White-line ratio

Mapping the Valence States of Co Using the White-Line Ratio. 102... 

The second experiment is performed on the reduction of Mn02. Similarly, the plot of composition, o/ Mn, and white-line intensity, Mn L3/L2, are shown in Figure 4.4, where the shadowed bands indicate the white-line ratios for Mn " ", Mn +, and Mn" + as determined from the standard specimens of MnO, Mn203, and Mn02, respectively. The reduction of Mn02 occurs at 300 C. As the specimen temperature increases, the O/Mn ratio drops and the L3/L2 ratio increases, which indicates the valence state conversion of Mn from 4+ to lower valence states. At r = 400°C, the speeimen contains the mixed valences of Mn, Mn +, and Mn +. As the temperature reaches 450°C, the specimen is dominated by Mn " " and Mn +and the composition is O/Mn = 1.3 0.5, in correspondence of Mn304, which is consistent with the mixed valence of Mn cations and implies the incomplete reduction of Mn02. 

Mapping the Valence States oe Co Using THE White-Line Ratio... 

The EELS is most sensitive to the divalent and trivalent Mn and Co ions, while the difference between Mn + and Mn" + or Co + and Co" + is small, leading to a larger error in the identification of the valence state because of experimental error. The only possible solution is to acquire high-quality EELS spectra. Erom the experimental point of view, we found that Mn and Co are the only transition metal elements whose white-line ratios are most sensitive to valence state variation, while the white lines of Ee are almost independent of its valence states. Therefore, more theoretical research is required to explore the origin of white lines. 

Krivanek, O.L. and Paterson, J.H. ELNES of 3d transition-metal oxides 1. Variations across the periodic table. Ultramicroscojiy 1990,32,313-318. Pease, D.M., Bader, S.D., Brodsky, M.B., Budnick, J.I., Morrison, T.L, and Zaluzec, N.J. Anomalous L3/L2 white line ratios and spin pairing in 3d transition metals and alloys Cr metals and Cr2oAugo- Phys. Lett 1986,114A, 491 94. 

Lloyd, S.J., Botton, G.A., andStobbs, W.M. Changes in the iron white-line ratio in the electron energy-loss spectrum of iron-copper. J. Microsc. 1995,180, 288-293. Yuan, J., Gu, E., Gester, M., Bland, J.A.C., and Brown, L.M. Electron energy-loss spectroscopy of Fe thin-fihns on GaAs(OOl). J. Appl. Phys. 1994, 75, 6501-6503. 

Fig. 5.12 Two different 3-D representations of the phase diagram of 3-methylpyridine plus wa-ter(H/D). (a) T-P-x(3-MP) for three different H2O/D2O concentration ratios. The inner ellipse (light gray) and corresponding critical curves hold for (0 < W(D20)/wt% < 17). Intermediate ellipses stand for (17(D20)/wt% < 21), and the outer ellipses hold for (21(D20)/wt% < 100. There are four types of critical lines, and all extrema on these lines correspond to double critical points, (b) Phase diagram at approximately constant critical concentration 3-MP (x 0.08) showing the evolution of the diagram as the deuterium content of the solvent varies. The white line is the locus of temperature double critical points whose extrema (+) corresponds to the quadruple critical point. Note both diagrams include portions at negative pressure (Visak, Z. P., Rebelo, L. P. N. and Szydlowski, J. J. Phys. Chem. B. 107, 9837 (2003))...

The L2,3 edges of the 4th period transition metals are marked by prominent "white line" features due to excitations of the 2p3/2 (L3) and 2pi/2 (L2) levels, following the allowed dipole transitions, to unoccupied d states. On the basis of the (2j + 1) degeneracy in a one electron model, the L3/L2 intensity ratio should be 2 1, but wide departures from this ratio have been observed in transition metals and their oxides [21, 22, 29, 30]. Even though no single factor has been found to account for these observations, these extensive studies form the basis of an empirical catalogue of L3/L2 ratios to be used in future determinations of the oxidation states. Further, positive chemical shifts are also observed as a function of oxidation states for Tj 3+- Ti4+ (2 eV), Mn2+ - Mn4+ (2 eV), Fe2+... 

Leapman et al. (159, 160) have examined the general features (threshold energies, widths, and intensity ratios) of L1UI white lines in 3d transition-metal oxides (Ti02, Cr203, FeO, NiO, CuO), which arise from transition into a partially filled, large d density of states the relative white-line intensities remain as yet unexplained. 

Muller et al. (206) have been concerned with the Lii ni white lines for Ca, Ti, Cr, Co, and Cu and LHi white lines for Sr, Zr, Nb, Ru, Rh, and Pd. In the latter series the shape of the white lines with increasing atomic number is determined by (i) the narrowing and increase of the 4d density of states and (ii) progressive filling of the 4d band. Crystal structure effects are much less conspicuous in the L-edge spectra than in the K-edge spectra. The shapes of the individual L, white lines of the 3d elements Ca, Ti, Cr, Co, Ni, and Cu are similar to those encountered in the 4d series, but the 2p1/2-2p3/2 spin-orbit splitting here is so small (from 6 eV for Ca to 20 eV for Cu) that the Lji and LfH spectra are superimposed. The relative size of the Lm and L white lines follows approximately the multiplicity ratio 2 to 1 of the 2p3/2 and 2pi/2 core states. 

Fig. 23. Comparison of the Lj and Lj absorption spectra. The spectra has been multiplied by a factor of 2.1 to overlap the high energy part of the spectra. A difference can be observed at the white line over a range of about 10 eV. At the white line maximum the intensity ratio Lj/Lj is 2.75, indicating a larger density of unoccupied states with total angular momentum number J = 5/2...

The difference and the ratio are between high and low oxidation states, raiiorelativity intensity of the white line. for solution samples is dependent upon the relative concentration of Ce and Ce (Ref. 36). The calculation was done with the Herman Skillman program, for example, configurations 2p - 4f 6d - and 2p, 4f 4d° for Ce and Ce, respectively were used only the difference in the transition energy was considered. 

Figure 4.3 An overlapped plot of the white-line intensity ratio of Co L3/L2 and the corresponding chemical composition of o/ Co function of the in situ temperature of the C03O4 specimen, showing the abrupt change in valence state and oxygen composition at 400°C. The error bars are determined from the errors introduced in background subtraction and data fluctuation among spectra...

For characterizing advanced and functional materials that usually contain cations with mixed valences, EELS is a very powerful approach with a spatial resolution higher than any other spectroscopy techniques available. Based on the intensity ratio of white lines, it has been demonstrated that the valence states of Co and Mn in oxides can be determined quantitatively. This information is important in studying valence transition in oxides. 

Based on the intensity ratio of white lines, a new experimental approach has been demonstrated for mapping the valence states of Co and Mn in oxides using EFTEM. Resulting L3/L2 images are almost independent of either the specimen thickness (provided f/A < 0.8) or the diffraction effects, and are reliable for mapping the distribution of cation valences. An optimum spatial resolution of... 

Figure 6.33 (A) Microscopic pictures of a hyphal tip (Al), branching region (A2), and the fully grown hypha (A3). False color plots of the absolute intensity of the cytochrome marker band (1573cm ) within the mapped regions of the hyphal tip cell (B1), the branching region (B2), and the central compartment (B3). The normalized cytochrome content is determined by the 1573-1652 cm ratio along the white line - beginning from the star and ending...

In this example, we see that Active Therapy vs. Placebo, or drug therapy, has a significant odds ratio because the 95% confidence interval line does not cross 1. It appears that patients on active therapy are almost four times as likely to experience clinical success as those who are not on active therapy, while controlling for the variables White vs. Black, Male vs. Female, and Baseline Pain (continuous). ... 

Fig. 28. The cumulative COj/CO ratio for coke bum-off on spherical catalyst beads versus combustion temperature in air (O) white amorphous silica-alumina ( ) green Cr02-containing amorphous silica-alumina (M) macroporous white catalyst. The weight (mg) of the bead tested is denoted by the numerals adjacent to the respective symbol. Dashed line represents intrinsic ratios from carbon combustion research. From Weisz (1966).

Fig. 2. Kriged cross-section of C02/CaO molar ratio along A - A on McIntyre grid line 3500E through the HMC deposit has been modified by hand to reflect section geology. White dots indicate sample locations.

Synthesis of CHDM/BA and CHDM/PDA Polyester Resins Described in Tables III and IV. CHDM, brassylic acid (or dodecandioic acid) and "Fascat 4100 in a mol ratio of 2/1/0.005 and 5 wt % of xylene were placed in a three-necked, 250-mL round-bottomed flask fitted with line, a thermometer, an Ace temperature controller, a heating mantle, a mechanical stirrer, a steam-heated Allihn partial condenser with a xylene-filled Barrett moisture test receiver below the Allihn condenser and a total condenser above it. The mixture was heated to about 140 without stirring to melt the reactants and stirring was started. Heating was continued to 205 C. A slow N sweep was maintained throughout the reaction. About 95 to 100% of the theoretical water was collected in the Barrett receiver. Upon cooling the reaction mixtures partially solidified to white waxy solids which liquified when heated to about 40 C. Acid numbers were < 1 mg of KOH/g of resin. 

Figure 8 shows effect of recirculation ratio and space velocity. Horizontal line shows total PO4 as P in the influent and vertical line does total phosphate in the effluent. Black circles were data obtained from the experiments in case that recirculation ratio was 0 and space velocity 38 1/h. White circles were obtained, in case that recirculation was 2 and space velocity 13 1/h. Solid line and dotdash line shows theoretical values calculated from eq.(8), to agree well with experimental results. Increasing in recirculation ratio and decreasing in space velocity was recognized to improve phosphate removal efficiency. 

---