Search results for "engineering.material"
showing 10 items of 2352 documents
A new simple approach to evaluate pedogenic clay transformation in a Vertic Calcisol
2006
The aim of this study is to characterize the pedogenic clay minerals by using simple approach: Mixing mineralogical and geochemical findings. The fine clay fractions (< 0.1 μm) of a Vertic Cambisol profile were studied by means of X-ray diffraction (XRD), infrared spectroscopy (FTIR) and cation exchange capacity (CEC). Qualitative and quantitative mineralogical compositions of the clay mixture were determined. Moreover, chemical equilibria and thermodynamic stabilities of minerals (calcite, gypsum, kaolinite, smectites and illites) were studied using results of ionic activities obtained from total concentration of various aqueous species in water extracts from soil-saturated pastes. XRD ana…
Modeling red coral (Corallium rubrum) and African snail (Helixia aspersa) shell pigments: Raman spectroscopyversusDFT studies
2016
Pigments from red coral (Corallium rubrum) and African snail (Helixia aspersa) shell were studied non-invasively using Raman spectroscopy with 1064-nm laser beam. The two observed bands because of organic pigments confined in biomineralized CaCO3 matrix at about 1500 and 1100 cm−1 were assigned to ν(CC) and ν(C―C), respectively. Both signals originate from polyene(s) of largely unknown structure, containing several conjugated CC bonds. The small peak at 1016 cm−1 in the Raman spectrum of coral pigment was assigned to in-plane ―CH3 rocking or structural deformation of polyene chain because of spatial confinement in the mineral matrix. The organic pigments in red coral and snail shell were pr…
Small scale secondary CaCO3 accumulations in selected sections of the European loess belt. Morphological forms and potential for paleoenvironmental r…
1997
Eighteen important Quaternary loess paleosoil sites have been studied across the European loess belt. They included approximately 50 buried soils, the over and/or underlying loess and the present-day surface soils (where possible). From the numerous types of secondary CaCO3 accumulations recognized, only the small scale accumulations are discussed in this paper, including calcified root cells, CaCO3 hypocoatings, needle-fiber calcite, powdery calcite coatings, earthworm biospheroliths, and calcite pseudomorphs on gypsum. Most of the features studied are found in the rhizosphere microecosystem. Each of these features showed a unique relationship with organic matter, micro-organism and plant …
Refining the temperature dependence of the oxygen and clumped isotopic compositions of structurally bound carbonate in apatite
2019
Abstract Clumped isotope data from carbonated apatite from in vivo and in vitro samples are presented to refine the relationship between mineral growth temperature and carbonate clumped isotopic composition (Δ47). Δ47, δ18O and δ13C data were obtained from phosphoric acid digestion (T = 110 °C) of chemically untreated teeth from an African elephant, Greenland sharks, sand tiger sharks and synthetic apatites. These data cover a temperature range between 1 °C and 80 °C and enlarge the calibration dataset presented in Wacker et al. (2016) by a factor of five. Taxon-specific analyses of tooth enamel(oid) and dentine reveal that both tissues show identical Δ47 values even though the content of o…
Lithium isotopes and partition coefficients in inorganic carbonates: Proxy calibration for weathering reconstruction
2021
We report Li measurements from cave-analogue carbonate-precipitation experiments in order to: i) assess the expected isotope fractionation factors applicable to speleothem growth, and ii) contribute to the wider understanding of lithium incorporation in carbonates. The experimental setup closely mimics natural processes (e.g. precipitation driven by CO2 degassing, low ionic strength solution, thin solution film) but within a laboratory setting that allows for controlled growth conditions (temperature, pCO2, drip rate, carbonate saturation index and the composition of the initial solution). For the main batch of calcite growth experiments our average 1000lnαcalcite-solution is -8.5&plu…
Determination of aragonite trace element distribution coefficients from speleothem calcite–aragonite transitions.
2016
The processes that govern the incorporation of (trace) elements into speleothems can often be linked to environmental changes. Although element incorporation into speleothem calcite is now reasonably well understood, current knowledge regarding trace element variability in speleothem aragonite is very limited. Of particular interest is whether trace element distribution coefficients are above or below one in order to assess the extent to which prior aragonite precipitation has affected speleothem aragonite trace element records. This study uses nine calcite-to-aragonite transitions in seven speleothems from diverse environmental settings to derive the first quantitative estimates of the dis…
Coarse-grained cryogenic aragonite as end-member of mineral formation in dolomite caves
2018
Abstract Cryogenic carbonate particles (single crystals and aggregates) have recently been recognized as important witnesses of permafrost dynamics, as they can be used to estimate the thickness and timing of development of permafrost. In this study, the petrography and geochemistry of coarse-grained cryogenic aragonite (CGCAr) identified in Zoolithen Cave in NE Bavaria, Germany, are described in detail for the first time. We provide a sequence of carbonate precipitation during freezing, where CGCAr mark the final crystallization phase in freezing water on ice. Our results support the notion that host rock composition, solution chemistry, and cave ventilation play an important role for arag…
Geochemistry and mineralogy of travertine deposits of the SW flank of Mt. Etna (Italy): Relationships with past volcanic and degassing activity
2007
Abstract Travertine deposits outcropping in the lower SW flank of Mt. Etna were studied for their mapping, as well as for their chemical, mineralogical and isotopic compositions. These deposits are dated to about 24 to 5 ka in the Adrano area, located at the western limit of the study area. In this area travertines show high Mg contents and are composed mostly of dolomite, thus apparently ruling out any primary deposition in favour of a diagenetic origin. Travertines outcropping near Paterno, in the east part of the study area, should be younger than 18 ka. Those located to the SSW of Paterno (Paterno–Diga) show high Sr contents and aragonite as dominant mineralogical phase, thus suggesting…
Deep-water stromatolites andFrutexites Maslov from the early and Middle Jurassic of S-Germany and Austria
1993
Despite extensive discussions during the last 20 years stromatolites are still used by many geologists as unequivocal indicators of very shallow-water conditions. We investigated four stratigraphic units from the Lower and Middle Jurassic of southern Germany (Posidonien-Schiefer, Amaltheen-Ton) and of the Northern Calcareous Alps (Adneter Kalk, Klauskalk), which were formerly interpreted as shallow marine sediments by some authors due to the occurrence of stromatolites. Our interpretations of the macro-, micro- and ultrafacies of these sediments are not compatible with shallow-water settings. We therefore propose a deep-marine, aphotic origin of these stromatolites. Former interpretations o…
A biphasic calcium phosphate coating for potential drug delivery affects early osseointegration of titanium implants.
2016
Background Calcium phosphate (CaP) surface coatings may accelerate osseointegration and serve as a drug delivery system for mineral-binding biomolecules. In a pilot study, the impact of a commercially available, thin CaP coating on early osseous bone remodeling was compared with a modern, subtractive-treated rough surface (SLA-like) in an animal trial. Methods In 16 rabbits, 32 endosseous implants (CaP; n = 16, SLA-like; n = 16) were bilaterally inserted in the proximal tibia after randomization. After 2 and 4 weeks, bone-implant contact (BIC;%) in the cortical (cBIC) and the trabecular bone (sBIC) as well as volume of bone within the screw thread with the highest amount of new-formed bone …