DE2128878C3 - Reusable composite cathode made of metal - Google Patents

Description

The invention relates to a reusable composite cathode made of metal, the surface of which by means of a net-like coating made of an electrically non-conductive, chemically resistant material is divided into numerous delimited electrically conductive sections for the electrodeposition of Metals, in particular nickel, in which the metal on the electrically conductive cathode sections in considerable thickness, semi-adherently and then in lump form from the cathode Will get removed.

From the German patent specification 1 202 005 and the USA patent specification 3 419 901 it is known to Electro refining of nickel as a cathode to use a flexible shaped body made of sheet metal on its Surface of electrically conductive islands with the help of interconnected lines of non-conductive Material are limited. A nickel coating of substantial thickness will be semi-adherent to the islands cast down from a bath that reduces a certain amount of the internal tensions

which contains the agent which causes a metal deposit with low internal stress. The shaped body covered with an electrolytically deposited coating emerges from the bath removed and the deposited agent detached by bending the shaped body.

By suitable choice of the dimensions of the electrically conductive islands, the agent can even be obtained in pieces of any suitable shape and the shaped body can be used again.

According to German patent specification 1 202 005, a non-conductive material can enter between the islands Adhesive paint, varnish, varnish, tape or the like, for example materials made of plastic or rubber, such as epoxy resins, acrylic resins and polyethylene.

These coatings have to be replaced from time to time, and the process also has the disadvantage that conventional sulphate-chloride-nickel baths cannot be used, since these baths usually lead to deposits with an internal tensile stress of at least 14 kp / mm ² and this high internal stress tends to cause the nickel coating to peel off the shaped body before the desired thickness is reached. The invention is therefore based on the object of avoiding these disadvantages.

The solution to the aforementioned problem is that in a composite cathode of the initially mentioned type according to the invention the electrically non-conductive coating of one on the at least in the area of the coating there is a roughened metallic cathode melted glass-like enamel.

Roughening the metal base not only improves the adhesion of the vitreous enamel coating under electroplating conditions, but also, if this roughened surface extends over the conductive islands, also enables metal precipitates of suitable thickness to be deposited from electrolytic baths which lead to precipitation with high internal tensions. Advantageously, the metal base has a surface roughness of 1.8 to 2.5 µm RMS as measured using a profilometer (Type QB, Model 1 from Micrometrical Manufacturing Co., Ann Arbor, Michigan). This surface roughness can advantageously be achieved by sandblasting with a fairly coarse sand and is ^{suitable for depositing nickel with an internal stress of 14 to 45 kgf / mm 2} , as shown in FIG

Sulphate-chloride-nickel baths are precipitated.

The metal base of the cathode must be sonicated

ensure that the electrodeposited metal does not adhere too strongly to it. It advantageously consists of stainless steel; however, other metals such as nickel or enameling iron or steel can also be used if they are suitably passivated. Enamel iron or steel can through

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Chromium plating in the area of the electrically conductive in-treatment in the furnace are then carried out

being passivated; however, this has the disadvantage of removing acidic etching, and ultimately the loading

that the chromium contaminate the electroplating bath stratified cathode rinsed with water. The cathode

can. _ is then ready to use.

Regardless of what material is used, the cathodes of the present invention must be sufficiently compact to allow for the electrorefining of nickel. If -to enable repeated use, and the surface of the electrically conductive islands is therefore advantageously at least 0.5 mm thick. If it is rough, advantageously up to a surface roughness, the thickness is no more than about 0.8 mm, a speed of 1.8 to 2.5 [in RMS, can advantageously be bent slightly to the metal deposits io the used to be removed from aqueous solutions, which can be done, for example, by guiding between with a content of 50 to 90 g / l nickel as nickel rubber rollers. With regard to the sulfate, 15 to 75 g / l chloride as sodium chloride and practical implementation of the electric refinery is 10 to 40 g / l boric acid and a pH value, however, it is advantageous to have thicker and stronger cathodes, from 2 to 4.5 . The electrolytic low for example with a thickness of 3.5 to 6.5 mm to 15 beat from these baths can use at 43 to 66 ^C C to ensure good contact of the cathode with the at a current density of 0.5 to 2.7 A / dm ² take place. Strcimzuführungsschiene for the cathode to ensure the precipitated nickel from these baths and a warping and short circuit in which has a high voltage. Avoid nickel deposits with a gas aniseing vessel. The deposits on the lower internal tensile stress of, for example, these more rigid cathodes can be removed by measures such as up to 4.2 kp / mm- \ such as electrolytic vibration or hammering. Genes nickel with a content of about 0.02 "η

The glass-like enamel coating should be made of sulfur, adhere much more firmly. If, therefore, it is necessary for baths to adhere well to the metal substrate and be used, which lead to such deposits being relatively non-porous, non-conductive, scratch-resistant and peeling, the electrically conductive islands should be relatively stable and resistant under the chemical and smooth surfaces, for example from 1.25 to 1.8 µm electrochemical conditions which exist in the Me-RMS for the separation of the precipitate medium of the electro refining prevail. Especially to facilitate. This surface quality can be suitable enamels are alkali borosilicate glasses with mechanical grinding, chemical or electronic silicic acid content of more than 50% and a trolytic polishing of the exposed roughened titanium dioxide content of 3 to 10% or more. The 30 metal surface areas of the composite cathode will maintain the linear thermal expansion coefficient of the enamel, after which the vitreous enamel layer should be fairly close to that of the substrate. applied and fired. According to another example, a stainless steel should be embodied in one embodiment, the parts of the original expansion coefficients of 9.6-10 ~ ⁷ / 'C can be combined with a relatively smooth surface of the metal substrate, an enamel, which has an expansion correspond to electrically conductive islands, coefficient of graduation of a similar size, approximately of covered and only the uncovered parts, at -8 · 10 ~ ⁷ / ° C to 12 · 10 "V ⁰ C. For example by sandblasting, roughened and with

The vitreous enamel can be covered in a predetermined vitreous enamel. The cover

The pattern on the roughened metal surface of the kung can then be removed and the enamel fired

Cathode as an aqueous slurry or in an- 4 °.

their form, for example an oil-based PaMc, As an example, a 3.5 mm thick sheet was made from by spraying, brushing, dipping, or a Type 304 austenitic stainless steel up to another suitable method can be applied. a surface roughness of 1.8 to 2.5 11 sand-die interconnected areas of vitreous blasted, degreased, with numerous 3.5 mm thick Gen Fmaille should be at least as wide as the 45 rubber discs with a diameter of 17.5 mm of the deposit to be deposited on the mold, which covers in a regular pattern with center metal (generally about 3.5 bit 6.5 mm). The point spacings of 32 mm with the help of glue desired pattern can be attached to the sheet metal surface by using a. The sheet Stencil can be made such as was then made with an aqueous slurry the silk screen process. 5 ° of a chemically resistant glass-like enamel

Although the electrically conductive islands can each be sprayed on the basis of an alkali borosilicate glass, the

have desired shape; electrolytic low 10 ⁰ O TiO ₂ , 2% BaO and 2% PbO contained. the

suggest on rectangular islands, however, tend to enamel had such a grain size that no more

to grow together at the edges so that it is as 1 to 2% on a Tyler sieve with 200 mesh

it becomes difficult to separate the pieces. 55 (74 µm) were retained. Before burning

The electrically conductive islands are therefore advantageous, the coating layer was two hours at 77 ^r C

circular or elliptical. dried and the rubber discs after

After removing excess material drying removed.

For example, the coated cathode is placed in an oven for five minutes

Drying cabinet heated to 38 to 93 ° C to heat the surface to 870 "C to create a coating of glass

to dry the slurry and remove excess moisture-like enamel with a thickness of 0.75 mm.

ability to remove from the coating. You will then form that has a coefficient of thermal expansion of

in an oven, for example, at a temperature of 10.5 · 10 " ⁷ /" C. Compared to it possessed

Fired from 760 to 900 ° C to give the enamel to the steel sheet a coefficient of thermal expansion

melt and bond with the substrate. The 65 of 9.6 · 10 ~ ⁷ / ° C.

Thickness of the molten vitreous enamel can be The amount of oxide formed during firing

be about 0.025 to 0.25 mm or more. Oxyde, was anodized in 25% vväs-

which is on the exposed metal during the seriger sulfuric acid at room temperature and one

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Current density of 27 A / dm ² removed. The cleaned contains, in which the tendency to more alkaline sheet metal was then in an aqueous electrolyte conditions as: n most of the electro-immersed, the 60 g / nickel ate nickel sulfate (NiSO ₄ , lyten. It was observed that an extraordinarily- 6H., O), 50 g / l chloride as sodium chloride (NaCl) and very thin and interrupted nickel film containing 20 g / l boric acid and a pH value of 4.5 glass-like enamel in the narrow area. Nickel was produced from this bath at 60 ° C and beats, in which the growing nickel closely approaches that of a current density of 2.2 A / dm- in a thickness of the glass surface. This film can be tolerated down to 2.5 mm on the electrically conductive islands as long as it is present in places; slay. After removing the sheet from the, however, it should be removed (for example, the circular disks were removed with a diameter of about 19 mm by immersing in nitric acid between individual water by the electrolysis process), before connecting the sheet with a bath Metal rod has been struck, and the electrically conductive areas of the mold are enlarged with the patterned surface.
The cathode was practically not damaged. The invention was made specifically with regard to

After rinsing, the cathode was again subjected to the electrolytic deposition of nickel Bath brought back. Even after ten galvanic letters; a versing cycles designed according to the invention The quality of the cathode was not the Merk- bund electrode, but it can be used in connection with public worsened. speaking electrolytes also to electrolytic

Deposits of other metals are used in the course of electrolytic deposition,

the nickel disks showed the tendency to over the um- ao For example, copper and zinc, which deal with

outgrowth giving glass-like enamel. The relatively low internal stresses are deposited, never-

Nickel deposits do not seem to cloud the enamel, nor do metals such as co-

stir, and there seems to be a narrow area between bait and manganese, which deals with relatively high inner

the two surfaces to exist, the electrolyte tensions precipitate.

Claims (8)

Patent claims: 1. Reusable composite cathode made of metal, the surface of which is covered by a reticulated Coating of an electrically non-conductive chemically resistant material in numerous limited electrically conductive sections are divided for the electrodeposition of metals, in particular nickel, in which the metal on the electrically conductive cathode sections in Precipitate considerable thickness semi-adherent and then in lump form from the cathode is removed, characterized in that the electrically non-conductive coating from a metallic cathode roughened at least in the area of the coating fused glass-like enamel. 2. Cathode according to claim 1, characterized in that it is round on its surface or elliptical electrically conductive islands. 3. Cathode according to claim 1 or 2, characterized in that the entire surface is roughened is. 4. Cathode according to claims 1 to 3, characterized in that at least the coated Areas of the metal surface up to a surface roughness of 1.8 to 2.5 µm RMS are roughened. 5. Cathode according to claims 1 to 4, characterized in that the metal base consists of stainless steel. 6. Method for the electrolytic refining of nickel using a cathode according to the claims 1 to 5, characterized in that the nickel at a temperature of 43 to 66 C is precipitated from a bath containing 50 to 90 g / l of nickel as nickel, 5 to 75 g / l Contains chloride as NaCl and 10 to 40 g / l boric acid and has a pH of 2 to 4.5. 7. The method according to claim 6, characterized in that the nickel is ^{deposited with an internal tensile stress of 14 to 45 kp / mm 2} on the composite cathode. 8. The method according to claim 6, characterized in that the nickel with an inner Tensile stress up to 4.2 kp / mm- 'is deposited on tiner cathode, whose electrically conductive Islands have a surface roughness of 1.25 to 1.8 (in the RMS.