Criteria chromium

Proposed chromium criteria for the protection of human health and natural resources... 

Table 2.6 Proposed Chromium Criteria for Protection of Human Health and Natural Resources...

As reported here, adverse effects of chromium to sensitive species have been documented at 10.0 pg/L (ppb) of Cr+6 and 30.0 pg/L of Cr+3 in freshwater and 5.0 pg/L of Cr+6 in saltwater and, to wildlife, 10.0 mg of Cr+6 per kilogram of diet (ppm). Tissue levels in excess of 4.0 mg total Cr/kg dry weight should be viewed as presumptive evidence of chromium contamination, although the significance of tissue chromium residues is unclear. Some of these findings are in sharp contrast to chromium criteria proposed by regulatory agencies. 

The enthalpy of decomposition, which is rather low compared with criterion C, in the CHETAH programme (see p.117), was determined by DSC and corresponds to 0.76 KJ/g at 230-260°C. In a confined atmosphere the decomposition conditions would be explosive. This reaction has been used many times because of its spectacular aspect. This is why it is called Vesuvius fire by artificers and green volcano by lecturers. These demonstrations should be stopped because of the detonation risks they represent as well as chromium (III) oxide toxicity. 

Category and Criterion (units in parentheses) Chromium Concentration Reference8... 

Another interesting point is the relative rates of the reactions of the azido and thiocyanatopentaammines. The relative rates of these two reactants with iron (I I) ion are similar to those with chromium (I I), that is, the azide is four to five powers of ten more rapid than is the thiocyanato. I am suggesting that this might be a criterion for inner sphere activated complex as opposed to an outer sphere complex. With trisdipyridylchromium(II) ion, which must react via an outer sphere process, the azido and thiocyanato rates are relatively comparable, and the same also for vanadium (I I) ion which also probably procedes via an outer sphere activated complex. 

It is well known, even from old literature data (ref. 1) that the presence of metal promotors like molybdenum and chromium in Raney-nickel catalysts increases their activity in hydrogenation reactions. Recently Court et al (ref. 2) reported that Mo, Or and Fe-promoted Raney-nickel catalysts are more active for glucose hydrogenation than unpromoted catalysts. However the effects of metal promotors on the catalytic activity after repeated recycling of the catalyst have not been studied so far. Indeed, catalysts used in industrial operation are recycled many times, stability is then an essential criterion for their selection. From a more fundamental standpoint, the various causes of Raney-nickel deactivation have not been established. This work was intended to address two essential questions pertinent to the stability of Raney-nickel in glucose hydrogenation namely what are the respective activity losses experienced by unpromoted or by molybdenum, chromium and iron-promoted catalysts after recycling and what are the causes for their deactivation ... 

As soon as the quartet-quartet luminescence of chromium(III) compounds was discovered by Porter and Schlafer the criterion for it being feasible (it may need low temperature and small chromium concentration, as discussed in 9.d, and it may still be undetectable for obscure reasons) was recognized to be a short-lived T2 being trapped... 

Chromium reduction to measure reduced inorganic sulfur compounds in sediments was proposed by Zhabina and Volkov (1978). Since then it has found wide use internationally (Sullivan etal. 1999), particularly when pyritic sediments and acid volatile mono-sulfides are expected. The method is not measurably affected by sulfur in organic matter or sulfates (Canfield etal. 1986 Morse Cornwell 1987). Accordingly, this chromium reducible sulfur method (SCr) is especially useful on samples with appreciable organic matter and also for sandy soils where the %S action criterion is very low (e.g. as low as 0.03%S). 

From the viewpoint of chemical and physical requirements the permissible indicators involve a number of criteria mercury, selenium, cadmium, vanadium, chromium, arsenic, silver, lead, barium, cyanides, hydrogen sulphide, fluorides, phenols, oil and oil substances, COD(Mn), colour, odour, taste and turbidity. The most stringent criterion concerns the content of mercury, followed by selenium, cadmium, vanadium, cyanides, oil and oil substances. Another important indicator is the content of organic matters characterized by COD(Mn). 

In a electronic system all transitions are determined by these relations, in a high-spin i system, however, only the quintet-quintet transitions. The latter may be distinguished from the quintet-triplet transitions by their band positions, as in chromium(II) fluorides, or at least by their band intensities, as in manganese(III) fluorides. The intensity criterion must be handled with some care, however, as the maximum extinction coefficients of intercombination bands may well reach the order of magnitude of spin-allowed bands. Thus the absorption maxima at higher energies, which are of interest here, cannot be definitely localized least in MnFs 18) but neither in the other manganese(III) compounds (see Fig. 6). 

Resource and Criterion (Units in Parentheses) Effective Chromium Concentration... 

A criterion of this book is that only those carbides and nitrides having a melting point above 1800"C and good chemical resistance are considered. Chromium carbide is a marginal case as mentioned in Ch. 3, Sec. 

The area under the dialysis curve for chromium(III) in dilute HCl may, therefore, be used as a standard of comparison this area is found to be 95,5 % of the rectangular area defined by the coordinates (Fig. 1). A numerical criterion of the relative eflfectiveness of a ligand is the ratio F defined as follows ... 

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