Particle Bath Concentration

Sautter16 found that the volume percentage of AI2O3 particles in a Ni-matrix increases with particle bath concentration. In further investigations4 9 11 23 26 30 33 42 this behavior was 

For incorporation of polystyrene particles in copper55 56 and zinc54 75 76 a deviation from the Langmuir adsorption behavior at high particle bath concentration was observed (Fig. 7). The obtained particle composite content is higher than expected from the extrapolated curve at 

Composites are deposited using both electroless62-64 and electrolytic plating processes. In the latter case composite deposition occurs in the presence of an applied electrical field, which is characterized by the cathodic potential or current density. The current density is the most extensively investigated process parameter. Roughly two types of current density dependencies can be distinguished. The particle composite content against current density curve either decreases or increases continuously or exhibits one or two 

The nature of the current density dependence of particle codeposition is the most disputed aspect in the mechanism of composite plating (Section IV). In the simplest case the particle deposition rate is not affected by the current density, either because of particle mass transfer limitations or a current density independent particle-electrode interaction. Since the metal deposition rate increases with current density, this results in a continuously decreasing particle composite content. In other cases the particle-electrode interaction has to be current density dependent. An unambiguous explanation for this dependence has not yet been found, but it is apparent that the metal deposition behavior is involved. 

The peaks in particle incorporation often55 56,77,85,89 occur at the same current density as kinks in the polarization curve for metal deposition. For Au-Ai203 composite deposition77 the peaks and kinks also correlate with the preferred orientation of the Au crystallites. Similarly, for zinc-polystyrene composites54,76 the peak in polystyrene codeposition corresponds to a change in morphology of the zinc deposit. Polarization 

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The mechanism of particle incorporation is treated extensively in the next section, but a generalized mechanism is given here to better comprehend the effects of the process parameters. Particle incorporation in a metal matrix is a two step process, involving particle mass transfer from the bulk of the suspension to the electrode surface followed by a particle-electrode interaction leading to particle incorporation. It can easily be understood that electrolyte agitation, viscosity, particle bath concentration, particle density etc affect particle mass transfer. The particle-electrode interaction depends on the particle surface properties, which are determined by the particle type and bath composition, pH etc., and the metal surface composition, which depends on the electroplating process parameters, like pH, current density and bath constituents. The particle-electrode interaction is in competition with particle removal from the electrode surface by the suspension hydrodynamics. 

The deposition variables are the process parameters most suited to regulate the particle composite content within the limits set by the particle properties and plating bath composition. Particle bath concentration is the most obvious process variable to control particle codeposition. Within the limits set by the metal plating process and the practical feasibility also current density, bath agitation and temperature can be used to obtain a particular composite. Consequently the deposition process variables are the most extensively investigated parameters in composite plating. The models and mechanisms discussed in Section IV almost exclusively try to explain and model the relation between these process parameters and the particle codeposition rate. 

Guglielmi validated his model for Ni-Ti02 and Ni-SiC composite deposition. From the obtained values for k it was found using Eq. (1) that 0 crand it was concluded that the strong adsorption step is rate determining. The model was also successful in describing the variation of the particle composite content with the particle bath concentration and current density of several other composites.57,59,60 66 79 84 For example,... 

Reynolds number (-) gas constant (J K 1 mol 1) radial distance (m) modified Sherwood number (-) dimensionless number for particle bath concentration (-)... 

The inconsistency in these various investigations is possibly due to the choice of the units in which the particle content is expressed. Just as ion concentrations are expressed in moles, that is the number of ions per volume, the parameter to be considered is the number of particles suspended and incorporated.61 Volume or weight particle bath and composite content in fact yield an erroneous comparison of data obtained at different particle sizes. It was found62 that the weight percentage of SiC particles incorporated in Ni increases, whereas the number of SiC particle... 

Figure 4 shows that in an electroless Ni(P) bath the H2P02 bath concentration reduces on addition of SiC or A1203 particles. The Ni2+ bath concentration and pH, not shown in Fig. 4, in contrast is not affected by particle addition. Very likely a negative charge is inferred on the particles... 

The extent of solubilization of the oily soil depends on the chemical structure of the surfactant, its concentration in the bath, and the temperature (Chapter 4, Section IB). At low bath concentrations only a relatively small amount of oily soil can be solubilized, whereas at high surfactant concentrations (10-100 times the CMC), solubilization is more similar to microemulsion formation (Chapter 8, Section II) and the high concentration of surfactant can accommodate a much larger amount of oily matter (Schwartz, 1972). With ionic surfactants, the use concentration is generally not much above the CMC consequently, solubilization is almost always insufficient to suspend all the oily soil. When insufficient surfactant is present to solubilize all the oily soil, the remainder is probably suspended in the bath by macroemulsification Antiredeposition agents, such as the POE terephthate polyesters mentioped in Section 1 above, help prevent redeposition of suspended oily soil particles. 

The authors [42 4] continued to study autoacceleration effect at DMDAACh radical polymerization within the frameworks of fractal and scaling approaches. In paper [39], two hmiting asymptotic regimes for the description of dynamical scaling of the aggregates growth in bath with particles initial concentration c. were considered. For these regimes definition the authors [39] introduced the... 

The composition of the codeposition bath is defined not only by the concentration and type of electrolyte used for depositing the matrix metal, but also by the particle loading in suspension, the pH, the temperature, and the additives used. A variety of electrolytes have been used for the electrocodeposition process including simple metal sulfate or acidic metal sulfate baths to form a metal matrix of copper, iron, nickel, cobalt, or chromium, or their alloys. Deposition of a nickel matrix has also been conducted using a Watts bath which consists of nickel sulfate, nickel chloride and boric acid, and electrolyte baths based on nickel fluoborate or nickel sulfamate. Although many of the bath chemistries used provide high current efficiency, the effect of hydrogen evolution on electrocodeposition is not discussed in the literature. 

In the concentrated environment of electroplating baths, the diffusiophoretic force is the only force that can counteract the attractive London-van der Waals force. An appreciable diffusiophoretic force is, however, only present in binary electrolytes. In practice, particles are codeposited from supported electrolytes. In supported electrolytes, the diffusiophoretic force is absent, and Valdes model predict that under... 

The amounts oi adsorption of the polymer on latex and silica particles were measured as follows. Three milliliters of the polymer solution containing a known concentration was introduced into an adsorption tube(lO ml volume) which contained 2 ml of latex (C = l+.O wt %) and silica(C = 2.0 wt %) suspensions. After being rotated(l0 rpm) end-over-end for 1 hr in a water bath at a constant temperature, the colloid particles were separated from the solution by centrifugation(25000 G, 30 min.) under a controlled temperature. The polymer concentration that remained in the supernatant was measured colorimetrically, using sulfuric acid and phenol for the cellulose derivatives(12), and potassium iodide, iodine and boric acid for PVA(13). From these measurements, the number of milligrams of adsorbed polymer per square meter of the adsorbent surface was calculated using a calibration curve. 

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