Cobalt impurities

Other impurities levels are quite low as exemplified in Table 9.2.4 for cobalt. Impurities such as Ca, Fe, or Na, which may be present as cations in the precursor, are considerably lower because these elements can not be reduced to the zero-valence state by the polyol and then are retained in the solution. 

The generation of crud is controlled by adopting the material with low cobalt impurities, and maintaining the pH of reactor coolant water in the range of 6.9 to 7.4. 

In most cases, as a fluence monitor small disks or wires of an Al-Co alloy with 0.1 to 1% Co are used by such a dilution of the monitor substance, self-shielding and flux depression effects are avoided. In general, since interfering radionuclides produced in the diluting element are small, chemical separations before activity measurement of Co are normally not needed. Frequently, the cobalt impurities in stainless steels, which are in the range of 100 to 1000 ppm, can be directly used as a fluence monitor in such cases, however, the accurate cobalt concentration in the material has to be additionally determined by chemical analysis. 

The highly beneficial effect of Stellite replacement in the newer Siemens PWRs was confirmed by a comparative study performed by Garbett (1992). In this study it was emphasized that cobalt impurities in the primary circuit materials are only minor contributors to the radiation fields in the areas surrounding the piping, components and systems. 

Special considerations moisture in excess of 0.1% will cause bubbling iron, copper, manganese, cobalt impurities catalyze oxidation... 

Impure C0O2 (oxidizing agent on alkaline Co(ll)) and some mixed oxides of cobalt(lV) and (V), e.g. K.3C0O4, are known. 

Germanium tetrachloride refined for use in making optical fibers is usually specified to contain less than 0.5 to 5 ppb of each of eight impurities vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc. Limits are sometimes specified for a few other elements. Also of concern are hydrogen-bearing impurities therefore, maximum limits of 5 to 10 ppm are usually placed on HCl, OH, CH2, and CH contents. 

Cementation is also an efficient way of putifyiag a pregnant solution by removing impurities that are more noble than the metal being processed. An example is the cementation of copper, cadmium, cobalt, and nickel from ziac solutions prior to electrowinning. 

Other Meta.Is, Although most cobalt is refined by chemical methods, some is electrorefined. Lead and tin are fire refined, but a better removal of impurities is achieved by electrorefining. Very high purity lead is produced by an electrochemical process using a fluosiUcate electrolyte. A sulfate bath is used for purifying tin. Silver is produced mainly by electrorefining in a nitrate electrolyte, and gold is refined by chemical methods or by electrolysis in a chloride bath. 

Most of the heavy-metal impurities present in 2inc salt solutions must be removed before the precipitation reaction, or these form insoluble colored sulfides that reduce the whiteness of the 2inc sulfide pigment. This end is usually achieved by the addition of 2inc metal which reduces most heavy-metal ions to their metallic form. The brightness of 2inc sulfide can be improved by the addition of a small amount of cobalt salts (ca 0.04% on a Co/Zn basis) (20). Barium sulfate [7727-43-7] formed in the first step is isolated and can be used as an extender. 

Aeration must be avoided since it can oxidize and resolubiUze the cemented (precipitated) impurities. Filter presses are used after each step and the cakes are leached to recover various values. For example, cadmium is dissolved, recemented with zinc, and recovered on site either electrolyticaHy or by distillation. A copper residue of 25—60% copper is sold for recovery elsewhere. The other impurities cannot be recovered economically with the exception of cobalt in some plants. 

Hypobromites, the salts of hypobromous acid, do not keep well because they gradually disproportionate to bromide and bromate. Solutions are best prepared as needed from bromine and alkafl with cooling. Because disproportionation is catalyzed by cobalt, nickel, and copper (70), these impurities should be avoided. SoHd alkaline earth hypobromites, or more properly, bromide hypobromites such as calcium bromide hypobromite [67530-61 CaBr(OBr), have been known for many years, but the pure crystalline hydrates sodium hypobromite pentahydrate [13824-96-9] NaOBr 5H20, and potassium hypobromite tribydrate [13824-97-0], KOBr 3H20, were not described until 1952 (71). Hypobromites are strong bleaching agents, similar to hypochlorites. 

Cr C Cr C chromium iton(l l) [12052-89-0] CrFe (c phase), and chromium iron molybdenum(12 36 10) [12053-58-6] Cr 2F 36 o Q phase), are found as constituents in many alloy steels Ct2Al23 and CoCr ate found in aluminum and cobalt-based alloys, respectively. The chromium-rich interstitial compounds, Ci2H, chromium nitrogen(2 l) [12053-27-9] Ct2N, and important role in the effect of trace impurities on the... 

Many different values for room temperature mechanical properties can be found in the Hterature. The lack of agreement depends, no doubt, on the different mixtures of a and y phases of cobalt present in the material. This, on the other hand, depends on the impurities present, the method of production of the cobalt, and the treatment. 

Zaffer, m. zaffer, zaffre (impure oxide of cobalt). Zaffetika, /. asafetida. 

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