Co systems

Figure A3.14.6. P-T ignition limit diagram for CO + system in a flow reactor showing location of...

Figure 10 presents the Curie temperature (T ) vs the TM-content (x) for Co- and Fe-based biaary alloys. Alloying rare-earth elements with small amounts of transition metals (x < 0.2) leads to a decrease ia Curie temperature. This is particularly obvious ia the Gd—Co system where it corresponds to a nonmagnetic dilution similar to that of Cu (41,42). This iadicates that TM atoms experience no exchange coupling unless they are surrounded by a minimum number j of other TM atoms. The critical number is j = 5 for Fe and j = 7 for Co. The steep iacrease of for Co-based alloys with x about 0.7 is based on this effect. 

FIra Supprassion Systams 4. 3.1 CO, Systems 4.2.3.2 Water Svstems 4.2.3.3 Dry Powder Systems 4.2.3.4 Halon Systems b. Faulty Indication... 

We observe that for the Fe-Co system a sim le spin polarized canonical model is able to reproduce qualitatively the results obtained by LMTO-CPA calculations. Despite the simplicity of this model the structural properties of the Fe-Co alloy are explained from simple band-filling arguments. 

In a previous work we showed that we could reproduce qualitativlely the LMTO-CPA results for the Fe-Co system within a simple spin polarized canonical band model. The structural properties of the Fe-Co alloy can thus be explained from the filling of the d-band. In that work we presented the results in canonical units and we could of course not do any quantitative comparisons. To proceed that work we have here done calculations based on the virtual crystal approximation (VGA). In this approximation each atom in the alloy has the same surrounding neighbours, it is thus not possible to distinguish between random and ordered alloys, but one may analyze the energy difference between different crystal structures. 

Also neglected have been kinetic studies concerned with comparison of the rates of the decarbonylation of different M(COR)CO systems. Heck 109) reports that at 25 °C MeCOCo(CO)4 dissociates CO about 2250 times more rapidly than MeCOMn(CO)5. This may well be an approximate ratio of the respective rates of the decarbonylation. Qualitative, synthetically oriented experiments seem to indicate that RCOMn(CO)5 decarbonylate faster than their rhenium counterparts (Section V,C). 

Table. Intensities (Arbitrary Units) of SIMS Clusters for the Ni(100)/CO System...

Typical Mossbauer spectra for the fresh, reduced, carblded and used Fe/ZSM-5 system are shown in a composite Fig. 5. Similar spectra were obtained for the Fe-Co/ZSM-5 system. The product distribution for the F-T reaction, using the Fe and Fe-Co systems, are shown in Table 1. The gasoline range hydrocarbon yield increased from 75 to 94%, when the Fe-Co clusters were used in place of Fe only. In a typical CEMS (Conversion Electron Mossbauer Spectroscopy) of the Fe-Co system, no spectrum for 57pg vas observed even after one week from this. It was concluded that in the Fe-Co clusters Co was predominantly in the "mantle" and Fe species were In their "core," in the parlance of metallurgy/geophysics. This model Is sometimes referred to as the cherry model. 

For the reduction of NO with propene, the catalyst potential dependence of the apparent activation energies does not show a step change and is much less pronounced than it is for the CO+O2 and NO+CO systems. There is persuasive evidence [20] that the step change is associated with a surface phase transition - the formation or disruption of islands of CO. It is reasonable to assume that this phenomenon cannot occur in the NO+propene case, since there is no reason to expect that large amounts of chemisorbed CO can be present under any conditions. That there should be a difference in this respect between CO+O2/CO+NO on the one hand, and NO+propene on the other hand, is therefore understandable however, the chemical complexity of the adsorbed layer in the NO+-propene precludes any detailed analysis of the Ea(VwR> effect. 

SO2 nearly completely deactivated the Cu-ZSM-5, resulted in an inhibition for Co-ZSM-5 and an enlargement of the N2O conversion over Fe-ZSM-5 (figure 9). Both the Fe and the Co systems returned to their original activity after removal of the SO2, this took several hours. 

Severson MW, Stuhlmann C, Villegas I, Weaver MJ. 1995. Dipole-dipole coupling effects upon infrared spectroscopy of compressed electrochemical adlayers Application to the Pt(lll)/CO system. J Chem Phys 103 9832-9843. 

A frequent theme in high-pressure STM is the possibility of artefact structures developing due to low levels of impurities present in the gaseous reactants it is an aspect that has been discussed13 for the Pt (llO)-CO system. 

Practitioners must have a good understanding of cardiovascular physiology to diagnose, treat, and monitor circulatory problems in critically ill patients. Eugene Braunwald, a renowned cardiologist, described the interrelationships between the major hemodynamic variables (Fig. 10-1).1 These variables include arterial blood pressure, cardiac output (CO), systemic vascular resistance (SVR), heart rate (HR), stroke volume (SV), left ventricular size, afterload, myocardial contractility, and preload. While an oversim-... 

Both the Co and the Fe systems have very similar chemistry for the 1 1 codimerization reaction. Although they are almost identical in catalytic selectivity, they do differ in other catalytic properties, especially the rate of reaction (66). In practice, the Co system is superior to the Fe system our discussion will therefore focus mainly on the former system. 

The Co system is more reactive as well as much more selective than the Ni and Rh catalyst systems (Table XVII). The best systems allow almost 100% conversion with almost 100% yield of c -l,4-hexadiene. The best of the Ni and Rh systems known so far are still far from such amazing selectivity. The tremendous difference between the Ni system and the Co or Fe system must be linked to the difference in the nature of the coordination structures of the complexes, i.e., hexacoordinated (octahedral complexes) in the case of Co and Fe and tetra- or penta-coordinated (square planar or square pyramidal) complexes in the case of Ni. The larger number of coordination sites allows the Co and Fe complex to utilize chelating phosphines which are more effective than monodentate phosphines for controlling the selectivity discussed here. These same ligands are poison for the Ni (and Rh) catalyst system, as shown earlier. 

With dienes and acetylenes, only M = Fe, Co or Ni showed activity. The Fe and Co systems gave many side products. Therefore, the Ni catalyst was studied in greater detail. Bis-(7r-cycloocta-l,5-diene)nickel(0) was equivalent to the Ziegler catalyst in hydrosilation of penta-1,3-diene. 

Tab. 3.4 Shift of the C-O and Fe-C stretch frequencies relative to the isolated heme-CO system for each of the protein conformations l-V. Hydrogen bond energies are also listed. Distances are given in A, frequencies in cm-1 and energies in kcal mol-1.

Electrophilic metal complexes that have shown Markovnikov-type selectivity include catalysts based on Ru(n),383-386 Fe(m),387 Au(i) and Au(m),380,388 and Ir(m).389 Notable among these examples are Zeise s salt390 (entries 1 and 2) and the PtCl4/CO system (entry 3), the latter of which has proved to be effective for the hydration of a wide... 

From Bulk to Monatomic Wires An Ab Initio Study of Magnetism in Co Systems with Various Dimensionality. 

It is a somewhat surprising fact that information about vibrational frequencies and bond lengths in very common and important ions is very sparse. Clearly, many more such determinations are necessary. Only this year, for example, have data become available which enable metal-ligand displacements on electron removal for the aquo Fe(II)/Fe(III) and Co(II)/Co(III) systems to be obtained. In view of the importance of these partially unpublished data, I have reproduced them in Table VI. The values of A for the Fe and Co systems are 0.128-0.137, and 0.208 8 respectively. The variability of the Fe results points to the fact that caution must be exercised in using data obtained in crystal lattices for a solution environment. Spin-polarized neutron diffraction studies on the structure of solu-... 

The multilayered Cu/Co systems discussed here can be grown as described next (6b). Electrolyte composition is based on a cobalt/copper ratio of 100 1 and consists of a solution of 0.34 M cobalt sulfate, 0.003 M copper sulfate, and 30g/L boric acid. The pH is fixed around 3.0, and there is no forced convection while deposition is carried out. The electrodeposition may usually be carried out potentiostatically at 45°C between —1.40 V versus SCE for the cobalt and —0.65 V versus SCE for the copper with an 3 cell potential interrupt between the cobalt-to-copper transition to avoid cobalt dissolution, which can occur when there is no interrupt. 

In Rh catalysed systems, where the metal acyl species also clearly contained iodide, a further possibility was introduced, compared with the mechanism postulated by BASF for their Co systems, that elimination of Acl could occur. The earliest publications from Monsanto which described the proposed mechanism noted that they could not distinguish between a final step involving (i) reductive elimination of Acl followed by hydrolysis of Acl (Eq. (32)), (Eq. (33)) and (ii) hydrolysis at the metal center followed by some other initially unspecified mechanism of recycling HI to Mel (Eq. (34)) [3]. 

Despite these drawbacks remarkably good results have been obtained in the equi-atomic region of the Fe-Co system (Inden 1977) which are virtually indistinguishable from those obtained by CVM calculations (Colinet 1993). However, this... 

Figure 10.72 Calculated vertical section through die Fe-Cr-Co system at a constant ratio JF.yfco of 83 17 (from Inden 1987, Homma et ah 1981). is the Curie temperature.

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