DETERMINATION OF THE PHASE COMPOSITION OF INTERMEDIATE AND FINAL PRODUCTS OF SYNTHESIS OF SPINEL TYPE CATALYSTS Cu1Cr2O4 AND Cu1Fe2O4 BY DIFFERENTIATING DISSOLUTION METHOD

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 Cu₁Cr₂O₄ and Cu₁Fe₂O₄ 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 Cu₁²⁺Cr₂³⁺O₄ and structures with different degree of ordering. In the case of copper-iron systems at 600 °C, stoichiometric compounds of the Cu_1-x²⁺Fe₂³⁺O₄ spinel composition and structure are defective in copper. The 900°C temperature pro­vides the formation of compounds of a given spinel composition Me₁²⁺Me₂³⁺O₄ 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.

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