Enhancing the Incorporation of Particles during Electrocodeposition by Surface Modification (Het verhogen van de inbouw van deeltjes tijdens elektrocodepositie door middel van oppervlaktemodificatie)

Electrocodeposition is a coating technology where particles are added to an electroplating bath in order to deposit composite coatings. Unfortunately, the presence of particles in the plating solution is insufficient to obtain composite coatings. In this work, it is attempted to increase particle codeposition by modification of the particle surface. This should increase the attractive interaction force between particle and electrode, and consequently, the incorporation probability. From literature, three beneficial particle properties could be readily identified, namely hydrophobicity, specific metal affinity and electrical conductivity.An attempt was made to unequivocally determine the influence of a fourth surface property, the surface charge or potential of the particle. By smart selection criteria, BaSO4, CaF2 and K1.33Mn8O16 were identified as having potential determining ions (pdi) that are electrochemically silent. It was shown that in water and in diluted plating baths the article surface potential could be controlled by additions of the pdi. A clear relation between surface potential and codeposition was shown by codeposition tests in three different metals under acid as well as alkaline conditions. Although current step measurements proved that these pdi-additions had an influence on the electroplating process itself, the correlation between current steps and codeposition changes was close to zero. It was concluded that a positive surface potential or surface charge is a promoting surface quality for particle incorporation.In following parts of the thesis, three techniques were explored to apply favorable surface properties to particles that show low incorporation rates. TiO2, Al2O3 covered TiO2 and Al2O3 were chosen as particles to be modified with these techniques. The first proposed method made use of coupling agents, specific molecules that assist in increasing the compatibility of two different surfaces. The surface of TiO2 was grafted using a large selection of commercially available coupling agents, having two types of reactive head groups, silanes and phosphonic acids. Phosphonic acids showed a higher grafting density on TiO2 than silanes for the same functional group. For bulkier functional groups, a limited grafting density was obtained. With respect to codepositon, hydrophobic modifications were the most efficient, followed by mercapto groups. Heterocyclic functional groups proved disappointing. An explorative study was started for usi