Crystallite Size Distribution Research Articles

Crystallization of Cu60Zr20Ti20 bulk metallic glass by high pressure torsion

Abstract Bulk metallic glass of Cu60Zr20Ti20 composition has been synthesized by copper mold casting. Slices of the as-cast glass has been subjected to severe plastic deformation by high-pressure torsion for different whole turns. The microstructure and the thermal behavior of the deformed disks have been investigated by X-ray diffraction and differential scanning calorimetry. It was confirmed that the initial compression preceding the high pressure torsion induces crystallized structure, which shows only minor further changes upon the severe plastic shear deformation achieved by twisting the sample. The X-ray line profiles have been evaluated by the Convolutional Whole Profile Fitting algorithm in order to determine the evolution of the microstructural parameters, such as the median and variance of the crystallite size distribution, average crystallite size and dislocation density as a function of the number of revolutions. Hardness measurements by nanoindentation have also been carried out on the as-cast alloys and the deformed disks.

Microstructure Optimization of Mg-Alloys by the ECAP Process Including Numerical Simulation, SPD Treatments, Characterization, and Hydrogen Sorption Properties.

Both numerical simulation and hardness measurements were used to determine the mechanical and microstructural behavior of AZ31 bulk samples when submitted to the Equal Channel Angular Pressing (ECAP) technique. Billets of this representative of Mg-rich alloys were submitted to different numbers of passes for various ECAP modes (anisotropic A, isotropic BC). The strain distribution, the grain size refinement, and the micro-hardness were used as indicators to quantify the effectiveness of the different processing routes. Structural characterizations at different scales were achieved using Scanning Electron Microscopy (SEM), micro-analysis, metallography, Small Angle Neutron Scattering SANS, X-Ray Diffraction (XRD), and texture determination. The grain and crystallite size distribution and orientation as well as defect impacts were determined. Anelastic Spectroscopy (AS) on mechanically deformed samples have shown that the temperature of ECAP differentiate the fragile to ductile regime. MgH2 consolidated powders were checked for using AS to detect potential hydrogen motions and interaction with host metal atoms. After further optimization, the different mechanically-treated samples were submitted to hydrogenation/dehydrogenation (H/D) cycles, which shows that, for a few passes, the BC mode is better than the A one, as supported by theoretical and experimental microstructure analyses. Accordingly, the hydrogen uptake and (H/D) reactions were correlated with the optimized microstructure peculiarities and interpreted in terms of Johnson-Avrami- Mehl-Kolmogorov (JAMK) and Jander models, successively.

Photocatalytic and antibacterial activities study of prepared self-cleaning nanostructure surfaces using synthesized and coated ZnO nanoparticles with Curcumin nanodispersion

Abstract Zinc oxide nanoparticles had been synthesized and encapsulated using Curcumin nanoemulsions, Zn(Cur)O NPs, under subcritical water conditions. The effects of temperature (120, 140 and 160 °C) and pH values of the reaction solution (4, 7 and 10) on the particle size, grain size, cristallinity, specific surface area, band gap, Urbach energy, morphology, photocatalytic activity and antibacterial properties of the prepared Zn(Cur)O NPs were evaluated using XRD, FT-IR, SEM, EDX and UV-Vis spectroscopy analysis. The obtained results indicate that the prepared spherical and rod shapes Zn(Cur)O NPs had a crystallite size distribution of 10–100 nm. Furthermore, the results reveal that most uniform Zn(Cur)O NPs with highest photocatalytic activity, quantum yield (0.161 mol·m−2 s−1), specific surface area (242 m2/g), minimum band gap (2.62 eV) and Urbach energy (0.125 meV) were formed at 160 °C and natural pH. The highest antibacterial activities against both Gram positive and negative bacteria strains, were achieved using the synthesized Zn(Cur)O at 160 °C and basic pH(10).

Thermal and crystallization behavior of SiO2‐PbF2 glass system in the presence of ErF3 and Al2O3

AbstractOxyfluoride glass‐ceramics have been introduced as one of the best bulk hosts for upconversion process of rare‐earth ions. However, less attention to the technological topics in the process of glass crystallization has hindered the development of them in industrial scale applications. In this research, SiO2–PbF2 glasses were investigated to clarify the ambiguous role of rare‐earth ions and alumina content in the microstructure and crystallization behavior. Results indicated that Er3+ addition caused a liquid‐liquid phase separation via nucleation and growth mechanism, which led to single phase crystallization of β‐PbF2:Er3+ solid solution. Moreover, Er3+ had a significant effect on the crystallite size, size distribution, and PbF2 crystallization temperature. On the other hand, increasing Al2O3 content enhanced the transparency and thermal stability of glass samples, whereas it reduced the amount of fluorine loss and increased the dissolution of Er3+ in fluoride crystalline structure. These results address some of the most controversial issues about crystallization behavior of rare‐earth‐doped oxyfluoride glasses.

Structural and Magnetic Properties of Co‒Mn Codoped ZnO Nanoparticles Obtained by Microwave Solvothermal Synthesis

Zinc oxide nanoparticles codoped with Co2+ and Mn2+ ions (Zn(1−x−y)MnxCoyO NPs) were obtained for the first time by microwave solvothermal synthesis. The nominal content of Co2+ and Mn2+ in Zn(1−x−y)MnxCoyO NPs was x = y = 0, 1, 5, 10 and 15 mol % (the amount of both ions was equal). The precursors were obtained by dissolving zinc acetate dihydrate, manganese (II) acetate tetrahydrate and cobalt (II) acetate tetrahydrate in ethylene glycol. The morphology, phase purity, lattice parameters, dopants content, skeleton density, specific surface area, average particle size, average crystallite size, crystallite size distribution and magnetic properties of NPs were determined. The real content of dopants was up to 25.0% for Mn2+ and 80.5% for Co2+ of the nominal content. The colour of the samples changed from white to dark olive green in line with the increasing doping level. Uniform spherical NPs with wurtzite structure were obtained. The average size of NPs decreased from 29 nm to 21 nm in line with the increase in the dopant content. Brillouin type paramagnetism and an antiferromagnetic interaction between the magnetic ions was found for all samples, except for that with 15 mol % doping level, where a small ferromagnetic contribution was found. A review of the preparation methods of Co2+ and Mn2+ codoped ZnO is presented.

Synthesis of NiFe2O4 nanofibers by joint sol-gel and electrospinning technique

In this study, electrospinning combined with sol-gel technique is applied in order to produce magnetic nickel ferrite (Ni-ferrite) nanofibers. The prepared Ni-ferrite gel was mixed with poly(vinylpyrrolidone) (PVP) solution which was used as a spinning aid to enable spinnability of the mixture. Structural and morphological characteristics of the as-spun ferrite gel/PVP composite web structure and calcinated Ni-ferrite nanofibers were analyzed using scanning electron microscopy (SEM). Phase composition analysis was carried out by Fourier-transform infrared (FT-IR) spectroscopy, X-Ray diffraction analysis (XRD) and 57Fe Mössbauer spectroscopy (MS). The obtained results suggest that the pure nanocrystalline NiFe2O4 dense mat to the almost coral-like structure of fibers with diameters ranging from hundreds of nanometers to few micrometers was obtained. The results of MS analysis revealed the existence of a crystallite size distribution within the material as well as the existence of a superparamagnetic fraction with very small crystallite sizes (<13nm). Magnetic behavior of the obtained material at elevated temperatures was also scrutinized using thermomagnetic measurements (TM) up to 800 °C.

X-ray diffraction Warren–Averbach mullite analysis in whiteware porcelains: influence of kaolin raw material

ABSTRACTCompositional and microstructural analysis of mullites in porcelain whitewares obtained by the firing of two blends of identical triaxial composition using a kaolin B consisting of ‘higher-crystallinity’ kaolinite or a finer halloysitic kaolin M of lower crystal order was performed. No significant changes in the average Al2O3 contents (near the stoichiometric composition 3:2) of the mullites were observed. Fast and slow firing at the same temperature using B or M kaolin yielded different mullite contents. The Warren–Averbach method showed increase of the D110 mullite crystallite size and crystallite size distributions with small shifts to greater values with increasing firing temperature for the same type of firing (slow or fast) using the same kaolin, as well as significant differences between fast and slow firing of the same blend at different temperatures for each kaolin. The higher maximum frequency distribution of crystallite size observed at the same firing temperature using blends with M kaolin suggests a clearer crystallite growth of mullite in this blend. The agreement between thickening perpendicular to prism faces and mean crystallite sizes <D110> of mullite were not always observed because the direction perpendicular to 110 planes is not preferred for growth.

Facile synthesis of La-doped In2O3 hollow microspheres and enhanced hydrogen sulfide sensing characteristics

The undoped and 1.0–5.0 mol% La–doped In2O3 hollow microspheres have been successfully synthesized via a simple hydrothermal method without template and gas sensor have been fabricated basing on them. The nanostructures and morphologies of the maintained hollow spheres were characterized by various experimental techniques. The gas sensing properties of these hollow microspheres were investigated systematically. The results indicated that among all the samples (pure, 1.0, 3.0 and 5.0 mol% La–doped In2O3), 3.0 mol% La–doped In2O3 exhibited the highest response toward 10 ppm hydrogen sulfide (H2S) at 200 °C, having a response value of 17.8, approximately 4.8 times higher than pure In2O3. Furthermore, excellent selectivity, good repeatability and outstanding long-term stability were also achieved. The significantly enhanced sensing properties to H2S could be attributed to the changes in distribution of different oxygen components, crystallite size and specific surface area caused by La doping.

Yttrium promoted Ni-based double-layered hydroxides for dry methane reforming

Abstract Yttrium modified Ni-based double-layered hydroxides were tested as novel catalysts in dry methane reforming. The catalysts were characterized by XRF, BET analysis, XRD, TPR-H2, TPD-CO2, TGA/DSC-MS, H2 chemisorption and TEM. Co-precipitation with yttrium (III) nitrate hexahydrate resulted in increased specific surface area, smaller Ni crystallite size, enhanced reducibility, and higher distribution of weak and medium basic sites as compared to Y-free material. The DRM catalytic tests, carried out in the temperature range of 850–600 °C, led to a significant improvement of activity, with the 1.5 wt % Y-promoted catalyst being the most efficient in converting both CH4 and CO2. Moreover, the 10 h test at 700 °C further confirmed enhanced stability for this HTNi-Y1.5 catalyst. Higher CO2 conversion than CH4 conversion and less CO compared to H2 proves that side reactions are occurring simultaneously.

Size and Shape Distribution of Bipyramidal TiCh Nanoparticles by Transmission Electron Microscopy - an Inter-Laboratory Comparison

Extraction of true, 3D shape (and size) of non-spherical nanoparticles (NPs) is associated with errors by conventional 2D electron microscopy using projection images. Significant efforts within the ISO technical committee TC 229 ‘Nanotechnologies’ are aimed at establishing accurate TEM and SEM measurement of NP size and shape as robust, standard procedures. Study groups have been organizing inter-laboratory comparisons on well-selected NP systems according to the market needs, such as aggregated titania nano-powder for which size and shape distribution of primary crystallites of irregular shape must be measured accurately. To be noticed is e. g. the fact that the measurement procedure allows only manual selection of the particles clearly distinguishable for analysis as well as manual definition of the contour of the imaged NPs. An inter-laboratory exercise on titania NPs (pure anatase, grown by hydrothermal synthesis) of well-defined non-spherical shape, i.e. bipyramidal has been recently started within ISO/TC 229 under similar conditions as for the irregular shaped titania. Overlapped particles were allowed to be considered, as long as they are clearly distinguishable. One decisive NP selection criterion was to analyze only those NPs with a roundness value below 0.7, i.e. the NPs laying on the support foil and, hence, with projection areas clearly deviating from perfect circles (R=1). The overall evaluation (for 15 labs) of the size descriptors (area, Feret, minFeret, perimeter) and shape descriptors (aspect ratio, roundness, compactness, extent) by analysis of variance is just to be finished and included in ISO/WD 21363 Nanotechnologies -- Protocol for particle size distribution by transmission electron microscopy.

Effects of ordered mesoporous bimodal structures of Fe/KIT-6 for CO hydrogenation activity to hydrocarbons

Highly ordered mesoporous bimodal structures of KIT-6 with average pore diameters of 3.6 and 5.4 nm originated from its different wall thickness were newly synthesized and applied for CO hydrogenation to hydrocarbons through Fischer-Tropsch Synthesis (FTS) reaction using the supported iron nanoparticles. The ordered bimodal mesopore structures of the KIT-6 with smaller than 5.4 nm in size showed a significantly enhanced FTS activity by selectively forming heterogeneous bimodal crystallite size distributions of iron nanoparticles. The positive effects of the mesoporous bimodal structures of the KIT-6 were mainly attributed to the facile formation of the spatially confined smaller iron nanoparticles, which can be strongly interacted with the structurally stable ordered mesoporous KIT-6 with the co-presence of the larger iron nanoparticles on the outer surfaces of the mesoporous bimodal KIT-6. After adding small amount of potassium promoter with 2 wt%K on the mesoporous bimodal Fe/KIT-6, a slight increase of CO conversion as well as C5+ selectivity with less extent of CO2 formation was observed due to the suppressed activity of water-gas shift reaction. However, the structurally unstable monomodal KIT-6 having a relatively larger mesopore above 7.3 nm showed a lower FTS activity by preferentially forming an inactive amorphous carbon species. A superior FTS activity on the ordered mesoporous bimodal Fe/KIT-6 was attributed to the easy formations of smaller iron carbides, where the active smaller iron carbides were strongly interacted and spatially confined inside of the highly ordered mesoporous bimodal KIT-6 surfaces.

Full-section otolith microtexture imaged by local-probe X-ray diffraction

An optimized synchrotron-based X-ray diffraction method is described for the direct and efficient measurement of crystallite phase and orientation at micrometre resolution across textured polycrystalline samples of millimetre size (high scale dynamics) within a reasonable time frame. The method is demonstrated by application to biomineral fish otoliths. Otoliths are calcium carbonate accretions formed in the inner ears of vertebrates. Fish otoliths are essential biological archives, providing information for individual age estimation, the study of population dynamics and fish stock management, as well as past environmental and climatic conditions from archaeological specimens. Here, X-ray diffraction mapping is discussed as a means of describing the mineralogical structure and microtexture of otoliths. Texture maps could be generated with a fewa priorihypotheses on the aragonitic system. Full-section imaging allows quantitative intercomparison of crystal orientation coupled to microstructural description, across the zones of the otoliths that represent distinctive mineral organization. It reveals the extents of these regions and their internal textural structure. Characterization of structural and textural correlations across whole images is therefore proposed as a complementary approach to investigate and validate the local in-depth nanometre-scale study of biominerals. The estimation of crystallite size and orientational distribution points to diffracting domains intermediate in size between the otolith nanogranules and the crystalline units, in agreement with recently reported results.

Microstructural evolution of aluminum hydroxide gel during the hydration of calcium sulfoaluminate under different alkali concentrations

The present paper discusses the microstructural evolution of aluminum hydroxide (AH3) formed during the hydration of calcium sulfoaluminate in neutral and alkaline solutions (0-M NaOH, 0.01-M NaOH, 0.1-M NaOH, 1-M NaOH, 5-M NaOH and 8-M NaOH). Rietveld method and field emission scanning electron microscopy measurements were used to observe the evolution of crystallite size and particle size distribution, respectively. Furthermore, various characterization methods were used to complement the microstructure of AH3 phase. The result of 27Al MAS-NMR spectroscopy indicated the absence of the amorphous AH3 phase in all hydrated pastes. The degree of crystallinity, with respect to the AH3 phase, improved with increasing alkali concentration. However, AH3 phase can also react with OH− ion and even disappear in high alkaline conditions. In low alkaline conditions (i.e., 0-M NaOH, 0.01-M NaOH, 0.1-M NaOH), the AH3 phase had a nanocrystalline structure with an average crystallite size of about 8–9 nm and particle size distribution ranging from 110 nm to 210 nm. In high alkaline conditions (i.e., 5-M NaOH and 8-M NaOH), the AH3 phase presented a well-crystalline nature. The average crystallite size increased up to about 30–40 nm and the particle size distribution was mostly 800–1400 nm (5-M NaOH) or 1000–1500 nm (8-M NaOH).

Structural and elastic properties of nickel–zinc ferrite nano-particles doped with lithium

The X-ray and Fourier transform infrared (FTIR) spectroscopy are used to studying the structural and elastic properties of Ni-Zn ferrite doped lithium according to the chemical formula Ni1−xZnx−2yLiyFe2+yO4, where (0 ≤ x ≤ 0.5) and (y = 0, 0.01, 0.02, 0.03, and 0.04) which preparation by sol–gel method. Lattice constant (a), crystallite size, and cation distribution are deduced from XRD. FTIR measurement exhibits that two absorption bands (ν1 and ν2) around 400–800 cm−1 that confirm the existence of tetrahedral and octahedral sites of ferrite. Force constant, elastic wave velocity, bulk modulus, and young’s modulus also reported. The force constant for A-site is larger than for B-site which vary between (KA = 131.6–145.5 N/m) and (KB = 97.8–102.3 N/m) where can be found the values of elastic constant for nanoparticle is agreement with those of bulk material.

Size Control of Cobalt-Doped ZnO Nanoparticles Obtained in Microwave Solvothermal Synthesis

This article presents the method of size control of cobalt-doped zinc oxide nanoparticles (Zn1−xCoxO NPs) obtained by means of the microwave solvothermal synthesis. Zinc acetate dihydrate and cobalt(II) acetate tetrahydrate dissolved in ethylene glycol were used as the precursor. It has been proved by the example of Zn0.9Co0.1O NPs (x = 10 mol %) that by controlling the water quantity in the precursor it is possible to precisely control the size of the obtained Zn1−xCoxO NPs. The following properties of the obtained Zn0.9Co0.1O NPs were tested: skeleton density (helium pycnometry), specific surface area (BET), dopant content (ICP-OES), morphology (SEM), phase purity (XRD), lattice parameter (Rietveld method), average crystallite size (FW1/5/4/5M method and Scherrer’s formula), crystallite size distribution (FW1/5/4/5M method), and average particle size (from TEM and SSA). An increase in the water content in the precursor between 1.5% and 5% resulted in the increase in Zn0.9Co0.1O NPs size between 28 nm and 53 nm. The X-ray diffraction revealed the presence of only one hexagonal phase of ZnO in all samples. Scanning electron microscope images indicated an impact of the increase in water content in the precursor on the change of size and shape of the obtained Zn0.9Co0.1O NPs. The developed method of NPs size control in the microwave solvothermal synthesis was used for the first time for controlling the size of Zn1−xCoxO NPs.

Helium diffusion parameters of hematite from a single-diffusion-domain crystal

This contribution reports new parameters for helium diffusion in hematite useful for interpretation of cosmogenic 3He and radiogenic 4He chronometry. Fragments of a coarse, euhedral single crystal of hematite from Minas Gerais, Brazil were subjected to bulk step-heating helium diffusion experiments after proton irradiation to make a uniform distribution of 3He. Aliquots of three different grain sizes ranging from ∼300 to ∼700 μm in equivalent-sphere radius yielded helium diffusion activation energies Ea ∼ 170 kJ/mol, very similar to previous estimates for Ea in hematite. Uniquely in this specimen, diffusivity varies with the dimensions of the analyzed fragments in precisely the fashion expected if the diffusion domain corresponds to the physical grain. This contrasts with previous studies that concluded that the analyzed hematites consist of polycrystalline aggregates in which helium migration is governed by the size distribution of the constituent crystallites. These new data permit a direct estimate of the helium diffusivity at infinite temperature for hematite of ln(Do) = −0.66 ± 0.35 in cm2/s.The major implication of the new diffusion parameters is that hematite is very retentive of helium even at very small crystal sizes. For example, a 20 nm radius hematite crystal, at the smallest end of the size range so far described in dated polycrystalline hematite specimens, will retain more than 99% of its ingrown He over 1 Myr at 30 °C, and more than 90% over 100 Myr. Under most conditions, hematite is close to quantitatively helium-retentive on the Earth's surface, simplifying radiogenic and cosmogenic helium dating of this phase. In a system cooling at 10 °C/Myr, the 20 nm hematite crystal has a He closure temperature of ∼70 °C, similar to a typical ∼100 μm apatite crystal.Helium is likely held tightly in hematite owing to its dense hexagonal closest packing structure and absence of migration-enhancing channels. The isostructural minerals corundum and ilmenite are likely to be similarly helium retentive.

Tunable Crystallization and Nucleation of Planar CH3NH3PbI3 through Solvent-Modified Interdiffusion.

A smooth and compact light absorption perovskite layer is a highly desirable prerequisite for efficient planar perovskite solar cells. However, the rapid reaction between CH3NH3I methylammonium iodide (MAI) and PbI2 often leads to an inconsistent CH3NH3PbI3 crystal nucleation and growth rate along the film depth during the two-step sequential deposition process. Herein, a facile solvent additive strategy is reported to retard the crystallization kinetics of perovskite formation and accelerate the MAI diffusion across the PbI2 layer. It was found that the ultrasmooth perovskite thin film with narrow crystallite size variation can be achieved by introducing favorable solvent additives into the MAI solution. The effects of dimethylformamide, dimethyl sulfoxide, γ-butyrolactone, chlorobenzene, and diethyl ether additives on the morphological properties and cross-sectional crystallite size distribution were investigated using atomic force microscopy, X-ray diffraction, and scanning electron microscopy. Furthermore, the light absorption and band structure of the as-prepared CH3NH3PbI3 films were investigated and correlated with the photovoltaic performance of the equivalent solar cell devices. Details of perovskite nucleation and crystal growth processes are presented, which opens new avenues for the fabrication of more efficient planar solar cell devices with these ultrasmooth perovskite layers.

Role of copper and silver modified titania photoanode on performance engineering of dye sensitized solar cells

Effective charge carrier separation and charge transport at the interface layers of dye sensitized solar cells (DSSC) play a vital role in attaining superior photo conversion efficiency. The charge carrier separation and transport at the interfaces of DSSC can be improved by preparing suitable material interfaces based on the band edge offset. Present work reports the preparation of copper (Cu) and silver (Ag) modified titania as an efficient photoanode for DSSC. The structural analyses confirm the crystallinity of the samples in anatase phase with nanoscale crystallite size distribution. The optical analyses show an elevated absorption of the modified samples compared to the pristine titania. A prototype dye sensitized solar cell was fabricated using pristine and modified photoanodes, and the performance have been evaluated through I–V analysis with and without illumination. Cu and Ag modified titania photoanode showed 4.4 and 15 times enhanced photo conversion efficiency (PCE) respectively, compared to the pristine titania and this may be attributed to the effective charge separation and charge transport. The above result opens up a new area of research in modifying the photoanode of the next generation solar cells.

On the Intrinsic Limits of the Convolution Method to Obtain the Crystallite Size Distribution from Nanopowders Diffraction

The present work briefly reviews the convolution of crystallite shape functions and discusses its experimental limitations. The diffraction from a theoretical spherical shape powder is used to exemplify the limits of the convolution procedure. Mean lattice distortions were not considered since the discussed limitations are inherent to the convolution method using Fourier transforms. The diffraction pattern and the convolution were calculated using appropriate macros for the Topas program. It is shown that very small crystallites require a large 2θ convolution span and the smallest subdivision for the distribution will depend on this convolution span. To show the importance of the convolution limits and its application, the nanocrystalline CeO2 round-robin diffraction pattern was evaluated. The chord frequency distribution by XRD showed conformity with the chord distribution calculated from a grain size histogram obtained by transmission electron microscopy for this sample.

Dislocation, crystallite size distribution and lattice strain of magnesium oxide nanoparticles

The oxide of magnesium nanoparticles synthesized using sol-gel method and analysis of the structural properties was conducted. The functional groups of nanoparticles has been analysed by Fourier Transform Infrared Spectroscopy (FT-IR). Dislocations, average size of crystal, strain, stress, the energy density of crystal, crystallite size distribution and morphologies of the crystals were determined based on X-ray diffraction profile analysis. The morphological of the crystal was analysed based on the image resulted from SEM analysis. The crystallite size distribution was calculated with the contention that the particle size has a normal logarithmic form. The most orientations of crystal were determined based on the textural crystal from diffraction data of X-ray diffraction profile analysis. FT-IR results showed the stretching vibration mode of the Mg-O-Mg in the range of 400.11-525 cm−1 as a broad band. The average size crystal of nanoparticles resulted is 9.21 mm with dislocation value of crystal is 0.012 nm−2. The strains, stress, the energy density of crystal are 1.5 x 10−4; 37.31 MPa; 0.72 MPa respectively. The highest texture coefficient value of the crystal is 0.98. This result is supported by morphological analysis using SEM which shows most of the regular cubic-shaped crystals. The synthesis method is suitable for simple and cost-effective synthesis model of MgO nanoparticles.