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- earth block masonry (2)
- partial safety factors (2)
- uniaxial compression test (2)
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The potential of electrospray deposition, for the controlled preparation of particles for imaging in electron microscopes, is evaluated on various materials: from mono-modal suspensions of spherical particles to multimodal suspensions and to real-world industrial materials. It is shown that agglomeration is reduced substantially on the sample carrier, compared with conventional sample preparation techniques. For the first time, it is possible to assess the number concentration of a tri-modal polystyrene suspension by electron microscopy, due to the high Deposition efficiency of the electrospray. We discovered that some suspension stabilizing surfactants form artifact particles during electrospraying. These can be avoided by optimizing the sprayed suspension.
Ziel der vorliegenden Untersuchung war es zu überprüfen, inwiefern eine Bemessungsvorschrift auf Basis von Teilsicherheitsbeiwerten im Lehmmauerwerksbau möglich ist. Bemessungsvorschriften im konventionellen Mauerwerksbau und im Lehmmauerwerksbau waren aufgrund des prinzipiell gleichen Tragverhaltens stets eng miteinander verknüpft. Die im Rahmen dieser Arbeit durchgeführten Druckversuche an Lehmmauermörtel, Lehmsteinen und Lehmmauerwerk konnten zeigen, dass die Streuungen der Festigkeiten von Lehmbaustoffen aufgrund der industriellen Herstellung sehr gering sind. Es konnte festgestellt werden, dass eine Bemessung auf Grundlage des semiprobabilistischen Bemessungskonzeptes in Anlehnung an den konventionellen Mauerwerksbau möglich ist. Neben einem ersten Vorschlag des Teilsicherheitsbeiwertes für den Lastzustand Druck werden Vorschläge für Prüfvorschriften im Lehmbau beziehungsweise deren Modifikation unterbreitet und künftige Forschungsschwerpunkte herausgearbeitet.
The potential of electrospray deposition, for the controlled preparation of particles for imaging in electron microscopes, is evaluated on various materials: from mono-modal suspensions of spherical particles to multimodal suspensions and to real-world industrial materials. It is shown that agglomeration is reduced substantially on the sample carrier, compared with conventional sample preparation techniques. For the first time, it is possible to assess the number concentration of a tri-modal polystyrene suspension by electron microscopy, due to the high deposition efficiency of the electrospray. We discovered that some suspension stabilizing surfactants form artifact particles during electrospraying. These can be avoided by optimizing the sprayed suspension.
The goal of the present study is to assess the feasibility to develop a first reliable database of materials parameters for Earth Block Masonry (EBM). The database is crucial when defining the materials safety factors. In the first part an experimental campaign of compressive tests were carried out on two types of earth block and two types of earth mortar. The results showed that the mean variation of the compressive strength was remarkably less than expected. This low variation is related to a production with high quality standards of the materials employed. In the second part a partial safety factor for EBM under uniaxial compression was determined through the reliability method. The results proved the reliability of a common calculation method for EBM based on partial safety factors following the current standards.
In the beginning of the 1980s earth building has undergone a renaissance, which nowadays leads to an increasing use of load-bearing earth constructions and in particular, earth block masonry. At present there are no common structural standards according to the semi-probabilistic calculation concept, which is the state-of-the-art in European standards. A solid database is needed for the determination of the materials partial safety factor. Therefore, compressive strength tests were carried out with two types of earth blocks and two types of prefabricated earth mortar. The evaluation showed that the variation of the compressive strength was remarkably less than expected, which seems to indicate high quality standards of the components earth block and mortar with regard to industrial production. On the basis of these results and together with the reliability method, a partial safety factor for earth block masonry subjected to compression was determined. The main aim of the research was the development of a first valid database for material parameters of earth block masonry with particular regard to statistical characteristics. The results showed that a common calculation method for earth block masonry based on partial safety factors following the valid masonry construction standard is feasible.
Evaluation of electron microscopy techniques for the purpose of classification of nanomaterials
(2016)
One current and much-debated topic in the characterization of nanomaterials (NM) is the implementation of the recently introduced recommendation on a definition of a nanomaterial by the European Commission. According to this definition, a material is a NM when for 50% or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm-100 nm. The European NanoDefine Project was set up to develop and validate a robust, readily implementable and cost-effective measurement approach to obtain a quantitative particle size distribution and to distinguish between NMs and non-NMs according to the definition.
All currently available sizing techniques able to address nanoparticles were systematically evaluated. It was demonstrated that particle sizing techniques like: analytical centrifugation, particle tracking analysis, single-particle inductively coupled plasma mass-spectrometry, differential electrical mobility analysis, dynamic light scattering, small angle X-ray scattering, ultrasonic attenuation spectrometry, but also gas adsorption analysis based on the BET-method can be applied for a screening classification. However, the quality of the results depends on the individual material to be classified. For well-dispersed, nearly spherical (nano)particles most of the sizing techniques can be applied in a quick and reliable way. In contrast, the classification of most real-world materials is a challenging task, mainly due to non-spherical particle shape, large polydispersity or strong agglomeration/aggregation of the particles. In the present study it was shown that these issues can be resolved in most cases by electron microscopy as a confirmatory classification technique.
Electron microscopy techniques such as TEM, STEM, SEM or TSEM (transmission in SEM) are capable of assessing the size of individual nanoparticles accurately. Nevertheless the challenging aspect is sample preparation from powder or liquid form on the substrate, so that a homogeneous distribution of well-separated (deagglomerated) particles is attained. The systematic study in this work shows examples where the extraction of the critical, smallest particle dimension - as the decisive particle parameter for the classification as a NM - is possible by analysing the sample after its simple, dry preparation. The consequences of additional typical issues like loss of information due to screening of smaller particles by larger ones or the (in)ability to access the constituent particles in aggregates are discussed.
By means of practical examples the inherent statistical evaluation of the particle size is highlighted together with all its pitfalls such as setting of a suitable threshold for delimitation of the particle .
Evaluation of electron microscopy techniques for the purpose of classification of nanomaterials
(2016)
Electron microscopy techniques such as TEM, STEM, SEM or TSEM (transmission in SEM) are capable of assessing the size of individual nanoparticles accurately. Nevertheless, the challenging aspect is sample preparation from powder or liquid form on the substrate, so that a
homogeneous distribution of well-separated (deagglomerated) particles is attained. The systematic study in this work shows examples where the extraction of the critical, smallest particle dimension - as the decisive particle parameter for the classification as a NM - is possible by analysing the sample after ist simple, dry preparation. The consequences of additional typical issues like loss of information due to screening of smaller particles by larger ones or the (in)ability to access the constituent particles in aggregates are discussed.
Evaluation of electron microscopy techniques for the purpose of classification of nanomaterials
(2016)
One current and much-debated topic in the characterization of nanomaterials (NM) is the implementation of the recently introduced recommendation on a definition of a nanomaterial by the European Commission.
All currently available sizing techniques able to address nanoparticles were systematically evaluated. It was demonstrated that particle sizing techniques like: analytical centrifugation, particle tracking analysis, single-particle inductively coupled plasma mass-spectrometry, differential electrical mobility analysis, dynamic light scattering, small angle X-ray scattering, ultrasonic attenuation spectrometry, but also gas Adsorption analysis based on the BET-method can be applied for a screening classification. However, the quality of the results depends on the individual material to be classified. For well-dispersed, nearly spherical (nano)particles most of the sizing techniques can be applied in a quick and reliable way. In contrast, the classification of most real-world materials is a challenging task, mainly due to non-spherical particle shape, large polydispersity or strong agglomeration/ aggregation of the particles. In the present study it was shown that these issues can be resolved in most cases by electron microscopy as a confirmatory classification technique.
Electron microscopy techniques such as TEM, STEM, SEM or TSEM transmission in SEM) are capable of assessing the size of individual nanoparticles accurately (see Figures 1 and 2). Nevertheless the challenging aspect is sample preparation from powder or liquid form on the substrate, so that a homogeneous distribution of well-separated (deagglomerated) particles is attained. The systematic study in this work shows examples where the extraction of the critical, smallest particle dimension - as the decisive particle parameter for the classification as a NM - is possible by analysing the sample after its simple, dry preparation. The consequences of additional typical issues like loss of information due to Screening of smaller particles by larger ones or the (in)ability to access the constituent particles in aggregates are discussed.
In the beginning of the 1980s earth building has undergone a renaissance, which nowadays leads to an increasing use of load-bearing earth constructions and in particular, earth block masonry. At present, there are no common structural standards according to the semi-probabilistic design concept, which is the state-of-the-art in European standards.
A solid database is needed for the determination of the partial safety factor on the resistance side. Therefore, compressive strength tests were carried out with two types of earth blocks and two types of prefabricated earth mortar. The evaluation showed that the variation of the compressive strength was remarkably less than expected, which seems to indicate high quality standards of the components earth block and mortar with regard to industrial production.
On the basis of these results and together with the reliability method, a partial safety factor for earth block masonry subjected to compression was determined. The main aim of the research was the development of a first valid database for material parameters of earth block masonry with particular regard to statistical characteristics. The results showed that a common calculation method for earth block masonry based on partial safety factors following the valid masonry construction standard is feasible.
Condensed-phase mechanisms play a major role in fire-retardant polymers. Generations of development have followed the concept of charring to improve fire properties. Whereas the principal reactions are believed to be known, the specific description for multicomponent systems is lacking, as is the picture across different systems. A two-step approach is proposed in general, and also presented in greater detail. The second step covers the specific reactions controlling charring, whereas the actual reactants are provided in the preceding step. This model consistently incorporates the variety of structureproperty relationships reported. A comprehensive case study is presented on seven phosphorus flame retardants in two epoxy resins to breathe life into the two-step approach.