Title of Invention	A PROCESS FOR ELECTROLESS COMPOSITE COATING.
Abstract	A process for electroless composite coating of Ni-P-Al2O3-Al3Zr-ZrO2 has been developed by obtaining a fine (submicron) and uniform sized particles of Al2O3 and ZrO2 and co-depositing them within the Ni-P electroless bath. This novel method not only reduces the processing steps but alsxo improves the process economy through sizing of particle.

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This invention relates to a process for electroless composite coating. More particularly, this invention relates to a process for an electroless composite coating of nickel- phosphorous - alumina - aluminium zirconate - zirconium oxide (Ni-P-Al2O3-Al3Zr- Zr02). Electroless coating or auto catalytic deposition method as it is referred to by some investigators is basically the deposition of a metallic coating by a controlled chemical reduction that is catalyzed by the metal or alloy being developed. In the case of composite coating, a composite-combination of two or more materials will be used in place of single matrix such as a metal. The electroless coatings are becoming more and more popular in industries. [1. Donald W. Boudrand. "Electroless Plating", ASM Hand book. Surface Engg., Vol. 75, pp 200-3 JO, (1994). 2. Apachitei, J. Duszyk, L. Katgerman and P.J.B. Overkamp, Scripta Materialia, vol.38, 9, pp 1347-1353, (1998), 3. Apachitei, J. Duszyk, L. Katgerman and P.J.B. Overkamp, Scripta Materialia, vol. 38, 9, pp 1383-1389, (1998), 4. Jim Henry, Metal Finishin, vol. 82, 9, pp 93-94, (1984), 5. N. Feldstein, Metal Finishing, Vol.82, 1A, pp 408-416, (1984), 6. N. Feldstein, T. Lancsk, D. Lindsay and L. Salerno, Metal Finishing, vol.81, 8, pp 35-41, (1983), 7. R.C. Agarwala, "Strucutral Studies and Crystalline Behaviour of Electroless Ni-P Films",- Ph.D. Thesis, University of Roorkee, Roorkee, (1987), 8. S.M. Moonir-Vagheli, A. Saatchi and J. Hedjazi, Z. Metallkde, vol.88, 6, pp 498-501, (1997), 9. Srinivasan K.N., John S. Vasudean T. and Deepa B., Proc. of Ninth National Congress on Corrosion Control, held at The International Centre, Goa, 16-18 Sept., pp 108-112, (1999), 10.V.V.N. Reddy, B. Ramamoorthy and P. Keshavan Nair. Proc. of 18th AIMTDR Conference held at IIT, Kharagpur, Dec. 21-23, pp 440-444, (1998).]. All these references include development of electroless composite coatings such as nickel-phosphorous-alumina (Ni-P-Al2O3), nickel-phosphorous-silicon carbide (Ni-P-SiC), Ni-P-M0S2 (molybdenum disulphide), Ni-P-C(carbon), Ni-P-Mo (molybdenum), Ni-P-WC (tungsten carbide), Ni-Co (cobalt)-P, Ni-Cu (copper)-P etc., which are Ni-P matrix based. They also cover all the methods to synthesise composite electroless coatings involving suspension of particulates of composites in the matrix like Ni-P. The draw back of these methods is the dependence of rate of Coating and other properties on particle size. Also, Ni-P-Al2O3-Al3Zr-Zro2) type of coatings have not been found to be reported so far in the available literature. Another objective of the invention is to reduce the energy consumption by eliminating some steps such as stirring while improving the process economy through sizing of particles. Accordingly, the present invention provides a process for electro less composite coating which comprises; preparing an alkali bath by adding nickel sulphate, sodium hypo phosphite, sodium citrate and ammonium chloride at a pH ranging between 8.5 - 9.5, adding an aqueous solution of zirconium oxychloride and aluminum chloride to the above electrolyte bath in the presence of ammonium sulphite to co precipitate the aluminum chloride of chromium oxychloride, immersing the cleaned and sensitized specimen to the above said electrolyte bath to obtain the desired homogeneous composite coating Ni-P-Al2O3-Al3Zr-Zro2) on the catalytic surface. In an embodiment of the present invention the present invention provides, the composite coating as prepared in Ni-P-Al2O3-Al3Zr-Zro2) In another embodiment of the present invention the present invention provides, the composite electrolyte bath used is comprising a) Nickel sulphate ranging from 34-34 g/1 b) Sodium citrate ranging from 82-86 g/1 c) Aluminum Chloride - ranging from 19-20 g/1 d) Ammonium Chloride - ranging from 23 - 26 g/1 e) Sodium hypo phosphite ranging from 18-20 g/1 f) Ziroconium oxychloride ranging from 5-6 g/1 g) Ammonium Sulphite ranging from 23-26 g/1 The novel process of the present invention is illustrated by the following examples and a few trials which should not be construed to limit the scope of the present invention. Several experiments were carried out to synthesize the coating and the results as regards appearance and adherence of coatings gave the appropriate range of process parameters. These include coating weights of 100, 150 and 60 mg by varying pH of 9 and 9.5 time between 3 to 45 minutes and temperature between 85 and 90. This range of process parameters has been used to carry out a set of experiments with three variables at two levels of each. An orthogonal array "L4" (Table 1) has been selected to conduct experiments. The effect of process parameters, viz., pH, time and temperature have been studied by ANOVA TECHNIQUE. The details of experimental design is as follows. The ANOVA (analysis of variance) results are also shown in Table 2 (Table Removed) Table 1 : An Experimental lay out using 'L4' array Trial No. 1: First set of experiments were carried out without any pooling factor. Results are shown in Table2. Table 2; ANOVA table for experiments conducted as per array 'L4' (Table Removed) The X-Ray Diffraction study of coatings reveals the presence of many phases namely Al3Zr, A12O3, Ni12P5, Ni5Zr, Ni (amorphous). The X-ray diffraction result is shown in Figurel. Trial No. 2 Another set of experiments were carried out with pooling of temperature factor. These results are also shown in Table 2. By referring to Figure 1, the various phases present in as plated composites electroless are reported in Table 3. Table 3: Various phases present in Ni-P-Al2O3-Al3Zr-ZrO2 composite electroless coating (As coated) (Table Removed) N= number of peaks, ; A, = wave length, 1.542 for CuKK The EPMA point analysis (quantitative analysis) of the coating revealed the phases of the coating and the average values of three different places obtained are given in Table 4: Table 4:Amount of different phases present in the coating (Table Removed) The scanning electron micrographs shows the remarkable grain refinement due to Al3Zr, A12O3 & ZrO2 phases present in as coated conditions. This is clearly evident from comparing SEM photographs of Ni-P electroless coating (Figure 2) and electroless composite coating, Ni-P-AlO3-Al3Zr-ZrO2 (Figure 3). In Figure 3 the globules of Ni-P are seen which are of uniform size and smaller, when compared with Figure 2. In the start of coating process nuclei form at discrete sites on the substrate. With time, the growth these nuclei occur vertically as well as critically filling the whole space with Ni-P coating. The composite coating obtained by this method consists of oxides of aluminum and zirconium, (A12,O3 and ZrO2) and intermetallics, (Al3Zr) in Ni-P matrix. From the experiment lay out and responses (Table 1), the weight of the coating has been considered as quality characteristic. With the above experiments, the performance of trials conducted is calculated using the following Equation: Y= T/N+(A,-T/N) + B2-T/N) + C2-T/N)=150±⌂Y Where T = Grand total of all results N = Number of results AI = pH , S2 = Temperature (°C), and C1 = Time.( min). A Y = small change in g due to local variable time AI, B2 and C2 are average effect of corresponding factors in different experiments as regard weight of the coating, the main effect. The factors AI, B2 and C2 are selected due to maximum weight of the coating obtained by using these variables from the array 'L4'. The calculated Y is the result obtained in agreement to experiment 2, therefore the process conditions weere optimized thus. [Ranjeet K. Roy. "A Primer on Taguchi Method", Published by Van Nostrcmd Reimbold, New York, 1990]. It is found that pH and time of coating have got predominant effect on weight of coating by this process. One of the advantages of the present invention is co-precipitation of alumina-zirconia in the bath itself followed by co-deposition which is an improved method for composite coatings by electroless method. Another advantage of the present invention is grain size refinement due to the in situ co-precipitation reaction in electroless bath. Yet another advantages of the present invention include: higher coating rate than that obtained with conventional electroless Ni-P coating; presence of an intermetallic compound Al3Zr as one of the phases in the electroless composite coating and submicron size A12O3 and ZrO2 particles embedded in the Ni-P matrix. We Claim: 1. A process for electroless composite coating which comprises; preparing an alkali bath by adding nickel sulphate, sodium hypo phosphite, sodium citrate and ammonium chloride at a pH ranging between 8.5 - 9.5, adding an aqueous solution of zirconium oxychloride and aluminum chloride to the above electrolyte bath in the presence of ammonium sulphite to co precipitate the aluminum chloride of chromium oxychloride, immersing the cleaned and sensitized specimen to the above said electrolyte bath to obtain the desired homogeneous composite coating Ni-P-Al2O3Al3Zr-ZrO2 on the catalytic surface. 2. A process as claimed in claim 1, wherein the composite electrolyte bath used is comprising; a) Nickel sulphate ranging from 32-34 g/1 b) Sodium citrate ranging from 82-86 g/1 c) Aluminum Chloride - ranging from 19-20 g/1 d) Ammonium Chloride - ranging from 23-26 g/1 e) Sodium hypo phosphite ranging from 18-20 g/1 f) Zirconium oxychloride ranging from 5-6 g/1 g) Ammonium Sulphite ranging from 23-26 g/1 3. A process for electro less composite coating substantially herein described with reference to the examples and drawing accompanying this specification.

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