Study of the preparation of ruthenia based catalytic materials by heating their precursors

Thermal behaviour of hydrous ruthenia (RuO₂·nH₂O) and ruthenia containing 10% titania ((RuO₂)_0.9–(TiO₂)_0.1nH₂O) was characterised on heating in air by emanation thermal analysis (ETA), thermogravimetry (TG), differential thermal analysis (DTA) and evolved gas analysis (EGA). The anhydrous ruthenia and ruthenia containing 10% titania samples were prepared by heating their hydrous precursors at 500°C in air. The temperature intervals of the samples dehydration and crystallisation were determined. XRD, TEM and surface area measurements were also used for the characterisation of the samples. The ETA results, evaluated by a mathematical model, brought about new information about surface area and microstructure development of the intermediate products of the oxides under in situ conditions of the heating in air. A good agreement between ETA and the results of other methods was obtained. The NO_x reduction by CO was used to test the catalytic properties of these samples.     

Reaction study of various mixtures of tetra ethyl ortho silicate and aluminum nitrate

Several studies on the formation of amorphous aluminosilicate phase during heating slow hydrolysis (SH) or Type 1 mullite gel prior to formation of 2:1 mullite is briefly reviewed. Tetra ethyl ortho silicate (TEOS) and aluminum nitrate nonahydrate (ANN) are isothermally heated on water bath at 80 °C. It has been shown that these react in an exothermic manner. The resultant isothermally heated gel (ISG) removes organics, moisture on heating and forms alumino silicate (A) precursor phase. Among the various mixtures of the two components, the batch composition corresponds to Al/Si ratio of 3/1 generates highest evolution of heat which suggests that precursor analogous to the composition of 3:2 mullite is most stable. Slow hydrolysis gels of different Al₂O₃:SiO₂ ratios synthesized out of similar sources exhibit 980 °C exotherm on DTA analysis which is a function of Al₂O₃ content. The highest exotherm is observed for the gel/precursor analogous to the same composition of the batch synthesized above by isothermal condition. Corroborating heat evolution behavior of ISG gels with DTA analysis of SH gels, it is suggested that the various compositions of intermediate aluminosilicate (A) phase may form. The composition corresponds to 3:2 mullite may be most stable.

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Application of inert radioactive gases in the study of solids

The behaviour of different iron salts (FeSO₄.7 H₂O, FeC₂O₄.2 H₂O, Mohr's salt, and basic iron carbonate) was studied by means of the emanation method, DTA and dilatometry. The salts were heated within the temperature range of 20 to 1100 C, under identical conditions. The results obtained are compared and the process of thermal decomposition of the different salts is discussed.The activity of ferric oxide obtained by decomposition of various iron salts is estimated, and it is suggested that the low activity of the sulphate-derived ferric oxides is related to a low thermal annealing rate, while the higher activities of the other two resultant ferric oxides are similarly related to higher thermal annealing rates.     

Preparation and study of YSTZ-Al2O3 nanocomposites

Yttria stabilized zirconia-alumina (YSTZ-Al₂O₃) nanocomposite system with various Al₂O₃ concentrations has been synthesized by sol-gel route. The experimental techniques XRD, DTA, TGA, FT-Raman, FT-IR, SEM, Vickers hardness measurements, density measurements and Impedance spectroscopy were used to characterize the synthesized specimens. DTA result shows two exothermic reactions: one around 760°C and another around 960°C. XRD results confirm that the specimen starts to crystallize on heating above 750°C. Well resolved XRD reflections corresponding to tetragonal (t) ZrO₂ were obtained after the specimens were heated at 1000°C. FT-Raman results confirmed that the crystallites developed above 750°C was t-ZrO₂. It was observed from the XRD and DTA results that the bulk and grain boundary region crystallize independently in two different temperatures with a difference in temperature of about 200°C. The crystallization temperatures increase with Al₂O₃ contents. At 1300°C, the pure YSTZ and 5 and 10 wt % Al₂O₃ added YSTZ specimens underwent structural transformation from tetragonal to monoclinic ZrO₂. But, the tetragonal symmetry remains stable at 1300°C with an addition of 15 wt % Al₂O₃. The system which retain its tetragonal symmetry at its processing temperature (1300°C) gives high hardness and maximum density values. Almost 100% theoretical density value was obtained at 1300°C with an addition of 15 wt % of Al₂O₃.     

Evaluation of crystallization kinetics of glasses by non-isothermal analysis

Based on Johnson-Mehl-Avrami transition equation, this paper proposes a new non-isothermal method for evaluating the crystallization kinetics of glasses. An equation relating the kinetic parameters of the crystallization activation energy, E, and the frequency factor, v, to the inflection-point temperature, T _f, and the heating rate, , of differential thermal analysis (DTA) experiment is established. The inflection-point temperature, T _f, can be easily determined from the derivative differential thermal analysis (DDTA) curves. The validity of the proposed method is ascertained by applying it to Li₂O·2SiO₂ glass. The acquired values of the crystallization kinetic parameters by this method are excellent agreement with the isothermal analysis results. In contrast, the traditional non-isothermal methods give much higher values.     

FTIR,DTA and XRD study of sphene (CaTiSiO5) crystallization in a ceramic frit and a non-borate base glass

The primary objective of this study has been the application of Fourier transform infrared (FTi.r.) absorption spectroscopy for both qualitative and quantitative characterization of sphene (CaTiSiO₅) crystallization in test materials; namely, a CaO-TiO₂-B₂O₃ bearing ceramic frit-S and a similar non-borate base glass-S. Differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscope/electron probe X-ray microanalysis (SEM/EPMA) techniques have also been used. FTi.r. absorption spectra have been shown to be capable of providing both qualitative and quantitative characterizations of crystal nucleation and growth in a frit-S and glass-S, being annealed between 800–1100° C. CaTiSiO₅ appears as the dominant phase and-cristobalite as the transitional phase in frit-S; whereas, -CaSiO₃ is dominant, CaTiSiO₅ being a minor phase in the non-borate glass-S. As given by DTA data, the intense stage of crystal growth for frit-S is about 120–125° C lower than that of glass-S. B₂O₃ content and the relative amounts of CaO and TiO₂ in the test specimens have been shown to give different modes of phase evolution and the onset temperature of nucleation. The activation energies,E _c, of crystal nucleation/growth was estimated by two different methods, namely, via DTA data and FTi.r. absorption spectra under the dominant surface nucleation mode for powder pellet specimens.E _c for CaTiSiO₅, -CaSiO₃ and-cristobalite in the frit-S and the non-borate base glass-S were estimated to be 219.6, 107.2 and 51.5 kJ mol^–1, respectively, parallel to the decreasing order of chemical complexity of the glass-forming system. Similar quantitative FTi.r. studies in the determination ofE _c for a broader scope of glass compositions, and compared with that based on XRD and DTA data, are to be encouraged so that the application of FTi.r. spectroscopy in glass-ceramics may be advanced.     

The critical properties of binary mixtures containing carbon dioxide: Krichevskii parameter and related thermodynamic properties

The values of Krichevskii parameter are given, which are calculated using the data on critical lines for binary CO₂ + solute mixtures (n-alkanes, alcohols, refrigerants, inert gases, water, diatomic gases, and other organic compounds), and detailed comparison is made with the results of other researchers obtained using different measuring techniques. In this review, special attention is given to the investigation of the thermodynamic (partial molar properties, Henry’s constant, distribution coefficient, solubility, and others) and structural (direct and total correlation integrals, size of clusters) properties of infinitely dilute solutions (IDS) of CO₂ + solute in the vicinity of the critical point (CP) of pure solvent (CO₂), for which purpose the values of Krichevskii parameter and the properties of pure solvent are used. The procedure is given of estimating the effect of small impurities on the accuracy of determination of the critical parameters of pure substances. The importance of critical lines (pattern and qualitative form) and of the Krichevskii parameter in the investigation of the scaling behavior (renormalization of the critical behavior) of thermodynamic functions of IDS in the vicinity of the CP of pure CO₂ is discussed in detail. The boundaries are determined of regions in the T-x and Δρ-x planes, in which the renormalization is observed of the critical behavior of weakly divergent (isochoric heat capacity) and highly divergent (isobaric heat capacity and isothermal compressibility) properties in CO₂ + solute mixtures.     

The synthesis of amorphous M-Si (M=transition metal) alloy powders by mechanical alloying

Crystalline powders of Si and M (transition metal) in the composition ratio Si M = 2 1 were mechanically alloyed by a laboratory ball mill in an inert atmosphere. The progress of the mechanical alloying was identified by X-ray diffraction. The amorphization reaction between Si and M proceeded according to a second-order reaction. The sequence of the rate of amorphization reaction for the Si-M system was Mn > Ti > V > Ni > Co. The sequence of the rate was correlated to the volume ratio (V _M/V_Si) of the Si-M system except for Si-Ni system. The crystallization of Si-Mn, of which the MA rate was fastest, was studied by means of X-ray diffraction, differential thermal analysis (DTA) and electrical resistivity measurement. We observed parallel changes on crystallization between the thermal event in the DTA tracing and the change of electrical resistance.     

Conversion of polycarbosilane (PCS) to SiC-based ceramic Part 1. Characterisation of PCS and curing products

A commercial polycarbosilane (PCS) preceramic polymer has been characterised as-received and following curing under a variety of conditions. Elemental analysis, gel permeation chromatography (GPC), infra-red spectroscopy (FT-IR), simultaneous thermogravimetric analysis-differential thermal analysis (TG-DTA) and solid state nuclear magnetic resonance (NMR) have been employed. A number average molar mass of 1200 was found with a broad molar mass distribution ( / = 2.97). Elemental analysis gave an empirical formula of SiC_2.2H_5.3O_0.3. IR and Solid state ²⁹Si and ¹³C NMR spectra showed the presence of Si-O-Si, SiC₄, SiC₃H, Si-Si, Si-CH₃ and Si-CH₂ groups. Simultaneous TG-DTA performed under an argon flow showed that there was a weight gain which started at approximately 240 °C. DTA showed an exotherm starting at this temperature showing that there was oxidation of the polymer even in an inert atmosphere. This is perhaps due to the oxygen in the PCS and there may also be some impurities in the inert atmosphere. Evidently the PCS is very sensitive to oxygen. Above 500 °C, weight loss dominated although the exotherm continued to approximately 700 °C. The effect of heating rate and dwell time at 200 °C on the changes in the chemical composition during curing have been explored using IR and solid state NMR spectroscopies, and elemental analysis. The longer the cure time the higher was the weight gain and greater was the extent of the oxidation reactions. Elemental analysis showed that the ratio of H and C to Si decreased with holding time at the cure-temperature while the amount of oxygen increased. Use of a higher heating rate resulted in a lower weight gain when the same holding time was used. From this it is clear that curing starts below the holding temperature.     

The crystallization of diabase glass

The crystallization behaviour of diabase glass at elevated temperatures was studied in samples prepared by melting the diabase rock. DTA and X-ray analyses revealed the crystallization of diopside (CaO · MgO · 2SiO₂) at 865 C and anorthite (CaO · Al₂O₃ · 2SiO₂) at 1060 C. Further, the kinetics of crystallization of diopside were studied. The phenomenological Johnson-Mehl-Avrami equation was used and the exponentn=3/2 determined from the dependency of the volume fraction of the crystal phase (diopside) on time. The activation energy of crystallization of diabase glass 248 kJ mol^–1 was estimated on the basis of DTA measurements carried out at different heating rates and found to be in good agreement with literature data for similar glass.     

Nucleation and crystallization kinetics of CaO-Al2O3-2SiO2 in powdered anorthite glass

The nucleation and crystallization kinetics of CaO-Al₂O₃-2SiO₂ crystals in powdered anorthite glass with particle size <44 m in which CaO-Al₂O₃-2SiO₂ crystals were found to crystallize in the heating process of the glass, were studied by nonisothermal measurements using differential thermal analysis (DTA). The temperature of maximum nucleation rate was determined from the DTA curves of samples heat treated at different temperatures. The activation energy and kinetic parameters were simultaneously calculated from the DTA data using previously reported kinetic models. The crystallization process of a sample heat treated at the temperature of the maximum nucleation rate was fitted to kinetic equations with an Avrami constant, n2 and a dimensionality of crystal growth, m2, indicating that the constant number of nuclei of CaO-Al₂O₃-2SiO₂ precipitated in a glass matrix grew two-dimensionally with an activation energy taken as an average of the values calculated by the Kissinger and also the Augis and Bennett method of 679±4 kJ mol^–1.     

Investigations of Ultrasound Propagation in Porous Impurity-Helium Solids

The velocity and attenuation of ultrasound passing through porous impurity-helium solids immersed in liquid ⁴He have been measured in the temperature range 1.1–2.3 K. These solids were formed by injecting a mixture of impurity (e.g. D₂, Ne, N₂ or Kr) and helium gases into superfluid ⁴He. The sound signal seemed to propagate mainly in the helium contained in the pores, rather than through the solid sample itself. We found that the speed of sound at low temperatures is close to and decreases more rapidly with temperature than first sound in bulk helium, similar to behavior observed in aerogel. The attenuation of sound in helium in the compressed impurity-helium solids is bigger than in bulk helium and increases rapidly with temperature up to 1.65 K, after which a crossover to a much weaker temperature dependence was observed.     

Thermal expansion and phase transformations of copper sulfides

The microstructure and phase transformations of copper sulfides have been studied by thermal analysis, microstructural analysis, and x-ray diffraction during heating in an inert atmosphere. The unit-cell parameters of Cu_1.8S, CuS, Cu_1.96S, and a Cu_1.8+x S (0 < x ≤ 0.2) solid solution have been determined as functions of temperature.     

The synthesis of the Nb3(Al-Ge) system by sputtering

The variation of the superconducting transition temperatureT _chas been studied in the Nb₃Al _1–x Ge _x system for0x1 for samples produced by rf sputtering onto heated substrates. The effect that different sputtering gas pressures have upon the rate of energy loss of the sputtered atoms due to collisions with neutral sputtering gas atoms is considered. Also considered is how thermalization can be achieved in the fewest number of collisions by matching the mass of the sputtering gas atoms to that of the sputtered atoms. For the case of Nb ₃ (Al-Ge) we show that it is advantageous to use a mixture of sputtering gases so that the light Al atoms can be thermalized as well as the heavier Nb and Ge atoms. It is also thus shown that the same sputtering conditions that are optimal for forming high-T _cNb₃Ge onto heated substrates are not optimal for forming high-T _cNb ₃ Al.Supported by CUNY FRAP and National Science Foundation DMR 74-18138.     

Effect of mechanical activation on thermal energy storage properties of Co3O4/CoO system

The heat produced by a solar receiver during on-sun operation can be employed to drive the endothermic reduction reaction of Co₃O₄ to CoO; then the consumed thermal energy can be recovered completely by the exothermic reverse oxidation reaction of CoO to Co₃O₄ which can take place during off-sun operation. In this research, the effect of mechanical activation duration (1, 2, 4, 8, and 16?h) on thermal energy storage by Co₃O₄/CoO redox pair was investigated. It was found that increasing the mechanical activation duration increases the sintering and particle size of the cobalt oxide powder after one cycle redox, and subsequently the thermal energy storage properties are declined. The weight loss was about 4–5?wt.% for samples heated by 1, 3, and 5?$°\text{C}$/min, while it was about 2?wt.% for 10?$°\text{C}$/min heating rate and less than 1?wt.% for 15?$°\text{C}$/min heating rate. The comparison of cycleability of as-received and 1?h mechanical activated cobalt oxide showed that mechanical activation weakens the cycleability of redox reactions of cobalt oxide. The as-received cobalt oxide cycleability continued up to three cycles, although the reduction and oxidation capacities gradually declined. The cycleability of 1?h mechanical activated sample entirely diminished after two cycles.     

Weak Binding Potentials and Wetting Transitions

We present ab initio calculations of the adsorption potentials V(Z) of inert gases and hydrogen on the surfaces of various metals. The ratio of the adsorption well depth to that of the adsorbate pair potential is 3.5, 2, 1.5, 1, 0.9 and 0.9 for adsorption on Mg, Li, Na, K, Rb, and Cs, respectively, with some variation between gases (always smallest for Ne). When this ratio is small, a wetting transition occurs; we predict the wetting temperature T _w using a model of Cheng et al. Comparison is made with other calculations and with experiments.     

Selection of ferrite powder for thermal coagulation therapy with alternating magnetic field

Selection of ferrite powder was carried out to realize a thermal coagulation technique in which tumors are locally heated by an application of alternating magnetic field from external coils. Magnesium ferrite (MgFe₂O₄) showed the largest increase in temperature (T) under an alternating magnetic field in all the ferrites examined. For all the samples, T value under alternating magnetic field was increased with an increase in frequency (200–500 kHz). The heating ability for the Mg-ferrite was ca. 1.4 W/g under alternating magnetic field of 4.0 kA/m (200 W, 370 kHz). The heating ability in alternating magnetic field was clearly depended on the magnitude of the hysteresis loss for the ferrite powder.     

Rare-gas mobility in some anisotropic ceramic oxides: Al2O3, Cr2O3, Fe2O3, TiO2, U3O8

The mobility of the inert gases xenon or radon in five anisotropic oxides (hexagonal corundum Al₂O₃, Cr₂O₃, Fe₂O₃, tetragonal rutile TiO₂, and orthorhombic U₃O₈) was studied. The gases were introduced by ion bombardment. The oxides were in the form of powders, sinters, or single crystals. Normal volume diffusion was found at low gas concentration, the activation energies in kilocalories per mole being 85 for Al₂O₃, 73±5 for Cr₂O₃, 68±5 for Fe₂O₃, 78±5 for TiO₂, and 85±8 for U₃O₈, and the pre-exponential termsD ₀ falling into the ideal range of about 3×10^–1±1 cm²/sec. Structural radiation damage, the annealing of which coincided with gas release at low temperatures, and, in some cases, retardation of the gas release were found at higher gas concentrations. Some evidence is presented that grain boundaries, pre-existing vacancy clusters, and dislocation loops may act as trapping sites for gas atoms (or bubbles) and may be stabilised after trapping of the gas.     

Electrical and thermal properties of ammonium and potassium oxalates

The d.c. electrical conductivity () and the relative permittivity () were accurately measured as a function of temperature in the range 300 < T < 450 K for ammonium oxalate monohydrate (AOX), (NH₄)₂ C₂O₄H₂O and potassium oxalate monohydrate (POX), K₂C₂O₄H₂O. Differential thermal analysis (DTA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) from 300 K up to 520 K were also performed for each compound. The data of the electrical parameters combined with the DTA and/or DSC thermograms suggest the existence of a possible change in the electrical conduction at 350 K for AOX and at 355 K for POX. Like most hydrogen-bonded molecules, the charge carriers may be protons and the electrical conduction is therefore protonic. At somewhat higher temperatures, dehydration and/or decomposition takes place in each compound and is reflected as a sudden loss in weight in the TGA plot.     

Post-deposition thermal treatments for improving the interconnection strength of a Ti-W/Au/Cu bonding system

The bonding combination of Ti-W/Au/Cu laminate strips deposited on an SiO₂/Si passivated substrate is strengthened through post-deposition age-hardening thermal treatment of the deposited metals in the amorphous state. For creating a copper layer of 10 m thickness at the top, both electrodeposition and physical vapour deposition (evaporation) methods are applied to obtain different strip properties. Peel tests, which can simulate the strip delamination process, are conducted to evaluate the strip-substrate bonding strength. A micro-mechanics analysis indicates that weak strip stiffness is a key cause for the frequent strip-substrate separations. Consequently, the laminate composite system is heated and cooled after deposition under different treatment conditions to strengthen the strip. The specimens are heated to a temperature of 220 to 400C, held there for a time and cooled quickly in air or water. The strengthening effect of the amorphous metals is obvious but complicated. The improved bonding strength will decrease again if the heating temperature is lower than 200C or the heating time is shorter than 50 min. At room temperature, indices of performance for strip-substrate bonding strength such as average peel force, peel energy and peak peel load continuously vary within approximately 100 h, depending upon the heating treatment history. Significant improvements of up to approximately 300% have been achieved according to peel strength tests. The sticking strength becomes so high after the thermal treatment that no part of a strip can initially leave its substrate during the tests.