Mechanically Stimulated Thermal Synthesis of Lithium Pentaaluminate from Lithium Carbonate and Aluminum Hydroxide

It is shown that the phase composition of lithium aluminates formed when aluminum hydroxide in the form of gibbsite interacts with lithium carbonate in their mixture with Al: Li atomic ratio of 5: 1 depends on the duration of a preliminary mechanical activation of the mixture and on the temperature of the subsequent thermal treatment. A thermal treatment of the starting mixture at temperatures exceeding 800°C yields LiAl₅O₈ with a substantial admixture of α- and γ-LiAlO₂. Raising the duration of the mechanical activation to 5 min and more makes it possible to obtain highly dispersed single-phase LiAl₅O₈ with a specific surface area larger than 20 m² g^–1     

Dehydration of lithium iodide crystal hydrate in vacuum

Dehydration of the LiI · 3H₂O crystal hydrate in vacuum has been investigated at 20–25°C. The decomposition of the LiI · 3H₂O crystal hydrate in vacuum proceeds to monohydrate. During heating of lithium iodide monohydrate, evolution of water vapor is observed at 30–100 and 100–170°C. Above 200°C, evolution of molecular oxygen is observed, possibly, because of the decomposition of lithium peroxide that is formed in side reactions during the decomposition of lithium iodide crystal hydrate.     

Broad-Range Detection of Water Vapor using Cavity Ring-down Spectrometer

Quantitative measurement of water vapor is essential in many fields including semiconduc-tor industry, combustion diagnosis, meteorology, and atmospheric studies. We present an optical hygrometer based on cavity ring-down spectroscopy. The instrument is high-vacuum compatible, self-calibrated by using the free-spectral-range of the ring-down cavity made of low-thermal-expansion Invar. Using a single tunable diode laser working at 1.39 μm, detection of trace water vapor in vacuum and in high-purity helium gas, and also determination of humidity at ambient conditions, have been demonstrated. It indicates that the instrument can be used to detect the partial pressure of water vapor in a very broad range from 10^-7 Pa to 10³ Pa. Such an optical hygrometer can be potentially applied as a primary moisture standard to determine the vapor pressures of water (ice) at low temperatures.     

Thermal stability of aluminium hydroxycarbonates with monovalent cations

Dawsonite-type compounds of formula MAl(OH)₂CO₃ (M = Na. K, NH₄) as well as a laminar hydrotalcite-type hydroxycarbonate of composition [Al₂Li(OH)₆]₂CO₃·4H₂O. have been hydrothermally synthesized The thermal decomposition of these compounds was monitored by DTA and TG, and the resulting products have been studied by X-ray and IR techniques. Sodium and potassium dawsonites are destroyed at 335°C. yielding a poorly crystalline compound in which part of the overall carbonate is present; the remaining carbonate is lost between 600 and 700°C, yielding NaAlO₂ and KAlO₂, respectively Ammonium dawsonite and lithium hydrotalcite are less stable, their thermal decomposition occurring at about 240°C. The ammonium dawsonite heated at 680°C shows the presence of A1₂O₃ with a poorly ordered structure, while lithium hydrotalcite yields poorly crystalline γ-Al₂O₃ at 500°C and a mixture of γ-LiAlO₂ and LiAl₅O₈ when the compound is heated at higher temperatures ( ~ 1000°C).     

Zur Koordination des Aluminiums im β-LiAlO2

On the Coordination of Al in β-LiAlO₂ By using ²⁷Al-NMR and the determination of the contribution of Al₂O₃ to the molar refractivities, the octahedral coordination of Al in α-LiAlO₂ respectively the tetrahedral coordination in γ-LiAlO₂ has been confirmed. For β-LiAlO₂ the results show that there only tetrahedrally coordinated Al occurs, contrary to earlier statements given in literature.     

Thermal behaviour of the copper-substituted cobalt hydroxide fluoride series CuxCo1−x(OH)F

The basic salt cobalt(II) hydroxide fluoride was obtained by partial hydrolysis of a 0.2M solution CoF₂. Mixed Co(II)·Cu(II) hydroxide fluorides with an isomorphic substitution of Co(II) by Cu(II) ions up to 20% were also prepared. XRD data obtained on these compounds indicate that they are single-phase compounds, their X-ray powder patterns being almost identical to the Co(OH)_0.7F_1.3 diagram, with Zn(OH)F-type structure. However, their stoichiometries are very close to Co_1?xCu_x(OH)F (0≤x≤0.2). Thermal analysis studies carried out up to 1273 K in still air or under dynamic vacuum conditions show that in air CoO or a mixture of CoO and CuO is formed as final product. In vacuum, at high temperature, with a Ta heating surface, pure α-Co or a mixture of α-Co and Cu is formed at about 973 K.     

On the Reactions Occurring in the CaO?Cr2O3?O2 system

The reactions occurring in the system CaO? Cr₂O₃? O₂ have been investigated. In the mixture of two oxides heated in air to higher temperature calcium chromate and chromite are being formed. The rate and the ratio of the two reactions is very sensitive to the composition of gaseous atmosphere, especially to the partial pressure of oxygen. The formation of spinel was accelerated by a small amount of oxygen but was partly or fully suppressed at a higher oxygen pressure on the expense of chromate formation. The oxidation of CaO? Cr₂O₃ was also studied kinetically. Detailed measurements in different gaseous atmospheres were performed with doped CaO and Cr₂O₃. The results were interpreted in the light of the defect structure of the reacting oxides.     

Mass spectrometric studies of lithium-containing oxides at high temperature

The sublimation and vaporization of various lithium containing oxides have been studied by high temperature mass spectrometry. The installed Knudsen cell apparatus gave some useful information about the vapor species, appearance potentials, partial pressures and heats of reactions involved. The investigated oxides are Li₂O, Li₂O-Al₂O₃, Li₂O-MoO₂ and Li₂O-SiO₂ systems. This paper mainly presents the most recent data for the Li₂O-SiO₂ system. A relationship for the decomposition reaction of ortho-Li₄SiO₄ was deduced. The heat of the reaction was determined by the third law method.The activity of the Li₂O component in the double oxides was estimated from the partial pressures of the vapor species. γ-LiAlO₂ and meta-Li₂SiO₃ showed fairly low activities in comparison with Li₂O oxide. The activity coefficients decreased with the Li₂O mole fraction in the lithium compounds.The heats of formation and atomization of LiO and Li₂O gaseous species were determined.     

Thermal decomposition of managanese oxyhydroxide

Temperature-programmed thermal decomposition of γ- and α-manganese oxyhydroxide has been studied between 20 and 670°C under vacuum and under a low pressure (10 Torr) of oxygen. Solid products at various temperatures have been analyzed by X-ray diffractometry. Under vacuum γ-MnOOH decomposed below 400°C to a mixture of Mn₅O₈, α-Mn₃O₄, and water according to the reaction scheme: 8MnOOH → Mn₅O₈ + Mn₃O₄ + 4H₂O. Above this temperature Mn₅O₈ was converted to α-Mn₃O₄ as a result of oxygen removal. The vacuum dehydration at 250°C of oxyhydroxide rich in α-MnOOH led to the formation of a new modification of Mn₂O₃ isostructural with corundum (α-Al₂O₃). In oxygen both oxyhydroxides decomposed to β-MnO₂. γ-MnOOH transformed directly to β-MnO₂ while α-MnOOH appeared to transform via corundum-phase Mn₂O₃ as an intermediate.     

High-temperature X-ray study of the formation and delamination of manganese-alumina spinel Mn<Subscript>1.5</Subscript>Al<Subscript>1.5</Subscript>O<Subscript>4</Subscript>

The behavior of the manganese-alumina system with Mn:Al = 1:1 on heating in air and vacuum was studied. The starting samples were mixtures of β-Mn₃O₄, α-Mn₂O₃, and γ-Al₂O₃. On heating to 950°C in air, the samples were partially oxidized into α-Mn₂O₃, and corundum α-Al₂O₃ formed along with mixed manganese-alumina cubic spinel, whose composition was close to Mn₂AlO₄. In vacuum at 1200°C, the starting sample with a ratio of Mn:Al = 1:1 transformed into the manganese-alumina spinel Mn_1.5Al_1.5O₄, which retained its cubic structure after slow cooling in vacuum. When cooled in air, this solid solution delaminated, and a nanocrystalline Mn_2.8Al_0.2O₄ phase formed, whose structure was β-Mn₃O₄ type tetragonal spinel.     

A novel approach for synthesis of nanocrystalline γ-LiAlO2 from spent lithium-ion batteries

Synthesis of nanocrystallite γ-LiAlO₂ from spent lithium-ion batteries has been investigated. XRD results show that γ-LiAlO₂ phase can be synthesized by thermal treatment of the cathode material over its aluminum sheet at 800–900 °C for 2 h. This is accompanied with the formation of Co₃O₄ and CoO phases as colored powders. SEM investigation revealed the formation of dense grains as coconut-like shape structure of γ-LiAlO₂ phase. Comparatively, reaction of chemical grade Al powder with LiOH in stoichiometric ratio at 800 °C gives γ-LiAlO₂ phase of cotton-like morphology.     

The effect of different atmospheres on structural changes of titanate nanotubes during heating

Thermal stability of titanate nanotubes (Ti-NT) was studied in temperature range from room temperature up to 1000 °C in three different atmospheres—in air, vacuum and helium—and differences were observed. In air, vacuum and helium, the release of adsorbed and crystal water was detected in temperatures up to 200 °C. Transformation of the initial structure to anatase form of TiO₂ was found independently of the atmosphere used. But in air the transformation to anatase occurred at lower temperature. The difference between these atmospheres was approximately 100 °C. However, only in air, the transformation to sodium hexatitanate and rutile form of TiO₂ occurred at higher temperatures. In vacuum, only the anatase phase was detected up to 800 °C. In helium, the transformation to rutile was observed but not to sodium hexatitanate. The changes of the initial structure of Ti-NT during the elevation of temperature were studied by combination of in situ powder X-ray diffraction, differential scanning calorimetry, thermal gravimetric analysis and mass spectroscopy.     

Experimental Vapor Pressures and Derived Thermodynamic Properties of Aqueous Solutions of Lithium Nitrate from 423 to 623 K

Vapor pressures of six aqueous lithium nitrate solutions with molalities of (0.181, 0.526, 0.963, 1.730, 2.990, and 5.250) mol-kg^–1 have been measured in the temperature range 423.15–623.15 K with a constant-volume piezometer immersed in a precision liquid thermostat. The static method was used to measure the vapor pressure. The total uncertainty of the temperature, pressure and composition measurements were estimated to be less than 15 mK, 0.2%, and 0.014%, respectively. The vapor pressures of pure water were measured with the same apparatus and procedure to confirm the accuracy of the method used for aqueous lithium nitrate solutions. The results for pure water were compared with high-accuracy P_S–T_S data calculated from the IAPWS standard equation of state. Important thermodynamic functions (activities of water and lithium nitrate, partial molar volumes, osmotic coefficient, excess relative partial molar entropy, and relative partial molar enthalpy values of the solvent) were derived using the measured values of vapor pressure for the solution and pure water. The measured and derived thermodynamic properties for solutions were compared with data reported in the literature. The present results are consistent with most previous reported thermodynamic data for the pure water and H₂O + LiNO₃ solutions at low temperatures.     

Physical and chemical properties of silicon carbonitride nanocrystalline films

Nanocrystalline transparent films SiC_xN_y were obtained by plasma-enhanced chemical deposition within the temperature range 473–1173 K from low pressure gas phase from a mixture of hexamethyldisilazane vapor, ammonia, and helium. Physical chemical properties of the films obtained were studied by IR and Raman spectroscopy, ellipsometry, X-ray photoelectron spectroscopy, scanning electron microscopy, high resolution transmission electron spectroscopy and synchrotron radiation powder diffaction. Voltage-capacity and voltage-current measurements were also made. The dependence of chemical and phase composition of the films on deposition conditions was determined, and the formation of approximately 2 nm sized spherical nanocrystals within the films was established. The nanocrystals are formed by a phase similar to usual α-Si₃N₄, with silicon atoms partially substituted by carbon ones.     

Electric properties of oxyfluorides Ba2In2O5−0.5x F x with brownmillerite structure

Synthesis of fluoro-substituted substances based on brownmillerite Ba₂In₂O₅ is carried out. The width of the homogeneity region of the Ba₂In₂O_5?0.5x F _x (0 < x ≤ 0.25) solid solution was established using X-ray analysis. Measurement of temperature dependences of conductivity in atmospheres with different partial pressure of water vapor (pH₂O = 3.3 and 2 × 10³ Pa) showed an increase in conductivity at T ≤ 550°C in a humid atmosphere, which is due to appearance of proton transport. The dependence of conductivity on partial oxygen pressure (pO₂ = 0.21 × 10⁵ to 10^?15 Pa) is studied in the temperature range of 500–1000°C; ion transport numbers are calculated. The method of polarization measurements was used to determine transport numbers of fluoride. Total conductivity is divided into ion (proton, oxygen, and fluoride ion) and electron components. Analysis of concentration dependences of conductivities showed that low concentrations of fluoride allow increasing both the total and partial conductivities (oxygen-ion and proton) and, besides, allow shifting the “order-disorder” phase transition by 100°C to the low temperature range.     

Synthesis of lithium ferrite by precursor and combustion methods: A comparative study

The thermal decomposition of lithium hexa(carboxylato)ferrate(III) precursors, (Li₃[Fe(L)₆]·xH₂O, L = formate, acetate, propionate, butyrate), has been carried out in flowing air atmosphere from ambient temperature upto 500 °C. Various physico-chemical techniques, i.e., TG, DTG, DTA, XRD, SEM, IR, Mössbauer spectroscopy, etc., have been employed to characterize the intermediates and end products. After dehydration, the anhydrous complexes undergo decomposition to yield various intermediates, i.e., lithium oxalate/acetate/propionate/butyrate, ferrous oxalate/acetate and α-Fe₂O₃ in the temperature range of 185–240 °C. A subsequent decomposition of these intermediates leads to the formation of nanosized lithium ferrite (LiFeO₂). Ferrites have been obtained at much lower temperature (255–310 °C) as compared to conventional ceramic method. The same nano-ferrite has also been prepared by the combustion method at a comparatively lower temperature (400 °C) and in less time than that of conventional ceramic method.     

Influence of Water Vapor on Silica Membrane: Adsorption Properties and Percolation Effect

The influence of water vapor on silica membrane with pore size of 4 ? has been investigated in terms of adsorption properties and percolation effect at 50 and 90 oC. Two methods are employed: spectroscopic ellipsometry for water vapor adsorption and gas permeation of binary mixture of helium and H₂O. The adsorption behaviors on the silica membrane comply with the first-order Langmuir isotherm. The investigation demonstrates that helium flux through the silica membrane decreases dramatically in presence of H₂O molecules. The transport of gas molecules through such small pores is believed not to be continuous any more, whereas it is reasonably assumed that the gas molecules hop from one occupied site to another unoccupied one under the potential gradient. When the coverage of H₂O molecules on the silica surface increases, the dramatic decrease of helium flux could be related to percolation effect, where the adsorbed H₂O molecules on the silica surface block the hopping of helium molecules.     

Higher hydrates of lithium chloride,lithium bromide and lithium iodide

For lithium halides, LiX (X = Cl, Br and I), hydrates with a water content of 1, 2, 3 and 5 moles of water per formula unit are known as phases in aqueous solid–liquid equilibria. The crystal structures of the monohydrates of LiCl and LiBr are known, but no crystal structures have been reported so far for the higher hydrates, apart from LiI·3H₂O. In this study, the crystal structures of the di‐ and trihydrates of lithium chloride, lithium bromide and lithium iodide, and the pentahydrates of lithium chloride and lithium bromide have been determined. In each hydrate, the lithium cation is coordinated octahedrally. The dihydrates crystallize in the NaCl·2H₂O or NaI·2H₂O type structure. Surprisingly, in the tri‐ and pentahydrates of LiCl and LiBr, one water molecule per Li⁺ ion remains uncoordinated. For LiI·3H₂O, the LiClO₄·3H₂O structure type was confirmed and the H‐atom positions have been fixed. The hydrogen‐bond networks in the various structures are discussed in detail. Contrary to the monohydrates, the structures of the higher hydrates show no disorder.     

High-Temperature Oxidation Resistance of PDC Coatings in Synthetic Air and Water Vapor Atmospheres

This work is aimed at the development and investigation of the oxidation behavior of ferritic stainless-steel grade AISI 441 and polymer-derived ceramic (PDC) protective coatings. Double-layer coatings of a PDC bond coat below a PDC top coat with glass and ceramic passive fillers’ oxidative resistance were studied at temperatures up to 1000 °C in a flow-through atmosphere of synthetic air and in air saturated with water vapor. Investigation of the oxide products formed at the surface of the samples in synthetic air and water vapor atmospheres, at different temperatures (900, 950, 1000 °C) and exposure times (24, 96 h) was carried out on both uncoated steel and steel coated with selected coatings by scanning electron microscopy (SEM) and X-Ray diffraction (XRD). The Fe, Cr₂O₃, TiO₂, and spinel (Mn,Cr)₃O₄ phases were identified by XRD on oxidized steel substrates in both atmospheres. In the cases of the coated samples, m- ZrO₂, c- ZrO₂, YAG, and crystalline phases (Ba(AlSiO₄)₂–hexacelsian, celsian) were identified. Scratch tests performed on both coating compositions revealed strong adhesion after pyrolysis as well as after oxidation tests in both atmospheres. After testing in the water vapor atmosphere, Cr ions diffused through the bond coat, but no delamination of the coatings was observed.     

Irradiation of some polysiloxanes in various gases

The changes produced by γ-irradiations on two polysiloxanes in several gaseous atmospheres were studied by both sequential and parallel exposures with an in-situ vibrating reed technique. Irradiation in atmospheres of N₂O, He, air, and a mixture of 20% NO₂ and 80% N₂, caused reduction in the crosslinking rates of the polymers as compared to vacuum. Marked discolorations of the samples occurred when irradiations were conducted in air, N₂O, and 20% NO₂–80% N₂. Similarities in crosslinking rates and color changes were obtained when the polymers were irradiated in either air or the gas mixture.