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  • METALLIC MATERIALS  (3)
  • long-term trends  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Long-term trends in stream chemistry and biology in North-East Scotland: Evidence for recovery (1995)
    Springer
    Water, air & soil pollution 85 (1995), S. 689-694 
    Details
    ISSN: 1573-2932
    Keywords: reversibility ; recovery ; long-term trends ; hydrochemistry ; acidification ; macroinvertebrates ; Scotland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Since 1983 stream chemistry and macroinvertebrate ecology were monitored in ten streams draining the eastern Cairngorms. All streams have exhibited a decline in sulphate concentrations in response to reduced acid deposition; in the more acidic systems this has been reflected by a parallel increase in acid neutralizing capacity (ANC). In some streams this coincides with an increase in the abundance of acid-sensitive mayflies which may provide evidence for biological recovery. In the most chronically acidified systems no increased abundance has been observed despite significant increases in ANC. This suggests that further reductions in deposition and sufficient time for a reversal of soil acidification is required before any biotic recovery occurs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00476909
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    Paper (German National Licenses)
    Fulltext
  • 2
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    Unknown
    The undercooling of liquids (1984)
    In:  CASI
    Details
    Publication Date: 2006-06-08
    Description: The formation by melt quenching of such metastable structures as glassy or microcrystalline solids and highly supersaturated solutions is made possible by the extreme resistance of most melts to homophase crystal nucleation at deep undercooling. This nucleation resistance contrasts sharply with the very low kinetic resistance to the movement of crystal-melt interfaces, once formed, in metals and other fluid systems at even minute undercooling. The methods of nucleation study which have proven especially effective in bypassing nucleation by heterophase impurities thereby exposing the high resistance of melts to homophase nucleation may be summarized as follows: observation of the crystallization behavior of dispersed small droplets; drop tube experiments in which liquid drops solidify, under containerless conditions, during their fall in the tube; and observation of the crystallization of bulk specimens immersed in fluxes chosen to dissolve or otherwise deactivate (e.g., by wetting) heterophase nucleants. This method has proven to be remarkably effective in deactivating such nucleants in certain pure metals.
    Keywords: METALLIC MATERIALS
    Type: NASA. Lewis Research Center Fundamentals of Alloy Solidification Appl. to Industrial Processes; p 11-14
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Crystal nucleation in glass-forming alloy and pure metal melts under containerless and vibrationless conditions (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The undercooling behavior of large spheroids of Pd40Ni40P40 was investigated. By surface etching, supporting the specimens on a fused silica substrate, and successive heating and cooling, crystallization can be eliminated, presumable due to the removal of surface heterogeneities. By this method samples up to 3.2g with a 0.53 mm minor diameter, were made entirely glassy, except for some superficial crystals comprising less than 0.5% of the volume. These experiments show that a cooling rate of approximately 1 K/sec is adequate to avoid copious homogeneous nucleation in the alloy, and that by eliminating or reducing the effectiveness of heterogeneous nucleation sites, it is possible to form bulk samples of this metallic glass with virtually unlimited dimensions.
    Keywords: METALLIC MATERIALS
    Type: NASA-CR-162075 , NAS 1.26:162075
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Crystal nucleation in glass-forming alloy and pure metal melts under containerless and vibrationless conditions (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Crystal nucleation behavior in metallic alloys known to form glasses in melt quenching was characterized and from this characterization the possibility that massive amounts of certain alloys could be slow cooled to the glass state was assessed. Crystal nucleation behavior of pure liquid metals was examined experimentally, under containerless conditions, and theoretically.
    Keywords: METALLIC MATERIALS
    Type: NASA-CR-161267
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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