Fused Silica Particles Research Articles

Spectroscopic study of organic coatings on fine particles, exposed to ozone and simulated sunlight

This work intends to quantify the variation in optical properties of aerosol by in-situ spectroscopic monitoring the ozonolysis of a mixture of typical biomass burning compounds. The reaction occurs on silica and glass particles in the presence of simulated sunlight. Fused silica particles (Aerosil) were coated with a thin film of a 1:1 mixure of 4-phenoxyphenol with 4-carboxyphenone as a photosensitizer. UV–VIS spectra of dichloromethane extracts from the particles recorded before and after treatment, show development of a new band after prolonged ozone and light exposure. Changes in optical properties are reported, and variations of spectroscopic features are discussed. We show that the ozone-induced heterogeneous photochemical reaction does produce species absorbing light in the solar spectral range. Further, we demonstrate that the heterogeneous photosensitized reactions at 200 ppb ozone (strongly ozone polluted regions) for a time period of 7 h aging process, can increase light absorption of atmospheric aerosols in the tropospheric actinic window (>290 nm) by 0.4 absorption units ng-C−1 O3 ppm−1 in the region 290–358 nm and by 1.0 absorption units ng-C−1 O3 ppm−1 in the region 360–448 nm. Chemical changes of such surface films were identified by diffuse reflectance infrared Fourier transform spectroscopy of coated glass spheres, and we suggest formation of humic-like substances comparable to those reported in continental aerosol.

シリコーン含有ポリイミドから調製したSi/C/Oコンポジットのリチウムイオン挿入脱離特性

Si/C/O composites were formed by carbonization of Kapton type polyimide films containing 0–10 at% Si. About 24 mass% of Si was present in the composite derived from the polyimide containing 7 at% Si at 1350°C and, by 29Si MAS NMR, they were mainly Si(O)4 type components around −110 ppm with unidentifiable components in a range of −100 to −20 ppm. This composite showed the best performance of Li+ ion insertion/extraction: the coulomb efficiency was nearly 100% except for the 1st cycle and the extraction capacities were 648 mA h g−1 after 10 cycles at 50 mA g−1 and 393 mA h g−1 after 50 cycles at 500 mA g−1, and the latter was increased to ca. 470 mA h g−1 by preliminary cycles at low current densities. After 10 cycles at 50 mA g−1 the components around −110 ppm almost disappeared from the NMR spectrum and a broad and noisy band was observed in a range of −100 to −50 ppm. Since sub-micrometer fused silica particles did not react as the composites performed, the components around −110 ppm are not necessarily silica. The mechanism of reversible insertion/extraction of Li+ ion for the composites was not completely clarified, but the results by cyclic voltammetry and MAS NMR left room for doubt about an alloying/dealloying mechanism between Si and Li.

Heating/melting of a fused silica particle by convection and radiation

The effect of internal absorption and emission of radiation on the heating/melting process of small fused silica particles is analyzed. The particle is considered to be semitransparent to radiation, and the radiative transfer theory is used to predict the local volumetric absorption/emission rate. The transient energy equation with conduction and radiation accounted for is solved to predict the temperature distribution in the particle and the solid–liquid interface position after the melting has started. The radiative transfer calculations are carried out on the spectral basis using published spectral optical property data for fused silica. Results of parametric calculations for different diameter particles, surroundings temperatures and external flow conditions are reported and discussed.

X-ray tomography of powder injection moulded micro parts using synchrotron radiation

Powder injection moulding is one of the most promising replication methods for the mass production of metal and ceramic micro parts. The material for injection moulding, a so-called feedstock, consists of thermoplastic binder components and inorganic filler with approximately equal volume fractions. Injection moulding of the feedstock leads to a green part that can be processed to a dense metal or ceramic micro part by debinding and sintering.During the injection moulding process extremely high shear rates are applied. This promotes the separation of powder and binder leading to a particle density variation in the green part causing anisotropic shrinkage during post-processing. The knowledge of introducing density gradients and defects would consequently allow the optimization of the feedstock, the moulding parameters and the validation of a simulation tool based on the Dissipative Particle Dynamics which is currently under development, as well.To determine the particle density and defect distribution in micro parts synchrotron radiation tomography in absorption mode was used. Due to its parallel and monochromatic character a quantitative reconstruction, free of beam hardening artifacts, is possible. For the measurement, bending bars consisting of dispersed fused silica particles in a polymeric matrix were used. The presented results using this set-up show that crucial defects and density variations can be detected.

Prevention Against Adhesion of Contamination to End Surface of Optical Fiber Connectors in Lapping Film Finishing

The end surface of optical fiber connector is finished by using the lapping film with colloidal silica as abrasive in order to obtain fine optical characteristic. However, the adhesion of some contamination to the finished end surface very often occurs. In the practical manufacturing process, after finishing, a cleaning process of wiping with cloth is adopted, which induces higher production costs and generation of scratches. In this study, two new types of lapping films are proposed to overcome the above problem, namely, to prevent the contamination from adhering to the end surface in the finishing process. Then the lapping film with addition of titanium oxide particles and the lapping film utilizing spherical fused silica particles as abrasives were developed. The finishing experiments revealed that the scratch-free end surface quality without contamination could be achieved by using the developed films.

Movement of Triboelectrically Charged Particles in Toner Display

The mechanism of toner display based on an electrical movement of black and white charged particles has been investigated. Two types of black conductive toner and white fused silica particles charged in the different electric polarity are enclosed between a two electrodes coated with charge transport layer. The particle movement is controlled by the external electric field applied between two transparent electrodes. The toner is fixed on the cathode by an electrostatic force across the CTL to display a black image. The toners can be put back to the counter electrode by applying a reverse electric field, and a white image is formed.The black and white solid images are displayed by the switch of polarity of applied voltage in toner display cell. The polarity of charge and the value of charge to mass ratio of two particles were measured by observation of the particle separation on the surface-type electrodes and using q/m meter, respectively.

Adsorption of Comb Macromolecule on Fused Silica Particles and the Calculation of Interparticle Potential Energy

We have discussed the effect of comb macromolecule adsorbed on fused silica particles to the dispersion of the particle. The effect of the amount and thickness of the polymers adsorbed on the fused silica particles on the total interparticle potential energy was investigated. The evaluation of dispersed property of the particles in solvent was considered by magnitude of interparticle potential energy. The total interparticle potential energy was calculated by summing up the steric hindrance effect and London-van der Waals interaction. The amount of polymers adsorbed were not influenced by the minimum of the total potential energy. The maximum radius of the particles that can be dispersed in polymer solution was in proportion to the thickness of the adsorbed layer.

The formation of SiO2 from hexamethyldisiloxane combustion in counterflow methane-air flames

Silica formation from hexamethyldisiloxane (HMDS) oxidation was studied by means of a CH 4 −N 2 /air opposed diffusion flame technique to which vaporized HMDS was added to the fuel flow. The CH 4 −N 2 /air flame changed color from a pale-blue flame to whitish pink color when small amounts of HMDS were introduced in the flame. Increasing concentrations (1.3 mol %) made the flame more luminous, and a second thin-flame zone, orange in color, appeared on the fuel side. Emission spectroscopy revealed the existence of Si−H and Si−O species. SiO 2 particles were observed only in the postcombustion gases, and the analysis of solid materials suggested the formation of fused silica particles, which were initially about 10 nm in size, forming outside the flame zone in these experiments. The overall mechanism in addition to that for methane oxidation is suggested as follows: C 6 H 18 Si 2 O+OH=2C 3 H 9 SiO+H C 6 H 18 Si 2 O+O 2 =2C 3 H 9 SiO+O C 6 H 18 Si 2 O+HO 2 =2C 3 H 9 SiO+OH C 3 H 9 SiO+M=3CH 3 +SiO+M SiO+HO 2 =HSiO+O 2 SiO+OH=SiO 2 +H SiO+O+M=SiO 2 +M SiO+O 2 =SiO 2 +O together with the formation of SiOH and SiO(OH) species. The agreement between the model predictions using Sandia code OPPDIF and the experimental data was found to be satisfactory. The model appears to be a useful tool in elaboration of chemistry of formation of SiO 2 in flames used to synthesize pure silica in this way.

Zeta potential measurement of muscovite mica basal plane-aqueous solution interface by means of plane interface technique

The zeta potentials of muscovite mica basal plane were investigated by means of the plane interface technique as a function of pH in the presence of 0.001 M KCl, compared with those of fused silica. For the plane interface technique, the negative zeta potentials of a large muscovite mica sheet, i.e., the mica basal plane, were uniformly higher in magnitude than those of a large silica plate over the pH range from 2 to 11, whereas the zeta potentials of the mica basal plane were markedly dependent on pH in the pH range of 3 to 6. In the pH range of 2 to 3, the zeta potenteials of the mica basal plane showed remarkably negative values of −80 to −60 mV and became more insensitive to the reduction in pH. In particular, we could not observe the presence of an isoelectric point (iep) of the mica basal plane, which has never been encountered normally in the case of pure oxides. For comparison, the electrophoresis measurements were made for both mica and silica particles. The negative mobility zeta potentials of mica particles were smaller in magnitude than those of fused silica particles in the pH range of 3 to 11 even though the positively charged alumina-type sites on the mica particles were neutralized by sodium dodecyl benzene sulfonate (SDBS). This result was quite the reverse of the trend obtained from the plane interface technique. However, the variation in flotation recovery of the muscovite mica with dodecyl ammonium chloride (DAC) as a collector at pH 3 was very consistent with that of crystalline quartz (ζ ∼ −65 mV) with dodecyl trimethyl ammonium bromide (DTAB) at pH 7.4. This observation provided justification for the remarkably negative zeta potential (∼ −75 mV) of the mica basal plane obtained from the plane interface technique at pH 3.

Thermal-Expansion Behavior of Two-Phase Solids

The thermal expansion behavior of the two duplex systems, lead-fused silica and aluminum-silicon, has been investigated experimentally above and below room temperature. The microstructure in the first case consisted of fused silica particles in a lead matrix, while silicon constituted the dispersed phase in the second. The expansion coefficients always fell below those predicted by the simple rule of mixtures. A model is proposed and a new formula for the calculation of the thermal expansion coefficient of duplex materials is derived. The new formula fits experimental results better than Turner's formula. The role of microplastic yielding in high-inclusion-content composites is discussed.