@article{ShkilnyySchoeneRumplaschetal.2011,
  author    = {Shkilnyy, Andriy and Sch{\"o}ne, Stefanie and Rumplasch, Claudia and Uhlmann, Annett and Hedderich, Annett and G{\"u}nter, Christina and Taubert, Andreas},
  title     = {Calcium phosphate mineralization with linear poly(ethylene imine) a time-resolved study},
  series = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft},
  volume    = {289},
  journal   = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft},
  number    = {8},
  publisher = {Springer},
  address   = {New York},
  issn      = {0303-402X},
  doi       = {10.1007/s00396-011-2403-2},
  pages     = {881 -- 888},
  year      = {2011},
  abstract  = {We have earlier shown that linear poly(ethylene imine) (LPEI) is an efficient growth modifier for calcium phosphate mineralization from aqueous solution (Shkilnyy et al., Langmuir, 2008, 24 (5), 2102). The current study addresses the growth process and the reason why LPEI is such an effective additive. To that end, the solution pH and the calcium and phosphate concentrations were monitored vs. reaction time using potentiometric, complexometric, and photometric methods. The phase transformations in the precipitates and particle morphogenesis were analyzed by X-ray diffraction and transmission electron microscopy, respectively. All measurements reveal steep decreases of the pH, calcium, and phosphate concentrations along with a rapid precipitation of brushite nanoparticles early on in the reaction. Brushite transforms into hydroxyapatite (HAP) within the first 2 h, which is much faster than what is reported, for example, for calcium phosphate precipitated with poly(acrylic acid). We propose that poly(ethylene imine) acts as a proton acceptor (weak buffer), which accelerates the transformation from brushite to HAP by taking up the protons that are released from the calcium phosphate precipitate during the phase transformation.},
  language  = {en}
}
@article{BalckeHahnOswald2011,
  author    = {Balcke, Gerd U. and Hahn, M. and Oswald, Sascha},
  title     = {Nitrogen as an indicator of mass transfer during in-situ gas sparging},
  series = {Journal of contaminant hydrology},
  volume    = {126},
  journal   = {Journal of contaminant hydrology},
  number    = {1-2},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0169-7722},
  doi       = {10.1016/j.jconhyd.2011.05.005},
  pages     = {8 -- 18},
  year      = {2011},
  abstract  = {Aiming at the stimulation of intrinsic microbial activity, pulses of pure oxygen or pressurized air were recurrently injected into groundwater polluted with chlorobenzene. To achieve well-controlled conditions and intensive sampling, a large, vertical underground tank was filled with the local unconfined sandy aquifer material. In the course of two individual gas injections, one using pure oxygen and one using pressurized air, the mass transfer of individual gas species between trapped gas phase and groundwater was studied. Field data on the dissolved gas composition in the groundwater were combined with a kinetic model on gas dissolution and transport in porous media. Phase mass transfer of individual gas components caused a temporary enrichment of nitrogen, and to a lower degree of methane, in trapped gas leading to the formation of excess dissolved nitrogen levels downgradient from the dissolving gas phase. By applying a novel gas sampling method for dissolved gases in groundwater it was shown that dissolved nitrogen can be used as a partitioning tracer to indicate complete gas dissolution in porous media.},
  language  = {en}
}