Molecular dynamics simulations of structural disordering and forming defects in a milling process for selenium

In our previous paper, structural changes of selenium powders ground by a planetary ball mill at various rotational speeds were investigated for the nanostructural modification of particles using mechanical grinding process. The experimental results indicated that the amorphisation of Se by grinding accompanies lattice strain, and the lattice strain arises from impact energy which is more than an energy related to intermolecular interaction. In this paper, molecular dynamics simulations of selenium have been carried out under compressing conditions of various pressure strengths for obtaining information of the lattice strain at atomic level. Then, dynamical behaviour of atomic configuration has been discussed in this process. The structural disordering and formation of the structural defects were estimated by deviations of bond length and angle and the number of created defects before and after compressing from simulated results. The disordering took place during compressing at various pressure strengths, and the disordered atoms return to their initial positions at lower pressure. Stable disordered state and defects after the compression can however remain by compression at more than a certain pressure strength mainly associated with binding energy of selenium.     

Macroscale and microscale evolutions of mechanically alloyed FeZn systems

The present work aims to correlate, in time, macroscale and microscale phenomenological evolutions of the microstructure of Fe and FeZn alloys processed by mechanical milling (MM) and alloying (MA), respectively. Powders were characterized for particle size distribution (PSD), particle morphology (optical microscopy, OM, scanning electron microscopy, SEM), microhardness, crystallite size, differential scanning calometry (DSC) and transmission electron microscopy (TEM). Two macroscopic regimes of PSD behavior were distinguished: the first one dominated by the cold welding process; and, the other where both fracture and agglomeration play a significant role. Solid solubilization of Zn on bcc Fe was found to reduce the final microhardness as well as increase the lattice parameter and is very well predicted by Miedema's thermodynamical approach. Microhardness and solid solution formation kinetics were correlated in time and both could be precisely described by a logistic function. After 5 h of planetary milling, microhardness and the lattice parameter become stable as well as the PSD and particle morphology, indicating that the system has already reached steady state. Indeed, this condition can be monitored by both macroscopic and microscopic parameters. Prior to an homogeneous powder, DSC results suggest an endothermic solid-state amorphization reaction for samples processed for up to 1 h as a result of the formation of clean Fe/Zn interfaces during MA.     

Size-induced effect on nano-crystalline CoFe2O4

Cobalt ferrite (CoFe₂O₄) nano-particles have been synthesized successfully and we studied the effect of temperature on them. The particles have been annealed at different temperatures ranging from 373 to 1173 K. Significant effect on the physical parameters like crystalline phase, crystallite size, particle size, lattice strain and magnetic properties of the nano-particles has been investigated. The studies have been carried out using a powder X-ray diffractometer (XRD), a transmission electron microscope (TEM) and a vibrating sample magnetometer (VSM). A thorough study of the variation of specific surface area and particle size with annealing is presented here, with their effects on saturation magnetization.     

Effect of lattice strain on the Debye-Waller factors of Mg, Zn and Cd

Lattice strains in Mg, Zn and Cd powders produced by grinding have been analyzed by X-ray powder diffraction. The lattice strain (ɛ) and Debye-Waller factor (B) are determined from the half-widths and integrated intensities of the Bragg reflections. In all three cases viz. Mg, Zn and Cd, the Debye-Waller factor is found to increase with the lattice strain. From the correlation between the strain and effective Debye-Waller factor, the Debye-Waller factors for zero strain have been estimated for Mg, Zn and Cd. The variation of energy of vacancy formation as a function of lattice strain has been studied.     

The influence of annealing temperature on the slip plane activity and optical properties of nanostructured ZnO films

The zinc oxide films were prepared by the sol-gel method on the ordinary glass substrates. The activity of slip systems were evaluated by X-ray diffraction line broadening analysis using convolution multiple whole profile (CMWP) fitting procedures. It was found that in all temperatures the 〈a〉 type dislocations is dominating and its fraction increases with the rise of annealing temperature in the range of 350-600 °C. The investigation on the optical properties of films showed that the optical band gap energy increases linearly with the annealing temperature and crystallite size but decreases with the lattice strain.     

Dry grinding effect on pyrophyllite–quartz natural mixture and its influence on the structural alternation of pyrophyllite

Infrared spectroscopy (IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM) with energy dispersive X-ray analysis (EDS) were used to investigate the evolution of mechanical destruction of the pyrophyllite structure and final ground products upon grinding with a laboratory planetary ball mill. The raw ore used in this present work was mainly composed of pyrophyllite and quartz. This pyrophyllite was more resistant toward mechanical destruction, and the crystalline order of pyrophyllite was not completely destroyed until grinding for 240 min with a 20:1 of weight ratio of the balls to powder. The existing crystalline phase in the final ground product was found to be quartz, which served as the associated phase in the original pyrophyllite mineral. The rate of destruction of pyrophyllite structure depended on the types of chemical bonds. Additionally, increasing the intensity of grinding resulted in acceleration of the mechanically induced amorphization of the pyrophyllite structure, whereas the associated quartz grains contributed to the deceleration of the amorphization of pyrophyllite.     

Dry Grinding of Mefenamic Acid Particles for Enhancement of its Water Dissolution Rate

This paper details an investigation into the enhancement of the water dissolution rate of mefenamic acid (MA) by means of a dry grinding treatment. The physico‐chemical properties of the ground MA particles were analyzed by measurements of specific surface area, powder X‐ray diffraction patterns, differential scanning calorimetry thermograms and infrared spectra, and the effects of the change in the physico‐chemical properties (especially, crystalline structure) on the dissolution rate were studied. The polymorphic transition from Form I (original) to II and the change of the molecular structure of MA did not occur in the grinding treatments. However, the specific surface area of the MA particles increased, and the crystallinity decreased (i.e., the amorphization level increased) as the grinding progressed. Hydrogen bonds formed between the carboxyl groups of the opposed asymmetric MA molecules were broken gradually after the grinding limit was attained in the grinding system, resulting in an effective improvement of the initial dissolution rate.     

Anisotropy models in precise crystallite size determination of mechanically alloyed powders

Nanocrystalline AA 4032 alloy powder was synthesized by high-energy ball milling from elemental powders for 30 h duration. XRD and TEM results reveal that the powder is cubic and nanocrystalline in nature. X-ray peak broadening analysis was used to evaluate the lattice strain and the crystallite size using the Williamson-Hall analysis with three different models viz., uniform deformation, uniform deformation stress and uniform deformation energy density. The root mean square (RMS) strain was calculated from the interplanar spacing and the strain estimated from the three models. The three models yield different strain values due to the anisotropic nature of the material. The energy density model is proposed to be the best fit model among the three as severe lattice strain is associated with ball milled powders.     

Microstructural characterisation of nanoparticles using, XRD line profiles analysis, FE-SEM and FT-IR

In this investigation, the structural characteristics of α- Fe₂O₃ nanoparticles synthesised by a mechanical milling have been explored. The structure and morphology of samples were characterized by X-ray powder diffraction, field-emission scanning electron microscope (FE-SEM) and FT-IR measurements. The crystallite size and internal strain were evaluated by XRD patterns using Williamson-Hall and Scherrer methods. The results did not reveal any phase change during the milling. The average particle size decreases with a prolongation of milling times, while the lattice parameters and internal strain increase. It was found that using this method allowed the formation of hematite nanoparticles.     

晶面偏角对利用Voigt函数法计算硅单晶本征晶格应变的影响

研究并制备了不同晶面偏角的Si(111)单晶,经过研磨和抛光使表面粗糙度低至3.4?达到超光滑水平,消除了表面和亚表面损伤层以及其所产生的应力变化.利用高精度X射线衍射仪分别测定了在不同晶面偏角条件下衍射曲线的半高全宽和积分宽度.应用Voigt函数法分析计算了微观应变,通过理论计算和实验对比可知,Si(111)单晶在晶面偏角达到0.749o时,偏角本身所带来的衍射峰半高全宽变化使计算出的应变值误差大于5%.研究结果为其他晶体类似研究提供了重要参考.     

Study on the lattice distortion of the As-prepared nanosized TiO2 particles via detonation method

Quantitative XRD measurements of the nanosized TiO₂ particles obtained from the detonation soot have been carried out. The lattice parameters, such as grain size, cell volume, lattice constants and lattice strain were obtained. The relationships between the change ratio of cell volume (the reciprocal of the particles size, or the mass ratio of explosive and TiO₂ precursor) and the lattice strain of the different TiO₂ phases were also discussed. The relationship between the change ratio of cell volume and the particle size of TiO₂ particles was also studied. The results demonstrated that with the decreasing of the particles size, the lattice strain of anatase phase increased, while the lattice strain of rutile phase increased firstly and then decreased to some extent. It is different from the linear relationship between the lattice distortion and the reciprocal of the particles size reported in other literatures. In the meantime, the lattice strains were different with the different mass contents of RDX in the microstructures of the TiO₂ particles. The direct reflection of microstructure changes is the changes of the particle size of TiO₂ particles. Based on the XRD results, the particular characteristics of the detonation process and interfacial effects of nanocrystalline materials, a crude explanation was also given.     

Analysis of ball-milled Mo powder using X-ray diffraction

X-ray diffraction measurements and analysis were carried out on ball-milled Mo powder. During the ball milling of Mo powder, several stages of deformation could be identified. After short durations of ball milling, still undeformed starting powder was present and the volume fraction of this was determined. The initial aggregates of deformed powder particles exhibited a deformation texture. On prolonged ball milling, the particle size decreased, the deformation texture disappeared and internal strains built up. By simulation and matching of the corresponding line profiles using a Monte Carlo type of line-profile simulation based on a simple three-dimensional model of the distribution of straight dislocations, an estimate of the dislocation density in the ball-milled particles was obtained.     

Controlled synthesis of photoluminescent Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> nanoparticles from metal-organic polymeric precursor

Bi₄Ti₃O₁₂ (BIT) nanoparticles with a narrow average particle size distribution in the range of 11–46 nm was synthesized via a metal-organic polymeric precursor process. The crystallite size and lattice parameter of BIT were determined by XRD analysis. At annealing temperatures >550 °C, the orthorhombic BIT compound with lattice parameters a = 5.4489 Å, b = 5.4147 Å, and c = 32.8362 Å was formed while at lower annealing temperatures orthorhombicity was absent. Reaction proceeded via the formation of an intermediate phase at 500 °C with a stoichiometry close to Bi₂Ti₂O₇. The particle size and the agglomerates of the primary particles have been confirmed by FESEM and TEM. The decomposition of the polymeric gel was ascertained in order to evaluate the crystallization process from TG-DSC analysis. Raman spectroscopy was used to investigate the lattice dynamics in BIT nanoparticles. In addition, investigation of the dependence of the visible emission band around the blue–green color emission on annealing temperatures and grain sizes showed that the effect of grain size plays important roles, and that oxygen vacancies may act as the radiative centers responsible for the observed visible emission band.     

Mechanical Properties of Rubber Sheets Produced by Direct Molding of Ground Rubber Tire Powder

The so called “direct powder molding” is a compressions molding process which can be directly applied to ground rubber tire (GRT). This study shows that the GRT can be re-used to produce medium-size parts with good mechanical properties without any addition of virgin rubber. For rubber sheets prepared from the mechanically ground rubber tire (MGRT) and the cryogenically ground rubber tire (CGRT), the densities and crosslink densities of the rubber sheets increased with a decrease of the particle size of the waste tire powder. The tensile strength of the rubber sheets increased with the decreasing of the particle size for the two types of waste tire powder to 250 μm and 120 μm, respectively, and then became level. The moulding pressure had no effect on the densities, tensile strength or elongation at break of the rubber sheets. These results suggested that the effect of the particle size is important and is correlated with the mechanical properties of the rubber sheets produced by direct powder moulding technology. In general, the best mechanical properties were obtained with waste tire rubber with a size of about 250 μm for the rubber particles obtained from the mechanical grinding method of waste tire powdering.     

Ultrasonic de-agglomeration of barium titanate powder

BaTiO3 (BT) powder, with average particle size of 1.4 microm, was synthesized by solid-state reaction. A high-intensity ultrasound irradiation (ultrasonication) was used to de-agglomerate micro-sized powder to nano-sized one. The crystal structure, crystallite size, morphology, particle size, particle size distribution, and specific surface area of the BT powder de-agglomerated for different ultrasonication times (0, 10, 60, and 180 min) were determined. It was found that the particles size of the BT powder was influenced by ultrasonic treatment, while its tetragonal structure was maintained. Therefore, ultrasonic irradiation can be proposed as an environmental-friendly, economical, and effective tool for the de-agglomeration of barium titanate powders.     

Rapid synthesis and characterization of silicon substituted nano hydroxyapatite using microwave irradiation

Nano sized hydroxyapatites with silicon substitution of three different silicon concentrations were successfully prepared first time by a rapid microwave assisted synthesis method, with a time saving and energy efficient technique. The effects of the Si substitution on crystallite size, particle size and morphology of the powders were investigated. The crystalline phase, microstructure, chemical composition, and morphology and particle size of hydroxyapatite and silicon substituted hydroxyapatites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and dynamic light scattering. The crystallite size and particle size decreases with increase in silicon content and particle morphology spheroidal for pure hydroxyapatite changes to elongated ellipsoidal crystals while silicon substitution increases. Fourier Transform Infrared Spectroscopy analysis reveals, the silicon incorporation to hydroxyapatite lattice occurs via substitution of silicate groups for phosphate groups. Substitution of phosphate group by silicate in the apatite structure results in a small increase in the lattice parameters in both a-axis and c-axis of the unit cell.     

One-step,template-free hydrothermal synthesis of CuO tetrapods

The present investigation reports one-step template-free hydrothermal synthesis of CuO tetrapods (CuO-T) and its characterization. The CuO tetrapods have been prepared in moderate condition without using any surfactant. The prepared sample was characterized by powder X-ray diffraction (PXRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR) spectroscopy, UV–vis–NIR (DRS) spectroscopy and Photoluminescence (PL) spectroscopy. The X-ray diffraction and Fourier transform infrared spectrum analysis confirm clearly the formation of a pure phase high-quality CuO with monoclinic crystal structure. X-ray peak broadening analysis was used to evaluate the average crystallite size (∼30 nm) and lattice strain by the Williamson–Hall (W–H) method. Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) result reveals that the particles are tetrapods in shape with an average length ∼50 nm. Additionally the optical properties were investigated by using UV–vis reflectance spectra with considerable blue-shift in the optical band gap (Eg = 1.45 eV) due to quantum confinement effect. Photoluminescence (PL) spectrum showed both UV as well as visible emission peaks indicating their good optical properties.     

The effects of strain and atomic mobility on the amorphization of Al by Mn implantation at RT

The crystalline to amorphous phase transformation was studied by performing Mn implantations into Al thin films and single crystals at RT. Structural changes and the lattice site occupation of the Mn atoms were directly observed as a function of Mn concentration by X-ray diffraction, Rutherford backscattering (RBS) and channeling experiments. A detailed analysis of the strain distribution upon implantation is given taking into account the lattice site occupation of the Mn atoms and the atomic mobility during implantation at RT. At Mn concentrations 1–2 at% the mainly substitutionally incorporated Mn atoms distort the Al lattice considerably. These distortions provide the driving force for local lattice rearrangements that lead to the formation of amorphous clusters. Experimental results are further consistent with the assumption that the atomic density of these amorphous clusters is equal to the fcc value thus minimizing the strains after transformation. From the results it is concluded that the strain energy is the single most important factor in the amorphization process, determining both the instability of the supersaturated solid solution and the transformation to the amorphous state.     

Microstrain in hydroxyapatite carbon nanotube composites

Synchrotron radiation diffraction data were collected from hydroxyapatite–carbon nanotube bioceramic composites to determine the crystallite size and to measure changes in non‐uniform strain. Estimates of crystallite size and strain were determined by line‐profile fitting of discrete peaks and these were compared with a Rietveld whole‐pattern analysis. Overall the two analysis methods produced very similar numbers. In the commercial hydroxyapatite material, one reflection in particular, (0 2 3), has higher crystallite size and lower strain values in comparison with laboratory‐synthesized material. This could indicate preferential crystal growth in the [0 2 3] direction in the commercial material. From the measured strains in the pure material and the composite, there was a degree of bonding between the matrix and strengthening fibres. However, increasing the amount of carbon nanotubes in the composite has increased the strain in the material, which is undesirable for biomedical implant applications.