Rate of Cu

Copper. Some 15 copper compounds (qv) have been used as micronutrient fertilizers. These include copper sulfates, oxides, chlorides, and cupric ammonium phosphate [15928-74-2] and several copper complexes and chelates. Recommended rates of Cu appHcation range from a low of 0.2 to as much as 14 kg/hm. Both soil and foHar appHcations are used. 

In gas reforming plants, e.g. the hot potassium carbonate process for CO removal, sodium metavanadate is used to prevent mild-steel corrosion". Banks reports" that this treatment does not reduce the rather high corrosion rate of Cu-30Ni in these plants. 

Employing a specially constructed electrical circuit to avoid use of a salt bridge and its associated IR drop, and a two compartment cell, Weise and Weil [80] also confirmed that, in the absence of H2CO, the deposition rate of Cu was significantly lower than would be obtained in a full electroless solution. They employed solutions somewhat similar to Feldman and Melroy [79], but carried out their experiments at room temperature. 

The feasibility of the above model rests on the formation of Cu(I) in the copper(II)-ascorbic acid system. A recent study firmly established that Cu(I) can indeed accumulate in the presence of a stabilizing ligand, Cl-, and in the absence of 02 (14). The actual form of the rate law is determined by the relative rates of Cu(I) formation and consumption, and further studies should clarify how the stability and reactivity of copper(I) are affected by the presence of various components and the conditions applied. 

Amino acids accelerate and proteins retard the rate of Cu(II)-catalyzed oxidation of di-2-pyridyl ketone hydrazone (173) yielding fluorescent compounds. This has been applied for the analysis of amino acids and proteins378. 

Indirect evidence of isotopic fractionation among different complexes was obtained by Marechal et al. (1999) and Marechal and Albarede (2002) who observed different elution rates of Cu and Cu on anion-exchange columns (Fig. 11). These experiments were confirmed by Zhu et al. (2002) and Rouxel (2002) with similar results on fractionation coefficients. Figure 11 shows that, in HCl medium, the heavier isotope 65 is less well retained on the column than the lighter isotope 63. Marechal and Albarede (2002) used an error function approximation to the elution curve to derive the ratio of fractionation coefficients for the 63 and 65 isotopes between the resin and the eluent. From the relationship between the elution volume (position... 

In contrast, the rate of Cu(II)-catalyzed hydrolysis of 3-pyridylme thyl-phosphate shows an enhancement of twenty-fold at a pH where the reactive species is probably the 1 1 complex represented in (59)144 145. 

The importance of the measurements that we have presented so far for the diffusion of embedded tracer atoms becomes evident when we now use these measurements and the model discussed in Section 3 to evaluate the invisible mobility of the Cu atoms in a Cu(00 1) terrace. The results presented in Section 2 imply that not just the tracer atom, but all atoms in the surface are continuously moving. From the tracer diffusion measurements of In/Cu(0 0 1) we have established that the sum of the vacancy formation energy and the vacancy diffusion barrier in the clean Cu(0 01) surface is equal to 717 meV. For the case of self-diffusion in the Cu(0 01) surface we can use this number with the simplest model that we discussed in Section 3.2, i.e. all atoms are equal and no interaction between the vacancy and the tracer atom. In doing so we find a room temperature hop rate for the self-diffusion of Cu atoms in a Cu(00 1) terrace of v = 0.48 s-1. In other words, every terrace Cu atom is displaced by a vacancy, on average, about once per two seconds at room temperature and about 200times/sec at 100 °C. We illustrate this motion by plotting the calculated average displacement rate of Cu terrace atoms vs. 1 /kT in Fig. 14. 

Surface vacancies were shown to be responsible for the motion of embedded In and Pd atoms in the Cu(00 1) surface. The density of surface vacancies at room temperature is extremely low, but they diffuse through the surface at an extremely high rate leading to significant diffusion rates of Cu(00 1) terrace atoms. In the STM measurements the rapid diffusion of these vacancies leads to long jumps of embedded tracer atoms. Measurements of the jump length distribution show a shape of the distribution that is consistent with the model that we discussed in Section 3. In turn, this shows that the vacancy-mediated diffusion process can be accurately described with the model that is presented in Section 3, provided that the interaction between the tracer atom and the surface vacancy is properly taken into... 

Popel (1994) reported results obtained by Ishimov et al. (1971) showing that the initial spreading rate of Cu on A12Oj at 1350°C, i.e. for a system for which Op 90° (see Table 6.1), is close to 1 m/s which is similar to that observed in metal/metal systems where 0F <3C 90°. 

Rates of Cu+ to Ru + electron transfer also have been measured in modified mutants of spinach plastocyanin, a blue copper protein from the photosynthetic ET chain [79], Ru-bipyridine complexes were introduced at surface sites, with Cu-Ru distances ranging from 13 to 24 A. ET rate constants, measured using laser flash-quench techniques, vary from 10" to 10 s. ET in Ru-modified plastocyanin is not activationless as it is in Ru-modified azurin, suggesting a slightly greater reorganization energy for the photosynthetic protein. The distance dependence of ET in Ru-modified plastocyanin is exponential with a distance decay factor identical with that reported for Ru-modified azurin (1.1 A ). 

Figure 6 shows the etch rate of Cu in 500.T DHF as a function of Oj partial pressure. The etch rate is linear with Oj concentration. 

The reactions (20) to (22) form the copper equilibrium on the electrode surfaces. Concentration of Cu(I) on the cathode surface affects the deposition rate. The maximum net rate of Cu+ production is at about —50 mV versus Cu/CuSC>4 and at higher overpotentials it decreases. Disturbing the Cu(II)—Cu(I)—Cu equilibrium can cause the formation of copper powder, but this is more a problem on the anode. For the current densities commonly used in electrorefining, the cathode overpotential is between 50 and 100 mV. The system is mainly charge transfer controlled and the effect of mass-transfer polarization is small. If Cu(I) concentration on the cathode surface decreases, mass-transfer polarization will increase, causing more uneven deposit. 

Cu from aqueous solutions increase with initial concentrations of Cu", 4nd are independent of solution quantities. (2) Removal rates of Cu from aqueous solutions decrease slightly in the presence of Ni", but are otherwise independent of Ni concentration. (3) Regeneration rates of spent resins are dependent on NH4OH concentrations. The reaction rates are dependent on the mass ratios of ammonia solution to resin at low NH4OH concentrations, but are independent of the mass ratios at high NH OH concentrations. (4) Instantaneous regeneration fractions of spent resins are independent of mass ratios and NH OH concentrations. Regeneration rate constants are independent of mass ratios and dependent on NH OH concentrations. 

Fig. 15.14 Effects of PEG concentration on the rate of Cu deposition (open diamond) and the deposition potential (solid diamond) on an unpatterned substrate...

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