Silica Aerosol Research Articles

Research on ballistic performance of green shear thickening functionalized fabric based on solid waste modification

Based on the solid waste-based modification, green shear-thickening functionalized ballistic composites were prepared. Silica aerosols were obtained from solid waste diatomaceous earth through sol–gel preparation, gel aging, and supercritical drying. The modified silica aerosols acted as the dispersed phase, regulating the green shear-thickening liquid. A comparison was made between the performance of the modified shear-thickening liquid (SG@STF) and traditional shear-thickening liquids. By modifying solid waste based shear thickener (SG@STF) Combined with aramid fabric (AF) to test Ballistic performance. Characterization tests revealed that the rheological properties of SG@STF were significantly enhanced by increasing the volume fraction of the dispersed phase in STF from 50 % to 60 %. This enhancement was attributed to the addition of reactive functional groups on the surface of the silica sol. Yarn pull-out tests demonstrated that SG@STF/AF improved the tensile strength by 120 % compared to AF fabric, thanks to its superior friction properties. Ballistic tests showed that SG@STF increased the ballistic ultimate velocity of AF fabric by 105 %, elevating AF’s ballistic limiting velocity from 51 m/s to 105 m/s. Consequently, SG@STF/AF exhibited superior ballistic properties compared to AF fabric. The doping of SG enhanced the friction between yarns and increased the load-bearing area of the fabrics, thereby improving the ballistic properties of SG@STF/AF and achieving the desired modulation of their ballistic properties.

Efficient acidic CO2 electroreduction to formic acid by modulating electrode structure at industrial-level current

Acidic CO2 electroreduction has the potential to synthesize low carbon footprint chemicals using renewable electricity. However, proton-rich environments can lead to strong hydrogen evolution reaction (HER) and severe degradation of electrochemical CO2 reduction reaction (CO2RR) performance. Modulating electrode structure plays a critical role in improving the local microenvironment of CO2RR electrolytes. Here, by covering the catalyst layer with a hydrophobic silica aerosol layer, the surface of the catalyst is protected from corrosion, thereby increasing the efficiency and stability of the system. In the flow cell, the Sn-C/SiO2-3 catalyst has high formic acid (HCOOH) selectivity at high current density (∼90 % at −400 mA cm−2). Importantly, the Sn-C/SiO2-3 catalyst can operate stably for 45 h at −400 mA cm−2. Combined in situ infrared analysis reveals that hydrophobic SiO2 aerosol layer can engineer the local microenvironment over the Sn-C catalyst surface by increasing the coverage of *OCHO to improve the CO2RR, which ultimately promotes high-efficiency CO2 conversion to HCOOH in strong acidic media. This surface coating strategy for adjusting the interface microenvironment can also be used for other electrocatalytic reactions.

Modified silica-based double-layered hydrophobic-coated stainless steel mesh and its application for oil/seawater separation

A double-layered hydrophobic-coated stainless steel mesh (CSSM) was successfully prepared by vapor deposition of polydimethylsiloxane (PDMS) to form aerosol silica (SiO2) particles on SSM followed by coating with the in situ modified SiO2 generated in the natural rubber (NR) latex for use in oil/seawater separation. The in situ SiO2 particles were modified with octyltriethoxysilane (OTES) or hexadecyltrimethoxysilane (HDTMS). Transmission electron microscopy, 29Si solid-state nuclear magnetic resonance, and Fourier transform infrared spectroscopy were used to determine the structure of the in situ modified SiO2 generated in the NR latex. Scanning electron microscopy and water contact angle analyses were applied to characterize the morphology and hydrophobicity of the CSSM, respectively. The presence of aerosol SiO2 particles from PDMS and in situ modified SiO2 by OTES (MSi-O) or HDTMS (MSi-H) generated in the NR could enhance the surface roughness and hydrophobicity of the CSSM. The hydrophobic CSSM was then applied for the separation of chloroform/seawater and crude oil/seawater mixtures. A high separation efficiency (up to 99.3%) with the PDMS/NR/MSi-H CSSM was obtained and the mesh was reusable for up to 20 cycles.

66 A New Raman Spectroscopy Approach for the Measurement of Respirable Crystalline Silica Aerosols Collected onto Filters: Practical Considerations and Advantages

Abstract It is estimated that 560,000 workers in the United Kingdom are potentially exposed to respirable crystalline silica (RCS), which can cause disabling diseases such as silicosis and cancer. The incidence of silicosis in exposed workers can occur at levels below current workplace exposure limits and sensitive analytical techniques are needed to measure low RCS concentrations. The analytical performance of a new Raman spectroscopy method was compared with current X-ray diffraction (XRD) methods. The study investigated limits of detection, measurement uncertainty and measured samples collected from inside respirators. In total, 119 respirable, thoracic, and samples from the Sioutas impactor (PM10 to PM2.5) were also collected from cutting and polishing of engineered and natural stones and analysed for RCS. The LOD for Raman of 0.26 µg is lower than those published for current XRD or infrared methods (5 to 10 µg). The coefficients of determination were between 0.97 and 0.94. The Raman response is as stable as XRD when measuring samples with different median particle sizes (from 0.5 to 7 µm). Raman measurements were significantly different at the 95 % confidence level for the respirable samples (slope = 1.11) but not for thoracic samples (slope = 1.03). Raman spectroscopy has an advantage when measuring quartz in the presence of some minerals that cause interferences with XRD such as zircon. Raman spectroscopy is a promising alternative to XRD for RCS measurements. It has a low LOD and few modifications of current protocols would be necessary to adopt a Raman analysis approach. 2022© Crown copyright

Low-speed gas knife protection for the large aperture optical component in high-power laser systems

In high-power laser systems, fused silica aerosols produced by laser-induced damage to optical components impede further improvement in operation efficiency. To mitigate aerosol threats, low-speed gas knives are an attractive online option. Herein, we investigate the protective mechanism of a low-speed gas knife (<20 m/s) against aerosol invasion on the optical component. First, aerosol particles invaded the surface experimentally in two ways and were detected both in the core and non-core regions, depending on the coverage area of the protection flow. Particle sedimentation percentages can directly reflect the protection capability of the gas knife flow. Since a “midstream defect” is readily apparent, a CFD model was developed to explain the phenomenon from the perspective of velocity distribution. Additionally, the Euler-Lagrange method was used to track airflow particle motions and reappear the protective process. The numerical and experimental results on protection efficiency are closely correlated. The numerical calculation indicates that the “midstream defect” manifested in the core region is possibly attributed to the turbulent dispersion and anisotropic near-wall effects of particles of various diameters, while in the non-core region, the mechanism differs. This work provides a framework for airflow clean designs inside high-power laser systems.

Mie scattering from optically levitated mixed sulfuric acid-silica core-shell aerosols: observation of core-shell morphology for atmospheric science.

Sulfuric acid is shown to form a core-shell particle on a micron-sized, optically-trapped spherical silica bead. The refractive indices of the silica and sulfuric acid, along with the shell thickness and bead radius were determined by reproducing Mie scattered optical white light as a function of wavelength in Mie spectroscopy. Micron-sized silica aerosols (silica beads were used as a proxy for atmospheric silica minerals) were levitated in a mist of sulfuric acid particles; continuous collection of Mie spectra throughout the collision of sulfuric acid aerosols with the optically trapped silica aerosol demonstrated that the resulting aerosol particle had a core-shell morphology. Contrastingly, the collision of aqueous sulfuric acid aerosols with optically trapped polystyrene aerosol resulted in a partially coated system. The light scattering from the optically levitated aerosols was successfully modelled to determine the diameter of the core aerosol (±0.003 μm), the shell thickness (±0.0003 μm) and the refractive index (±0.007). The experiment demonstrated that the presence of a thin film rapidly changed the light scattering of the original aerosol. When a 1.964 μm diameter silica aerosol was covered with a film of sulfuric acid 0.287 μm thick, the wavelength dependent Mie peak positions resembled sulfuric acid. Thus mineral aerosol advected into the stratosphere would likely be coated with sulfuric acid, with a core-shell morphology, and its light scattering properties would be effectively indistinguishable from a homogenous sulfuric acid aerosol if the film thickness was greater than a few 100 s of nm for UV-visible wavelengths.

The Effect of Type of Filler on Microphase Separation and Reinforcement in Polyurethane Based Composites

In order to investigate the effect of hydrophilicity and size of a filler on the reinforcement and supramolecular structure of polyurethane (PU) based composites, a sequence of polymer composites based upon oligomeric 4,4'-diphenylmethane diisocyanate (MDI) and propylene diol with molecular weight equal to 1000 were prepared via a simple in-situ method. Titanium (IV) dioxide (TO) was used as a microsized filler and an aerosol silica (AS) was used as a nanosized filler, both with hydrophilic surfaces. Carbon black (CB) was used as a microsized filler with a hydrophobic surface. The maximal degree of filling was varied from 5 wt% for AS, 25 wt% for CB, and up to 50 wt% for TO. It was shown that maximal reinforcement of the PU composites (up to one order of magnitude in improvement) could be obtained if the filler increases the microphase separation in the PU matrix. This effect was maximal for CB filler, although this filler was not active in the formation of hydrogen bonds. Thus, the neutral filler also changed the supramolecular structure of the polymer matrix. The strong reinforcement by the CB was connected with their nucleating ability, i.e. the possibility to produce a maximal number of rigid domains by CB/PU interactions in the PU matrix.

Influence of particle properties on measuring a low-particulate-mass concentration by light extinction method

The influence of particle size variation on particle concentration measurement via light extinction is a major challenge in the field, particularly when particle shape and composition can alter the size effect. In this study, a white-cell extinction system was used to characterize the extinction properties of several mineral and ash aerosols to illustrate the size effect among particles with different optical properties. The extinction coefficients of the aerosols were derived from real-time data and compared with the Mie calculation and modeled optical properties of ensembles of aerosol particles (MOPSMAP) simulation. The experimentally derived extinction coefficients of irregularly shaped silica aerosols were larger than those of spherical silica aerosol with an equivalent size in the range 0.5–3 μm. The deviation increased with particle shape deformity, which was consistent with the MOPSMAP simulation. Variations in the mass extinction coefficient, caused by a fixed size variation, increased with particle shape deformity, thereby demonstrating that particle shape deformity intensifies the influence of size variation on particulate extinction. The sensitivity of particulate extinction to size variation varied slightly among the alumina and silica aerosols. However, this sensitivity was negligible compared with the sensitivity of silica aerosols with different morphologies. According to the experimental results for ash aerosols, particle shape deformity is likely to introduce a systematic error of 25%–100% to the extinction-calculated concentration through the alteration of the extinction coefficient, indicating that stringent limitations for the acceptable particle size variation of non-spherical particles should be considered to guarantee the reliability of the extinction-calculated concentration.

Light Extinction Method for Measuring a Low Particle Concentration with White Cell Optics: Relationship between Light Transmittance and Particle Properties

Because particulate matter (PM) emission standards of coal-fired power plants in China are becoming increasingly stricter, a higher sensitivity of traditional PM emission monitoring systems is required to adapt to the proposed ultralow emission (ULE) levels. In this study, a commercial optical structure, white cell optics, was introduced into the traditional extinction system to enhance particulate extinction and lower the detection limit by increasing the light path length. By connecting an aerosol generator and an electrical low-pressure impactor system, the white cell light extinction (WC-LE) system was tested to predict the low particle concentration of spherical silica aerosol and fly ash aerosol. According to the results of real-time testing with spherical silica aerosol, a good response between extinction signal and particle concentration was generally observed over the concentration range of 0–10 mg/m³. An excellent linear correlation between the extinction and particle concentration was obtained from data from short periods without violent feeding fluctuation. Based on the linear correlation, the particle concentration was calculated from the real-time extinction signal. For silica aerosols with different size distributions, the calculated concentration generally showed good correlation with the experimental value; the variation in extinction coefficients derived from the linear correlations was smaller than the theoretical values calculated with the measured size distribution, which seemed to be related to the in-cell mass loss. By testing the system with fly ash aerosols, the real-time response, linear correlation between signals, and concentration measurement also showed satisfactory results. The results of this study show that the WC-LE system is sensitive to small fluctuations in the particle concentration and provides a reliable correlation between the extinction signal and particle concentration, which allows the system to be considered a promising solution for particle emission monitoring at ULE levels.

Influence of relative humidity on real-time measurements of particulate matter concentration via light scattering

As the particulate-matter (PM) emission standards in China become increasingly rigorous (their upper limit has decreased to 10 mg/m3 in the power industry), considerable attention has been paid to PM emissions from coal-fired power plants. However, there is a large amount of water vapour in flue gas from power plants, which poses a great challenge to the measurement of the PM mass concentration via light scattering. Although water vapour does not affect the light scattering, changes in the properties of particles caused by water vapour influence it. To investigate the effects of the aerosol relative humidity on the PM mass-concentration measurement via light scattering, a test rig was constructed for wet aerosol light-scattering measurements. Light-scattering and hygroscopic properties, as well as morphological features of fly ash aerosol and pure mineral aerosol (pure powder silica) under different relative-humidity conditions were compared in a laboratory. The linear least-squares method was used to fit the relationship between the scattered light intensity and the PM mass concentration under four different humidity conditions. With increase in relative humidity, the R-squared values and the slopes of the fitted line were 0.9941, 0.9941, 0.9926, and 0.9854 and 35.14, 35.90, 28.59, and 26.91, respectively. Thus, the intensity of light scattering was directly proportional to the PM mass concentration, and the mass sensitivity, i.e. the slope of the fitted curve, changed with respect to relative humidity. From low to high relative-humidity conditions, the enhancement factors at a scattering angle of 20° were 0.868 ± 0.045, 0.814 ± 0.053, and 0.706 ± 0.029 for powder silica and 0.905 ± 0.010, 0.918 ± 0.015, and 0.984 ± 0.019 for fly ash. Thus, humidity had a greater influence on the mass-concentration measurement of powder silica aerosol via light scattering than on that of fly ash aerosol. Scanning electron microscopy results for aerosol particles under different humidity conditions indicated that the agglomeration characteristics of these particles increased with the relative humidity. Considering previous reports on the response characteristics of the hygroscopic particles with respect to their optical properties to relative humidity in the atmosphere, we found that the hygroscopic growth and agglomeration of aerosol particles together determine the measurement accuracy, which is very useful for onsite measurements of the PM mass concentration via the light-scattering method.

Passivation Threshold for the Oxidation of Liquid Silicon and Thermodynamic Non-equilibrium in the Gas Phase

The present study focuses on a specific step of the metallurgical path of purification to provide solar-grade silicon: the removal of boron through the injection of H2O(g)-H2(g)-Ar(g) (cold gas process). A progressive increase of the oxidant H2O(g) concentration at injection increases the speed of the process until a silica layer appears at the surface of the liquid silicon to be purified. It then stops the purification. During the process, silica aerosols may form in the gas boundary layer. This modifies the flows of oxidants and the gas concentrations at the liquid silicon surface. Using a monodimensional model, this article shows that a hypothesis of thermodynamic equilibrium of silica aerosols with the gas phase in the boundary layer has to be dropped in order to explain the appearance of a silica passivating layer. The passivation threshold is defined as the limit concentration of the oxidant at the injection below which there is no silica on the liquid silicon surface and beyond which silica particles appear on the liquid silicon surface. Three experiments of estimation of the passivation threshold with the injection of water vapor are used to confirm an empirical criterion for the prediction of the appearance of the silica layer. Two other sets of experiments with the injection of Ar-O2 are also being studied where the kinetics of the formation of silica aerosols seems to be slower than when water vapor is used. An optimization of the speed of boron removal under the assumption of a maximal concentration of water vapor before the appearance of a passivating silica layer would require an increase of the liquid silicon surface temperature from the fusion temperature of silicon.

Effect of bioactive glass-containing resin composite on dentin remineralization

ObjectivesThe purpose of this study was to evaluate the effect of bioactive glass (BAG)-containing composite on dentin remineralization. MethodsSixty-six dentin disks with 3 mm thickness were prepared from thirty-three bovine incisors. The following six experimental groups were prepared according to type of composite (control and experimental) and storage solutions (simulated body fluid [SBF] and phosphate-buffered saline [PBS]): 1 (undemineralized); 2 (demineralized); 3 (demineralized with control composite in SBF); 4 (demineralized with control composite in PBS); 5 (demineralized with experimental composite in SBF); and 6 (demineralized with experimental composite in PBS). BAG65S (65% Si, 31% Ca, and 4% P) was prepared via the sol-gel method. The control composite was made with a 50:50 Bis-GMA:TEGDMA resin matrix, 57 wt% strontium glass, and 15 wt% aerosol silica. The experimental composite had the same resin and filler, but with 15 wt% BAG65S replacing the aerosol silica. For groups 3–6, composite disks (20 × 10 × 2 mm) were prepared and approximated to the dentin disks and stored in PBS or SBF for 2 weeks. Micro-hardness test, attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) and field-emission scanning electron microscopy (FE-SEM) was investigated. ResultsThe BAG-containing composite significantly increased the micro-hardness of the adjacent demineralized dentin. ATR-FTIR revealed calcium phosphate peaks on the surface of the groups which used BAG-containing composite. FE-SEM revealed surface deposits partially occluding the dentin surface. No significant difference was found between SBF and PBS storage. Clinical SignificanceBioactive glass is a potentially useful material for remineralization of tooth structure. When incorporated into a resin composite, it may aid in remineralizing the adjacent demineralized dentin, thus preventing further destruction of the tooth. ConclusionBAG-containing composites placed in close proximity can partially remineralize adjacent demineralized dentin.

CFD Modeling of Boron Removal from Liquid Silicon with Cold Gases and Plasma

The present study focuses on a specific step of the metallurgical path of purification to provide solar-grade silicon: the removal of boron through the injection of H2O(g)-H2(g)-Ar(g) (cold gas process) or of Ar-H2-O2 plasma (plasma process) on stirred liquid silicon. We propose a way to predict silicon and boron flows from the liquid silicon surface by using a CFD model (©Ansys Fluent) combined with some results on one-dimensional diffusive-reactive models to consider the formation of silica aerosols in a layer above the liquid silicon. The comparison of the model with experimental results on cold gas processes provided satisfying results for cases with low and high concentrations of oxidants. This confirms that the choices of thermodynamic data of HBO(g) and the activity coefficient of boron in liquid silicon are suitable and that the hypotheses regarding similar diffusion mechanisms at the surface for HBO(g) and SiO(g) are appropriate. The reasons for similar diffusion mechanisms need further enquiry. We also studied the effect of pressure and geometric variations in the cold gas process. For some cases with high injection flows, the model slightly overestimates the boron extraction rate, and the overestimation increases with increasing injection flow. A single plasma experiment from SIMaP (France) was modeled, and the model results fit the experimental data on purification if we suppose that aerosols form, but it is not enough to draw conclusions about the formation of aerosols for plasma experiments.

Characterization of a silica-aerosol in a sintering process by wide-angle light scattering and principal component analysis

In nanoparticle synthesis, a large variety of sizes and morphologies can be observed depending on the process parameters. Besides fractal-like aggregates built from primary particles and non-aggregated spherical particles also mixtures of particle fractions are obtained. For industrial process control, real-time capable algorithms for multi-variate parameter determination are required. In this work, principal component analysis is employed for inverting scattering data from elastic light scattering measurements to obtain information about the size distribution of particle fractions like fractals and spheres and the mixing ratio. Additionally in the case of fractals their fractal dimension is determined. The method is employed on simulated data and experimental data from wide-angle light scattering (WALS) measurements on a silica aerosol synthesized in a chemical vapor synthesis process with a proceeding sintering step of variable degree.

The Complex Refractive Index of Volcanic Ash Aerosol Retrieved From Spectral Mass Extinction

AbstractThe complex refractive indices of eight volcanic ash samples, chosen to have a representative range of SiO2 contents, were retrieved from simultaneous measurements of their spectral mass extinction coefficient and size distribution. The mass extinction coefficients, at 0.33–19 μm, were measured using two optical systems: a Fourier transform spectrometer in the infrared and two diffraction grating spectrometers covering visible and ultraviolet wavelengths. The particle size distribution was measured using a scanning mobility particle sizer and an optical particle counter; values for the effective radius of ash particles measured in this study varied from 0.574 to 1.16 μm. Verification retrievals on high‐purity silica aerosol demonstrated that the Rayleigh continuous distribution of ellipsoids (CDEs) scattering model significantly outperformed Mie theory in retrieving the complex refractive index, when compared to literature values. Assuming the silica particles provided a good analogue of volcanic ash, the CDE scattering model was applied to retrieve the complex refractive index of the eight ash samples. The Lorentz formulation of the complex refractive index was used within the retrievals as a convenient way to ensure consistency with the Kramers‐Kronig relation. The short‐wavelength limit of the electric susceptibility was constrained by using independently measured reference values of the complex refractive index of the ash samples at a visible wavelength. The retrieved values of the complex refractive indices of the ash samples showed considerable variation, highlighting the importance of using accurate refractive index data in ash cloud radiative transfer models.

Measurement of Crystalline Silica Aerosol Using Quantum Cascade Laser\u2013Based Infrared Spectroscopy

Inhalation exposure to airborne respirable crystalline silica (RCS) poses major health risks in many industrial environments. There is a need for new sensitive instruments and methods for in-field or near real-time measurement of crystalline silica aerosol. The objective of this study was to develop an approach, using quantum cascade laser (QCL)-based infrared spectroscopy (IR), to quantify airborne concentrations of RCS. Three sampling methods were investigated for their potential for effective coupling with QCL-based transmittance measurements: (i) conventional aerosol filter collection, (ii) focused spot sample collection directly from the aerosol phase, and (iii) dried spot obtained from deposition of liquid suspensions. Spectral analysis methods were developed to obtain IR spectra from the collected particulate samples in the range 750–1030 cm−1. The new instrument was calibrated and the results were compared with standardized methods based on Fourier transform infrared (FTIR) spectrometry. Results show that significantly lower detection limits for RCS (≈330 ng), compared to conventional infrared methods, could be achieved with effective microconcentration and careful coupling of the particulate sample with the QCL beam. These results offer promise for further development of sensitive filter-based laboratory methods and portable sensors for near real-time measurement of crystalline silica aerosol.

Mass extinction spectra and size distribution measurements of quartz and amorphous silica aerosol at 0.33–19 µm compared to modelled extinction using Mie, CDE, and T-matrix theories

Simultaneous measurements were made of the spectral extinction (from 0.33–19 µm) and particle size distribution of silica aerosol dispersed in nitrogen gas. Two optical systems were used to measure the extinction spectra over a wide spectral range: a Fourier transform spectrometer in the infrared and two diffraction grating spectrometers covering visible and ultraviolet wavelengths. The particle size distribution was measured using a scanning mobility particle sizer and an optical particle counter. The measurements were applied to one amorphous and two crsystalline silica (quartz) samples. In the infrared peak values of the mass extinction coefficient (MEC) of the crystalline samples were 1.63 ± 0.23 m2g−1 at 9.06 µm and 1.53 ± 0.26 m2g−1 at 9.14 µm with corresponding effective radii of 0.267 and 0.331 µm, respectively. For the amorphous sample the peak MEC value was 1.37 ± 0.18 m2g−1 at 8.98 µm and the effective radius of the particles was 0.374 µm. Using the measured size distribution and literature values of the complex refractive index as inputs, three scattering models were evaluated for modelling the extinction: Mie theory, the Rayleigh continuous distribution of ellipsoids (CDE) model, and T-matrix modelling of a distribution of spheroids. Mie theory provided poor fits to the infrared extinction of quartz (R2 < 0.19), although the discrepancies were significantly lower for Mie theory and the amorphous silica sample (R2=0.86). The CDE model provided improved fits in the infrared compared to Mie theory, with R2 > 0.82 for crsytalline sillica and R2=0.98 for amorphous silica. The T-matrix approach was able to fit the amorphous infrared extinction data with an R2 value of 0.995. Allowing for the possibility of reduced crystallinity in the milled crystal samples, using a mixture of amorphous and crystalline T-matrix cross-sections provided fits with R2 values greater than 0.97 for the infrared extinction of the crystalline samples.

Active Oxidation of Liquid Silicon in the Presence of Hydrogen: Extension of the Ratto Model

The rate of oxidation of silicon has been studied in the presence of hydrogen, in order to predict the rate of boron removal from liquid silicon in liquid/gas processes where a chemical equilibrium exists at the surface. A new 1D model for the reactive boundary layer above liquid silicon has been developed from existing literature, adding two gaseous species H2 and H2O. The classical model (O2 only) gives a layer of silica aerosol just above the surface, for oxygen pressures above some pascals. Adding some hydrogen, this layer is displaced away from the silicon and vanishes if the hydrogen ratio is sufficient. We applied this model on liquid silicon oxidation experiments with theoretically predicted mass boundary layer thicknesses for impinging jets. The needed thickness to reproduce the experimental purification rate on our plasma process is compatible with our model.

Risk assessment of workers exposed to crystalline silica aerosols

ABSTRACTThis study was conducted to determine the concentration of airborne respirable crystalline silica (ARCS) particles and to evaluate its risk level among workers employed in eight different workplaces in Iran. They included sandblasting operations, ceramic production, sand and gravel work, brick production, asphalt manufacturing, foundry operation, glass making, and stone cutting. Personal exposure to ARCS was measured in randomly selected samples from each workplace. The maximum and minimum average of ARCS concentration in the eight workplaces were observed in foundry operation (0.338 ± 0.110 mg/m3) and glass manufacturing (0.125 ± 0.093 mg/m3), respectively. The average concentration of ARCS in all assessed working conditions were higher than the permitted limit of occupational contact recommended by Technical Committee of the Iranian Ministry of Health, treatment and medical education (0.025 mg/m3). Overall, the results showed a serious lack of control in Iranian industries with respect to workers' exposures to ARCS.

Bioactive glass fillers reduce bacterial penetration into marginal gaps for composite restorations

ObjectiveBioactive glass (BAG) is known to possess antimicrobial and remineralizing properties; however, the use of BAG as a filler for resin based composite restorations to slow recurrent caries has not been studied. Accordingly, the objective of this study was to investigate the effect of adding 15wt% BAG to a resin composite on bacterial biofilms penetrating into marginal gaps of simulated tooth fillings in vitro during cyclic mechanical loading. MethodsHuman molars were machined into approximately 3mm thick disks of dentin and 1.5–2mm deep composite restorations were placed. A narrow 15–20 micrometer wide dentin-composite gap was allowed to form along half of the margin by not applying dental adhesive to that region. Two different 72wt% filled composites were used, one with 15wt% BAG filler (15BAG) and the balance silanated strontium glass and one filled with aerosol silica and silanated strontium glass without BAG (0BAG—control). Samples of both groups had Streptococcus mutans biofilms grown on the surface and were tested inside a bioreactor for two weeks while subjected to periods of cyclic mechanical loading. After post-test biofilm viability was confirmed, each specimen was fixed in glutaraldehyde, gram positive stained, mounted in resin and cross-sectioned to reveal the gap profile. Depth of biofilm penetration for 0BAG and 15BAG was quantified as the fraction of gap depth. The data were compared using a Student's t-test. ResultsThe average depth of bacterial penetration into the marginal gap for the 15BAG samples was significantly smaller (∼61%) in comparison to 0BAG, where 100% penetration was observed for all samples with the biofilm penetrating underneath of the restoration in some cases. SignificanceBAG containing resin dental composites reduce biofilm penetration into marginal gaps of simulated tooth restorations. This suggests BAG containing composites may have the potential to slow the development and propagation of secondary tooth decay at restoration margins.