ORCID Profile
0000-0002-6986-2982
Current Organisation
Eberhard Karls Universität Tübingen
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Elsevier BV
Date: 02-2015
Publisher: Trans Tech Publications, Ltd.
Date: 05-2004
Publisher: Elsevier BV
Date: 2004
Publisher: Elsevier BV
Date: 03-1996
Publisher: Wiley
Date: 08-2003
Publisher: Elsevier
Date: 2012
Publisher: Elsevier BV
Date: 08-2015
DOI: 10.1016/J.JHEVOL.2015.05.001
Abstract: South Africa has in recent years gained increasing importance for our understanding of the evolution of 'modern human behaviour' during the Middle Stone Age (MSA). A key element in the suite of behaviours linked with modern humans is heat treatment of materials such as ochre for ritual purposes and stone prior to tool production. Until now, there has been no direct archaeological evidence for the exact procedure used in the heat treatment of silcrete. Through the analysis of heat-treated artefacts from the Howiesons Poort of Diepkloof Rock Shelter, we identified a hitherto unknown type of organic residue - a tempering-residue - that sheds light on the processes used for heat treatment in the MSA. This black film on the silcrete surface is an organic tar that contains microscopic fragments of charcoal and formed as a residue during the direct contact of the artefacts with hot embers of green wood. Our results suggest that heat treatment of silcrete was conducted directly using an open fire, similar to those likely used for cooking. These findings add to the discussion about the complexity of MSA behaviour and appear to contradict previous studies that had suggested that heat treatment of silcrete was a complex (i.e., requiring a large number of steps for its realization) and resource-consuming procedure.
Publisher: Wiley
Date: 10-2000
DOI: 10.1002/1521-4117(200010)17:3<113::AID-PPSC113>3.0.CO;2-Z
Publisher: Elsevier BV
Date: 2005
Publisher: Elsevier BV
Date: 07-2011
Publisher: Wiley
Date: 20-12-2004
Publisher: Royal Society of Chemistry (RSC)
Date: 1996
DOI: 10.1039/JM9960600595
Publisher: Informa UK Limited
Date: 17-01-2020
Publisher: Elsevier BV
Date: 03-2009
Publisher: Elsevier BV
Date: 2004
Publisher: Wiley
Date: 20-06-2011
Publisher: IMAPS - International Microelectronics Assembly and Packaging Society
Date: 07-2018
DOI: 10.4071/IMAPS.661015
Abstract: Enhancements on power electronic systems with reduced chip area and miniaturized passive components are subject of several research activities in academics and industry. To realize such future electronic devices, it is necessary to incorporate wide bandgap semiconductor technology such as silicon carbide and gallium nitride operating at higher temperatures. Therefore, the development of novel materials with high thermal conductivities and stability, withstanding harsh environments up to 300°C is of major interest. Especially, polymeric encapsulation materials have to be improved because of common degradation effects above 175°C. Ceramic (nonpolymeric) materials with thermal conductivities above 5 W/(m·K) already illustrated promising results for the encapsulation of power electronics. The present work illustrates recent developments and improvements on novel ceramic encapsulation materials, which finally avoid critical interactions with the chip surface. Furthermore, advances in reliability will be discussed in terms of passed high-temperature reverse bias and humidity tests correlated with relevant material properties.
Publisher: Wiley
Date: 10-07-2009
DOI: 10.1002/JRS.2361
Publisher: Elsevier BV
Date: 2005
Publisher: Elsevier BV
Date: 07-2005
Publisher: Elsevier BV
Date: 08-2010
Publisher: Springer Science and Business Media LLC
Date: 09-1985
DOI: 10.1007/BF00429426
Publisher: AIP Publishing
Date: 04-1997
DOI: 10.1063/1.364340
Abstract: Combining hardness indentation tests and micro-Raman spectroscopy it is shown that metallic Si-II is produced near the interface of a diamond indenter and silicon to a depth of about 0.5 μm, where the highest stresses (hydrostatic and deviatoric) exist. At fast unloading rates Si-II transforms to the amorphous state, whereas a mixture of the r8 high pressure polymorph Si-XII and the bc8 phase Si-III forms upon a slow load release. The region of Si-III+Si-XII is surrounded by the wurtzite structured Si-IV, where the stresses during the indentation had not been high enough to cause the transition to the metallic state. Thus, because of shear deformation a direct transformation to Si-IV takes place. Outside the phase-transformed regions the classical aspects of indentation-induced deformation by dislocation glide, twinning and crack formation are observed. Annealing of the high pressure phases leads to the formation of Si-IV at moderate temperatures and to the reversal to the original diamond structure (Si-I) at temperatures above 500 °C. Using the laser beam of the Raman spectrometer to anneal the s les the phase transitions could be monitored directly. The formation of silicon polymorphs other than amorphous or metallic structures during hardness indentation is, to the best of our knowledge, reported here for the first time. The results compare well with the polymorphism in Si that is known from diamond anvil cell experiments.
Publisher: Elsevier BV
Date: 04-2003
Publisher: Springer Science and Business Media LLC
Date: 2011
DOI: 10.1557/PROC-499-225
Abstract: High-pressure phase transformations occurring in materials are important for a wide range of problems in materials science and engineering. Most of the results in this field have been obtained using high-pressure cells. In this work, we demonstrate that high-pressure phase transformations also take place during mechanical contact of hard solid materials. These solid-state transformations can be studied by simply combining hardness indentation tests with micro-Raman spectroscopy. In contrast to diamond anvil cell (DAC) experiments, the stress conditions during mechanical contacts are highly non-hydrostatic, i.e. very high shear stresses affect the transformation behavior. Nevertheless, the obtained results can be discussed in the light of the phase transformations as known from DAC experiments. The ex les of our research presented here include Si, Ge, SiO 2 and ZrO 2 , and show that phase transformations and amorphization at mechanical contacts are a quite common phenomenon, which has important implications.
Publisher: Elsevier BV
Date: 2021
Publisher: Elsevier BV
Date: 2005
Publisher: AIP Publishing
Date: 08-2008
DOI: 10.1063/1.2965210
Abstract: The hydrothermal diamond anvil cell (HDAC) is an excellent tool for high-temperature, high-pressure (hydrothermal) experiments. For an accurate determination of pressure induced by a certain temperature in an isochoric s le chamber volume, an equation of state (EOS) of water can be used instead of direct measurement. This paper reviews the theoretic background and provides all needed equations for the application of EOS of water to HDAC experiments summarizing state-of-the-art knowledge and incorporating up-to-date thermodynamic data. The p-T conditions determined using the IAPWS-95 formulation for the thermodynamic properties of ordinary water are in agreement with values obtained from direct methods or other established EOS formulations. In particular, (1) the calculation of density through the (a) melting point or (b) homogenization method along with determining (2) pressure as a function of density and temperature or (3) density as a function of pressure and temperature is explained. As a new aspect in the context of HDAC operations, the critical influence of nucleation and a strategy to overcome this problem are discussed. Furthermore, we have derived new polynomial equations, which allow the direct calculation of the fluid phase’s density from the melting temperature. These are implemented in a spreadsheet program, which is freely available for interested users.
Publisher: Springer Science and Business Media LLC
Date: 09-2009
Publisher: Elsevier BV
Date: 10-1998
Publisher: Springer International Publishing
Date: 2016
Publisher: Trans Tech Publications, Ltd.
Date: 04-2007
DOI: 10.4028/WWW.SCIENTIFIC.NET/KEM.336-338.1823
Abstract: Sodium-rich glasses of the system Na2O-SiO2 are well known to be easily soluble in water. This is not true for silica-rich compositions. We have manufactured quenched glasses with silica contents between 65 and 80 wt.% SiO2 and followed the water interaction at 100°C by measuring mass and s le dimensions in intervals. Comparing the path of edge length, mass and volume to a general shrinking core model for cuboids we conclude that only compositions between 65 and 70 wt% SiO2 can be described well by a simple dissolution process. The logarithm of the dissolution rate constant varies linearly with the SiO2 content. At higher silica contents the mechanism changes towards leaching of sodium. We propose changing glass structures to be responsible for the change in mechanism.
Publisher: Springer International Publishing
Date: 2016
Publisher: John Wiley & Sons, Inc.
Date: 04-2009
Publisher: Wiley
Date: 25-08-2022
DOI: 10.1111/ARCM.12820
Abstract: Birch tar was the first adhesive produced by humans. Its study has consequences for our understanding of human evolution and the development of specialised craftsmanship. One of the better‐documented birch tar making methods is the ‘double‐pot’ technique, where two containers are used, one containing bark, the other collecting the tar. Birch tar made with double‐pots has low viscosity and bad adhesive properties. To obtain a usable adhesive, it must be reduced in volume by cooking. We investigate the evolution of tar’s mechanical properties during cooking. We use lap‐shear tests to investigate strength, stiffness and failure behaviour. We found that tar must be cooked for 90 min to acquire adhesive properties. When cooked for longer, strength and stiffness increase over a 30 min lasting time span. Cooking for even longer, beyond this 30 min window, produced a substance that could no longer be used as an adhesive. The implications are that tar cooking requires a high level of skill because specific signs indicating the desired properties must be recognised during the process. Tar cooking constitutes a supplementary investment in time and resources and appears to be associated with a certain degree of risk.
Publisher: Springer Science and Business Media LLC
Date: 20-09-2018
Publisher: Wiley
Date: 03-2006
Publisher: WIP
Date: 2017
Publisher: AIP Publishing
Date: 08-1998
DOI: 10.1063/1.368198
Abstract: The stability of diamond under pressure and the structure of hypothetical high-pressure phases have been a controversial issue for a long time. “Will diamond transform under megabar pressures?” asked Yin and Cohen in the title of their paper [Phys. Rev. Lett. 50, 2006 (1983)] which attempted to predict an answer to this question 15 years ago. Before and after that, many other scientists tried to find the answer doing both modeling and experiments. However, the cubic structure of diamond seems to be experimentally stable up to the highest static pressures that the modern high-pressure technology can achieve. We addressed the problem by decreasing the contact area of pressurization instead of increasing the total load. Experimentally this can be easily done in indentation tests using a sharp diamond indenter. In addition to hydrostatic stresses, such a test creates shear stresses as well. Here deformations may be realized, which are either impossible or would require much higher pressures when utilizing only hydrostatic stresses. By coupling the indentation loading with micro-Raman spectroscopy, we were able to drive and monitor phase transformations in diamond. A very similar phenomenon can be observed by scratching a diamond with another diamond. Thus, phase transformations in diamond may in fact be a very common feature of wear.
Publisher: Trans Tech Publications, Ltd.
Date: 04-2007
DOI: 10.4028/WWW.SCIENTIFIC.NET/KEM.336-338.1780
Abstract: Corrosion experiments on a number of rare earth di-silicates containing Y, Yb and Lu have been conducted in flowing air with 30 vol.% H2O at 1500°C. Nominally the corrosion rate is slower by a factor 5 to 10 compared to silica. However, alumina impurity incorporation has a profound influence on the process of corrosion as it masks not only the gravimetric results but also changes the surface phase assemblages to contain rare earth garnets and liquid phases. It is presumed that silica loss occurs under those conditions via the liquid phase and does not necessarily follow the same kinetics as direct silicate corrosion. Furthermore, atmospheric silicon hydroxide saturation effects contribute to the corrosion process. Currently all determined corrosion rates of rare earth silicates are viewed as system specific only.
Publisher: IOP Publishing
Date: 19-12-2018
Abstract: The calcitic spines of the sea urchins Heterocentrotus mamillatus and H. trigonarius are promising role models for lightweight applications, bone tissue scaffolds and energy dissipating processes due to their highly porous and organized structure. Therefore, mechanical properties including Young's Modulus, strength, failure behaviour and energy dissipation efficiency have been investigated in depth with uniaxial compression experiments, 3-point bending tests and resonance frequency d ing analysis. It was found that despite a very similar structure, H. trigonarius has a significantly lower porosity than H. mamillatus leading to a higher strength and Young's Moduli, but limited ability to dissipate energy. In order to show reliable energy dissipation during failure in uniaxial compression, a transition porosity of 0.55-0.6 needs to be exceeded. The most effective structure for this purpose is a homogeneous, foam-like structure confined by a thin and dense shell that increases initial strength and was found in numerous spines of H. mamillatus. Sharp porosity changes induced by dense growth layers or prominent wedges of the spines' radiating building principle act as structural weaknesses, along which large flakes can be spalled, reducing the energy dissipation efficiency considerably. The high strength and Young's Modulus at the biologically necessary high porosity levels of the spines is useful for Heterocentrotus and their construction therefore remains to be a good ex le of biomimetics. However, the energy dissipative failure behaviour may be regarded as a mere side effect of the structure.
Publisher: Elsevier BV
Date: 10-1985
Publisher: Elsevier BV
Date: 06-2018
Publisher: Elsevier BV
Date: 07-2009
Publisher: Springer International Publishing
Date: 2016
Publisher: Wiley
Date: 10-1999
DOI: 10.1002/(SICI)1097-4555(199910)30:10<939::AID-JRS460>3.0.CO;2-C
Publisher: Informa UK Limited
Date: 06-1997
Publisher: Trans Tech Publications, Ltd.
Date: 11-2012
DOI: 10.4028/WWW.SCIENTIFIC.NET/KEM.529-530.589
Abstract: This work follows a study on hydrothermal aged 3Y-TZP bioceramics, which showed that the surface X-ray diffraction data from moisture exposed s les give distorted results, reflecting a simple linear growth of a partially transformed layer from the surface into the interior. There is no indication for a leveling off or retardation of this growth at elevated temperatures (134°C) and here we present evidence that this is probably true at body temperatures as well. However, the rate constants at body temperature for the studied material are low and indicate a long lifetime. It should be noted that this statement is specific and other materials with minor changes to chemistry or microstructure may behave much better or much worse under those conditions. Furthermore slow crack growth and crack interactions are not yet investigated and may necessitate a minimum of low-temperature degradation susceptibility to ensure reliable long-time use.
Publisher: Informa UK Limited
Date: 13-02-2008
Publisher: Elsevier BV
Date: 2007
Publisher: Springer Science and Business Media LLC
Date: 09-1998
Publisher: Elsevier BV
Date: 12-1998
Publisher: Springer Science and Business Media LLC
Date: 15-12-2010
Publisher: Elsevier BV
Date: 02-2014
DOI: 10.1016/J.ACTBIO.2013.09.033
Abstract: We present new findings on the low-temperature degradation of yttria-stabilized zirconia at 37°C over several years and at high and low partial pressures of water. With the aid of focused ion beam cross-section confirmation studies we are able to show an extensive linear, continuous degradation without retardation, even at low temperatures and low water pressures. The characteristic layer growth and its inferred rate constant imply a lifetime of tens of years under simple tension and open the possibility of studying the longevity of these ceramics more rigorously. In addition, we show reproducibility complications of accelerated aging tests by the use of different autoclaves and possible implications for standardized procedures.
Publisher: AIP Publishing
Date: 07-2009
DOI: 10.1063/1.3159035
Abstract: The structural stability of the layered ternary carbide Ti3AlC2 was studied up to 35 GPa using x-ray diffraction with a Merrill–Basset-type diamond anvil cell and ab initio calculations. The structure (P63/mmc) was stable in the present pressure range without any phase transition. The Birch–Murnaghan equation of state was employed to fit the experimental pressure-volume date, from which the isothermal bulk modulus of Ti3AlC2 was determined as 156±5 GPa, which was also supported by theoretical results. In addition, theoretical calculations described anisotropic pressure dependences of the lattice parameters, electronic structure, and bonding properties of Ti3AlC2.
Publisher: Elsevier BV
Date: 05-1997
Publisher: Springer Science and Business Media LLC
Date: 06-2017
Publisher: Elsevier BV
Date: 1997
Publisher: Springer Berlin Heidelberg
Date: 15-11-2010
Publisher: Elsevier BV
Date: 06-2011
Publisher: Wiley
Date: 04-2010
Publisher: IEEE
Date: 05-2018
Publisher: Springer Science and Business Media LLC
Date: 04-2011
Abstract: This paper supplies new interpretation of nanoindentation data for silicon, germanium, and gallium arsenide based on Raman microanalysis of indentations. For the first time, Raman microspectroscopy analysis of semiconductors within nanoindentations is reported. The given analysis of the load-displacement curves shows that depth-sensing indentation can be used as a tool for identification of pressure-induced phase transformations. Volume change upon reverse phase transformation of metallic phases results either in a pop-out (or a kink-back) or in a slope change (elbow) of the unloading part of the load-displacement curve. Broad and asymmetric hysteresis loops of changing width, as well as changing slope of the elastic part of the loading curve in cyclic indentation can be used for confirmation of a phase transformation during indentation. Metallization pressure can be determined as average contact pressure (Meyer's hardness) for the yield point on the loading part of the load-displacement curve. The pressure of the reverse transformation of the metallic phase can be measured from pop-out or elbow on the unloading part of the diagram. For materials with phase transformations less pronounced than in Si, replotting of the loaddisplacement curves as average contact pressure versus relative indentation depth is required to determine the transformation pressures and/or improve the accuracy of data interpretation.
Publisher: Springer Science and Business Media LLC
Date: 2010
Abstract: Amorphous hydrogenated Si 1-x C x /SiC multilayers consisting of alternating Si 1-x C x and stoichiometric SiC layers were prepared using Plasma Enhanced Chemical Vapour Deposition (PECVD). Annealing at temperatures up to 1100°C was done targeting the size controlled crystallization of Si nanocrystals (NCs) in a SiC matrix. The influence of annealing temperature on the nanostructure of the multilayers was studied using Glancing Incidence X-ray Diffraction (GIXRD), Raman spectroscopy and Transmission Electron Microscopy (TEM). GIXRD reveal the crystallization of Si and SiC, when annealing temperatures exceed 900°C. The crystallization of Si and SiC was confirmed by TEM bright-field imaging and electron diffraction. Annealing at 900°C, leads to the formation of Si NCs with a size of 3 nm, whereas the SiC NCs also have a size of 3 nm. However, a large amount of Si is still amorphous as shown by Raman spectroscopy. Annealing at temperatures exceeding 900°C reduces the amorphous phase and a further growth of Si NCs occurs.
Publisher: Wiley
Date: 26-07-2015
DOI: 10.1111/IJAC.12434
Publisher: Proceedings of the National Academy of Sciences
Date: 19-08-2019
Abstract: We found a previously unknown way to produce birch tar. Instead of creating cognitively demanding structures (underground or in containers), this method consists of simply burning bark close to cobbles in a hearth. The tar is deposited on the stones and can be scraped off for use. This approach to interpreting early tar resolves the mystery of the associated and still not understood early technical complexity and provides a “discoverable” pathway to one of the earliest pyrotechnologies. These results have implications for our interpretation of birch tar in the archaeological record: Birch tar from early archaeological contexts alone can no longer indicate the presence of modern cognition and/or cultural behaviors in Neanderthals.
Publisher: Elsevier BV
Date: 08-2012
Publisher: Trans Tech Publications Ltd
Date: 27-10-2010
DOI: 10.4028/WWW.SCIENTIFIC.NET/AST.64.1
Abstract: Cordierite Mg2Al4Si5O18 is a material for diesel particulate filters (DPF) with high potential. Its resistance to a simplified model ash has been tested on single crystals at temperatures up to 1050°C, which are realistic for use under ‘worst case’ conditions. A mixture of Ca, Mg and Zn phosphates, which are typical main constituents of many DPF ashes, was used as model ash. Single crystals were examined in order to investigate the orientation dependence of attack due to the strongly anisotropic nature of the Cordierite crystal lattice. Strong corrosion by the ash occurs at 1050 °C, connected to excessive ash melting. The molten ash attacks Cordierite by fast dissolution of the substrate with melt (super)saturation within minutes. Anisotropy of the dissolution process could not be detected. The initial kinetics are dominated by saturation effects, which slow down corrosion. The saturated melt attacks Cordierite by reaction processes leading to the formation of new crystalline phases. This process is much slower than the initial dissolution process but may significantly contribute to the destruction of Cordierite substrates if large contact areas between ash melt and Cordierite exist.
Publisher: The Royal Society of Chemistry
Date: 19-06-2003
Publisher: AIP
Date: 2010
DOI: 10.1063/1.3482347
Publisher: Springer Science and Business Media LLC
Date: 10-1999
DOI: 10.1038/44323
Publisher: American Geophysical Union (AGU)
Date: 10-09-1990
Publisher: Wiley
Date: 12-01-2020
Publisher: Elsevier BV
Date: 08-2013
Publisher: Elsevier BV
Date: 03-2010
Publisher: Elsevier BV
Date: 04-2006
Publisher: Springer Science and Business Media LLC
Date: 04-1986
DOI: 10.1007/BF00374427
Publisher: Public Library of Science (PLoS)
Date: 22-04-2022
DOI: 10.1371/JOURNAL.PONE.0265640
Abstract: The study of lithic raw material quality has become one of the major interpretive tools to investigate the raw material selection behaviour and its influence to the knapping technology. In order to make objective assessments of raw material quality, we need to measure their mechanical properties (e.g., fracture resistance, hardness, modulus of elasticity). However, such comprehensive investigations are lacking for the Palaeolithic of Kazakhstan. In this work, we investigate geological and archaeological lithic raw material s les of chert, porphyry, and shale collected from the Inner Asian Mountain Corridor (henceforth IAMC). Selected s les of aforementioned rocks were tested by means of Vickers and Knoop indentation methods to determine the main aspect of their mechanical properties: their indentation fracture resistance (a value closely related to fracture toughness). These tests were complemented by traditional petrographic studies to characterise the mineralogical composition and evaluate the level of impurities that could have potentially affected the mechanical properties. The results show that materials, such as porphyry possess fracture toughness values that can be compared to those of chert. Previously, porphyry was thought to be of lower quality due to the anisotropic composition and coarse feldspar and quartz phenocrysts embedded in a silica rich matrix. However, our analysis suggests that different raw materials are not different in terms of indentation fracture resistance. This work also offers first insight into the quality of archaeological porphyry that was utilised as a primary raw material at various Upper Palaeolithic sites in the Inner Asian Mountain Corridor from 47–21 ka cal BP.
Publisher: Elsevier BV
Date: 06-2009
Publisher: Oxford University Press (OUP)
Date: 12-1990
Publisher: Trans Tech Publications, Ltd.
Date: 1992
Publisher: Elsevier
Date: 2010
Publisher: De Gruyter
Date: 18-12-2017
Publisher: Elsevier BV
Date: 09-2018
DOI: 10.1016/J.ACTBIO.2018.07.010
Abstract: According to the Weibull theory for brittle materials, the mean experimental strength decreases with test specimen size. For the brittle parts of an organism this would mean that becoming larger in size results automatically in reducing strength. This unfavorable relationship was investigated for two porous, biological materials that are promising concept generators for crack deflective and energy dissipative applications in compressive overloading: the quasi-brittle coconut endocarp and the brittle spines of the sea urchin Heterocentrotus mamillatus. Segments in different volumes were prepared and tested in uniaxial compression experiments. Failure of both materials is Weibull distributed underlining that it is caused by statistically distributed flaws in the structure. However, the coconut endocarp has a much higher Weibull modulus (m = 14.1-16.5) than the spines (m = 5). The more predictable failure of the endocarp is probably attributed to a rather homogeneous microstructural design and water bound in the structure. In terms of the spines it was found that the Weibull modulus is structure dependent: More homogeneous spines feature a higher Weibull modulus than spines with a heterogeneous structure. Whereas the nearly dense endocarp exhibited, although less pronounced, the expected decrease in strength with increase in size, the spines showed a failure independently of size. This remarkable behavior may be explained with their highly porous internal structure. Small and large spines consist of struts of similar size, which constitute the porous internal structure, potentially limiting the flaw size to the size of the strut regardless of the spine size. Scaling is an important aspect of the biomimetic work process, since biological role models and structures have rarely the same size as their technical implementations. The algorithms of Weibull are a standard tool in material sciences to describe scaling effects in materials whose critical strength depends on statistically distributed flaws. The challenge is to apply this theory (developed for homogeneous, isotropic technical materials) to brittle and quasi-brittle biological materials with hierarchical structuring. This study is a first approach to verify whether the Weibull theory can be applied to the coconut endocarp and to sea urchin spines in order to model their size/volume roperty-relations.
Publisher: Springer Science and Business Media LLC
Date: 20-01-2010
Publisher: De Gruyter
Date: 17-06-2019
Publisher: Elsevier BV
Date: 05-2010
Publisher: De Gruyter
Date: 17-06-2019
Publisher: Elsevier BV
Date: 1998
Publisher: Elsevier BV
Date: 06-2006
Publisher: Springer Science and Business Media LLC
Date: 11-2021
DOI: 10.1186/S40494-021-00621-1
Abstract: Birch tar is one of the oldest adhesives known in human history. Its production has been discussed in the framework of early complex behaviours and sophisticated cognitive capacities. The precise production method used in the Palaeolithic remains unknown today. Arguments for or against specific production pathways have been based on efficiency or process complexity. No studies have addressed the question whether birch tar made with different techniques is more or less performant in terms of its properties. We therefore investigate the adhesive performance of birch tar made with three distinct methods: the open-air condensation method and two variations of underground structures that approximate the double-pot method in aceramic conditions. We use lap-shear testing, a standard mechanical test used for testing the strength of industrial adhesives. Tar made in 1 h with the condensation method has a shear strength similar to, although slightly higher than, tar made underground if the underground process lasts for 20 h. However, tars from shorter underground procedures (5 h) are significantly less strong (by a factor of about 3). These findings have important implications for our understanding of the relationship between the investment required for Palaeolithic birch tar production and the benefits that birch tar represented for early technology. In this regard, the simple and low-investment open-air condensation method provides the best ratio.
Publisher: Elsevier BV
Date: 05-2001
Publisher: Wiley
Date: 12-05-2011
Publisher: Elsevier BV
Date: 04-2003
Publisher: Royal Society of Chemistry (RSC)
Date: 2000
DOI: 10.1039/A908030I
Publisher: Wiley
Date: 12-04-2011
Publisher: SAGE Publications
Date: 11-2009
DOI: 10.1366/000370209789806975
Abstract: This study provides experimentally determined values for the actual μ-Raman spectroscopy s ling depth in zirconia ceramics (ZrO, 2 ) via line scans on a wedge-shaped s le. Common instrumental settings with metallurgical objective lenses in dry air, argon-ion, and helium-neon laser radiation of approximately 10 mW were chosen. Under those conditions effective s ling depths, defined as the depth at which 99% of the information is recorded, range from 20 to more than 50 μm, depending on the numerical aperture of the lens and the laser wavelength. These results elucidate the pitfalls of the investigation of surface phenomena in zirconia ceramics such as low-temperature degradation or mechanically induced phase transformations by Raman spectroscopy.
Publisher: ASME International
Date: 1993
DOI: 10.1115/1.2906689
Abstract: The problems of high-temperature oxidation and corrosion of Si3N4 and SiC are discussed. Other ceramics usually do not meet the requirements of structural applications at high temperatures. If the application has to meet very defined limits of size change, it is necessary to specify the exact material composition, as well as the atmosphere composition and physical environment to be able to specify the limits. This is in any case true for extremely reducing conditions or very high temperatures. Under oxidizing conditions, the region between ≈850 and 1100°C should be avoided when salty, sulfurous, and wet fuel conditions are expected. High temperature limits for long-time applications of Si3N4 in oxidizing environments are between 1200 and 1400°C, corresponding to eutectic temperatures of the glass phase. The ultimate limit for long-time use of SiC is likely to be between 1700 and 1800°C, where bubble formation and spallation may become inevitable.
Publisher: Elsevier BV
Date: 02-2003
DOI: 10.1016/S0968-4328(03)00018-0
Abstract: Superconducting MgB(2) ceramics were prepared and yield superconducting transition temperatures of about 39 K. For covering the various length scales on which inhomogeneities appear in MgB(2), electron-probe micro-analysis (EPMA) and analytical transmission electron microscopy (TEM) were applied for a phase analysis. Particularly useful were the preliminary electron spectroscopic imaging (ESI) results in the TEM. It could be shown by EPMA that the microstructure consists of a Mg-B-O matrix and boron-rich secondary phases of composition close to MgB(12). It was unclear in which form oxygen was present in the superconducting matrix. By combining the acquisition of B-K and O-K edge jump ratio images and energy-dispersive X-ray spectroscopy in the TEM, we could prove that the matrix consists of superconducting MgB(2) and MgO. Most of the MgO precipitates and grains appear with diameters between 20 and 300 nm. The size distribution of MgO was inhomogeneous and oxygen-rich areas of dimensions >1 microm were also observed. Edge jump ratio images obtained by ESI were analysed for determining the signal values and effects of multiple inelastic scattering.
Publisher: John Wiley & Sons, Inc.
Date: 1998
Publisher: Wiley
Date: 03-2009
Publisher: Springer Science and Business Media LLC
Date: 10-07-2023
DOI: 10.1007/S12520-023-01798-1
Abstract: Pottery kilns are a common feature in the archaeological record of different periods. However, these pyrotechnological installations are still seldom the target of interdisciplinary investigations. To fill this gap in our knowledge, an updraft kiln firing experiment was run at the C us Galli open-air museum (southern Germany) by a team consisting of experimental archaeologists, material scientists, geoarchaeologists, and palaeobotanists. The entire process from the preparation of the raw materials to the firing and opening of the kiln was carefully recorded with a particular focus on the study of the raw materials used for pottery making, as well as on fuel usage. The temperatures were monitored by thermocouples placed at different positions in the combustion and firing chambers. In addition, thermocouples were installed within the kiln wall to measure the temperature distribution inside the structure itself. Unfired raw materials as well as controlled and experimentally thermally altered ceramic s les were then characterised with an integrated analysis including ceramic petrography, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and portable X-ray fluorescence (pXRF). Our work provides data about mineralogical and microstructural developments in both pottery kiln structures and the ceramics produced in this type of installations. This is helpful to discuss the limits and potential of various scientific analyses commonly used in ancient ceramic pyrotechnological studies. Overall, our work contributes to a better understanding of updraft kiln technology and offers guidelines on how to address the study of this type of pyrotechnological installations using interdisciplinary research strategies.
Publisher: Elsevier BV
Date: 08-2010
Publisher: Wiley
Date: 08-2009
Publisher: Elsevier BV
Date: 06-2017
Publisher: IOP Publishing
Date: 03-06-2003
Publisher: Elsevier BV
Date: 10-2008
Publisher: SAGE Publications
Date: 07-1998
Publisher: Elsevier BV
Date: 03-2009
Publisher: Springer Science and Business Media LLC
Date: 06-08-2016
Publisher: IOP Publishing Ltd
Date: 2004
Publisher: Elsevier BV
Date: 2013
DOI: 10.1016/J.ACTBIO.2012.08.032
Abstract: The kinetics of the tetragonal to monoclinic (t-m) transformation of zirconia in a hydrous environment at 134°C and 3 bar pressure was studied. As surface X-ray diffraction, which is conventionally used to explore the progress, has a very limited depth of information, it distorts the quantitative results in a layer-on-layer situation and by itself is ill suited for this reason. Analyzing cross sections is more suitable therefore, focused ion beam techniques were used to prepare artifact-free cuts. The material was subsequently investigated by scanning electron microscopy, electron backscatter diffraction and Raman spectroscopy. Only the combination of methods makes it possible to resolve the quantifiable details of the process. The transformation starts in the near-surface areas, forms a layer, and the growth of this layer proceeds into the bulk material following a simple linear time law (0.0624 μm h(-1) for material in the chosen condition), without apparent retardation or limit. The progress yields a gradientless layer with a fixed amount of residual tetragonal zirconia (~27% for 3Y-TZP in the present conditions) separated from unaffected material by a boundary, which has a roughness only in the grain size range. The kinetics indicates a reaction rate control, where the hydration reaction is the key factor, but is modified by the stepwise access of water to the reaction front opened by the autocatalytic transformation of zirconia with a critical hydration level.
Publisher: Trans Tech Publications, Ltd.
Date: 07-1995
Publisher: Trans Tech Publications, Ltd.
Date: 10-1999
Publisher: International Union of Crystallography (IUCr)
Date: 22-08-2011
Publisher: Elsevier BV
Date: 12-2014
Publisher: Springer Science and Business Media LLC
Date: 04-11-2017
Publisher: Royal Society of Chemistry (RSC)
Date: 1995
DOI: 10.1039/JM9950502313
Publisher: Trans Tech Publications Ltd
Date: 27-10-2010
Publisher: Public Library of Science (PLoS)
Date: 19-10-2016
Publisher: Wiley
Date: 10-1989
Publisher: MDPI AG
Date: 31-05-2021
DOI: 10.3390/BIOMIMETICS6020036
Abstract: The spine of the lance sea urchin (Phyllacanthus imperialis) is an unusual plant-akin hierarchical lightweight construction with several gradation features: a basic core–shell structure is modified in terms of porosities, pore orientation and pore size, forming superstructures. Differing local strength and energy consumption features create a biomimetic potential for the construction of porous ceramics with predetermined breaking points and adaptable behavior in compression overload. We present a new detailed structural and failure analysis of those spines and demonstrate that it is possible to include at least a limited number of those features in an abstracted way in ceramics, manufactured by freeze-casting. This possibility is shown to come from a modified mold design and optimized suspensions.
Publisher: Public Library of Science (PLoS)
Date: 02-12-2022
DOI: 10.1371/JOURNAL.PONE.0278643
Abstract: We propose a quantitative framework for understanding the knapping force requirements imposed by different raw materials in their unheated and heat-treated states. Our model interprets stone tool knapping as being the result of cracks formed during the first impact with a hammer stone, followed by continued stressing of these cracks that eventually leads to flake detachment. We combine bending strength, indentation fracture resistance and “Griffith” crack lengths of flint and silcrete to obtain functions identifying critical forces for flaking without or after heat treatment. We argue that these forces are a key factor for understanding the “knappability” of different raw materials, because only forces with 100N or less can be used for very precise strike control. Our model explains for the first time why experimental knappers frequently observe that flint (a stronger material, which, in our case, has a strength above 100 MPa) is easier to knap than silcretes (which is relatively weaker with strength values at or below 60 MPa). Our findings allow for understanding the differences between heat-treated and untreated flint and silcrete in terms of knapping quality, and they allow to compare the qualities of different raw materials.
Publisher: Springer Science and Business Media LLC
Date: 08-1984
DOI: 10.1007/BF00371400
Publisher: Springer Science and Business Media LLC
Date: 12-2009
Publisher: Elsevier BV
Date: 10-2010
Publisher: Springer International Publishing
Date: 2016
Publisher: Informa UK Limited
Date: 11-04-2008
Location: Germany
No related grants have been discovered for Klaus Nickel.