الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
The nature of the entities present at the early stage of the precipitation pathways from solutions is largely debated in the literature. These entities might drive the entire nucleation and
growth mechanisms of the precipitation. Understanding the formation of these entities is of
fundamental relevance in order to achieve an appropriate control at the macroscopic level of
the solid formation, for instance in terms of morphology, physicochemical properties, and
crystalline phase. In this thesis, targets of investigations of the early stage of the precipitation
kinetics (i.e. pre-nucleation stage) from supersaturated solutions are calcium carbonate (CaC)
and phosphate (CaP), being the most studied biominerals. Despite the high scientific relevance
across a broad spectrum of applications, little is known about their early stage formations.
In order to investigate the precipitation pathway from CaC and CaP systems, a series of
synchrotron wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS)
experiments were performed at the MS-X04SA beamline of the Swiss Light Source (SLS)
at the PSI, Villigen, Switzerland. In particular, the SAXS signal is important for detecting
amorphous entities in suspension−such as clusters or nanodroplets with a density higher than
that of the solvent−and their size and shape. For the CaC and CaP systems, in-situ SAXS
experiments were performed with horizontal liquid microjet specifically designed for such
measurements. The jet was generated using a capillary connected to a mixer, where four HPLC
pumps were delivering solutions in order to obtain the desired pH and saturation level of
the systems. The saturation level was evaluated thanks to an accurate thermodynamic-kinetic
precipitation model of CaC and CaP systems. The liquid was collected in a catcher where the
temperature (T) and pH of the solution, under stirring, are monitored on line. The microjet was
highly stable, with tunable diameter, pulsation-free and the delay between the mixing point and
measuring point can be tuned. Time-resolved measurements using the WAXS regime were also
conducted on calcium carbonate-forming solutions system in quartz capillary.
A practical procedure for absolute intensity calibration for SAXS studies on liquid microjets
was established, using a gold nanoparticle suspension as a standard. In this way, the intercept of the corresponding SAXS scattering curve could provide a scaling reference pertaining to the
experiments. The SAXS data collected from liquid microjets of amorphous calcium carbonate
(ACC) and amorphous calcium phosphate (ACP) suspensions were modeled using parametric statistical models. Insights about the size and shape distribution of denser matter in the
liquid jet are provided. Theoretical implications on the early stage of solid formation pathway are inferred. Furthermore, the pair distribution function (PDF) analysis was utilized to
extract information from the WAXS data about the evolving structure of calcium carbonate.
The feasibility of the WAXS data collection yields a clear signal in moderate acquisition times,
of the order of minutes−it is able to distinguish between amorphous clumps and crystalline
nanoparticles.