Micromachining of hardened Portland cement pastes using femtosecond laser pulses

Femtosecond laser pulses (30fs in length) of various energies were utilised for production of single and multiple overlapping ablation sites on flat polished surfaces of hardened Portland cement pastes. In order to assess the sizes of the ablation sites and possible subsurface laser-induced damage, the ablation sites were investigated using environmental scanning electron microscopy (ESEM) - both from normal top-down view and in cross-sections. Furthermore, approximately 10-µm wide notches were produced using femtosecond pulses on cylindrical microspecimens (150µm in diameter) of hardened Portland cement pastes. In addition to electron microscopy observations, several microspecimens were investigated using synchrotron-based X-ray computed microtomography (SRμCT). The results suggest that production of "damage-free” samples for micromechanical testing of hardened Portland cements pastes is possibl

A Monte Carlo approach for scattering correction towards quantitative neutron imaging of polycrystals

The development of neutron imaging from a qualitative inspection tool towards a quantitative technique in materials science has increased the requirements for accuracy significantly. Quantifying the thickness or the density of polycrystalline samples with high accuracy using neutron imaging has two main problems: (i) the scattering from the sample creates artefacts on the image and (ii) there is a lack of specific reference attenuation coefficients. This work presents experimental and simulation results to explain and approach these problems. Firstly, a series of neutron radiography and tomography experiments of iron, copper and vanadium are performed and serve as a reference. These materials were selected because they attenuate neutrons mainly through coherent (Fe and Cu) and incoherent (V) scattering. Secondly, an ad hoc Monte Carlo model was developed, based on beamline, sample and detector parameters, in order to simulate experiments, understand the physics involved and interpret the experimental data. The model, developed in the McStas framework, uses a priori information about the sample geometry and crystalline structure, as well as beamline settings, such as spectrum, geometry and detector type. The validity of the simulations is then verified with experimental results for the two problems that motivated this work: (i) the scattering distribution in transmission imaging and (ii) the calculated attenuation coefficients.</jats:p

Aspects of micromechanical properties of cement-based materials

Available from British Library Document Supply Centre-DSC:DX214217 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Micromachining of hardened Portland cement pastes using femtosecond laser pulses

ISSN:1359-5997ISSN:0025-5432ISSN:1871-687

Hard X-ray Phase-Contrast Tomographic Nanoimaging

Synchrotron‐based full‐field tomographic microscopy established itself as a tool for noninvasive investigations. Many beamlines worldwide routinely achieve micrometer spatial resolution while the isotropic 100‐nm barrier is reached and trespassed only by few instruments, mainly in the soft x‐ray regime. We present an x‐ray, full‐field microscope with tomographic capabilities operating at 10 keV and with a 3D isotropic resolution of 144 nm recently installed at the TOMCAT beamline of the Swiss Light Source. Custom optical components, including a beam‐shaping condenser and phase‐shifting dot arrays, were used to obtain an ideal, aperture‐matched sample illumination and very sensitive phase‐contrast imaging. The instrument has been successfully used for the nondestructive, volumetric investigation of single, unstained cells