ELSEVIER Materials Chemistry and Physics 53 (1998) 235-238 MATERIALS CHEMISTRYAND PHYSICS Materials Science Communication Improving the throwing power of nickel electroplating baths Z. Abdel-Hamid * Central Metallurgical Research and Development Institute, PO Box 87, Helwan, Cairo, Egypt Received 28 May 1997; received in revised form 30 October 1997; accepted 5 December 1997 Abstract The throwing power of nickel electroplating baths was measured from the extent of plating penetration inside a tube by applying a new formula which relates the degree of penetration to the crevice dimensions and plating current. The effect of different factors such as pH value, anion or cation additives on the throwing power of different composition baths were investigated. The throwing power was shown to improve with the increase of pH value and the addition of sodium ions in the form of chloride, sulphate, borate or hypophosphite salts. High values of throwing power of nickel baths were achieved in hypophosphite, chloride, sulphate and borate baths. © I998 Elsevier Science S.A. All rights reserved. Keywords: Nickel electroplating baths 1. Introduction Improving the throwing power of electroplating and elec- troforming is essential from an economic point of view as well as the performance of the coatings. Most of the methods used to measure the throwing power of electroplating solu- tion, such as the Hull cell [ 1 ], bent cathode [2] and Haring Blum [3], expressed the value numerically or as a percentage without a specified unit. The field formula is the most popular one used to evaluate quantitatively the throwing power of plating solutions. This depended on the primary current dis- tribution (linear ratio) Lr/L,, where Lr is the distance from the anode to the far cathode, Ln is the distance from the anode to the near cathode and on the metal distribution Mn/Mr. There are many objections against using this method [4]. A more reliable measuring method was recently proposed by the authors [4,5] based on measuring the extent of plating penetration inside a tube. The throwing power is expressed by the value of K in the following simple formula p2 = Kd) log i+ C, where C is a constant, P is the coating penetration inside the tube, q5 is the diameter of the tube, i is the current and K is the throwing power. The throwing power of electroplating solution was gener- ally affected by different factors, such as * Corresponding author. 0254-0584/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PIIS0254-0584(97) 02070- 1 1. Operating conditions (current density, temperature, pH and agitation)--any change leading to an increase in polarization would result in an improvement in throwing power [ 6]. 2. Effect of chemical additives--organic compounds have been found to reduce the throwing power of nickel baths, while salts of alkali or alkaline earth metals increase con- ductivity with a consequent improvement in throwing power. The aim of this work is to set a new reliable equation for the quantitative estimation of the throwing power of nickel Watt's baths by the tube penetration method rather than the earlier equation. The effect of pH values and some additives such as sodium salts on the throwing power were investigated. 2. Experimental The throwing power was measured using the penetration method. A plastic block with drilled cylindrical holes of dif- ferent diameters (5-20 mm) is placed in a rectangular cell (20 X 12 × 10 cm) facing the anode plate. The plastic tubes are lined with copper foil (0.05 mm). The copper foil is connected to a d.c. source through a fine hole in the block to act as the cathode. The plating was conducted at a current density of 1-4 A dm -2 for 5 min at 50-60°C, the distance between anode and cathode is 10 cm. After plating, the foils