SurTec 717 R Alkaline Zinc/Nickel Process

Transcription

1 Protection upgraded SurTec 717 R Alkaline Zinc/Nickel Process Properties optimized for rack plating tolerates higher temperatures with high burning limit achieves superior metal distribution produces uniform Zn/Ni alloy deposits with % nickel in the layers in the current density range from 1 to 4 A/dm 2 deposits homogenous grain-refined, semi-bright to bright Zn/Ni layers alkaline process with high current efficiency of % IMDS-number: Application SurTec 717 R is used for rack application. The process (based on sodium) includes the following products: SurTec 700 EN Sodium Zincate Electrolyte, 3x Concentrate is the electrolyte concentrate for the initial bath make-up; it guarantees a good and proofed salt quality, a reliable maintaining of the initial desired values, as well as a fast and safe make-up without formation of irritating and dangerous highly alkaline aerosols SurTec 717 I Carrier controls the metal distribution and the alloy composition SurTec 717 II Brightener supplies the brightness and is dosed optional and only if needed according to Hull cell test SurTec 717 LCD Booster is used as secondary brightener and works at low current density SurTec 717 Ni Nickel Solution for make-up and maintenance contains 100 g/l nickel and is necessary to keep the nickel concentration constant SurTec 717 R-C Complexing Agent contains the complexing agent in order to control the right composition of the alloy layer SurTec 717 CA Corrective Additive is especially needed for higher working temperatures In order to improve the deposition conditions, special additives are available for the addition to the already prepared make-up of the alkaline zinc electrolyte, if required (see separate product information sheet SurTec 700 x Tools); for example: SurTec 700 RN Conditioner is only added to the electrolyte if using steel anodes page 1

2 make-up values: SurTec 700 EN Electrolyte 300 ml/l sodium hydroxide (NaOH) 25 g/l SurTec 717 I Carrier 4 ml/l (3-8 ml/l) SurTec 717 LCD Booster 0.5 ml/l ( ml/l) SurTec 717 Ni Nickel Solution 22 ml/l (20-30 ml/l) SurTec 717 R-C Complexing Agent 70 ml/l (60-90 ml/l) SurTec 700 RN (for steel anodes) 10 ml/l (0-20 ml/l) SurTec 717 CA Corrective Additive 1-10 ml/l SurTec 717 II Brightener 0-2 ml/l analytical values: zinc (Zn) 8 g/l (7-9 g/l) nickel (Ni) 2.2 g/l ( g/l) sodium hydroxide (NaOH) 135 g/l ( g/l) sodium carbonate (Na 2 CO 3 ) 30 g/l (max. 70 g/l) sodium sulfate (Na 2 SO 4 ) 10 g/l (max. 30 g/l make-up: Steps for make-up: 1. Pour the calculated amount of SurTec 700 EN Sodium Zincate Electrolyte, 3x Concentrate (30 g/l Zn) into a clean plating tank. 2. Add additional 25 g/l sodium hydroxide. 3. Dilute with deionised water to approx. 80 % of the final volume and stir well. Before addition of the additives make sure that the temperature of the electrolyte is not higher than 30 C. 4. Pour the calculated amount of SurTec 717 R-C Complexing Agent cautiously into an area with good agitation. 5. Mix the bath for at least 30 min (e.g. with filter pumps). 6. Next, slowly add in the following order SurTec 717 Ni Nickel Solution, SurTec 717 I Carrier and SurTec 717 LCD Booster. 7. If required, add SurTec 717 II Brightener. 8. If using steel anodes, add 10 ml/l SurTec 700 RN Conditioner. 9. Fill the bath to the final volume with deionised water. 10. Mix the bath and filter for min. 1 hour. 11. Plate a scrap cathode for at least Ah/l to electrolyse the bath. By this way the zinc content will be worked down from 9 g/l to the desired value of 8 g/l. temperature: 28 C (25-35 C) The selected temperature must be kept as exactly as possible, optimal ± 1 C current density: 2.0 A/dm 2 ( A/dm 2 ) current efficiency: % (depending on current density and bath temperature) plating speed: 0.2 µm/min at 2 A/dm 2 agitation: strong agitation by venturi nozzles is needed (please ask SurTec technical support for details) page 2

3 backside front-side faced to the parts (cathode) tank material: filtration: heating/ cooling: exhaust: hints: polypropylene, or steel with PP, PVC or rubber coating continuously, with 2-3 times the total bath volume per hour; pore size: µm necessary; out of Teflon or stainless steel required for worker s protection remove carbonates and sulfates regularly (please ask SurTec technical support for details) Anodes Pure nickel anodes or steel anodes with additional protection additive (ask SurTec technical support for details). SurTec recommends the using of inert anodes in combination with an external zinc generator. Operation with inert anodes and external zinc generator Anodes: optimal are pure nickel anodes, but also anodes of expanded metal out of mild steel with piccolo mesh 30 mm x 8 mm, rib width 6 mm, material thickness 2 mm are possible. If using steel anodes, 10 ml/l SurTec 700 RN must be added to the electrolyte. The expanded metal should be installed with the ribs horizontally oriented for driving the gas evolution to the backside. It should be vertically stiffened with flat irons leading to the anode hooks. For optimal current distribution, the anodes should be placed at both sides of the cathode along the full width of the plating tank. Zinc generator: SurTec recommends a zinc generator with catalytically coated baskets. These relatively small-sized high-performance zinc generators generate a zinc concentrate which provides the necessary zinc ions reliably. The zinc content in the bath can be controlled by the exchange rate between bath and generator. We would be pleased to calculate the optimum conditions for your line, we also offer the specially coated baskets please contact us! page 3

4 recommended process sequence (for iron parts): 1. hot degreasing with SurTec SurTec hydrochloric acid pickling with SurTec 420 or SurTec 424 (for hardened steel) 3. anodic electrolytic cleaning with SurTec neutralisation with SurTec Zn/Ni Electrolyte SurTec 717 R 6. activation in hydrochloric acid at ph passivation, e.g. SurTec 675, SurTec 680 or SurTec 696 (sealer or post-dip is required) 8. optional: sealer or post-dip 9. hot air drying at C for 15 Minutes Between each step, there has to be rinsed. The rinsing methods have to be adapted to the plating line. Maintenance and Analysis Analyse and adjust the content of zinc, nickel and sodium hydroxide regularly. Daily control analyses are recommended to prevent large variations of the metal composition in the bath. Keep the zinc content constant by an external zinc generator. Correct deposited nickel by adding SurTec 717 Ni Nickel Solution. A dosage of 10 ml/l SurTec 717 Ni is equivalent to 1 g/l nickel. Dose the additives according to ampere-hours and Hull cell tests. Sodium carbonate and sodium sulfate can be analysed by SurTec Lab. If carbonates and sulfates reach the limit values they must be removed by regeneration systems If there are not enough dosing pumps available the additive can be pre-mixed: Mix dosing pump 1: SurTec 717 Ni and SurTec 717 R-C Mix dosing pump 2: SurTec 717 I and SurTec 717 LCD (Please ask SurTec technical support for details.) Overview of Methods and Frequency of Analysis Substance Method Frequency in Customer Lab Frequency in SurTec Lab zinc titration, AAS, X-ray,ICP 1 x per shift every 2-4 Ah/l nickel titration, AAS, X-ray, ICP 1 x per shift every 2-4 Ah/l NaOH titration 1-2 times/ week every Ah/l 1-2 times/month 1-2 times/month 1-2 times/month Na 2 CO 3 titration times/month Na 2 SO 4 titration, ICP times/month page 4

5 Sample Preparation Take a sample at a homogeneously mixed position. If the sample is turbid, let the turbidity settle down and decant or filter the solution. For the analysis the samples must be clear. Zinc Analysis by Titration reagents: 0.1 mol/l EDTA solution (Titriplex III) buffer solution (100 g/l NaOH ml/l 98 % acetic acid in DI-water) dimethyl glyoxime solution (2 % alcoholic solution) indicator: xylenol orange tetra sodium salt (1 % blended in KNO 3 ) Double determination: 1. Pipette 5 ml bath sample into a 250 ml beaker. 2. Dilute with approx. 25 ml deionised (DI-)water. 3. Add buffer solution, until the solution gets clear and the colour changes (approx. 20 ml). 4. Add approx. 20 ml dimethyl glyoxime solution. 5. Heat up to 60 C while stirring. 6. After cooling down to room temperature filtrate the solution and wash the filter cake with some DI-water. 7. Add a spatula tip of indicator to the filtrate (inclusive the water from the washed filter cake). 8. Titrate with 0.1 mol/l EDTA solution from red to yellow. calculation: hint: consumption in ml = A (ml) A in ml = g/l zinc The colour changes from purple to yellow-grey. It is not possible to describe the colour exactly; it depends on the matrix of the bath sample (e. g. metal impurities). Adjust the circulation rate from the zinc generator. Zinc Analysis by AAS instruments: reagents: atomic absorption spectrometer (AAS): wave length: nm; slit: 0.7 nm hydrochloric acid (HCl, ½ conc.) p.a. laboratory standard solutions of 1 to 5 ppm zinc Prepare a 1:5000 dilution: 1. Pipette 10 ml bath sample into a 100 ml volumetric flask. 2. Fill up with deionised water and mix well. 3. Pipette 1 ml from this solution into a 500 ml volumetric flask. 4. Acidify with 20 ml half conc. hydrochloric acid. 5. Fill up with deionised water and mix well. 6. Measure this solution in the AAS at nm in comparison to laboratory standards of 1 to 5 ppm. calculation: 1 ppm = 5 g/l zinc (dilution of 1:5000) Adjust the zinc generator to reach the correct zinc content. page 5

6 Nickel Analysis by Titration reagents: 0.1 mol/l EDTA solution (Titriplex III) buffer solution (100 g/l NaOH ml/l 98 % acetic acid in DI-water) indicator: xylenol orange tetra sodium salt (1 % blended in KNO 3 ) Double determination: 1. Pipette 5 ml bath sample into a 250 ml beaker. 2. Dilute with approx. 100 ml deionised water. 3. Add approx. 20 ml buffer solution, until the solution gets clear. 4. Heat up to 80 C while stirring. 5. Add a spatula tip of indicator. 6. Titrate at 80 C with 0.1 mol/l EDTA solution from red to yellow. calculation: consumption in ml = B (ml) (B in ml A in ml) = g/l nickel rise by 1 g/l nickel = addition of 10 ml/l SurTec 717 Ni Nickel Analysis by AAS equipment: atomic absorption spectrometer (AAS): wave length: nm slit: 0.2 nm reagent: hydrochloric acid (½ conc.) p. a. barium chloride solution (15 % BaCl 2 in DI-water) laboratory standard solution of 5-10 ppm nickel 1. Pipette 5 ml bath sample into a 100 ml beaker. 2. Cautiously add 10 ml ½ conc. hydrochloric acid. Attention: gas evolution (CO 2 )! 3. Fill 20 ml BaCl 2 solution into a second 100 ml beaker. 4. Warm up both beakers to approx. 70 C. 5. Add the barium chloride solution to the bath sample: a precipitation is formed. 6. Let the solution cool down. 7. Fill the solution together with the precipitation quantitatively into a 50 ml volumetric flask. 8. Fill up to the final volume with DI-water, mix well and let the precipitate settle down. This is the pre-dilution of 1: From the clear solution from top of the flask, pipette 5 ml into a 100 ml volumetric flask. 10. Add 5 ml half conc. hydrochloric acid. 11. Fill up to the mark with deionised water and mix well. This is the final dilution of 1:200 (in summary). 12. Measure this solution in the AAS at nm in comparison to laboratory standards of 5 to 10 ppm. calculation: 5 ppm = 1 g/l nickel (dilution 1:200) rise by 1 g/l nickel = addition of 10 ml/l SurTec 717 Ni page 6

7 Sodium Hydroxide Analysis by Titration reagents: 0.5 mol/l sulfuric acid (= 1 N) barium chloride solution (15 % BaCl 2 p.a. in DI-water) indicator: thymolphthalein calculation: hint: 1. Pipette 5 ml bath sample into a 250 ml Erlenmeyer flask. 2. Add 15 ml of the barium chloride solution. 3. Dilute with 50 ml of deionised water. 4. Add 3 drops of indicator. 5. Titrate with 0.5 mol/l sulfuric acid from blue to colourless. consumption in ml 7.98 = g/l sodium hydroxide For the dosage of NaOH, the quality (concentration) of the raw material has to be considered. Sodium Carbonate Analysis by Titration reagents: barium nitrate solution (5 %) 1 mol/l hydrochloric acid (= 1 N) 1 mol/l sodium hydroxide solution (= 1 N) indicator: methyl orange solution (0.04 %) calculation: 1. Pipette 10 ml bath sample into a 250 ml Erlenmeyer flask. 2. Dilute with 50 ml deionised water. 3. Heat the dilution up until it starts boiling. 4. Add 75 ml barium nitrate solution (a precipitate appears). 5. Allow it to cool and let the precipitate settle down for 30 minutes. 6. Filter the complete sample through a blue-ribbon filter (first pour the clear upper phase into the filter, then add the precipitate, rinse the flask with little water). 7. Wash the filter residue min. 5 x thoroughly with deionised water, therefore elutriate and drain completely but don t let it dry out. The Precipitate must be free of hydroxide. (Test: Mix few drops of filtrate with one drop nitric acid and one drop silver nitrate solution: if the washing process is sufficient, no white precipitate will be formed.) 8. Put the filter paper with the well rinsed precipitate into a clean 250 ml Erlenmeyer flask. 9. Add 100 ml deionised water. 10. Acidify with exactly 20 ml 1 mol/l hydrochloric acid. 11. Let the solution boil up briefly. 12. After cooling down, add 3 drops of indicator. 13. Titrate the excessive hydrochloric acid with 1 mol/l sodium hydroxide from red to orange-yellow. (20 - consumption in ml) 5.3 = g/l sodium carbonate If the carbonate content is higher than 70 g/l a regeneration system must be used. (ask SurTec technical support for details). page 7

8 Hull Cell Test Perform all tests in a standard 250 ml Hull cell. Before plating, prepare well the Hull cell panel (pickling and anodic cleaning - it has to be free of zinc and oil). Plate the freshly cleaned panel in the Hull cell at 1 A for 15 min at bath working temperature (± 1 C). Rinse the panel with tap water and dry it with hot or compressed air. An ideal panel is bright and has an equal nickel content over the whole current density area, measurable with X-ray. Because of the high current applied (1 A, 15 min), it is recommended to use fresh electrolyte samples for each variation in the Hull cell test. The Hull Cell Test must be done daily and documented for further optimization from the SurTec technical support. Technical Specification (at 20 C) Appearance Density (g/ml) ph-value (conc.) SurTec 717 I liquid, colourless-yellowish, clear ( ) 7.0 ( ) SurTec 717 II liquid, yellowish-brownish, clear ( ) 5.4 (3-8) SurTec 717 LCD liquid, yellowish-brownish, clear ( ) 10.6 (8,5-13) SurTec 717 Ni liquid, blue, clear ( ) 7.2 (6.4-8) SurTec 717 R-C liquid, colourless, clear ( ) 12.2 ( ) SurTec 717 CA liquid, colourless-yellowish, clear ( ) > 13 SurTec 700 EN liquid, colourless, clear ( ) > 11 SurTec 700 RN liquid, colourless, ( ) ca. 12 clear to slightly turbid Consumption and Stock Keeping The consumption depends heavily on the drag-out. To determine the exact amounts of drag-out, see SurTec Technical Letter 11. Dose SurTec 717 R-C, 717 Ni, 717 I, 717 II and 717 LCD according to ampere hours (Ah). The following values per 10,000 Ah can be taken as estimated average consumption: SurTec 717 I SurTec 717 II SurTec 717 LCD SurTec 717 Ni SurTec 717 R-C l 0-2 l l 6-10 l 2-3 l In order to prevent delays in the production process, per 1,000 l bath the following amounts should be kept in stock: SurTec 717 I SurTec 717 II SurTec 717 LCD SurTec 717 Ni SurTec 717 R-C SurTec 717 CA SurTec 700 RN 25 kg 25 kg 25 kg 50 kg 50 kg 25 kg 90 kg page 8

9 Product Safety and Ecology Classification and designation are noted in the Material Safety Data Sheets (according to the European legislation). The safety instructions and the instructions for environmental protection have to be followed in order to avoid hazards for people and environment. Please pay attention to the explicit details in our Material Safety Data Sheets. Warranty We are responsible for our products in the context of the valid legal regulations. The warranty exclusively accesses for the delivered state of a product. Warranties and claims for damages after the subsequent treatment of our products do not exist. For details please consider our general terms and conditions. Further Information and Contact If you have any questions concerning the process, please contact your local technical department. For further information and contact details please visit our homepage: 28 November 2016/DK, MR page 9