Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS


MODSTEEL Streszczenie raportu

Project ID: G5RD-CT-1999-00066
Źródło dofinansowania: FP5-GROWTH
Kraj: Greece

Model deposition studies of calcium phosphate precipitation

Simulated Milk Ultra-Filtrate (SMUF) solutions were employed to investigate calcium phosphate precipitation characteristics, under various conditions, in two types of tests. Spontaneous precipitation of calcium phosphate was studied in narrow ranges of pH (5.7 to 7.0) and temperature (55 to 75 Co). The morphology and size of precipitated particles depends primarily on solution super saturation; reduction of pH leads to relatively larger particles. The precipitated solids are identified as poorly crystallized hydroxyapatite. The presence of citrate ions results in morphological changes of precipitated crystals.

Calcium phosphate precipitation was also investigated under continuous flow conditions by employing a tubular test section, at temperatures 60 and 70 Co, pH 5.8 to 7.0 and two Reynolds numbers (7.000 and 17.000). Deposition rate is affected by both temperature and pH, through solution super saturation. At the maximum deposition rate, an initially thin layer is formed, covering entirely the substrate within minutes from the onset of flow. Further deposition occurs mostly in the form of overgrowths consisting of clusters of sub micron particles. With increasing flow velocity the deposition rate tends to increase, and more compact deposit layers are obtained.

These tests did not provide clear evidence that the deposited mass is affected by the surface treatment or type of substrate; however, SEM deposit observations indicate that adhesion strength of modified surfaces might by reduced, compared to steel substrate, possibly facilitating clean up. The techniques employed in this work are useful in testing heat exchanger surface characteristics as regards deposition in dairy and other processes.

Reported by

Centre for research and technology Hellas - CERTH
6th km. Charilaou – Thermi Road
57001 Thermi, Thessaloniki
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