Differential Dissolution Method Research Articles

Determining the Phase Composition of Copper Ferrite Samples by a Standardless Differential Dissolution Method

Determining the Phase Composition of Copper Ferrite Samples by a Standardless Differential Dissolution Method

Mixed Films Based on MgO for Secondary Electron Emission Application: General Trends and MOCVD Prospects

Doping process is widely used to improving emission performance of MgO films thicker than 10 nm via assisting the surface recharge and changing in electron structure. The present paper briefly reviews this strategy in a search for the new materials and structures being effective for secondary electron emission (SEE) and their diagnostics. Then, Metal-Organic Chemical Vapor Deposition (MOCVD) coupled with the specially selected precursor is suggested here as a new technique that transforms the refractory oxides to nanoscale, defect-disordered materials able to solid-solid interaction at 450 °C. Primary experiments have been performed for demanded mixed films based on MgO with ZrO2 and CeO2 additions. A dopant impact on facilitating the formation of oxygen vacancies in the host oxide and on the features of new mixed phases have been studied by new diagnostic means, based primarily on chemical method of differential dissolution. The method brought out the effective solvents that were the probes for identifying the nanoscale and amorphous phases possessing by the different defects on the surface of MgO films and determining contents of these phases. This approach allowed us to explain the origin of mixed phases and to estimate contribution of each from them in the macroscopic SEE properties.

Invisible Surface Oxygen Vacancies in a Thin MgO Film: Impacts on the Chemical Activity and Secondary Electron Emission.

Today, Fs defects in MgO as isolated surface neutral oxygen vacancies are in the focus of surface science, catalysis research, and emission coating of microchannel plates. With the 10-4 atom % content at 750 K and under pO2 = 10-9 Torr, estimated by us from the known equilibrium T-x and p-T-x diagrams of MgO, Fs defects remain invisible or difficult-to-detect objects. The MgO(100) → MgO(100) + Fs + 1/2O2 phase transition was studied in MgO films deposited by the metal-organic chemical vapor deposition (MOCVD) procedure from the mixed-ligand Mg precursor on Si substrates at 725 K in the O2 flow where the nonstoichiometric phase (MgO/Fs) is formed in the gas medium containing simultaneous H2, CO, H2O, CO, and O2 species in unbalanced concentrations. Realization of the above transition was proven theoretically and experimentally through kinetic-thermodynamic analysis of the nonequilibrium system with revealing thermodynamic motive forces, i.e., the positive enthalpy and entropy, as well as through a new combination of diagnostic methods including the original differential dissolution method, due to which separate determination of the point and morphological defects was achieved. It was found that Fs defects occur when oxygen in the immediate vicinity to the substrate surface is replaced practically completely by the oxidized products of the precursor and the resulting oxygen pressure becomes enough for this process. The 90 mass % of the as-deposited MgO-film-involved (MgO/Fs) phase; its chemical activity is demonstrated through dissolution in hot water, while the electron donor activity is through 9 at 750 eV secondary electron yield. A good understanding of gas-phase reactions between the precursors and oxygen provides the fundamental basis of the MOCVD process to deposit MgO films that are dense, free from carbon, and of homogeneous texture. This makes the MOCVD process suitable also for use as coatings of microchannel plates.

Effect of Lithium Nitrate Doping on the Phase Composition of Alumina–Chromium Catalysts

The effect of a lithium nitrate (LiNO3) modifying additive on the genesis of the phase composition of alumina–chromium catalysts has been studied using the differential dissolution (DD) and X-ray diffraction (XRD) methods. It has been shown that LiNO3 reacts with a pure support (Al2O3) to form lithium aluminate, double oxide Al4Li2O7 with a spinel structure, and mixed hydroxide LiAl2(OH)7(H2O)2. The reaction of an alumina–chromium catalyst with LiNO3 also leads to the formation of lithium aluminate and double oxide Al4Li2O7; however, a mixed hydroxide is not formed. In addition, the reaction of lithium cations with the Cr(VI) catalyst active component leads to the formation of lithium chromate. A comparative analysis of the phase compositions of alumina–chromium catalysts with LiCl and LiNO3 additives has been conducted. It has been found that, depending on the nature of the additive, the phase composition of the catalyst partially changes. In the case of the introduction of lithium chloride, solid solutions of Cr(III) and Li(I) in alumina are formed; the use of lithium nitrate leads to the formation of double oxide Al4Li2O7 and lithium aluminate. The results of studying the activity of 0.5–3% Li + 9.5% Cr + Al2O3 catalyst samples (Li being introduced from LiCl and LiNO3) have shown that the replacement of the LiCl modifying additive by LiNO3 leads to a change in the catalytic properties of the alumina–chromium catalysts. The activity of the sample doped with lithium nitrate is 4–8% higher than the activity of the sample doped with lithium chloride. This finding can be attributed to the fact that, in the case of the LiNO3 additive, the concentration of the formed active phases Li2CrO4 and Cr2O3 is higher. The selectivities of the catalysts modified with lithium salts (chloride and nitrate) differ only slightly owing to the formation of identical active phases.

SYNTHESIS OF IRON OXIDE FROM METAL POWDERS

A comparative analysis of various methods for obtaining highly dispersed iron oxides has been carried out. The advantages and disadvantages of traditional and developing methods of synthesis of iron oxides for catalysts, sorbents and ceramic materials are identified. The advantages of the method of mechanochemical synthesis of obtaining highly dispersed iron oxides for catalysts for the medium-temperature conversion of CO in the production of ammonia and the oxidation of methanol to formaldehyde are shown. The methods of X-ray phase, X-ray structural, synchronous thermal analysis and Mössbauer spectroscopy were used to study the process of mechanochemical oxidation of iron and cast iron powders in order to obtain iron oxides. The phase composition and specific surface area of the obtained oxides are investigated. It was found that in the process of mechanical activation of iron-containing powders in the aquatic environment, the system Fe-Fe3O4-FeOOH is formed. Heat treatment at 450 °C for 6 h causes decomposition of FeOOH to α-Fe2O3 and partial oxidation of metallic iron. By the method of differential dissolution, it was established that the cast iron in the presence of water in a roller-ring vibratory mill for 60 min is oxidized to 77.6%, and the iron is oxidized to 88%. Also in the process of dissolving metal powders in oxalic acid solutions using ultrasound FeC2O4 · 2H2O is formed, which under the conditions of thermolysis decomposes to maghemite – γ-Fe2O3 with the release of CO and CO2, and at 400 °C to hematite – α-Fe2O3. The possibility of using the produced iron oxides for obtaining iron-chromium catalysts for the medium-temperature conversion of CO in the production of ammonia and iron-molybdenum catalysts for formaldehyde synthesis is shown. The CO degree conversion is 92.0% at 340 °C, and the productivity by formaldehyde is 13.0 µmol/(g∙s).

Stoichiographic determination of the composition and concentration of phases encapsulated in the bulk of a solid matrix phase

A two-step method of stoichiographic calculations used in the determination of the formulas of phases encapsulated in the bulk of matrices of another composition is proposed. At the first stage of calculations, the stoichiometric composition of the encapsulated phase is determined and, at the second step, the concentrations of this phase and the matrix are found. The use of this method in the analysis of oxide La–Cu catalysts by the method of differential dissolution ensures the detection of the phase La1Cu1 (La2Cu2O5), incorporated within the matrix La1Cu0.5 (La2CuO4) phase.

Contribution of Chemical Methods to the Study of Nanostructure of Ultrafine and Amorphous Materials

Controlling the hydrolysis conditions of the solution TiOSO4•xH2SO4•yH2O, the h-TiO2 and A-TiO2 single phases were prepared in amorphous/crystalline state. With scanty structural and electron microscopy data, the unique capability of differential dissolution method was used to perform quantitative phase analysis of the samples and identify phases where two from them (TiO)(HSO4)0.4(OH)and TiO(OH)2 were found to be amorphous. New results were obtained that the amorphous TiO(OH)2 is transformed to ~ 5-nm crystallites TiO2-x•0.95H2O which then turned into ~ 3-nm crystallites TiO2•0.25H2O when drying the gels at 90°C. New structural models for the crystallites were proposed explaining differences in their chemical and thermal characteristics.

Determination of chemical and phase compositions of mixed oxides with the perovskite-like structure based on strontium titanates by differential dissolution method

The results of the application of stoichiographic method of differential dissolution (DD) to analyze mixed oxides with the perovskite-like structure are presented. The samples of Sr1Ti0.9Mg0.1O3 with the ABO3 stoichiometry of perovskite and samples of Sr2Ti0.9Mg0.1O4 with the A2BO4 stoichiometry of layered perovskite (where A = Sr2+; B = Ti4+, Mg2+) are prepared by a mechanochemical method and analyzed before and after catalytic tests. Conditions of the detection, identification, and quantitative determination of different phases in the compositions of the samples are described. The surface comppositions of the initial samples are determined by the DD method, and changes observed after the catalytic tests are noted. The DD results are compared with the powder XRD results.

Determination of the phase composition of catalyst precursors for multiwall carbon nanotubes by the stoichiographic differential dissolution method

The standardless stoichiographic differential dissolution (DD) method is used for phase analysis of superfine multicomponent oxide precursors of Fe-Co MWCNT synthesis catalysts obtained by the Pechini method. The analysis identifies the individual phases in the studied samples of Fe2Co/Al2O3, Fe2Co/MgO, and Fe2Co/CaCO3 and determines their stoichiometric composition and quantitative content. It is found that the samples are a complex mixture of superfine oxide phases the composition of which corresponds to a spinel structure and may simultaneously include both active (Fe and Co) and carrier elements (Al and Mg) to form solid solutions. It is only the Fe2Co/CaCO3 samples that contain a carrier-free phase the composition of which corresponds to a spinel structure.

The structure and catalytic properties of amorphous phase in MoVTeO catalysts for propane ammoxidation

This work presents an investigation of the chemical and phase composition of Mo1.0V0.3Te0.23Ox catalyst prepared by spray drying. The changes in the catalyst after heat treatment at 220–550°C were characterized by IR and Raman spectroscopy, XRD, HRTEM and differential dissolution methods. In the range of temperature 400–420°C HRTEM revealed the presence of nanoscaled crystallites that are structurally and chemically related to M1 and M2 phases and randomly distributed in the amorphous matrix. The characteristic diffraction pattern of the amorphous product can be described by a model of nano-sized clusters built from the structure of M1 phase. Nanostructured catalysts are active and selective in propane ammoxidation. The increase of temperature of heat treatment of the catalyst above 450°C leads to decomposition of nanostructured M1 phase and crystallization of M2 and a series of vanadium–molybdenum phases. The process is accompanied by a decrease in activity.

Determination of the chemical composition of modified fiber glass silicate materials by differential dissolution

The paper presents the results of application of the stoichiographic method of differential dissolution (DD) to the analysis of modified aluminosilicate and zirconium silicate fiberglass materials (FGM) and related catalysts. Na-Al-Si and Na-Zr-Si FGM have been studied after sodium leaching-out and subsequent modification with Al, Co, and Pt additives. The conditions of detection, identification, and determination of different forms of FGM modifiers and the analysis of the surface of these samples are provided. The DD method has been used for the precise correction of the composition of the fiber glass sample surface.

Developing methods to compare tablet formulations of atorvastatin

Atorvastatin (ATV) is an antilipemic drug of great interest to the pharmaceutical industry. ATV does not appear in the monographs of Brazilian pharmacopoeia, and analytical methodologies for its determination have been validated. The chromatographic conditions used included: RP-18 column-octadecylsilane (250 x 4.6 mm, 5 mm), detection at 238 nm, mobile phase containing 0.1% phosphoric acid and acetonitrile (35:65% v/v), flow at 1.5 mL min-1, oven temperature at 30ºC, and injection volume of 10 mL. ATV is classified as a class II product, according to the biopharmaceutical classification system. As such, a dissolution test was proposed to evaluate pharmaceutical formulations on the market today, under the following conditions: water as a dissolution medium, 1000 mL as a volume, paddle apparatus at a rotation speed of 50 rpm, 80% (Q) in 15 minutes with UV spectrophotometer readings at 238 nm. In the pattern condition proposed as the ideal dissolution test, which appropriately differentiates amongst formulations, the generic product was not considered pharmaceutically equivalent; however, in other less differential dissolution methods, which also fall within appropriate legal parameters, this product could come to be regarded as generic.

Determination of chemical composition of solid inorganic substances and materials using the principles of stoichiography and voltammetry

The state of the art in determination of the phase composition of complex inorganic solids by chemical and electrochemical methods is discussed. The theoretical and practical essentials of stoichiography and the new stoichiographic method of differential dissolution (DD) are reported. The unique feature of this method is that reference samples of the analyzed solid phases are not necessary. The development of this stoichiographic method was strongly affected by voltammetry. The application of the DD method for determining the chemical composition of various substances and materials is presented. The complementary use of voltammetry and DD for the detection, identification, and quantitative determination of inhomogeneity of the chemical composition of high-temperature superconductors was shown to be efficient.

Diagenesis in bone and enamel apatite carbonate; the potential of density separation to assess the original composition

This paper presents a new approach to the isotopic measurement of diagenetically altered archaeological bone apatite carbonate. We describe how the existing differential dissolution method may be combined with a new approach to remove diagenetically reformed material on the basis of its greater specific gravity. We show that heavier, more diagenetically altered fraction has a higher (altered) δ13C and also increased crystallinity within one individual. In addition, we proposed one potential tool to check the validity of bone carbonate by comparing bone collagen, enamel carbonate and bone carbonate values of δ13C and radiocarbon content from the same individual. In the case of Danebury cattle, we estimated the biogenic δ13Capa value for DC83 and DC89, although it is still difficult to overcome diagenesis in order to meet the expected value, which is shown to be 1.9‰ (DC83) and 3.5‰ (DC89).

Stable Isotope Chemistry of Bone Collagen and Carbonate Assessed by Bone Density Fractionation

This paper presents a stable isotope chemistry of bone collagen and carbonate. Bone carbonate has the potential to provide additional isotopic information. However, it remains controversial as to whether archaeological bone carbonate retains its original biogenic signature. I used a novel application of bone density fractionation and checked the integrity of <TEX>${\delta}^{13}C_{apa}$</TEX> values using radiocarbon dating. Diagenesis in archaeological bone carbonate still remains to be resolved in extracting biogenic information. The combined use of bone density fractionation and differential dissolution method shows a large shift in the <TEX>${\delta}^{13}C_{apa}$</TEX> values. Although <TEX>${\delta}^{13}C_{apa}$</TEX> values are improved in lighter density fractions, a large percentage of contamination in bone carbonate was reported via <TEX>$^{14}C$</TEX> dating compared to that noted with bone collagen.

Determination of the chemical composition of fiberglass silicate materials by the differential dissolution method

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.

Phase equilibrium and intermediate phases in the Eu–Sb system

Rapid heating rate thermal analysis, X-ray diffraction, fluorescence spectrometry, and differential dissolution method were used to study the high-temperature phase equilibrium in the Eu–Sb system within the composition range between 37 and 96 at% Sb. The techniques were effective in determination of the vapor–solid–liquid equilibrium since intermediate phases except Eu 4Sb 3 evaporated incongruently after melting. A thermal procedure was developed to determine the liquidus and solidus lines of the T−x diagram. Six stable phases were identified: two phases, EuSb 2 and Eu 4Sb 3, melt congruently at 1045±10 °C and 1600±15 °C, the Eu 2Sb 3, Eu 11Sb 10, Eu 5Sb 4, and Eu 5Sb 3 phases melt incongruently at 850±8 °C, 950±10 °C, 1350±15 °C, and 1445±15 °C, respectively. The exact composition shifting of Sb-rich decomposable phases towards Eu 4Sb 3, the most refractory compound, was determined. The topology of the Eu–Sb phase diagram was considered together with that of the Yb–Sb system.

Calculations and interpretation of the results of stoichiographic analysis of solid multi-element multi-phase compounds and materials

Methods and approaches to the calculations and interpretation of the results of stoichiographic analysis of solid multi-element multi-phase compounds and materials using the flow mode of the differential dissolution (DD) method are reported. Special features of calculationls as well as the objective reasons for the necessity of obtaining more or less precise results of stoichiographic calculations are discussed. The details of the procedure of stoichiographic calculations, refinement, and interpretation of the results are considered on an example of the DD-analysis of the Co-Ni-Fe-Bi-K-P-Mo-O/SiO2-catalyst for the selective oxidation and oxidative ammonolysis of hydrocarbons. The specific details and methods used for the estimation of the performance characteristics of the DD analytical procedure are discussed.

Determination of the chemical composition of supported vanadium-containing oxide catalysts by the differential dissolution method

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.

Stoichiography for investigation of the functional materials composition, structure, and properties

Principles of the stoichiography and differential dissolution method (DD) providing deep insight into the composition of mixtures containing unknown chemical compounds are considered. Compounds can be identified using their primary feature — the stoichiometry of elemental composition; reference samples of the compounds are not needed. The DD method makes it possible to analyze mixtures of crystalline and/or amorphous phases with constant and/or variable composition in the form of dispersed powders, ceramics, crystals, thin films and nanosize objects. Various aspects of the stoichiography and DD method application to investigation of composition, structure and properties of the functional materials are discussed.