Composition, silicate anion structure and morphology of calcium silicate hydrates (C-S-H) synthesized by silica-lime reaction and by the controlled hydration of tricalcium silicate (C3S)

The main product of Portland cement hydration is C-S-H. Despite constituting more than half of the volume of hydrated pastes and having an important role in strength development, very little is known about the factors that determine its morphology. To investigate the relationship between the chemical composition, silicate anion structure and morphology of C-S-H, samples were synthesized via silica-lime reactions and by the hydration of C3S under controlled lime concentrations and with/ without accelerators. The silicate anion structure of the samples was studied by 29Si MAS NMR and the morphology and chemical composition by TEM and SEM. All samples prepared via silica-lime reactions with bulk Ca/Si up to 1.5 were foil-like. The hydration of C3S at fixed lime concentration yielded foil-like C-S-H for [CaO]22mmol/L. A relationship between the silicate anion structure and the morphology of C-S-H was found for the samples fabricated with accelerators

EBSD, SEM and FIB characterisation of subsurface deformation during tribocorrosion of stainless steel in sulphuric acid

The tribocorrosion behaviour of a 304L stainless steel/alumina contact was investigated in sulphuric acid at two imposed potentials (cathodic and passive) The metal deformation below the surface was investigated by analyzing cross sections using secondary electron microscopy (SEM) and electron back scatter diffraction (EBSD) Cross sections were also prepared using focussed ion beam (FIB) and analyzed by in situ SEM. AES depth profiling was used to analyze surface composition Metal subsurface deformation resulted in the build up of a deformed layer of approximately 20 mu m thickness in the near surface zone within the wear track This layer exhibited a deformation gradient with high deformation close to the surface resulting in grain refinement down to 10 nm The applied potential influenced the deformation at passive applied potential more strain was accumulated below the surface resulting in more pronounced grain refinement and higher density of defects. Using AES analysis no alumina transfer from the counter body or any significant burying of oxide below the surface could be detected (C) 2010 Elsevier B.V All rights reserved

EBSD: a powerful microstructure analysis technique in the field of solidification

This paper presents a few examples of the application of electron back-scatter diffraction (EBSD) to solidification problems. For directionally solidified Al-Zn samples, this technique could reveal the change in dendrite growth directions from to as the composition of zinc increases from 5 to 90 wt%. The corresponding texture evolution and grain selection mechanisms were also examined. Twinned dendrites that form under certain solidification conditions in Al-X specimens (with X = Zn, Mg, Ni, Cu) were clearly identified as dendrite trunks split in their centre by a (111) twin plane. In Zn-0.2 wt% Al hot-dip galvanized coatings on steel sheets, EBSD clearly revealed the preferential basal orientation distribution of the nuclei as well as the reinforcement of this distribution by the faster growth of dendrites. Moreover, in Al-Zn-Si coatings, misorientations as large as 10 degrees mm(-1) have been measured within individual grains. Finally, the complex band and lamellae microstructures that form in the Cu-Sn peritectic system at low growth rate could be shown to constitute a continuous network initiated from a single nucleus. EBSD also showed that the alpha and beta phases had a Kurdjumov-Sachs crystallographic relationship

Relation between microstructure and Charpy impact properties of an elemental and pre-alloyed 14Cr ODS ferritic steel powder after hot isostatic pressing

This article describes the microstructure and Charpy impact properties of an Fe-14Cr-2W-0.3-Ti-0.3Y(2)O(3) oxide dispersion strengthened (ODS)-reduced activation ferritic (RAF) steel, manufactured either from elemental powders or from an Fe-14Cr-2W-0.3Ti pre-alloyed powder. ODS RAF steels have been produced by mechanical alloying of powders with 0.3 wt% Y2O3 nanoparticles in either a planetary ball mill or an attritor ball mill, for 45 and 20 h, respectively, followed by hot isostatic pressing (HIPping) at 1,150 degrees C under a pressure of 200 MPa for 4 h and heat treatment at 850 degrees C for 1 h. It was found that the elemental ODS steel powder contains smaller particles with a higher specific surface area and a two times higher oxygen amount than the pre-alloyed ODS steel powder. After HIPping both materials exhibit a density higher than 99%. However, the pre-alloyed ODS steel exhibits a slightly better density than the elemental ODS steel, due to the reduced oxygen content in the former material. Charpy impact experiment revealed that the pre-alloyed ODS steel has a much larger ductile-to-brittle transition temperature (DBTT) (about 140 degrees C) than the elemental ODS steel (about 25 degrees C). However, no significant difference in the upper shelf energy (about 3.0 J) was measured. TEM and SEM-EBSD analyses revealed that the microstructure of the elemental ODS steel is composed of smaller grains with a larger fraction of high-angle grains (>15 degrees) and a lower dislocation density than the pre-alloyed ODS steel, which explains the lower DBTT value obtained for the elemental ODS steel