This paper presents the comparative analysis of the properties of highly dispersed silicas synthesized by pyrogenic and fluoride methods. Raw materials and synthesis conditions differ significantly for the considered methods. The structure and surface properties of synthesized silica samples was characterized by a number of methods such as IR, nitrogen adsorption, SEM, microcalorimetry, temperature programmed desorption time-of-flight with mass-spectrometry (TPDM), thermogravimetric analysis. IR spectra showed presence of characteristic absorption bending bands at 468 сm− 1 (Si-O-Si) and at 800 сm− 1 (O-Si-O) and stretching vibrations bands in the range of 1000–1200 сm− 1 (Si-O-Si) for all the studied samples regardless of their synthesis method. The absorption band at 3750 cm− 1 attributed to free silanol groups ≡ Si-OH confirms the presence of this main sorption centers evenly distributed on the surface for all silica samples. The intensity of this band is quite low for samples obtained by the fluoride synthesis method due to the high water content. This fact is also confirmed by the TGA and TPDM methods. The distribution functions of the activation energy of water desorption demonstrates several maxima: (i) at 60–80 kJ/mol and 100 kJ/mol refers to desorption of molecularly adsorbed water; (ii) at 160–180 kJ/mol is due to the associatively desorbed water. All studied silica samples are hydrophilic according to values of the heat of immersion in water and n-decane, and their Rebinder’s hydrophilicity index Kh > 1. The BET surface area and pore volume of samples significantly depend both on the method of synthesis and on the raw materials.

Highly dispersed powders of amorphous silica (silicon dioxide) with a purity of 99.98 % using ammonium fluoride were synthesized from the man-made waste of copper-smelting production. The amorphous state of the obtained silica samples was confirmed by XRD analysis. It was found that the particle size distribution of SiO2 in an aqueous medium is mainly represented by aggregates (100-220 nm) and agglomerates of aggregates (1300 and 5500 nm). It is shown that an increase in the time of ultrasonic treatment does not significantly affect the bi-or trimodal character of the particle size distribution. The effective diameter Def of agglomerates of silica particles decreases by 3 times during the first 10 min of ultrasonic treatment. With a subsequent increase in the processing time, Def does not change significantly, but fluctuates around some specific value. IR spectra of silica samples have characteristic bands related to bending vibrations of Si-O-Si at 468 cm -1 (intense) and O-Si-O at 800 cm -1 (average intensity), as well as bands related to stretching vibrations of Si-O-Si in the range 1000-1200 cm -1 , which are responsible for the reactivity. It was found that the process of thermal desorption from the surface of the SiO2 sample proceeds in several stages, with the most intense release of the following main volatile products: O (m/z 16), OH (m/z 17), H2O (m/z 18), and CO (m/z 28). The textural characteristics of the synthesized powders were determined by the method of low-temperature nitrogen adsorption. It is shown that the shape of the adsorption isotherm and the hysteresis loop corresponds to the texture porosity of aggregates of non-porous nanomaterials. The adsorption isotherm is well linearized, which made it possible to calculate the specific surface area according to BET (64 m 2 /g) and Langmuir (93 m 2 /g), the total pore volume, micropores, and the total area of micropores.

Показана возможность получения высокодисперсных порошков аморфного диоксида кремния из техногенных металлургических отходов, представляющих собой отвальные шлаки медеплавильного производства и пылевидные отходы производства кремния и ферросилиция (микрокремнезема). Описан достаточно простой и экономичный метод синтеза с использованием одного реагента (фторида (бифторида) аммония) при невысоких температурах (до 400°С). Синтезированный диоксид кремния имеет высокую степень чистоты (≈99.96%) и является аморфным, что подтверждается данными масс-спектрометрии и рентгенофазового анализа. Методом лазерной корреляционной спектроскопии показано, что распределение частиц по размерам в водной среде является бии тримодальным, диаметр агломератов частиц преимущественно 1300 и 5500 нм, такжеприсутствуют агрегаты размером 130−250 нм. Эффективный диаметр частиц диоксидакремния уменьшается с увеличением времени ультразвуковой обработки.

Comparative characteristics of the structure and physicochemical properties of silica synthesized by pyrogenic and fluoride methods