Amorphous SiO2 Research Articles

HfO2/SiO2 nanolaminate-based composites prepared by ion beam sputtering for low-loss optics

HfO2 prepared by ion beam sputtering (IBS) is widely used as a high-refractive index material for making low-loss laser films. The challenge of a high-performance HfO2 film is to simultaneously obtain an amorphous morphology with low scattering and a stoichiometric structure with low absorption. Furthermore, nanometer-sized voids are commonly present in IBS films due to excessive oxygen and argon adsorption during deposition, which is the primary barrier to achieve a smooth surface and low optical loss of HfO2. Thin amorphous SiO2 layers were added periodically into HfO2 coatings using the IBS process to synthesize amorphous HfO2 / SiO2 nanolaminate-based composites. The resulting composites exhibited excellent comprehensive performance with a dense amorphous microstructure and a void-free smooth surface. High-temperature annealing was performed to ensure superior stoichiometry and lower absorption. However, the crystalline states and microstructure of some composites evolved during the gradual annealing. We present a detailed study of the crystallization, surface topography, and absorption evolution in HfO2 / SiO2 nanolaminates as a function of HfO2 sublayer thickness and thermal annealing temperature. Moreover, the interplay between crystallization, surface topography, and absorption is elucidated. The HfO2 / SiO2 nanolaminate with 19 thin layers maintained a dense amorphous structure with low absorption after annealing. Finally, a 1064-nm HfO2 / SiO2 nanolaminate-SiO2 high-performance reflector was prepared and achieved lower absorption with a smooth surface after annealing, which demonstrated the great potential of the HfO2 / SiO2 nanolaminates for considerably improving optical loss.

Alkylsiloxane/alkoxysilane sols as hydrophobic treatments for concrete: A comparative study of bulk vs surface application

Water and waterborne decay agents (e.g. salts, microorganisms) are commonly associated with undesired alterations and damages on concrete elements. A strategy to mitigate their impact is to decrease water retention in the material either by surface treatments or admixtures. In this work, hydrophobic concretes were developed by the addition of a hydrophobic sol containing TEOS and PDMS oligomers, synthetized by a surfactant-assisted sol-gel route, either as an admixture or as a surface treatment. The hydrophobic performance was similar for both application modes (>70% capillary absorption reduction) and higher than concrete containing a commercial (calcium stearate) admixture or a nanosilica-based hydrophobic coating. Addition as an admixture led to a higher durability in the rain and abrasion tests.The hydrophobic sol as an admixture promotes an increase of surface roughness and porosity, as well as the formation of C–S–H like reaction products with the cement matrix components, as evidenced by AFM, MIP, SEM and FTIR. Despite the higher porosity, impact resistance and material cohesion were not negatively affected respect to the plain concrete. Application as a surface treatment decreased porosity and led to a higher amorphous SiO2 content. The material cohesion and impact resistance was increased by this application, although penetration was limited to the first 4 mm and the hydrophobic properties were more susceptible to mechanical damages to the surface.

Ultrahigh-strength carbon aerogels for high temperature thermal insulation

Carbon aerogels with nanoporous structure are attractive for thermal insulation under extreme conditions, but their practical applications are usually plagued by the inherent brittleness and easy-oxidation characteristic at high temperature. Herein, silica-modified carbon aerogels (SCAs) with extraordinarily high strength are prepared via a facile sol-gel polymerization of phenolic resin and siloxane, followed by ambient pressure drying and carbonization. The resulting SCAs possess medium-high density of ∼0.5 g·cm−3 and mesoporous structure with the mean pore size of 33 nm. During carbonization process, the siloxane could be gradually transformed into the amorphous SiO2 particles and crystalline SiC particles, which are coated on the surface of carbon nanoparticle and consequently improve the oxidation-resistance of carbon aerogels. Due to the density-porosity trade-off, the SCAs have high compressive strength of 10.0 MPa and satisfied thermal conductivities of 0.118 W·m−1·K−1 at 25 °C and 0.263 W·m−1·K−1 at 1000 °C. Furthermore, needled carbon fiber-reinforced SCAs (CF-SCAs) with ultrahigh compressive strength of 210.5 MPa are prepared, which exhibit good thermal conductivities of 0.207 W·m−1·K−1 at 25 °C and 0.407 W·m−1·K−1 at 1000 °C. The ultrahigh mechanical strength, good oxidation-resistance, good thermal insulation as well as the facile preparation make the SACs great promising in high-temperature insulations especially under harsh conditions.

Carbonated wollastonite - An effective supplementary cementitious material?

Carbonated wollastonite clinker (CS) may be suitable as supplementary cementitious material (SCM) for mortar and concrete. The microstructure of unground CS clinker, carbonated CS slurry and a mortar blended with carbonated CS are investigated by scanning electron microscopy. Additionally, a reference mortar with pure Portland cement and one with a cement replacement level of 30 mass‐% by carbonated CS are produced to assess its contribution to compressive strength development. The calcium silicates are decalcified during carbonation resulting in CaCO3 and amorphous SiO2. The latter reacts when used as SCM in mortar influencing the Ca/Si ratio of calcium‐silicate‐hydrate and contributing to compressive strength development.

Super-hard “Tanghulu”: cubic BP microwire covered with amorphous SiO2 balls

Superhard materials, which are widely used in metallurgy, petroleum drilling, and mechanical processing, have become the key to the development of processing and manufacturing industry. Boron phosphide is an excellent Superhard candidate material with excellent inert, high thermostability and heat conductivity. However, since synthesizing BP is a hard task, studies of its basic physical properties and applications are hindered to some extent. Here, we obtained a micron-scale “Tanghulu”, in the process of synthesizing boron phosphide single crystals using high-temperature flux method. Under a special appearance, "Tanghulu" is a superhard BP microwire covered by melted or amorphous SiO2 and the hardness of the BP microwires is 40.16GPa. On the basis of a comprehensive material analysis, we established the formation mechanism of this Superhard “Tanghulu” as follows: during the heating process with continuous high temperature, SiO2 molecules on the wall of quartz tube escape and diffuse freely and adhere to the boron phosphide rod-shaped single crystal, which will aggregate then under the effect of surface tension to form an isotropic spherical amorphous SiO2 and form the “Tanghulu” finally. Our work can help to broaden the understanding of micro-scale materials.

Investigation of dye removal ability and reusability of green and sustainable silica and carbon-silica hybrid aerogels prepared from paddy waste ash

In this study, the paddy waste ash (PA) was utilized for producing carbon-silica hybrid (PCS) and silica (PS) aerogels. X-ray fluorescence (XRF) spectrometer analysis revealed a high silica content in PA. Crystalline SiO2-cristobalite structure was observed in the X-ray diffraction (XRD) patterns of PA. As expected, the PCS and PS samples exhibited an amorphous SiO2 phase. The pore enlargement and structural improvement after aerogel synthesis were determined using a N2 adsorption-desorption analysis. The specific surface area of the PCS and PS samples were found to be 519 and 652 m2/g, respectively. From the zeta potential results, the points of zero charge (pHPZC) of the samples were found below “2” except for the PCS sample (pHPZC = 2.08). In the first stage of the Remazol Turquoise GN (RTGN) adsorption experiments, the effect of initial pH (2–8) was examined for PA, PCS, and PS sorbents. The highest dye removal value of the PCS sorbent was 61% at pH = 2, while this value was 17.9% and 21.4% for PS and PA sorbents, respectively. The removal percentage curve exhibited a similar trend to the zeta potential curve of the samples. In the experiments conducted with different amounts of sorbents, the dye removal percentage increased with increasing amounts of sorbents. The experimental results and thermodynamic calculations showed that the RTGN adsorption onto PCS was an endothermic process. Pseudo-first order, pseudo-second order and intra-particle diffusion equations were applied to determine the adsorption kinetics of RTGN onto PCS, and it was found that the experimental data was well-fitted to the pseudo-second order kinetic model. The Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) adsorption isotherm models were used to define the adsorption mechanism of RTGN onto PCS. The Freundlich and Langmuir isotherm models were in agreement with our experimental data and it was concluded that RTGN adsorption on PCS surface occurred both as single layer and multi-layer, as well as took place on heterogeneous and homogeneous surfaces. Characterization analyses were conducted for the PCS sorbent after use to understand the structural changes after dye removal. The regeneration and reusability of the PCS sorbent were investigated and it was found that it preserved its initial removal ability by about 95% after four cycles. The dye removal percentage of PCS decreased by 28% after five cycles.

Novel TCAD Approach for the Investigation of Charge Transport in Thick Amorphous SiO2 Insulators

A TCAD approach for the investigation of charge transport in thick amorphous silicon dioxide is presented for the first time. Thick oxides are investigated representing the best candidates for integrated galvanic insulators in future power applications. The large electric fields, such devices experience and the preexisting defects in the amorphous material, give rise to a leakage current, which leads to degradation and failure. Hence, it is crucial to have a complete understanding of the main physical mechanisms responsible for the charge transport in amorphous silicon oxide. For this reason, metal–insulator–metal structures have been experimentally characterized at different high-field stress conditions and a TCAD approach has been implemented in order to gain insight into the microscopic physical mechanisms responsible for the leakage current. In particular, the role of charge injection at contacts and charge build-up due to trapping–detrapping mechanisms in the bulk of the oxide layer has been investigated and modeled to the purpose of understanding the oxide behavior under dc- and ac-stress conditions. Numerical simulations have been compared against experiments to quantitatively validate the proposed approach.

Corrosion of a dense, co-continuous SiC/Si composite in CO2 and synthetic air at 750 °C

The heat-to-electricity conversion efficiency of concentrated solar power plants may be enhanced, for lower cost electricity generation, by using high-temperature (750 °C) supercritical CO2 as a working fluid to drive the turbines in these plants. Unfortunately, such operation has been inhibited by the reduction in thermomechanical performance at ≥550 °C of metal alloys used, or considered for use, in compact heat exchangers for heat transfer to supercritical CO2. Co-continuous, melt-infiltration-processed SiC/Si composites possess an attractive combination of high-temperature mechanical and thermal properties for use in such compact heat exchangers. However, the corrosion behavior of melt-infiltration-processed, equivolume SiC/Si composites in CO2 at 750 °C has not been reported. In this work, the oxidation kinetics of SiC/Si composites, fabricated by Si liquid infiltration into porous SiC preforms, have been examined in CO2 and in air at 750 °C for up to 700 h. Continuous, thin, slow-growing external amorphous SiO2 scales formed on the SiC/Si composites during oxidation in both gases, without detectable oxide formation at internal (subsurface) SiC/Si interfaces. Corrosion-induced SiC formation in CO2, and Si3N4 formation in air, were also not detected below the SiO2 scales. The weight gains were small, with a significantly lower rate of weight gain detected in CO2 than in air. SiO2 scales formed on SiC in both gases were thinner than the scales formed on Si. The SiO2 scales formed on Si in air were notably thicker than the scales formed on Si in CO2, whereas SiO2 scales formed on SiC in air and CO2 were of similar thickness.

Role of Interfacial Oxide in the Preferred Orientation of Ga2O3 on Si for Deep Ultraviolet Photodetectors.

It is generally known that a layer of amorphous silicon oxide (SiO2) naturally exists on the surface of silicon, resulting in the growth of gallium oxide (Ga2O3) that is no longer affected by substrate crystallinity during sputtering. This work highlights the formation energy between the native amorphous nano-oxide film formed on the Si substrate and monoclinic β-Ga2O3 dominating the preferred orientation prepared for deep ultraviolet photodetectors. The latter were deposited on p-type silicon (p-Si) with (111) orientation using radio frequency sputtering at 600 °C and post rapid thermal annealing (RTA). The X-ray diffraction (XRD) results indicate both as-deposited and postannealing films with the (400) preferred orientation for a layer thickness of 100 nm. However, slight random orientation with the amorphous structure is mixed in the preferred one for the as-deposited film with a thickness of 200 nm and reduced after being annealed at 800 °C, which is observed by XRD and transmission electron microscopy. Meanwhile, thermal-induced massive twin boundaries (TBs) and stacking faults (SFs) were generated when annealed at 1000 °C, owing to the relaxation of lattice strain by the coherent interface. The interfacial bonding energy per unit area (Ei) between β-Ga2O3 films with various facets ((001), (010), (100), and (2̅01)) and amorphous SiO2 was calculated using density functional theory. The Ei of β-Ga2O3 (100)/SiO2 reveals the highest value (0.289 eV/Å2), which is consistent with the (100) preferred orientation of deposited films. The (100) preferred orientation is the driving force for TBs and SFs. The discrimination of responsivities and the photo/dark current contrast ratio (Iph/Idark) are inversely proportional to the amorphous structure, grain boundaries, TBs, and SFs. Therefore, optimum metal–semiconductor–metal photodetector performance is achieved for RTA-treated samples at 800 °C with an Iph/Idark of 3.91 × 102 and a responsivity of 0.702 A/W (λpeak = 230 nm) at 5 V bias for a 200 nm thin film.

Plasma electrolytic oxidation of zircaloy-4 in a mixed alkaline electrolyte

Characteristics of coating resulted from plasma electrolytic oxidation (PEO) of zircaloy-4 in an electrolyte containing phosphate, silicate, and hydroxide were investigated. The mixed electrolyte is proposed to reduce power consumption. PEO was conducted in a DC mode at a current density of 30, 50, and 70 mA/cm2. Plasma was generated at a relatively low breakdown voltage of 150 V, independent of the current density. The resulting coating was composed of amorphous SiO2 and crystalline monoclinic (m) and tetragonal (t) ZrO2 phases. XRD analysis revealed that the porous outer layer developed at 30 mA/cm2 was dominated by the m phase. The percentage of the m phase decreased while the t phase increased with increasing current density. Therefore, the coating formed at 70 mA/cm2 showed the highest abrasive wear resistance, three times higher than the substrate. Similarly, the polarization curve and electrochemical impedance spectroscopy showed that the highest corrosion resistance, more than two orders of magnitude higher than the substrate, was obtained in the coated-70 mA/cm2 specimen. The use of low power and a mixed electrolyte is beneficial in producing PEO coating with high wear resistance and excellent anti-corrosion characteristic.

Formation of Aligned α-Si3N4 Microfibers by Plasma Nitridation of Si (110) Substrate Coated with SiO2

Plasma nitridation of an amorphous SiO2 layer on Si (110) substrate can form well-aligned α-Si3N4 crystallites in fibrous morphology. Nitriding is performed at a temperature in the range of 800–1000 °C by using microwave plasma with a gas mixture of N2 and H2. Raman spectroscopy shows the characteristics of an α-Si3N4 phase without other crystalline nitrides. As shown by scanning electron microscopy, the formed α-Si3N4 microfibers on the Si substrate can be in a dense and straight array nearly along with Si <11¯0>, and can have a length over 2 mm with a diameter in the range of 5–10 μm. Structural characterization of scanning transmission electron microscopy in cross section view reveals that the elongated α-Si3N4 crystallites are formed on the surface of the nitrided SiO2/Si (110) substrate without any interlayers between Si3N4 and Si, and the longitudinal direction of α-Si3N4 appears mainly along <112¯0>, which is approximately parallel to Si <11¯0>.

Effect of CO2 treatment on the microstructure and properties of steel slag supplementary cementitous materials

Accelerated carbonation was employed to pretreat steel slag supplementary cementitious materials (SCMs) to improve its hydration reactivity and volume stability. The microstructures of carbonated steel slag SCMs and their impact on the hydration, soundness and compressive strengths of cement materials were investigated. Results indicated that nano-CaCO3 and amorphous SiO2 gel were the main carbonation products of steel slag, which constructed a porous microstructure, leading to an obvious increase in specific surface area by 77.11%. The nano-CaCO3 and amorphous SiO2 were involved in cement hydration to form monocarboaluminate and C-S-H respectively, which increased the hydration degree, enhanced the interface between the steel slag and hydrated cement matrix. For instance, compressive strength of cement paste mixed with 30 wt% carbonated steel slag was increased by 9.7 % compared with that of the paste incorporating noncarbonated steel slag. The autoclave expansion of cement paste containing 30 wt% carbonated steel slag was 0.17% whereas that of the paste containing uncarbonated steel slag was disintegrated as a result of excessive expansion. This study provides a novel way to utilize the steel slag to prepare high quality SCMs for being used as a replacement of cement.

Composite Films of HDPE with SiO2 and ZrO2 Nanoparticles: The Structure and Interfacial Effects.

Herein, we investigated the influence of two types of nanoparticle fillers, i.e., amorphous SiO2 and crystalline ZrO2, on the structural properties of their nanocomposites with high-density polyethylene (HDPE). The composite films were prepared by melt-blending with a filler content that varied from 1% to 20% v/v. The composites were characterized by small- and wide-angle x-ray scattering (SAXS and WAXS), small-angle neutron scattering (SANS), Raman spectroscopy, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). For both fillers, the nanoaggregates were evenly distributed in the polymer matrix and their initial state in the powders determined their surface roughness and fractal character. In the case of the nano-ZrO2 filler, the lamellar thickness and crystallinity degree remain unchanged over a broad range of filler concentrations. SANS and SEM investigation showed poor interfacial adhesion and the presence of voids in the interfacial region. Temperature-programmed SANS investigations showed that at elevated temperatures, these voids become filled due to the flipping motions of polymer chains. The effect was accompanied by a partial aggregation of the filler. For nano-SiO2 filler, the lamellar thickness and the degree of crystallinity increased with increasing the filler loading. SAXS measurements show that the ordering of the lamellae is disrupted even at a filler content of only a few percent. SEM images confirmed good interfacial adhesion and integrity of the SiO2/HDPE composite. This markedly different impact of both fillers on the composite structure is discussed in terms of nanoparticle surface properties and their affinity to the HDPE matrix.

Photonic response and temperature evolution of SiO2/TiO2 multilayers

The microstructural and optical reflectivity response of photonic SiO2/TiO2 nanomultilayers have been investigated as a function of temperature and up to the material system’s melting point. The nanomultilayers exhibit high, broadband reflectivities up to 1350 °C with values that exceed 75% for a 1 μm broad wavelength range (600–1600 nm). The optimized nanometer sized, dielectric multilayers undergo phase transformations from anatase TiO2 and amorphous SiO2 to the thermodynamically stable phases, rutile and cristobalite, respectively, that alter their structural morphology from the initial multilayers to that of a scatterer. Nonetheless, they retain their photonic characteristics, when characterized on top of selected substrate foils. The thermal behavior of the nanometer sized multilayers has been investigated by differential thermal analysis (DTA) and compared to that of commercially available, mm-sized, annealed powders. The same melting reactions were observed, but the temperatures were lower for the nm-sized samples. The samples were characterized using X-ray powder diffraction before DTA and after annealing at temperatures of 1350 and 1700 °C. The microstructural evolution and phase compositions were investigated by scanning electron microscopy and energy-dispersive X-ray spectroscopy measurements. The limited mutual solubility of one material to another, in combination with the preservation of their optical reflectivity response even after annealing, makes them an interesting material system for high-temperature, photonic coatings, such as photovoltaics, aerospace re-entry and gas turbines, where ultra-high temperatures and intense thermal radiation are present.

Room Temperature Growth of Silica Nanowires on Top of Ultrathin Si Nanowires Synthesized with Sn‐Cu Bimetallic Seeds

Si nanowires (NWs) are grown by the vapor–liquid–solid method using Cu–Sn bimetallic catalysts in a plasma‐enhanced chemical vapor deposition (PECVD) reactor. The microstructure of the NWs is analyzed by transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. An amorphous SiO2 region, much larger than the native oxide, is present on top of each crystalline SiNW: in SiNWs with diameter below 10 nm, it takes the form of a silica NW of up to 50 nm in length. The new NW separates the initial catalyst particle into one that stays in contact with the SiNW and one or more that lies at the top of the new NW. The former is made of Cu and Cu3Si and contains no Sn, whereas the latter keeps amounts of both elements. The observed microstructure appears to be the result of a mechanism of Si oxidation catalyzed by Cu3Si. The deposit after SiNW growth, in the PECVD reactor, of a protecting 2 nm thick layer of hydrogenated amorphous Si, completely suppresses this mechanism. Reference for future applications based on Cu–Sn‐catalyzed quantum‐sized SiNWs is provided.

Oxygen atom ordering on SiO2/4H-SiC {0001} polar interfaces formed by wet oxidation

In the processing of 4H-SiC MOSFET devices, it is crucial to optimize the condition of wet oxidation based on the wafer surface orientation to obtain excellent electronic properties. However, the mechanism of surface oxidation and the effect of surface polarity remain unclear. The atomic structures of SiO2/4H-SiC (0001) [Si-face] and (0001¯) [C-face] interfaces can be analyzed by aberration-corrected STEM and first-principles MD calculations. On the Si-face, interfacial O atoms on the amorphous SiO2 layer show clear atomic ordering with a rigid O-Si bridge structure across the SiO2/4H-SiC interface, involving a slow oxidation rate. The C-face can be rapidly oxidized, resulting in dangling bonds, bond bending, rough interface, and residual carbon in the SiO2. A key feature is the formation of a stable and flat oxidation front by O atom ordering and then the suppression of interface defects or residual C, which provides an approach for designing high-performance 4H-SiC MOSFET devices.

Effects of precipitation treatment and oxygen dispersions on thermoelectric properties of CoSi

Effects of a precipitation treatment on the thermoelectric properties in a CoSi thermoelectric material are investigated by scanning and transmission electron microscopy. The Seebeck coefficient and electrical conductivity are explained based on electron-phonon scattering by considering relaxation time approximation and its electronical structure in the framework of the Boltzmann transport equation in the as-sintered (AS) sample fabricated by spark plasma sintering. A precipitation treatment at 1073 K for 30 min is applied to the AS sample. The high Seebeck coefficient and electrical conductivity are obtained, while low thermal conductivity is achieved by dispersing metallic Co2Si phases and insulating amorphous SiO2 nanoparticles in addition to small grain size of ≈ 3 µm due to enhancement in phonon scattering. The dispersion of the amorphous SiO2 is also beneficial in reducing the matrix grain size by the Zener drag.

Porosity of Calcium Silicate Hydrates Synthesized from Natural Rocks.

In this work, the suitability of natural raw materials with various modifications of SiO2—granite sawing waste (quartz) and opoka (a mixture of cristobalite, tridymite, quartz, and an amorphous part)—for the 1.13 nm tobermorite and xonotlite synthesis is examined, and their specific surface area, pore diameter and volume, and the predominant pores are determined. Hydrothermal syntheses were carried out at 200 °C for 12 and 72 h from mixtures with a molar ratio of CaO/SiO2 = 1.0. X-ray diffraction analysis, simultaneous thermal analysis, and scanning electronic microscopy were used, which showed that in the lime–calcined opoka mixture the formation of crystalline calcium silicate hydrates takes place much faster than in the lime–granite sawing waste mixture. The high reactivity of amorphous SiO2 results in the rapid formation of 1.13 nm tobermorite and xonotlite (12 h). According to Brunauer, Emmet and Taller (BET) analysis data, this product features a specific surface area of ~68 m2/g, a total pore volume of 245 × 10−3 cm3/g, and has dominating 1–2.5 nm and 5–20 nm diameter pores. This porosity of the material should provide good thermal insulation properties of the products made from it as no air convection occurs in the fine pores.

Microstructure evolution and mechanical behavior of a mullite fiber heat‐treated from 1100 to 1300°C

AbstractIn this paper, the effect of phase transformation on microstructure evolution and mechanical behaviors of mullite fibers was well investigated from 1100 to 1300°C. In such a narrow temperature range, the microstructure and mechanical properties showed great changes, which were significant to be studied. The temperature of the alumina phase transformation started at below 1100°C. The main phases in fibers were γ‐Al2O3 and δ‐Al2O3 with amorphous SiO2 at 1150°C. The stable α‐Al2O3 formed at 1200°C. Then the mullite phase reaction occurred. As the alumina phase reaction took place, the tensile strength increased with the increasing temperature. In particular, the filaments achieved the highest strength at 1150°C with 1.98 ± 0.17 GPa, and the Young's modulus was 163.08 ± 4.69 GPa, showing excellent mechanical performance. After 1200°C, the mullite phase reaction went on with the crystallization of orthorhombic mullite. The density of surface defects increased rapidly due to thermal grooving, which led to mechanical properties degrade sharply. The strength at 1200°C was 1.01 ± 0.15 GPa with a strength retention of 63.13%, and the Young's modulus was 184.14 ± 10.36 GPa. While at 1300°C, the tensile strength was 0.64 ± 0.14 GPa with a strength retention of only 40.00%.

Assessment of cytotoxicity of an original industrial aerosol containing a high percentage of amorphous silica in the nanometer range

Introduction. At the current stage of hygienic evaluation, the substantiation of at least approximate safe concentrations in the ambient air of populated areas for nanoparticles is an up-to-date challenge. Its persistence dissolves the guidelines for risk management and divests the supervisory bodies of legal support. A comparative toxicological evaluation of the studied substance and its chemical analogue is one of the guidelines for the academic substantiation of the hygienic standards for the permissible content of hazardous substances in the air. It already has previously defined exposure standards. Materials and methods. To investigate the cytotoxicity of the studied particles, a shift of the cellular composition of the bronchoalveolar lavage fluid (BALF) was used. Also, some biochemical measurements of the BALF supernatant were investigated. Outbred female rats were instilled with a suspension of particles in the volume of 1 ml of various concentrations in the form of an intratracheal suspension. Distilled water was used as a solvent. Statistical analysis of the data obtained was performed using the Student’s t-test. Results. The comparative assessment of the cytotoxicity of an original industrial aerosol containing 72% amorphous silica with an average particle size of 90 nm (SiO2 IA) was performed. It also included engineered particles of amorphous silica with an average size of 43 nm (SiO2 NPs), a commercial, an industrial sample of 100% amorphous silica with a particle size of 5 to 60 nm (amorphous SiO2), and a reference sample of standard quartz DQ12 in a volume of 1 ml of water suspension. Under the findings of changes in the cellular composition of the bronchoalveolar lavage fluid 24 hours after the intratracheal instillation of these particles, it was revealed that the biological power (in terms of the NL/AM ratio) of both SiO2 NPs and amorphous SiO2 is statistically much higher than the industrial aerosol under study. It is also higher than the standard quartz dust DQ12. In this regard, the cytotoxicity of SiO2 IA may be explained by the predominant content of amorphous silica nanoparticles in it. Conclusion. Under the obtained results, the appropriateness of using indicative safe exposure levels (ISEL) of 0.02 mg/m3 for amorphous silica needs to be reviewed. The safe reference level of impact guideline does not contain data concerning the particle size and the percentage of amorphous SiO2 in the aerosol. Nevertheless, it is impossible to pollute the ambient air with an aerosol containing only this substance.