JPS61221390A - Coating type lead dioxide electrode - Google Patents

Abstract

PURPOSE:To improve adhesiveness, strength, dimensional stability and electricity conduction capacity and to facilitate production by coating lead dioxide via intermediate layers on a blanked plate which is specified in the diameter and thickness of the blanked parts. CONSTITUTION:The blanked plate of which the max. diameter of the blanked parts and the shortest spaces between the adjacent blanked parts are respectively 1.5-12mm and 1.5-7.0mm and the thickness is 1.0-7.0mm is prepd. The intermediate layers 2 consisting of an acid resistant and conductive platinum group (alloy), etc. are coated on the plate 1. The lead dioxide layer 3 is coated to about 0.3-8mm thickness over the entire surface of the layers 2 to form electrodes. The coating type lead dioxide electrodes exhibit substantial durability against a corrosive electrolyte. There is no need for a welding stage in production and the increase of the size to some extent is possible.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention can be used as an anode for the electrolytic production of chlorates, perchlorates, periodates, persulfates, etc. This invention relates to a coated lead dioxide electrode used as an anode for electrolytic treatment of waste liquids, electroplating, and especially fluorosilicide baths in chrome plating.

[Conventional technology]

Electrodes used in industrial electrolysis must be sufficiently satisfactory in terms of performance, durability, electrode form, mechanical strength, workability, economic efficiency, etc. In recent years, metal electrodes in which a platinum group metal compound is coated on a substrate such as titanium have appeared, and due to their excellent performance as well as the advantages of good strength and dimensional stability, they have brought about significant advances in the salt electrolysis industry and elsewhere.

On the other hand, the lead dioxide electrode, which has been recognized in the past, is an excellent and inexpensive electrode that has a high oxygen overvoltage second only to platinum and has a unique electrocatalytic ability. However, the reason why this electrode has not been put into full-scale practical use is the lack of mechanical strength and workability of this electrode.
This is caused by a lack of dimensional stability.

Conventionally, plate-shaped lead dioxide electrodes have been produced by electrodepositing concave anodic electrodes from a lead nitrate bath, etc., and then extracting the electrodes.
Due to the presence of internal strain, it was brittle and large, and its shape was also limited. For this reason, attempts have been made to electrodeposit lead dioxide directly onto graphite plates and titanium plates, but these attempts have not been successful due to cracks, poor adhesion, etc., resulting in peeling and falling off. Recently, there is a method of electrodepositing titanium wire mesh as a core material. However, although adhesion is improved, it is weak in strength and bends easily, so cracks are likely to occur, and it is difficult to pass much current, making it impossible to increase the size.

In order to improve these drawbacks, we welded titanium extractor metal (VF Publication No. 58-30957), punching metal, and wire mesh (Special Publication No. 58-31396) to the titanium plate as a base together with a holding plate, and then applied carbon dioxide through the intermediate layer. A method of electrodepositing lead was tried. This method significantly improved adhesion, mechanical strength, and dimensional stability.

However, since the titanium is exposed around the periphery of the holding plate and electrodes, electrolytes that do not have the corrosion resistance of the titanium base, such as silica fluoride baths for chrome plating, will corrode the holding plate and exposed parts, causing them to peel off and fall off. sometimes occurred. In addition, the manufacturing process of the electrode becomes complicated and requires many man-hours, resulting in an expensive electrode. [Problems to be solved by the invention] The present inventors have developed We conducted various studies in order to obtain an electrode that maintains good physical strength and dimensional stability, can be used even with electrolytes that corrode the base metal, can be made large to a certain extent, and is easy to manufacture. As a result, this was finally completed.

[Means for solving problems]

That is, in the present invention, the maximum diameter of the punched part and the shortest distance between adjacent round punched parts are 1.5 to 12 m and 1.5 to 7.0 m, respectively.
a punched plate having a thickness in the range of 1.0 to 7.0 mm, an intermediate layer coated on the punched plate, and an intermediate layer electrodeposited on the intermediate layer. This is a coated lead dioxide electrode made of lead dioxide.

Next, the present invention will be explained based on the drawings. 1 and 3 are cross-sectional views of an electrode according to the invention, consisting of a stamped plate 1, an oxidation-resistant and electrically conductive intermediate layer 2, and a lead dioxide layer 3. FIG.

The punching plate 1 is coated with a solvent such as trichlene or alkali 1. I
After degreasing with K and then etching with hydrofluoric acid or hot oxalic acid to roughen the surface, a lead dioxide layer 3 is formed on the entire surface by anode electrodeposition via the intermediate layer 2. The material of the punched plate 1 used in the present invention includes iron, iron alloy,
Nickel, chromium, aluminum, titanium, tantalum,
It is made of zorconium, niobium, or an alloy mainly composed of these, and can have a size of about 1.000 to 1.500 cm in length and width, and can be shaped into a cylindrical shape as well as a flat plate. Further, the shape of the punched portion 4 is generally round, but it may be of any other shape such as an ellipse, a square, a cross, or a mixture thereof.

Next, the present invention will be described in detail with reference to FIG. 2, taking a general round shape as the shape of the punched portion 4 as an example. The shortest distance Ll between adjacent punched parts 4 is preferably in the range of 1.5 to 7.0 cm. 1
．． If the length is smaller than 5 m, the strength of the plate will be insufficient, and when the electrode is handled, it will bend and the electrodeposited lead dioxide layer will crack and peel off. Moreover, if it is larger than 7.0, the flat part becomes too wide and the adhesion of the lead dioxide layer decreases. The maximum diameter L2 of the punched part should preferably be in the range of 1.5 to 12 mm. If it is smaller than 1.5 mm, oxygen bubbles generated on the substrate surface during electrodeposition of lead dioxide will accumulate in the punched part 4. A lead dioxide layer containing pinholes is formed. If such an electrode is used as an anode in a fluorosilicide bath for chromium plating, the base of the punched portion 4 will corrode and the lead dioxide layer will fall off. Moreover, if it is larger than 12 m, it is not preferable in view of the current distribution of the counter electrode. The plate thickness is also 1.0 to 7. The range of Ofi is good, and if it is thinner than 1.0 dew, the strength is weak, and the problem of heat generation remains when carrying out large current.
If it is thicker than 7+III, oxygen bubbles cannot be removed during electrodeposition and pinholes will occur in the lead dioxide layer.

The intermediate layer 2 is interposed to prevent oxidation of the surface of the punched plate 1, and is made of oxidation-resistant and conductive platinum group metals, alloys thereof, or oxides thereof, silver, manganese dioxide, cobalt oxide, molybdenum oxide. It consists of at least one type. The platinum group metals used are platinum, iridium, rhodium, palladium, ruthenium, etc., and the coating is prepared by electroplating or by dissolving the chlorides of these metals in alcohol and coating them on a punched plate, and then using a pyrolysis method. Ru.

Silver, manganese dioxide, cobalt oxide, and molybdenum oxide are similarly coated by dissolving the nitrates of these metals in water or alcohol. When using iron, stainless steel, etc. as the punched plate, the thermal decomposition method produces hydrochloric acid during the thermal decomposition process of the platinum group metal chloride-containing coating solution, which corrodes the substrate and impairs the adhesion of the intermediate layer. If the lead dioxide is insufficient, the electrodeposition of lead dioxide will be poor, so coating with a coating solution containing sulfate, nitrate or organic metal salt or by electroplating is desirable. Further, a thickness of about 0.5 to 5 μm is sufficient for the intermediate layer.

The lead dioxide layer of the present invention is entirely coated on the intermediate layer applied to the surface of the punched plate by anodic electrodeposition, and the electrodeposition liquid consists of lead salt and copper salt, and the lead salt includes lead nitrate, lead nitrate, Lead sulfamate, lead acetate, etc. are used, and copper nitrate is mainly used as the copper salt. The concentrations of lead and copper in the electrodeposition solution are 100 to 210 g/l and 4 to 209/l, respectively, and the liquid temperature is maintained at 60 to 80° C. and -3.5 to 4.5. The anode current density is 1 to 5 A/dm, and stainless steel is used as the cathode for electrolysis. During this time, adjust the liquid to pH 3.5-4.
．． To maintain the temperature at 5, adjust by adding lead oxide, lead carbonate, lead hydroxide, etc. If these conditions are not met, island-like electrodepositions or lump-like electrodepositions tend to occur, internal strain increases, cracks in the coating and peeling of the electrodeposit material tend to occur, which is not preferable.

The thickness of the lead dioxide coating is set to 0.3 to 8 thick as required, but this is adjusted by the length of the electrodeposition time. Third
The figure shows an example of an electrode manufactured by not filling the punched portion 4 with lead dioxide coating. Electrodeposition is completed in this way, but there are no cracks, holes or pinholes, and a uniform coating is obtained depending on the surface of the substrate. Good adhesion can be obtained by fulfilling the important role and releasing internal strain.

〔Example〕

Next, embodiments of the present invention will be illustrated by examples, but the gist thereof is not limited in any way by these examples.

Example 1 A titanium plate measuring 12011II11 in length and 50m in width and 3+a+ in thickness was punched in parallel with round shapes having a hole diameter of 3m and a punching part interval of 3m to produce an electrode substrate. This electrode substrate was degreased by trichlene cleaning, and then surface-treated by immersing it in a 5-thihydrofluoric acid solution. Next, a coating solution consisting of 3 parts by weight of platinum chloride, 1 part by weight of iridium chloride, and 36 parts by weight of isopropyl alcohol was applied, dried, and then heat-treated at 500° C. to form an intermediate layer of 0.7 μm. Using this electrode substrate as an anode and a stainless steel plate as a cathode, electrodeposition was carried out for 30 hours in an electrodeposition solution consisting of lead nitrate and steel nitrate.
A lead dioxide coating of m thickness was obtained. At this time, the concentration of lead and copper ions was 200 fi/l and 6.5 g/l, the anode current density was 2.5 A/dm2, the average liquid temperature was 65°C, and the liquid pH was around 4.2. I kept it. The lead dioxide coating was electrodeposited almost uniformly over the entire surface, with no cracks on the surface and excellent flatness.

Example 2 Hole diameter 5 on an iron plate with length 120, width 50+W, thickness 3.2W
m, round punching with a punching part interval of 3fi in a staggered manner (60 degrees)
An electrode substrate was fabricated. This electrode substrate was degreased by trichlene cleaning, and the surface was etched by immersing it in industrial 35% hydrochloric acid for 1 hour. Next, a 0.5M silver nitrate aqueous solution was applied, dried, and then repeatedly baked at 450° C. for 30 minutes to form a 2 μm intermediate layer, followed by electrodeposition for 12 hours in the same manner as in Example 1. The coating thickness of the obtained lead dioxide electrode was 1.0 m, and it was electrodeposited uniformly on the punched part and the flat part.

Comparative example 1 120m in length to learn about the effects of the electrodes of the present invention.

A titanium plate with a width of 50 m and a thickness of 3 fl was used as a base, pretreatment, intermediate layer coating, and lead dioxide coating were performed under the same conditions as in Example 1. Gum tape was adhered to the coated surface, pressure was applied with a roll, and the tape was pulled. It was peeled off and adhesion was observed. The results are shown in Table 1.

Table 1 Example 3 Using the electrode produced in Example 1 as an anode and a stainless steel plate as a cathode, perchlorate was electrolytically produced under the following electrolytic conditions.

Electrolysis conditions Anode: Electrode manufactured in Example 1 Cathode: Stainless steel plate (50x130x3
) Electrolyte---NNaC403soo/l, Na
F 2ji/l distance between electrodes...5m Conventional lead dioxide electrodes require a distance between electrodes of 15 to 30 meters, but with this electrode, the sliding voltage is 0.2 to 0.2 meters at 5 meters.
With a reduction of 0.5v and an average current efficiency of 88ch, the required power was saved by 5-10ch. This electrode continued to operate stably for over 6 months, and no changes in shape, cracking, or peeling were observed during this period.

Example 4 Using an electrode manufactured in the same manner as in Example 1 as an anode and a stainless steel plate as a cathode, electroless plating waste liquid was subjected to COD reduction electrolytic treatment under the following conditions.

Electrolytic conditions Anode... Electrode of the present invention Cathode... Stainless steel plate electrolyte... Electroless plating waste liquid COD --- 48,000 ppm (Start) Current density... ...10 A/dm2 temperature
...60℃ COD was 48,000 ppm at the start of electrolysis, but it was 24
After time electrolysis, the amount could be reduced to about 800 ppm.

Patch electrolysis treatment was performed 10 times under the same conditions, and stable results were obtained. There was no peeling of the electrode after electrolysis, and no change in shape was observed.

Example 5 Chromium plating was performed on mild steel using the electrode manufactured in Example 2 as an anode. The plating bath composition is as follows:
Plating was carried out at a current density of 50 A/dm2 and a bath temperature of 60°C. For comparison, an expanded plate was spot welded onto a titanium plate, and a presser plate was spot welded to its periphery for reinforcement.The electrode was coated with lead dioxide through an intermediate layer only in the area excluding the presser plate. Plating was also carried out under the same conditions for the reference electrode (abbreviated as reference electrode).

Plating solution composition Chromic anhydride 250 g/l Sodium silicate 10 g/l Sulfuric acid
1,! iI/1
During electrolysis for four months, the electrode of the present invention showed no voltage increase, no change in shape, no peeling, and had a good surface condition, fully exhibited the characteristics of lead dioxide, and exhibited stable performance. However, after one month had passed, the exposed titanium of the holding plate and substrate of the reference electrode had corroded, and even though the elution of lead dioxide was minute, it was no longer possible to carry out electrolysis.

〔effect〕

The coated lead dioxide electrode of the present invention has a strong punched plate as a base, and the entire surface is coated with lead dioxide through an intermediate layer.
In addition to improving adhesion, strength, dimensional stability, and current carrying capacity, it also eliminates the need for a welding process in manufacturing.

It also showed sufficient durability against corrosive electrolytes.

[Brief explanation of drawings]

1 and 3 are cross-sectional views of the electrode of the present invention, and FIG. 2 is a diagram showing the distance between the ends of the punched parts. DESCRIPTION OF SYMBOLS 1... Punching board, 2... Intermediate layer, 3... Lead dioxide layer, 4... Punching part, L! ...The shortest interval between adjacent punched parts, C2...The maximum diameter of the punched parts. Patent Applicant: Former Hon Carlit Co., Ltd.

Claims (1)

[Claims] 1 The maximum diameter of the punched part and the shortest distance between adjacent punched parts are in the range of 1.5 to 12 mm and 1.5 to 7.0 mm, respectively, and the plate thickness is in the range of 1.0 to 7.0 mm. 1. A coated lead dioxide electrode comprising: a punched plate, an intermediate layer coated on the punched plate, and lead dioxide electrodeposited on the intermediate layer.