Formation Of Flakes Research Articles

Ways to Improve the Quality of Die Steel 5KhNM

There was performed an analysis of influence of the deoxidation technology, hydrogen content and high concentration of titanium in steel 5KhNM (Rus. “5XHM”) on quality of die blanks, evaluated based on the results of the ultrasonic test.The fractographic examinations of fractures and the X-ray microprobe analysis of chemical composition of non-metallic inclusions were conducted, the evaluation of macro- and micro-structure of a die blank with high titanium content was performed.It is demonstrated that defects of dies from steel 5KhNM (Rus. “5XHM”) are cracks from merged flakes and micro-flakes; in most cases large concentrations of sulphides appeared to be hydrogen collectors for formation of flakes and micro-flakes.

Magnetic and structural anisotropic properties of magnetostrictive Fe-Ga flake particles and their epoxy-bonded composites

Flake shaped particles of grain-oriented Fe80Ga20 and Fe73Ga27 alloys were prepared using a high-energy wet ball-milling process. The surface of flakes produced were predominantly parallel to the (1 0 0) crystallographic plane in flakes. These flakes possess two in-plane 〈1 0 0〉 easy axes of magnetization, which enhances magnetostrictive performance and sensitivity for use in composite materials. The deformation mechanism leading to formation of (1 0 0) grain-oriented flakes is associated with small angel crystal reorientations along slip lines similar to what occurs during rolling. Data are presented on the in-plane magnetic properties of these flakes, which were characterized using field-dependent magnetization measurements. The epoxy-bonded composites with the particle alignment exhibited high magnetostriction values of ∼103 ppm.

Surface Texture-Induced Enhancement of Optical and Photoelectrochemical Activity of Cu2ZnSnS4 Photocathodes

The objective of this work is to understand and improve the photocatalytic activity of Cu2ZnSnS4 (CZTS) through postgrowth modification techniques to create surface textures. This objective can be achieved using a combination of solvents, etching agents, and anodization techniques. One of the most effective surface treatments for enhancing the surface properties of photovoltaic materials is formation of nanoscale flakes, although other surface modifications were also evaluated. The superior performance of textured films can be attributed to enhanced surface area of absorber material exposed to electrolyte, ZnS deficiency, and high catalytic activity due to reduced charge-transfer resistance. Fine-tuning of ion flux and electrolyte stoichiometry can be used to create a controlled growth algorithm for CZTS thin films. The resulting information can be utilized to optimize film properties. The utility of nanostructured or engineered surfaces was evaluated using photoelectrochemical measurements. Finite-difference time-domain (FDTD)-assisted simulations were conducted for selected texturing, revealing enhanced surface area of absorbing medium that ultimately resulted in greater power loss of light in the medium.

Formation of anodic zirconia nanotubes in fluorinated ethylene glycol electrolyte with K2CO3 addition

The influence of K2CO3 on the morphology of anodic zirconia (ZrO2) nanotubes array were investigated by anodizing zirconium (Zr) foil at 60V in fluorinated ethylene glycol (EG) electrolyte added to it varying amount of K2CO3: 0.5vol.%, 1vol.%, 2vol.% and 3vol.%. The adhesion of ZrO2 on Zr is affected by the volume of K2CO3 added whereby at lower volume, i.e. 0.5vol.% and 1vol.%, poor adhesion of anodic film was observed leading to the formation of loose ZrO2 flakes. At higher 2vol.% and 3vol.% addition the adhesion was improved. All anodic films are comprised of nanotubes with length increases when more K2CO3 was added in EG. Nanotubes grown in 3vol.% K2CO3 are 9.4μm long with 48.8nm outer diameter and 9.1nm wall thickness. Reducing the applied potential to 20V resulted in compact oxide and at 40V, nanotubes with smaller diameter of <50nm were produced. Crystallization of the ZrO2 nanotubes was achieved by annealing at 400°C. The crystalline ZrO2 nanotubes (mostly in monoclinic and tetragonal phases) grown in 3vol.% K2CO3 exhibits the highest photocurrent density (0.12mA/cm−2) and rapid methyl orange (MO) degradation under ultra-violet (UV) radiation. This is attributed to the good adhesion of ZrO2 on Zr, longer length of the tubes and perhaps from the effect of adsorbed carbonate ions on the surface of the oxide.

Production of carbon nanostructures in biochar, bio-oil and gases from bagasse via microwave assisted pyrolysis using Fe and Co as susceptors

In this study, the production of nanostructured biochar from lignocellulosic biomass, sugarcane bagasse, is demonstrated via microwave assisted pyrolysis by using iron (Fe) and cobalt (Co) particles as susceptors. The experiments were performed in a bench scale pyrolysis reactor at 600W microwave power up to a temperature of 500°C. The effect of bagasse:susceptor composition on the quality of biochar was evaluated using a range of characterization techniques like scanning electron microscopy, porosimetry, X-ray diffraction, and Raman spectroscopy. The addition of Fe as the susceptor resulted in the formation of nanoparticles and nanotubes of average diameter in the range of 30–120nm and 20–50nm, respectively. The addition of more Fe particles resulted in an increase in size of nanoparticles and nanotubes due to enhanced rate of localized heating, which led to fusion of small particles and tubes. The biochar obtained by the addition of Fe susceptor was rich in carbon content compared to that obtained without the addition of susceptor. The addition of a mixture of Fe and Co as susceptor led to the formation of small graphitic flakes and fine nanotubes. Besides biochar, bio-oil and non-condensable gases were also characterized for their composition. The major organic functionalities in bio-oil included furan derivatives, simple phenols, guaiacol, syringol and their derivatives. Maximum energy recovery of 49% was observed in bio-oil when 20wt.% Fe and 33.3wt.% of Fe+Co were used as susceptors. The addition of Fe resulted in high yield of H2 and CH4 gases, besides CO2 and CO. Thus, microwave pyrolysis is shown to be a promising technique to tailor the morphological features of biochar by using metallic susceptors, and simultaneously produce good quality bio-oil and gases.

Avaliação de diferentes fontes de carboidratos para o sistema de bioflocos e crescimento do camarão branco

O trabalho teve como objetivo avaliar o resí­­duo de cervejaria e outras diferentes fontes de carboidratos para o sistema de bioflocos e diferentes densidades para o crescimento do camarão branco, Litopenaeus vannamei (peso inicial de 0,35 ± 0,05g). O experimento foi realizado durante o perí­­odo de 55 dias, utilizando 6 tratamentos com 3 repetições cada, com duas densidades de estocagem (300 e 500 camarões/m²) e três substratos (resí­­duo de cervejaria, melaço de cana e farinha de mandioca). Os parí­¢metros abióticos foram monitorados diariamente e as biometrias ocorreram semanalmente, para a avaliação do desempenho. Os parí­¢metros fí­­sico-quí­­micos da água encontraram-se adequados para a espécie, entretanto os compostos nitrogenados alcançaram ní­­veis pouco elevados, porém os í­­ndices zootécnicos foram satisfatórios, apresentando médias de sobrevivência, ganho de peso e peso final entre 74-82%; 3,5-5,0g e 4,2-5,7g, respectivamente. Verificou-se que tratamentos com o resí­­duo de cervejaria apresentaram parí­¢metros zootécnicos superiores e também, maior formação de flocos microbianos. Os tratamentos com menores densidades apresentaram melhores í­­ndices zootécnicos. Os resultados demonstraram que a produtividade dos flocos nos diferentes tratamentos é eficiente como complemento alimentar para o crescimento de L. vannamei e para a qualidade da água, e que entre os substratos, o resí­­duo de cervejaria revela-se como excelente composto orgí­¢nico para a formação do bioflocos.

Sequential Solvent Exchange Method for Controlled Exfoliation of MoS2 Suitable for Phototransistor Fabrication.

In this study, flakes of molybdenum disulfide (MoS2) with controlled size and thickness are prepared through sequential solvent exchange method by sonication in dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP) solvents. While NMP acts more effectively in reducing the thickness of flakes, DMF shows better potential in conserving the lateral size of nanosheets. The distribution of size and thickness of nanoflakes as a function of sonication time verifies that extended sonication results in dramatic drop of the dimension of the exfoliated flakes. This technique leads to the formation of few-layered MoS2 flakes without further drop of their lateral dimensions. It has been observed that by exposing the bulk MoS2 powders to oxygen plasma, the exfoliation process is accelerated without converting to 2H-MoS2 structures. Finally, a phototransistor has been fabricated based on few-layered MoS2 layers with a field effect mobility of ∼2.1 cm2 V-1 s-1 showing a high response to laser excitation of 532 nm wavelength.

Study of photo-structural changes under the influence of laser and e-beam irradiations in (Ag3AsS3)0.9(As2S3)0.1 thin films

(Ag3AsS3)0.9(As2S3)0.1 thin films with high concentration of silver were deposited by a rapid thermal evaporation, their structural properties were studied using SEM and AFM. Roughness analysis of as-deposited films surfaces was performed. The influence of laser and e-beam irradiation on structural and optical properties was analysed. It is shown that e-beam, as well as laser illumination, causes a formation of flakes, bubbles on the surface of the films. Holographic gratings were recorded on the given films using green laser. Optical transmission kinetics with laser illumination shows its increase with illumination time.

Comparative study of deterioration forms on nearby granitic bridges from an urban setting in the NW Iberian Peninsula

Stone coatings, biological colonization, efflorescence and detachments are frequent on granitic surfaces of our cultural heritage infrastructure. In order to find the different origins for each deterioration form, this paper studies and compares several coatings, efflorescence and flakes found on granitic surfaces of bridges from different ages built in the same area (Ourense in NW Iberian Peninsula at 90km from the sea) under the same environmental and traffic conditions. The most recent bridge was the New Bridge built in the beginning of 20th century and the oldest one was the Roman Bridge with the 1st century AD foundations but its current structure was built in 17th century. The New Bridge has exhibited a greater variety of deterioration forms such as black crusts, carbonate crusts, efflorescence and biological colonization. On the Roman Bridge, black crusts, efflorescence to a greater extent, and flakes associated with salt crystallization processes have been identified. Scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray diffraction and Fourier transform infrared (FTIR) spectroscopy studies were carried out in order to establish their composition, and optical and electronic microscopies and X-ray microtomography were used to study their morphologies. As a result, anthropogenic factors (industrial activities, traffic pollution and fertilizers) are considered to be the main contributors to crusts, efflorescence and flake formation on both studied substrates (granite ashlars and mortars). To a lesser extent, natural factors (marine influence and bird droppings) should be taken into account.

Vapor transport growth of MoS2 nucleated on SiO2 patterns and graphene flakes

Vapor transport growth of atomically thin MoS2 layers on patterned substrates is investigated, as it is a step towards the self-aligned growth and formation of heterojunctions, which could be useful in future applications. Enhanced formation of MoS2 flakes at the pattern edges is observed on both the substrates examined, namely, patterned thermal SiO2 on Si(100) and graphene flakes on SiO2. The diffusion driven growth leads to the formation of MoS2 monolayers (MLs) with sizes of tens of micrometers around the edges of SiO2 patterns. The growth mode and the optical quality of the MoS2 flakes can be controlled by varying the substrate temperature. Besides the lateral growth, 3R-type pyramids are obtained on prolonging the growth. Lateral MoS2-graphene heterostructures are obtained by using graphene flakes on SiO2 as a substrate.

A Contribution to the Understanding of the Combined Effect of Nitrogen and Boron in Grey Cast Iron

Inoculation is an essential part of controlling material properties in grey cast iron. Inoculation practice has for decades been based on the addition to the melt of small amounts of elements with a strong affinity to O (and S) just before casting takes place. This method is proven—both in theory and in practice—to be effective in most cases. But it has the disadvantage that the nucleation effect fades away over time. In particular, in heavy castings (slow cooling) this effect may cause non-uniform and unacceptable material properties in some parts of the casting. Nitrogen is also known to influence grey iron microstructure. Both graphite flake formation and matrix formation are influenced. However, the obtained effects differ considerably between different reported investigations. This investigation deals with the combined effect of nitrogen and boron and how it is possible to utilize this effect to enhance material properties in heavy grey iron castings. It is shown that the controlled additions of nitrogen and boron can be used to control the microstructure of thick section grey iron castings. A plausible theory for the formation of boron nitride nuclei effective for graphite growth is presented.

Variation of cavity hydrogen pressure in the forming process of heavy forging

Flake is an irreparable crack type defect in many huge steel products, especially in heavy forging. Lots of previous studies have revealed that flake is usually originated at cavities within heavy forging. In addition, whether it is generated and what size after it is formed both largely depend on the hydrogen pressure within the cavity. However, the most part of previous studies only related cavity hydrogen pressure to steel hydrogen concentration, and few studies considered the metal forming effect. In this paper, the relationship between cavity hydrogen pressure and metal forming process of heavy forging is addressed from a simulation perspective. Different from previous research, this paper wants to emphasize the importance of metal forming process in the flake formation. There are four parts in this paper. We start with a brief introduction to the flake and the importance of cavity hydrogen pressure in its formation. Then, we propose a cavity hydrogen pressure calculation model. After that, the simulation results and discussions are provided. We end the study with the conclusion. We find in our research that metal forming has a great influence on cavity hydrogen pressure, especially with large deformation. Based on these findings, we may conclude that flake formation not only depends on the steel hydrogen content, but also very depends on the way of forming. Admittedly, what we have discussed in this study is far from complete. And some improvements we want to make in our further research include (1) studying the influence of metal forming on flake formation in micro-scale, such as in grain scale; (2) verifying the simulation results with experiment; and (3) considering the hydrogen diffusion process in metal forming process.

Preparation of Mg-MgH2 flakes by planetary ball milling with stearic acid and their hydrogen storage properties

Many studies preparing magnesium hydride using catalyst addition were performed, resulting in the preparation of additive-containing magnesium hydride. Preparation of a sample with a MgH2 phase without additives requires high pressure and high temperature and is time-demanding. In order to prepare an additive-free sample with a MgH2 phase, 90 wt% Mg+10 wt% MgH2 (named 90Mg+10MgH2) was milled under a hydrogen atmosphere with 6 wt% stearic acid as a process-controlling agent, which led to a formation of Mg-MgH2 flakes. The hydrogen storing and releasing properties of the prepared flakes were investigated and compared with those of purchased MgH2. A sample with a majority fraction of MgH2 phase was prepared by planetary ball milling of 90 Mg+10 MgH2 with 6 wt% stearic acid. The resultant particles of 90 Mg+10 MgH2 obtained after hydridingdehydriding cycling were much smaller and had significantly more cracks and defects than those of MgH2 after hydriding-dehydriding cycling. 90 Mg+10 MgH2 released 0.12 wt% hydrogen for 4 min, 3.70 wt% for 20 min, and 5.30 wt% for 60 min at 648 K at the first cycle.

Effect of milling on the structure and magnetic properties in Mn54Al46 flakes prepared by surfactant-assisted ball milling

MnAl flakes with different size were prepared using the surfactant-assisted ball-milling method. Depending on the sequence of ball milling and anneal, different microstructures and magnetic properties were obtained. [001] textured ε-phase MnAl flakes were obtained by surfactant-assisted ball-milling isotropic powders. After annealing the textured flakes, high purity τ-phase MnAl have been obtained from milled powders. Regardless of the sequence between anneal and ball milling, the coercivities of the milled powders are much higher than those of bulk ingots. The magnetic properties are dependent on the fraction of the τ-phase and ball milled time. A high coercivity of 234.9kA/m and a saturation magnetization of 0.47T have been obtained in milled powders. Addition of oleic acid and oleyl amine in the ball milling were found to be critical to the formation of MnAl flakes.

Spectroscopic and morphological studies of laser ablated silver

The spectroscopic and morphological studies of silver has been investigated after irradiation of Nd:YAG laser by employing Laser Induced Breakdown Spectroscopy (LIBS) and Scanning Electron Microscope (SEM) analyses. Silver targets were exposed to various laser fluences ranging from 5.2Jcm−2 to 41.7Jcm−2 under ambient environment of argon at a pressure of 100Torr. LIBS analysis revealed that when the laser fluence was increased from 5.2Jcm−2 to 10.4Jcm−2, an increasing trend for both electron temperature and electron number density of plasma was observed due to enhanced energy deposition. Afterwards, with increasing fluence from 10.4Jcm−2 to 15.6Jcm−2, a decreasing trend was achieved which was attributed to the shielding effect. With further increase in fluence from 15.6Jcm−2 to a maximum value of 41.7Jcm−2, a saturation region was achieved and insignificant changes in both plasma parameters were observed. This saturation is explainable on the basis of the formation of a self-regulating regime. SEM analysis revealed the formation of flakes and ridges on the surface of silver at the lowest fluence of 5.2Jcm−2. For increased fluences ranging from 10.4Jcm−2 to 41.7Jcm−2, distinct and unorganized melted channels were the dominant features. However, at a maximum fluence of 41.7Jcm−2, micro and nano crystallites of lamellar (tabular) shape were also formed. At peripheral ablated areas, flakes, cavities, cones and craters with multiple ablated layers were formed. The modifications in surface morphology of laser-ablated silver have been correlated with plasma parameters.

Influence of furfuryl moulding sand on flake graphite formation in surface layer of ductile iron castings

The influence of the use of moulding sand with furan resin, prepared both with fresh sand and reclaimed matrix, on the formation of a flake graphite formation at the surface layer of ductile iron castings has been investigated. A series of experimental heats of ductile iron cast in moulds made of moulding sand characterised by different levels of surface active elements (sulphur, oxygen) were performed. The effect of the wall thickness and the initial temperature of the metal in the mould cavity on the formation of flake graphite in the surface layer of the casting is shown in the paper. Investigations carried out by means of scanning electron microscopy (energy dispersive X-ray spectroscopy and wavelength dispersive X-ray spectroscopy) showed concentration of gradient profiles of surface active elements in the castings surface layer, which are responsible for their quality. Finally, it has been shown that there exists a significant effect of the quality of the sand on the formation of the flake graphite layer and the surface characteristics of ductile iron castings.

Characterisation of thin films of graphene-surfactant composites produced through a novel semi-automated method.

In this paper we detail a novel semi-automated method for the production of graphene by sonochemical exfoliation of graphite in the presence of ionic surfactants, e.g., sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB). The formation of individual graphene flakes was confirmed by Raman spectroscopy, while the interaction of graphene with surfactants was proven by NMR spectroscopy. The resulting graphene–surfactant composite material formed a stable suspension in water and some organic solvents, such as chloroform. Graphene thin films were then produced using Langmuir–Blodgett (LB) or electrostatic layer-by-layer (LbL) deposition techniques. The composition and morphology of the films produced was studied with SEM/EDX and AFM. The best results in terms of adhesion and surface coverage were achieved using LbL deposition of graphene(−)SDS alternated with polyethyleneimine (PEI). The optical study of graphene thin films deposited on different substrates was carried out using UV–vis absorption spectroscopy and spectroscopic ellipsometry. A particular focus was on studying graphene layers deposited on gold-coated glass using a method of total internal reflection ellipsometry (TIRE) which revealed the enhancement of the surface plasmon resonance in thin gold films by depositing graphene layers.

Metal Flake Defect and Its Formation Mechanism during Replacement Metal Gate CMP Process

Replacement metal gate (RMG) has been introduced in semiconductor fabrication since 45 nm gate scaling era. RMG process has advantages in prevention of damage by gate etch and thermal process, and it gives work function material stability. Moreover, improvement of device performance is expected as well. Therefore it has been employed as industry standard process for advanced node transistor fabrication. However, the complexity of RMG process flow emphasizes the importance of metal gate chemical mechanical polishing (CMP) which plays a key role in the success of RMG formation. Three complementary CMP steps (gate poly-Si CMP, poly-Si open CMP, metal gate CMP) are involved in RMG formation and comprehensive understanding of interplay among these CMP steps is the key to achieve uniform gate height across the wafer. In addition to extremely tight control of final gate height, post metal gate CMP defects are one of the most critical parameters affecting device performance as well as yield. Among various kinds of defects, metal flakes are most serious defect which fails transistor function by providing gate leakage channel. This paper approaches both integrational and CMP process aspect to reveal the mechanism of metal flake formation.

Microstructure evolution and mechanical properties of drop-tube processed, rapidly solidified grey cast iron

The microstructure, phase composition and microhardness of rapidly solidified grey cast iron BS1452 Grade 250 are compared against the conventionally solidified alloy. Powder samples were prepared using containerless processing via the drop-tube technique. The rapidly cooled droplets were collected and sieved into size range from ≥850µm to ≤53µm diameters corresponding to estimated rates of 200–23,000Ks−1. Microstructure evaluations were made by optical and scanning electron microscopy, while XRD was used for identification and analysis of evolved phases. The control sample showed extensive graphite flake formation which was absent in virtually all the droplets samples. With decreasing particle size (increasing cooling rate) we observed an increase in the proportion of Fe3C present and the retention of γ-Fe in preference to α-Fe, with the proportion of retained austenite increasing with increasing cooling rate. At the highest cooling rates utilised a Martensitic or acicular ferrite structure was observed. Cooling rates of 200Ks−1 resulted in a doubling of the measured microhardness relative to the as-received (slowly cooled) material. Cooling at the highest rates achieved resulted in a further doubling of the measured microhardness.

Fundamental investigation of micro-scale wear characteristics of ultra-fine gold wires under low contact force and long sliding distance

Micro-scale wear characteristics of ultra-fine gold wires with a diameter of ~28μm was investigated under a low contact force over a long sliding distance up to ~200km. The tip of the wire was slid against a silicon wafer under a low normal force of 5μN. Wear of the gold wire was quantified from the images of the tip obtained by a 3D laser microscope and a scanning electron microscope before and after the wear test. The dimensionless Archard relationship wear coefficient was in the order of 10−7 which was extremely low considering that sliding was carried out in dry condition. Such a low wear characteristics was attributed to low contact pressure that could be achieved by formation of a conformal contact due to flattening of the wire tip as sliding wear progressed. Wear behavior of the gold wire could be characterized by formation of thin flakes of wear debris that were generated as a result of adhesive shear stress imparted at the sliding interface. As an effort to reduce the wear coefficient even further, octadecyltrichlorosilane self-assembled monolayer was deposited on the silicon to serve as a nano-lubricant. It was effective in improving the wear resistance by about two-fold.