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  • 2000-2004
  • 1975-1979  (4)
  • 1970-1974  (1)
  • 1900-1904
  • Thermodynamics  (3)
  • Current induced transition  (2)
  • 1
    Electronic Resource
    Electronic Resource
    A thermodynamic analysis of the secondary transition in the spontaneous precipitation of calcium phosphate (1978)
    Springer
    Calcified tissue international 25 (1978), S. 209-216 
    Details
    ISSN: 1432-0827
    Keywords: Thermodynamics ; Kinetics ; Apatite ; Octacalcium phosphate ; Tricalcium phosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary A thermodynamic analysis has been made of the secondary transition stage in the spontaneous precipitation of calcium phosphate following the amorphous-crystalline transformation. The first formed crystalline material has a solubility similar to that of octacalcium phosphate (OCP) and the computed thermodynamic solubility product remains invariant in the pH range 7.00–8.60. The duration of the secondary stage is sensitive to pH and the transition appears to occur by hydrolysis of the first formed OCP-like phase to a more basic apatitic phase with a tricalcium phosphate (TCP) stoichiometry. The crystalline material at the end of this transition has an invariant solubility product, in the pH range 7.00 to 8.60, when the TCP-like molecular formula is assumed. Changes in the solution chemistry which accompany the solid-tosolid transitions are consistent with the above conclusions. The results of this study are also consistent with those of a previous study which suggest that the stability of the amorphous calcium phosphate phase is dependent upon the instability of the solution phase with respect to OCP formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02010771
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Negative differential resistance in theV(I)-characteristic of superconducting Sn-whiskers (1975)
    Springer
    Applied physics 7 (1975), S. 127-130 
    Details
    ISSN: 1432-0630
    Keywords: Superconductivity ; Non-equilibrium transport properties ; Current induced transition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The current-induced step structure in the phase transition from the superconducting to the normal conducting state of whiskers of tin shows hysteretic behaviour. By shunting the whisker by a small normal conductor a stable reentrant part of theV(I)-characteristic (negative differential resistance) could be measured for the first step both by de and ac instruments. If the condition of stabilization is not fullfilled, the voltage in the hysteretic region shows oscillations. These oscillations were measured and calculated with a simple model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00884222
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Spannungsstufen in denU (T)-Übergangskurven undU (I)-Kennlinien stromtragender Zinn-Whisker (1973)
    Springer
    Applied physics 2 (1973), S. 303-320 
    Details
    ISSN: 1432-0630
    Keywords: Superconductivity ; Non-equilibrium transport properties ; Current induced transition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The current induced phase transition from the superconducting to the normalconducting state is studied in whiskers of tin. Transition curves were taken byU(T)-measurements at steady currents as well as characteristic curves byU (I)-measurements at fixed temperatures. For larger current intensities these curves show voltage steps which increase linearly with current intensity. The onset of voltage reading appears at the critical current density, as predicted by theory. The step structures are, however, observed at current densities which are several times larger than the critical ones. The influence of a magnetic field on the location and the structure of the curves was measured and is compared to theoretical predictions. At temperatures close toT co whiskers are onedimensional with respect to the superconducting orderparameter because of their small diameters. Therefore, intermediate state pattern and flux flow are rejected as an explanation of the observed structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00896936
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    A thermodynamic analysis of the amorphous to crystalline calcium phosphate transformation (1978)
    Springer
    Calcified tissue international 25 (1978), S. 59-68 
    Details
    ISSN: 1432-0827
    Keywords: Amorphous calcium phosphate ; Thermodynamics ; Apatite ; Octacalcium phosphate ; Tricalcium phosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary A thermodynamic analysis of the precipitation of amorphous calcium phosphate (ACP) and its transformation to crystalline apatite has been made. A nearly constant ion product, over a wide variety of conditions, was obtained for a tricalcium phosphate (TCP)-like phase suggesting that the molecular unit which governs the solubility of ACP may be similar in composition to TCP. The introduction of 10% acid phosphate into the formula for the TCP ion product improves the fit of experimental data and results in an invariant ion product. The stability of ACP in solution was found to be dependent upon its thermodynamic instability with respect to an octacalcium phosphate (OCP)-like phase. The dependence of the induction period for the amorphous to crystalline transformation upon the pH and the Ca/P ratio of the solution is best explained by the assumption that an OCP-like phase is initially nucleated on the surfaces of the ACP particles. The events that occur in the immediate post-transition period suggest the hydrolysis of this OCP-like material to an apatitic phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02010752
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Hydroxyl content of solution-precipitated calcium phosphates (1979)
    Springer
    Calcified tissue international 27 (1979), S. 153-160 
    Details
    ISSN: 1432-0827
    Keywords: Hydroxide ; Hydroxyapatite ; Titration ; Precipitation ; Thermodynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary A method is described for determination of the titratable hydroxide ion in calcium phosphate precipitates. The procedure requires accurate analysis of the other titratable species in the crystal lattice but is unaffected by the presence of other lattice constituents or impurities. The method was applied to precipitates that had been previously analyzed by solution thermodynamic techniques, and the results were consistent with the earlier observations. The hydroxide content of the precipitates increased with crystal maturity and with increasing pH of the precipitation medium. The hydroxide content of the amorphous phase and the immediate post-amorphous-crystalline transformation phase was shown to be nearly zero. After 3 to 4 days' maturation, the hydroxide content of precipitates prepared at pH values of 7, 8, and 9 was shown to increase to approximately 23, 40, 56% of that required for pure hydroxyapatite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02441178
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    Paper (German National Licenses)
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