Influence of Cold Rolled Deformation Degree and Heating Rates on Crystallite Dimension and Recrystallization Fraction of Aluminum Plates

In order to study the microstructure evolution rule of pure aluminum plates during different cold-rolled (CR) deformation degrees and annealing processes, samples with aCR deformation of 50~85%, heating rates of 60~100 °C/min and annealing at the target temperature of 350~500 °C were investigated. The microstructure, crystallite dimension and grain boundary characteristics were characterized by the methods of polarizing microscope (PM) and electron backscattered diffraction (EBSD). The results showed that the crystallite dimension of the initial state was 102 μm and ends up completely broken with an increase in the CR deformation degree. When the CR deformation increases to 85%, the deformed micro-bands were very small, with a band spacing of 5~10 μm. At this time, the grain distortion is more serious, there are more high-density grain defects, such as dislocations, and there is a high deformation of the storage energy, which is the energy preparation for the subsequent finished products to withstand the annealing process. The recrystallization fraction was higher with an increase in annealing temperature. After completed recrystallization, the grains showed an equiaxed shape. Orientation imaging and misorientation angle analysis showed that the red-oriented grains of the (001) plane, which had preferred nucleation, recrystallization and rapid grain growth. Final grains of the completed recrystallization are relatively coarse. Under the same deformation, the average crystallite dimension of the recrystallized grains decreases with an increase in annealing heating rate.

Removal of diclofenac from aqueous solutions by adsorption on thermo-plasma expanded graphite

The adsorption of diclofenac on thermo-plasma expanded graphite (a commercial product) from water solutions was investigated. The adsorbent material was characterized by SEM, TEM, BET, Raman and X-ray diffraction analyses. Typical diffractogram and Raman spectrum of graphitic material, dimension of 24.02 nm as crystallite dimension and a surface area of 47 m2 g−1 were obtained. The effect of pH on the adsorption capacity was evaluated in the range 1–7 and the adsorption mechanism was described by kinetic and isothermal studies. Pseudo-second order and Dubinin–Radushkevich models agreed with theoretical values of adsorption capacity (i.e. 400 and 433 mg g−1, respectively) and resulted to be the best fit for kinetics and isothermal experimental data. The thermodynamics of the process was evaluated by plotting the adsorption capacity/concentration ratio at the equilibrium as a function of different values of the multiplicative inverse of temperature. Moreover, the adsorbent regeneration was also investigated, comparing two different remediation techniques. Solvent washing performed with NaOH 0.2 M and thermo-treatment carried out by heating in an oven at 105 °C for 2 h and then at 200 °C for 4 h. The thermo-treatment was the best technique to regenerate the adsorbent, ensuring same performance after 4 cycles of use and regeneration.

The Effect of Extended Ball-Milling upon Three-Dimensional and Two-Dimensional Perovskite Crystals Properties

The ball-milling of materials is a mechanical grinding method that has different effects on treated materials, and can be used for the direct synthesis of organometal halide perovskite (OHP) crystals. Herein, the effect of such a process, extended over a large temporal window, is related to the properties of referential three-dimensional (3D) MAPbI3 (MA = methylammonium) and two-dimensional (2D) PEA2PbI4 (PEA = phenylethylammonium) perovskite crystals. For both 2D and 3D systems, the ball-milling induces a reduction of the crystallite dimension, accompanied by a worsening of the overall crystallinity, but without any sign of amorphization. For MAPbI3, an intriguing room temperature structural transition, from tetragonal to cubic, is observed. The processing in both cases impacts on the morphology, with a reduction of the crystal shape quality connected to the particles’ agglomeration tendency. All these effects translate to a “blue shift” of the absorption and emission features, suggesting the use of this technique to modulate the 3D and 2D OHPs’ properties.

Структурные, оптические и фоточувствительные свойства пленок PbS, осажденных в присутствии CaCl-=SUB=-2-=/SUB=-

Polycrystalline lead-sulfide (PbS) films doped with calcium are synthesized on sitall and glass substrates by chemical bath deposition with the use of thiocarbamide and a CaCl_2 additive at concentrations of up to 5 mM. Introduction of the CaCl_2 additive into the reaction solution greatly prolongs the induction period of the process of synthesis. The thicknesses of the PbS and PbS(Ca) films are, correspondingly, 200 and 150 nm at an average crystallite dimension of ~100 nm. The maximum calcium content in the films is 0.06 at % for layers on sitall substrates and 0.11 at % for layers on glass substrates. Doping with calcium does not influence the crystal structure of lead sulfide (the cubic B 1 structure, space group Fm 3 $$\bar {m}$$ ) but brings about an increase in the crystal-lattice period from a = 0.59343(2) nm to a = 0.59413(1) nm, an increase in microstrains, and partial ordering of the crystallites forming the film. Upon the introduction of calcium, the band gap decreases from E _ g = 0.40 eV at 295 K (0.38 eV at 90 K) to E _ g = 0.38 eV (0.37 eV). The introduction of up to 5 mM of CaCl_2 into the reaction mixture increases the voltage–power sensitivity of the films by a factor of ~1.7, which is attributed to oxygen-containing compounds formed in the films as a result of the increase in the induction period of the process of synthesis.

Mineralogy of the clay fraction of Alfisols in two slope curvatures: III - spatial variability

A good knowledge of the spatial distribution of clay minerals in the landscape facilitates the understanding of the influence of relief on the content and crystallographic attributes of soil minerals such as goethite, hematite, kaolinite and gibbsite. This study aimed at describing the relationships between the mineral properties of the clay fraction and landscape shapes by determining the mineral properties of goethite, hematite, kaolinite and gibbsite, and assessing their dependence and spatial variability, in two slope curvatures. To this end, two 100 × 100 m grids were used to establish a total of 121 regularly spaced georeferenced sampling nodes 10 m apart. Samples were collected from the layer 0.0-0.2 m and analysed for iron oxides, and kaolinite and gibbsite in the clay fraction. Minerals in the clay fraction were characterized from their X-ray diffraction (XRD) patterns, which were interpreted and used to calculate the width at half height (WHH) and mean crystallite dimension (MCD) of iron oxides, kaolinite, and gibbsite, as well as aluminium substitution and specific surface area (SSA) in hematite and goethite. Additional calculations included the goethite and hematite contents, and the goethite/(goethite+hematite) [Gt/(Gt+Hm)] and kaolinite/(kaolinite+gibbsite) [Kt/(Kt+Gb)] ratios. Mineral properties were established by statistical analysis of the XRD data, and spatial dependence was assessed geostatistically. Mineralogical properties differed significantly between the convex area and concave area. The geostatistical analysis showed a greater number of mineralogical properties with spatial dependence and a higher range in the convex than in the concave area.

Cristallochemical characterization of synthetic Zn-substituted maghemites (g-Fe2-xZn xO3)

Maghemite (g-Fe2O3) is the most usually found ferrimagnetic oxide in red basalt-derived soils. The variable degrees of ionic substitution of Fe3+ for different metals (e.g. Ti4+, Al3+, Mg2+, Zn2+, and Mn2+) and non-metals in the maghemite structure influence some cristallochemical features of this iron oxide. In this study, synthetic Zn-substituted maghemites were prepared by co-precipitation in alkaline aqueous media of FeSO4.7H2O with increasing amounts of ZnSO4.7H2O to obtain the following sequence of Fe3+ for Zn2+ substitutions: 0.0, 0.025, 0.05, 0.10, 0.15, 0.20, and 0.30 mol mol-1. The objective of this work was to evaluate the cristallochemical alterations of synthetic Zn-substituted maghemites. The dark black synthetic precipitated material was heated to 250 °C during 4 h forming a brownish maghemite that was characterized by chemical analysis as well as X ray diffraction (XRD), specific surface area and mass-specific magnetic susceptibility. The isomorphic substitution levels observed were of 0.0013, 0.0297, 0.0590, 0.1145, 0.1764, 0.2292 and 0.3404 mol mol-1, with the formation of a series of maghemites from Fe2Zn0O3 to Fe(1.49)Zn(0.770)O3 . The increase in Fe3+ for Zn2+ substitution, [Zn mol mol-1] increased the dimension a0 of the cubic unit cells of the studied maghemites according to the regression equation: a0 = 0.8343 + 0.02591Zn (R² = 0.98). On the other hand, the mean crystallite dimension and mass-specific magnetic susceptibility of the studied maghemites decreased with increasing isomorphic substitution.

Phonon Confinement in SiC Nanocrystals: Comparison of the Size Determination Using Transmission Electron Microscopy and Raman Spectroscopy

Silicon carbide fibers of different generation/processing routes (NLM-Nicalon and Tyranno SA3) were thermally treated to trigger the growth of nanocrystals, which were analyzed using Raman spectroscopy and transmission electron microscopy (TEM). The nanocrystals were also aged in molten sodium nitrate to investigate their reactivity. The spatial correlation model has been used to model the Raman spectra and extract accurate and statistical information on the nanocrystallites' structure and dimension. For the NLM fibers, an average size of 2.5 to 7.0 nm was calculated, which was in good agreement with TEM observations. For the Tyranno SA3 fiber, despite the heavily faulted stacking sequence, the Raman peaks remained sharp, indicating that the crystallite dimension calculated from the Raman spectra is only dependent on the actual size of the nanocrystals and is not affected by the sequence of the stacking faults.

Hydrothermal Synthesis and Properties of Ce1−xMxO2-δ(M = La, Bi, Sm, Pr, Tb) Solid Solutions

ABSTRACTA systematic study of hydrothermally prepared Ce1−x,MxO2−δ, (M= Sm, Bi, Pr, Tb; x= 0-0.30) solid solutions, promising materials for application in solid oxide fuel cells and oxygen membranes is presented. Ultrafine particles of uniform crystallite dimension, ∼ 20 nm can be formed in 30 min. under hydrothermal conditions (260°C, 10 MPa). The small particle size (20-50 nm) of the hydrothermally prepared materials allows sintering of the samples into highly dense ceramics at 900-1350°C, significantly lower temperatures than 1600-1650°C required for samples prepared by solid state techniques. The solubility limit of Bi2O3, in CeO2, was determined to be around 20 mol. %. The maximum conductivity, σ600°C ∼ 4.4 × 10−3 S/cm with Ea = 1.01 eV, and σ600°C = 5.7 × 10−3 S/cm with Ea ≈ 0.9 eV was found at x= 0.20 and x= 0.17 for Bi and Sm, respectively. In the Ce-Pr/Tb oxide systems, in addition to the high oxide ion conductivity, electronic conductivity occurs through the hopping of small polarons by a thermally activated mechanism (electron hopping from the Pr3+/Tb3+ to a neighboring Pr4+/Tb4+ ion).

Characterization of Silicon Carbide thin Films Deposited by Laser Ablation on [001] and [111] Silicon Wafers

ABSTRACTStoichiometric films of 3C SiC, 50 to 1000 nm thick were deposited on Si wafers by laser ablation of ceramic stoichiometric SiC targets. Films grown at substrate temperatures above 1000° C on [001] and above 900° C on [111] show orientation epitaxial to the Si substrate along the film normal. Depending on the deposition conditions, the oriented crystallite dimension along this direction ranges from 20 nm to over 100 nm. The crystallite dimensions in the film plane range from 20 to 70 nm. Raman spectra show the expected TO and LO lines from SiC but indicate that the films sometimes contain other material, for example (30 to 50 Å) graphitic inclusions or small amounts of polycrystalline silicon.