HYDROTHERMAL CEMENT METAL INTERFACES

We investigated the adherence of two cementitious materials, calcium p hosphate cement (CPC) and silica flour-filled class G cement (CGC), to metal substrates, such as cold-rolled steel (CRS), stainless steel (S S), electroplated zinc-coated steel (EZS), and zinc phosphate-coated s teel (ZPS) after autoclaving at 200 degrees C. In CPC/metal joints, th e gamma-AlOOH phase, which segregated from the hydroxyapatite phase of the CPC matrix, was preferentially precipitated on the CRS and SS sur faces and also mixed with the reaction products formed at the interfac es between CPC and EZS or ZPS, Precipitation of gamma-AlOOH caused the formation of a weak boundary layer at the interfacial transition zone s, thereby resulting in a low shear-bond strength, Although CGC accele rated the rate of corrosion of CRS and SS surfaces, the growth of Fe2O 3 clusters, formed as the corrosion products of metals at interfaces, aided the anchoring effect of xonotlite crystals as the major phase of CGC matrix, thereby conferring a high shear-bond strength, The EZS an d ZPS surfaces were susceptible to alkali dissolution caused by the at tack of the high-pH interstitial fluid of CGC pastes to the Zn and zin c phosphate coatings, Thus, the bond strengths of the CGC/EZS and /ZPS joints were lower than those of the joints made with CRS and SS.