Abstract: It has been known experimentally that, additives, such as LaCl3, lactic acid, Fe2(SO4)3, thiourea and 2,2’-bipyridine, regularly influence the electroless deposition rate, that is, there is a maximum deposition rate with increasing additives concentration. In order to explore this regularity, an adsorption model is proposed and a deposition rate formula is deduced. The deposition rate formula is used to operate nonlinear curve fitting. The fitting curves obtained, correspond with the experimental results. Some parameters can be obtained from the fitting results, such as adsorption equilibrium constants of additives. It is found that the adsorption equilibrium constant on the naked surface (K1) is larger than that on the adsorbed reductant (K2). The larger K1 means that additives adsorb on the naked surface more easily than on the adsorbed reductant. The adsorption ability of different additives also can be illustrated through K1 and K2. For example, the K1, K2 of LaCl3, thiourea and 2,2’-bipyridine are greater than that of lactic acid and Fe2(SO4)3. The comparison indicates that the adsorption ability of LaCl3, thiourea and 2,2’-bipyridine is stronger than that of lactic acid and Fe2(SO4)3. Thus the concentration of LaCl3, thiourea and 2,2’-bipyridine, which corresponds to maximum deposition rate, is smaller than that of lactic acid and Fe2(SO4)3.

Key words: Electroless deposition rate, LaCl₃, Lactic acid, Fe₂(SO₄)₃, Thiourea, 2,2’-bipyridine