Precipitation of calcium sulfates has been investigated on modified cellulose interfaces and in situ. Spin-coated cellulose thin films were used as model substrates to investigate the crystallization of calcium sulfate dihydrate (gypsum) under industrially relevant conditions using highly concentrated dispersions of calcium sulfate hemihydrate (bassanite). The films were pre-treated in aqueous solutions of calcium, magnesium or iron ions, where regeneration in a solution of Ca 2 + promoted gypsum crystallization on the polysaccharide substrate in the presence of bassanite or in control solutions comprising supersaturated calcium sulfate. Cellulose-bassanite hybrid thin films were also applied as crystallization substrates for gypsum from a dispersion of bassanite. Hybrid thin films were prepared by adding bassanite into a mixture of dissolved polymeric cellulose and nmethyl- morpholine-n-oxide (NMMO) before regeneration of the cellulose structure. The bassanite aggregates acted as crystal growth sites for gypsum, which promoted the crystal growth of gypsum on the hybrid thin film substrate. In situ characterisation of the precipitation of gypsum on the cellulose interface with Raman spectroscopy and X-ray diffraction showed the crystallization to proceed via a bassanite intermediate phase in a solution of calcium and sulfate ions. The existence of the otherwise thermodynamically unstable phase was attributed to the stabilizing effect of dissolved polymeric cellulose and dehydrated NMMO. Precipitation of calcium sulfates in situ produced nanoparticulate amorphous calcium sulfate within a cellulose polymer network. The composite material was prepared by adding aqueous solutions of calcium and sulfate ions into NMMO prior to the dissolution of cellulose, where the hydration of NMMO controlled the transformation of amorphous calcium sulfate to crystalline gypsum.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:683938 |
| Date | January 2014 |
| Creators | Nissinen, Tomi Pekka Bernhard |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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