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Eingeladener Vortrag
- nein (17)
Bioglass® 45S5 is mainly used clinically as powders, granules or pastes instead of sintered compacts. This is due to the inherent problem of crystallization during the sintering, which results in poor mechanical properties and reduced bioactivity. Recently, new bioactive glasses with improved crystallization stability have been developed as promising candidates for manufacturing of sintered powder compacts for bone regeneration, which combine improved sintering behavior with bioactivity. Compared with the well-known Bioglass® 45S5 (SiO2-P2O5-CaO-Na2O) the calcium/alkali oxide ratio was increased, sodium oxide was partially replaced by potassium oxide and up to 3 mol% calcium fluoride were added, in order to stabilize the glass against crystallization. The aim of this study was to investigate the sintering and crystallization behavior of these new bioactive glasses.
Sintering and crystallization were characterized by heating microscopy, XRD, FTIR, SEM, and DTA. The results show that a sintered density of 88-99 % is achieved in contrast to only 57-67% for Bioglass® 45S5. In addition, FTIR and XRD analyses show that Bioglass® 45S5 crystallized during sintering while for the new glasses no crystalline phases are detected. The thermal properties of all glasses were studied by DTA measurements, and the influence of grain size was characterized. These studies showed that full densification can be attained for particle size < 32 µm, whereas coarser particles progressively increase residual porosity. Observed foaming phenomena, are strongly retarded by crystallization of beta-HAp.
Nowadays, the use of bioactive glasses is established for bone regeneration; however glasses are used mostly as powders, granules or in a paste. Sintered scaffolds are not used clinically, because of the in inherent problem of crystallization during the sintering process, resulting in poor mechanical properties and reduced bioactivity. The aim of this study was therefore to design new bioactive glasses, which combine improved processing and sintering with bioactivity.
Compared with the well-known Bioglass® 45S5 (SiO2-P2O5-CaO-Na2O) the calcium/alkalioxide ratio was increased, sodiumoxide was partially replaced by potassiumoxide and up to 8 mol% calciumflorid were added, in order to stabilize the glass against crystallization.
The sintering behavior of the new glasses was characterized by heating microscopy and compared to Bioglass® 45S5. The results showed that the new glasses achieved a sintered density of 88-99 % in contrast to only 57-67% for Bioglass® 45S5. In addition FTIR and XRD analyses showed that Bioglass® 45S5 crystallized during sintering while for the new glasses no crystalline phases were detected. The thermal properties of all glasses were studied by DTA and DSC measures, and the influence of grain size and heating rate were characterized. These studies showed a shift of start and end temperature of sintering process as well as the final density. The structure of sintered specimens during and after sintering was examined using light and electron microscopy (REM).
Phänominilogische Studien des Blähens von bioactiven Gläsern verschiedener Zusammensetzung und Unteruschung des Einflusses einer Kristallisation. Die ausgasenden Komponenten wurden mittels Vakuumheißextraktion(VHE) und Infrarotspektroskopie identifiziert sowie der Einfluss von Korngröße, Mahldauer und -atmosphäre auf das Blähen unterucht.
SASfit: a tool for small-angle scattering data analysis using a library of analytical expressions
(2015)
SASfit is one of the mature programs for small-angle scattering data analysis and has been available for many years. This article describes the basic data processing and analysis workflow along with recent developments in the SASfit program package (version 0.94.6). They include (i) advanced algorithms for reduction of oversampled data sets, (ii) improved confidence assessment in the optimized model parameters and (iii) a flexible plug-in system for custom user-provided models. A scattering function of a mass fractal model of branched polymers in solution is provided as an example for implementing a plug-in. The new SASfit release is available for major platforms such as Windows, Linux and MacOS. To facilitate usage, it includes comprehensive indexed documentation as well as a web-based wiki for peer collaboration and online videos demonstrating basic usage. The use of SASfit is illustrated by interpretation of the small-angle X-ray scattering curves of monomodal gold nanoparticles (NIST reference material 8011) and bimodal silica nanoparticles (EU reference material ERM-FD-102).
A user-friendly open-source Monte Carlo regression package (McSAS) is presented, which structures the analysis of small-angle scattering (SAS) using uncorrelated shape-similar particles (or scattering contributions). The underdetermined problem is solvable, provided that sufficient external information is available. Based on this, the user picks a scatterer contribution model (or 'shape') from a comprehensive library and defines variation intervals of its model parameters. A multitude of scattering contribution models are included, including prolate and oblate nanoparticles, core-shell objects, several polymer models, and a model for densely packed spheres. Most importantly, the form-free Monte Carlo nature of McSAS means it is not necessary to provide further restrictions on the mathematical form of the parameter distribution; without prior knowledge, McSAS is able to extract complex multimodal or odd-shaped parameter distributions from SAS data. When provided with data on an absolute scale with reasonable uncertainty estimates, the software outputs model parameter distributions in absolute volume fraction, and provides the modes of the distribution (e.g. mean, variance etc.). In addition to facilitating the evaluation of (series of) SAS curves, McSAS also helps in assessing the significance of the results through the addition of uncertainty estimates to the result. The McSAS software can be integrated as part of an automated reduction and analysis procedure in laboratory instruments or at synchrotron beamlines.
The combination of tomographic, microstructural data with other experimental techniques and with modeling is paramount, if we want to extract the maximum amount of information on material and component properties. In particular, quantitative image analysis, statistical approaches, direct discretization of tomographic reconstructions represent concrete possibilities to extend the power of the tomographic 3D representation to insights into the material and component performance. This logic thread holds equally for industrial and academic research, and valorizes expensive experiments such as those carried out at synchrotron sources, which cannot be daily repeated.
I will show a few examples of possible use of X-ray tomographic data for quantitative assessment of damage evolution and microstructural properties, as well as for non-destructive testing. Examples of micro-structured inhomogeneous materials will be given, such as Composites, Ceramics, Concrete, and Additively manufactured parts. I will also show how X-ray refraction computed tomography (CT) can be highly complementary to classic absorption CT, being sensitive to internal interfaces.
Mg-Y,RE-Zn systems present second phases with high thermal stability, promoting the increase of strength and creep resistance at high temperatures.
Mg and its alloys have a potential application as biomaterials due to their biocompatibility and degradation behaviour. The dominant corrosion mechanism in those alloys is the microgalvanic corrosion through coupling of the more noble second phases with the Mg matrix, and therefore a low concentration of those was sought.
This paper deals with the initiation and propagation of corrosion in mortar specimens precracked under mechanical loading and carbonated in climate accelerated conditions (50 % CO2–65 % RH)for 15–23 weeks. Mechanical loading led to transverse macro-cracks and damage at the steel-mortar interface characterized by micro-cracks (cover controlled cracking) which favour the carbonation of crack walls and the interface with the steel bar. Wetting–drying cycles performed after carbonation favoured corrosion initiation all along the steel bar because of the carbonated interface and corrosion propagation because of the creation of corrosion cracks which appear to develop from the micro-cracks induced by the mechanical load. Results also show that rust develops all around the perimeter of the carbonated steel bar but that the corrosion layer is thicker in the lower half surface of the reinforcement than that observed in the upper half. Results indicate that the distribution and composition of corrosion products depend on the thickness of the rust layer and that the multilayered structure of rust depends mainly on its thickness.
The new standard ‘ISO 17636-2:2013: Non-destructive testing of welds — Radiographic testing — Part 2: X- and gamma-ray techniques with digital detectors’, defines the practice for radiographic inspection of welded pipes for manufacturing and in-service inspection. It is applied in Europe for inspections of pipe welds in nuclear power plants as well as in chemical plants and allows a faster inspection with digital detector arrays (DDA) than with film. Nevertheless, it does not allow the evaluation of the depth and shape of volumetric and planar indications. In 2001 a planar tomography scanner, TomoCAR, was introduced for mechanized radiographic testing (RT) inspection and non-destructive measurement of cross sections. The project TomoWELD is based on a new concept of the scan geometry, an enhanced GPU based reconstruction, and the application of a new generation of photon counting DDAs based on CdTe crystal CMOS hybrids. The new detector permits the selection of energy thresholds to obtain an optimum energy range and reduction of the influence of scattered radiation. The concept and first measurements are presented. Flaw depth and shape of volumetric and planar irregularities can be determined.