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  • 1
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    Dependence of growth rate of quartz in fused silica on pressure and impurity content (1980)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The effects of pressure, temperature, and some variations in impurity content on the growth rate u of quartz into fused silica were measured. Under all conditions the growth rate was interface controlled and increased exponentially with pressure with an activation volume averaging -21.2 cu cm/mole. The activation enthalpy for all specimens is extrapolated to a zero pressure value of 64 kcal/mole, within the experimental uncertainty. At a given stoichiometry the effect of hydroxyl content on growth rate is described entirely by a linear term C(OH) in the prefactor of the equation for the growth rate. The effect of chlorine impurity can be described similarly. Also u is increased as the ideal stoichiometry is approached from the partially reduced state.
    Keywords: SOLID-STATE PHYSICS
    Type: Journal of Applied Physics; 51; Sept
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  • 2
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    The mechanism of growth of quartz crystals into fused silica (1980)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: It is proposed that the growth of quartz crystals into fused silica is effected by a mechanism involving the breaking of an Si-O bond and its association with an OH group, followed by cooperative motion of the nonbridging oxygen and the hydroxyl group which results in the crystallization of a row of several molecules along a crystalline-amorphous interfacial ledge. This mechanism explains, at least qualitatively, all the results of the earlier experimental study of the dependence of quartz crystal growth upon applied pressure: large negative activation volume; single activation enthalpy below Si-O bond energy; growth velocity constant in time, proportional to the hydroxyl and chlorine content, decreasing with increasing degree of reduction, and enhanced by nonhydrostatic stresses; lower pre-exponential for the synthetic than for the natural silica.
    Keywords: SOLID-STATE PHYSICS
    Type: Journal of Applied Physics; 51; Dec. 198
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  • 3
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    Undercooling of molten silicon (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Droplets of uncoated molten Si(0.4-0.8 mm diameter) have been undercooled 250 C. Ge droplets of similar size have been undercooled 280 C in a B2O3 flux. The observed nucleation onset temperatures of both Si and Ge droplets are at or below the predicted amorphous phase melting temperatures T(al). The solidified structures were polycrystalline. The nucleation frequency I, calculated from the Si data (20,000/cu cm s at 240 + or - 20 C undercooling), should be an upper limit of the homogeneous nucleation frequency of the crystal phase, since it has not been established that nucleation was homogeneous in these experiments. However, this limiting I for Si indicates that homogeneous nucleation of crystal would not become appreciable in laser pulsing experiments until the liquid Si is undercooled to well below T(al).
    Keywords: SOLID-STATE PHYSICS
    Type: Applied Physics Letters (ISSN 0003-6951); 46; 844
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  • 4
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    Formation of bulk metallic glass by fluxing (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Bulk specimens (0.4-4 g mass) of the alloy Pd40Ni40P20 have been undercooled consistently to the glass state, with no detectable superficial crystallinity, in a molten flux of dehydrated boron oxide. The minimum dimension of the most massive glass specimen, so formed, was 1.0 cm. The absence of crystallinity in the specimens was confirmed by X-ray diffraction, scanning electron microscopy, and calorimetry.
    Keywords: SOLID-STATE PHYSICS
    Type: Applied Physics Letters (ISSN 0003-6951); 45; 615
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  • 5
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    Bulk formation of a metallic glass - Pd40Ni40P20 (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Molten spheroids of Pd40Ni40P20, of up to 0.53-cm minor diameter, were slowly cooled (1.4 K/s) on a fused silica surface under 10 to the -6 torr vacuum to a form which was entirely glassy except for some superficial crystallinity comprising less than 0.5% of the volume. The occurrence of crystallization was eliminated by subjecting the specimens to surface etching followed by a succession of heating and cooling cycles. The absence of crystallization in bulk was confirmed by X-ray diffraction, transmission electron microscopy, and calorimetry. Using the last technique, the heat of crystallization of the glass was measured to be 5.3 + or - 0.3 kJ/g atom.
    Keywords: SOLID-STATE PHYSICS
    Type: Applied Physics Letters; 41; Oct. 15
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  • 6
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    Melting of Ni40Pd40P20 glass (1985)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Upon reheating, most glassy metal alloys crystallize at a temperature not far removed from the glass temperature Tg and far below the liquidus temperature T1. It has been reported by Kui et al. (1984) that the alloy Ni40Pd40P20, which exhibits a scaled glass temperature of about 0.68, has been melt quenched, under a flux of dehydrated B2O3, to a glass at rates as low as 1 deg/s. Here some specimens of this alloy, when similarly fluxed during reheating, have been reheated to temperatures within 50 deg of T1 and 280 deg above Tg at rates of about 2.5 deg/s, and then cooled again to Tg, without crystallization. From this behavior it is inferred that the steady frequency of homogeneous nucleation of crystals in the alloy is less than 0.1/cu cm s.
    Keywords: SOLID-STATE PHYSICS
    Type: Applied Physics Letters (ISSN 0003-6951); 47; 796
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