L. T. Zhuravlev’s research while affiliated with Russian Academy of Sciences and other places

The physicochemical properties of the surface of silica precipitated from a hydrothermal solution have been studied. The concentration of physically adsorbed water, and the net concentration of surface and bulk (internal) hydroxyl groups have been found by low-temperature adsorption of nitrogen and thermogravimetric data. The concentration of internal silicone (internal water) under different temperatures of the silica specimens under study has been estimated from the difference between the net concentration and the Zhuravlev physicochemical constants. The type of noncrystalline silica containing substantial amounts of internal water has been identified. The difference in mechanisms involved in internal and surface water extraction has been established.

The physicochemical properties of amorphous silica precipitated from a hydrothermal solution were studied. Low-temperature nitrogen adsorption in conjunction with the BET method was used to determine the specific surface area of this silica. Based on thermogravimetry data, the total content of water was estimated. A comparison of the thermogravimetry data with the Zhuravlev physicochemical constants made it possible to determine the temperature dependences of the concentration of surface and internal silanols over a temperature range of from 200 to 1200°C. A new type of amorphous silica with enhanced internal water content was revealed. The distinctions between the mechanisms of the removal of surface and internal water were established.

The physicochemical characteristics of amorphous silica precipitated from a hydrothermal solution are investigated. The specific surface of silica is determined by the Brunauer-Emmett-Teller method from the data on low-temperature nitrogen absorption. The limits of the total water content are estimated according to the thermogravimetric data. The temperature dependences of the concentration of surface and internal silanol groups in the range 200–1200°C are determined by comparing the thermogravimetric data with the Zhuravlev physicochemical constants for the silica samples under consideration. A new type of amorphous silica with a considerable concentration of internal water is revealed. It is established that the mechanisms of the removal of surface and internal water differ from each other.

A review article is presented of the research results obtained by the author on the properties of amorphous silica surface. It has been shown that in any description of the surface silica the hydroxylation of the surface is of critical importance. An analysis was made of the processes of dehydration (the removal of physically adsorbed water), dehydroxylation (the removal of silanol groups from the silica surface), and rehydroxylation (the restoration of the hydroxyl covering). For each of these processes a probable mechanism is suggested. The results of experimental and theoretical studies permitted to construct the original model (Zhuravlev model-1 and model-2) for describing the surface chemistry of amorphous silica. The main advantage of this physico-chemical model lies in the possibility to determine the concentration and the distribution of different types of silanol and siloxane groups and to characterize the energetic heterogeneity of the silica surface as a function of the pretreatment temperature of SiO2 samples. The model makes it possible to determine the kind of the chemisorption of water (rapid, weakly activated or slow, strongly activated) under the restoration of the hydroxyl covering and also to assess of OH groups inside the SiO2 skeleton. The magnitude of the silanol number, that is, the number of OH groups per unit surface area, αOH, when the surface is hydroxylated to the maximum degree, is considered to be a physico-chemical constant. This constant has a numerical value: αOH,AVER=4.6 (least-squares method) and αOH,AVER=4.9 OH nm−2 (arithmetical mean) and is known in literature as the Kiselev–Zhuravlev constant. It has been established that adsorption and other surface properties per unit surface area of silica are identical (except for very fine pores). On the basis of data published in the literature, this model has been found to be useful in solving various applied and theoretical problems in the field of adsorption, catalysis, chromatography, chemical modification, etc. It has been shown that the Brunauer–Emmett–Teller (BET) method is the correct method and gives the opportunity to measure the real physical magnitude of the specific surface area, SKr (by using low temperature adsorption of krypton), for silicas and other oxide dispersed solids.

Research of Soviet scientists is surveyed. Contributions to various aspects of the colloid chemistry of silica are examined: preparation and stabilization of silica hydrosols; preparation of silica gels; structural characterization of silicas; surface chemistry elucidation; adsorption and ion-exchange property examination; and geometric and chemical modification of silicas, silica coatings, and so forth.

A short survey is presented of results on the dehydration, dehydroxylation and rehydroxylation of the surface of amorphous silica.

A survey is presented of the research results obtained by the author on the properties of amorphous silica. It covers the following topics: physically adsorbed water; dehydration of the surface and the temperature boundary of this process; dehydroxylation of the surface; concentration of hydroxyl groups on the silica surface, depending on the conditions of activation of silica; the energetic non-uniformity of the surface; chemisorption of water (rehydroxylation of the surface); the difference between the hydroxyl groups on the silica surface and structurally bound water inside the silica particles. For each of these processes a probable mechanism is suggested.

Using meta-nitrobensoates of hexamethyleneamine, morpholine and ammonia, the authors studied the effect of cation (amine component) on the interaction of these inhibitors with St3 steel. Electrochemical, ellipsometric and mass-spectrometric methods were used in this study. It is found that the amine nitrobenzoates studied do not differ fundamentally in their action on anodic and cathodic reactions. Inhibition is closely related to the nature and strength of adsorption of amine nitrobenzoates on the steel.

Using the method of mass-spectroscopic thermal analysis, it has been shown that when the surface of rutile is modified with n-butylamine and acetic acid, it is possible for the two substances to interact in the surface layer, with the result that the order in which the amine and the acid are adsorbed affects the structure of the resulting adsorbed layers. The chemisorbed layer on the surface of a sample of TiO2-AA-BA consists of molecules of both modifiers and the product of their surface reaction. Acetic acid adsorbed on TiO2-BA displaces the coordinatively bound amine molecules from the surfaces, leading to the formation of butylacetamide and the chemisorption of the acid molecules on unoccupied areas of the TiO2 surface.

1. When silicas are modified with amines, not all surface silanol groups participate in the chemical reaction. 2. When amine-modified silica gels are heated, water is produced; the maximum rate of the formation of gas occurs at 625 and 750 K. Destruction of the modifying layer begins with the liberation of ammonia at T > 640 K. 3. Adsorption of SO2 and CO2 on aminated silicas is determined by the surface concentration of amino groups, by their nature, and by their mutual position.