Carbonate dissolution evidence

Ku TCW, Walter LM, Coleman ML, Blake RE, Martini AM (1999) Coupling between sulfur recycling and syndepositional carbonate dissolution evidence from oxygen and sulfur isotope composition of pore water sulfate, South Florida Platform, USA, Geochim Cosmochim Acta 63 2529-2546... 

Murray RW, Leinen M, Isem AR (1993) Biogenic flux of A1 in the central equatorial Pacific Ocean Evidence for increased productivity during glacial periods. Paleoceanogr 8 651-670 Murray RW, Knowlton C, Leinen M, Mix AC, Polski CH (2000) Export production and carbonate dissolution in the central equatorial Pacific Ocean over the past 1 Ma. Paleoceanogr 15 570-592 Nancollas GH, Amjad Z, Koutsoukas P (1979) Calcium phosphates-speciation, solubility, and kinetic considerations. Am Chem Soc Symp Ser 93 475-497... 

Figure 7 shows the joint interfaces in ground C-SiC/Cu-clad-Mo joints made using Ticusil. There is evidence of good braze/composite interaction (Figs. 7a b), and relatively large quantities of Ti (18,6 atom%). Mo (36.4 at%) and Ag (45 at%) are detected within the C-SiC composite (point I, Fig. 7b). The SiC coating on the composite surface has been removed by grinding and an intimate composite-to-braze contact established. Silicon is detected at -15-20 pm distance within the braze region near the interface (point 4, Fig. 7b). As before, the braze matrix displays the Ag-rich and Cu-rich two-phase eutectic structure with the Ag-rich phase preferentially segregating at the C-SiC surface (Fig. 7b). The Ag-rich phase has also preferentially deposited at the interface on the Cu-clad-Mo side (Fig. 7c). Interestingly, there is some carbon dissolution and diffusion in braze (points 1 2, Fig. 7c) and also in Mo (point 5, Fig. 7c) to a depth of -30 pm. Additionally, some Cu (10.6 at%) from the clad layer was detected within the Mo substrate (point 5, Fig. 7c).

Dissolved arsenic is correlated with ammonia (Fig. 4), consistent with a release mechanism associated with the oxidation of organic carbon. Other chemical data not shown here provide clear evidence of iron, manganese and sulfate reduction and abundant methane in some samples indicates that methanogenesis is also occurring. It is not clear however if arsenic is released primarily by a desorption process associated with reduction of sorbed arsenic or by release after the reductive dissolution of the iron oxide sorbent. Phreeqc analysis shows PC02 between 10"12 and 10"° bars and that high arsenic waters are supersaturated with both siderite and vivianite. 

The major problems with Ni-based anodes and NiO cathodes are structural stability and NiO dissolution, respectively (9). Sintering and mechanical deformation of the porous Ni-based anode under compressive load lead to severe performance decay by redistribution of electrolyte in a MCFC stack. The dissolution of NiO in molten carbonate electrolyte became evident when thin electrolyte structures were used. Despite the low solubility of NiO in carbonate electrolytes ( 10 ppm), Ni ions diffuse in the electrolyte towards the anode, and metallic Ni can precipitate in regions where a H2 reducing environment is encountered. The precipitation of Ni provides a sink for Ni ions, and thus promotes the diffusion of dissolved Ni from the cathode. This phenomenon... 

The main impurity, not unexpectedly, is oxygen (ca. 11 atomic %). Evidence was presented to show that this O was probably mainly in the forms of carbonate and adsorbed water. The carbonate could come from two sources dissolution of atmospheric CO2 and (see Eq. (3.11)) from decomposition of thiourea. 

Lead and mercury are deposited as micron-sized clusters, predominantly at intercrystallite boundaries [105] so does lithium from the polyethylene oxide solid electrolyte. What is more, Li intercalates into the sp2-carbon [22, 138], Thus, observations on the Li intercalation and deintercalation enable one to detect non-diamond carbon on the diamond film surface. Copper is difficult to plate on diamond [139], There is indirect evidence that Cu electrodeposition, whose early stages proceed as underpotential deposition, also involves the intercrystallite boundaries [140], We note that diamond electrodes seem to be an appropriate tool for use in the well-known electroanalytical method of detection of traces of metal ions in solutions by their cathodic accumulation followed by anodic stripping. The same holds for anodic deposition, e.g. of, Pb as PbCh with subsequent cathodic reduction [141, 142], Figure 30 shows the voltammograms of anodic dissolution of Cd and Pb cathodically predeposited from their salt mixtures on diamond and glassy carbon electrodes. We see that the dissolution peaks are clearly resolved. The detection limit for Zn, Cd, and Pb is as low as a few ppb [143]. 

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