Apparent Crystallite Size Research Articles

Determination of the average crystallite size and the crystallite size distribution: the envelope function approach EnvACS.

A procedure is presented to exactly obtain the apparent average crystallite size (ACS) of powder samples using standard in-house powder diffraction experiments without any restriction originating from the Scherrer equation. Additionally, the crystallite size distribution within the sample can be evaluated. To achieve this, powder diffractograms are background corrected and long-range radial distribution functions G(r) up to 300 nm are calculated from the diffraction data. The envelope function f env of G(r) is approximated by a procedure determining the absolute maxima of G(r) in a certain interval (r range). Fitting of an ACS distribution envelope function to this approximation gives the ACS and its distribution. The method is tested on diffractograms of LaB6 standard reference materials measured with different wavelengths to demonstrate the validity of the approach and to clarify the influence of the wavelength used. The latter results in a general description of the maximum observable average crystallite size, which depends on the instrument and wavelength used. The crystallite site distribution is compared with particle size distributions based on transmission electron microscopy investigations, providing an approximation of the average number of crystallites per particle.

Influence of purification methods on the extraction of nanocrystals from bio-hydroxyapatite under consideration of the coalescence phenomenon

The coalescence of nanocrystals that occurs during low-temperature thermal treatments during the purification of hydroxyapatite from pigs has not yet been studied in the context of low-temperature environmentally friendly purification. To preserve the nature of hydroxyapatite, two extraction methods were investigated: Route 1 (autoclave and Soxhlet) and Route 2 (calcination at low temperatures with different times). The focus is on observing the effectiveness of removing fats and proteins while maintaining crystallite size and morphology. DSC showed that coalescence of crystallites occurred at 452, 566, 648, and 704 °C. Raw has a higher IR FWHM (phosphate band) due to the organic material; R1 had a lower FWHM (partial removal of lipids and proteins). Increasing the calcination temperature decreases the FWHM, indicating a shift in vibrational states from surface to bulk, leading to an increase in apparent crystallite size due to coalescence. For 20–80 h at quasi-stable temperatures of 400 and 500 °C, no significant changes occur in the IR spectrum. X-ray diffraction indicates the removal of organic material during calcination, as the peaks become clearer with increasing temperature. The crystallite size is not affected and remains in similar ranges. Purification with hydroxide shows an increase in both lattice parameters, in addition to the fluctuations that occur due to the ionic substitutions that naturally occur in biogenic HAp. And the TEM study confirms that the changes in apparent size from 2D to 3D are the result of the phenomenon of interplanar coalescence at low temperatures that occurs in sintering processes.

Ternary nanocomposite comprising MnO2, GQDs, and PANI as a potential structure for humidity sensing applications

Humidity sensing has been offering a noticeable contribution in different industrial, medical, and agricultural activities. Here, graphene quantum dots doped with polyaniline (PANI) and MnO2 were successfully prepared. The synthesized system is exposed to a set of structural, morphological, and optical investigations. The apparent crystallite size is less than 30 nm, reflecting the nanoscale of the structure, and thus validating the preparation route as evident on XRD pattern. SEM images show a fibrous structure where polyaniline dominates and covers most of the structure’s surface. The evident bands of the FTIR spectrum are designated to the component used in synthesis confirming the chemical structure of the fabricated system. The humidity sensing study of the synthesized structure is carried out through a wide range of relative humidity (RH) levels range of 11–97%. The response and recovery times of the fabricated structure are found to be around 120 and 220s, respectively.

Promising nanocomposites for food packaging based on cellulose – PCL films reinforced by using ZnO nanoparticles in an ionic liquid

The fact that most composites consist of polluting synthetic materials has prompted a search for biodegradable replacements based on cellulose fibers and polycaprolactone as potential packaging materials. In this work, we developed a green, efficient approach to rendering hydrophobic polycaprolactone (PCL) compatible with hydrophilic cellulose fibers by using an ionic liquid as a nanowelding agent in the presence of zinc oxide nanoparticles (ZnONPs). Transparent biobased nanocomposite films were thus directly obtained by in situ ring-opening polymerization (ROP) of ε-caprolactone (CL) monomers onto the dissolved cellulose matrix by using the ionic liquid 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac). [EMIM]Ac and ZnONPs were efficiently catalyzed ε-caprolactone ROP under mild conditions. Cellulose-grafted PCL nanocomposite films were obtained by adding variable amounts of CL and ZnONPs to the cellulose matrix. The maximum grafting of 40% was achieved by using 5▒wt% ZnONPs and 70% CL. FTIR spectra confirmed the presence of PCL in the nanocomposites. Also, FE-SEM revealed uniform dispersion of ZnONPs and PCL in the regenerated cellulose matrix, and trapping of nanoparticles in nanofibrils after the cellulose matrix was regenerated. X-ray diffraction (XRD) spectra showed a decreased apparent crystallinity and crystallite size. The XRD results also confirmed that the crystal properties of the nanocomposite films and an all-cellulose composite (ACC) were almost identical. The mechanical, barrier and optical properties of the nanocomposite films were significantly better than those of the ACC film by effect of the incorporation of ZnONPs and PCL especially with 5▒wt% ZnONPs and 70% CL). The nanocomposite films exhibited acceptable antioxidant activity and UV-light barrier properties, so they hold promise for used in food packaging. Nanocomposite films are in fact multifunctional materials with the potential for use in cellulose-based food packaging by virtue of their being transparent and bio-based, and possessing very good water vapor and oxygen barrier properties.

Photocatalytic Degradation of Alizarin Red S by Using a Layered Zn/Al-NO3 Double Hydroxides

This research presents the use of layered Zn-Al-NO3 layered double hydroxides (LDH) which photocatalytically degraded Alizarin Red S (ARS) under a UV source. The prepared photocatalytic material was characterized by employing the use of X-Ray Diffraction (XRD) analysis, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), Fourier Transform Infrared (FTIR) spectroscopy and Band gap Energy using Tauc plot. The analyzed XRD patterns of Zn-Al-NO3 show characterized diffraction angles typical of LDH. Also, the XRD patterns were used to calculate the apparent crystallite size (32.5 nm). The bandgap energy of the LDH was determined to be 3.2 eV. The effect of the initial concentration of the ARS dye, catalyst amount or dose and pH were also determined. The Zn-Al-NO3 efficiently degraded ARS at (69.91%), which could be attributed to its smaller crystallite size. The kinetic study (reaction rate and half-life) of the photodegradation appeared to be R 2 = 0.9886 and (t1/2) = 76.7 min, the data fit the Langmuir Hinshelwood expression, which follows the pseudo-first-order kinetic model.

Facile Synthesis and Characterization of Molybdenum Carbides/Carbon Nanocomposites by Laser Pyrolysis

This short communication reports on the facile and scalable synthesis and characterization of molybdenum carbides/carbon nanocomposites prepared by laser pyrolysis in a one-step process. Water and commercial molybdenum oxide were used as low-cost environmentally friendly precursors. The nanocomposites are mainly composed of two types of carbides with different apparent crystallite sizes, 21 ± 1 nm and 9 ± 1 nm for Mo2C and MoC1−x, respectively. Thanks to a simple annealing at 500 °C under argon, it was possible to increase the specific surface area around 50 m2/g without changing the morphology of the nanocomposite.

X-ray diffraction analysis by Rietveld refinement of FeAl alloys doped with terbium and its correlation with magnetostriction

Fe81Al19 polycrystalline alloys doped with Tb (0–0.25 at%) were obtained by arc melting. The introduction of Tb favors the formation of columnar grains in the microstructure of the alloys, which develops a texture in the [100] crystal direction. Microstructural examination shows that the alloys are composed in great proportion by the disordered body-centered cubic (bcc), A2 phase and by a small proportion of the ordered bcc, B2 phase. As a consequence of doping with Tb, the lattice parameter increases, so the calculated apparent crystallite size increases, indicating a decrease in dislocation density and therefore in microstrains. The change in the magnetostriction with the magnetic field, dλT/dH, is directly related to strain anisotropy that can favor the iron easy magnetization axis on the [100] direction. An increase in total magnetostriction is found in the doped alloys with a maximum of 90 × 10−6 at 300 K for the alloy containing 0.027 at% Tb. This enhancement is a threefold value of the undoped alloy, which is attributed to the smaller maximum strain value and the preferential orientation formation by the columnar grains.

WAXS in-situ study of R-BAPB polyetherimid double-melting behavior

Reactor particles of nascent polyetherimid (PI) R-BAPB powder consist of numerous morphological units of the lamellar type, which have semicrystalline structure. Two endo-peaks at 318 °C and 340 °C were observed in the DSC thermogram of the PI powder. A unique in-situ thermo-WAXS experiment showed no significant difference in X-ray peak profiles when the sample was heated from room temperature up to 330 °C, (the valley between the low- and high-temperature endo-peaks). At that point the WAXS reflections became sharper and much better resolved without a visible crystal cell transformation. It was revealed that the degree of crystallinity dropped near 330 °C and continued decreasing until the complete melting of the sample. The low-temperature endo-peak is associated with melting of numerous small crystallites leading to the sharp amorphization of the sample and to a significant increase in the apparent crystallite size at 330 °C. The high-temperature endo-peak can then be attributed to melting of the larger crystallites formed from the melt during isothermal crystallization at 330 °C. Using WAXS profiles, it was also possible to evaluate the volumetric coefficient of thermal expansion of the crystalline part of the studied polymer as CTEvol = 3.8·10−4 K−1.

Near band edge and defect emissions in wurtzite Cd0.025Mg0.10Zn0.875O nanocrystals

We report on near band edge and local defects emissions in Cd0·025Mg0·10Zn0·875O (CdMgZnO) nanoparticles (NPs) as a function of temperature, where a strong temperature-dependent near-infrared emission around 1.7 eV (~730 nm) has been observed. The NPs were synthesized by a modified sol-gel method and were annealed at 750 °C after growing. The crystallographic parameters have been determined by 2-dimensional synchrotron x-ray diffraction (XRD) and conventional XRD analysis, confirming their growth within the wurtzite phase with a preferred orientation along the (101) plane and an apparent crystallite size of 52.72 ± 0.18 nm. This apparent crystallite size is consistent with the nearly hexagonal particle shape (50.15 ± 0.38 nm) obtained from high resolution transmission electron microscopy. Valence Electron Energy Loss Spectroscopy (VEELS) has been conducted to gain information on the band structure and interband transitions. From the VEELS spectrum, an onset bandgap of 3.2 ± 0.3 eV was attributed to Cd/Mg co-doped ZnO. The temperature-dependent photoluminescence properties and enhancement of the optically active local defects emission have been analyzed.

On the structural evolution of textile grade polyacrylonitrile fibers during stabilization and carbonization: Towards the manufacture of low‐cost carbon fiber

We made an attempt to produce low cost carbon fibers using textile grade polyacrylonitrile (Tex-PAN) fibers. Here, we examined fibers collected from each zone of the stabilization and carbonization furnaces and mechanical and physical properties were measured with the aim to evaluate their chemical stability and final properties. Thermal studies revealed a cyclization peak at 308 °C and an extent of reaction of 66.2% after stabilization process. The apparent crystallite size after carbonization was determined by X-ray diffraction and it was found to be smaller in Tex-PAN fibers than commercial PAN fibers. Raman spectroscopy confirmed the development of the graphitic structures within the carbon fibers produced from Tex-PAN. Interestingly, the tensile properties (3.25 GPa) of carbon fibers from Tex-PAN fibers were found to be comparable with those of commercial PAN fibers. Precursor fibers take more than half of total production cost for producing carbon fibers (CFs), Tex-PAN precursor can be an indispensable candidate for low cost CF production.

Apparent crystallite domain size growth in metal oxide nanocrystal ensembles: The importance of surface reactivity of powders for processing

A major challenge related to metastable oxide nanoparticles as starting materials for ceramics is to achieve control over their processing related property changes. We compared MgO nanoparticles with those of Ba2+-admixtures exhibiting enhanced surface reactivity. The enhanced surface reactivity promotes particle coarsening and gives rise to a multimodal particle size distribution with a fine fraction of nanocubes (d ​< ​10 ​nm) and a coarse fraction of larger particles. Water adsorption from the ambient has a key influence on sintering and resulting microstructures. After sample exposure to water vapor there arise significant changes in structure and crystallite domain size that originate from size dependent dissolution effects transforming only the fine fraction of particles (<10 ​nm) into hydroxides. Thus, controlled Ba-admixture and segregation at the single particle level provides means to address the impact of surface basicity, hydration and consecutive surface chemistry on microstructure evolution during processing.

Rietveld‐based quantitative phase analysis of B‐type starch crystals subjected to ultrasound and hydrolysis processes

AbstractThe functional properties of starch could be improved with structural tuning through a number of processing techniques, intensely explored in the past few years by several industries such as food, pharmacology, paper and cosmetics. The current work proposes a model for determining the crystallinity of B‐type Starch based only on X‐ray diffraction (XRD) and Rietveld refinement method (RM). A sample of food grade potato starch (described as B‐type Starch) was submitted to structural modifications using high energy ultrasound followed by acid hydrolysis. The sample was thereby studied by powder XRD measurements and later refined using RM. Apparent crystallite sizes were found to be stable after ultrasound processing, while the crystallinity increased 10% after hydrolysis. Hence, this procedure provides an easy and alternative approach for estimating the crystallinity and the crystallite sizes of the starch sample.

Investigation of structural, microstructural and magnetic properties of YbxY1-xF3 solid solutions

In this investigation, we have synthesized YbxY1-xF3 solid solutions by fluorination of yttrium and ytterbium sesquioxides with ammonium hydrogen difluoride. According to the XRD analysis, all synthesized YbxY1-xF3 samples have an orthorhombic crystal structure belonging to the β-YF3 structural type. The refinement of crystal structure was done by the Rietveld method within the Pnma space group using the TCH pseudo-Voigt function. The anisotropic peak broadening was analyzed, and the average apparent crystallite size is about 50 nm with a small anisotropy of shape, while the significant microstrain that is highly anisotropic is present in all samples. The temperature-dependent magnetic susceptibility was analyzed by applying the model of a free ion perturbed by the crystal field. We have obtained the effective magnetic quantum numbers Mieff of four Kramer's doublets of Yb3+ ion along with the entire crystal field splitting of the 2F7/2 manifold of Yb3+ in YF3. The acquired maximum energy splitting of the ground level is about 150 K in our most diluted samples. The field-dependent isothermal magnetization measurements were carried out at various temperatures and analyzed by classical Langevin function. Results obtained from magnetic measurements show that all YbxY1-xF3 (x ≠ 0) solid solutions exhibit pure paramagnetic behavior in the whole temperature range from 2 to 300 K, with a predominant antiferromagnetic exchange interactions.

A simple mixing method for polyamide 12/attapulgite nanocomposites: structural and mechanical characterization

In this work, the attapulgite (ATP) was used as a promising mineral clay to prepare polyamide 12 (PA12) matrix polymer nanocomposites. ATP has a relatively low cost compared to other nanoclays and is a very abundant raw material in the northeast region of Brazil. The ATP was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy and field emission gun scanning electron microscopy (FEG-SEM). The PA12/ATP nanocomposites with 0, 1, 2.5, 5, 7.5 and 10 wt% of ATP were prepared using a simple blending method in a high-speed thermokinetic homogenizer (3000 rpm) in which the melting of the PA12 and the mixture with ATP occurred by friction, followed by hot pressing and stamping of the specimens. The nanocomposites were characterized by mechanical properties, the degree of crystallinity and crystallite size were calculated by XRD, and the morphological characteristics were observed by SEM. The addition of ATP in the PA12 matrix increased the modulus of elasticity, hardness, degree of crystallinity and the apparent crystallite size of the nanocomposites. The addition of up to 5 wt% of ATP increased tensile strength and deformation at break; for higher concentrations, the dispersion was not efficient. A major advantage of using ATP as a reinforcement agent for PA12 is the low cost of this material plus the great interaction with PA12 which can dispense the use of compatibilizer agents and/or surface modification in the ATP, making it a potential material to extend PA12’s range of applications.

Defect mediated modification of structural, optical and magnetic properties of Xe3+ ions irradiated GaN/sapphire films

We report tailoring of structural, optical and magnetic properties of PLD grown GaN films by 500 keV Xe3+ ions at irradiation fluences of 1 × 1016 and 5 × 1016 ions-cm−2. Deterioration in the crystallinity is observed after irradiation; however, average apparent crystallite size is increased at fluence of 5 × 1016 compared to 1 × 1016 ions-cm−2. In pristine film, broad yellow luminescence peak at ~2.2 eV along with characteristic peak at ~3.4 eV has been observed by photoluminescence spectroscopy. Appearance of peaks at 2.06, 2.65 and 3.06 eV after irradiation suggests defect states generation within the band-gap. Origin of yellow luminescence in GaN films is attributed to Ga vacancy related defects, point defect complexes with unintentional impurities (C and O) on the surface. Lattice disorder examined by RBS/C supports the structural and optical measurements/observations. Films remain diamagnetic as investigated by SQUID magnetometer for all fluences as the concentration of defects is not sufficient to trigger ferromagnetism.

Influence of the reaction time during the treatment of bacterial cellulose with sulfuric acid solution

Biomaterials are one of the most important parts of the medical device industry. Being used frequently in the development of Scaffolds for the tecidual regeneration. Bacterial cellulose is a biomaterial widely used in tissue regeneration. Due to its high content of hydrogen bonds, its crystallinity is high and its solubility is low, which makes its use difficult. Studies carried out with anteriority showed the modification suffered by bacterial cellulose treated with sulfuric acid solutions. The objective of this work was to study the influence of reaction time on crystallinity in the treatment of bacterial cellulose with sulfuric acid solution. Bacterial cellulose was modified by acid hydrolysis with sulfuric acid solutions of 48 or 64% for 60, 120 and 240 min. In all cases, the hydrolysed cellulose was washed with distilled water until pH 7, subsequently the cellulose was washed with ethanol and dried in an oven at 37 ° C until a constant mass. The samples obtained were characterized by X-ray diffraction and the crystallinity index, the apparent crystallite size, the crystallite inner chains and the Z-discriminant function were determined. The results showed that the reaction time has a statistically significant influence on the crystallinity of bacterial cellulose.

Highly dense Ca5(PO4)2SiO4 bioceramics with ultrafine microstructure prepared by pressureless sintering

Si-containing ceramics are regarded as promising materials for bone regeneration. And microstructure is a key factor for both mechanical and biological properties of bioceramics. In the present work, nanocrystalline Ca5(PO4)2SiO4 (CPS) powders were prepared by ultrasound-assisted precipitation method. The sintering behavior of CPS ceramics was investigated by pressureless sintering. Results showed that the synthesized CPS powders with an apparent crystallite size of 84 nm exhibited an excellent sintering capability. Grain growth of CPS ceramics could be effectively suppressed via TSS method, and the mean grain size, relative density and Vickers hardness of CPS ceramics obtained under the optimized conditions were 0.42 μm, 98.40% and 5.22 GPa, respectively. Therefore, TSS process provides a facile method to fabricate highly dense CPS bioceramics with ultrafine microstructure, which are expected to be promising materials with improved mechanical and biological properties for bone regeneration applications.

The enhanced activity of base metal modified MgAl mixed oxides from sol-gel hydrotalcite for ethylic transesterification

MgAl hydrotalcite was successfully prepared through the sol-gel method and modified by in situ addition of base metals (Me = K, Ba, Sr and La). The Me–MgAl hydrotalcites were calcined and the obtained oxides were evaluated as catalysts for ethylic transesterification in order to investigate their potential application for biodiesel production. The Me–MgAl characterization revealed that the materials present different crystalline structures and the metal addition caused surface area reduction and increased the apparent crystallite size. On the other hand, the addition of the base metals to hydrotalcite deeply affected the base properties of the oxides, increasing their catalytic activity. Particularly, the Ba–MgAl presents the highest amount of strong base sites which resulted in a high conversion (≈90%) in the model transesterification reaction between methyl acetate and ethanol. Furthermore, an ester conversion of about 80% was reached in soybean oil transesterification. Moreover, the Ba–MgAl can be reused for 3 batch cycles with low deactivation. These results suggest that Ba–MgAl can be considered a promising heterogeneous catalyst for biodiesel production.

Exploring the lignolytic potential of a new laccase producing strain Kocuria sp. PBS-1 and its application in bamboo pulp bleaching

The pulp and paper industry is one of the largest polluting industries in the world employing chlorine-based bleaching processes. The hazardous impact on the environment can be mitigated by either removal of chlorine or minimizing its use by developing alternative bleaching methods. This study was undertaken to explore the applicability of a new laccase isolated from Kocuria sp. PBS-1 for bamboo pulp bleaching. The enzyme was optimally active at 50 °C and pH 7 and the Km, Vmax and Kcat were 39.45 ± 5.47 mM, 407.40 ± 4.9 μmol min−1 and 124.5 s−1 respectively. Further, the t1/2 was found to be 13 h at 30 °C. This laccase produced a significant increase in the ISO brightness to 80.03 ± 1.68% after LMPZ (Laccase, Mediator, Peroxide and Ozone) bleaching. A significant reduction in the kappa number was recorded for L, LM, LMP and LMPZ treated pulp samples. The FTIR peak at ~1118 cm−1 attributed to lignin present in spectra of the control pulp sample was not observed in spectra of the treated pulps. A new band at 1162 cm−1 in treated pulps indicated degradation of syringyl groups along with an increase in the total crystallinity index, empirical crystallinity index and apparent crystallite size of the cellulose. XRD data of treated pulp samples revealed an increase in the cellulose crystallinity index as per A1430/897 ratio. The SEM of treated pulps showed a change in morphology of pulps like the appearance of cracks, crevices, grooves and peeling of fibrils due to lignolytic activity. These findings may provide leads for the development of new cleaner and alternative methods for pulp bleaching.

Time Dependent Structure and Property Evolution in Fibres during Continuous Carbon Fibre Manufacturing.

Here we report on how residence time influences the evolution of the structure and properties through each stage of the carbon fibre manufacturing process. The chemical structural transformations and density variations in stabilized fibres were monitored by Fourier Transform Infrared Spectroscopy and density column studies. The microstructural evolution and property variation in subsequent carbon fibres were studied by X-ray diffraction and monofilament tensile testing methods, which indicated that the fibres thermally stabilized at longer residence times showed higher degrees of structural conversion and attained higher densities. Overall, the density of stabilized fibres was maintained in the optimal range of 1.33 to 1.37 g/cm3. Interestingly, carbon fibres manufactured from higher density stabilized fibres possessed lower apparent crystallite size (1.599 nm). Moreover, the tensile strength of carbon fibres obtained from stabilized fibres at the high end of the observed range (density: 1.37 g/cm3) was at least 20% higher than the carbon fibres manufactured from low density (1.33 g/cm3) stabilized fibres. Conversely, the tensile modulus of carbon fibres produced from low density stabilized fibres was at least 17 GPa higher than those from high density stabilized fibres. Finally, it was shown that there is potential to customize the required properties of resultant carbon fibres suiting specific applications via careful control of residence time during the stabilization stage.