Chromium atomic properties

On the basis of temperature programmed reduction and oxidation (TPR-TPO) measurements, it was proposed that the calcination of chromia used as a catalyst for the selective fluorination of CF3CH2C1 into CF3CH2F depends strongly on the gas used to calcine the precursor [50], Furthermore, the fluorination of CF3CH2C1 depends directly on the number of reversibly oxidizible chromium atoms in the catalysts. The oxidation/reduction properties are related closely to the atmosphere of pre-treatment and a linear relationship between the catalytic activity and the hydrogen uptake during the second reduction step has been found [51],... 

The morphology and properties of heterostructures depend on the thickness of the deposited chromium layer. Moreover, the number of chromium atoms deposited on the substrate surface also affects the structure of the emerging islands. At small thicknesses of chromium layers (1-2 monolayers) almost all the chromium atoms are embedded into the silicon crystal lattice, thus forming CrSi2. However, with increase in the layer thickness up to seven monolayers not all atoms turn out to be built-in and even after the deposition of silicon a certain amount of unbound chromium atoms remain inside the islands. 

A study of the properties of (C Hs)3C HF)3 demonstrates how n-arene complexes may be formed from bonded aryl conqdexes. If the tris-tetrahydrofuranate is washed with ether the tetrahydrofuran is removed and a black powder is formed. This powder is at first strongly paramagnetic and the paramagnetism decreases with time. Hydrolysis of the powder forms 7r-arene chromium complexes. These properties suggest that the black powder contains radical species and the formulations, exemplified in Figure 57, have been suggested [91]. The formation of diphenyl has been proposed to occur by the /u>rn-coupling of phenyl radicals, within the environment of the chromium atom [95]. 

Rocha, E. R. P. Nobrega, J. A. Effects of Solution Physical Properties on Copper and Chromium Signals in Plame Atomic Absorption Spectrometry, /. Chem. Educ. 1996, 73, 982-984. 

Physical Properties. Molybdenum has many unique properties, leading to its importance as a refractory metal (see Refractories). Molybdenum, atomic no. 42, is in Group 6 (VIB) of the Periodic Table between chromium and tungsten vertically and niobium and technetium horizontally. It has a silvery gray appearance. The most stable valence states are +6, +4, and 0 lower, less stable valence states are +5, +3, and +2. 

The discussion so far has been limited to the structure of pure metals, and to the defects which exist in crysteds comprised of atoms of one element only. In fact, of course, pure metals are comparatively rare and all commercial materials contain impurities and, in many cases also, deliberate alloying additions. In the production of commercially pure metals and of alloys, impurities are inevitably introduced into the metal, e.g. manganese, silicon and phosphorus in mild steel, and iron and silicon in aluminium alloys. However, most commercial materials are not even nominally pure metals but are alloys in which deliberate additions of one or more elements have been made, usually to improve some property of the metal examples are the addition of carbon or nickel and chromium to iron to give, respectively, carbon and stainless steels and the addition of copper to aluminium to give a high-strength age-hardenable alloy. 

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