Regular Grain Research Articles

Two-Step Spark Plasma Sintering Process of Ultrafine Grained WC-12Co-0.2VC Cemented Carbide.

Ultrafine grained WC-12Co-0.2VC (named UYG12V) cemented carbides were prepared via the two-step spark plasma sintering (SPS) in this study. First, the effects of the sintering temperature on the relative density and WC grain size of UYG12V cemented carbides were studied. The results show that regular WC grains form when sintered at 1300 °C. The sintered body begins to rapidly densify and WC grains grow slowly when sintered at 1200 °C. Thus, the first-step (T1) and the second-step (T2) temperatures in the two-step SPS of UYG12V are 1300 °C and 1200 °C, respectively. The effect of the holding time during the first and second steps on the mechanical properties was also studied. The results show that the UYG12V cemented carbide sintered at 1300 °C for 3 min and then at 1200 °C for 5 min has the best comprehensive mechanical properties, exhibiting the average particle size, Vickers hardness, fracture toughness, relative density, and bending strength of 271 nm, 18.06 GPa, 12.25 MPa m1/2, 99.49%, and 1960 MPa, respectively.

Characterization of electrodeposited ZnTe thin films

ZnTe thin films were deposited on FTO-coated glass substrates by a low-cost, easy and simple electrodeposition method. The grown layers of ZnTe have been characterized by photoelectrochemical cell (PEC) measurement for determining carrier type, UV–visible spectrophotometer for optical characterization, X-ray diffraction (XRD) for structural analysis and scanning electron microscopy (SEM) for the surface morphology. An annealing effect of the as-deposited thin films has also been investigated. PEC measurements of ZnTe film showed p type electrical conductivity. Optical measurement showed that ZnTe films have very high transmittance in the UV–visible region; moderate transmittance in the visible range; and moderate to lower transmittance in the visible–infrared region and have higher absorbance in the middle of the visible region to near-infrared region. Band gap values are estimated to vary from 2.3 to 1.90 eV for the ZnTe films deposited at different conditions. Band gap of ZnTe films is observed to decrease when the films are annealed at different temperatures in nitrogen environment. From the XRD and SEM study, ZnTe films are found to be polycrystalline with (111) preferential orientation of the cubic structure and appeared dense crack-free surfaces with regular granular-shaped grains without any cauliflower-like appearance. After annealing the as-deposited film transmittance, absorbance and intensity in XRD pattern are observed to increase and a good ZnTe crystal structure is observed to form. The values of average crystallite size are estimated to be 22.82 nm and 30.82 nm for as-deposited and annealed ZnTe films, respectively.

Surface Quality of AMg2 Aluminum Alloy with Ultrafine Grain Structure after Machining 2. Milling

The influence of cutting on the surface roughness and undulation of AMg2 aluminum alloy with regular and ultrafine grain structure is considered. The quantitative influence of profile filters on its surface roughness and undulation is established, on the basis of 2D parameters. In the machining of materials with ultrafine grain structure, the surface quality is better than for materials with regular grain structure.

Synthesis and spectroscopic studies of carbon nanosheets (CNSs) produced by pyrolysis of phthalazinium betaines at relatively lower temperature

The main scope of this comprehensive study is to investigate the annealing temperature effects (300 °C ≤ T ≤ 500 °C) on the crucial properties as regards the characteristic bond structures, surface morphology, crystallinity, crystal plane alignments, phase purity, local elemental compositions and distributions of the carbon nanosheets (CNSs). The materials are prepared by the solid-state air pyrolysis of the compound, 2-phenylphthalazin-2-ium-4-olate (phthalazinium betaine). Characterization of compounds prepared in air atmosphere conditions is performed by thermal gravimetric analysis, Fourier transformation-infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy and electron-dispersive X-ray techniques. It is found that the temperature value of 350 °C favors the formation velocity of CNSs due to the transition in more turbostratic structure of the system. In fact, the product (prepared at 350 °C) exhibits the largest nucleation and growth rates on the surface. Thus, the distribution (regular grain orientation) of CNSs is observed to be most homogenous, leading to the larger nestlike structures with more corrugated and bunched forms (much sharper edges) in the crystal structure. All the results obtained demonstrate that the best product with unique features is an intriguing material for potential applications in nanoelectronics and biomedical systems.

Experimental and analytical study of failure behavior in TiB2-B4C composite under shock loading

Abstract The shock response of the TiB2-B4C composite has been studied by experimental and theoretical analysis. The plate impact experiments and the Doppler pin test system (DPS) were used to collect the free surface velocity of sample. Results showed that regular grain of TiB2 was distributed uniformly in the grown grain of B4C. The intergranular fracture was mainly occurred along the grain boundary of the TiB2 phase, while the transcrystalline fracture was mainly happened within the B4C particles. The free surface history of the composite showed that Hugoniot elastic limit (HEL) of the TiB2-B4C composite was 16.09 GPa. The analytical models of failure wave propagation were established when the delayed effect of crack propagation was ignored and considered respectively. It can be concluded that the failure wave velocity of the composite was increased from 0.67C0 to 0.69 C0 at the shock pressure of 5.46–12.17 GPa, and attenuated with the propagation distance. The delayed effect had a great effect on the failure wave propagation, which were increased with shock pressure, and decreased with propagation distance.

Glyphosate Levels in American Food Products Meet Government Safety Levels Yet Exceed Concentrations Associated with Negative Effects

Glyphosate, the active ingredient in the weed killer Roundup, is the most popular herbicide in the agricultural industry, with 6.1 billion kilograms sprayed worldwide in the past decade. Residue findings in breakfast foods and alcoholic beverages have prompted quantitative human and vertebrate studies yielding contradictory results . This study tested the hypothesis that glyphosate concentrations in frequently consumed food products exceed the levels legally allowed in Australia, the European Union, and the United States. The enzyme linked immunosorbent assay (ELISA) method was utilized to measure glyphosate concentrations in cereal, gluten-free white and yellow corn tortillas, regular and whole grain pasta, white and whole wheat bread, and soy chocolate milk. The results showed that mean glyphosate residues were the highest in cereal (1903 parts per billion [ppb]) and significantly higher in whole grain pasta (45 ppb) than regular pasta (19 ppb), in gluten-free yellow corn tortilla (35 ppb) than gluten-free white corn tortilla (none detected), and in whole wheat bread (888 ppb) than white bread (56 ppb). Mean glyphosate concentrations in 25% of samples exceeded the threshold (500 ppb) at which negative effects were observed in previous studies. However, glyphosate concentrations in none of the samples exceeded government-imposed limits. These results raise concerns about whether government-imposed limits are sufficient to protect human health. Future research should quantify glyphosate residues in a wider variety of foods and conduct epidemiological studies to reassess the sufficiency of current safety limits.

Kinetics of Grain Boundary Networks Controlled by Triple Junction and Grain Boundary Mobility

The kinetics of a triple junction of grain boundaries with distinct specific energies and mobilities and a finite mobility of the triple junction is investigated. The microstructure is approximated by different 2D settings consisting of typical structural elements. First, the migration of the triple point together with the adjacent grain boundaries, is simulated, assuming that the grains are infinitely large. Secondly, growth or shrinkage of finite n-sided grains is simulated by altering the boundary conditions and the results are compared to the already published analytical solution. The numerical results coincide with the corrected analytical solution. This solution can be derived either by applying the principle of maximum dissipation, or by applying the force balance at the triple junction within the framework of linear irreversible thermodynamics. The change of the area of infinite and finite grains is investigated analytically and numerically. By comparing the results of both approaches, the influence of the initial topology of the structural elements on the kinetics of grain growth can be estimated. Furthermore, the kinetics of grain growth of different idealized grain boundary networks is investigated. It is shown that square shaped grains surrounded by hexagons and dodecagons result in a more realistic grain growth scenarios than squares surrounded by octagons. A deviation from idealized grain boundary arrangements is e.g., observed, due to different triple junction mobilities, and the initially n-sided regular grain deforms in a complex manner.

Preparation of Dielectric Films via Thermal Oxidation of MnO2/GaAs

MnO2 nanolayers (~29 nm) produced on the surface of single-crystal GaAs wafers by magnetron sputtering have been shown to act as oxygen transfer agents for the thermal oxidation of the semiconductor. The presence of MnO2 increases the oxide film growth rate by three to nine times relative to stimulator-free oxidation of GaAs. The films thus grown range in thickness from 35 to 200 nm and possess good dielectric properties (resistivity on the order of ~1010 Ω cm and dielectric strength in the range (5–8) × 106 V/cm). According to X-ray diffraction data, the films are enriched in oxidized arsenic and have a regular grain structure in the surface layer, with a roughness height within 30 nm (according to atomic force microscopy data).

A study of thermomechanical behaviour and grain size evolution of AA7050 under hot forging conditions

A series of compression tests have been carried out using Gleeble (3800) thermomechanical simulator to investigate the viscoplastic behaviour of AA7050 as well as its microstructural characteristics under hot forging conditions. The thermomechanical tests were conducted at the temperatures of 350–450 °C with strain rates of 0.0005–0.5 s−1, which covers the range of hot forging conditions for AA7050. Interrupted tests have also been carried out to track the microstructural evolution under various thermomechanical deformation conditions. Particular attention has been focused on the criteria of dynamic recrystallisation in AA7050 during the uniaxial compression at high temperatures, which could help to obtain regular homogeneous grain structures for hot forged components. It was found that AA7050 has a strong viscoplastic behaviour and flow stress is more than halved from 350 to 450 °C. A suitably low strain rate and high temperature are required for significant dynamic recrystallisation (0.05 s−1 and 400 °C in current deformation level). The average grain size decreases with increasing strain and deformation temperature due to dynamic recrystallisation, but the relationship between average grain size and strain rate is not monotonic. Present findings provide a guideline for the selection of hot forging parameters so that quality components could be achieved with low forging force.

Thermoelectric voltage switching in gold atomic wire junctions

We explore the thermoelectric properties of gold atomic chains bridging gold electrodes by means of \textit{ab initio} and semi-empirical calculations, and heuristic reasoning. We predict the thermoelectric voltage induced by a temperature difference across such junctions to oscillate, repeatedly changing sign, as a function of the number of atoms $N$ making up the atomic chain. We also predict the amplitude of the oscillations to be proportional to $N$ for long atomic chains. Further we predict the thermoelectric voltage to change sign, in some cases, if the junction is stretched without changing $N$. Our predictions apply regardless of whether regular or irregular electrode grain boundaries are present and whether the electrodes are symmetric or asymmetric. Our findings may pave the way to the realization of new mechanically controllable voltage switches enabling direct conversion of heat into electricity in energy harvesting applications.

Multiferroic properties of novel lead-free KNN-LT/20NZCFO magneto-electric composites

Novel multiferroic composites of 0.95Na0.52K0.48Nb03-0.05LaTiO3 (KNN-LT) as ferroelectric matrix and 20 vol% Ni0.2Zn0.3Co0.5Fe2O4 (NZCFO) as ferromagnetic reinforcement successfully prepared by a conventional sintering process. In X-ray spectra, both the characteristics peaks of ferroelectric KNN-LT and ferromagnetic NZCFO phases without any impurity phase were clearly observed. Both in pure ferroelectric and composite samples the orthorhombic symmetry of KNN based piezoceramic was detected. In FESEM images, the characteristic cube-like morphology of KNN-LT phase and regular polygonal grains of NZCFO ferrite indicates the successful sintering process of multiferroic composites. The simultaneous ferroelectric (based on P-E loop) and ferromagnetic (according to M-H curve) behaviors of KNN-LT/NZCFO approves that this composite can be known as a novel lead free multiferroic composite. The excellent values of Ps ∼ 9 µC/cm2 and Ms ∼ 14 emu/g for this magnetoelectric composite were obtained.

Structure and photoluminescence properties of ZnWO4 film prepared by depositing WO3/ZnO/WO3 heterolayer via magnetron sputtering technique

Novel ZnWO4 thin films were achieved by annealing sandwich WO3/ZnO/WO3 (WZW) heterolayer that were deposited on clean fused silica substrates by RF magnetron sputtering technique. The crystal structures, surface morphologies and photoluminescence (PL) properties of the annealed WZW heterolayers were characterized by x-ray diffraction (XRD), Raman, scanning electron microscopy (SEM) and PL measurements. The XRD and Raman patterns show that the ZnWO4 thin films formed from WZW heterolayers possess the monoclinic wolframite structure with a preferential orientation along the a-axis. The annealing temperature of WZW heterolayer plays a vital role in determining the crystallization, surface morphologies and PL properties of the formed ZnWO4 films. The SEM graphs and PL spectra indicate that the annealing treatment at about 750 °C for 30min is very effective for deposited WZW heterolayer to form the flat ZnWO4 thin film with the regular nanometer grains (200–400 nm) and the strongest PL emission near about 495 nm, while further increasing annealing temperature to 850 °C leads to a rough surface and weakened PL intensity. The PL spectra from all the annealed WZW films display a broad and asymmetrical shape and are depend on the excitation wavelengths in the range of 240–290 nm as well as annealing temperature. The related PL mechanisms were analyzed and discussed according to the excitation spectra monitored at 410 nm and 495 nm, respectively. It is suggested that the coexistence of the ZnWO4 and ZnO excitation bands in the film should be responsible for the evolving of PL shapes with the excitation wavelengths. Finally, the average PL decay time of the formed ZnWO4 film was determined to be about 22μs by time-resolving the three intrinsic emissions of the ZnWO4 crystallites. This work illustrates that magnetron sputtering is an effective technique to prepare the fluorescing ZnWO4 film.

Theoretical modeling of the regular olivine intergrowths in the mimetic paramorphosis after ringwoodite and wadsleyite

Theoretical modeling of regular olivine grains misorientations in mimetic paramorphoses after ringwoodite and wadsleyite, the formation of which during the ascension of matter from the Mantle Transition Zone is expected, has been carried out. The coordinates of the misorientation axes and the misorientation angles, characterizing 10 operations of alignment in the pair intergrowths of olivine grains, eight of which are twins, are calculated. Possible conditions for the formation of mimetic paramorphoses predicted here, and the chances of their persistence are discussed. The calculated orientations are compared with the known twinning laws of olivine.

The Effect of the Morphology of Coarse Aggregate on the Properties of Self-Compacting High-Performance Fibre-Reinforced Concrete.

When understanding the effect of the morphology of coarse aggregate on the properties of a fresh concrete mixture, the strength and deformability of self-compacting high-performance fibre-reinforced concrete (SCHPFRC) can be seen to be critical for its performance. In this research, regular and irregular grains were separated from granite coarse aggregate. The morphology of these grains was described while using digital image analysis. As a result, the aspect ratio, roundness and area ratio were determined in order to better understand this phenomenon. Then, the principal rheological, physical, and mechanical properties of SCHPFRC were determined. The obtained results indicated that the morphology of the grains of coarse aggregate has an impact on the strength and stiffness properties of SCHPFRC. Moreover, significant differences in the transverse strain of concretes were observed. The morphology of the coarse aggregate also has an impact on the rheological parameters of a fresh concrete mixture. To better understand this phenomenon, the hypothesized mechanism of the formation of SCHPFRC caused by different morphology of coarse aggregate was proposed at the end of the article.

Morphometric and sediment analysis of beach cusp in correlation to rip currents: a case study from tropical coast, West coast of India

The presence of rhythmic beach cusps in foreshore regions are of persistent research interest to coastal researchers, engineers with respect to their formation in beaches. Morphometric and sediment analysis were used to study beach cusp morphology at Vengurla beach, a gentle slope beach characterized by medium sand. The cusp dimensions such as spacing, elevation, amplitude and depth were measured for detailed analysis. The distinctive sediment characteristics between the horn and the bays of the cusp are different and cusp measurements show a high level of irregularity. Horns and bays have medium sand, but sorting is varying. Sorting variations clearly demonstrated the difference in energy condition between horns and bay. Negative skewness of few horn samples has been correlated with erosional trend. Based on the grain size analysis result, it was observed that Vengurla beach cusps follow the regular grain size distribution pattern. Additionally, the low-intensity rip currents were also noticed in the study area. The rate of occurrence and strength of rip currents are decided by the nearshore bathymetry and play an imperative role in rip current formation. The present study is based upon the field measurements along Vengurla coast and contributes to morphometric analysis of beach cusps. Regarding beach cusps, there are no documented databases along the Indian coast. Understanding the beach cusp formation and its seasonal changes along the beaches will be useful for effective coastal management.

The experimental investigation and modeling on the mechanical behavior of dual-phase approximate equiaxial nanocrystalline AgCu alloy

Nanostructured dual-phase equiaxial alloy (DPEA) possesses the unique mechanical properties of high strength and ductility. However, the characterization of mechanical behavior and its elastic-plastic response of DPEA remain to be solved. In this paper, in-situ consolidation dual-phase approximate equiaxial nanocrystalline (NC) AgCu alloys have been synthesized and relevant tensile and nanoindentation tests have been carried out. Experimental results indicates that dual-phase approximate equiaxial NC AgCu alloys have good strength, ductility and a certain creep resistance. Moreover, a theoretical model based on mechanics has been proposed to simulate the stress-strain relationship, strain hardening rate and creep strain rate of dual-phase equiaxial NC AgCu alloy. The plastic property of regular grain interior (GI) phase and amorphous grain boundary (GB) phase has been addressed by the strain gradient plasticity model. Based on the calculated results of the proposed model is consistent with the experimental results. Our analysis revealed that mechanical properties of DPEA are sensitive to the grain size, content of GI phase, volume fraction of solute cluster and thickness of GB. This research has provided a theoretical framework to design excellent mechanical property of DPEA by optimizing material structure parameters.

Interface Engineering for All-Inorganic CsPbI2 Br Perovskite Solar Cells with Efficiency over 14.

In this work, a SnO2 /ZnO bilayered electron transporting layer (ETL) aimed to achieve low energy loss and large open-circuit voltage (Voc ) for high-efficiency all-inorganic CsPbI2 Br perovskite solar cells (PVSCs) is introduced. The high-quality CsPbI2 Br film with regular crystal grains and full coverage can be realized on the SnO2 /ZnO surface. The higher-lying conduction band minimum of ZnO facilitates desirable cascade energy level alignment between the perovskite and SnO2 /ZnO bilayered ETL with superior electron extraction capability, resulting in a suppressed interfacial trap-assisted recombination with lower charge recombination rate and greater charge extraction efficiency. The as-optimized all-inorganic PVSC delivers a high Voc of 1.23 V and power conversion efficiency (PCE) of 14.6%, which is one of the best efficiencies reported for the Cs-based all-inorganic PVSCs to date. More importantly, decent thermal stability with only 20% PCE loss is demonstrated for the SnO2 /ZnO-based CsPbI2 Br PVSCs after being heated at 85 °C for 300 h. These findings provide important interface design insights that will be crucial to further improve the efficiency of all-inorganic PVSCs in the future.

High Temperature Superconductors (${\rm Y}_{1-x}{\rm Nd}_{x}$ )Ba2Cu3O7-δ Obtained by Acetate Method

Bulk ceramic samples with chemical composition (Y 1-x Nd x )Ba 2 Cu 3 O 7-δ , where x = 0, 0.1, 0.2, 0.5, and 1 were sintered by a proposed acetate method. The samples were then submitted to structural characterization by X-ray diffraction with crystal structure refining using the Rietveld method. AC electrical resistivity measurements from ambient temperatures down to 4.2 K were performed, as well as magnetic measurements of magnetic moment as function of temperature and magnetic hysteresis loop. Results have shown superconductivity with critical temperatures of about 91 and 60 K for pure YBa 2 Cu 3 O 7-δ (x = 0) and pure NdBa 2 Cu 3 O 7-δ (x = 1) samples, respectively. Scanning electron microscopy images were also analyzed, revealing a regular parallel-piped grain shape. The proposed method showed as an advantage to reduce the grinding time without any considerable degradation on structural or superconducting properties of pure YBa 2 Cu 3 O 7-δ (x = 0) or pure NdBa 2 Cu 3 O 7-δ ( x = 1), as related to samples prepared by a conventional solid state route.

Geomorphology of the Al Wahbah crater at Harrat Kishb west of the Kingdom of Saudi Arabia

The main objective of this research is to conduct a geomorphic study of the Al Wahbah crater located in Harrat Kishb, west of Saudi Arabia. The crater is considered as one of the well-known national tourist places, which attracted many visitors a year. This study handles the geomorphic framework of the crater to draw a digital elevation model. It is a step to designate slopes of the crater and its surroundings, as well as other morphometric characteristics. The lithologic units of the crater and its surroundings have been updated using geologic maps and SPOT 5 (2.5 m) satellite image. The research aims also at analyzing the deposits of the crater floor through mechanical analysis of the field-collected samples. In this process, the circular floor of the crater had been classified into two halves. Then, field samples were collected from the radius of the crater at three places apart from each other. The lab analyses include porosity and hydraulic conductivity. The results of analyzing these samples disclosed high percentages of porosity. The porosity of all samples is homogeneous as well in the samples collected from the three profiles of different depths. As well the mechanical analysis indicates a regular and homogeneous grain size distribution. The current study elucidates the impact of the mutual interaction between the natural variable forming the Al Wahbah crater geomorphic system. The interaction resulted in a dynamic and complex geomorphic system along with distinctive associations of landforms and surficial deposits. The study is considered among the pioneer research efforts that tackled the Al Wahbah crater from different scientific and applications perspectives.

Effect of thermal annealing on properties of polycrystalline Titanium dioxide (TiO2) thin film prepared by simple chemical method

Titanium dioxide (TiO2) thin film prepared in a simple chemical method, on an optically flat a glass substrate. The effect of the annealing temperature on a structural and the optical properties of TiO2 films is studied systematically by X-ray diffraction (XRD), Atomic Force Microscopy (AFM), UV–VIS spectroscopy . The XRD patterns show that the deposited films and the annealed films are polycrystalline and the average grain size of the crystallite grains ranges from 41 to 50 nm in films. AFM images reveal a regular grain distribution of grains in films and the grains in the nanoscale dimension. The UV–Vis rays results show that increase in transmittance with increase the annealing temperature, also, the energy gap decreases from 3.6 to 2.6 volts, due to the effect of quantum volume.