Flake Sizes Research Articles

Effect of Oxidation Level on Methanol and Proton Transport Characteristics of Graphene Oxide (GO) Based Proton Exchange Membrane (PEM)

Development of a PEM with insignificant methanol permeability at highly concentrated methanol supply is considered a major advancement in the direct methanol fuel cell (DMFC) technology. GO, a popular precursor for graphene synthesis, is decorated with surface oxidative groups (-COOH, -OH, C=O, etc.), which render proton conductivity to GO under hydrated conditions [1]. Its proton conductivity, along with a highly impermeable graphene backbone makes GO a suitable material for a highly selective PEM. We prepared a GO membrane, which exhibited two orders of magnitude higher proton to methanol selectivity, as compared to Nafion [2]. The membrane didn’t suffer any open cell voltage drop, even at 5 and 10 M methanol solution.GO is prepared by chemically exfoliating graphite flakes via oxidation. Different recipes have been reported in literature for oxidation of graphite, which result in GO with different oxidation levels. Oxidation level of GO is known to impact its physiochemical properties (flake size, surface defects), which should affect mass transport of species across it. Herein, we present effect of oxidation level of GO on its proton and methanol transport characteristics. At first, we studied the impact of mean flake size on these transport processes, by preparing GO using Hummer’s method, and varying its mean flake size via sonication, while keeping a constant oxidation level. A 10 µm thick GO laminate is prepared by vacuum filtration of its aqueous dispersion. Methanol permeability of the GO laminate is observed to be varying linearly with flake size (Fig.1). This is because, being similar in size to water, methanol molecules also follow a tortuous transport path around a GO flake [3]. Hence, changing the flake size changes the diffusion path length for methanol. On the contrary, proton conductivity changed rather insignificantly with flake size (Fig.1). This could be due to the presence of proton selective atomic formations on the GO surface, which allows protons to be transported through the GO flake (Fig.3). We conducted a TEM study on the GO flakes, which revealed presence of surface defects of different sizes. Based on the size of these defects, possible proton transport paths across the GO flakes is discussed in Fig.4.GO with three different oxidation levels is prepared using process developed by Marcano et al. [4] by varying the weight ratio of graphite flakes to KMnO4. GO 1 to 3 (refers to products with an increasing oxidation level) is prepared by using weight ratios (Graphite: KMnO4) of 1:2, 1:4 and 1:6 respectively. Mean flake size of GO is reduced with increase in the oxidation level; mean flake sizes for GO-1, GO-2 and GO-3 measuring 77, 56 and 34 µm. Reduction in flake size is due to unzipping of GO flakes under oxidative environments. Therefore, methanol permeability across the GO laminate changes with oxidation level (Fig.2). However, unlike in Fig.1, methanol permeability doesn’t change linearly with flake size; rather it varies polynomially (order 3). This is because, in addition to breaking down of flakes, surface defects on GO surface also enlarge under the oxidative environment. This further adds to the methanol permeability across the GO laminate. Proton conductivity also increases with increase in the oxidation level. As mean flake size doesn’t have a significant effect on proton conductivity of GO flakes, this increase is primarily due to increase in the number of surface oxidative groups, which are responsible for the in-plane ionic conductivity of the GO flakes.[1] Karim et al. J. Am. Chem. Soc. 135 (2013) 8097−8100.[2] Paneri et al. J. Power Sources (2013)(Under review).[3] Boukhvalov et al.Nano Lett. 13 (2013) 3930.[4] Marcano et al. ACS Nano 4 (2010) 4806.

Effect of surface texture on color appearance of metallic coatings

• Effect of aluminum flake on visual texture and consequently color appearance of metallic coatings was investigated. • Statistical texture analysis methods were applied to quantify texture features of metallic coatings. • Correlation between perceptual appearance differences and texture differences was investigated. • Analysis of variation (ANOVA) was applied to find the best texture analysis method. In this study, the effect of aluminum flake size on the color appearance of metallic coatings has been investigated. To this end, metallic solvent-borne basecoat-clear coat systems with seven different surface textures using different sizes of aluminum flakes were prepared corresponding to nine color centers including blue, yellow, red, green, purple, cyan, orange, greenish yellow and gray. The color changes via texture differences were assessed by visual experiments carried out by 25 observers including 14 women and 11 men using gray scale method and under semi-diffuse illumination conditions. The assessed pairs had the same color center and different visual texture caused by different aluminum flake sizes. Texture analysis was performed using autocorrelation function and fractal dimension on gray scale images of the samples, captured by a scanner, and texture difference for each assessed pair was computed. The results showed that different aluminum flake size can cause different visual texture and consequently different color appearance. The correlation between perceptual color differences and the texture differences showed that autocorrelation function and fractal dimension have a pretty good performance for quantifying texture feature of the metallic coatings while the texture is caused by aluminum flakes.

Are bigger flakes always better? An experimental assessment of flake size variation on cutting efficiency and loading

Previous studies have indicated that the cutting efficiency of flake tools increases with increased tool size. Here, we undertook to examine the relationship between flake size and efficiency parameters using a larger and more variable flake dataset than used in previous analyses. Our analyses were specifically designed to assess whether there is an absolute relationship between ever-increasing flake size and increased efficiency and/or loading potential. An alternative hypothesis is merely that only the smallest flakes are inefficient, and it is this factor which has been driving previous statements linking increasing flake size with increased efficiency. Our first set of analyses, using all experimental flakes, determined that a statistically significant relationship existed between increased flake sizes and increased cutting efficiency, as measured by two different efficiency measures (‘Time taken’ and ‘Number of cutting strokes required’). This analysis also demonstrated a statistically significant positive relationship between flake size and loading forces. However, our second analysis, which excluded the smallest flakes in our sample, revealed a different pattern. In this second set of analyses, increasing flake size did not indicate a statistically significant relationship with our two measures of cutting efficiency. A statistically significant relationship between increased flake size and increased loading was, however, still evinced. In sum, these results suggest that there is not an unconditional or absolute relationship between increased flake size and increased cutting efficiency in all circumstances. Rather, there is a threshold below which flakes of a certain size will become markedly inefficient. Our results have particular implications relating to flake utility, optimality, and factors potentially influencing flake selection by hominins.

Relationship between Graphite Flake Sizes and the Mechanical Properties of Grey Iron

Cast Irons are important engineering materials which possess a wide range of attractive properties. Their properties are significantly dependent on the microstructure of the cast, cast iron components. A way of controlling the microstructure of cast iron is through the control of cooling rates during solidification. To control cooling rate, the heat storage capacity of the mould is important. This paper presents the report of a study on the characteristic effects of graphite flake sizes on some mechanical properties of grey cast iron. Six mould materials with heat storage capacities ranging from 1.52 kJ.m-2.K-1.s-1/2 to 2.16 kJ.m-2.K-1.s-1/2 were prepared and used to cast some grey cast iron samples whose microstructures were observed by optical microscopy. Mechanical properties of the grey iron were evaluated. The results show that the properties increased with the heat storage capacity of the mould. Also, the microstructures show a dependence on heat storage capacity of the mould.

Size and synergy effects of nanofiller hybrids including graphene nanoplatelets and carbon nanotubes in mechanical properties of epoxy composites

We study mechanical reinforcement in a widely used epoxy matrix with the addition of graphene nanoplatelets (GnPs) and various mixture ratios of carbon nanotubes (CNTs) with GnPs. Two different dimensions of GnPs were used with flake sizes of 5μm and 25μm to investigate the influence of nanofiller size on composite properties. In GnP reinforced composites, bigger flakes showed greater reinforcement at all GnP concentrations as they actively control the failure mechanisms in the composite. In the mixture samples, highest CNT content (9:1) showed marked improvement in fracture toughness of 76%. The CNT:GnP ratio is an interesting factor significantly influencing the properties of the epoxy based nanocomposites. The combination of high aspect ratio of CNTs and larger surface area of GnPs contribute to the synergistic effect of the hybrid samples. Thermal conductivity consistently increases with incorporation of GnPs in the matrix. Transmission electron microscopy (TEM) images confirm the uniform nanofiller dispersion achieved in the composites. For the hybrid samples CNTs are seen to align themselves on the GnP flakes creating an inter-connected strong nanofiller network in the matrix. The homogeneous nanofiller dispersions have been achieved by high shear calendaring which is a method capable of being industrially scaled up.

Characterization of Graphite Flakes in Grey Iron Microstructure

Cast irons are important engineering materials which possess a wide range of attractive properties. Their properties are significantly dependent on the microstructure of the cast and cast iron components. A way of controlling the microstructure of cast iron is through the control of cooling rates during solidification. To control cooling rate, the heat storage capacity (HSC) of the mould is important. This paper presents the report of a study on the characteristic effects of graphite flake sizes on some mechanical properties of grey cast iron. Six mould materials with HSCs ranging from 1.52 to 2.16 kJ m−2 K−1 s−1/2 were prepared and used to cast some grey cast iron samples whose microstructures were observed by optical microscopy. Mechanical properties of the grey iron were evaluated. The results show that the properties increased with the HSC of the mould. In addition, the microstructures show a dependence on HSC of the mould.

Raman Studies of Defects in Graphene Grown on SiC

Raman Studies of Defects in Graphene Grown on SiC K. Grodecki, R. Bozek, J. Borysiuk, W. Strupinski, A. Wysmolek, R. Stepniewski and J.M. Baranowski Institute of Electronic Material Technology, Wolczynska 133, 01-919 Warsaw, Poland Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Hoza 69, 00-681 Warsaw, Poland Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warsaw, Poland The Raman scattering studies of multi-layer graphene obtained by high temperature annealing of carbon terminated face of 4H-SiC(000-1) substrates are presented. Intensity ratio of the D and G bands was used to estimate the average size of the graphene flakes constituting carbon structures. The obtained estimates were compared with flake sizes from atomic force microscopy data. We found that even the smallest structures observed by atomic force microscopy images are much bigger than the estimates obtained from the Raman scattering data. The obtained results are discussed in terms of different average flake sizes inside and on the surface of the multi-layer graphene structure, as well as different type of defects which would be present in the investigated structures apart from edge defects.

Influence of Mould Heat Storage Capacity on Properties of Grey Iron

Grey cast iron is characterized by presence of a large portion of its carbon in the form of graphite flakes which are observable in their microstructures. Their properties are significantly dependent on the micro-constituents of the, cast iron components. A way of controlling the microstructure of cast iron is through the controlled cooling rates during solidification. To control cooling rate, the heat storage capacity of the mould is important. This paper presents the characteristic effects of graphite flake sizes on some mechanical properties of grey cast iron. Six mould materials with heat storage capacities ranging from 1.52 kJ.m-2.K-1.s-1/2 to 2.16 kJ.m-2.K-1.s-1/2 were prepared and used to cast some grey cast iron samples whose microstructures were observed by optical microscopy. Mechanical properties of the grey iron were evaluated. The results show that the properties increased with the heat storage capacity of the mould. Also, the microstructures show a dependence on heat storage capacity of the mould.

COMBUSTION OF AEROSOLIZED SPHERICAL ALUMINUM POWDERS AND FLAKES IN AIR

Combustion rates and completeness of aerosolized spherical aluminum powders and flakes are compared using constant volume explosion experiments. The comparison of particles and flake sizes was made based on their specific surface areas determined using the Brunauer–Emmett–Teller (BET) method and respective “BET diameters.” It is observed that the rates of pressure rise and respective rates of flame propagation were higher for spherical aluminum powders with BET diameters of about 2 to 5 µm compared to aluminum flakes for which the respective BET diameters were under 1 µm. In agreement with the flame propagation rates, the overall completeness of combustion was also higher for spherical powders compared to flakes. It is suggested that aerosolized flakes could be agglomerated in gas flows more than spherical particles causing their inferior combustion performance.

Gray Cast-Iron Water Pipe Metallurgy

The results of a metallographic study of gray cast-iron water pipes are reported. These pipes were installed between 1885 and 1973 in eight different water systems. Each pipe had been extracted during scheduled maintenance or failure repairs to provide data for a larger study to produce a methodology for determining the residual life of gray cast-iron pipes. This metallographic study was conducted to determine the causes of variations in the mechanical properties of these pipes. Pit-cast and spun-cast pipes were found to have distinctly different types of graphite flakes, flake sizes, and metallic matrices. These differences were directly responsible for the variations in the mechanical properties between the two types of pipes, with the larger flake sizes of the pit-cast pipes, in particular, producing weaker material. Examples of anomalous pipes that did not have the standard appearance of either type of manufacture were also found and the reasons for their appearance identified. The results of the study show that the metallurgy of the pipes may be a major contributing factor, along with external forces such as corrosion or poor installation practices. Metallographic analysis therefore can assist water utilities managers in making decisions in repairs, rehabilitation, and replacement.

Electrical conduction models for isotropically conductive adhesive joints

An electrical conduction model for silver filled isotropically conductive adhesives (ICA) was developed. The model combines the microscopic resistance of the bulk silver particles and the contact between silver flakes with the macroscale resistor network calculation by percolation theory. The resistivities of the composites were calculated by resistor network simulations considering both contact effects and particle size effects. Three different types of film typically exist on the silver surface: residual organic films; tarnish films; and a thin epoxy layer. The contact resistance between silver flakes can be due to a constriction resistance, to the tunneling resistance through insulating films, or to the resistance of more conductive layers. The constriction resistance is produced by the restriction of the current flow by small contact spots and is controlled by the actual contact spot area (metallic contact), which is dependent on the contact force between flakes. The tunneling resistance is caused by the very thin layer which may reside on the silver flakes between the metallic contact spots, and is dependent on a barrier film thickness and potential. Oxide and sulfide tarnish films are typically degenerate semiconductors. Two- and three-dimensional (2-D and 3-D) computer simulations were performed to predict the effects of particle sizes, shapes, and distribution on the percolation conduction thresholds and cluster sizes. The model predicts that the percolation threshold decreases with broad particle size distributions and high aspect ratio particles. The effective resistivity of the adhesive depends on the thickness dimension of the adhesive pad geometry, with very thin layers resulting in high percolation thresholds and high resistivities. Resistivity does not change with the pad thicknesses greater than a certain thickness level. Silver flake orientation on the surface increases the resistivity of the conductive adhesive pads, but in the same magnitude range. The resistivities of the materials are controlled by silver flake sizes and the nature of the contacts.

Barrier membranes with tipped impermeable flakes

AbstractDiffusion of carbon dioxide through silicone‐polycarbonate membranes containing oriented mica flakes is proportional to the square of the volume fraction of the flakes, to the square of the aspect ratio, and to the square of the cosine of the angle at which the flakes are oriented. These experiments are consistent with Monte Carlo simulations. The simulations allow investigation of more complex geometries, including other flake orientations and polydisperse flake sizes.

SENSORY AND OBJECTIVE EVALUATION OF A RESTRUCTURED BEEF PRODUCT

ABSTRACTA study was undertaken to determine the effect of connective tissue, flake size and NaCl level on the texture of restructured beef steakettes; to examine the effect of these factors on the acceptability of restructured steakettes; and to develop sensory and instrumental texture profiles of the product. Restructured beef steakettes were manufactured with two levels of connective tissue (high, low), three flake sizes (3 mm, 6 mm, 13 mm) and three NaCl levels (0.25%, 0.50%, 0.75%). The textural attributes of these products were measured by a trained sensory panel and by objective measures of compression texture profile analysis, Warner‐Bratzler shear and three tensile tests. Most sensory texture attributes could be predicted accurately using instrumental methods. Reduction of the sensory attributes by Principal Components Analysis revealed two underlying dimensions of connective tissue and bind strength. A consumer panel rated steakettes manufactured with 6 mm flakes and 0. 75% NaCl at either connective tissue level to be the most acceptable of the 18 products manufactured for this study.

The effects of the preparation conditions on the electrochemical properties of graphite-CrO 3 intercalation compounds in acid electrolyte—I. the studies on lower chromium oxides

A slow potentiodynamic method (10 mV min −1) has been used to characterize the dilute intercalation compounds of graphite with CrO 3 (GIC-CrO 3's) prepared by the dry and the impregnation-dry method from two kinds of natural graphite of different flake sizes. The characteristic anodic peak at 1.3–1.4 V vs nhe obtained for GIC-CrO 3's in 0.25 M H 2SO 4 was evidenced to be associated with the oxidation of the lower oxides of Cr such as Cr 3O 8 and/or Cr 2O 5 remaining in the compounds after their treatment in hot 6 M HCl. The amount of these oxides and their electrochemical activity are dependent on the kind of graphite subjected to the intercalation process as well as the method of intercalation. The comparison of the results obtained for GIC-CrO 3's with those achieved for the same compounds after heat treatment and with the physical mixture of pristine graphite with Cr 2O 3 led to assumption that lower oxides were formed due to the partial reduction of CrO 3 intercalated and that between them and the graphite structure, occurs the chemical interaction.

The dilute intercalation compounds of graphite with chromium trioxide

The dilute intercalation compounds of graphite with CrO 3 were prepared by two methods using natural graphites of different flake sizes. The first method consisted of the impregnation of graphite in an aqueous solution of CrO 3 at 70°C followed by heating dry semiproduct at 200°C for 10 hr. In the second method the impregnation process was omitted and graphite was directly subjected to reaction with molten CrO 3. Although the C Cr ratio of the compounds was always higher than 13, it was shown that in the case of the dry method (without impregnation) this parameter is lower for the finer graphite, whereas in the case of preimpregnated compounds it is distinctly lower for the coarser graphite. The reasons for this difference are discussed. Because of the equivocal data of X-ray analysis the compounds were examined in detail by the electrochemical method in 0.25 M H 2SO 4 including the measurements of electrode potential and the potentiodynamic runs. Data obtained are consistent with the results of other studies made in this work and evidence that CrO 3 is intercalated in graphite and coexists with lower oxides insoluble in 6 M HCl. While the compounds are unaffected by 6 M HC1 and 0.5 M H 2SO 4, they are deintercalated in alkaline solutions. After heating up to 260°C and/or pressing at 600 at Cr 6+ ions are easily leached from the compounds by cold water. The mechanism of deintercalation is considered.

Physical and Sensory Properties of Restructured Beef Steaks Formulated with Various Flake Sizes and Mixing Times

Restructured cow beef steaks were made using six different flake size formulations: (a) coarse, (b) medium, (c) fine, (d) coarse + medium, (e) medium + fine and (f) coarse + fine meat flakes. Each formulation was mixed for 0, 5, 10 or 15 min, pressed into “logs”, frozen and cut into steaks. Steaks were evaluated for physical appearance, fat and moisture content, cooking properties, texture and sensory attributes. Steaks made from the coarse flakes had large fat particles and therefore received lower (P<0.05) ratings for physical appearance. Restructured steaks made from the fine particles were more tender (P<0.05) and received significantly higher (P<0.05) textural desirability and overall palatability ratings than restructured steaks made from coarse particles. A mixing time of 5 min resulted in higher scores (P<0.05) for juiciness and tenderness as compared to restructured steaks made from meat mixed for 15 min. Mixing time had no significant effect on cooking losses or binding strength.

Precooking and Flake Size Effects on Spent Fowl Restructured Steaks

Four formulations of spent fowl muscle, each made to contain 40% dark muscle and 60% white muscle, were prepared as follows: (a) raw meat, large flake size; (b) raw meat, small flake size; (c) precooked meat, large flake size and (d) precooked meat, small flake size. Each formulation was mixed with 0.3% NaCl, 0.25% Na tripolyphosphate and 0.25% hydrolyzed vegetable protein for 10 min, pressed into logs under 400 psi, frozen and cut into steaks. Steaks were evaluated for moisture and fat content, cooking properties, texture and sensory attributes. Restructured steaks made from precooked chicken muscle had lower initial moisture contents and lost less moisture during cooking than restructured steaks made from raw meat. Flake size had no significant effect on cooking losses; however, the smaller flake sizes contributed to a more tender product. Steaks made from the raw chicken meat were of a more acceptable flavor. Restructured steaks made from raw flakes were significantly more desirable in texture and overall palatability and were more tender and juicy than restructured steaks made from precooked chicken.

Structure and properties of a splat cooled 2024 aluminum alloy

Pound lots of splat cooled 2024 aluminum flake materials were produced by rapidly quenching the atomized melt against a rotating copper disc. Three flake sizes were selected, cold compacted into aluminum cans, and extruded at 300°C at a reduction ratio of 20 to 1. The extruded rods were reduced 50 pct by cold swaging, solution treated at 495°C, water quenched, and naturally aged. The splat cooled 2024 alloy had constituent particles of 1 fim and finer (compared to 5 to 20 μm for the commercial alloy); further, one of the complex constituent phases (AlCuFeMn) was essentially eliminated by the rapid quench. Compared to commercial 2024-T4, the splat cooled 2024 alloys showed 14 to 17 pct increase in yield and tensile strength (no loss of ductility) a seven-fold increase in fatigue life at 30,000 psi, and a large improvement in the 300°F (150°C) stress rupture life in tests beyond 100 h. The fracture characteristics of the splat alloys, while exhibiting excellent to superior ductility, appear inhomogeneous due to the presence of finely dispersed oxide films scattered in the structure.

A search for intercalation in the graphite-chlorine system

The mass of chlorine gas or liquid adsorbed by graphite was measured with a recording silica spring balance designed to operate at pressures to saturation and sample temperatures to 25°C. The rates of absorption in saturated vapor and the isotherms were determined for several sources and flake sizes of graphite. All behaviour in the range −25° to +20°C was characteristic of condensation of chlorine in a pore system. Some of the behaviour was also characteristic of intercalation but the other behaviour was not. It is therefore concluded that chlorine does not intercalate graphite.

The mechanism of bromine exchange in the bromine-graphite lamellar compounds

The rates of exchange of normal and radioactive bromine in bromine-graphite were studied at temperatures of 20–45°C. A range of natural graphite flake sizes from 50–2000 μ were used to prepare the compounds. The dependence of the rate of exchange on particle size, a, changed abruptly from 1 a at large particle sizes to 1 a 2 at small particle sizes. The apparent activation energy varied by a factor of three over the temperature range investigated. A mechanism of exchange is proposed which explains the observed particle size dependence, temperature dependence and the form of the rate curves in terms of two consecutive surface processes and the structural features of the natural graphite flakes.