Microstructural characterization of dental zinc phosphate cements using combined small angle neutron scattering and microfocus X-ray computed tomography

Objective To characterize the microstructure of two zinc phosphate cement formulations in order to investigate the role of liquid/solid ratio and composition of powder component, on the developed porosity and, consequently, on compressive strength. Methods X-ray powder diffraction with the Rietveld method was used to study the phase composition of zinc oxide powder and cements. Powder component and cement microstructure were investigated with scanning electron microscopy. Small angle neutron scattering (SANS) and microfocus X-ray computed tomography (XmCT) were together employed to characterize porosity and microstructure of dental cements. Compressive strength tests were performed to evaluate their mechanical performance. Results The beneficial effects obtained by the addition of Al, Mg and B to modulate powder reactivity were mitigated by the crystallization of a Zn aluminate phase not involved in the cement setting reaction. Both cements showed spherical pores with a bimodal distribution at the micro/nano-scale. Pores, containing a low density gel-like phase, developed through segregation of liquid during setting. Increasing liquid/solid ratio from 0.378 to 0.571, increased both SANS and XmCT-derived specific surface area (by 56% and 22%, respectively), porosity (XmCT-derived porosity increased from 3.8% to 5.2%), the relative fraction of large pores ≥50 μm, decreased compressive strength from 50 ± 3 MPa to 39 ± 3 MPa, and favored microstructural and compositional inhomogeneities. Significance Explain aspects of powder design affecting the setting reaction and, in turn, cement performance, to help in optimizing cement formulation. The mechanism behind development of porosity and specific surface area explains mechanical performance, and processes such as erosion and fluoride release/uptake

The effect of firing temperature on the composition and microstructure of a geocement-based binder of sodium water-glass

The fire performance of a geocement-based binder was investigated with a combination of analytical techniques, in terms of changes in composition and microstructure. Geocement, formulated as Na2O∙Al2O3∙6SiO2∙20H2O, was prepared using metakaolin, sodium water-glass, rotten stone and sodium hydroxide. The mixture was homogenized by passing through a hydrodynamic cavitator. Cubes of 20 mm were prepared, hardened at laboratory conditions for 28 days, and subsequently burnt at 600, 800 and 1200 °C in a laboratory furnace. Cavitation treatment resulted in a highly amorphous binder; amorphous fraction decreased upon firing up to 800 °C due to crystallization, and increased above 1000 °C because of melt formation. Porosity increased with firing temperature and pores larger than 1 mm in diameter prevailed at 1200 °C. The material remained stable up to 1200 °C. The results indicate the adequacy of this geocement-based binder for preparing fire-protecting materials

Composition and Technology of the 17th Century Stucco Decorations at Červená Lhota Castle in Southern Bohemia

A high relief stucco decoration from the Great Chamber of the castle Červená Lhota in the Southern Bohemia was surveyed and characterised as a part of its planned conservation. A detailed analytical work was undertaken in order to provide support for the repair works that aimed to be based on a good knowledge of the original materials and application techniques. The main research focus was on the fruit pieces decorating the ribs of vaults. Altogether, over 20 mortar samples were collected from the vault bedding mortar, plaster, stucco elements and the stucco pieces themselves. Additionally, some pieces of stucco (fruits), that were loose and had to be temporarily removed, were studied macroscopically and by X-ray CT. The characterisation of binder, aggregate and additives was carried out using OM, SEM, TA, acid attack, sieve analysis of insoluble residue, XRD, FTIR and nL-MS. It led to an understanding of the uses of various mortar mixes and determination of their composition. The results are discussed as an example of an analytical procedure that aimed at understanding in detail of this historically significant technique from a material and technological standpoint