CR ratio

The species CrCN was characterised by means of its behaviour to ion-exchange, its absorption spectrum, and analysis of the CN /Cr ratio in the separated complex. The existence of the species CrNC " was less clearly established from its absorption spectra. 

Scheme 7 Initiation mechanisms proposed in literature for the CO-reduced Cr/Si02 catalyst. Vertical direction shows evolution of the initial species upon addition of one ethylene molecule. Horizontal direction shows all the possible isomeric structures characterized by an average C2H4/Cr ratio equal to 1, 2, and 3...

Cr ratio of solid to gas heat capacities [dimensionless—see just after Eq. (49)]... 

Trace element concentrations in Canada, Commonwealth, and Howard glaciers were 100% nSS. In fact, all trace elements measured had median element Cr ratios 3 or more orders of magnitude greater than seawater averages (Nozaki, 1997). 

Chromium is a common anthropogenic contaminant in surface waters, therefore Cr isotope fractionations are of potential interest in tracking Cr + pollution in groundwaters. Ellis et al. (2002, 2004)) and Izbicki et al. (2008) analyzed ground-water samples from contaminated sites and observed an increase in Cr/ Cr ratios up to 6%c during the reduction of chromate. Equilibrium fractionations between Cr(VI) and Cr (III) have been estimated by Schauble et al. (2002), who predicted Cr isotope fractionations >l%c between Cr species with different oxidation states. 

Figures 10.52(a,b) show phase % vs temperatiu plots for a standard IN625 alloy. It is predominantly strengthened at low temperatures by the formation of 6 and is characterised by the formation of three types of carbide, MC, M C and M23C6. It is further unstable with respect to both a and p at low temperatures. This behaviour shows that the alloy lies close to a boundary which is controlled by the Mo/Cr ratio where, at lower Mo/Cr ratios, the alloy would contain MC and the more Cr rich phases M23C6 and a, while at higher Mo/Cr ratios the alloy would contain MC and the more Mo-rich phases M C and p.

The Mn- Cr system can be studied by TIMS, ICPMS, and SIMS techniques. For TIMS and ICPMS work, bulk samples or mineral separates are dissolved and the solutions are passed through ion-exchange columns to produce clean solutions of manganese and chromium. For minerals with high Mn/Cr ratios SIMS can obtain isotopic data while retaining the petrographic context of the measurements. The chromium isotopic compositions may have to be corrected for small additions of chromium from spallation reactions induced by cosmic rays. This is particularly important in iron-rich meteorites. 

Mixed hydroxide was prepared by a method previously described [9]. A mixture of 10% metal nitrate aqueous solution with a Zn Cr ratio of 0.5 was prepared. This solution was heated to 70 °C, while a 5% ammonia (Merck) aqueous solution was added drop wise under constant stirring, with the pH maintained at approximately 7.0. The mixture was digested for another 2 hours at 80 °C in order to complete the precipitation. The precipitate was filtered, washed and dried in air at 110 °C for 12 hours. Chemical analysis yielded Zn 21.4%, Cr 34.1%, O 41.9% and H 2.6%. 

To prepare the spinel oxide by solid-state reaction of a mixture of the individual metal cation oxides, the following procedure was used [8] a mixture of powdered ZnO (Aldrich >99%) and C CL (Aldrich >99%) (0.5 Zn Cr ratio), was carefully grounded for 10 minutes in order to obtain a good dispersion of the compounds in the solid mixture. This mixture was then heated at 900 °C for 12 hours in a N2 atmosphere. 

The PXRD patterns for both the LDH and MH are shown in Figure 1. The LDH showed a PXRD pattern with very intense and sharp peaks, characteristic of a very well ordered hydrotalcite-like compound. The basal spacing obtained was 7.68 A, very close to the reported data [17,20,21] for carbonate containing LDH. From the chemical analysis we obtain the following molecular formula Zn2 9Cr(OH)7 8(C03)o5-2,3H20 (normalized to Cr = 1). The Zn Cr ratio obtained, 2.9, was slightly lower than the one expected, 3, indicating a preferential solubilisation of Zn(II) cations, a feature widely reported in the synthesis of LDHs [11]. 

The mixed hydroxide (MH), however, gave no significant PXRD reflections. The identified formula for this compound was Zni.oCr2(OH)8 0 (normalized for Cr = 2), with a Zn Cr ratio of 0.5, exactly as expected, showing the complete precipitation of the metal cations. 

The same trend as that reported by the Nozaki group upon dilution was observed. The copolymerization conditions were 60°C and 40 bar CO2, with a PO/Cr ratio of 20,000 1, the TOF of the optimal dinuclear complex was 82 h, whereas the mononuclear analogue showed a TOF of just 7 h ... 

The chromium analogue of 16, [(mesitylene)Cr(CO)3] (17) also undergoes a net two-electron oxidation in MeCN, but the chemistry involved is entirely different for the two complexes. With 17+, attack by solvent leads to rapid loss of arene and CO ligands, accompanied by further oxidation. (At fast scan rates, the 17+/17 couple becomes a reversible one-electron process.) A comparison of the relative reactivity of the 17-electron complexes 16+ and 17+ toward associative attack by MeCN led to the rate order W > Cr (ratio of ca. 104 1). It was suggested that this reactivity order reflects less steric congestion for nucleophilic attack at the... 

Patients showed a negative correlation between NAA/Cr ratio in FL and negative symptom ratings 4 NAA/Cr in Flippo area of both patients and their unaffected siblings as compared with healthy controls suggesting heritability of trait 4 NAA/Cr in TL and FL of patients Cho/Cr f in FL, [ in TL of patients... 

J, NAA in left and right Hippo of patients trend toward 4 Cr in left Hippo as compared with the right in patients 4 NAA in left and right ACC of schizophrenic patients no correlation between NAA and medication dose or Dl No difference in the metabolites (NAA, ml, Cho) in thalamus, PFC or Hippo between groups 4 NAA/Cr ratio in the pons of patients found no difference in cerebellum... 

J, NAA/Cr ratio in left medial TL of patients subjects with family history of schizophrenia showed greater deficit than subjects without history J, NAA/Cr ratio in left medial TL of patients J, NAA/Cr and Cho/Cr ratios in patients with disorganized and undifferentiated types of schizophrenia than with paranoid schizophrenia... 

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