Title of Invention

PROCESS FOR COATING AN ARTICLE WITH NICKEL AND BORON, AND AN ARTICLE HAVING SUCH COATING.

Abstract

present invention relates to a process for depositing a metal coating containing nickel and boron on a substrate, said process comprising the steps of: preparing a plating bath having a pH in the range of about 10.5 to 14 and a temperature above ambient temperature, comprising. (a) nickel ions according to a nickel concentration in the range of about 4.76 to about 5g/1 of coating bath; (b) an effective amount of a stabilizer, (c) a metal ion complexing agent in an amount effective to inhibit precipitation of said metal ions from the plating bath; (d) an effective amount of a borohydride reducing agent; and (e) optionally up to 0.25 moles of cobalt per liter of plating bath; immersing said substrate to be coated into said bath, such electrolessly depositing the coating on the substrate and optionally heat treating said metal coating for about one to about 24 hours subsequently. The process according to the present invention is characterized in that the plating bath is prepared on the basis of deionized water having a conductivity in the range of about 0.05 [m]S. Futhermore, the present invention relates to a platin bath for use in said process, and to a coated article as manufactured by means of such a process.

Full Text

The present invention relates to a process for coating an article with nickel and boron and an article having such a coating and more particularly to electroless nickel plating. The document US 6,066,406 discloses corrosion and wear resistant metallic coatings containing nickel and boron. The coatings as described according to said prior art reference are preferably deposited on catalytically active substrates from an electroless coating bath containing nickel ions, a stabilizer, a metal ion complexing agent, and a borohydride reducing agent, at a pH of about 10 to about 14. However, the hardness of said coating layers is still limited as well as the other properties being important for technical applications, which limitations result from the insuppressible occurrence of substantive co-depositing of impurities during the plating process. Especially, the coating baths according to the state of the art tend to spontaneous decomposition caused by the presence of unwanted elements that themselves would become activated plating sites that, once plating become larger in mass until they become so large that they fall out of solution, thereby dropping to the bottom of the plating tank causing said tank to plate or worse, additionally falling onto the work item to be plated, resulting thereby in a rough coating surface. Furthermore, in most cases the coating baths according to the state of the art additionally do not provide a proper reduction of the present nickel ions, leading to a bath solution that requires discarding, thereby also contributing to a worse quality of the coating surface. Therefore, there remains a strong demand for a process for depositing a metal coating containing nickel and boron on a substrate, which avoids completely such phenomenon being caused by undesired co-depositing of impurity particles, affecting unfavourably the application properties of the resulting nickel containing coatings as produced according to the state of the art. This problem is solved by the process of the present invention as described further in the specification making use of the plating bath having the specific parameters as described. Especially, the process according to the present invention is characterized by the use of most accurately deionized water with a conductivity in the range of about 0.05 to about 0.1 µS for the preparation of the plating bath, which measure in particular avoids completely the undesired co-deposition of impurity particles in the coatings, resulting surprisingly in coatings with exceptionally unexpected physical properties in regard of particular hardness, corrosion resistance, wear resistance, abrasion resistance, etc. (see below under section "K" of the working example). In particular, the use of said deionized water prevents spontaneous decomposition of the coating bath by removing unwanted elements that themselves would become larger in mass until they become so large in mass that they fall out of the solution dropping to the bottom of the plating tank, thereby causing the tank to plate or worse, additionally falling onto the work item to be coated, thereby resulting in a rough coating surface. Furthermore, when using deionized water, the elements found in tap water, which usually tend to interfere with the stabilizing elements of the bath, are absent, resulting in a proper reduction of the nickel. Therefore, the above-discussed decomposition of the coating bath can be avoided. The further details of the teaching according to the present invention are described by means of the following working example. WORKING EXAMPLE A. BATH COMPONENTS Cemkote A = Make-up ( = premixed solution of 24g/l of total tank volume of Sodium Hydroxide pellets (Electronic Grade) mixed with high-quality deionized water. Cemkote B = Reducer ( = solution comprising an effective amount of a borohydride reducing agent and an effective amount of a metal ion complexing agent, preferably of ethylenediamine); Cemkote C = Stabilizer ( = preferably a solution comprising an effective amount of lead tungstate). Cemkote D = Nickel Replenisher ( = a solution comprising both Ni-based plating solution, ammonium hydroxide, and a metal ion complexing agent, preferably ethylenediamine according to effective amounts, respectively). B. MAKE-UP PROCEDURE a. Rinse tank thoroughly with deionized water. Tank must be free of debris and plate-out residue. b. Place new 5-micron filters in the filter chamber. c. Fill the tank half way with deionized water having a conductivity in the range of 0.05 to 0.1 µS. d. Add 20% by volume of the total tank volume of Cemkote A. e. Add premixed solution of 24g/l of total tank volume of Sodium Hydroxide pellets (Electronic Grade) mixed with high-quality deionized water. Caution: this solution heats up when mixed. f. Fill tank to working level with high-quality deionized water. g. Start pump. C. BATH PARAMETERS Temperature 90 -92 degrees Celsius; pH 10.5 to 14; Bath load 0.12 dm2 / ml to 0.16 dm2 / ml; Nickel concentration 4.76 to 5.6 g/l; Plating rates 18 to 24 µm per hour. D. PLATING After proper preparation, parts are to be placed into the Cemkote solution for the required time in order to obtain the desired thickness of plating. E. AGITATION Air agitation is not recommended for this process. Continuous filtration with 5-micron filters and the total tank turnover rate of 10 times per hour is recommended. F. TANK CLEANING A solution of 30% to 50% Nitric acid solution should be placed into the tank after every third day of plating to clean out all the plate-out, if any, as well as passivate the tank. Let circulate over night. After Nitric acid solution is removed, refill the tank with a 2% to 3% ammonium hydroxide solution to neutralize any residual nitric acid (pH to be 10.5 or higher). Let circulate for one to two hours, then drain and flush with high-quality DI water. G. NICKEL REPLENISHMENT Nickel Titration Apparatus: a. 250 ml Erlenmeyer flask b. 2 ml pipette c. 10 ml graduated cylinder d. 25 ml burette e. Stir plate f. Pipette bulb g. Stir bar PROCEDURE: a. Add 100 ml of deionized water to a 250 ml Erlenmeyer flask. b. Pipette 2 ml sample of the plating solution into same flask. c. Add 10 ml of concentrated Ammonium Hydroxide solution to flask. d. Place flask on the stir plate and turn on stirrer. e. Add one Murexide indicator tablet (4mg). f. Zero burette with 0,0575 EDTA standard solutions. g. Titrate. h. Color change is from yellow to purple. Monitor nickel level every half hour to maintain within recommended range. When adding Cemkote D to an operating plating bath, add slowly. H. REDUCER REPLENISHMENT a. Cemkote B and Cemkote C components are first mixed together before adding them to an operating plating bath. b. Adds should be made per addition schedule every half hour of plating, c. These adds should be made as slow as possible. I. ADDITION SCHEDULE Please note that this schedule is based on a Total Tank Volume (TTV) of 100 Gallons ( = about 500 liters), and will vary based on the Total Tank Folume (TTV) of your particular tanks. LOAD [dm*] CEMKOTE "B" Addition [ml] CEMKOTE "C" Addition [ml] 135 1087.5 870 162 1305.0 1044 203 1631.25 1305 243 1957.5 1566 270 2175.0 1740 310 2501.25 2001 350 2827.5 2262 404 3262.5 2610 444 3588.75 2871 485 3915.0 3132 539 4350.0 3480 579 4676.25 3741 620 5002.5 4002 674 5437.5 4350 K. PHYSICAL PROPERTIES OF RESULTING COATINGS 1. Composition: approximately 95 wt.-% nickel and. 5 wt.-% boron. 2. Coating density: 8.0 to 9.4 g/cm3. 3. Deposition thickness range: 1 µm to preferably approximately 250 µm (maximum deposit thickness generally unlimited), particularly 25-50 µm averagely for common industrial standard applications. 4. Structure: columnar growth; nodular topographic surface. 5. Uniformity of deposit: +/- 10 % of total deposit. 6. Magnetic Properties: slightly magnetic. 7. Surface finish distortion: increase of 20 -32 RMS from starting value of 1 RMS (mild steel, standard grit-blasted preparation, 25 µm deposit). 8. Bond Strength: metallurgical bond to metallic substrates, exceeds known bond tests resulting in secondary attachment material failure, epoxy/silver solder. Greater than 3200 kilo/2.54cm3, 6061 t aluminium (epoxy failure). Greater than 5000 kilo/2.54cm3, 6061 t titanium (epoxy failure). Greater than 35,000 kilo/2.54cm3, ferrous alloys. 9. Hydrogen Embrittlement: Less than 1 % induction of hydrogen; ASTM-F1940, Hard chrome: 38-44 %; Electroless nickel: 23-27 %. 10. Internal Stresses; Extremely low tensile: 30 MPa. Hard Chrome: 1000 MPa. 11. Corrosion resistance. ASTM B-117. Although Cemkote® should not be considered for corrosion resistance alone, in applications requiring wear resistance along with some corrosion resistance, a duplex layer should be incorporated. With an underlying layer of nickel 10 - 12 µm, the coatings as produced in accordance with the teaching of the present invention can resist oxide development up to 240 hours. In addition, post-plating sealers have been employed to further enhance corrosion resistance. It should also be mentioned that due to the durability of the coatings produced in accordance with the teaching of the invention, in common, practical applications, these coatings far exceed the useful life of other coatings such as cadmium and zinc. 12. Wear Resistance, Falex ASTM-D2714, ring and.block; mass loss: 0.0002g. Electroless nickel, mass loss: 0.0022 g. Hard chrome, mass loss: 0.0017 g. Tungsten Carbide, mass loss: 0.0014 g. 13. Abrasion resistance, ASTM-G65, Abrasive sand, mass loss: 0.008 g; Thermal spray tungsten carbide, mass loss: 0.009 g; PVD titanium nitride, mass loss: 0.065 g; PVD Cr nitride, mass loss: 0.0039 g; Hard chrome, mass loss: 1.1g; Electroless nickel, mass loss: 1.4 g. 14. Ductility: Extremely ductile because of the true columnar growth. 15. Hardness: The coatings as manufactured according to the teaching of the present invention represent an alloy coating comprising of a softer nickel and boron matrix with harder nickel boride crystalline clusters dispensed through-out the deposit. Knopp and Vickers indenters capture mostly the softer matrix and not the much harder nickel boride clusters. So reading are commonly found to be 1100 — 1400 KpH. The nickel-boride clusters 1600 - 2000 KpH. 16. Temperature limitations: -100 °C to 980 °C. 17. Melting Point: 1400 °C. 18. Electrical conductivity: about 15 - 190 microOhms. 19. Coefficient of friction: 0.08 - 0.06 ASTM-D2714; Hard chrome: 1.3 - 1.35. WE CLAIM: 1. A process for coating an article with nickel and boron and an article having such a coating, the process comprising the following steps: - Preparing a plating bath having a pH in the range of 10.5 to 14 and a temperature above ambient temperature, comprising: (a) nickel ions according to a nickel concentration in the range of 4.75 to 5 g/l of plating bath; (b) a stabilizer; (c) a metal ion complexing agent to inhibit precipitation of said metal ions from the plating bath; and (d) a borohydride reducing agent; - immersing said substrate to be coated into said plating bath, electrolessly depositing the coating on the substrate, characterized in that the plating bath is prepared on the basis of deionized water having a conductivity in the range of 0.05 to 0.1µS. 2. The process for coating an article with nickel and boron as claimed in claim 1, wherein the prepared plating bath further comprises up to 0.25 moles of cobalt per litre of plating bath. 3. The process as claimed in claim 1, wherein the said metal coating comprising nickel and boron, is heat-treated for 1 to 24 hours. 4. The process as claimed in claim 1, wherein the temperature of the plating bath is selected in the range between 90°C to 95°C, preferably in the range of 91.5°C to 92.5°C. 5. The process as claimed in any of claims 1 to 4, wherein 0.0006 to 0.075 g stabilizer per litre of plating bath is used. 6. The process as claimed in any of claim 1 to 5, wherein the stabilizer used is lead tungstate. 7. The process as claimed in any of the claims 1 to 6, wherein the metal ion complexing agent comprises a compound selected from the group consisting of ethylenediamine, ethylenediaminetetracaetate (EDTA), water soluble salts of tartaric acid and ammonia. 8. The process as claimed in claim 1 to 7, wherein the metal complexing agent is ethylenediamine. 9. The process as claimed in any of claims 1 to 8, wherein the borohydride reducing agent is selected from the group consisting of sodium borohydride, potassium borohydride, sodium trimethoxyborohydride, and potassium trimethoxyborohydride. 10. The process as claimed in claim 9, wherein the borohydride reducing agent is sodium borohydride. 11. The process as claimed in claim 1, wherein the said plating bath has a pH in the range of 10.5—14 and a temperature above ambient temperature, comprising the following components: (a) nickel ions according to a nickel concentration in the range of 4.76 to 5 g/l of plating bath; (b) stabilizer; (c) a metal ion complexing agent for inhibiting precipitation of said metal ions from the plating bath; (d) a borohydride reducing agent; (e) upto 0.25 moles of cobalt per litre of plating bath; wherein the plating bath comprises of deionized water having a conductivity in the range of 0.05 to 0. 1µS. 12. The plating bath as claimed in claim 11, wherein the plating bath has a temperature in the range of 90°C to 95°C, preferably in the range of 91.5°C to 92.5°C. 13. The plating bath of any of claims 11 or 12, wherein it comprises 0.0006 to 0.0075g stabilizer per litre of plating bath. 14. The plating bath of any of the claims 11 to 13, wherein the stabilizer is lead tungstate. 15. The plating bath of any of the claims 11 to 14, wherein the metal ion complexing agent comprises a compound selected from the group consisting of ethylenediamine, ethylenediaminetetraacetate (EDTA), water soluble salts of tartaric acid and ammonia. 16. The plating bath of claim 15, wherein the metal complexing agent is ethylenediamine. 17. The plating bath of any of claims 11 to 16, wherein the borohydride reducing agent is selected from the group consisting of sodium borohydride, potassium borohydride, sodium trimethoxyborohydride, and potassium trimethoxyborohydride. 18. The plating as claimed in claim 17, wherein the borohydride reducing agent is sodium borohydride. The present invention relates to a process for depositing a metal coating containing nickel and boron on a substrate, said process comprising the steps of: preparing a plating bath having a pH in the range of about 10.5 to 14 and a temperature above ambient temperature, comprising: (a) nickel ions according to a nickel concentration in the range of about 4.76 to about 5g/l of coating bath; (b) an effective amount of a stabilizer; (c) a metal ion complexing agent in an amount effective to inhibit precipitation of said metal ions from the plating bath; (d) an effective amount of a borohydride reducing agent; and (e) optionally up to 0.25 moles of cobalt per liter of plating bath; immersing said substrate to be coated into said bath, such electrolessly depositing the coating on the substrate and optionally heat treating said metal coating for about one to about 24 hours subsequently. The process according to the present invention is characterized in that the plating bath is prepared on the basis of deionized water having a conductivity in the range of about 0.05 µS. Futhermore, the present invention relates to a platin bath for use in said process, and to a coated article as manufactured by means of such a process.

Documents:

846-KOLNP-2003-CORRESPONDENCE.pdf

846-KOLNP-2003-FORM 27.pdf

846-kolnp-2003-granted-abstract.pdf

846-kolnp-2003-granted-claims.pdf

846-kolnp-2003-granted-correspondence.pdf

846-kolnp-2003-granted-description (complete).pdf

846-kolnp-2003-granted-examination report.pdf

846-kolnp-2003-granted-form 1.pdf

846-kolnp-2003-granted-form 18.pdf

846-kolnp-2003-granted-form 2.pdf

846-kolnp-2003-granted-form 26.pdf

846-kolnp-2003-granted-form 3.pdf

846-kolnp-2003-granted-form 5.pdf

846-kolnp-2003-granted-letter patent.pdf

846-kolnp-2003-granted-reply to examination report.pdf

846-kolnp-2003-granted-specification.pdf