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1Author    ChrL. Teske, Hk Müller-BuschbaumRequires cookie*
 Abstract    h e rm o a n a ly tis c h e U n te rs u c h u n g e n z u r R ü c k o x id a tio n von B a 2Y C u 30 6 + :c Thermoanalytical Investigations about the Reoxidation of Ba2YCu3Ob + x The reoxidation reaction of Ba,YCu30 6+x forming the superconducting ceramic material Ba2YCu30 6 93 is studied by thermoanalytical methods (DTA and TG). The exothermal oxygen uptake in pure 0 2-atmosphere is at a maximum rate in the range of 230-330 C (% 150 min). The reoxidation temperature can be lowered by treatment of Ba2YCu3Oe 0 in Ar: H2 = 1:1 atmosphere but the uptake of greater amounts of hydrogen prevents the material from becoming super-conducting again at low reoxidation temperatures. The process has an activation energy Ea = 70.9 + 2kJ/Mol and a reaction enthalpy AH = — 86.7kJ/Mol Ba2YCu30 6 0 (normalized to a 1/2 0 2 basis) which is estimated from DTA-data. 
  Reference    Z. Naturforsch. 43a, 965—970 (1988); eingegangen am 8. August 1988 
  Published    1988 
  Keywords    Ba2YCu30 6 + x, Thermoanalysis, Reoxidation, Activation Energy, Reaction Enthalpy 
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 TEI-XML for    default:Reihe_A/43/ZNA-1988-43a-0965.pdf 
 Identifier    ZNA-1988-43a-0965 
 Volume    43 
2Author    J. Jadżyn, G. Czechowski, B. Żywucki, C. Legrand, P. Bonnet, R. DąbrowskiRequires cookie*
 Title    Dielectric Properties of Mesomorphic n-TPEB's in Isotropic Phase  
 Abstract    Dielectric relaxation studies have been performed for the isotropic phase of a series of mesogenic molecules of l-[3-n-alkyl-biphenyl]-2-[4-isothiocyanatophenyl]ethane, CnH 2n+ 1 -(f)-(t>-CH 2 CH 2 -<p-NCS (n-TPEB), for n = 7, 8 and 9. Two Debye-type dielectric absorption bands have been interpreted as corresponding to the rotation around the short and long molecular axis. 
  Reference    Z. Naturforsch. 48a, 871—874 (1993); received May 29 1993 
  Published    1993 
  Keywords    Dielectric relaxation, Molecular dynamics, Mesomorphic molecules, Relaxation time, Activation energy 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0871.pdf 
 Identifier    ZNA-1993-48a-0871 
 Volume    48 
3Author    Takahiro Ueda, Katsuyuki Shimizu, Hiroshi Ohki, Tsutomu OkudaRequires cookie*
 Title    C CP/MAS NMR Study of Motion and Local Structure of Phenethyl- ammonium Ion in [C 6 H 5 CH 2 CH 2 NH 3 ] 2 PbX 4 (X = Cl, Br, I)  
 Abstract    Ionic motion and local structure of phenethylammonium ion (C 6 H 5 CH-,CH 2 NH 3 +) in a series of phenethylammonium lead(II) halides, [C 6 H 5 CH 2 CH 2 NH 3 ] 2 PbX 4 (X = Cl, Br, I) were studied by means of 13 C cross polarization/magic angle sample spinning (CP/MAS) NMR technique. Among the three salts, remarkable differences in the spectra were observed in the signals corresponding to the phenyl carbons. The peaks from C2, C3, C5, and C6 in the phenyl group were split into three for the chloride and into two for the bromide, although in the iodide those were observed as a single peak. Coalescence of those peaks, as well as line broadening were observed on heating. This indicated that peak split brings about disorder of the orientation in the phenyl group around the C1-C4 axis, suggesting to have three and two orientations for the chloride and the bromide, respectively. Above room temperature the phenyl group undergoes chemical exchange among these orientations, and at higher temperature, reorientation with a large amplitude takes place around its axis. The apparent activation energies of the reorientation of the phenyl group for the chloride and bromide were estimated from the temperature dependence of the linewidth of the resonance peaks to be about 24 kJ mol -1 , 25 kJ mol -1 , respectively, which is similar to in the iodide (25.0 kJ mol -1). Ab initio molecular orbital energy calculation was carried out to evaluate the potential barrier of the internal rotation of the phenyl group in a free phenethylammonium ion. The intramolecular interaction was evaluated to be 13.9 kJ mol -1 from the calculation, and the intermolecular interaction results to be 10 kJmol -1 . 
  Reference    Z. Naturforsch. 53a, 983—988 (1998); received April 30 1998 
  Published    1998 
  Keywords    13 C CP/MAS NMR, Layered compound, Disorder, Reorientation, Activation energy 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0983.pdf 
 Identifier    ZNA-1998-53a-0983 
 Volume    53 
4Author    Yukihiro Yoshimura, Seiji Sawamura, Yoshihiro TaniguchiRequires cookie*
 Abstract    f fe c ts o f P r e s s u r e , T e m p e r a tu r e , a n d C o n c e n tr a tio n o n th e V is c o s ity o f A q u e o u s A m m o n iu m B ro m id e S o lu tio n Dedicated to Prof. Hitoshi Ohtaki on the occasion of his 60th birthday The viscosity of aqueous ammonium bromide solutions is measured at 0.1-1.0 mol kg-1, 278.2-323.2 K, and 0.1-375 MPa, using a high-pressure rolling-ball viscometer. The activation energy (£v) for viscous flow and Jones-Dole's B coefficient are estimated. Ev against pressure yields a concave curve with a minimum and B yields a convex one with a maximum. These phenomena are attributed to pressure, temperature, and concentration effects on the water-structure. 
  Reference    Z. Naturforsch. 50a, 316—322 (1995); received December 14 1994 
  Published    1995 
  Keywords    Viscosity, High pressure, Ammonium bromide, Activation energy, Jones-Dole's B coef­ ficient 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0316.pdf 
 Identifier    ZNA-1995-50a-0316 
 Volume    50 
5Author    Hsin-Yi Hsu, Chao-Cheng YangRequires cookie*
 Title    Conductivities of Room Temperature Molten Salts Containing AICI3, Measured by a Computerized Direct Current Method  
 Abstract    The conductivities of the binary room-temperature molten salt systems AlCl3-yV-«-butylpyridinium chloride (BPC), AlCl3-l-ethyl-3-methylimidazolium chloride (EMIC) and AlCl3-benzyltriethylammo-nium chloride (BTEAC) have been measured at different temperatures and compositions by a d.c. four-probes method. There is a maximum of the conductivity at 50 mol% A1C13 in the A1C13-BPC and A1C13-EMIC systems at 40 to 80 °C, their activation energies being relatively low (20.79 and 14.76 kJ/mol, respec­ tively). As to the A1C13-BTEAC system, there is an irregular change in the conductivity at 40-70 mol% A1C13 in the temperature range 50 to 80 °C. The conductivities of the three RTMS are in the order A1C13-EMIC > A1C13-BPC > A1C13-BTEAC, the reason being discussed. 
  Reference    Z. Naturforsch. 56a, 670—676 (2001); received July 23 2001 
  Published    2001 
  Keywords    Conductivity, Room-temperature Molten Salts, Activation Energy, Direct Current Method, Computerized Measurement System 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0670.pdf 
 Identifier    ZNA-2001-56a-0670 
 Volume    56