RU2056635C1 - Method of phase analysis of solid substances - Google Patents

Abstract

FIELD: chemical analysis. SUBSTANCE: starting solid material is worked with solvent. Composition of solvent or its temperature is changed. Increase of temperature and change of composition of solvent are conducted either by increase of rate and degree of change of temperature and/or composition of solvent with proviso that process of dissolution of phases is slowed down or stopped or by decrease of rate and degree of change of temperature and/or composition of solvent. In this case process of dissolution of at least one element out of mix of analysed substance goes on with significant rate. EFFECT: improved authenticity of phase analysis. 3 cl, 1 tbl

Description

 The invention relates to the field of chemical analysis, mainly chemical methods of phase analysis of solids of complex and unknown phase composition: mineral raw materials and products of its processing, building materials, solid products of chemical and other industries, soil and other environmental objects, forensic objects and other solids of various origin and destination.

The use of known chemical methods for phase analysis of objects of a previously unknown phase composition is impossible without first determining the elemental composition, crystal structure, chemical and physico-chemical properties of each of the individual phases, for which these phases must be pure (isolated from a mixture or synthesized). The method of differentiating dissolution does not require preliminary phase separation, but no methods are known that ensure that this method conducts phase analysis of objects of a previously unknown phase composition [1]
The known method of phase analysis, which consists in the complete dissolution of a sample sample of a multiphase solid and recording the speed of this process. The determination of the qualitative and quantitative phase composition of the analyte is carried out on the basis of the laws of change over time of the ratios of the rates of dissolution of chemical elements from the composition of the sample, without using standards of individual phases. The composition and temperature of the solvent for each specific solid sample are pre-selected according to the rules adopted in the quantitative elemental analysis, and the composition and temperature of the solvent are changed, going from low concentrations of solvent components and temperatures to higher values during the process of sample dissolution [2]
However, the existing method of phase analysis does not allow you to quickly, in one or a limited number of experiments, determine the composition and content of each phase in the analyte, but only provides information about the single or multiphase composition of this substance.

 The purpose of the invention is the determination of the elemental composition and quantitative content of individual phases of unknown structure in substances with known elemental, but unknown qualitative and quantitative phase composition, increasing the information content, correctness, reproducibility, sensitivity and acceleration of phase analysis.

 This goal is achieved by the fact that in chemical methods of selective and differentiating dissolution in the phase analysis of solids of known qualitative and quantitative elemental composition, but unknown qualitative and quantitative phase composition, including the process of sequential dissolution of solid phases from a sample of the analyte, conducting elemental analysis of the resulting solution and determining the rate of transition into the solution of chemical elements from a sample sample, finding to qualitative and quantitative phase composition of the sample by calculating on the basis of patterns of change in the ratios of the elements that pass into the solution, the process of successive dissolution of solid phases is carried out gradually increasing the temperature of the solvent and / or gradually adding a small amount of components to the solvent of the "soluble substance-solvent" system, agree on the frequency and degree of change temperature and composition of the solvent with the rate of transition into the solution of chemical elements from the composition of the sample as follows ohm: increase the frequency and degree of change in temperature and composition of the solvent during periods of time when the process of dissolution of all elements from the composition of the sample slows down or stops, and vice versa, reduce the frequency and degree of change in temperature and composition of the solvent until it stops completely when the dissolution process is at least one , from the elements from the composition of the sample comes at a significant speed. The kinetic dependences recorded in such a process serve as initial data for calculating the qualitative and quantitative phase composition of the sample. The significance (insignificance) of the recorded values of the dissolution rate of elements in each case is established based on the specified values of metrological criteria for the accuracy of the results of elemental and phase analysis of a particular sample.

PRI me R 1. Phase analysis of the supported copper-chromium catalyst for the complete oxidation of hydrocarbons. The catalyst is prepared by impregnating alumina applying to the surface of copper dichromate, followed by heat treatment at 700 ^C. The elemental composition of the catalyst, wt. Cu 1.33; Cr (III) 1.64; Cr (VI) n.a. Al 43.4. Due to the low content of copper and chromium, the phase composition of the active component of the catalyst by the method of x-ray phase analysis has not been established.

In the phase analysis of the catalyst proposed method (static method) weighed catalyst sample having a particle size ≅ 0,05 mm, weight 1 g was placed into a glass reactor containing 100 ml of HCl (1: 4) at 50 ^{° C} and stirring process was performed dissolution. Every 5 minutes, a sample of the solution was taken, in which the content of copper, chromium and aluminum was determined by atomic absorption (AA) spectrophotometry. Since after 5-10 minutes the dissolution of copper ceased, and aluminum and chromium did not start, the solvent composition was changed, adding 20 ml of a mixture of acids (H ₂ SO: H ₃ PO ₄ : HClO ₄ 3,5: 1: 1,5) continued heating by evaporation of H ₂ O and HCl. After that, the mixture of high boiling acids continued to be heated, increasing the temperature of the solvent over time according to a linear law, continuing to take samples of the resulting solution and analyze them for the content of all three elements. When the dissolution rate of all elements fell to zero due to their complete dissolution, heating was stopped. Based on the parametric dependences of the process of differentiating dissolution of the sample, its qualitative and quantitative phase composition was calculated. An assumption was made about the oxide nature of the phases, since the transition to the solution from the oxygen sample was not controlled. The empirical formulas of the phases were calculated based on the slope of the linear sections of the parametric functions, and the number of phases in the sample according to the length of these linear sections. In the analyzed sample, the composition and content of two phases were found: copper oxide CuO 0.5 ± 0.05 wt. solid solution of copper and chromium (III) oxides in alumina, composition 0.46 CuO · 0.50 Cr ₂ O ₃ · 28.0 Al ₂ O ₃ 99.5 ± 4.7 wt.

 PRI me R 2. Phase analysis of high silica zeolites (CVC). CVCs are highly effective catalysts for the synthesis of liquid fuels from non-hydrocarbon feedstocks; they are prepared by hydrothermal synthesis methods. CVCs contain 0.5-0.3% aluminum and about 40% silicon. The content of CVCs in the products of their synthesis is determined by the method of x-ray phase analysis, the correctness of the results of which is uncertain, because it depends on the used reference samples of CVCs, the composition of which does not cover all possible variations in the elemental composition of CVCs in the analyzed samples.

When phase analysis of CVC samples by the proposed method (static method), a sample of a CVC sample, crushed to particles with a size of ≅ 0.05 mm, weighing 0.3 g was placed in a glass reactor containing 100 ml of HCl (1: 4), at 20 ^o With and with stirring, the dissolution process was carried out, taking samples of the solution after 0.5-2 minutes, in which the aluminum and silicon contents were determined by AA spectrophotometry. Since after 3-5 minutes aluminum dissolution ceased, then further conducted titration solution HF (1:19) at ²⁰ ° C at a constant rate of 0.25 ml / min, and when the aluminum dissolution process and silicon slowed and stopped with a solution of aluminum HF (1 : 5) at 20 ^o C.

 As an example of phase analysis by the proposed method, the results of titration of a sample N: 1, which according to x-ray phase analysis completely consisted of the CVC phase, as well as two samples N: 2 and N: 3, synthesized under the same conditions, but differing in the aluminum content and phase, are presented CVC, according to x-ray phase analysis (see table).

The kinetic curve and parametric functions of the N: 1 sample show that the sample really completely represents the CVC phase. From the kinetic curve of sample N: 3 and the parametric functions of samples N: 2 and N: 3 it follows that these samples, in addition to the CVC phase, contain a silicon phase (without aluminum) SiO ₂ . At different contents of aluminum in the N: 2 and N: 3 samples, the CVC phase in them is characterized by the same Si: Al ratio of 18.4. During the titration, measures were taken to prevent the loss of silicon in the form of SiF ₄ . The reactor and other devices are made of fluoroplastic. When calculating the results of the analysis, corrections were introduced related to a change in the volume of titrated contents of the reactor due to the introduction of titrant and sampling of the solution.

PRI me R 3. Phase analysis of the superconducting ceramics Y-Ba-Cu-O. A sample of superconducting ceramics was prepared by solid-phase sintering of yttrium, barium, and copper oxides. According to elemental analysis and x-ray phase analysis, the composition of the sample corresponded to a single phase Y ₁ Ba ₂ Cu ₃ O _x . When phase analysis of ceramic samples of the proposed method (static method), a sample of ceramic samples, crushed to particles with sizes ≅ 0.05 mm, weighing 0.05-0.1 g was placed in a glass reactor containing 100 ml of 0.03 M HCl at 3 ^about C and with stirring, the dissolution process was carried out. Every 5 s, and then after 1-2 min, samples of the resulting solution with a volume of 0.5 ml were taken, in which the contents of yttrium, barium, and copper were determined by AA spectrophotometry. Within 10-20 s, only yttrium and barium passed into the solution, then their dissolution slowed down, and therefore, titration of the contents of the HCl reactor was started (d 1.19), adding ≈0.05 ml (dropwise) every 2- 3 min. When the dissolution of the elements slowed down, the rate of addition of HCl (d1.19) was increased 2-10 times. Simultaneously, the solution was heated from room temperature up to ≈70 ° ^C. At the end of the titration solution is passed in only a small amount of copper, yttrium and barium, and dissolving completely ended. For the accurate determination of these small amounts of copper against the background of its bulk having already passed into the solution, the following was done. In a parallel experiment, at the end of the titration, the formed sample solution was filtered and the titration of the residue not dissolved at this time was continued. The phase composition of the ceramic sample was calculated, wt. Y ₁ Ba ₂ Cu ₃ O 96.0 ± 1.3; Y ₂ O ₃ 1.1 ± 0.2; BaO 1.8 ± 0.3; CuO 1.6 ± 0.2. Thus, in addition to the main phase Y ₁ Ba ₂ Cu ₃ O, the sample contains impurity phases of yttrium, barium, and copper oxides. The high dissolution rate of yttrium and barium oxides indicates their very high dispersion, which increases the information content of the results obtained by the proposed method.

PRI me R 4. Phase analysis of the solid product of the coprecipitation of hydroxides of copper, zinc and aluminum. The elemental composition of the product, wt. Cu 11.8; Zn 39.5; Al 7.31. According to x-ray phase analysis, the product consists of an amorphous and crystalline phase of a layered pyroaurite structure of undetermined elemental composition and in an unknown quantity. To determine the phase composition of the product by the proposed method (flow method), a weighed sample with a particle size of ≅ 0.05 mm, weighing 2-5 mg, was placed in a flow microreactor with a filter through which a solvent stream of a given composition and temperature was created. The entire resulting solution was sent for analysis, which was carried out continuously every 15 s using an atomic emission spectrometer with inductively coupled plasma and a polychromator, determining the content of copper, zinc and aluminum. Titration of the sample was carried out with a solution of sulfuric acid. For this, a solution of H ₂ SO ₄ (1: 3) was gradually added dropwise from the burette to a glass containing 300 ml of water. The contents of the beaker were continuously mixed and, using a peristaltic pump, the resulting solution of H ₂ SO _{4 of} increasing concentration at room temperature was sent through a capillary to a microreactor with a weighed sample and then to an ICP spectrometer. Kinetic dissolution curves of elements were recorded during the process. Depending on the course of the curves, the concentration and the amount of added titrant were increased or stopped, as required by the proposed method. Calculations show that the analyzed sample contains two phases with molar ratios between the elements: Cu: Zn: Zl 1: 3.82: 1.63 and Cu: Zn: Al1: 2.85: 2.03. Based on metal oxides in the oxidation states of 2+ and 3+, these phases of variable composition are described by the formulas:
5.95 MeO · Al ₂ O ₃ ≈ 6 MeO · Al ₂ O ₃ 35.2 wt.

3.85 MeO · Al ₂ O ₃ ≈ 4 MeO · Al ₂ O ₃ 27.0 wt. where Me (Cu ²⁺ + Zn ²⁺ ). With this representation of the composition of the phases, their total content is equal to 62.2 wt. those. less than 100% The imbalance is due to the fact that, in addition to metals, the composition of these phases of the layered pyroaurite structure includes a large number of OH ^- , CO ^{3 -} or NO ^{3 -} anions, depending on the composition of the components used in the synthesis of the product. This type of phase may, for example, have the composition Me $\genfrac{}{}{0ex}{}{\text{2+}}{\text{3}}$ , Me $\genfrac{}{}{0ex}{}{\text{3+}}{\text{1}}$ (OH) ₈ (CO $\genfrac{}{}{0ex}{}{\text{2-}}{\text{3}}$ ) _0.5 (H ₂ O) ₂ . The application of the proposed method made it possible to determine the number of phases forming the sample, the atomic relations between metals in these phases, and the amount of metals in each phase.

PRI me R 5. Phase analysis of a multicomponent bismuth-molybdenum selective oxidation catalyst. The elemental composition of the catalyst corresponds to the gross formula:
Bi ₁ M _o12 Fe ₃ Co _4.5 Ni _2.5 P _0.5 K _0.05 · O _x .

Phase analysis of the catalyst sample by the proposed method (flow method) was carried out according to the titration method described in example 4, using a flow microreactor ICP spectrometer with a polychromator as an analyzer of the resulting solution and a computer for recording and calculating the analysis results. As starting materials for titration, water and a HCl solution (1: 3) were used, which were added dropwise from a burette into a glass of water, then the solution was passed through a capillary into a microreactor and then to an ICP spectrometer. Data on the composition of the solution was obtained every 10 s. First, water was sent to the reactor, which led to the dissolution of all potassium and a small fraction of molybdenum. Since the dissolution of the sample in water stopped, acid titration was started, adjusting its concentration growth rate and dosing the added quantities depending on the course of the kinetic dissolution curves of the elements recorded on the display screen during titration. At the end of the titration was conducted heating the solution from 20 to ⁸⁰ C. From the kinetic curves and stehnogramm follows that present in the sample at least four phases:
phase 1 contains all of the potassium and part of the molybdenum in the form of potassium molybdate;
phase 2 contains most of bismuth, part of iron, cobalt, nickel and molybdenum, for example bismuth molybdate, in which part of bismuth is replaced by other elements;
phase 3 and 4 according to preliminary calculations, respectively, have the composition:
Co _0.39 Ni _0.21 Fe _0.29 Bi _0.030 Mo ₁ O _x (N: 3) and
Co _0.60 Ni _0.35 Fe _0.06 Bi _0.036 Mo ₁ O _x (N: 4) The phosphorus contained in the sample is most likely distributed between the last two phases.

Using the proposed method of phase analysis of solids provides compared with existing methods the following advantages:
rapid determination of the qualitative and quantitative phase composition of solid multiphase substances of a previously unknown phase composition without the use of phase reference samples and preliminary isolation of phases in a pure form;
determination of the phase composition of amorphous and X-ray amorphous solids;
determination of impurity phases, phase purity of individual phases, precision determination of the elemental composition (stoichiometry) of individual phases;
determination of the distribution of impurity, including trace, amounts of elements over individual phases of a multiphase substance;
determination of the elemental composition of phase samples, variable composition of the same crystalline structure.

 This method can be implemented in the static version, when the solvent components are added to the reactor with the soluble substance and the solvent, as well as in the flow-through version, in which the solvent with the added components passes through the reactor with the soluble substance. Components in such systems can be introduced in a solid, liquid or gaseous state at a constant or variable speed, continuously or discontinuously. The components of the solvent in the required concentration can be generated directly in the titratable system, for example, as a result of chemical reactions or by evaporation of the solvent. Patterns of temperature changes in the system during dissolution can be different.

Claims (3)

 1. METHOD OF PHASE ANALYSIS OF SOLIDS, including treating the starting material with a solvent as the temperature rises and changing the composition of the solvent with successive dissolution of the phases, conducting an elemental analysis of the resulting solution, determining the dissolution rate of the elements contained in each phase, and establishing patterns of change in the rate of transition of the elements into the solution with the subsequent calculation based on these laws of the qualitative composition of the phases and their quantitative content in the analyte tv, characterized in that the temperature increase and the change in the composition of the solvent is carried out either by increasing the frequency and degree of change of the temperature and / or composition of the solvent, provided that the phase dissolution process is slowed or stopped, or by reducing the frequency and degree of change in the temperature and / or composition of the solvent, provided that the process of dissolution of at least one element from the composition of the analyte is at a significant speed.  2. The method according to claim 1, characterized in that the change in the composition of the solvent is carried out by introducing at least one component, forming with the soluble phase the product, passing into the solution.  3. The method according to claim 1, characterized in that the composition of the solvent is changed by evaporation.

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