Alumina particles, effect

This paper reviews the recent experimental results and mathematical modeling from the literature on electrocodeposition of particles in a metallic matrix. Although many different particle/metal systems are discussed, the electrocodeposition of alumina particles in copper matrix is highlighted as this widely-studied system illustrates the various effects of process variables and it exemplifies the types of contradictions concerning these results in the literature. 

Perhaps even more noteworthy is the effect of crystallographic phase. While one phase of a specific composition may readily incorporate from a particular bath composition, another phase of the same composition may incorporate to a much lower extent or not at all. For instance, in the alumina particle system, the alpha phase has been found to readily incorporate from an acidic copper bath while the gamma phase incorporates at less than one tenth the amount of alpha, if at all, as shown in Table 1 [2, 11, 27, 31, 33],... 

Figure 1 Effect of pH on the adsorption of a non-ionic polyacrylamide on fine alumina particles (after Rayf ...

Calculations carried out by Johnson and Morrison [Jj for alumina particles of 0.25 pm radius covered by 22.5 A shells show that the potential energy of interaction is reduced from about —175 kT to about —25 kT. The major effect of the shell is to eliminate the short-range attraction by separating the particles. Differences due to the Hamakcr constant of the shell arc also significant, the difference between the shallowest and deepest well being 20 kT. 

Table IV gives the Attrition Indexes for the commercial and experimental samples. These values are reported for microspheres that were spray dried before the viscosity of the slurry exceeded 100 cP. The data show, again, that sol age and particle size of the CP alumina affect attrition. Sol age also seems to reduce the influence of the CP-2 as a binder. The Reference (4) has an AI of about 3 which is comparable to the index for CP-2(4). The important point here is that the alumina particles can be incorporated into a standard FCC formula to change catalytic activity without a detrimental effect on attrition resistance.

The small number of charge carriers in the semiconductor is partially compensated for by the small size of metal particles. By using Schwab s magnetic measurements as a clue to the number of electrons transferred to the nickel across the nickel-alumina interface it can be estimated that a change of 0.05 electron per atom would produce detectable catalytic effects. By extrapolation to the small dispersed type of metal particle being considered here, it is seen that for a particle containing 2000 atoms the equivalent transfer would be produced by 100 electrons. Despite this, if one considers contact between a 2000-atom platinum particle and a 100 alumina particle (volume 4 x 10 cc) the flow of electrons to the metal would be drastically limited by the small number of charge... 

Activity Tests with Model Compounds. Activity tests with model compounds were also carried out for the fresh, regenerated, and aged catalysts in a fixed bed reactor under a vapor phase condition at 5.0 MPa. 3 cm of crushed catalyst (0.35 - 0.5mm) was diluted with 9 cm of inactive alumina particles. Catalyst activities, such as hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and hydrogenation (HG), were measured, feeding a mixture of 1 wt% carbon dioxide, lwt% dibenzothiophene, 1 wt% indole, and 1 wt% naphthalene in n-heptane. The catalysts were presulfided with a 5% H2S/H2 mixture at 400 °C for two hours and aged with a liquid feed at a reaction condition for 24 hours. Tests for HDS and HDN reactions were conducted at 275 °C, while those for a HG reaction were done at 325 °C. Condensed liquid products were analyzed with gas chromatography. Since all the reactions took place with the crashed catalysts in the vapor phase, we assumed that effectiveness factors were unity (9). 

The effect of pressure and velocity on the polish rates of copper was determined in DI water and in the presence of ferric nitrate, H202/glycine, and NH4OH with alumina particles as the abrasives. The polish rate shows a stronger dependence on velocity than that predicted by the Preston equation in the case of ferric nitrate, a highly reactive chemical. The velocity dependence is weaker for the other two less reactive chemicals, and is the same as that predicted by Preston equation for DI water. Our earlier empirical model, R = KPV + BV + Rc, where K, B, and Rc are constants, describes all the polish rate data satisfactorily. 

The presence of other materials in the impregnating solution can have a marked effect on the location of the metal within the support particle. These additives have been conveniently divided into three classes. Class 1 additives consist of simple inorganic electrolytes which influence the electrostatic interactions at the solution-support interface. Simple salts such as sodium nitrate, sodium chloride, or calcium chloride do not adsorb strongly enough on alumina to compete with platinum salts for adsorption. Fig. 13.9a 0 shows the concentration profile of platinum on an alumina particle when the impregnation of chloroplatinic acid was done in the absence of any additives. This a somewhat diffused egg shell profile. Fig. 13.9b shows the adsorption profile for the catalyst prepared by impregnation in the presence of an amount of sodium nitrate equimolar to the chloroplatinic acid. Here the amount of platinum adsorbed decreases while the adsorption profile approaches a uniform distribution. It is... 

---