DK169354B1 - Melting bath and method for electrolytic surface coating with refractory metals from fluoride-containing salt melts - Google Patents

Abstract

The invention relates to a molten bath for plating with high-melting metals, in particular niobium and tantalum. The bath consists of an alkali metal fluoride melt, which contains oxide ions and ions of the metal to be precipitated. The molar ratio between the metal to be precipitated and the oxide ions, or the other cations in the melt, must be held within given ratios. The redox level must be held at a value which corresponds to that which is reached when the molten bath is in contact with the particular high-melting metal in the metallic form. The invention also relates to a process in which the bath in question is used.

Description

i DK 169354 B1in DK 169354 B1

Opfindelsen angår et smeltebad af den i krav l's indledning angivne art.The invention relates to a melt bath of the kind set forth in the preamble of claim 1.

Refractory-metaller (niob, tantal, zirkon, molybdæn, wolf-5 ram m.v.) er generelt meget modstandsdygtige overfor korrosion i sure og oxiderende medier, fx angribes Nb og Ta kun i ringe grad af 200°C varm koncentreret svovlsyre og af elementært chlor. Desuden kan de modstå høje temperaturer (smeltepunkter > 2000°C) under ikke oxiderende atmosfære.Refractory metals (niobium, tantalum, zircon, molybdenum, wolfram, etc.) are generally very resistant to corrosion in acidic and oxidizing media, for example Nb and Ta are attacked only to a small extent by 200 ° C hot concentrated sulfuric acid and of elemental chlorine . In addition, they can withstand high temperatures (melting points> 2000 ° C) under non-oxidizing atmosphere.

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Anvendelsesmulighederne for belægninger af niob- og tantal metal til korrosionsbeskyttelse af specielt udsatte dele i ventiler, flowmetre, pumper og lignende vil være store i den kemiske industri og andre industrier, hvor der kræves 15 stor korrosionsresistens.The applications of niobium and tantalum metal coatings for the corrosion protection of specially exposed parts of valves, flowmeters, pumps and the like will be great in the chemical and other industries where 15 high corrosion resistance is required.

Belægninger af refractory metaller kan udfældes elektroly-tisk fra chlorid- og fluoridholdige saltsmelter. Der er i litteraturen beskrevet metoder hertil (G.W. Mellors and S.Refractory metal coatings can be electrolytically precipitated from chloride and fluoride-containing salt melts. Methods are described in the literature (G.W. Mellors and S.

20 Senderoff, US Pat. 3,444,058 (1969), J.E. Perry, US Pat.20 Senderoff, U.S. Pat. 3,444,058 (1969), J.E. Perry, US Pat.

3,371,020 (1968), G.P. Capsimalis, E.S. Chen, R.E. Peterson and I. Ahmad, J. Appl. Electrochem. 17, 253 (1987), P.3,371,020 (1968), G.P. Capsimalis, E.S. Chen, R.E. Peterson and I. Ahmad, J. Appl. Electrochem. 17, 253 (1987), P.

Los and J. Joslak, B. Electrochem. 5, 829 (1989), P. Taxil and J. Mahenc, J. Appl. Electrochem. Γ7, 261 (1987)), men 25 det har i praksis vist sig vanskeligt at opnå teknisk og økonomisk tilfredsstillende resultater særlig med hensyn til niobbelægninger. Problemerne består blandt andet i at undgå udfældninger, der indeholder alkalimetaller, oxider og komplekse oxosalte af refractory metallerne.Los and J. Joslak, B. Electrochem. 5, 829 (1989), P. Taxil and J. Mahenc, J. Appl. Electrochem. Γ7, 261 (1987)), but in practice it has proved difficult to obtain technically and economically satisfactory results, especially with regard to niobium coatings. The problems include avoiding precipitates containing alkali metals, oxides and complex oxo salts of the refractory metals.

30 Fælles for de tidligere beskrevne badtyper til elektroly-tisk overfladebelægning er, at de som anioner kun indeholder fluorid og komplekse fluorider og i enkelte tilfælde chlorider (V.I. Konstantinov, E.G. Polyakov and P.T. Stan-35 grit, Electrochemica Acta 26., 445 (1981) , A.N. Baimakov, S.A. Kuznetsov, E.G. Polyakov and P.T. Stangrit, Elektrok- DK 169354 B1 2 him 2J-, 597 (1985)). Bade indeholdende chlorider har dog oftest givet dendrittiske udfældninger eller har bevirket dannelse af lavere positive oxidationstrin af refractory metallerne. Det har hidtil været antaget, at selv små 5 mængder oxid er skadelig for udfældningskvaliteten, når rene fluoridbade blev anvendt. Der er dog i litteraturen beskrevet processer, hvor niob udfældes på katoden fra blandede fluorid-chlorid smelter tilsat K2NbF7 og Nb205 (V.I. Konstantinov, E.G. Polyakov and P.T. Stangrit, Elec-10 trochemica Acta 26., 445 (1981), A.N. Baimakov, S.A. Kuznetsov, E.G. Polyakov and P.T. Stangrit, Elektrokhim 21, 597 (1985)).30 Common to the previously described bath types for electrolytic coating are that as anions they contain only fluoride and complex fluorides and in some cases chlorides (VI Konstantinov, EG Polyakov and PT Stan-35 grit, Electrochemica Acta 26. 445 (1981 ), AN Baimakov, SA Kuznetsov, EG Polyakov and PT Stangrit, Elektrok- DK 169354 B1 2 him 2J-, 597 (1985)). However, baths containing chlorides have most often produced dendritic precipitates or have resulted in the formation of lower positive oxidation steps of the refractory metals. It has been hitherto assumed that even small amounts of oxide are detrimental to the precipitation quality when pure fluoride baths were used. However, processes have described in the literature that niobium precipitates on the cathode from mixed fluoride chloride melts added with K2NbF7 and Nb205 (VI Konstantinov, EG Polyakov and PT Stangrit, Elec-10 trochemica Acta 26, 445 (1981), AN Baimakov, SA Kuznetsov, EG Polyakov and PT Stangrit, Elektrokhim 21, 597 (1985)).

Fra US patentskrift nr. 1,815,054 kendes desuden en pro-15 ces, hvor refractory metaller, specielt tantal kan fremstilles ved elektrolyse af smeltebade af alkalimetalhali-der (specielt fluorid), tilsat alkalimetal-refractoryme-talhalogenid dobbeltsalte og et ioniserbart oxygenholdigt salt af refractory metallet. Refractory metallet kan ved 20 denne proces kun fås på pulverform og ikke som et sammenhængende overfladelag på katoden. Der anvendes ikke reduktion af smeltebadet, og den oxygenholdige forbindelse de-komponeres ved anoden.U.S. Patent No. 1,815,054 also discloses a process wherein refractory metals, especially tantalum, can be prepared by electrolysis of alkali metal halide melting agents (especially fluoride), with double alkali metal refractory metal halide and an ionizable oxygen-containing salt of the refractory metal. . In this process, the refractory metal can only be obtained in powder form and not as a coherent surface layer on the cathode. No reduction of the melt bath is used and the oxygen-containing compound is decomposed at the anode.

25 Den foreliggende opfindelse, der er af den i krav l's indledning angivne art, er ejendommelig ved det i krav l's kendetegnende del angivne. Ved anvendelse af saltsmelte-bade ifølge opfindelsen undgås de hidtil kendte ulemper, som urene og usammenhængende overfladelag, og pletteringen 30 med de nævnte metaller kan udføres kontinuert med et økonomisk og teknisk tilfredsstillende resultat.The present invention, which is of the kind set forth in the preamble of claim 1, is characterized by the characterizing part of claim 1. The use of salt melt baths according to the invention avoids the known drawbacks such as impure and incoherent surface layers, and the plating 30 with said metals can be carried out continuously with an economically and technically satisfactory result.

Opfindelsen angår ligeledes en fremgangsmåde som angivet i krav 4's indledning, der er ejendommelig ved det i krav 35 4's kendetegnende del angivne.The invention also relates to a method as claimed in the preamble of claim 4, which is characterized by the characterizing part of claim 35 4.

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Saltsmeltebadene ifølge opfindelsen indeholder foruden fluorid-anioner en væsentlig mængde oxidanioner. Bade med denne sammensætning kan anvendes til elektrolytisk plettering af finkrystalliske, coherente og adhæderende overfla-5 delag af refractory metaller.The salt melt baths of the invention contain, in addition to fluoride anions, a substantial amount of oxide anions. Baths of this composition can be used for electrolytic plating of fine crystalline, coherent and adhesive surface layers of refractory metals.

Plettering med refractory metaller fra fluoridbade tilsat oxidanioner har ikke tidligere været kendt, og anvendelsen af disse bade medfører som nævnt store fordele såvel af 10 teknisk som af økonomisk art. Dette er eftervist ved undersøgelse af strømudbyttet og ved elektronmikroskopi og EDX-analyser af det udfældede metal.Plating with refractory metals from fluoride baths with oxide anions has not been known in the past, and the use of these baths, as mentioned, brings great advantages both technically and economically. This has been demonstrated by the current yield and by electron microscopy and EDX analyzes of the precipitated metal.

Ved pletteringen skal smeltebadets indhold af metalioner 15 af det refractory metal, der skal udfældes, ligge mellem 1 og 8 atom %, og molforholdet mellem oxid og metal skal ligge i intervallet 0,1 til 1,5, for at der fås coherente overfladelag af rent metal ved arbejdstemperaturer mellem smeltepunktet og ca. 900°C.In plating, the molten bath's content of metal ions 15 of the refractory metal to be precipitated must be between 1 and 8 atomic% and the molar ratio of oxide to metal must be in the range 0.1 to 1.5 to obtain coherent surface layers of pure metal at working temperatures between the melting point and approx. 900 ° C.

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Smeltebadets redoxniveau skal holdes på en passende værdi ved tilsætning af et redoxmiddel. Dette kan være refractory metallet på metalform eller en forbindelse, der har en tilsvarende effekt.The redox level of the melt bath must be maintained at an appropriate value by the addition of a redox agent. This may be the refractory metal in metal form or a compound having a similar effect.

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Den elektrolytiske udfældning skal udføres i en inert, ikke oxyderende atmosfære af fx argon, neon,' tørt kvælstof eller under vacuum.The electrolytic precipitation must be carried out in an inert, non-oxidizing atmosphere of, for example, argon, neon, dry nitrogen or under vacuum.

30 Badsammensætningen ifølge opfindelsen er ikke mere korro siv, end at man kan anvende beholdere og lignende af et hvilket som helst materiale, der ikke reagerer væsentligt med smelten, fx glasagtigt kulstof, grafit, stabiliserende zirkonoxider, nikkel og nikkelholdige materialer, sialoner 35 og aluminiumnitrid.The bath composition according to the invention is no more corrosive than can be used for containers and the like of any material which does not significantly react with the melt, e.g. glassy carbon, graphite, stabilizing zirconium oxides, nickel and nickel-containing materials, sialones 35 and aluminum nitride. .

DK 169354 B1 4DK 169354 B1 4

Katoden, på hvilken metaller udfældes, skal bestå af et elektrisk ledende fast materiale, som ikke reagerer i for stor grad med smelteelektrolytten. Dette kan fx være stål, legeret stål, grafit, nikkel, nikkelholdige legeringer 5 eller kobber.The cathode on which metals are deposited must consist of an electrically conductive solid which does not react excessively with the melting electrolyte. This may be, for example, steel, alloy steel, graphite, nickel, nickel-containing alloys 5 or copper.

Anoden kan bestå af det metal, der skal udfældes, fx i form af stænger, metalfolie eller plade i forskellige geometriske udformninger. Anoden virker således som kilde for 10 det metal, der skal udfældes, og fastholder desuden oxidationstrinnet af refractory metallet i smeltebadet på den ønskede størrelse.The anode may consist of the metal to be precipitated, for example in the form of rods, metal foil or plate in various geometric designs. Thus, the anode acts as a source of the metal to be precipitated, and further maintains the oxidation step of the refractory metal in the melt bath at the desired size.

Elektrolytbadet kan også anvendes som metalkilde. I så 15 tilfælde kan der anvendes en inert anode fx af grafit, glasagtigt kulstof eller platin. Når elektrolytbadet anvendes som metalkilde, må der tilsættes metalioner til smelten, således at koncentrationen af det metal, der udfældes, holdes indenfor det ønskede interval. Desuden skal 20 der tilsættes et reduktionsmiddel, fx det pågældende refractory metal, for at oxidationstrinnet bliver korrekt.The electrolyte bath can also be used as a metal source. In such cases, an inert anode, for example, of graphite, vitreous carbon or platinum, may be used. When the electrolyte bath is used as a metal source, metal ions must be added to the melt so that the concentration of the precipitated metal is kept within the desired range. In addition, a reducing agent, such as the refractory metal in question, must be added in order for the oxidation step to be correct.

Badsammensætningen ifølge opfindelsen er baseret på, at der som elektrolyt er anvendt alkalifluoridsmelteblandin-25 ger tilsat niob/tantal fluorider, niob/tantal oxider, niob/tantal oxofluorider eller blandinger af disse samt tilstrækkeligt oxid til, at metal/oxid forholdet ligger i det ønskede interval.The bath composition according to the invention is based on the addition of alkali fluoride melt mixtures as an electrolyte with added niobium / tantalum fluorides, niobium / tantalum oxides, niobium / tantalum oxofluorides or mixtures thereof and sufficient oxide to keep the metal / oxide ratio in the desired ratio. interval.

30 Den foretrukne grundsmelte (opløsningsmiddel) er den eu-tektiske blanding af LiF-NaF-KF. Denne blanding tilsættes niob/tantal i form af fluorider, oxofluorider, komplekse fluorider/oxofluorider eller oxider. For at opnå det rette oxidindhold i smelten justeres denne eventuelt med tilsæt-35 ning af oxider fra 1. eller 2. hovedgruppe og/eller oxider DK 169354 B1 5 eller oxofluorider af det metal, der skal udfældes. Disse bestanddele udgør elektrolytbadet.The preferred base melt (solvent) is the eectectic mixture of LiF-NaF-KF. This mixture is added to niobium / tantalum in the form of fluorides, oxofluorides, complex fluorides / oxofluorides or oxides. In order to obtain the correct oxide content in the melt, it is optionally adjusted with the addition of oxides from the first or second main group and / or oxides DK 169354 B1 5 or oxofluorides of the metal to be precipitated. These components make up the electrolyte bath.

Eksempel 1.Example 1.

5 Niob blev pletteret på en stang af lav-kulstofstål fra en smelte, som indeholdt 2,7 mol % niob og 2,7 mol % oxid med eutektisk LiF-NaF-KF som grundsmelte. Niob blev tilsat som K2NbF7 og oxidet som Na20. Anoden bestod af 1 mm tyk niob-plade. Procestemperaturer 700°C, strømtæthed (katodisk) 77 10 mA/cm2. Før elektrolysen var niob-anoden neddyppet i 3 timer i elektrolytbadet. Det katodiske strømudbytte var 95%.Niobium was plated on a low carbon steel rod from a melt containing 2.7 mole% niobium and 2.7 mole% oxide with eutectic LiF-NaF-KF as the primary melt. Niob was added as K2NbF7 and the oxide as Na2O. The anode consisted of 1 mm thick niobium plate. Process temperatures 700 ° C, current density (cathodic) 77 10 mA / cm2. Prior to electrolysis, the niobium anode was immersed for 3 hours in the electrolyte bath. The cathodic current yield was 95%.

Det udfældede overfladelag var krystallinsk, coherent og hæftede godt til substratet af lav-kulstofstål. EDX-ana-lyser viste, at det bestod af 100% niob.The precipitated surface layer was crystalline, coherent and adhered well to the low carbon steel substrate. EDX analysis revealed that it consisted of 100% niobium.

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Eksempel 2.Example 2.

Niob blev pletteret på kulstofstål under samme procesbetingelser som i eksempel 1. Smelteelektrolytten var en eutektisk blanding af LiF-NaF-KF med et niobindhold på 20 3,2 mol % og et oxidindhold på 3,2 mol %. Det udfældede overfladelag bestod af rent niob (EDX-analyse), var finkrystallinsk, coherent og hæftede godt til substratet. Det katodiske strømudbytte var 77%.Niobium was plated on carbon steel under the same process conditions as in Example 1. The melt electrolyte was a eutectic mixture of LiF-NaF-KF with a niobium content of 3.2 mole% and an oxide content of 3.2 mole%. The precipitated surface layer consisted of pure niobium (EDX analysis), was fine crystalline, coherent and adhered well to the substrate. The cathodic current yield was 77%.

25 Eksempel 3.Example 3.

Niob blev udfældet på kulstofstål under samme procesomstændigheder som i eksempel 1. Smelteelektrolytten var en eutektisk blanding af LiF-NaF-KF tilsat oxidholdigt NbF5. Indhold af niob og oxid var henholdsvis 2,7 og ca.Niobium was precipitated on carbon steel under the same process conditions as in Example 1. The melt electrolyte was a eutectic mixture of LiF-NaF-KF added to oxide-containing NbF5. Niobium and oxide contents were 2.7 and ca.

30 3,2 mol %. Det udfældede lag var coherent, finkrystallinsk og hæftede godt til underlaget af stål. EDX-analyser viste, at overfladelaget var 100% niob. Det katodiske strømudbytte var 56%.3.2 mole%. The precipitated layer was coherent, fine crystalline and adhered well to the substrate of steel. EDX analyzes showed that the surface layer was 100% niobium. The cathodic current yield was 56%.

35 Eksempel 4.Example 4.

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Tantal blev udfældet på kulstofstål fra en grundsmelte af eutektisk LiF-NaF-KF tilsat K2TaF7 og Na20. Mol % af tantal og oxid var henholdsvis 2,7 og ca. 2,0. Som anode anvendes en cylinder af 1 mm tykt tantalfolie. Anoden var neddyppet 5 3 timer, før elektrolysen blev igangsat. Procestemperatu ren var 700°C. Det udfældede overfladelag bestod af rent tantalmetal, var coherent, finkrystallinsk og hæftede godt til underlaget af lav-kulstofstål. Det katodiske strømudbytte var 78%.Tantalum was precipitated on carbon steel from a basic melt of eutectic LiF-NaF-KF added with K2TaF7 and Na2O. Mol% of tantalum and oxide were 2.7 and ca. 2.0. As an anode, a cylinder of 1 mm thick tantalum film is used. The anode was immersed for 3 hours before electrolysis was initiated. The process temperature was 700 ° C. The precipitated surface layer consisted of pure tantalum metal, was coherent, fine crystalline and adhered well to the low carbon steel substrate. The cathodic current yield was 78%.

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Eksempel 5.Example 5

Zirkonium blev udfældet fra en eutektisk LiF-NaF-KF smelte tilsat K2ZrF6. Mol % Zr og oxid var begge 2,7%. Som anode anvendtes 1 mm tykt zirkonmetalfolie. Den katodiske strøm-15 tæthed var 40 mA/cm2 og procestemperaturen 700°c. Det udfældede zirkonmetallag hæftede godt til substratet af lavkulstof stål. Strømudbyttet var 58%.Zirconium was precipitated from a eutectic LiF-NaF-KF melt added with K2ZrF6. Mol% Zr and oxide were both 2.7%. As the anode, 1 mm thick zircon foil was used. The cathodic current density was 40 mA / cm 2 and the process temperature 700 ° C. The precipitated zircon metal layer adhered well to the low carbon steel substrate. The current yield was 58%.

Claims (4)

1. Smeltebad til elektrolytisk overfladebelægning med et 5 refractory metal valgt blandt Nb, Ta; Zr, W eller Mo, især niob eller tantal, på basis af en saltsmelte af alkalimetalfluorider og et fluorid af refractory metallet, kendetegnet ved, at badets indhold af metalioner af refractory metallet ligger 10 mellem 1 og 8 atom %, at badet indeholder oxidanioner og er i kontakt med refractory metallet på metalform eller indeholder et tilsvarende redoxmiddel, og at molforholdet mellem oxid og refractory metallet ligger i intervallet 0,1 til 1,5. 151. Electrolytic surface coating melt bath with a 5 refractory metal selected from Nb, Ta; Zr, W or Mo, especially niobium or tantalum, on the basis of a salt melt of alkali metal fluorides and a fluoride of the refractory metal, characterized in that the bath content of metal ions of the refractory metal is between 1 and 8 atom%, that the bath contains oxide anions and is in contact with the refractory metal in metal form or contains a corresponding redox agent and that the molar ratio of oxide to the refractory metal is in the range 0.1 to 1.5. 15 2. Bad ifølge krav 1, kendetegnet ved, at det indeholder oxidanioner i form af et alkalimetaloxid eller et oxid, oxofluorid eller komplekst oxo-fluorid af refractory metallet. 20Bath according to claim 1, characterized in that it contains oxide anions in the form of an alkali metal oxide or an oxide, oxofluoride or complex oxofluoride of the refractory metal. 20 3. Bad ifølge krav 1 eller 2, kendetegnet ved, at det indeholder refractory metallet i form af et fluorid, et komplekst fluorid, et oxofluorid eller et komplekst oxofluorid af refractory metallet. 25Bath according to claim 1 or 2, characterized in that it contains the refractory metal in the form of a fluoride, a complex fluoride, an oxofluoride or a complex oxofluoride of the refractory metal. 25 4. Fremgangsmåde til elektrolytisk overfladebelægning med et refractory metal valgt blandt Nb, Ta', Zr, W eller Mo, især niob og tantal, i en inert, ikke oxyderende atmosfære eller under vakuum, kendetegnet 30 ved, at der til elektrolysen anvendes et bad med en sammensætning ifølge et af kravene 1-3.Method of electrolytic surface coating with a refractory metal selected from Nb, Ta ', Zr, W or Mo, especially niobium and tantalum, in an inert, non-oxidizing atmosphere or under vacuum, characterized in that a bath is used for the electrolysis with a composition according to any one of claims 1-3.