Facile synthesis and characterization of monocrystalline cubic ZrO2 nanoparticles

Crystalline ZrO₂ nanoparticles were prepared from zirconium isopropoxide by slow hydrolysis and subsequent hydrothermal treatment of solutions containing various amounts of sodium hydroxide at 180 °C. Whereas moderately basic solutions lead to the formation of nanoparticles of monoclinic ZrO₂ with plate-like morphology, and nanoparticles of the cubic ZrO₂ high-temperature polymorph with diameters of approx. 5 nm were obtained from strongly basic solutions. The morphology, structure and properties of as-synthesized nanoparticles were characterized using HRTEM, XRD, Raman spectroscopy, UV–vis, PL spectroscopy and BET measurements. The formation of both, the monoclinic and the cubic polymorph, was confirmed by electron microscopy and Raman spectroscopy. The crystallinity and morphology of the resulting ZrO₂ nanoparticles can be adjusted by the choice of the reaction conditions. The cubic ZrO₂ nanoparticles have a high surface area (300 m²/g) and exhibit a strong photoluminescence in the UV region.     

Morphosynthesis of strontianite nanowires using polyacrylate templates tethered onto self-assembled monolayers

Strontianite nanowires have been synthesized on self-assembled monolayers (SAM) in the presence of polyacrylate templates. The morphology of this product exhibits characteristic differences from that of products obtained in the absence of polyacrylate. It is demonstrated that the template-induced crystallization process involves the interaction between the SAM surface, polyacrylate (a dissolved polyelectrolyte), and the cations/anions in solution. By the combination of these components, hierarchically ordered mineral hybrid structures are formed.     

Crystal structure of Zn4Na(OH)6SO4Cl·6H2O

The structure of Zn₄Na(OH)₆SO₄Cl·6H₂O, a secondary mineral from Hettstedt, Germany, was determined by single-crystal X-ray diffraction. The crystals are hexagonal,a=8.413(8),c=13.095(24) Å, space group $P\bar 3$ , Z=2. The structure was refined to R=0.0554 and R_w=0.0903 for 970 reflections with I≥3σ(I). The structure can be described as zinc hydroxide layers perpendicular toc, from which sulfates and chlorides extend. The layers are held together by a system of hydrogen bonds involving hexaaquo Na⁺ ions which occupy the interlayer space.     

Probing cooperative interactions of tailor-made nucleation surfaces and macromolecules: a bioinspired route to hollow micrometer-sized calcium carbonate particles

It is well known that the formation of biominerals by living organisms is governed by the cooperation of soluble and insoluble macromolecules with peculiar interfacial properties. To date, most of the studies on mineralization processes involve model systems that account only for the existence of one organic matrix and thus disregard the interaction between the soluble and insoluble organic components that is crucial for a better understanding of the processes taking place at the inorganic-organic interface. We have set up a model system composed of a matrix surface, which is composed of a self-assembled monolayer (SAM) and a soluble component, poly(aspartic acid). It could be demonstrated that the phase selection of calcium carbonate and the morphology of the resulting particles are determined by the stabilization of amorphous precursor particles by the polymer and the interaction between polymer and SAM. The morphology of the hollow vaterite microspheres are reminiscent to a 3D analogue of the so-called "coffee-stain effect", where the transformation from a voluminous hydrated, amorphous material to a more dense crystalline material leads to the formation of hollow spheres from massive spherical microparticles.     

Determination of Yield Surfaces in Accordance With ISO 16842 Using an Optimized Cruciform Test Specimen

Background: For the standard ISO 16842 cruciform test specimen, stresses obtained from the gauge area are far below the ultimate tensile strength due to high stress concentrations at the slit ends which lead to premature failure. Objective: To introduce a new cruciform specimen design which has been optimized with respect to the determination of yield surfaces. Methods: The proposed design differs from the ISO standard by an additional thinning of the gauge area and wider slits in the arms to avoid stress singularities. Compared to other cruciform test piece designs found in the literature, the stress distribution is still homogeneous and there is no need to reduce the size of the gauge area, thanks to the specimen’s well-balanced proportions. Results: Biaxial tensile tests have been conducted with aluminium 5754 alloy samples of different thicknesses. For the standard cruciform test piece, the maximum strain achieved at the gauge area is only 25% of the fracture strain. The optimized cruciform test piece can attain about 66% of the fracture strain before breaking. Conclusions: The optimized specimen design enables the measurement of yield surfaces at higher stress levels. In case of other materials such as elastomers, the slit length has be to adjusted accordingly.