Study Of Solid-state Reaction Research Articles

Application of thermogravimetric analysis in study of solid-state reaction between barium oxalate and uranyl oxalate

Alkaline earth metals and their oxides have an important role while deciding the postirradiation processing of irradiated fuels from the reactors. The reaction between uranyl oxalate and barium oxalate has been studied using thermogravimetric analysis. Oxalates of uranium and barium were prepared, and their thermal decomposition in argon environment has been studied. It has been observed that uranyl oxalate decomposes into mixture of U3O8 and UO2.13 with the evolution of carbon monoxide, oxygen and carbon dioxide in the temperature range of 573–673 K, but beyond this temperature U3O8 and UO2.13 appeared as intermediate and the final product has been found to be UO2.12. In case of solid-state reaction of barium oxalates, it has been observed that the reaction pathway of its decomposition is altered in the presence of uranium oxide. Barium oxalate first decomposes to barium carbonate followed by the reaction with uranium oxide at a relatively high temperature during the next step in TG. XRD characterization of the intermediates and end products indicated that BaUO4 is formed which gets partially reduced to BaUO3 at elevated temperature.

Study of solid-state reactions and order-disorder transitions in Pd/α-Fe(001) thin films

The formation of the hard-magnetic ordered L10-FePd phase in thin bilayer Pd/α-Fe(001) films has been experimentally studied. Solid-state reactions initiated by thermal heating in bilayer Pd/α-Fe(001) films with a thickness of 50–60 nm (the atomic ratio Pd: Fe ≈ 50: 50) separated from the substrate have been studied using the in situ electron diffraction methods. It has been shown that the solid-state reaction between the palladium and iron layers in Pd/α-Fe(001) starts at 400°C with the formation of the disordered Fe-Pd phase. At 480°C, the ordered L10-FePd phase is formed. The order-disorder phase transition has been studied. It has been established that the transition of the ordered L10-FePd phase to the disordered FePd phase starts at 725°C. At 740°C, only the disordered FePd phase is present over the whole volume of the film. The observed temperature of the order-disorder phase transition is shifted from the equilibrium value by 35°C to higher temperatures. This effect is assumingly associated with the higher concentration of palladium atoms at the boundaries of the Fe-Pd crystal grains owing to the grain-boundary adsorption.

Solid-state Reaction Study on Physically and Tribochemically Prepared BaC2O4-SnC2O4 Mixtures

The synthesis of barium metastannate, BaSnO3, by heating mixtures of metal oxalates, either physically mixed or subjected to a phase of mechanical activation, up to temperatures in the range 750- 1200 °C has been studied. Simultaneous thermogravimetric-differential scanning calorimetric (TGDSC) analyses and powder X-ray diffractometry have been applied to check the advancement of the reactions. BaSnO3, though slightly contaminated by BaCO3, can be obtained by heating the activated mixture up to T ≥ 1000 °C while heating a sample of a physical mixture at temperature as high as 1200 °C resulted in a mixture of BaSnO3, SnO2 and Ba2SnO4. The heat capacities of BaSnO3 samples prepared at temperatures between 1000 and 1200 °C have been measured by modulated temperature differential scanning calorimetry (MTDSC) in the temperature range 50-400 °C.

Thermal and electrochemical study of solid-state reaction of mercury with Pt–20% Rh alloy

Thermogravimetry (TG), energy dispersive X-ray microanalysis (EDX), scanning electron microscopy (SEM), mapping surface and X-ray diffraction (XRD) have been used to study the reaction of mercury with platinum–rhodium (Pt–Rh) alloy. The results suggest that, when heated, the electrodeposited Hg film reacts with Pt–Rh to form intermetallic compounds each having a different stability, indicated by separate third mass-loss steps. In the first step, between room temperature and 170 °C, only the bulk Hg is removed. From this temperature to about 224 °C, the mass loss can be attributed to decomposition of the intermetallic PtHg4. The third step, from 224 to 305 °C, can be ascribed to thermal decomposition of solid solution composed of intermetallic species RhHg2 and PtHg2. Intermetallic compound such as PtHg4, PtHg2, and RhHg2 was characterized by XRD. These intermetallic compounds were the main products formed on the surface of the samples after partial removal of the bulk mercury via thermal desorption.

Study of solid-state reaction in Pb(Zr,Ti)O3ceramics doped with (Fe2+, Ni2+, Sb3+) ions

Study of solid-state reaction in Pb(Zr,Ti)O₃ceramics doped with (Fe²⁺, Ni²⁺, Sb³⁺) ions

In situsimultaneous Raman/XRPD study of solid-state reactions at non-ambient conditions

<i>In situ</i>simultaneous Raman/XRPD study of solid-state reactions at non-ambient conditions

Study of solid-state reactions in Sm(Co, Fe, Cu, Zr) z 2:17-type alloys by means of in situ electrical resistivity measurements

In the present work, solid-state reactions in Sm 2(Co, Fe, Cu, Zr) 17-type alloys have been investigated by means of in situ electrical resistivity measurements. Changes in the electrical resistivity of a Sm(Co 0.74Fe 0.1Cu 0.12Zr 0.04) 8.5 alloy after solid solution treatment at 1190 °C, quenching to room temperature, and during isothermal ageing at temperatures between 400 and 900 °C, have indicated microstructural/phase changes occurring at temperatures below those commonly used for the development of high coercivity in Sm(Co, Fe, Cu, Zr) z -type materials. Subsequent crystallographic and magnetic transition measurements have shown a high degree of correlation with respect to the changes observed in the electrical resistivity during isothermal ageing.

Differential scanning calorimetry in studies of solid-state reactions in photochromic materials

Differential scanning calorimetry (DSC) was employed to study the kinetics of reverse thermally driven reactions in polycrystalline samples of three photochromic compounds. Results obtained on two dihydropyridine derivatives were critically re-examined and compared with results of the experiments performed with an acridizinium salt. Heat flow curves, measured on samples previously irradiated with UV, exhibited broad exothermic anomalies at elevated temperatures (above ca. 320K for dihydropyridines and above ca. 490K for the acridizinium salt), observed only once after irradiation and attributed to bleaching reactions. The activation energies of bleaching reactions in the dihydropyridine derivatives, determined from fractional heating experiments, amount to ca. 90–170kJ/mol. Exact determination of the distribution of activation energies proved difficult due to uncertainties with a proper setting of baselines.

Microbalance and Related Studies of High-temperature Superconductors

Many properties of oxide superconductors depend on the oxygen concentration and its distribution in the samples. The microgravimetric method is very useful to study of oxide superconductors, as it allows investigations in vacuum and controlled environments in classical applications: thermogravimetric analysis for the study of solid-state reactions, determinations of oxygen contents in redox reactions and the combined measurement of mass and additional parameters, e.g. evolved gas analysis etc. Single-phase samples of high-temperature superconductors were synthesized from stoichiometric mixtures of high-purity oxides and carbonates. Appropriate amounts of the precursor powders were homogenized manually or by a mechanical ball mill and subsequently calcined at temperatures in the 800 to 950°C range with intermediate grinding to ensure homogenous reaction. The lattice parameters of all preparations were controlled, in both initial and final experiments, by the X-ray powder method (CuKα radiation), using a Stadi P (Stoe) diffractometer with a position-sensitive detector. It is well known that temperature and mass can be measured with an accuracy higher by orders of magnitude than it is still possible for the thermoanalyst to determine the transformation temperatures or the mass changes due to overlapping partial reactions. Applications of Cahn microbalance to study of high-temperature superconductors are presented.

Use of Pt Markers in the Study of Solid-State Reactions in the Presence of an Electric Field

The use of Pt to mark the initial location of heterophase boundaries in solid-state reactions was extended to investigate the motion of interfaces during a thin-film solid-state reaction between In2O3 and MgO in the presence of an electric field. The Pt markers were prepared by sputtering a thin Pt film onto a single-crystal substrate. The resulting multilayer was then heated prior to thin-film deposition to de-wet the Pt film and thus form an array of small, isolated particles. These particles serve as fine-scale markers for tracking the motion of interfaces. However, there are certain situations in which the markers can move with the interface.

TEM studies of solid-state reactions in sputter-deposited Nb/Al multilayer thin films

Solid state reactions in sputter-deposited Nb/Al multilayer thin films have been studied by transmission and analytical electron microscopy (TEM/AEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The Nb/Al multilayer thin films for TEM studies were sputter-deposited on (1102)sapphire substrates. The periodicity of the films is in the range 10-500 nm. The overall composition of the films are 1/3, 2/1, and 3/1 Nb/Al, corresponding to the stoichiometric composition of the three intermetallic phases in this system.Figure 1 is a TEM micrograph of an as-deposited film with periodicity A = dA1 + dNb = 72 nm, where d's are layer thicknesses. The polycrystalline nature of the Al and Nb layers with their columnar grain structure is evident in the figure. Both Nb and Al layers exhibit crystallographic texture, with the electron diffraction pattern for this film showing stronger diffraction spots in the direction normal to the multilayer. The X-ray diffraction patterns of all films are dominated by the Al(l 11) and Nb(l 10) peaks and show a merging of these two peaks with decreasing periodicity.

A new approach to the study of solid-state reactions in oxide ceramics

Thin-film reactions have potential applications for the production of buffer layers in heterojunctions and for the reaction bonding of materials. The main drawback to these applications at present isthat the effect of interface morphology on the initial kinetics of solid-state reactions is not well understood. In order to study the kinetics and mechanisms of thin-film reactions in oxide ceramics, a new method has been developed. The approach relies on the production of a well characterized high-quality oxide thin film on a single-crystal oxide substrate which makes up the idealized reaction couple-a ‘single-crystal’ thin film in intimate contact with a single crystal substrate. The thin-film approach localizes the reaction near the surface of the specimen so that conventional cross-sectioning techniques can be utilized. Additionally, the scale of the reaction is of the order of tens of nanometers or less which is ideally suited to high-resolution SEM or conventional TEM.NiO/α-Al2O3 is a model system for the study of solid-state reactions.

Thermoanalytical study of the formation of compounds in the PbO−MO (M=Ca, Sr, Ca+Sr) system

In order to clarify the effect of PbO addition on the formation steps of the superconducting phases in the system Bi2O3−SrO−CaO−CuO, a study of solid-state reactions under non-isothermal conditions, in the PbO−MO (M=Ca, Sr, Ca+Sr) system has been carried out.

Solid-state reaction study on the system Ni-Li 2CO 3

Thermogravimetry, differential scanning calorimetry, X-ray diffractometry and scanning electron microscopy have been used to investigate the formation reaction of the solid solution Li x Ni 1− x O in the solid-state system Ni-Li 2CO 3. Thermogra vimetric results show that carbonate decomposition takes place well below its usual temperature when nickel is being oxidized and that as a consequence of the simultaneous oxidation and decomposition processes, a solid solution forms in a temperature range where no appreciable volume diffusion can occur. X-ray diffraction measurements confirm this conclusion showing that lattice constant values of thermogravimetric samples linearly decrease with increasing mixture lithium content. Notwithstanding all experimental evidences agree in indicating that all lithium oxide participates to solid solution formation, sensible departures from the linear relationship arise for mixtures of high lithium content (X Li>0.2010). It is shown that cation vacancies are responsible of such a behaviour and that their concentration increases with increasing the relative amount of lithium oxide produced by spontaneous carbonate decomposition that enters solid solution.

The Early Stages of the Spinel-Alumina Phase Transformation

ABSTRACTThe initial stage of topotactic growth of Ni-Al spinel into Al2O3has been examined using transmission electron microscopy. A new experimental approach to the study of solid-state reactions, which may be adapted for in-situ experiments for low-temperature systems, has been used in this study. In its present form, the technique involves heating a thin film of one oxide in the presence of a vapor of the second oxide. In the study of the growth characteristics of Ni-Al spinel phase, the orientation of the Al2O3substrate has been found to influence greatly both the structural and morphological aspects of the spinel growth. In particular, the topotactic relationship between the spinel and the alumina are very different for (0001) and {1120} substrate orientations. The very early stage of the kinetics of the spinel growth, in which the length and the width of the spinel particles are only a few hundred angstroms, is illustrated with the results obtained from the re-heating experiments. The structure of the spinel-alumina interface has also been studied using high-resolution electron microscopy. These results are discussed in relation to the different models proposed for the spinel-alumina phase transformation.

A new approach to the study of solid-state reactions

Abstract A new technique for the study of solid-state reactions is described. The new approach uses a thin-film specimen geometry and is ideal for transmission-electron-microscopy studies of the same specimen before and after the Occurrence of solid-state reactions. The technique of illustrated by an investigation of the growth of Ni-Al spinel on, and into, an alumina substrate. Near-topotactic relationships and exact topotactic alignment of the spinel and the alumina were both found. The {111} plane of the spinel is parallel either to the (00011) plane of the alumina or to the {1120} plane of the alumina. Further heat treatment of such samples directly reveals the mechanism by which the spinel particles grow.

Study of solid-state reactions in the NiO/Fe2O3 system

Solid-state reactions in the NiO/Fe2O3 system have been investigated in the temperature range 1100 to 1300° C, The optical microscope and the electron probe microanalyser were used. Kinetic parameters of the calcination process of this system: the reaction rate, time exponent and activation energy, have been determined by observing the changes in the reaction layer thickness with time and temperature. The analysis of the reaction layer composition was the basis for discussion concerning the possible mechanism of this reaction.

Precautions a prendre dans l'emploi des thermobalances

Based on 25 years of experience of the pyrolysis of several thousands of inorganic and organic substances with. reference to gravimetric analysis, studies of volumetric standards and studies of solid-state reactions, the author attempts to explain the disagreements in results obtained by users of various models of thermobalances. These differences are traced to 10 main causes: the type of apparatus, the thermocouple, the nature of the substance involved, the weight of this substance, the rate of heating, the nature of the atmosphere around the crucible, the gas flow-rate in the furnace, the nature and shape of the crucible, the sensitivity of the recorder trace, and the nature and weight of the residue.

Compound Formation and Crystal Structure in the System ZnO-TiO2

In addition to the well-known zinc orthotitanate (Zn2TiO4) and zinc metatitanate (ZnTiO3), the study of solid-state reactions in the system ZnO-TiO2 disclosed a previously unrecognized compound, Zn2Ti3O8. This compound was obtained when sulfate-containing hydrous titanium oxide of anatase structure was reacted with ZnO at 700° to 900° C. It crystallized in a defect spinel structure with eight Zn2+ ions occupying the tetrahedral positions and twelve Ti4+ ions distributed in sixteen octahedral positions (a0= 8.395 ± 0.002 a.u.). Crystallographic data are given for zinc orthotitanate and metatitanate. Formation of the latter compound appeared to be favored by rutile TiO2 sources and those readily convertible to rutile under the reaction conditions.

Synthetic Mica Investigations: II, Role of Fluorides in Mica Batch Reactions

Various fluorides were studied to determine which might be suitable for the synthesis of fluor‐phlogopite mica (K2Mg6Al2Si6O20F4). K2SiF6, MgF2, K2AlF5, and K3AlF6 are preferred in that order. KF, KMgF3, AlF3, KAlF4, and MgSiF6· 6H2O are less suitable for the purpose. Solid‐state reaction studies were made on the following binary partial systems of the mica batch: MgF2+ MgO, 3MgF2+ Al2O3, 2MgF2+ SiO2, 3MgF2+ KAlSi3O8, K2SiF6+ 3MgO, K2SiF6+ Al2O3, K3AlF6+ 3MgO, and K3AlF6+ 3SiO2. Solid‐state reaction studies on various types of fluor‐phlogopite batches showed that this mica compound can be synthesized at temperatures as low as 750°C. For best results, however, it should be done at 1000° to 1300°C. in closed containers, using anhydrous batch materials to minimize hydrolysis of the fluorides and loss of HF. Many of the mica batches expand as they react in the solid state, and there is danger in large‐scale experiments that the container may break unless heating is rapid between 750° and 1200°C.