Germanate anomaly

Addition of alumina to alkali germanate glasses results in a shift in the position of the germanate anomaly to higher R2O concentrations. The anomaly eventually disappears for glasses which contain equimolar concentrations of alkali oxide and alumina. The low alkali anomaly in... 

Addition of alkali oxides to germania initially reduces the thermal expansion coefficient, which passes through a minimum at 2 to 5 mol% alkali oxide. Further additions of alkali oxides result in a continuous increase in the thermal expansion coefficient out to the limit of glass formation. The position of the minimum in thermal expansion coefficient is near the low alkali germanate anomaly in viscosity and glass transformation temperature, which occurs at 2 mol% alkali oxide. No unusual behavior in the thermal expansion coefficient is found in the 15 to 20 mol% alkali oxide region where the traditional germanate anomaly in density and refractive index occurs. Replacement of alkali oxides by alumina reduces the thermal expansion coefficient, but has little effect on the shape of the thermal expansion coefficient versus composition curve, which still displays a minimum at 2 to 5 mol% alkali oxide. 

Hartwich G, Schwanitz G, Becker J. 1969. Chromosome anomalies in a case of benzene leukaemia. German Medical Monthly 14 449-450. 

German C R, Elderfield H (1990) Application of the Ce anomaly as a redox indicator The ground rules. Paleoceanography 5 823-833... 

Figure 8 The vertical profiles of La, Ce, and Nd (A) and calculated Ce-anomaly (B) in the Black Sea. After German eta/. (1991).

Karthikeyan A., Almeida RM. Structural anomaly in sodium germanate glasses by molecular dynamics simulation. J. Non-Cryst. Sohds 2001 281 152-161 Klug H.P., Alexander L.E. X-ray Diffraction Procedures for Polycrystalline and Amorphous Materials. John Wiley Sons, New York, USA, 1994 Loshmanov A.A., Sigaev V.N., Yamzin LI. Sov. Phys. Cryst. 1974 19 168 Manaila R., Zaharescu. Medium range order in high surface area amorphous silicas. J. Mater. Sci. 1990 25 2095-2099... 

Processes invoked to explain the development of Ce anomalies include (1) biologically-mediated oxidation of Ce(III) to Ce(IV) in coastal and open oceans (Moffett 1990, 1994a,b, Sholkovitz and Schneider 1991, Sholkovitz et al. 1994) (2) Ce(III)-Ce(lV) redox shifts across anoxic/oxic interfaces in the water columns of marine basins (De Baar et al. 1988, German and Elderfield 1989, Schijf et al. 1991, Sholkovitz et al. 1992) and (3) the development of the largest Ce anomalies in rivers with the highest pH (Goldstein and Jacobsen 1988a,b, Elderfield et al. 1990). Each of these subjects will be covered in more depth in subsequent sections. 

Fig. 14. Two vertical profiles of dissolved La, Nd, Er, and Ce concentrations and the Ce anomaly, parts a-e respectively a comparison of the South Atlantic station of German et al. (1995) and the western North Pacific station ( 271-1) of Piepgras and Jacobsen (1992).

There is slow but progressive oxidation of dissolved Ce(HI) to particulate Ce(IV) in the deep waters as they age in transport from the North Atlantic to the North Pacific and Indian Oceans (Elderfield 1988, German et al. 1995). This redox-driven oxidation is reflected in the development of more negative Ce anomalies along the path of deep water transport. This feature is apparent when one compares the deep water samples of the western North Pacific with those of the South Atlantic (figs. 14d, e). Between these two locations the Ce anomalies change by about 50% (from 0.12 to 0.06). 

Fig. 23. Plots vs. dissolved Si for (a) Nd, (b) Er, and (c) Ce anomaly for the Atlantic, Indian, and Pacific oceans. Data from this study and from Elderfield and Greaves (1982), De Baar et al. (1983, 1985a,b), Klinkhammer et al. (1983), Palmer (1983), Elderfield (1988), Piepgras and Jacobsen (1988, 1992), Greaves et al. (1989, 1991), German and Elderfield (1990), Sholkovi.tz and Schneider (1991), and Dickie and Elderfield (unpublished data). From Bertram and Elderfield (1993).

Fig. 31. A comparison of vertical profiles of the Ce anomaly for seawater fipom the Atlantic, Indian and Pacific Oceans. Stations shown in legend. Data from Elderfield and Greaves (1982), Sholkovitz and Schneider (1991), Piepgras and Jacobsen (1992) and German et al. (1995).

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