KR800000591B1 - Electrode assembly for cathodic protection - Google Patents

Abstract

Spinel-structured sinterde materials consisting of Fe2O3 55-90 mole % and MC(where M is >=1 of Mn, Ni, Co, Mg, Cu and Zn) 10-45 mole 5 had a good corrsion resistance and a thermalshock resistance, and hence they are useful as the counter electrode for electrochemical protection of boilers and water heaters. Thus mixtures of composition Fe2O3 50-95 and NiO 5-50 mole % were presintered at 800≰C(3hr) in the air, then sintered at 1,400≰C(5hr) under N to give 110mm 15mm 15mm electrodes.

Description

Sintered Body Electrode for Preventing Electrical Corrosion

1 is a diagram showing the relationship between the composition and the resistivity when the composition of the metal oxide sintered body is converted.

2 is a diagram showing the relationship between the composition when the composition of the metal oxide sintered body is changed and the thermal shock cycle in which the sintered body is destroyed.

3 is a diagram showing current and voltage characteristics of electrodes of the water heater shown in FIG.

4 is a structural diagram of a water heater using the metal oxide sintered body of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode made of a metal oxide sintered body having a spinel crystal structure, and an object thereof is to improve thermal shock resistance of the electrode.

When storing water or seawater containing electrolyte in a metal container, in order to prevent the metal container from being corroded by water or the like, the metal container is used as a cathode, and the other electrode ( The metal corrosion prevention method which prevents corrosion of a metal container by applying a voltage between anodes and making a current flow, using a counter electrode as an anode below, has been performed widely conventionally.

Recently, however, household electric water heaters and boilers have been actively used as effective methods of using late-night power. However, the counter electrodes used to prevent corrosion of metal containers of such electric water heaters and boilers are not only corrosion resistant but also cold water and hot water. Because it is always exposed to, it is required to withstand the heat shock of rapid quenching and quenching sufficiently. Conventionally known carbon electrodes and magnetite electrodes are inferior in corrosion resistance and thermal shock resistance as counter electrodes for water heaters, and development of excellent electrodes has been desired.

The inventors of the present invention, previously described, is 99.9-60 mol% of iron oxide and MO (M represents Mn, Ni, Co, Mg, Cu, or Zn) in terms of Re ₂ O ₃ , and 0.1-40 mol% of manganese oxide, It is proposed that a metal oxide sintered body having a spinel crystal structure of at least one of nickel oxide, cobalt oxide, magnesium oxide, copper oxide or zinc oxide is most suitable for use as an electrode having excellent resistivity and corrosion resistance.

In the composition of the metal oxide sintered electrode having such a spinel crystal structure, the present invention provides 90 to 55 mol% of iron oxide and MO (M represents Mn, Ni, Co, Mg, Cu, or Zn) in terms of Fe ₂ O ₃ . It has a resistivity of 0.004 to 1.0 Pa.cm by having a sintered body having a spinel structure of at least one of 10 to 45 mol% of manganese oxide, nickel oxide, cobalt oxide, magnesium oxide, copper oxide or zinc oxide. The present invention has been found to have a thermal shock resistance of not less than 50 mg / cm < 2 > It was accomplished.

As the shape of the electrode of the present invention, one of a desired type can be used. For example, as used in a conventional magnetic iron oxide electrode, the metal oxide sintered body of the present invention is made into a hollow cylinder, and is hollow. An electric conductor such as copper may be plated on the inner surface, and a conductive wire may be connected to the plated layer, or the plate-like metal oxide sintered body of the present invention may be fixed to the plated copper plate. have.

It goes without saying that when the electrode of such a type is used, the plating layer must be in direct contact with water or the like.

Next, the general manufacturing method of the metal oxide sintered electrode which has the spinel crystal structure of this invention is shown.

90-55 mol% of Fe ₂ O ₃ and at least one 10-45 mol% of MO (M represents Mn, Ni, Co, Mg, Cu or Zn) are mixed, for example, sufficiently mixed in a bowl mill. After heating in the air or in an atmosphere containing a predetermined amount of hydrogen gas in nitrogen gas, carbon dioxide gas and inert gas at a temperature of 700 to 1,000 ° C. for 1 to 15 hours, the rate of spinelization is 80% or more, and then cooled and pulverized. To obtain fine powder.

) 성형하는 것에 의해서, 혹은 기타의 방법 예를 들면 압출성형하는 것에 의해서 소망하는 형상을 갖는 성형체를 얻고, 이 성형체를 O₂가스함유량을 조정한 N₂가스 또는 CO₂가스와 같은 불활성의 가스분위기중에 있어서 소결하므로서 본 발명의 전극이 얻어진다.By injection molding the fine powder or by adding water to the fine powder

) Molding or other method, for example, extrusion molding, to obtain a molded article having a desired shape, and the molded article is inert gas atmosphere such as N ₂ gas or CO ₂ gas in which O ₂ gas content is adjusted. By sintering in the air, the electrode of the present invention is obtained.

In the case where the rate of spinelization of the metal oxide after the temporary firing is 80% or less, the metal oxide sintered body obtained by the main firing is likely to be dispersed in the thermal shock characteristics. It is preferable that the rate of spinelization is between 80%.

In a starting material in the above, Fe ₂ O ₃ and MO but using (M is Mn, Ni, Co, Mg, Cu or Zn represents a), Fe ₂ O ₃ instead of in terms of Fe ₂ O ₃ 90~55 One or two mixtures of Fe, FeO, and Fe ₂ O ₃ may be used so as to be mole%, and a compound which becomes a metal oxide by heating instead of a metal oxide such as MO, such as carbonate or oxalate, may also be used. .

In order to explain the invention in more detail, the following examples are presented.

Example 1

Oxide material of 95-50 mol% iron oxide in terms of Fe ₂ O ₃ and nickel oxide in terms of NiO was temporarily baked in air at 800 ° C. for 3 hours, and then 1,400 ° C. for 5 hours, N _It baked in ₂ gases and obtained the plate-shaped sintered compact of 110 mm in length, 15 mm in width, and 15 mm in thickness, respectively. The measurement results of the resistivity and thermal shock characteristics of these samples are shown in FIGS. 1 and 2.

In addition, it is possible to vary the power supply of the water heater shown in FIG. 4, and the result of measuring the current-voltage characteristics of the counter electrode is shown in FIG. In addition, the resistivity was measured by a two-point stylus method.

In terms of thermal shock characteristics, normally, the thermal shock of cold heat applied to the corrosion preventing electrode for water heaters is an average of 1,000 cycles per year with a temperature difference of 100 ° C.

Furthermore, there should be no breakdown of electrodes by thermal stress for five years. In general, it is said that the deterioration of the strength of an object due to thermal stress is proportional to the repetition speed of the thermal shock cycle if the thermal shock temperature is constant. The cold heat cycle of the water heater provided for practical use is 1,000 (cycles / year), as described above, which is about 3 (cycles / day). It was judged that the actual test of the thermal gun resistance suitable for the degree of the thermal gun cycle of this degree can be provided for practical use if it withstands the thermal shock of 200 (cycle) or more under the following acceleration conditions.

The sample was measured as 1.0 cycle / hour of acceleration conditions here, and the sample which can endure 200 cycles or more was made into the composition range of this invention.

As apparent from the relationship between the composition and the resistivity of the metal oxide sintered body of FIG. 1, it can be seen that the resistivity increases as the water% of NiO increases.

In the relationship between the composition of the metal oxide sintered body of FIG. 2 and the thermal shock cycle in which the sample is destroyed, when the content of NiO is 10 mol% or less, it is not preferable as an electrode for a water heater, but rather it is used in a place where the content of NiO is high. It can be seen that it is most suitable.

On the other hand, the difference in resistivity of the counter electrode in the range of 0.01 to 1 Ω.cm is not seen in FIG. 3, but when the resistance is greater than 1 Ω.cm, the characteristics deteriorate, and the resistivity of the counter electrode for the water heater is at least 1 Ω.cm. It turns out that it is necessary to make the following.

Moreover, content of NiO in this electrode of resistivity 1 ohm * cm was 45 mol%.

Even if the resistivity of the counter electrode is relatively high (around 1Ω.cm), practically no problem is found because the liquid for the water heater is industrial water, tap water, well water, etc., and therefore the liquid itself has a resistance (about 1,000Ω.cm). It is considered that the resistance of the electrode itself does not affect the current-voltage characteristic as far as 1?

Example 2

As in Example 1, the measurement results of the resistivity, thermal shock characteristics, and voltage-current characteristics of the sample obtained by firing one or two or more of Fe ₂ O ₃ , NiO, CoO, MgO, CnO, and ZnO were measured. The same result was obtained.

In addition, the representative example is shown to the following 1st table for reference.

Moreover, it was confirmed that the obtained sintered compact has a spinel structure by X-ray diffraction analysis.

[Table 1]

In addition, the loss of corrosion was measured by the following electrolytic conditions by making the loss (mg) per 1m <2> by the analytical method in the case of using as an anode for electrolysis in standard seawater.

As described above, the electrode for preventing corrosion of water for water heaters and boilers having excellent resistivity of 0.004 to 1.0 Ω.cm and having thermal shock resistance is 90 to 55 mol% of iron oxide and MO in terms of Fe ₂ O ₃ . Spinel crystal structure of at least one of 10 to 45 mol% of manganese oxide, nickel oxide, cobalt oxide, magnesium oxide, copper oxide, or zinc oxide in terms of (M represents Mn, Ni, Co, Mg, Cu, or Zn). It is obtained by setting it as the sintered compact which has a.

Reference Example 1

The ferrite material having a high thermal shock resistance obtained in Example 2 was molded and heat-treated under a sintering condition suitable for each material to prepare a 120 × 10 × 5 mm columnar ferrite electrode sample. This sample was actually mounted in a water heater as shown in FIG. 3, and subjected to a thermal shock mounting test automatically under the following thermal shock conditions.

Under the above conditions, each sample was mounted in a water heater, and a thermal shock of about 100 (° C.) was applied at 40 (min / cycle) at 1,050 cycles, but no destruction of the ferrite electrode occurred.

In the drawings, (1) is an iron container, (2) is an electrical drainage terminal, (3) is the sintered body of the present invention, (4) is an attachment block, and (5) is a socket.

Reference Example 2

In order to confirm that the ferrite electrode for corrosion prevention with a strong thermal shock resistance obtained in the above Example was insoluble, the following electrolytic test was carried out. The tap water was heated to 98 ° C., and the ferrite electrode was inserted into the boiling water as an anode.

A nickel plate was used for the cathode electrode, and the plate was energized for 8 hours at a current density of 0.5 (A / dm 2).

As a result, the iron ion elution concentration in tap water was 0.007 ppm. In addition, while energizing for one week under the same conditions, the elution of Fe was 0.15 (ppm).

In all cases, it was found to be less than the food sanitation standard value (Fe <0.3 ppm), and was an insoluble electrode sufficiently applied to a water heater for drinking water.

As apparent from the above-described examples and the like, a ferrite electrode for preventing water heater corrosion, which was excellent in corrosion resistance and high in thermal shock resistance, was obtained.

Claims (1)

10 to 45 mol% of manganese oxide, nickel oxide and cobalt oxide in terms of iron oxide and MO (M represents Mn, Ni, Co, Mg, Cu or Zn) in terms of Fe ₂ O ₃ An anticorrosion sintered body electrode having a spinel crystal structure of at least one of magnesium oxide, copper oxide and zinc oxide.

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