Hydrothermal light-weight calcium phosphate cements: use of polyacrylnitrile-shelled hollow microspheres: Fid-Bau Portal

Hydrothermal light-weight calcium phosphate cements: use of polyacrylnitrile-shelled hollow microspheres

Sugama, T. / Lipford, B.

Calcium phosphate cement (CPC) slurries with a very low density of less than 1.0 g.cm^-3 were prepared by incorporating polyacrylnitrile (PAN)-shelled hollow microspheres with calcite sizing ito CPC pastes consisting of sodium metaphosphate, high alumina cement and water. Their characterizations were then investigated to assess their value as temperatures up to 300 deg C. This light-weight cement showed the following four main features: firstly the chemical inertness of the PAN shells to CPC served to extend thickening time of the slurry; secondly the microsphere surfaces preferentially absorbed Al ions from among the various ionic species in the interstitial fluid of CPC at 100 deg C, thereby forming amorphous Al-enriched sodium phosphate hydrates as interfacial intermediate layers which tightly linked the microspheres to the CPC matrix; thirdly although the thermal decomposition of PAN shells around 200 deg C generated numerous voids in the cement body, these open spaces were filled by well-grown wardite crystals formed by the in-situ phase transformation of amorphous sodium aluminate phosphate hydrates, thereby preventing a serious loss in strength of the light-weight calcium phosphate cement (LCPC) specimens; fourthly the major phase composition of CPC matrix at 200 deg C and 300 deg C consisted of well-crystallized hydroxyapatite and boehmite compounds which can be categorized as alkali carbonation-resistant phases. The integration of these characteristics was responsible for maintaining the compressive strength of greater than 0.6 MPa for LCPC specimens derived from a very-low-density (0.98 g.cm^-3) slurry exposed for 6 months to a 0.05 M Na2CO3-laden solution at 250 deg C.