Influence of Synthesis Conditions on the Properties of Zinc Oxide Obtained in the Presence of Nonionic Structure-Forming Compounds

This work investigated the influence of synthesis conditions, including the use of nonionic structure-forming compounds (surfactants) with different molecular weights (400–12,600 g/mol) and various hydrophilic/hydrophobic characteristics, as well as the use of a glass substrate and hydrothermal exposure on the texture and structural properties of ZnO samples. By X-ray analysis, it was determined that the synthesis intermediate in all cases is the compound Zn5(OH)8(NO3)2∙2H2O. It was shown that thermolysis of this compound at 600 °C, regardless of the physicochemical properties of the surfactants, leads to the formation of ZnO with a wurtzite structure and spherical or oval particles. The particle size increased slightly as the molecular weight and viscosity of the surfactants grew, from 30 nm using Pluronic F-127 (MM = 12,600) to 80 nm using Pluronic L-31 (MM = 1100), PE-block-PEG (MM = 500) and PEG (MM = 400). Holding the pre-washed synthetic intermediates (Zn5(OH)8(NO3)2∙2H2O) under hydrothermal conditions resulted in the formation of hexagonal ZnO rod crystal structures of various sizes. It was shown that the largest ZnO particles (10–15 μm) were observed in a sample obtained during hydrothermal exposure using Pluronic P-123 (MM = 5800). Atomic adsorption spectroscopy performed comparative quantitative analysis of residual Zn2+ ions in the supernatant of ZnO samples with different particle sizes and shapes. It was shown that the residual amount of Zn2+ ions was higher in the case of examining ZnO samples which have spherical particles of 30–80 nm. For example, in the supernatant of a ZnO sample that had a particle size of 30 nm, the quantitative content of Zn2+ ions was 10.22 mg/L

Synthesis of Hydrophobic Nanosized Silicon Dioxide with a Spherical Particle Shape and Its Application in Fire-Extinguishing Powder Compositions Based on Struvite

Textural and morphological features of hydrophobic silicon dioxide, obtained by the hydrolysis of tetraethoxysilane in an ammonia medium followed by modification of a spherical SiO2 particles surface with a hydrophobic polymethylhydrosiloxane, were studied in this work. The size of silicon dioxide particles was controlled during preparation based on the Stöber process by variation of the amount of water (mol) in relation to other components. The ratio of components, synthesis time and amount of the hydrophobizing agent were determined to obtain superhydrophobic monodisperse silicon dioxide with a spherical particle size of 50–400 nm and a contact angle of more than 150°. In the case of the struvite example, it was demonstrated that the application of spherical- shaped hydrophobic silicon dioxide particles in powder compounds significantly improves the flowability of crystalline hydrates. The functional additive based on the developed silicon dioxide particles makes it possible to implement the use of crystalline hydrates in fire-extinguishing powders, preventing agglomeration and caking processes. The high fire-extinguishing efficiency of the powder composition based on struvite and the developed functional additive has been proven by using thermal analysis methods (TGA/DSC)

Assessment of Extremely Cold Subarctic Climate Environment Destruction of the Basalt Fiber Reinforced Epoxy (BFRE) Rebar Using Its Moisture Uptake Kinetics

A quite simple method is proposed for the assessment of extremely cold subarctic climate environment destruction of the basalt fiber reinforced epoxy (BFRE) rebar. The method involves the comparison of experimentally obtained long-term moisture uptake kinetic curves of unexposed and exposed BFRP rebars. A moisture uptake test was carried out at the temperature of 60 °C and relative humidity of 98 ± 2% for 306 days. The plasticization can be neglected because of low-level moisture saturation (<0.41% wt.); the swelling and structural relaxation of the polymer network can be neglected due to the high fiber content of BFRP rebar; moisture diffusion into the basalt fibers can be neglected since it is a much lesser amount than in the epoxy binder. These assumptions made it possible to build a three-stage diffusion model. It is observed that an increase in the density of defects with an increase in the diameter of the BFRP rebar is the result of the technology of manufacturing a periodic profile. The diffusion coefficient of the BFRP rebar with a 6, 10, or 18 mm diameter increased at an average of 82.7%, 56.7%, and 30%, respectively, after exposure to the climate of Yakutsk during 28 months, whereas it was known that the strength indicators had been increased