Thermoelectric characterization of NaxMx/2Ti1−x/2O2 (M=Co, Ni and Fe) polycrystalline materials

Layered -titanate materials, Na_xM_x/2Ti_1−x/2O₂ (M=Co, Ni and Fe, x=0.2–0.4), were synthesized by flux reactions, and electrical properties of polycrystalline products were measured at 300–800 °C. After sintering at 1250 °C in Ar, all products show n-type thermoelectric behavior. The values of both d.c. conductivity and Seebeck coefficient of polycrystalline Na_0.4Ni_0.2Ti_0.8O₂ were ca. 7×10³ S/m and ca. −193 μV/K around 700 °C, respectively. The measured thermal conductivity of layered -titanate materials has lower value than conductive oxide materials. It was ca. 1.5 Wm⁻¹ K⁻¹ at 800 °C. The estimated thermoelectric figure-of-merit, Z, of Na_0.4Ni_0.2Ti_0.8O₂ and Na_0.4Co_0.2Ti_0.8O₂ was about 1.9×10⁻⁴ and 1.2×10⁻⁴ K⁻¹ around 700 °C, respectively.     

A new experimental device for pyrolysing coal particles under controlled conditions over a wide range of heating rates

CSIRO has designed and built a new device for pyrolysing coal under closely controlled conditions over a range of heating rates from 10⁻¹ to 10⁴ °C/s. The coal is placed in a stainless-steel mesh which is heated electrically in a cell under a controlled atmosphere. The heating rate is precisely rectilinear even at the highest or lowest heating rates. The terminal temperature (up to 1000 °C) can be held on a selected plateau for 10⁻² to 10² s before the sample cools by simple heat dissipation.     

Electrical conductance of KI in anhydrous acetonitrile

The electrical conductivity of KI solutions in anhydrous acetonitrile has been determined at 0, 25 and 35°C in the concentration range 0·9– 600 × 10⁻⁴ mole/l. The values of Λ₀, K and a calculated from the results are, respectively: 145·9 mho/cm, 0·95 × 10 ⁻² and 1·72 Å at 0°C; 186·2 mho/cm, 8·98 × 10⁻² and 4·6 Å at 25°C; and 204·8 mho/cm, 5·17 × 10⁻² and 3·5 Å at 35°C. The phoreograms at all the three temperatures are catabatic at lower concentration, but become anabatic at 0·017, 0·022 and 0·024 respectively, at 0, 25 and 35°C.     

Comparative study of lithium ion conductors in the system Li1+xAlxA2−x (PO4)3 with A=Ti or Ge and 0≤x≤0·7 for use as Li sensitive membranes

Preparations and physico-chemical characterizations of NASICON-type compounds in the system Li_1+xAl_xA_2−x^IV(PO₄)₃ (A^IV=Ti or Ge) are described. Ceramics have been fabricated by sol-gel and co-grinding processes for use as ionosensitive membrane for Li⁺ selective electrodes. The structural and electrical characteristics of the pellets have been examined. Solid solutions are obtained with Al/Ti and Al/Ge substitutions in the range 0≤x≤0·6. A minimum of the rhombohedral c parameter appears for x about 0·1 for both solutions. The grain ionic conductivity has been characterized only in the case of Ge-based compounds. It is related to the carrier concentration and the structural properties of the NASICON covalent skeleton. The results confirm that the Ti-based framework is more calibrated to Li⁺ migration than the Ge-based one. A grain conductivity of 10⁻³ S cm⁻¹ is obtained at 25°C in the case of Li_1·3Al_0·3Ti_1·7(PO₄)₃. A total conductivity of about 6×10⁻⁵ S cm⁻¹ is measured on sintered pellets because of grain boundary effects. The use of such ceramics in ISE devices has shown that the most confined unit cell (i.e. in Ge-based materials) is more appropriate for selectivity effect, although it is less conductive.©     

Mercury-mercurous propionate electrode: standard potentials at different temperatures and related thermodynamic quantities

The standard molal potentials E°_m of the Hg/Hg₂(OPr)₂, OPr⁻ electrode at 15°, 20°, 25°, 30° and 35° C have been determined. The E°_m values obtained are 0.5114, 0.5072, 0.5031, 0.4988 and 0.4942 V respectively, which can be fitted to the equation Edg_m/V = 0.5031 −8.56 × 10⁻⁴ (itt/°C − 25)−3.0588 × 10⁻⁶ (t/ °C -25)². The changes in standard free energy, entropy and enthalpy for the cell reaction have been calculated.     

水蒸气/氧流化床两段煤气化制备低焦油合成气工艺实验

由下行床热解和提升管（或输送床）气化组合形成的流化床两段气化将煤气化反应过程解耦为煤热解和半焦气化两个反应阶段,热解产物完全进入气化反应器,利用其中的高温环境和输送的半焦催化作用分别实现焦油的热裂解与催化裂解,完成低焦油气化。利用该流化床两段气化的10 kg/h级实验室工艺实验装置,以榆林烟煤为原料、水蒸气/氧气作为气化剂,变化过量氧气系数ER、蒸汽炭比S/C、热解及气化温度等参数,研究水蒸气/氧流化床两段煤气化制备低焦油合成气的特性。结果表明,流化床两段气化系统可实现稳定运行（实验3 h以上）,在ER=0.36和S/C=0.15时,热解和气化的代表温度分别稳定在735℃和877℃,合成气的CO、CO₂、H₂、CH₄、C _n H _m 和N₂含量分别为14.33%、10.07%、18.39%、9.89%、1.82%和45.50%,相应的合成气产量达到1.8 m³/kg,低位热值8.99 MJ/m³,焦油含量0.437 g/m³,展示了制备低焦油合成气的技术特征。对于实际的长时间连续运行,更高的气化温度将使流化床两段气化具有更好的低焦油特性。     

水蒸气/氧流化床两段煤气化制备低焦油合成气工艺实验

由下行床热解和提升管（或输送床）气化组合形成的流化床两段气化将煤气化反应过程解耦为煤热解和半焦气化两个反应阶段,热解产物完全进入气化反应器,利用其中的高温环境和输送的半焦催化作用分别实现焦油的热裂解与催化裂解,完成低焦油气化。利用该流化床两段气化的10 kg/h级实验室工艺实验装置,以榆林烟煤为原料、水蒸气/氧气作为气化剂,变化过量氧气系数ER、蒸汽炭比S/C、热解及气化温度等参数,研究水蒸气/氧流化床两段煤气化制备低焦油合成气的特性。结果表明,流化床两段气化系统可实现稳定运行（实验3 h以上）,在ER=0.36和S/C=0.15时,热解和气化的代表温度分别稳定在735℃和877℃,合成气的CO、CO₂、H₂、CH₄、C _n H _m 和N₂含量分别为14.33%、10.07%、18.39%、9.89%、1.82%和45.50%,相应的合成气产量达到1.8 m³/kg,低位热值8.99 MJ/m³,焦油含量0.437 g/m³,展示了制备低焦油合成气的技术特征。对于实际的长时间连续运行,更高的气化温度将使流化床两段气化具有更好的低焦油特性。     

In situ XAFS investigation of Ca and K catalytic species during pyrolysis and gasification of lignite chars

A newly developed X-ray absorption fine structure (XAFS) spectroscopy technique was used to examine, in situ, the catalytic behaviour and properties of highly dispersed carboxyl-bound Ca and K in lignites, chars and related materials during pyrolysis and gasification. With this technique, the spectral changes noted for Ca at temperatures up to 420 °C were relatively minor (peak broadening, enhancement of minor pre-edge features, and slight Ca---O bond distance contraction) and not fully reversible. Such changes are consistent with rearrangement of the Ca site due to loss of volatile species molecules from the immediate coordination sphere around Ca. For K, similar minor changes were found during pyrolysis to 420 °C, but upon exposure to O₂ and an increase in temperature to 500 °C, significant nonreversible spectral changes were observed that appeared consistent with transformation of the K catalytic species into K₂CO₃.     

Conductivity of Na5+xYAlxSi4-xO12 ceramics

A series of ceramics samples, Na_5+xYAl_xSi_4-xO₁₂, has been prepared by a solid state reaction with the starting materials of SiO₂, Y₂O₃, Al₂O₃ and Na₂CO₃. Their crystalline structure and morphology have been studied by the determination of XRD, IR, TG, DTA and SEM. Their conductivity has been measured by means of the complex impedance method. The dependence of the conductivity and density of the samples on the amount of the added Al₂O₃ and the reaction between the conductivity and the temperature have been discussed. When x = 0, the density of the sintering sample is 90% T.D., and the conductivity is 1·48 x 10⁻¹ (ωcm)⁻¹ at 300°C; when x = 0·1, the density is up to 97% T.D., and the conductivity up to 1·74 x 10⁻¹ (ω cm)⁻¹ at 300°C.     

Methacryl-terminated macromers by living polymerization as precursors of IPN polymer electrolytes

A new class of polymer electrolytes, based on the interpenetrating polymer network approach, was obtained starting from functionalised macromers, of poly-ether nature, in the presence of a lithium salt (LiBF₄, LiClO₄, LiCF₃SO₃) and propylene carbonate (PC) or tetraethyleneglycol dimethylether (TGME), as plasticizers.

The macromers were synthesised by living polymerisation employing a HI/I₂ system as the initiator. The macromer has a polymerisable end group, which can undergo radical polymerisation, attached to a monodisperse poly-vinylether, containing suitable ethylene oxide groups for ion coordination. Monomers and macromers were characterised by FTi.r., u.v.–vis, ¹H- and ¹³C-n.m.r.

Self-consistent and easily handled membranes were obtained as thin films by a dry procedure using u.v. radiation to polymerise and crosslink the network precursors, directly on suitable substrates, in the presence of the plasticizer and the lithium salt. The electrolytic membranes were studied by complex impedance and their thermal properties determined by differential scanning calorimetry analysis.

Ionic conductivities (σ) were measured for PC and TGME-based membranes at various plasticizer and salt contents as a function of T (60 to −20°C). LiClO₄/PC/PE electrolytes, with 3.8% (w/w) salt and 63% PC, have the highest σ (1.15×10⁻³ and 3.54×10⁻⁴ S cm⁻¹ at 20°C and −20°C, respectively). One order of magnitude lower conductivities are achieved with TGME; samples with 6% (w/w) LiClO₄ and 45% (w/w) TGME exhibit σ values of 2.7×10⁻⁴ and 2.45×10⁻⁵ S cm⁻¹ at 20°C and −20°C.     

Adsorption of methane/ethane mixtures on dry coal at elevated pressure

The binary adsorption characteristics of methane and ethane on dry coal to 40 atm pressure have been calculated from pure-component isotherms. In some coal seams, pressures exceeding 40 atm have been recorded and the methane sampled from the virgin coal often shows a few percent of ethane. The binary adsorption characteristics were calculated by employing the ideal adsorbed solution theory of Myers and Prausnitz, and experimentally-determined (Type I) pure gas isotherms at 0, 30 and 50 °C. The coal used in this investigation was high-volatile ‘A’ bituminous (hvab) from the Pennsylvania Pittsburgh seam. Gas nonideality was accounted for by replacing pressure with fugacity. Adsorption of methane on dry coal is purely physical; the isosteric heat of adsorption does not exceed 2.4 kcal/mol^* at 30 °C on the above coal. Isobars on the resulting binary equilibrium diagram exhibited an unexpected phenomenon of intersecting each other which might be attributable to the above nonideality considerations. The region of a few percent of ethane, which is of practical importance from the viewpoint of coal seams, was expanded and reduced to an equation: V(CH₄) = −21.52 + 7.18(VF) + 16.88(VF)² −0.395(P) − 0.00661(P)² + 0.824(T) − 0.00030(T)² + 0.928(VF)(P) − 0.858(VF)(T). V(Total) = 25.9 − 23.6(VF) + 0.655(P) − 0.00875(P)² − 0.795(T) + 0.743(VF)(T) where V(CH₄) and V(Total) = cm³(STP)CH₄ and total gas respectively adsorbed per g dry coal; VF = vol. fraction of methane as analysed at 1 atm (0.94 VF 1.0); P = seam pressure, atm (0 P 40); T=seam temperature, °C(−10 T 50).     

Catalytic decomposition of nitrous oxide over Ru-exchanged zeolites

We report that ultrastable faujasite-based ruthenium zeolites are highly active catalysts for N₂O decomposition at low temperature (120–200°C). The faujasite-based ruthenium catalysts showed activity for the decomposition of N₂O per Ru³⁺ cation equivalent to the ZSM-5 based ruthenium catalysts at much lower temperatures (TOF at 0.05 vol.-% N₂O: 5.132 × 10⁻⁴ s⁻¹ Ru⁻¹ of Ru-HNaUSY at 200°C versus 5.609 × 10⁻⁴ s⁻¹ Ru⁻¹ of Ru-NaZSM-5 at 300°C). The kinetics of decomposition of N₂O over a Ru-NaZSM-5 (Ru: 0.99 wt.-%), a Ru-HNaUSY (Ru: 1.45 wt.-%) and a Ru-free, Na-ZSM-5 catalyst were studied over the temperature range from 40 to 700°C using a temperature-programmed micro-reactor system. With partial pressures of N₂O and O₂ up to 0.5 vol.-% and 5 vol.-%, respectively, the decomposition rate data are represented by: −dN₂O/dt=itk(P_N2O) (P_O2)^−0.5 for Ru-HNaUSY, −dN₂O/dt=k(P_N2O) (P_O2)^−0.1 for Ru-NaZSM-5, and −dN₂O/dt=k(P_N2O)^−0.2 (P_O2)^−0.1 for Na-ZSM-5. Oxygen had a stronger inhibition effect on the Ru-HNaUSY catalyst than on Ru-NaZSM-5. The oxygen inhibition effect was more pronounced at low temperature than at high temperature. We propose that the negative effect of oxygen on the rate of N₂O decomposition over Ru-HNaUSY is stronger than Ru-NaZSM-5 because at the lower temperatures (<200°C) the desorption of oxygen is a rate-limiting step over the faujasite-based catalyst. The apparent activation energy for N₂O decomposition in the absence of oxygen is much lower on Ru-HNaUSY (E_a: 46 kJ mol⁻¹) than on Ru-NaZSM-5 (E_a: 220 kJ mol⁻¹).     

Synthesis of nanocrystalline 8 mol% yttria stabilized zirconia powder from sucrose derived organic precursors

An organic precursor synthesis of 8 mol% yttria stabilized zirconia (YSZ) powder from Zr–Y composite nitrate solution and sucrose has been studied. Oxidation of sucrose in Zr–Y composite nitrate solution containing excess nitric acid in situ generates hydroxy carboxylic acids that forms a white sol which showed peaks at 1640 cm⁻¹ and 1363 cm⁻¹ in IR spectrum corresponding to hydroxy carboxylic acid complexes of Zr and Y. Precursor mass obtained by drying the sol on calcinations at 600 °C produced loosely agglomerated particles of cubic YSZ. Deagglomerated YSZ contain submicron particles with D₅₀ value of 0.5 μm and the particles are aggregates of nanocrystallites of nearly 10 nm size. Compacts prepared by pressing the YSZ powder sintered to 96.7% TD at 1450 °C. The sintered YSZ ceramic showed an average grain size of 2.2 μm.     

Electrical conductivity and thermal expansion of Bi2O3 doped with Pr

Electrical conductivity and thermal expansion of Bi₂O₃ doped with 15 and 25 mol% prasoeodymia have been studied, named BP15 and BP25 respectively. The crystal phases formed in the sintered oxides and their lattice parameters were determined by X-ray diffraction (XRD). The electrical conductivity was measured in air by means of both impedance spectroscopy and the four-point DC technique within the temperature range 100–850°C. Thermal expansion coefficient measurements were carried out using the dilatometry technique. The results derived show the formation of a single rhombohedral phase in both cases which appears to be stable up to 680°C. The electrical conductivity is thermally activated exceeding 1·0 and 0·7 S/cm at 850°C for the compositions BP15 and BP25 respectively. The thermal expansion coefficient is highly non-linear and varies between 6 and 13 × 10⁻⁶ K, presenting an increase up to 500°C followed by a decrease above this temperature region.     

Conductivity, charge transfer and transport number—an ac-investigation of the polymer electrolyte LiSCN-poly(ethyleneoxide)

In this paper a series of impedance measurements in the frequency range 10⁻⁴−2 × 10⁵ Hz and in the temperature range 20–170°C is reported for the cell: Li-metal/LiSCN [dissolved in poly (ethyleneoxide)]/Li-metal. On the basis of the measurements a whole range of electrical properties such as the conductivity, the charge transfer resistance, the transport number for the Li⁺-ion, the double layer capacity and the dielectric constant were determined for the polymer complex. The most important findings were (1) two regions with linear log σ vs 1/T plots and a transition temperature between the regions of 80°C and (2) the fact that both ions were mobile in the polymer complex with the Li⁺-ion having a transport number of 0.54 independent of temperature.     

Electrochemical reduction of thermally prepared oxides of iron and iron-chromium alloys studied by in situ Raman spectroscopy

Pure Fe and Fe/Cr alloys (3% and 12% Cr) were oxidized at 250–260°C and subsequently electrochemically reduced in borate buffer, pH 8.4. The reduction was followed by in situ Raman spectroscopy as well as chronopotentiometric and chronoamperometric measurements. At several time intervals ex situ Raman control investigations and ESCA analyses were undertaken. Although at −0.7 V vs sce partial reduction of the oxide film was observed, -Fe₂O₃ remained unchanged and reduced at −0.9 V. A mixture of spinel structured oxide, possibly Fe₃O₄, and a ferrous deposit were observed when the oxide film was galvanostatically reduced at 100 μA cm⁻²; after prolonged reduction the bare metal resulted. The thermally created oxide of the Cr alloy possessed an inner Cr rich layer which during the galvanostatic reduction of the oxide film at 50 μA cm⁻² is most likely responsible for an increase in the overpotential of more than 80 mV.     

E.s.r. spectroscopic study on the chemistry of coal oxidation

A better understanding of the mechanisms of pre-oxidation could lead to improved methods for prevention of coal weathering, which has a deleterious influence on liquid yield during pyrolysis. Previous Morgantown Energy Technology Center studies demonstrated that the extractable fractions of coal are more susceptible to oxidative weathering than the residue. To better understand the chemistry of coal weathering and the influence of pre-oxidation on subsequent devolatilization, in situ electron spin resonance (e.s.r.) spectroscopic studies were performed on coal, weathered coal and on the corresponding untreated and preoxidized fractions (extract and residue). In this technique, pyrolysis is performed in an e.s.r. cavity and the concentration of free radicals is followed as the sample is pyrolysed. Elemental analysis of the pre-oxidized and untreated samples indicated that H/C ratio of the extract and the coal sample was reduced slightly during 48 h of oxidation at 150 °C in air whereas the H/C ratio of the residue was essentially unchanged. The influence of pre-oxidation (48 h at 150 °C) was to increase the e.s.r. spin concentration of the weathered coal slightly compared to the raw coal when devolatilized at 460 °C. The e.s.r. experiments performed at 460 °C also showed that pre-oxidation significantly enhanced free radical concentration in the extract but had a lesser effect on the residue. The enhanced free radical formation of the pre-oxidized extract relative to the untreated extract implies that mild pre-oxidation affects hydrogen-rich components (extract) more than the primarily hydrogen-poor components (residue) of coal.     

Hallspannungsmessungen in wässrigen elektrolyten

In measuring the Hall effect in aqueous solutions some aspects of electrochemistry and electrode kinetics have to be considered. The described apparatus is based on a constant magnetic field and an alternating electrical field of variable frequency and on three Hall electrodes. The hall mobility in 0·1 N HNO₃, 0·01 N AgNO₃ at 20°C is 2·58 × 10⁻³ cm/Vs.

Résumé

Quelques aspects électrochimiques et électrocinétiques des mesures de l'effet Hall dans les solutions aqueuses sont discutés. L'apparaillage décrit en détail fonctionne au moyen d'un champ magnétique continu, d'un champ électrique alternatif de fréquence variable et avec trois sondes d'Hall. La mobilité d'Hall trouvée dans un électrolyte de 1/10 n HNO₃, 1/100 n AgNO₃ est = 2,58 · 10⁻³ cm²/Vs à 20°C.     

Hydrogen production from coal-alkali interaction

The interaction between Poniati-Girimint coal and alkali has been studied at temperatures from 400 °C to 700 °C and with various ratios of alkali to coal from O to 1.4, using a heating rare of 5 °C min⁻¹ or shock heating at 600 °C. With slow heating, the optimum temperature and alkali to coal ratio for maximum yield of hydrogen at atmospheric pressure were 600 °C and 1.25, respectively. Under these conditions the yields of hydrogen and methane were 505 m³ and 76 m³ per tonne of coal, respectively. In shock pyrolysis the corresponding yields were 370 m³ and 34 m³ per tonne of coal, respectively. The recovery of alkali was 87%, 13% having reacted with the mineral matter of the coal. X-ray diffraction and infrared studies of the washed residual char indicated that the mineral matter present was highly dispersed and had probably been converted into sodium and aluminosilicates.     

An evaluation of Ce-Pr oxides and Ce-Pr-Nb oxides mixed conductors for cathodes of solid oxide fuel cells: Structure, thermal expansion and electrical conductivity

Ceria doped with praseodymia and niobia has been studied in order to evaluate the possibility of applying these materials as cathodes for solid oxide fuel cells. The content of crystallographic phases and their lattice parameters have been determined by X-ray diffraction, the thermal expansion coefficient has been characterised by the dilatometry technique and the electrical conductivity has been measured by complex impedance spectroscopy and by the four probe DC technique. The results have shown the presence of one fluorite phase in binary compositions (CeO₂-PrO_2−x) for PrO_2−x concentrations up to about 20 mol% and two fluorite phases with different lattice parameters for higher PrO_2−x concentrations. The addition of 3 mol% NbO_2·5 has allowed the stabilisation of a single fluorite phase up to 50 mol% PrO_2−x. The thermal expansion coefficient varies between 0 and 30 × 10⁻⁶/K depending on composition and temperature. The electrical conductivity is mainly electronic and thermally activated. The conductivity exceeds 0·1 S/cm at 800°C for compositions with 40 to 50 mol% PrO_2−x.