Search results for "amor"
showing 10 items of 1531 documents
Reactions and textures in grossular–wollastonite–scapolite calc–silicate granulites from Maligawila, Sri Lanka: evidence for high-temperature isobari…
2001
Grossular–wollastonite–scapolite calc–silicate granulites from Maligawila in the Buttala klippe, which form part of the overthrusted rocks of the Highland Complex of Sri Lanka, preserve a number of spectacular coronas and replacement textures that could be effectively used to infer their P–T–fluid history. These textures include coronas of garnet, garnet–quartz, and garnet–quartz–calcite at the grain boundaries of wollastonite, scapolite, and calcite as well as calcite–plagioclase and calcite– quartz symplectites or finer grains after scapolite and wollastonite respectively. Other textures include a double rind of coronal scapolite and coronal garnet between matrix garnet and calcite. The r…
High biocompatibility and improved osteogenic potential of amorphous calcium carbonate/vaterite.
2020
In human bone, amorphous calcium carbonate (ACC) is formed as a precursor of the crystalline carbonated apatite/hydroxyapatite (HA). Here we describe that the metastable ACC phase can be stabilized by inorganic polyphosphate (polyP) that is also used as a phosphate source for the non-enzymatic carbonate/phosphate exchange during HA formation. This polymer was found to suppress the transformation of ACC into crystalline CaCO3 at a percentage of 5% [w/w] ("CCP5") with respect to CaCO3 and almost completely at 10% [w/w] ("CCP10"). Both preparations (CaCO3/polyP) are amorphous, but also contain small amounts of vaterite, as revealed by XRD, FTIR and SEM analyses. They did not affect the growth/…
Mechanochemical Access to Defect-Stabilized Amorphous Calcium Carbonate
2018
Amorphous calcium carbonate (ACC) is an important precursor in the biomineralization of crystalline CaCO3. The lifetime of transient ACC in nature is regulated by an organic matrix, to use it as an intermediate storage buffer or as a permanent structural element. The relevance of ACC in material science is related to our understanding of CaCO3 crystallization pathways. ACC can be obtained by liquid–liquid phase separation, and it is typically stabilized with the help of macromolecules. We have prepared ACC by milling calcite in a planetary ball mill. The ball-milled amorphous calcium carbonate (BM-ACC) was stabilized with small amounts of Na2CO3. The addition of foreign ions in form of Na2C…
Pseudomorphic transformation of amorphous calcium carbonate films follows spherulitic growth mechanisms and can give rise to crystal lattice tilting
2015
Amorphous calcium carbonate films synthesized by the polymer-induced liquid-precursor (PILP) process convert into crystallographically complex calcite spherulites. Tuning the experimental parameters allows for the generation of crystal lattice tilting similar to that found in calcareous biominerals. This contribution evidences the role of spherulitic growth mechanisms in pseudomorphic transformations of calcium carbonate.
Partial high-pressure aragonitization of micritic limestones in an accretionary complex, Tavşanlı Zone, NW Turkey
2006
Pelagic micritic limestones within an upper Cretaceous accretionary complex in the Tavsanli Zone, NW Turkey, preserve textures indicating incomplete prograde transformation of micritic calcite to aragonite, representing the only known example of this type. Aragonitization starts at the central parts of the micritic limestone beds and advances towards the lower and upper parts of the layers at the expense of micrite. Micrite is very fine grained (<0.003 mm) and contains radiolaria, foraminifera and thin shell fragments. Aragonite forms large crystals, up to 3 cm across, with straight grain boundaries and c-axis mostly subparallel to the carbonate beds. Relict micritic portions are devoid of …
Flexible minerals: self-assembled calcite spicules with extreme bending strength.
2013
Flexi-Fibers Glass or metal fibers can show incredible flexibility. Natalio et al. (p. 1298 ; see the Perspective by Sethmann ) used the protein silicatein-α, which is responsible for the biomineralization of silicates in sponges, to guide the formation of spicules made of calcite. These synthetic spicules could be bent to a high degree because of their inherent elasticity, whilst retaining the ability to guide light.
Early homogenous amorphous precursor stages of calcium carbonate and subsequent crystal growth in levitated droplets.
2008
An in situ study of the contact-free crystallization of calcium carbonate in acoustic levitated droplets is reported. The levitated droplet technique allows an in situ monitoring of the crystallization while avoiding any foreign phase boundaries that may influence the precipitation process by heterogeneous nucleation. The diffusion-controlled precipitation of CaCO3 at neutral pH starts in the initial step with the homogeneous formation of a stable, nanosized liquid-like amorphous calcium carbonate phase that undergoes in a subsequent step a solution-assisted transformation to calcite. Cryogenic scanning electron microscopy studies indicate that precipitation is not induced at the solution/a…
Stable amorphous calcium oxalate: synthesis and potential intermediate in biomineralization.
2014
Amorphous calcium oxalate nanoparticles with sizes of 10–30 nm were synthesized at room temperature by the hydrolysis of a dimethyl oxalate from ethanol solution.
The Understanding of the Metazoan Skeletal System, Based on the Initial Discoveries with Siliceous and Calcareous Sponges
2017
Initiated by studies on the mechanism of formation of the skeletons of the evolutionary oldest still extant multicellular animals, the sponges (phylum Porifera) have provided new insights into the mechanism of formation of the Ca-phosphate/hydroxyapatite skeleton of vertebrate bone. Studies on the formation of the biomineral skeleton of sponges revealed that both the formation of the inorganic siliceous skeletons (sponges of the class of Hexactinellida and Demospongiae) and of the calcareous skeletons (class of Calcarea) is mediated by enzymes (silicatein: polymerization of biosilica; and carbonic anhydrase: deposition of Ca-carbonate). Detailed studies of the initial mineralization steps i…
Amplified morphogenetic and bone forming activity of amorphous versus crystalline calcium phosphate/polyphosphate.
2020
Amorphous Ca-phosphate (ACP) particles stabilized by inorganic polyphosphate (polyP) were prepared by co-precipitation of calcium and phosphate in the presence of polyP (15% [w/w]). These hybrid nanoparticles showed no signs of crystallinity according to X-ray diffraction analysis, in contrast to the particles obtained at a lower (5% [w/w]) polyP concentration or to hydroxyapatite. The ACP/15% polyP particles proved to be a suitable matrix for cell growth and attachment and showed pronounced osteoblastic and vasculogenic activity in vitro. They strongly stimulated mineralization of the human osteosarcoma cell line SaOS-2, as well as cell migration/microvascularization, as demonstrated in th…