Materials Surgery – Reactivity Differences of Organic Groups in Hybrids

Synergistic properties in hybrid materials can emerge if the inorganic matrix has an electronic influence on the organic constituents and vice versa. This paper describes the drastic effect of SiO₂ in periodically ordered mesoporous organosilica materials (PMOs) on ethylene groups. A sophisticated, in situ solid‐state NMR spectroscopy study showed that the ozonolysis of ethylene groups follows an entirely different mechanism than is normal for organic, molecular groups. Ultimately, this leads to the topotactic transformation of the PMO material. Only if silicon is not in the alpha position to the double bond does it became possible to establish a new method to functionalize PMOs materials: the targeted scission of the ethylene group and the creation of functionalized pockets inside the pore walls of the mesoporous solid.     

Synthesis and luminescence properties of novel LiSrPO4:Dy phosphor

Novel LiSrPO₄:Dy³⁺ phosphors for white light-emitting diodes (w-LEDs) were synthesized by the conventional solid-state reaction. X-ray powder diffraction (XRD) analysis confirmed the phase formation of LiSrPO₄:Dy³⁺ materials. Luminescence properties results showed that the phosphor could be efficiently excited by the UV–vis light region from 250 to 460 nm, and it exhibited blue (483 nm) and yellow (574 nm) emission corresponding to ⁴F_9/2 → ⁶H_15/2 transitions and ⁴F_9/2 → ⁶H₁₃/₂ transitions, respectively. The luminescence intensity of LiSrPO₄:xDy³⁺ phosphor firstly increased and then decreased with increasing Dy³⁺ concentration, and reached the maximum at x = 0.03. It was found that concentration quenching occurred as a result of dipole-dipole interaction according to the Dexter's theory. The decay time was also determined for various concentrations of Dy³⁺ in LiSrPO₄.     

Synthesis and characterization of Co-Sn substituted barium ferrite particles by a reverse microemulsion technique

A series of Co-Sn substituted barium ferrite particles have been successfully synthesized by a reverse microemulsion technique. The effects of heteroatom contents and precipitating agents were investigated, respectively. It was found that the presence of heteroatoms could enhance lattice parameters, affect morphology evolution and modulate magnetic properties. Particularly, an unusual saturation magnetization (>70.0 emu/g) could be achieved under low heteroatoms concentration due to preferential occupation in specific sites. Precipitating agents played a critical role in forming barium ferrite phase, only sufficient precipitating agents could produce high-purity phase. Besides, this method is not limited in the synthesis of Co-Sn substituted barium ferrite, it can be extended to other heteroatoms, such as Ni-Zr and La, and resultant products also show well crystalline phase and unique magnetic properties.     

Morphology-controlled hydrothermal synthesis of MnCO3 hierarchical superstructures with Schiff base as stabilizer

MnCO₃ with hierarchical superstructures such as chrysanthemum, straw-bundle, dumbbell and sphere-like were synthesized in water/ethanol system under environment-friendly hydrothermal condition. In the synthesis process, the CO₂ in atmosphere was used as the source of carbonate ions and Schiff base was used as shape guiding-agent. The different superstructures of MnCO₃ could be obtained by controlling the hydrothermal temperature, the molar ratio of manganous ions to the Schiff base, or the volume ratio of water to ethanol. A tentative growth mechanism for the generation of MnCO₃ superstructures was proposed based on the rod–dumbbell–sphere model. Furthermore, the MnCO₃ as precursor could be further successfully transferred to Mn₂O₃ microstructure after heating in the atmosphere at 500 °C, and the morphology of the Mn₂O₃ was directly determined by that of the MnCO₃ precursor.     

Synthesis of acid-base bifunctional mesoporous materials by oxidation and thermolysis

A novel and efficient method has been developed for the synthesis of acid-base bifunctional catalyst SO₃H-MCM-41-NH₂. This method was achieved by co-condensation of tetraethylorthosilicate (TEOS), 3-mercaptopropyltrimethoxysilane (MPTMS) and (3-triethoxysilylpropyl) carbamicacid-1-methylcyclohexylester (3TAME) in the presence of cetyltrimethylammonium bromide (CTAB), followed by oxidation and then thermolysis to generate acidic site and basic site. X-ray diffraction (XRD) and transmission electron micrographs (TEM) show that the resultant materials keep mesoporous structure. Thermogravimetric analysis (TGA), X-ray photoelectron spectra (XPS), back titration, solid-state ¹³C CP/MAS NMR and solid-state ²⁹Si MAS NMR confirm that the organosiloxanes were condensed as a part of the silica framework. The bifunctional sample (SO₃H-MCM-41-NH₂) containing amine and sulfonic acids exhibits excellent acid-basic properties, which make it possess high activity in aldol condensation reaction between acetone and various aldehydes.     

Solution precursor plasma deposition of nanostructured ZnO coatings

Zinc oxide (ZnO) is a wide band gap semiconducting material that has various applications including optical, electronic, biomedical and corrosion protection. It is usually synthesized via processing routes, such as vapor deposition techniques, sol-gel, spray pyrolysis and thermal spray of pre-synthesized ZnO powders. Cheaper and faster synthesis techniques are of technological importance due to increased demand in alternative energy applications. Here, we report synthesis of nanostructured ZnO coatings directly from a solution precursor in a single step using plasma spray technique. Nanostructured ZnO coatings were deposited from the solution precursor prepared using zinc acetate and water/isopropanol. An axial liquid atomizer was employed in a DC plasma spray torch to create fine droplets of precursor for faster thermal treatment in the plasma plume to form ZnO. Microstructures of coatings revealed ultrafine particulate agglomerates. X-ray diffraction confirmed polycrystalline nature and hexagonal Wurtzite crystal structure of the coatings. Transmission electron microscopy studies showed fine grains in the range of 10-40 nm. Observed optical transmittance (∼65-80%) and reflectivity (∼65-70%) in the visible spectrum, and electrical resistivity (48.5-50.1 mΩ cm) of ZnO coatings are attributed to ultrafine particulate morphology of the coatings.     

Experiments and mesoscopic modelling of dynamic testing of concrete

Due to their large aggregates size and their heterogeneous microstructure, concretes are difficult materials to test at high strain-rates. Direct tensile tests, spalling tests and edge-on impact experiments have been especially developed and performed on a standard concrete (max grain size of 8 mm). The influence of free water on the high strain rate behaviour has been carefully evaluated. Numerical simulations of dynamic testing have been also performed using a mesoscopic approach in which the matrix and the aggregates are differentiated. Numerical and analytical homogenization methods have been employed to define a model-concrete which fits experimental data of simple and œdometric compression tests. Then, the numerical simulations with several random distributions of aggregates were conducted to validate the processing methods applied to the experimental data of the dynamic tests. Moreover an anisotropic damage model coupled to the mesoscopic approach has been used to simulate the dynamic behaviour of concrete under impact. It allows predicting the increase of strength and cracking density with strain-rate and the free water influence on the dynamic behaviour of concrete.     

Crack propagation in quasi-brittle two-dimensional isotropic lattices

Materials with cellular structure are gaining prominence in recent years due to improvements in production processes, that enable the manufacture of new materials, and biomechanics, that requires mechanical analysis of cellular structures such as bones. The possibility to use the Fracture Mechanics tools developed for the continua to the fracture of cellular materials is analyzed in the present paper. As proposed by Maiti et al. the fracture toughness of cellular solids can be obtained through two procedures: taking into account the stress at crack tip or the fracture toughness of the base material. Both procedures are analyzed and the equivalent R-curve and a cohesive law is obtained in function of the cell size and structure morphology. A critical truss length exists from which crack propagation goes from being governed by the energy dissipated to being governed by the stress field.     

Microstructural effects on ductile fracture in heterogeneous materials. Part I: Sensitivity analysis with LE-VCFEM

Ductile failure of heterogeneous materials, such as cast aluminum alloys and discretely reinforced aluminums or DRA’s, initiates with cracking, fragmentation or interface separation of inclusions, that is followed by propagation in the matrix by a ductile mechanism of void nucleation and growth. Damage localizes in bands of intense plastic deformation between inclusions and coalesces into a macroscopic crack leading to overall failure. Ductile fracture is very sensitive to the local variations of the microstructure morphology. This is the first of a two part paper on the effect of microstructural morphology and properties on the ductile fracture in heterogeneous ductile materials. In this paper the locally enhanced Voronoi cell finite element method (LE-VCFEM) for rate-dependent porous elastic–viscoplastic materials is used to investigate the sensitivity of strain to failure to loading rates, microstructural morphology and material properties. A model is also proposed for strain to failure, incorporating the effects of important morphological parameters.     

Study on conductivity and redox stability of iron orthovanadate

FeVO₄ was synthesised by conventional solid state technique. Impedance measurements using a silver electrode were unsuccessful due to a solid state reaction between FeVO₄ and Ag, forming α-AgVO₃ and α-Fe₂O₃ at the interface. Impedance measurements, with a platinum electrode, reaffirmed that FeVO₄ exhibits semiconductor behaviour in air. In a reducing atmosphere, 5% H₂/Ar, high electronic conductivity, from 1 S cm⁻¹ at 300 °C to 2 S cm⁻¹ at 700 °C, was observed with an activation energy of 0.13(1) eV. X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry data determined that the change in electronic conductivity was due to the degradation of the material into FeV₂O₄ and α-Fe₂O₃. It is believed that the conduction was due to electron hopping between vanadium d-orbitals. Neither FeVO₄ nor FeV₂O₄ are deemed suitable as anode materials for solid oxide fuel cells, due to redox instability.