Rau Electroless Nickel Plating Baths ntawm 90℃(pH 4.5), Cov ntsiab lus phosphorus siab tshaj plaws hauv chav da dej puas tuaj yeem titanium qib 2 tiv taus yam tsis muaj hydrogen embrittlement?

Electroless npib tsib xee (EN) plating da dej yog khiav ntawm 85-95 degree, pH 4.0-5.5 thiab muaj nickel sulfate los yog npib tsib xee hypophosphite ua hlau qhov chaw, sodium hypophosphite li txo tus neeg sawv cev thiab ntau yam complexing agents (citrates, acetates los yog glycolates). Lub da dej chemistry yog me ntsis acid thiab muaj ob qho tib si oxidizing thiab txo hom. Titanium Qib 2 feem ntau yog siv rau immersion rhaub nyob rau hauv EN da dej vim nws broad corrosion kuj. Txawm li cas los xij, muaj hom tsis ua haujlwm, hydrogen embrittlement, uas cov hypophosphite txo tus neeg sawv cev decomposes rau phosphorus thiab hydrogen. Phosphorus yog codeposited nrog npib tsib xee rau ntawm titanium nto thiab cov hydrogen tsim thaum lub sij hawm electroless txheej txheem yuav absorbed rau hauv titanium lattice. Thaum kub da dej ntau dua qhov kev cuam tshuam ntawm absorbed hydrogen nrog phosphorus nto txheej ua rau hydride ntau lawm thiab tawg. Cov kab lus hais txog qhov siab tshaj plaws tso cai ntawm phosphorus, tso tawm los ntawm decomposition ntawm hypophosphite, uas Qib 2 titanium yuav dais yam tsis muaj qhov tshwm sim ntawm hydrogen embrittlement hauv EN da dej ntawm 90℃thiab pH 4.5.

Hydrogen evolution hauv electroless nickel da dej
Cov tshuaj tiv thaiv electroless nickel plating yog autocatalytic: Ni2+ + 2H2PO2- + 2H2O → Ni0 + 2H2PO3- + H2 + 2H+. Rau txhua mole ntawm nickel plated, ib mole ntawm hydrogen gas yog tsim los ntawm cov tshuaj tiv thaiv. Qee qhov ntawm cov hydrogen no yog atomic hydrogen (H.) thaum lub sijhawm tsim, thiab qee qhov ntawm cov atomic hydrogen no tuaj yeem nqus tau rau hauv ib qho xim hlau rau hauv da dej -xws li titanium heater sheaths. Tus nqi ntawm kev nqus yog nyob ntawm qhov chaw ntawm titanium, muaj cov hlau catalytic (xws li npib tsib xee nws tus kheej), thiab qhov kub thiab txias.

Thaum absorbed atomic hydrogen diffuses hauv titanium lattice. Thaum lub zos concentration ntawm hydrogen mus txog qhov solubility txwv (ca. 150 ppm ntawm 90 degree), brittle titanium hydride (TiH2) precipitates. Hydride ntau lawm ua rau lub ntim nthuav dav (15%) thiab kev ntxhov siab sab hauv uas yuav ua rau tawg, tshwj xeeb tshaj yog nyob rau hauv qhov chaw uas muaj kev ntxhov siab ntxiv, xws li cov pob qij txha welded los yog lub raj khoov.

Lub luag haujlwm ntawm Phosphorus hauv Hydrogen Uptake
Hypophosphite tawg ua lub luag haujlwm nyuaj hauv phosphorus. Nyob rau ntawm cov hlau ua haujlwm ntawm qhov chaw hypophosphite raug txo kom muaj phosphorus: 2H₂PO₂⁻ + 2H⁺ → 2P + 4H₂O. Qhov no phosphorus deposits nyob rau hauv ib tug nyias zaj duab xis nyob rau hauv lub titanium nto, tshwj xeeb tshaj yog nyob rau hauv cov cheeb tsam uas passive zaj duab xis yog nyias los yog puas. Cov txheej phosphorus no catalyses ntxiv kev puas tsuaj ntawm hypophosphite thiab hydrogen evolution, ua rau muaj kev nce hauv zos hydrogen flux rau hauv titanium.

Qhov tseem ceeb tshaj, cov phosphorus txheej tiv thaiv kev sib txuas ntawm atomic hydrogen rau molecular hydrogen (2H· → H2). Ntawm qhov chaw phosphorus cov tshuaj tiv thaiv recombination qeeb, yog li ib feem loj ntawm cov hydrogen tsim nyob rau hauv daim ntawv atomic thiab muaj rau nqus mus rau hauv titanium. Rau EN da dej yam tsis muaj qhov tseem ceeb phosphorus deposition qhov nqus ntawm hydrogen tsim yog li ntawm 1-5%. Absorption feem yuav yog 15-30% nrog phosphorus nto txheej.

Cov ntsiab lus phosphorus siab tshaj plaws rau Qib II
Cov ntsiab lus phosphorus nyob rau hauv EN da dej (los ntawm decomposition ntawm hypophosphite thiab kev puas tsuaj ntawm hypophosphite ion) yog feem ntau qhia raws li lub orthophosphite (H 2 PO 3 - ) concentration los yog raws li ib tug elemental phosphorus equivalents. Hauv ib da dej EN ib txwm ua haujlwm ntawm 90℃thiab pH 4.5 qib orthophosphite mus ntawm 0 g / L ntawm da dej ua rau- txog 100-200 g / L dhau lub neej ntawm da dej thaum da dej tawm.

Kev tshuaj ntsuam xyuas hydrogen permeation ntawm Qib 2 titanium daim nyias nyias raug rau EN da dej nrog tswj cov qib orthophosphite ua cov nram qab no hydrogen absorption fluxes ( ntsuas electrochemically):

Nrog orthophosphite concentrations qis dua 20 g / L (nyob ib ncig ntawm 5 g / L elemental phosphorus hauv lub xeev txo) hydrogen absorption yog 0.02 txog 0.05 ppm ib teev - tsis tseem ceeb rau 10 xyoo lub neej rhaub.

Uptake nce mus rau 0.10-0.30 ppm / teev nrog orthophosphite ntawm 20-50 g / L (5-12 g / LP sib npaug). Ntawm tus nqi no, qhov pib hydrogen concentration ntawm 150 ppm yog mus txog hauv 500-1500 teev (3-9 lub lis piam ua haujlwm tas li). Cov cua sov hauv cov tshuaj da dej no feem ntau ua tsis tiav los ntawm kev tawg tom qab 3-6 lub hlis.

For orthophosphite, absorption is more than 0.5 ppm/hr at concentrations above 50 g/L (>12 g / LP sib npaug) qhov tseem ceeb concentration yog ua tiav hauv tsawg dua 300 teev. Hauv 1-2 lub hlis embrittlement thiab tawg.

Qhov siab tshaj plaws kev nyab xeeb ntawm orthophosphite rau Qib 2 titanium hauv EN da dej ntawm 90℃thiab pH 4.5 yog 15 g / L. Saum toj no qhov kev pheej hmoo ntawm hydrogen embrittlement dhau 6 lub hlis ua haujlwm tshaj li qhov tau txais.

Cov tswv yim rau Mitigation
Ntau cov txheej txheem ua haujlwm tuaj yeem ua kom lub neej ntev ntawm Qib 2 titanium hauv EN da dej:

Kev hloov pauv hauv chav da dej: Hloov lossis rov txuas dua EN da dej thaum lub orthophosphite concentration nyob nruab nrab ntawm 15-20 g / L. Qhov no feem ntau yog 6-10 hlau tig.

Titanium nto kho: Electropolished los yog anodized titanium nto muaj tsawg qhov chaw catalytic rau phosphorus deposition thiab muaj 30-50% qis hydrogen absorption tus nqi tshaj pickled los yog raws li-drawn nto.

Periodic acid tu: Immersing nyob rau hauv 20% nitric acid ntawm 50℃rau 30 feeb txhua 1-2 lub lis piam tshem tawm phosphorus deposits, replenishes titanium passive zaj duab xis thiab tshem tawm catalytic phosphorus txheej.

Kev tiv thaiv Cathodic: Los ntawm kev sib txuas lub tshuab cua sov titanium rau cov hlau zoo dua qub (xws li platinum lossis kub), lub peev xwm saum npoo tau hloov pauv thiab kev puas tsuaj hypophosphite qis dua. Qhov no tsis yog qhov ua tau zoo hauv EN da dej.

Titanium Heater Daim Ntawv Thov Matrix rau EN Baths
EN Bath Condition Titanium Qib Recommended Actions Orthophosphite ConcentrationHeater Life Expected (1.65 mm wall)
Tshiab da dej, lub teeb loading<10 g/LGrade 2 Normal operation >5 xyoo
Nruab nrab-lub neej da dej, nruab nrab loading 10-15 g/L Qib 2 Lub lim tiam acid tu pom zoo 2-4 xyoos
Hnub nyoog da dej, siab loading 15-25 g/L Qib 2 Hloov da dej lossis siv Qib 7 6-12 hli
Hnub nyoog da dej, siab loading 15-25 g / L Qib 7 Txais, Qib 7 zoo tshaj ntawm kev tiv thaiv embrittlement 2-3 xyoos
Bath stressed >25 g / L Txhua yam titanium dhau lub neej Hloov da dej tam sim < 3 lub hlis
High phosporus bath (deposit contains 10 to 12 % P)Variable, normally >20 g / LHastelloy C-276 Titanium tsis pom zoo Siv Hastelloy
Alternative Qib 7
EN da dej. Qib 7 titanium (Ti-0.15Pd) absorbs hydrogen ntawm li 1/3 tus nqi ntawm Qib 2. Lub xub ntiag ntawm palladium txhim kho cov recombination ntawm hydrogen nyob rau saum npoo, yog li txo cov flux ntawm atomic hydrogen rau hauv cov hlau. Qib 7 hauv da dej uas muaj orthophosphite ntawm 15-25 g / L nqus ntawm tus nqi ntawm 0.05-0.10 ppm / hr. Qhov no txhais tau hais tias 1,500-3,000 teev (3-6 lub hlis) yuav tsum ua kom muaj qhov tseem ceeb. Qib 7 yuav kav 2-3 xyoos hauv da dej uas yuav rhuav tshem Qib 2 hauv 6 lub hlis yog tias lawv ntxuav txhua lub lim tiam nrog cov kua qaub kom tshem tawm cov phosphorus deposits.

Ntawm 90℃thiab pH 4.5, titanium Qib 2 tuaj yeem tiv taus orthophosphite concentrations txog li 15 g / L hauv electroless nickel plating da dej yam tsis muaj hydrogen embrittlement. Nyob rau hauv cov ntaub ntawv embrittlement yuav nce ceev heev tshaj 15 g / L, cua sov yuav poob nyob rau hauv ib lub hlis. Cov kws kho tsheb yuav tsum saib xyuas orthophosphite tsis tu ncua thiab npaj rau da dej kom tig mus ua ntej 20 g / L. Qib 7 titanium nrog electropolished nto tiav rau da dej xav tau ntau dua ntawm orthophosphite. Muab cov kua qaub ntxuav txhua lub lim tiam. Ntawm orthophosphite tshaj 25 g / L titanium yog incompatible thiab Hastelloy C-276 los yog quartz heaters raug pom zoo. Thaum muas titanium rhaub rau EN kev pab cuam nug rau cov ntaub ntawv ntawm qhov chaw tiav thiab xav txog kev ntxiv cov tshuaj hydrogen (nyias hlau hydrogen sojntsuam) rau cov da dej tseem ceeb.