Papers by Keyword: Acid-Base Properties

Abstract: The article presents potentiometric (pH-metric) methods that are used to study the acid-base properties of the surface of dispersed materials of different chemical nature. It is shown that the surface of any solid body has a surface hydroxyl-hydrate layer with a set of active adsorption centers (ACA) of different chemical structure and a wide range of acid-base properties. It has been proven that potentiometric (pH-metric) methods of studying dispersed materials in suspensions allow obtaining the most complete information about surface acid-base properties.

Abstract: The paper presents studies on the properties of various types of micro-reinforcing fibers to assess their role and effectiveness in the structure formation of the cellular composite. Based on the data on the weight loss after exposure in a model medium of cement, analysis of the alkali resistance of fibers of five different types – basalt fiber, heat-treated basalt fiber, polymer fiber and glass fibers from two different manufacturers – was carried out. It is shown that the fibers have a sufficiently high durability in the medium of hardening cement, which is expressed by a relatively insignificant weight loss of the original fiber after exposure in a model medium for 28 days in ambient conditions. The weight loss for some fibers sharply increases when hardening conditions are changed to hydrothermal ones. The images of fibers exposed in a model medium of cement, obtained using scanning microscopy, were also analyzed, and the character of distribution of acidic and basic adsorption sites on the surface of fibers depending on the type was assessed. Based on the analysis of the obtained data, we can talk about a high number of active sites on the surface of basalt and glass fibers, which ensures the formation of crystalline new formations on them and makes it possible to predict their high adhesion to the cement matrix.

Abstract: Gd₂O₂S:Tb phosphors with different terbium content are prepared in a reducing atmosphere at various synthesis conditions. The effect of an activator and Na₄P₂O₇ flux concentrations upon photo-and X-ray induced luminescence of the synthesized samples as well as on their acid-base properties and morphology is studied. The addition of Na₄P₂O₇ flux into the charge mixture leads to a significant increase of the phosphor particle size. A positive correlation is found between the particle size and pH value of the phosphor aqueous slurry. The photoluminescence intensity is found to mostly depend on the activator concentration, while X-ray luminescence intensity primarily depends on the particle size and crystal structure perfectness of the phosphor matrix. Charge mixture compositions and synthesis conditions providing Gd₂O₂S:Tb phosphors with the highest photo-and X-ray luminescence intensity are determined. A Gd₂O₂S:Tb phosphor with X-ray luminescence intensity exceeding the values for the commercial phosphor KEP-45 of a similar composition is developed. The obtained phosphors can be used for the manufacture of intensifying screens applied in industrial X-ray flaw detection.

Abstract: The urgency of the problem concerning the rapid assessment of moisture absorbing power of powdery substances is discussed in the given article. The theoretical prerequisites for the determination of moisture absorbing power by an acid-base interaction in the system “solid body-water” are considered. The advantages of the pH analytic signal of aqueous suspension are shown. Some practical recommendations of the new experimental data processing and interpretation by pH metry used for the assessment of moisture absorbing power of powdery substances are developed. It is shown that the velocity of mass transfer analytic signal undergoes changes with time depending on functional groups of the surface. These functional groups are initially predetermined by the inner structure of the object of the research. The explanation of the deceleration mechanism of acid-base reaction interaction in the system “solid body-water” is supplied. It allows examining the hydrophilic behavior (hydrophobic behavior) of the surface of the polycrystalline substance.

Abstract: The article demonstrates how acid-base properties of the surface of tin (II) oxide powders influence its photocatalytic activity in reaction of photodegradation of methylene blue. The experiment shows that the photocatalytic activity of the tin (II) oxide depends on the number and the strength of surface acid centers of the Lewis.

Abstract: Humic substances are the major components of soil, peat and brown coal. They can be fractionating into fulvic acids (FA), brown humic acids (BHA) and gray humic acids (GHA). In this work we investigated the influence of mechanochemical modifications on structural composition of HAs main fractions using the methods of IR and ¹H MRS spectroscopy. The IR spectroscopy results has shown that HA has different chemical composition in comparison with GHA and BHA. Potentiometric titration showed that mechanoactivation (MA) with thiourea increases the amount of oxygen-containing groups up to 2.5. For the first time we studied the impact of modifying agent of thiourea on the structural composition and acid-base properties of HAs major fractions - GHA and BHA during the mechanoactivation process.