A Mottled, Non-Lithified Paleosol in Brazil: Diagnosis by Morphological and Mineralogical Features

The identification of paleosols is difficult when no buried horizons or lithification occur. Here, we described the identification of a possible paleosol, its characterization, and which features supported its positive diagnosis. In a construction site, a vertical cut exposed an unusual red–yellow mottling with massive structure and channels (probably faunal), in contrast with the overlying homogeneous red Oxisol with fine granular structure. A similar but more deferrified section with white–yellow mottling also occurred nearby, and both were sampled as large clods. In thin sections, many oriented clay coatings occur along channel voids, suggesting illuviation, as well as dissolving Fe nodules and Mn coatings along planar and channel voids. X-ray diffraction showed a clay dominated by kaolinite, traces of illite, and absence of gibbsite, again contrasting with the gibsitic-kaolinitic clay of the Oxisol. We confirmed the diagnosis of a Paleoultisol due to the following incompatibilities with the overlying Oxisol: (1) massive, apedal structure, and higher bulk density; (2) clay coatings indicative of illuviation as key soil-forming process; (3) low clay contents in particle-size analysis due to cementation; (4) very low organic carbon consistent with long-term inhumation; and (5) kaolinitic–illitic clay. The unusual granular microstructure of the B horizon of the Oxisol is partly derived from disintegration and desilication of the Paleoultisol.

Wear behavior and microstructure of Fe-C-Si-Cr-B-Ni hardfacing alloys

This study aims to investigate the relationship between wear resistance and microstructure of a hardfacing alloy Fe-C-Si-Cr-B-Ni system as well as investigating ways of improving the hardness of the hard facing layer through the addition of nickel to achieve a finer granular microstructure. Three hardfacing alloys are used for overlaying. Ferroboron (FeB) and Ferronickel(FeNi), are added to the massive wire during the welding process. A hardness test, microscopic characterization and wear analysis are carried out on the samples. The surfaces of the samples are examined using scanning electron micsoscope in order to better understand the wear mechanism. At room temperature, wear occurs through a combination of abrasive grooving and local delamination. Microstructure and hardness affect the wear resistance of the alloys. Test results shows that as hardness increases, wear resistance increases.

Packing density of bi-disperse mixtures under one-dimensional compression

This work aims to investigate the effect of fines in different type of bi-disperse grain size distributions in terms of minimum/maximum density, compressibility and crushing. The material adopted is the Light Expanded Clay Aggregate (LECA), an artificial granular material characterized by light, porous and crushable grains. The bi-disperse grading are firstly analysed in terms of packing density, measuring experimentally the minimum and the maximum porosity for different combination of sizes and volume proportions. Then, some selected mixtures are subjected to one-dimensional compression tests up to high pressures. Evolution of grain size due to grain crushing phenomena and compressibility are therefore measured and interpreted. Finally a theoretical model is adopted in order to predict the mechanical material response accounting grain crushing and granular microstructure.

Spin stress contribution to the lattice dynamics of FePt

Invar-behavior occurring in many magnetic materials has long been of interest to materials science. Here, we show not only invar behavior of a continuous film of FePt but also even negative thermal expansion of FePt nanograins upon equilibrium heating. Yet, both samples exhibit pronounced transient expansion upon laser heating in femtosecond x-ray diffraction experiments. We show that the granular microstructure is essential to support the contractive out-of-plane stresses originating from in-plane expansion via the Poisson effect that add to the uniaxial contractive stress driven by spin disorder. We prove the spin contribution by saturating the magnetic excitations with a first laser pulse and then detecting the purely expansive response to a second pulse. The contractive spin stress is reestablished on the same 100-ps time scale that we observe for the recovery of the ferromagnetic order. Finite-element modeling of the mechanical response of FePt nanosystems confirms the morphology dependence of the dynamics.

Structural Changes in TiO2 Films Formed by Anodizing of Electro-Polished Titanium

Anodizing is a surface modification technique that is applied to growing oxide films on Ti to accelerate the osseointegration of an implant. Besides the surface roughness, the crystalline structure of these films can affect its performance as a biomaterial. For this reason, this technique has been refined to produce crystalline films without requiring heat treatments. For this purpose, TiO2 films were grown on Ti (grade 2) by anodizing with direct current at different potentials. Images obtained by optical microscopy with polarized light revealed a granular microstructure in various colors, as consequence of different crystalline orientations of the grains and films thickness. Raman spectroscopy showed that the films crystallinity is affected by variations in the applied potential and anodizing time.

The Effect of Different Salt Additions on the Microstructure of YBCO Synthesized by a Biomimetic Method

The effect of different salt additions on the granular microstructure of samples of the high temperature superconductor YBa2Cu3O7δ (YBCO) synthesized by a biomimetic method has been investigated. Attempting biotemplating using salts with the rock-salt structure, most such salts were found to be chemically compatible with the YBCO biosynthesis, but only NaCl and KCl were observed to result in the desirable strongly anisotropic platelet growth to form clusters with localized orientational alignment. Broadening the range of additions to other chloride salts of varying structures resulted in an increase in the CuO impurity content of the samples, but with all the YBCO formed exhibiting platelet growth. Chloride salts are therefore considered to be good candidates for addition to the biomimetic YBCO synthesis in order to achieve anisotropic platelet growth.