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  • Ostwald ripening  (4)
  • CHEMISTRY AND MATERIALS (GENERAL)  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Morphological instabilities in pattern formation by precipitation and crystallization processes (1996)
    Springer
    Geologische Rundschau 85 (1996), S. 19-28 
    Details
    ISSN: 0016-7835
    Keywords: Key words Anastomoses ; Crystal zoning ; Snow bands ; Liesegang rings ; Ostwald ripening ; Self organization ; Siderite ; Supersaturation theory ; Zebra rock
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Morphological instabilities in periodic patterns occurring both in precipitation and crystallization processes (Liesegang rings and crystal zoning) are investigated and compared with similar patterns in geological samples (zebra rocks and mud bands in snow sediments). In classical Liesegang systems, undisturbed parallel or concentric precipitation bands are emanated from even or concentric diffusion sources in homogeneous diffusion matrices of gelatine or other gels. In the case of superposing diffusion sources, sources with undulatory curvatures or local diffusion barriers there may occur several types of instabilities within the sequence of regular patterns: (a) gaps within the bands forming radial alleys free of precipitate, (b) transition from broken bands to speckled patterns and (c) apparent branching of bands linked together by so-called anastomoses. Calculations with a competitive particle growth (CPG) model show that lateral instabilities in Liesegang bands (gaps and radial alleys of gaps) are the result of Ostwald ripening effects taking place after precipitation. Apparent branching of bands or formation of anastomoses can be simulated with a prenucleation model according to Ostwald's supersaturation theory. Similar irregularities can be observed in zebra rocks (e.g. banded siderite) whose bandings are commonly explained by sequential sedimentation processes. A very different mechanism is assumed to be responsible for the origin of mud bands in snow sediments. An initially homogeneous distribution of intrinsic mud in snow sediments can be arranged into parallel bands according to a crystal zoning mechanism which is based on repeated thawing and freezing of the snow sediment due to the daily alternation of sun and darkness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192056
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Self-organization of recent rhythmic iron–manganese precipitations in underground mines in the Harz mountains (1996)
    Springer
    Geologische Rundschau 85 (1996), S. 29-37 
    Details
    ISSN: 0016-7835
    Keywords: Key words Banded mineralization ; Harz mountains ; Self-organization ; Iron ; manganese ; ferrihydrite ; birnessite ; Time-series analysis ; Aquatic systems ; Iron bacteria ; Ostwald ripening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  A recent early diagenetic banded iron–manganese mud has been forming underground in a closed lead–zinc mine for approximately 40 years. The processes leading to the banded structure of the precipitate were studied during a period of 2 years. Therefore, 19 physical and chemical parameters were measured regularly in short intervals. The resulting time series were analysed with respect to the data sets of the monthly chemical analyses of the descendent mine water, the daily rainfall and the mineral content. The results reveal that the precipitated material undergoes internal self-organization due to interaction of redox, colloid-chemical, microbial, electrical and ripening processes, and not exclusively produced by seasonal fluctuations of material input. Thus, the primary banding of the material, caused by externally forced fluctuations of the redox conditions within the mine water, is reorganized after a short time. The finally observed bands are controlled by non-linear coupling of reaction and transport processes within the mud. A genetic model for the banded mineralization was developed and verified by numerical simulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192057
    Location Call Number Expected Availability
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Morphological instabilities in pattern formation by precipitation and crystallization processes (1996)
    Springer
    International journal of earth sciences 85 (1996), S. 19-28 
    Details
    ISSN: 1437-3262
    Keywords: Anastomoses ; Crystal zoning ; Snow bands ; Liesegang rings ; Ostwald ripening ; Self organization ; Siderite ; Supersaturation theory ; Zebra rock
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Morphological instabilities in periodic patterns occurring both in precipitation and crystallization processes (Liesegang rings and crystal zoning) are investigated and compared with similar patterns in geological samples (zebra rocks and mud bands in snow sediments). In classical Liesegang systems, undisturbed parallel or concentric precipitation bands are emanated from even or concentric diffusion sources in homogeneous diffusion matrices of gelatine or other gels. In the case of superposing diffusion sources, sources with undulatory curvatures or local diffusion barriers there may occur several types of instabilities within the sequence of regular patterns: (a) gaps within the bands forming radial alleys free of precipitate, (b) transition from broken bands to speckled patterns and (c) apparent branching of bands linked together by so-called anastomoses. Calculations with a competitive particle growth (CPG) model show that lateral instabilities in Liesegang bands (gaps and radial alleys of gaps) are the result of Ostwald ripening effects taking place after precipitation. Apparent branching of bands or formation of anastomoses can be simulated with a prenucleation model according to Ostwald's supersaturation theory. Similar irregularities can be observed in zebra rocks (e.g. banded siderite) whose bandings are commonly explained by sequential sedimentation processes. A very different mechanism is assumed to be responsible for the origin of mud bands in snow sediments. An initially homogeneous distribution of intrinsic mud in snow sediments can be arranged into parallel bands according to a crystal zoning mechanism which is based on repeated thawing and freezing of the snow sediment due to the daily alternation of sun and darkness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192056
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Self-organization of recent rhythmic iron-manganese precipitations in underground mines in the Harz mountains (1996)
    Springer
    International journal of earth sciences 85 (1996), S. 29-37 
    Details
    ISSN: 1437-3262
    Keywords: Banded mineralization ; Harz mountains ; Self-organization ; Iron, manganese, ferrihydrite, birnessite ; Time-series analysis ; Aquatic systems ; Iron bacteria ; Ostwald ripening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract A recent early diagenetic banded iron-manganese mud has been forming underground in a closed lead-zinc mine for approximately 40 years. The processes leading to the banded structure of the precipitate were studied during a period of 2 years. Therefore, 19 physical and chemical parameters were measured regularly in short intervals. The resulting time series were analysed with respect to the data sets of the monthly chemical analyses of the descendent mine water, the daily rainfall and the mineral content. The results reveal that the precipitated material undergoes internal self-organization due to interaction of redox, colloid-chemical, microbial, electrical and ripening processes, and not exclusively produced by seasonal fluctuations of material input. Thus, the primary banding of the material, caused by externally forced fluctuations of the redox conditions within the mine water, is reorganized after a short time. The finally observed bands are controlled by non-linear coupling of reaction and transport processes within the mud. A genetic model for the banded mineralization was developed and verified by numerical simulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192057
    Location Call Number Expected Availability
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    Paper (German National Licenses)
    Fulltext
  • 5
    facet.materialart.
    Unknown
    Phase relations in the Fe-Ni-Cr-S system and the sulfidation of an austenitic stainless steel (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The stability fields of various sulfide phases that form on Fe-Cr, Fe-Ni, Ni-Cr and Fe-Cr-Ni alloys were developed as a function of temperature and the partial pressure of sulfur. The calculated stability fields in the ternary system were displayed on plots of log P sub S sub 2 versus the conjugate extensive variable which provides a better framework for following the sulfidation of Fe-Cr-Ni alloys at high temperatures. Experimental and estimated thermodynamic data were used in developing the sulfur potential diagrams. Current models and correlations were employed to estimate the unknown thermodynamic behavior of solid solutions of sulfides and to supplement the incomplete phase diagram data of geophysical literature. These constructed stability field diagrams were in excellent agreement with the sulfide phases and compositions determined during a sulfidation experiment.
    Keywords: CHEMISTRY AND MATERIALS (GENERAL)
    Type: NASA-TM-78465 , A-7309
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
    facet.materialart.
    Unknown
    Stability of chromium (III) sulfate in atmospheres containing oxygen and sulfur (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The stability of chromium sulfate in the temperature range from 880 K to 1040 K was determined by employing a dynamic gas-solid equilibration technique. The solid chromium sulfate was equilibrated in a gas stream of controlled SO3 potential. Thermogravimetric and differential thermal analyses were used to follow the decomposition of chromium sulfate. X-ray diffraction analysis indicated that the decomposition product was crystalline Cr2O3 and that the mutual solubility between Cr2(SO4)3 and Cr2O3 was negligible. Over the temperature range investigated, the decomposition pressure were significantly high so that chromium sulfate is not expected to form on commercial alloys containing chromium when exposed to gaseous environments containing oxygen and sulfur (such as those encountered in coal gasification).
    Keywords: CHEMISTRY AND MATERIALS (GENERAL)
    Type: NASA-TM-78504 , A-7508
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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