Oxidation by X-rays

Table 12.6 Results of inorganic carbon analysis of calcareous soils by potentiometry compared with those for calcium oxide by X-ray fluorescence spectrometry... 

Harrison, P.M. Fischbach, F.A. Hoy, T.G. Haggis, G.H. (1967) Ferric oxyhydroxide core of ferritin. Nature 216 1188-1190 Harvey, D.T. Linton, R.W (1981) Chemical characterization of hydrous ferric oxides by X-ray photoelectron spectroscopy. Anal. 

Greegor RB, Lytle FW, Ewing RC, Haaker RF (1984) Ti-site geometry in metamict, armealed and synthetic complex Ti-Nb-oxides by X-ray absorption spectroscopy. Nucl Instr Meth B1 587-594 Greegor RB, Lytle FW, Chakoumakos BC, Lumpkin GR, Ewing RC (1985a) An investigation of metamict and armealed natural pyrochlore by X-ray absorption spectroscopy. Mater Res Soc Symp Proc 44 655-662... 

A convenient starting point for such an assessment involves two independent investigations of the surface composition of tin-antimony oxides by X-ray photoelectron spectroscopy (XPS) in 1979 (/J, 27). The study by Pyke and Cross (13) followed their earlier work on the phase composition (72) and showed the extent of surface enrichment in antimony to depend on bulk composition and calcination conditions. For example, the surface of a material with a bulk antimony content of 20% and calcined at 600 C for 16 hr was found to be enriched by a factor of about 2.7, with the degree of enrichment decreasing rapidly with depth from surface until the bulk composition was attained at 50A. Although the surface enrichment factor was found to vary with bulk composition at constant temperature, the dependence of the surface composition on calcination temperature represented an even more interesting feature of the study and is depicted in Fig. 2. 

Dodd CG, Glen GL (1968) Chemical bonding studies of silicates and oxides by X-ray K-emissionspectroscopy. J. Appl Phys 39 5377-5384... 

Many contributors have determined the transitional metals valence states in oxides by X-ray spectroscopy methods. The sophisticated unique specialized equipment fitted with high-vacuum systems and significant time expenditure is necessary for its implementation. 

Harvey, D. T. Linton, R. W. (1981). Chemieal Charaeterization of Hydrous Ferric Oxides by X-ray Photoeleetron Speetroseopy. Chemistry, 53, 1684-1688. 

Salinas-Sanchez A, Garcia-Munoz JL, Rodriguez-Carvajal J, Saez-Puche R, Martinez JL (1992) Structural characterization of R2BaCuOs (R = Y, Lu, Yb, Tm, Er, Ho, Dy, Gd, Eu and Sm) oxides by X-ray and neutron diffraction. J Solid State Chem 100 201-211... 

The many possible oxidation states of the actinides up to americium make the chemistry of their compounds rather extensive and complicated. Taking plutonium as an example, it exhibits oxidation states of -E 3, -E 4, +5 and -E 6, four being the most stable oxidation state. These states are all known in solution, for example Pu" as Pu ", and Pu as PuOj. PuOl" is analogous to UO , which is the stable uranium ion in solution. Each oxidation state is characterised by a different colour, for example PuOj is pink, but change of oxidation state and disproportionation can occur very readily between the various states. The chemistry in solution is also complicated by the ease of complex formation. However, plutonium can also form compounds such as oxides, carbides, nitrides and anhydrous halides which do not involve reactions in solution. Hence for example, it forms a violet fluoride, PuFj. and a brown fluoride. Pup4 a monoxide, PuO (probably an interstitial compound), and a stable dioxide, PUO2. The dioxide was the first compound of an artificial element to be separated in a weighable amount and the first to be identified by X-ray diffraction methods. 

Analyses of alloys or ores for hafnium by plasma emission atomic absorption spectroscopy, optical emission spectroscopy (qv), mass spectrometry (qv), x-ray spectroscopy (see X-ray technology), and neutron activation are possible without prior separation of hafnium (19). Alternatively, the combined hafnium and zirconium content can be separated from the sample by fusing the sample with sodium hydroxide, separating silica if present, and precipitating with mandelic acid from a dilute hydrochloric acid solution (20). The precipitate is ignited to oxide which is analy2ed by x-ray or emission spectroscopy to determine the relative proportion of each oxide. 

Ruthenium—Titanium Oxides. The x-ray diffractioa studies of mthenium—titanium oxide coatiags show that the coatiag components are preseat as the metal dioxides, each ia the mtile form as weU as ia soHd solutioa with each other (13). The developmeat of the crystal stmcture begias to occur at a bake temperature of about 400°C. By foUowiag the diffractioa line for the mtile stmcture, an iacrease ia crystallinity can be seen as temperatures are iacreased to the 600—700°C range. Above these temperatures, the peak begias to separate iato two separate peaks, iadicative of phase separatioa iato iadividual mtile oxides, oae rich ia mthenium and one rich ia titanium. 

Na[Sb(OH)g], respectively. The latter compound is one of the least soluble sodium salts known and is useful in sodium analysis. Numerous polyantimonate(V) derivatives are prepared by heat treatment of mixtures of antimony trioxide and other metal oxides or carbonates. Of these, K Sb O [12056-59-6] and K Sb O [52015-49-3] have been characterized by x-ray. These consist of three-dimensional networks of SbO in which corners and edges are shared with K" ions located in tunnels through the network (23). Simple species such as SbO and Sb20 2, analogous to orthophosphate and pyrophosphate, apparendy do not exist. 

The simplest analytical procedure is to oxidize a sample in air below the fusion point of the ash. The loss on ignition is reported as graphitic carbon. Refinements are deterrninations of the presence of amorphous carbon by gravity separation with ethylene bromide, or preferably by x-ray diffraction, and carbonates by loss of weight on treating with nitric acid. Corrections for amorphous carbon and carbonates are appHed to the ignition data, but loss of volatile materials and oxidation may introduce errors. 

X-Ray diffraction studies on the 3-imino-l-azetine (205 Ar = p-FC6H4), show that the four-membered ring is planar with an unusually long endocyclic C=N bond (74ZN(B)399). The structure of the 1-azetine A7-oxide (275) has also been determined by X-ray crystallographic techniques (79CC993). 

An important property of the surface behaviour of oxides which contain transition metal ions having a number of possible valencies can be revealed by X-ray induced photoelectron spectroscopy. The energy spectrum of tlrese electrons give a direct measure of the binding energies of the valence electrons on the metal ions, from which the charge state can be deduced (Gunarsekaran et al., 1994). 

Long-term exposure to fenie oxide dust ean eause ehanges to the lungs whieh are deteetable by X-rays. For this reason an 8 hr TWA TLV of 5 mg/m has been set. Good ventilation is important for proeesses involving this eompound. For regular use routine medieal examination and exelusion of staff with pulmonary disease may be neeessary. 

FIGURE 15.29 The arrangement of snbnnits in horse methemoglobin, the first hemoglobin whose strnctnre was determined by X-ray diffraction. The iron atoms on metHb are in the oxidized, ferric (Fe ) state. (Irving Gets)... 

Optical resolution of the dithiirane 1-oxides 2 and 3 was accomplished by HPLC equipped with a chiral column (97T12203). Absolute configurations of 2a and 2b were determined by X-ray crystallography. Tire stereospecific isomerization (epimerrzation) of 2a to 3b and 2b to 3a was observed during the resolution study. 

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