Title of Invention

AN ELECTROLESS NICKEL COATING COMPOSITION

Abstract

The main object of the present invention is to provide an electroless nickel coating solution for coating thermo-mechanical treated (TMT) rebar with an increased stability without interfering with the formation of the nickel coating. Another object of the present invention is to provide a process for electroless nickel coating of thermo-mechanical treated (TMT) rebar without removing oxide scales. Yet another object of the present invention is to provide a nickel-phosphorus alloy coating on rebar surfaces for obtaining the desired bond strength with concrete and significant improvement of corrosion resistance property. These and other objects of the present invention are achieved by using an electroless nickel plating composition for coating thermo mechanical treatement (TMT) rebars with nickel-phosphorus alloy. In one preferred embodiment the present invention provides an electroless nickel coating composition comprising at least one each of a water soluble nickel salt, a reducing agent, a complexing agent, and a stabilizer. Nickel is derived from the water soluble nickel salt. The water soluble nickel salt is selected from a group consisting of any one, some, or all of nickel chloride, nickel sulphate, nickel formate, nickel acetate and nickel hypophosphide. The nickel salt is preferably nickel sulphate. The composition of the present invention having nickel- phosphorus, nickel-boron, or close to 100 % pure nickel will depend on the reducing agent used. The reducing agent used is selected from a group consisting of any one, some or all of hypophosphorus acid, hypophosphites, borohydrides, dimethylamine borane, trimethylamine borane, hydrazine, thiosulphates, and ascorbates. The reducing agent is preferably hypophosphide and hydrazine. The complexing agent can be selected from a group consisting of any one, some or all of ammonia and organic complex forming agents containing one or more functional groups selected from the group consisting of primary amino, secondary amino, tertiary amino, amino, carboxy and hydroxy. The complexing agent can be selected from a group consisting of any one, some or aU of ethylenediamine, diethylene triamine, triethylene tetramine, triethylenetriamine, sodium citrate, sodium pyrophosphate, organic acids, water soluble salts of organic acids, and amino acids. The organic acid can be selected from a group consisting of maleic acid, succinic acid, lactic acid, oxalic acid, citric acid, tartaric acid, and ethylene diamine tetra acetic acid. The stabilizers used can be divided into the following classes, (i) compounds of group VI elements: S; Se; Te; (ii) compounds containing oxygen: As02,103, M0O4 ; (iii) heavy metal cations : Sn + +, Pb + +, Hg +, Sb + + +; and (iv) unsaturated organic acids: maleic, itaconic. The electroless nickel layer can be deposited on a substrate by contacting the substrate with the composition of the present invention. The composition of the electroless nickel coating will depend on the bath chemistry and pH. The deposition rate of Ni depends on the bath temperature and pH and the Ni percentage in the coating will depend mainly on the bath pH. The electroless process can be used for depositing a Ni-P alloy layer on a substrate, for example TMT rebar surface by contacting the substrate with the composition of the present invention. The deposition of nickel phosphorus alloy on the rebar surface depends on the composition, the pH and temperature of the bath. The pH of the composition is preferably between 3 and 11. The bath temperature can be maintained at 70 - 95° C for alloy deposition at the optimum rate. The presence of stabilizer hastens the deposition rate upto a certain ppm level. Above the critical limit the stabilizer can even stop the deposition completely. A bath temperature of 85 - 95° C and pH 5 - 7 can be provided when organic acid is used as complexing agent and sodium hypophosphorus is used as reducing agent.

Full Text

FIELD OF APPLICATION The present invention relates to an electroless nickel coating composition for coating re-enforcement bars. In particular, the invention relates to an electroless nickel coating of thermo-mechanical treated (TMT) re-bar, without removing the oxide scale. The invention provides a nickel-phosphorus alloy coating composition and a method of depositing a nickel-phosphorus alloy coating by electroless process. BACKGROUND OF THE INVENTION The formation and stability of the passivating film on bare steel surfaces is dependent on the pH level of the solution surrounding the steel. In the absence of interfering chloride or other ions, such a film has been shown to be produced and indefinitely maintained so as to effectively prevent corrosion when the pH is greater than 11.5. Thus, the high pH concrete pore solution is sufficient to maintain stable passivation films and corrosion should not occur. However, in practice this favourable state of affairs may change and depassivation may occur under two specific sets of conditions: (i) reduction of pH due to reaction with atmospheric CO2 (carbonation); and (ii) penetration of chloride ions into the concrete pore solution around the steel. It is known that, at sufficiently high concentrations, chloride ions can effectively destabilize the passivating film even when the normally high pH level associated with concrete water solutions remains unchanged. Hence, some pretreatment of the rebar is required to prevent this corrosion problem. Electroless metal deposition solutions (electroless plating solutions) deposit metal over a catalytically active surface by chemical reduction in the absence of an external electric circuit. Those solutions containing nickel are used in a wide range of industrial applications. Nickel-boron and nickel-phosphorus coatings are recognized in the art for their corrosion resistance, hardness and associated wear-resistance. See, for example, U.S. Patent Nos. 2,726,170; 3,045,334; 3,378,400; 3,738,849; 3,674,447; 3,432,338; 3,918,137; 4,395,442; 4,567,066; 4,706,616; 4,724,819; 5,019,163; 5,148,780; and 6,178,306. Typical electroless nickel plating solutions generally comprise a water-soluble nickel salt, a water-soluble alloying salt (if an alloy is present), a reducing agent, and a chelating or complexing agent. Additives may also be added in relatively low concentrations to enhance various characteristics of the solution of plated article. One continuing need with respect of electroless nickel plating solutions has been the need to increase the stability of the solution. It has been found, however, that in certain instances the addition of stabilizers to meet this need interferes with the formation of the nickel coating, in that during the formation of the nickel coating the accelerator co-deposits in the nickel. Some stabilizers are also known to cause discoloration of the deposit. SUMMARY OF THE INVENTION The main object of the present invention is to provide an electroless nickel coating solution for coating thermo-mechanical treated (TMT) rebar with an increased stability without interfering with the formation of the nickel coating. Another object of the present invention is to provide a process for electroless nickel coating of thermo-mechanical treated (TMT) rebar without removing oxide scales. Yet another object of the present invention is to provide a nickel-phosphorus alloy coating on rebar surfaces for obtaining the desired bond strength with concrete and significant improvement of corrosion resistance property. These and other objects of the present invention are achieved by using an electroless nickel plating composition for coating thermo mechanical treatement (TMT) rebars with nickel-phosphorus alloy. In one preferred embodiment the present invention provides an electroless nickel coating composition comprising at least one each of a water soluble nickel salt, a reducing agent, a complexing agent, and a stabilizer. Nickel is derived from the water soluble nickel salt. The water soluble nickel salt is selected from a group consisting of any one, some, or all of nickel chloride, nickel sulphate, nickel formate, nickel acetate and nickel hypophosphide. The nickel salt is preferably nickel sulphate. The composition of the present invention having nickel- phosphorus, nickel-boron, or close to 100 % pure nickel will depend on the reducing agent used. The reducing agent used is selected from a group consisting of any one, some or all of hypophosphorus acid, hypophosphites, borohydrides, dimethylamine borane, trimethylamine borane, hydrazine, thiosulphates, and ascorbates. The reducing agent is preferably hypophosphide and hydrazine. The complexing agent can be selected from a group consisting of any one, some or all of ammonia and organic complex forming agents containing one or more functional groups selected from the group consisting of primary amino, secondary amino, tertiary amino, amino, carboxy and hydroxy. The complexing agent can be selected from a group consisting of any one, some or aU of ethylenediamine, diethylene triamine, triethylene tetramine, triethylenetriamine, sodium citrate, sodium pyrophosphate, organic acids, water soluble salts of organic acids, and amino acids. The organic acid can be selected from a group consisting of maleic acid, succinic acid, lactic acid, oxalic acid, citric acid, tartaric acid, and ethylene diamine tetra acetic acid. The stabilizers used can be divided into the following classes, (i) compounds of group VI elements: S; Se; Te; (ii) compounds containing oxygen: As02,103, M0O4 ; (iii) heavy metal cations : Sn + +, Pb + +, Hg +, Sb + + +; and (iv) unsaturated organic acids: maleic, itaconic. The electroless nickel layer can be deposited on a substrate by contacting the substrate with the composition of the present invention. The composition of the electroless nickel coating will depend on the bath chemistry and pH. The deposition rate of Ni depends on the bath temperature and pH and the Ni percentage in the coating will depend mainly on the bath pH. The electroless process can be used for depositing a Ni-P alloy layer on a substrate, for example TMT rebar surface by contacting the substrate with the composition of the present invention. The deposition of nickel phosphorus alloy on the rebar surface depends on the composition, the pH and temperature of the bath. The pH of the composition is preferably between 3 and 11. The bath temperature can be maintained at 70 - 95° C for alloy deposition at the optimum rate. The presence of stabilizer hastens the deposition rate upto a certain ppm level. Above the critical limit the stabilizer can even stop the deposition completely. A bath temperature of 85 - 95° C and pH 5 - 7 can be provided when organic acid is used as complexing agent and sodium hypophosphorus is used as reducing agent. When pyrophosphate or ammonia is used as complexing agent and hydrazine is used as reducing agent, the bath temperature 70 - 80° C and pH is ~ 10.5. The stabiiizer concentration in the composition is ~ 0.05 to 10 mg/l, preferably between 0.5 to 1.5 ppm thiourea . The coating thickness is directly proportional to treatment time. After electroless nickel (EN) treatment all samples are rinsed in tap water and dried in open atmosphere subsequently. Surface appearance of the electroless nickel (EN) coated samples are bright. The plating composition preferably has an effective nickel ion concentration of 0.01 to 1 mol/l. The effective concentration of reducing agent in the plating composition is 0.01 to 1.0 mol / I. The effective concentration of complex agent in the composition is ~ 0.01 to 2.0 mol/l. The electroless nickel coating of the present invention on the surface of rebar bundle provides significant improvement in corrosion resistance property in a concrete environment. According to the present invention separate pickling operation to coat nickel- phosphorous alloy on steel substrate is not required. The surface treatment can be done on individual rebar as well as on a bundle consisting of multiple rebars. The coating developed on TMT rebar according to this invention is also applicable for TMT, TMT CRS as well as CTD bars. Electroless nickel coated rebar satisfy the requirement of bond strength with concrete. The electroless nickel coated material shows significant improvement in corrosion resistance against chloride / simulated alkaline concrete environments compared to bare steel. The thermo-mechanical treated (TMT) bar in the present invention is coated by nickel-phosphorus alloy through electroless route without removing oxide scale from the steel substrate. Coating property very much depends on composition, temperature, dipping time and pH of the bath solution, electro-less nickel (EN) coated reinforcing bars showed significant improvement in corrosion resistance against chloride and it satisfy the requirement of bond strength with concrete. In the present invention, by developing the optimum electroless nickel (EN) process, it has been possible to provide adequate corrosion protection of thermo- mechanical treated (TMT) rebar in concrete environment. The electroless coating of the present invention can also be applied on thermo-mechanical treated (TMT), cold rolled steel (CRS) and CTD bars. WE CLAIM 1. An electroless nickel coating composition comprising at least one each of a water soluble nickel salt, a reducing agent a complexing agent, and a stabilizer. 2. The nickel coating composition as claimed in claim 1, wherein said water soluble nickel salt is selected from a group comprising any one, some or all of nickel chloride, nickel sulfate, nickel formate, nickel acetate and nickel hypo-phosphide. 3. The nickel coating composition as claimed in claim 1, wherein said water soluble nickel salt is nickel sulfate. 4. The nickel coating composition as claimed in claim 1, wherein said reducing agent is selected from a group comprising any one, some, or all of hypo-phosphorus acid, hypophosphites, borohydrides, dimethylamine borane, thimethylamine borane, hydrazine, thiosulfates. 5. The nickel coating composition as claimed in claim 1, wherein said reducing agent comprises sodium hydrophosphide and hydrazine. 6. The nickel coating composition as claimed in claim 1, wherein said complexing agent is selected from a group comprising any one, some or all of ammonia and organic complex forming agents comprising one or more functional groups selected from a group consisting of primary amino, secondary amino, tertiary amino, amino carboxy and hydroxy. 7. The nickel coating composition as claimed in claim 6, wherein said complexing agent is selected from a group comprising any one, some or all of ethylenediamine, diethylene triamine, triethylene tetramine, triethylenetriamine, sodium citrate, sodium pyrophosphate, organic acids, water soluble salts of organic acids, and amino acids. 8. The nickel coating composition as claimed in claim 7, wherein said organic acids are selected from a group comprising maleic acid, succinic acid, lactic acid, oxalic acid, citric acid, tartaric acid, and ethylene diamine tetra acetic acid. 9. The nickel coating composition as claimed in claim 1, wherein said stabilizer is selected from four classes of stabilizers, - compounds of group VI elements S, Se, Te; - compounds containing oxygen, like AsO2, IO3, MoO4; - heavy metal cations Sn++, Pb++, Hg+, Sb+++; and - unsaturated organic acids like maleic, itaconic. 10. The nickel coating composition as claimed in claims 1 to 3, wherein effective concentration of Ni ions is 0.01 to 1.0 mol / litre. 11. The nickel coating composition as claimed in claim 1, wherein the pH value of the composition is 3 to 11. 12. The nickel coating composition as claimed in claims 1, 4 and 5, wherein effective concentration of said reducing agent is 0.01 to 1.0 mol / I. 13. The nickel coating composition as claimed in claims 1,6, 7 and 8, wherein effective concentration of said completing agent is 0.01 to 2.0 mol /1. 14. The nickel coating composition as claimed in claims 1 and 9, wherein concentration of said stabilizer is 0.05 to 10 mg / I and preferably 0.05 to 1.5 ppm thiourea. 15. A method of depositing an electroless nickel layer on a substrate comprising the step of contacting the substrate with an electroless nickel coating composition as claimed in the preceding claim. 16. A method of depositing a nickel phosphorus alloy layer by electroless process on a substrate like TMT rebar surface comprising the step of contacting the substrate with a composition as claimed in the preceding claims. 17. The method as claimed in claim 15, wherein the process parameters are 85-95° C temperature and 5-7 pH for the bath when organic acid is used as complexing agent and sodium hypohosphide is used as reducing agent. 18. The method as claimed in claim 15, wherein the process parameters are 70-80° C temperature and 10.5 pH for the bath when pyrophosphates or ammonia is used as complexing agent and hydrazine is used as reducing agent. 19. A steel substrate with oxides scale deposited with a nickel phosphorus alloy layer by the method as claimed in claim 16. 20. An electroless nickel coating composition comprising at least one each of a water soluble nickel salt, a reducing agent a complexing agent, and a stabilizer, substantially as herein described. The main object of the present invention is to provide an electroless nickel coating solution for coating thermo-mechanical treated (TMT) rebar with an increased stability without interfering with the formation of the nickel coating. Another object of the present invention is to provide a process for electroless nickel coating of thermo-mechanical treated (TMT) rebar without removing oxide scales. Yet another object of the present invention is to provide a nickel-phosphorus alloy coating on rebar surfaces for obtaining the desired bond strength with concrete and significant improvement of corrosion resistance property. These and other objects of the present invention are achieved by using an electroless nickel plating composition for coating thermo mechanical treatement (TMT) rebars with nickel-phosphorus alloy. In one preferred embodiment the present invention provides an electroless nickel coating composition comprising at least one each of a water soluble nickel salt, a reducing agent, a complexing agent, and a stabilizer. Nickel is derived from the water soluble nickel salt. The water soluble nickel salt is selected from a group consisting of any one, some, or all of nickel chloride, nickel sulphate, nickel formate, nickel acetate and nickel hypophosphide. The nickel salt is preferably nickel sulphate. The composition of the present invention having nickel- phosphorus, nickel-boron, or close to 100 % pure nickel will depend on the reducing agent used. The reducing agent used is selected from a group consisting of any one, some or all of hypophosphorus acid, hypophosphites, borohydrides, dimethylamine borane, trimethylamine borane, hydrazine, thiosulphates, and ascorbates. The reducing agent is preferably hypophosphide and hydrazine. The complexing agent can be selected from a group consisting of any one, some or all of ammonia and organic complex forming agents containing one or more functional groups selected from the group consisting of primary amino, secondary amino, tertiary amino, amino, carboxy and hydroxy. The complexing agent can be selected from a group consisting of any one, some or aU of ethylenediamine, diethylene triamine, triethylene tetramine, triethylenetriamine, sodium citrate, sodium pyrophosphate, organic acids, water soluble salts of organic acids, and amino acids. The organic acid can be selected from a group consisting of maleic acid, succinic acid, lactic acid, oxalic acid, citric acid, tartaric acid, and ethylene diamine tetra acetic acid. The stabilizers used can be divided into the following classes, (i) compounds of group VI elements: S; Se; Te; (ii) compounds containing oxygen: As02,103, M0O4 ; (iii) heavy metal cations : Sn + +, Pb + +, Hg +, Sb + + +; and (iv) unsaturated organic acids: maleic, itaconic. The electroless nickel layer can be deposited on a substrate by contacting the substrate with the composition of the present invention. The composition of the electroless nickel coating will depend on the bath chemistry and pH. The deposition rate of Ni depends on the bath temperature and pH and the Ni percentage in the coating will depend mainly on the bath pH. The electroless process can be used for depositing a Ni-P alloy layer on a substrate, for example TMT rebar surface by contacting the substrate with the composition of the present invention. The deposition of nickel phosphorus alloy on the rebar surface depends on the composition, the pH and temperature of the bath. The pH of the composition is preferably between 3 and 11. The bath temperature can be maintained at 70 - 95° C for alloy deposition at the optimum rate. The presence of stabilizer hastens the deposition rate upto a certain ppm level. Above the critical limit the stabilizer can even stop the deposition completely. A bath temperature of 85 - 95° C and pH 5 - 7 can be provided when organic acid is used as complexing agent and sodium hypophosphorus is used as reducing agent.

Documents:

00242-kol-2006-description provisional.pdf

00242-kol-2006-form 1.pdf

00242-kol-2006-form 2.pdf

00242-kol-2006-form 3.pdf

00242-kol-2006-gpa.pdf

242-KOL-2006-(30-06-2014)-CLAIMS.pdf

242-KOL-2006-(30-06-2014)-CORRESPONDENCE.pdf

242-KOL-2006-(30-06-2014)-FORM-1.pdf

242-KOL-2006-(30-06-2014)-FORM-2.pdf

242-KOL-2006-(30-06-2014)-PA.pdf

242-KOL-2006-(31-10-2011)-CORRESPONDENCE.pdf

242-kol-2006-abstract.pdf

242-kol-2006-claims.pdf

242-kol-2006-correspondence.pdf

242-kol-2006-description (complete).pdf

242-kol-2006-form 1.pdf

242-KOL-2006-FORM 18.pdf

242-kol-2006-form 2.pdf

242-kol-2006-form 3.pdf

242-kol-2006-form 5.pdf

242-kol-2006-gpa.pdf

242-kol-2006-specification.pdf