwdarw.6.3a, HF 50 ppm 40.degree. C. reference samples: A17, B17N Present invention: from H.sub.2 SO.sub.4 150 g/l 500 A/m.sup.2 6.1b.fwdarw.6.3b, HF 300 ppm 50.degree. C. reference samples: A18, B18O Present invention: from H.sub.2 SO.sub.4 150 g/l 1000 A/m.sup.2 6.1c.fwdarw.6.3c, H.sub.2 SiF.sub.6 1000 ppm 60.degree. C. reference samples: A19, B19P Present invention: from H.sub.2 SO.sub.4 150 g/l 5000 A/m.sup.2 6.1d.fwdarw.6.3d, H.sub.2 SiF.sub.6 1000 ppm 60.degree. C. reference samples: A20, B20______________________________________
The characterization comprised:
detecting the electrode potential as a function of the operating time
detecting the possible noble metal loss at the end of the test
visual inspection.
The results are summarized in Table 6.3
TABLE 6.3______________________________________Results of the characterization Potential V/NHEElectrolyte Samples initial 100 h 1000 h 3000 h Morphology______________________________________M 6.1a 1.74 1.80 1.83 1.89 No variation 6.2a 1.80 1.80 1.80 1.85 " 6.3a 1.81 1.80 1.81 1.88 No variation A17 1.66 3.19 Corrosion B17 1.67 2.41 CorrosionN 6.1b 1.80 1.81 1.84 1.88 No variation 6.2b 1.80 1.81 1.81 1.86 " 6.3b 1.81 1.82 1.82 1.82 " A18 1.62 2.95 Corrosion B18 1.66 2.26 CorrosionO 6.1c 1.83 1.89 1.90 1.95 No variation 6.2c 1.83 1.84 1.84 1.91 " 6.3c 1.84 1.85 1.84 1.92 " A19 1.67 3.19 Corrosion B19 1.74 2.61 CorrosionP 6.1d 1.91 1.94 1.97 2.38 No variation 6.2d 1.90 1.91 1.91 1.96 " 6.3d 1.92 1.94 1.93 1.94 " A20 1.84 >6.0 Corrosion B20 1.90 >5.0 Corrosion______________________________________
The analysis of the results leads to the following considerations
all the electrodes of the invention are more stable than those of the prior art;
in particular, the best performance was recorded by the samples prepared with the longest treatment time in the molten salt bath.
EXAMPLE 7
18 electrode samples having the dimensions of 40 mm.times.40 mm.times.2 mm, were prepared applying an interlayer based on tungsten, by plasma jet deposition of a tungsten powder having an average grain size of 0.5-1.5 micron. An electrocatalytic coating was then applied as described in Table 7.1.
TABLE 7.1______________________________________Method of application of the interlayer and electrocatalytic coating Interlayer ThicknessSample No. (micron) Electrocatalytic coating______________________________________7.1a,b,c,d,e,f 15-25 Thermal decomposition of precursor salts of Ta--Ir (64%) as in Example 1.7.2a,b,c,d,e,f 30-40 Thermal decomposition of precursor salts of Ta--Ir (64%) as in Example 1.7.3a,b,c,d,e,f 70-80 Thermal decomposition of precursor salts of Ta--Ir (64%) as in Example 1.______________________________________
The samples thus prepared were subjected to electrochemical characterization as anodes in six types of electrolytes simulating the industrial operating conditions as shown in Table 7.2.
TABLE 7.2______________________________________Electrochemical characterization OperatingSeries Sample No. Electrolyte conditions______________________________________M Present invention: from H.sub.2 SO.sub.4 150 g/l 500 A/m.sup.2 7.1a.fwdarw.7.3a, HF 50 ppm 40.degree. C. reference samples: A21, B21, 2.4 (Example 2).N Present invention: from H.sub.2 SO.sub.4 150 g/l 500 A/m.sup.2 7.1b.fwdarw.7.3b, HF 300 ppm 50.degree. C. reference samples: A22, B22, 2.4 (Example 2).O Present invention: from H.sub.2 SO.sub.4 150 g/l 1000 A/m.sup.2 7.1c.fwdarw.7.3c, H.sub.2 SiF.sub.6 1000 ppm 60.degree. C. reference samples: A23, B23, 2.4 (Example 2).P Present invention: from H.sub.2 SO.sub.4 150 g/l 5000 A/m.sup.2 7.1d.fwdarw.7.3d, H.sub.2 SiF.sub.6 1500 ppm 60.degree. C. reference samples: A24, B24, 2.4 (Example 2).Q Present invention: from H.sub.2 SiF.sub.6 50 g/l 500 A/m.sup.2 7.1e.fwdarw.7.3e, 60.degree. C. reference samples: A25, B25, 2.4 (Example 2).R Present invention: from HBF.sub.4 50 g/l 500 A/m.sup.2 7.1f.fwdarw.7.3f, 60.degree. C. reference samples: A26, B26, 2.4 (Example 2).______________________________________
The characterization comprised:
detecting the electrode potential as a function of the operating time
detecting the possible noble metal loss at the end of the test
visual inspection.
The results are summarized in Table 7.3.
TABLE 7.3______________________________________Results of the electrochemical characterization Potential V(NHE)Electrolyte Samples initial 100 h 1000 h 3000 h Morphology______________________________________M 7.1a 1.7 1.71 1.73 1.78 No variation 7.2a 1.71 1.70 1.70 1.71 " 7.3a 1.68 1.67 1.68 1.68 " A21 1.63 3.05 Corrosion B21 1.66 2.44 Corrosion 2.4 1.58 1.64 1.70 1.69 No variationN 7.1b 1.71 1.72 1.75 1.82 " 7.2b 1.70 1.70 1.69 1.69 " 7.3b 1.67 1.70 1.68 1.68 " A23 1.63 2.89 Corrosion B23 1.67 2.36 Corrosion 2.4 1.63 1.70 1.83 1.90 No variationO 7.1c 1.72 1.74 1.78 1.86 " 7.2c 1.70 1.70 1.72 1.72 " 7.3c 1.70 1.70 1.71 1.69 " A24 1.66 3.47 Corrosion B24 1.76 2.81 Corrosion 2.4 1.63 1.70 1.72 1.80 No variationP 7.1d 1.74 1.76 1.86 1.89 " 7.2d 1.73 1.75 1.75 1.75 " 7.3d 1.73 1.73 1.74 1.74 " A24 1.84 3.05 Corrosion B24 1.94 3.10 Corrosion 2.4 1.75 1.77 1.84 2.00 Initial corrosionQ 7.1e 1.66 1.69 1.83 1.86 Initial corrosion 7.2e 1.68 1.68 1.68 1.67 Initial corrosion 7.3e 1.67 1.69 1.68 1.68 Initial corrosion A25 1.65 >4.0 Initial corrosion B25 1.68 >4.0 Corrosion 2.4 1.70 1.90 2.1 CorrosionR 7.1f 1.65 1.70 1.77 1.79 No variation 7.2f 1.67 1.67 1.68 1.69 " 7.3f 1.65 1.66 1.66 1.66 " A26 1.66 >4.0 Corrosion B26 1.70 >5.0 Corrosion 2.4 1.75 1.95 2.5 Corrosion______________________________________
The analysis of the results lead to the conclusions that all the samples according to the present invention are more stable than those prepared according to the prior art teachings, in particular, the electrodes provided with the tungsten interlayer are stable also in concentrated fluoboric or fluosilicic baths where the samples of the previous examples became corroded.
EXAMPLE 8
36 electrode samples having the dimensions of 40 mm.times.40 mm.times.2 mm, were prepared by applying an interlayer based on suicides, precisely tungsten silicide and titanium silicide, by plasma jet deposition after the same pretreatment as described in Example 1. An electrocatalytic coating was then applied as described in Table 8.1.
TABLE 8.1______________________________________Method of application of the interlayer and electrocatalytic coatingInterlayer Compo- Thickness ElectrocatalyticSample No. sition (micron) Method coating______________________________________8.1a,b,c,d,e,f WSi.sub.2 20-30 Plasma jet Ta--Ir (64%), by deposition of thermal WSi.sub.2 powder decomposition (0.5-1.5 starting from micron) precursor salt paints as in Example 18.2a,b,c,d,e,f WSi.sub.2 40-50 Plasma jet Ta--Ir (64%), by deposition of thermal WSi.sub.2 powder decomposition (0.5-1.5 starting from micron) precursor salt paints as in Example 18.3a,b,c,d,e,f WSi.sub.2 70-80 Plasma jet Ta--Ir (64%), by deposition of thermal WSi.sub.2 powder decomposition (0.5-1.5 starting from micron) precursor salt paints as in Example 18.4a,b,c,d,e,f TiSi.sub.2 20-30 Plasma jet Ta--Ir (64%), by deposition of thermal TiSi.sub.2 (0.5-1.5 decomposition micron) starting from powder precursor salt paints as in Example 18.5a,b,c,d,e,f TiSi.sub.2 40-50 Plasma jet Ta--Ir (64%), by deposition of thermal TiSi.sub.2 (0.5-1.5 decomposition micron) starting from powder precursor salt paints as in Example 18.6a,b,c,d,e,f TiSi.sub.2 70-80 Plasma jet Ta--Ir (64%), by deposition of thermal TiSi.sub.2 (0.5-1.5 decomposition micron) starting from powder precursor salt paints as in Example 1______________________________________
The samples thus prepared were subjected to electrochemical characterization as anodes in six types of electrolytes simulating industrial operating conditions as shown in Table 8.2. For each type of operating conditions a comparison was made with some reference samples prepared according to the prior art teachings as described in Example 1 and a sample of Example 2 of the invention (sample 2.4).
TABLE 8.2______________________________________Electrochemical characterization OperatingSeries Sample No. Electrolyte Conditions______________________________________M 8.1a.fwdarw.8.3a, H.sub.2 SO.sub.4 150 g/l 500 A/m.sup.2 reference samples: HF 50 ppm 40.degree. C. A27, B27, 2.4 (Example 2)N 8.1b.fwdarw.8.3b, H.sub.2 SO.sub.4 150 g/l 500 A/m.sup.2 reference samples: HF 300 ppm 50.degree. C. A28, B28, 2.4 (Example 2)O 8.1c.fwdarw.8.3c, H.sub.2 SO.sub.4 150 g/l 1000 A/m.sup.2 reference samples: H.sub.2 SiF.sub.6 1000 ppm 60.degree. C. A29, B29, 2.4 (Example 2)P 8.1d.fwdarw.8.3d, H.sub.2 SO.sub.4 150 g/l 5000 A/m.sup.2 reference samples: H.sub.2 SiF.sub.6 1500 ppm 60.degree. C. A30, B30, 2.4 (Example 2)Q Present invention: from H.sub.2 SiF.sub.6 50 g/l 500 A/m.sup.2 8.1e.fwdarw.8.3e, 60.degree. C. reference samples: A31, B31, 2.4 (Example 2)R 8.1f.fwdarw.8.3f, HBF.sub.4 50 g/l 500 A/m.sup.2 reference samples: 60.degree. C. A32, B32, 2.4 (Example 2)______________________________________
The characterization comprised:
detecting the electrode potential as a function of the operating time
detecting the possible noble metal loss at the end of the test
visual inspection.
The results are summarized in Table 8.3.
TABLE 8.3______________________________________Results of the electrochemical characterization Potential V(NHE)Electrolyte Samples initial 100 h 1000 h 3000 h Morphology______________________________________M 8.1a 1.74 1.74 1.78 1.81 No variation 8.2a 1.72 1.73 1.75 1.75 No variation 8.3a 1.70 1.71 1.71 1.72 No variation 8.4a 1.75 1.75 1.80 1.84 No variation 8.5a 1.74 1.74 1.77 1.77 No variation 8.6a 1.69 1.71 1.70 1.73 No variation A27 1.63 3.05 Corrosion B27 1.69 2.44 Corrosion 2.4 1.58 1.64 1.70 1.69 No variationN 8.1b 1.72 1.76 1.77 1.82 No variation 8.2b 1.71 1.71 1.71 1.74 No variation 8.3b 1.70 1.71 1.72 1.72 No variation 8.4b 1.77 1.78 1.77 1.90 No variation 8.5b 1.72 1.73 1.73 1.73 No variation 8.6b 1.73 1.72 1.70 1.72 No variation A28 1.62 2.89 Corrosion B28 1.71 2.36 Corrosion 2.4 1.63 1.70 1.83 1.90 No variationO 8.1c 1.75 1.75 1.79 1.84 No variation 8.2c 1.70 1.70 1.75 1.75 No variation 8.3c 1.70 1.73 1.73 1.74 No variation 8.4c 1.76 1.81 1.82 1.86 No variation 8.5c 1.72 1.76 1.77 1.79 No variation 8.6c 1.72 1.75 1.76 1.77 No variation A29 1.67 3.47 Corrosion B29 1.76 2.81 Corrosion 2.4 1.63 1.70 1.72 1.80 No variationP 8.1d 1.75 1.76 1.79 1.90 No variation 8.2d 1.74 1.74 1.76 1.77 No variation 8.3d 1.75 1.75 1.75 1.78 No variation 8.4d 1.76 1.77 1.78 1.88 No variation 8.5d 1.74 1.76 1.75 1.77 No variation 8.6d 1.76 1.77 1.77 1.79 No variation A30 1.84 3.05 Corrosion B30 1.94 3.10 Corrosion 2.4 1.75 1.77 1.84 2.00 Initial corrosionQ 8.1e 1.68 1.68 1.75 1.84 No variation 8.2e 1.67 1.67 1.71 1.74 No variation 8.3e 1.65 1.70 1.70 1.70 No variation 8.4e 1.66 1.66 1.74 1.89 No variation 8.5e 1.71 1.70 1.73 1.76 No variation 8.6e 1.73 1.72 1.73 1.78 No variation A31 1.64 >2.0 No variation B31 1.68 >4.0 Corrosion 2.4 1.70 1.90 2.1 Corrosion (Ex. 2)R 8.1f 1.66 1.67 1.68 1.92 No variation 8.2f 1.67 1.67 1.71 1.73 No variation 8.3f 1.70 1.72 1.72 1.73 No variation 8.4f 1.70 1.72 1.78 1.89 No variation 8.5f 1.74 1.74 1.73 1.73 No variation 8.6f 1.70 1.70 1.72 1.75 No variation A32 1.66 >4.0 Corrosion B32 1.70 >5.0 Corrosion 2.4 1.75 1.95 2.5 Corrosion (Ex. 2)______________________________________
The analysis of the results lead to the following conclusions:
all the samples according to the present invention are more stable than those prepared according to the prior art teachings;
in particular, the electrodes provided with the titanium or tungsten silicide interlayer are stable also in concentrated fluoboric or fluosilicic baths wherein the samples of the previous example 2 became corroded.
The above discussion clearly illustrates the distinctive features of the present invention and some preferred embodiments of the same. However, further modifications are possible without departing from the scope of the invention, which is limited only by the following appended claims.

Number	Name	Date
4765879	Matsumoto et al.	Aug 1988
4956068	Nguyen et al.	Sep 1990
5435896	Hardee et al.	Jul 1995

Anode for oxygen evolution in electrolytes containing fluorides or fluoride-complex anions

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (1)

US Referenced Citations (3)