Absorbed cerium

Fractions of absorbed cerium depositing in gonads were calculated from data in Table 20 by taking average ratios of radioactivity in testes or ovaries to that in liver and skeleton and multiplying these by the above liver and skeletal deposition fraction. 

Nucleated by gold and/or silver nanoparticles, themselves photonucleated with the aid of UV-absorbing cerium (3 ) ions Crystallized (at about 600°C) to dendritic form of lithium metasilicate (LijSiOj), which is soluble in HF add Photonucleation plus heat treatment at higher temperatures (850°C) produces stable hthium disihcate (Li2Si205) and a-quartz... 

Cerous salts in general are colorless because Ce " has no absorption bands in the visible. Trivalent cerium, however, is one of the few lanthanide ions in which parity-allowed transitions between 4f and Sd configurations can take place and as a result Ce(III) compounds absorb in the ultraviolet region just outside the visible. 

The role of cerium in these lighting phosphors is not as the emitting atom but rather as the sensitizer. The initial step in the lighting process is the efficient absorption of the 254 nm emission Ce ", with broad absorption bands in the uv, is very suitable. This absorbed energy is then transferred to the sublattice within the crystalline phosphor eventually the activator ion is fed and emission results. Cerium, as a sensitizer ion, is compatible in crystal lattices with other lanthanide ions, such as Eu and Tb, the usual activator atoms. 

Discussion. Iron(III) (50-200 fig) can be extracted from aqueous solution with a 1 per cent solution of 8-hydroxyquinoline in chloroform by double extraction when the pH of the aqueous solution is between 2 and 10. At a pH of 2-2.5 nickel, cobalt, cerium(III), and aluminium do not interfere. Iron(III) oxinate is dark-coloured in chloroform and absorbs at 470 nm. 

The cobalt complex is usually formed in a hot acetate-acetic acid medium. After the formation of the cobalt colour, hydrochloric acid or nitric acid is added to decompose the complexes of most of the other heavy metals present. Iron, copper, cerium(IV), chromium(III and VI), nickel, vanadyl vanadium, and copper interfere when present in appreciable quantities. Excess of the reagent minimises the interference of iron(II) iron(III) can be removed by diethyl ether extraction from a hydrochloric acid solution. Most of the interferences can be eliminated by treatment with potassium bromate, followed by the addition of an alkali fluoride. Cobalt may also be isolated by dithizone extraction from a basic medium after copper has been removed (if necessary) from acidic solution. An alumina column may also be used to adsorb the cobalt nitroso-R-chelate anion in the presence of perchloric acid, the other elements are eluted with warm 1M nitric acid, and finally the cobalt complex with 1M sulphuric acid, and the absorbance measured at 500 nm. 

The reaction between Co(III) and Ce(III) has been the subject of a detailed study in a series of papers by Sutcliffe and Weber . Of particular value is the thorough investigation of the influence of anions on the rate in perchlorate media. The reaction was followed by measuring the disappearance of Co(IIl) at its absorption maximum of 650 m/i, a wavelength where both oxidation states of cerium are transparent and Co(II) absorbs only slightly. Changes in temperature and ionic strength affect the spectrum of Ce(III) at the 296 m/i maximum, but the... 

Radiocerium absorbed into the systemic circulation will be transported by blood proteins and be deposited predominantly in liver and bone. Deposition fractions will be about 0.45 for liver, 0.35 for bone, and 0.1 for other soft tissues with the remainder excreted in urine and feces. The retention times in liver and bone are long compared to the radioactive half-lives of the cerium isotopes. Therefore, their effective biological half-times in these organs will be approximately equal to their physical half-lives. Experimental data on internal organ distri-... 

Fig. 17. Biological model recommended for describing the uptake and retention of cerium by humans after inhalation or ingestion. Numbers in parentheses give the fractions of the material in the originating compartments which are cleared to the indicated sites of deposition. Clearance from the pulmonary region results from competition between mechanical clearances to the lymph nodes and gastrointestinal tract and absorption of soluble material into the systemic circulation. The fractions included in parentheses by the pulmonary compartment indicate the distribution of material subject to the two clearance rates however, these amounts will not be cleared in this manner if the material is previously absorbed into blood. Transfer rate constants or functions, S(t), are given in fractions per unit time. Dashed lines indicate clearance pathways which exist but occur at such slow rates as to be considered insignificant compared to radioactive decay of the cerium isotopes.

With Cerium. —If hydrogen is passed over hot metallic cerium the hydrogen is absorbed —... 

This shifts the maximum light transmission towards the yellow by absorbing more in the blue. Several of the more popular materials have been arsenic and manganese. In recent years, cerium has been substituted for these materials. An advantage of cerium is solarization does not occur as long as arsenic is not present. Also, when the cerium is used in conjunction with selenium and cobalt, the addition of 2-3 ounces per ton of batch can give a reduction in the usage of these two materials. ( )... 

The method of establishing the concentrations of reactant species from the measured absorbances at various times during the early stages of reaction will be illustrated for the cerium(IV) reaction with oy-Cr(OH2)2(C 204)2 ... 

It is apparent that Cr(C2C>4)3 3, m-Cr(OH2)2(0204)2 , and Cr(0H2)4C2044 react smoothly with cerium(IV) in acidic-sulfate media, 1 mole of oxalate being oxidized for each 2 moles of cerium(IV) consumed. The observations made are consistent with the view that the three reactions proceed, at least initially, according to the stoichiometries represented by the respective Reactions 3,1, and 2. The initial absorbances of reactant solutions (values obtained by extrapolation of measured absorbances to zero time) agree well with the values calculated, on the basis of Beer s law, from the absorptivity coefficients of the components. Further, as the reactions in 1.83Af sulfuric acid proceed, the absorbances of the solutions move toward the values expected for the assumed products at rates which demonstrate the reactions are first order in cerium(IV) and complex—see, for example, Figure 2. We thus find no indication that reaction intermediates contribute measurably to the absorbances of reactant solutions, or that reaction conditions cause the rapid equilibration of any of the oxalato complexes with other species... 

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