DE1284811B - Process for reducing or preventing the hydrogen brittleness of objects made of non-ferrous metals - Google Patents

Description

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The invention relates to a method for vermin- It is known to use metals against the oxidative change or prevention of electrochemical corrosion in aqueous media electrochemically induced hydrogen brittleness. protect their surface completely with a It is known that metals are coated by chemical and coating of a more noble metal. This measure of electrochemical influences is subject to corrosion, but does not necessarily protect the metal against it being an oxidation of the free metal and thus the hydrogen embrittlement, but can in certain Destruction of the metal occurs. In contrast to cases, even accelerate the attack, It is these forms of corrosive attack on a metal From "The Industrial Chemist", 1958, p. 285

If the hydrogen embrittlement does not lead to destruction, it leads to anodic dissolution of the metal titanium of the metal by chemical reaction, but the io anodes made of titanium with small amounts of platinum or Metal suffers a decrease in its pliability to cover a platinum group metal. Farther d. H. an embrittlement that often leads to failure. is known from the Austrian patent specification The types of failure by hydrogen brittleness 187 896 and the German patent 386 514 die range from extreme brittleness and cracking to the use of oxidizing anolyte liquids to the formation of bubbles on the surface. It is used 15 tantalum anodes in contact, which are used as assume that this embrittlement by diffusion of effective anode surface serving platinum layer or atomic hydrogen in the metal causes platinum to partially cover the surface. The influences that cause embrittlement wear a coating.

depend on the metal and on the formation of atomic The Swiss patent specification 101 816 describes

Hydrogen in the vicinity of the metal. The at 20 an electrode, which consists of a platinum coating on a the surface of a metal is electrochemically inert carrier material such as glass, magnesia, chemical processes can result in the formation of ato- porcelain, quartz, carborundum, clay, produce marem hydrogen. This is particularly true according to the previous state of the art

the case in acidic electrolytes. known, molded body made of tantalum or titanium, which as

Metals that are immersed in an oxidizing anolyte liquid during electrolysis are loaded and therefore not to be coated with platinum in an oxidative manner in order to assimilate them in an oxidative manner exposed to can prevent exposure to the solution.

be exposed to atomic hydrogen. The invention is completely different

The speed of penetration of water- based on the hydrogen brittleness, the task substance generally depends on the concentration of 30 due to the absorption of atomic hydrogen in it Hydrogen on the metal surface. The reducing media without dissolving the relevant To prevent the existence of residual stresses in the metal, which is caused by the metal. Because of for example during cold forming, it seems that the task could be different to increase the rate of absorption. Sulfur-known measures to protect anodes Hydrogen solutions also increase the penetration, no indication of the method according to the invention speed of hydrogen in steel. give.

The hydrogen embrittlement are subject to many Me- The subject of the invention is a method for

talle. This phenomenon was found in tantalum and niobium, reducing or preventing them in aqueous certain titanium alloys, vanadium and some media electrochemically induced hydrogen alloys these metals as well as the corrosive fragility of objects made of non-ferrous metals, resistant pure chrome steels and for some such as tantalum, niobium, vanadium, tantalum-titanium alloys Types of carbon steels, especially edge steel, or tantalum-manganese alloys, which thereby observed. is characterized in that only a small part

Many attempts have been made to avoid this disruptive surface of these objects in a known manner to overcome the influence, for example by over- 45 with ruthenium, rhodium, palladium, osmium, monitoring of the purity of the metal and application of iridium, platinum, gold, rhenium or their alloys special heat treatments. However, it was being covered.

no perfect solution to the problem found. This partial covering of the surface can be done in

While it is still known the corrosion of a known manner due to plating with the noble non-oxidizable steels, such as chromium-50 metal, by welding, by rubbing the metal or Chrome-nickel steels, through the installation of surface, for example with a powder or the Prevent electrodes made of precious metals. End of a rod made of the noble metal, through bare As is known, these steels consist essentially of mechanical contact or the addition of a Iron and are therefore classified as ferrous metals. soluble salt to the aqueous solution, which is to From the fact that the corrosion that wets iron and protective metal takes place, predominantly made of iron alloys mostly the precious metals ruthenium, rhodium, palladium,

by chemical conversion of iron into iron osmium, iridium, platinum, gold and rhenium Bonding is effected by the galvanic Ab- than metals with low hydrogen overvoltage Divorce from small amounts of palladium, be considered platinum. It is believed that the or copper or through the installation of electrodes 60 mechanism according to which the metals with lower Precious metals or coal prevent hydrogen overvoltage from embrittling, but it was not to be concluded that it is completely based on this property. The atomic one other types of non-hydrogen due to absorbed hydrogen accumulates on the metal with lower levels Corrosion caused by ferrous metals - at the hydrogen overvoltage and not on the upper part Metal in its elementary state retains the area of the base metal or base alloy stays on - especially with tantel, niobium, vanadium. While the presence of atomic water-tantalum-titanium alloys and tantalum-manganese alloy on the surface of the base metal for diffusion wrestling can be reduced. of the hydrogen would lead to the base metal,

has the accumulation of atomic hydrogen on the metal with low hydrogen overvoltage only results in the binding of atomic hydrogen, whereby molecular hydrogen is released. hydrogen in the molecular state does not penetrate easily into the base metal or alloy, so that the Embrittlement by hydrogen absorption is prevented.

The amount of low hydrogen overvoltage metal required for effective protection is different. It depends on the metal to be protected, the influences on this metal and the the electrochemical conditions present, d. i.e. whether it is corrosive or cathodic Load, as well as the precious metal used. In many cases it will be an effective protection already achieved through tiny amounts of the precious metals mentioned.

For example, the hydrogen brittleness of tantalum was prevented by using a piece of platinum foil attached to the tantalum surface by spot welding. It was found that one Ratio of the effective platinum area to the tantalum area of only 1: 5000 the tantalum is still effective was protected.

In another experiment, tantalum was protected against embrittlement by hydrogen ions in hydrochloric acid achieved by rubbing platinum powder onto the surface of the tantalum sample or with the end of a Platinum wire was painted over the tantalum surface.

An annealed sample of a tantalum sheet was in electrical contact with a platinum wire in concentrated Hydrochloric acid kept at 190 ° C. After 90 hours the sample was still pliable and showed none Cracks when bent 180 ° C so that the ends lay flat on top of each other. One not with platinum Protected comparison sample was brittle and broke when

ίο bending. A number of other experiments were carried out in which the connection between the metals to be protected and platinum and other precious metals was established in various ways. The results of these tests are shown in Table 1. 3.67 cm ² strips of commercially available, annealed tantalum sheet were used. In some cases, the precious metal was attached to the tantalum sheet by spot welding. In other cases, pieces of precious metal foil were attached to the tantalum

ao samples attached. Furthermore, cores of a strand of the noble metal were wound around the tantalum sample. In the In cases where the tantalum sheet was clad with a noble metal, the coating was extremely thin and interrupted. Its thickness was only 1.02 μm. Of the

The coating was not always continuous, but in most cases it was sufficient if only a part the surface of the samples was coated. In some experiments, salts of the precious metals were the most active Media added.

Tabel

Influence of precious metals on the hydrogen brittleness of tantalum in concentrated hydrochloric acid

at 19O ⁰ C

Point-
welds
of 0.25 mm 0 per sample 2 3 6th Type of connection 0 Pieces 4th V Strands
veins, G 6th V < ^b ) of Precious metal with the tantalum sample proportion of 1/ 1/ completely ver powder Precious metal salt Diameter; V 1 G G G Foils
pieces of
2.54 cm V 1 G 0.635 mm G Sample surface plated; the plated area / 2 /1 scratches in surface the acid Precious metal Number of point V G G G Edge- V G G thick, G G G G rubbed in added; welds V V G G 15.875 mm G") 1/ G G 0.005 g chloride V G G G länae. V G G GW long G G <°) / 4 G in solution V G Zahfder V G G 0 j 1 G G V G V V j U G G platinum V V ^T
V V G G G Palladium ... V V V V G G gold V V V V G G iridium V G G G Rhodium .... G osmium G G Ruthenium .. G Rhenium .... V silver V

V = embrittled, cracked when bent.

G = pliable, no signs of brittleness, no tearing when bent by 180 ^° C.

(a) = Only two pieces of foil were used in this case.

(b) = One third of the sample surface covered with the film.

(c) = Three pieces of iridium wire were spot welded to each side of the sample.

The results in Table 1 show that the presence of the noble metals in the form of a coating, Wire, powder, foil, spot welds and as chloride in the acidic medium cause embrittlement prevented. The extremely small amounts of platinum that are effective are interesting. It can also be seen that silver does not belong to this group of metals with low hydrogen overvoltage.

It has been found that tantalum, especially the metal in cold rolled form, becomes very brittle when

it is used as a cathode in electrolysis. Tests were therefore carried out to determine whether through the presence of platinum or gold also the hydrogen brittleness under these conditions would be prevented. The results of these tests are given in Table 2. :

Tabel

Influence of precious metals on the hydrogen brittleness of tantalum under cathodic loading in 1 n-sulfur

acid at room temperature

Shape of the precious metal

Condition of the sample

Current density hours mA / cm ² 30th 16.5 30th 16.5 10 20th 10 20th 20th 1.25 20th 1.25 10 1.5 10 1.5

Result of bending tests

Without precious metal

Fully platinum plated

Without precious metal

Fully platinum plated

Without precious metal

Platinum-plated and scarred

Without precious metal

Completely gold plated

cold rolled

cold rolled

cold rolled

cold rolled

cold rolled from a short billet cold rolled from a short billet cold rolled from a short billet cold rolled from a cruciform block torn no cracks cracked no cracks cracked no cracks cracked no cracks

From the values in Table 2 it can be seen that the presence of platinum reduces the hydrogen brittleness of Tantalum under cathodic loading prevents, however, the required ratio of platinum to Tantalum seems to be higher than it is to prevent fragility under the influence of more concentrated Hydrochloric acid at 190 ° C is necessary. This is undoubtedly due to the fact that under the conditions During electrolysis, hydrogen atoms are present on the surface of the tantalum to a greater extent than in the experiments with hydrochloric acid. It is more than likely the low ratio of platinum to tantalum would also be applicable for the electrolysis experiments if the current density were adjusted so that the Hydrogen evolution would be the same as in the experiments with hydrochloric acid. As a result of persistence of the platinum-plated tantalum samples against hydrogen brittleness when used as cathodes they are particularly useful as electrodes.

Alloys of tantalum and titanium containing 10 to 50% titanium are in terms of corrosion resistance in some respects comparable to tantalum, but with regard to some highly corrosive influences not as stable as tantalum. Since these alloys also tend to become brittle in certain media, Attempts have been made to prevent this type of damage by using precious metals. An annealed alloy of 60% tantalum and 40% titanium in 15% hydrochloric acid at 190 ° C. was examined. The results of these tests are summarized in Table 3.

Table 3
Influence of precious metals on the hydrogen brittleness of an alloy made from 60% tantalum and 40% titanium

Precious metal present as Condition of the sample Acting medium Results of
Bending tests - cold rolled and in
concentrated HF
etched 15% HCl
190 ° C, 67 hours brittle - annealed ^ 15% HCl,
190 ⁰ C, 66 hours brittle Platinum-plated all around annealed ^<a> 15% HCl,
19O ⁰ C, 66 hours no cracks Cathodically loaded in 1 nH ₂ SO ₄
as an electrolyte - annealed ^<a> Current density 83 mA / cm ² ,
16 hours brittle Platinum-plated all around annealed ^ Current density 83 mA / cm ² ,
16 hours no cracks annealed ^ Current density 100 mA / cm ² ,
28 hours brittle

(a) Annealed at 1230 ^° C. for 30 minutes.

(b) annealed for 1 hour at 1250 ⁰ C under a vacuum of 0.1 x ΙΟ- ³ mm Hg.

From the results in Table 3, it can be seen that 6g was found to be an unclad alloy

that a very thin platinum coating on the surface of 60% tantalum and 40% titanium became brittle,

the alloy prevented embrittlement. In the meantime a thin platinum coating on the surface

look for a cathodic load that protected the alloy against embrittlement.

In general, niobium does not have the corrosion resistance of tantalum, but it is one of the metals which can be described as good in this regard. Niobium also tends to be hydrogen brittle, and to a greater extent than tantalum, possibly due to the somewhat poorer corrosion resistance and the higher amount of hydrogen evolved during corrosion.

Versprödungsversuche in 10 ° / ₀ hydrochloric acid at

190 ° C were carried out with niobium samples with and without platinum on the surface. Here were the unplated annealed samples brittle, while samples that were half-plated with platinum stayed lithe. In experiments with cathodic loading it was found that niobium by plating with Platinum can be protected against hydrogen brittleness can. The results of the tests are given in Table 4.

Table 4 Influence of noble metals on the hydrogen brittleness of niobium

Precious metal present as State
the sample Acting medium Results of
Bending tests Platinum-plated, surface of the sample for
Half coated annealed *
annealed *
annealed *
annealed *
annealed * 10% HCl at 190 ° C
10% HCl at 190 ° C brittle
no cracks Cathodically loaded in 1 nH ₂ SO ₄ Platinum-plated all around Current density 69 mA / cm ² , 2 hours
Current density 10 mA / cm ^a , 24 hours
Current density 10 mA / crn ⁸ brittle
brittle
no cracks

* Annealed for 30 minutes at 1175 ° C under a vacuum of 0.1 x 10 ^-3 mm Hg.

Vanadium metal is extremely susceptible to nascent hydrogen and is enhanced by its presence extremely brittle. Tests were carried out to determine whether the metals were lower with Hydrogen overvoltage the embrittlement of van

prevent dium. These tests were carried out both in acidic solutions and under cathodic loading carried out. The results of the tests are given in Table 5.

Table 5 Influence of noble metals on the hydrogen brittleness of vanadium

Precious metal present as State
the sample Acting medium Results
of bending tests cold rolled boiling 5% HCl very brittle * Platinum wire, 4 cores ** cold rolled boiling 5% HCl could loop
be bent Platinum foil, 2.54 cm square
Edge length cold rolled boiling 5 ° / _o HCl could loop
be bent Half of the surface
platinum plated cold rolled boiling 5% HCl could loop
be bent Platinum-plated all around cold rolled boiling 5% HCl could loop
be bent Cathodically loaded in 1 nH ₂ SO ₄
as an electrolyte - cold rolled 10 mA / cm ² , 3 hours brittle Platinum-plated all around cold rolled 10 mA / cm ² , 3 hours no cracks - cold rolled 67 mA / cm ^a , 2 hours brittle - cold rolled 10 mA / cm ² , 3 hours brittle Platinum-plated all around and
scarred cold rolled 10 mA / cm ² , 3 hours better than nothing-
plated sample

* Original sample in the cold-rolled condition could be bent 180 °. ** Area of the samples examined 3.23 to 4.52 cm ² . Length of one wire of the Pt litz wire approx. 15.875 mm.

809640/1674

The experiments with boiling 5% hydrochloric acid showed that unalloyed cold-rolled vanadium was extremely high becomes brittle. The presence of platinum in the form of wire or as a coating causes embrittlement greatly reduced. The platinum coating prevents embrittlement under cathodic loading.

About damage to titanium or titanium alloys due to hydrogen brittleness due to corrosion is not reported often. In spite of this, in a few cases this phenomenon occurred in certain batches a titanium alloy containing 8% manganese

10

posed. Studies have shown that the brittleness is prevented by the presence of platinum in contact with the claimed metal during the test in a 10 ° / ₀ hydrochloric acid solution while the bare metal crack in a few minutes. In further tests with this alloy it was found that platinum plating of part of the surface as well as palladium wire prevented the brittleness. The test results are given in Table 6.

Tabel

Influence of precious metals on the prevention of hydrogen embrittlement of a titanium special alloy (8% Mn) in 10 ° / _o hydrochloric acid at room temperature

Shape of the precious metal Results of the exams
on clamped samples * Without precious metal
Platinum wire, multiple cores
Half surface platinum-plated
The entire surface is platinum-plated
Several palladium wire cores broke in 30 minutes
no embrittlement after 120 hours **
no embrittlement after 100 hours **
no embrittlement after 100 hours **
no embrittlement after 120 hours **

* Sheet metal sample 114.3 mm long, 12.7 mm wide, by fastening in a holder made of the same material with a 101.6 mm long slot

bent by 180 °.

** Attempt terminated after this time.
Note: length of a platinum wire core approx. 25.4 mm.

Claims (1)

Claim: Process for reducing or preventing those electrochemically induced in aqueous media Hydrogen brittleness of objects made of non-ferrous metals such as tantalum, niobium, vanadium, Tantalum-titanium alloys or tantalum-manganese alloys that are in contact with atomic Hydrogen, characterized in that only a small part of the surface these objects in a known manner with ruthenium, rhodium, palladium, osmium, iridium, Platinum, gold, rhenium or their alloys is covered.