DE1521875A1 - Process for protecting titanium against etching - Google Patents

Description

PATENTANWÄLTE * 4l 1 IAC · DR.-INQ. H. FINCKE - · munOMEN β, | ·. hpfl * 9W

DIPL.-ING. H. BOHR DIPL.-ΙΝΘ. 8. STAEQER

i.r.r. ». JJ4 »4I I OZ I O / D

U 20 684 Case 5 * 9

Dr. Expl,

Description mm Patentgeeueh

of the company IUiT CHEUIOlIS »0., New York, N.T. UNITED STATES"

concerning

"Proceedings sub protect ron Titan against the · Xtsen ". '

* s: April 14, 1965 - U. 8. A.

The invention relates to a new method of preventing the etching of titanium surfaces.

Because of its resilience to the unequal attack becomes titanium metal in the diffusion process of devices or apparatus which are exposed to corrosive materials during use, used. For example, titanium is used in heating elements, respectively Heat registers, heat exchangers, racks, etc., which are in Metal plating process or metal coating process

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It has been found, however, that even corrosion-resistant titanium can be severely etched by solutions containing halide ions, especially if the solution is acidic and contains an oxidizing agent. Such solutions can be overlooked with ear? , When plating or about Siehen with many · !, in the acid plating or on loan with copper, in the acid plating besiehungsweise About Siehen with tin in the acid plating or coating with zinc, etc. is used · Blder sum plating are besiehungsweise About Siehen with chromium for the \ Ren oxidizing baths with a content of halides are typical and it will be referred to below for the sake of simplicity

Baths for plating or coated with chromium typically contain high concentrations of chromic acid, for example about 130 to 500 g / l. Warden These baths can by fluoride ions, including simple fluoride and complex fluorides such as Silicofluoride besiehungsweise fluosilikate, fluoalumlnate fluoborate _v, etc., catalyzes Fluotitanate · The plating or coating is generally conducted at elevated temperatures, for example, 34-72 ⁰ O performed. Under these conditions, heat exchangers, coils, hot elements or the like made of titanium, which may be in the bathroom, are quickly attacked and watered. The service life or durability of such a device or apparatus is reduced as a result, which leads to excessive replacement and replacement costs and undercutting or maintenance costs. So far there has not been a satisfactory process for

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prevention of this corrosion found, tack ·, overlay, streaks or ligaments and the like loosen, crumble or relationally leaf or fall off into the bath and also reduce the heat transfer drastically, which is of course very undesirable.

E * is an object of the invention, a new way of protecting archery of titanium against itsen on contact with corrosive ones Provide baths. The invention is also directed to a method of preventing titanium metal from coming into contact with baths for plating or plating with chrome. Other goals can be found in the following description

According to certain features, the erfindungsgemtfie retracts, for protecting titanium umfabt against the Itzen upon immersion in an aqueous acidic solution bringing the coagulated th Titanes ta intimate electrical contact with a metal with low hydrogen overvoltage, and maintaining a low cathodic current density on said titanium Regarding on an anode in the solution mentioned

The method according to the invention is typically a shooter of titanium in the form of exposed or exposed titanium surfaces, effective Surface the surface of a plating or coating device or a plating or covering apparatus, such as of heating coils, heating elements respectively Heating registers, heat exchangers, partitions, tubes

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or the like, his * The device or apparatus can made of titanium plates, titanium rods, titanium clad plates, etc. be made. Bas titanium can be technically pure titanium or an alloy with a high titanium content, for example n with a content of at least 93% titanium.

During use, the Titanrorrlohtuag or over apparatus in an aqueous acidic solution including Plattierbader or baths sun plating or coat, etc. immersed Reinigungebäder, stripping or decals (w stripping baths). The acidic solution can typically be dissolved ealide ions, such as chloride ions, simple ι clay ions. Fluorides, ions of complex fluorides, etc., contain »The method according to the invention is particularly useful when the aqueous acidic solution is a solution plating or coating with chromium containing chromic acid and fluoride, either as simple fluoride or as complex fluoride, such as Silicofluorid or fluoailikat, Fluoaluminat, Fluotitanat, Fluoboraty etc. is.

According to the invention, the titanium surface to be protected is provided with a * Metal with low hydrogen overvoltage made intimate electrical contact · The hydrogen overvoltage is a UaB the work that is required to release or develop hydrogen at the cathode, among other things. It is traditionally like that than the difference between the potential of the electrode if hydrogen was released during the electrolysis, respectively is developed, and the potential of reversible respectively

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reversible hydrogen electrode in electromotive force (in emf), where both potentials are related to the same electrolyte. A cathode with a lower water overvoltage therefore produces hydrogen at a lower voltage than a cathode or ol; a higher hydrogen voltage. Metals with a low hydrogen concentration, "as the designation is used in this application, are those metals which have a lower hydrogen or activation overvoltage than that of the well-known metals with intermediate hydrogen overvoltage, such as clay copper," fyplschly the metals which may be used in performing the Sr * finding that have an overvoltage equal to or less than the overvoltage of a clean solid wrap. These metals with a lower overvoltage have an overvoltage of less than about 0.3 V at a current density of 0.1 A per dm ² , for example as described in "Xhe Corrosion Handbook ¹ * by Ξ. Ühlig (John Wiley 1948) * page 1 144. As will be understood by those skilled in the art, the wafer coating of a metal can be modified by a method of treating the metal surface.

Typical metals with low hydrogen overvoltage according to the Invention include platinum, palladium, rhodium, gold, iridium and ffickel including black nickel and "Kleotrolese-Hicksls", preferably in finely divided ode; » active catalytic Jörn.

These metals can be used in a:; ur delivery of a low Wa * - Substantial overvoltage suitable Po3 «m in intimate electrical contact

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be brought with the su protective utan surface, you can used in various ways in connection with the KLtan surface will. A very useful procedure for use The metal with a low hydrogen overvoltage is the electrolytic or galvanic deposition Precipitation of the same from a solution with a content of ions of the metal with low hydrogen! overvoltage »Vorsogewele · if the solution is a washable solution of a water-soluble compound » which in solution are ions of the metal at low waaaeretoff overvoltage results «

Tuck compounds of the metals bit lower Waseerstoffüberapannung uafaaeen salts, acids ADRs · _t can be the metal with low Vasseratoffüberspannung in the form of ions resulting from simple ions or Komplexionon. For example, solutions of chloroplatinic acid can be used as halogenated metals, cyanides, and, for example, the ions of gold, cyanide, and halogenated salts, for example the ions of gold and halogenated salts, can also be used as the ions of gold, cyanide, and salts of the platinum ion source and solutions of chlorogollic acid can be used as tetrachlorooldic acid Poreel AuOj (aurations), etc. ^ be used. Ss vx ^ ntr * unlohe Koulvalente metal compounds are TerWendtt · If there "metal old lower faseeretofjraberspanmmg can exist in more than 1 oxidation" - or valence mute, each of these can be used for the plating bath or bath for flatting or coating.

Typical water-soluble compounds of metals that can be used old low hydrogen tension include palladium dichloride,

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Chloroplatinic acid, platinum chloride, platinum i inrtnodlnltrlt or diasdnoplatinum & initrite, Ealiuachloroplatinit, Potassium chloroplatinit, Tetramainplatln (XI) -HLorid, Tetr * jeinplatin (II) -fluorid (II) -fluoride, chloro-di-urol (II) -fluoride, chloro-diurol (II) -fluoride, chloro-diurolate, gold, fluoride chloride, chloro-di-urolium chloride, gold compounds eind Falladiumchlorid, gold chloride and chloroplatinic acid and preferably they are turned rt in aqueous solution.

The titanium surface, which is to be protected, can be lower than the metal Hydrogen overvoltage through gÄlranieche separation atie- | hitting the metal with low hydrogen overvoltage on the surface of the bench in intimate electrical contact to be brought. Typically this can be done by dipping the Titanium surface as a cathode in a solution containing ions of the metal with low hydrogen overvoltage and sending it through an electric current Bwiachen the said titanium surface and an anode accomplished in said solution will.

Preferably the metal is with a low hydrogen overvoltage electrodeposited from an aqueous solution besiehungoweise precipitated. Typiacherwaiee the aqueous solution can etwe. 0.5 to 20 g / l, preferably 2 to 10 g / l, for example 5 g / l, Contains metal ions with a low hydrogen overvoltage, calculated as metal. It can be compatible acids, for example Hydrochloric acid or salts vo.a complexing agent ions, for example se sodium cyanide, can be added to lower the metal nit

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Keep hydrogen overvoltage in solution by the desired pH value or an excess of complexing agent ions is »maintained ·

The aqueous solutions can during the galvanic deposition or deposition dee metal with low hydrogen overvoltage, typically at a temperature ron about 20 to 90 ° C _t be kept preferably 25 to 60 ⁰ O, for example 40 ⁰ O _9,! Typically dl "electrodeposition can beziehungeweise Precipitation at a cathode etrom density of about 0.5 Me 5 Vdm ² , preferably 0.8 to 2 Α / δ « ² , for example 1 A / dm ² , for about 0.2 to 5 minutes, preferably 0.5 to 2 meows, for example 1 minute. Oils Thickness of the deposition of the metal with low hydrogen overvoltage or the coating of the metal with low hydrogen overvoltage can typically be of the order of 0.05 to 0.5 yu, preferably 0.1 to 0.2 / u, for example 0.15 yu. If necessary, thicker deposits or coatings can be used, but this does not result in any substantial European tortelle.

You can use other methods to bring the fits Intimate electrical contact with the metal with low water • tofoverapension be used. For example, the Vitas can be filled with a full of the metal with low hydrogen overburdening covered or covered. It can be done by dipping into a hot melt, by dusting with metal powder with lower Waoaorstoff overvoltage and subsequent melting, by flattening

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be sucked over by dipping, etc. The low hydrogen overvoltage metal can make thin holes having (foraminous) plate or film including Siebo beZiehungaweise agitation, bloomed or expanded metals or expanded metal, perforated or perforated metals, etc. in heartfelt electrical contact with the surface to be protected, preferably in the immediate vicinity of the titanium surface to be protected or directly adjacent to them and in electrical connection with the titanium surface to be protected been. The plate or foil having holes can be made from the metal with a low hydrogen overvoltage or it can be one with a metal with low hydrogen overvoltage, like platinum coated with palladium, in the above given way be coated metal, for example steel. The titanium to be protected against etching is preferably surface covered or occupied with the plate or solid having thin holes and adjoins or adjoins them is this adjacent.

The amount of des Metal with low hydrogen overvoltage can be very low be. Larger amounts can be used, however, it has been found that such larger meogens, that is, thicker layers are not significantly better with regard to the prevention of undesired X-etching. The preferred amount of metal can be included low hydrogen overvoltage approximates that of the formation of a Monomolecular layer of the same on the treated area

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be required, but it can be established that an uninterrupted or steady "onomolecular layer" cannot form. Instead, the low hydrogen overvoltage metal can be in the form of separate "islands" and a significant percentage of the treated surface can be seen to be exposed to contact with the flatting solution or plating. It would be expected that such exposed or exposed surfaces would not be protected and would be drilled in the same way as a completely untreated surface.Surprisingly, it was found that even these relatively uneven treatments were very much in terms of removing the undesirable etching of the entire treated surface of the titanium object more ⁴ "oind sam, when used under corrosive conditions in the manner described below ·

During the period during which the titanium surface is immersed in intimate electrical contact with the metal with low hydrogen overvoltage in the aqueous acidic solution, a cathode potential of low current density is maintained on this in relation to an anode in the solution mentioned. In this way, the titanium surface is kept in intimate electrical contact with the metal with a low hydrogen overvoltage in relation to an anode in the cathodic solution. By running a current with a low current density between them. The low current density which can be used is typically 0.1 to 2 A / dm ² , preferably 0.5 to 1 A / dm ² , for example 0.8 A / dm ² .

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All anode, in relation to which the cathodic © potential is held up, kern, relate s-areiee to whom. the aqueous acidic solution is a Flattierüttgslöstn, 5 or solution sum Flattieren or coating, the anode or anodes normally used in the plating or overshooting operation. Other parts of the door direction, for example partition walls, container walls, etc., can also act as anodes. The desired current density can be supplied by a direct current source with relatively low power (low output source of direct current), which is electrically connected both to the anode and to the tube and stand.

The invention is explained in more detail with reference to the following examples, which are not to be interpreted as limiting.

Examples 1 to 5

There were 5 tests strips with a size of 2.54 cm × 7.62 cm × 0.08 approx. Cut from a plate made of a titanium alloy with a composition of 9β # Ti and 2 $ Bl. 5 of the strips were coated with a platinum coating with a platinum silver plating of 0.15 M by electrolyzing them as cathode for 1 minute in an aqueous solution containing 6 g platinum / l (16 g H ₂ FtCl-. 6 H ₂ OA) and 300 cm ^{3 of} aqueous hydrochloric acid with a specific weight of 1 _r 19 per 1 at a current density of etse 1 A / dm ² . The remaining ?. Strips were not plated bazie-

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in other words not excessive "

Each strip was cleaned, weighed and placed in a Okrotelureplattierungsbad or CFCC? Omeaurebad sua Flat animals be · relationship as the following composition at 55 ⁰ O tibet pull submerged.

Component concentration (in g / l)

CrO ₃ 225

(ala SrSO _4. added) 1.2

1 plated or coated strip and 1 unplated or uncoated strip were simply immersed in the solution without electricity. 2 plated or coated strips and 1 unplated or uncoated strip were made cathodic during the Eintauohena bit 0.8 k / Qar (0.05 asl). Ak Έ * & 9 of the experiment, the strips were weighed again and the dissolved titanium tightness was harvested and calculated as the weight loss in g per cm of surface per hour · Cg / approx. ² / hour). The results of this comparison are summarized in the following table *

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BATH ORIGINAL Tabel

example surface conditions duration
of the BIn- weight
before the
Dew
chen
(in g) weight
after this
Dew
chen
(in g) Weight
under
divorced Weight change
in g / cm / hour 1 Pt electroplating
at or gal
vanish Pt coating (in hours
the) 7.33 ** 7.33 * 3 -0.0001 negligible Pt electroplating
bezi »ftun £ Rwn * ee gal
vanish Pt coating cathodic 40 7.5570 7.5573 ♦ 0.000, ▼ negligible 3 Pb electroplating
respectively gal
vanic Pt oversug cathodic 63 7.5728 7.5 * 10 -0.0318 -0.000031 & 4th no electroplat
relationship
wise no electroplating
shear coating no electricity 40 7.2738 7.2578 -0.0160 -0.000016 5
ι no blelctroplat-
relationship
wise no electroplating
shear coating no electricity 40 7,156 * 6.5 * 78 -0.6086 -0.00059 cathodic 40

As can be seen from the table, see the examples 1 and 2, which illustrate the practice of the invention, there was essentially no change in weight during the experiment. By this new inventive method protected titanium surfaces therefore remain free of corrosion even after a long period of use and etchings · In contrast to this, the strips of Examples 3t 4- and 5 by the solution sum plating and coating, respectively badly etched with chrome. It is noteworthy that the plate electroplating or the galvanic flatin oversugation in example 3 did not protect the titanium, but in reality the corrosion compared to bare titanium without plating, deposition respectively coating of example 4 increased to twice the · Be It is also noteworthy that the bare titanium of Example · · 5 through the catholic treatment alone was not protected, but instead of deaasn it corroded about 38 times as fast as bare titanium, which was simply swapped into the solution (Example 4)

Various modifications of the invention are possible. Claims

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Claims (1)

Claims e 1 ») Process for protecting titanium against etching when immersing it in an aqueous acidic solution, thereby £ jekenn5; calibrates, that the titanium is treated with a metal with a low hydrogen bias voltage brings into intimate electrical contact and on the titanium a low cathodic current density in Maintains reference to an anode in said solution. 2o) Method according to claim 1, characterized in that one as an aqueous, acidic solution, it is one which contains large halide ions contains, used. 3.) The method according to claim 1 or 2, dadirch gekennzoic. ^ Inet that non al3 aqueous acidic solution a solution for plating or coating with chromium with a content of Chromic acid and fluoride used. 4 ") Method according to claim 1 to 3, characterized in that the metal with low hydrogen overvoltage on the Electroplated titanium. 5.) Method according to claim 1 to 4, characterized in that the metal with a low hydrogen overvoltage is platinum, Palladium, rhodium, gold, iridium or nickel used, where platinum is reprimanded before. 6o) method no.ch claim 1 bLs 5 »characterized in that one as a metal with a low hydrogen overvoltage 9098A3 / U07 BATH ORIGINAL those with a hydrogen overvoltage of less than about 0.3 V at a current density of 0.1 A / dm ² are used. 7.) Method according to claim 1 to 6, characterized in that the low cathodic current density used is about 0.1 to 2 Λ / dcr, preferably about 0.5 to 1 A / am . MIMTAMMlfl ML- (NO H Vienna Mti. · «· PWC4N · 1.CTAIMl BATH ORIGINAL 9098A3 / U07