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The influence of modifying additives and synthesis conditions on the genesis of the phase composition of alumina–chromium catalysts was studied by differential dissolution (DD) and X-ray diffraction (XRD) analysis. The salts of potassium (KNO3) and lithium (LiCl) were added as additives. It was found that the individual nature of the additives affected the formation of phases. Although potassium and lithium cations occur in the same group of the periodic system, they differently react with a phase of γ-Al2O3 in the support: lithium forms a LixAl1 solid solution with the crystallized finely dispersed γ-Al2O3 species, whereas potassium mainly remains on the surface of the finely dispersed Al2O3 species and partially forms potassium aluminate. The interaction of lithium cations with the active component Cr(VI) of the catalyst leads to the formation of lithium chromate analogously to the reaction of the potassium cation with $${\text{CrO}}_{4}^{{2 - }}.$$ However, a portion of lithium cations is introduced into the structure of the substitution solid solution of Cr(III) in γ‑Al2O3 to form addition solid solutions (Al1Crx1– x2Liy1 –y2).

Traditionally, the X-ray analysis (XRD) method is used to study the phase composition of a solid. But phases with structural defects, poorly crystallized (with disordered structure and amorphous), microphases, phases of variable composition, surface phases and phases, distributed in various ways throughout the entire volume of the sample, often turn out to be X-ray amorphous. In these situations, the stochiographic DR method proves to be more effective, since it allows qualitatively and quantitatively to detect both the crystalline and X-ray amorphous phases listed above. The phase compositions of the spinel type catalysts Cu 1 Cr 2 O 4 and Cu 1 Fe 2 O 4 were studied by the stoichiographic method of differentiating dissolution (DR). It is established that the nature of the element and temperature influence the formation of the spinel structure, creating new shapes. The paper describes phase transformations occurring in the synthesis of catalysts, which was carried out by coprecipitation from a mixture of solutions of nitrate salts. It was found that the temperature of 85°C forms various stoichiometric formations, which are precursors of spinels. The 600°C temperature in the case of copper-chromium systems forms stoichiometric compounds of the spinel composition Cu 1 2+ Cr 2 3+ O 4 and structures with different degree of ordering. In the case of copper-iron systems at 600 °C, stoichiometric compounds of the Cu 1-x 2+ Fe 2 3+ O 4 spinel composition and structure are defective in copper. The 900°C temperature pro­vides the formation of compounds of a given spinel composition Me 1 2+ Me 2 3+ O 4 and structures in both systems. The results by the DR method were compared with the results of the XRD method. A comparative analysis has shown that the ordered or crystallized forms of spinels and oxides are detected by both methods, while disordered and defective forms of spinels, the shapes of disordered solid solutions, and also small amounts of oxides show only the DR method.

The process of mechanical alloying in the 33Al-45Cu-22Fe (at.%) powder mixture subjected to high-energy ball milling was studied. Due to complexity of the alloy formation in this system, several methods – X-ray diffraction phase analysis, Differential Dissolution, thermal analysis and Transmission and Scanning Electron Microscopy – were combined to obtain the detailed information on the structure and composition of the mechanical alloying products. Possible formation mechanisms of these phases during mechanical alloying are discussed. No crystalline phase containing Fe and Cu, Al has been found in the products of mechanical alloying of the 33Al-45Cu-22Fe mixture. The formation of Cu-Al phases followed the sequence of Al2Cu → Al4Cu9 → Cu(Al) solid solution. When only those phases that were detected by the XRD analysis were taken into account, the mass balance of Al and Fe in the products of mechanical alloying was not satisfied. The Differential Dissolution and high-resolution Transmission Electron Microscopy data suggest the formation of non-stoichiometric X-ray amorphous phases containing all three elements. Reasons for the retardation of the solid-state interaction between aluminum and copper in the ternary powder mixture are discussed.

Intermediate and final products of the synthesis of Cu–Al cermets have been studied by a differential dissolution (DD) stoichiographic method. Their qualitative and quantitative phase compositions have been determined. The phase composition of the intermediate products has been shown to differ from that of the final products. It has been shown that the first stage of the synthesis is the formation of a solid solution and intermetallic phase. In the final stage, the latter decomposes to give a solid solution, copper, and aluminum. The degree of decomposition depends on the mechanical activation time of the constituent metals: milling for 12 min leads to complete decomposition of the intermetallic phase. We also observe the oxidation of the forming aluminum and copper to their oxides and partial interaction between them, resulting in the formation of solid solutions of aluminum oxide in copper oxide. A comparative analysis of DD data with results obtained by physical methods— X-ray diffraction (XRD) and nuclear magnetic resonance (NMR)—demonstrates that they do not always agree. The reason for such discrepancies is that the three methods have different capabilities. We thus conclude that the use of both DD and XRD is crucial for obtaining reliable results.

We report the phase and microstructure evolution of the Cu–13 wt.% Al mixture during treatment in a high-energy planetary ball mill with a particular focus on the early stages of mechanical alloying. Several characterization techniques, including X-ray diffraction phase analysis, nuclear magnetic resonance spectroscopy, differential dissolution, thermal analysis, and electron microscopy/elemental analysis, have been combined to study the evolution of the phase composition of the mechanically alloyed powders and describe the microstructure of the multi-phase products of mechanical alloying at different length scales. The following reaction sequence has been confirmed: Cu + Al → CuAl 2 (+Сu) → Cu 9 Al 4 + (Cu) → Cu(Al). The phase evolution was accompanied by the microstructure changes, the layered structure of the powder agglomerates disappearing with milling time. This scheme is further complicated by the processes of copper oxidation, reduction of copper oxides by metallic aluminum, and by variation of the stoichiometry of Cu(Al) solid solutions with milling time. Substantial amounts of X-ray amorphous phases were detected as well. Differential dissolution technique has revealed that a high content of aluminum in the Cu(Al) solid solution-based powders is due to the presence of Al-rich phases distributed between the Cu(Al) crystallites.

The standardless method of differential dissolution (DD) was used for determining the chemical composition of aluminosilicate and zirconium silicate glass-fiber clothes at different stages of their preparation and modification. Conditions for the detection, identification, and quantitative determination of various forms of heterogeneity in the elemental, phase, and surface compositions of these materials are considered. The distribution of the elements that constitute the glass-fiber clothes between various forms—surface ion-exchange (Na), hydrated (Al, Si), and framework (Al, Si) species—was quantitatively determined for the first time.

The technical and experimental aspects of creating the conditions of differential dissolution in a flow stoichiographic system are discussed; the scheme of the experimental apparatus, stoichiograph, is presented. The construction, operation conditions of the main units of the stoichiograph, and sample treatment issues are considered. The principles of the creation and optimization of the conditions of the dynamic differential dissolution for the analysis of compounds and materials of the known and unknown phase composition are discussed: the composition of solvents and temperature, and the principles of their variation in time, including those in the processes of stoichiographic titration.

The results of the application of the stoichiographic method of differential dissolution (DD) in the determination of the chemical composition of vanadium-containing catalysts are presented. In the studied catalyst series, amounts of vanadium were deposited onto TiO2, SiO2, Al2O3, ZrO2, and Nb2O5. The catalysts were prepared by the impregnation method or by the spray drying method and thermally treated at different temperatures. The DD method was used for the precise correction of the phase composition of the V2O5/TiO2 catalyst samples in order to determine the nature of the active component of these catalysts and obtain the correct information on their structure using the NMR method.

The phase composition of La1 – xCaxFeO3 – 0.5x perovskites synthesized from preactivated oxides was studied by powder X-ray diffraction analysis and differential dissolution. The system does not form a continuous series of homogeneous solid solutions. No intermediate samples from this series are monophasic. It was found that the synthesis under nonequilibrium conditions (mechanical activation + calcination at 900°С for 4 h) resulted in nonequilibrium microheterogeneous solid solutions with degrees of calcium substitution for lanthanum of no higher than 0.5. A longer calcination (for 16 h) or an increase in the calcination temperature of solutions up to 1100 °С decreased the calcium content of the samples down to x ∼ 0.2 because of the formation of a brownmillerite phase. The catalytic activity of the test samples in the oxidation of CO changed nonmonotonically with x, and it was maximum at x = 0.5–0.6, which correlates with the maximum density of interphase boundaries in these samples.

The phase analysis of La1-xCaxFeO3-0.5x perovskites prepared by a ceramic process from oxides is studied by X-ray diffraction and differential dissolution methods. Atx 0.5, the formation of the structures of a brownmillerite-based homological series is found. The catalytic activity of perovskites depends nonmonotonically on thex value and reaches the maximum atx = 0.6.

X-ray powder diffraction, transmission electron microscopy and differential dissolution were used for investigation of the phase transformation peculiarities of biphasic manganese-alumina catalysts during their thermal treatment. An effect of interaction between aluminium and manganese oxides depending on the sample preparation procedure was found.