DE2100178A1 - Process for electrolytic polishing of metal objects ^ - Google Patents

Description

concerning

Process for electrolyte polishing of metal objects

The invention relates to a method for the electrolytic polishing of metals and metal alloys, in particular of Aluminum, copper and its alloys as well as corrosion-resistant Stole.

It is known to polish the metal objects electrolytically by dissolving the surface of the metal which is connected as an anode in the electrolyte. In this process, the metal body is in a corresponding electrolyte, is connected as an anode in the direct current circuit, in the same electrolyte there is a second electrode, which is connected as a cathode, so that the direct current circuit is thus closed.

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It is also already known that a metal • To detach the body cathodically by immersing it in nitric acid under the influence of the current flow, you want to remove it has taken place (Israel patent specification 26 224, French patent specification 1,549,365, British Patent 1,129,750 and Belgian patent 704 472).

It has long been known that an in an electrolyte Fully immersed metal body experiences destruction, primarily as intergranular corrosion or corrosion can be described at the grain boundaries (G.V. Akimov, N.D. Thomashov, "Theory et Mgthodes d'Essai de la Corrosion des MStaux ", Dunod, Paris 1957» pp. 7t 290-296). This phenomenon has been called a disadvantage so far and no one has tried 1 to use this effect for any purpose do*

According to the invention, it has now surprisingly been found that the intergranular corrosion of the metals is electrolytic can be favored, i.e. by placing the metal object inside an electrolyte as one of the electrodes in a DC circuit is electrolyzed. To now this intergranular corrosion at a certain time on a certain To limit degree, the voltage, current density, temperature and composition of the electrolyte must be carefully selected and be brought into a certain interdependence so as not to have a negative influence or an overall attack on the Cause metal body. In the following is called "conditions for the electrolytically caused, intergranular corrosion "the combination of the values for voltage, current density, Understand temperature and electrolyte composition. These conditions are determined empirically for all metalworking

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substances through simple experiments, with the metal in different electrolytes at different voltages, current densities and temperatures is electrolyzed, whereupon the structure or the fine structure of the surface (with a profilograph) is determined. As part of these tests, the electrical

lysis time determined for the targeted, limited, intergranular Corrosion is needed.

Surprisingly, it was also according to the invention found that in the course of the electrolysis for intergranular corrosion when reversing the polarity of the metal object intergranular corrosion broken off and in its place the elevations and flat areas between the gaps caused by intergranular corrosion, which smooths the metal surface. The metal object receives a highly polished, mirror-like shiny surface, whereby the surface quality is essential is better than what can be obtained from conventional polished processes. This applies both to the case where the subject matter is in the same Electrolyte remains or when it is transferred to another.

If the second process stage is followed by measurements on the metal surface with the aid of a "profilograph", it is found that the degree of polishing increases up to a certain time when it is generally practically unchanged remain. It is assumed that this state has been reached when the elevations and flat areas have been completely removed are and you have reached the root of the columns, which in the first process stage in the generation of the intergranular Corrosion has been caused · However, the exact processes have not yet been fully clarified.

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The invention thus relates to a method for the electrolytic polishing of a metal object in two stages, wherein in the first stage an electrolysis is carried out in an aqueous electrolyte to produce an intergranular • cause corrosion to the extent desired. In the second stage, the direction of the current is reversed, i.e. the Polarity of the body changes, whereby it can either remain in the same electrolyte or in a different one Electrolyte is transferred · It is electrolyzed in the second stage until the desired polish is achieved.

The electrolysis time of the first stage for intergranular corrosion in a certain metal material can be determined experimentally determine, as will be explained in the following

In addition to an aqueous system, the electrolyte for carrying out the method according to the invention can also be various Contain proportions of organic solvents, in particular lower aliphatic alcohols or polyhydroxy compounds. Depending on the type of metal to be polished, it can be acidic, basic or neutral.

The ones required for the first and second process stages Voltages are in the order of magnitude from 5 to 150 V, the current densities in the range from 1 to 150 A / dm.

The electrolysis temperature should be within the range of 20 to about 90 ⁰ C.

The quality of the polishing by the method according to the invention is superior to any known polishing method, as is the case can easily be determined with the naked eye

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The appropriate method is therefore particularly suitable for those cases where highly polished metal surfaces are required, e.g. for for making reflectors and mirrors and for creating highly polished areas on various metal objects for decorative purposes.

A special area of application is in high vacuum technology * In such systems, the inner surfaces of all Parts must be polished to prevent gas adsorption as much as possible. The polishing methods used so far had however, in this regard * not yet fully complied with. ™ It was found, however, that the metal surfaces polished according to the invention are practically unable to adsorb gas, so that the method according to the invention is particularly suitable for polishing surfaces that are used in high vacuum systems to find.

If desired, the method according to the invention can also be used for the selective polishing of metal surfaces. One can so only partially immerse the object in the electrolyte for the second process stage. The object thus obtained has two zones, one polished and one unpolished.

Another possibility of selective polishing is that surface areas are used for the second process stage is selectively covered with an insulating material which is not attacked by the electrolyte. The polishing in this case only takes place on the free area part. After finishing the polishing process, the mask is removed from the insulating metal removed again. As an insulating or masking material, for example, a lacquer or an artificial

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material applied by spraying, brushing or the like Way is applied. After finishing the polishing process, it can be removed again.

In some cases it can be useful to place the object to be polished before it is immersed in the electrolyte to switch into the circuit in order to ensure that the reaction aimed at by the electrolysis is possible purely chemical reactions prevail, which under certain circumstances would take precedence in the opposite case.

The objects to be polished are contacted in the usual way and are not the subject of the invention.

The following examples illustrate the method of the invention for polishing a number of metal materials. In each case the metal objects were first degreased, e.g. chemically with the help of an organic solvent or electrochemically or both, after which it is rinsed off with water. After completing the second stage of the Electrolysis, the items are rinsed with water and dried.

Examples 1-4

Objects made of aluminum and aluminum alloys were immersed in an electrolyte, the composition of which is given in the second column of Table 1 is given. The objects are designed cathodically, voltage and current density are in the Table listed, as well as the electrolysis time. The polarity was reversed while the object was in the same electrolyte, and then continued with the same voltage and current density electrolyzed. Table 1 also contains the electrolyte temperature. The phosphoric acid solution in the electrolyte was 85% strength by weight

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and the sulfuric acid solution 66 ° BS. With all percentages it is # V / V. The current density was determined on the objects to be polished.

Table 1

₉ min min Example electrolyte VA / dnT 1st stage 2nd stage ⁰ C

1 x NaOH 120 g / l _{± z} ^ _{0 2 6} _ ₈ g _Q

60g / l

+ ■ ^w

+ ₁₂

_{5 10} . ₃₀ 3 5 80 CrO ₃ 7.5 g / l
+ H ₂ O 55

₃ ^
Glycerin

₂₄ + 12-15 5-10 2 5 85 ENT ₃ 50 g / l

Excellent polished surfaces were obtained in all examples.

The above electrolytes can also be used for polishing objects made of copper, copper alloys or corrosion-resistant steel.

Examples 5-9

Articles made of corrosion-resistant steel of the American specification 30 ^ -10 / 8 were treated as in Examples 1-k. - 8th -

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min »in

Example electrolyte VA / dm ² i. Level 2. Level ⁰ G

H ₃ PO ^ + ■,

Propyl alcohol 10-15 5-30 3 5 55

^H 3 ^po if

Butyl alcohol 10-15 5 - ** 0 3 6 40

₃ + _l0 . ₁₅ 5.40 ψ ₈

Glycerin $ 33

ENT ,, 100 g

HF 50 g / l ¹⁰ - ¹² ^ ^{30 3 3 60}

NH ^ NO ₃ 50 g / l

HNO ₃ 50 g / 1 ₂₀ 20-100 1 2 60 methyl alcohol

100 g / l

H ₃₂₁ ,

H ₂ SO ^ i * 0% + 10-15 10-150 1 5 80 CrO ₃ 7.5

Here, too, one received excellently polished objects These electrolytes can also "under the same conditions for objects made of copper, aluminum or their Applying alloys

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Examples 11-14

Objects made of copper, a copper-zinc alloy and copper-zinc-nickel alloys were used in the sense of the examples 1-4 treated.

Table 3

ρ »in min _n example electrolyte VA / dra 1st stage 2nd stage C

12 H ₃ PO ^ 6Of ₀ +

Isopropyl 12 5-30 2 5 30 • alcohol

13 H ₃ PO ₄ ? 5f> +

sec. butyl 15 5-30 2 8

alcohol

Glycerin $ 20 + 5-30 2 8 40 butyl alcohol $ 20
+ H ₂ O $ 20

Here, too, one received excellently polished objects. The electrolytes can also be used for polishing aluminum, Use aluminum alloys and corrosion-resistant steel.

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In the previous examples, the metal objects of the two process stages remained in the same electrolyte. But you can also, for example, an aluminum alloy in the first process step with an electrolyte from Example 1 of Treat table 1 and in the second stage with a different electrolyte. In the same way, this is possible for corrosion-resistant Steels from table 2 and for copper and copper alloys from table 3

Claims

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Claims (12)

P a fent claim.e IJ method for electrolytic polishing of metal articles, characterized gekennzeichne t, one dag in a first Verfaftrensstufe in an aqueous electrolyte electrolyzed _t until the desired Ausmas the intergranular corrosion occurred hati be followed in a second process stage reverses the polarity and now electrolytically to achieve the desired polishing amount removes the surface of the metal object 2. The method according to claim l _t characterized ge ke η η that the same electrolyte is used for both process stages 3. The method according to claim 1 or 2, characterized draws that the metal object is in the first Process stage as a cathode. switches. 4. The method according to claim 1 to 3 »characterized in that in both process stages with a voltage between 5 and 150 V. 5 «method according to claim 1 to ^ ₁ thereby marked draws that one in both process stages with a current density in the range of 1 - 150 A / dm. - 12 - 109829/1655 - 12 - lA-39 6. The method according to claim 1 to 5 »thereby geke η η draws ti that one works at an electrolyte temperature ^{between 20 and 90 0 C in both process stages.} 7. The method according to claim 1 to 6, characterized · that one for polishing in areas of the metal object provides it with an insulating mask before the second process stage. 8. The method according to claim 1 to 7, characterized in that the object to be polished turns on before immersing in the electrolyte in the circuit. 9. The method according to claim 1 to 8, characterized in that g e k e η η drawing χι et that the electrolyte contains phosphate ions. 10. The method according to claim 9i, characterized in that the electrolyte is an aqueous solution of sodium hydroxide and sodium phosphate. 11. The method according to claim 9ι, characterized in that the electrolyte is an aqueous solution of phosphoric acid, sulfuric acid and chromic acid. 12. The method according to claim 9, characterized in that the electrolyte is an aqueous solution of phosphoric acid, sulfuric acid and nitric acid. 13 · Method according to claim 9, characterized in that g e k e η η - draws that the electrolyte is an aqueous solution of phosphoric acid and an alcohol, especially propyl alcohol, butyl alcohol or glycerin. - 13 -10982 * 9/1655 - 13 - LA-39 026 Method according to Claims 1 "to 8, characterized in that the electrolyte is nitric acid and optionally hydric acid or ammonium nitrate and methyl alcohol contains. 10992 * 8/1658