Metal Flakes Research Articles

Flaking behavior and microstructure evolution of nickel and copper powder during mechanical milling in liquid environment

To prepare metal flakes with a high flaking level and investigate the microstructure of metal flakes, nickel and copper powder were mechanically milled in liquid environment and the microstructure of powders was investigated by X-ray diffraction. The milling process can be divided into flaking and broken stages. At the flaking stage, milled metal powders exhibited high flaking level and flaky microshape, and 〈2 0 0〉 became preferred orientation. While at the broken stage, the milled powders presented a low flaking level and irregular microshape, and 〈2 0 0〉 was not preferred orientation any longer. The grain size, microstrain and dislocation density along 〈2 0 0〉 direction varied with milling time differently from that along 〈1 1 1〉 direction. The flaking level of the milled powders was related to the 〈2 0 0〉 preferred orientation, and more closely to the deformation mechanism. We can strengthen the formation of 〈2 0 0〉 preferred orientation to obtain metal powders with a high flaking level.

RESEARCH ON WATER BASED COATING CONTAINING NANO-SILICA FOR MAGNESIUM ALLOY

Due to magnesium's active chemical property, a novel environmental protective water based metallic coating was developed, which mainly contains metal flake, nano-silica, silicate and silane. The coating's properties were investigated by neutral salt spray test, micro-hardness testing, adhesion test and electrochemical technique etc. Meanwhile the coating surface and microstructure was observed by scanning electron microscopy (SEM). Furthermore, the effect of nano silica on the coating was also explored. Results showed that an excellent adhesive, heat-resisting, protective coating for AZ91D magnesium alloy could be achieved by this technique. It also indicated that nano silica could greatly improve the properties of coating. In the paper, mechanism of nano silica coating was also discussed.

A Novel Anti-Corrosion Coating for Aluminium Alloy

A novel environmental protective water based metallic coating was developed for aluminum alloys, which mainly contains metal flake, silicate and silane. The coating's properties were investigated by neutral salt spray test, micro-hardness testing, adhesion test and electrochemical technique etc. Meanwhile the coating's surface and microstructure was observed by scanning electron microscopy (SEM). Furthermore, the film forming matter was examined by Fourier transform infrared spectroscopy (FTIR) test. Results showed that an excellent adhesive, heat-resisting, protective coating for aluminum alloy could be achieved by this technique. An interpenetrating polymer network (IPN) was formed in the coating by means of cross linking reaction of organosilicone and inorganic silicate. In thesis, the film forming mechanism and protection of coating were also discussed.

Impact of real-time magnetic axis sweeping on steady state divertor operation in LHD

Steady state divertor operation with high performance plasmas (ne ∼ 0.7 × 1019 cm−3, Ti ∼ 2 keV) was demonstrated for half an hour in the Large Helical Device (LHD), the superconducting helical device (R = 3.6–3.9 m, a = 0.6 m, B = 3 T, l/m = 2/10). The high performance plasmas have been sustained with an averaged heating power of 680 kW and achieved an injected energy of 1.3 GJ. This required both advanced technological integration of heating systems and divertor heat flux control. In particular, optimization of divertor heat flux distribution along the divertor leg trace on divertor plates and real-time magnetic axis sweeping (R = 3.67–3.7 m) have allowed LHD to access a steady state regime with a margin of safety for the actively cooled divertor plates. The distribution of divertor heat load along the traces was investigated with calorimetric measurements and it was found that there was a localized heat load connected with the loss of high-energy ions produced by ion cyclotron radio frequency near-fields. Orbit analysis shows that the behaviour of high-energy ions is qualitatively in good agreement with the experimental result. Long-pulse discharges were terminated by radiation collapse due to penetration of metallic flakes into the plasma.

1064-nm laser fragmentation of thin Au and Ag flakes in acetone for highly productive pathway to stable metal nanoparticles

The laser-induced fragmentation of thin Au and Ag flakes in acetone by 1064-nm nanosecond laser (with the fluence typically ∼2J/cm2) potentially offers a highly productive pathway to stable metal nanoparticles in liquid. Acetone serves as a superior liquid medium that keeps fine metal nanoparticles free from precipitation even in such concentrated nanoparticle solutions exceeding ∼0.1M. Thin metal flakes have good capability to absorb the 1064-nm laser energy as efficiently as in the visible region. A part of the thus laser-heated molten flakes explosively split into submicroparticles, and some other significant part directly into fine nanoparticles. Both kinds of product particles have minor absorption cross-sections for subsequent laser pulses at 1064nm, and thus no longer fragment further. One of the two kinds of Ag flakes studied in this work yielded fine Ag nanoparticles at a remarkable high production rate of 1.1mg/min for the input laser power of only ∼0.65W.

Thirty-minute plasma sustainment by real-time magnetic-axis swing for effective divertor-load-dispersion in the Large Helical Device

Achieving steady-state plasma operation at high plasma temperatures is one of the important goals of worldwide magnetic fusion research. A high temperature of approximately 2keV, and steady-state plasma-sustainment operation of the Large Helical Device (LHD) [O. Motojima, K. Akaishi, H. Chikaraishi et al., Nucl. Fusion 40, 599 (2000)] is reported. High-temperature plasmas were created and maintained for more than 30min with a world record injected heating power of 1.3GJ. The three-dimensional heat-deposition profile of the LHD helical divertor was modified and during long-pulse discharges it effectively dispersed the heat load using a magnetic-axis swing technique developed at the LHD. A sweep of only 3cm of the major radius of the magnetic axis position (less than 1% of the major radius of the LHD) was enough to disperse the divertor heat load. The modification of the heat-load profile was explained well by field-line tracing. The steady-state plasma was heated and sustained mainly by hydrogen minority ion heating using ion cyclotron range of frequencies. The operation lasted until a sudden increase of radiation loss occurred, presumably because of wall metal flakes dropping into the plasma. The sustained line-averaged electron density was approximately 0.7–0.8×1019m−3. The average input power was 680kW, and the plasma duration was 31min 45s. This successful long operation shows that the heliotron configuration has a high potential as a steady-state fusion reactor.

Research on Water Based Coating for Magnesium Alloy

Magnesium and its alloys have many applications for theirs excellent physical and mechanical properties. Due to magnesium’s active chemical properties and difficulties in direct painting, a novel environmental protective water based coating was developed, which mainly contains metal flake, silicate, silane and sodium polyphosphate etc. The properties and structure of the coating were investigated by adhesion test, hardness test, heat resistance test, neutral salt spray test and Scanning Electron Microscopy (SEM) et al. Meanwhile, the effect of sodium polyphosphate was also examined by hydrogen evolution test and electrochemical test. Furthermore, the film forming mechanism of the coating was explored by Fourier Transform Infrared spectroscopy (FTIR). Results showed that the coating had a stepped structure which could achieve extraordinary adhesion, 350°C temperature heat resistance, HV0.50/30 210 hardness and 300 hours anti-corrosion time in salt spray test. In the coating, the addition of sodium polyphosphate could greatly improve the corrosion resistance of the coating because of the barrier film formed by sodium polyphosphate. The mechanism of interpenetrating polymer network (IPN) was preliminary put forward based on the results of FTIR.

Getting the Lead Out of Electronics

The electronics industry is learning to do without: it is having to abandon one of its long-time staples, lead–tin solder. For decades lead–tin solder has been used to attach electronic components to printed wiring boards. However, with the body of evidence pointing to serious adverse health effects of lead, the search for a replacement has spawned intense effort in the electronics industry and in universities. Now scientists think they may have found some promising leads: solders made of alternative alloys and polymer formulations known as electrically conductive adhesives (ECAs).

Conducted noise suppression up to GHz range by spin-sprayed Ni 0.2Zn xFe 2.8−xO 4 ( [formula omitted], 0.6) films having different natural resonance frequencies

In order to apply to a novel, flexible type of GHz noise suppressors, we prepared Ni 0.2Zn x Fe 2.8− x O 4 films with x = 0.3 and 0.6 and thicknesses of 2 and 5 μm, by spin spray ferrite plating from an aqueous solution on polyimide sheets at 90 °C. Placing the films onto a microstrip line, we measured transmission loss Δ P loss and reflection parameter S 11 at 10 MHz–10 GHz. As x increased from 0.3 to 0.6, f r (natural resonance frequency) decreased from 350 to 50 MHz, which resulted in decreasing f c (a frequency from which Δ P loss begins rising) from 400 to 100 MHz. This means we can tune f c of the films by changing the Zn concentration x. At 8 GHz, Δ P loss obtained by the ferrite films increased from 40% to 70% when their thickness increased from 2 to 5 μm. We obtained S 11 < 10 % , irrespective of Zn concentration, in the whole measurement frequency range. By the films with x = 0.3 and 2 μm thickness we obtained Δ P loss = 40 % , which was as strong as that obtained by a commercially available composite sheet type noise suppressor of 25 μm thickness that are made of ferromagnetic metal flakes embedded in a flexible polymer matrix. Moreover, Δ P loss by the ferrite film increased to 70% when the thickness was increased to 5 μm. Therefore, our NiZn ferrite films are promising to be actually used as GHz noise suppressors with tunable working frequencies that exhibit stronger noise suppression than the commercialized composite type of noise suppressors.

Modelling infrared extinction of high aspect ratio, highly conducting small particles

Infrared extinction cross sections and volume extinction coefficients have been calculated for high aspect ratio cylindrical fibres and thin disc flakes with microscale and nanoscale minor dimensions. The extinction dependence on conductivity and particle dimension has been predicted. A range of scattering models have been employed and include the method of moments, the finite difference time domain method and the exact analytical solutions for an equivalent surface area sphere (Mie theory) and an infinite cylinder. Choice of model depended upon particle size, geometry and conductivity. Experimental measurements of extinction for metal flake samples were also performed and compared to the theoretical predictions. Extremely large volume extinction coefficients (>1000 m2 cm−3) are predicted for selected major dimension and sufficiently large aspect ratios and conductivity. Corrections to the bulk conductivity have been made due to the particle minor dimension being of the order of the mean free electron path length. Optimum particle minor dimensions resulting in maximum volume extinction have been identified for a given conductivity.

Laser lithography on resist bi-layer for nanoelectromechanical systems prototyping

We present a laser lithography technique based on lift-off, for fast and flexible prototyping of micro and nanoelectromechanical systems (MEMS/NEMS). The technique is based on direct laser writing on substrates coated with a resist bi-layer consisting of polymethyl methacrylate (PMMA) on lift-off resist (LOR). Laser writing melts and evaporates the PMMA exposing the LOR. Oxygen ashing removes PMMA residues within the lithography pattern. A resist solvent is used to transfer the pattern down to the substrate. The LOR is dissolved isotropically while the PMMA is unaffected by the solvent, hence creating an undercut profile. After metal evaporation a two-step lift-off process prevents metal flakes from adhering to the surface. First, warm acetone dissolves the PMMA and lifts off the metal layer, then warm Remover PG removes the LOR and any remaining metal. Metal structures with line widths down to 600 nm and dots with 600 nm diameters are presented.

Laser lithography on resist bi-layer for nanoelectromechanical systems prototyping

We present a laser lithography technique based on lift-off, for fast and flexible prototyping of micro and nanoelectromechanical systems (MEMS/NEMS). The technique is based on direct laser writing on substrates coated with a resist bi-layer consisting of polymethyl methacrylate (PMMA) on lift-off resist (LOR). Laser writing melts and evaporates the PMMA exposing the LOR. Oxygen ashing removes PMMA residues within the lithography pattern. A resist solvent is used to transfer the pattern down to the substrate. The LOR is dissolved isotropically while the PMMA is unaffected by the solvent, hence creating an undercut profile. After metal evaporation a two-step lift-off process prevents metal flakes from adhering to the surface. First, warm acetone dissolves the PMMA and lifts off the metal layer, then warm Remover PG removes the LOR and any remaining metal. Metal structures with line widths down to 600 nm and dots with 600 nm diameters are presented.

04/00986 Coloured paints based on coated flakes of metal as the pigment, for enhanced solar reflectance and cooler interiors: description and theory: Smith, G. B. et al. Solar Energy Materials and Solar Cells, 2003, 79, (2), 163–177

04/00986 Coloured paints based on coated flakes of metal as the pigment, for enhanced solar reflectance and cooler interiors: description and theory: Smith, G. B. et al. Solar Energy Materials and Solar Cells, 2003, 79, (2), 163–177

Ray model of light scattering by flake pigments or rough surfaces with smooth transparent coatings.

We derive expressions for the intensity and polarization of light singly scattered by flake pigments or a rough surface beneath a smooth transparent coating using the ray or facet model. The distribution of local surface normals is used to calculate the bidirectional reflectance distribution function (BRDF). We discuss the different distribution functions that can be used to characterize the distribution of local surface normals. The light-scattering model is validated by measurements of the BRDF and polarization by a metallic flake pigmented coating. The results enable the extraction of a slope distribution function from the data, which is shown to be consistent over a variety of scattering geometries. These models are appropriate to estimate or predict the appearance of flake pigment automotive paints.

Infrared reflection-absorption spectra of metal-effect coatings.

The results of studies of infrared reflection-absorption spectra of metal-effect coatings are presented in this paper. Such coatings consist of metallic flakes that are dispersed in a polymer binder. The spectra show two distinct phenomena. One is due to the polymer matrix. The other is due to metallic flakes that are dispersed inside the layer. The polymer binder causes narrow spectral lines that give a thickness-dependent intensity and position. Metallic flakes change the average baseline of this spectrum over the entire infrared spectral region. This particular effect was evaluated using a simple rough-surface model. Two parameters of the model, the root-mean-square roughness and the correlation length of the rough surface, described the reflection of the partial beams on the metal flake surfaces and scattering on flakes boundaries. The other two parameters are the specular reflectance and the diffuse reflectance of the plane untextured interface between the polymer matrix and the metal flake surface. Various metal-effect coatings within the same polymer binder were analyzed. The effect of each metal flake dispersion was evaluated by the parameters within the rough-surface model. The results were analyzed in terms of the size and the loadings of flakes that were used in the coatings.

Lift-off process for nanoimprint lithography

We report a novel a lift-off method for nanoimprint lithography. This is a bi-layer method, using a polymethyl methacrylate (PMMA) on lift-off layer (LOL) resist scheme. For the imprint step, direct evidence for good pattern transfer down to 20 nm is shown. Oxygen plasma ashing is required to remove residual PMMA. A liquid solvent, MF 319, is used to transfer the pattern down to the silicon. The LOL is dissolved isotropically while the PMMA is unaffected. Ashing time can kept to a minimum through the wet etch method. This reduces the line widening effect. After metal evaporation a two-step lift-off process prevents metal flakes from adhering to the surface electrostatically. At first warm acetone breakes apart the metal layer and dissolves the PMMA, then warm Remover S-1165 removes the LOL and remaining metal. Structures of lines down to 50 nm and dots with a diameter of sub 20 nm are presented.

Coloured paints based on coated flakes of metal as the pigment, for enhanced solar reflectance and cooler interiors: description and theory

Flakes of metal coated with thin dielectric films, when used as various coloured paint pigments, can reflect much more of the near infra red component of solar radiation than standard paints of equivalent colour, which makes them attractive for reducing cooling loads in cars and under metal roofs, while maintaining a wide range of decorative options. Spectral responses, solar absorptance and CIE colour co-ordinates are explored theoretically for a single layer, and two layers of different refractive index, on smooth aluminium flakes. Results in air, and in a clear matrix of refractive index close to that of the paint binder, are presented to highlight the colour shifts that are observed in a matrix when colour is due to interference. Thin film models show that the single layers have weak angle of incidence dependence while double layers have attractive variations in reflected colour while retaining their high NIR reflectance. This adds to decorative appeal. The origins and impact of diffuseness are briefly discussed.

Dehydration process and structural development of cordierite ceramic precursors derived from FTIR spectroscopic investigations

Cordierite precursors were prepared by a sol-gel process using tetraethoxysilane, aluminum sec.-butoxide, and Mg metal flakes as starting materials. The precursors were treated by 15-h heating steps in intervals of 100 °C from 200 to 900 °C; they show a continuous decrease in the analytical water content with increasing preheating temperatures. The presence of H2O and (Si,Al)–OH combination modes in the FTIR powder spectra prove the presence of both H2O molecules and OH groups as structural components, with invariable OH concentrations up to preheating temperatures of 500 °C. The deconvolution of the absorptions in the (H2O,OH)-stretching vibrational region into four bands centred at 3584, 3415, 3216 and 3047 cm−1 reveals non-bridging and bridging H2O molecules and OH groups. The precursor powders remain X-ray amorphous up to preheating temperatures of 800 °C. Above this temperature the precursors crystallize to μ-cordierite; at 1000 °C the structure transforms to α-cordierite. Close similarities exist in the pattern of the 1400–400 cm−1 lattice vibrational region for precursors preheated up to 600 °C. Striking differences are evident at preheating temperatures of 800 °C, where the spectrum of the precursor powder corresponds to that of conventional cordierite glass. Bands centred in the “as-prepared” precursor at 1137 and 1020 cm−1 are assigned to Si–O-stretching vibrations. A weak absorption at 872 cm−1 is assigned to stretching modes of AlO4 tetrahedral units and the same assignment holds for a band at 783 cm−1 which appears in precursors preheated at 600 °C. With increasing temperatures, these bands show a significant shift to higher wavenumbers and the Al–O stretching modes display a strong increase in their intensities. (Si,Al)–O–(Si,Al)-bending modes occur at 710 cm−1 and the band at 572 cm−1 is assigned to stretching vibrations of AlO6 octahedral units. A strong band around 440 cm−1 is essentially attributed to Mg–O-stretching vibrations. The strongly increasing intensity of the 872 and 783 cm−1 bands demonstrates a clear preference of Al for a fourfold-coordinated structural position in the precursors preheated at high temperatures. The observed band shift is a strong indication for increasing tetrahedral network condensation along with changes in the Si–O and Al–O distances to tetrahedra dimensions similar to those occurring in crystalline cordierite. These structural changes are correlated to the dehydration process starting essentially above 500 °C, clearly demonstrating the inhibiting role of H2O molecules and especially of OH groups.

Microstructure analysis of metal-effect coatings

The microstructure of a system of metal-effect coatings was studied with respect to the types of metal falkes used, their dispersion and their orientation. Some indirect and some direct methods were applied on the same silver metallic acrylic coatings and blue metallic acrylic coatings, prepared with various amounts of different types of metallic flakes. Indirect methods were used to measure the influence of coating microstructure on their optical properties. Diffuse reflectance in D/8° geometry at various incidence planes was measured in order to detect the tilted flakes. Gonio-spectrophotometry was used to evaluate the lightness flop. The angular dependence of specularly reflected infrared light was used to detect the effect of optical screening. SEM micrographs of metallic flakes in the dry coating were obtained on plasma-etched surfaces where the parameters of the flake/binder geometry were quantified. A three-dimensional distribution of aluminum in upper layers of coating was determined by ion microbeam analysis, where the vertical resolution was higher than the lateral resolution. Vertical grouping of flakes was detected and their inclination angle was determined. The advantages of applied methods are discussed and compared.

Analysis of metallic pigments by ion microbeam

Metallic paints consist of metallic flakes dispersed in a resinous binder, i.e. a light-element polymer matrix. The spatial distribution and orientation of metallic flakes inside the matrix determines the covering efficiency of the paint, glossiness, and its angular-dependent properties such as lightness flop or color flop (two-tone). Such coatings are extensively used for a functional (i.e. security) as well as decorative purpose. The ion microbeam analysis of two types of silver paint with imbedded metallic flakes has been performed to determine the spatial distribution of the aluminum flakes in paint layer. The average sizes of the aluminum flakes were 23 μm (size distribution 10–37) and 49 μm (size distribution 34–75), respectively. The proton beam with the size of 2×2 μm 2 at Ljubljana ion microprobe has been used to scan the surface of the pigments. PIXE mapping of Al Kα map shows lateral distribution of the aluminum flakes, whereas the RBS slicing method reveals tomograms of the flakes in uppermost 7 μm of the pigment layer. The series of point analysis aligned over the single flake reveal the flake angle in respect to the polymer matrix surface. The angular sensitivity is well below 1 angular degree.