Formation Of Flakes Research Articles

Intriguing Carbon Flake Formation during Microwave‐Assisted Hydrothermal Carbonization of Sodium Lignosulfonate (Global Challenges 8/2020)

Intriguing Carbon Flake Formation during Microwave‐Assisted Hydrothermal Carbonization of Sodium Lignosulfonate (Global Challenges 8/2020)

Laboratory intercomparison for the evaluation of the delamination propensity of glass containers for pharmaceutical use

AbstractThis paper is the result of two round robin activities run by the Technical Committee TC12, Pharma Packaging, of the International Commission on Glass (ICG). It deals with the phenomenon of delamination, that is, the formation of lamellae or flakes in drug products due to specific and localized corrosion of glass vials, and it follows a first paper PDA J Pharm Sci Technol. 2018, 72, 553–565where a testing protocol for the evaluation of the delamination propensity was proposed. The results showed that the protocol gives information on the quality of vials with respect to the propensity to corrosion, but no direct correlation with delamination could be demonstrated, as no lamellae formation was observed.In response, further testing was carried out on five sets of vials with expected low delamination propensity, compared to a set of vials with high expected delamination propensity using both the proposed protocol and a more aggressive protocol. The objective was to observe lamellae at least in the high propensity vials to show a correlation to initial test protocols.The results show that there is a very good consistency between the results of the two testing protocols and therefore, with a good level of reliability, the degree of glass surface corrosion can be estimated by the testing protocol proposed by the Technical Committee. In some cases, the glass surface corrosion results may indicate an increased risk of delamination (depending on the individual interaction between the pharmaceutical solution and the inner vial surface).

Effects of different industrial processes on the phenolic composition of white and brown teff (Eragrostis tef (Zucc.) Trotter)

Teff is currently being incorporated into a range of foodstuffs, especially gluten-free flakes and extruded products. The main objective of this work was to assess the effects of different treatments (industrial milling, formation of flakes and extrusion) on the phenolic composition of two types of teff grains differing in their colour (white and brown). Fifty-nine phenolic compounds were detected by HPLC-DAD-MSn. C-glycosyl flavones accounted for more than 90% of the total phenolic contents in both teff types. White teff mostly contained apigenin-derived flavones (86–92%), whereas luteolin derivatives prevailed in brown teff (91–94%). The industrial processes, mainly flaking and extrusion, caused marked changes in the phenolic composition, some of which were dependent on the teff type. In both teff types, processing changed the phenolic profiles similarly by increasing C-monoglycosyl flavones and decreasing acylated derivatives. However, the total content was increased in flakes and extruded products made only from brown teff grains.

Relationships among American popcorn and their links with landraces conserved in a microcenter of diversity

This study describes the genetic diversity and the population structure of 66 popcorn landrace collections in a recently discovered microcenter of maize (Zea mays L.) diversity in southern Brazil. Furthermore, we elucidate their phylogenetic relationships with a diverse panel of 575 popcorn populations from 18 countries of American Continent. The germplasm, representing distinct landraces, was genetically characterized as population bulks using single nucleotide polymorphism markers (SNPs). Five main groups were identified for the popcorn germplasm of the southern region of Brazil. This pattern was associated with phenotypic diversity in grain shape and color. The germplasm of the American Continent was structured in nine groups associated with geographical region with significant differences in terms of genetic diversity and expansion capacity or popping expansion (the formation of large flakes after the kernels explode in response to heating). The popping expansion pattern of the American groups displayed a North-South geographical continuum, in which the average values increased with geographical distance from the center of origin in Mexico. The highest averages were obtained for the Lowland groups of South America. These results raise two hypotheses: the first one is the possibility of a continuous evolution of this characteristic, which is popcorn did disperse North - South, but interbreeding with local varieties drove up the diversity of the gene pool, and at the same time allowed more efficient selection on the trait of expansion capacity. The second is the possibility of a second domestication event of Zea mays ssp. mays L., in South America, which would assume an independent origin of popcorn, but not an independent domestication of maize. Both hypotheses would be based on popcorn populations brought from Mexico by human migrations. The germplasm collected in the microcenter of diversity in southern Brazil, most of them originated in the Lowlands of South America, a part of germplasm established phylogenetic relationships closer to the popcorn populations of Brazil collected in the last century. The study contributes to improved understanding of the origin and phylogenetics of this maize group and as such to conservation of those valuable genetic resources and future breeding efforts. This is valuable genetic research which led to better insight into grouping and dispersion of studied genotypes in the target region, but also its place vis-a-vis origin and migration of popcorn genotypes in South America in general.

Comparative Study of Microstructure, Mechanical and Reciprocating Wear Properties of Unmodified and Sr-Modified A383 Alloy and Composite

The present study focused on strontium (Sr)-induced A383 alloy and composite reinforced with 6 wt% boron carbide (B4C) particles processed by stir casting technique. From metallographic analysis, it was confirmed that Sr addition modified needle structures of α-Si to fine α-Si. This grain refinement enhanced the hardness of A383-Sr alloy by 52.72% and A383-Sr/B4C by 73.6%, and tensile strength of A383-Sr by 69.93% and A383-Sr/B4C by 81% when compared to A383 unmodified alloy. Fractography analysis proved that both Sr-induced alloy and composite had brittle failure with clear formation of flakes and cleavages. Reciprocating wear test was conducted at various loads (15 N, 25 N, 35 N) and at sliding distances (500 m, 1000 m, 1500 m). It was observed that wear rate was proportional to the applied load. Wear rate increased with increase in sliding distance, but after 1000 m, there was decline in wear rate. Worn surface analysis revealed the presence of oxide layer after 1000 m which enhanced wear resistance. A383-Sr/B4C composite possessed superior wear resistance compared to other.

Feasibility of removal of graphene oxide particles from aqueous suspensions by DC/AC electrocoagulation

Graphene oxide (GO) particulates offer an inexpensive route for the formation of graphene flakes. Their fine size and high degree of dispensability in aqueous media have raised environmental safety concerns in processing plants. This manuscript describes a novel electrocoagulation based method that enables the removal of GO particles from acidic aqueous suspensions in the form of copper-ion containing GO films. Specifically, copper ions were generated near a copper anode and adsorbed onto negatively surface-charged GO particles, driving the anodic deposition of GO films. The experimental variables included the type of electric field (DC and AC) and the use of a copper-ion induced bulk pre-coagulation step. A direct current (DC) potential gradient of 3 V/cm applied to a baseline suspension with a GO concentration of 0.8 mass percent solids removed approximately 3% of the GO particles in a minute in the form of compact films of thickness ranging from approximately 10 to 50 microns containing copper ions. Use of AC fields led to lower deposition rates and copper content. On the other hand, pre-coagulation of GO dispersions with copper ions led to films with enhanced copper concentrations. Characterization of GO films using XPS and Raman techniques has shown that copper is present in the bivalent form in GO.

Cathodically Deposited Birnessite As the Electrode Material

Various manganese oxides are considered as rather active ORR catalysts and/or supercapacitor materials for operation in alkaline medium. However all these oxides are thermodynamically unstable at high pH and undergo more or less slow transformations to non-stoichiometric oxides containing alkali metal cations M (MxMnO2*nH2O, known also as birnessite mineral). We report a possibility to deposit birnessite thin layers by means of permanganate cathodic reduction. We consider ORR activities and reversible recharging data for birnessite deposited at various potentials with account for XRD information on birnessite cell disordering and microscopic data on the morphology of the deposits.Deposition is complicated by formation of soluble Mn(V) and Mn(VI) species and their disproportionation. However fortunately these by-side reactions appear to be strongly inhibited by forming birnessite solid, and the resulting current efficiencies are high enough. We compare deposition efficiency and adhesion for Pt, Ni, and glassy carbon supports. The best adhesion is found for Ni support.Deposits morphology strongly depends on deposition potential. Thin deposits formed at low overvoltage demonstrate homogeneously distributed pores, and only starting from sub-mkm thickness branched flakes appear, which are typical for natural birnessite morphology. Contrary, at higher overvoltage the deposits start to branch from the very beginning, and consist from thin flakes exclusively. This morphology is unfavorable for electrode behavior because of too high material resistance. Deposition transients allow to monitor the morphology. For flakes formation, oscillatons at deposition transients are observed, which can be associated with layer-by-layer growth.The recharging of all birnessite materials is reversible, but the specific capacity strongly depends on deposition potential and deposit thickness. The best results (ca. 500 mkF/cm2 at scan rates up to 0.1 V/s) are found for thin deposits fabricated at low overvoltage. ORR mass activity is comparable with observed earlier for MnO2, which is believed to undergo slow transformation to birnessite in alkaline solutions. The important advantage of electrodeposited birnessite as compared to the majority of chemically synthesized manganese oxides is a possibility to operate in the absence of conducting binder.

An Easy and Ecological Method of Obtaining Hydrated and Non-Crystalline WO3-x for Application in Supercapacitors.

In this work, we report the synthesis of hydrated and non-crystalline WO3 flakes (WO3−x) via an environmentally friendly and facile water-based strategy. This method is described, in the literature, as exfoliation, however, based on the results obtained, we cannot say unequivocally that we have obtained an exfoliated material. Nevertheless, the proposed modification procedure clearly affects the morphology of WO3 and leads to loss of crystallinity of the material. TEM techniques confirmed that the process leads to the formation of WO3 flakes of a few nanometers in thickness. X-ray diffractograms affirmed the poor crystallinity of the flakes, while spectroscopic methods showed that the materials after exfoliation were abundant with the surface groups. The thin film of hydrated and non-crystalline WO3 exhibits a seven times higher specific capacitance (Cs) in an aqueous electrolyte than bulk WO3 and shows an outstanding long-term cycling stability with a capacitance retention of 92% after 1000 chronopotentiometric cycles in the three-electrode system. In the two-electrode system, hydrated WO3−x shows a Cs of 122 F g−1 at a current density of 0.5 A g−1. The developed supercapacitor shows an energy density of 60 Whkg−1 and power density of 803 Wkg−1 with a decrease of 16% in Csp after 10,000 cycles. On the other hand, WO3−x is characterized by inferior properties as an anode material in lithium-ion batteries compared to bulk WO3. Lithium ions intercalate into a WO3 crystal framework and occupy trigonal cavity sites during the electrochemical polarization. If there is no regular layer structure, as in the case of the hydrated and non-crystalline WO3, the insertion of lithium ions between WO3 layers is not possible. Thus, in the case of a non-aqueous electrolyte, the specific capacity of the hydrated and non-crystalline WO3 electrode material is much lower in comparison with the specific capacity of the bulk WO3-based anode material.

Van der Waals Epitaxy of Earth-Abundant Zn3P2 on Graphene for Photovoltaics

Earth-abundant semiconducting materials are a potential solution for large-scale deployment of solar cells at a lower cost. Zinc phosphide (Zn3P2) is one such Earth-abundant material with optoelectronic properties suitable for photovoltaics. Herein, we report the van der Waals epitaxy of tetragonal Zn3P2 (α-Zn3P2) on graphene using molecular beam epitaxy. The growth on graphene progresses by the formation of Zn3P2 triangular flakes, which merge to form a thin film with a strong (101) crystallographic texture. Photoluminescence from the Zn3P2 thin films is consistent with previously reported Zn3P2. This work demonstrates that the need for a lattice-matched substrate can be circumvented by the use of graphene as a substrate. Moreover, the synthesis of high-quality Zn3P2 flakes and films on graphene brings new material choices for low-cost photovoltaic applications.

Intriguing Carbon Flake Formation during Microwave-Assisted Hydrothermal Carbonization of Sodium Lignosulfonate.

Elongated carbon structures, here denoted as carbon flakes (CF), are revealed after microwave‐assisted hydrothermal carbonization of sodium lignosulfonate. The morphology of formed CF is investigated by transmission electron microscopy and atomic force microscopy. Interestingly, a wide range of length distributions (between 100 and 700 nm) and a relatively constant aspect ratio and thickness are observed, indicating structures clearly different from the carbon spheres commonly formed during hydrothermal carbonization of lignocellulosic biomass. Moreover, X‐ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, and X‐ray photoelectron spectroscopy provide further information of the chemical structure, which consist mainly of nanographitic domains with a high degree of defects such as oxygenated functional groups, hybridized sp3 carbon, and aliphatic side chains. Furthermore, new insights into the formation mechanisms are uncovered and the formation is speculated to proceed through the combined effect of microwave irradiation and a heterogeneous solid–solid conversion. The formed CF are anticipated as highly interesting products for a variety of material applications.

Synthesis of few-layer graphene flakes by magnetically rotating arc plasma: effects of input power and feedstock injection position

A magnetically rotating arc plasma system is used for the synthesis of graphene flakes by methane decomposition. Effects of input power and feedstock injection position on product microstructures are investigated. The morphology and composition of the products are characterized by transmission electron microscopy, Raman spectroscopy, X-ray diffraction, etc. Results show amorphous spherical particles with a diameter in the range of 10–40 nm and graphene flakes with 1–20 layers are generated in the plasma process. The graphene flakes are produced under a high gas temperature and long thermal history, while the spherical particles are favored by the opposite conditions. As the gas temperature increases, the products change from spherical particles to graphene flakes; moreover, the graphene flakes have larger size, fewer layers, straighter graphitic layers and better crystalline structure under a higher gas temperature. Emission spectral analysis indicates there exist lots of H atoms when the feedstock gas has a long thermal history in the plasma, revealing the importance of H atoms in the graphene flake formation. It is suggested that a high temperature and rich H environment can suppress the formation of curved or closed structures, leading to the production of graphene flakes with high crystallinity.

OPTIMIZATION OF ROLL COMPACTOR VARIABLES AND FORMULATION OF ANTI-RETROVIRAL TABLET BY ROLL COMPACTION METHOD

Objective: This study emphasis on roll compaction variable and how the processing parameters influence the formation of granules in process of formulations of antiretroviral IR Tablet with help of optimization technique.
 Methods: In this present work we aimed to develop a stable pharmaceutical dosage form with anti-retroviral drug tenofovir disoproxil fumarate. % retention of granules over # 60 mesh in roll compaction method by sizing with 50G co-mill screen was assessed by optimization and results were evaluated by Design expert 12.0 software. Various parameters and optimization of the parameter for formulation for better product was done by using 23 factorial design and dry granulation technique for manufacturing tablets. Three operating parameters the roller speed, the hydraulic pressure and the gap width on the Chamunda CPMRC-200/150 Roll Compactor were varied. The planned response variable for study was % retention over #60 ASTM mesh. % retention of granules was calculated by weighing granules on digital electronic balance with respect to how much premix material was taken for compaction.
 Results: Excipients compatibility study gave positive way showing no change in physical appearance of drug-excipients mix. It reviled that drug was compatible with excipients used.
 By formation of granules with required ratio, the value of Compressibility index changed from 29 to 21.89, showed that flow properties were improved i.e. from poor to passable.
 Design expert 12.0 gave optimized solution for formation of required quantity of granules. Pareto chart showed envaulted positive and negative impact of factors on response as explained in results.
 The results clearly indicate that how granules manufacturing in roll compaction process are influenced by roller pressure, roller gap and speed. 70 % flakes formation and granules retention were observed with 4000 kg/cm2 pressure, 1 mm roller gap width and 6 rpm speed of roller.
 Pareto chart clearly indicate major impact is of roller pressure. Comparative dissolution profile graph showed that drug release pattern is similar with the innovator tablet.
 A stable, robust tablets were formed at the end of process.
 Conclusion: In this study, by optimizing processing variables stable antiretroviral immediate release oral solid dosage form was formed.

Elucidating the mechanism for the chemical vapor deposition growth of vertical MoO2/MoS2 flakes toward photoelectrochemical applications

To control the growth of layered two-dimensional transition metal dichalcogenide (TMD) materials or complex structures such as heterostructures, it is important to understand the growth mechanism. In this study, we demonstrated the chemical vapor deposition (CVD) growth of vertically aligned MoO2/MoS2 flakes by using sulfur and molybdenum trioxide (MoO3) powders as precursors. Moreover, based on various experimental measurements, a detailed growth mechanism is proposed for elucidating the conversion of MoO2 to MoS2 in the CVD process to achieve vertically aligned MoO2/MoS2 flakes. Our results reveal that two competing pathways for sulfurization reactions occur during the CVD growth process: the dominance of the reactions in the vapor-phase pathway facilitates the formation of parallel-aligned MoS2 flakes, while the dominance of the reactions in the solid-phase pathway determines the formation of vertically aligned MoO2/MoS2 flakes. In addition, the photoelectrochemical (PEC) activity of the vertically aligned MoO2/MoS2 flakes was evaluated for hydrogen production applications based on PEC water splitting. Our results open the door to promote the process for designing the growth of other TMD materials or complex structures, which can be beneficial for use in various applications.

Effect of alloying elements W, Ti, Sn on microstructure and mechanical properties of gray iron 220

Experiments were carried out to observe the variation in microstructure and mechanical properties of gray cast iron by adding pearlite promoting alloying elements such as Ti, Sn and W. Results show that adding Sn, Ti, and W with different concentrations improve the microstructure, Brinell hardness and tensile strength of gray cast iron. With the increase of alloying element concentration, the average graphite length and graphite content increase linearly. At the same time, average cell size and the maximum graphite length also decrease linearly. Brinell hardness and tensile strength of gray cast iron also increase with an increase in alloying elements contents, and attain the maximum when Ti = 0.561%, Sn = 0.561% and W = 0.945%. However, at higher concentrations of Ti = 0.810%, Sn = 0.631% and W = 1.351%, the tensile strength decreases from 333 MPa to 297 MPa and the Brinell hardness decreases from 248 HB to 225 HB. The decrease in tensile strength and Brinell hardness at the higher concentration level is attributed to the formation of coarse and thick graphite flakes.

A pH-dependent partial electrochemical exfoliation of highly oriented pyrolytic graphite for high areal capacitance electric double layer capacitor electrode

High electrolyte resistance severely limits the response time and energy efficiency of an electric double layer capacitor electrode. Vertically oriented graphene nanosheets (VOG) having open, straight channel morphology is a new, attractive morphology with low electrolyte resistance. While CVD remains the dominant synthesis method for VOG electrodes, electrochemical exfoliation of graphite, a facile, economical and scalable method for production of loose graphene flakes, can also provide a VOG electrode. Here we show, that the conditions of electrochemical exfoliation for producing VOG morphology is substantially different from using it to produce loose graphene flakes. In particular, a low pH solution leads to a better expansion of the graphite and substantially better VOG density while a high pH solution leads to the formation of loose graphene flakes. Sulfuric acid is better than other sulfate salt-based electrolyte solutions for the synthesis of a VOG electrode. The electrolyte concentration, exfoliation time, and current density also affect the electrode capacitance. The optimal process conditions provide a VOG electrode of areal capacitance 750 mF/cm2. A capacitor consisting of two identical VOG electrodes shows a volume capacitance density of 1.56 F cm−3 higher than most of the literature values for supercapacitors.

Surface features on aged 238Pu-doped Eu-monazite

Abstract Several 238Pu-doped Eu monazite single crystals stored at ambient conditions are monitored for 15 years using Scanning and Transmission electron microscopy, spectroscopy, diffraction and optical microscopy. Despite preservation of high crystalline quality, mechanical cracking and formation of small flakes is observed. After several month of aging, a new phase appeared on surfaces of the crystals, which later formed a continuous shell of most crystallographic faces. Electron diffraction indicated that the shell consists of submicron Pu-containing rhabdophanes. Its formation likely occurs due to combined action of atmospheric moisture and recrystallisation of radiation damage in monazite domains adjacent to external and internal surfaces. Extent of the rhabdophane formation appears to be influenced by crystallography and Pu content of corresponding growth sectors of the parent monazite. Whereas macroscopic rhabdophanes and monazites are relatively stable against irradiation, formation of sub-microscopic particles is a point of concern for development of monazite-based ceramic forms for actinide immobilization.

Facile synthesis of amorphous Ti-peroxo complex for photocatalytic activity under visible-light irradiation

Abstract In this paper, amorphous Ti-peroxo complexes (ATPC) were successfully synthesized by a facile exothermic sol-gel method without annealing process. The TiH2 and H2O2 are used as starting precursor and oxidative polymerization agent. The color of prepared ATPC powder was changed from green to yellow with increase of H2O2 which directly induce the formation of small flakes on the ATPC, resulted in high surface area (154.1 m2/g). Raman and FT-IR spectra shows that the more peroxo groups such as Ti–OOH, Ti–O–O–Ti and -O-Ti-O- in yellow colored ATPC are formed than that of green colored ATPC. These peroxo groups not only accelerate the photocatalytic activity by abundant superoxide anion radicals, but also induce the formation of oxygen vacancies which can lead the visible-light activity. The prepared yellow colored ATPC shows remarkable visible-light induced photocatalytic activity with 95% decolorization of Rhodamine B within 30 min. Compare with previous researches related with titania based photocatalyst, the yellow colored ATPC shows excellent recycling property with maintained decolorization rate.

Microstructure and carbon storage capacity of hydrated magnesium carbonates synthesized from different sources and conditions

Recently, the mineral carbonation via the reaction of CO2 with saline aquafers received much attention as one of the most promising ways for geologic CO2 storage. This paper reports microstructure and carbon storage capacity of hydrated magnesium carbonates (HMCs) synthesized from different sources, i.e., reject brine and commercial Mg(OH)2 slurry, and under different conditions, i.e., pH (8–14) and Mg(OH)2:CO2 molar ratio (1:1–1:7). Results show that dypingite (Mg5(CO3)4(OH)2·5H2O) is the main phase forming at lower Mg(OH)2:CO2 ratios. An increase in the Mg(OH)2:CO2 ratio and/or pH leads to the precipitation of nesquehonite (MgCO3·3H2O). A unique “house of cards” texture, involving formation of the rosette-like dypingite flakes on the surface of nesquehonite needles, is discovered under elevated pH and Mg(OH)2:CO2 ratios. HMCs synthesized from reject brine exhibit a much higher carbon storage capacity of 82.6% than that produced from the commercial Mg(OH)2 slurry (43.7%). Findings from this study advance understanding of mineral recovery from reject brine and the capture and long-term storage of CO2 in the form of HMCs.

Growth of quadrilateral graphene flakes with a sulfur atomic template on the surface of Ni (110)

The relationship between the properties and substrates of graphene is important to research the graphene synthesized by a bottom-up approach. Here, we synthesized graphene with a surface segregation method and demonstrated that a quadrilateral graphene was formed by using Ni(110) as a substrate. Most of the graphene edges were parallel to the [101] or [100] directions of Ni(110). We found that sulfur impurities in Ni that segregated to the surface with a C(2 × 2) surface reconstruction during the graphene growth played critical roles in the formation of the quadrilateral graphene flakes.

Hydrogen Anti-flaking Heat Treatment in VAR89S Rail Steel

Hydrogen content in the diffusible range and beyond a critical level in steel is detrimental to the formation of hydrogen flakes that show up in ultrasonic testing. It is observed that the hydrogen content in any hot-rolled steel has a gradient with lowest hydrogen at the surface and higher towards the core. This is associated with the secondary phase transformation of high hydrogen-soluble austenite phase to a low-soluble ferrite phase, occurring last towards the core. Anti-flaking heat treatment was carried out in a flake-sensitive pearlitic rail steel grade, VAR89S, with an initial hydrogen level of 1.86 ppm at the core and 1.58 ppm in the surface of a 160-mm diameter hot-rolled bar. The heat treatment involved holding at 650 °C for times varying between 8 and 36 h, which decreased the hydrogen content. The decrease in hydrogen during anti-flaking heat treatment was correlated using Fick’s law model which took into account the initial hydrogen gradient across the bar cross section. The model predicted the experimental trend for hydrogen distribution at surface, mid-radius, and core. The hydrogen distribution at surface showed higher than predicted values, which could be attributed to the carbide spheroidization at the surface.