الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 159 |  |  |
| | | from | 159 | | |
Abstract
Our study concerned with electroless nickel plating from acid bath containing sodium hypophosphite as reducing agent and sodium acetate as complexing agent.
It can be possible to deposit nickel-phosphorus, nickel-tungsten - phosphorus, nickel – phosphorus - polymer (polyvinyl pyrrolidone) and nickel – tungsten - polymer composites. At relatively low bath temperature (80oC).The optimum composition and operating conditions for obtaining low temperature electroless nickel bath for Ni-P(●), Ni-W-P (▲) deposits and Ni-PVP (■) , Ni-W-PVP (♦) composites are shown in the following table.
Chemical Name Chemical Formula Concentration
Nickel sulphate NiSO4.6H2O 30 g/l ●
Sodium hypophosphite NaH2PO2.H2O 25 g/l ●
Sodium acetate CH3COONa.H2O 20 g/l ●
Lactic acid CH3CH(OH)COOH 10 ml/l ●
Propionic acid C2H5CO2H 10 ml/l ●
Sodium lauryl sulphate NaC12H25SO4 0.3 g/l ●
Sodium tungstate Na2WO4.2H2O 20, 40, 60 g/l ▲
Polyvinyl pyrrolidone (C6H9NO)n 5, 10, 20 g/l ■
Sodium tungstate + polyvinyl pyrrolidone 60 g/l +5, 10, 20 g/l ♦
Ammonium hydroxide NH4OH pH adjust (pH=4)
Plating temperature 80-85o C
Coating time 1hr
Part I:
The element percentage of the constituents in Ni-P and Ni-W-P deposits, deposited from acidic bath are shown in the following table.
Type of coating Weight percent (wt.%)
P W Ni
Ni-P 11.66 ........ 88.66
Ni-W-P I 9.88 3.13 86.99
Ni-W-P II 6.40 5.02 87.58
Ni-W-P III 4.92 7.01 88.07
The as deposited alloys of the acidic bath had amorphous structure, whereas crystallinity was observed at 400oC for 60 minutes. The sharp peaks formation of nickel and nickel phosphide Ni3P were detected at 400oC i.e. heat treatment leads to crystallization of all deposits and extensive is capable of improving it.
The morphology of electroless nickel alloy coating on low carbon steel has a nodular shape.
The results showed that the best adhesion was obtained in all samples, excellent adhesion and no gap. Percentage inhibition increases with increasing additive concentration (sodium tungstate 20, 40 and 60 g/l) approaching to complete protection, this is due to complete coverage by Ni-P and Ni-W-P coatings.
The electroless nickel coatings showed excellent corrosion resistance in both 3.5% sodium chloride solution and 2 M hydrochloric acid solution. This is because of the absence of the defects in crystalline alloys such as grain absence, dislocation, stacking faults and aggregation.
Part II A:
The thin film x-ray diffraction of Ni-PVP composites show amorphous nature .The grain size is increased from Ni-P deposit to Ni-PVP composite. The crystalline size increased as the polymer concentration increase in the plating bath in cases Ni-PVP composites.
The surface morphology of Ni-PVP composite coatings shows a nodular shape.
The protection of corrosion of Ni-PVP in 3.5% NaCl and 2 M HCl solutions were studied. The corrosion protection in 3.5% NaCl solution show a protection follow the sequence Ni-PVP III > Ni-PVP II > Ni-PVP I > Ni-P. Also the corrosion resistance in 2M HCl solution show the sequence Ni-PVP III > Ni-PVP II > Ni-PVP I > Ni-P.
Part II B:
The thin film x-ray diffraction of Ni-W-PVP composites show amorphous nature .The grain size is increased from Ni-W-P deposit to Ni-W-PVP composite with increasing the polymer concentration in the plating bath. The surface morphology of Ni-W-PVP composite coatings shows a nodular shape. The corrosion protection of Ni-W-PVP in 3.5% NaCl and 2 M HCl solutions were studied.
The electroless plating of Ni-W-P and Ni-W-PVP alloys on low carbon steel improve its corrosion protection. The corrosion protection of coated low carbon steel in 3.5% NaCl and 2 M HCl solutions follow the sequence Ni-W-PVP III > Ni-W-PVP II > Ni-W-PVP I > Ni-W-P. The excellent corrosion protection is due to the absence of the defects in crystalline alloys such as grain absence, dislocation stakes faults and segregation.