Synergistic effect of 2-butyne-1,4-diol and pulse plating on the structure and properties of nickel nanocrystalline deposits

Nanocrystalline nickel deposits were produced by applying both direct current (DC) and pulse current electroplating (PC) from an additive-free Watts type bath and in the presence of 2-butyne-1,4-diol (BD). The surface morphology, the preferred orientation, the grain size and the microhardness of the deposits were investigated. Under DC conditions, the addition of BD enhanced the perfection of [100] preferred crystal orientation and promoted a considerable grain refinement. The application of PC technique in presence of small amount of BD (CBD = 0.25 mmol L− 1) accelerated the textural modification from [100] to [211] with respect to DC conditions and deposits with grain size of 20–60 nm were produced. A significant enhancement of microhardness of the produced bright deposits was observed compared to those deposits prepared under DC regime, which could be correlated to the observed crystal orientation mode [211], as well as to the corresponding nanosized crystallites. Progressive addition of BD promoted a peculiar textural modification from [211] to [100] and a possible mechanism of action of BD is proposed taking into account as inhibiting species of the Ni crystal growth not only Ni(OH)2 but also cis-butene-1,4 diol.