Durability and thermal cycling of Ni/YSZ cermet anodes for solid oxide fuel cells

The long-term properties of Ni/yttria stabilized zirconia (YSZ) cermet anodes for solid oxide fuel cells were evaluated experimentally. A total of 13 anodes of three types based on two commercial NiO powders were examined. The durability was evaluated at temperatures of 850 C, 1000 C and 1050 C over 1300 to 2000h at an anodic d.c. load of 300mA cm^–2 in hydrogen with 1 to 3% water. The anode-related polarization resistance, R _P, was measured by impedance spectroscopy and found to be in the range of 0.05 to 0.7 cm². After an initial stabilization period of up to 300h, R _P varied linearly with time within the experimental uncertainty. At 1050 C no degradation was observed. At 1000 C a degradation rate of 10 m cm² per 1000 h was found. The degradation rate was possibly higher at 850 C. A single anode was exposed to nine thermal cycles from 1000 to below 100 C at 100 C h^–1. An increase in R _P of about 30m cm² was observed over the first two cycles. For the following thermal cycles R _P was stable within the experimental uncertainty.     

Cooperative inclusion of sodium 1-pyrenesulfonate by γ-cyclodextrin

Summary The interaction of -cyclodextrin(-CD) with sodium 1-pyrenesulfonate(PS) was studied spectrophotometrically. -CD was found to cause much larger decrease in the absorption maxima of PS than -CD. The fluorescence spectra of PS in the presence of -CD showed excimer emission, while those of PS with -CD showed only monomer emission, indicating that -CD forms 12 (-CDPS) complexes in which two PS molecules are included in the -CD cavity in a face-to-face fashion. The binding isotherm showed a sigmoidal curve. The association constants were estimated by computer simulation of the binding curve. The 12 (CDPS) complex was found to be much more stable (K=10⁶ M^–1) than the 11 complex (K=1 M^–1). At high concentration of -CD another -CD cooperates in binding two PS molecules, resulting in the formation of a 22 complex.     

Molybdenum nitride for the direct decomposition of NO

The physico-chemical properties of passivated -Mo₂N have been investigated. The material showed high activities for NO direct decomposition: nearly 100% NO conversion and 95% N₂ selectivity were achieved at 450C. The amount of O₂ taken up by -Mo₂N increased with temperature rise and reached 3133.9 molg^–1 at 450C; we conclude that there formation of Mo₂O_xN_y occurred. This oxygen-saturated -Mo₂N material was catalytically active: NO conversion and N₂ selectivity were 89 and 92% at 450C. We found that by means of H₂ reduction at 450C, Mo₂O_xN_y could be reduced back to -Mo₂N and the oxidation/reduction cycle is repeatable; such a behaviour and the high oxygen capacity (3133.9 molg^–1) of -Mo₂N suggest that -Mo₂N is a promising catalytic material for automobile exhaust purification.     

Processing of boron-nitrogen preceramic polymers

A number of new oligomeric and polymeric reagents rich in boron and nitrogen have recently been derived by several research groups. These reagents offer potential for the formation of boron nitride (BN) as controlled morphology powders as well as nonpowder forms. Specifically, it has been found that a family of 3-point and 2-point poly(borazinylamine) reagents may be processed by techniques used in organic polymer chemistry, with subsequent formation of BN ceramic fibers, coatings, xerogels, aerogels, and aerosols.     

Synthesis of statistical polydiene networks by reaction of liquid polyenes with telechelic siloxanes

The present investigation concerns the synthesis of statistical networks similar to vulcanized rubber. We have used liquid precursor polymers: polybutadiene (PB) and polyisoprene (PI) with telechelic siloxanes. The reactivity of the polydienes can be classified as follows: PB units 1,2 PI units 3,4 PI units 1,4 0. The network formation is a function of the ratio R = nb, of pendent double bonds/nb. of SiH. For R 1 the networks are rather hard and brittle, for 8 R 10 they are soft and elastic, whereas for R 16 the gels obtained are very soft and sticky.     

Effects of gas bubbles on the current and potential profiles within porous flow-through electrodes

This paper presents a mathematical model to calculate the distributions of currenti(x), potentialE(x), gas void fraction (x) and pore electrolyte resistivity (x) within porous flow-through electrodes producing hydrogen. It takes into consideration the following effects: (i) the kinetics of the interfacial charge transfer step, (ii) the effect of the non-uniformly generated gas bubbles on the resistivity of the gas-electrolyte dispersion within the pores of the electrode (x) and (iii) the convective transport of the electrolyte through the pores. These effects appear in the form of three dimensional groups i.e.K=i _o L where i_o is the exchange current density, is the specific surface area of the electrode andL its thickness.= ⁰ L where ⁰ is the pore electrolyte resistivity and =/Q where is a constant, =tortuosity/porosity of the porous electrode andQ is the superficial electrolyte volume flow rate within it. Two more dimensionless groups appear: i.e. the parameter of the ohmic effect =K/b and the kinetic-transport parameterI=K. The model equations were solved fori(x),E(x), (x) and (x) for various values of the above groups.Nomenclature specific surface area of the bed, area per unit volume (cm^–1) - b RT/F in volts, whereR is the gas constant,T is the absolute temperature (K) - B =[1–(I ² Z/4)], Equation 9a - C =(1–B ²), Equation 9b - E(L) potential at the exit face (V) - E(0) potential at the entry face (V) - E(x) potential at distancex within the electrode (V) - E _rev reversible potential of the electrochemical reaction (V) - F Faraday's constant, 96500 C eq^–1 - i _o exchange current density of the electrode reaction (A cm^–2 of true surface area) - i(L) current density at the exit face (A cm^–2 of geometrical cross-sectional area of the packed bed) - I K =i _oL(/Q) (dimensionless group), Equation 7d - K =i _oL, effective exchange current density of the packed bed (A cm^–2) Equation 7a - L bed thickness (cm) - q tortuosity factor (dimensionless) - Q superficial electrolyte volume flow rate (cm³ s^–1) - x =position in the electrode (cm) - Z =exp [(0)], Equation 7f - transfer coefficient, =0.5 - =K/b=(i ₀ L ⁰ L)/b (dimensionless group) Equation 7e - (x) gas void fraction atx (dimensionless) - = ⁰ L, effective resistivity of the bubble-free pore electrolyte for the entire thickness of the electrode ( cm²) - (0) polarization at the entry face (V) - (L) polarization at the exit face (V) - =q/, labyrinth factor - constant (cm³ C^–1), Equation 3a - =/Q (A ^–1) conversion factor, Equation 3b - porosity of the bed - (x) effective resistivity of the gas-electrolyte dispersion within the pores ( cm) - ⁰ effective resistivity of the bubble-free pore electrolyte ( cm)     

New polymer syntheses

Summary Various poly(ether sulfide)s were prepared by polycon-densation of 4-mercaptophenol or silylated 4-mercaptophenol with 2,6-dichloropyridine or 3,6-dichloropyridazine. A two step and an one-pot procedure were compared. The poly-(ether-sulfide)s were characterized by elemental analyses, inherent viscosities, ¹³C-NMR spectroscopy, gel-permeation chromatography and DSC-measurements.     

New polyisobutylene based model ionomers

Three-arm star polyisobutylene ionomers (¯M_n=8800) with terminal SO₃ M (M=K or Ca²) groups were synthesized and their mechanical properties investigated. Compression molded films displayed high elongations, i.e., -1000% for Ca² ionomers with lower values for the K counterions. Strain induced crystallinity was observed at higher elongations. Mechanical properties in general compared favorably with conventional covalently linked rubbery networks and were comparable and in some cases superior to EPDM-based ionomers carrying randomly distributed SO₃ M groups.For the first two parts see Proceedings, 28th IUPAC Macromolecular Symposium, Amherst, MA, July 11–16, 1982, p. 905 and 906     

Adsorption Isotherm and Pore Characteristics of Nano Alumina Derived from Sol-Gel Boehmite

This paper deals with a systematic investigation on the synthesis of aluminium oxide starting from mono hydroxy aluminium oxide (boehmite, (AlOOH)) which in turn is synthesized from aluminium nitrate. Boehmite on heating forms , transitional alumina and -alumina phases in the temperature range 400–600, 800–1050 and 1050–1100°C respectively. Calculation from XRD, using Scherer equation shows that -alumina has crystallite size in the range 5–10 nm, while and -alumina are in the range 10–20 nm and -alumina is about 33 nm. The textural features of aqueous sol-gel boehmite samples calcined at various temperatures were analyzed by specific surface area measurements and adsorption isotherm features. Maximum specific surface area of 266 m²/g is observed for the precursor calcined at 400°C and a minimum of 5 m²/g at 1100°C. Total pore volume is maximum for the precursor calcined at 600°C (0.2653 cm³/g). Average pore size ranges from 3 nm (400°C) to 11 nm (1100°C). The adsorption isotherms also show a change from Type IV to Type II with increase in temperature showing difference in surface properties. The information from t-plots, pore size distribution and cumulative pore volume data also indicates differences in porosity features of boehmite on calcination. The adsorption isotherm and pore size distribution analysis show maximum microporosity at 400°C, while maximum mesoporosity is observed at 600°C. At higher temperatures, porosity decreases, even though small fraction of pores in the mesopore range is still retained. At 1100°C, there is structural transformation from transitional to -alumina, with very low specific surface area 5 m²/g and pores in the size range of 11 nm. The various data presented in this study will be useful in the synthesis of alumina with tailor made properties.     

Dynamic mechanical properties of crosslinked polyisoprene under deformation

Summary Molecular motions of elastomers under deformations were observed through dynamic mechanical measurements. Composite master curves of dynamic moduli E and E and loss tangent tan over a wide range of frequency and in a state of elongation were obtained by the time-temperature superposition procedure. It is found that both moduli increase with strain, . The slope of the dispersion curve of E become more gradual with the increase in , while that of E is almost unchanged. The increment of E is generally larger than that of E, which does not agree with the N. W. Tschoegl prediction, E ^* ()=f() E _o ^* (), where E ^* () and E _o ^* () are complex moduli at the strain of and O, respectively, and f() is the function of only . The difference in the strain dependence of E from E was found to correspond to the strain dependence of the equilibrium modulus.     

Antifungal polyoxygenated fatty acids fromAeollanthus parvifolius

Two polyoxygenated fatty acids with antifungal activity have been isolated from aerial parts ofAeollanthus parvifolius (Labiatae) using bioassay-guided isolation procedures. Spectroscopic analysis was used to identify the compounds as (Z)-4,9-diacetoxy-6,7-epoxy-5-hydroxy-8-oxododeca-2-enoic acid and (Z)-4,6,7,9-tetraacetoxy-5-hydroxy-8-oxododeca-2-enoic acid. Both of these compounds inhibited spore germination ofCladosporium cucumerinum. Minimum inhibitory doses were 1 µg and 5 µg, respectively, but only the former inhibited germination ofAspergillus niger at a dose of 5 µg. Neither compound exhibited antibacterial activity. (Z)-4,9-Diacetoxy-6,7-epoxy-5-hydroxy-8-oxododeca-2-enoic acid reduced the hyphal growth ofPythium ultimum. The mode of action was not resolved but did not involve either the disruption of the cell wall membrane or the inhibition of extracellular enzymes. Application of (Z)-4,6,7,9-tetraacetoxy-5-hydroxy-8-oxododeca-2-enoic acid to seedling plants did not give any protection against fungal attack, and indeed the compound appeared to be phytotoxic.     

Thermally stable alumina–gallia aerogel as a catalyst for NO reduction with C3H6 in the presence of excess oxygen

In order to improve thermal stability, an alumina–gallia aerogel was prepared and the catalyst performance for NO reduction with C₃H₆ was compared with that of an alumina–gallia xerogel. Basically, both were prepared by a sol–gel method with supercritical drying for the former, while with oven drying for the latter. Upon heating at 800, 900, and 1000°C, the aerogel exhibited higher NO conversion than the xerogel at reaction temperature <400°C, while NO conversion was lower on the former than on the latter at >500°C. At 450°C, NO conversion was almost the same for these two catalysts. A marked difference was observed upon heating them at 1100°C: the aerogel still maintained quite a high activity, while the xerogel greatly lost it. After heating the aerogel at 1100°C, -phase alumina remained untransformed with its surface area of 80 m²/g, while the xerogel was completely transformed to -alumina with its surface area of 6 m²/g. The high activity remaining on the aerogel heated at 1100°C was ascribed to its large surface area.     

Water vapor absorption and aqueous retention of hydrolyzed starch polyacrylonitrile graft copolymers — “superabsorbent starch”

Summary Starch copolymers with polyacrylonitrile grafts were prepared using the Mn³⁺ initiation method and different amounts of acrylonitrile. The product was hydrolyzed in aqueous alkali (nitrile groups to amide and carboxyl groups) to enhance the hydrophilic character of the copolymer and achieve superabsorbent properties. At relative humidities (RH) up to 95–97 % the modified starch shows normal water vapor absorption like cellulose and other polysaccharides. When in contact with liquid distilled water, the modified starch forms a superabsorbent gel which retains very large amounts of water (up to 800 g/g). At low and high pH and in aqueous salt solutions (NaCl, CaCl₂ and synthetic urine) the water retention is strongly reduced. This is interpreted as due to the ionic strength (salt effect) and for Ca²⁺ ions probably also crosslinking by salt formation with carboxyl groups on adjacent chains or chain segments.     

Change in degree of polyamidation of polycaproamide during orientation stretch

Conclusions The effect of stretch ratio, the ratio of stretch ratios in the cold and hot zones, and of the relative viscosity of polycaproamide on the degree of its breakdown during stretching have been examined.The degree of breakdown decreases if the viscosity stays within the range 3.25–3.35, and the stretch ratio in the cold zone is the maximum possible.Translated from Khimicheskie Volokna, No. 5, pp. 26–27, September–October, 1983.     

On the NiMoO4 oxidative dehydrogenation of propane to propene: some physical correlations with the catalytic activity

The - and -phases of NiMoO₄ have been investigated with different techniques (X-ray diffraction, electrical conductivity, IR spectroscopy) in order to tentatively rationalise the different catalytic activities observed in the oxidative dehydrogenation of propane to propene. XRD analyses have shown that at 595 ° C, the -phase is already present but a temperature of 700 ° C is required to obtain a full conversion into a pure -phase. Electrical conductivity showed the presence of anionic vacancies. It is proposed that propene is formed by the reaction of propane with surface O^2- anions. The -phase is almost twice more selective in propene formation than the -phase for comparable conversion at identical temperatures. This could derive from different oxygen environments on the active catalytic site.     

Recovery and recrystallization of electrodeposited bright copper coatings at room temperature. II. X-ray investigation of primary recrystallization

X-ray investigations of the recrystallization processes occurring at room temperature in electrodeposited bright copper coatings were carried outin situ. As a result of the orientation transformation of the growth texture with 311, 111 and 110 components, a recrystallization texture with 100, 110 and 111 components was obtained. It was established that one of the factors which influence the microhardness of copper coatings is the orientation distribution of crystallites.     

Critical solution point and chain dimension of branched-polystyrene solutions

Summary Critical solution point and chain dimension were measured for branched polystyrene(BPS) in solution as a function of molecular weight(M) and compared with those for linear polystyrene(LPS). The critical concentration _c of BPS was quite different from that of LPS at a fixed M, but the same at a fixed overlap-concentration ^*, i.e., plots of _c vs. ^* fall on a single straight line for both BPS and LPS (gf_c ^*). Reduced critical temperature _c defined by gt_c=(–T_c)/ [T_c: critical temperature, : the -temperature] was related to _c as _{c c} ² for BPS, whereas _{c c} for LPS.     

Inhibition of β-Glucosidase and Esterase by Tannins from Betula, Salix, and Pinus Species

The reaction of tannin fractions isolated from the bark of Betula, Salix, and Pinus species with two enzymes, -glucosidase and esterase, was investigated. The influence of precipitation to the hydrolytic capacity of -glucosidase also was studied. All tannins studied precipitated -glucosidase and esterase, and moderate differences in the precipitating capacities of the tannins were observed. Interestingly, complex formation between -glucosidase and tannin did not markedly affect the activity of the enzyme. Therefore, complex formation during the insect/herbivore feeding does not necessarily change the defense activity of phenolic glycosides or decrease activity of digestive enzymes.     

Partial oxidation of methane to synthesis gas

Partial oxidation of methane to synthesis gas has been carried out over a number of transition metal catalysts under a range of conditions. It is found that the metals Ni, Ru, Rh, Pd, Ir and Pt, either supported on alumina or present in mixed metal oxide precursors, will bring the system to equilibrium. The yield of CO and H2 improves with increasing temperature in the range 650–1050 K, and decreases with increasing pressure between 1 and 20 atm. An excellent yield (92%) is obtained with a 421 N₂CH₄O₂ ratio at 1050 K and atmospheric pressure, with a space velocity of 4×10⁴ hour^–1.     

Studies on electrical conductivity of gamma irradiated polyaniline

Summary de electrical conductivity at surface of -irradiated polyaniline (PAn) has been studied. EPR spectroscopic results indicate that the variation of spin concentration is consistent with the increase of _de. Electrical conductivity (_de) versus temperature (T) characteristics of unirradiated and irradiated PAn were performed, which demonstrate that the unirradiated curve can fit to ln_deT₁, while the irradiated curve fit to ln_deT_1/4.