Eco-friendly Geopolymer Composite Based on Non-heat-treated Phosphate Sludge Reinforced With Polypropylene Fibers

Silicon - Geopolymers produced with metakaolin (MK) and thermally untreated phosphate sludge (PS) are beneficial and environmentally advantageous materials, but their fragility limits its...     

Optical and magnetic properties of perovskite materials: Ba0.3La0.7Ti0.3Fe0.7O3 and Ba0.1La0.9Ti0.1Fe0.9O3

Structural, optical and magnetic properties are reported for new synthesized perovskite materials. Ba_0.3La_0.7Ti_0.3Fe_0.7O₃ and Ba_0.1La_0.9Ti_0.1Fe_0.9O₃ compositions were prepared via solid state reaction. X-ray analysis confirms that both compositions show feature of perovskite structure. Rietveld refinement method was used to confirm the phase formation and investigate the structure and space group. The study demonstrates the formation of orthorhombic structure with Pnma space group for Ba_0.3La_0.7Ti_0.3Fe_0.7O₃ while the composition Ba_0.1La_0.9Ti_0.1Fe_0.9O₃ structure adopts Pbnm symmetry. UV–vis spectroscopy measurements show very broad and intense UV–visible light absorption, the estimated band gap ranges between 2.07 and 2.15 eV. Magnetic measurements were carried out for the compositions Ba_0.3La_0.7Ti_0.3Fe_0.7O₃ and Ba_0.1La_0.9Ti_0.1Fe_0.9O₃. The hysteresis loops of both samples at 300 and 10 K show a strong ferromagnetic behavior. The temperature dependent magnetization at 0.05 T under field-cooled (FC) and zero field cooled (ZFC) modes shows magnetic frustration or spin glass-like behavior.     

The stress–strain behavior of refractory microcracked aluminum titanate: The effect of zigzag microcracks and its modeling

The stress–strain behavior of ceramics, such as aluminum titanate, has certain features that are unusual for brittle materials—in particular, a substantial nonlinearity under uniaxial tension, and load–unload hysteresis caused by the sharp increase of the incremental stiffness at the beginning of unloading. These features are observed experimentally and are attributed to microcracking. Here we compare different degrees of stress–strain nonlinearity of aluminum titanate materials and quantitatively model them. We use advanced mechanical testing to observe the mechanical response at room and high temperature; electron microscopy, and X-ray refraction radiography to observe the microstructural changes. Experiments show that two types of microcracks can be distinguished: (i) microcracks induced by cooling from the sintering temperature (due to heterogeneity and anisotropy of thermal expansion), with typical sizes of the order of grain size, and (ii) much larger microcracks generated by the mechanical loading. The two microcrack types produce different effects on the stress–strain curves. Such microcracks and the features of the stress–strain behavior depend on the density of the cooling-induced microcracks and on the distribution of grain sizes. They are modeled analytically and numerically.