DE2546937A1 - ELECTRODE FOR ELECTRIC CORROSION PROTECTION AND PROCEDURES FOR ITS USE - Google Patents

Description

DR. BERG DIPL.-ING. STAPF

PATENTANWÄLTE 8 MÜNCHEN 86, POSTFACH 860245

Dr. Berg Dipl.-Ing. Stapf, 8 Munich 86, P. O. Box 86 0245

Our symbol 8 MONKS 80? Π Π KT

Our ref. Mauerkircherstraße 45 *. U · U l \ I.

Attorney file 26 451
Be / Ro

TDK Electronics Co., Ltd, Tokyo, Japan

"Electrode for electrical corrosion protection and methods for its use"

It is generally known that a metal vessel such as an iron kettle water with electrolyte dissolved therein, "for example, seawater contains gradually corroded, and that the corrosion of such a boiler to ver-FPA-1689 6 033 20/1116 ~ ² ~

Avoid using an electrical device called "electrical corrosion protection". The electric Corrosion prevention is also referred to as "cathodic protection". In such electrical corrosion prevention, the metal kettle is used as the cathode and a carbon, magnetite or platinum-coated titanium electrode as an anode and applies a DC voltage to the electrodes. In this case an electrode 'Which is used as an anode, have good corrosion resistance. Furthermore it is required to the corrosion of the "iron boiler for heating water" or the "iron water heater" by means of the cathode - Protective procedures to prevent an electrode that is designated as a Anode is used, have both good thermal shock resistance and good corrosion resistance must because the heating and cooling are repeated in the water heater.

It was found that the carbon electrode had poor corrosion resistance and the magnetite electrode characterized by a low _ corrosion resistance and low thermal shock resistance: Lt is. The platinum-coated titanium electrode is admittedly with respect to excellent in their electrical conductivity and thermal shock resistance, but has only a low level Resistance to pulsating or undulating currents «,

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The present invention relates to an electrode excellent in thermal shock resistance, corrosion resistance and, furthermore, lower in electrical power Resistance.

The present invention relates to an electrode for electrical Corrosion protection as well as a method for electrical Corrosion prevention using the electrode.

The electrode of the present invention comprises a sintered body of a mixture of iron oxide of 90 Ms 55 mol%, "calculated as" Pe ₂ O, and a metal oxide of 10 to 45 mol%, calculated as MO (where M is at least one Metal of the group Mn, Ni, Co, Mg, Cu and / or Zn is The sintered body is a solid solution of 15.7 to 87.1 mol $ MPepO * (where M has the meaning defined above) and 84.3 to 12.9 mol # Pe ₅ O _4. In the sintered body, the iron atoms are present in both "ferric" and ferrous porms. Accordingly, the term "calculated as" means that "all in the iron oxides present in the sintered body in the form of Pe ₂ O, "are calculated or stated.

Electrodes of the present invention can be made, for example, as follows: Iron (II) oxide (Pe ₂ O ₅ ) and a metal oxide (MnO, NiO, CoO, CuO, MgO or ZnO) are made in the ratio of 90 to 55 M0I96

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mixed at 10 to 45 Mo1 $ in a ball mill. The mixture is heated for about 1 to about 15 hours in air, nitrogen or carbon dioxide at a temperature of about 700 to about 1000 ^° C. Hydrogen can be present in the nitrogen gas in an amount up to about 10%. After cooling, the heated mixture is pulverized to form a fine powder. The fine powder is molded into a molded body, for example, by compression molding or extrusion. The molded body is heated at a temperature of about 1100 ⁰ C to about 145 ° ⁰ C in nitrogen or carbon dioxide, which may contain up to about 20 oxygen, from about 1 to about 4 hours "the heated body is cooled slowly in nitrogen or carbon dioxide containing up to about 5 Yolfo of oxygen, abo The desired sintered body, ie, an electrode of the present invention, is thus obtained. The electrodes produced in this way have a relatively low resistance, good corrosion and thermal shock resistance.

Instead of Fe ₂ O, ferrous metal or FeO can also be used. Instead of the metal oxide, compounds of the metals which produce metal oxides, for example metal carbonate or oxalate, when heated can be used «

The following examples serve exclusively to illustrate the invention.

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example 1

As shown in Table 1.1, ¥ eJD ^ and NiO were weighed out in the appropriate amounts to prepare Samples 1-6, which _{contain various molar percentages of Fe 2} O. and NiO.

(Mon 196) Table 1 .1 NOK
(*) sample
No. 95: 5 Pe ₂ O ₃
f Ö * /
ν FS / 4.82 1 90:10 195.18 9.88 2 90; 20th 190.12 20.94 3 70:30 179.06 33.40 4th 60:40 166.60 47.54 5 55 J 45 152.46 55.36 6th 144.64

In each case, Pe ₂ O ₅ and NiO were mixed in a ball mill for 20 hours. The mixtures were then preheated at a temperature of 800 ° C. for about 3 hours and then cooled. The obtained mixtures were pulverized using a ball mill to form powders having a particle size of less than 20 µm. The powders were compression-molded with a pressure of about 1 to / cm to form molded bodies with a size of 110 × 15 × 15 mm. The formed bodies were heated for 5 hours at a temperature of 1440 ⁰ O in nitrogen gas and then slowly in nitrogen gas

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cooled for 10 hours to form desired sintered bodies, i.e., electrodes.

The electrical resistance of the obtained sintered bodies (Electrode Nos. 1-6) was measured by the four-contact method. The values obtained are given in Table 1.2. The corrosion resistance of each sintered body (i.e. _, the anodes) was evaluated by measuring the weight loss of each anode in the electrolysis of standard seawater under the following conditions.

The values obtained are given as "Corrosion Loss" in Table 1.2.

Conditions of electrolysis

Anode area 0.25 dm ²

Cathode platinum mesh 100 200 χ 1.0 mm

Distance between the electrodes 5 cm

Voltage (direct current) 5 Amp / dm

Solution temperature 50 C + 1

Electrolysis duration 4 hours

The thermal shock resistance of each sintered body, i.e. the anodes, was evaluated by taking the number the repetitions of "heating" and "cooling" as follows:

The sintered body is immersed in hot water at a temperature of 98 ^° C. for 3 minutes and then in cold water

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immersed at a temperature of 5 ° C for 5 minutes. This "Heating" and "Cooling", hereinafter referred to as a heating cycle and cooling "is repeated until the sintered Body breaks. The number of repetitions obtained are given in Table 1.2,

resistance
{SI * cm) Table 1.2 Number of again
recoveries of
heating and cooling sample
No. 0.01 Corrosion loss
(mg / am ² ) 165 1 0.01 6.10 205 2 0.05 2.70 225 5 0.05 1.55 250 4th 0.10 1.55 240 VJl 0.50 1.55 250 6th 1.55

From the above results it can be seen that the
Sample 1 has low resistance but is inferior in corrosion resistance and thermal shock resistance.

In Fig. 1 of the accompanying drawings, curves A and B respectively show the change in resistance and corrosion loss with changes in the relative molar percentages of ^ e ₂ O ₅ and ITiO.

Example 2

As can be seen in Table 2.1, Fe ₂ O ,, MnO,

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CoO, MgO, CuO, ZnO and NiO each weighed to obtain Samples 7-15, which contain various molar percentages of Fe ₂ O ,, MnO, CoO, MgO, CuO, ZnO and NiO,

Table 2.1

Sample Fe ₉ O, MnO CoO MgO CuO ZnO NiO No. _M r _fl / - ^> Mo 1 $ Mol $ Mol $ Mo 1 $ Mo 1 $ Mo 1 $ ^M fg ° (g) (g) (g) (g) (g) (g)

7 90 10
(19O, 59) (9.41)

8 90 10
(190.09) (9.91)

9 90 10 (194.54) (5.46)

10 90 10 (189.51) (10.49)

11 90 10 (189.28) (10.72)

12 60 40
(152.34) (47.66)

13 60 10 15 15 (151.66). (11.23) (17.79) (19.32)

14 _M 60 _9Q n 20 20 ^{(15Ύ '29)} (25.12) (23.59)

15 60 10 10 20 (152.32) (11.28) (12.64) (23.75)

The sintered bodies (electrodes 7-15) were obtained by the same procedure as in Example 1 except for that the "preheating" and the "heating" were carried out according to the conditions given in Table 2.2.

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Tabel

Sample Preheat No. Temperature Atmosphere ⁰ C

Time (hours)

Heating temperature ( ⁶ C)

800

800

800

800

N _2, with the common ^, just $ 3 H ₂

N ₂ , with the salary of $ 7 H ₀

Np, with the salary of $ 7 H ₂

N ₂ , with the salary of $ 3 H ₀

800 N ₂ , with to the Ge VJl stop by 7 ⁰ I. i H ₂ 800 air 3 800 air 3 800 air 3 800 air 3

1250 1250

1250 1200 1250

1300 1250 1200 1200

The electrical resistance, the value of the corrosion resistance and the number of WM-repetitions of "heating" and cooling "of the sintered bodies (Electrode Nos. 7 to 15) is shown in Table 2.3.

resistance
(Jl -cm) Table 2.3 Number of again
fetches of the he
heating and cooling sample
No. 0.008 Corrosion loss
(mg / dm ² ) 205 7th 0.007 1.20 252 8th 0.020 1.15 213 9 0.010 1.25 231 10 1.20

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Continued table 2.3

Sample resistance Corrosion loss No. (Jl cm) (mg / dm ² )

Number of repetitions of heating and cooling

0.009 0.250

0.330 0.450 0.470

1.20 1.00

1.20 1.20 1.25

207

245 273 298 243

From the above results it can be seen that electrodes for use in cathodic protection with low electrical resistance, high corrosion resistance and high thermal shock resistance are made from a sintered body of a mixture of iron oxide of 90 to 55 Mo 1 $ ιέ, calculated as Fe ₂ O, and metal oxide of 10 to 45 Mo 1 $, calculated as MO, wherein M is at least one metal from the group Mn, Hi, Go, Mg, Cu and / or Zn can be obtained.

Further investigations were carried out as follows: The electrodes 2-6 with dimensions of 120 χ 10 mm were prepared by repeating the procedures of Example 1 with Samples 2-6 and becoming the thermal shock resistance of electrodes 2-6 and corrosion tests of electrode 2 are carried out as follows:

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1. Thermal shock analysis:

The electrodes 2-6 were immersed in an iron kettle equipped with an electric heater. Cold water was poured into the kettle at a temperature of 5 ^° C. over 6 minutes and then the cold water was heated by the electric heater for 30 minutes. The temperature of the water reached 98 ^° C. The current was then switched off, the hot water was drained from the kettle for 4 minutes and cold water at a temperature of 5 C was poured into the kettle for 6 minutes. The second heating then took place. The heating and cooling of the electrodes as mentioned above were repeated 1050 times by means of an automatic controller. No breakage of the electrodes No. 2-6 could be found.

2. Corrosion tests:

Electrode No. 2 was placed in a kettle (enamelled Iron), which contained hot water, was used. The tests were carried out under the following conditions:

Anode * Electrode No. 2

Cathode nickel plate

Voltage (direct current) 5 V

Current density 0.5 amp / dm

Temperature of the water 98 ⁰ C

The energy supply took place for 8 hours and 7 days | the

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The concentration of iron ions in water was 0.007 ppm (for 8 hours) and 0.15 ppm (for 7 days). These values are lower than the standard values of the Food Sanitation Law (Fe ions 0.3 ppm). The electrode of this invention, can therefore be used as an anode for a water heater (boiler) for drinking water or for pleasure purposes.

Ι claims -13-

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Claims (14)

Patent claims: 1. Electrode for electrical corrosion protection, characterized in that it is a sintered body of a mixture of (1) an iron oxide in an amount of 90 to 55 mol $, calculated as 3Te ₂ OZ and (2) a metal oxide in an amount of 10 to 45 moles $ calculated as MO, where M is at least one metal from the group Mn, Ni, Co, Mg, Cu and / or Zn. 2. Electrode according to claim 1, characterized in that the sintered body is a solid solution of (1) MFe ₂ O., wherein M is at least one metal from the group Mn, Ni, Co, Mg, Cu and / or Zn in an amount of 15.7 to 87.1 moles and (2) ^ e ₅ O, in an amount of 84.3 Ms 12.9 moles. 3. Electrode according to claim 1, characterized in that it _{comprises a sintered body of Fe 0} P ₅ and NiO. 4. Electrode according to claim 3, characterized in that the Mo1 $ ratio of Fe ₂ O ₅ and NiO varies from about 90 ι 10 to about 55:45 » 5. An electrode according to claim 1, characterized in that it _{comprises a sintered body of Fe 2} O ₅ and CoO. -H- 603820/1116 6. Electrode according to claim 5, characterized in that the mol $ ratio Fe ₂ O to CoO = 90:10. 7. An electrode according to claim 1, characterized in that the sintered body _{comprises Fe 3} O ₅ , MnO, CoO and ZnO. 8. Electrode according to claim 7, characterized in that the sintered body comprises 60 moles of Fe ₂ O ₃ , 10 moles of MnO, 15 moles of CoO and 15 moles of ZnO. 9. An electrode according to claim 1, characterized in that a sintered body _{comprises Fe 2} O ₃ , MgO and IiO. 10. An electrode according to claim 9, characterized in that the sintered body comprises 60 mol% Fe ₂ O ₃ , 20 mol% MgO and 20 mol% UiO _β 11. Electrode according to claim 1, characterized in that it _{comprises Fe 2} O ₅ , MnO, CuO and NiO. 12. Electrode according to claim 11, characterized in that it _{comprises 60 mol $ Fe 2} O ₅ , 10 MnO, 10 MoI ^ CuO and 20 MoI ^ NiO. 609820/1116 13 · - Procedure for electrical corrosion protection under Use of an electrode as an anode, thereby characterized in that the electrode is a sintered body made of a mixture of (1) iron oxide from 90 to 55 mol $, calculated as ΡβρΟ, and (2) a Metal oxide of 10 to 45 mol%, calculated as MO, where M is at least one metal from the group Mn, Ni, Go, Mg, Cu and / or Zn is used. 14. The method according to claim 13, characterized in that an electrode is used, the sintered body of which is a solid solution of (1) MFe ₂ O., wherein M is at least one metal from the group Mn, Wi, Co, Mg, Cu and / or Zn is from 15.7 to 87.1 moles # and (2) Pe ₅ O _{4 is} from 84.3 to 12.9 moles $. 609820/1116 Blank page