Aragonite synthetic

Romanek CS, Grossman EL, Morse JW (1992) Carbon isotopic fractionation in synthetic aragonite and calcite Effects of temperature and precipitation rate. Geochim Cosmochim Acta 56 419-430 Rowe MW, Clayton RN, Mayeda TK (1994) Oxygen isotopes in separated components of Cl and CM meteorites. Geochim Cosmochim Acta 58 5341-5347... 

Kim ST, O Neil JR (1997) Equilibrium and nonequUibrium oxygen isotope effects in synthetic carbonates, Geochim Cosmochim Acta 61 3461-3475 Kim S-T, Mucci A, Taylor BE (2007) Phosphoric acid fractionation factors for calcite and aragonite between 25 and 75°C, Chem Geol 246 135-146... 

The applicability of scanning Auger spectroscopy to the analysis of carbonate mineral surface reactions was demonstrated by Mucci and Morse (1985), who carried out an investigation of Mg2+ adsorption on calcite, aragonite, magnesite, and dolomite surfaces from synthetic seawater at two saturation states. Results are summarized in Table 2.5. 

The most complete study of the inhibition of calcium carbonate precipitation by organic matter was carried out by Berner et al. (1978), where primary concern was the lack of carbonate precipitation from supersaturated seawater. Both synthetic organic compounds and organic-rich pore waters from Long Island Sound were used to measure the inhibition of aragonite precipitation. Natural marine humic substances and certain aromatic acids were found to be the strongest inhibitors. The rate of precipitation in pore waters was also found to be strongly inhibited. 

Morse J.W., deKanel J. and Harris J. (1979) Dissolution kinetics of calcium carbonate in seawater. VII The dissolution kinetics of synthetic aragonite and pteropod tests. Amer. J. Sci. 279, 482-502. 

Mucci A. and Morse J.W. (1985) Auger spectroscopy determination of the surface-most adsorbed layer composition on aragonite, calcite, dolomite, and magnesite in synthetic seawater. Amer. J. Sci. 285, 306-317. 

The rate of dissolution of synthetic and deep sea biogenic (pteropods) aragonite in seawater have also been determined in the laboratory by the pH-stat method (57). The results of the experiments to determine the change in the rate of dissolution as a function of undersaturation are presented in Figure 16. The pteropods were found to dissolve at. only about 3% the rate, per unit surface area, of the synthetic aragonite. The results also indicate a change in the empirical reaction order from 2.92 to 7.37 at = 0,44. The rate equations for pteropod dissolution are ... 

Figure 16. Log of the dissolution rate vs. the log of (1 — Cl) for synthetic aragonite and pteropods (after Ref. 57)...

Figure 17. Log of the dissolution rate vs. total carbonate ion concentration for synthetic aragonite, pteropods, calcitic Pacific Ocean sediment, and foraminifera in the 125-500 iim size fraction. (A) indicates ihe aragonite equilibrium total carbonate ion concentration at 25°C, 1 atm (26). (C) indicates the calcite equilibrium total carbonate ion concentration at 25°C, 1 atm (25).

Figure 19. Change in the rate of synthetic aragonite dissolution, relative to dissolution in very low phosphate seawater, as a function of time (57)...

Morse, J.W., de Kanel, J., and Harris, K. The dissolution kinetics of calcium carbonate in seawater VII. The dissolution kinetics of synthetic aragonite and pteropods, Amer. Jour. Sci. (in press). 

Synthetic calcite and aragonite were studied in [2450] by electrophoresis. Samples with CaCl2 added (0.0005-0.05 M, different pH) were positively charged and samples with Na2CO3 added (0.0005-0.05 M, different pH) were negatively charged. At pH 9.1, in the presence of 0.01 M NaCl, both minerals were positively charged. 

Calcined kaolin, scalenohedral PCC, aragonitic PCC and amorphous silicates are examples of aggregated fillers, i.e. these products consist of crystals which are synthetically clustered into repetitive shapes of similar size throughout the... 

R(C03)(0H), synthesized by Sawyer et al. (1973), can be described as a polymorph of hydroxylbastnasite. This synthetic R(C03)(OH) and hydroxyl bastnasite are related as are aragonite and vaterite, the polymorphs of CaC03, respectively. 

While amorphous precursors were already found and discussed for biomineral systems as a sophisticated way towards minerals as they avoid high salt concentrations with their associated high osmotic pressures, the other mechanisms emerged from purely synthetic systems. Only very recently, the first evidence was reported that, for example, mesocrystals can be found in biominerals like aragonite platelets in nacre [114] or cal-cite nanocrystals in sea urchin spines [116]. Much has still to be done to understand the forces that control the perfect nanoparticle alignment in mesocrystals, as well as the exact building mechanism and the possibilities for manipulating these structiues. However, the toolbox of crystalUzation is clearly extended now. 

There also existed another use of synthetic polymers besides synthetic gels as the hard template to influence crystal growth discussed above. In this case, sohd synthetic polymers were used as a real hard template . It has been demonstrated that calcium carbonate favored the formation of the vaterite phase on the poly(vinyl chloride-co-vinyl acetate-co-maleic acid) substrate in the supersatiuated solution prepared from calcium nitrate and sodium dicarbonate solutions at pH 8.50 [238]. Commercial polymer fiber (Nylon 66 and Kevlar 29) can induce crystallization of calcite in solution, but the vaterite phase tends to crystallize on the surface of polymers in the presence of soluble polymer (PVA), and aragonite favors forming on the siuface of polymers modified with acid or alkah accompanying PVA [239]. 

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