E2S2 2010 Denver Convention Center Denver, Colorado Paul Brezovec, CEF, CTC Michael Miller, CTC Testing Room Temperature Ionic Liquid Solutions for Depot Repair of Aluminum Coatings Wednesday, June 16, 2010
Outline A. Background of need B. Problem with incumbent coating C. Reason for ionic liquids as electrolytes D. Safety issues 2
Background Need to repair aluminum (Al) coatings a) Pure (> 99%) Al coating electrodeposit b) Steel part surfaces c) Coating is not all within the line of sight There would be two major requirements: a) The repair process would comply with facility environment, safety and occupational health (ESOH) b) The coating would conform with MIL-DTL-83488, Detail Specification Coating, Aluminum, High Purity 3
Incumbent Aluminum Coating The incumbent Al coating is electrodeposited on the part by original equipment manufacturers It serves as a cadmium coating replacement The Al coating itself is considered to be safe However, adopting this Al coating technology poses processing issues for a repair facility Uses an aluminum organyl and salt in an aromatic solvent electrolyte, which is air/moisture sensitive Ignites spontaneously in air Requires stringent controls to eliminate moisture contact, and mitigate the fire hazard in the facility 4
Ionic Liquid: Definition An ionic liquid (IL) is a salt in the liquid state Discussion will be limited to a room-temperature IL (RTIL) which has a melting point that is less than 100 C For example, BMIM-PF 6 is an RTIL; table salt is not Source: Wikipedia sodium (Na + ) chloride (Cl - ) Table Salt (NaCl) Crystal Melting Point = 801 C Source: Wikipedia 1-butyl-3-methylimidazolium (BMIM + ) hexafluorophosphate (PF 6- ) Ionic Liquid (BMIM-PF 6 ) Melting Point = 11 C 5
Example RTIL Anions/Cations Cations Alkylated imidazolium Alkylpyridinium Dialkylpyrrolidinium / Dialkylpiperidinium Tetraalkylammonium Tetraalkylphosphonium Anions Trifluoroacetate Bromide (Cl ) Chloride (Br ) Hexafluorophosphate Tri-fluoromethane sulfonate Tricyanomethide Tetrafluoroborate Trialkylsulfonium RTIL anion/cation pairings Bis(trifluoromethyl sulfonyl)imide They are used to dissolve metal salts and additives for electroplating They become the electrolyte in place of an aqueous solution 6
RTIL Features Negligible vapor pressure Non-flammable Remain liquid within a wide temperature range Other properties may be tailored by the anion/cation selection Physicochemical properties Electrochemical properties Instances of existing equipment used for conversion to RTIL-based processing but expect some equipment modifications 7
Claimed Plating Opportunities Inert 1 H IIA IIIA IVA VA VIA VIIA He 2 Li Be B C N O F Ne 3 Na Mg IIIB IVB VB VIB VIIB ------ VIIIB ------ IB IIB Al Si P S Cl Ar 4 5 6 7 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr = As Metal = As Alloy = As Metal and Alloy Reference: Endres, F., A.P. Abbott, and D.R, MacFarlane, Ed., Electrodeposition from Ionic Liquids, Wiley-VCH, Weinheim, Germany, 2008. Opportunity of new plating alloys (e.g., Nb) Plating of active elements (e.g., Mg, Mo, Ta, Ti) Quality of plating is not quantitatively reported 8
Select Al Electroplating in RTIL Options based on the research literature Cation Dialkyimidazolium Tetraalkylammonium Tetraalkylphosphonium Dialkylpyrrolidinium Anion Chloride Bis(trifluoromethylsulfonyl)imide ( TFSI ) Down-select, based on commercial availability 1-ethyl,3-methylimidazolium chloride ([EMIM]Cl) 9
Electroplating Al in [EMIM]Cl Aluminum chloride (AlCl 3 ) dissolves in [EMIM]Cl, forming [EMIM]chloroaluminates: [EMIM]Cl + AlCl 3 [EMIM]AlCl 4, and [EMIM]AlCl 4 + AlCl 3 [EMIM]Al 2 Cl 7 Electrolyte is supplied pre-mixed Al plates (Al ) when there are more dissolved Al atoms than EMIM molecules: 4[EMIM]Al 2 Cl 7 + 3e Al + 4[EMIM]AlCl 4 + 3AlCl 4 100% plating efficiency at 4 amperes/decimeter 2 (A/dm 2 ), claimed 10
Al Plating from RTIL Electrolyte Overview: 1. Remove soils/corrosion products/plating from surfaces 2. Activate the substrate (standard method); dry 3. Electroplate Al onto the activated areas: Pure Al anodes Elevated electrolyte temperature improves activity Mechanical agitation Current density of 4 A/dm 2 (example) 4. Rinse and dry plating; Inspect the plating quality 11
Safety Considerations 1. Water (H 2 O) contamination Reacts with chloroaluminate (AlCl 4 ) anions: AlCl 4 + H 2 O AlOCl 2 + 2HCl Liberates hydrogen chloride (HCl) gas Forms oxychloroaluminate (AlOCl 2 ) ) Slows plating rate; requires AlCl 3 additions Build-up of AlOCl 2 requires recycling Design limits H 2 O contamination Process allows for < 0.1 % H 2 O by weight 12
Safety Considerations (continued) 2. Voltage excursion above ~2.7 volts Chloride anion oxidize to chlorine at anode 4AlCl 4 2Al 2 Cl 7 + Cl 2 + 2e. 3. Electrolyte handling Electrolyte is a superacid Personal protective equipment required Face shield, goggles Nitrile gloves with elbow extension 13
Summary 1. A method to repair electroplated aluminum is a option using a near-commercial RTIL electrolyte, [EMIM]Cl-AlCl 3. 2. The specification for pure aluminum deposits, MIL-DTL-83488, may apply. 3. Compliance with ESOH requirements require further hands-on review, including designs for container covers. 14
Contacts Paul Brezovec, CEF Concurrent Technologies Corporation 100 CTC Drive Johnstown, PA 15904 Ph: (814) 269-2844 E-mail: brezovec@ctc.com Michael Miller Concurrent Technologies Corporation 7995 114 th Avenue Largo, FL 33773-5026 Ph: (727) 549-7285 E-mail: MillerMi@ctc.com 15
Putting ideas into action. SM 1-800-CTC-4392 www.ctc.com