Phase Composition of the Products of Fe Oxidation in Fe + C + NaCl + H2O + O2 Exothermic Mixtures

Using thermodynamic analysis of the Fe–C–NaCl–H₂O–O₂ system and experimental studies (x-ray diffraction and Mössbauer spectroscopy) of exothermic mixtures containing Fe metal, activated carbon, water, and NaCl, we identified the state of Fe and determined the phase composition of the reaction products at different stages of oxidation with atmospheric oxygen. The calculation and experimental results are in reasonable agreement. Under the conditions of restricted access for air, the main oxidation product is magnetite, Fe₃O₄. Free access for air leads to the formation of hydrous ferric oxide, Fe₂O₃ · nH₂O. The most stable phase under the conditions of interest is goethite, Fe₂O₃ · H₂O (-FeOOH). Storage of incompletely oxidized samples away from air for 7–14 days leads to partial reduction of iron(III) oxide phases to Fe₃O₄ and -Fe.     

Supercapacitive performance of hydrous ruthenium oxide (RuO<Subscript>2</Subscript>·<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O) thin films deposited by SILAR method

The amorphous hydrous ruthenium oxide (RuO₂·nH₂O) thin films were deposited by a simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method. These films were characterized for their structural, surface morphological, and compositional study by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDAX) techniques. The wettability test was carried out by measuring the water contact angle. The scanning electron microscopy study showed small RuO₂ particles are grouped together to form porous agglomerates. The FT-IR study confirmed the formation of hydrous ruthenium oxide films. The hydrophilic nature of ruthenium oxide (RuO₂·nH₂O) thin films was observed from water contact angle measurement. The presence of Ru and O in the film was confirmed by EDAX analysis. The supercapacitor behavior of these films studied in 0.5 M H₂SO₄ electrolyte showed maximum specific capacitance of 162 F g⁻¹ at 10 mV s⁻¹ scan rate. These films exhibit 80% cycling performance after 2,000 cycles. The charge–discharge studies carried at 1 mA cm⁻² current density revealed the specific power of 3.5 KW kg⁻¹ and specific energy of 29.7 W Kg⁻¹ with 93% coulombic efficiency.     

Formation of niobium-tantalum pentoxide orthorhombic solid solutions under chlorine-bearing atmospheres

This paper studies, by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDXS), the structural changes suffered by amorphous hydrated Nb oxide and mixtures of amorphous and crystalline Nb and Ta oxides subjected to thermal treatments in air and chlorine atmospheres. The air heating of amorphous Nb₂O₅·nH₂O leads to different crystalline phases depending on the working temperature. The hexagonal phase of Nb₂O₅ is obtained at 773 K and the monoclinic phase -Nb₂O₅ is obtained at 1173 K. The thermal treatment of amorphous Nb oxide in chlorine atmosphere decreases the temperature at which phase -Nb₂O₅ appears and at 1173 K the stable monoclinic phase -Nb₂O₅ is obtained. Air calcination for 5 hours at temperatures between 973 and 1273 K of different amorphous Nb₂O₅·nH₂O - Ta₂O₅·nH₂O mixtures does not lead to solid solution of these oxides. Thermal treatment in chlorine atmosphere of amorphous Nb and Ta oxides leads to the formation of Nb₂O₅ and Ta₂O₅ orthorhombic solution in one hour at 973 K and in 24 hours at 1223 K, when starting from crystalline oxides. The effect of chlorine is due to the dissolution-recrystallization of the metallic chlorides and the oxygen formed, when the system evolves to chemical equilibrium between solid phases and gaseous chlorine.     

Superconducting Properties of the 3-K Phase of Sr2RuO4 near Hc2

The superconducting transition temperature, T _c , of the impurity-free, intrinsic Sr₂RuO₄ is as high as 1.50 K. However, we recently showed that T _c is remarkably increased up to 3 K in the Sr₂RuO₄–Ru eutectic system, in which plate-like microdomains of Ru metal are embedded in the primary-phase Sr₂RuO₄. The phase diagram of the anisotropic upper critical field of the 3-K phase indicates that H _c2 for the field parallel to the RuO₂ plane is strongly suppressed at low temperatures. We argue that the reorientation of the Cooper-pair spin direction near the Sr₂RuO₄–Ru interface may be responsible for this suppression. In addition, we observed unusual hysteresis in the out-of-plane resistivity, _c , at low temperatures and near H _c2, only when the field was applied parallel to the RuO₂ plane.     

Synthesis and Properties of Neptunium(V) Propionates

From propionate-containing solutions of Np(V), the crystalline compounds NpO₂OOCC₂H₅·nH₂O with n = 1 or 2 and M(NpO₂)₂(OOCC₂H₅)₃·H₂O with M = NH₄ or Cs were separated. Their X-ray powder patterns were recorded and behavior at heating was studied. The IR and electronic absorption spectra suggest that, in these compounds, the NpO₂ ⁺ ions are coordinated with each other to form cation-cation bonds involving all yl oxygen atoms.     

Synthesis, Structure, and Properties of Ammonium Polyvanadomolybdate Xerogels

Powders and films of (NH₄)_{2 – x} H _x V_{12 – y} Mo _y O_{31 ±} · nH₂O (0 x 2, 0 y 3) xerogels with a layered structure were prepared for the first time. According to IR spectroscopy data, the V–O–Mo layers in the xerogels are similar to those in the delta vanadium bronze (NH₄)_0.5V₂O₅. X-ray photoelectron spectroscopy shows that the vanadium and molybdenum in the xerogels are mainly in the oxidation states 5+ and 6+, respectively. The materials also contain small amounts of V⁴⁺and OH^–. The thermal stability of the materials increases with Mo content. The electrical conductivity of the films depends on air humidity and reaches a maximum at the composition (NH₄)_1.5H_0.5V₉Mo₃O_{31 +} · nH₂O. At temperatures in the range 20–70°C and air humidity between 12 and 59%, the activation energy of conduction is very low.     

The Superconducting and Normal-State Transport Properties in Pure, Pr-Doped, and Ca-Doped NdBa2Cu3O7?y

We report detailed studies of the superconducting and normal-state transport properties in NdBa₂Cu₃O_7–y , Nd_0.9Ca_0.1Ba₂Cu₃O_7–y , and Nd_0.8Pr_0.2Ba₂Cu₃O_7–y , systems. We found a linear temperature dependence of resistivity and the Hall number n _H above T _c. For a given sample n _H, which is inconsistent with any simple transport model in science (1/n). However, and n _H at a fixed temperature for these three samples follow a relation 1/n _H. This is evidence that n _H could scale with actual mobile carrier concentration. The unit cell volume V is a linear function of n _H. The T _c –V–n _H diagram indicates that there exist an optimal concentration n _H and an optimal V for T _c in these systems.     

Structural changes of glass-ceramics of the Cu2O-Al2O3-SiO2 system on heating in air

The behaviour of copper ions in low thermal expansion glass-ceramics prepared from Cu₂O · Al₂O₃ ·_nSiO₂ glasses, or in-spodumene type Cu₂O · Ae₂O₃ ·nSiO₂ crystals included in the glass-ceramics on heating in air was investigated. On hewing at 300 to 500° C, the copper ions behaved as in the corresponding glasses. Cuprous ions in the glass-ceramics or-spondumene type crystals were oxidized into the cupric state, and at the same time an equal amount of cuprous ions to those oxidized were expelled out of the specimen for the requirement of electrical charge neutrality and then reacted with oxygen to form CuO on the surface. The oxidation of cuprous ions and the decrease of the copper content of the-spondumene type crystals brought about a considerable decrease in the lattice spooings.     

Hydrous zirconium dioxide: interfacial properties,the formation of monodisperse spherical particles,and its crystallization at high temperatures

The characteristics of hydrous zirconia gels obtained by hydrolysis of highly acidic ZrOCl₂ · 8H₂O solutions at 100C are described. Under adequate conditions, monodisperse spherical hydrous zirconia is obtained. The role of sulphate and chloride ions is described. The gel has a large water content, indicating only modest crosslinking. Crystallization upon heating takes place with the formation of both monoclinic and tetragonal zirconia polymorphs; X-ray line widening studies do not indicate a particle size-crystal structure correlation. On the basis of this observation and using Stranki's rule, the crystallization sequence upon heating is rationalized. Surface properties of hydrous zirconia are discussed on the basis of electrophoretic measurements, and compared with those of baddeleyte. The site binding model is not very adequate to describe these systems, and the existence of a very thin gel-like region at the baddeleyte-water interface is postulated.     

Surface roughness and mechanical properties of melt-spun Al-Cu ribbons

Al, Al-5.23, Al-13.46 and Al-33 wt% Cu ribbons with different thicknesses,t, have been prepared by chilled block melt spinning under different processing conditions. Surface roughness, taken as peak to valley values,R _t, measured on both the substrate and air sides of the ribbon, shows great dependence on substrate velocity,v, ejection gas pressure,P, nozzle height above the substrate,H, and a lesser dependence on substrate thermal conductivity,k, and melt superheat, T. The bulk density over all the zones shows an increase over conventionally cast alloys of 7.4% for Al-33 wt% Cu and about 3% for aluminium. Microhardness,H _n, measurements inside each of the three microstructure zones, which were identified across the ribbon section, show variation witht asH _n =H _o t ^–m, where the constantH _o depends on the microstructure zone andm depends on the alloy composition. The zone at the substrate side has the highestH _n values and that at the air side has the lowest ones. The number of bending cycles to fracture, which is taken as a measure of ductility, increased with ribbon thickness and decreased with copper content.     

Quarter-wave design criteria for omnidirectional structural colors

Structural colors are caused by light interference from periodic multi-layer dielectric stacks and exhibit rich, highly-chromatic colors. However, avoiding a color shift due to angular variation remains a challenge. The design criteria for angle-independent structural colors have been studied by treating a quarter-wave stack of alternating dielectric material layers as a one-dimensional photonic crystal. A refractive index zone has been identified that exhibits narrowband omnidirectionality for structural colors in the visible wavelength range. It was found that a quarter-wave stack of high refractive index (RI) paired-layers (n _H = 2.85 and n _L = 2.5), which have low RI contrast (n _H /n _L = 1.14), is key in fabricating omnidirectional structural color materials. The theoretical predictions discussed here are verified experimentally using a titania/halfnia (TiO₂/HfO₂) multilayer stack.     

Study of some aspects of the reactivity of La2O3 with CO2 and H2O

The behaviour of three different samples of La₂O₃ on exposure to atmoshperic CO₂ and H₂O and the influence of the origin is discussed. The thermal evolution of the samples, stabilized in air for months or even years, has been studied by TG, TPD, IR spectroscopy and X-ray diffraction. BET surface areas of the samples were determined from the corresponding nitrogen adsorption isotherms at 77 K. In all three samples, hydration and carbonation occur in bulk. In accordance with our results, lanthana samples stabilized in air would consist of lanthanum hydroxide, La(OH)₃, partially carbonated, La₂(OH)_6–3x (CO₃) _x ,(x1). When hexagonal phases of La₂O₃, obtained by calcining, at 1130 K, the samples stabilized in air were re-exposed, hydration and carbonation levels similar to those observed in the stabilized samples were reached after less than 24 h. Some lanthana samples were soaked in water, at 298 K, and then dried at 380 K. In this way, the evolution of the oxide when treated under similar conditions to those used in both impregnation and ion exchange techniques for preparation of supported metal phases, could be investigated.     

Magnetic relaxation rates in spin-polarized hydrogen

A self-contained discussion is presented of the longitudinal (T ₁ ^–1 ) and transverse (T ₂ ^–1 ) relaxation rates in bulk and surface samples of spin-polarized atomic hydrogen (H), at sufficiently low temperatures that only the lowest two atomic hyperfine levels are thermally populated. The nonhydrodynamic contribution to the rates, due to binary collisions between hydrogen atoms, in both normal and Bose condensed samples of H are emphasized. However, the approach is general and is equally well suited for treating long-wavelength, hydrodynamic relaxation processes. Most of the discussion pertains to samples close to thermodynamic equilibrium. The calculation of the longitudinal relaxation rate for some states far from equilibrium, particularly relevant for real samples of H, is also presented. Some of the interesting results are:(1) the potentially long surface longitudinal relaxation time (T ₁) in samples with most of the available surface area oriented perpendicular to the direction of the stabilizing field; (2) the possibility of extracting the condensate fractionn _o(T)/n from aT ₁ measurement in the Bose condensed state, and finally (3) an amusingGedanken experiment that would allow us to detect the onset of Bose condensation in aT ₁ measurement in the absence of recombination.     

Polymorphic transformation of titanium dioxide by mechanical grinding

The effect of mechanical grinding on the structural transformation of titanium dioxide was studied by using several anatase samples prepared from different starting materials and with various particle sizes. Three anatase samples were prepared by hydrolysis of Ti(O·i-C₃H₇)₄, TiCl₄, and TiOSO₄·2H₂O and one is commercial reagent grade anatase. Each of the as-prepared or heat-treated samples (1.0 g) was ground in a mortar of sintered alumina for up to 96 h in air. The stability of brookite synthesized by grinding was examined by heating in air and under hydrothermal pressure. From the relative amount of the phases estimated by the measurement of the integrated intensity of X-ray line profile and of X-ray crystallite size, DTA and TG, IR spectra, and observation by electron microscope, it is concluded that: 1. the transformation proceeds by a consecutive process from anatase to rutile through brookite by grinding; 2. the smaller the initial particle size of anatase, the more stable the intermediate phase of brookite; 3. the very fine crystals of 520 nm of anatase can be grown to 50150 nm of rutile by grinding for 96 h; 4. the rate process of the transformation depends on the initial particle size and is independent of the difference in starting materials or of surface adsorbants; 5. an appropriate lattice distortion introduced by grinding is considered to stabilize the brookite phase; and 6. the lattice constant and the density of brookite synthesized by grinding,a ₀=0.5447±0.005 nm,b ₀=0.9150±0.0005 nm,c ₀=0.5141±0.0005 nm, andD _x =4.14 g cm^–3 agree with those in natural brookite.     

Ion exchange of intercalation compounds from WOP2O7 and intercalation ofn-alkylamines

Ion exchange of Na _x WOP₂O₇ ·nH₂O (x 1.4) prepared from WOP₂O₇ was attempted, using alkaline and alkaline earth ions. The degree of exchange was observed to be >50% at 90° C except for Mg²⁺. The basal spacing of ion-exchanged materials for the hydrated phase were dependent on the number of water molecules in the interlayer spaces, while those for the dehydrated phase increased with the size of ions in the interlayer spaces. The network of water molecules linked by the hydrogen bond in the interlayer spaces seems to determine the basal spacing. By the ion-exchange reaction,n-alkylammonium ions were intercalated into the interlayer spaces of Na _x WOP₂O₇ ·nH₂O (x 1.4) and Sn _x H _y WOP₂O₇ ·nH₂O (2x +y 0.5). In spite of the difference in the charge density of the host layer, a similar arrangement of alkyl chains in the interlayer spaces resulted, and neutral amines were considered to be intercalated as well as ammonium ions. Direct reaction ofn-alkylamine with WOP₂O₇ produced an intercalation compound without reduction of tungsten. The arrangement of the amines in the interlayer spaces is similar to that supposed to the ion-exchanged derivatives when heated at 140° Cin vacuo.     

Reactions between mercury-wetted aluminium and liquid water

The reaction of solid aluminium with liquid water has been studied by several investigators. In this paper, the reaction between mercury-wetted aluminium and liquid water is described. At 25 and 90 °C, the reaction products were identified by X-ray diffraction analysis as bayerite,-Al₂O₃.3H₂O, and boehmite,-Al₂O₃.H₂O, respectively. The transitions of these hydrates to-Al₂O₃ upon heating were indicated by endothermic peaks on DTA thermograms and weight-loss measurements by TGA.The wetting mercury film acts as a medium for rapid transport of aluminium in solution from the solid-liquid interface to the liquid-vapour or liquid-liquid interface. This unique condition produces readily identifiable materials since it avoids some of the difficulties encountered by other investigators in their attempts to study the reactions of air and liquid water directly with aluminium foil or bulk samples.     

Cobalt basic salts as inorganic precursors of cobalt oxides and cobalt metal: Thermal behaviour dependence on experimental conditions

The influence of heating rates and environment conditions on the thermal behaviour of two cobalt basic salts,-Co₂(OH)₃Cl and Co₅(OH)_8.5Cl_1.5 · 2.5H₂O, have been studied. The processes were followed using thermogravimetric and differential thermal analysis, X-ray diffraction, and infrared spectroscopy. When decomposition reactions are carried out in a nitrogen atmosphere, Co₃O₄ is always formed in quantities that seem to depend on the heating rates. When decomposition processes are carried out in an X-ray high-temperature diffraction chamber, pure cobalt is obtained at 750° C as the final product. Green cobalt hydroxychloride, the composition of which determined from chemical analysis seems to correspond to the formula Co₅(OH)_8.5Cl_1.5 · 2.5H₂O or alternatively 4Co(OH)₂. CoCl_1.5(OH)_0.5 · 2.5H₂O, has been isolated as a stable compound and the evolution of this material during the ageing process has been followed by X-ray diffraction, electron microscopy and BET surface-area determination.     

Kinetics of gas-phase conversion of U<Subscript>3</Subscript>O<Subscript>8</Subscript> into water-soluble compounds in nitrating atmosphere at 25–30°С

The kinetics of the gas-phase conversion of U₃O₈ in NO_x–H₂O (vapor)–air and HNO₃ (vapor)–H₂O (vapor)–air atmospheres was fitted by the Kazeev–Kolmogorov–Erofeev equation. The following parameters n and K were obtained: for experiments in NO_x–H₂O (vapor)–air atmosphere, n = 0.2 ± 0.1 and K = 0.2 ± 0.2 h^–1; for experiments in HNO₃ (vapor)–H₂O (vapor)–air atmosphere, n = 0.3 ± 0.2 and K = 0.03 ± 0.02 h^–1 (confidence probability p = 0.95). For the U₃O₈ conversion in both media, n < 0.5, which suggests the diffusion control of the U₃O₈ conversion under the action of both HNO₃ and NO_x.     

The synthesis and thermal behaviour of zinc diphosphates

Zinc diphosphates (Zn₂P₂O₇ · 5H₂O, Zn₂P₂O₇ · 3H₂O, 5K_1.4Zn_1.3P₂O₇ · 16H₂O, and 5K_0.8Zn_1.6P₂O₇ · 9H₂O) were made by the wet process. The composition of the products was dependent on the conditions (concentration, pH, and dropping rate of the solution) of the process. When the products were heated, decomposition of the diphosphates to orthophosphate took place below about 150 ·C. Polymerization of the phosphates to phosphates with longer chains was observed in the temperature range 150 to 400 ° C. The amorphous phosphates thermally produced by heating diphosphates other than 5K_1.4Zn_1.3P₂O₇ · 16H₂O, showed reorganization to diphosphate above 400 ° C according to the reaction M₂O₃PO[P(O₂M)O] _n PO₃M₂ +nM₃PO₄(n + 1)M₄P₂O₇ where M represents K and/or 1/2Zn.     

Characterization and metastability of alkoxy-derived tetragonal zirconia powder

The zirconia powders were synthesized through the hydrolysis of zirconiumn-butoxides with air moisture as well as with aqueous solutions of different pH values to investigate the metastability of tetragonal (t)-ZrO₂. The SEM and TEM observations reveal that powders prepared with air moisture hydrolysis consist of spherical particles of 0.5–3.5 m diameter, while gel-like powders composed of finer particles were obtained with aqueous solution hydrolysis. The samples obtained show different crystallization and tetragonal/monoclinic transformation temperatures on differential thermal analysis. The metastability of t-ZrO₂, investigated in terms of relative content with X-ray diffraction, was not explicable through the crystallite size effect. Instead, the existence of unpaired electrons, detected using electron paramagnetic resonance, and the strain within the powders, were found to be probably influential in affecting the metastability of t-ZrO₂.